Long-term effects of vitamin C supplementation on glomerular changes in streptozotocin-induced diabetic rats

Background. Deficiency of vitamin C (L-ascorbic acid; AA) may induce renal glomular dysfunction in diabetes. Few data are available for the role of continuous supplementation of AA on glomerular dysfunction and pathology induced during diabetes. Objective: To investigate long-term effects of AA supplementation on glomerular changes in streptozotocin (STZ)-induced diabetic rats. Methods: Diabetes was induced in Sprague-Dawley rats (180-220 g) by injection of STZ (55 mg/kg bw, iv). The rats were divided into controls (CON), AA-supplemented controls (CON-AA), diabetic. (STZ) and AA-supplemented diabetic rats (STZ-AA). AA (1 g/L) was continuously supplemented to the rats for 4, 8, 16 and 24 weeks. The glomerular filtration rate (GFR), effective renal plasma flow (ERPF), renal vascular resistance (RVR) malondialdehyde (MDA) and transforming growth factor-beta 1 (TGF-beta 1) levels were measured in the renal cortex. Glomerular morphology was examined histologically. Renal hypertrophic index was calculated using kidney-to-body weight ratio (KW/BW). Results: Decreases in GFR and ERPF were ameliorated at week 16 and deteriorated at week 24 after AA supplementation in STZ-AA rats. High blood glucose concentration was attenuated only at week 16. MAD and TGF-beta 1 levels in renal cortex decreased significantly in STZ-AA rats at week 16 but not at week 24. The number of abnormal glomeruli and KW/BW decreased significantly at week 16 in STZ-AA rats. Conclusion: Long-term supplementation of AA may ameliorate the glomerular changes induced by diabetes.