Total Antioxidant Capacity, Superoxide Dismutase and Glutathion Peroxidase in Diabetic Patients

In diabetic patients, the persistence of hyperglycemia has been reported as a cause of increased production of oxygen-free radicals through glucose autoxidation and nonenzymatic glycation. The antioxidant capacity is always decreased in diabetic patients, but it seems necessary to measure all the components to ascertain the reasons. The aim of this study was to determine the plasma total antioxidant capacity (TAC) and changes in the activities of two antioxidant enzymes; superoxide dismutase (SOD) and glutathion peroxidase (GPX) in diabetic patients and to estimate their relationship to levels of glycated hemoglobin, fasting blood sugar and duration of diabetes.
The changes in the status of antioxidant enzymes were evaluated in erythrocyte samples obtained from 125 diabetic patients (types I and II) and 120 apparently healthy sex and age matched subjects as control group. The activities of SOD and GPX were determined by standard spectrophotometric methods. Total antioxidant status was measured using Randox kit. Level of fasting blood glucose was measured by enzymatic method and that of glycated hemoglobin (GHb), by colorimetric method employing thiobarbituric acid reaction.
Serum glucose and GHb levels were high in two types of diabetic patients versus the control group. Compared with the control, the total antioxidant capacity was depleted in two diabetic groups, but depletion was more severe in second type. The activities of SOD and GPX were significantly low in two types of diabetic patients. Marked differences in the activities of the enzymes in good, fair and poor controlled patients were noticed. The enzyme activities in first type were higher than that of type II, but the differences were not significant. In diabetic patients, significant correlation between the total antioxidant capacity and levels of GHb, fasting blood sugar and duration of diabetes was observed, but in the case of SOD and GPX it was not marked.
In view of low activities of the enzymes in both types of diabetic patients and lack of correlation between their enzymes activities, levels of glycated hemoglobin, fasting blood sugar and duration of disease it may be concluded that reduction in the activities of the enzymes are partially involved in depletion of the total antioxidant capacity. It seems that the reduction in levels of other antioxidant enzymes and substances are involved in the decreased antioxidant capacity in diabetic patients. In view of low activities of SOD and GPX in patients supplementary trace elements such as Selenium, Copper, Zinc and Manganese, the essential components of the enzymes structures may be useful in prevention of oxidative stress. The meaningful correlation between depletion of total antioxidant capacity and poor glycemic control suggests that measurement of total antioxidant capacity in diabetic patients can be used as an index of glycemic control and development of diabetic complications in both types of diabetes.