Age-associated alteration of blood thiol-group-related antioxidants in smokers

Total blood glutathione and nonglutathione free sulfhydryl compounds, glutathione peroxidase, and glutathione S-transferase in erythrocytes and plasma and also lipid peroxides in plasma were investigated in 48 male smokers and 42 male nonsmokers. We found that the level of total blood glutathione was significantly increased in young smokers (age <40) but no such change was noted in aging smokers (age>/=40). The activities of glutathione peroxidase and glutathione S-transferase in plasma were significantly decreased in young smokers and the plasma levels of these two enzymes and nonglutathione free sulfhydryl compounds were more drastically decreased in aging smokers. The average concentration of plasma lipid peroxides of the aging smokers (2.76+/-0.46 nmol/ml) was significantly higher than that of the aging nonsmokers (2.32+/-0. 41nmol/ml, P=0.049). On the other hand, the level of total blood glutathione was negatively correlated with the level of plasma lipid peroxides (r=-0.305, P=0.002) and was positively correlated with the smoking index (r=0.307, P=0.019) of all the study subjects under age control. These results indicate that the activities of glutathione peroxidase and glutathione S-transferase declined to a great extent under smoking-mediated oxidative stress in the blood of both young and aging smokers. Moreover, the compensatory generation of total blood glutathione may effectively prevent plasma lipids from peroxidation in young smokers, although the activities of glutathione peroxidase and glutathione S-transferase in plasma were decreased. By contrast, total blood glutathione was inadequate for such protection in the aging smokers. We suggest that supplementation of thiol-group-related agents may be considered for the prevention or alleviation of oxidative stress in aging smokers, whose capability and capacity for the disposal of smoking-mediated free radicals and reactive oxygen species are compromised.