Differential binding of PGE-1 and PGF-2alpha to the human spermatozoa membrane

Long chain polyunsaturated fatty acid (LC-PUFA) composition of fish sperm: nexus of dietary, evolutionary, and biomechanical drivers

Long-chain polyunsaturated fatty acids (LC-PUFA) like arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) constitute one-third to half of fish sperm lipids. Fish sperm is rich in phospholipid (PL)-primarily phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin. DHA is generally the most abundant LC-PUFA in each PL class, followed by competition between ARA and EPA. While the total n-6: n-3 PUFA ratio does not correlate significantly with sperm biomechanics, LC-PUFA do. DHA positively influences sperm biomechanics, while ARA and EPA may be negatively associated. Fish sperm maintains lower (≤1) total n-6 PUFA per unit of n-3 PUFA but keep a higher (>1) ARA per unit EPA. A weak dietary influence on sperm EPA and DHA exists but not on ARA. The DHA: EPA ratio in fish sperm is often >1, though values <1 occur. Certain species cannot fortify DHA sufficiently during spermatogenesis, diverging through whole genome duplications. Fish sperm can show ARA: EPA ratios greater or less than 1, due to shifts in prostaglandin pathways in different evolutionary eras. DHA-rich PL bilayers provide unique packing and fusogenic properties, with ARA/EPA-derived eicosanoids guiding sperm rheotaxis/chemotaxis, modulated by DHA-derived resolvins. Docosapentaenoic acid (DPA, 22:5n-3) sometimes substitutes for DHA in fish sperm.

Arachidonic Acid Pathways and Male Fertility: A Systematic Review

Arachidonic acid (AA) is a polyunsaturated fatty acid that is involved in male fertility. Human seminal fluid contains different prostaglandins: PGE (PGE₁ and PGE₂), PGF_2α, and their specific 19-hydroxy derivatives, 18,19-dehydro derivatives of PGE₁ and PGE₂. The objective of this study is to synthesize the available literature of in vivo animal studies and human clinical trials on the association between the AA pathway and male fertility. PGE is significantly decreased in the semen of infertile men, suggesting the potential for exploitation of PGE agonists to improve male fertility. Indeed, ibuprofen can affect male fertility by promoting alterations in sperm function and standard semen parameters. The results showed that targeting the AA pathways could be an attractive strategy for the treatment of male fertility.

Prostaglandin synthesis by cumulus-oocyte complexes: effects on in vitro fertilization in mice

Cumulus-oocyte complexes, obtained from superovulated Balb/C virgin female mice, released to the incubation media significant amounts of PGE1, PGE2 and PGF2 alpha, as estimated by bioassay. Fertilization rates in vitro decreased sharply when cumulus-oocyte complexes were treated with indomethacin (10(-6) M) and then inseminated with 5000 sperm per oocyte. In order to explore if the reduced prostaglandin (PG) concentration was responsible for diminished fertilization rates, PGE1, PGE2 and PGF2 alpha (10(-9) M) were added to the fertilization media of treated oocytes. PGE1 and PGE2 but not PGF2 alpha returned fertilization rates to control levels. Besides, PGE1 (10(-9) M) enhanced fertilization rates with reduced sperm numbers (1000 sperm per oocyte) of untreated cumulus-oocyte complexes. In conclusion, PG synthesis and release of mouse cumulus-oocyte complexes affects fertilization in vitro, and it is suggested that PGs of the E series modulate sperm function at the moment of fertilization.

Evidence for a cannabinoid receptor in sea urchin sperm and its role in blockade of the acrosome reaction

Delta-9-tetrahydrocannabinol ((-)delta 9 THC), the primary psychoactive cannabinoid in marihuana, reduces the fertilizing capacity of sea urchin sperm by blocking the acrosome reaction that normally is stimulated by a specific ligand in the egg's jelly coat. The bicyclic synthetic cannabinoid [3H]CP-55,940 has been used as a ligand to demonstrate the presence of a cannabinoid receptor in mammalian brain. We now report that [3H]CP-55,940 binds to live sea urchin (Strongylocentrotus purpuratus) sperm in a concentration, sperm density, and time-dependent manner. Specific binding of [3H]CP-55,940 to sperm, defined as total binding displaced by (-)delta 9THC, was saturable: KD 5.16 +/- 1.02 nM; Hill coefficient 0.98 +/- 0.004. This suggests a single class of receptor sites and the absence of significant cooperative interactions. Sea urchin sperm contain 712 +/- 122 cannabinoid receptors per cell. Binding of [3H]CP-55,940 to sperm was reduced in a dose-dependent manner by increasing concentrations of CP-55,940, (-)delta 9THC, and (+)delta 9THC. The rank order of potency to inhibit binding of [3H]CP-55,940 to sperm and to block the egg jelly stimulated acrosome reaction was: CP-55,940 > (-)delta 9THC > (+)delta 9THC. These findings show that sea urchin sperm contain a stereospecific cannabinoid receptor that may play a role in inhibition of the acrosome reaction. The radioligand binding data obtained with live sea urchin sperm are remarkably similar to those previously published by other investigators using [3H]CP-55,940 on mammalian brain and nonneural tissues. The cannabinoid binding properties of this receptor appear to have been highly conserved during evolution. We postulate that the cannabinoid receptor may modulate cellular responses to stimulation.

Biosynthesis of prostaglandins by human spermatozoa in vitro and their role in acrosome reaction and fertilization

Five homogenates of human sperm cells were separately incubated with [14C]arachidonic acid in the presence of reduced glutathione, L-tryptophan, and haematin as cofactors. The cyclooxygenase products of arachidonic acid metabolism were extracted, separated, and measured for their radioactivity. The rate of formation of prostaglandin (PG)D2, PGE2, PGF2 alpha, 6-keto PGF1 alpha, and thromboxane (TX)B2 were 18.0 +/- 1.11, 10.9 +/- 0.68, 5.8 +/- 0.21, 3.9 +/- 0.13 and 6.6 +/- 0.52 pmol/10(6) cells/min, respectively. These results are discussed in relation to the hypothesis that cyclooxygenase metabolites of certain polyunsaturated fatty acids play an important part in the sperm acrosome reaction and fertilization.

Analysis of the role of prostaglandins in the fertilization process

This study was designed to elucidate the role of prostaglandins (PG) in the fertilization process, using indomethacin (ID), an inhibitor of PG biosynthesis, and mouse in vitro fertilization as a model for analysis. Spermatozoal viability, as assessed via motility, was not suppressed by ID at 100 and 150 micrograms/ml in 3-h incubation, but markedly by 200 micrograms/ml in 1-h incubation. On the other hand, ovum viability was not affected even by 200 micrograms/ml ID in 5-h incubation, as assessed via dye-excretion and morphology. Fertilization rates for 0, 100, 150 and 200 micrograms/ml ID were 58.8, 54.8, 24.3 and 18.9%, respectively; at 150 micrograms/ml and more, significant inhibition was noted. The reduction in spermatozoal viability at 200 micrograms/ml ID was not detected after supplementation of 50 micrograms/ml PGF2 alpha. Fertilization rates were 23.1 and 20.7% in the groups at 150 and 200 micrograms/ml ID with PG solvent, respectively. After supplementation of 50 micrograms/ml PGF2 alpha, the rates were 55.8% and 64.0%, respectively. The degenerated eggs significantly increased. The polyspermic eggs also tended to increase in the ID 200 micrograms/ml groups; however, after PGF2 alpha supplementation, the number of such eggs tended to decrease. Based on these facts, it is concluded that PG may play their role in fertilization not only via sperm, but also via eggs.

Molecules that initiate or help stimulate the acrosome reaction by their interaction with the mammalian sperm surface

This review deals with exogenous molecules that stimulate the acrosome reaction (AR) of mammalian sperm in vitro, presumably by acting at the sperm surface. Such molecules may exert their effect(s) by stimulating capacitation and/or by stimulation or initiation of the AR, and they are probably present at one of three putative in vivo sites (also discussed here) for the AR of a fertilizing sperm: the oviductal fluid, the cumulus oophorus matrix, and the zona pellucida. The molecules discussed include serum albumin, hydrolytic enzymes (particularly proteases); hormones including biogenic amines, estradiol, and arachidonic acid metabolites; sulfur-containing beta-amino acids; glycosaminoglycans such as hyaluronic acid; and a zona pellucida glycoprotein. Possible mechanisms to explain the effects of these molecules are also discussed. Several conclusions and suggestions are offered in this review: There is more than one site for the AR of a fertilizing sperm in vitro, depending on experimental conditions and species, but the site(s) at which the AR of a fertilizing sperm occur(s) in vivo is/are still a matter of disagreement; there are a number of molecules that can stimulate or initiate the AR in vitro, and such molecular duplication may also exist in vivo to ensure fertility; and synergistic interaction between some of those exogenous molecules may occur in the stimulation of capacitation and the stimulation or initiation of the AR.

The effects of products and inhibitors of arachidonic acid metabolism on the hamster sperm acrosome reaction

The mammalian sperm acrosome reaction (AR) is a fusion and fenestration of sperm head membranes which is essential for fertilization. Our earlier work demonstrated that arachidonic acid could stimulate the AR 15 min after addition to hamster sperm capacitated by incubation for 4.5 h. The present study was undertaken to determine whether inhibitors of arachidonic acid metabolism could affect the stimulation of the AR by arachidonic acid and whether products of its metabolism could stimulate the AR. Phenidone or nordihydroguaiaretic acid, inhibitors of both the cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism, and docosahexaenoic acid, a cyclo-oxygenase pathway inhibitor, inhibited the AR induced by arachidonic acid. PGE2, a product of the cyclo-oxygenase pathway of arachidonic acid metabolism and 5- or 12-hydroxyeicosatetraenoic acid (HETEs) products of the lipoxygenase pathway, stimulated the AR when added to sperm capacitated by incubation for 4.5 h. Prostaglandins not derived from arachidonic were also tested: PGE1 stimulated the AR, but PGF1 alpha and PGA2 did not. We suggest that arachidonic acid metabolites produced by the sperm and by the female reproductive tract are important for the mammalian sperm AR.

Prostaglandins in semen and their relationship to male fertility: a study of 145 men

Prostaglandin (PG) F2 alpha and PGE were measured in 163 semen samples from 145 men attending our male infertility clinic. In addition, each semen sample was analyzed for 13 different fertility parameters. Blood plasma levels of testosterone, follicle-stimulating hormone, and luteinizing hormone were also determined in many of the patients. The data obtained were then analyzed using multiple regression analyses on each PG for all of the parameters studied. The results indicate seminal PGF2 alpha and PGE concentrations were 2.78 +/- 0.24 micrograms/ml and 46.0 +/- 4.5 micrograms/ml, respectively. The seminal parameters that were significant predictors of seminal PGF2 alpha included: Ca++ concentration (P less than 0.001), Zn++ concentration (P less than 0.01), and percentage of tapered sperm (P less than 0.05). The seminal parameters that were significant predictors of seminal PGE included: Ca++ concentration (P less than 0.01) and sperm motility (P less than 0.05). Plasma testosterone was also a significant predictor of seminal PGE (P less than 0.05). These results suggest that seminal PGs are important to the human male fertility potential in that their levels are significantly interdependent with specific parameters of male fertility.

The influence of prostaglandins on sperm motility

Prostaglandin E2 and F2 alpha were measured in ejaculates from 10 fertile and 55 infertile men. Prostaglandin F2 alpha was negatively correlated with motility (r = 0.77; p less than 0.01) in normal men. In patients with disturbed fertility, prostaglandin F2 alpha was always higher than in the controls, while prostaglandin E2 was elevated only in patients with persisting varicocele and in those with very low sperm counts and severely impaired motility. There was neither de novo synthesis of prostaglandins in spermatozoa nor were binding sites for prostaglandin E2 and F2 alpha detectable. Inactivation of seminal prostaglandins by incubation with prostaglandin 15-hydroxydehydrogenase resulted in a dramatic fall in motility. The results suggest that prostaglandin F2 alpha act on motility, but the action is not mediated by receptors.