Effects of the lipid peroxidation product ( <i>E</i> )-4-hydroxy-2-nonenal on ram sperm function

Abstract

(E)-4-hydroxy-2-nonenal (HNE) is a lipid peroxide end-product which exerts powerful biological effects in a variety of cell and tissue systems. The effects of exogenous HNE on ram spermatozoa were examined in vitro. HNE inhibited the motility of diluted ram spermatozoa in a dose-dependent (100–400 μmol l−1) manner (P &amp;lt; 0.05). The extent of motility loss varied with sperm concentration as well as with HNE concentration, and was manifested as a progressive decrease in mean sperm velocity. The suppressive effect of 250–500 mmol HNE l−1 on the motility of reactivated ram sperm models (P &amp;lt; 0.05) was prevented by the addition of 1 mmol reduced glutathione l−1 to the reactivation medium, suggesting that HNE inhibits ram sperm motility via oxidation of sulfhydryl groups in the axoneme. Oxygen uptake by ram spermatozoa was inhibited (P &amp;lt; 0.05) by the addition of 100 or 200 μmol HNE l−1. Glucose utilization was maintained in the presence of 200 μmol HNE l−1. suggesting that fructolysis was unaffected by HNE. As was the case with motility, the inhibition of oxidative metabolism by HNE was not reversed by washing the spermatozoa. The activity of ram sperm acrosomal enzymes released by cold shock, as measured by hydrolysis of N-benzoyl-dl-arginine p-nitroanilide (BAPNA), was reduced in the presence of 100 μmol HNE l−1 (P &amp;lt; 0.05). No evidence was found of disruption of the acrosomal outer membrane or the sperm plasma membrane as a result of exposure to HNE. The effects of HNE on the motility, oxidative metabolism and enzyme activity of ram spermatozoa are in keeping with the effects of lipid peroxides on spermatozoa, and of HNE in other biological systems, reported elsewhere. The lack of membrane disruption by HNE is surprising, given the ability of exogenous peroxide mixtures to disrupt sperm membranes, and the powerful haemolytic activity of HNE.