In vitro fertilization and the effect of progesterone and 17 alpha-hydroxyprogesterone on acrosome reaction of mouse epididymal spermatozoa

This study assessed the effect of progesterone and 17 alpha-hydroxyprogesterone (17 alpha-OH-progesterone) at concentrations of 0.01-10 micrograms/ml, on the acrosome reaction and in vitro fertilizing ability of mouse epididymal spermatozoa. Cumulus masses containing oocytes were cultured in Brinster's medium, to which were added capacitated epididymal spermatozoa which had been incubated in medium with various concentrations of progesterone or 17 alpha-OH-progesterone for 90 min. IVF success rate was assessed 20-24 h following insemination. Progesterone was found to increase the fertilization rate at the 1 microgram/ml and 10 microgram/ml concentrations while lower concentrations had no effect. However, 17 alpha-OH-progesterone failed to show any effect on fertilizing ability. Incubation of epididymal spermatozoa in medium containing 1 microgram/ml and 10 micrograms/ml progesterone significantly increased the acrosome reaction as monitored by a chlortetracycline fluorescence assay. 17 alpha-OH-progesterone, however, failed to show any effect on the acrosome reaction. The results suggest direct effects of progesterone, but not of 17 alpha-OH-progesterone, on fertilization and the acrosome reaction of mouse spermatozoa.

Relationship between acrosome reactions and hamster egg penetration after ionophore challenge in absence of teratozoospermia

OBJECTIVE

To determine the relationship between acrosome reactions and hamster egg penetration after ionophore challenge in nonteratozoospermic semen samples.

SETTING

A tertiary care center, the Andrologic Clinic, Department of Internal Medicine, University of L'Aquila.

PATIENTS

Twenty-five nonteratozoospermic patients with infertile marriages and nine fertile men.

INTERVENTIONS

The hamster egg penetration assay and the acrosome reaction assessment were performed on capacitated sperm suspensions in basal conditions and after ionophore challenge with ionomycin.

MAIN OUTCOME MEASURE

The relationship between the acrosome reactions and the hamster egg penetration was analyzed.

RESULTS

Although in basal conditions the spontaneous acrosome reaction rate was not correlated with the hamster egg penetration, after ionophore challenge both the induced acrosome reaction rate and the acrosome reaction increase (induced minus spontaneous acrosome reaction rate) correlated with the hamster egg penetration. The highest correlation was observed between the induced acrosome reaction rate and the penetration index. Considering a penetration index = 2 as the threshold of a good response of the hamster egg penetration assay to the ionophore challenge, significantly lower acrosome reaction rates and increases were associated with poor hamster egg penetration. However, different penetration indexes occurred at the same level of induced acrosome reaction rate.

CONCLUSIONS

The capability of sperm to react after ionophore challenge reflects to some extent the capability of the acrosome-reacted sperm to undergo the changes of the plasma membrane that are necessary for sperm-oocyte fusion. The simple evaluation of the acrosome reactions may represent a useful complement rather than a substitute for the hamster egg penetration assay in monitoring the responses of human sperm to the ionophore challenge. An impaired inducibility of the acrosome reactions may account for poor hamster egg penetrations exhibited by nonteratozoospermic semen samples.

The acrosome reaction in digitonin-permeabilized sea urchin sperm in the absence of the natural inducer

In many species, the acrosome reaction of sperm is an obligatory step in fertilization. Increases in [Ca2+]i and pHi, activation of adenylyl cyclase and inositol trisphosphate generation accompany the egg jelly-induced acrosome reaction of sea urchin sperm. The signaling mechanisms involved are unknown. We used digitonin, a cholesterol-complexing compound, to selectively permeabilize the plasma membrane of sea urchin sperm suspended in a medium that mimics the cytosolic ion composition. Within 6 to 8 min, 30 to 50 microM digitonin allowed incorporation of the membrane-impermeant dye Hoechst 33258 into the sperm, staining exclusively the nucleus. No alterations in sperm morphology were caused by digitonin at the concentrations used, however, it irreversibly permeabilized the plasma membrane. Permeabilized sperm retained lactate dehydrogenase and actin. When incubated in Ca(2+)-containing permeabilization buffer (pH 7.8), sperm were capable of undergoing spontaneously the acrosome reaction; this reaction was pH dependent and displayed an absolute Ca2+ requirement. Electron microscopy indicates that the acrosome reaction undergone by permeabilized sperm resembled that induced by egg jelly. Additionally, rhodaminyl-phalloidin staining of sperm reacted under permeabilizing conditions revealed a fluorescent filament in the acrosomal tubule region, demonstrating the occurrence of actin polymerization. Thus, in permeabilized sperm the machinery necessary to perform a [Ca2+]i- and pHi-sensitive acrosome reaction is functionally preserved. Permeabilized sperm offer new avenues to study the molecular bases of the sea urchin sperm acrosome reaction.

Importance of bicarbonate to the progesterone-initiated human sperm acrosome reaction

Progesterone, a putative in vivo initiator of the human sperm acrosome reaction (AR), has previously been shown to act at the sperm plasma membrane to initiate the AR in vitro. Here, we have investigated whether bicarbonate (HCO3-) was required for the progesterone-initiated human AR and whether HCO3(-)-dependent cAMP activation might be involved. Capacitated human sperm were suspended in the presence of high (25 mM) or low (1 mM) HCO3- media. The AR was assayed using fluorescein isothiocyanate (FITC)-conconavalin A with sperm fixed 5 minutes after progesterone or solvent control addition. Progesterone initiated the AR in both high and low HCO3- media, but the percentage of AR was significantly lower in the latter medium. In the presence of high HCO3-, 20-minute preincubation with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), a blocker of HCO3- transport, inhibited the progesterone-initiated AR in a dose-dependent manner. The maximum inhibition (85%) was obtained with 18 microM DIDS. Inhibition by DIDS was reversed by washing sperm after treatment. Preincubation of sperm with dibutyryl cAMP (0.1 microM-1 mM) plus DIDS almost completely eliminated the inhibition of the progesterone-initiated AR by DIDS. Dibutyryl cAMP alone did not have a stimulatory effect on the progesterone-initiated AR, when high HCO3- was present, but it was able to partially overcome the reduction of AR by low HCO3-. These results are the first to demonstrate the importance of HCO3- to: 1) mammalian AR initiation by the putative physiological initiator progesterone, and 2) the human sperm AR.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of angiotensin-converting enzyme (ACE) from human spermatozoa during capacitation and acrosome reaction

The present study examines the release of angiotensin-converting enzyme (ACE) from human spermatozoa during capacitation conditions and in correlation to acrosome reaction and cell death. The ACE content of spermatozoa was measured by treating the cells with different detergents. Glass wool-filtered and washed human spermatozoa were incubated for 3 hours at 37 degrees C. Percentages of acrosome-reacted and dead spermatozoa did not change significantly, but the ACE release increased from 0 to 2.93 +/- 0.44 mU/100 x 10(6) spermatozoa after 180 minutes (P < 0.001). In order to study the influence of acrosome reaction on ACE release, the acrosome reaction of noncapacitated spermatozoa was induced by 10 microM calcium ionophore A23187. The percentages of acrosome reaction and viability in noncapacitated spermatozoa as well as the ACE release were compared to corresponding data from experiments using capacitated spermatozoa (3 hours, 37 degrees C) from the same donors. Although the number of living acrosome-reacted spermatozoa after ionophore treatment (30.5 +/- 4.0%) was significantly higher than after capacitation (13.3 +/- 2.8%, P < 0.001), ACE release from ionophore-treated, noncapacitated spermatozoa was lower (P < 0.05). The data indicate that ACE release from human spermatozoa during capacitation is independent of acrosome reaction. Measurement of ACE release may be a clinically useful assay for human sperm capacitation.

Dual effect of spermine on acrosomal exocytosis in capacitated bovine spermatozoa

The influence on spermine on the acrosomal exocytosis of capacitated bovine spermatozoa was studied. Dual effect of spermine was observed, depending on its concentration. It was shown that 10 microM spermine stimulated acrosomal exocytosis and prostaglandin F2 alpha production, whereas higher concentrations of spermine inhibited these processes. Acrosomal exocytosis induced by spermine was inhibited by staurosporine, a specific protein kinase C (PKC) inhibitor, indicating that PKC may be involved in this stimulation. Also, acrosomal exocytosis induced by the PKC activator phorbol 12-myristate-13-acetate was inhibited by 10 mM spermine. Therefore, these data indicate that spermine is involved in signal transduction events leading to exocytosis. We suggest that the concentration-dependent reversal of the stimulatory action of spermine could be explained by the existence of two binding sites for spermine: high affinity sites involved in inducing acrosomal exocytosis by low spermine concentration and low affinity sites mediating inhibition of acrosomal exocytosis by high concentration of spermine.

Oligosaccharide constructs with defined structures that inhibit binding of mouse sperm to unfertilized eggs in vitro

During fertilization in mice, free-swimming sperm bind to mZP3, an 83-kDa glycoprotein present in the egg extracellular coat, the zona pellucida [Wassarman, P. M. (1990) Development 108, 1-17]. Mouse sperm recognize and bind to a specific class of serine/threonine-linked (O-linked) oligosaccharides present on mZP3. After binding to mZP3, sperm undergo a form of cellular exocytosis, the acrosome reaction, thereby enabling them to penetrate the zona pellucida and fertilize the egg. Thus, gamete interactions in mice are carbohydrate-mediated. In this context, we tested 15 O-linked-related oligosaccharide constructs with defined structures for their ability to inhibit binding of mouse sperm to ovulated eggs and to induce sperm to undergo the acrosome reaction in vitro. Thirteen of the oligosaccharides were constructed and characterized in our laboratory [Seppo, A., Pentillä, L., Niemelä, R., Maaheimo, H., Renkonen, O., & Keane, A. (1995) Biochemistry 34, 4655-4661]; two were obtained commercially. We found that, while none of the oligosaccharides induced sperm to undergo the acrosome reaction, a few of them inhibited binding of sperm to eggs at relatively low concentrations (ID50 < 5 microM). In certain cases, sperm formed head-to-head aggregates in the presence of the oligosaccharides. The results suggest that the ability of oligosaccharides to inhibit binding of sperm to eggs is dependent on several parameters, including the size and branching pattern of the oligosaccharide, as well as on the nature of the sugar residue at the nonreducing end of the oligosaccharide.

Superoxide anion production by human spermatozoa as a part of the ionophore-induced acrosome reaction process

The involvement of superoxide anion (O2o-) in human sperm capacitation and/or acrosome reaction was investigated. Addition of superoxide dismutase (SOD) to the medium at the beginning of the capacitation process or 15 min before induction of the acrosome reaction, decreased the level of ionophore-induced acrosome reaction. Hyperactivation was unaffected by the presence of SOD during the capacitation process. Addition of calcium ionophore to the sperm suspension increased production of O2o- by the spermatozoa by four to five-fold and induced the acrosome reaction. In the presence of SOD, superoxide anion could not be detected in the medium and the rate of induced-acrosome reaction was decreased greatly. The presence of an inhibitor of protein kinase C inhibited the production of O2o- in the medium and reduced the induced-acrosome reaction. The production of O2o- and the acrosome reaction were also increased by exposure of spermatozoa to 12-myristate 13-acetate phorbol ester, a specific activator of protein kinase C. While the level of spontaneous acrosome reaction was not increased by the direct addition of O2o- to the medium, its presence induced the release of unesterified fatty acids from membrane phospholipids. These findings suggest that the production of O2o- by spermatozoa could be involved in the ionophore-induced acrosome reaction, possibly through the de-esterification of membrane phospholipids. However, this production of superoxide anion is not sufficient on its own to induce the acrosome reaction.

The effect of alpha-amylase on the acrosomal membrane of human sperm

PURPOSE

Sperm capacitation and the acrosome reaction are prerequisites to accomplishing fertilization. The object of this research was to induce capacitation and the acrosome reaction of human sperm, comparing the acrosome status of fertile and infertile men, using alpha-amylase.

METHODS

Acrosome status was measured using indirect immunofluorescence (IIF; monoclonal antibody GB24, Thèramex), hemizona assay (HZA), and transmission electron microscopy (TEM).

RESULTS

Acrosome-reacted sperm without alpha-amylase treatment was significantly more abundant in the fertile versus the infertile group utilizing IIF, HZA, and TEM. alpha-Amylase-treated spermatozoa from the fertile and infertile groups showed a significant increase in the number of sperm bound to the hemizona (P < 0.05).

CONCLUSIONS

The percentage of acrosome-reacted sperm in the infertile group was significantly enhanced by alpha-amylase, utilizing IIF and TEM.

Atrial natriuretic peptide: a chemoattractant of human spermatozoa by a guanylate cyclase-dependent pathway

Atrial natriuretic peptide (ANP), found in mammalian ovarian granulosa cells and oocytes (Kim et al., 1992, 1993), induces the human acrosome reaction (Anderson et al., 1994). The purpose of the present study was to determine whether ANP, as egg-derived peptides from sea urchins, can act as a chemoattractant to human spermatozoa. Small lengths of capillary tubing that contained different concentrations of ANP were suspended over a suspension of washed spermatozoa. The number of spermatozoa that entered the tubing was determined. More than twice the number of spermatozoa moved into the tubing that contained a maximally effective concentration of ANP, as compared with tubing that contained only medium. The concentration of ANP that produced a half-maximal effect was 0.7 nM. The effect was blocked by LY83583, an inhibitor of guanylate cyclase. ANP produced more than a twofold increase in the rate of cGMP formation, an effect that was blocked by LY83583. Human ANP (5-27), a fragment of the intact peptide, had no chemoattractant activity. These findings suggest that a specific sperm receptor exists for the chemoattractant activity of ANP that is associated with guanylate cyclase. The chemoattractant activity of ANP is independent of the presence of extracellular calcium ions and is independent of the action of ANP as a stimulus of the acrosome reaction. There is no association between the chemoattractant activity of follicular fluid and the follicular fluid concentration of ANP. These data suggest that factors besides ANP are responsible for the chemoattractant activity of follicular fluid.(ABSTRACT TRUNCATED AT 250 WORDS)

Relevance of acrosome function in the evaluation of semen in vitro fertilizing ability

OBJECTIVES

To determine whether or not acrosome evaluation can enhance the prediction of IVF results when associated to conventional semen parameters.

DESIGN

Acrosome reaction, sperm concentration, motility, and morphology were recorded in 131 semen samples from patients undergoing an IVF attempt.

MAIN OUTCOME MEASURES

Spontaneous acrosome loss after a 24-hour incubation in B2 medium and after induction by calcium ionophore A23187 and phorbol ester, phorbol 12-myristate 13-acetate 4-O-methyl ether (TPA).

RESULTS

Statistically significant differences between fertilization failures and successes were found for concentration, viability, spontaneous and induced acrosome reaction, and most parameters of motility and morphology. However, none of the parameters could predict > 64% of IVF results when studied alone. A progressive discriminant analysis allowed to predict up to 83% of IVF results, by classifying sperms through their normal forms, rapid motility, spontaneous acrosome loss, enlarged heads, multiflagellar forms, vitality, linear motility, and acrosome response to TPA. The other parameters, including concentration and response to calcium ionophore, had no additive value.

CONCLUSION

The study of acrosome function, through spontaneous acrosome loss and response to TPA, is of great interest in clinical practice when associated to some parameters of motility and morphology. However, it appears that response to calcium ionophore, one of the most studied parameters, is of poor practical interest.

Activation of a Gi protein in digitonin/cholate-solubilized membrane preparations of mouse sperm by the zona pellucida, an egg-specific extracellular matrix

Mammalian sperm possess guanine nucleotide-binding regulatory proteins (G proteins) that are involved in signal transduction pathways leading to zona pellucida (ZP)-mediated acrosomal exocytosis. We have previously examined ZP-G protein dynamics in mouse sperm homogenates, as well as cell-free membrane preparations, and our data support the existence of ZP receptor-G protein complexes in sperm membranes. However, the composition of this complex has not been identified due to experimental limitations of the membrane preparations. In the present study, a detergent-solubilized preparation from mouse sperm membranes that retained the signaling properties of cell homogenates and cell-free membrane preparations was developed using buffers containing digitonin and cholate. GTP gamma S, a poorly hydrolyzable analogue of GTP, bound to these solubilized preparations in a specific and concentration-dependent fashion that reached saturation at 100 nM. Incubation of this solubilized membrane preparation with heat-solubilized ZP resulted in an increase in specific GTP gamma S binding in a concentration-dependent manner, with a maximal response at 4-6 ZP/microliters. Mastoparan (50 microM) increased GTP gamma S binding to levels similar to that seen with solubilized ZP. Mastoparan plus ZP stimulated GTP gamma S binding to the same extent as mastoparan or ZP alone. Pertussis toxin completely inhibited ZP-stimulated GTP gamma S binding and decreased mastoparan-stimulated GTP gamma S binding by 50-60%. Purified ZP3, the ZP component that possesses quantitatively all of the sperm binding and acrosomal exocytosis-inducing activities of the intact ZP, stimulated GTP gamma S binding to an extent similar to that of solubilized ZP.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of protein tyrosine phosphorylation by platelet-activating factor and progesterone in human spermatozoa

Tyrosine phosphorylation of proteins is involved in several sperm functions, including capacitation, motility, and acrosome reaction of spermatozoa. This study was undertaken to determine changes of tyrosine phosphorylation during 'in vitro' capacitation as well as the ability of platelet-activating factor (PAF) and progesterone (P), two known activators of sperm functions, to stimulate tyrosine phosphorylation of human sperm proteins. Spermatozoa were capacitated in BSA-containing medium and incubated with PAF (10-1000 nM) and progesterone (0.1-1 microgram/ml). After SDS-PAGE, sperm proteins were transferred to nitrocellulose and tyrosine phosphorylated proteins immunodetected by reacting with anti-phosphotyrosine antibody. The antibody mainly reacted with two proteins of approximately 97 and 75 kDa. The level of phosphorylation increased in these two proteins as a function of capacitation time, with a maximum between 120 and 180 min. In addition, phosphorylation in these two proteins was increased in capacitated spermatozoa by treatment with progesterone and PAF and was greatly reduced by pre-incubation with the tryosine kinase inhibitor erbstatin. Furthermore, pre-incubation with the two tyrosine kinase inhibitors erbstatin and genistein inhibited the induction of acrosome reaction by progesterone and, partially, by PAF. Our results suggest a role for tyrosine kinase(s) in the mechanism of capacitation and activation of human spermatozoa by PAF and progesterone.

Ca(2+)-regulating mechanisms that modulate bull sperm capacitation and acrosomal exocytosis as determined by chlortetracycline analysis

We have used chlortetracycline (CTC) analysis to investigate mechanisms that may play important roles during bull sperm capacitation in a culture medium (containing glucose, heparin, and caffeine) known to promote capacitation and fertilization in vitro. In initial experiments employing the Ca2+ ionophore A23187, we identified three discrete CTC patterns so similar to those described for mouse and human sperm that we have employed the same nomenclature: "F," characteristic of uncapacitated, acrosome-intact cells; "B," characteristic of capacitated, acrosome-intact cells; "AR," characteristic of capacitated, acrosome-reacted cells. Over a 60-min period, A23187 stimulated significant increases in B and AR pattern cells, with concomitant decreases in F pattern cells, suggesting a very rapid transition from the uncapacitated to the capacitated state and then on to exocytosis. Without ionophore, significant changes in the proportions of F and B pattern cells were also observed, but the maximum responses required 4 hr; the proportion of AR cells was consistently approximately 15% throughout, indicating a low incidence of spontaneous acrosome loss. Analysis of cells in media with altered composition indicated that the inclusion of either heparin or caffeine significantly promoted capacitation to about the same extent, but together, heparin plus caffeine had an even more stimulatory effect. Despite this, none of these treatments triggered acrosome loss above the levels seen in media lacking these constituents. In the presence of caffeine, with or without heparin, the inclusion of glucose had little effect on responses, but in the presence of heparin there were fewer B cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting fertilization: endometrial placental protein 14 reduces the capacity of human spermatozoa to bind to the human zona pellucida

OBJECTIVE

To examine whether placental protein 14 (PP14) may affect directly those sperm functions crucial to fertilization and early embryo development.

DESIGN

In these prospective studies, we evaluated semen samples of fertile men incubated under capacitating conditions with and without PP14.

SETTING

Academic tertiary institution.

INTERVENTIONS

Biologically active PP14 was purified from human midtrimester amniotic fluid by anion exchange and immunoaffinity chromatography. After separation of the motile fraction, spermatozoa were incubated for 30 minutes with or without PP14 (concentration range of 0.01 to 100 micrograms/mL), washed, and then aliquots were prepared for use in the different assays. Human sperm-zona pellucida (ZP) binding was assessed using the hemizona assay (HZA) in a 4-hour gametes coincubation period. Sperm motility parameters were evaluated using a computerized semen analyzer. The acrosome reaction (AR) was determined by fluorescein isothiocyanate-conjugated Pisum sativum agglutinin and indirect immunofluorescence.

MAIN OUTCOME MEASURES

Sperm-ZP binding, sperm motility patterns, and AR.

RESULTS

Preincubation of sperm (and not the hemizonae) with PP14 produced a significant and dose-dependent inhibition of binding in the HZA. Monoclonal antibodies generated against PP14 showed no direct effect in the HZA and partially neutralized the inhibitory activity of PP14 in the HZA. Insulin-like growth factor binding protein-1 (IGFBP-1), an endometrial stromal cell product, showed no effect in the HZA. Neither PP14 nor IGFBP-1 interfered with sperm motility parameters or the AR.

CONCLUSIONS

Placental protein 14 produced a potent, fast, and dose-dependent inhibition of binding of human spermatozoa to the human ZP without affecting other prefertilization events (i.e., hyperactivated motility or AR). The detrimental effect on sperm-zona interaction seems to be specific for this endometrial epithelial protein (not observed with an endometrial stromal product) and may have fundamental bearance to the fertilization process thus providing a mechanism for endometriosis-related infertility.

Monoclonal antibodies which recognize equatorial segment epitopes presented de novo following the A23187-induced acrosome reaction of guinea pig sperm

Acrosome-intact mammalian sperm can adhere to zona pellucida-free oocytes but are only capable of fusing if they have previously undergone the acrosome reaction. This suggests that the acrosome reaction results in presentation of at least one novel epitope which plays a role in sperm-oocyte fusion. Monoclonal antibodies were raised against unfixed acrosome-reacted guinea pig sperm and screened by indirect immunofluorescence for binding to the equatorial segment. They were back-screened against unfixed acrosome-intact sperm for absence of binding. Using this approach, two antibodies, G11 and M13, were identified which detect equatorial segment epitopes presented de novo by sperm following an A23187-induced acrosome reaction. The localization of these epitopes to the equatorial segment was confirmed at the ultrastructural level by indirect immunogold-labelling. Fluorescein isothiocyanate-labelled Fab fragments of these two antibodies also localized to the equatorial segment. Affinity chromatography and western blotting established that the two mAbs recognize the same proteins, which have M(r)s of 34, 46, 48 and 51 × 10(3). When sperm were induced to undergo the acrosome reaction with A23187 and incubated with their discharged acrosomal contents, a further band was produced with an M(r) of 30 × 10(3). Production of this band was inhibited in the combined presence of 100 microM phenylmethylsulphonyl fluoride and 100 microM p-aminobenzamidine even though these compounds do not inhibit acrosomal exocytosis. Neuraminidase and O-glycosidase were without effect on the proteins detected by antibodies G11 and M13. Endoglycosidase F, however, eliminated the bands of M(r) 46, 48 and 51 × 10(3) and replaced them with a strong band of M(r) 44 × 10(3) and two minor bands of M(r) 43 and 45 × 10(3). Formaldehyde fixation of acrosome-intact sperm caused partial rupture of the acrosome with loss of the characteristic rouleaux (stacks) of guinea pig sperm. Indirect labelling of these formaldehyde-fixed sperm with fluorescein isothiocyanate- or gold-labelled second antibody, with or without permeabilization with 0.05% Triton X-100, showed dense labelling on the cytoplasmic face of the plasma membrane overlying the convex surface of the acrosome but little labelling elsewhere. Cryosections of acrosome-intact sperm labelled indirectly with immuno-gold showed labelling consistent with the same location, as well as sporadic labelling at other intracellular sites overlying the acrosome. Since there is no evidence that sperm can translocate intact membrane protein from the cytoplasmic face to the extracellular face of the plasma membrane during the acrosome reaction, the evidence suggests that there are two isolated antigen pools.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of acrosome reaction in fresh and frozen-thawed bovine spermatozoa by platelet activating factor

In vitro capacitation has been induced in fresh and frozen spermatozoa of Karan Swiss (KS) and Karan Fries (KF) crossbred cattle by using a phospholipid-platelet activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine). The capacitation was monitored by examining acrosome reaction (AR) and motility at various levels of platelet activating factor (PAF) and at the end of each incubation time. On an average, with the increase in incubation time, there was a gradual decrease in motility and increase in acrosome reaction in both fresh as well as frozen spermatozoa. As PAF level increased, the motility of fresh sperms decreased and their acrosome reaction increased dramatically. However, in frozen-thawed semen, the motility remained almost the same and increase in AR of frozen spermatozoa was not pronounced. PAF level of about 100 microM was observed to be most optimum as at this level AR improved significantly without much loss of motility.

Reactive oxygen species, lipid peroxidation and enzymatic defence systems in human spermatozoa

The reactive oxygen species, hydrogen peroxide (H2O2) and superoxide anion (O2o-), were generated with a xanthine-xanthine oxidase system and their effect on human sperm function was studied. The action of reactive oxygen species on selected human spermatozoa resulted in a decreased capacity for ionophore-induced acrosome reaction, a decrease in sperm motility, an increase in the concentration of lipid hydroperoxides and a loss of membrane polyunsaturated fatty acids. H2O2 was the key intermediate of the deleterious effects exerted by the xanthine and xanthine oxidase. Among these parameters, the acrosome reaction appeared most susceptible to the reactive oxygen species generated by the xanthine-xanthine oxidase system, and was decreased without sperm motility being affected. Treatment with H2O2 was shown to inactivate several enzymatic activities involved in the antioxidant defence of spermatozoa: glutathione peroxidase, superoxide dismutase and glucose-6-phosphate dehydrogenase. H2O2 and O2o- were shown to be involved in the lipid alterations triggered by the xanthine-xanthine oxidase system. Singlet oxygen is proposed to intervene in the lipoperoxidation process. The inefficacy of mannitol in protecting spermatozoa suggests that hydroxyl radicals were not produced in the extracellular medium.

Intracellular calcium increase and acrosome reaction in response to progesterone in human spermatozoa are correlated with in-vitro fertilization

In this study we have investigated responsiveness to progesterone in spermatozoa from a group of unselected male partners of couples undergoing in-vitro fertilization (IVF). We evaluated progesterone-stimulated intracellular Ca2+ ([Ca2+]i) and percentage increase in acrosome reaction in the same sperm sample used for oocyte inseminations. [Ca2+]i was measured with a fluorimetric method, while the acrosome reaction was assessed using a fluorescent probe (fluorescein isothiocyanate-labelled peanut lectin). The average percentage [Ca2+]i as well as the rate of increase in the frequency of acrosome reaction following progesterone challenge were significantly lower (P < 0.005) in the group of patients with a fertilization rate < 50%. In addition, significant correlations between the fertilization rate and the progesterone-stimulated [Ca2+]i and acrosome reaction increases (r = 0.78 and r = 0.79 respectively) were observed. Furthermore, in cases of fertilization failure, no increase of [Ca2+]i or acrosome reaction was observed in response to progesterone with the exception of one case. Our results indicate that [Ca2+]i and acrosome reaction increases in response to progesterone can be of value in the prediction of sperm fertilizing ability. As the two parameters were significantly correlated to each other (r = 0.86), the two assays have similar IVF predictive value and might be used interchangeably as a diagnostic tool in the assignment of male patients to the different kinds of assisted fertilization techniques.

Capacitation in vitro of stallion spermatozoa: comparison of progesterone-induced acrosome reactions in fertile and subfertile males

Mammalian sperm that have completed capacitation are capable of undergoing the acrosome reaction in response to a number of biological and chemical stimuli. In the present report, we have investigated the ability of progesterone to stimulate acrosome reactions of stallion sperm capacitated in vitro. Motile sperm were selected by a two-layer Percoll gradient centrifugation and were incubated in TALP medium modified by the 1:1 (v/v) addition of TEST-yolk medium for 5 hours at 39 degrees C, under 5% CO2 in humidified air. Sperm incubated in vitro in TALP-TEST medium had a higher percentage of acrosome reactions following the addition of progesterone (3.18 mumol/L) compared to controls (P < 0.05). Furthermore, sperm from stallions classified as fertile on the basis of breeding history had higher percentages of progesterone-induced acrosome reactions in comparison with stallions classified as subfertile (P < 0.05). Acrosome reactions were assessed routinely by fluoresceinated lectin binding, but the physiological appearance of induced acrosome reactions was confirmed at the ultrastructural level by transmission electron microscopy. We conclude that 1) TALP-TEST medium supports stallion sperm capacitation in vitro, 2) progesterone-induced acrosome reactions are physiological, and 3) sperm from fertile stallions may be more responsive to progesterone-induced acrosome reactions than those of subfertile stallions. This is the first report in a nonhuman species that differences exist between the sperm of fertile and subfertile males in the ability to capacitate and acrosome react in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of mannose-binding sites on human spermatozoa and their role in sperm-zona pellucida binding

A D-mannosylated albumin (DMA) neoglycoprotein was assessed to validate experimentally a probe capable of detecting mannose-binding sperm receptors involved in human sperm-egg interaction. DMA specifically blocked zona binding of swim-up human spermatozoa in a concentration-dependent manner. While no considerable effect was observed on sperm-zona initial contact, almost 50% of spermatozoa bound to the zona during a 2-hour period detached from it when DMA was introduced in the incubation medium. DNA inhibition was evident when 10% fetal bovine serum, but not 3.5% human serum albumin (HSA), was used as Ham's F10 medium supplementation. This may be due to the amount of free calcium in the medium since addition of 40 mM CaCl2 to F10-HSA restored DMA inhibition. Furthermore, the higher the calcium concentration in the incubation buffer, the greater the DMA blockage of sperm-zona binding. Unfixed sperm presented fluorescent DMA label over the entire acrosomal area (cap pattern), or concentrated at the equatorial segment (bar pattern). These patterns increased during capacitation, appearing on an average of 20% of the sperm after overnight incubation. They also increased, especially the bar pattern, following calcium ionophore treatment. Nearly all of methanol-fixed spermatozoa displayed the fluorescent label at the head level. Concomitant assessment of sperm membrane integrity and DMA fluorescent patterns revealed that DMA fluorescence coincided mostly with permeabilized or altered sperm plasma membrane. In conclusion, DMA is a suitable probe to identify human sperm mannose-binding sites crucially involved in sperm-zona interaction. These sites appear to require free calcium concentrations to operate, and their expression changes with capacitation and acrosome reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

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.