Protective role of enalapril for chronic tubulointerstitial lesions of hyperoxaluria

Purpose: Hyperoxaluria is a recognized cause of tubulointerstitial lesions and it may contribute to chronic renal failure. In previous studies we demonstrated that enalapril was effective against the progression of tubulointerstitial lesions in a 4-week hyperoxaluria rat model. We evaluated whether the action of enalapril on the tubulointerstitial lesions produced by hyperoxaluria persisted for a long period. Materials and Methods: Two-month-old male Sprague-Dawley rats were divided into 4 groups of 12 each, including 1-control animals given tap water, 2-animals with hyperoxaluria, 3-animals with hyperoxaluria plus enalapril, 4-animals with enalapril. Hyperoxaluria in groups 2 and 3 rats was induced by administering 1% ethylene glycol, a precursor for oxalates, in the tap water continuously throughout the whole study. Meanwhile, groups 3 and 4 received 20 mg./l. enalapril in the drinking water. At the end of the study renal tubulointerstitial lesions were evaluated by immunostaining using monoclonal antibodies against macrophage infiltrates (ED1), tubulointerstitial alpha -smooth muscle actin and transforming growth factor-beta1. The lesions were quantified by semiquantitative scores. Creatinine clearance and urinary albumin excretion were also determined. Results: There was no difference in urine oxalate excretion in groups 2 and 3. Group 3 rats treated with enalapril showed fewer tubulointerstitial lesions than nontreated group 2 rats, as indicated by the mean scores plus or minus standard error of mean for inflammatory infiltrate (2.16 +/- 0.2 versus 0.83 +/- 0.16), tubular atrophy (2 +/- 0.27 versus 0.66 +/- 0.14), interstitial fibrosis (2.5 +/- 0.15 versus 0.5 +/- 0.1), glomerular ED1 (1.75 +/- 0.25 versus 0.16 +/- 0.11), interstitial ED1 (2.33 +/- 0.18 versus 0.58 +/-: 0.10) tubular transforming growth factor-beta1 (2.09 +/-. 0.08 versus 0.91 +/- 0.14), interstitial transforming growth factor-beta1 (2.33 +/- 0.22 versus 0.66 +/- 0.12), tubulointerstitial alpha -smooth muscle actin (2.91 +/- 0.22 versus 0.83 +/- 0.16), lower urinary albumin excretion (35.5 +/- 2.7 mg. daily versus 10.9 +/- 1) and higher creatinine clearance (2.29 +/- 0.04 ml. per minute versus 2.54 +/- 0.03, all p <0.05). Conclusions: Based on our results we believe that enalapril would provide a beneficial effect against chronic tubulointerstitial lesions caused by oxalates.