RESUMO
OBJECTIVE: To investigate whether ruboxistaurin (a selective PKC-ß inhibitor) mediates renoprotective effect via interference with TGF-ß1/Smad-GRAP cross-signalling. METHOD: Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (55 mg/kg). Then, the diabetic rats were treated with ruboxistaurin (10 mg/kg, p.o) for 6 weeks. Valsartan (15 mg/kg, p.o) was used as a positive control. After 6 weeks of treatment, diabetic nephropathy biomarkers were assessed. TGF-ß1, Smad2, and Smad3 mRNA and protein levels were detected using qPCR and western blot analysis. KEY FINDINGS: Data showed that serum creatinine, kidney/body weight ratio and urinary albumin excretion significantly increased in diabetic rats. These changes were significantly attenuated by treatment with ruboxistaurin. A significant up-regulation of TGF-ß1, Smad2 and Smad3 mRNA expression was observed in diabetic rats, which was alleviated by administration of ruboxistaurin. Furthermore, immunoblotting showed a significant improvement in protein levels of TGF-ß1 (P < 0.01), Smad2/3 (P < 0.01) and p-Smad3 (P < 0.001) in diabetic rats treated with ruboxistaurin compared to untreated. Importantly, the reduction in GRAP protein expression in diabetic kidney was prevented by treatment with ruboxistaurin. CONCLUSION: These data suggest that the renoprotective effect of ruboxistaurin is possibly due to down-regulation of TGF-ß1/Smad pathway and normalization of GRAP protein expression.