Insulin and heparin suppress superoxide production in diabetic rat glomeruli stimulated with low-density lipoprotein

Patients with diabetic nephropathy frequently show increased levels of circulating low-density lipoprotein (LDL) and oxidized LDL, which have been reported to be related to the generation of oxygen-free radicals. In the present study, we evaluated the effects of insulin and heparin on the superoxide production of glomeruli, which were isolated from rats with streptozotocin-induced diabetes for one week, one month, and three months, respectively, and the glomeruli were stimulated with native and oxidized LDL. LDL was isolated from normal subjects with normolipidemia, and the superoxide was measured by using a spectrophotometer. The results demonstrated that the poorly controlled diabetic rat glomeruli showed a significantly higher production of superoxide than normal glomeruli under basal status and after stimulation, and this production increased further with the progression of diabetes. Insulin suppressed both the basal and stimulated production of superoxide in diabetic glomeruli, but not in normal glomeruli. Heparin suppressed superoxide production of diabetic glomeruli stimulated by either native or oxidized LDL, and it also partly suppressed superoxide production of normal glomeruli stimulated by oxidized LDL. Our results suggest that glomeruli injury in diabetics with hyperlipidemia may be mediated through enhanced generation of oxygen-free radicals, which can be partially attenuated by insulin and heparin.