Antioxidative effects of azelnidipine on mesangial cell proliferation induced by highly concentrated insulin

Insulin resistance combined with hyperinsulinemia is involved in the generation of oxidative stress. There is known to be a relationship between increased production of reactive oxygen species and the diverse pathogenic mechanisms involved in diabetic vascular complications including nephropathy. The present study found that high doses of insulin affect mesangial cell proliferation through the generation of intracellular reactive oxygen species and the activation of cell signaling pathways. We also examined whether azelnidipine, a dihydropyridine-based calcium antagonist with established antioxidant activity, has the potential to inhibit mesangial cell proliferation. Cell proliferation was increased in a dose-dependent manner by high doses of insulin (0.1-10 mu M), but was inhibited by 0.1 mu M azelnidipine. Phosphorylation of extracellular signal-regulated kinase (ERK)-1/2 was found to be increased by insulin in a dose-dependent manner (0.1-10 mu M). This increased phosphorylation of ERK- 1/2 was inhibited by treatment with 0.1 mu M azelnidipine. Intracellular oxidative stress was also increased by insulin stimulation in a dose-dependent manner (0.01-10 mu M), and 0.1 mu M azelnidipine was found to block intracellular reactive oxygen species production more effectively than 0.1 mu M nifedipine. The NAD(P)H oxidase inhibitor, apocynin (0.01-0.1 mu M), prevented insulin-induced mesangial cell proliferation. Taken together, these results suggest that azelnidipine inhibits insulin-induced mesangial cell proliferation by inhibiting the production of reactive oxygen species. Given these pharmacological characteristics, azelnidipine may have the potential to protect against the onset of diabetic nephropathy and slow its progression. (C) 2007 Elsevier B.V. All rights reserved.