A simple comet assay for archived sperm correlates DNA fragmentation to reduced hyperactivation and penetration of zona-free hamster oocytes

Identification of bi-allelic KIF9 loss-of-function variants contributing to asthenospermia and male infertility in two Chinese families

Introduction

Asthenozoospermia (AZS) is a leading cause of male infertility, affecting an estimated 18% of infertile patients. Kinesin proteins function as molecular motors capable of moving along microtubules. The highly conserved kinesin family member 9 (KIF9) localizes to the central microtubule pair in the flagella of Chlamydomonas cells. The loss of KIF9 expression in mice has been linked to AZS phenotypes.

Methods

Variant screening was performed by whole exome sequencing from 92 Chinese infertile patients with AZS. Western blot was used to was used for analyzing of candidate proteins expression. Patients' sperm samples were stained with immunofluorescent to visualise proteins localization and were visualised by transmission electron microscopy (TEM) to determine axoneme structures. Co-immunoprecipitation assay was used to verify the binding proteins of KIF9. In vitro fertilization (IVF) was used to evaluate the efficiency of clinical treatment.

Results

Bi-allelic KIF9 loss-of-function variants were identified in two unrelated Chinese males exhibiting atypical sperm motility phenotypes. Both of these men exhibited typical AZS and suffered from infertility together with the complete absence of KIF9 expression. In contrast to these KIF9-deficient patients, positive KIF9 staining was evident throughout the flagella of sperm from normal control individuals. KIF9 was able to interact with the microtubule central pair (CP) component hydrocephalus-inducing protein homolog (HYDIN) in human samples. And KIF9 was undetectable in spermatozoa harboring CP deletions. The morphologicy of KIF9-deficient spermatozoa appeared normal under gross examination and TEM. Like in mice, in vitro fertilization was sufficient to overcome the fertility issues for these two patients.

Discussion

These findings indicate that KIF9 associates with the central microtubules in human sperm and that it functions to specifically regulate flagellar swinging. Overall, these results offer greater insight into the biological functions of KIF9 in the assembly of the human flagella and its role in male fertility.

Conventional semen analysis and advanced sperm function tests in diagnosis and management of varicocele

Clinical varicoceles are a common cause of male infertility and affect sperm parameters as measured in a conventional semen analysis. Varicocelectomy has been shown in prospective studies to improve semen parameters in men with a clinical varicocele. Clinical varicoceles are also a well-known source of oxidative stress which may affect the quality of spermatozoa. Spermatozoa are particularly susceptible to oxidative stress due to a limited capacity for DNA repair. The susceptibility of spermatozoa to oxidative stress is modulated by a balance between ROS and antioxidants, which can be quantified by various laboratory assays. Varicocelectomy has been consistently shown to reduce both ROS and sperm DNA fragmentation, and various assays should be utilised in the diagnosis and treatment of infertile men with a clinical varicocele.

Declining BRCA-Mediated DNA Repair in Sperm Aging and its Prevention by Sphingosine-1-Phosphate

Recent data suggest that paternal age can have major impact on reproductive outcomes, and with increased age, there is increased likelihood of chromosomal abnormalities in the sperm. Here, we studied DNA damage and repair as a function of male aging and assessed whether sphingosine-1-phosphate (S1P), a ceramide-induced death inhibitor, can prevent sperm aging by enhancing DNA double-strand breaks (DSB) repair. We observed a significant increase in DNA damage with age and this increase was associated with a decline in the expression of key DNA DSB repair genes in mouse sperm. The haploinsufficiency of BRCA1 male mice sperm showed significantly increased DNA damage and apoptosis, along with decreased chromatin integrity when compared to similar age wild type (WT) mice. Furthermore, haploinsufficiency of BRCA1 male mice had lower sperm count and smaller litter size when crossed with WT females. The resulting embryos had a higher probability of growth arrest and reduced implantation. S1P treatment decreased genotoxic-stress-induced DNA damage in sperm and enhanced the expressions of key DNA repair genes such as BRCA1. Co-treatment with an ATM inhibitor reversed the effects of S1P, implying that the impact of S1P on DNA repair is via the ATM-mediated pathway. Our findings indicate a key role for DNA damage repair mechanism in the maintenance of sperm integrity and suggest that S1P can improve DNA repair in sperm. Further translational studies are warranted to determine the clinical significance of these findings and whether S1P can delay male reproductive aging. There is mounting evidence that sperm quality declines with age, similar to that of the oocyte. However, the reasons behind this decline are poorly understood and there is no medical intervention to improve sperm quality. Our study suggests a strong role for DNA damage repair in maintenance of sperm quality, and for the first time, a potential pharmaceutical approach to prevent sperm aging.

The progesterone-induced sperm acrosome reaction is a good option for the prediction of fertilization in vitro compared with other sperm parameters

Progesterone (P₄ ) is crucial for the physiological function of spermatozoa. In the study, we investigated the correlation between P₄ -induced sperm acrosome reaction (AR) and parameters including sperm progressive motility, normal morphology and sperm DNA fragmentation (SDF), and compared the in vitro fertilization (IVF) predictive values of these indicators based on the multivariate regressions analysis and receiver operator characteristics (ROC) curve analyses. The results demonstrated a negative correlation between P₄ -induced sperm AR and the SDF, with the correlation -9.05 (-17.25 to -0.84), p<0.05, n = 47). No relationship was found between the sperm progressive motility, normal morphology and the induced AR. The P₄ -induced AR and SDF were both significantly correlated to the fertilization rate. ROC curve analyses indicated that P₄ -induced AR was a better prognostic predictor for the fertilization rate compared with the SDF, with the areas under the curve 0.729 (0.580-0.849), p<0.01 and 0.637 (0.484-0.772), p=0.16 respectively. The cut-off value for P₄ -induced AR to predict "50% fertilization rate" was 23.4% with sensitivity and specificity of 63.3% and 88.2% respectively. The overall results indicated that the assessment of P₄ -induced AR seemed to be a more sensitive indicator for fertilization rate in vitro compared with other sperm parameters.

Effect of Spermatic Nuclear Quality on Live Birth Rates in Intracytoplasmic Sperm Injection

Background:

Our study defines the clinical role of sperm DNA damage in the assisted reproductive technology procedure.

Aim:

To investigate if the compaction of chromatin explored added to the analysis of the sperm DNA fragmentation allows obtaining a new indicator for sperm genome quality linked to live birth rate (LBR).

Design:

This was a prospective study, undergoing 101 cycles in the intracytoplasmic sperm injection (ICSI) program.

Materials and Methods:

The sperm DNA fragmentation index (DFI) has been measured with sperm chromatin dispersion examination. The sperm decondensation index (SDI) of chromatin has been measured with aniline blue procedure; with these indexes, a new parameter has been created: DFI × SDI.

Statistical Analysis:

Pearson's correlation coefficient, Student's t-test, and Chi-square test were used. The quantitative variables were described as mean ± standard deviation. Multivariate logistic regressions were performed with live birth as outcome.

Results:

The sperm concentration, motility, and normal morphology were lower when the DFI was high (P = 0.001). The fertilization rates and the number of obtained embryos were not statistically significant different according to the DFI groups. The SDI does not appear to be linked either with the spermatic parameters or with the ICSI parameters. A low DFI seems to be a beneficial factor to obtain a live birth in ICSI procedure (P = 0.064). In case of high DFI, a high SDI allows to obtain a higher LBR than a low SDI.

Conclusion:

The DFI is a good prognostic for a delivery rate in ICSI procedure, and the SDI could be added to DFI to create a new parameter of sperm nuclear quality. This new parameter seems to be linked to LBR.

Investigation on the origin of sperm morphological defects: oxidative attacks, chromatin immaturity, and DNA fragmentation

DNA fragmentation can be deleterious on spermatozoon morphology but the pathogenesis of teratozoospermia associated with DNA breaks is not fully understood, even if oxidative attacks and defects in chromatin maturation are hypothesized. Therefore, this study is one of the first to clarify on the underlying hypothesizes behind such observations. The objectives of our study were to assess the role of oxidative attacks in DNA damage pathogenesis in ejaculated spermatozoa from patients with isolated teratozoospermia. We aimed to assess the correlation of DNA breaks with morphologically abnormal spermatozoa, as well as ROS level and impairment chromatin condensation. A total of 90 patients were divided into two groups, men with isolated teratozoospermia (n = 60) and men with normal semen parameters (n = 30) as controls. DNA fragmentation was evaluated by TUNEL assay; chromatin immaturity was studied using acridine orange and toluidine blue staining. We evaluated the ability of spermatozoa to produce reactive oxygen species with nitro blue tetrazolium staining. Patient with teratozoospermia when compared to fertile men showed significantly higher rates of semen ROS production, sperm hypocondensated chromatin, denaturated DNA, and fragmented DNA. All these parameters were positively correlated with abnormal sperm morphology. The studied DNA integrity markers were also correlated with ROS production. Fragmented DNA is the main pathway leading to morphology defects in the sperm. In fact, impaired chromatin compaction may induce DNA breaks and free radicals, which can break the DNA backbone indirectly, by reducing protamination and disulphide bond formation, as oxidative attack appears to be the major cause of poor semen morphology.

Sperm DNA and detection of DNA fragmentations in sperm

The questionable effectiveness of routine sperm parameters in determining male factor infertility problems and increasing the success rates of assisted reproductive techniques have led to the investigation of more detailed sperm parameters that could affect the male fertility and reproduction. Thus, the effects of different sperm parameters such as sperm DNA integrity was started to be investigated thanks to the previously described methods such as single cell gel electrophoresis (COMET) assay, sperm chromatin structure assay (SCSA), acridine orange test (AOT), terminal deoxynucleotidyl transferase-mediated deoxyuridine (TdT) triphosphate (dUTP) nick end labeling (TUNEL) assay and sperm chromatin dispersion (SCD) test. However, studying on sperm DNA might be very complex because the sperm DNA differs from the somatic cell DNA with its unique structure. Also, the sperm DNA undergoes many changes during spermatogenesis and it is condensed by being packaged tightly with different types and numbers of protamines in different species. Despite all these difficulties, these methods provide important information about the reasons and consequences of DNA damages in sperm and the effects of these damages on reproduction.

Improvement in pregnancy outcomes in couples with immunologically male infertility undergoing prednisolone treatment and conventional in vitro fertilization preceded by sperm penetration assay: a randomized controlled trial

PURPOSE

Anti-sperm antibodies (ASA) in men impair not only sperm motility but also fertilization and conception. However, utilization of corticosteroids to suppress ASA has shown variable pregnancy outcomes. This controversy is also extended to include the usefulness of conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in treatments of men with ASA. This study was therefore designed to define factors contributing to these inconsistent results.

METHODS

Infertile men having ASA (n = 241) were randomly assigned for treatment with or without prednisolone for three cycles each of 21 days of their partner's menstrual cycles. Control and treated men underwent then human sperm penetration assay (SPA), of hamster oocytes, to diagnose men with impaired sperm fusogenic capacity. Men with positive or negative SPA results were admitted to conventional IVF or ICSI programs, respectively.

RESULTS

Treated patients had improved sperm motility and progressive motility when compared to control patients (P < 0.001). Fertilization (P = 0.04), embryo cleavage (P = 0.01), and chemical (P = 0.02) and clinical (P = 0.04) pregnancy rates were higher in treated patients than in control patients undergoing conventional IVF but not ICSI cycles.

CONCLUSIONS

Men with ASA may also have compromised sperm fusogenic capacity, which can mask the clinical significance of corticosteroids. Corticosteroid administration in men with ASA, but without compromised sperm fusogenic capacity, improves conventional IVF but not ICSI outcomes; the reason being that ICSI bypasses issues of compromised fusogenic capacity. Inclusion of SPA in infertility clinics that offer both conventional IVF and ICSI services may be useful to identify which patients with ASA benefit from corticosteroid treatments.

ICSI significantly improved the pregnancy rate of patients with a high sperm DNA fragmentation index

Objective

Correlations between semen parameters and sperm DNA fragmentation index (DFI) were investigated to identify characteristics of sperm without DNA damage that could be used in selecting sperm for intracytoplasmic sperm injection (ICSI). Pregnancy outcomes were compared to determine whether in vitro fertilization (IVF) or ICSI is a better choice for patients who have sperm with a high-DFI.

Methods

Semen analysis was carried out in 388 patients who visited our IVF center for the first time to investigate correlations between sperm DFI and semen parameters. In addition, 1,102 IVF cycles in 867 patients were carried out in the present study; 921 cycles in the low-DFI group (DFI <30%) and 181 cycles in the high-DFI group (DFI ≥30%). Both the low- and high-DFI groups were subdivided into IVF and ICSI cycle groups.

Results

Sperm DFI showed significant inverse correlations with sperm motility (r=−0.435, p<0.001) and morphology (r=−0.153, p<0.05). Sperm DFI also showed significant correlations with rapid motility (r=−0.436, p<0.001), and the kinetic parameters of average-path velocity (r=−0.403) and linearity (r=−0.412). Although there was no significant difference in the pregnancy rates between IVF (48.6%) and ICSI (44.8%) in the low-DFI group, the pregnancy rate of ICSI cycles (44.8%, p<0.05) was significantly higher than IVF cycles (25.0%) in the high-DFI group. No significant difference was observed in the abortion rates between the low-DFI (52 of 921, 5.6%) and high-DFI groups (7 of 181, 3.8%).

Conclusion

ICSI is a better choice than IVF for improving the pregnancy outcomes of patients who have sperm with a high DFI.

Does sperm DNA fragmentation affect the developmental potential and the incidence of apoptosis following blastomere biopsy?

Common methods employed in assisted reproduction technology (ART) include intracytoplasmic sperm injection (ICSI) with an unspecified level of sperm DNA fragmentation (SDF) and preimplantation genetic diagnosis (PGD). The aim of this study was to investigate the impact of SDF on human preimplantation embryo development and the incidence of apoptosis following a single blastomere biopsy. Using sperm chromatin dispersion (SCD) to assess SDF, a total of 20 processed semen samples were categorized into two groups; group I: SDF ≤30% and group II: SDF >30%. After ICSI, fertilization, cleavage, and embryo quality score were assessed. A single blastomere was biopsied from day 3 embryos and development was monitored on day 4. The frequency of apoptosis in biopsied embryos was assayed by TUNEL and the level of BCL-2, BAX, hsa-mir-15a, and hsa-mir-16-1 were assessed by quantitative real-time polymerase chain reaction (qRT-PCR). SCD was found to be negatively correlated with sperm motility and normal form spermatozoa (p < 0.05). The rate of fertilization, cleavage, and embryo quality score were not significantly different between the two groups (all p > 0.05). SDF >30% had no negative effect on potential development and did not increase the proportion of apoptotic cells and the level of apoptosis-related genes and microRNAs (miRNAs) in group II vs. group I (p > 0.05). It appears that at the levels assessed paternal genome damage had little if any negative effect on preimplantaton embryo development and apoptosis following single blastomere biopsy. This may reflect the selection of morphologically normal sperm for ICSI and the repair capacity of the oocyte.

Biomonitoring of polycyclic aromatic hydrocarbons from coke oven emissions and reproductive toxicity in nonsmoking workers

The objective of the cross-sectional study was to assess whether exposure to polycyclic aromatic hydrocarbons (PAHs) from coke oven emissions contributed to alteration of semen quality and sperm DNA integrity in nonsmoking workers. Nonsmoking coke oven workers from a steel plant in Taiwan served as the exposure groups (topside-oven workers for the high exposure group and side-oven workers for the low exposure group), and administrators and security personnel in the plant served as the control. An exposure assessment was conducted to determine both particulate and gaseous phase of PAH levels and urinary 1-hydroxypyrene (1-OHP) levels. Semen quality was analyzed according to WHO guidelines. DNA fragmentation and bulky DNA adducts were measured to assess sperm DNA integrity. There was no significant difference in sperm concentrations, vitality, and DNA fragmentation between the exposed group and the control. The high exposure group experienced significantly lower percentages of normal morphology as compared with the control (p=0.0001). Bulky DNA adducts were detected in the exposed group that were significant higher than the control (p=0.04). Exposure to PAHs from coke-oven emissions could contribute to increased levels of bulky DNA adducts in sperm.

Are sperm DNA fragmentation, hyperactivation, and hyaluronan-binding ability predictive for fertilization and embryo development in in vitro fertilization and intracytoplasmic sperm injection?

OBJECTIVE

To determine the diagnostic value of the following sperm function tests in predicting the fertilizing ability of spermatozoa in conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI): hyaluronan-binding assay (HBA), DNA fragmentation (Halosperm), and hyperactivity.

DESIGN

Prospective study.

SETTING

University medical center.

PATIENT(S)

133 couples undergoing infertility treatment with IVF/ICSI.

INTERVENTION(S)

Analysis of sperm DNA fragmentation, hyaluronan-binding ability, and hyperactivation on washed semen samples used for the insemination of oocytes.

MAIN OUTCOME MEASURE(S)

Correlation between the results of sperm function tests and the fertilization rate (FR) or embryo quality (EQ) after IVF and ICSI. Comparison of the sperm DNA fragmentation, hyperactivation, and hyaluronan binding ability between cycles with less than 50% (group 1) and more than 50% (group 2) of oocytes fertilized after IVF.

RESULT(S)

Both FR and EQ in IVF cycles negatively correlated with sperm DNA fragmentation. Furthermore, a positive correlation was observed between FR and hyaluronan-binding ability or induced hyperactivity. The semen samples from the IVF cycles with low FR (group 1) were characterized by statistically significantly higher sperm DNA fragmentation and lower hyaluronan-binding ability in comparison with semen samples from the group with high levels of fertilization (group 2). In ICSI cycles, no relationship was found between sperm function tests and FR or EQ.

CONCLUSION(S)

The Halosperm test, the HBA test, and induced hyperactivity are useful in predicting the ability of spermatozoa to fertilize oocytes in IVF and are helpful in distinguishing semen samples suitable for IVF or ICSI.

Sperm DNA damage measured by comet assay

Measurement of sperm DNA damage is a useful tool in the evaluation of male infertility, as the sperm nucleus lacks protection against oxidative stress and is vulnerable to oxidation-mediated DNA damage. The Comet assay or single-cell gel electrophoresis is a relatively simple and sensitive method for measuring strand breaks in DNA in individual sperm. During this procedure, sperm cells are embedded in a thin layer of agarose on a microscope slide and lysed with detergent under high salt conditions. This process removes protamines and histones allowing the nucleus to form a nucleoid-like structure containing supercoiled loops of DNA. Alkaline pH conditions result in unwinding of double-stranded DNA, and subsequent electrophoresis results in the migration of broken strands towards the anode, forming a comet tail, when observed under fluorescence microscope. The amount of DNA in the head and tail is reflected by its fluorescent intensity. The relative fluorescence in the tail compared with its head serves as a measure of the level of DNA damage. In this chapter, we describe the alkaline version of the Comet assay, which is highly sensitive for measuring single- and double-strand DNA breaks.

Clinical value of DNA fragmentation evaluation tests under ART treatments

Male reproductive health has been under scrutiny recently. Many studies in the literature have concluded that semen quality is declining and that the incidence of testicular cancers is increasing. The reason for this change has been attributed to damage in sperm chromatin. During in vivo reproduction, the natural selection process ensures that only a spermatozoon with normal genomic material can fertilize an oocyte. However, the assisted reproduction technique (ART) is our selection process, leading to the possibility that abnormal spermatozoa could be used to fertilize an oocyte. We could avoid this by quantifying the amount and type of genomic damage in sperm using well-accepted laboratory methods. The sperm deoxyribonucleic acid (DNA) integrity is important for success of natural or assisted fertilization as well as normal development of the embryo, fetus and child. Intra cytoplasmic sperm injection (ICSI) is bypassing natural sperm selection mechanisms, which increases the risk of transmitting damaged DNA. The significance of required investigations and multiple techniques is that they could evaluate DNA defects in human spermatozoa. The ability of these techniques to accurately estimate sperm DNA damage depends on many technical and biological aspects. The aim of this review is to evaluate the most commonly used methods.

Sperm DNA integrity assays: diagnostic and prognostic challenges and implications in management of infertility

Sperm is not a simple carrier of paternal genetic information but its role extends clearly beyond fertilization. Integrity of sperm genome is an essential pre-requisite for birth of healthy offspring and evaluation of sperm should entail DNA integrity analysis. DNA integrity analysis is a better diagnostic and prognostic marker of sperm reproductive potential. Conventional semen analysis emphasizes on sperm concentration, viability, motility and morphology and has been proven to be a poor indicator of reproductive potential and pregnancy outcome. To overcome the drawbacks associated with conventional semen analysis more useful fertility tests and molecular biomarkers have been explored. Among the different tests which have evolved for assessing the sperm reproductive potential, tests for sperm DNA quality are most promising. Sperm DNA damage has been closely associated with numerous indicators of reproductive health including fertilization, embryo quality, implantation, spontaneous abortion, congenital malformations and childhood diseases. It therefore has great potential as a prognostic test for both in vitro and in vivo conception. This review presents an updated account of tests that have better diagnostic and prognostic implications in the evaluation of sperm DNA damage. The basic principles, outline of methodology, advantage, disadvantage, clinical significance of each technique and implications of these tests have been discussed. The logistics of each test with respect to available resources and equipment in an andrology laboratory, the feasibility of performing these tests in routine diagnostic workup of infertile men and the opportunities and challenges provided by DNA testing in male fertility determination are also presented.

Integrity of human sperm DNA assessed by the neutral comet assay and its relationship to semen parameters and clinical outcomes for the IVF-ET program

Objective

To explore potential relationships between sperm DNA integrity and both semen parameters and clinical outcomes.

Methods

Semen analysis of 498 samples was performed according to the 2010 criteria of the World Health Organization. The sperm DNA fragmentation Index (DFI) of the semen samples was assessed using a neutral comet assay.

Results

Sperm DFI showed a significant correlation with semen parameters, including the patient's age, sperm viability, motility, morphology, and number of leukocytes (p<0.05). The sperm DFI values for asthenozoospermic (15.2%), oligoteratozoospermic (18.3%), asthenoteratozoospermic (17.5%), and oligoasthenoteratozoospermic semen samples (21.3%) were significantly higher than that observed in normozoospermic semen samples (10.5%, p<0.05). A sperm DFI value of 14% was used as a threshold of sperm DFI in assessing whether DNA was highly damaged. In 114 IVF-ET cycles, the fertilization rate of the sperm DFI <14% group (70 cycles, 61.7%) was significantly higher than that observed for the ≥14% group (44 cycles, 55.3%), but there was no difference in the other clinical outcomes between the two groups. In the ≥14% group, the pregnancy rates of the ICSI cycles (40.0%) and half-ICSI (44.0%) were higher than conventional IVF cycles (30.7%), but the difference was not statistically significant.

Conclusion

Along with the conventional semen analysis, the sperm DFI assessed using the comet assay was shown to improve the quality of the semen evaluation. To evaluate the precise effect of ICSI on pregnancy rates in the patients who demonstrate high sperm DFI values, further study is necessary.

Sperm chromatin structure assay parameters are not related to fertilization rates, embryo quality, and pregnancy rates in in vitro fertilization and intracytoplasmic sperm injection, but might be related to spontaneous abortion rates

OBJECTIVE

To investigate the relationship between sperm chromatin structure assay (SCSA) parameters, DNA fragmentation index (DFI) and high DNA stainability (HDS), and outcomes of IVF and intracytoplasmic sperm injection (ICSI).

DESIGN

Retrospective review and prospective study.

SETTING

Academic human reproduction laboratory.

PATIENT(S)

Two hundred twenty-three couples undergoing conventional IVF (n = 137) and ICSI (n = 86).

INTERVENTION(S)

Testing with SCSA on a semen aliquot taken from ejaculate used for assisted reproductive technology (ART).

MAIN OUTCOME MEASURE(S)

Conventional semen parameters, DFI, HDS, outcomes of IVF and ICSI.

RESULT(S)

There were no significant differences in IVF and ICSI fertilization rate, good embryo rate, and pregnancy rate (PR) between high, moderate, and low DFI or HDS groups. Men with HDS >15% had significantly higher IVF abortion rates. There was a statistically insignificant trend toward an increased abortion rate in the high DFI (>27%) group. The DFI correlated negatively with sperm motility, and HDS correlated negatively with sperm morphology and concentration.

CONCLUSION(S)

Neither DFI nor HDS scores can provide independent information about embryo quality, fertilization, and PRs for infertility patients undergoing ART. Sperm DNA fragmentation probably affects sperm motility. The relationship between HDS and IVF abortion rates provides preliminary evidence that ICSI may be indicated for men with HDS >15%. The potential adverse effect of sperm DNA damage on the quality of postimplantation embryo and spontaneous abortion should be a concern.

The comet assay in male reproductive toxicology

Due to our lifestyle and the environment we live in, we are constantly confronted with genotoxic or potentially genotoxic compounds. These toxins can cause DNA damage to our cells, leading to an increase in mutations. Sometimes such mutations could give rise to cancer in somatic cells. However, when germ cells are affected, then the damage could also have an effect on the next and successive generations. A rapid, sensitive and reliable method to detect DNA damage and assess the integrity of the genome within single cells is that of the comet or single-cell gel electrophoresis assay. The present communication gives an overview of the use of the comet assay utilising sperm or testicular cells in reproductive toxicology. This includes consideration of damage assessed by protocol modification, cryopreservation vs the use of fresh sperm, viability and statistics. It further focuses on in vivo and in vitro comet assay studies with sperm and a comparison of this assay with other assays measuring germ cell genotoxicity. As most of the de novo structural aberrations occur in sperm and spermatogenesis is functional from puberty to old age, whereas female germ cells are more complicated to obtain, the examination of male germ cells seems to be an easier and logical choice for research and testing in reproductive toxicology. In addition, the importance of such an assay for the paternal impact of genetic damage in offspring is undisputed. As there is a growing interest in the evaluation of genotoxins in male germ cells, the comet assay allows in vitro and in vivo assessments of various environmental and lifestyle genotoxins to be reliably determined.

Clinical relevance of sperm DNA damage in assisted reproduction

Many studies have shown how a 'paternal effect' can cause repeated assisted reproduction failures. In particular, with increasing experience of intracytoplasmic sperm injection (ICSI), it became evident that spermatozoa from some patients repeatedly fail to form viable embryos, although they can fertilize the oocyte and trigger early preimplantation development. Many authors have shown how this paternal effect can be traced back to anomalies in sperm chromatin organization: the spermatozoa of subfertile men are characterized by numerical abnormalities in spermatozoal chromosome content, Y chromosome microdeletions, alterations in the epigenetic regulation of paternal genome and non-specific DNA strand breaks. In particular, pathologically increased sperm DNA fragmentation is one of the main paternal-derived causes of repeated assisted reproduction failures in the ICSI era. The intention of this review is to describe nuclear sperm DNA damage, with emphasis on its clinical significance and its relationship with male infertility. Assessment of sperm DNA damage appears to be a potential tool for evaluating semen samples prior to their use in assisted reproduction, helping to select spermatozoa with intact DNA or with the least amount of DNA damage for use in assisted conception.

Relationship between sperm DNA damage, induced acrosome reaction and viability in ICSI patients

The DNA damage in human spermatozoa is a relevant predictor of prognosis in male infertility, whereby increased sperm DNA damage impairs the outcomes of artificial reproduction. Theoretically, DNA damage should alter the special cellular functions of human spermatozoa, and lead to diminished acrosome reaction with reduced fertilization rates. Nevertheless, intracytoplasmic sperm injection (ICSI) has been reported to alleviate such negative outcomes due to DNA damage. This study investigated the relationship between DNA fragmentation and acrosome reaction as well as viability in ICSI patients. The study enrolled 42 men undergoing ICSI due to poor sperm parameters. The DNA fragmentation indexes (DFI) were 4-10% in 38% of the cases, and > or = 10% in 19% of the cases. The results of both acrosome reaction and viability assays showed negative correlations with DFI values in all cases and especially in cases with fertilization rates <60% (P < 0.05). However, such correlations were not found in cases with fertilization rates >60%. There were no live deliveries in patients with high DFI levels (>10%). In conclusion, negative correlations were identified between increased DNA damage, and acrosome reaction and/or viability of human spermatozoa, especially in cases with reduced fertilization rates.

Value of the sperm deoxyribonucleic acid fragmentation level, as measured by the sperm chromatin dispersion test, in the outcome of in vitro fertilization and intracytoplasmic sperm injection

OBJECTIVE

To determine the prognostic value of sperm DNA fragmentation levels, as measured by the sperm chromatin dispersion (SCD) test, in predicting IVF and ICSI outcome.

DESIGN

Double-blind prospective study.

SETTING

University-affiliated private IVF setting.

PATIENT(S)

A total of 85 couples undergoing infertility treatment with IVF/ICSI.

INTERVENTION(S)

Analysis of DNA fragmentation by the SCD test in 170 aliquots obtained from the ejaculate and from the processed semen used for assisted reproductive technologies (ART).

MAIN OUTCOME MEASURE(S)

Percentage of spermatozoa with fragmented DNA was statistically correlated with embryo quality and reproductive success.

RESULT(S)

Fertilization rate was inversely correlated with DNA fragmentation (r = -0.245 P = .045). Higher DNA fragmentation rate gave an increased proportion of zygotes showing asynchrony between the nucleolar precursor bodies of zygote pronuclei (73.8% vs. 28.8% P < .001). In addition, the slower embryo development and worst morphology on day 6 was correlated with higher sperm DNA fragmentation (47.7% vs. 29.4% P = .044). We also observed a negative correlation between DNA fragmentation and the implantation rate (r = -0.250 P = .042). However, SCD test values were not statistically different in cycles that resulted in a pregnancy compared with those that did not (33.2 vs. 28.2 and 32.4 vs. 34.7).

CONCLUSION(S)

This is the first report that describes a correlation between sperm DNA integrity, as measured by the SCD test, and fertilization rate, embryo quality, and implantation rate in IVF/ICSI. The degree of DNA fragmentation was inversely correlated with fertilization rate, synchrony of the nucleolar precursor bodies' pattern in pronuclei, embryo ability to achieve blastocyst stage, and embryo morphological quality. Because SCD test values were correlated with embryo quality and blastocyst rate, the lack of correlation between sperm DNA fragmentation and pregnancy outcome in IVF might be due to embryo selection before transfer. The ability of the SCD test to predict the blastocyst rate after IVF/ICSI warrants further study.

Sperm DNA fragmentation negatively correlates with velocity and fertilization rates but might not affect pregnancy rates

OBJECTIVE

To evaluate sperm DNA fragmentation in correlation with sperm parameters and IVF/intracytoplasmic sperm injection (ICSI) outcomes.

DESIGN

Retrospective review.

SETTING

A tertiary infertility referral clinic.

PATIENT(S)

We collected 303 semen samples from patients undergoing IVF with or without ICSI.

INTERVENTION(S)

Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) assay, measurement of fertilization rates, good embryo rates, and pregnancy rates for the IVF/ICSI program.

MAIN OUTCOME MEASURE(S)

The percentage of sperm with DNA fragmentation, correlated with semen analysis parameters and IVF/ICSI outcomes.

RESULT(S)

Sperm DNA fragmentation rates were significantly higher in patients with abnormal sperm parameters than in those with normal sperm parameters. When sperm DNA fragmentation was >10%, fertilization rates were affected. Sperm DNA fragmentation rates were negatively correlated with sperm velocity parameters but did not affect pregnancy outcomes.

CONCLUSION(S)

The results indicated that sperm DNA fragmentation affects fertilization rates and sperm motility but might not affect pregnancy rates.

DNA damage to spermatozoa has impacts on fertilization and pregnancy

DNA damage in the male germ line has been associated with poor semen quality, low fertilization rates, impaired preimplantation development, increased abortion and an elevated incidence of disease in the offspring, including childhood cancer. The causes of this DNA damage are still uncertain but the major candidates are oxidative stress and aberrant apoptosis. The weight of evidence currently favours the former and, in keeping with this conclusion, positive results have been reported for antioxidant therapy both in vivo and in vitro. Resolving the causes of DNA damage in the male germ line will be essential if we are to prevent the generation of genetically damaged human embryos, particularly in the context of assisted conception therapy.

Relationship between human semen parameters and deoxyribonucleic acid damage assessed by the neutral comet assay

OBJECTIVE

To explore the association between semen parameters and sperm DNA damage.

DESIGN

Cross-sectional.

SETTING

Andrology clinic.

PATIENT(S)

Two hundred fifty-seven men undergoing infertility assessment.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Sperm concentration and motility were measured using computer-assisted sperm analysis; morphology was scored using the strict criteria. The neutral comet assay was used to measure sperm DNA damage. Comet assay parameters included comet extent, percent DNA in the comet tail, and tail distributed moment, an integrated measure of length and intensity. We also scored cells that were too long to measure (>300 microm), which we referred to as cells with high DNA damage.

RESULT(S)

Men older than 35 years had a statistically significant increase in the number of cells with high DNA damage as compared with younger men. In age-adjusted regression analyses, the most consistent associations were found between semen parameters and the number of cells with high DNA damage. For an interquartile range change in the number of cells with high DNA damage, sperm concentration declined 14.2 x 10(6)/mL, motility declined 4.3%, and morphology declined 0.5%. Comet extent and percent DNA in the comet tail were also associated with a decline in sperm concentration and motility, respectively.

CONCLUSION(S)

Although there were associations between semen and comet assay parameters, their magnitudes were weak, suggesting that the comet assay provides additional independent information on sperm function.

Embryo quality and IVF treatment outcomes may correlate with different sperm comet assay parameters

BACKGROUND

Standard semen parameters have proven poor at predicting the outcomes of IVF treatment cycles. As recent studies suggest that the male genome may play an important role in early embryogenesis, this study attempts to correlate the level of sperm DNA damage in fresh semen and prepared sperm with the outcomes of conventional IVF treatment cycles.

METHODS

Forty patients embarking on IVF treatment were recruited into this prospective observational study. Both fresh semen and PureSperm-prepared sperm were processed using a modified comet assay 3-6 months prior to the patients' IVF treatment cycles. Comet head DNA (mean and integrated head density) and tail DNA parameters (length and moment) were measured separately.

RESULTS

Significant correlations between total sperm concentration and between comet length, moment, mean head density with embryo quality were detected in fresh semen and prepared sperm. Surprisingly, no significant correlations between head and tail parameters were detected.

CONCLUSIONS

Comet head and tail DNA parameters appear to be potentially useful as predictors of embryo quality and IVF outcomes, especially in couples with unexplained subfertility. The lack of correlation between head and tail parameters may be due to a different mechanism of DNA damage within these two compartments.

A simple DNA disc chip in a microarray design based on modified comparative genomic hybridization for sperm DNA analysis

OBJECTIVE

A DNA disc chip assay, based on comparative genomic hybridization, was designed to measure changes in sperm DNA intensities. The objective was to analyze the DNA integrity of hyperactive sperm cells after mild heat treatment.

DESIGN

The assay based on a multiple cell comet assay was used to analyze changes in genomic DNA. Washed sperm DNA were tested on the assay and images stored in a microarray design.

SETTING

Clinical and academic research environment.

PATIENT(S)

Frozen-thawed washed sperm from different donors (n = 7).

INTERVENTION(S)

Discarded sperm leftover from trial washes carried out at 37 degrees and 40 degrees C were frozen and processed for the DNA disc chip assay.

MAIN OUTCOME MEASURE(S)

Fluorescent intensities of DNA disc chips and sperm variables.

RESULT(S)

Heat treatment resulted in more than eightfold increase in sperm hyperactive motility with little degradation in DNA integrity. Sperm with low hyperactivation was associated with alterations in DNA after heat treatment.

CONCLUSION(S)

The DNA disc chip assay was simple, inexpensive, and permitted assisted reproduction technologies laboratories to use comparative genomic hybridization for cytogenotoxicity testing. However, the assay required manual processing, a fluorescent microscope, and computer. The data showed an association between sperm hyperactivation and DNA integrity suggesting that the hyperactivation marker may be used for selecting quality sperm for intracytoplasmic sperm injection. More studies are needed to examine temperature effects on ejaculated human sperm.

Chromatin remodeling during spermiogenesis: a possible role for the transition proteins in DNA strand break repair

An important chromatin remodeling process is taking place during spermiogenesis in mammals and DNA strand breaks must be produced to allow the accompanying change in DNA topology. Endogenous DNA strand breaks are indeed detected at mid-spermiogenesis steps but are no longer present in mature sperm. Both in vitro and in vivo evidence suggests that the DNA-binding and condensing activities of a set of basic nuclear "transition proteins" may be crucial to the integrity of the chromatin remodeling process. We propose that these proteins are necessary for the repair of the strand breaks so that DNA fragmentation is minimized in the mature sperm.

Induction of the acrosome reaction and zona-free hamster oocyte penetration by a bull with complete teratospermia versus a half brother with normal sperm

A fertile bull producing normal sperm and a sterile half brother exhibiting 100% teratospermia were available to study an induced sperm acrosome reaction and oocyte penetration. Pedigree analysis indicated that this condition was inherited. Experiments were undertaken to study the induction of the acrosome reaction using dilaurylphosphatidylcholine (PC12) liposomes, because this procedure was previously established to be highly correlated with bull fertility. The sperm from each bull were incubated with several PC12 concentrations for varying time periods. The initial percentages of sperm from the sterile bull with intact, partially intact, and lost acrosomes were 67%, 18%, and 14%, respectively, vs 82%, 13%, and 5% for the fertile bull (P < .05). After incubation for 15 minutes with 50 microM PC12 liposomes the corresponding values were, respectively, 51%, 26%, and 19%; and 60%, 28%, and 12%. Thus, the differences after induction of the acrosome reaction, although significant (P < .05), were small. The number of sperm adhered to each oocyte averaged 22 and 10, respectively, for the fertile and sterile bulls, whereas 74% of the fertile bull sperm and only 11% of the sterile bull sperm penetrated oocytes. Mixing the sperm-oocyte complex during incubation and increasing the sperm concentration during incubation to compensate for differences in sperm motility did not markedly affect oocyte penetration by teratogenic sperm, which is consistent with this bull being sterile. In other studies, microinjection of this type of sperm was demonstrated to induce fertilization, so the consequences of using sperm with hereditary defects in assisted reproductive programs to overcome human male sterility may be a concern.

Cryopreservation of human cumulus cells for co-cultures and assessment of DNA damage after thawing using the comet assay

PURPOSE

Cumulus cells have been shown to be beneficial for blastocysts formation in co-cultures but information on cumulus cryopreservation is lacking. The objective was to use the fixed cell comet assay to analyze for DNA damage in cumulus cells after cryopreservation.

METHODS

Discarded cumulus cells from follicular aspirates obtained during assisted reproduction procedures (N = 4 cases) were pooled and cryopreserved in either 40% ethylene glycol and 0.5 M sucrose, 12:20% glycerol-egg yolk medium, 28% glycerol hypoosmolar medium or control medium. The cells were processed and stored in liquid nitrogen for 48 h. The thawed cells were smeared on glass slides, fixed, stained with acridine orange, embedded in a mini-agarose layer, and electrophoresis carried out. Fluorescent images were analyzed.

RESULTS

The cumulus tail moment, a calculated index of DNA damage, was significantly lower for each of the three cryoprotectant when compared with the control. The two cryoprotectants containing glycerol were associated with higher cumulus cell viability. However, the glycerol-egg yolk combination yielded the highest cell viability.

CONCLUSIONS

The cumulus comet assay demonstrated similar DNA integrity in cells frozen in each of the three cryoprotectants. The glycerol-egg yolk medium had the highest cell viability with little or no DNA damage after freeze-thaw. More studies are needed to examine the long-term effect of the cryoprotectants on thawed cumulus cell viability.

Human sperm deoxyribonucleic acid fragmentation by specific types of papillomavirus

OBJECTIVE

Human papillomaviruses are present in up to 64.3% of patients' sperm. The objectives were (1) to determine human papillomavirus deoxyribonucleic acid effects on sperm deoxyribonucleic acid integrity and (2) to assess human papillomavirus differential effects on the sperm cell.

STUDY DESIGN

Two-layer colloid washed sperm were exposed to E6-E7 deoxyribonucleic acid fragments generated from human papillomavirus types 16, 18, 31, 33, 6/11, or control (DQA1) for 24 hours. The motility parameters were measured and analyzed. Pilot studies were performed to develop a fixed sperm comet assay to assess deoxyribonucleic acid fragmentation.

RESULTS

Significant sperm deoxyribonucleic acid fragmentation occurred after exposure to deoxyribonucleic acid of human papillomavirus types 16 and 31. Human papillomavirus deoxyribonucleic acid fragment size was not a factor. Human papillomavirus types 18, 33, and 6/11 did not compromise sperm deoxyribonucleic acid integrity. Washed sperm motility was higher in the presence of human papillomavirus deoxyribonucleic acid except for type 6/11. Amplitude of head displacement was lower for human papillomavirus types 16 and 6/11. Sperm linearity was increased for all human papillomavirus types except type 18.

CONCLUSION

Human papillomavirus type 16 and 31 deoxyribonucleic acid caused deoxyribonucleic acid breakages characteristic of apoptotic but not necrotic sperm. The data suggest that these human papillomavirus types may adversely affect subsequent embryonic development after fertilization. Sperm deoxyribonucleic acid appears to resist human papillomavirus types 18, 33, and 6/11 or repairing mechanisms occurred. Although enhanced motility was found in human papillomavirus-exposed sperm, important velocity parameters were decreased, suggesting impaired sperm function.