Experimental Study Of Protective Effects Of α-Lipoic Acid On Kidneys Of Diabetic Rats

Backgroud:Diabetic nephropathy is one of the common chronic complications of diabetes mellitus. Increasing number of diabetic nephropathy has gone along with the rising incidence of diabetes mellitus year by year. But the exact pathogenesis of diabetic nephropathy is not fully elucidated, and brings some difficulties for the treatment. The recent researches founded that oxidative stress and its mediated apoptosis in kidneys participated the development of diabetic nephropathy. Hence, it will be a new way to look for a drug against oxidative damage which can reduce cell apoptosis and delay the aggravation of kidney functions in diabetic mellitus.Objective: To explore the role of oxidative stress and its mediated apotosis in the pathogenesis of diabetic nephropathy , and elucidate the protecting effects of a-lipoic acid on kidneys.Methods: Diabetic model was induced by intraperitoneal injection of streptozotocin (STZ), and the diabetic rats were randomly divided into two groups: untreated-diabetic group(DM group) and a-lipoic acid treated group (LA group), and the normal rats were served as a normal control group (NC group). Blood glucose(BG),Blood Urea Nitrogen (BUN),Serum Creatinine (Scr) and urinary albumin excrection rate (UAER)were detected 12 weeks later. The removed kidneys were used for detecting the levels of malondialdehyde (MDA) and the activities of antioxidant enzymes in renal cortex , including superoxide dismutase (SOD),catalase(CAT) and glutathione peroxidase (GSH-Px). Histomorp-hologic changes were observed by optics microscope and electron microscope, respectively. Apoptotic cells in kidneys were identified by terminal-deoxynucleotidyl transferase mediated d-UTP nick end labeling (TUNEL). The expression of apoptosis-associated gene caspase-3 was detected by immunohistochemistry.Results:1. Compared with the NC group, BG,BUN,Scr and UAER were significantly increased in DM group (P<0.01); BUN,Scr and UAER were decreased in LA group compared with the DM group (P<0.01 or P<0.05); no statistic differences of BG were founded between DM group and LA group.2.Compared with the NC group, the levels of MDA were significantly increased (P<0.01)in renal cortex of DM group, it was decreased in LA group compared with the DM group(P<0.01).The activities of SOD and CAT were significantly reduced (P<0.01), the activity of GSH-Px was significantly increased in DM group(P<0.01) ; the activities of the above antioxidant enzymes were all increased in LA group compared with the DM group(P<0.01 or P<0.05 ).3. The number of apoptotic cells in glomeruli and tubules was significantly increased (P<0.01), and the expression of caspase-3 in tubules was upregulated in DM group (P<0.01); above indices were improved in LA group compared with the DM group (P<0.01) .4. Glomerular hypertrophy,mesangial cell proliferation,extracellular matrix accumulation were observed by optics microscope in DM group. The result of electron microscope showed that podocytes were tumefied,foot processes were fusioned into a band and adhered to the basement membrane in DM group. Above abnormal histomorphologic changes were significantly improved in LA group.5. Urinary albumin excrection rate was positively correlated with MDA,GSH-Px,cell apoptosis rate in kidney cortex and the semiquantitative expression of caspase-3,respectly (r=0.735, P<0.01; r=0.689, P<0.01; r=0.866, P<0.01; r=0.785, P<0.01) , and negatively correlated with the activities of SOD and CAT (r=-0.723,P<0.01; r=-0.540, P<0.05) . MDA was positively correlated with cell apoptosis rate in kidney cortex and the semiquantitative expression of caspase-3, respectly (r=0.841,P<0.01; r=0.889, P<0.01) .Conclusion:Diabetes mellitus can cause high level of oxidative stress and excessive apoptosis in kidneys ,caspase-3 was involved in the regulation of apoptosis. The above mechanisms participated the deveploment of diabetic nephropathy together .a-Lipoic acid can improve renal function, decrease proteinuria, alleviate renal histopathological damage and play the role of protecting diabetic kidneys by eliminating free radicals,inhibiting oxidative stress and interfering in apoptosis by downregulating the expression of caspase-3, and this role is independent of its hypoglycemic effects.