Control of the fertilization process by the egg coat: how does it work in humans

Alleviation of acrosome reaction prematurity by sperm treatment with egg yolk

OBJECTIVE

To examine the effects of egg yolk on the spontaneous and ionophore-induced acrosome reaction (AR) and sperm-zona pellucida (ZP) binding in spermatozoa from patients with AR prematurity.

DESIGN

Prospective analysis.

SETTING

Private hospital, public research center, and a university-based laboratory.

PATIENTS

In vitro fertilization patients selected on the basis of previous AR testing.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Frequency of the AR, number of ZP-bound spermatozoa.

RESULTS

The pretreatment of spermatozoa with egg yolk decreased the frequency of AR occurring spontaneously during subsequent sperm incubation in capacitating medium but did not modify the sperm response to ionophore. The egg yolk-treated spermatozoa also showed a greater capacity of binding the ZP than their untreated counterparts.

CONCLUSIONS

The pretreatment of spermatozoa with egg yolk alleviates the sperm-ZP binding deficiency resulting from premature initiation of the AR and may be helpful in IVF with patients showing this anomaly.

Sperm:oocyte ratios in an in vitro fertilization (IVF) program

PURPOSE

During the past few years, many oocyte insemination techniques, including microinjection, have evolved in the treatment of male-factor infertility. This preliminary study was designed to evaluate whether microdroplet insemination could be considered a reliable technique, especially for semen samples with male-factor defects. The first objective was to assess fertilization rates obtained by inseminating sibling oocytes using both the conventional IVF and the microdroplet method (Group 1). The second objective was to evaluate subsequent embryo development and pregnancy rates resulting from microdroplet insemination, in addition to formulating adequate sperm:oocyte ratios for various semen categories (Group 2). Four semen categories were studied including fresh normal sperm, frozen/thawed normal sperm, and male-factor sperm with one defect and two or three defects.

RESULTS

Group 1 consisted of 54 couples; no statistical significance was found in the fertilization rates between test tube and microdroplet insemination in all four semen categories. Based on these results, patients from Group 2 (48 couples) had their oocytes inseminated only in microdroplets with sperm:oocyte ratios ranging from 2000 to 10,000 motile sperm:1 oocyte. The average fertilization rate for male-factor sperm was 55%, with a 91% cleavage rate.

CONCLUSION

Higher fertilization rates were observed in the lowest range of sperm:oocyte ratios (2000-4000:1) for male-factor sperm with one defect and in the highest range (8000-10,000:1) for male-factor sperm with two or three defects. Polyspermy occurred in only 0.4% of the oocytes inseminated. Microdroplet insemination is an alternative treatment for moderate to moderately severe male-factor infertility, establishing a bridge between conventional IVF and microinjection. With adequate sperm:oocyte ratios, this technique allows the natural selection process of fertilization in vitro to take place, without the high incidence of polyspermy or mechanical damage frequently observed in assisted fertilization techniques.

A plasma-membrane progesterone receptor in human sperm is switched on by increasing intracellular free calcium

Recent studies have revealed the presence of an atypical progesterone receptor on the plasma membrane of a relatively small subpopulation of human sperm cells. In this study, we show that the receptor is present in many cells in a latent form and that the receptor function in these cells is switched on asynchronously by increasing intracellular free Ca2+ levels. Under physiological conditions, this process occurs during sperm capacitation, but it can be mimicked by a short sperm exposure to the Ca(2+)-mobilizing agent thapsigargin. These observations suggest a role of Ca2+ as a modulator of nongenomic steroid effects on the cell surface.

Solubilized human zona pellucida competes with a fucosylated neoglycoprotein for binding sites on the human sperm surface

OBJECTIVE

To evaluate the implication of fucose binding sites on the sperm surface in the sperm-zona pellucida (ZP) binding by examining the ability of a fucosylated neoglycoprotein to compete with solubilized zona proteins for sperm binding.

DESIGN

The binding of a fucosylated neoglycoprotein to spermatozoa was analyzed in relation to sperm capacitation and the actual acrosomal status. The effect of solubilized ZP material on the binding was examined.

SETTING

Private hospital, public research center, and university department.

PATIENTS, PARTICIPANTS

Healthy volunteers with normal sperm parameters.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Fluorescence signal detected by fluorescence-activated cell sorting or fluorescence microscopy on spermatozoa incubated with fluorescein isothiocyanate-labeled fucosylated neoglycoprotein.

RESULTS

There was a small subpopulation of spermatozoa that showed a strong binding activity for the fucosylated neoglycoprotein, and the size of this subpopulation increased with the time of exposure to capacitating conditions. The binding sites were located on the head (mainly on the acrosomal region) of acrosome-intact spermatozoa. The neoglycoprotein binding was competitively inhibited by solubilized ZP.

CONCLUSIONS

The data show that a commercially available fucosylated neoglycoprotein competes with solubilized ZP proteins for binding sites on the sperm surface. Further research into the relationship between the neoglycoprotein binding and zona binding is warranted to evaluate the potential diagnostic usefulness of this neoglycoprotein.

Sperm treatment with pentoxifylline improves the fertilizing ability in patients with acrosome reaction insufficiency

OBJECTIVE

To test whether pentoxifylline, a drug previously shown to sensitize spermatozoa from normal samples to the action of acrosome reaction stimuli, can be used to improve the fertilizing ability of spermatozoa from patients with acrosome reaction insufficiency.

DESIGN

Prospective analysis of pentoxifylline effects on the acrosome reaction and zona-free egg penetration; retrospective comparison of IVF results with and without the use of pentoxifylline.

SETTING

Private hospital, public research center, and university-based laboratory.

PATIENTS

In vitro fertilization patients selected on the basis of a previous acrosome reaction test.

INTERVENTIONS

None in the experimental part; IVF-ET in the clinical part of this study.

MAIN OUTCOME MEASURES

Frequency of the acrosome reaction, rate of penetration of zona-free eggs, normal fertilization in IVF attempts.

RESULTS

Pentoxifylline improves the acrosome reaction scores and zona-free egg penetration rates in patients with acrosome reaction insufficiency. Preliminary clinical experience shows an improvement of IVF results in these patients.

CONCLUSIONS

In vitro pentoxifylline treatment of spermatozoa to be used in IVF improves the sperm fertilizing ability in patients with acrosome reaction insufficiency. However, the effect of pentoxifylline on the acrosome reaction should be tested individually in each patient before the application of the drug in this new indication.