The presence of platelet-activating factor-like activity in human spermatozoa

Ether lipids and a peroxisomal riddle in sperm

Sperm are terminally differentiated cells that lack most of the membranous organelles, resulting in a high abundance of ether glycerolipids found across different species. Ether lipids include plasmalogens, platelet activating factor, GPI-anchors and seminolipid. These lipids play important roles in sperm function and performance, and thus are of special interest as potential fertility markers and therapeutic targets. In the present article, we first review the existing knowledge on the relevance of the different types of ether lipids for sperm production, maturation and function. To further understand ether-lipid metabolism in sperm, we then query available proteomic data from highly purified sperm, and produce a map of metabolic steps retained in these cells. Our analysis pinpoints the presence of a truncated ether lipid biosynthetic pathway that would be competent for the production of precursors through the initial peroxisomal core steps, but devoid of subsequent microsomal enzymes responsible for the final synthesis of all complex ether-lipids. Despite the widely accepted notion that sperm lack peroxisomes, the thorough analysis of published data conducted herein identifies nearly 70% of all known peroxisomal resident proteins as part of the sperm proteome. In view of this, we highlight open questions related to lipid metabolism and possible peroxisomal functions in sperm. We propose a repurposed role for the truncated peroxisomal ether-lipid pathway in detoxification of products from oxidative stress, which is known to critically influence sperm function. The likely presence of a peroxisomal-derived remnant compartment that could act as a sink for toxic fatty alcohols and fatty aldehydes generated by mitochondrial activity is discussed. With this perspective, our review provides a comprehensive metabolic map associated with ether-lipids and peroxisomal-related functions in sperm and offers new insights into potentially relevant antioxidant mechanisms that warrant further research.

Platelet-activating factor induces acrosome reaction via the activation of extracellular signal-regulated kinase in human spermatozoa

Platelet-activating factor (PAF) affects capacitation, acrosome reaction and fertilisation potential of spermatozoa. This study investigated the underlying mechanism(s) through which PAF regulated sperm function. Our data demonstrated that PAF dose-dependently induced, whilst lyso-PAF (PAF precursor) showed no effect on acrosome reaction of capacitated human spermatozoa. Treatment with PAF for 90 min enhanced tyrosine phosphorylation and expression of extracellular signal-regulated protein kinases (ERK) 1 and 2 in human spermatozoa. Moreover, pre-treatment with the ERK inhibitor U0126 significantly and dose-dependently suppressed PAF-induced acrosome reaction. Therefore, PAF may be actively involved in the modulation of sperm acrosome reaction by interacting with ERK. The role of PAF in fertilisation warrants further investigation.

Effects of n-6 and n-3 polyunsaturated acid-rich soybean phosphatidylcholine on membrane lipid profile and cryotolerance of human sperm

OBJECTIVE

To study the effects of n-6 and n-3 polyunsaturated acid-rich soybean phosphatidylcholine (soy-PC) on sperm cryotolerance with regard to sperm membrane lipid profile, membrane surface integrity, and routine semen parameters.

DESIGN

Experimental study.

SETTING

University-affiliated tertiary hospital.

PATIENT(S)

A total of 20 normospermic fertile men.

INTERVENTION(S)

Semen samples examined for differences in semen parameters, sperm membrane lipid profile, and plasma membrane surface both before and after cryopreservation using basic freezing medium with N-tris(hydroxymethyl)-methyl-2-aminoethane sulfonic acid (TES) and tris-(hydroxymethyl)-aminomethane (TRIS) supplemented with purified soy-PC (TEST-PC) or egg yolk (TEST-Y), both alone or in association (TEST-Y-PC).

MAIN OUTCOME MEASURE(S)

Conventional semen parameters and membrane lipid profile by matrix-assisted laser/desorption ionization mass spectrometry (MALDI-MS).

RESULT(S)

Postthaw sperm cell motility, vitality, and morphology parameters were similar for soy-PC (TEST-PC) and egg yolk (TEST-Y) cryoprotectants. However, sperm exposed to TEST-Y-PC presented better kinetic parameters, which were similar to the original quality of the fresh semen. Human sperm MALDI-MS lipid profiles revealed that the relative abundance of glycerophospholipids of m/z 760.44 [PC (34:1)+H]+, 781.55 [SM (20:0) +Na]+, 784.55 [PC (36:3) +H]+, 806.64 [PC (38:6) +H]+, 807.64 [SM (22:1) +Na]+, and 809.64 [SM (22:0) +Na]+ increased in soy-PC samples (TEST-PC). Nonetheless, only one lipid (m/z 781.55, [SM (20:0) +Na]+) statistically significantly changed when sperm was cryopreserved in TEST-Y-PC.

CONCLUSION(S)

Sphingomyelin was defined as a prospective biomarker of soy-PC treatment, and it could be related to the positive cryoprotective effects of soy-PC in human sperm, opening new perspectives to design of a more efficient synthetic cryoprotectant medium containing purified egg yolk biomolecules combined with soy-PC.

Effects of the platelet-activating factor (PAF) on selected quality parameters of cryopreserved bull semen (AI) with reduced sperm motility

The aim of the study was to determine the effects of platelet-activating factor (PAF) on selected quality parameters of cryopreserved bull semen with reduced sperm motility used for artificial insemination. The aim of experiment 1 was to identify the optimal concentration of the phospholipid able to preserve sperm viability. Cryopreserved semen was treated with different PAF concentrations: 1×10-5M, 1×10-6M, 1×10-7M, 1×10-8M and 1×10-9M. The experiment demonstrated that PAF at concentration 1×10-9M increased most the sperm viability parameters (motility parameters, plasma membrane integrity and mitochondrial function) after 120 min of incubation of thawed semen at 37°C. Cryopreserved bull semen with reduced sperm motility (below 70%) was supplemented with PAF in a concentration of 1×10-9M. A statistically significant increase in sperm motility, percentage of linear motile spermatozoa and VSL value was observed after 120 min incubation of sperm with 1×10-9M PAF. Sperm supplementation with PAF also had positive effects on plasma membrane integrity and percentage of spermatozoa with preserved mitochondrial transmembrane potential, but the differences were not statistically significant. The results indicated positive effects of PAF supplementation at a concentration of 1×10-9M on the selected sperm quality parameters in cryopreserved bull semen with reduced motility.

The role of intrauterine insemination in male infertility

Male infertility is a common condition and intrauterine insemination (IUI) is used to treat the mild to moderate forms. Male subfertility determination is usually based on routine semen analysis but recent publications have questioned its diagnostic and prognostic accuracy as well as the effectiveness of IUI itself, as a treatment modality. We carried out a structured review of the literature to assess the current evidence regarding the diagnosis of male infertility, the effectiveness and cost effectiveness of IUI in male infertility and factors that affect the outcome of IUI. There is still uncertainty regarding the criteria for diagnosing male infertility and predicting treatment outcome based on standard semen parameters. The presence of seminal defects compromises the outcome of IUI in comparison with unexplained infertility. The total motile sperm count (TMSC) appears to have a consistent, direct relationship with treatment outcome, but there is no definite predictive threshold for success. However, it is reasonable to offer IUI as first-line treatment if TMSC is greater than 10 million when balancing the risk and cost of alternate treatments, such as in vitro fertilization (IVF). Sperm DNA studies and sperm preparation techniques warrant further studies in order to establish their clinical relevance. There are limited data on the clinical and cost-effectiveness of IUI in male infertility and large high-quality randomized controlled trials are warranted. However the difficulties in organizing such a study, at the present time, are a matter for discussion.

Exogenous platelet-activating factor improves the motility of human spermatozoa evaluated with C.A.S.A.: optimal concentration and incubation time

The objective of this study is to determine the optimal conditions for human semen incubation treated with exogenous platelet activating factor (ePAF) for intra-uterine insemination (IUI). This prospective study was carried out on 32 infertile men and each semen sample was processed with the ISolate Sperm Separation Medium, washed with sperm washing medium (SWM) and resuspended either in SWM alone (control samples), or with ePAF 0.1, 0.5, and 1.0 μM. Each concentration was subsequently incubated and evaluated at 5, 15, 30, and 60 min. The motility parameters were evaluated by the computer-aided sperm analysis (C.A.S.A.) system. Curvilinear velocity, straight line velocity, average path velocity, rapid and progressive motility significantly increased compared to control samples at an ePAF concentration of 0.1 μM (with at least 15 min of incubation). The best results were obtained with ePAF concentrations of: 0.1 μM (60 min of incubation) and 0.5 μM (30-60 min of incubation). In conclusion, results are enhanced when ePAF is added to standard semen preparation for IUI. An ePAF concentration of 0.1 μM, with an incubation time of 15 min, can be used for semen samples with normal motility. Whilst, for semen samples with poor motility, the ePAF concentration is best increased to 0.5 μM and/or the incubation time prolonged to 60 min.

Intravenous infusion of PAF affects ovulation, fertilization and preimplantation embryonic development in NZB x NZW F1 hybrid mice

Platelet Activating Factor (PAF) is a bioactive phospholipid, which exhibits a variety of biological activities and plays a significant role in all aspects of reproduction. In this work, a single intravenous injection of various concentrations of PAF shortly after Human Chorionic Gonadotropin (HCG) administration as well as 24 and 48 h before HCG administration was studied in NZB x NZW F1 hybrid mice. Optimum results were observed when PAF was injected just after the administration of HCG. In this protocol, the concentrations of PAF exhibited bell-shaped response to every stage of development. Any concentration of PAF between 5.5 x 10(-11) and 5.5 x 10(-15)g/g b.w., caused an improved ovulation rate, an increased fertilization rate, an increased rate of cell cycle and an enhanced hatching blastocyst rate (P<0.05 for all stages). Injection of lyso-PAF had no effect in any stage. Our data show that the effect of PAF on early stages of embryo development in vitro is dependent on its way of administration, on the concentrations used as well as on the time PAF is injected.

Platelet-activating factor acetylhydrolase activity affects sperm motility and serves as a decapacitation factor

OBJECTIVE

To determine the relationship between platelet-activating factor acetylhydrolase (PAFah) content in semen and sperm motility.

DESIGN

The PAFah levels in semen were measured and correlated with sperm motility.

SETTING

Clinical laboratory in a private assistant reproductive technology clinic.

PATIENT(S)

Three hundred and twelve men seeking diagnosis and treatment of infertility.

INTERVENTION(S)

Semen samples were collected from 312 healthy mature men seeking infertility treatment. Sperm motility and PAFah activity were measured in seminal plasma. Data was analyzed by Student's t test and regression analysis.

MAIN OUTCOME MEASURE(S)

PAFah activity and sperm motility.

RESULT(S)

Seminal PAFah content ranged from a low of 179 IU/L to a high of 2,457 IU/L. The overall mean PAFah content in semen was 780.59 IU/L. Linear regression analysis revealed a significant (R2 = 0.655) and negative relationship between PAFah content in semen and sperm motility. Semen specimens with high percent motility (> or = 50%) had significantly lower PAFah concentrations (442.03 +/- 14.37 IU/L) than those with the lower percent sperm motility (< 50%) (882.16 +/- 18.45 IU/L).

CONCLUSION(S)

The data confirm the presence of PAFah in human semen and that activity is significantly and negatively correlated with sperm motility. The PAFah is proven to be a candidate for sperm decapacitation factors, whereas PAF is qualified to be a candidate for sperm capacitation factors.

Effect of sperm treatment with exogenous platelet-activating factor on the outcome of intrauterine insemination

OBJECTIVE

To evaluate the effect of sperm treatment with exogenous platelet-activating factor (PAF) on IUI clinical pregnancy rate.

DESIGN

Prospective randomized study.

SETTING

Assisted Reproduction Unit, 2nd Department of Obstetrics and Gynecology, University of Athens, Aretaieion Hospital, Athens, Greece.

SUBJECT(S)

Fifty-two couples with unexplained infertility, candidates for IUI.

INTERVENTION(S)

Sperm treatment with an exogenous mixture of PAF (final concentration, 10(-7) mol/L) in sperm-washing medium, direct swim-up technique of sperm preparation, a maximum of six IUI cycles per couple with or without PAF treatment.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy rate (pregnancies confirmed by ultrasonography per hundred cycles).

RESULT(S)

The overall clinical pregnancy rate after a maximum of six IUI cycles was significantly higher when sperm was treated with PAF compared with the rate after the direct swim-up technique (23.07% vs. 7.92%).

CONCLUSION(S)

Treatment of sperm with exogenous PAF might improve the clinical outcome of IUI in cases of unexplained infertility.

The significance of platelet-activating factor and fertility in the male primate: a review

Since its discovery nearly 30 years ago platelet-activating factor (PAF) has emerged as one of the more important lipid mediators known. PAF (1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphorylcholine) exists endogenously as a mixture of molecular species with structural variants of the alkyl moiety. PAF is a novel potent signaling phospholipid that has unique pleiotropic biological properties in addition to platelet activation. PAF also plays a significant role in reproduction and is present in the sperm of a number of primate species. PAF content in squirrel monkey sperm is significantly higher during the breeding season than the non-breeding season. PAF content in rhesus sperm has a significant relationship with sperm motility. PAF content in human sperm has a positive correlation with seminal parameters and pregnancy outcomes. The enzymes (lyso-PAF-acetyltransferase and PAF-acetylhydrolase) necessary for PAF activation and deactivation are present in primate sperm. PAF-acetylhydrolase may act as a "decapacitation factor". Removal of this enzyme during capacitation promotes PAF synthesis increasing primate motility and fertilization. PAF also plays a significant role in the fertilization process, enhancing the fertilization rates of oocytes. Enhanced embryo development has also been reported in oocytes fertilized with PAF-treated sperm. Exogenous PAF will also significantly improve primate artificial insemination pregnancy outcomes. PAF antagonists inhibit sperm motility, acrosome reaction, and fertilization thus suggesting the presence of receptors for PAF. The PAF-receptor is present on primate sperm, with altered transcript levels and distribution patterns on abnormal cells. Whereas, the exact mechanism of PAF in sperm function and reproduction is uncertain, its importance in normal primate fertility is substantial.

Platelet-activating factor significantly enhances intrauterine insemination pregnancy rates in non-male factor infertility

OBJECTIVE

To determine the efficacy of treating semen specimens with platelet-activating factor (PAF) before IUI.

DESIGN

Prospective randomized double-blinded study of PAF treatment of sperm for patients with a history of infertility undergoing IUI.

SETTING

Private infertility center.

INTERVENTION(S)

Patients had ovulation induction therapy with clomiphene citrate (CC) or gonadotropin, two IUIs per month with PAF treatment.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy rates.

RESULT(S)

There was a significant difference in IUI pregnancy rates per cycle between control (10/56; 17.9%) and PAF (14/47; 29.8%) treatment groups in the normal male study arm. There was a significant difference in cumulative IUI pregnancy rates between control (10/35; 28.6%) and PAF (14/26; 53.9%) patient groups in the normal male study arm. There was no significant difference in IUI pregnancy rates per cycle between control (12/124; 9.7%) and PAF (14/119; 11.8%) treatment groups in the male factor study arm. There was no significant difference in cumulative IUI pregnancy rates between control (12/46; 26.1%) and PAF (14/38; 36.8%) patient groups in the male factor study arm. There was a significant difference in overall cumulative IUI pregnancy rates between control (21/81; 25.9%) and PAF (27/64; 42.2%) patient groups.

CONCLUSION(S)

The inclusion of PAF into the IUI sperm wash procedure significantly improves pregnancy rates. However, the significant improvement can only be shown to affect men presenting with normal semen parameters.

Sperm preparation for ART

The onset of clinical assisted reproduction, a quarter of a century ago, required the isolation of motile spermatozoa. As the indication of assisted reproduction shifted from mere gynaecological indications to andrological indications during the years, this urged andrological research to understand the physiology of male germ cell better and develop more sophisticated techniques to separate functional spermatozoa from those that are immotile, have poor morphology or are not capable to fertilize oocytes. Initially, starting from simple washing of spermatozoa, separation techniques, based on different principles like migration, filtration or density gradient centrifugation evolved. The most simple and cheapest is the conventional swim-up procedure. A more sophisticated and most gentle migration method is migration-sedimentation. However, its yield is relatively small and the technique is therefore normally only limited to ejaculates with a high number of motile spermatozoa. Recently, however, the method was also successfully used to isolate spermatozoa for intracytoplasmic sperm injection (ICSI). Sperm separation methods that yield a higher number of motile spermatozoa are glass wool filtration or density gradient centrifugation with different media. Since Percoll as a density medium was removed from the market in 1996 for clinical use in the human because of its risk of contamination with endotoxins, other media like IxaPrep, Nycodenz, SilSelect, PureSperm or Isolate were developed in order to replace Percoll. Today, an array of different methods is available and the selection depends on the quality of the ejaculates, which also includes production of reactive oxygen species (ROS) by spermatozoa and leukocytes. Ejaculates with ROS production should not be separated by means of conventional swim-up, as this can severely damage the spermatozoa. In order to protect the male germ cells from the influence of ROS and to stimulate their motility to increase the yield, a number of substances can be added to the ejaculate or the separation medium. Caffeine, pentoxifylline and 2-deoxyadenosine are substances that were used to stimulate motility. Recent approaches to stimulate spermatozoa include bicarbonate, metal chelators or platelet-activating factor (PAF). While the use of PAF already resulted in pregnancies in intrauterine insemination, the suitability of the other substances for the clinical use still needs to be tested. Finally, the isolation of functional spermatozoa from highly viscous ejaculates is a special challenge and can be performed enzymatically to liquefy the ejaculate. The older method, by which the ejaculate is forcefully aspirated through a narrow-gauge needle, should be abandoned as it can severely damage spermatozoa, thus resulting in immotile sperm.

Fertilization potential of human sperm is correlated with endogenous platelet-activating factor content

PURPOSE

Platelet-activating factor (PAF) is a potent signaling phospholipid that is found in mammalian sperm and has a positive correlation with fertility. Whereas PAF is present in human sperm, there are no relational reports on its content and the cells fertilization potential. Therefore, the study objective was to determine if PAF content in capacitated-induced sperm is related to fertilization potential as determined by the sperm penetration assay (SPA).

METHODS

Endogenous sperm lipids were measured for PAF content by a specific radioimmunoassay following insemination of zona pellucida-free hamster ova. Data were analyzed by regression analysis and Student's t test.

RESULTS

Regression analysis revealed a positive and significant relation (R2 = 0.806; P < 0.05) between PAF content in human sperm and SPA outcome (pass: > or = 5.0; fail: < 5.0, penetrations/ova). Patients that passed (22.61 +/- 5.21 picomoles/10(6)) the SPA had significantly (P < 0.01) higher PAF levels in their sperm than patients that failed (12.91 +/- 1.76 picomoles/10(6) cells) the test.

CONCLUSIONS

PAF content in capacitated-induced sperm has a significant and positive relationship with fertilization potential. Fertilization potential may be predicted by measuring PAF levels in capacitation-induced human sperm. Determining PAF content in capacitated human sperm may be a beneficial diagnostic tool for the infertility specialist.

Relationship between platelet-activating factor concentration in rhesus monkey (Macaca mulatta) spermatozoa and sperm motility

Platelet-activating factor (PAF) is a potent signaling phospholipid that has been implicated in a number of biological activities. PAF concentration in primate spermatozoa has a positive correlation with fertility. While PAF is present in rhesus spermatozoa, there are no relational reports on its concentration and the cell's motility. The study objective was to determine if PAF concentration in rhesus spermatozoa was correlated with motility indices (percent motility and forward progression). Semen was collected from sexually mature males and cell counts, and percent motilities and forward progressions were recorded prior to PAF measurement by radioimmunoassay. Spermatozoa-derived PAF concentration ranged from a low of 0.9 picomoles/10(6) cells to a high of 13.0 picomoles/10(6) cells. The overall mean (+/-SEM) PAF concentration was 4.6 (+/-1.6) picomoles/10(6) spermatozoa. Regression analysis revealed a positive and significant relationship between PAF concentration in the spermatozoa and percent motility (R2 = 0.914; P < 0.01) as well as forward progression (R2 = 0.849; P < 0.05). A receiver-operator characteristic curve and the calculation of the probability that a positive forward progression will be predicted indicated a cutoff limit of 1.5 picomoles/10(6) cells for PAF concentration in rhesus sperm. Rhesus monkey spermatozoa motility was significantly greater (P < 0.01) in the high-PAF (> or =2 picomoles/10(6) cells) group (31.0 +/- 7.6) than in the low-PAF (<2 picomoles/10(6) cells) group (6.8 +/- 2.1). Rhesus monkey spermatozoa forward progression was significantly greater (P < 0.05) in the high-PAF (> or =2 picomoles/10(6) cells) group (3.0 +/- 1.0) than in the low-PAF (<2 picomoles/10(6) cells) group (0.7 +/- 0.3). The data demonstrate that PAF concentration in rhesus spermatozoa has a significant relationship with percent motility and the cell's forward progression. Determining PAF concentration in spermatozoa may be a significant predictor of fertility in the primate. Additional studies will elucidate the role of PAF in spermatozoa function and the significance PAF plays in primate fertility.

Platelet-activating factor content in boar spermatozoa correlates with fertility

The objective of this study was to evaluate the level of platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine; PAF] content in spermatozoa between two groups of boars that differ in farrow rate percentages. The boar farrow rate was defined as High if it was > or = 70% and Low if it was < 70%. Fresh, extended semen was collected from sexually mature boars and used in the PAF extractions. Platelet-activating factor was detected in all semen samples assayed. The amount of PAF detected in spermatozoa obtained from the High group ranged from 1.90 to 11.30 pM/10(6) cells. The level of PAF in the Low group ranged from 0.92 to 4.96 pM/10(6) cells. Regression analysis revealed a positive (R2 = 0.369) and significant (P = 0.021) relationship between PAF content in boar spermatozoa and farrow rate. Spermatozoa-derived PAF levels (mean +/- SEM) were significantly higher (P = 0.015) in the High-farrow group (6.75 +/- 1.25 pM/10(6) cells) than in the Low-farrow group (2.45 +/- 0.51 pM/10(6) cells). The PAF content in spermatozoa was significantly higher (P = 0.035) in the High-average (> or = 10.5/litter) number of piglets born group (5.78 +/- 1.24 pM/10(6) cells) than in the Low-average (< 10.5/litter) number of piglets born group (3.34 +/- 1.19 pM/10(6) cells). Additionally, PAF content in spermatozoa was significantly higher (P = 0.034) in the High-average (> or = 9/litter) number of piglets born alive group (6.82 +/- 1.35 pM/10(6) cells) than the Low-average (< 9/litter) number of piglets born alive group (3.00 +/- 0.87 pM/10(6) cells). The data demonstrate that PAF is present in boar spermatozoa and that levels are significantly higher in individuals with a high-farrow rate status and high-number of piglets born and born-alive.

The effects of follicular fluid and platelet-activating factor on motion characteristics of poor-quality cryopreserved human sperm

PURPOSE

To evaluate the effects of follicular fluid and platelet-activating factor on sperm motion characteristics of cryopreserved oligospermic and normospermic samples.

METHODS

Sperm motion characteristics were evaluated prior to cryopreservation, immediately after thawing and following incubation in human tubal fluid, follicular fluid, or 1-microM platelet-activating factor cultures. Sixteen oligospermic samples and 20 normospermic samples were examined. Sperm motion characteristics were analyzed manually according to WHO criteria (1999) and also with an automated videomicrography system.

RESULT(S)

Incubation in follicular fluid increased overall motility and the percentage of sperm with fast progressive motility in normospermic but not oligospermic samples. Incubation with platelet-activating factor increased overall motility and the percentage of sperm showing nonprogressive motility in both oligospermic and normospermic samples.

CONCLUSION(S)

The stimulatory effects of culture in follicular fluid as seen in normospermic samples do not show a significant benefit in oligospermic cryopreserved samples. Platelet-activating factor and follicular fluid increase motility via different mechanisms. Incubation of oligospermic cryopreserved sperm with PAF increases the number of motile sperm, thereby enabling easier identification of viable sperm for intracytoplasmic sperm injection in samples with severe asthenozoospermia.

Impact of blood serum insulin-like growth factor I on platelet-activating factor in bull spermatozoa

The objective of this study was to examine differences in platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine; PAF] in spermatozoa between two lines of Angus beef cattle divergently selected for blood serum insulin-like growth factor I (IGF-I) concentration. Endogenous lipids were extracted from the spermatozoa and endogenous PAF content was determined by radioimmunoassay. The amount of PAF detected in spermatozoa obtained from high IGF-I bulls (n = 8) ranged from 0.145 to 3.571 pM/10(6) cells. The level of PAF extracted from spermatozoa obtained from low IGF-I- bulls (n = 5) ranged from 0.001 to 1.024 pM/10(6) cells. Polynomial regression analysis revealed a significant cubic relationship (R(2) = 0.374; F = 6.292; P < 0.05) between spermatozoa PAF content and blood serum IGF-I concentration. Spermatozoa-derived PAF levels (mean +/- SEM) were significantly higher (P < 0.05) in the high IGF-I group (1.90 +/- 0.39 pM/10(6) cells) than in the low IGF-I group (0.59 +/- 0.20 pM/10(6) cells). High IGF-I bulls have a greater than three-fold higher PAF content in their spermatozoa than low IGF-I bulls. The data demonstrate that not only is PAF present in bull spermatozoa but that levels are significantly higher in individuals with high serum IGF-I concentrations.

Presence of platelet-activating factor in squirrel monkey (Saimiri boliviensis) spermatozoa: seasonal differences

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphoryl-choline) (PAF) is a potent signaling phospholipid which has pleiotropic biological properties in addition to platelet activation. PAF has been detected in the spermatozoa in a number of species. The concentration of PAF is inversely related to human spermatozoa quality. There are no reports on the presence of PAF in nonhuman primate spermatozoa. Therefore, the primary objective of this study was to determine if PAF is present in the spermatozoa from the squirrel monkey (which is a seasonal breeder). A second objective was to determine if PAF levels change from the breeding to the nonbreeding season. Endogenous lipids were extracted from mature Bolivian squirrel monkeys (Saimiri boliviensis) spermatozoa and assayed for the presence of PAF by [125I] radioimmunoassay. PAF was detected in all samples assayed. PAF levels were significantly higher (P < 0.01) during the breeding season (mean: 3.58 ng/10(6) spermatozoa) than the nonbreeding season (mean: 0.76 ng/10(6) spermatozoa). The data demonstrate that PAF is present in squirrel monkey spermatozoa, with higher levels found during the breeding season. Additional studies are warranted to elucidate the role of PAF in spermatozoa function.

Platelet-activating factor content in human spermatozoa and pregnancy outcome

OBJECTIVE

To determine whether platelet-activating factor (PAF) content in human spermatozoa from an isolated population is related to fertilization and pregnancy outcome.

DESIGN

Prospective analysis of PAF content in human spermatozoa after a Percoll gradient wash and its relation to fertilization and pregnancy outcome.

SETTING

University-based reproductive genetics laboratory.

SUBJECT(S)

Couples undergoing assisted reproduction.

INTERVENTION(S)

Lipids extracted from Percoll gradient spermatozoa were quantitated for PAF content by a specific radioimmunoassay.

MAIN OUTCOME MEASURE(S)

The relation between spermatozoa-derived PAF levels and motility, concentration, morphology, and fertilization and pregnancy rates were determined by using regression analysis and the Student t-test.

RESULT(S)

Radioimmunoassay and regression analysis showed a significant and positive relation between PAF content in human spermatozoa and concentration and motility indices and implantation rate. Patients who became pregnant had a significantly higher PAF content in the spermatozoa used (7.285 pmol/10(6) cells) than did patients who did not become pregnant (2.990 pmol/10(6) cells).

CONCLUSION(S)

The PAF content in human spermatozoa has a significant and positive relation with motility and concentration indices and implantation rate. Pregnancy rates but not fertilization rates may be predicted by measuring PAF levels in an isolated subpopulation of human spermatozoa.

Effects of platelet activating factor on capacitation and acrosome reaction in mouse spermatozoa

Platelet activating factor (PAF) plays an important role in mammalian reproduction. The aim of this study was to investigate the effects of PAF on capacitation and acrosome reaction of mouse spermatozoa by chlortetracycline (CTC) fluorescence assay and coomassie blue staining. The percentage of capacitated mouse spermatozoa was increased (P < 0.05) by incubation with 50 ng/ml PAF for 20-120 min. The peak response occurred between 80 to 100 min of exposure to PAF. In contrast, the effects of PAF on acrosome reaction may be not receptor-mediated since lyso-PAF had the same effects. Ionophore A23187 stimulated an increase in acrosome-reacted spermatozoa of PAF-treated spermatozoa, but not of lyso-PAF-treated ones. These results suggest that PAF mainly acts on sperm capacitation.

Expression of the platelet-activating factor receptor in human spermatozoa: differences in messenger ribonucleic acid content and protein distribution between normal and abnormal spermatozoa

OBJECTIVE

To determine the expression and distribution of the platelet-activating factor (PAF) receptor in normal and abnormal specimens of human spermatozoa.

DESIGN

Prospective analysis of membrane-bound PAF receptors by immunofluorescence and PAF receptor messenger RNA by quantitated reverse transcription-polymerase chain reaction in normal and abnormal spermatozoa.

SETTING

University-based reproductive genetics laboratory.

PATIENT(S)

Men undergoing routine semen analysis.

INTERVENTION(S)

Normal and abnormal spermatozoa were exposed to rabbit anti-PAF receptor antibody, fluorescein isothiocyanate-conjugated goat anti-rabbit antibody, and fluorescent microscopy or subjected to RNA isolation by acid-phenol extraction and quantitated (MIMIC Construction Kit [Clontech Laboratories, Inc., Palo Alto, CA]) reverse transcription-polymerase chain reaction.

MAIN OUTCOME MEASURE(S)

Fluorescent intensities at six locations along spermatozoa (end piece, principal tail, midpiece, neck, proximal head, and acrosomal region) and PAF receptor expression (messenger RNA) levels.

RESULT(S)

Immunofluorescence demonstrated a significant difference in PAF receptor distribution between normal and abnormal human spermatozoa, specifically at the neck region. Additionally, abnormal spermatozoa were found to have statistically significantly more PAF receptor messenger RNA than normal spermatozoa.

CONCLUSION(S)

Platelet-activating factor receptor expression and distribution are significantly altered in abnormal spermatozoa and this may be the result of some defect in gene transcription.

Presence of platelet-activating factor in rhesus (Macaca mulatta) spermatozoa

Platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-phosphocholine; PAF] is a unique signaling phospholipid which has been implicated in a number of biological activities (e.g., reproduction). PAF has been detected in the spermatozoa from a number of laboratory and domestic species, including, but not limited to, rabbit, bovine, and the mouse. The concentration of PAF is inversely related to human (Homo sapien) spermatozoal quality. Additionally, PAF levels are significantly higher in Bolivian squirrel monkey (Saimiri sciureus) spermatozoa obtained during the breeding season than spermatozoa obtained during the nonbreeding season. There are no reports on the presence of PAF in rhesus (Macaca mulatta) spermatozoa. Therefore, the primary objective of this study was to detect the presence of PAF in rhesus spermatozoa. A second objective was to determine if PAF spermatozoa levels differ between animals housed individually (single-caged) versus free-ranging (open corrals). Semen were collected from mature rhesus via electro-ejaculation. Spermatozoa were washed free of ejaculatory plug and quick frozen in PBS. Endogenous lipids were extracted from thawed spermatozoa and ejaculatory plugs then assayed for the presence of PAF by [125I]-radioimmunoassay. PAF was not detected in any ejaculatory plugs. PAF levels were significantly higher (P < 0.01) in spermatozoa obtained from free-ranging males (mean: 1.16 pmol/10(6) spermatozoa) than males housed individually in single cage units (mean: 0.53 pmol/10(6) spermatozoa). PAF was present in rhesus spermatozoa. Additionally, PAF levels were higher in spermatozoa obtained from corral-housed animals. Additional studies are warranted to elucidate the role of PAF in spermatozoa function.

Bovine seminal platelet-activating factor acetylhydrolase: association properties in seminal plasma and with lipoproteins

The enzyme responsible for most of the phospholipase A2 (PLA2) activity present in bovine seminal plasma was recently purified to homogeneity. Sequencing revealed that the enzyme is also a platelet-activating factor acetylhydrolase (PAF-AH) of the serum type with kinetic properties generally similar to its serum homologue. In the present work, we have attempted to clarify its physiological function by studying its association properties in seminal plasma. As was observed previously for its PLA2 activity, its PAF-AH activity was also inhibited by the major proteins of bovine seminal plasma (BSP proteins). Sequential dilution experiments as well as centrifuging semen on Percoll did not reveal detectable association of PAF-AH with spermatozoa. Neither did the enzyme interact with lipid particles reported to be present in bovine seminal plasma. The purified PAF-AH, however, did display lipoprotein association properties in vitro similar to those demonstrated by the serum enzyme in vivo. At pH 7.4, it could associate with both low density lipoproteins and very low density lipoproteins but not with high density lipoproteins. Overall the data presented here indicate that the enzyme is strongly inactivated as a PAF-AH in seminal plasma and that it does not associate with lipid particles or spermatozoa.

Effects of platelet-derived growth factor (PDGF) on the in vitro production of bovine embryos in protein-free media

The purpose of our experiments was to explore the effects of platelet-derived growth factor (PDGF)-supplementation at the various steps of in vitro production of bovine embryos using protein-free media. Cumulus-oocyte-complexes (COC) were collected by slicing abattoir ovaries and then dividing the COC into 2 morphological categories. After maturation for 24 h in TCM-199 supplemented with hormones and either 20% estrous cow serum (ECS) or 1 mg/ml polyvinyl-alcohol (PVA), oocytes were co-incubated for 19 h with frozen/thawed spermatozoa from bull of proven fertility. The semen was diluted in Fert-Talp supplemented with heparin, hypotaurine and epinephrine and either 6 mg/ml bovine serum albumin (BSA) or 1 mg/ml PVA. Presumptive zygotes were transferred into embryo culture medium containing either 20% ECS or 1 mg/ml PVA for a total of 10 d. The PDGF was added at concentrations of 1, 10 or 100 ng/ml to the maturation medium (Experiment 1), fertilization medium (Experiment 2) or culture medium from Day 1 on (Experiment 3), respectively, or at 1 ng/ml PDGF to both the fertilization and culture medium from Day 3 on (Experiment 4), with each medium supplemented with PVA. Oocytes/embryos incubated in the absence of PDGF in media supplemented with either ECS or PVA served as controls. An average of 20 COC was incubated in 1 droplet under silicone oil, and each experiment contained 4 to 6 replicates. No significant differences were found among the various concentrations of PDGF, nor did PDGF-supplementation during maturation (Experiment 1) or embryo culture on Day 1 (Experiment 3) significantly affect development of oocytes/embryos (34.7 +/- 3.5 to 40.4 +/- 2.5% morulae, 11.9 +/- 2.4 to 18.8 +/- 2.5% blastocysts; and 23.2 +/- 2.3 to 27.5 +/- 3.4% morulae, 11.5 +/- 2.6 to 12.7 +/- 2.3% blastocysts, respectively; x +/- SEM). In the presence of 10 ng/ml PDGF in the fertilization medium development to morulae and blastocysts was similar to that of the ECS-group, and was higher (P < 0.05) than that of the PVA-control (ECS: 32.1 +/- 4.6 and 13.8 +/- 2.7%; PVA: 17.5 +/- 0.8 and 6.1 +/- 1.3%; PDGF: 30.6 +/- 3.0 and 14.0 +/- 2.2%, respectively). Development to morulae/blastocysts was increased, and was at the same level as in the ECS-group when the fertilization and/or embryo culture medium on Day 3 contained PDGF compared with the PVA-control group (morulae: ECS 25.3 +/- 4.4%, PVA 13.9 +/- 2.2% [P < 0.05], PDGF 16.7 +/- 3.2 to 19.1 +/- 1.1%; blastocysts: ECS 5.3 +/- 2.1%, PVA 5.0 +/- 1.7%, PDGF 7.1 +/- 1.6 to 9.1 +/- 1.7%, respectively). These results indicate that under our laboratory conditions PDGF can elevate low rates of development and the addition of PDGF to the fertilization medium enhances bovine preimplantation embryonic development. Thus, PDGF can be potentially an important factor in a completely defined medium to substitute the effects of serum.

The biochemical role of platelet-activating factor in reproduction

The presence of Co-A independent transacylase activity in amnion cells and the preferential transfer of arachidonic acid to acceptor-ethanolamine plasmalogen provide a satisfactory explanation to the questions raised by the observation that arachidonate-enriched ethanolamine plasmalogen increases in amnion late in gestation without alteration in the total amount of ethanolamine glycerophospholipids. The proposed mechanism also serves as a link between the observed changes in glycerophospholipid composition and the generation of PAF. We have emphasized a role for PAF in fetal lung maturation, the initiation and maintenance of parturition, and in certain complications associated with a premature delivery. Although PAF is known to be the most potent lipid mediator yet described and its importance in reproductive biology is well documented, it is our view that these events cannot be attributed solely to PAF and in all likelihood a number of autacoids participate in these processes.

Platelet activating factor and conception

PURPOSE

This review provides evidence for the involvement of platelet activating factor (PAF) in the several facets of pregnancy establishment.

METHODS

A comprehensive literature review and new data.

RESULTS

PAF has a role in spermatozoal function, fertilization, embryo development, and implantation.

CONCLUSIONS

PAF is intimately involved in conception.

Platelet activating factor treatment of spermatozoa enhances rabbit oocyte fertilization following subzonal sperm insertion

PURPOSE

The objective of this study was to evaluate the effects of spermatozoal platelet activating factor (PAF) treatment on fertilization rates employing subzonal sperm insertion in the rabbit.

STUDY DESIGN

Oocytes (n = 130) with distinct first polar bodies were injected with three to seven motile spermatozoa. Half (n = 65) of the oocytes were injected with PAF-treated sperm, whereas the other half (n = 65) served as controls and were injected with nontreated sperm. Fertilization rates were assessed by the formation of two pronuclei followed by cleavage to the two-cell stage.

RESULTS

In the group of oocytes injected with PAF-treated sperm, we noted a significant (P < 0.001) improvement in fertilization rates, 61.5% (40/65), vs. control nontreated sperm, 20.0% (13/65). Subsequent cleavage to the two-cell stage was noted for 95% (38/40) in the treated vs 92.3% (12/13) in the nontreated fertilized zygotes.

CONCLUSION

We conclude that PAF treatment of rabbit spermatozoa prior to subzonal insertion improves fertilization rates and may be of clinical significance in assisted reproductive programs.

Platelet activating factor and pentoxifylline as human sperm cryoprotectants

OBJECTIVE

To explore whether the addition of platelet-activating factor (PAF) or pentoxifylline before cryopreservation improves the recovery of motile viable sperm and what role cyclic adenosine monophosphate (cAMP) plays in this recovery.

DESIGN

Washed sperm was cryopreserved in the absence of and in the presence of PAF and pentoxifylline. After 2 weeks these samples were quick-thawed and evaluated before and after washing for sperm motility and other motion characteristics. Sperm viability and cAMP concentration were determined to compare the effects of these cryoprotectants.

RESULTS

When sperm samples were cryopreserved in the presence of PAF or pentoxifylline, an improvement in the recovery of motile sperm in unwashed and washed post-thaw samples was observed. There were 38% more motile sperm recovered with PAF and 15% more with pentoxifylline when compared with untreated samples. In comparison with the unwashed samples, sperm motility in post-thaw samples was lowered by the washing procedure. When PAF was used as a cryoprotectant, a significant improvement in the linearity and straight line velocity of the post-thaw sperm was observed. When pentoxifylline was used as a cryoprotectant, lateral head displacement was significantly improved in the post-thaw samples than in the control group. Both PAF-and pentoxifylline-treated samples contained a greater number of viable sperm than the control. The cAMP concentrations in post-thaw samples were 12-fold higher in pentoxifylline-treated samples and 4-fold higher in PAF-treated samples when compared with the untreated control. A 4-fold decrease in cAMP concentration was observed in post-thaw control samples compared with fresh-washed sperm.

CONCLUSIONS

The results of this study suggest that both PAF and pentoxifylline are useful cryoprotectants for the increased recovery of motile, viable sperm. Although increased recovery of motile sperm in pentoxifylline-treated samples is related to higher cAMP levels, the cryoprotective effect of PAF does not appear to be due to increased cAMP.

Embryonic platelet activating factor production in the rabbit increases during the preimplantation phase

OBJECTIVE

This study measured platelet activating factor (PAF) production by rabbit embryos in vitro and ascertained if there is increased PAF production associated with advancing embryonic development.

STUDY DESIGN

Two-cell rabbit embryos were recovered from superovulated New Zealand White does and cultured in vitro for 96 hr. Every 24 hr embryos were scored for developmental stage and PAF activity from the corresponding culture medium was measured by platelet aggregation and organic phosphate analyses.

RESULTS

PAF was detected in culture medium at all stages from two cells to blastocysts and rose significantly (P < 0.001) at each 24-hr interval, reaching maximal levels at the expanded blastocyst stage.

CONCLUSION

Maximal PAF production by expanded blastocysts may be an embryonic paracrine signal that facilitates implantation.

Stimulation of platelet-activating factor synthesis by progesterone and A23187 in human spermatozoa

The presence of platelet-activating factor (PAF) has been demonstrated recently in mammalian spermatozoa, together with evidence for a role of this phospholipid in enhancing sperm motility and fertilizing ability. To investigate whether PAF synthesis and release occurs in human spermatozoa following incubation with stimuli that induce acrosome reaction, spermatozoa were incubated with progesterone and A23187, two known inducers of the exocytotic event. PAF synthesis (remodelling pathway) was assessed by [3H]acetate incorporation into PAF. Treatment of spermatozoa with progesterone and A23187 resulted in an increase of [3H]acetate incorporation into PAF. Most of the newly synthesized [3H]PAF formed in response to acrosome reaction was found in the supernatant, suggesting a release of the phospholipid from spermatozoa. PAF-like material extracted from human spermatozoa was able to induce aggregation of rabbit platelets and showed identical retention time and the same ion m/e values as authentic PAF when analysed with g.c.-m.s. Lyso-PAF:acetyl-CoA acetyltransferase (EC 2.3.1.67) activity in human spermatozoa was also studied and showed similar kinetic parameters to those described for other cell systems. Stimulation of spermatozoa with progesterone and A23187 induced an increase of [3H]arachidonic acid release, suggesting an activation of phospholipase A. In conclusion, our results demonstrated increased production and release of PAF in human sperm following stimulation with progesterone and A23187 and suggest a role for this phospholipid in the activation of spermatozoa.

Platelet-activating factor treatment of human spermatozoa enhances fertilization potential

OBJECTIVE

The purpose of this study was to evaluate the effects of platelet-activating factor treatment on human spermatozoa fertilizing capability, as assessed by the zona-free hamster penetration assay.

STUDY DESIGN

Twenty-three semen specimens were divided into two groups on the basis of initial motile sperm count greater or less than 20 x 10(6)/ml. Each sample served as its own treatment control. Twice-washed spermatozoa were treated with 1 x 10(-7) mol/L of platelet-activating factor before performing the sperm penetration assay. For the two groups the percent penetrations and penetration index were compared with the paired t test, and an independent t test was used to compare parameters between groups.

RESULTS

Significant enhancement of both percent penetrations (p < 0.0001) and penetration index (p < 0.005) were noted on platelet-activating factor treatment in both groups. Enhancement of both indices were noted to be independent of initial motile sperm counts.

CONCLUSION

Platelet-activating factor treatment of human spermatozoa may be of potential therapeutic value in certain cases of asthenospermia or fertilization failure in human in vitro fertilization.

Enhanced embryo development of rabbit oocytes fertilized in vitro with platelet activating factor (PAF)-treated spermatozoa

PURPOSE

The purpose of this study was to determine the effects of PAF treatment of rabbit spermatozoa on in vitro fertilization and subsequent blastocyst formation. Rabbit spermatozoa were exposed to PAF (10(-7) M), lyso-PAF (10(-7) M), or HIS (385 mOsm/kg) for 15 min prior to insemination of ovulated oocytes. Fertilized oocytes were cultured to the hatched blastocyst stage.

RESULTS

Fertilization rates with PAF were significantly higher than those of fresh (P < 0.001), lyso-PAF-treated (P < 0.01), HIS-treated (P < 0.05) spermatozoa. Two-cell embryos produced from oocytes inseminated with PAF-treated spermatozoa had significantly higher hatched blastocysts than oocytes inseminated with fresh (P < 0.01), lyso-PAF-treated (P < 0.05), or HIS-treated (P < 0.05) spermatozoa.

CONCLUSION

We conclude that PAF treatment of spermatozoa increases fertilization rates and subsequent embryonic development.

Effects of platelet activating factor on mouse sperm function

Platelet activating factor (PAF) has been implicated in a variety of reproductive processes. This study was designed to investigate the effect of PAF and the specific PAF receptor antagonist, CV-3988, on capacitation and the acrosome reaction in mouse spermatozoa using an in vitro fertilization (IVF) system. When spermatozoa were preincubated for 30 min in medium containing PAF (10(-7) to 10(-11) M), a significant increase in the fertilization rate with both cumulus-free and zona-free oocytes was observed. In contrast, treatment of the spermatozoa with 10(-5) M CV-3988 caused a significant decrease in both sperm motility and fertilization rates with zona-intact and zona-free oocytes. This suppression was reversed by the addition of PAF. Furthermore, the acrosome reaction was enhanced by PAF treatment of spermatozoa in a dose-dependent manner. This stimulation of the acrosome reaction by PAF required the presence of calcium ions in the medium. While 10(-5) M CV-3988 inhibited the acrosome reaction, the inhibition was also reversed by the addition of PAF. These results suggest that PAF can stimulate not only the capacitation process but also the acrosome reaction, both of which are dependent on extracellular calcium.

Coagulation and fibrinolysis markers in seminal plasma of patients under evaluation for involuntary childlessness

Semen specimens from four groups of patients were evaluated for coagulation and fibrinolysis factors: a group of patients with infertile semen and involuntary childlessness (n = 35), a group with fertile semen and involuntary childlessness (n = 39), a group with fertile semen and proven fertility before vasectomy (n = 34) and a group with infertile semen after vasectomy (n = 147). The third patient group with proven fertility before vasectomy was considered as a control group. Only small amounts of fibrinogen, factor VIII:c, plasminogen, antithrombin III, fibrin monomers and plasminogen activator inhibitor-1 were detected in seminal plasma. The thrombin-antithrombin III, D-dimer and tissue plasminogen activator regular concentrations were measured and the D-dimer/thrombin-antithrombin III ratios calculated. The reference ranges were assessed and the quantities were compared in the different patient groups. Significant differences were demonstrated between the prevasectomy group (= control group) and both the postvasectomy and the infertility groups with respect to D-dimer and D-dimer/thrombin-antithrombin III ratio. We conclude that both coagulation and fibrinolysis play a part in coagulum formation and liquefaction of seminal plasma. The balance between coagulation and fibrinolysis (expressed as D-dimer/thrombin-antithrombin III ratio) was significantly different between the control group and the three patient groups. The coagulation/fibrinolysis balance was impaired in the semen from post vasectomy patients and from those with involuntary childlessness and the D-dimer/thrombin-antithrombin III ratios in both these patient groups were very similar.

Human spermatozoa produce C16-platelet-activating factor

Recent data indicate that human spermatozoa produce platelet-activating factor as determined by the rabbit platelet [3H]serotonin release bioassay. In this report, we examined by fast atom bombardment/mass spectrometry the molecular species of platelet-activating factor generated by these germ cells. Extracted spermatozoal samples that contained platelet-activating factor bioactivity underwent straight-phase high-performance liquid chromatography, and fractions which coeluted with authentic C16- and C18-platelet-activating factor standards were subjected to fast atom bombardment/mass spectrometry. Our mass spectral data indicate that human spermatozoa synthesize C16-platelet-activating factor but not C18-platelet-activating factor.

Platelet-activating factor stimulates motion parameters of cryopreserved human sperm

Platelet-activating factor is a naturally occurring molecule that does not appear to cause the detrimental effects to sperm as have been reported for other synthetic stimulatory agents. Incubation of freeze-thawed sperm with low motility with PAF at concentrations greater than or equal to 1.0 microM significantly improved a number of motion parameters (% motility, VSL and LIN). Optimal incubation conditions for PAF were defined at 1 hour and at 25 degrees C. The success of assisted reproductive techniques employing cryopreserved sperm with poor motility may be enhanced by stimulation protocols employing PAF.