Sperm-zona interaction and recombinant DNA technology

Recombinant DNA technology has revolutionized our understanding of many biological systems. However, such techniques and their application have not been fully exploited in the study of sperm zona interaction. Using examples from other biological systems, we ourline several experimental approaches that are likely to significantly enhance our understanding of the gamete recognition process.

Semen donors and STD screening

AIM

The British Andrology Society recommends screening semen donors for sexually transmitted infections to minimise the risk of pathogen transmission to the mother and fetus. The aim was to review recent findings of semen donor screening and, if appropriate, recommend changes to the screening protocol.

SUBJECTS

175 consecutive men attending for STD screening between January 1992 and December 1995 who had been preselected by the Department of Obstetrics and Gynaecology as suitable semen donors.

METHODS

Retrospective review of case notes and group comparison of demographic and sexual history data.

RESULTS

11 men (6%) had evidence of infection, excluding CMV seropositivity, at their first STD screen. After semen donation, 109 men (63%) were rescreened and, of these, 12% had positive findings. Positive findings at initial screening were predicted by a history of more than one partner in the preceding 6 months (OR 7.11, 95% CI 1.66-30.4) but it did not predict rescreening findings. Other factors such as age, marital status, employment status or past STDs were not predictive for either screen.

DISCUSSION

Less than 20% of initial volunteers meet the full criteria of high quality post-thaw semen, no transmissible genetic disorders, and no transmissible pathogens. Sexual history may predict but would not alone preclude all positive STD screening findings. It is essential that sequential STD screening of donors continues and that genitourinary physicians should be involved in this process. Validation of newer diagnostic techniques as screening tests in this setting is required.

The potential shortcomings of measuring hyperactivated motility by computer-aided sperm analysis when sperm motion is multiphasic

This paper was written from the standpoint that computer-aided sperm analysis (CASA) instruments, which capture a 'snapshot' of sperm trajectories in order to generate their data, may provide a poor measure of hyperactivated motility in a sperm population where hyperactivation is multiphasic in nature. To illustrate this point, a series of theoretical sperm populations were constructed which varied subtly but significantly in the nature of the hyperactivated behaviour expressed by spermatozoa. The parameters which were manipulated were: (i) the number of hyperactivated phases exhibited within a given period of time; (ii) the duration of these phases; and (iii) proportion of spermatozoa within the population which exhibited hyperactivated phases. These populations were then subject to an analysis in which snapshots of sperm motion were examined to determine the percentage of hyperactivated spermatozoa for that population. The results indicated that whilst this snapshot approach to quantifying hyperactivation could provide a figure for the percentage of hyperactivated spermatozoa within the sample window, this often inaccurately described the underlying behaviour of the population. Since there is very likely to be a significant amount of biological information contained within the nature of multiphasic behaviour, this paper has argued that this aspect of snapshot analysis is one which requires serious consideration by CASA manufacturers and medical researchers.

Continuous assessment of human spermatozoa viability during cryopreservation

Cryomicroscopy has enabled direct observation of freezing and thawing of human spermatozoa. When used with a fluorescent viability kit, sperm membrane damage was not apparent down to temperatures of -5 degrees C, but significant damage occurred after thawing (55% of spermatozoa had damaged membranes). Semen samples were cooled or frozen to temperatures (at decrements of 10 degrees C) from 0 degree C to -110 degrees C. At all these temperatures the proportion of live to membrane-damaged cells remained constant. Samples held at temperatures above -30 degrees C were not adversely affected. Below -30 degrees C there was a gradual increase in the proportion of membrane-damaged cells on thaw and a decrease in the number of live cells recovering motility. At temperatures between -50 degrees C and -60 degrees C there was an equal proportion of live motile, immotile, and membrane-damaged cells. It is concluded that some irreversible damage to spermatozoa was a result of freezing processes in cells frozen to -30 degrees C or less, but most of the cryodamage was incurred during thawing, possibly due to recrystallization.

Direct assessment of cryopreservation of human spermatozoa using a cryomicroscope and computer-aided sperm analysis

Use of a cryostage has enabled direct observation of human spermatozoa as they are cryopreserved and thawed. Crystallization and recrystallization events are readily observed. In combination with computer-aided semen analysis (CASA) equipment it was possible to determine the consequence of altering the cooling, freezing and thawing rates of a temperature-rate profile on sperm motility. Increasing the cooling rate to 50 degrees C/min resulted in significantly lower pre-freeze to post-thaw ratios for average path velocity (VAP, 13%), mean straight line velocity (VSL, 35%), mean linearity (LIN, 28%) and straightness (STR, 24%), while the ratio of the number of cells crossing the field of view (NCF) significantly increased (30%) compared to a standard freeze-thaw temperature rate profile. The NCF pre-freeze to post-thaw ratio was associated with the percentage of cell recovery after cryopreservation. Faster thaw rates resulted in better survival of the cells, perhaps due to the shorter time during which recrystallization occurred. The NCF ratios were significantly higher (33 and 30% for thaw rates of 50 and 100 degrees C/min respectively) than for the standard profile samples. Previous studies on cell survival have shown a link between the cooling and thaw rates. The cryostage should prove invaluable in future studies to identify the causes of cryodamage to spermatozoa. When used in combination with CASA, changes to sperm function during cryopreservation can be accurately measured.

Biological activity of recombinant human ZP3 produced in vitro: potential for a sperm function test

The human zona binding test is the most predictive test of sperm function yet the availability of human zona severely restricts its clinical use. The primary aim of this study was to use a commercially available in-vitro transcription and translation system to produce immobilized recombinant human ZP3 (rhuZP3) on agarose beads. The biological activity of this preparation was examined using sperm binding and the acrosome reaction. Significantly higher levels of sperm binding to rhuZP3 beads (n = 12, P < 0.05) compared with controls were observed and there was a significant induction (n = 12, P < 0.01) in the acrosome reaction after overnight incubation at 37 degrees C in 5% CO2 in air. In conclusion, the in-vitro transcription and translation system can produce sufficient quantities of purified immobilized biologically active rhuZP3. These preliminary experiments will enable further refinements to be made so that a solid-phase sperm function test based on rhuZP3 coated beads is likely to be developed in the near future.

Recombinant human zona pellucida glycoprotein 3 induces calcium influx and acrosome reaction in human spermatozoa

Recombinant human ZP3 (rhuZP3) generated by Chinese hamster ovary cells transfected with a plasmid containing human ZP3 cDNA was used to study the acrosome reaction (AR) and intracellular calcium fluxes in capacitated human spermatozoa. Conditioned medium containing rhuZP3 significantly induced the AR (P < or = 0.005) in 59.4 +/- 4.7% of spermatozoa (control = 8.5 +/- 3.1%) and caused complete acrosomal loss in a further 17.2 +/- 3.8% of cells (control = 3.7 +/- 0.7%; mean +/- SEM, n = 5). Sperm motility was not affected and acrosomal exocytosis in response to rhuZP3 was also shown to be time-dependent. Basal concentrations of sperm intracellular calcium were measured (82 +/- 7 nM; mean +/- SEM, n = 9). A transient increase in intracellular calcium (typically up to 400-450 nM) occurred within 1 min of rhuZP3 addition and was followed by sustained lower values of calcium (200-400 nM). These responses were dependent on the amount of rhuZP3. This is the first report of zona protein-induced changes in intracellular calcium levels in human spermatozoa. The results support the premise that ZP3 is an agonist of the human sperm AR and that rhuZP3 generated in a eukaryotic cell is effective in this respect.

Comparative study of the effect of human cervical mucus and a cervical mucus substitute, Healonid, on capacitation and the acrosome reaction of human spermatozoa in vitro

The present study was designed to investigate the effect of human cervical mucus on capacitation and the acrosome reaction of human spermatozoa and compare its effect to that of a cervical mucus substitute, sodium hyaluronate (Healonid). Spermatozoa from donors of proven fertility were isolated from semen using cervical mucus, Healonid or a direct swim-up (acting as the control). Sperm capacitation and the acrosome reaction were monitored by the chlortetracycline assay. In the mucus-treated group, there was a significantly higher percentage of capacitated spermatozoa, but a low incidence of spontaneous and A23187-induced acrosome reactions compared to the control. The use of Healonid during sperm isolation mimicked the effect of mucus relatively successfully. Since mucus and Healonid show very little chemical similarity, this finding would imply that cervical mucus exerts a physical effect during its interaction with spermatozoa, although a chemical effect cannot be completely dismissed. In conclusion, this study confirms early reports describing the ability of cervical mucus to capacitate spermatozoa but at the same time conserve sperm function. The finding that Healonid exerts an almost identical effect on spermatozoa would lend support to its use as a cervical mucus substitute during in-vitro fertility assessments and research studies.

Measurement of intracellular pH in human spermatozoa by flow cytometry with the benzo[c]xanthene dye SNAFL-1: a novel, single excitation, dual emission, molecular probe

In numerous animal species the acrosome reaction of spermatozoa has been linked to elevations in intracellular pH (pHi). However, whether or not this is merely a passive consequence of calcium ion influx is not known. Studies into the fluctuations in pHi in sperm cells have been hampered by the lack of a pH-sensitive probe that could be used in conjunction with flow cytometry. In this study, flow cytometric analysis of pHi in human spermatozoa was accomplished by using one of the new benzo[c]xanthene dyes (SNAFL-1). SNAFL-1 was then observed in situ with conventional fluorescent microscopy and was found to be located in the post-acrosomal cytoplasm of the head. It was then used to measure the differences in pHi between acrosome intact populations of spermatozoa, and populations that had been induced to acrosome-react with human follicular fluid or the calcium ionophore A23187 to mimic the calcium influx. It was concluded that the human sperm acrosome reaction is also accompanied by a rise in pHi and the natural agonist-induced rise could not be accounted for by calcium ion influx alone.

A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility

OBJECTIVE

To determine the effectiveness of the in vivo administration of vitamin E as treatment for reactive oxygen species-associated male infertility.

SETTING

University-based center for reproductive medicine.

DESIGN

Double-blind randomized placebo cross-over controlled trial.

PATIENTS, PARTICIPANTS

Thirty healthy men with high levels of reactive oxygen species generation in semen and a normal female partner.

INTERVENTIONS

Patients were allocated to two groups according to the blinded randomization. Each patient received either 600 mg/d of vitamin E (Ephynal, 300 mg tablets; F. Hoffman-La Roche Ltd., Basle, Switzerland) (order A) or identical placebo tablets (order B) for 3 months. Then after a 1-month wash-out period the patients were crossed-over to the other treatment.

MAIN OUTCOME MEASURES

Improvement in the in vitro function of the spermatozoa measured by conventional semen analysis, computerized motility assessment, determination of reactive oxygen species generation, binding to the zona pellucida of the unfertilized human oocyte in a competitive zona binding assay, development of hyperactivated motility (both spontaneous and in the presence of 20% of the natural agonist, human follicular fluid) and pregnancy.

RESULTS

Rise in the blood serum vitamin E levels after treatment accompanied by improvement in one of the sperm function tests: the zona binding assay. The zona binding ratio for order A improved from 0.2 (range 0 to 0.5) before treatment to 0.5 (range 0.1 to 1.0) after treatment, the corresponding values for order B were 0.2 (range 0 to 1.0) before treatment and 0.3 (range 0.1 to 0.7) after treatment.

CONCLUSION

Oral administration of vitamin E significantly improves the in vitro function of human spermatozoa as assessed by the zona binding test.

Hyperactivation may assist human spermatozoa to detach from intimate association with the endosalpinx

The behaviour of human spermatozoa was observed during incubation with epithelial cells isolated from the isthmic and ampullary sections of human uterine (Fallopian) tubes. During incubation, spermatozoa were observed to bind to the epithelial cells of the tube (the endosalpinx), and individual spermatozoa attached and detached at intervals. The kinematic characteristics of spermatozoa during these behaviour patterns were determined. The results showed that detached spermatozoa typically had an increased curvilinear velocity and amplitude of lateral head displacement, accompanied by a decrease in their linearity. Significantly (P < 0.01) more of the detaching spermatozoa were hyperactivated than were spermatozoa prior to attachment for both isthmic (35.3 +/- 5.5 versus 4.0 +/- 3.3%; mean +/- SEM) and ampullary (26.0 +/- 7.0 versus 2.0 +/- 1.4%) regions. Incubation with epithelial cells from either region produced no differences in any category of sperm behaviour. Furthermore, there was no significant difference between regions in the amount of time spermatozoa spent bound (33.6 +/- 12.9 and 20.6 +/- 3.0 s for isthmic and ampullary tissue respectively). These results support the hypothesis that hyperactivation may assist spermatozoa in breaking connections with epithelial cells.

Implementing comprehensive quality control in the andrology laboratory

Comprehensive quality control procedures were integrated into the routine semen analysis workload of a large university-based andrology laboratory. Methods were chosen to match as far as possible those which have been used successfully for many years in disciplines such as clinical chemistry. Levey-Jennings and cusum charts were plotted in order to monitor the immunobead-binding test for antisperm antibodies and a video-taped control sample for computerized semen analysis. A cryopreserved semen control was also charted. Daily manual sperm counts were plotted against the corresponding computer-assisted semen analysis (CASA) value. Multiple readings of 30 slides were used to monitor morphology assessments. Monthly means for morphology were also calculated regularly. Coefficients of variation were calculated for all variables and were found to be more appropriate for some aspects, such as CASA, than for others, such as morphology, when difference from the previous reading of the same slide was found to be more useful. These integrated quality control procedures had a direct influence on the production of results from the laboratory. Together with a high standard of technician training, comprehensive routine quality control based on repeated analyses of control samples is an effective way of assuring the validity of semen analysis results.

A time course study of capacitation and the acrosome reaction in human spermatozoa using a revised chlortetracycline pattern classification

OBJECTIVE

To study the time course of capacitation, spontaneous, and A23187-induced acrosome reaction of human spermatozoa during 8 hours incubation in vitro using the chlortetracycline (CTC) assay with a revised fluorescent pattern classification.

DESIGN

Fertile donor spermatozoa were isolated by direct swim-up and incubated in Earle's balanced salt solution for up to 8 hours. At hourly intervals, spermatozoa were stained with CTC before and after the addition of A23187 to induce the acrosome reaction.

SETTING

The University Clinic, Jessop Hospital for Women, Sheffield, United Kingdom.

PATIENTS

Donors participating in the Donor Insemination Program.

MAIN OUTCOME MEASURES

Eight fluorescent patterns identified by the CTC assay and acrosome-reacted spermatozoa detected by indirect immunofluorescence using 18.6 monoclonal antibody.

RESULTS

Using a statistical model defined by analysis of deviance allowed rationalization of the CTC pattern classification by grouping together patterns that showed a similar and significant change over time. In addition, spontaneous and A23187-induced acrosome-reacted spermatozoa identified by the CTC assay were shown to be correlated significantly to those identified by indirect immunofluorescence.

CONCLUSION

The CTC assay using a revised pattern classification offers a more precise description of human spermatozoa capacitation in vitro. Also, CTC-identified acrosome reaction (both spontaneous and A23187 induced) was confirmed independently by indirect immunofluorescence.

Clinical value of sperm morphology for in-vivo fertility: comparison between World Health Organization criteria of 1987 and 1992

The World Health Organization (WHO, 1992) has suggested new criteria for scoring sperm morphology. This study compares the clinical value of the new criteria, i.e. classification of a man as fertile or infertile, to those previously established by the WHO (1987). Papanicolaou-stained semen smears from 166 men attending our infertility clinic, whose fertility status was known, were scored using both methods. Using logistic discriminant analysis for compositional data, no difference between these two sets of criteria with respect to predicting pregnancy outcome was observed. The categorization of the abnormalities (head, midpiece, tail) provides no extra clarification. The WHO (1992) cut-off point of 30% for normal forms is not appropriate, as approximately half of the men in the fertile group had a normal sperm morphology below this limit. In conclusion, the present WHO (1992) classification of sperm morphology is of no additional clinical value. Studies on sperm morphology should concentrate on obtaining biological data on, and measurements of, spermatozoa which are functionally active. Only then can the definition of normal be achieved and clinically useful criteria be adopted.

The interaction in vitro of human spermatozoa with epithelial cells from the human uterine (fallopian) tube

The physical interaction between human spermatozoa and the epithelium of the human uterine (Fallopian) tube was investigated in vitro using a variety of techniques. The 'live' observation of human spermatozoa incubated with 1 day old cultures of tubal epithelium demonstrated that spermatozoa can show a strong physical interaction with epithelial cells; contact with the epithelium appeared to be random and there was no evidence of any taxis toward epithelial cells. The physical interaction (or 'binding') was resistant to gentle washing and was maintained following the addition of glutaraldehyde fixative. The intimate nature of the interaction was confirmed ultrastructurally where both spermatozoa and epithelial membranes were observed to be in close apposition. These results are the first descriptions of sperm-epithelial 'binding' in the human. They are similar to other observations made in a variety of non-human mammalian species. It is suggested that this interaction may be an important feature of normal sperm transport in the human uterine tube in vivo.

Oral steroid therapy for subfertile males with antisperm antibodies in the semen: prediction of the responders

This study was performed to examine the effectiveness of steroid therapy in subfertile men with antisperm antibodies and infertility lasting > 1 year, to predict those who would respond positively, and to evaluate the effect of the therapy on semen parameters and antisperm antibodies. The patients included 48 subfertile couples in whom the male partner had > or = 20% motile spermatozoa with bound antibodies of immunoglobulin (Ig)G, IgA or a combination of both, and were treated with prednisolone, 40 mg a day, for the first 10 days, then 5 mg on days 11 and 12 of the partner's cycle for 9 months. Twelve couples became pregnant; a cumulative conception rate of 30.2% was achieved at 9 months. The pregnant group started with significantly higher concentrations of IgG (tail) and grade I motility (P = 0.03 and P = 0.02 respectively). Multi-covariate discrete logistic regression analysis on the initial screening semen samples predicted a higher chance of conception for those with high levels of IgG (tail) (P = 0.006, sensitivity = 33%, specificity = 93%, correct = 75%, false positive = 33% and false negative = 24%). In the pregnant group, prednisolone caused a significant increase in grade I motility (P = 0.03). In the non-pregnant group, there was a significant increase in grade I motility (P = 0.0002), amplitude of lateral head displacement (P = 0.03), curvilinear velocity (P = 0.02) and decrease in grade IV motility (P = 0.03) following prednisolone treatment. In both groups there was suppression of the total antisperm antibody concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

A morphometric comparison of the nuclear morphology of fresh and frozen-thawed human zona-bound and unbound sperm

The role of sperm nuclear morphology in zona binding and the effect of cryopreservation on sperm nuclear morphology have been investigated using objective criteria. The nuclear dimensions of fresh and frozen-thawed sperm heads that had been prepared by the swim-up (SU) technique, and bound to human oocytes in vitro, were measured using a computer-assisted image analyzer. These were compared with each other and also to sperm in the SU samples and those that had not bound to the zona pellucida. The unbound (UB) sperm and SU sperm had very similar nuclear morphology. In contrast, the nuclear morphology of the zona-bound (ZB) sperm differed significantly (P < 0.05) from that of the SU and UB sperm. These differences were found specifically between area, breadth, and roundness in the SU and ZB sperm preparations, and between area and roundness in the UB and ZB sperm preparations; the ZB sperm had smaller but rounder nuclei than either the SU or UB sperm. In addition, the frozen-thawed sperm in the SU and UB groups showed a trend towards smaller nuclei than the corresponding fresh groups, whereas the frozen-thawed ZB sperm had significantly (P < 0.05) smaller nuclear dimensions than the fresh ZB sperm. From the present study it appears that the ZB sperm are a morphologically distinct population, although it is not yet clear whether these differences reflect functional events that occur in the sperm head during its maturation or changes at the level of the sperm's DNA after the initial stage of zona binding.(ABSTRACT TRUNCATED AT 250 WORDS)

The sequential effects of human cervical mucus, oviductal fluid, and follicular fluid on sperm function

OBJECTIVE

To compare the sequential effects of human cervical mucus (CM), oviductal fluid, and follicular fluid (FF) on sperm motility, hyperactivation, and the acrosome reaction during 9 hours of incubation in vitro.

DESIGN

Spermatozoa from a fertile donor were allowed to penetrate human CM in vitro and then were recovered and incubated in either 30% human oviductal fluid or a simple salt solution for 3 hours before challenge with 20% FF. Thus, the sequential effects of the fluids collected from the female reproductive tract on sperm hyperactivation and acrosome reaction were examined.

SETTING

The donor insemination program at the University Clinic within the Jessop Hospital for Women, Sheffield, United Kingdom.

PATIENTS

All donors used in this study were involved in the donor insemination program.

MAIN OUTCOME MEASURES

Sperm motility, hyperactivation, and percentage of acrosome-reacted spermatozoa were measured.

RESULTS

This study used an in vitro technique to mimic sperm transport in vivo. Spermatozoa sequentially incubated with female reproductive tract secretions in vitro showed a maintenance in the level of FF-induced hyperactivated motility and a decreased response to the FF-induced acrosome reaction when compared with sperm challenged with FF in the absence of prior incubation with human oviductal fluid.

CONCLUSION

It is suggested that human oviductal fluid may serve to delay the FF-induced acrosome reaction.

Computer-assisted measurement of hyperactivation in human spermatozoa: differences between European and American versions of the Hamilton-Thorn motility analyser

Spermatozoa from healthy donors of proven fertility were analysed for percentage hyperactivation, mean curvilinear velocity (VCL), mean progressive velocity (VSL), amplitude of lateral head displacement (ALH) and percentage linearity (LIN) using two versions of the Hamilton-Thorn motility analyser (HTMA) running at different frame rates. The sort fraction criteria developed using a machine utilizing 30 Hz gave comparable figures for the percentage spermatozoa displaying motility patterns concomitant with hyperactivation when compared to that developed for a machine using a frame rate of 25 Hz. Statistically significant differences were observed when criteria developed using 30 Hz machines were transferred to those using 25 Hz. The frame rate dependency of VSL and VCL are thought to account for these differences; values for ALH and LIN were largely unaffected by frame rate. These results have implications for workers using the European version of the HTMA (at 25 Hz) with sort criteria, containing frame rate-dependent variables, which have been developed by American colleagues using the machines of a higher frame rate. More appropriate sort criteria for workers using European (25 Hz) machines are suggested.