Mannose ligand receptor assay as a test to predict fertilization in vitro: a prospective study

Lactoferrin affects in vitro and in vivo fertilization and implantation in rats

Lactoferrin (LF) is present in the oviduct, reduces in vitro gamete interaction, and affects sperm capacitation parameters in humans. Our aim was to investigate LF actions on further stages of the reproductive process in the Wistar rat model. Motile sperm were obtained from cauda epididymis to assess LF binding by direct immunofluorescence and LF effect on acrosome reaction (AR) using a Coomassie blue staining. After ovarian hyperstimulation of female rats, oocytes were surgically recovered and coincubated with motile sperm and different doses of LF to estimate the in vitro fertilization (IVF) rate. To evaluate the LF effect on pregnancy and embryo implantation, female rats (80 days old) were placed with males and received daily intraperitoneal injections of LF during one complete estrous cycle (pregnancy experiments) or during the first 8 gestational days (implantation experiments). The number of pregnant females and live born pups was recorded after labor. Moreover, the number of implantation sites was registered during the implantation period. LF was able to bind to the sperm head, midpiece, and tail. 10 and 100 μg/ml LF stimulated the AR but reduced the IVF rate. The administration of 100 and 200 mg/kg LF significantly decreased the number of implantation sites and the litter size, whereas 100 mg/kg LF declined the pregnancy rate. The results suggest that LF might interfere with the reproductive process, possibly interfering with gamete interaction or inducing a premature AR; nevertheless, the mechanisms involved are yet to be elucidated.

Effects of lactoferrin, a protein present in the female reproductive tract, on parameters of human sperm capacitation and gamete interaction

In a recent study, lactoferrin (LF) was detected in human oviductal secretion. The protein was able to bind to oocytes and sperm, and modulated gamete interaction. The aim of the present study was to investigate the effect of LF on parameters related to human sperm capacitation and sperm-zona pellucida interaction. Semen samples were obtained from healthy normozoospermic donors (n = 7). Human follicular fluids and oocytes were collected from patients undergoing in vitro fertilization. Motile sperm obtained by swim-up were incubated for 6 or 22 h under capacitating conditions with LF (0-100 μg/mL). After incubations, viability, motility, presence of α-d-mannose receptors (using a fluorescent probe on mannose coupled to bovine serum albumin), spontaneous and induced acrosome reaction (assessed with Pisum sativum agglutinin conjugated to fluorescein isothiocyanate), and tyrosine phosphorylation of sperm proteins were evaluated. Sperm-zona pellucida interaction in the presence of LF was investigated using the hemizone assay. The presence of LF did not affect sperm viability or motility, but caused a dose-dependent significant decrease in sperm α-d-mannose-binding sites, and the effect was already significant with the lowest concentration of the protein used after 22 h incubation. Dose-dependent significant increases in both induced acrosome reaction and tyrosine phosphorylation of sperm proteins were observed in the presence of LF. The present data indicate that LF modulates parameters of sperm function. The inhibition of gamete interaction by LF could be partially explained by the decrease in sperm d-mannose-binding sites. The presence of the LF promoted sperm capacitation in vitro.

d-Mannose-binding sites are putative sperm determinants of human oocyte recognition and fertilization

The aim of the present study was to further evaluate the participation of D-mannose in the process of human sperm-egg interaction. Zona pellucida binding competitive assays in the presence of D-mannose were carried out using discarded oocytes from IVF. Spermatozoa were capacitated and D-mannose-binding site (MBS) expression, sperm viability and follicular fluidinduced acrosome reaction (AR) were evaluated. MBS were visualized using a fluorescein-neoglycoprotein probe. The capacity of free D-mannose and mannosylated albumin to induce the AR was also tested. MBS and the IVF outcome were also analysed. The involvement of D-mannose in sperm binding to the zona pellucida was verified by the inhibitory effect produced when the sugar was present during binding assays. MBS expression increased during capacitation, in parallel with the ability to undergo the induced AR. Mannosylated albumin, but not the free sugar, induced the AR. In acrosome-reacted spermatozoa, the MBS was located at the plasma membrane, as shown by confocal analysis. No significant difference in the increase in MBS expression was observed among the different IVF groups of patients. The data show that D-mannose is involved in the sperm-zona pellucida interaction, and that the expression of MBS on the sperm surface occurs during the acquisition of in-vitro sperm fertilizing ability.

The role of mannose receptor on HIV-1 entry into human spermatozoa

In this opinion article we consider the possibility that human spermatozoa have receptors for human immunodeficiency virus-1 (HIV-1). It is clear that sperm cells have the potential for transmitting HIV-1, but the mechanisms responsible for spreading or the virus by this vector are not known. In contrast to the traditional HIV-1 target cells, spermatozoa do not express CD4 receptors or the CCR5/CXCR4 co-receptors. Recent evidence indicates that astrocytes, which also do not express these molecules, can be infected with HIV-1 through the mannose receptor. Furthermore, a 160-kDa sperm receptor that interacts with the HIV gp 120 has been described. Therefore, we hypothesize that the mannose receptor, of 165-175 kDa, is the receptor that HIV-1 uses to invade spermatozoa, which could lead to both vertical and horizontal transmission of HIV-1.

Doses of levonorgestrel comparable to that delivered by the levonorgestrel-releasing intrauterine system can modify the in vitro expression of zona binding sites of human spermatozoa

BACKGROUND

The levonorgestrel-releasing intrauterine system (LNG-IUS) exerts its contraceptive effect by interfering with sperm transport through the female genital tract and with ovulation. However, the possibility cannot be discarded that the device exerts a direct effect on sperm function, thus, helping prevent fertilization.

OBJECTIVES

The purpose of this study is to evaluate whether LNG at doses comparable to that measured in the uterus during the use of the LNG-IUS affects the detection of D-mannose binding sites or zona pellucida (ZP) receptors on human spermatozoa. The association with acrosomal status was also investigated.

METHODS

Seventeen semen samples from fertile men were used, and spermatozoa were separated using a Percoll gradient and incubated for 22 h at 37 degrees C under 5% CO(2) in air. Capacitated spermatozoa were exposed for 30 min to 1,000 or 10,000 ng/mL of LNG or control medium. D-Mannose binding sites were detected using commercial D-mannosylated bovine serum albumin conjugated with fluorescein isothiocyanate, and the percentage of specific patterns (II and III) was recorded. The acrosome reaction was evaluated using the Pisum sativum technique.

RESULTS

Levonorgestrel releasing significantly increased (p < .001) the percentage of spermatozoa with D-mannose receptors localized in pattern III, and this increase was dose dependent and a significant increase (p < .001) in the percentage of acrosome-reacted spermatozoa. Double staining confirmed an association between the location of the zona receptor and acrosomal status.

RESULTS

The in vitro exposure of capacitated spermatozoa to the assayed doses of LNG increased the proportion of spermatozoa with fewer chances of interacting with the ZP. Further studies should be carried out to confirm whether this mechanism is part of the contraceptive action of the LNG-IUS.

Inhibition of bovine sperm-oocyte fusion by the p-aminophenyl derivative of D-mannose

Several steps in the process of mammalian fertilization are mediated by carbohydrates. This study investigated the role of the p-aminophenyl derivative of d-mannose (APMP) during bovine fertilization. Inseminating cumulus-oocyte complexes (COCs) in the presence of increasing APMP concentrations resulted in a significant dose-dependent decrease of the fertilization rate (P < 0.05). No negative effect of 50 mM APMP on total sperm motility and progressive motility was found. Subsequently, the fertilization steps at which this blocking effect could be exerted were investigated, i.e., sperm penetration of the cumulus oophorus, sperm-zona binding, acrosome reaction, sperm-oolemma binding, and/or sperm-oocyte fusion. Inseminating cumulus-enclosed and cumulus-denuded oocytes in the presence of 50 mM APMP significantly decreased the fertilization rate to a comparable minimum level (P < 0.05). There was no significant relationship between the number of spermatozoa bound to the zona pellucida and the APMP concentration, and APMP nor d-mannosylated bovine serum albumin (BSA) suppressed or stimulated sperm acrosomal status. Inseminating zona-free oocytes in the presence of 50 mM APMP did not influence sperm-oolemma binding, but significantly inhibited sperm-oocyte fusion (P < 0.05). Preincubating zona-free oocytes with 200 microg/ml Con A but not with 50 mM APMP inhibited the sperm-oocyte fusion rate to the same extent as when the gametes were simultaneously exposed to 50 mM APMP. These data indicate that the blocking effect of APMP on bovine fertilization is mainly due to an inhibition of sperm-oocyte fusion, probably by specific obstruction of the sperm receptor sites that are responsible for the fusion process.

Comprehensive office evaluation in the new millennium

The success of a comprehensive office-based evaluation of male-factor infertility depends on the physician's thorough understanding of risk assessment in the history, identification of pertinent physical examination findings, and correct assessment of laboratory data. Office-based ultrasonographic techniques have already increased the urologist's ability to visualize suspected anatomic abnormalities, and the use of functional tests of sperm has given greater depth to the limited, but essential, prognostic capabilities of the routine semen analysis.

Receptors and channels regulating acrosome reactions

Prospective clinical studies informed by cloning and sequencing of sperm surface receptors and metal ion channels have elucidated critical early steps in the acrosome reaction that explain aspects of metal ion-related male infertility. Induction of the acrosome reaction is proposed to include non-nuclear progesterone receptor activation of Shaker-related sperm head voltage-gated potassium ion channels (VGKC). Men express VGKC isoforms with differing sensitivities to lead (Pb(2+)) inhibition, thus explaining interindividual variabilities in Pb(2+)-related male infertility. VGKC opening induces calcium (Ca(2+)) transients, and a signalling cascade induced by zona receptor aggregation requires an actin cytoskeleton created by the VGKC-induced Ca(2+) transients. Actin polymerization and stabilization, favoured by zinc (Zn(2+)) and depolymerized by cadmium (Cd(2+)), may mediate low Zn(2+) and high Cd(2+) infertile states. Zona receptor aggregation induces phosphotyrosine signals at sites, including sperm voltage-dependent Ca(2+) channels (VDCC), intermediate in electrophysiology between T- and L-type channels. Sperm surface VDCC localize at the sperm equatorial segment, the terminus of zona receptor translocation. Opening of VDCC admits a second Ca(2+) wave that activates phospholipase C phosphorylated in the zona receptor cascade. Phospholipase C induces fusogenic lipids and activates actin-severing proteins, depolymerizing the actin cytoskeleton and permitting apposition and fusion of acrosomal and plasma membranes.

Effect of freezing-thawing on the expression of mannose-ligand receptors on human spermatozoa: the impact on sperm capacitation and acrosome reaction

The aim of this study was to evaluate the change in the expression of mannose-ligand receptors following a freezing-thawing procedure, in order to assess its impact on sperm capacitation and acrosome reaction. Twenty semen samples were obtained from fertile donors. Sperm samples were divided into two equal volumes. One aliquot was cryopreserved and the other aliquot was incubated at 32 degrees C. After 2 h the frozen sample was thawed and both samples were further incubated at 32 degrees C to allow capacitation. Mannose receptors were examined following 4 and 22 h of incubation using a mannosylated-BSA-FITC probe. The expression of mannose-ligand receptors on the sperm plasma membrane was determined according to the fluorescence pattern: pattern I represents pre-capacitation, pattern II represents capacitated spermatozoa and pattern III represents acrosome-reacted spermatozoa. After 4 h incubation in capacitating medium, the percentages of patterns I, II and III were 90, 7 and 3% for fresh spermatozoa and 89, 8 and 3% for frozen-thawed spermatozoa, respectively (P > 0.05). Following 22 h of incubation, the percentages of patterns I, II and III were 84, 11 and 5 for fresh spermatozoa and 83, 11 and 6% for frozen-thawed spermatozoa, respectively (not significant at P > 0.05). The percentages of patterns II and III in fresh and frozen-thawed spermatozoa were increased by the same magnitude with longer incubation in the capacitating conditions. It was concluded that the freezing-thawing procedure for human spermatozoa does not affect the expression of mannose-ligand receptors and the dynamics of sperm pre-fertilization processes.

Metal ions and human sperm mannose receptors

Zinc and lead concentrations were measured in seminal plasma from fertile donors, infertile men with varicocoele and men undergoing work-ups for in vitro fertilization. Ejaculated spermatozoa from these subjects were incubated in vitro with various metal ions and/or dibromoethane and dibromochloropropane. Mannose receptor expression was correlated with metal and toxicant levels. Sperm distributions of potassium channels were compared with lead ions and calcium channels with zinc ions. Mannose receptor expression by capacitated spermatozoa increased linearly with seminal plasma zinc levels, and correlated inversely with lead levels. Cobalt had no effect on mannose receptor expression, but nickel had a concentration-dependent biphasic effect. Mannose receptor expression was not affected by dibromoethane and dibromochloropropane if the cholesterol content of the sperm membrane was high, but mannose receptor expression was decreased in low cholesterol spermatozoa by exposures below estimated permissive exposure limits. Potassium channels and lead ions co-localized over the entire head of human spermatozoa, while both calcium channels and zinc ions were confined to the equatorial segment of the head. Mannose receptor expression on the external surface of the human sperm plasma membrane is a biomarker for the effects of transition and heavy metals and organic toxicants on sperm fertility potential.

Numerical dose-compensated in vitro fertilization inseminations yield high fertilization and pregnancy rates

OBJECTIVE

To evaluate in cases with morphologically abnormal sperm whether fertilization and pregnancy rates are increased by normalizing the number of sperm inseminated and whether biomarkers can identify cases of reduced or failed fertilization.

DESIGN

Prospective studies of sperm morphology and function.

SETTING

University hospital assisted human reproduction program.

PATIENT(S)

Partners of 308 women undergoing IVF.

INTERVENTION(S)

Motile sperm populations were assessed for sperm head morphology, for surface receptors for mannose and progesterone binding, and the ability to undergo a free mannose-induced acrosome reaction. Zinc in seminal plasma was determined by atomic absorption spectroscopy.

MAIN OUTCOME MEASURE(S)

Sperm morphology was associated with fertilization and clinical pregnancy rates. Biomarker analyses were correlated with fertilization rates using Kruskal-Wallis tests, chi2 tests, and Spearman rank order correlations.

RESULT(S)

Fertilization and pregnancy rates after numerical dose compensation inseminations were indistinguishable between men with differing percentages of normal sperm. Biomarker deficits were identified irrespective of sperm head morphology in 96% of cases of reduced or failed fertilization.

CONCLUSION(S)

Fertilization and pregnancy rates in cases of abnormal morphology are optimized by inseminating at least 25,000 sperm/mL with normal acrosomes. Reduced or failed fertilization can be predicted by testing for molecular deficits in mannose receptor expression and mannose-stimulated acrosome loss.