Oxidant stress is believed to be enhanced in patients with diabetes mellitus, which may lead to endothelial dysfunction and the development of atherosclerosis. In diabetes, hyperglycemia drives non-enzymatic glycation and oxidation of proteins and lipids which enhances the formation of advanced glycation end products (AGEs), which may be involved in the pathogenesis of diabetic vascular disease. The macrovascular complications of diabetes seem to be due to enhanced cellular oxidant stress by the interaction of AGEs with their receptor. It would be worthwhile to devise methods to reduce this oxidant stress. In alloxan-induced diabetic rats lipid peroxidation products were increased, while levels of nitric oxide glutathione peroxidase and superoxide dismutase were reduced. Melatonin restored these biochemical abnormalities to normalcy independent of hyperglycemia. This model can be used to study the role of oxidant stress in the development of macrovascular complications in diabetes mellitus.

Autoxidation of pyrogallol in alkaline medium is characterized by increases in oxygen consumption, absorbance at 440 nm, and absorbance at 600 nm. The primary products are H2O2 by reduction of O2 and pyrogallol-ortho-quinone by oxidation of pyrogallol. About 20 % of the consumed oxygen was used for ring opening leading to the bicyclic product, purpurogallin-quinone (PPQ). The absorbance peak at 440 nm representing the quinone end-products increased throughout at a constant rate. Prolonged incubation of pyrogallol in alkali yielded a product with ESR signal. In contrast the absorbance peak at 600 nm increased to a maximum and then declined after oxygen consumption ceased. This represents quinhydrone charge-transfer complexes as similar peak instantly appeared on mixing pyrogallol with benzoquinones, and these were ESR-silent. Superoxide dismutase inhibition of pyrogallol autoxidation spared the substrates, pyrogallol, and oxygen, indicating that an early step is the target. The SOD concentration-dependent extent of decrease in the autoxidation rate remained the same regardless of higher control rates at pyrogallol concentrations above 0.2 mM. This gave the clue that SOD is catalyzing a reaction that annuls the forward electron transfer step that produces superoxide and pyrogallol-semiquinone, both oxygen radicals. By dismutating these oxygen radicals, an action it is known for, SOD can reverse autoxidation, echoing the reported proposal of superoxide:semiquinone oxidoreductase activity for SOD. The following insights emerged out of these studies. The end-product of pyrogallol autoxidation is PPQ, and not purpurogallin. The quinone products instantly form quinhydrone complexes. These decompose into undefined humic acid-like complexes as late products after cessation of oxygen consumption. SOD catalyzes reversal of autoxidation manifesting as its inhibition. SOD saves catechols from autoxidation and extends their bioavailability.

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