Graphene is a new type of carbon material with a flexible, two-dimensional structure. Due to the excellent stability of its lattice structure and its mechanical flexibility, graphene-based materials can be applied in flexible humidity sensors. At present, the application of graphene-based flexible humidity sensors in the fields of medical care and environmental monitoring is attracting widespread attention. In this review, the basic properties of graphene oxide (GO) and reduced graphene oxide (rGO) as moisture-sensitive materials and methods for their preparation were introduced. Moreover, three methods for improving the performance of moisture-sensitive materials were discussed. The working principle of different types of graphene-based humidity sensors were introduced. The progress in the research on graphene-based flexible humidity sensors in four respects: Human respiration, skin moisture, human sweat, and environmental humidity were discussed. Finally, the future research, following the development trends and challenges, to develop the potential of integrated, graphene-based flexible humidity sensors were discussed. Flexible electronic sensors are sensors made of flexible materials that can be stretched, bent, and even folded . AccordiThe selection of flexible moisture-sensitive materials is the key to preparing flexible humidity sensors. In recent years, graphene has attracted a great deal of attention for various sensing applications. The excellent electrical and mechanical properties of graphene have made it a widely used material in lithium-ion batteries, supercapacitors, electronic products, and optical devices ,6,7,8,9.In the 1990s, researchers began to use stretchable materials with a certain degree of flexibility to prepare electronic sensors, and related research has developed significantly in recent years. In 2004, single-layer graphene was isolated for the first time. The first graphene-based gas sensor detected a single water molecule in 2007. Since that time, a number of graphene-based humidity sensors have been prepared by researchers. Capacitive and quartz crystal microbalance (QCM) humidity sensors based on a GO film coating appeared in 2011. Over the next few years, flexible humidity sensors based on graphene appeared. With the development of materials science, researchers have begun to explore humidity-sensitive materials with higher sensitivity, and have attempted to use different sensing mechanisms to prepare better-quality humidity sensors. In 2016, a multi-functional all-graphene flexible sensor capable of detecting pressure, temperature, and humidity appeared. In recent years, in order to further develop flexible devices, researchers have conferred a number of innovative functions on sensor systems, including self-powering and self-repairing functions. This was a brief timeline of the development of graphene-based flexible humidity sensors ,22.In this paper, we review materials and methods for the preparation of graphene-based flexible humidity sensors, and report methods for improving sensor performance. Then, according to the different sensing mechanisms, we summarize progress in the research on graphene-based flexible humidity sensors in terms of capacitance, resistance, and other mechanisms, and discuss their application and prospects in the fields of human respiration, skin moisture, human sweat, and environmental humidity.The core material of a humidity sensor is its humidity-sensitive material. When the humidity-sensitive material interacts with humidity , it can change the quality, thickness, and optical, mechanical, and electrochemical characteristics of the humidity-sensitive material, thereby changing the impedance between the detection electrodes. So, information about humidity can be obtained by detecting the impedance output signal.GO is a derivative of graphene. Its structure maintains the hexagonal shape of graphene. After the oxidation process, a large number of polar oxygen-containing groups, such as hydroxyl, epoxy, and carbonyl groups, will be introduced onto the graphene layer. So, it can absorb a large number of water molecules and, with an increase in humidity, it will agglomerate into a water molecular film using the interaction between water molecules and GO materials. Due to the principle and the change in structure after the action, GO is an outstanding humidity-sensitive material that is used in humidity sensors ,25,26,27GO, as a humidity-sensitive material, has many excellent properties. In terms of composition and structure, GO has good hydrophilicity due to the presence of oxygen-containing functional groups. Medheker put forward a theoretical analysis of the hydrophilicity of GO . When thMoreover, the irregular oxygen-containing region of the intermediate structure of the GO sheet, that is, the six-membered ring skeleton of carbon atoms, has hydrophobic properties, so the GO can also be dispersed in a large number of organic solvents, which demonstrates its amphiphilicity. By means of a comparison of the dispersion of GO after ultrasonic treatment and after 3 weeks of standing, GO was shown to be able to be stably dispersed in water, acetone, ethanol, ethylene glycol, and other organic solvents, which is helpful for further processing and obtaining stable GO . Obtaini3O+). Through the Grotthuss chain reaction (H2O + H3O+ → H3O+ + H2O), proton transfer and charge transfer take place in the GO, thus reducing the resistance of the GO membrane. Additionally, there is another sensing mechanism that produces the opposite result and is worthy of discussion. When GO interacts with water molecules, GO materials can act as electron donors and exhibit p-type semiconductor properties. As the electron density increases, the number of holes in the sensing material itself decreases, so that the resistance of the sensing layer increases. In addition, when the humidity is high, the resistance of the sensitive layer increases significantly. This effect may be caused by the increase in molecular distance due to expansion and the subsequent decrease in penetration pathways [In terms of electrical properties, GO will change the dielectric constant after adsorbing water molecules. A mechanism analysis of the influence of GO on the dielectric constant of water molecules was performed by Bi’s group . Under apathways ,33,34. Mpathways . By drawIn terms of mechanical properties, due to the presence of oxygen-containing functional groups, the adsorption of water molecules from the environment will affect a GO membrane’s mechanical properties. With the increase of humidity, the elastic modulus and tensile strength of the GO membrane decrease. However, increasing the number of oxygen-containing functional groups will increase the number of hydrogen bonds, which are directly connected to the adjacent GO sheets. This will improve the elastic modulus and toughness of GO-based humidity-sensitive films, which is conducive to their application to flexible substrates ,28,36,37GO can be partially reduced by the controlled removal of oxygen-containing groups. The product of the reduction is rGO. Compared with GO, it has higher electrical conductivity . The str4 to deoxidize graphite powder, which greatly improves the experimental safety. Moreover, rGO can be more easily and quickly prepared using Hummers’ method. In addition, this preparation method has the advantages of rapidness, simplicity, and a low preparation cost, which make industrial production easier to realize [At present, there are three methods for preparing GO: Hummers’ method, the Staudenmaier method, and Brodie’s method. The most commonly used preparation method is Hummers’ method ,39,40. T realize ,41,42. N realize ,44.The performance of rGO is related to the process for the reduction of GO, which can be reduced by many methods, such as thermal reduction, chemical reduction, and light reduction. Controlled removal of oxygen-containing functional groups on the surface of GO can change the properties and structure of the material. The thermal reduction method uses the instability of oxygen-containing functional groups on the surface of GO and can remove and form hole defects in the material through thermal annealing reduction .The chemical reduction method uses chemical reagents to remove oxygen-containing functional groups on the surface of GO to achieve the reduction of GO. This method has less-stringent requirements for equipment and the environment than thermal reduction methods, and the preparation process is simpler and the cost is lower. Therefore, the chemical reduction method is suitable for use in the large-scale production of rGO.The reduction of GO using the above-mentioned two methods requires the consumption of a large amount of energy and is not suitable for long-term development. It is also difficult to achieve the integration of flexible devices using these two methods, which limits the application of rGO in flexible electronics . PhotoreOne of the most important components of a humidity sensor is the humidity-sensitive thin film. The commonly used methods for preparing GO composite films include titration, dip coating, spraying, spin coating, electrophoresis, Langmuir–Blodgett (L-B) membrane technology, vacuum filtration, in-situ polymerization, the sol-gel method, chemical vapor deposition, magnetron sputtering, and vacuum evaporation ,53,54,55The performance of a flexible humidity sensor is closely related to the physical and chemical properties of its humidity-sensitive materials. Combined with the physical and chemical properties of humidity-sensitive materials, we can improve the performance of humidity-sensitive materials in the following three respects.Controlling the morphology (structure) of the composite. Hosseini and others developed a highly sensitive flexible humidity sensor based on graphene quantum dots (QGDs) . The QGD2 composite film [2 were different with different annealing temperatures, which would affect the humidity sensitivity response characteristics of the sensor. Phan and others used rapid thermal annealing (RTA) to control the number of oxygen-containing functional groups in the GO [Finding the best preparation conditions and methods, such as finding the most suitable annealing temperature to control the number of oxygen-containing functional groups and using the self-assembly method to make the structure stable and firm. Li prepared a flexible resistive humidity sensor based on an rGO/WSite film . It was n the GO . Throughn the GO .Modifying the structure of the graphene derivative according to need, such as using functional group materials to modify the GO to enhance the humidity sensitivity response, doping heteromorphic semiconductor materials to form a Schottky barrier, and preparing composite materials to improve the self-adsorption capacity and permeability structure. Su’s group modified graphene using GO as a precursor material ,68,69. IA flexible humidity sensor is generally composed of a flexible substrate, a humidity-sensitive film, and a metal detection electrode. At present, there are many kinds of graphene-based flexible humidity sensors ,72,73. AThe biggest challenges for flexible humidity sensors involve their manufacture, their mechanical properties, the stability of the electrochemical performance, and their ability to maintain sensitivity after repeated bending deformations. The key to their manufacture lies in the flexibility of the electrodes/circuits. At present, the theoretical research on the design and manufacturing of graphene-based flexible electronic devices mainly focuses on the flexible substrate transfer method and the strain structure design method, as shown in The flexible substrate transfer method is a method for sequentially transferring one electrode structure to another flexible substrate. It has the advantages of strong technical compatibility and simplicity, and the operation is carried out at a normal temperature, avoiding the possibility of the temperature affecting the device’s function. Polydimethylsiloxane (PDMS) is often selected to be the flexible substrate for the transfer method. PDMS is a stretchable material that is highly transparent, chemically inert, and non-toxic. It can be applied to human skin, implanted in the body, or applied in wearable devices. In addition, polyurethane (PU), polyester resin (PET), and so on can be chosen . These oThe strain structure design method is used mainly to provide the electrode material with a higher degree of flexibility by designing the strain structure, which can not only avoid significant deformation of the electrode material under normal working conditions, but also alleviate damage during stretching. According to the shape of the conductive layer, there are serpentine structures, paper-cut structures, three-dimensional network structures, and so on ,79,80,81Rhumidity is the resistance measured under humid conditions and Rair is the resistance measured under dry air conditions [The working principle of a resistive humidity sensor is that the moisture-sensitive film changes its impedance characteristics by adsorbing water molecules. These sensors measure the environmental humidity by changing the output electrical signal. The sensitivity of a resistive humidity sensor can be defined as:nditions . ResistiCpu is the capacitance value, S is the effective electrode area of the capacitive sensor, d is the thickness of the moisture-sensitive polymer film layer, ε0 is the dielectric constant of classical vacuum, and εr is the dielectric constant of the moisture-sensitive polymer material. The structure of a capacitive flexible humidity sensor is similar to that of the resistance type, and the dielectric layer is covered on two of the flexible cross finger electrodes. At present, most humidity sensors use capacitance sensing technology [The working principle of a capacitive humidity sensor is that it detects the environmental humidity by changing the dielectric constant of the humidity-sensitive film through changing the transmission capacitance value. The capacitance value can be expressed by the following formula:chnology ,83. ThisIn addition to resistive flexible humidity sensors and capacitive flexible humidity sensors, there are also high-performance humidity sensors based on other technologies and instruments, such as optical fiber humidity sensors and QCM humidity sensors. In addition to GO-based and rGO-based humidity sensors, graphene derivatives, such as graphene quantum dots prepared from GO, can be used to prepare flexible humidity sensors. GQDs have also been combined with optical fiber technology to prepare a new type of humidity sensor with higher sensitivity . The senThe humidity sensing mechanism of a fiber-optic humidity sensor is that the properties of refracted or reflected light waves are changed after the moisture-sensitive material adsorbs water molecules. The changes in properties can be detected by the amplitude, polarization amplitude, frequency shift, or phase shift of the light waves. Because of their small volume and light weight, optical fiber sensors have low transmission loss and a strong multiplexing ability and can also realize multi-parameter and long-distance detection. Because of their excellent corrosion resistance and anti-electromagnetic interference ability, optical fiber sensors are suitable for use under strong magnetic conditions and in harsh environments ,85,86.f0 is the resonance frequency of the QCM, A is the effective area, and ρ and μ are the density and shear modulus of the quartz crystal, respectively [QCM is a non-destructive technology. The sensing mechanism of a QCM humidity sensor is to coat a layer of humidity-sensitive film on the electrode. After the moisture-sensitive material is deposited on the electrode, Sauerbrey’s equation can be used to convert the dynamic adsorption mass into a resonance frequency shift.ectively ,88. CompGQD material is an important graphene derivative whose sheet size is smaller than 100 nm, and it has a quantum confinement electron state. GQD material has excellent hydrophilicity, a large specific surface area, and a small sheet size ,90. The Due to their high sensitivity, excellent flexibility, good stretchability, and stability, graphene-based flexible humidity sensors have great potential for application in such fields as electronic skin, personal health monitoring, and wearable and stretchable humidity sensors ,100,101.Respiratory rate can be considered to be a key indicator of human health, and monitoring changes in an individual’s respiratory rate and depth of breath can be used in medical diagnosis ,103. TraThe moisture content of human skin is also a key indicator of human health. Graphene-based flexible humidity sensors can detect skin moisture and show great potential for use in wearable devices suitable for evaluating moisturizing products. At present, there are few research results on this kind of sensor. On the one hand, for contact sensor equipment, when in contact with skin, the sensor needs to have a certain degree of flexibility, a better fit for the skin, and be harmless to the skin to prevent damage with long-term use. On the other hand, the preparation of non-contact sensor equipment needs theoretical guidance. Graphene-based flexible humidity sensors for the detection of moisture and humidity in the skin have yet to be developed. However, researchers have attempted to establish a functional relationship between the sensitivity of PIM-based sensors and the moisture content of human skin and developed high-precision skin moisture measurement instruments that may provide a solution for graphene-based flexible humidity sensors .There are many ions in human sweat. The composition and content of ions in human sweat are also key indicators of human health. It is very important to personal health monitoring and exercise monitoring to sample and analyze fresh sweat using sensors. At present, there are many types of studies on the implementation of personalized health monitoring by means of wearable sensor technology. The monitoring of ions in sweat requires the wearable sensor to capture fresh sweat. Guijun Li and others reported on the development of wearable sweat capture devices using patterned graphene arrays with controllable wetness and conductivity for the simultaneous capture and electrochemical measurement of sweat droplets . Sweat dLife depends on environmental moisture. Life needs to sense the humidity and temperature of the outside world and provide feedback. As an important organ for sensing the outside world, the skin needs to be repaired by electronic equipment and medical means if it is damaged or even necrotic. Electronic skin is a system that can simulate human skin, sense the external pressure, temperature, and humidity, obtain other information, and provide feedback, which also requires the integration of flexible humidity sensors in the electronic skin. Most sensors that can sense pressure, temperature, and humidity are rigid and cannot perform synchronous monitoring. Recently, a multifunctional sensor was prepared by means of spraying a mixture of carbon black (CB) and rGO on a paper substrate . It can In general, graphene-based flexible humidity sensors are widely used in the field of respiratory monitoring. Moreover, the technology for their preparation is becoming increasingly simple, their cost is gradually being reduced, and their performance is constantly being improved, which should also promote the development of wearable medical systems.Due to its large specific surface area and the large number of hydrophilic oxygen-containing functional groups, GO has an excellent capacity for water absorption. GO and rGO are two common humidity-sensitive materials. By controlling and optimizing these materials’ structure, improving the preparation conditions and methods, or directly modifying them, the sensing performance of the sensor can be improved. In addition, GQD material has a small sheet size that enables a film formed by stacking to contain a large number of voids, which enable water molecules to penetrate into the humidity-sensitive film more quickly and accelerate the humidity-sensitive response of the sensor. GQD material is a graphene-based material with the potential for broad application in humidity-sensitive materials.The large-scale production of high-quality humidity-sensitive materials is a basic premise of the application of graphene-based flexible humidity sensors. The existing spin-coating and inkjet printing technologies can be used to realize the preparation of low-cost humidity-sensitive films ,106,107.In the process of preparing graphene-based flexible sensors, the flexible substrate transfer method and the stress structure design method can be used to obtain a high degree of flexibility. Different graphene-based materials have different sensing mechanisms. QCM sensors and fiber-optic sensors use QCM sensing devices and fiber-optic sensing technologies, respectively. As new types of sensors that integrate multiple technologies, they have excellent humidity sensing characteristics, including a short response time, low humidity hysteresis, and high sensitivity. In addition, these two new types of flexible humidity sensors have high repeatability, good long-term stability, and a long life. They have very broad future research prospects.Finally, the actual application of graphene-based flexible humidity sensors in human respiratory monitoring, skin moisture detection, sweat analysis, and environmental humidity detection requires us to integrate sensor technology with other technologies. Currently, the main problem of multi-function sensors is that the recognition accuracy between multiple signals still needs to be improved. Sensor materials need to have a high degree of stability in order for us to complete the integration of data transmission and processing units and ultimately achieve the goals of minimizing equipment size and optimizing performance.


The ultimate memristor, which acts as resistive memory and an artificial neural synapse, is made from a single atomic layer. In this manuscript, we present experimental evidence of the memristive properties of a nanopatterned ferroelectric graphene field-effect transistor (FET). The graphene FET has, as a channel, a graphene monolayer transferred onto an HfO The influence of the charge traps at the graphene/HfZrO interface can degrade transistor performance . However2O3/Si FETs can act as memtransistors. The memtransistors were previously never fabricated at the wafer scale, and only on MoS2 flakes at a reduced scale. The combination of HfZrO and graphene monolayer is beneficial for graphene monolayer transfers since the average surface roughness of HfZrO, as measured with an AFM, was 0.2 nm—one order of magnitude lower than the roughness of SiO2.In conclusion, we demonstrated that nanopatterned graphene/HfZrO/Al


Graphene-based van der Waals (vdW) heterojunction plays an important role in next-generation optoelectronics, nanoelectronics, and spintronics devices. The tunability of the Schottky barrier height (SBH) is beneficial for improving device performance, especially for the contact resistance. Herein, we investigated the electronic structure and interfacial characteristics of the graphene/AlN interface based on density functional theory. The results show that the intrinsic electronic properties of graphene changed slightly after contact. In contrast, the valence band maximum of AlN changed significantly due to the hybridization of Cp and Np orbital electrons. The Bader charge analysis showed that the electrons would transfer from AlN to graphene, implying that graphene would induce acceptor states. Additionally, the Schottky contact nature can be effectively tuned by the external electric field, and it will be tuned from the p-type into n-type once the electric field is larger than about 0.5 V/Å. Furthermore, the optical absorption of graphene/AlN is enhanced after contact. Our findings imply that the SBH is controllable, which is highly desirable in nano-electronic devices. Fortunately, the construction of the heterojunction by vertically stacking two 2D materials provides a new avenue to extend the application possibility of their individual components ,18,19. TAlN is a rather significant wide bandgap semiconductor due to its small or even negative electron affinity, excellent chemical stability, a superior mechanical strength, and a high thermal conductivity ,28. Furtheterojunction. To describe the stability of the heterostructure, the binding energy is defined by Equation (1) [A denotes the x–y in-plane area of the heterojunction.The Vienna ab-initio simulation package (VASP) , which hy Grimme  was emplirection ,40. The rst–Pack  approachrst–Pack . The banrst–Pack . The hettion (1) ,44:(1)Ebheterojunction, the graphene/AlN heterojunction was built with a new lattice constant of a = b = 12.33 We first optimized the graphene and AlN primitive cells, and the lattice constants of graphene and AlN were  that in ,45. By utructure ,44.We first calculated the electronic structures of the graphene and monolayer AlN, as shown in p orbital electrons while the CBM is contributed by Ns orbital electrons.The typical Dirac-point of graphene is found to occur at the Fermi level. The conduction band minimum (CBM) of AlN rides at the ulations . The proThe work function is defined as nterface . The pronterface  discusseThe plane-averaged charge density difference (PCDD) between the graphene/AlN interface is represented by Equation (2) ,21:(2)ΔρThe Schottky barrier height (SBH) plays a vital role in the metal/semiconductor interfacial system or Schottky-based devices. In the theory of the Schottky–Mott model ,51, the F shown in Usually, a high SBH will seriously increase the contact resistance and further degrade the contact performance of the field-effect transistor (FET). Thus, the tunability of SBH is rather meaningful for Schottky devices. The common methods of modulating the SBH include in-plane strain engineering , verticaL is the slab thickness in the graphene/AlN heterojunction. Finally, the normalized absorbance A material needs to be corrected in the case of a two-dimensional (2D) material ,55. Thisfined as (5)σ3D(ωribed in ; ε0 is tIn conclusion, the structural, electronic, and optical properties of the graphene/AlN interface under external electric field were investigated through density functional theory. The results of the projected band structure, the charge density differences, and the Bader charge showed that graphene acts as an acceptor while AlN acts as a donor. By applying the external electric field from −0.5 V/


GRN mutation. This was achieved using single and double-labeling immunohistochemistry, and double-labeling immunofluorescence and confocal microscopy. In the sALS spinal cord, P-TDP43 Ser403-404 deposits were elongated and parallel to the lumen, whereas others were granular, seldom forming clusters. In the frontal cortex, the inclusions were granular, or elongated and parallel to the lumen, or forming small globules within or in the external surface of the blood vessel wall. Other deposits were localized in the perivascular space. The present findings are in line with previous observations of TDP-43 vasculopathy in a subset of FTLD-TDP cases and identify this pathology in the spinal cord and frontal cortex in a subset of cases within the sALS/FTLD-TDP spectrum.Sporadic amyotrophic lateral sclerosis (sALS) and FTLD-TDP are neurodegenerative diseases within the spectrum of TDP-43 proteinopathies. Since abnormal blood vessels and altered blood-brain barrier have been described in sALS, we wanted to know whether TDP-43 pathology also occurs in blood vessels in sALS/FTLD-TDP. TDP-43 deposits were identified in association with small blood vessels of the spinal cord in 7 of 14 cases of sALS and in small blood vessels of frontal cortex area 8 in 6 of 11 FTLD-TDP and sALS cases, one of them carrying a  TARDBP gene, as the major pathological protein in the inclusions of FTLD-U (hereinafter FTLD-TDP) with or without motor neuron disease, and in sALS  and most cases of frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) are considered to be within the same spectrum . This is in sALS . Aggrega in sALS .TARDBP  in the cytoplasm of neurons and glial cells, and in neuronal processes , 10, 11.TARDBP .Abnormalities in the wall of blood vessels, and altered blood-brain barrier (BBB) and SCBB, occur in sALS. Alterations affect the endothelial cells, pericytes, thigh junctions, matrix metalloproteinases, transport systems, aquaporin 4, free radicals, cytokines, and VEGF receptors, among others . A majorLittle information is available on blood vessels in FTLD-TDP, except for microbleeds . HoweverC9orf72 expansions and mutations in SOD1 and TARDP were not found in any case. Small DNs and/or TDP-43-positive granules and/or small cytoplasmic globules in cortical neurons in the contralateral frontal cortex area 8 were observed in 8 of 14 cases but were only abundant in 3 cases.Postmortem brain cases were obtained from the Institute of Neuropathology biobank, now a branch of the HUB-ICO-IDIBELL biobank, following the Spanish legislation , and the approval of the local ethics committee . The brain and spinal cord were obtained at autopsy, and selected samples were rapidly dissected, kept in labeled plastic bags, and immediately frozen and stored at –80°C for further biochemical studies, or fixed in 4% buffered formalin for no <3 weeks. Thirty selected regions of the brain and spinal cord were embedded in paraffin; 4-µm-thick sections were obtained with a sliding microtome, dewaxed, and processed for current histological and immunohistochemical methods, including hematoxylin and eosin, Luxol fast blue-Klüver Barrera, Sudan black, and periodic acid Schiff. Other sections were processed for phospho-tau (AT8), β-amyloid, α-synuclein, phospho-neurofilament medium and heavy chain, ubiquitin, TDP-43, P-TDP-43 Ser409-410, glial fibrillary acidic protein (GFAP), Iba1, and myelin basic protein immunohistochemistry, as detailed elsewhere . sALS caGRN mutation A303AfsX57; the female patient presented with late-onset frontotemporal dementia and had eye-shaped NIIs in addition to NCIs and DNs , Parkinson disease, tauopathies, vascular diseases, neoplastic diseases affecting the nervous system, metabolic syndrome, hypoxia, and prolonged axonal states, such as those occurring in intensive care units were excluded. Cases with infectious, inflammatory, and autoimmune diseases, either systemic or limited to the nervous system, were not included.2O2. The immunoreactions resulted in a brown precipitate.Single-labeling immunohistochemistry was carried out on de-waxed sections 4-μm-thick in every case. The sections were boiled in citrate buffer to enhance antigenicity and blocked for 30 minutes at room temperature with 10% fetal bovine serum diluted in PBS. Then, the sections were incubated at 4°C overnight with the primary antibody, washed, and thereafter incubated with EnVision + system peroxidase  for 30 minutes at room temperature. The peroxidase reaction was visualized with diaminobenzidine and H2O2 as a brown precipitate. Then, the sections were incubated at 4°C overnight with the second primary antibody, washed and incubated with the appropriate secondary antibody/HRP. The peroxidase reaction was visualized with diaminobenzidine, NH4NiSO4, and H2O2. The immunoreaction resulted in a blue-gray precipitate. Control of the immunostaining included omission of the primary antibody; no signal was obtained following incubation with only the secondary antibodies.Double-labeling immunohistochemistry was done in 2 steps. The sections were incubated at 4°C overnight with the first primary antibody, washed and incubated with the appropriate secondary antibody liked to horseradish peroxidase (HRP); the immunoreaction was visualized with diaminobenzidine and HPrimary antibodies were rabbit polyclonal antibodies TDP43 (G400)  used at a dilution of 1:100, P-TDP43 Ser403-404  diluted 1:2000; rat anti-P-TDP43 Ser409-410 antibody  diluted 1:100; and mouse monoclonal GFAP antibody  used at a dilution of 1:1000, and MCAM/CD146 antibody  used at a dilution of 1:100. The secondary antibodies were swine anti-rabbit immunoglobulins/HRP , goat anti-mouse immunoglobulins/HRP , and donkey anti-rat IgG (H + L)/HRP , all used at a dilution of 1:100. Combinations for double-labeling immunohistochemistry were P-TDP43 Ser403-404 and MCAM/CD146 antibody, and P-TDP43 Ser403-404 and GFAP.Double-labeling immunofluorescence was carried out in de-waxed 4-μm-thick sections which were stained with a saturated solution of Sudan black B  for 15 minutes to block the autofluorescence of lipofuscin granules present in cell bodies, and then rinsed in 70% ethanol and washed in distilled water. Some sections were incubated at 4°C overnight with anti-GFAP and anti-P-TDP43 Ser403-404 antibodies; other sections with CD68  and anti-P-TDP43 Ser403-404 antibodies. After washing, the sections were incubated with Alexa488 or Alexa546  fluorescence secondary antibodies against the corresponding host species. Nuclei were stained with DR . After washing, the sections were mounted in Immuno-Fluore mounting medium , sealed, and dried overnight. Sections were examined with a Leica TCS-SL confocal microscope. No attempt was made to quantify blood vessels with TDP-43-immunoreactive deposits in line with the lack of studies quantifying the number of NCIs, NIIs, and DNs in FTLD-TDP cases.In the normal spinal cord, TDP-43 immunoreactivity was observed in the nucleus of neurons and glial cells. In sALS, TDP-43 was preserved in the nuclei of some motor neurons of the anterior horn and the vast majority of nuclei of glial cells. TDP43 was translocated to the cytoplasm in a case-dependent number of motor neurons in sALS to form skein-like inclusions, dot-like inclusions, and granular and spicular deposits . AbnormaGRN mutation. In the frontal cortex area 8 type C and the 3 sALS cases with cortical TDP-43 pathology, TDP-43 immunoreactivity was preserved in the nucleus of the majority of neurons, glial cells and cells of the blood vessels. However, variable numbers of thick TDP-43-immunoreactive neurites (DNs) were present, mainly in the upper cortical layers and the sixth layer. NCIs were seldom observed, and in small numbers, whereas NII and glial inclusions were almost absent.In the normal frontal cortex, TDP-43 immunoreactivity was present in the nuclei of neurons, glial cells, and the nuclei of the cells of the blood vessel walls . In fronGRN mutation  in frontal cortex area 8 of FTLD-TDP; some inclusions appeared to be within the blood vessel wall, but others were located outside the blood vessel wall close to the external layer .Similarly, double-labeling immunohistochemistry in sALS cases using the same antibodies displayed P-TDP-43 inclusions outside the MCAM/CD146-immunoreactive blood vessel wall in the perivascular space  or in coTo learn about the relationship between TDP-43-immunoreactive inclusions and astrocytes, double-labeling immunohistochemistry with P-TDP43 Ser403-404 and GFAP antibodies was carried out in the frontal cortex of cases with FTLD-TDP pathology. GFAP immunoreactivity was rarely seen in the proximity of P-TDP-43-immunoreactive deposits. In most cases, it was difficult to ascertain the relationship between some inclusions and astrocytes; this occurred when astrocyte processes wrapped small neurons with NCIs , and wheGRN mutation .The present study identifies TDP-43 proteinopathy in a very few blood vessels of the spinal cord in 7 of 14 sALS, in the frontal cortex area 8 in one of 3 sALS, and in the frontal cortex area 8 in 5 of 8 FTLD-TDP cases, one of them bearing a Progranulin deficiency is linked to TDP-43 pathology, including altered autophagy, TDP-43 accumulation, TDP-43 translocation, and abnormal truncation . The proThe present observations are in line with pioneering descriptions of TDP-43 vasculopathy in FTLD-TDP . HoweverRNA processing is essential for regulated gene expression; therefore, defects at some stages of gene regulation may contribute to disease-RNA specific alterations . TDP-43 Little is known about TDP-43 and blood vessels. However, the function of TDP-43 in blood vessels is probably similar to that reported in other settings including RNA transcription, RNA splicing, and protein interactions. Therefore, it may be posited that TDP-43 pathology in blood vessels may have deleterious effects in vascular homeostasis and compromise normal BBB and BSCB function in subgroups of patients with sALS/FTLD-TDP. In this line, altered blood vessels of the spinal cord are found in TDP-43 conditional knockout mice . EndotheThe significance of perivascular and vascular TDP-43 pathology in a subset of ALS/FTLD cases is currently unknown but could be better understood through mechanistic and clinicopathological correlation studies. Not all sALS/FTLD-TDP cases contain vascular TDP-43-immunoreactive deposits, and when they are present, the number of blood vessels with positive deposits is very small. Yet, the low density of deposits could be compatible with a toxic impact on vascular cells and perivascular astrocytes.These observations also suggest that sALS and FTLD-TDP are degenerative diseases not limited to neurons and oligodendrocytes as other cell types are affected. ALS-derived fibroblasts show cytoplasmic TDP-43 aggregation under certain experimental paradigms . DownregIn conclusion, the present observations show the presence of TDP-43 vasculopathy in the cerebral cortex and spinal cord in a subset of patients within the spectrum of sALS/FTLD-TDP. Since diverse abnormalities converge in the wall of blood vessels and alter BBB and SCBB in sALS, and vascular alterations are reported in animal models showing downregulation or overexpression of TDP43 it is tempting to speculate that TDP-43 vasculopathy contribute to the altered vascular function in sALS/FTLD-TDP43 spectrum.


Graphene and its oxide are nanomaterials considered currently to be very promising because of their great potential applications in various industries. The exceptional physiochemical properties of graphene, particularly thermal conductivity, electron mobility, high surface area, and mechanical strength, promise development of novel or enhanced technologies in industries. The diverse applications of graphene and graphene oxide (GO) include energy storage, sensors, generators, light processing, electronics, and targeted drug delivery. However, the extensive use and exposure to graphene and GO might pose a great threat to living organisms and ultimately to human health. The toxicity data of graphene and GO is still insufficient to point out its side effects to different living organisms. Their accumulation in the aquatic environment might create complex problems in aquatic food chains and aquatic habitats leading to debilitating health effects in humans. The potential toxic effects of graphene and GO are not fully understood. However, they have been reported to cause agglomeration, long-term persistence, and toxic effects penetrating cell membrane and interacting with cellular components. In this review paper, we have primarily focused on the toxic effects of graphene and GO caused on aquatic invertebrates and fish (cell line and organisms). Here, we aim to point out the current understanding and knowledge gaps of graphene and GO toxicity. It is dnar axis . Howevernar axis . The idenar axis ,6.It is the strongest and thinnest known material known to man . GraphenThese advantages of graphene make it desirable for the development of graphene composites through the incorporation of different functional materials. Graphene-based composites have been achieved successfully with organic crystals ,31, inorOn the other hand, graphene oxide (GO) is an intermediate product obtained during the synthesis of reduced GO (rGO) ,44,45. IAt this increasing phase of commercial production, the presence of graphene is evident in the environment at a significant level ,51. IrreIn this present review, we will analyze the biocompatibility and toxicology of graphene and GO in order to evaluate the safety limits needed for the implementation of upcoming researches. We will also try to draw attention towards knowledge gaps to attain valuable insights on the fate and risks presented by graphene and GO on fish in the aquatic environment. Furthermore, we will discuss the key physiological factors involved in influencing the toxicity of graphene and GO in fish in the surrounding water medium, degradation pathways, and the exposure and administration pathways. We believe that the critical study in this field will lead to collection of current information leading to the production of better modified materials emerging in healthcare, diagnostic, and therapeutics.Graphene is inert in chemistry because of the immense delocalized π electron system . The graCrassostrea virginica), both 1 and 10 mg/L GO exhibited a dose-dependent elevated lipid peroxidation. No significant changes in glutathione S-transferase (GST) levels were observed, but a reduction in the total protein levels was found in tissues of the digestive glands at both concentrations (1 and 10 mg/L) of the GO. Overall, the study indicated that short-term GO exposures can induce oxidative stress, epithelial inflammation and adversely affected the overall health of Crassostrea virginica [Crassostrea virginica, elevated lipid peroxidation and changes in glutathione-s-transferase (GST) were observed in tissues of gills and digestive gland exposed at 2.5 and 5 mg/L. Reactive oxygen species (ROS) induced oxidative damage. Therefore, the study suggested that detoxification enzyme such as GST are thought to be involved in stress signaling, leading to harmful effects on cellular health [Invertebrates are important organisms utilized for environmental toxicological studies. They have a relatively short life span, fast reproduction, and high sensitivity towards pollutants. They are also cost-effective and contribute quick results. These organisms are regarded as convenient test species for ecotoxicity studies of new chemicals and nanoparticles . The invirginica . In a sir health .Diopatra neapolitana (a polychaete species) for 28 days. The analysis of physiological (regenerative capacity) and biochemical  depicted negative effects of GO on regenerative capacity of Diopatra neapolitana, the organisms exposed to higher concentrations of GO took long periods to complete regeneration. GO also altered the energy-related responses, such as glycogen content with high polychaetes, which might have resulted from decreased metabolism. The research work concluded that cellular damage happened despite higher activities of antioxidant and biotransformation enzymes in Diopatra neapolitana exposed to GO [Daphnia magna with and without the presence of humic acid (HA). The GO induced significant toxicity to Daphnia magna with a median lethal concentration of 48 h LC50 equal to 84.2 mg/L and 21-day LC50 as 3.3 mg/L. The HA mitigated the acute and chronic toxicity in Daphnia magna, as in the presence of HA, the decreased toxicity of GO was attributed to alleviation of oxidative damage by HA [Daphnia magna was done by Guo and colleagues. Their results demonstrated the accumulation of graphene at 1% of organism’s dry mass. During the time for depuration, these organisms bore roughly constant body burdens after 24 h regardless of initial graphene concentration, whereas, after addition of an algae and humic acid, the depuration resulted in significant release of accumulated graphene but leaving some graphene in the organism. The study concluded that the remaining graphene in Daphnia magna might possess a risk to be passed on to neonates and thus require further risk assessment and relevant evaluation [Ceriodaphnia dubia in acute and chronic assay. The mean effective concentration (EC50) estimated during acute exposure was 1.25 mg/L, whereas chronic exposure of GO resulted in significant decrease in number of neonates, feeding rates, and ROS generation. Their research group concluded that in the presence of GO, there was a shift in the available energy for self-maintenance instead of feeding and reproduction activities [Palaemon pandaliformis, results suggested that GO did not cause acute toxicity at concentration up to 5.0 mg/L after 96 h exposure. However, GO in association with Cd and Zn increased toxicity of the trace elements as suggested by 96 h LC50 of Cd associated with GO 1.7 times less than the 96 h LC50 of Cd alone and 96 h LC50 of Zn associated with GO 1.8 times less than 96 h LC50 of Zn alone. Likewise, co-exposure of GO with trace elements impaired the routine metabolism of Palaemon pandaliformis. The study recommended that more researches and evaluation of data need to be done to understand the toxicity criteria of GO in aquatic organisms or aquatic bodies [Further in a study by De Marchi et al., different concentrations of GO  toxicity were tested over ed to GO . In anotge by HA . Furtheraluation . In anottivities . Moreovec bodies .In determining the cytotoxicity of environmental pollutants, cell lines derived from fish are considered very suitable experimental model. Testing the toxicity of nanomaterials is more complex than other chemical compounds. In nanomaterials, various physiochemical properties such as size, shape, surface area, and surface modification need to be considered prior to experimentation. Other factors including agglomeration, aggregation, sedimentation, dissolution, concentration need to be studied as well their fate in the test systems. If these aspects of nanomaterials are not investigated prior to experimentation, they might interfere with the results and misleading conclusions can be drawn. A study by Lamel et al. was done by exposing topminnow fish hepatoma cell line PLHC-1 cells to a single layer GO and carboxyl graphene (CXYG) (16 µg/mL GO or CXYG) suspensions with an aryl hydrocarbon receptor (AhR). Their results demonstrated pre- and co-exposure of cells to GO and CXYG nanoplatelets induced cytochrome P450 1A (cyp1A) expression, suggesting that graphene nanoplatelets increased the effective concentration of AhR agonists by facilitating passive diffusion into cells by damaging the plasma membrane or transporting them over the plasma membrane via a Trojan horse-like mechanism. Based on their results, it was found that there is an existence of combination effects between nanomaterials and environment pollutants . In a siIn another study, bluegill sunfish (BF-2 cells) were exposed to GO at concentrations of 0, 10, 20, 40, 60, 80, and 100 μg/mL for 24 h. Two biological assays -2,5-diphenyl tetrazolium bromide) MTT assay and neutral red uptake (NR) resulted in cytotoxicity and oxidative stress in BF-2 cells. The tested biomarkers of oxidative stress such as lipid peroxidation, superoxide dismutase, catalase, reactive oxygen species, and 8-hydroxy-2′-deoxyguanosine levels increased, and glutathione level was decreased in BF-2 after treatment with GO. The GO induced a dose- and time-dependent cytotoxicity on BF-2 cells . In addip < 0.05) decreased at 100 mg/L at 48 hpf. Furthermore, rGO and MWCNTs decreased the length of hatched larvae at 96 hpf but no mortality and morphological malformation were observed, which further requires more results and analysis at various concentrations at different time periods [A reliable way of nanomaterials administration to an aquatic organism is oral and direct injection . For dirFurther in a different study, when the zebrafish embryos were exposed to a concentration of 1–100 μg/L to analyze the developmental toxicity, the results yielded impaired DNA modification, protein carbonylation, and excessive generation of ROS. The work also highlighted nonmonotonic response of zebrafish developmental toxicity to GO at μg/L to mg/L levels. On further analysis, transcriptomics revealed deficiencies in the collagen and matrix metalloproteinase (MMP) related genes, which in turn affected the skeletal and cardiac development of zebrafish. Moreover, to contribute to the results of developmental toxicity, metabolomics assay showed inhibition in amino acid metabolism and disturbance in the ratio of unsaturated fatty acids (UFAs) to saturated fatty acids (SFAs). The work, therefore, demonstrated developmental toxicity on the basis of involved molecular mechanism at trace concentration equal to 10 µg/L .In an interesting study of Hu et al. with parent and offspring zebrafish when GO nanosheets were administered to parental zebrafish at a concentration of 0.01–1 µg/L, GO translocated from water to the brain of parent fish and the offspring with major loss of claudin5a . However, GO did not induce neurotoxicity in the parent fish and significant neurotoxicity occurred in the offspring, exhibiting loss of dopaminergic neurons and reduction in acetylcholinesterase (AChE) activity. Moreover, endoplasmic reticulum damage, autophagy promotion, ubiquitin down-regulation, and increase in β-galactosidase activities were observed, attributing to the failures in the carbohydrate and fatty acid metabolisms. Their work suggested that more researches and data compilation for the toxicity of GO on fish offspring at environmentally relevant concentration are required to do reliable analysis and to establish conclusions . Similar∙OH, and changes in the secondary structure of protein, which, in contrast, were relieved by HA. On the other hand, humic acid reduced interactions between GO and chorion mitigating chorion damage by regulating the morphology, structure, and surface negative charges of GO, indicating a feasible antidotal mechanism for GO in presence of HA [In a study by Clemente and co-workers, zebrafish embryos were analyzed after 5 and 7 days of GO exposure at 100 mg/L and humic acid (HA) at 20 mg/L either individually or together. Regardless of the presence of HA, the larvae exposed to GO for 5 days demonstrated increase in the locomotor activity, reduction in yolk sac size, total length, and inhibition of AChE activity. The larvae exposed to GO for 7 days did not show any significant differences in the locomotor activity, but the RT-PCR gene expression analysis depicted an increase in AChE expression. The work suggested that HA is associated with toxicity risk modulation by GO and some compensatory homeostatic mechanisms might be involved in the effects observed in zebrafish . In a sisynapsin IIa expression at 5 mg/L with down-regulation of dat expression were observed, showing potential compensatory mechanism. At 10 mg/L GO exposure, increase in heart rate, absolute turn angle, brain cell damage, and decrease in dopamine levels were observed. However, no changes were observed on higher concentrations of GO exposure, which is attributed to GO agglomeration. The work concluded that the results of the toxic effects of GO were not dose-dependent and are pre-eminent at lower concentrations, and hence more studies are required to gather relevant data and analysis [hcrt and hcrtr mRNA, while graphene did not obviously disturb the sleep behavior and gene expression patterns [In another study, zebrafish embryos were treated with GO at 0, 0.01, 0.1, 1, and 100 mg/L for 24, 48, and 96 hpf. Results revealed that the GO adhered to and enveloped the chorion of zebrafish embryos via the hydroxyl group interactions and it blocked the pore canals of the chorionic membrane causing hypoxia and hatching delay. Furthermore, GO penetrated the chorion of embryo via endocytosis, damaged the mitochondria, and primarily translocated to the eye, heart, and yolk sac regions involved in circulatory system of zebrafish. In these organs, GO induced excessive generation of reactive oxygen species, thus increasing oxidative stress, DNA damage, and apoptosis. The work highlighted specific adverse effects of GO on embryogenesis and emphasized the potential ecological and health risks of GO . Furtheranalysis . In the analysis . The gropatterns .Fusobacteria and the genus Cetobacterium and Lactobacillus and decreasing the abundance of Firmicutes and the genus Pseudomonas; GR caused marked shifts in the diversity of the gut microbiota. The GFMs also altered the intestinal morphology and antioxidant enzyme activities by inducing more vacuolation and generating more goblet cells [Acute toxicity, oxidative stress, and immune-toxicity of GO were analyzed at 1, 5, 10, or 50 mg/L for 14 days were done in a study using the zebrafish adult model. Histological analysis of the liver and intestine showed cellular alterations including vacuolation, loose arrangement of cells, histolysis, and disintegration of cell boundaries. Malondialdehyde (MDA) level and superoxide dismutase (SOD) and catalase (CAT) activities were increased and glutathione was decreased in the liver after treatment with GO. Moreover, levels of tumor necrosis factor alpha (TNF-α), interleukin-1B, and interleukin-6 depicted induction in immune response. Hence, the work suggested GO exposure in aquatic system caused oxidative stress and immune toxicity in adult zebrafish . Moreoveet cells .Anabas testudineus (the climbing perch) revealed accumulation of cellular lipid peroxides specifically in the mitochondria. Activity of SOD, CAT, and, GST was augmented in contrast to lowered level of reduced glutathione titer. The results also indicated oxidative stress in cell and mitochondria in fish after exposure to GO, thus suggesting compilation of more data for comparison of results and establishments [p ≤ 0.05 for RBC (0.770 cells/μL × 106) in T1 and 0.850 cells/μL × 106 in T2 compared with negative control (1.410 cells/μL × 106). There was no significant decrease p > 0.05 of each PCV in T1 and T2 (31 and 27%), respectively, compared with control negative (35%) and hemoglobin (10.30 and 9 mg/dL) in T1 and T2, respectively, compared with negative control (11.65 mg/dL), while the addition of graphene nanoparticles did not affect the number of WBC in T1 and T2 (15.1 and 19.1 cells/μL × 103), respectively, compared with negative control (15.6 cells/μL × 103) [The effects of GO were observed on the antioxidant metabolism of zebrafish; after 48 h exposure, SOD activity was significantly increased in 20 mg/L, CAT activity in 2, 10, and 20 mg/L, and lipid peroxidation (LPO) had an increase in 2 mg/L, whereas glutathione peroxidase (GPx) was inhibited at 20 mg/L. Later after 168 h recovery in clean water, SOD remained elevated in 20 mg/L, CAT activity remained unchanged and GPx activity was inhibited at 2, 10, and 20 mg/L, and LPO decreased in 2 mg/L. The study suggested that GO exposure disrupted antioxidant metabolism of adult zebrafish in which it was not restored even after 168 h recovery period in clean water . The toxishments . In a seL × 103) . The sumThe unique properties of graphene and GO along with other carbon nanomaterials such as carbon nanotubes and fullerenes have been used for various applications and can be released in environment at significant amounts, posing threat to aquatic species as well as humans. Once released in the bodies of water, graphene and GO can also interact with existing inorganic ions and natural organic matter (NOM), posing threat for significant adverse effects on the ecosystem. However, intentional exposure of graphene in biomedical applications is of interest. The literature cites approximately 60% graphene-related materials applications in biomedical engineering as stated by Mao et al. . This siHere in the present review, we have compiled, presented, and compared the current toxicological scenarios of graphene and GO in aquatic invertebrates and fish model organisms. We compared the paper published number  during the past 16 years (from 2004 to 2020). Results show the relative paper published number for graphene-based nanomaterial toxicity is around 50% less than their fullerene or carbon nanotube counterparts . In addiIn case of continuous waterborne exposure, the developmental stages of the embryo and the duration of exposure are very critical. The embryos exposed in waterborne graphene and GO might agglomerate in the exposure media or on the chorion depleting embryo of oxygen supply and may cause developmental deformities or worst, mortality. The chorion has been reported as a major barrier to prevent nanomaterial uptake by fish embryos . In thisIn this review paper, we hereby summarize that research of graphene and GO toxicity specifically on aquatic organisms is relatively limited. The research on graphene-based nanomaterials toxicity has started taking place progressively in the last decade. Thus, a comprehensive understanding of interaction of graphene and GO with environment, aquatic organisms, and other living systems in vitro and in vivo is essential for their safe usage and further development. The large part of available current literature indicates that graphene-based nanomaterials are cytotoxic. Although the particular mechanism for their toxicity has not yet been established, ROS elevation, lipid peroxidation, nutrient/oxygen depletion, and inflammation have been most widely recognized mechanisms for graphene-based nanomaterials toxicity in aquatic organisms.The applications and uses of graphene and GO are rising evidently in fields of biomedical sciences, supercapacitors, sensors, and construction materials. The release of waste material from these industries can prove to be harmful for environment, aquatic organisms, and humans. Graphene-based nanomaterials interact with natural organic material (NOM), aggregates, adsorbs, and colloids, which in turn can cause toxicity to aquatic organisms through many different body mechanisms. Furthermore, the physiochemical properties of graphene and GO such as particle size, surface functional groups, and oxygen content/surface charges may affect the toxicity upon interaction with aquatic organisms. The data we accumulated demonstrated a lot of information gaps that does not allow establishing a concrete statement regarding the toxicity criteria guidelines. It is also difficult to compare the toxicological effects of graphene and GO between different studies due to diversity in size, shape, surface modification, synthetization techniques, and model organisms. It is, hence, important to understand the toxicity caused by graphene nanomaterials for aquatic organisms in order to facilitate the practical applications of these promising new graphene-based nanomaterials.


A lesser-acknowledged role of Propionibacterium acnes is its effect on the development of sarcoidosis. This literature review not only further explores this association but also that of Propionibacterium acnes and other inflammatory conditions, such as ulcerative colitis and pyoderma gangrenosum, acne, ulcerative colitis syndrome (PAC syndrome). This article reviews the effect that isotretinoin, a commonly used treatment of acne, has on the pathogenesis of ulcerative colitis, and the immune dysregulation and genetic susceptibility of individuals prone to developing acne, sarcoidosis, and ulcerative colitis.Literature for this article review was obtained from PubMed by utilizing both regular keywords and medical subject heading (MeSH) subheadings for data gathering. Regular keywords were: Propionibacterium acnes, sarcoidosis, ulcerative colitis, and isotretinoin. MeSH subheadings used were: Propionibacterium acnes/immunology, Propionibacterium acnes/pathogenicity, Propionibacterium acnes/genetics, sarcoidosis/immunology, and sarcoidosis/genetics.Following the application of inclusion and exclusion criteria, a total of 5172 publications were obtained. A total of 5086 publications were removed due to a lack of relevancy to outcomes of interest. The remaining 86 publications from all the regular and MeSH keywords were selected due to relevancy to outcomes of interest. Following this, a refined manual search was done, with the removal of duplicates, and 33 publications from PubMed were selected for review.Following a review of these records, Propionibacterium acnes was repeatedly concluded to be a causative agent of sarcoidosis. Variable results for the association between Propionibacterium acnes and ulcerative colitis were found. Most studies showed no significant association between the use of isotretinoin and the development of ulcerative colitis. A strong overlapping role of genetic susceptibility and immune dysregulation in the pathogeneses of sarcoidosis, ulcerative colitis, and Propionibacterium acnes was found. Propionibacterium acnes (P. acnes) is a gram-positive bacterium, found ubiquitously as a commensal on the surface of the skin, the bowel, the conjunctival surface, the oral mucosa, and even the external ear canal. Perhaps the most well-known disease association with P. acnes is its role in the development of acne. This bacterium thrives in an anaerobic environment and has a predilection for the pilosebaceous unit of the skin, leading to epidermal inflammation and scarring, as seen in Figure Sarcoidosis is a systemic granulomatous inflammatory condition characterized by widespread noncaseating granulomas, which are most frequently formed in the skin, eyes, lymphatic system, and the lungs. Depending on the ethnicity of the population, the annual incidence of sarcoidosis varies significantly; the highest incidence is seen among African Americans , followed by Caucasians , and the lowest incidence is reported in the Asian and Hispanic populations  [Possible triggers of sarcoidosis include infectious agents, organic particles, and inorganic environmental factors, as shown in Figure Like sarcoidosis, ulcerative colitis (UC) is also a multi-system condition, although it mainly involves the colon and rectum. As shown in Figure In addition, a particularly interesting association that has been repeatedly hypothesized in current literature is that the use of isotretinoin in the treatment of P. acnes is associated with an increased incidence of ulcerative colitis. If significant, this association could make it necessary to avoid isotretinoin use in patients prone to developing ulcerative colitis and its associated autoimmune conditions, such as primary sclerosing cholangitis .The types of acne implicated in the development of sarcoidosis and ulcerative colitis will also be reviewed in this article. More specifically, repeated inflammation of the apocrine glands, also known as hidradenitis suppurativa (HS), or ‘acne inversa’ has also been associated with systemic inflammatory syndromes ,7. All tBoth these conditions share quite a few similarities in their pathogenicity; they are both the result of cellular immune dysregulation ,9. This MethodLiterature for this article review was obtained from PubMed by utilizing both regular keywords and medical subject heading (MeSH) subheadings for data gathering. Table Inclusion CriteriaAll records published in the last 10 years, in the English language, which had the availability of the abstract, free full texts, and full text, were included. All records consisting of the following article types were included: case reports, classical article, clinical conference, clinical study, clinical trial, clinical trial protocol, controlled clinical trial, journal article, meta-analysis, multicenter study, newspaper article, observational study, randomized controlled trial, review, and systematic review. The species included humans and other animals. The journal category included was MEDLINE.Exclusion CriteriaAll records published more than 10 years ago or not in the English language were excluded. All records consisting of the following article types were excluded: address, autobiography, bibliography, biography, books and documents, clinical trial-phase I, clinical trial-phase II, clinical trial-phase III, clinical trial-phase IV, clinical trial-veterinary, comment, comparative study, congress, consensus development conference, consensus development conference, NIH, corrected and republished article, dataset, dictionary, directory, duplicate publication, editorial, electronic supplementary materials, English abstract, evaluation study, government publication, guideline, historical article, interactive tutorial, interview, introductory journal article, lecture, legal case, legislation, letter, and news. The journal categories excluded were dental journals and nursing journals.ResultsTable For both the regular and MeSH keywords, following the application of inclusion/exclusion criteria in PubMed, a total of 5172 publications were obtained. A total of 5086 publications were removed due to lack of relevancy to outcomes of interest: association of P. acnes with sarcoidosis, association of isotretinoin use (P. acnes treatment) with ulcerative colitis, and association of sarcoidosis with ulcerative colitis. The remaining 86 publications from all the regular and MeSH keywords were selected due to relevancy to outcomes of interest. Following this, a refined manual search was done, with the removal of duplicates, and 33 publications from PubMed were selected for review as follows: twelve case-control studies, five article reviews, three observational studies, four animal studies, three case studies, two cohort studies, two case reports, and two human studies. All the articles reviewed are available for reference. A more in-depth review was performed for the available publications after inclusion/exclusion to include the relevant topic of interest and its significant associations. Figure DiscussionThe Role of Genetics and the Immune System in the Development of P. acnes InfectionMany factors contribute to the development of P. acnes infection, and it is evident that the interaction between P. acnes and host immunity plays a significant role in this. The ubiquitous nature of P. acnes was previously thought to be due to the overproduction of the organism in all areas with high sebum production. However, more recent studies, through genomic sequencing of the P. acnes organism, have shown that specific individuals may be more predisposed to developing P. acnes infection. The genes most commonly involved in the pathogenesis of P. acnes are those that code for components of the innate immune system, such as TLRs, interleukins (ILs), and other inflammatory signaling pathways in the host.P. acnes aggravates acne by promoting the synthesis of lipids, the formation of comedones, and by inducing and precipitating inflammation in the host's skin. The inflammatory action of P. acnes occurs through the activation of TLR-2 and TLR-4 on keratinocytes, which in turn activates the mitogen-activated protein kinase (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B cell (NF-kB) pathways of inflammation. NF-kB is a transcriptional factor that is responsible for the regulation of gene expression in the inflammatory cascade. This demonstrates the ability of P. acnes to selectively activate certain innate immunity genes . These iCommonly thought to be found only in patients suffering from acne vulgaris, P. acnes can also be found in healthy subjects who are not suffering from acne. Genomic studies of P. acnes have revealed that varying strains are associated with different degrees of acne. Strains RT4/5 are more strongly associated with acne, while strains RT2/6 are associated with healthy human skin. Specific pathogenic factors encoded in the acne-inducing strains were identified in genomic studies of P. acnes. In a murine model of acne, done by inoculating P. acnes with a synthetically produced human sebum, very little loss of viability was observed after one week (indicating intracellular persistence of P. acnes). The acne-associated P. acnes strains (RT4/5), compared with the health-associated P. acnes strains (RT2/6), induced significantly higher levels of IL-8, IL-1α, IL-1β, and IL-6 in vitro and in vivo . This stP. acnes can induce particular genetic expression at the cellular level, such as increased expression of the genes coding for caspase-1 and inflammasomes in monocytes, subsequently causing the release of IL-1β from these cells. Through this mechanism, P. acnes triggers mononuclear cells to release IL-6, IL-1β, and transforming growth factor-β (TGF-β) and stimulates the differentiation of CD4+ T lymphocytes into helper T cells 1 and 17 (Th1 and Th17) cells. These derived cells are responsible for the upregulation of IL-17 and that of interferon-gamma .In an observational study done to better understand the body’s adaptive immune responses to P. acnes, it was shown that infiltrating immune cells consisted mostly of CD4+ T cells in the area surrounding the follicles affected by P. acnes. By studying specific CD4+ T cells in vitro, the results of this study showed that P. acnes induces a mixed helper T cell (Th17/Th1) response by inducing the secretion of IL-17A and interferon-gamma from these cells .Interferon-gamma is a cytokine best known for its role in the activation of macrophages and the synthesis and maintenance of granulomas, which are the pathognomic findings of sarcoidosis. In a human study of a macrophage cell line, the intracellular persistence of P. acnes was demonstrated. The P. acnes-containing phagosome did not fuse with lysosomes, preventing the formation of the phagolysosome, and therefore allowing P. acnes to persist intracellularly . This meHow the Innate Immune System Plays a Role in the Pathogenesis of Sarcoidosis and Ulcerative ColitisThe development of sarcoidosis can be attributed to several factors involved in the innate immune system. In order to demonstrate this, an animal study was conducted where mice were injected with a viable strain of P. acnes isolated from a patient with sarcoidosis. The mice deficient in the innate immunity adapter proteins MyD88 and cytochrome B-245 beta chain (CybB) had larger and more granulomas compared to the wild-type mice injected with P. acnes. Typically, in response to P. acnes administration in wild-type mice, proinflammatory markers are synthesized by the body, and neutrophils are transported into the lung, a response that is dependent on MyD88 and CybB . In the A case-control study was done to determine possible genetic and functional differences in TLR-9 between patients with sarcoidosis and healthy controls. To assess any genetic differences in these groups, the promoter region of the TLR-9 gene was sequenced. However, no genetic differences were found between the patients and controls. Additionally, in assessing the functional aspect of TLR-9, patients with sarcoidosis produced significantly less interferon-gamma upon stimulation with different stimuli. IL-23 and IL-6 productions were also measured. A significant difference between the case-control groups was not found here either, except when stimulated by a TLR-9 agonist, which increased IL-23 production. The study concluded that the decreased production of interferon-gamma could reflect the anergic state seen in the peripheral blood T lymphocytes of patients with sarcoidosis, and also concluded that the ability of TLR-9 to increase the production of IL-23 could indicate that functional defects in the immune pathway of TLR-9 could increase the susceptibility to sarcoidosis .Moreover, reiterating these results about TLR-9, a randomized controlled trial was done to test the ability of TLRs to act as drug targets for immunomodulation in ulcerative colitis. The medication, DIMS0150 (a TLR-9 agonist), was given to patients, and the study compared a control group with a placebo. Significantly (p=0.0073) higher mucosal healing and histological improvement were seen in the TLR-9 agonist group after four weeks [In another study involving TLRs, their role in the development of sarcoidosis was studied. Bronchoalveolar (BAL) lavage cells from patients with sarcoidosis and healthy controls were stimulated with ligands taken from TLR-2 and TLR-4. Results were measured based on the production of tumor necrosis factor-α and IL-6. Patients with sarcoidosis showed a significantly higher cytokine response than the controls . A subseLet us consider the case report of a 30-year-old patient with ulcerative colitis, who was in remission and on maintenance Infliximab therapy. He was admitted with symptoms of dyspnea, nocturnal sweating and, nonproductive cough. Following further investigations, he was found to have drug-induced stage II pulmonary sarcoidosis. This report demonstrates the importance of monitoring patients under biological therapy using agents such as anti-tumor necrosis factor-α. Monitoring such patients can identify paradoxical adverse effects of inflammation, such as the development of sarcoidosis .In addition to its role in the pathogenesis of sarcoidosis, the innate immune system also can be implicated in other inflammatory conditions, such as ulcerative colitis. One case-control study investigated whether immune-mediated diseases are more frequent in patients with inflammatory bowel disease (IBD). Results showed a significantly (p<0.05) greater percentage of comorbidity in the IBD groups than the controls. Odds ratios were significantly increased (p<0.00125) for primary sclerosing cholangitis, celiac disease, type 1 diabetes, sarcoidosis, asthma, iridocyclitis, psoriasis, pyoderma gangrenosum, rheumatoid arthritis, temporal arteritis, and atrophic gastritis .In an animal study conducted to study the goblet cell dysfunction that underlies the pathology of ulcerative colitis, the role of the immune system in the pathogenesis of ulcerative colitis is exemplified. The mucosal barrier of the intestine is responsible for mediating the commensal bacteria in the gut. This mucosa is maintained by the goblet cells, which synthesize the protective mucus layer. When this layer is impaired, ulcerative colitis ensues. IL-18 is the main factor that can cause the barrier integrity in a model of colitis to be broken down. In fact, when the IL-18 or its receptor in the intestinal epithelial cells were deleted in mice, this resulted in the lack of ulcerative colitis development and a lack of mucosal damage .The Role of P. acnes in the Development of SarcoidosisIn assessing the role of P. acnes in the development of sarcoidosis, a case-control study was done. This study aimed to detect P. acnes-derived immune complexes in sarcoid lesions. Lymph node samples from patients with sarcoidosis and a P. acnes-specific monoclonal antibody were used to react with the bacterium P. acnes. Results showed that insoluble immune complexes (IICs)-forming P. acnes were present in 89% of the sarcoid samples, and only 20% of the control samples with lymphadenitis. In addition, no insoluble immune complexes were detected in control samples without lymphadenitis. Results also showed a high number of P. acnes-derived IICs in macrophages in sarcoid lymph nodes [In another case-control study done to assess the link between P. acnes and sarcoidosis, the ability of P. acnes to induce granuloma formation in the lungs of patients was assessed. When stimulated with heat-killed P. acnes, the production of tumor necrosis factor-α and GM-CSF by BAL cells were measured. The BAL cells of patients with sarcoidosis induced significantly higher levels of the inflammatory cytokines when stimulated by P. acnes, as compared to the controls . This fuAn interesting case study, further supporting this association, showed that patients developed sarcoidosis six months following the use of etanercept (a tumor necrosis factor-inhibitor) for the treatment of rheumatoid arthritis. Here, immunohistochemistry revealed P. acnes in the noncaseating granulomas. This shows that even when Sarcoidosis is drug-induced, the primary pathogenic agent is commonly P. acnes .Myocardial tissue from patients with known cardiac sarcoidosis, myocarditis, and other cardiomyopathies was obtained for an observational study. All three types of samples were formalin-fixed paraffin-embedded using immunohistochemistry with a P. acnes-specific monoclonal antibody. Results showed that P. acnes showed significantly high positive reactivity in the cardiac sarcoidosis group, with massive inflammation. In contrast, no reactivity was noted in the myocarditis and cardiomyopathy samples . This reA recent case-control study examined bacterial lymph node biopsy samples using 16SrRNA gene sequencing in patients with sarcoidosis to test the strength of association between P. acnes and sarcoidosis. P. acnes 16SrRNA was solely detected in all the samples of the sarcoidosis groups, and none was detected in the controls or tuberculosis (TB) groups. The quantitative amount of P. acnes bacterium found was also significantly (p=0.0010) higher than that amount found in tuberculosis samples . These rIn one case-control study, the idea that P. acnes occurs more commonly in genetically susceptible individuals, and therefore causes sarcoidosis in these patients, was explored. Currently, the most common causative agents thought to cause sarcoidosis are both P. acnes and mycobacterium. However, on actual bacterial culture, only P. acnes is detected in the sarcoid lesions. In this case-control study, the P. acnes antibody was formalin-fixed and paraffin-embedded with both sarcoidosis and control samples. The immunohistochemistry showed that 74% of the lung samples reacted with the sarcoid samples. The antibody did not react with non-sarcoid granulomas or any of the 45 tuberculosis samples, strongly implicating P. acnes as the causative organism for the formation of granulomas in sarcoidosis .Specific strains of Propionibacterium are implicated in sarcoidosis. In a previous study, complete genomic sequencing of a particular C1 strain of P. acnes was done, and this strain was the primary bacterial isolate from the granulomas of sarcoidosis cases. In a more recent observational study done, the genetic makeup of this C1 strain was further evaluated. The analysis showed that the C1 strain was phylogenetically unique and found primarily in the sarcoid isolate, identified by its unique 18.8-kilobase pairs (kbp) transposon sequence. Specific sequence types (STs) were identified, namely ST26 isolates, which carry the transposon insertion [Some studies have gone a step further by evaluating the diagnostic value of using P. acnes rRNA as a biomarker for sarcoidosis. This potential biomarker was studied in a case-control study by using reverse-PCR to measure the amount of rRNA of P. acnes present in sarcoidosis and control cases. P. acnes rRNA was detected in 48 of the 65 sarcoidosis samples, but only four of the 45 tuberculosis samples and only three of the 50 controls. The number of copies determined as a cut-off from this study was 50.5 copies per milliliter. This study suggests the diagnostic ability to quantify P. acnes rRNA for distinguishing between sarcoidosis and tuberculosis .The Role of P. acnes in the Development of Ulcerative ColitisAccording to several existing studies, there is a recognized association between P. acnes and the gastrointestinal tract. It has been long hypothesized that the commensal bacteria in the gut could be causative in the pathogenesis of P. acnes infection. For example, when an individual is depressed or has anxiety, there has been evidence of exacerbation of acne due to the subsequent gut microbiome alteration and increased skin inflammation. There indeed is evidence of a gastrointestinal-dermal axis that interlinks the intestinal microbiota, oral commensal bacteria, and diet to acne. It has been suggested that the mechanism that allows the gut microbiome to influence skin homeostasis comes from its altering effects on innate immunity .One pathway suggested to influence acne is the mechanistic target of rapamycin (mTOR) pathway when interacted with by intestinal flora. This pathway controls the intestinal barrier, and in the case of a disturbance of this barrier, a positive feedback loop that stimulates proinflammatory cytokines can be formed. As discussed earlier, this disturbance of the intestinal mucosal barrier by the organism P. acnes in the gut is the same mechanism by which ulcerative colitis can develop. Probiotics have been shown to directly inhibit P. acnes through their antimicrobial proteins .In a cohort study done to evaluate the effect of isotretinoin on the development of ulcerative colitis, participants who were recently treated with isotretinoin or topical acne medications were studied. The result was no significant association between isotretinoin use and the development of IBD. However, in an additional prespecified secondary analysis, isotretinoin was associated with IBD in patients aged 12-19 years, and topical acne medications were also found to be associated with IBD. Since the primary study did not find a significant association in either group, but there was an association in prespecified secondary analyses, it was suggested that there is a possible association between IBD and P. acnes itself . SimilarDoes Isotretinoin Use, for the Management of Acne, Increase the Risk of Developing Ulcerative Colitis?Isotretinoin is a form of vitamin A commonly used to manage cases of severe acne vulgaris, such as nodulocystic acne. It has been hypothesized that this medication can trigger IBD, namely ulcerative colitis. A human study was conducted to review the effect of isotretinoin on the immune system. This study hypothesized that isotretinoin could cause acne to subside by normalizing the innate immune response to the commensal P. acnes. The blood monocytes of these patients with acne showed significantly high quantities of TLR-2 expression when stimulated by P. acnes. However, when treated with isotretinoin, this TLR-2 expression was significantly suppressed, and this effect lasted even six months following the therapy . This deThe possible association between isotretinoin use and the development of ulcerative colitis was first documented in 1986 when a young woman developed proctitis during isotretinoin use. She reported relief of her bowel symptoms after withholding the isotretinoin medication. Since that time, several case-control and cohort studies have been done to study the possibility of this etiological link further. A case-control study done with a population of women using oral contraceptives concluded no association between the vitamin A analogue and ulcerative colitis  [Although the causal link is not proven to date, some studies do suggest some relationship between isotretinoin use and ulcerative colitis. A case-control study was done by following a population of IBD cases, all exposed to isotretinoin for a one-year duration. In this study, results were different from those of the cases discussed above. Ulcerative colitis was strongly associated with previous isotretinoin exposure . No association was found between the medication use and Crohn’s disease, or in the controls group. This study concluded that this association between ulcerative colitis and isotretinoin is dose-dependent, and the higher the dose, the more the risk. The absolute risk for developing ulcerative colitis following isotretinoin use is small. However, it is useful for clinicians to know this possible correlation when prescribing isotretinoin .The Role of Genetic Susceptibility in Developing Hidradenitis Suppurativa With the Auto-Inflammatory PAC SyndromeHidradenitis suppurativa (HS), also known as ‘acne inversa’, is often associated with other auto-inflammatory conditions that can become severe if left undiagnosed or untreated. Hidradenitis suppurativa is caused by a dysfunction of the innate immune system, with abnormal IL-1 signaling that leads to repetitive inflammation by neutrophils at affected sites. This same abnormal pathway is shared with the other auto-inflammatory conditions such as acne, pyoderma gangrenosum, psoriatic arthritis, and ulcerative colitis . When pyA case study was done to evaluate the genetic susceptibility of patients who develop pyoderma gangrenosum, acne, and ulcerative colitis (PAC) syndrome. It is known that the gene PSTPIP1 is involved in immune regulation, and possibly the increased susceptibility to developing PAC syndrome. Considering this, a 33-year-old man with chronic ulcerative colitis, severe acne, and multiple non-healing ulcers in the lower limbs (PAC syndrome) was studied. The PSTPIP1 gene was sequenced and studied for any abnormalities. A heterozygous mutation was found that damaged the function of the resulting encoded protein, affecting the IL-1-signaling pathway. Following this, the human IL-1 antagonist anakinra was used to treat this patient, and his condition improved greatly. This study concluded that there is a commonality in the pathogenesis of pyoderma gangrenosum, acne, and ulcerative colitis, due to this mutation . These PAn observational study evaluated a possible association between hidradenitis suppurativa and IBD. The prevalence and risk of IBD in patients with hidradenitis suppurativa compared to the general population were studied. It was concluded that the risk of both new-onset Crohn’s disease and ulcerative colitis was significantly increased in patients with hidradenitis suppurativa. However, the actual prevalence was still low . These rAlthough sarcoidosis has a multifactorial etiology, P. acnes has repeatedly been shown as a causative agent of sarcoidosis in several well-designed, reproducible studies. The link between P. acnes and ulcerative colitis, on the other hand, requires far more research because an association is suspected, but clinical studies have shown variable results. In addition, most studies showed no significant association between the use of isotretinoin and the development of ulcerative colitis. Based on the several studies reviewed, it can be established that there is indeed an overlapping role of genetic susceptibility and immune dysregulation in the pathogeneses of sarcoidosis, ulcerative colitis, and P. acnes. However, many of these results are obtained from animal studies, and further exploration in the form of human studies is required. This will help clinicians determine novel ways to direct their management of these conditions in the future by targeting these specific genetic and immune vulnerabilities.