The Penetration Test with Zona pellucida as a Predictor of the Fertilizing Capacity of Native and Cryopreserved Human Spermatozoa

In order to fertilizate oocyte the sperm need to penetrate into Zona pellucida surrounding the female gamete and consisting of glycoprotein. The purpose of this work was to evaluate the penetration activity of native and cryopreserved sperm with normo- and oligoastenoteratozoospermia. Control group 1 consisted of 10 samples of ejaculates with normozoospermia. Group 2 included the samples of 22 men with oligoasthenoteratozoospermia. Cryopreservation of spermatozoa was carried out by vitrification. The penetration rate and index were calculated by counting the number of spermatozoa associated with empty ZP oocytes. The average number of spermatozoa in group 1 was 46.7 ± 8.8, in group 2 it made 12.4 ± 3.6 million/ml (p <0.01). The fractions of progressive motile spermatozoa were 27.9 ± 3.5 and 8.2 ± 1.1% (p <0.001), for group 1 and 2, respectively. We found significant differences in the ability of spermatozoa from group 1 and 2 to penetrate ZP. The penetration rate of spermatozoa with normozoospermia was 86.6 ± 8.5%, with oligoasthenoteratozoospermia it made 17.9 ± 4.5% (p <0.001). After cryopreservation, the penetration rate of spermatozoa with normozoospermia did not change and made 84.4 ± 9.2% (р<0.05), however, with oligoasthenoteratozoospermia was significantly decreased down to 9.9 ± 3.3% (р <0.001). The penetration index was 0.85 ± 0.19 and 0.17 ± 0.07% for groups 1 and 2, respectively (p <0.01). After cryopreservation, the penetration index for spermatozoa from normozoospermic ejaculates remained at the same level, whereas in oligoastenoteratozoospermia was decreased up to 0.03 ± 0.06% (p<0.01). ZP penetration rate and index of spermatozoa from normozoospermic ejaculates is significantly higher than with oligoastenoteratozoospermia. Cryopreservation factors do not affect to spermatozoa ability to bind with ZP in normozoospermic group and significantly reduce this index at oligoasthenoteratozoospermic group. The penetration test with Zona pellucida can be used as a predictor of fertilizing ability of native and cryopreserved human spermatozoa. These results should be considered when choosing the tactics of fertilization with cryopreserved spermatozoa, especially in the case of oligoasthenoteratozoospermic semen samples. Promising is the elucidation of the correlation between the frequency and the index of penetration and fertilizing capacity of spermatozoa, that will be the subject of further studies.