Sperm DNA fragmentation, recurrent implantation failure and recurrent miscarriage

Unexplained recurrent miscarriages are associated with an aberrant sperm protamine mRNA content

STUDY QUESTION

Are unexplained recurrent miscarriages associated with abnormal protamine-1 and protamine-2 mRNA levels in spermatozoa?

SUMMARY ANSWER

Both protamine-1 and protamine-2 mRNA levels as well as the protamine-1 to protamine-2 mRNA ratio in spermatozoa from men whose female partners experienced two or more consecutive miscarriages were significantly different compared to those from both healthy control men and subfertile couples undergoing IVF/ICSI.

WHAT IS KNOWN ALREADY

Aberrant sperm protamine ratios are known to be associated with male-factor infertility. Data from this study suggest that the protamine mRNA ratio may additionally affect early embryo development.

STUDY DESIGN, SIZE, DURATION

The study population was recruited from men whose female partners presented with two or more consecutive unexplained miscarriages in a consultation for recurrent pregnancy loss between 2014 and 2016. At the research laboratory of the Urological Clinic of the University Giessen, spermatozoa from cases and controls were subjected to reverse transcription quantitative PCR (RTqPCR) using specific primer pairs for protamine-1 and protamine-2.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Protamine-1 and protamine-2 mRNA levels were analysed in semen samples from 25 men whose female partners experienced at least two consecutive idiopathic miscarriages before the 20th week of gestation. The couples were recruited during consultation at the Fertility Center of the LMU Munich, Germany, and at the Clinical Division of Gynecologic Endocrinology and Reproductive Medicine of the Medical University of Vienna, Austria. Results were compared with those from 32 healthy donors (WHO, 2010) recruited at the Department of Urology, Pediatric Urology and Andrology, Giessen, Germany, and 107 men whose partners participated in an IVF/ICSI program at the Fertility Center of the LMU Munich, Germany.

MAIN RESULTS AND THE ROLE OF CHANCE

Protamine-1 and protamine-2 mRNA levels as well as the protamine mRNA ratio and all routine semen parameters revealed significant differences between recurrent miscarriage couples and healthy volunteers (P < 0.01). When comparing recurrent miscarriage couples with couples undergoing IVF/ICSI, Ct-values of protamine-1 and protamine-2 mRNAs were significantly higher and the protamine mRNA ratio was significantly lower in RM couples (P < 0.01). When comparing protamine mRNA levels and the protamine mRNA ratio with routine semen parameters, a significant negative correlation was evident between progressive motility and the protamine-2 mRNA level (P = 0.015), as well as between non-progressive motility and the protamine mRNA ratio (P = 0.023).

LIMITATIONS REASONS FOR CAUTION

Although our data demonstrate significant abnormalities in RM, larger sample sizes will be needed to confirm our results. Larger sample sizes should also balance the fact that we had to focus mainly on median protamine mRNA levels. Finally, men in the healthy control group were younger in age than those in the case group, which might have introduced some bias, at least concerning the classic semen parameters. Moreover, only protamine mRNA instead of protein levels could be measured.

WIDER IMPLICATIONS OF THE FINDINGS

Although the exact mechanism remains to be elucidated, our data suggest that protamine mRNA levels in spermatozoa are not only important for successful fertilization, but also for proper development of the early embryo.

STUDY FUNDING/COMPETING INTEREST(S)

Grant from the University Clinic Giessen and Marburg (UKGM 29/2015GI). There are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

The effect of human sperm chromatin maturity on ICSI outcomes

Because sperm chromatin may play a key role in reproductive success, we verify the associations between sperm chromatin abnormalities, embryo development and the ability to achieve pregnancy. The evaluation of sperm chromatin maturity using aniline blue (AB), chromomycin A3 (CMA3) and toluidine blue (TB) staining were carried out in group of males from infertile couples that underwent ICSI. Low levels of sperm chromatin abnormalities (< 16%) were found in most subjects (> 50%). A higher percentage of TB-positive sperm cells were discovered in the men from couples who achieved ≤ 50% fertilized oocytes compared to men who achieved > 50%. No significant differences were discovered by the applied tests between the men from couples who achieved ≤ 50% and those who achieved > 50% high-quality embryos on the 3rd or 5th day after fertilization, nor between the men from couples who achieved pregnancy and those who failed. The sperm chromatin maturity did not correlate with the ICSI results. However, the ROC analysis revealed a significant predictive value of TB-positive spermatozoa only for fertilization. Therefore, the TB assay can be considered as a useful test for the prediction of fertilization. Our findings suggest that the level of sperm chromatin abnormalities of the examined men was not clinically significant. No found associations between sperm chromatin maturity and embryo development and the ability to achieve pregnancy. We could not exclude the effects of the repairing processes in the fertilized oocyte. The use of complementary tests that verify the status of the sperm chromatin seems justified.

Impact of a mild scrotal heating on sperm chromosomal abnormality, acrosin activity and seminal alpha-glucosidase in human fertile males

The aim of this study was to observe sperm aneuploidy, DNA integrity, seminal alpha-glucosidase (NAG) and acrosin activity (AA) under testicular heat stress (SH). Spermatozoa were obtained from 30 healthy adult volunteers subjected to scrotal warming at 43°C for 30-40 min on two successive days per week for 3 months between February 2012 and September 2016. Aniline blue (AB), acridine orange (AO) staining, TUNEL assay and FISH analysis to evaluate sperm function, sperm DNA integrity and chromosomal abnormalities were carried on before, during and after SH. Sperm AA and NAG was measured by microplate reader. The mean parameters of sperm parameters, AA and NAG were significantly decreased. In contrast, the mean percentage of sperm DNA fragmentation and the proportion of aneuploidy of chromosomes 13, 18, 21, X and Y were significantly increased for spermatozoa collected during SH versus before SH (p < .01-.001). After stopping scrotal heating for 3 months, most parameters were completely restored to pre-SH levels. Sperm parameters, sperm DNA integrity, chromosomes, AA and NAG are affected by scrotal exposure to constant SH temperatures several degrees over normal physiological temperature, and after treatment, these parameters were reversibly restored to the level before SH in adult men.

Sperm DNA fragmentation in donors and normozoospermic patients attending for a first spermiogram: Static and dynamic assessment

Static assessment of sperm DNA Fragmentation (SDF at the time of ejaculation or sperm thawing when cryopreserved) and the dynamic assessment of SDF (SDF assessed after T2 hr, T6 hr and T24 hr of sperm thawing) were used to establish cut-off values associated with sperm donors when compared with closely related normozoospermic patients. Cryopreserved samples from donors revealed SDF levels two times lower in comparison with the patients. Donor sperm DNA exhibited a 2.5 times higher longevity when compared with the patients. Static values of SDF after thawing of approximately 11% identify the donors with a 71% of sensitivity and 84% specificity. With respect to the dynamic assessment, SDF increases of 2.3 per hr during the first 2 hr of incubation identify the donors with 70% of sensitivity and 66% of specificity. Creating the Rate of Combined Damage (RCD) defined as the product of SDF-T0 by the increase in the damage registered during the first 2 hr of incubation (r-SDF-T0-2 ), an index of RCD = 22.2 units has an identification capacity of donors with a 78% sensitivity and 77% specificity. Such cut-off values could be used to characterise donors with high chromatin resistance to damage when meeting the above-established criteria.

DNA fragmentation in spermatozoa: a historical review

Sperm DNA Fragmentation has been extensively studied for more than a decade. In the 1940s the uniqueness of the spermatozoa protein complex which stabilizes the DNA was discovered. In the fifties and sixties, the association between unstable chromatin structure and subfertility was investigated. In the seventies, the impact of induced DNA damage was investigated. In the 1980s the concept of sperm DNA fragmentation as related to infertility was introduced as well as the first DNA fragmentation test: the Sperm Chromatin Structure Assay (SCSA). The terminal deoxynucleotidyl transferase nick end labelling (TUNEL) test followed by others was introduced in the nineties. The association between DNA fragmentation in spermatozoa and pregnancy loss has been extensively investigated spurring the need for a therapeutic tool for these patients. This gave rise to an increased interest in the aetiology of DNA damage. The present decade continues within this research area. Some of the more novel methods recently submerging are sorting of cells with increased DNA fragmentation and hyaluronic acid (HA) binding techniques. The clinical value of these tests remains to be elucidated. In spite of half a century of research within the area, this analysis is not routinely implemented into the fertility clinics. The underlying causes are multiple. The abundance of methods has impeded the need for a clinical significant threshold. One of the most promising methods was commercialized in 2005 and has been reserved for larger licensed laboratories. Myriads of reviews and meta‐analyses on studies using different assays for analysis of DNA fragmentation, different clinical Artificial Reproductive Treatments (ART), different definitions of successful ART outcome and small patient cohorts have been published. Although the area of DNA fragmentation in spermatozoa is highly relevant in the fertility clinics, the need for further studies focusing on standardization of the methods and clinical implementation persists.

Inter-and Intra-Laboratory Standardization of TUNEL Assay for Assessment of Sperm DNA Fragmentation

The functional aspects of sperm activity such as sperm chromatin integrity and ability to fertilize cannot be characterized by routine semen parameters. Men with unexplained infertility and idiopathic infertility, as well as men with normozoospermic semen profiles, show high DNA fragmentation. Molecular anomalies in the sperm can be detected by a sperm DNA fragmentation (SDF) assay which can be used in adjunct to conventional semen analysis. While the sperm chromatin structure assay (SCSA) remains the "gold standard," the TUNEL assay using flow cytometry is becoming popular among the different tests that are currently available to measure sperm DNA fragmentation. In this unit, we describe the inter-laboratory and intra-laboratory standardization of the TUNEL assay using a benchtop cytometer. The article also provides a step-by-step protocol for measuring sperm DNA fragmentation using the TUNEL assay and a bench-top flow cytometer, and also points out the inherent challenges with this test. © 2017 by John Wiley & Sons, Inc.