Nitric oxide generation ameliorates the tubulointerstitial fibrosis of obstructive nephropathy

Angiotensin-converting enzyme (ACE) inhibitors have been shown to minimize fibrosis of the kidney tubulointerstitium in several diseases. In addition to lowering angiotensin II levels, ACE inhibitors can increase kinin levels and subsequently increase nitric oxide formation. To determine whether nitric oxide generation is a component of the beneficial effect of ACE inhibitors on renal fibrosis, enalapril, enalapril plus NG-nitro-L-arginine methyl ester (L-NAME) or L-arginine was administered to rats that had undergone unilateral ureteral obstruction (UUO). Ureteral obstruction caused significant increases in interstitial volume, monocyte macrophage infiltration, interstitial collagen IV and alpha-smooth muscle actin expression, transforming growth factor-beta 1 mRNA, collagen IV mRNA, and tissue inhibitor of metalloproteinase-1 mRNA. Enalapril treatment significantly blunted the increase in all parameters during UUO. Cotreatment of the animals with enalapril and L-NAME reversed the beneficial effect of enalapril in the obstructed kidney for all parameters. Treatment of animals with UUO with L-arginine significantly blunted the increase in all parameters except for transforming growth factor-beta 1 mRNA expression. In the enalapril- plus-L-NAME-treated animals, there were modest but significant increases in monocyte/macrophage infiltration of the interstitium and glomerulus, and collagen IV and alpha-smooth muscle actin expression in the interstitium of the contralateral unobstructed kidney. The urine nitrite concentration was significantly increased by either enalapril or L-arginine treatment, whereas L-NAME significantly reduced urine nitrite concentration. These results suggest that treatment modalities that increase nitric oxide formation have a beneficial effect on the progression of cellular and molecular parameters of tubulointerstitial fibrosis caused by obstruction of the ureter.