Insulin decreases circulating vitamin E levels in humans (original) (raw)

1996, Metabolism-clinical and Experimental

Both hyperinsulinemia and free oxygen radicals have been implicated in the pathogenesis of atherosclerosis, but the relationshi p between insulin levels or insulin action and the oxidant/antioxidant balance has not been explored. We measured the effect of physiologic hyperinsulinemia on plasma concentrations of vitamin E, a major free radical scavenger molecule. Isoglycemic clamps (at an insulin infusion rate of 6 pmol • min -1 • kg -1) were performed in fou r groups of subjects: (1) 12 nOn-insulin-dependent diabetic (NIDDM) patients, (2) eight patients with essential hypertension, (3) 11 nondiabetic obese individuals, and (4) 12 healthy subjects. In 10 healthy volunteers, a time-control experiment was performed by replacing the insulin infusion with normal saline. Vitamin E and plasma lipid levels were determined at baseline and after 2 hours of insulin/saline infusion. Insulin sensitivity was reduced in diabetic, obese, and hypertensive groups in comparison to healthy controls, but fasting plasma vitamin E concentrations were similar in all groups. A consistent decrement in plasma vitamin E concentrations (averaging 12% of baseline, p < .000!' ) was observed in all subjects receiving insulin regardless of the level of insulin sensitivity, whereas no significan t changes in plasma vitamin E were Seen in subjects receiving saline infusion (P < .001 v insulin infusion groups). The insulin-induced decrement persisted in all study groups when plasma vitamin E concentrations were corrected for total serum cholesterol levels (-8.9% _+ 1.2% v -0.4 +_ 2.3% of saline controls, P = ,0004) or serum low-density lipoProtein (LDL (-10.0% -+ 1,2% v -0,4% -+ 2.2%, P = .0002}. We conclude that insulin infusion acutely depletes vitamin E in circulating iipids regardless of insulin resistance. This effect may represent a physiologic means of transferring vitamin E into cell membranes, alternatively, it might reflect a pro-oxidant action of insulin in vivo.