Comparative analysis of three sperm DNA damage assays and sperm nuclear protein content in couples undergoing assisted reproduction treatment

STUDY QUESTION

Is there an association between sperm DNA damage, measured by three different assays, sperm nuclear protein content and clinical outcomes in assisted reproduction treatment (ART)?

SUMMARY ANSWER

Sperm DNA damage measured by terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling (TUNEL) and the Comet assay were significantly associated with ART outcomes in our single institution study.

WHAT IS KNOWN ALREADY

Abnormal protamine expression is known to be associated with sperm DNA damage and male infertility. A number of studies have shown a significant relationship between sperm DNA damage and ART outcomes. To date, there are no large studies providing direct comparisons of DNA damage tests within the same study population. Thus, the prognostic value for each method remains unknown.

STUDY DESIGN, SIZE, DURATION

Cross-sectional study of 238 men from infertile couples undergoing ART at the University Center for Reproductive Medicine, Utah, USA, between April 2011 and March 2013.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm from men undergoing ART were tested for DNA damage using the alkaline Comet assay, TUNEL and flow cytometric chromatin evaluation (FCCE) assays. Histone retention was analysed using the aniline blue staining method, whereas protamine content (proteins P1 and P2) and ratio were analysed using acid urea gel electrophoresis. The prognostic value of each sperm DNA test to predict clinical pregnancy was calculated.

MAIN RESULTS AND THE ROLE OF CHANCE

Histone retention was associated with sperm DNA damage (P < 0.001), reduced embryo quality (P = 0.005) and clinical pregnancies (P < 0.001). The mean percentage of sperm with DNA damage was significantly higher in sperm from non-pregnant couples compared with that from pregnant couples, as measured by TUNEL assay (15.04 ± 1.16% versus 8.79 ± 0.56%; P < 0.001) and alkaline Comet assay (72.79 ± 2.49% versus 55.86 ± 2.29%; P < 0.001). There was no association between clinical pregnancies and DNA fragmentation index measured by FCCE (12.97 ± 1.46 versus 14.93 ± 1.65; P = 0.379). Of the protamine parameters analysed, only the P1/P2 ratio was associated with sperm count (P = 0.013), men's age (P = 0.037), maturity (P = 0.049) and blastocyst quality (P = 0.012). Histone retention and sperm DNA damage measured by Comet and TUNEL assays were associated with fertilization rate (P < 0.05), embryo quality (P < 0.05) and implantation rate (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

A potential drawback of this study is that it is cross-sectional. Generally in such studies there is more than one variable that could cause the effect. Analysing sperm is one part of the equation; there are also a number of female factors that have the potential to influence ART outcomes. Therefore, given the large and well-established role of female factors in infertility, normal sperm DNA integrity and protamination do not necessarily ensure clinical pregnancy in ART. Thus, female factors can reduce the prognostic value of sperm DNA tests. Further, our use of native semen instead of prepared sperm may have iatrogenically increased the DNA damage.

WIDER IMPLICATIONS OF THE FINDINGS

Alteration in sperm nuclear protein affects sperm DNA integrity. Further, with the current dataset, TUNEL and Comet assays appeared more predictive of ART success than FCCE.

STUDY FUNDING/COMPETING INTEREST(S)

No personal or direct financial support has been received for any of this work. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Assessment of the reproductive toxicity of inhalation exposure to ethyl tertiary butyl ether in male mice with normal, low active and inactive ALDH2

No data are available regarding aldehyde dehydrogenase 2 (ALDH2) polymorphisms related to the reproductive toxicity possibly caused by ethyl tertiary butyl ether (ETBE). In this study, two inhalation experiments were performed in Aldh2 knockout (KO), heterogeneous (HT) and wild type (WT) C57BL/6 male mice exposed to ETBE, and the data about general toxicity, testicular histopathology, sperm head numbers, sperm motility and sperm DNA damage were collected. The results showed that the 13-week exposure to 0, 500, 1,750 and 5,000 ppm ETBE significantly decreased sperm motility and increased levels of sperm DNA strand breaks and 8-hydroxy-deoxyguanosine in both WT and KO mice, the effects were found in 1,750 and 5,000 ppm groups of WT mice, and all of the three exposed groups of KO mice compared to the corresponding control; furthermore, ETBE also caused decrease in the relative weights of testes and epididymides, the slight atrophy of seminiferous tubules of testis and reduction in sperm numbers of KO mice exposed to ≥500 ppm. In the experiment of exposure to lower concentrations of ETBE (0, 50, 200 and 500 ppm) for 9 weeks, the remarkable effects of ETBE on sperm head numbers, sperm motility and sperm DNA damage were further observed in KO and HT mice exposed to 200 ppm ETBE, but not in WT mice. Our findings suggested that only exposure to high concentrations of ETBE might result in reproductive toxicity in mice with normal active ALDH2, while low active and inactive ALDH2 enzyme significantly enhanced the ETBE-induced reproductive toxicity in mice, even exposed to low concentrations of ETBE, mainly due to the accumulation of acetaldehyde as a primary metabolite of ETBE.

ICSI outcome is significantly better with testicular spermatozoa in patients with necrozoospermia: a retrospective study

OBJECTIVE

To determine whether intracytoplasmic sperm injection (ICSI) outcome with testicular sperm is superior to that of ejaculated sperm in men with incomplete necrozoospermia, defined as sperm viability ≥5 to ≤45%.

STUDY DESIGN

Retrospective study at a Reproductive Medicine Center of a tertiary referral hospital. A total of 231 couples with male infertility due to incomplete necrozoospermia underwent 342 ICSI cycles with freshly ejaculated sperm (ICSI-ejaculated) and 182 cycles with testicular sperm (ICSI-TESE).

RESULTS

Overall 1624 MII oocytes were injected in the ICSI-ejaculated group with a fertilisation rate of 60.8%, while in ICSI- TESE cycles the fertilisation rate was 59.6% in 874 MII oocytes. The cleavage rate was higher in ICSI-ejaculated cycles than in ICSI-TESE cycles (96.3% versus 92.9%; p = 0.004). However, the pregnancy and implantation rates per cycle were significantly higher in the ICSI-TESE group (67/182, 36.8% versus 68/342, 19.9% (p = 0.0001); and 23.7% versus 12.7% (p = 0.0001), respectively). The miscarriage rate was similar (ICSI-ejaculated 26.5% versus ICSI-TESE 17.9%, p = 0.301). Live birth rate per cycle in the ICSI-ejaculated group was significantly lower than in the ICSI-TESE (13.7% versus 28.6%, p = 0.0001).

CONCLUSIONS

In cases of persistent necrozoospermia, testicular sperm should be favoured over ejaculated sperm. These data call for more research to understand the pathophysiology of refractory necrozoospermia.

Sperm selection: effect on sperm DNA quality

The selection of spermatozoa without DNA fragmentation and chromosomal diseases prior to assisted reproductive techniques helps to optimize the outcome of the treatment; in particular, sperm selection prior to in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) is crucial. In fact, although ICSI has been successfully and safely applied worldwide for almost 20 years, at the present time we have no real knowledge regarding the hypothetical long-term side effects on ICSI adults, given the increased likelihood of spermatozoa with defective nuclear content fertilizing oocytes.In the case of DNA damage, the basal sperm DNA fragmentation rate can be significantly reduced by some sperm processing procedures that improve the percentage of spermatozoa with normal chromatin structure by filtering out DNA-damaged spermatozoa. After this first step, new advances in micromanipulation can be performed to choose the "ideal" mature spermatozoa for ICSI, reducing potential damage to the gametes. In fact, it is possible to prevent fertilization by DNA-damaged and chromosomal-unbalanced spermatozoa by selecting ICSI sperm by maturation markers such as hyaluronic acid or other zona pellucida receptors. Furthermore, novel noninvasive imaging techniques can be valid tools for helping in the morphological selection of ICSI spermatozoa.

Evaluation of potential protein biomarkers in patients with high sperm DNA damage

The laboratory evaluation of male infertility remains an essential area of research as 40-60% of infertility cases are attributable to male-related factors. Current sperm analysis methods add only partial information on sperm quality and fertility outcomes. The specific underlying cause of infertility in most cases is unknown, while a proportion of male infertility could be caused by molecular factors such as the absence or abnormal expression of some essential sperm proteins. The objective of this study was to screen for associations between sperm protein profiles and sperm concentration, motility, and DNA fragmentation index in patients undergoing fertility evaluation in a clinical setting. Based on those parameters, semen samples were categorized as either normal or abnormal. We screened 34 semen samples with various abnormal parameters and compared them to 24 normal control samples by using one dimensional (1-D) gel electrophoresis and mass-spectrometry. In this study, we anticipated to establish a normal sperm parameter profile which would be compared to abnormal sperm samples and reveal candidate proteins. Our preliminary results indicate that no normal uniform profile could be established, which affirms the complexity of male fertility and confirms the limitations of standard semen analysis. Four main protein groups were identified in correlation with abnormal DNA fragmentation and/or motility. The first group included sperm nuclear proteins such as the SPANX (sperm protein associated with the nucleus on the X chromosome) isoforms and several types of histones. The second group contained mitochondria-related functions and oxidative stress proteins including Mitochondrial Ferritin, Mitochondrial Single-Stranded DNA Binding Protein, and several isoforms of Peroxiredoxins. Two other protein groups were related to sperm motility such as microtubule-based flagellum and spindle microtubule as well as proteins related to the ubiquitin-proteasome pathway. Further research is required in order to characterize these potential biomarkers of male fertility potential.

Evaluation of human sperm chromatin status after selection using a modified Diff-Quik stain indicates embryo quality and pregnancy outcomes following in vitro fertilization

Sperm chromatin/DNA damage can be measured by a variety of assays. However, it has been reported that these tests may lose prognostic value in Assisted Reproductive Technology (ART) cycles when assessed in post-prepared samples, possibly due to the normalizing effect promoted by sperm preparation procedures. We have recently implemented a modified version of the Diff-Quik staining assay that allows for the evaluation of human sperm chromatin status in native samples, together with standard sperm morphology assessment. However, the value of this parameter in terms of predicting in vitro fertilization (IVF) and Intracytoplasmic sperm injection (ICSI) outcomes after sperm selection is unknown. In this study, data from 138 couples undergoing in vitro fertilization (IVF) or Intracytoplasmic sperm injection (ICSI) treatments showed that sperm chromatin integrity was significantly improved after density gradient centrifugation and swim up (p < 0.001), but no correlations were found with fertilization or embryo development rates (p > 0.05). However, sperm samples presenting lower percentages of damaged chromatin were associated with better quality (Grade I) embryos in both ART procedures (p < 0.05) and clinical pregnancy among IVF couples (p < 0.05). Furthermore, regression analysis confirmed the clinical value of Diff-Quik staining in predicting IVF (but not ICSI) clinical pregnancy (OR: 0.927, 95% CI: 0.871-0.985, p = 0.015), and a threshold value of 34.25% for this parameter was established. The proportion of IVF couples achieving a clinical pregnancy was reduced 1.9-fold when the percentage of abnormal dark staining was ≥34.25% (p = 0.05). In conclusion, the Diff-Quik staining assay provides useful information regarding ART success, particularly in IVF cycles, where some degree of 'natural' sperm selection may occur; but not in ICSI, where sperm selection is operator dependent. This quick and low-cost assay is suggested as an alternative method to detect sperm chromatin status in minimal clinical settings, when no other well-established and robust assays (e.g. Sperm chromatin structure assay, terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling) are available.

Diagnostic value of sperm DNA fragmentation and sperm high-magnification for predicting outcome of assisted reproduction treatment

Over the last years, major improvements in the field of male infertility diagnosis have been achieved. The aim of this study was to determine the diagnostic usefulness of sperm DNA integrity and sperm vacuolisation for predicting outcome in infertile couples undergoing in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) treatments. A cohort study from 152 infertile couples undergoing sperm DNA fragmentation and high-magnification tests prior to an assisted reproduction treatment was designed. We found that the most predictive cutoff for pregnancy was 25.5% of DNA fragmentation with a negative predictive value of 72.7% (P=0.02). For the degree of vacuolisation, the best predictor of pregnancy was 73.5% of vacuolated sperm grades III+IV with a negative predictive value of 39.4% (P=0.09), which was not statistically significant. In conclusion, sperm DNA fragmentation greater than 25.5% could be associated with higher probability of failure IVF treatment. Regarding the results of the sperm analysis at high magnification, they do not allow us to predict whether or not patients will become pregnant.

The impact of sperm DNA damage in assisted conception and beyond: recent advances in diagnosis and treatment

Sperm DNA damage is a useful biomarker for male infertility diagnosis and prediction of assisted reproduction outcomes. It is associated with reduced fertilization rates, embryo quality and pregnancy rates, and higher rates of spontaneous miscarriage and childhood diseases. This review provides a synopsis of the most recent studies from each of the authors, all of whom have major track records in the field of sperm DNA damage in the clinical setting. It explores current laboratory tests and the accumulating body of knowledge concerning the relationship between sperm DNA damage and clinical outcomes. The paper proceeds to discuss the strengths, weaknesses and clinical applicability of current sperm DNA tests. Next, the biological significance of DNA damage in the male germ line is considered. Finally, as sperm DNA damage is often the result of oxidative stress in the male reproductive tract, the potential contribution of antioxidant therapy in the clinical management of this condition is discussed. DNA damage in human spermatozoa is an important attribute of semen quality. It should be part of the clinical work up and properly controlled trials addressing the effectiveness of antioxidant therapy should be undertaken as a matter of urgency. Sperm DNA damage is a useful biomarker for male infertility diagnosis and prediction of assisted reproduction outcomes. It is associated with reduced fertilization rates, embryo quality and pregnancy rates, and higher rates of spontaneous miscarriage and childhood diseases. With all of these fertility check points, it shows more promise than conventional semen parameters from a diagnostic perspective. Despite this, few infertility clinics use it routinely. This review provides a synopsis of the most recent studies from each of the authors, all of whom have major track records in the field of sperm DNA damage in the clinical setting. It explores current laboratory tests and the accumulating body of knowledge concerning the relationship between sperm DNA damage and clinical outcomes. The paper proceeds to discuss the strengths and weaknesses and clinical applicability of current sperm DNA fragmentation tests. Next, the biological significance of DNA damage in the male germ line is considered. Finally, as sperm DNA damage is often the result of increased oxidative stress in the male reproductive tract, the potential contribution of antioxidant therapy in the clinical management of this condition is discussed. As those working in this field of clinical research, we conclude that DNA damage in human spermatozoa is an important attribute of semen quality which should be carefully assessed in the clinical work up of infertile couples and that properly controlled trials addressing the effectiveness of antioxidant therapy should be undertaken as a matter of urgency.

[Evaluation of sperm functional parameters in normozoospermic infertile individuals]

OBJECTIVE

This study evaluated the integrity of the chromatin structure, reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP), DNA damage and lipid peroxidation of semen samples from infertile men classified as unexplained infertility.

METHODS

Between February 2010 and July 2011 semen parameters and functional tests were evaluated in 10 subjects with proven fertility, 10 that belong to general population and 8 with idiopathic infertility. In addition to the conventional semen analysis, the following unconventional seminal analysis were conducted: evaluation of ROS, MMP, sperm chromatin structure assay (SCSA) by flow cytometry, assessment of sperm membrane lipid peroxidation by spectrophotometry, and alkaline comet assay by electrophoresis.

RESULTS

We observed a significant increase (P<.05) in the production of ROS and the fragmentation or sperm DNA damage in the population of infertile men. There were no statistically significant differences (P>.05) in the analysis of sperm membrane integrity between the groups. Moreover, we observed significant correlations (P<.05) between SCSA and comet assay (r=0.86) and the production of intracellular ROS (r=-0.588).

CONCLUSION

The sperm from individuals with idiopathic infertility showed high levels of intracellular ROS and increased levels of DNA fragmentation in the sperm. These results suggest that these two parameters are related to unexplained infertility and therefore have clinical importance as a possible diagnostic and prognostic tool in the evaluation of idiopathic male infertility.

Telomere lengths in human pronuclei, oocytes and spermatozoa

Telomeres are chromosome ends that control functions related to cell division. Short telomeres are proposed to underlie infertility, female reproductive ageing and abnormal embryogenesis, but there is little direct evidence on telomere length in gametes and embryos. The aim of this study was to measure telomere lengths in individual human oocytes, spermatozoa, male and female pronuclei, in order to compare parental contributions to telomere lengths in the human zygote. Quantitative fluorescence in situ hybridization was used to measure average telomere length in pronuclei of oocytes fertilized for research using a known fertile sperm sample. Pronuclei derived from male and female gametes were distinguished by 5-methylcytosine staining. Results were compared with those for unfertilized mature and immature oocytes and individual spermatozoa decondensed in vitro. Fifty unselected men and one sperm donor provided semen samples and 32 women donated oocytes surplus to IVF treatment. Telomeres in mature oocytes and female pronuclei were significantly longer than those in individual spermatozoa and male pronuclei (P < 0.0001). Telomeres were longer in immature oocytes than in mature oocytes (P < 0.04). Sperm telomere length increased with male age (P < 0.05). Neither sperm nor oocyte telomere lengths were significantly associated with clinical parameters or outcome of treatment. In conclusion, telomere length measurements directly comparing human pronuclei under identical conditions show that male-derived telomeres are shorter on average than female-derived telomeres at fertilization. We propose that from this starting point, telomere lengths are probably modified by recombination events in the oocyte until telomerase increases at the blastocyst stage. Our findings do not support the use of gamete telomere lengths as a fertility diagnostic tool.

Assessment of DNA damage in sperm after repeated non-invasive sampling in zebrafish Danio rerio

Repeated non-invasive sampling of zebrafish Danio rerio sperm was conducted, sperm counts were obtained and a method for measurement of DNA damage in sperm was developed and validated (single-cell gel electrophoresis, comet, assay). DNA damage in sperm increased with concentration of hydrogen peroxide (H2 O2 , 0-200 µM), and in vitro exposure of sperm to 200 µM H2 O2 produced 88·7 ± 3·9% tail DNA compared to unexposed controls [12 ± 0·7% tail DNA (mean ± s.e., n = 3)]. Frequency of sperm sampling (sampled every 2, 4 or 7 days) did not affect DNA damage in sperm, but sperm counts decreased 57 and 22% for fish sampled every 2 or 4 days, respectively.

The clinical utility of sperm DNA integrity testing: a guideline

Sperm DNA damage is more common in infertile men and may contribute to poor reproductive performance. However, current methods for assessing sperm DNA integrity do not reliably predict treatment outcomes and cannot be recommended routinely for clinical use.

Cell membrane proteins from oviductal epithelial cell line protect human spermatozoa from oxidative damage

OBJECTIVE

To study the potential protective action in vitro of oviductal epithelial cell membrane proteins against oxidative damage in human spermatozoa.

DESIGN

Prospective in vitro study.

SETTING

University research laboratory and infertility clinic.

PATIENT(S)

Semen from men attending the infertility clinic at the Queen Mary Hospital with normal semen parameters (World Health Organization, 2010).

INTERVENTION(S)

We studied the effect of oviductal epithelial cell membrane proteins on the sperm functions and endogenous antioxidant enzyme activities.

MAIN OUTCOME MEASURE(S)

Sperm motility, lipid peroxidation, DNA fragmentation, intracellular reactive oxygen species (ROS) level, superoxide dismutase, and glutathione peroxidase activities.

RESULT(S)

Oviductal epithelial cell membrane proteins bind to the human spermatozoa and protect them from ROS-induced damages in terms of sperm motility, membrane integrity, DNA integrity, and intracellular ROS level. Spermatozoa-oviduct epithelial cell interaction also enhances the antioxidant defenses in spermatozoa.

CONCLUSION(S)

Our results demonstrated the protective effects of spermatozoon-oviductal epithelial cell interaction against oxidative stress in human spermatozoa. The results enhance our understanding of the protective mechanism of oviduct on sperm functions.

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.

Novel insights into the genetic and epigenetic paternal contribution to the human embryo

The integrity of the sperm genome and epigenome are critical for normal embryonic development. The advent of assisted reproductive technology has led to an increased understanding of the role of sperm in fertilization and embryogenesis. During fertilization, the sperm transmits not only nuclear DNA to the oocyte but also activation factor, centrosomes, and a host of messenger RNA and microRNAs. This complex complement of microRNAs and other non-coding RNAs is believed to modify important post-fertilization events. Thus, the health of the sperm genome and epigenome is critical for improving assisted conception rates and the birth of healthy offspring.

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.

Effect of smoking on sperm vitality, DNA integrity, seminal oxidative stress, zinc in fertile men

OBJECTIVE

To assess the effect of smoking on sperm vitality, sperm DNA integrity, semen reactive oxygen species, and zinc levels in fertile men.

METHODS

One-hundred sixty men were investigated. They were divided into 2 equal groups: healthy fertile nonsmokers and healthy fertile smokers. They were subjected to history taking, clinical examination, and semen analysis. In their semen, sperm hypo-osmotic swelling test, sperm DNA fragmentation test, seminal reactive oxygen species, and zinc were assessed.

RESULTS

Compared with fertile nonsmokers, fertile smokers were significantly associated with lower hypo-osmotic swelling test and seminal zinc levels and significantly associated with higher sperm DNA fragmentation percent and seminal reactive oxygen species levels.

CONCLUSION

Smoking (cigarettes/day and duration) has detrimental effects on sperm motility, viability, DNA fragmentation, seminal zinc levels, and semen reactive oxygen species levels, even in fertile men, and it is directly correlated with cigarette quantity and smoking duration.

Sperm DNA damage: how relevant is it clinically?

PURPOSE OF REVIEW

The true impact of the current sperm DNA fragmentation testing needs further scrutiny to assess whether clinically meaningful information is conveyed.

RECENT FINDINGS

Various studies have suggested different or no threshold values with assorted tests for the percentage of DNA fragmentation in the ejaculated sperm above which natural conception, fertilization or embryo development and/or clinical pregnancy rates are compromised. Current DNA fragmentation assessment methods provide very little specific information on the nature and severity of the DNA damage detected. Although sperm DNA fragmentation is associated with lower pregnancy rates through natural conception or intrauterine insemination, it does not seem to affect intracytoplasmic sperm injection outcome. Although animal studies demonstrated adverse reproductive effects of sperm DNA fragmentation, any conclusive evidence in humans is yet to be demonstrated. It is not clear whether interventions aimed at enrichment of sperm with decreased DNA fragmentation are effective in preventing the potential adverse effects of sperm DNA fragmentation in humans. Major concern about the use of sperm DNA integrity tests as prognostic parameters is that the direct evaluation of DNA fragmentation in individual sperm fertilizing the oocyte is not possible.

SUMMARY

The lack of consensus in defining a clinically relevant standard DNA fragmentation test with a meaningful cut-off level brings challenges in implementing the routine use of sperm DNA integrity assessment in daily practice.

Single-cell pulsed-field gel electrophoresis to detect the early stage of DNA fragmentation in human sperm nuclei

Single-cell pulsed-field gel electrophoresis (SCPFGE) with dual electrode pairs was developed to detect the early stage of DNA fragmentation in human sperm. The motile sperm were purified by the commonly used density-gradient centrifugation technique and subsequent swim-up. The sperm were embedded in a thin film of agarose containing bovine trypsin (20 µg/mL) and were then lysed. Prior to SCPFGE, proteolysis of DNA-binding components, such as protamine and the nuclear matrix was essential to separate the long chain fibers from the fibrous and granular fragments derived from a single nucleus. The overall electrophoretic profiles elucidated the course of DNA fragmentation. A few large fibrous fragments were observed at the beginning of the process, however, as the fragmentation advanced, the long chain fibers decreased and shortened, and, conversely, the granular fragments increased until finally almost all the DNA was shredded. Although the ejaculate contained sperm with heterogeneous stages, the purified motile sperm exhibited several dozens of uniformly elongated fibers arising from the tangled DNA at the origin, whereas a part of these fibers gave rise to fibrous fragments beyond the tip of the elongated fibers, and their numbers and sizes varied among the sperm. Conventional intra-cytoplasmic sperm injection (ICSI) usually depends on intra-operative light microscopic observation to select a sperm for injection. The present results revealed that sperm motility could not give full assurance of DNA integrity. SCPFGE is likely to serve an important role in the preoperative differential diagnosis to determine the competence of the sperm population provided for injection.

The effect of sperm DNA fragmentation on miscarriage rates: a systematic review and meta-analysis

STUDY QUESTION

Is there an association between high levels of sperm DNA damage and miscarriage?

SUMMARY ANSWER

Miscarriage rates are positively correlated with sperm DNA damage levels.

WHAT IS KNOWN ALREADY

Most ejaculates contain a subpopulation of sperm with DNA damage, also referred to as DNA fragmentation, in the form of double or single-strand breaks which have been induced in the DNA prior to or following ejaculation. This DNA damage may be particularly elevated in some subfertile men, hence several studies have examined the link between sperm DNA damage levels and conception and miscarriage rates.

STUDY DESIGN, SIZE, DURATION

A systematic review and meta-analysis of studies which examined the effect of sperm DNA damage on miscarriage rates was performed. Searches were conducted on MEDLINE, EMBASE and the Cochrane Library without any language restrictions from database inception to January 2012.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We used the terms 'DNA damage' or 'DNA fragmentation' combined with 'miscarriage', 'abortion' or 'pregnancy' to generate a set of relevant citations. Data extraction was performed by two reviewers. Study quality was assessed using the Newcastle-Ottawa Scale. Meta-analysis of relative risks of miscarriage was performed with a random effects model. Subgroup analyses were performed by the type of DNA damage test, whether the sperm examined were prepared or from raw semen and for pregnancies resulting from IVF or ICSI treatment.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified 16 cohort studies (2969 couples), 14 of which were prospective. Eight studies used acridine orange-based assays, six the TUNEL assay and two the COMET assay. Meta-analysis showed a significant increase in miscarriage in patients with high DNA damage compared with those with low DNA damage [risk ratio (RR) = 2.16 (1.54, 3.03), P < 0.00001)]. A subgroup analysis showed that the miscarriage association is strongest for the TUNEL assay (RR = 3.94 (2.45, 6.32), P < 0.00001).

LIMITATIONS, REASONS FOR CAUTION

There is some variation in study characteristics, including the use of different assays and different thresholds for DNA damage and the definition of pregnancy loss.

WIDER IMPLICATIONS OF THE FINDINGS

The use of methods which select sperm without DNA damage for use in assisted conception treatment may reduce the risk of miscarriage. This finding indicates that assays detecting DNA damage could be considered in those suffering from recurrent pregnancy loss. Further research is necessary to study the mechanisms of DNA damage and the potential therapeutic effects of antioxidant therapy.

STUDY FUNDING/COMPETING INTEREST(S)

None.

Epididymis response partly compensates for spermatozoa oxidative defects in snGPx4 and GPx5 double mutant mice

We report here that spermatozoa of mice lacking both the sperm nucleaus glutathione peroxidase 4 (snGPx4) and the epididymal glutathione peroxidase 5 (GPx5) activities display sperm nucleus structural abnormalities including delayed and defective nuclear compaction, nuclear instability and DNA damage. We show that to counteract the GPx activity losses, the epididymis of the double KO animals mounted an antioxydant response resulting in a strong increase in the global H₂O₂-scavenger activity especially in the cauda epididymis. Quantitative RT-PCR data show that together with the up-regulation of epididymal scavengers (of the thioredoxin/peroxiredoxin system as well as glutathione-S-transferases) the epididymis of double mutant animals increased the expression of several disulfide isomerases in an attempt to recover normal disulfide-bridging activity. Despite these compensatory mechanisms cauda-stored spermatozoa of double mutant animals show high levels of DNA oxidation, increased fragmentation and greater susceptibility to nuclear decondensation. Nevertheless, the enzymatic epididymal salvage response is sufficient to maintain full fertility of double KO males whatever their age, crossed with young WT female mice.

The clinical benefit and safety of current and future assisted reproductive technology

Since the first birth by IVF was achieved in 1978, the techniques involved in assisted reproductive technology have grown at an enormous rate. However, new technology has rarely been robustly validated before clinical use and developing scientific understanding of the available techniques has done little to alter their use. Furthermore, there are inconsistencies in the available clinical studies and endpoints. The benefits of some technologies already established for routine use are currently dubious and there are clear ethical concerns with providing them to patients when their scientific basis is not clear. As the uptake of assisted reproductive technology increases and newer technologies continue to push the boundaries of science, it is important to consider the clinical benefits and safety of all assisted reproductive technologies. This review will discuss aspects of some of the more recent techniques, including sperm DNA-damage tests, intracytoplasmic morphologically selected sperm injection, amino acid and metabolomics profiling, preimplantation genetic screening and time-lapse imaging, and those that may have substantial impacts on the field of reproductive medicine in the future including artificial gametes, ovarian transplantation and gene therapy.

Mechanisms and clinical correlates of sperm DNA damage

Among the different DNA anomalies that can be present in the male gamete, DNA fragmentation is the most frequent, particularly in infertile subjects. There is now consistent evidence that a sperm containing fragmented DNA can be alive, motile, morphologically normal and able to fertilize an oocyte. There is also evidence that the oocyte is able to repair DNA damage; however, the extent of this repair depends on the type of DNA damage present in the sperm, as well as on the quality of the oocyte. Thus, it is important to understand the possible consequences of sperm DNA fragmentation (SDF) for embryo development, implantation, pregnancy outcome and the health of progeny conceived, both naturally and by assisted reproductive technology (ART). At present, data on the consequences of SDF for reproduction are scarce and, in many ways, inconsistent. The differences in study conclusions might result from the different methods used to detect SDF, the study design and the inclusion criteria. Consequently, it is difficult to decide whether SDF testing should be carried out in fertility assessment and ART. It is clear that there is an urgent need for the standardisation of the methods and for additional clinical studies on the impact of SDF on ART outcomes.

Oxidative deoxyribonucleic acid damage in sperm has a negative impact on clinical pregnancy rate in intrauterine insemination but not intracytoplasmic sperm injection cycles

OBJECTIVE

To determine the level of DNA damage, both fragmentation and oxidative, in the sperm population used for intrauterine insemination (IUI) and intracytoplasmic sperm injection (ICSI) and its impact on fertilization and clinical pregnancy rates.

DESIGN

A prospective clinical study.

SETTING

A tertiary care fertility clinic.

PATIENT(S)

Couples undergoing ICSI (n = 48) and couples undergoing IUI cycles (n = 53).

INTERVENTION(S)

Assessment of both sperm DNA fragmentation using the TUNEL assay and oxidative DNA damage using the biomarker 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the samples prepared and used for insemination.

MAIN OUTCOME MEASURE(S)

Achievement of a clinical pregnancy.

RESULT(S)

Sperm DNA fragmentation and 8-OHdG were highly correlated (r = 0.55) and 8-OHdG was significantly lower in those who achieved a clinical pregnancy after IUI (8.9% vs. 20.2%). A threshold value of 11.5% 8-OHdG was identified as a useful predictor of IUI success. No differences were found in sperm DNA fragmentation or 8-OHdG between pregnant and nonpregnant couples in ICSI cycles.

CONCLUSION(S)

8-Hydroxy-2'-deoxyguanosine, a biomarker of oxidative DNA damage highly correlated with sperm DNA fragmentation, in human sperm DNA has significant value in predicting the chance of a clinical pregnancy after IUI but not ICSI in assisted reproductive technology.

Short-term storage of human spermatozoa in electrolyte-free medium without freezing maintains sperm chromatin integrity better than cryopreservation

Previous attempts to maintain human spermatozoa without freezing were based on short-term storage in component-rich medium and led to fast decline in motility and increased incidence of chromosome breaks. Here we report a new method in which sperm are maintained without freezing in an electrolyte-free medium (EFM) composed of glucose and bovine serum albumin. Human sperm were stored in EFM or human tubal fluid medium (HTFM) or were cryopreserved, and their motility, viability, and DNA integrity were examined at different intervals. Cryopreservation led to significant decline in sperm motility and viability and induced DNA fragmentation. Sperm stored in EFM maintained motility and viability for up to 4 and 7 wk, respectively, much longer than sperm stored in HTFM (<2 and <4 wk, respectively). DNA integrity, assessed with comet assay, was also maintained significantly better in EFM than in HTFM. One-week storage in EFM yielded motility and viability similar to that of cryopreserved sperm, but DNA integrity was significantly higher, resembling that of fresh sperm. After several weeks of storage in EFM, sperm were able to activate oocytes, undergo chromatin remodeling, and form normal zygotic chromosomes after intracytoplasmic sperm injection. This study demonstrated that human spermatozoa can be stored in EFM without freezing for several weeks while maintaining motility, viability, and chromatin integrity and that 1-wk storage in EFM offers better protection of sperm DNA integrity than cryopreservation. Sperm storage in EFM may become a viable option for the physicians working in assisted reproduction technology clinics, which would avoid cryodamage.

DNA damage and health in pregnancy

In healthy pregnancy reactive oxygen species and antioxidants remain in balance and DNA damage is repaired effectively. However, pregnancy is an inflammatory state exhibiting increased susceptibility to oxidative stress such that this balance can be easily disrupted. Increased DNA damage has been shown to be involved in many pathological states including pregnancy complications. Modern lifestyles including exposure to pollutants, poor diet, and lack of exercise cause excess inflammation, oxidative stress, and ultimately DNA damage. There is a growing body of literature providing evidence that these lifestyle changes are increasing our risk of infertility, miscarriage, and late-gestation pregnancy complications. Moreover, baseline DNA damage rises with age and couples in developed societies are delaying childbirth, placing them at further risk. In order to understand the effect of lifestyle and DNA damage on pregnancy health we require large prospective studies, with the collection of samples prior to conception and endpoints of time-to-pregnancy, early pregnancy loss, and late-gestation maternal and fetal health.

Sperm chromatin dispersion test in the assessment of DNA fragmentation and aneuploidy in human spermatozoa

Sperm DNA damage is thought to be increased in men with male factor infertility. Previous studies suggest a correlation between sperm DNA fragmentation and aneuploidy. The sperm chromatin dispersion (SCD) test was modified to produce the Halosperm Kit. The SCD-fluorescent in-situ hybridization (FISH) test allows the simultaneous detection of DNA fragmentation and aneuploidy on the same sperm cell. The objectives of this study were to validate the SCD, SCD-FISH and Halosperm tests for the analysis of sperm DNA fragmentation and compare them to the sperm chromatin structure assay (SCSA). Semen samples from 20 males undergoing IVF/intracytoplasmic sperm injection were processed using FISH, SCD-FISH, SCD and Halosperm, and compared with SCSA results. There was a significant difference between FISH and SCD-FISH results in the detection of aneuploidy (P=0.000) and the level of sperm DNA fragmentation in the samples subjected to SCSA and SCD (P=0.001) or SCSA and SCD-FISH (P=0.001). There was no significant correlation between DNA fragmentation and aneuploidy. If sperm aneuploidy is to be determined, more reliable results will be obtained if FISH is performed rather than SCD-FISH. A lack of validation and unknown clinical significance question the value of DNA fragmentation assays. DNA damage in the male germ line may result in adverse clinical outcomes and the pathophysiology and clinical consequences of sperm DNA damage are being actively researched. Many DNA fragmentation assays such as the Halosperm Kit have been developed recently and are now available at a commercial level. Unfortunately, aimed at vulnerable couples with difficulty conceiving, many of these tests have not been clinically validated. Despite its plausible appeal and fervour of its supporters, the benefits of widespread DNA testing that only achieves the distressing of couples with the knowledge that effectual therapeutic strategies are absent are questionable. Commercially, however, it is no doubt lucrative. Analysis of gametes prior to the initiation of an IVF cycle may improve the quality of embryos transferred. The clinical and scientific community considers it a matter of urgency to translate the basic science behind how a cell prepares for fertilization into routine clinical practice. However, it is equally important, if not more, to allow the science behind such applications to draw level with its practice before its widespread implementation.

Sperm DNA damage or progressive motility: which one is the better predictor of fertilization in vitro?

Sperm progressive motility has been reported to be one of the key factors influencing in vitro fertilization rates. However, recent studies have shown that sperm DNA fragmentation is a more robust predictor of assisted reproductive outcomes including reduced fertilization rates, embryo quality, and pregnancy rates. This study aimed to compare the usefulness of sperm progressive motility and DNA damage as predictive tools of in vitro fertilization rates. Here, 136 couples provided 1,767 eggs with an overall fertilization rate of 64.2%. The fertilization rate in vitro correlated with both sperm progressive motility (r² = 0.236; P = 0.002) and DNA fragmentation (r² = -0.318; P < 0.001). The relative risk of a poor fertilization rate was 9.5 times higher in sperm of men with high DNA fragmentation (>40%) compared with 2.6 times in sperm with poor motility (<40%). Further, sperm DNA fragmentation gave a higher specificity (93.3%) in predicting the fertilization rate than progressive motility (77.8%). Finally, the odds ratio to determine fertilization rate (>70%) was 4.81 (1.89-12.65) using progressive motility compared with 24.18 (5.21-154.51) using DNA fragmentation. This study shows that fertilization rates are directly dependent upon both sperm progressive motility and DNA fragmentation, but sperm DNA fragmentation is a much stronger test.

DNA mismatch repair and infertility

PURPOSE OF REVIEW

To highlight the significance of the abnormal DNA repair mechanism in male infertility.

RECENT FINDINGS

DNA repair defects cause a variety of spermatogenic defects in mouse models. Evidence is accumulating to demonstrate the importance of DNA repair defects in human nonobstructive azoospermia. Epigenetic changes may also play a crucial role in infertility.

SUMMARY

The DNA in the cell needs to be constantly repaired to ensure fidelity of DNA replication, to maintain genome stability and to ensure propagation of species. The DNA repair and recombination machineries are highly conserved across the species and inactivation of these pathways may lead to replication and recombination errors. This review summarizes the different types of DNA lesions and DNA repair pathways, particularly focusing on highly conserved meiotic regulators, the DNA mismatch repair proteins. Targeted deletions of some of these proteins result in infertility and predisposes to tumor in mutant mouse models. There is evidence for loss of some of these proteins in human male infertility. Because defective DNA repair is associated with a mutator phenotype, the risk of transmission to the offspring of these otherwise infertile men conceived using an assisted reproductive technology needs further evaluation.

Sperm chromatin structure assay (SCSA): a tool in diagnosis and treatment of infertility

Diagnosis of male infertility has mainly been based on the World Health Organization (WHO) manual-based semen parameter's concentration, motility and morphology. It has, however, become apparent that none of these parameters are reliable markers for evaluation of the fertility potential of a couple. A search for better markers has led to an increased focus on sperm chromatin integrity testing in fertility work-up and assisted reproductive techniques. During the last couple of decades, numerous sperm DNA integrity tests have been developed. These are claimed to be characterized by a lower intraindividual variation, less intralaboratory and interlaboratory variation and thus less subjective than the conventional sperm analysis. However, not all the sperm chromatin integrity tests have yet been shown to be of clinical value. So far, the test that has been found to have the most stable clinical threshold values in relation to fertility is the sperm chromatin structure assay (SCSA), a flow cytometric test that measures the susceptibility of sperm DNA to acid-induced DNA denaturation in situ. Sperm DNA fragmentation as measured by SCSA has shown to be an independent predictor of successful pregnancy in first pregnancy planners as well as in couples undergoing intrauterine insemination, and can be used as a tool in investigation, counseling and treatment of involuntary childlessness. More conflicting data exist regarding the role of sperm DNA fragmentation in relation to fertilization, pre-embryo development and pregnancy outcome in in vitro fertilization and intracytoplasmic sperm injection (ICSI).

Analysis of the relationships between oxidative stress, DNA damage and sperm vitality in a patient population: development of diagnostic criteria

BACKGROUND

DNA damage in human spermatozoa is known to be associated with a variety of adverse clinical outcomes affecting both reproductive efficiency and the health and wellbeing of the offspring. However, the origin of this damage, its biochemical nature and strategies for its amelioration, still await resolution.

METHODS

Using novel methods to simultaneously assess DNA fragmentation (modified TUNEL assay), DNA-base adduct formation (8-hydroxy-2'-deoxyguanosine [8OHdG]) and cell vitality, spermatozoa from a cohort of 50 assisted conception patients were examined and compared with a group of donors. Receiver operating characteristic (ROC) curve analysis was then used to examine the frequency distribution of the data and to determine optimized thresholds for identifying patients exhibiting abnormally high levels of DNA damage.

RESULTS

8OHdG formation and DNA fragmentation were highly correlated with each other and frequently associated with cell death. Percoll centrifugation improved sperm quality but, unexpectedly, increased 8OHdG formation in live cells, as did sperm fractionation using Puresperm gradients. ROC analysis indicated that the frequency distribution of 8OHdG and DNA fragmentation data were significantly different between patients and donors (P < 0.001), permitting the development of thresholds that would allow the accurate diagnosis of DNA damage in the male germ line.

CONCLUSION

The aetiology of DNA damage in spermatozoa involves a cascade of changes that progress from the induction of oxidative stress and oxidized DNA base adduct formation to DNA fragmentation and cell death. Preparation of spermatozoa on discontinuous density gradients aggravates the problem by stimulating the formation of 8OHdG in live cells. However, the development of novel methods and optimized thresholds for diagnosing oxidative DNA damage in human spermatozoa should assist in the clinical management of this pathology.