It has been previously shown that 2-hydroxyestradiol (2-OHE) attenuates the development of renal disease in genetic nephropathy associated with obesity and the metabolic syndrome. The purpose of this study was to test the hypothesis that 2-OHE, irrespective of its effects on metabolic status and/or obesity, exerts direct renoprotective effects in vivo. First, the effects of increasing doses of 2-OHE on mesangial cell growth, proliferation, and collagen synthesis in isolated rat glomerular

mesangial cells were evaluated in vitro. Second, the effects of 12-wk administration of 2-OHE (10 µg/h per kg) on renal function and structure in chronic puromycin aminonucleoside (PAN)–induced nephropathy in rats were evaluated in vivo. 2-OHE concentration-dependently (0.001 to 1 µmol/L; P<0.001) inhibited serum (2.5%)–induced cell growth (3H-thymidine incorporation), collagen synthesis (3H-proline incorporation), and cell proliferation (cell number). Importantly, the inhibitory effects of 2-OHE (0.1 µmol/L) were not blocked by ICI182780 (50 µmol/L), an estrogen receptor antagonist. In vivo, chronic administration of PAN (75 mg/kg + 5 × 20 mg/kg) over 12 wk induced severe chronic renal disease. Chronic treatment with 2-OHE significantly (P<0.05) attenuated PAN-induced decrease in glomerular filtration, reduced proteinuria, and the elevated BP, and it had no effect on PAN-induced increase in plasma cholesterol and triglycerides levels. 2-OHE had no effects on plasma testosterone levels in male nephropathic animals. Immunohistochemical staining for collagen IV and proliferating cell nuclear antigen (PCNA) in glomeruli and transforming growth factor–β (TGF-β) in renal tubular cells were significantly higher in PAN nephropatic rats versus control animals with intact kidneys. PAN also markedly increased glomerular and interstitial macrophage infiltration (ED1+ cells). 2-OHE had no effects on renal tubular cell TGF-β, but it significantly reduced glomerular PCNA and collagen IV and glomerular and interstitial macrophage infiltration. In summary, this study provides the first evidence that 2-OHE exerts direct renoprotective effects in vivo. These effects are mediated by estrogen receptor-independent mechanisms and are due, at least in part, to the inhibition of some of the key proliferative mechanisms involved in glomerular remodeling and sclerosis.