β-Carotene affects antioxidant status in non-insulin-dependent diabetes mellitus

Oxidative injury by reactive oxygen species (ROS) has been suggested to explain excess prevalence of vascular complications in diabetes mellitus. ROS are normally trapped by antioxidants such as β-carotene, vitamins C and E and glutathione. The consumption of reducing equivalents in the form of NADPH may interfere with the regeneration of glutathione and ascorbic acid in diabetes mellitus. We have compared 20 patients with non-insulin-dependent diabetes mellitus (NIDDM) with no vascular complications to age and sex matched healthy control subjects, and later treated them with natural (Dunaliella) β-carotene, 60 mg daily for 3 weeks. Compared with control patients there was a significant decrease in plasma glutathione by 50% (P<0.01) and in erythrocyte glutathione peroxidase by 30% (P<0.01) in the patients with NIDDM. Upon β-carotene treatment there was a 3.3-fold increase in plasma β-carotene as measured by high-performance liquid chromatography (HPLC; from 0.296±0.072 to 0.968±0.133 μg/ml, P<0.001). Plasma glutathione increased by 77%, erythrocyte glutathione increased by 39% (P<0.05) and glutathione peroxidase increased by 21% (P<0.01). Thus, basal plasma glutathione, erythrocyte glutathione and erythrocyte glutathione peroxidase levels are higher in age matched healthy controls than in NIDDM patients. Natural β-carotene affects the glutathione and part of its redox cycle enzymes by potential augmentation of its regeneration. Restoring antioxidant status may slow the rate of development of vascular complications in diabetes mellitus.