Effects of vitamin E administration on platelet function in diabetes mellitus.

A decrease in the vitamin E content of human diabetic platelets is closely associated with the accelerated platelet aggregation and platelet prostaglandin metabolism seen in patients with diabetes mellitus. We investigated the effect of vitamin E supplementation on these abnormalities of physiological function and prostaglandin metabolism in 14 non-insulin dependent diabetics with proliferative retinopathy. ADP-induced platelet aggregation was inhibited in vitro by the addition of vitamin E in a dose-dependent manner. However, in lower concentrations considered to be physiological doses in vivo, significantly greater inhibition was observed in diabetic platelets than in the control platelets. Next, alpha-tocopheryl nicotinate was administered to diabetics at a daily dose of 600 mg. The platelet vitamin E content was restored to control levels in 13 of the 14 patients after 2-4 weeks of daily administration. The ADP-induced platelet aggregation rate, platelet thromboxane B2 (TXB2, a stable metabolite of TXA2, a vasoconstrictor production, and plasma TXB2 level were low in all 14 diabetics. In contrast, plasma 6-keto-PGF 1 alpha (a stable metabolite of PGI2, a vasodilator) was significantly increased and therefore the 6-keto-PGF 1 alpha/TXB2 ratio in plasma was restored to within normal limits. These results indicate that vitamin E may improve platelet function and prostaglandin metabolism in diabetes mellitus and may be able to provide further beneficial effects in relation to the development of diabetic vascular complications.