The Role Of Renin Angiotensin System Activation In Chronic Cyclosporine A Nephropathy

Objective and Background Cyclosplorine A (CsA) remains one of the most important immunosuppressive drugs in the management of organ transplantation and autoimmune diseases. Chronic nephrotoxicity is the main side effect of cyclosporine A(CsA). It is characterized by chronic structural changes, which are manifested by increased extracellular matrix, tubular atrophy and arteriolopathy with hyalinization. The mechanisms of this disease have not been fully elucidated. Recently, a reproducible animal model of chronic CsA nephropathy was established on the observation that sodium depletion exacerbates CsA renal injury in rats. In this model, the renin angiotensin system (RAS) is activated. The elargement ofjuxtaglomerular apparatus (JGA) was found in the specimen from patients who received GsA for a long time. All this indicate that RAS activation is involved in chronic CsA nephrotoxicity. The present study was performed to explore the role of RAS activation in the CsA-induced tubulointerstitial fibrosis and the effects of blocking renin angiotensin system. Mater i 81 and Methods Adult male SD rats weighting 225 to250 g received low salt diet(O.05% sodium) with water ad libitum. After seven days, they were randomly divided into five groups: Vehicle (n7), CsA treated (n=7), CsA+Verapamil (lOmg kg? (n7), CsA+Enalapril (lOmg kg ?(n7) and CsA+Losartan (10mg kg? (n=7).Vehicle rats received a sc injection of olive oil daily, the other rats received CsA (15mg kg? by sc injection of CsA for 28 days. Plasma and renal renin activity were measured by radioimmunoassay. The expression of Angiotensin II type 1 receptor (AT1R) ,TGF 13 1 , biglycan, proliferating cell nuclear antigen (PCNA), Fas antigen and hepatocyte growth factor (HGF)in renal tissue were examined by Northern blot and/or by immunohistochemical staining. The apoptotic cells were identified by the TUNEL assay. The mRNA expression of HGF was additionally detected by in situ hybridization. During the experiment, tail systolic blood pressure was measured with a pleth~smograph(Shanghai Hypertension Institute). Urinary and plasma creatinine were measured by a Hitachi autoanalyzer. Urinary osmolality was measured by freezing point (Model3MQ,USA). N- acetyl- f3 -D-glucosaminidase (NAG) was measured by colorimetric analysis. Renal tissue samples were fixed in 10% buffered formalin and embedded in paraffin. Four micrometer-thick sections were stained with periodic acid- Schiff and trichrome. Semiquantitative score was used to assess the extent of tubulointerstitial and tubular atrophy in each category. A minimum of 20 fields at a magnification 200 X were assessed and graded in each biopsy specimen by an observer masked to treatment groups. Results 1 .CsA treated rats had a significant decreased GFR compared with VH (P<0.0 1). This change was not ameliorated by the use of Enalapril or Losartan. 2.GsA induced an impairment of urinary concentrating ability. Uosm was decreased significantly in CsA treated rats compared to that in VH group (P<0.05). It was not prevented by the use of Enalapril or Losartan. GsA treated rats had a significant increased NAG excretion compard to that in VH group (P<0.0 5). NAG enzymuria was reduced significantly by the administration of Verapamifl Enalapril or Losartan to GsA treated rats. 3 .Tubulointerstitial fibrosis score and tubule atrophy score were significantly elevated compared with to that in VH group (P<0.001 in all). These changes were reduced significantly in E...