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The aim of this study was to investigate the effect of HDL oxidation on PON1 paraoxonase activity. Also, we were interested in investigating the mechanism by which PON1 could be inactivated and the correlation between its enzymatic activity and the antioxidant properties of HDL. Three different oxidation systems were used for the HDL oxidation: (1) oxidation induced by THP1 cells, (2) oxidation induced by copper ions at a concentration 10 microM, and (3) oxidation induced by *OH and O2.- oxygen free radicals produced by gamma-radiolysis. HDL oxidation was followed by the measurement of lipid peroxide formation, and PON1 activity was determined by measuring the rate of paraoxon hydrolysis. Our results show that HDL oxidation is accompanied by a reduction in the PON1 paraoxonase activity. The extent of PON1 inactivation depends both on the extent of HDL oxidation and on the oxidation system used. The rates of HDL oxidation and PON1 inactivation were significantly correlated (r = 0.93, p < 0.0054). Our results show that oxidized HDL loses its protective effect toward LDL oxidation. The antioxidant action of HDL towards LDL oxidation and the degradation of PON1 paraoxonase activity were significantly correlated (r = 0.95, p < 0.04).

Chromatin remodelling steps in mammalian spermatids include posttranslational modifications of histones and DNA fragmentation. Histone H4 hyperacetylation (AcH4) establishes a chromatin state that facilitates DNA repair in somatic cells. So we sought to determine whether a similar link exists in spermatids by combining immunogold labelling with detection of DNA strand breaks, making use of gold particles of different sizes. DNA strand breaks were not detected in the vicinity of AcH4 chromatin, suggesting that this modified histone may not be involved in the aetiology of DNA fragmentation and repair in spermatids. The AcH4 reactivity, however, indicates that chromatin remodelling is distributed throughout the nucleus.

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