Changes in antioxidative mechanisms in elderly patients with non-insulin-dependent diabetes mellitus. Investigation of the redox dynamics of alpha-tocopherol in erythrocyte membranes.
BACKGROUND: Recently, it has been suggested that the onset and aggravation of diabetes are closely related to free radicals. Also, vitamin E is a lipophilic free radical scavenger that is localized mainly in biomembranes. OBJECTIVE: The purpose of this study was to clarify the defensive mechanisms against oxidative stress by investigating the differences in the redox dynamics of alpha-tocopherol in plasma and erythrocyte membranes between elderly patients with non-insulin-dependent diabetes mellitus (NIDDM) and healthy elderly subjects. METHODS: Total, alpha-, beta-, gamma- and delta-tocopherol and alpha-tocopherolquinone concentrations were determined by high-performance liquid chromatography with a redox detection mode using a series of four coulometric working electrodes. RESULTS: The alpha-tocopherolquinone/alpha-tocopherol ratio in plasma and erythrocyte membranes was not different between the two groups. Both the alpha-tocopherol concentrations in erythrocyte membranes and ratio of alpha-tocopherol in erythrocyte membranes to alpha- tocopherol in plasma was significantly lower in elderly NIDDM patients than in healthy subjects. CONCLUSION: These findings suggest that alpha-tocopherol is used normally in both plasma and erythrocyte membranes and alpha-tocopherol uptake in erythrocyte membranes is significantly decreased in elderly NIDDM patients. The functional disorder of the antioxidative activity of alpha-tocopherol in erythrocyte membranes due to impairment of this transfer mechanism may be associated with the pathogenesis of NIDDM.