Diagnostic value of the hamster oocyte penetration assay

Oxidative stress and male reproductive health

One of the major causes of defective sperm function is oxidative stress, which not only disrupts the integrity of sperm DNA but also limits the fertilizing potential of these cells as a result of collateral damage to proteins and lipids in the sperm plasma membrane. The origins of such oxidative stress appear to involve the sperm mitochondria, which have a tendency to generate high levels of superoxide anion as a prelude to entering the intrinsic apoptotic cascade. Unfortunately, these cells have very little capacity to respond to such an attack because they only possess the first enzyme in the base excision repair (BER) pathway, 8-oxoguanine glycosylase 1 (OGG1). The latter successfully creates an abasic site, but the spermatozoa cannot process the oxidative lesion further because they lack the downstream proteins (APE1, XRCC1) needed to complete the repair process. It is the responsibility of the oocyte to continue the BER pathway prior to initiation of S-phase of the first mitotic division. If a mistake is made by the oocyte at this stage of development, a mutation will be created that will be represented in every cell in the body. Such mechanisms may explain the increase in childhood cancers and other diseases observed in the offspring of males who have suffered oxidative stress in their germ line as a consequence of age, environmental or lifestyle factors. The high prevalence of oxidative DNA damage in the spermatozoa of male infertility patients may have implications for the health of children conceived in vitro and serves as a driver for current research into the origins of free radical generation in the germ line.

Kinetics of human male pronuclear development in a heterologous ICSI model

PURPOSE

To evaluate human sperm nuclear chromatin decondensation in a heterologous ICSI system using hamster ova injected with human sperm.

MATERIALS AND METHODS

Frozen hamster oocytes were injected with Triton X-100 treated sperm and fixed at different time points post ICSI. Oocytes injected with non-treated sperm served as controls. Male pronuclear decondensation was evaluated after staining with DAPI.

RESULTS

Sperm cells with partially destroyed membranes and depletion of the acrosome decondense more rapidly and to a greater extent than membrane/acrosome intact cells. Marked variability in pronuclear size was observed for any time point post ICSI, which most probably reflects the heterogeneity in the mature human sperm population.

CONCLUSION

Remodeling of male gamete nuclei in this heterologous ICSI mimics events that occur during natural fertilization in humans and therefore this approach may be used for studies of human sperm chromosomes transformations.

Diagnostic value of the zona-free hamster oocyte penetration test and sperm movement characteristics in oligozoospermia

A group of 27 oligozoospermic patients were followed up for 4.2 +/- 1.1 years in a prospective study designed to determine which aspects of semen quality are of value in the diagnosis of fertility. The semen analysis included the zona-free hamster oocyte penetration test, the assessment of sperm movement characteristics by time exposure photomicrography and a conventional semen profile. During the follow up period, 7 patients (25.9%) initiated a pregnancy. The identity of these fertile subjects could not have been ascertained by any single criterion of sperm movement or any feature of the conventional semen profile. The zona-free hamster egg penetration rates were also of little value in this respect since 4 of the 7 fertile patients scored 0% in this assay. Using a multivariate discriminant analysis, however, a combination of 7 criteria was identified, including hamster oocyte penetration and elements of both sperm movement and the semen profile, which could predict the fertility of these patients with 85.2% accuracy.

Prognostic value of the heterologous ovum penetration test for human in vitro fertilization

In order to evaluate the prognostic value of the heterologous ovum penetration test (HOP-test) the results of this test were compared with the fertilization rate of human ova in a programme for in vitro fertilization and embryo transfer (IVF/ET). Sperm from 29 husbands (23 normozoospermic and 6 with an abnormal semen profile) were exposed on one occasion to approximately 30 hamster ova in the HOP-test and on 1 to 3 occasions to 1 to 4 preovulatory oocytes obtained from the respective wives. The mean penetration rate (+/- SEM) of the hamster ova was 43 +/- 4% (range: 0-62%) for the normozoospermic men, and 23 +/- 6% (range: 0-47%) for the men with abnormal semen profiles. In 20 out of 23 couples in which the husbands were normozoospermic, sperm penetrated the hamster ova as well as they fertilized human ova; however, in one couple, a false-positive result was obtained (penetration of the hamster ova and no fertilization of the human oocytes) and in one couple a false-negative result occurred. One negative IVF result was correctly predicted by the HOP-test. In the 6 patients with disturbed sperm motility no correct positive or negative results were obtained, whilst 4 false-positive and 2 false-negative results occurred using the HOP-test. Although the number of patients with disturbed sperm motility was small, the data suggest that the HOP-test is of limited value in predicting fertility in an IVF program for couples with reduced fertility.