Attenuation of Renal Injury in db/db Mice Overexpressing Superoxide Dismutase

Attenuation of Renal Injury in db / db Mice Overexpressing Superoxide Dismutase Evidence for Reduced Superoxide−Nitric Oxide Interaction Frederick R. DeRubertis , Patricia A. Craven , Mona F. Melhem and Eman M. Salah From the Departments of Medicine and Pathology, Veterans Affairs Pittsburgh Healthcare System and University of Pittsburgh, School of Medicine, Pittsburgh, Pennsylvania Address correspondence and reprint requests to Frederick R. DeRubertis, MD, VA Pittsburgh Healthcare System, University Drive C, Pittsburgh, PA 15240. E-mail: frederick.derubertis{at}med.va.gov Abstract The effects of overexpression of Cu 2+ /Zn 2+ superoxide dismutase-1 (SOD-1) on indexes of renal injury were compared in 5-month-old nontransgenic (NTg) db/db mice and db/db mice hemizygous for the human SOD-1 transgene (SOD-Tg). Both diabetic groups exhibited similar hyperglycemia and weight gain. However, in NTg- db/db mice, albuminuria, glomerular accumulation of immunoreactive transforming growth factor-β, collagen α1(IV), nitrotyrosine, and mesangial matrix were all significantly increased compared with either nondiabetic mice or SOD-Tg- db/db . SOD-1 activity and reduced glutathione levels were higher, whereas malondialdehyde content was lower, in the renal cortex of SOD-Tg- db/db compared with NTg- db/db mice, consistent with a renal antioxidant effect in the transgenic mice. Inulin clearance (C IN ) and urinary excretion of guanosine 3′,5′-cyclic monophosphate (U cGMP ) were increased in SOD-Tg- db/db mice compared with corresponding values in nondiabetic mice or NTg- db/db mice. C IN and U cGMP were suppressed by N ω-nitro- l -arginine methyl ester in SOD-Tg- db/db but not in NTg- db/db mice, implying nitric oxide (NO) dependence of these increases and enhanced renal NO bioactivity in SOD-Tg- db/db . Studies of NO-responsive cGMP in isolated glomeruli supported greater quenching of NO in glomeruli from NTg- db/db compared with SOD-Tg- db/db mice. Evidence of increased NO responsiveness and the suppression of glomerular nitrotyrosine may both reflect reduced NO-superoxide interaction in SOD-Tg- db/db mice. The results implicate superoxide in the pathogenesis of diabetic nephropathy. AGE, advanced glycation product CCh, carbamylcholine CIN, inulin clearance cGMP, guanosine 3′,5′-cyclic monophosphate eNOS, endothelial nitric oxide synthase FCAlb, fractional clearance of albumin GPx, glutathione peroxidase GSH, reduced glutathione IL-2, interleukin-2 l-NAME, Nω-nitro-l-argi