A Comprehensive Review on the Medicinal Plants from the Genus Asphodelus

Plant-based systems continue to play an essential role in healthcare, and their use by different cultures has been extensively documented. Asphodelus L. (Asphodelaceae) is a genus of 18 species and of a total of 27 species, sub-species and varieties, distributed along the Mediterranean basin, and has been traditionally used for treating several diseases particularly associated with inflammatory and infectious skin disorders. The present study aimed to provide a general review of the available literature on ethnomedical, phytochemical, and biological data related to the genus Asphodelus as a potential source of new compounds with biological activity. Considering phytochemical studies, 1,8-dihydroxyanthracene derivatives, flavonoids, phenolic acids and triterpenoids were the main classes of compounds identified in roots, leaf and seeds which were correlated with their biological activities as anti-microbial, anti-fungal, anti-parasitic, cytotoxic, anti-inflammatory or antioxidant agents.


Introduction
The genus Asphodelus Linnaeus belongs to family Asphodelaceae Jussieu and is native to temperate Europe, the Mediterranean, Africa, the Middle East, and the Indian Subcontinent, and now naturalized in other places (New Zealand, Australia, Mexico, southwestern United States, etc.) [1]. It reaches its maximum diversity in the West of the Mediterranean, particularly in the Iberian Peninsula and in North-West Africa [2].
The family consists of three subfamilies: Asphodeloideae Burnett (including 13 genera), Hemerocallidoideae Lindley (including 19 genera) and Xanthorrhoeoideae M.W. Chase (with only one genus). This botanical family, now called Asphodelaceae, has had a complex history; its circumscription and placement in an order have varied widely. In the Cronquist system of 1981, members of the Asphodelaceae were placed in the order Liliales Perleb [3,4]. Cronquist had difficulty classifying the less obviously delineated lilioid monocots; consequently, he placed taxa from both the modern orders Asparagales Link and Liliales into a single family, Liliaceae Jussieu [5]. The decision to group three formerly separate families, Asphodelaceae, Hemerocallidaceae and Xanthorrhoeaceae, into a single family first occurred in 2003 as an option in the II Angiosperm Phylogeny Group (APG) classification for the orders and families of flowering plants. The name used for the broader family was then Xanthorrhoeaceae Dumortier [6], and the earlier references to this family were related only to subfamily Xanthorrhoeoideae. These changes were a consequence of improvements in molecular and morphological analysis and also a reflection of the increased emphasis on placing families within an appropriate order [5,7,8]. Later in Table 1 summarizes the ethnomedicinal data about the Asphodelus species including specific information on the plant parts as well as the geographical region where the plant is used. In Table 2 the principal chemical studies and identified compounds of the genus are presented. Tables 3 and 4 summarize the principals of in vitro and in vivo biological activity assays on the total extracts and isolated compounds.

Phytochemical Studies
Phytochemical studies as shown in Table 2, revealed the presence of different groups of compounds namely anthraquinones (either in the free or in the glycoside form), phenolic acids, flavonoids, and triterpenoids from A. acaulis, A. albus, A. aestivus, A. cerasiferus, A. fistulosus, A. microcarpus, A. ramosus, and A. tenuifolius.

Reported Biological Activities
In vitro and in vivo biological studies concerning Asphodelus extracts are presented in Table 3 and those reported from identified pure compounds are shown in Table 4. In some of the studies, no data were obtained concerning the tested doses and/or inhibitory values.
The ethanol and aqueous extracts of A. aestivus leaf showed moderate anti-fungal activity against Aspergillus niger [33], and whole plant ethanol extracts exhibited weak activity against Staphylococcus aureus with minimum inhibitory concentration (MIC) = 42 mg/mL) and Klebsiella pneumoniae (MIC = 60 mg/mL) [67]. Both leaf and root extracts showed strong antioxidant activity [15,68]. The root extract also showed significant anti-inflammatory properties, specifically anti-ulcer activity which is one of the documented uses in Turkish traditional medicine [32]. Root and leaf extracts showed antitumoral activity against human cancer cells (lung and prostate) through DNA damage [68,69].
Root extracts of A. ramosus showed positive in vivo anti-inflammatory activity, confirming the traditional uses of the plant in inflammatory disorders [23].
The whole plant extract showed in vivo hypotensive and diuretic activity in normotensive rats [74]. The root extract of this species showed anti-oxidant activity (DPPH test, IC 50 = 2.006 µg/mL) [25] and asphorodin, a compound isolated from the whole plant extract, exhibit a potent inhibition of lipoxygenase enzyme, (IC 50 = 18.1 µM) [26], which may have an important role as an anti-inflammatory agent. The biological properties of A. tenuifolius extracts prove their ethnomedical use mostly as anti-inflammatory or diuretic [24][25][26][27][28]30,31,34]. In vitro anti-fungal activity (A. niger)-Agar well diffusion method (zone of inhibition in cm −1 ) Ethanol extract (0.25 and 0.5 mg/mL) showed higher activity than aqueous extract (0.25 and 0.5 mg/mL) and similar activity for concentrations of 1 mg/mL. Both extracts were less active than Fluconazole (100 µ/mL) [33] In vitro antioxidant activity-β-carotene bleaching effect, metal chelating, total antioxidant activity, DPPH, ABTS, superoxide radical scavenging activity, hydroxyl radical scavenging activity, DMPD, nitric oxide scavenging activity Aqueous extract presented higher activity in metal chelating and radical scavenging assays (DPPH, IC 50 aqueous = 4.58 mg/mL and IC 50 methanol = 9.54 mg/mL, superoxide, hydroxyl, DMPD) Ethanol extract presented higher activity in β-carotene bleaching effect and total antioxidant activity Aqueous and ethanolic extracts presented similar radical scavenging activity in ABTS and NO assays. Both extracts presented significantly inferior results when compared to reference substances A. aestivus L Acetone, Methanol In vitro antioxidant activity-β-carotene, reducing power assay, DPPH, ABTS, inhibition of linoleic acid peroxidation, superoxide radical scavenging assays Reducing power and total antioxidant activity were higher in acetone extract; free radical and superoxide radical scavenging activity were higher in methanol extract (DPPH, IC 50 methanol = 0.16 mg/mL and IC 50 acetone = 0.50 mg/mL) Acetone extract presented higher activity in Reducing power and total antioxidant activity (inhibition of linoleic acid peroxidation) Methanol extract presented higher activity in superoxide radical scavenging and free radical scavenging activity (β-carotene, ABTS and DPPH, IC 50 methanol =0.16 mg/mL, IC 50acetone = 0.50 mg/mL) [15] A. aestivus L, R Dichloromethane n-Hexane In vitro cytotoxic activity-MTT assay against human lung cell cancer (A549) and prostate cell cancer (PC3)   All extracts showed antimicrobial activity, the methylene-chloride as the most active against S. aureus (MIC = 1.6 mg/mL), E. faecalis (MIC = 1.0 mg/mL), E. coli (MIC = 1.8 mg/mL) and P. aeruginosa (MIC = 0.15 mg/mL) All extracts showed antifungal activity against C. albicans, C. parapsilosis, C. glabrata, C. krusei. [30] A. tenuifolius

Materials and Methods
Ethnobotanical data was collected by our team in Portugal and relevant literature was reviewed until December 2017, by probing scientific databases (PubMed, Scopus, Google Scholar, b-on, Web of knowledge) and other web sources such as records from WCSP, IUCN, APG and the Missouri Botanical Garden database. Various keywords were used during the bibliographic research including: ASPHODELUS SPECIES; TRADITIONAL USES; ETHNOMEDICINAL EVIDENCE; BIOLOGICAL ACTIVITIES; ISOLATED MOLECULES; PHYTOCHEMISTRY. Information was gathered and summarized in table form where appropriate.

Conclusions
In conclusion, among the 18 species of the genus Asphodelus, only 30 percent of the species namely A. aestivus, A. fistulosus, A. microcarpus, A. ramosus, and A. tenuifolius have been documented for their traditional uses. In phytochemical studies 50 percent of the species (A. acaulis, A. aestivus, A. albus, A. cerasifer, A. fistulosus, A. macrocarpus, A. microcarpus, A. ramosus, A. tenuifolius) have been evaluated for their constituents however there is no documented data related to traditional uses of A. acaulis, A. albus and A. cerasiferus.
All the species with ethnomedical documented data were submitted to biological activity tests, showing a total or partial correlation with their traditional use as anti-microbial, anti-fungal, anti-parasitic, cytotoxic, anti-inflammatory, or antioxidant agents.
Root tubers plant part were mainly reported to have anthraquinone derivatives, triterpenoids, and naphthalene derivatives, while aerial parts mostly exhibited the presence of flavonoids, phenolic acids, and few anthraquinones.
Considering the previous phytochemical studies, 1,8 dihydroxyanthracene derivatives (e.g., aloe-emodin and chrysophanol) were the most common reported anthraquinones of A. aestivus, A. luteus and A. microcarpus extracts which could be responsible for the reported antimicrobial/fungal activities [78,80]. Aloe-emodin as a potent cytotoxic compound might be related to the reported anti-tumoral activity of A. aestivus [68,78].
Flavonoids namely luteolin and apigenin derivatives were frequently reported from the aerial parts of all studied Aphodelus species, which according to their known antioxidant and anti-inflammatory properties [81,82], could be correlated to their traditional uses in inflammatory diseases in agreement with the reported biological studies. Phenolic acids, namely caffeic acid and chlorogenic acid reported from aerial parts and root tubers might be responsible for the general antioxidant activity presented in the biological studies.
The present study allowed the importance and potential of the genus Asphodelus as a source of new compounds to be ascertained, with biological activity and new herbal products based on Asphodelus genus used in traditional medicine being ascertained, as well as its quality, mode of action, and safety of use. It should be pointed out that, to the best of our knowledge, the latter aspect (the safety of Asphodelus species) has not yet been the object of in-depth studies.