cardiovascular disease is one of the major causes of morbidity and mortality worldwide , especially among patients of chronic kidney disease ( ckd ) [ 1 , 2 ] . there is an increasing evidence of cardiometabolic syndrome ( cms ) involvement in ckd [ 3 , 4 ] , but a causal relationship has not been proven . cardiometabolic syndrome is a cluster of metabolic abnormalities combining obesity with 2 - 3 risk factors which include insulin resistance , hypertension , and high triglyceride or low high density lipoprotein ( hdl ) serum levels . it also increases the risk of cardiovascular disease ( cvd ) and type 2 diabetes . it is believed that atherosclerotic changes in blood vessels in chronic renal diseases contribute significantly to the high cardiovascular morbidity and mortality . morphological and functional abnormalities of the endothelium are considered as prodromal stage of atherosclerosis and early marker of cvd   that facilitate the progress of atherosclerosis [ 7 , 8 ] and contribute to the development of hypertension through the enhancement of vascular resistance . on the other hand , there is a strong evidence supporting the view that atherosclerosis is a disease characterized by low - level vascular inflammation [ 911 ] . inflammation , inflammatory action of local stimuli such as products of the oxidation process and glycation end products , oxidative stress , and degradation of extracellular matrix ( ecm ) change vasculature in terms of development of atherosclerosis . renal disease is associated with a graded increase in oxidative stress ( os ) markers even in early ckd . some studies have documented that peritoneal dialysis is associated with decreased levels of oxidative stress and inflammatory markers compared to haemodialysis . a small number of trials have been carried in order to determine associations between oxidative stress with vascular structure and function with equivocal results [ 14 , 15 ] . on the other hand , uncontrolled expression of matrix metalloproteinases ( mmps ) , enzymes that degrade extracellular matrix ( ecm ) , can result in tissue damage and the development of a number of destructive diseases such as arthritis , atherosclerotic plaque rupture , aortic aneurysm , and progression of tumors [ 16 , 17 ] . however , the relevance of malondialdehyde as a marker of oxidative stress which is generated by peroxidation of unsaturated fats as well as the role of matrix metalloproteinase-9 in atherosclerosis progression in patients ( pts ) with chronic kidney disease ( ckd ) not yet on dialysis compared to patients on peritoneal dialysis is less known , particularly with respect to cardiometabolic syndrome . the aim of this paper was to examine whether the serum concentration of malondialdehyde and matrix metalloproteinase-9 is involved in the process of atherosclerosis in patients with ckd not yet dialysis - dependent and those on peritoneal dialysis ( pd ) with signs of cms . this cross - section study was conducted at the clinic for nephrology , clinical center university in sarajevo , from june 2014 through december 2014 . fifty - two adult patients with cms and chronic kidney disease were included in the study . the subjects were divided into ckd patients not yet dialysis - dependent ( 30  pts ; egfr < 60 > 15  ml / min/1.73  m ) and patients on peritoneal dialysis for > 6 months ( 22  pts ) . all pd patients underwent 4 to 5 dialysis changes with 2 liters of dialysis solution . subjects who had an episode of peritonitis within the previous 3 months and patients with evidence of malignancy , autoimmune disease or chronic liver disease , active infection , history of cardiovascular or peripheral vascular disease , and diabetes and recent treatment with iron were excluded from the study . depending on the degree of severity of atherosclerotic changes in the carotid arteries all observed group patients were divided into three subgroups ( without atherosclerosis ( as0 ) , moderate atherosclerosis ( as1/2 ) , and severe atherosclerosis ( as3 ) ) . estimated glomerular filtration rate was performed using the mdrd ( abbreviated modification of diet in renal disease equation gfr ) . body mass index ( bmi ) was calculated as the ratio of body weight in kilograms and the square of height in meters ( bmi = kg / m ) . body weight for bmi in pd patients is measured with dry abdomen ( without dialysate solution ) . the blood pressure ( bp ) was measured with mercury sphygmomanometer after 15 minutes of rest , according to recommendation by the british hypertension society . hypertension was defined as systolic bp 140  mmhg and diastolic bp 90  mmhg or use of antihypertensive medications . informed consent was obtained from all participants and the local ethics committee approved the study . the concentration of malondialdehyde ( mda ) was analyzed at the center for cytogenetics and molecular medicine at the medical faculty in sarajevo using a competitive enzyme immunoassay test ( elisa ) , which was performed with commercial kit for the assessment of the overall level of mda ( manufacturer : uscn life science inc . , us - cea597ge ) . reading of the results is carried out at 450  nm on a plate reader stat fax 2100 , usa . the measurement concentration of mad was expressed in nanograms per milliliter ( ng / ml ) . the concentration of the enzyme matrix metalloproteinase-9 ( mmp-9 ) in serum was quantified by elisa at the clinic for immunology university clinical centre sarajevo , according to manufacturer 's instructions ( r&d systems , inc . reading of the results is carried out by spectrophotometry at 450  nm ( reader biotek elx50 ) , with the correction wavelength at 540  nm or 570  nm . the measurement concentration of mmp-9 was expressed in nanograms per milliliter ( ng / ml ) . the severity of carotid artery atherosclerosis was evaluated using the mean common carotid artery ( ca ) , intima media thickness ( imt ) , and plaque score ( ps ) . high - resolution b mode and color doppler and pulse doppler ultrasonography of both carotid arteries were performed with an ultrasound scanner ( wall - track system : w - t , maastricht , the netherlands ) equipped with a 7.5-mhz linear array transducer . measurement was done by the same angiologist who was not familiar with the clinical status of the study patients . after the carotid arteries were located by transverse scans , the probe was rotated 90 to obtain and record a longitudinal image of the anterior and posterior walls . the high - resolution images of the walls of the bilateral ca , internal carotid arteries ( ica ) , and carotid bulbs were examined according to recommendations of the american society of echocardiography carotid intima media thickness task force . the imt was defined as the distance between the leading edge of the lumen - intima echo and the leading edge of the media - adventitia echo in plaque - free area . at least three measurements ( a , b , and c ) were taken over one centimeter length of each wall segment ca , and these measurements on both sides were collected and divided to obtain the mean imt . the ps was calculated by adding the maximal thickness in millimeters of plaques in each segment on both sides ( a + b + c + thickness of the contralateral carotid artery plaques ) . the presence of atherosclerosis in cca is estimated as recommended by the mannheim consensus about atherosclerosis : ( 1 ) without atherosclerosis ( as0 ) : imt less than 80% of the reference interval ( ri ) , age- and gender - adjusted , with ri values obtained from previously published studies of monitoring , using the same ultrasound procedures;(2 ) mild atherosclerosis ( as1 ) : imt > 80% of the ri;(3 ) moderate atherosclerosis ( as2 ) : the presence of carotid plaque , with no significant stenosis ( psv < 125  cm / s);(4 ) severe atherosclerosis ( as3 ) : the presence of carotid plaque with threatening stenosis ( psv > 125  cm / s ) . without atherosclerosis ( as0 ) : imt less than 80% of the reference interval ( ri ) , age- and gender - adjusted , with ri values obtained from previously published studies of monitoring , using the same ultrasound procedures ; mild atherosclerosis ( as1 ) : imt > 80% of the ri ; moderate atherosclerosis ( as2 ) : the presence of carotid plaque , with no significant stenosis ( psv < 125  cm / s ) ; severe atherosclerosis ( as3 ) : the presence of carotid plaque with threatening stenosis ( psv > 125  cm / s ) . all data were expressed as the mean  sd or as median and interquartile range . the distribution of variables was tested by the kolmogorov - smirnov and/or shapiro - wilk test . student 's t - test was used to compare the means of variable with normal distribution . the difference in median with interquartile range between two groups was analyzed by the mann - whitney test . pearson 's test was used to correlate data with normal distribution and spearman 's test for data with a skewed distribution . a multiple regression analysis was applied to define the independent connection serum concentration of mda and mmp-9 with ultrasound parameters of ca . the significant independent variables were determined according to their standardized effect , defined as regression coefficient / standard error of the regression (  ) . all statistical calculations were performed with the spss 16 software ( version 16.0 , spss inc . , the average age of respondents was 59.84  5.16 years and was not different from the age of the control group . there was also no difference in age and smoking in cms patients with ckd without the need for dialysis treatment and those on peritoneal dialysis . all monitored ckd and pd patients were overweight , while bmi of control group patients was within the limits that are considered healthy ( between 20.1 and 24.5 ) . in our study , all observed ckd patients , dependent or not dependent on dialysis treatment , were hypertensive ( bp 140/90  mm hg ) , but significantly higher values of both systolic and diastolic blood pressure were registered in the group of patients on pd treatment compared to other ckd patients . although there were no significant intergroup differences in serum triglyceride levels , all groups of patients had an elevated level of serum triglycerides ( above the recommended value of 1.7 basal characteristics of the anthropometric profile , blood pressure values , metabolic pattern , and serum concentration of mda and mmp-9 in the whole group of ckd and pd subjects with cms and in two subgroups of ckd with and without dialysis ( pd ) are presented in table 1 . depending on the stages of atherosclerosis our data showed significant changes in serum concentration of mda and mmp-9 between the different subgroups of ckd nondialysis - dependent patients , as well as in patients on peritoneal dialysis ( table 2 ) . the level of serum mda through all the stages of atherosclerosis was significantly lower in pd patients compared to observed ckd nondialysis - dependent patients ( in as1/2 35.6 ( 28.339.1 ) versus 40.3 ( 31.945.6 )  ng / ml ; p < 0.05 and in as3 53.9 ( 49.863.2 ) versus 74.3 ( 68.276.3 )  ng / ml ; p < 0.05 ) . there were no significant differences in serum concentration of mda in the monitored pd and ckd patients without expressed atherosclerotic changes ( as0 20.6 ( 10.431.3 ) versus 24.1 ( 18.827 )  ng / ml ; p > 0.05 ) ( figure 1 ) . the level of serum concentration of mmp-9 was significantly different in pd patients compared to ckd nondialysis - dependent patients . significantly lower level of this biomarker is registered in the stage as1/2 of atherosclerosis in pd patients ( 374.8 ( 346.4397.7 )  ng / ml ) compared to the ckd patients treated conservatively ( 425.2 ( 405.5439.5 )  ng / ml ) ( p < 0.05 ) , whereas in stage as3 serum mmp-9 concentration was significantly higher in pd patients in comparison with other ckd patients ( p < 0.05 ) . such a relationship but lower concentration of mmp-9 in the serum was present in stage as0 in both groups ( figure 2 ) . significant correlation was confirmed between serum concentration of mda and imt - ca in all observed patients ( r = 0.859 ; p < 0.01 ) ( figure 3 ) , as well as between serum concentration of mda and value of plaque score ( rho = 0.869 ; p < 0.01 ) ( figure 4 ) . significant relation was also confirmed between serum concentration of mmp-9 and imt - ca ( r = 0.762 ; p < 0.01 ) ( figure 5 ) and between serum concentration of mmp-9 and value of plaque score in all observed ckd and pd patients ( r = 0.785 ; p < 0.01 ) ( figure 6 ) . in multiple regression model serum concentrations of mda and mmp-9 were significant predictors of imt - ca in all monitored ckd and pd patients ( p < 0.05 ) , as well as plaque score on carotid arteries in these populations ( p < 0.05 ) . this model is able to explain 70% of the variance in the results of imt ( r = 0.765 ) and about 79% ( r = 0.786 ) of the variation that occurs with the plaque score on carotid arteries in chronic kidney disease ( table 3 ) . the degree of intracellular and extracellular oxidative stress is related to the severity of renal failure . it was also noted that tissue damage caused by lipid peroxidation plays an important role in the developmentof various diseases including atherosclerosis , which is associated with high cardiovascular morbidity and mortality in ckd [ 23 , 24 ] . in recent years a few studies were published dealing with the status of oxidative stress in relation to various disorders that accompany chronic renal disease and renal replacement therapy [ 2529 ] . in the present paper we demonstrated that the serum concentration of mda did not statistically differ in ckd patients with cms treated conservatively and patients undergoing peritoneal dialysis . however , it was observed that serum concentration of mda progressively increases with severity of atherosclerotic changes in the carotid arteries within both groups of patients . on the other hand , we have also shown significant changes in serum concentration of mda between the different subgroups of ckd and pd patients according to the status of atherosclerotic changes in the carotid arteries . the highest levels of serum mda were in stage as3 in both groups of patients . significant correlation was confirmed between serum concentration of mda with imt - ca and plaque score in all study patients . in addition , our results indicate that the level of serum mda through all the stages of atherosclerosis was significantly lower in pd patients in comparison with observed ckd patients treated conservatively , which can be attributed to the influence of preserved residual renal function ( rrf ) and the absence of trusted signs of inflammation . since peritoneal dialysis is intrinsic type of dialysis through the peritoneum as biocompatible membrane , this result also suggests the possible influence of peritoneal dialysis on oxidative stress . a few studies reported increased os among pd patients , but other prooxidants ( tbars , tac ) were measured , associated with hypoalbuminemic state or loss of residual renal function ( rrf ) , and without comparing it with nondialysis ckd patients [ 25 , 27 , 30 ] . .   found that pd patients have markedly impaired endothelial function as documented by impaired flow mediated dilatation of brachial artery with higher serum concentration of os markers . furthermore , raju et al .   confirmed significant increase in serum mda in hemodialysis patients , compared with the same patients before they had started the hemodialysis treatment , which could be attributed to a bioincompatibility of dialysis membrane and diffusion of hydrophilic compounds to the dialysate and influx of endotoxin from the dialysate . these factors lead to activation of macrophages and production of reactive oxygen species ( ros ) and also a loss of antioxidants during hemodialysis sessions . all the above factors cause an increase in production of free radicals , peroxidation of lipids , and further rise in serum mda level after episodes of dialysis . our results suggest that oxidative stress is one of the factors that mediate the relationship between ckd , atherosclerosis , and cms . activity of mmp-9 is highly associated with the progression of ckd , diabetes , and coronary arterial disease [ 33 , 34 ] . this mmp is secreted by inflammatory cells in the adventitia or smooth muscle cells in the media . the degraded elastic fiber induces calcium deposition , which in conjunction with altered vascular structure is associated with vessel stiffening [ 35 , 36 ] . in ckd arterial stiffening increases cardiac afterload , left ventricular hypertrophy , reduces coronary artery perfusion and myocardial ischaemia , and increases pulse pressure that promotes atheroma formation and vascular remodeling . in our study , no significant difference was found in the serum concentration of mmp-9 between ckd patients treated conservatively and pd patients , but the significant increase was found in the value of this biomarker within both groups with progression of atherosclerotic process . these findings are in line with the findings of addabbo and associates , who have demonstrated that mmp-9 levels strongly correlated with carotid atherosclerosis burden irrespective of other factors in early , moderate , and advanced ckd . our data also showed the decreased serum concentrations of mmp-9 in the stage as1/2 of atherosclerosis in pd patients compared with ckd patients without dialysis treatment . however , it is our belief that the decrease in mmp-9 concentration in as1/2 stage of pd patients might occur due to the impact of peritoneal dialysis on mmp-9 serum concentration . mmp-9 was significantly higher in stage as3 in pd patients compared with ckd patients treated conservatively . to our knowledge , the impact of peritoneal dialysis on the concentration mmp-9 has not yet been clarified . some authors have demonstrated that the hemodialysis process leads to a reduction in plasma concentration of mmp-9 in some patients . a significant correlation of mmp-9 serum concentration with ca - imt and plaque score was found in all monitored patients in this study . also , in multiple regression model we confirmed a significant independent association of mda and mmp-9 with these ultrasonography parameters characterizing arterial wall and atherosclerotic changes of carotid arteries . the need for identification of risk factors and serum markers of atherosclerosis in the process of early detection and prediction of risk for cardiovascular disease has attracted a lot of attention in recent years . the significantly lower levels of mda in pd - cms patients in comparison with ckd - cms patients not yet dialysis - dependent and its increase with atherosclerosis progression , as well as obtained higher values of mmp-9 during progression of atherosclerosis especially in pd patients , could be a new contributing factor of our study . however , this study has certain limitations , such as the small number of respondents and a cross - sectional design of study . a question on the periodontal disease status of those patients was not included , although periodontal disease and kidney disease are highly associated and periodontal disease is alone associated with increases in mmp-9 . whether the longitudinal profile of mda and mmp-9 in ckd nondialysis - dependent patients and pd patients , both with signs of cms , provides additional information on the predictive power of these biomarkers for the progression of atherosclerosis remains a question for testing in future longitudinal studies with a larger number of patients . the results suggest that mda and mmp-9 could be mediators of ckd - related vascular remodeling in cms . the study data also suggest that that factors mediating relationship between cardiometabolic syndrome , chronic kidney disease , and atherosclerosis can include malondialdehyde and mmp-9 .