Susceptibility of human sperm to in situ DNA denaturation is strongly correlated with DNA strand breaks identified by single-cell electrophoresis

DNA damage in human sperm: The sperm chromosome assay

Background

Sperm DNA damage is a major cause of pre‐ and post‐implantation embryonic loss in humans. However, the factors that control how and when such DNA damage occurs in human sperm are poorly understood.

Methods

Here, I review information relating to sperm DNA damage that can be obtained from the sperm chromosome assays described in the existing literature.

Main findings

The sperm chromosome assays, which consist of interspecific in vitro fertilization or intracytoplasmic sperm injection using murine oocytes and subsequent chromosome analysis, indicate that the proportion of sperm showing DNA damage is initially low and there are larger numbers of sperm with potential membrane and DNA damage that are induced after ejaculation and separation from the seminal plasma. Other assays that directly detect sperm DNA (e.g., TUNEL assays, Comet assays, and acridine orange test) are not able to distinguish and detect the initial and potential DNA damage. Furthermore, the positive values in these direct assays are influenced by the frequency of immotile sperm and amorphous sperm populations.

Conclusion

The findings in the sperm chromosome assays show that further improvements in sperm preparation protocols may result in the reduction of sperm DNA damage, followed by more successful outcomes in infertility treatment.

Cytochemical tests to investigate sperm DNA damage: Assessment and review

Male factor infertility has been diagnosed as the cause of infertility in about 20% of infertile couples. Sperm analysis is the most common method for diagnosing infertility in a laboratory. However, approximately 15% of infertile men have a normal sperm analysis. Therefore, the result of a routine sperm analysis often cannot be a definitive diagnosis for male factor infertility. Also, approximately 8% of infertile men with normal sperm parameters have high levels of abnormal sperm DNA. This indicates the role of the integrity of sperm DNA in male infertility. Here, we review the current tests available to evaluate the sperm DNA integrity along with their benefits and limitations.

Improved methods of DNA extraction from human spermatozoa that mitigate experimentally-induced oxidative DNA damage

Current approaches for DNA extraction and fragmentation from mammalian spermatozoa provide several challenges for the investigation of the oxidative stress burden carried in the genome of male gametes. Indeed, the potential introduction of oxidative DNA damage induced by reactive oxygen species, reducing agents (dithiothreitol or beta-mercaptoethanol), and DNA shearing techniques used in the preparation of samples for chromatin immunoprecipitation and next-generation sequencing serve to cofound the reliability and accuracy of the results obtained. Here we report optimised methodology that minimises, or completely eliminates, exposure to DNA damaging compounds during extraction and fragmentation procedures. Specifically, we show that Micrococcal nuclease (MNase) digestion prior to cellular lysis generates a greater DNA yield with minimal collateral oxidation while randomly fragmenting the entire paternal genome. This modified methodology represents a significant improvement over traditional fragmentation achieved via sonication in the preparation of genomic DNA from human spermatozoa for downstream applications, such as next-generation sequencing. We also present a redesigned bioinformatic pipeline framework adjusted to correctly analyse this form of data and detect statistically relevant targets of oxidation.

DNA fragmentation in spermatozoa: a historical review

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

Fatherhood and Sperm DNA Damage in Testicular Cancer Patients

Testicular cancer (TC) is one of the most treatable of all malignancies and the management of the quality of life of these patients is increasingly important, especially with regard to their sexuality and fertility. Survivors must overcome anxiety and fears about reduced fertility and possible pregnancy-related risks as well as health effects in offspring. There is thus a growing awareness of the need for reproductive counseling of cancer survivors. Studies found a high level of sperm DNA damage in TC patients in comparison with healthy, fertile controls, but no significant difference between these patients and infertile patients. Sperm DNA alterations due to cancer treatment persist from 2 to 5 years after the end of the treatment and may be influenced by both the type of therapy and the stage of the disease. Population studies reported a slightly reduced overall fertility of TC survivors and a more frequent use of ART than the general population, with a success rate of around 50%. Paternity after a diagnosis of cancer is an important issue and reproductive potential is becoming a major quality of life factor. Sperm chromatin instability associated with genome instability is the most important reproductive side effect related to the malignancy or its treatment. Studies investigating the magnitude of this damage could have a considerable translational importance in the management of cancer patients, as they could identify the time needed for the germ cell line to repair nuclear damage and thus produce gametes with a reduced risk for the offspring.

Probiotic administration improves sperm quality in asthenozoospermic human donors

The objective of this study is to analyse the effect of the ingestion of two selected antioxidant probiotics strains (Lactobacillus rhamnosus CECT8361 and Bifidobacterium longum CECT7347) on sperm quality parameters in asthenozoospermic males after three and six weeks of administration. Nine asthenozoospermic men without any medical treatment under similar diet conditions participated in the study. The quality of individual sperm samples was evaluated before (previous to ingestion), during (after 3 and 6 weeks of ingestion) and after probiotic administration (3 and 6 weeks after finishing the treatment). Sperm motility was evaluated by computer-assisted sperm analysis system, DNA fragmentation by sperm chromatin structure assay, cell viability by flow cytometry and measurement of intracellular H₂O₂ (reactive oxygen species; ROS) by flow cytometry using dichloro-dihydrofluorescein diacetate. Sperm motility was drastically improved after the treatment (approximately 6 fold change), DNA fragmentation was statistically reduced after probiotic administration from (approximately 1.2 fold change) and intracellular H₂O₂ level was decreased (approximately 3.5 fold change). Cell viability was not affected by the treatment. The significant improvement in sperm motility and the decrease in DNA fragmentation reported in this study provide preliminary evidence that probiotics could be administrated to improve motility and decrease DNA fragmentation and ROS levels in asthenozoospermic human males.

p53 modulates the effect of ribosomal protein S6 kinase1 (S6K1) on cisplatin toxicity in chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) is characterized by the expression of the oncoprotein, BCR-ABL. BCR-ABL inhibitors revolutionized CML chemotherapy while blast crisis (BC) CML patients are less responsive. Since suppression of ribosomal protein S6 kinase1 (S6K1) phosphorylation reverses the resistance to BCR-ABL inhibitor in CML cells and S6K1 inhibitors augment cisplatin toxicity in lung cancer cells, we speculated that combination of S6K1 inhibitor and cisplatin may be beneficial for eliminating BC CML cells. To our surprise, S6K1 inhibition decreased cisplatin-induced DNA damage and cell death only in p53^-/- BC CML cells but not in p53^+/+ BC CML cells. During the progression of CML, p53 expression either decreases or mutates. Moreover, the expression of p53 affects drug response of CML cells. Our results confirmed that S6K1 inhibition reversed cisplatin toxicity is dependent on p53 expression in CML cells. Moreover, p53 attenuated the phosphorylation and localization of S6K1 via attenuating 3-phosphoinositide dependent protein kinase-1 (PDK1) phosphorylation. Furthermore, S6K1 acts via DNA-PKcs to regulate H2AX phosphorylation and PARP cleavage, respectively. Taken together, our results suggest that p53/PDK1/S6K1 is a novel pathway regulating cisplatin toxicity in BC CML cells.

Impact of tributyltin on antioxidant and DNA damage response in spermatozoa of freshwater prawn Macrobrachium rosenbergii

Effects of tributyltin (TBT) on antioxidant [total superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR)] and DNA damage levels in the spermatozoa were studied and reported here for the first time in the freshwater prawn Macrobrachium rosenbergii. Three groups of (n = 10 in each group) fishes were exposed to three different nominal concentrations of TBT viz., 1, 2, and 4 mg L(-1) along with control group for 90 days. Significant decrease of antioxidant and increased DNA damage levels were seen at higher doses of 2 and 4 mg L(-1). In prawn, the antioxidant level plays a vital role in sperm protection, activation, differential functions related to the physiology, and reproductive behavior. This study serves as a biomonitoring tool to assess the TBT effects on reproductive behavior of aquatic biota.

Sperm DNA fragmentation abnormalities in men from couples with a history of recurrent miscarriage

BACKGROUND

Previous studies have described an association between sperm with DNA damage and a history of recurrent miscarriage (RM), although it is not clear whether there is benefit in screening for sperm DNA fragmentation and to what extent DNA fragmentation impacts upon RM.

AIMS

To identify what proportion of couples experiencing RM are affected by DNA fragmentation abnormalities.

MATERIALS AND METHODS

In this retrospective study, between 2008 and 2013, couples with a history of recurrent miscarriage (≥3 first trimester miscarriages) were investigated comprehensively for known causes (karyotype, uterine, antiphospholipid syndrome, thrombophilia) and also by semen analysis, including DNA fragmentation [sperm chromatin structure analysis (SCSA)]. Statistical analysis was performed on SPSS software with significance taken as P < 0.05.

RESULTS

There were 108 couples with a median sperm DNA fragmentation index (DFI) of 9.50%. Normal levels were found in 70.5% of men (DFI < 15%), 23% had high levels (DFI 15-30%), and 6.5% had very high levels (DFI > 30%). Couples with otherwise unexplained recurrent miscarriage had significantly higher DFI than those with other causes identified on routine screening (P = 0.012).

CONCLUSIONS

In couples experiencing RM, 30% (32/108) of men had sperm with high levels of DNA fragmentation (DFI > 15%). This may be a contributing factor to the clinical syndrome of RM, and future clinical trials of therapies for these couples are warranted.

Sperm DNA quality evaluated by comet assay and sperm chromatin structure assay in stallions after unilateral orchiectomy

Unilateral orchiectomy (UO) may interfere with thermoregulation of the remaining testis caused by inflammation surrounding the incision site, thus altering normal spermatogenesis and consequently sperm quality. Two measures of sperm DNA quality (neutral comet assay and the sperm chromatin structure assay [SCSA]) were compared before UO (0 days) and at 14, 30, and 60 days after UO to determine whether sperm DNA changed after a mild testis stress (i.e., UO). The percent DNA in the comet tail was higher at 14 and 60 days compared to 0 days (P < 0.05) after UO. All other comet tail measures (i.e., length, moment, migration) were higher at all time periods after UO compared to 0 days (P < 0.05). Two SCSA measures (mean-αt, mode-αt) increased at 14 days after UO (P < 0.05), whereas two measures (SD-αt and COMP-αt) did not change. This study identified a decrease in sperm DNA quality using both the neutral comet assay and the SCSA, which was not identified using traditional measures of sperm quality.

Effect of cryopreservation on the sperm DNA fragmentation dynamics of the bottlenose dolphin (Tursiops truncatus)

Sperm DNA fragmentation is one of the major causes of infertility; the sperm chromatin dispersion test (SCDt) evaluates this parameter and offers the advantage of species-specific validated protocol and ease of use under field conditions. The main purpose of this study was to evaluate sperm DNA fragmentation dynamics in both fresh and post-thaw bottlenose dolphin sperm using the SCDt following different cryopreservation protocols to gain new information about the post-thaw differential sperm DNA longevity in this species. Fresh and cryopreserved semen samples from five bottlenose dolphins were examined for sperm DNA fragmentation dynamics using the SCDt (Halomax(®)). Sperm DNA fragmentation was assessed immediately at collection and following cryopreservation (T0) and then after 0.5, 1, 4, 8, 24, 48 and 72 h incubation at 37°C. Serially collected ejaculates from four dolphins were frozen using different cryopreservation protocols in a TES-TRIS-fructose buffer (TTF), an egg-yolk-free vegetable lipid LP1 buffer (LP1) and human sperm preservation medium (HSPM). Fresh ejaculated spermatozoa initially showed low levels of DNA fragmentation for up to 48 h. Lower Sperm DNA fragmentation (SDF) was found in the second fresh ejaculate compared to the first when more than one sample was collected on the same day (p < 0.05); this difference was not apparent in any other seminal characteristic. While there was no difference observed in SDF between fresh and frozen-thawed sperm using the different cryopreservation protocols immediately after thawing (T0), frozen-thawed spermatozoa incubated at 37°C showed an increase in the rate of SDF after 24 h. Sperm frozen in the LP1(℗) buffer had higher levels (p < 0.05) of DNA fragmentation after 24- and 48-h incubation than those frozen in TTF or HSPM. No correlation was found between any seminal characteristic and DNA fragmentation in either fresh and/or frozen-thawed samples.

Effect of cryopreservation and single layer centrifugation on canine sperm DNA fragmentation assessed by the sperm chromatin dispersion test

The aims of this study were: 1) to assess the effect of freezing and thawing on dog sperm DNA fragmentation index (sDFI) using the sperm chromatin dispersion test (SCDt); and 2) to determine whether or not the sperm selection by single layer centrifugation (SLC) using Androcoll-C improves sperm DNA longevity in SLC-selected frozen-thawed dog semen samples. Semen samples were collected from 4 dogs using digital manipulation. After collection, ejaculates were pooled and cryopreserved following a standard protocol. Sperm motility and morphology were assessed before freezing and after thawing as a control for the cryopreservation method used. In experiment 1, sDFI was analyzed immediately before freezing and after thawing (baseline values), showing no significant differences between fresh and frozen-thawed semen samples. In experiment 2, frozen-thawed semen samples were processed or not by SLC using Androcoll-C and longevity of DNA were assessed in terms of sDFI after 24h of in vitro incubation at physiological temperature (38°C). The results showed low values of sDFI in SLC-selected semen in comparison to unselected samples. In conclusion, no effect of cryopreservation was observed on baseline values of dog sperm DNA fragmentation. Additionally, SLC-selection using Androcoll-C improved longevity of frozen-thawed sperm DNA assessed by the SCDt.

[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.

Is ICSI Risky?

As assisted reproductive technology (ART) methods become the mainstream of infertility treatment, it has become even more critical to reassess its safety. Following the results of a study published by the Robinson Institute in the New England Journal of Medicine, the risk of ART, especially intracytoplasmic sperm injection (ICSI), has never been so closely scrutinized. This paper traces the origins and development of ICSI, assesses the risks documented in the literature, and finally interprets the implications of the study for couples contemplating therapy. We support the need for continued vigilance towards ICSI and the importance in investigating male-factor infertility as a prequel to its use.

Clinical management of male infertility in assisted reproduction: ICSI and beyond

The advent of in vitro fertilization and its augmentation with intracytoplasmic sperm injection (ICSI) has allowed a large number of couples suffering from moderate to severe male infertility, and also presenting with female pathologies, to achieve their reproductive dreams. Notwithstanding the existence of fundamental questions about the pathophysiological mechanisms leading to sperm dysfunction, and still unanswered concerns about health risks following ICSI, it appears that overall ICSI is safe and here to stay. Although on one hand ICSI possibly hampered advances of the knowledge in some areas of gamete biology and interaction, on the other it definitely gave impulse to studies designed to unveil the sperm contributions during and beyond fertilization, including the normalcy of the DNA/chromatin as well as molecular mechanisms of genetic/epigenetic control and nuclear organization status. In all, almost entering the fourth decade of assisted reproductive technologies, we should continue monitoring the safety of the technique and long-term development of offspring, whereas at the same time prioritizing areas of research addressing these fundamental questions.

DNA sperm damage correlates with nuclear ultrastructural sperm defects in teratozoospermic men

Sperm morphology has consistently been the best indicator of male fertility. Transmission electron microscopy currently provides the most information on the subcellular details of sperm structure. Recently, assessment of sperm DNA damage has been employed to assess fertility potential. The purpose of this work was to link sperm DNA damage, evaluated by an intercalated fluorescent dye, with the structural characteristics of sperm. Conventional semen analysis was performed on samples from men undergoing fertility evaluation. Thirty men were evaluated and assigned to three subgroups based on strict criteria for sperm morphology: normal morphology (>14% normal forms), intermediate morphology (5-14% normal forms), and poor morphology (<5% normal forms). By quantifying acridine orange-positive cells and ultrastructural sperm defects, we found that the poor morphology pattern group showed a positive association between sperm carrying damaged DNA and the percentage of sperm nucleus with vacuoles (P = 0.01). No statistically significant correlations were established in other ultrastructural characteristics of sperm, including immature chromatin, lytic changes, or abnormal sperm tails. These results suggest that zones without chromatin in the sperm nucleus reflect underlying chromosomal or DNA defects in severe teratozoospermic men. This association should be considered in the evaluation of male fertility.

DNA fragmentation in chicken spermatozoa during cryopreservation

Semen cryopreservation is fundamental both for the practice of artificial insemination, and for the conservation of genetic resources in cryobanks; nevertheless, there is still not an efficient standard freezing procedure assuring a steady and suitable level of fertility in fowl, and consequently there is no systematic use of frozen semen in the poultry industry. This study examined changes in motility (CASA), cell membrane integrity (Ethidium Bromide (EtBr) exclusion procedure and stress test) and DNA fragmentation (neutral comet assay) in fowl spermatozoa before, during and after cryopreservation and storage at -196 °C. An optimized comet assay for chicken semen was studied and applied to the analyses. Semen collected from 18 Mericanel della Brianza (local Italian breed) male chicken breeders was frozen in pellets and thawed in a water bath at 60 °C. Measurements were performed on fresh semen soon after dilution, after equilibration with 6% dimethylacetamide at 4 °C (processed semen) and after thawing. Sperm DNA damage occurred during cryopreservation of chicken semen and the proportion of spermatozoa with damaged DNA significantly increased from 6.2% in fresh and 6.4% in processed semen to 19.8% in frozen-thawed semen. The proportion of DNA in the comet tail of damaged spermatozoa was also significantly affected by cryopreservation, with an increase found from fresh (26.3%) to frozen-thawed (30.9%) sperm, whereas processed semen (30.1%) didn't show significant differences. The proportion of total membrane damaged spermatozoa (EtBr exclusion procedure) did not increase by 4 °C equilibration time, and greatly and significantly increased by cryopreservation; the values recorded in fresh, processed and frozen semen were 2.9, 5.6, and 66.7% respectively. As regards the proportion of damaged cells in the stress test, all values differed significantly (7.1% fresh semen, 11.7% processed semen, 63.7% frozen semen). Total motility was not affected by equilibration (52.1% fresh semen, 51.9% processed semen), whereas it decreased significantly after cryopreservation (19.8%). These results suggest a low sensitivity of frozen-thawed chicken spermatozoa to DNA fragmentation, therefore it should not be considered as a major cause of sperm injuries during cryopreservation.

An investigation of the potential effect of vacuoles in human sperm on DNA damage using a chromosome assay and the TUNEL assay

BACKGROUND

The aims of this study were to establish whether individual differences exist in the frequency and size of vacuoles found in human sperm and to ascertain whether such vacuoles are involved in causing DNA damage.

METHODS

Morphologically normal sperm were obtained from 15 IVF and 2 ICSI patients and 3 fertile donors. (i) Sperm heads were analyzed for the presence of vacuoles under a 1000× differential interference contrast microscope. (ii) In three patients and two donor samples, structural chromosomal damage was evaluated in normal sperm containing large vacuoles and selected at 1000× magnification for injection into mouse oocytes. (iii) In 10 patients and two donor samples, confocal laser microscopy detected DNA damage in sperm-exhibiting large vacuoles and stained with an in situ cell death detection kit.

RESULTS

(i) Vacuoles were observed in almost all normal sperm from patient and donor ejaculates and were mainly located at the tip or middle area of the sperm heads. However, average incidence of normal sperm exhibiting large vacuoles was 4.6 and 4.2% in the patient and donor groups, respectively. (ii) Sperm chromosome assays did not reveal any differences in the incidence of structural chromosome aberrations between sperm exhibiting large vacuoles and those without them (9.1 versus 4.1%). (iii) No significant difference in frequency of TUNEL-positive cells was found between normal sperm with large vacuoles and those without them in the samples examined. Among 227 sperm exhibiting large vacuoles, only 7 cells were TUNEL positive.

CONCLUSION

The results showed that large vacuoles were not responsible for DNA damage, suggesting that intra-cytoplasmic injection of morphologically selected sperm may not be required for patients who produce high-quality semen.

TUNEL as a test for sperm DNA damage in the evaluation of male infertility

OBJECTIVES

To standardize the TUNEL assay by establishing inter- and intraobserver variability, interassay variability, cutoff values, sensitivity and specificity of the assay, and studying the distribution of the DNA damage in a population of infertile men referred to a clinical andrology laboratory.

METHODS

Seminal ejaculates from 25 healthy male volunteers (controls) and 194 infertile men (with male factor infertility) referred to an andrology laboratory were examined for DNA damage by TUNEL assay using flow cytometric analysis.

RESULTS

Both the inter- and intraobserver variability and interassay variability was small (<10%). DNA damage in the controls was 11.9 ± 6.8% vs. 29.5 ± 18.7% in patients (P <.001). The cut-off value of 19.25% maximized the observed sensitivity (64.9%) and specificity (100%) of the assay. The distribution of DNA damage in the patients was as follows: 14.9% (29 of 194) with DNA damage between 0% and 10%; 22.7% (44 of 194) between 10% and 20%; 8.8% (17 of 194) between 20% and 30%; and 17.5% (34 of 194) between 30% and 40%. Finally, 27.3% (53 of 194) had TUNEL values >40%.

CONCLUSIONS

We report a detailed standardization of the TUNEL assay for clinical use, as well as reference ranges for DNA damage in normal healthy donors and infertile men. A cut-off of 19.25% with observed 100% specificity established in our program can differentiate infertile men with DNA damage from healthy men. This test can be offered to infertile patients who are idiopathic, have severe oxidative stress-related abnormal semen quality, and contribute to the infertility problem of the couple who are considering assisted reproductive techniques.

Sperm DNA damage in male infertility: etiologies, assays, and outcomes

Male factor infertility is the sole cause of infertility in approximately 20% of infertile couples, with an additional 30% to 40% secondary to both male and female factors. Current means of evaluation of male factor infertility remains routine semen analysis including seminal volume, pH, sperm concentration, motility, and morphology. However, approximately 15% of patients with male factor infertility have a normal semen analysis and a definitive diagnosis of male infertility often cannot be made as a result of routine semen analysis. Attention has focused on the role of sperm nuclear DNA integrity in male factor infertility. Here we review the structure of human sperm chromatin, the etiology and mechanisms of sperm DNA damage, current tests available to assess sperm DNA integrity, and effect of sperm DNA integrity on reproductive outcomes.

Evidence that single-stranded DNA breaks are a normal feature of koala sperm chromatin, while double-stranded DNA breaks are indicative of DNA damage

In this study, we have used single and double comet assays to differentiate between single- and double-stranded DNA damage in an effort to refine the interpretation of DNA damage in mature koala spermatozoa. We have also investigated the likelihood that single-stranded DNA breakage is part of the natural spermiogenic process in koalas, where its function would be the generation of structural bends in the DNA molecule so that appropriate packaging and compaction can occur. Koala spermatozoa were examined using the sperm chromatin dispersion test (SCDt) and comet assays to investigate non-orthodox double-stranded DNA. Comet assays were conducted under 1) neutral conditions; and 2) neutral followed by alkaline conditions (double comet assay); the latter technique enabled simultaneous visualisation of both single-stranded and double-stranded DNA breaks. Following the SCDt, there was a continuum of nuclear morphotypes, ranging from no apparent DNA fragmentation to those with highly dispersed and degraded chromatin. Dispersion morphotypes were mirrored by a similar diversity of comet morphologies that could be further differentiated using the double comet assay. The majority of koala spermatozoa had nuclei with DNA abasic-like residues that produced single-tailed comets following the double comet assay. The ubiquity of these residues suggests that constitutive alkali-labile sites are part of the structural configuration of the koala sperm nucleus. Spermatozoa with ‘true’ DNA fragmentation exhibited a continuum of comet morphologies, ranging from a more severe form of alkaline-susceptible DNA with a diffuse single tail to nuclei that exhibited both single- and double-stranded breaks with two comet tails.

EFFECT OF SPERM CHROMATIN DAMAGE ON FERTILIZATION RATIO AND EMBRYO QUALITY POST-ICSI

A total of 56 semen samples was collected from men in the ICSI program. The female partners of all men were under 35 years of age. Sperm chromatin integrity was evaluated by staining the spermatozoa with acridine orange. > 56% red fluorescence was taken as abnormal chromatin status. A significant negative association was found between the percentage of sperm with DNA fragmentation and fertilization rate. Increased red fluorescence indicated impaired fertilization outcome. Good quality embryo rates were significantly lower in abnormal AO stained group. Chromatin damage precedes the loss of fertilization potential and poor embryo quality.

Correlation between DNA damage and sperm parameters: a prospective study of 1,633 patients

OBJECTIVE

To investigate DNA fragmentation by using terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling in relation to World Health Organization parameters and computer-aided sperm analysis (CASA) in sperm to determine the possibility of obtaining a correlation among CASA parameters, sperm morphology, and DNA fragmentation.

DESIGN

Sperm analysis according to World Health Organization parameters, terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) for sperm DNA fragmentation, and CASA for sperm movement. Prospective study.

SETTING

All the patients were under clinical management, consulting for hypofertility at a fertility center in France.

PATIENT(S)

One thousand six hundred thirty-three men who were referred for infertility investigation, including a complete sperm analysis.

INTERVENTION(S)

Sperm analysis and DNA damage testing.

MAIN OUTCOME MEASURE(S)

Sperm morphology, DNA fragmentation, and movement characteristics.

RESULT(S)

One third of the patients had a TUNEL rate of >30%. Analysis of the 21 semen parameters tested revealed that 7 of them were significantly correlated with the TUNEL results.

CONCLUSION(S)

World Health Organization sperm parameters and DNA damage are complementary, rather than strongly linked. This should be considered to more fully understand the paternal contribution in assisted reproductive technologies failures.

Assessing sperm DNA fragmentation in the field: an adaptation of sperm chromatin dispersion technology

The sperm chromatin dispersion (SCD) test is a new technique that allows assessment of sperm DNA fragmentation (SDF) in different species. The application of this technique, like other techniques, is restricted to the laboratory. Our investigation was aimed at exploring the possibilities of extending SCD methodology for use in the field, where electric powered facilities such as freezers, microscopes or heaters are not available. Our results showed that SCD methodology, with minor modifications to the standard protocol, can be performed readily in the field, offering reliable information about SDF. An Light Emitting Diode (LED)-equipped microscope attached to a laptop, a gas heater and a CO(2) spray for cooling are sufficient to assess the quality of sperm DNA. The results obtained after assessing 10 different semen samples under different conditions (30 degrees C in the laboratory and at 17 degrees C and 4 degrees C in the field) showed that except after processing the slides at 4 degrees C, the results of SDF in different animals showed no significant differences. With the modifications suggested here, the SCD technique can be used to assess SDF in the wild. In particular, the DNA quality of spermatozoa obtained from animals post mortem can be assessed in the field.

The clinical utility of sperm DNA integrity testing

Sperm DNA damage is more common in infertile men and may contribute to poor reproductive performance. However, current methods for evaluating sperm DNA integrity do not reliably predict treatment outcomes, and no treatment for abnormal DNA integrity has proven clinical value.

A hierarchical zero-inflated log-normal model for skewed responses

Although considerable attention has been given to zero-inflated count data, research on zero-inflated lognormal data is limited. In this article, we consider a study to examine human sperm cell DNA damage obtained from single-cell electrophoresis (COMET assay) experiment in which the outcome measures present a typical example of log-normal data with excess zeros. The problem is further complicated by the fact that each study subject has multiple outcomes at each of up to three visits separated by six-week intervals. Previous methods for zero-inflated log-normal data are based on either simple experimental designs, where comparison of means of zero-inflated log-normal data across different experiment groups is of primary interest, or longitudinal measurements, where only one observation is available for each subject at each visit. Their methods cannot be applied when multiple observations per visit are possible and both inter- and intra-subject variations are present. Our zero-inflated model extends the previous methods by incorporating a hierarchical structure using latent random variables to take into account both inter- and intra-subject variations in zero-inflated log-normal data. An EM algorithm has been developed to obtain the Maximum likelihood estimates of the parameters and their standard errors can be estimated by parametric bootstrap. The model is illustrated using the COMET assay data.

Modern andrology: from semen analysis to postgenomic studies of the male gametes

A male factor is implicated in about 50% of couples treated with advanced assisted reproductive techniques (in vitro fertilization [IVF] or intracytoplasmic sperm injection [ICSI]). An important function of spermatozoa is to deliver the paternal genome to the oocyte. However, neither the routine testing of male fertility potential, nor its treatment, addresses the specific mechanisms by which spermatozoal factors may impact reproductive outcome. Recently, a number of screening tests for DNA integrity have been proposed to assess sperm chromatin abnormalities. These include nonspecific DNA strand breaks, numerical abnormalities in spermatozoal chromosome content, and alterations in the epigenetic regulation of the paternal genome. This minireview discusses methods to assess the influence of the paternal genome on reproduction beyond that which can be appreciated by simple quantitative and morphologic evaluation of spermatozoa. Finally, new data on how to select the "best fit" sperm for ICSI will be presented.