Impaired glutathione-related antioxidant defenses in the arterial tissue of diabetic patients

We studied the specific enzymatic activities of selenium-dependent (GSH-Px) and -independent (GST-Px) glutathione peroxidase, glutathione reductase (GSSG-Red), and glutathione S-transferase (GST) in internal mammary arteries (IMArt) specimens obtained during coronary artery bypass surgery in 18 patients with type 2 diabetes mellitus as compared to 18 non-diabetic controls; vascular lipid peroxidation, namely fluorescent damage products of lipid peroxidation (FDPL) as 4-hydroxynonenal-related oxidative stress indicators, was also studied. Moreover, in other 16 diabetic patients and 16 controls, total glutathione (TGlut) was determined in IMArt specimens specifically homogenized in sulfosalycilic acid to prevent vascular GSH depletion. The activities of GSH-Px, GSSG-Red, and GST were significantly lower, and FDPL levels higher, in the arterial tissue of diabetic patients than in that of controls; GST-Px was undetectable. Such enzymatic activities were inversely correlated with vascular lipid peroxidation, highlighting their antioxidant role in the arterial tissue, as were HbA1c and FDPL levels with the enzymatic activities, suggesting that glycation, oxidant species and lipoperoxidation aldehydes may be involved in glutathione-related enzyme inactivation. Further, in the diabetic patients HbA1c was correlated directly with lipid peroxidation but inversely with TGlut of the arterial tissue. In the patients considered for vascular enzymatic activities and FDPL assay, 3/4-vessel coronary artery disease (CAD) as expression of atherosclerosis severity was present in 9 diabetic patients and in 3 controls. Notably, vascular glutathione-related enzymatic activities were significantly lower, and FDPL levels higher, in the 9 diabetic patients with 3/4-vessel CAD than in the 9 without, as well as in the total of 12 patients with 3/4-vessel CAD than in the total of 24 patients without. Moreover, vascular TGlut content was significantly lower in the diabetic than in the control patients. Three/4-vessel CAD was present in 6 diabetic patients and in 2 controls considered for determination of vascular Tglut content, which was significantly lower in the diabetic patients with 3/4-vessel CAD than in those without, as well in the total of 8 patients with 3/4-vessel CAD than in the total of 24 patients without. Thus, weakened glutathione-related antioxidant capacity and oxidative stress of the arterial tissue are associated with the severity of atherosclerosis. In conclusion, impaired glutathione-related antioxidant defenses of the arterial tissue occur in diabetic patients, eventually favoring vascular oxidative stress and the severity of atherosclerosis.