Decreased Activity of Thiol Peroxidase (Glutathione Peroxidase 3) in Blood Plasma as an Indicator of Aging

Abstract

Thiol peroxidases is a superfamily of antioxidant enzymes catalyzing the thiol-dependent reduction of hydroperoxides. Thiol peroxidases of glutathione peroxidase (Gpx) family utilize reduced glutathione (GSH) as a reductant. Early studies recognized that plasma selenium-dependent Gpx (Gpx3) possesses a wide thiol specificity. Our previous study statistically confirmed the ability of rat Gpx3 to utilize reduced homocysteine (Hcy-SH) instead of GSH. Thus, GSH can be completely replaced by Hcy-SH in a reaction mixture, that allows to determine Gpx3 activity with higher selectivity. In present study, the hypothesis of the age-associated decline of thiol peroxidase activity in rat plasma was tested using Hcy-SH as a thiol substrate. The enzymatic activity in 23-24-month-old rats was significantly lower than in 6-8-month-old rats (p=0.0012, Wilcoxon-Mann-Whitney test). These data are in agreement with the results obtained by other authors revealed the diminished total Gpx activity in serum of 24-month-old rats. The progressive aging-associated decline of Gpx activity in human plasma is also known. Gpx3 activity in plasma may be an appropriate indicator of aging process due to its relatively high value in adult, not aged animals and humans, and its subsequent prominent aging-specific decline.