The Changes In Radial Aldosterone-mineralocorticoid Receptor System Activity In Patients With End Stage Renal Disease: Impact On Arterial Medial Calcification

Object i ve:Cardiovascular events due to vascular calcification remain the leading cause of mortality in the patients with end stage renal disease(ESRD) and clinical studies demonstrate that vascular calcification correlates with adverse cardiac events.A functional aldosterone(Ald)- mineralocorticoid receptor(MR) system(Ald-MR system) consists of Ald,aldosterone synthase 2(CYP11B2),MR,11β-hydroxysteroid dehydrogenase type 2(11β-HSD2).It was recently demonstrated that human vascular smooth muscle cells(VSMCs) express MR and Ald modulates expression of osteogenic genes including core-binding factorα1(Cbfα1),Osteopontin(OPN), CollagenⅠ(Col-Ⅰ) in an MR-depended pathway.These studies suggest that Ald activates the process of vascular calcification.However,the activity of Ald-MR system in human vascular tissues and its role in the pathogenesis of vascular calcification in ESRD condition are not well characterized.The purposes of this paper are to 1) examine the activity of Ald-MR system in the arteries in ESRD patients,and to 2) investigate the associations between the activity of Ald-MR system components and the extents of vascular calcification in these patients.Methods:Sixty ESRD patients underwent maintained hemodialysis and eight patients underwent splenectomy after acute trauma were collected as ESRD group and control group,respectively.The subjects in ESRD group were admitted in the General Hospital of Tianjin Medical University between January 2008 and June 2007,including 39 males and 21 females,with mean(51.5±11.7) years old.Their primary diseases included chronic glomerular nephritis,diabetic nephropathy,hypertensive nephropathy, polycystic kidney disease.Segments of radial arteries(about 0.5~1.0 cm) were obtained from all of uremic subjects in the initial operation of arteriovenous fistula prior to hemodialysis and fixed in 10%formalin.Meanwhile,fasting venous blood was collected for measurement of serum albumin,calcium,phosphate,parathyroid hormone (PTH),fasting lipid profile(total cholesterol,HDL and LDL cholesterol,and triglyceride),high sensitivity C-reactive protein(CRP).Vascular calcification was evaluated by van Kossa staining and categorized as non-calcified,mild-to-moderate calcified,and severe calcified subgroup.The expression of vascular 11β-HSD2,MR, Cbfα1,OPN,Col-Ⅰ,α-SMA were detected by immunostaining,and vascular 11β-CYP2 mRNA expression was determined by in situ hybridization assay.We evaluated the associations among MR expression,vascular calcification,and osteogenic proteins expressions.Data were analyzed by ANOVA,spearman correlation analyses,and unpaired t test,as appropriate.Differences between groups were considered significant at P<0.05.The software used for statistical analyses was the SPSS 11.5 standard version for Windows.Results:According to the results of van Kossa staining,the total calcification rate of radial artery was 31.67%in ESRD group,and the number of the patient in non-calcified,mild-to-moderate calcified,and severe calcified subgroup were 41,11,8, respectively.The pattern is medical calcification in all of the calcified arteries,and calcium deposited in medical layers and intimal elastic membranes.No vascular calcification was found in the patients in the control group.There was significant difference of the serum phosphorus concentration between the two groups(P<0.01), and statistical analysis showed a significant correlations between calcification extent and serum phosphorus,or PTH(r=0.257,0.351,P=0.026,0.003,respectively). Compared with the patients in the control group,whose arteries expressed osteogenic proteins faintly,the patients in ESRD group presented a pattern of co-expression of Cbfα1,OPN,and Col-Ⅰgenerally.These proteins expressions in the subjects from severe calcified subgroup increased significantly in contrast to the ones from the other two subgroups(P<0.01).Similarly,the arteries from the control group expressed MR and 11β-HSD2 faintly,but the arteries from ESRD group expressed these two Ald-MR system components obviously.MR presented in the paranuclear area of VSMC mainly, and its expression in severe calcified subgroup was higher than non-calcified subgroups(P<0.01).Unlike MR,11β-HSD2 presented another tendency that its expression in severe calcified subgroup was lower than mild-to-moderate calcified subgroups(P<0.05).On the contrary,artery wallα-SMA expression decreased in ESRD group than in the control group(P<0.01),although it did not change among the three subgroups obviously.Statistical analysis showed that MR expression was correlated with vascular calcification extent,OPN,Cbfα1,Col-Ⅰexpressions,and the correlation coefficients were 0.469,0.312,0.413,0.379,P<0.001,0.05,0.001,0.001, respectively.According in situ hybridization assay,all of the arteries from the two groups did not express CYP11B2 mRNA.Conclusions:(1) The expressions of Ald and 11β-HSD2 increase significantly in radial artery wall in ESRD patient.(2) The positive correlation between MR expression and vascular medial calcification in radial artery in ESRD patient suggests that the increment of Ald-MR system activity may play an important role in the pathogenesis of vascular calcification in ESRD condition,and provides a theoretical evidence for using MR antagonist in the early-stage-ESRD patients.(3) In ESRD patients,CYP11B2 mRNA does not express in radial artery,meanwhile,11β-HSD2 expression decreased markedly in severe calcified radial artery.(4) According to most of literatures,the increments of serum phosphorous and PTH concentration are considerable factors determinating the level of vascular calcification.