Differential incorporation of fatty acids into and peroxidative loss of fatty acids from phospholipids of human spermatozoa

Abstract

Intact human sperm incorporated radiolabelled fatty acids into membrane phospholipids when incubated in medium containing bovine serum albumin as a fatty acid carrier. The polyunsaturated fatty acids were preferentially incorporated into the plasmalogen fraction of phospholipid. Uptake was linear with time over 2 hr; at this time sufficient label was available to determine the loss of fatty acids under conditions of spontaneous lipid peroxidation. Loss of the various phospholipid types, the loss of the various fatty acids from these phospholipids, and the overall loss of fatty acids were all first order. The loss of saturated fatty acids was slow with first order rate constant k1 = 0.003 hr-1; for the polyunsaturated fatty acids, arachidonic and docosahexaenoic acids, k1 = 0.145 and 0.162 hr-1, respectively. The rate of loss of fatty acids from the various phospholipid types was dependent on the type, with loss from phosphatidylethanolamine being the most rapid. Among the phospholipid types, phosphatidylethanolamine was lost at the greatest rate. Analysis of fatty acid loss through oxidation products was determined for radiolabelled arachidonic acid. Under conditions of spontaneous lipid peroxidation at 37 degrees C under air in the absence of albumin, free arachidonic acid was found in the medium, along with minor amounts of hydroxylated derivative. All the hydroperoxy fatty acid remained in the cells. In the presence of albumin, all the hydroperoxy fatty acid was found in the supernatant bound to albumin; none could be detected in the cells. Albumin is known as a very potent inhibitor of lipid peroxidation in sperm; its action may be explained, based on these results, as binding the damaging hydroperoxy fatty acids. These results also indicate that a phospholipase A2 may act in peroxidative defense by excising a hydroperoxy acyl group from phospholipid and providing the hydroperoxy fatty acid product as substrate to glutathione peroxidase. This formulation targets hydroperoxy fatty acid as a key intermediate in peroxidative degradation.

Role of reactive oxygen species in the pathophysiology of human reproduction

“…The link between ROS and reduced motility may be due to a cascade of events that result in a decrease in axonemal protein phosphorylation and sperm immobilization, both of which are associated with a reduction in membrane fluidity that is necessary for spermoocyte fusion (1, 69). Another hypothesis is that H 2 O 2 can diffuse across the membranes into the cells and inhibit the activity of some enzymes such as G 6 PD. This enzyme controls the rate of glucose flux through the hexose monophosphate shunt, which in turn controls the intracellular availability of NADPH.…”

“…PMA-induced ROS ϭ levels of ROS in leukocyte-free sperm suspensions after stimulation of phorbol 12-myristate 13-acetate. Seminal leukocyte concentrations (ϫ10 6 /mL) and levels of ROS (ϫ10 6 counted photons per minute per 20ϫ10 6 sperm/mL) were log transformed.…”

“…Spermatozoa are particularly susceptible to OS-induced damage because their plasma membranes contain large quantities of polyunsaturated fatty acids (PUFA) (6) and their cytoplasm contains low concentrations of scavenging enzymes (1). Oxidative stress-mediated damage to the sperm plasma membrane may account for defective sperm function observed in a high proportion of infertility patients (7,8).…”

Effect of genistein supplementation of thawing medium on characteristics of frozen human spermatozoa

“…ROS-induced damage to spermatozoa is mediated by oxidative attack of bis-allylic methylene groups of sperm phospholipid-bound polyunsaturated fatty acids (PUFAs), leading to lipid peroxidation [9,10]. The effects of lipid peroxidation include irreversible loss of motility, leakage of intracellular enzymes, damage to sperm DNA [11] or deficiencies in oocyte penetration and sperm-oocyte fusion [12].…”

Effect of leukocytospermia and processing by discontinuous density gradient on sperm nuclear DNA fragmentation and mitochondrial activity

“…Sperm are especially susceptible to OS because they present high plasma membrane concentrations of polyunsaturated fatty acids (PUFA)-methylene groups present between double bonds in the carbon chain are sites where hydrogen molecules may easily be removed by ROS [14,15]-and lipid peroxidation will eventually lead to loss of mitochondrial activity [16] and increased DNA fragmentation [17].…”