Preventive effect of ACE inhibitor on interstitial myofibroblast formation and matrix deposition in a nephrotic model

The nephrotic mouse (ICGN strain) is a useful model for progressive nephrotic syndrome (NS). In the present study, we demonstrated the preventive effects of enalapril, an angiotensin converting enzyme (ACE) inhibitor, on the progression of renal dysfunction and tubulo-interstitial fibrosis in the NS mice. Administration of enalapril (5 mg/dL in drinking water) to the 4-week-old NS mice for a 4-week-period did not improve their nephrotic symptoms such as albuminuria and hypoalbuminemia, but significantly suppressed the increases in blood urea nitrogen and serum creatinine levels. Renal histopathology demonstrated that the administration of the ACE inhibitor significantly attenuated the progression of the tubular and interstitial lesions (tubular dilatation, luminal cast accumulation and interstitial expansion) rather than the glomerular sclerotic changes. The suppression of the increase in blood urea nitrogen level by enalapril depended on the attenuated tubular injury rather than on the unchanged glomerular matrix deposition. Immunohistochemical examination revealed that the administration of the ACE inhibitor suppressed the formation of myofibroblasts, identified by the alpha-smooth muscle actin-positive cells, in the interstitial spaces. Consequently, interstitial matrix deposition was significantly reduced in the NS mice treated with enalapril. From the results obtained with the spontaneous nephrotic model, we emphasize a possibility that ACE inhibitor may be effective for attenuating progression of renal dysfunction and fibrosis in human NS, even if the ACE inhibitor fails to improve nephrotic symptoms such as albuminuria and hypoalbuminemia.