Monitoring diabetic antioxidant status: a role for in vitro methaemoglobin formation

Diabetes leads to premature organ and system failure and considerably shortens lifespan. Careful control of glucose levels may not be enough to prevent the onset of complications in most diabetics. Compared with non-diabetics, diabetic tissues must not only resist a much greater long-term threat from hyperglycaemia-mediated reactive species but also defend themselves with compromised antioxidant systems. Although antioxidant therapy is a logical step in the prevention of oxidant and carbonyl stresses in the face of intermittent hyperglycaemia, this approach is not yet universally accepted to be effective in preventing complications. Although there are many biochemical indices of oxidant stress, piecemeal elevations of individual markers may not necessarily reflect true diabetic cellular antioxidant status. A dynamic process such as in vitro methaemoglobin generation may provide an opportunity to compare the response of a diabetic erythrocyte with that of a non-diabetic before and after corrective antioxidant therapy. Due to compromised cellular antioxidant capacity, diabetic cells generate less methaemoglobin in the presence of aromatic amine hydroxylamines, 4-aminophenol and nitrite compared with non-diabetics. Agents such as dihydrolipoic acid have been shown to correct methaemoglobin formation-mediated thiol deficits during in vitro studies. It is hoped that the progress of antioxidant supplementation studies in diabetics can be monitored with the aid of in vitro methaemoglobin generation using agents such as hydroxylamines, 4-aminophenol and nitrite. The most appropriate antioxidants and dosages can thus be recommended to diabetics worldwide to attenuate the development of complications.