Age-related decrease in high-density lipoproteins antioxidant activity is due to an alteration in the PON1's free sulfhydryl groups

The aim of this study was to evaluate the antioxidant activity of HDL with aging and to investigate the implication of PON1 in this process. The study involved 54 healthy subjects distributed in two age groups, young (20-25 years) and elderly (65-85 years). Lipid peroxidation was induced by *OH and O2*- oxygen free radicals produced by gamma-radiolysis of water. LDL oxidation was followed by the measurement of conjugated diene (CD), lipid peroxide (LP) and malondialdehyde (MDA) formation. PON1 was purified separately from young (Y-PON1) and elderly subjects (E-PON1). PON1 activity and structure was followed by measurement of PON1 paraoxonase (p.ase) activity, titration of the SH groups, and electrophoretic mobility by SDS-PAGE. Our results show a significant decrease in the HDL antioxidant activity: percentage of protection against CD formation=27.70% (p<0.01) for E-HDL versus 73.08% (p<0.001) for Y-HDL. Moreover, E-PON1 showed a lower antioxidant activity when compared to Y-PON1 47.08% versus 78.14%, respectively (p<0.0001). Exposition of PON1 to *OH and O2*- oxygen free radicals induced a significant decrease in PON1 p.ase activity as well as a reduction in the number of PON1's free sulfhydryl groups. Moreover, our results show a close association between PON1's free sulfhydryl groups and its capacity to protect LDL against lipid peroxidation. There was a significant decrease in the number of free sulfhydryls between Y-PON1 and E-PON1 with respect to cysteine-284 amino acid residues (p<0.0092).