GLUTATHIONE METABOLIC ENZYME-ACTIVITIES IN DIABETIC PLATELETS AS A FUNCTION OF GLYCEMIC CONTROL

Type 1 diabetic subjects categorized on the basis of the glycated haemoglobin content of their blood (low < 7 %; medium, > 7 % and < 11 %; high, > 11 %) were analyzed for total intraplatelet GSH as well as for the steady-state kinetic parameters (apparent K(M) and apparent V(max)) of some glutathione metabolic enzymes including glutathione reductase, glutathione peroxidase, gamma-glutamyltranspeptidase and glutathione-S-transferase. This study indicates that intraplatelet GSH content of subjects with low glycated-haemoglobin is approximately 2-fold higher than those with medium glycated-haemoglobin. There was no further decrease in intraplatelet-GSH in subjects with high glycated-haemoglobin. The kinetic parameters of the platelet-enzymes studied (glutathione reductase, gamma-glutamyltranspeptidase and glutathione-S-transferase) were essentially independent of the glycation state of the subject. However, the apparent K(M) of glutathione peroxidase was approximately 4-fold higher in the subjects with high glycated-haemoglobin, in comparison to low subjects. This decrease in affinity could possibly result from the susceptibility of this enzyme to non-enzymatic glucosylation as purified samples of glutathione peroxidase incubated in vitro with glucose showed similar increases in apparent K(M). These results are discussed in terms of the potential contribution of glutathione peroxidase impairment, to the hyperaggregability of the diabetic platelet.