Oxidant stress is increased within the glomerulus in experimental diabetic nephropathy

The mechanisms by which the metabolic consequences of hyperglycaemia induce diabetic renal injury remain ill-defined. We hypothesized that oxidant stress, a consequence of hyperglycaemia, is increased in glomeruli from Lewis rats with streptozotocin (STZ)-induced diabetes prior to major structural and functional glomerular damage. After 12 weeks of diabetes, Lewis rats had not developed proteinuria and their glomeruli appeared normal by light microscopy. However, kidneys of diabetic animals had higher levels of lipid peroxides and malondialdehyde (MDA) than control rats. Immunohistochemistry demonstrated MDA-lysine adducts in glomeruli of diabetic rats, and that lipid peroxides and MDA were increased in glomerular lysates of diabetic rats. A possible mechanism for this finding was suggested by the observation that freshly isolated whole glomeruli from STZ rats showed a greater capacity than glomeruli from control rats to produce H2O2. Activity of the inducible form of superoxide dismutase (SOD) Mn-SOD was increased in glomerular lysates from STZ rats, consistent with its induction by oxidant stress. Immunostaining for Cu,Zn SOD showed increased protein in glomeruli, although compared with the increase in Mn-SOD activity, Cu,Zn-SOD activity was not substantially increased, potentially as a result of partial inactivation of this enzyme by glycation. The increased oxidant stress in untreated diabetic rats was a consequence of hyperglycaemia and not due to a direct nephrotoxic effect of STZ, as at least some of these changes were attenuated by insulin treatment of diabetic animals. Collectively, these results demonstrate that experimental diabetes mellitus is accompanied by increased oxidant stress within glomeruli.