Protective effect of D-alpha-tocopherol on the function of human mesangial cells exposed to high glucose concentrations

Altered functions of mesangial cells (MCs) induced by high glucose levels are thought to play an important role in the pathogenesis of diabetic nephropathy. We investigate whether D-alpha-tocopherol (Toc), an antioxidant, can prevent malfunction of cultured human MCs induced by high-glucose media. Incubating MCs with 33 mmol/L glucose caused increased lipid peroxide (LPO) levels, disturbed cell replication, enhanced cytotoxicity, enhanced activity of the diacylglycerol (DAG)-protein kinase C (PKC) pathway, and overproduction of fibronectin and eicosanoids (6-keto prostaglandin F1 alpha [PGF1 alpha] and thromboxane B2 [TXB2]). The amount of LPO in MCs grown in 5 mmol/L glucose was reduced by the addition of Toc in a dose-dependent manner. Since the maximum effect of Toc on decreasing LPO was achieved at a concentration of 100 mumol/L, this dose was selected for the following experiments. Addition of Toc prevented increased LPO levels and [51Cr]-release from MCs induced by high-glucose media without affecting cell number. Toc decreased the total DAG level and PKC activity in membrane fractions in MCs cultured at both 5 and 33 mmol/L glucose. Furthermore, glucose-induced overproduction of fibronectin and eicosanoids from MCs was completely abolished by Toc. These results strongly suggest that Toc ameliorates glucose-induced malfunctions of MCs in vitro.