Effects of hydrogen peroxide on human spermatozoa

PURPOSE

Reactive oxygen species (ROS) have been reported widely to cause deleterious effects on sperm viability and function due to peroxidation of membrane lipids. However, their action appears more selective at low concentrations; recent evidence indicates that the superoxide anion can promote capacitation and induce hyperactivated motility (HA) in human spermatozoa and that hydrogen peroxide (H2O2) may participate in capacitation of hamster spermatozoa. The objective of these studies was to investigate the direct effects of H2O2 on functions crucial to fertilization in human spermatozoa.

METHODS

In these prospective studies, we examined the dose- and time-dependent effects of H2O2 on sperm membrane-mediated events (binding to the zona pellucida and changes in intracellular calcium concentration [Ca2+]i, motility patterns, and acrosome reaction). Sperm from fertile donors were used in the experiments under capacitating conditions after separation of the motile fraction by wash/swim-up. [Ca2+]i was measured by the fluorescent fura-2 indicator, and sperm-zona pellucida binding was assessed with the hemizona assay (HZA). Hyperactivated motility was evaluated by computerized analysis, and the percentage of acrosome reacted sperm was detected by FITC-Pisum sativum lectin and indirect immunofluorescence.

RESULTS

In the HZA, H2O2 did not influence sperm-zona pellucida binding at low concentrations (0.05 mM and 0.1 mM), but significantly reduced binding at 0.2 mM (P < 0.004 vs controls). H2O2 significantly decreased HA in a dose-dependent manner (P < 0.0001) and had a significant effect (P < 0.01) on acrosome reaction (stimulatory effect at 0.01 mM). H2O2 did not affect basal [Ca2+]i; however, H2O2 (0.1 mM through 10 mM) decreased the initial phase of progesterone-induced (P4: 1 microM) enhancement of [Ca2+]i in a dose- and time-dependent fashion. Preincubation of sperm with catalase (20 micrograms/ml) potentiated the P4-induced increase of [Ca2+]i. H2O2 did not significantly modify [Ca2+]i increase in response to inomycin (10 microM).

CONCLUSIONS

These experiments show that H2O2 directly affects sperm functions crucial to fertilization in a dose- and time-dependent fashion. Low concentrations maintain capacitation, whereas higher concentrations have deleterious effects, as determined by the end points of the capacitation process. The latter effects are probably dependent on modifications of plasma membrane and intracellular homeostasis by the oxidative process.

Ionic control of sperm function

Successful sperm function leads to fertilization. It is dependent on the extracellular environment, especially the array and concentration of various ions. Considerable evidence indicates that this is because of consequent effects on the intracellular ionic composition. Although both cations and anions undoubtedly play a role in a modulating sperm function, most of the evidence currently available concerns cations. Therefore, this review will concentrate on cations, focussing on Ca2+, Na+, K+ and H+. Their requirements for successful capacitation (mammalian sperm) and acrosomal exocytosis (both invertebrate and mammalian sperm) will be considered. In particular, the mechanisms which may control ion fluxes, leading to changes in the intracellular ionic composition and subsequently to changes in sperm functional potential, will be addressed.

Exocytosis in spermatozoa in response to progesterone and zona pellucida

Exocytosis in mammalian spermatozoa (the acrosome reaction) is a process essential for fertilization. Both progesterone and zona pellucida induce exocytosis in spermatozoa, which may encounter both during penetration of the oocyte's vestments. When mouse spermatozoa were exposed first to progesterone and then to zona pellucida, exocytosis was enhanced to a greater degree than that seen when the agonists were presented together or in the inverse order, which suggests that the steroid exerts a priming effect. Progesterone similarly primed the generation of intracellular messengers evoked by zona pellucida. The effects triggered by progesterone were mimicked by gamma-aminobutyric acid (GABA) and were blocked by bicuculline, which indicates that the steroid acts on a GABAA receptor.

Effects of pentoxifylline and progesterone on human sperm capacitation and acrosome reaction

This study was designed to test the effects of pentoxifylline and progesterone upon capacitation of fresh human spermatozoa. Capacitation and acrosomal integrity were assessed using the fluorescent probe chlortetracycline on spermatozoa co-stained with a supravital fluorescent dye, Hoechst 33258. Hyperactivated motility was measured using computer-assisted movement analysis. After exposure to pentoxifylline (1 mg/ml; 30 min), the fluorescent 'B' pattern, characteristic of capacitated, acrosome-intact cells, increased significantly (P < 0.01), though no increase in 'AR' pattern, characteristic of acrosome-reacted cells, was detected. There was a significant increase in hyperactive motility (P < 0.001). Exposure to progesterone (1 microgram/ml; 60 min) resulted in a significant increase in 'B' pattern (P < 0.05) and 'AR' pattern (P < 0.005), though no effect on the expression of hyperactivation was detected. No effect upon hyperactivation was detected on exposure of fresh or cryopreserved spermatozoa to a physiological range of progesterone concentrations (0.1-1000 ng/ml). Sequential exposure to pentoxifylline then progesterone resulted in a significant increase in 'B' pattern, acrosome loss and hyperactivation. Sperm viability was not affected in any treatment group. These observations suggest that pentoxifylline and progesterone affect capacitation through independent mechanisms. Stimulation of both capacitation and acrosome reaction resulted from sequential exposure to pentoxifylline and progesterone. This may have implications for sperm handling for assisted reproductive techniques.

Dithiothreitol effects on human sperm quality

Human semen normally coagulates immediately after ejaculation and then undergoes liquefaction during the next 15 to 60 minutes. Incomplete seminal liquefaction can result in impaired sperm motility and make clinical evaluation and manipulation difficult. Dithiothreitol, a mucolytic agent that reduces the mucoprotein disulfide bonds in sputum, has been found to induce liquefaction of incompletely liquefied semen in vitro. We studied the effects of dithiothreitol on sperm motility, viability, acrosomal integrity and morphology. A semen sample was provided by 45 healthy, young men at the University of Arizona. Of the specimens 10 (22%) demonstrated incomplete liquefaction. Sperm motility and motion characteristics of untreated (control) semen and semen treated with dithiothreitol were objectively evaluated using computer assisted semen analysis. Sperm cell membrane integrity and mitochondrial integrity were measured by fluorescence microscopy using the deoxyribonucleic acid specific fluorochrome propidium iodide and the mitochondria specific fluorochrome rhodamine-123, respectively. Acrosomal integrity was determined using the fluorescent stain chlortetracycline. Sperm morphology was evaluated using bright field microscopy. For completely liquefied semen (35 cases) dithiothreitol reduced sperm motility (59.1 +/- 1.2% untreated versus 53.2 +/- 1.2% treated, p < 0.01) and motion characteristics. However, dithiothreitol had no statistically significant effect on motility on sperm in the group with incompletely liquefied semen (10 cases). Sperm cell membrane, mitochondrial and acrosomal integrity was unaffected by dithiothreitol regardless of liquefaction status. Dithiothreitol caused a significant increase in abnormally large sperm head morphology in the group with completely liquefied semen. The minimal effects of dithiothreitol on sperm motility traits and viability support its use as a possible aid in the evaluation and manipulation of incompletely liquefied semen.

An in vitro promoting role for hydrogen peroxide in human sperm capacitation

A complex process of maturation called capacitation is an essential step for spermatozoa to fertilize oocytes. Recent studies have shown that reactive oxygen species (ROS) can enhance the capacitation of human spermatozoa and sperm-zona interaction. We have investigated whether hydrogen peroxide (H2O2) could trigger capacitation of human spermatozoa and the acrosome reaction. The addition of catalase, a specific H2O2 scavenger, at the beginning of the capacitation process decreased the levels of both hyperactivation and induced-acrosome reaction whereas catalase added 15 min before the induction of the acrosome reaction by the calcium ionophore had no effect. Supplementation of the medium with H2O2 resulted in increased levels of hyperactivation and the acrosome reaction, whereas H2O2 added 15 min before induction of the acrosome reaction did not have any stimulatory effect. These results suggest that H2O2 may be involved in the capacitation process of human spermatozoa but not in the acrosome reaction.

Solubilization and partial purification from mouse sperm membranes of the specific binding activity for 3-quinuclidinyl benzilate, a potent inhibitor of the zona pellucida-induced acrosome reaction

3-Quinuclidinyl benzilate (QNB), a potent antagonist of muscarinic acetylcholine receptors, has been demonstrated to inhibit specifically the zona pellucida (ZP)-induced acrosome reaction (AR) in mouse sperm (Florman and Storey, 1982; Dev Biol 91:121-130). In this study we describe the solubilization and partial purification of the mouse sperm QNB binding activity which may represent a component of the putative receptor complex for ZP on the sperm plasma membrane. Sperm membranes were isolated from cell homogenates of washed, capacitated, epididymal mouse sperm. Scatchard plots of QNB binding to these membranes indicated a single class of binding sites with KD = 7.2 nM and Bmax = 8700 sites/cell. These binding characteristics are similar to those seen with QNB binding to whole cells (Florman and Storey, 1982, J Androl 3:157-164). Sperm membranes were solubilized using 1% digitonin/0.2% cholate, and the resultant detergent-soluble fraction possessed QNB binding activity similar to that of intact membranes. The detergent-soluble fraction maintained intact ZP receptor(s)-G protein coupling in that treatment of this fraction with either ZP or mastoparan resulted in a 35% or 65% increase in specific GTP gamma S binding, respectively. The solubilized membrane preparation was fractionated by gel permeation HPLC. A majority of specific QNB binding activity was confined to one HPLC fraction. Analysis of this fraction by SDS-PAGE revealed a complex of approximately 5 proteins unique to this fraction. The most prominent protein had a M(r) of 72 kDa, which is within the M(r) range for muscarinic receptors. A protein with M(r) = 41 kDa was also present within this fraction. Subsequent pertussis toxin (PTX)-catalyzed ADP-ribosylation of this fraction revealed this protein to be the alpha subunit of the G(i) class of G proteins. Although the QNB binding activity could not be positively identified, we propose that it is contained in one or more of the proteins unique to this fraction and that these proteins, including G(i), may act as part of a sperm receptor complex for the ZP.

Comparison of the ability of progesterone and heat solubilized porcine zona pellucida to initiate the porcine sperm acrosome reaction in vitro

It has been previously shown that progesterone can initiate the acrosome reaction (AR) of capacitated human and hamster sperm in vivo. We report here that progesterone can initiate a morphologically normal AR in porcine sperm that have undergone capacitation in a Hepes-buffered medium in vitro. In addition, we have compared the abilities of progesterone and heat-solubilized porcine zona pellucida (zona) to initiate the porcine sperm AR. Capacitated porcine sperm were treated with 1 micrograms/ml progesterone, 150 micrograms/ml porcine zona, or solvent control for 10 min. After treatment, sperm were incubated with the supravital dye Hoechst 33258, fixed and the acrosomal status determined in the previously viable sperm by fluorescence microscopy with fluorescein isothiocyanate-labeled Pisum sativum agglutinin (FITC-PSA). There was no significant difference between the percentage of AR initiated by zona compared to that initiated by progesterone. In order to determine whether there was a synergistic interaction between the two AR initiators, both were added simultaneously to capacitated porcine sperm at optimal (1 microgram/ml progesterone, 150 micrograms/ml zona) and suboptimal (75 ng/ml progesterone and 75 micrograms/ml zona) concentrations. Simultaneous addition of the two AR-initiators at the two concentrations stimulated an additive AR-initiating response, rather than a synergistic one. Several possible explanations for the additive results are discussed.

Effects of pentoxifylline on human sperm parameters in vitro

PURPOSE

Pentoxifylline was tested in three raising concentrations (0.7 mM/l, 1.5 mM/l, 3.6 mM/l) on human sperm cells in vitro.

METHODS

On 143 samples, we examined drug effect on motile sperm concentration, grade of their motility, acrosome reaction and membrane status.

RESULTS

Obtained results show improvement in motile sperm concentration, as well as in the grade of progression in the majority of samples.

CONCLUSIONS

Spermatozoa membranes as well as occurrence of the acrosomal reaction were not affected by pentoxifylline.

Effects of cholic acid and 'Protectaid' formulations on human sperm motility and ultrastructure

Cholic acid (sodium cholate) and the other active ingredients of F-5 gel preparations in use for the impregnation of a new vaginal sponge (Protectaid) with contraceptive and anti-sexually transmitted disease properties, were assessed for their effects on human sperm motility and ultrastructure. Cholic acid (CA) produced an inhibition of motility which was both dose- and time-dependent. A complete suppression of motility was obtained at 30 s by a CA concentration of 1.25%. Nonoxynol-9 (NX9) compared with benzalkonium chloride (BZC) showed no significant difference at the concentration required (0.025%) to give a total inhibition of sperm motility after exposure for 30 s. The addition of F-5A gel containing 0.5% of each one of the spermicide ingredients (CA, NX9 and BZC) produced the total suppression of sperm motility within 30 s at a dilution of 1/50. Another preparation, F-5B gel, containing the spermicide ingredients at different concentrations (1.25% CA, 0.125% NX9 and 0.05% BZC) produced this same effect with a 1/10 dilution. Exposure of semen to a CA concentration of 1.25% or to 1/10 dilutions of F-5A gel for 30 s led to profound changes of sperm ultrastructure studied by scanning (SEM) and transmission (TEM) electron microscopy. SEM and TEM findings indicate that CA acts as a spermicide through its 'natural detergent' properties, damaging the outer plasma membrane of sperm cells. Protectaid formulations affect sperm motility and viability in a similar way.

Incubation of spermatozoa from asthenozoospermic semen samples with pentoxifylline and 2-deoxyadenosine: variability in hyperactivation and acrosome reaction rates

We examined hyperactivation and acrosomal loss in asthenozoospermic patients with a history of failed in-vitro fertilization (IVF). After selection by a Percoll gradient, spermatozoa were incubated with 3.6 mM pentoxifylline (PTX), 3.0 mM 2-deoxyadenosine (2-DXA) or both. Hyperactivation and ionophore A-23187-induced acrosome reaction were assessed immediately after sperm treatment and again after 180 min. In all groups studied, the mean hyperactivation rates were found to be low. No significant differences were noted between assessments immediately after treatment and 180 min later, except after treatment with both PTX and 2-DXA. The mean hyperactivation rates were found not to improve as a result of either PTX or 2-DXA, while the combination of both PTX and 2-DXA revealed a significant enhancement of total hyperactivation. When individual hyperactivation rates between control and treated sperm samples were compared, large differences in response were observed. Some sperm samples showed a marked increase in hyperactivation with one treatment, while another treatment led to a decrease. Acrosome reaction rates assessed immediately after ionophore A-23187 stimulation were found not to be significantly different from those assessed 180 min later. No significant effect could be demonstrated for either treatment, although, here too, marked interindividual variations were noted. It was concluded that an unselective use of PTX, 2-DXA or both compounds together, may restore sperm function in certain of these patients, and perhaps improve fertilization in vitro, but in others it may produce no change or may even be detrimental to sperm function.

The acrosome reaction to ionophore challenge test: assay reproducibility, effect of sexual abstinence and results for fertile men

Since the human acrosome reaction is considered a prerequisite for normal fertilization and the spontaneous acrosome reaction rate is low, laboratory tests using calcium ionophores to induce the acrosome reaction have been devised and applied to the investigation of patients. The introduction of any new laboratory test into routine clinical practice is usually accompanied by the determination of intra- and inter-subject variability within the normal population, and the derivation of reference values to distinguish between affected and unaffected populations. The acrosome reaction to ionophore challenge (ARIC) test was evaluated and found to have (i) intra- and inter-assay coefficients of variation of 10.8 and 18.8% respectively, (ii) a high degree of intra-subject variability for three subjects studied over a 10 week period, (iii) a high degree of inter-subject variability when aliquots of 20 ejaculates of donor semen of proven fertility were tested, and (iv) no effect of length of sexual abstinence on ARIC values. The results of this study suggest that the use of fresh semen samples from subjects of proven fertility for quality control purposes in the ARIC test may be inadequate due to the high degree of intra-subject variability, and that this problem may be overcome by utilizing a frozen quality control sample. The results also suggest that an isolated negative ARIC test is not necessarily indicative of functionally incompetent spermatozoa, and highlight the importance of examination of the normal population prior to the clinical application of such a test.

Calcium influx into mouse spermatozoa activated by solubilized mouse zona pellucida, monitored with the calcium fluorescent indicator, fluo-3. Inhibition of the influx by three inhibitors of the zona pellucida induced acrosome reaction: tyrphostin A48, pertussis toxin, and 3-quinuclidinyl benzilate

The fluorescent calcium indicator, fluo-3, was loaded as the membrane permeant tetraacetoxymethyl (AM) ester into cauda epididymal mouse sperm at 25 degrees C for 20 min in the absence of bovine serum albumin (BSA) and presence of the dispersant, Pluronic F-127. Excess indicator was removed by two centrifugation washes at 100g for 10 min, a procedure that did not impair sperm motility. Upon resuspension in medium containing 20 mg/ml BSA to promote capacitation, the sperm cells exhibited readily detectable fluorescence uniformly distributed in the cytoplasm. Cell fluorescence was stable over the time of the experiments and was responsive to changes in intracellular calcium concentration, [Ca2+]i. Initial [Ca2+]i was 231 +/- 58 nM (+/- SE, n = 43). Addition of heat-solubilized mouse zonae pellucidae to capacitated sperm increased [Ca2+]i by 106 +/- 19 nM (+/- SE, n = 18), the higher steady-state concentration being reached after 30 min. Subsequent addition of the non-fluorescent calcium ionophore Br-A23187 resulted in a further increase of 114 +/- 18 nM (+/- SE, n = 18), the higher steady-state concentration being reached after 6 min. The increase in [Ca2+]i induced by solubilized zonae pellucidae was largely blocked by 3-quinuclidinyl benzilate (QNB), an antagonist of muscarinic receptors that was earlier shown to block the zona pellucida induced acrosome reaction in mouse sperm (Florman and Storey, 1982: Dev Biol 91:121-130). This [Ca2+]i increase was completely blocked by the tyrosine kinase inhibitor, tyrphostin A48, and by the inactivator of G1 proteins, pertussis toxin. At the concentrations at which they blocked the zona pellucida-induced increase in [Ca2+]i, all three inhibitors also blocked the zona pellucida-induced acrosome reaction. These results indicate that [Ca2+]i increase in is an early, if not the initial, reaction in the sequence leading to zona pellucida induced acrosomal exocytosis in mouse sperm. The observation that the three inhibitors, each having a different mode of action, all block the zona pellucida induced [Ca2+]i suggests that the sperm plasma membrane receptors mediating the zona pellucida induced acrosome reaction may function as a complex, whose formation is activated by zona pellucida ligand binding.

Immunoglobulins from human follicular fluid induce the acrosome reaction in human sperm

The ability of human follicular fluid (hFF), retrieved from women undergoing IVF to induce the acrosome reaction (AR) in human sperm has been documented by several laboratories. However, the nature of the active factors in the hFF and the physiological meaning of the AR induction are highly controversial. We performed a three step purification scheme for hFF and all the fractions were screened for the AR-inducing activity. AR activity was associated with a protein fraction of M(r) > 180 kD that on further analysis under PAGE was found to be composed by subunits of apparent M(r) 50,000 and 29,000. The N-terminal sequences of these bands showed a 100% homology with the heavy and light chains of human IgG. A polyclonal antibody raised against the purified protein and anti-human IgG were both able to suppress the acrosome reaction-inducing activity of crude hFF. However, neither normal human serum nor a purified preparation of human IgG were able to mimic the AR-inducing activity of hFF. We concluded that the AR-inducing activity of hFF is, at least in part, due to the presence of antisperm antibodies.

Recombinant human zona pellucida protein ZP3 produced by chinese hamster ovary cells induces the human sperm acrosome reaction and promotes sperm-egg fusion

Studies on the role of specific molecules in the human fertilization process and additional assessments of potential applications for these proteins are hampered by the limited amount of available biological material. However, this drawback might be circumvented by the recent cloning of several gamete-specific genes, which opens possibilities for the production of recombinant proteins. By use of cDNA and genomic DNA fragments of the human ZP3 gene, which encodes a major constituent of the zona pellucida surrounding the oocyte, a 2.7-kb minigene was constructed containing the natural third and fourth introns of the gene and a truncated intron between exons 2 and 3. This ZP3 DNA was transfected to Chinese hamster ovary cells, and a single-cell clone producing the recombinant ZP3 protein (recZP3) was generated. Western blot analysis of culture medium from these cells showed that recZP3 has a molecular mass +/- 5 kDa smaller than that of natural ZP3. Under reducing conditions, it migrates at an apparent molecular mass of 55-60 kDa. RecZP3 induced the sperm acrosome reaction and promoted fusion of human spermatozoa with zona-free hamster oocytes, indicating that the recombinant protein is biologically active. RecZP3 provides an attractive tool for studying the initial stage of the human fertilization process. Furthermore, it might have clinical applications in the development of diagnostic tests for male infertility and serve as target antigen in the design of contraceptive vaccines.

Progesterone-induced acrosome reaction: potential role for sperm acrosome antigen-1 in fertilization

We have established a monoclonal antibody (mAb) AG7 defining a sperm acrosome antigen-1 (SAA-1) on spermatozoa from the human and several mammalian species. MAb AG7 inhibits fertilization of mouse eggs in vitro and in vivo. An important characteristic of mAb AG7 is its inhibition of the rise in intracellular calcium induced by progesterone in human spermatozoa. Here we show that, following the acrosome reaction, SAA-1 is lost from the cap of human spermatozoa but remains detectable in the equatorial region. Acrosome reaction assays demonstrated a clear difference between progesterone- and A23187-induced acrosome reactions. For induction of the acrosome reaction with progesterone, a minimum capacitation time of 6 h was required. A23187 induced the acrosome reaction regardless of capacitation time. MAb AG7 completely inhibited the progesterone-induced acrosome reaction, but not the A23187-induced acrosome reaction in human spermatozoa. Differences in the pattern of calcium flux induced by the two agents might account for this phenomenon. The inhibition of the progesterone-induced acrosome reaction by mAb AG7 implies a regulatory function of SAA-1 during the human sperm acrosome reaction.

Analysis of the extent to which sperm movement can predict the results of ionophore-enhanced functional assays of the acrosome reaction and sperm-oocyte fusion

This study has examined the extent to which the information generated by ionophore-enhanced bioassays of the acrosome reaction and sperm-oocyte fusion might be predicted from the computer-aided analysis of sperm motility. Strong correlations (r approximately 0.7) were observed between specific components of sperm movement in semen and the potential for A23187-induced sperm-oocyte fusion, generating a stepwise regression coefficient of R = 0.663 on the bais of two criteria, percentage progressive motility and amplitude of sperm lateral head displacement (ALH). The movement characteristics of the spermatozoa recovered from the Percoll gradients gave an even higher R value of 0.838 on the basis of four variables (percentage rapid, average path velocity, straightness and ALH). In contrast, the ability of human spermatozoa to undergo acrosome reaction in response to A23187 exhibited a limited correlation with sperm movement, whether these measurements were made in the original semen sample or following Percoll purification (R approximately 0.4). These results have diagnostic implications, since sperm-oocyte fusion and the acrosome reaction clearly differ in their relative dependence on sperm motility. In practical terms, it should be noted that the computer-aided analysis of sperm movement was shown to provide up to 70% of the information generated by the more laboured assessment of sperm-oocyte fusion.

Induced acrosome reactions as fertility predictor

PURPOSE

This study was conducted to determine the fertility predictive value of acrosome reaction rates and indices (induced minus control) of human spermatozoa. By comparison these outcomes with in vitro fertilization success. The effect of oocyte-cumulus complex exposure on the induction of the acrosome reaction was also analyzed. Patients attending our assisted reproduction unit for infertility treatment were included in the study. Acrosome reactions were determined on ethanol-permeabilized smears using FITC-conjugated Pisum sativum agglutinin. The acrosome reaction inducing agent used was calcium ionophore A23187 (10 microM/ml).

RESULTS

Poor correlations were found between all the acrosome reaction rates and indices and in vitro fertilization. The presence of oocyte-cumulus complexes had no effect on the spontaneous acrosome reactions, but had a significant effect on the inducibility of the acrosome reaction. Exposure to oocyte-cumulus complexes resulted in the mean percentage sperm induced to be 7.8% (SE = 3.1%) higher compared to the control samples.

CONCLUSIONS

Acrosome reaction rates and indices were therefore found to have no significant value in the prediction of male fertility and/or in vitro fertilization success. This study did, however, show that exposure to oocyte-cumulus complexes significantly increases the inducible sperm population.

The cell surface progesterone receptor which stimulates calcium influx in human sperm is unlike the A ring reduced steroid site on the GABAA receptor/chloride channel

Progesterone elicits a rapid, transient calcium influx in sperm that is a prerequisite for the progesterone-induced acrosome reaction. The possibility that the GABAA receptor/chloride channel was the receptor that mediated the progesterone-induced calcium influx in human sperm was examined. A-ring reduced 3 alpha-hydroxy pregnane steroids (e.g. alfaxalone, allopregnanolone, pregnanolone), which are active on the GABAA receptor/chloride channel, were found to be much weaker than progesterone at stimulating Ca2+ influx in sperm. The effects of a variety of progesterone metabolites and analogs and other steroids were compared for their ability to (i) stimulate GABA-induced 36Cl- uptake in synaptoneurosomes, (ii) stimulate GABA-induced Cl- currents in HEK-293 cells transfected with alpha 1, beta 2, and gamma 2 subunits of the GABAA receptor/chloride complex, and (iii) elicit a rapid Ca2+ influx in sperm. No correlation was observed between the ability of a given steroid to stimulate Ca2+ influx and efficacy in eliciting either 36Cl- uptake or chloride currents. Importantly, the action of progesterone to stimulate Ca2+ influx was not modified by GABA, diazepam, picrotoxin and pentobarbitol (known regulators of the GABAA receptor/chloride channel). It is concluded from these studies that the cell surface progesterone binding site on human sperm that mediates progesterone-induced changes in [Ca2+]i is unlike the steroid binding site on the GABAA receptor/chloride channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of monoclonal antibodies specific for human sperm: effect of CRL-10 on acrosome reaction

Monoclonal antibodies to human sperm were obtained from hyperimmunized BALB/c mouse spleen cells fused with myeloma NS-1 cells. Each antibody recognized definite regions in fresh unfixed sperm: equatorial region, acrosome, postacrosome, midpiece, tail. All the antibodies were specific for sperm. We selected CRL-10 monoclonal antibody, specific for acrosome, for a detailed study. The expression of the CRL-10 antibody-bound antigen was detected in other mammalian species. When CRL-10 antibody was added prior to sperm incubation in a capacitating medium, promotion of the acrosome reaction was observed.

Phosphatidylcholine enhances the acrosomal responsiveness of human sperm

Supplementing bovine serum albumin-containing medium with phosphatidylcholine (PC) accelerated the in vitro development of human sperm acrosomal responsiveness. Responsiveness was assessed by exposing the sperm to progesterone. The maximum effect was produced by incubation with 100 micrograms PC/ml, which resulted in 40% (23-56%) (mean, 95% confidence limits) of the sperm becoming responsive to progesterone at 24 hours, compared to 23% (10-40%) of control sperm. Enhancement was apparent after as little as 6 hours of incubation in vitro, and the number of responsive sperm was still increasing at the last time point tested (30 hours). PC had no apparent ill effects; it did not alter the percentage of motile sperm or the percentage of sperm stained with the supravital stain, Hoechst 33258. Enhanced responsiveness required prolonged incubation in PC, because PC was not effective when it was only applied at the same time as progesterone. Lysophosphatidylcholine did not enhance acrosomal responsiveness when used at concentrations from 10 ng/ml to 100 micrograms/ml, indicating that the effect of PC was not due to trace amounts of lysophosphatidylcholine. PC also increased the response of sperm to the Ca2+/H(+)-exchanging ionophore, ionomycin, suggesting that PC modifies an event that is coincident with or subsequent to the rise in intracellular free Ca2+ that is triggered by progesterone.

Disordered acrosome reaction of spermatozoa bound to the zona pellucida: a newly discovered sperm defect causing infertility with reduced sperm-zona pellucida penetration and reduced fertilization in vitro

It is believed that during the process of human fertilization, acrosome-intact spermatozoa bind to the surface of the zona pellucida which triggers the acrosome reaction and the enzymes released facilitate sperm penetration through the zona pellucida. We describe here reduced frequency of the acrosome reaction on the zona pellucida as a cause of infertility in 10 couples with long durations of infertility (average 6 years) and low (< 15%, n = 3) or zero (n = 7) fertilization rates in vitro. Sperm concentration, motility, velocity (Hamilton-Thorn), morphology and DNA normality were within the normal range in all the patients. Electron microscopy of spermatozoa did not reveal any specific ultrastructural defects. All couples were negative for antisperm antibodies by immunobead tests. Oocytes from other patients which failed to fertilize in in-vitro fertilization and normal donor spermatozoa were used as controls for sperm-zona pellucida binding and penetration experiments. Acrosome status of spermatozoa bound to the zona pellucida was assessed with a fluorescent lectin and electron microscopy. The mean number of spermatozoa bound to the zona pellucida was not significantly different between patients and controls. However, the acrosome reaction of spermatozoa bound to the zona pellucida after 2 h incubation was significantly lower (P < 0.001) in the patients (mean 5%, range 0-16) than in the controls (mean 68%, range 44-96). No zona pellucida (out of 40) was penetrated by patient spermatozoa whereas most (39/40) zonae were penetrated by control spermatozoa (average 27 spermatozoa/four zonae pellucidae).(ABSTRACT TRUNCATED AT 250 WORDS)

Anandamide (arachidonylethanolamide), a brain cannabinoid receptor agonist, reduces sperm fertilizing capacity in sea urchins by inhibiting the acrosome reaction

Anandamide (arachidonylethanolamide) is an endogenous cannabinoid receptor agonist in mammalian brain. Sea urchin sperm contain a high-affinity cannabinoid receptor similar to the cannabinoid receptor in mammalian brain. (-)-delta 9-Tetrahydrocannabinol (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. We now report that anandamide produces effects similar to those previously obtained with THC in Strongylocentrotus purpuratus in reducing sperm fertilizing capacity and inhibiting the egg jelly-stimulated acrosome reaction. Arachidonic acid does not inhibit the acrosome reaction under similar conditions. The adverse effects of anandamide on sperm fertilizing capacity and the acrosome reaction are reversible. The receptivity of unfertilized eggs to sperm and sperm motility are not impaired by anandamide. Under conditions where anandamide completely blocks the egg jelly-stimulated acrosome reaction, it does not inhibit the acrosome reaction artificially initiated by ionomycin, which promotes Ca2+ influx, and nigericin, which activates K+ channels in sperm. These findings provide additional evidence that the cannabinoid receptor in sperm plays a role in blocking the acrosome reaction, indicate that anandamide or a related molecule may be the natural ligand for the cannabinoid receptor in sea urchin sperm, and suggest that binding of anandamide to the cannabinoid receptor modulates stimulus-secretion-coupling in sperm by affecting an event prior to ion channel opening.

The use of anticlusterin monoclonal antibodies for the combined assessment of human sperm morphology and acrosome integrity

Clusterin is an abundant protein in the human male reproductive tract which appears to be produced by the testis, epididymis and the seminal vesicles. Using monoclonal antibodies and an amplified immunoperoxidase technique, we have identified two apparently biochemically distinct forms of clusterin on human spermatozoa. Morphologically abnormal spermatozoa have an extensive surface coating of conventional 80 kDa native clusterin, but this form of clusterin is not detectable on normal spermatozoa. Normal spermatozoa, however, contain within the acrosomal cap a different form of clusterin, reactive with an anticlusterin alpha-chain antibody. Agglutinated spermatozoa, most of which are grossly abnormal, were intensely labelled with the antibody against conventional 80 kDa clusterin, suggesting that the 'clustering' properties of this protein may play a role in the aggregation of abnormal spermatozoa. Anticlusterin monoclonal antibodies may be useful for semen analysis. Staining spermatozoa with anticlusterin monoclonal antibodies is a technically simple method which provides a visually obvious means of assessing spermatozoa morphology and acrosome status simultaneously. The current data also suggest that different functions of clusterin in the reproductive tract may be attributed to different molecular forms of the protein.

Pentoxifylline acts synergistically with A23187 to increase the penetration of zona-free hamster oocytes by cryopreserved human spermatozoa

The number of cryopreserved human spermatozoa which penetrated zona-free hamster oocytes after stimulation with 2 mumol A23187 per litre was increased by the further addition of 0.6 or 3.6 mmol pentoxifylline per litre. With spermatozoa prepared by washing by repeated centrifugation, the median numbers of sperm heads/egg were 1.9, 7.9 and 10.8 in the presence of 0, 0.6 or 3.6 mmol pentoxifylline per litre, respectively. A similar effect was observed with spermatozoa prepared on a Percoll gradient. As A23187 inhibited sperm motility, and this was exacerbated by pentoxifylline, the increased penetration rate of hamster oocytes cannot be explained by improved sperm motility. The number of spermatozoa stimulated to acrosome react by 2 mumol A23187 per litre was increased 3-fold by 3.6 mmol pentoxifylline per litre and 4-fold by 5 mmol caffeine per litre. These data suggest that cAMP may act synergistically with Ca2+ to stimulate the acrosome reaction. Pentoxifylline may improve the fertility of poor-quality human spermatozoa by enhancing their ability to respond to the Ca2+ signal produced by binding to the zona pellucida.