Effects of antioxidants on postprandial oxidative stress and endothelial dysfunction in subjects with impaired glucose tolerance and type 2 diabetes

Abstract

Aim: To compare changes in the oxidation-reduction balance and endothelial function before and after meal in patients with type 2 diabetes or impaired glucose tolerance and determine the effects of standard antioxidant supplementation.

Methods: Forty diabetics and 40 subjects with impaired glucose tolerance were compared with a control group. We assessed before and after a test meal (homogenized milkshake containing 80 g of saturated fat, amounting to 1,480 kcal), some reactive oxygen species, inflammation markers and flow-mediated vascular dilatation. These parameters were then reassessed after standard antioxidant treatment.

Results: After the meal, diabetics, subjects with impaired glucose tolerance and controls had higher levels of oxidant compounds compared to fasting levels. In subjects with diabetes and impaired glucose tolerance (IGT), Vascular Adhesion Molecule-1 and CRP were higher after the meal--diabetic subjects exhibited lower fasting flow-mediated dilatation, which deteriorated significantly after the meal. Antioxidant administration significantly improved the parameters investigated in all subjects.

Conclusions: In diabetic subjects, altered glycaemia and lipaemia are closely correlated with markers of systemic oxidative stress. Our results show that the abnormal changes in oxidative-reductive balance parameters are paralleled by similar changes in markers of endothelial dysfunction and inflammation at 4 h after ingestion of a fatty meal. Supplementation with a pool of antioxidants can reduce oxidative stress and inflammation in healthy subjects and, more importantly, in IGT patients. This previous aspect suggests that the timing of antioxidant supplementation has an important role in endothelium protection in healthy and pre-diabetic subjects, and along with prompt antioxidant treatment before irreversible endothelial damage has occurred, may have an important protective role in subjects with IGT-patients who require administration of adequate dietary antioxidants.