Abstract
The lipid composition of the sperm membrane has been shown to exert a significant effect upon the functional quality of spermatozoa. We have studied the effect of induced peroxidation and of the presence of polymorphonuclear white blood cells (WBCs) on the fatty acid composition of the phospholipids of human spermatozoa. The spermatozoa were fractionated by a discontinuous Percoll gradient in two fractions (47% and 90% Percoll). Induced peroxidation of spermatozoa was assessed by determining the production of thiobarbituric acid reactive substances (TBARS), mostly malondialdehyde, after incubation with ferrous sulphate and sodium ascorbate as a promoter of peroxidation. TBARS production after induction of peroxidation was correlated with the abundance of polyunsaturated fatty acids (PUFA) (r = 0.68, p < 0.0001), with the double bond index (r = 0.72, p < 0.0001), and with the oxidative potential index (r = 0.73, p < 0.0001) of fatty acids of phospholipids. In comparison with samples containing > 1 × 106 WBCs/mL, those with < 1 × 106 WBCs/mL contained higher proportions of PUFA (90% Percoll, p < 0.05; 47% Percoll, p < 0.05), total ω3 fatty acids (90% Percoll, p < 0.05; 47% Percoll, p < 0.001), docosahexaenoic acid (90% Percoll p < 0.05; 47% Percoll, p < 0.05), and double bond index (90% Percoll, p < 0.05; 47% Percoll, p < 0.001). In addition, mean melting point was significantly lower (90% Percoll, p < 0.05; 47% Percoll, p < 0.001) in samples with < 1 × 106 WBCs, indicating higher membrane fluidity. The increase of TBARS production by spermatozoa after incubation with the xanthine–xanthine oxidase system and/or ferrous sulphate as promoter of peroxidation was associated with a significant decrease of PUFA. Incubation of spermatozoa with WBCs, with or without activation by phorbol ester, decreased the PUFA ( p < 0.05). Also, TBARS production was increased ( p < 0.01) after activation of WBCs with phorbol ester. Our data provide evidence that oxidative stress induced by WBCs has a damaging effect on the polyunsaturated fatty acids of sperm phospholipids which may result, amongst other effects, in decreased membrane fluidity.
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