Interaction between osmotic and oxidative stress in diabetic precataractous lens - Studies with a sorbitol dehydrogenase inhibitor

Both sorbitol accumulation-linked osmotic stress and "pseudohypoxia" [incre ase in NADH/ NAD(+), similar to that in hypoxic tissues, and attributed to increased sorbitol dehydrogenase (1-iditol:NAD(+) 5-oxidoreductase; EC 1.1. 1.14; SDH) activity] have been invoked among the mechanisms underlying oxid ative injury in target tissues for diabetic complications. We used the spec ific SDH inhibitor SDI-157 [2-methyl-4(4-N,N-dimethylaminosulfonyl-1-pipera zino)pyrimidine] to evaluate the rule of osmotic stress versus "pseudohypox ia" in oxidative stress occurring in diabetic precataractous lens. Control and diabetic rats were treated with or without SDI-157 (100 mg/kg/day for 3 weeks). Lens malondialdehyde (MDA) plus 4-hydroxyalkenals (4-HA), MDA, GSH , and ascorbate levels, as well as the GSSG/GSH ratios, were similar in SDI -treated and untreated control rats, thus indicating that. SDI-157 was not a prooxidant. Intralenticular osmotic stress, manifested by sorbitol levels , was more severe in SDI-treated diabetic rats (38.2 +/- 6.8 vs 21.2 +/- 3. 5 mu mol/g in untreated diabetic and 0.758 +/- 0.222 mu mol/g in control ra ts, P < 0.01 for both), while the decrease in the free cytosolic NAD(+)/NAD H ratio was partially prevented (120 +/- 16 vs 88 +/- 11 in untreated diabe tic rats and 143 +/- 13 in controls, P < 0.01 for both). GSH and ascorbate levels were decreased, while MDA plus 4-HA and MDA levels were increased in diabetic rats versus controls; both antioxidant depletion and lipid aldehy de accumulation were exacerbated by SDI treatment. Superoxide dismutase (su peroxide:superoxide oxidoreductase; EC 1.15.1.1), GSSG reductase (NAD[P]H:o xidized-glutathione oxidoreductase; EC 1.6.4.2), GSH transferase (glutathio ne S-transferase; EC 2.5.1.18), GSH peroxidase (glutathione:hydrogen-peroxi de oxidoreductase; EC 1.11.1.9), and cytoplasmic NADH oxidase activities we re increased in diabetic rats versus controls, and all the enzymes but GSH peroxidase were up-regulated further by SDI. In conclusion, sorbitol accumu lation and osmotic stress generated oxidative stress in diabetic lens, wher eas the contribution of "pseudohypoxia" was minor. SDIs provide a valuable tool for exploring mechanisms of oxidative injury in sites of diabetic comp lications. (C) 1999 Elsevier Science Inc.