DNA fragmentation of human spermatozoa: Simple assessment of single- and double-strand DNA breaks and their respective dynamic behavioral response

Strong Correlation Between Double-Strand DNA Breaks and Total Sperm DNA Fragmentation in the Human Ejaculate

BACKGROUND

Double- and single-strand DNA breaks (DSBs and SSBs, respectively) in spermatozoa, which emerge from intrinsic and extrinsic degenerative processes, are likely related to the underlying male pathology.

AIM

To determine whether the incidence of DSBs in the human ejaculate is a consistent predictor of whole sperm DNA fragmentation (W-SDF = SSBs + DSBs).

METHODS

A correlation between the proportion of spermatozoa that showed whole W-SDF and those displaying only DSBs in DNA. Two patient cohorts were established: W-SDF ≤30% (low SDF; n = 153) and W-SDF ≥30% (high SDF; n = 222).

RESULTS

An increasing level of W-SDF is associated with an increased incidence of DSBs in the ejaculate. When data from both the low and high W-SDF groups were combined, a linear relationship was observed, with DSBs increasing by 0.799 units for each unit increase in W-SDF. However, when the cohorts were analyzed separately, the relationships differed. In the low SDF group, DSBs increased linearly by 0.559 units for each unit increase in W-SDF. In the high SDF group, DSBs increased exponentially by 0.602 units per unit of W-SDF. Furthermore, the data dispersion between the two variables was significantly different between the cohorts, with the high SDF group showing 0.8 times greater variability than the low SDF group.

CONCLUSIONS

While the presence of DSBs in sperm is correlated with the W-SDF present in raw semen samples, the biological mechanisms responsible for DSBs are expressed in different proportions and/or at different levels in ejaculates with higher levels of DNA damage.

Sperm DNA Fragmentation in Male Infertility: Tests, Mechanisms, Meaning and Sperm Population to Be Tested

Sperm DNA fragmentation (sDF) is a DNA damage able to predict natural conception. Thus, many laboratories added tests for the detection of sDF as an adjunct to routine semen analysis with specific indications. However, some points related to sDF are still open. The available tests are very different each from other, and a direct comparison, in terms of the prediction of reproductive outcomes, is mandatory. The proposed mechanisms responsible for sDF generation have not yielded treatments for men with high levels of sDF that have gained the general consent in clinical practice, thus requiring further research. Another relevant point is the biological meaning to attribute to sDF and, thus, what we can expect from tests detecting sDF for the diagnosis of male infertility. SDF can represent the "tip of iceberg" of a more extended and undetected sperm abnormality somehow impacting upon reproduction. Investigating the nature of such a sperm abnormality might provide novel insights into the link between sDF and reproduction. Finally, several studies reported an impact of native sDF on assisted reproduction technique outcomes. However, to fertilise the oocyte, selected spermatozoa are used where sDF, if present, associates with highly motile spermatozoa, which is the opposite situation to native semen, where most sDF associates with non-viable spermatozoa. Studies comparing the impact of sDF, as assessed in both native and selected spermatozoa, are needed.

Addendum to: The relationship between sperm nuclear DNA fragmentation, mitochondrial DNA fragmentation and copy number in normal and abnormal human ejaculates

BACKGROUND

While the kinetics of human sperm nuclear DNA fragmentation (SDF-nDNA) following ejaculation have been described, the dynamics and relationships of mitochondrial DNA copy number per spermatozoon (mtDNAcn) and fragmentation (SDF-mtDNA) remain unexplored.

OBJECTIVES

To compare post-ejaculatory kinetics of mtDNAcn, SDF-mtDNA and SDF-nDNA, global, single-strand DNA breaks (SDF-SSBs) and double-strand DNA breaks (SDF-DSBs) in normozoospermic and non-normozoospermic samples.

MATERIALS AND METHODS

28 normozoospermic and 43 non-normozoospermic ejaculates were evaluated at 0, 6, 24 and 48 h of incubation in vitro. SDF-nDNA was determined by sperm chromatin dispersion (SCD) assays. mtDNAcn and SDF-mtDNA were analysed by dPCR.

RESULTS

SDF-nDNA-global values increased as a consequence of quadratic SDF-SSBs and linear SDF-DSBs kinetics. Non-normozoospermic samples showed a slower SDF-global rate between 6-24 h, due to lesser SSBs production. Regarding SDF-DSBs, non-normozoospermic samples exhibited a faster initial increase rate, followed by a slower final increment. The mtDNAcn median value decreased linearly, being 3.2× higher in non-normozoospermics at all time points; mtDNAcn in both cohorts reduced to half of the baseline by 48 h. mtDNAcn was identified as a risk factor for discriminating non-normozoospermia, a finding that was further strengthen when combined with SDF-Global or SDF-DSBs values. SDF-mtDNA frequencies were identical, increasing over time correspondingly in both cohorts. The mtDNA fragmentation rate was initially fast, decreasing progressively with time for both cohorts; half of the initially unfragmented copies were fragmented after 48 h. Rates of mtDNAcn loss and SDF-mtDNA increase were only marginally correlated with the rates of nuclear fragmentation.

CONCLUSION

mtDNA fragmentation and loss occur post ejaculation. Their dynamics are likely to be associated with different and/or uncoupled mechanisms to that which cause nuclear DNA fragmentation. Our results indicate that while mtDNA fragmentation is not influenced by the sperm quality, the number of copies of sperm mtDNAcn can potentially serve as a risk factor for predicting non-normozoospermia.

The relationship between sperm nuclear DNA fragmentation, mitochondrial DNA fragmentation, and copy number in normal and abnormal human ejaculates

BACKGROUND

While it is common to clinically evaluate sperm nuclear DNA fragmentation, less attention has been given to sperm mitochondrial DNA. Recently, a digital PCR assay has allowed accurate estimation of the proportion of fragmented mtDNA molecules and relative copy number.

OBJECTIVES

To determine the correlation of classical sperm parameters, average mtDNA copies per spermatozoon and the level of mtDNA fragmentation (SDF-mtDNA) to that of nuclear DNA fragmentation (SDF-nDNA), measured as the proportion of global, single-strand DNA (SDF-SSBs) and double-strand DNA breaks (SDF-DSBs). To determine whether the level of nuclear and mitochondrial DNA fragmentation and/or copy number can differentiate normozoospermic from non-normozoospermic samples.

MATERIALS AND METHODS

Ejaculates from 29 normozoospermic and 43 non-normozoospermic were evaluated. SDF was determined using the sperm chromatin dispersion assay. mtDNA copy number and SDF-mtDNA were analyzed using digital PCR assays.

RESULTS

Relative mtDNA copy increased as sperm concentration or motility decreased, or abnormal morphology increased. Unlike SDF-mtDNA, mtDNA copy number was not correlated with SDF-nDNA. SDF-mtDNA increased as the concentration or proportion of non-vital sperm increased; the higher the mtDNA copy number, the lower the level of fragmentation. Non-normozoospermic samples showed double the level of SDF-nDNA compared to normozoospermic (median 25.00 vs. 13.67). mtDNA copy number per spermatozoon was 3× higher in non-normozoospermic ejaculates (median 16.06 vs. 4.99). Although logistic regression revealed SDF-Global and mtDNA copy number as independent risk factors for non-normozoospermia, when SDF-Global and mtDNA copy number were combined, ROC curve analysis resulted in an even stronger discriminatory ability for predicting the probability of non-normozoospermia (AUC = 0.85, 95% CI 0.76-0.94, p < 0.001).

CONCLUSION

High-quality ejaculates show lower nuclear SDF and retain less mtDNA copies, with approximately half of them fragmented, so that the absolute number of non-fragmented mtDNA molecules per spermatozoon is extremely low.

Development and integration of LensHooke® R10 for automatic and standardized diagnosis for sperm DNA fragmentation

BACKGROUND

The sperm chromatin dispersion assay is commonly used to assess sperm DNA integrity. This approach is time-consuming, demonstrates poor chromatin preservation, and provides an ambiguous and unstandardized evaluation of fragmented chromatin.

OBJECTIVES

We aimed to (i) develop an optimized sperm chromatin dispersion assay with reduced operation time, (ii) validate R10 test accuracy by comparing it to a conventional sperm chromatin dispersion assay, and (iii) standardize the sperm DNA fragmentation analysis procedure by integrating artificial intelligence optical microscopic technology.

MATERIALS AND METHODS

This cross-section study included 620 semen samples. Aliquots were analyzed by a conventional Halosperm® G2 assay (G2) and LensHooke® R10 assay (R10). The DNA fragmentation index was scored manually, and R10 slides were automatically determined by a LensHooke® X12 PRO semen analysis system (X12).

RESULTS

We demonstrated significant improvements in total assay time (40 vs. 72 min, p < 0.001) and in the halo-cytological resolution using R10 compared to G2. Comparing the G2 and R10, DNA fragmentation index results demonstrated good agreement between the two methods (Spearman's rank correlation, rho = 0.8517, p < 0.0001). We introduced the integration of an auto-calculation system to diagnose sperm DNA fragmentation. X12 interpretation showed excellent agreement with manual interpretation (Spearman's rank correlation, rho = 0.9323, p < 0.0001), but had a low coefficient of variation compared to manual interpretation (4% for R10 by X12 vs. 19% for R10 by manual scoring vs. 25% for G2 by manual scoring). DNA fragmentation index was more correlated with total motility (coefficients = -0.3607, p < 0.0001) than sperm morphology and was positively associated with asthenozoospermic semen samples (p = 0.0001).

CONCLUSION

The R10 sperm chromatin dispersion assay combined with the X12 semen analysis system is faster, more objective, and provides standardization for sperm DNA fragmentation.

Analysis of sperm chromatin packaging and reproductive biomarker to evaluate the consequence of advanced male age

In this study, the semen parameters, sperm chromatin integrity, antioxidant enzyme levels, and reproductive hormone levels of subfertile male subjects from Pakistan were assessed in relation to their age. Data on the demographic characteristics of the 750 study participants, including their general health, body mass index (BMI), and reproductive status, were collected from subfertile men from Pakistan. Semen and blood were collected to determine standard semen parameters, sperm chromatin dispersion (Halosperm-SCD), sperm chromatin integrity using toluidine blue (TB) staining, sperm chromatin maturity using chromomycin A3 (CMA3+) staining, and reproductive hormone (FSH, LH, prolactin and testosterone levels). The patients were divided into three groups according to their age: Group 1 included male subjects aged 30 years or less (n = 90), Group 2 included male subjects between the ages of 31 and 40 years (n = 330), and Group 3 included male subjects over 40 years of age (n = 330). Conventional semen parameters, reactive oxygen species (ROS), superoxide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), and lipid peroxidation (MDA) did not statistically (p > 0.05) differ with increasing male age or between different age groups. When compared to younger men (<30 years), sperm SCD (23.2 ± 0.88%) was significantly (p = 0.01) lower as compared to male patients aged >40 years (26.6 ± 0.6%). The concentration of LH, FSH, and testosterone levels were comparable between the groups (p > 0.05), while a significant (p = 0.04) increase in sperm chromatin immaturity CMA3+ (30 ± 0.71%) was observed in the old age group (>40 years) compared to the <30-year group (26.6 ± 1.03%). A positive association was observed between advanced male age and sperm chromatin dispersion (SCD) (r = 0.124, p = 0.001) and decondensation (CMA3+) (r = 0.1, p = 0.009). Despite potential limitations, this study has been carried out with extensive information on the potential risk of male age on sperm integrity. The present study demonstrated the impact of male age on male reproductive health, as these patients had a higher percentage of sperm chromatin damage (SCD) in their semen. Sperm DNA damage assessment will help in the evaluation and diagnosis of the underlying cause of poor fertility and can help clinicians in selecting the right treatment options. Male age is one of the factors that have an impact on the decline in male fertility. As a result, it is preferable for patients receiving assisted reproductive technology to be younger.

The influence of paternal overweight on sperm chromatin integrity, fertilization rate and pregnancy outcome among males attending fertility clinic for IVF/ICSI treatment

Background

Low and middle-income countries are facing a rapid increase in obesity and overweight burden, particularly in urban settings. Being overweight in men is associated with infertility and a higher risk to have a low sperm count or no sperm in their ejaculate. Despite potential limitations, this is one of few studies conducted to determine the potential risk of paternal overweight on sperm standard parameters, sperm chromatin integrity and assisted conception outcome including fertilization, embryo quality, cleavage rate, reduce blastocyst development, implantation, and cumulative live birth rate (CLBR).

Methods

A cross-sectional study of 750 infertile couples undergoing assisted reproduction technique at a single reproductive medicine center of Salma Kafeel Medical Centre Islamabad. Sperm from men undergoing ART were analyzed for chromatin integrity using sperm chromatin dispersion assay (SCD), Chromomycin A3 staining (CMA3), and toluidine blue (TB) staining, while other semen parameters were assessed on same day includes; standard semen parameters, reactive oxygen species (ROS), sperm deformity index (SDI), teratozoospermic index (TZI), and hypo-osmatic swelling test (HOST). Paternal body mass index (BMI) < 24.5–20 kg/m² served as the reference group, while the male patients with BMI > 24.5-30 kg/m² were considered to be overweight.

Results

In the analysis of the percentage of spermatozoa with chromatin maturity (CMA3) and chromatin integrity (TB) was reduced significantly in overweight men (p < 0.01) compared with a reference group. Increase in paternal BMI correlate with the increase in sperm chromatin damage (SCD r = 0.282, TB r = 0.144, p < 0.05), immaturity (CMA3, r = 0.79, p < 0.05) and oxidative stress (ROS) (r = 0.282, p < 0.001). Peri-fertilization effects were increased in oocytes fertilization in couples with overweight men (FR = 67%) compared with normal-weight men (FR = 74.8%), similarly, after univariant regression paternal weight remain predictor of sperm chromatin maturity, successful fertilization and CLBR. In the embryo, developmental stage number of the embryo in cleavage was higher in normal weight men, while day 3 (D3) embryos, percent good quality embryo D3, and blastocyst formation rate were compared able between the groups. The paternal overweight group had significant (p < 0.001) increased neonatal birth weight (2952.14 ± 53.64gm; within normal range) when compared with the reference group (2577.24 ± 30.94gm) following assisted reproductive technology (ART). CLBR was higher (p < 0.05) in normal weight men compared to couples with overweight male partners. CLBR per embryo transfer and per 2PN was a statistically significant (p < 0.05) difference between the two groups. An inverse association was observed in the linear regression model between paternal BMI with fertilization rate and CLBR.

Conclusion

The present study demonstrated the impact of paternal overweight on male reproductive health, as these patients had a higher percentage of immature sperm (CMA3) with impaired chromatin integrity (SCD, TB) in their semen and had decreased fertilization rate, CLBR following assisted reproductive treatments. The present study supports that paternal overweight should be regarded as one of the predictors for fertilization, CLBR and useful for counseling, to consider body mass index not only in women but also for men, in those couples opting for ART treatment, and warrant a poor reproductive outcome in overweight men.

Sperm DNA damage in men with spinal cord injury: the relative incidence of single- and double-strand DNA breaks

BACKGROUND

Men with spinal cord injury (SCI) show a high proportion of sperm DNA damage in their ejaculate but the underlying pathology remains elusive.

OBJECTIVE

To investigate the relative incidence of single (SSBs) and double-strand DNA breaks (DSBs) and DNase activity in men with SCI.

MATERIALS AND METHODS

This study included ejaculates of 20 men with SCI and 27 normozoospermic (sperm donors). A TwoTails comet assay (TTComet) allowed visualization of three categories of sperm DNA damage corresponding to SSBs, DSBs and those with a combination of SSBs and DSBs, facilitating accurate calculation of the total proportion of SSBs and DSBs. A subset of 15 individuals (sperm donors and SCI patients) was used to test for DNase activity in the seminal plasma.

RESULTS

While the proportion of DSBs in men with SCI (median-57.5%) was higher (P = 0.000) than normozoospermic samples (median-4.6%), the proportion of SSBs was higher (P = 0.022) in the normozoospermic ejaculates (median-6.0%) compared to men with SCI (median-2.5%). The relative proportion of the total DSBs with respect to the total SSBs was 3.3× in men with SCI but 0.9× in normozoospermic samples. We further confirmed the high DNase activity in the seminal plasma of men with SCI.

DISCUSSION

The TTComet assay provided new insights to the pathology of sperm DNA in men with SCI and may have diagnostic value in developing sperm selection methodologies to reduce DSBs prior to ART.

CONCLUSION

Men with SCI are characterized by a high proportion of sperm with DSBs and high levels of DNase activity in the seminal plasma compared to normozoospermic men.

Antibiotic toxicity on human spermatozoa assessed using the sperm DNA fragmentation dynamic assay

Sperm DNA fragmentation (SDF) dynamic assays were piloted on 4 fresh ejaculates to examine the possible sperm toxicity of three common antibiotics, ciprofloxacin, doxycycline and ampicillin, incubated at a concentration estimated to be reached in semen in vivo, and 100×, for 24 h. SDF was assessed in terms of single-strand DNA breaks (SSBs) and double-strand DNA breaks (DSBs). Low and high concentrations of ciprofloxacin and high concentration of doxycycline significantly increased the SDF rate, due to sperm containing SSBs. Ampicillin did not affect SDF dynamics at any dose. Based on these results, the effect of antibiotics on the global-SDF dynamics was further examined in 21 ejaculates assessed at 0, 4 and 6 h. Ciprofloxacin increased the rate of SDF at the low concentration in 17 from 21 subjects; the high concentration resulted in a stronger effect in all individuals. A significant increase in the rate of SDF in 17 ejaculates was also noted when spermatozoa were incubated with the high concentration of doxycycline. The dynamic SDF assay is a rapid and sensitive tool to evidence sperm toxicity. Ciprofloxacin should be avoided when it is necessary to preserve sperm quality for reproductive purposes and as additive in semen diluents.