Double-stranded sperm DNA damage is a cause of delay in embryo development and can impair implantation rates

Correlation between standard sperm parameters and sperm DNA fragmentation from 11,339 samples

Conventional semen parameters have long been considered fundamental in male fertility analyses. However, doubts have been raised regarding the clinical utility of the assessment of spermatozoa (sperm) DNA damage. In this retrospective study, we investigated the potential correlation between conventional semen parameters and semen DNA fragmentation (SDF) assessed as sperm DNA damage, in 11,339 semen samples collected between January 2019 and June 2022. We observed significant negative correlations between the DNA fragmentation index (DFI) and sperm viability (correlation coefficient [r] = -0.514) as well as progressive sperm motility (r = -0.512, p < 0.05). Samples were categorized into three groups according to DFI levels (Groups A, B, and C: ≤15%, 15 < DFI ≤30%, and >30%, respectively). Furthermore, the percentage of semen samples with normal sperm conventional parameters in Groups A, B, and C was 76.7% (4369/5697), 61.4% (2351/3827), and 39.7% (721/1815), respectively. Moreover, according to the reference values of conventional sperm parameters, the samples were divided into Groups F, G, and H with all normal, only one abnormal, and > two abnormal parameters, respectively. In addition, the proportions of samples with abnormal DFI values (>30) in Groups F, G, and H were 9.7% (721/7441), 23.1% (618/2676), and 39.0% (476/1222), respectively. Multivariate logistic regression models demonstrated that sperm vitality, progressive sperm motility, normal sperm form, total sperm count, semen volume, age, and some sperm kinematics collectively improved the area under the receiver operating characteristic curve (AUROC) to 0.861, surpassing the predictive value of a single predictor of pathologically damaged sperm DNA. Our study suggests that samples with abnormal sperm parameters may have a higher likelihood of high DNA fragmentation. Furthermore, certain semen parameters could be potential indicators of sperm DNA fragmentation, aiding sperm selection in assisted reproductive procedures.

The impact of microfluidics sperm processing on blastocyst euploidy rates compared with density gradient centrifugation: a sibling oocyte double-blinded prospective randomized clinical trial

OBJECTIVE

To compare the euploidy rates among blastocysts created from sibling oocytes injected with sperm and processed using microfluidics or density gradient centrifugation.

DESIGN

Sibling oocyte randomized controlled trial.

SETTING

Single university-affiliated infertility practice.

PATIENTS

A total of 106 patients aged 18-42 years undergoing fresh in vitro fertilization treatment cycles with preimplantation genetic testing between January 2021 and April 2022 contributed 1,442 mature oocytes, which were injected with sperm and processed using microfluidics or density gradient centrifugation.

INTERVENTION(S)

The sperm sample is divided and processed using a microfluidics device and density gradient centrifugation for injection into sibling oocytes.

MAIN OUTCOME MEASURE(S)

The primary outcome was the embryo euploidy rate. Secondary outcomes included fertilization, high-quality blastulation, and ongoing pregnancy rates.

RESULT(S)

The blastocyst euploidy rate per mature oocyte was not significantly different in the study group compared with the control group (22.9% vs. 20.5%). The blastocyst euploidy rate per biopsied embryo was also similar between the 2 groups (53.0% vs. 45.7%). However, the fertilization rate per mature oocyte injected was found to be significantly higher in the study group compared with the control group (76.0% vs. 69.9%). The high-quality blastulation rate per mature oocyte injected was similar between the 2 groups, as was the total number of embryos frozen. There were no differences in the number of participants with no blastocysts for biopsy or the number of participants with no euploid embryos between the 2 groups. Among the male factor infertility and recurrent pregnancy loss subgroups, there were no differences in euploidy rates, fertilization rates, blastulation rates, or total numbers of blastocysts frozen, although the study was underpowered to detect these differences. Seventy-seven patients underwent frozen embryo transfer; there were no significant differences in pregnancy outcomes between the 2 groups.

CONCLUSION(S)

Microfluidics processing did not improve embryo euploidy rates compared with density gradient centrifugation in this sibling oocyte study, although fertilization rates were significantly higher.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04744025.

Microfluidic sperm sorting selects a subpopulation of high-quality sperm with a higher potential for fertilization

STUDY QUESTION

Is a microfluidic sperm sorter (MSS) able to select higher quality sperm compared to conventional methods?

SUMMARY ANSWER

The MSS selects sperm with improved parameters, lower DNA fragmentation, and higher fertilizing potential.

WHAT IS KNOWN ALREADY

To date, the few studies that have compared microfluidics sperm selection with conventional methods have used heterogeneous study population and have lacked molecular investigations.

STUDY DESIGN, SIZE, DURATION

The efficiency of a newly designed MSS in isolating high-quality sperm was compared to the density-gradient centrifugation (DGC) and swim-up (SU) methods, using 100 semen samples in two groups, during 2023-2024.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen specimens from 50 normozoospermic and 50 non-normozoospermic men were sorted using MSS, DGC, and SU methods to compare parameters related to the quality and fertilizing potential of sperm. The fertilizing potential of sperm was determined by measurement of phospholipase C zeta (PLCζ) and post-acrosomal sheath WW domain-binding protein (PAWP) expression using flow cytometry, and the chromatin dispersion test was used to assess sperm DNA damage.

MAIN RESULTS AND THE ROLE OF CHANCE

In both normozoospermic and non-normozoospermic groups, the MSS-selected sperm with the highest progressive motility, PLCζ positive expression and PLCζ and PAWP fluorescence intensity the lowest non-progressive motility, and minimal DNA fragmentation, compared to sperm selected by DGC and SU methods (P < 0.05).

LIMITATION, REASONS FOR CAUTION

The major limitations of our study were the low yield of sperm in the MSS chips and intentional exclusion of severe male factor infertility to yield a sufficient sperm count for molecular experiments; thus testing with severe oligozoospermic semen and samples with low count and motility is still required. In addition, due to ethical considerations, at present, it was impossible to use the sperm achieved from MSS in the clinic to assess the fertilization rate and further outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

Our research presents new evidence that microfluidic sperm sorting may result in the selection of high-quality sperm from raw semen. This novel technology might be a key to improving clinical outcomes of assisted reproduction in infertile patients.

STUDY FUNDING/COMPETING INTEREST(S)

The study is funded by the Iran University of Medical Sciences and no competing interest exists.

TRIAL REGISTRATION NUMBER

N/A.

Embryo development is impaired by sperm mitochondrial-derived ROS

BACKGROUND

Basal energetic metabolism in sperm, particularly oxidative phosphorylation, is known to condition not only their oocyte fertilising ability, but also the subsequent embryo development. While the molecular pathways underlying these events still need to be elucidated, reactive oxygen species (ROS) could have a relevant role. We, therefore, aimed to describe the mechanisms through which mitochondrial activity can influence the first stages of embryo development.

RESULTS

We first show that embryo development is tightly influenced by both intracellular ROS and mitochondrial activity. In addition, we depict that the inhibition of mitochondrial activity dramatically decreases intracellular ROS levels. Finally, we also demonstrate that the inhibition of mitochondrial respiration positively influences sperm DNA integrity, most likely because of the depletion of intracellular ROS formation.

CONCLUSION

Collectively, the data presented in this work reveals that impairment of early embryo development may result from the accumulation of sperm DNA damage caused by mitochondrial-derived ROS.

Advanced Paternal Age: A New Indicator for the Use of Microfluidic Devices for Sperm DNA Fragmentation Selection

New social conditions and progress in ART have both contributed to the delay in parenthood in developed countries. While the effects of maternal age have been widely studied, paternal age is poorly understood, and there are no specific guides on ART techniques to treat its deleterious effects. It is known that there is an increase in sperm DNA fragmentation (SDF) in elderly men, and new sperm selection devices using microfluids have been developed. This study analyses 189 ICSI cycles with donor oocytes performed between January 2018 and February 2022. Spermatozoa were selected using an MSS device or density gradients, followed by ICSI fertilization and fresh/thawed embryo transfer. We assessed the association between the selection technique, paternal age (< or ≥45) and reproductive outcomes. Fertilization (FR), blastulation (BR), implantation (IR), live-birth (LBR) and miscarriage (MR) rates were calculated. The results showed significantly higher IR (57.7% vs. 42.5%) and LBR (42.9% vs. 30.3%) when applying MSS selection, and particularly higher BR, IR and LBR when the paternal age was equal to or over 45 years (BR: 64.4 ± 23% vs. 50.1 ± 25%, IR: 51.5% vs. 31.6% and LBR: 42.4% vs. 23.7%). We also found a negative correlation between BR and paternal age (r2 = 0.084). The findings show that MSS enhances success in assisted reproduction cycles with ICSI, especially in couples with advanced paternal age. We propose advanced paternal age as a new indicator for the application of sperm selection techniques that reduce fragmentation.

Repair mechanism of Yishen Tongluo formula on mouse sperm DNA fragmentation caused by polystyrene microplastics

CONTEXT

Plastics can break down into millions of microplastic (MPs, < 5 mm) particles in the soil and ocean. These MPs can then affect the function of the reproductive system. There is currently no effective solution to this problem aside from traditional Chinese medicine. We have previously used Yishen Tongluo formula (YSTL) to treat sperm DNA damage caused by some toxic substances.

OBJECTIVE

To investigate the mechanism underlying the repair of mouse sperm DNA fragmentation caused by polystyrene microplastics by YSTL.

MATERIALS AND METHODS

An animal model of polystyrene microplastic (PS-MP)-induced sperm DNA damage was replicated by gavage of SPF ICR (CD1) mice PS-MPs at 1 mg/d and treated with YSTL at 11.89, 23.78 and 47.56 g/kg, respectively, for 60 days. The Sperm DNA fragmentation index (DFI) of each group was detected and compared. The target genes of YSTL identified by transcriptomic and proteomic analyses were validated by qRT-PCR and western blotting.

RESULTS

The DFI of the PS group (20.66%) was significantly higher than that of the control group (4.23%). The medium and high doses of the YSTL group (12.8% and 11.31%) exhibited a significant repairing effect. The most enriched pathway was PI3K/Akt. TBL1X, SPARC, hnRNP0, Map7D1, Eps8 and Mrpl27 were screened and SPARC was validated.

DISCUSSION AND CONCLUSIONS

The precise mechanism by which YSTL inhibits PD-MPs DNA damage may be associated with the PI3K/Akt pathway and SPARC. It provides a new direction for using traditional Chinese medicine to prevent and repair reproductive system injury caused by MPs.

Chromatin condensation but not DNA integrity of pig sperm is greater in the sperm-rich fraction

BACKGROUND

Protamination and condensation of sperm chromatin as well as DNA integrity play an essential role during fertilization and embryo development. In some mammals, like pigs, ejaculates are emitted in three separate fractions: pre-sperm, sperm-rich (SRF) and post sperm-rich (PSRF). These fractions are known to vary in volume, sperm concentration and quality, as well as in the origin and composition of seminal plasma (SP), with differences being also observed within the SRF one. Yet, whether disparities in the DNA integrity and chromatin condensation and protamination of their sperm exist has not been interrogated.

RESULTS

This study determined chromatin protamination (Chromomycin A3 test, CMA3), condensation (Dibromobimane test, DBB), and DNA integrity (Comet assay) in the pig sperm contained in the first 10 mL of the SRF (SRF-P1), the remaining portion of the sperm-rich fraction (SRF-P2), and the post sperm-rich fraction (PSRF). While chromatin protamination was found to be similar between the different ejaculate fractions (P > 0.05), chromatin condensation was seen to be greater in SRF-P1 and SRF-P2 than in the PSRF (P = 0.018 and P = 0.004, respectively). Regarding DNA integrity, no differences between fractions were observed (P > 0.05). As the SRF-P1 has the highest sperm concentration and ejaculate fractions are known to differ in antioxidant composition, the oxidative stress index (OSi) in SP, calculated as total oxidant activity divided by total antioxidant capacity, was tested and confirmed to be higher in the SRF-P1 than in SRF-P2 and PSRF (0.42 ± 0.06 vs. 0.23 ± 0.09 and 0.08 ± 0.00, respectively; P < 0.01); this index, in addition, was observed to be correlated to the sperm concentration of each fraction (Rs = 0.973; P < 0.001).

CONCLUSION

While sperm DNA integrity was not found to differ between ejaculate fractions, SRF-P1 and SRF-P2 were observed to exhibit greater chromatin condensation than the PSRF. This could be related to the OSi of each fraction.

Innovative technology for evaluation of sperm DNA double-strand breaks diagnoses male factor infertility and prevents reproductive failures

Neutral comet assay has been available for two decades to evaluate sperm double-strand breaks (DSBs). However, its clinical usability is limited due to its complex and time-consuming procedure, as well as the lack of a standardized scoring system. The aim of this study was to: develop a rapid diagnostic method for DSBs, Sperm DNA Fragmentation Releasing Assay (SDFR), and explore the association between DSBs and reproductive outcomes. We pioneered the use of polyacrylamide (PA) for embedding sperm chromatin and optimized the porosity of PA to be between 10 and 13%. The refined PA network allowed the trapping of DSBs, which dispersed halo on an immunological slide; in contrast, intact chromatin failed to develop a halo. A strong correlation was showed between reproducible values obtained from SDFR and neutral comet assay. SDFR were responsive to dose-/time-dependent simulated DSBs, indicating high sensitivity and specificity. Furthermore, we conducted a retrospective study of couples with embryonic aneuploidy screening, and recording DSB profiles of the male partners. Our findings revealed that DSB enabled to predict embryonic aneuploidy whereas basic semen parameters did not. In conclusion, SDFR offers a rapid and user-friendly approach for evaluating DSBs, with potential implications for predictive healthcare in reproductive medicine.

Good practice recommendations on add-ons in reproductive medicine†

STUDY QUESTION

Which add-ons are safe and effective to be used in ART treatment?

SUMMARY ANSWER

Forty-two recommendations were formulated on the use of add-ons in the diagnosis of fertility problems, the IVF laboratory and clinical management of IVF treatment.

WHAT IS KNOWN ALREADY

The innovative nature of ART combined with the extremely high motivation of the patients has opened the door to the wide application of what has become known as 'add-ons' in reproductive medicine. These supplementary options are available to patients in addition to standard fertility procedures, typically incurring an additional cost. A diverse array of supplementary options is made available, encompassing tests, drugs, equipment, complementary or alternative therapies, laboratory procedures, and surgical interventions. These options share the common aim of stating to enhance pregnancy or live birth rates, mitigate the risk of miscarriage, or expedite the time to achieving pregnancy.

STUDY DESIGN, SIZE, DURATION

ESHRE aimed to develop clinically relevant and evidence-based recommendations focusing on the safety and efficacy of add-ons currently used in fertility procedures in order to improve the quality of care for patients with infertility.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ESHRE appointed a European multidisciplinary working group consisting of practising clinicians, embryologists, and researchers who have demonstrated leadership and expertise in the care and research of infertility. Patient representatives were included in the working group. To ensure that the guidelines are evidence-based, the literature identified from a systematic search was reviewed and critically appraised. In the absence of any clear scientific evidence, recommendations were based on the professional experience and consensus of the working group. The guidelines are thus based on the best available evidence and expert agreement. Prior to publication, the guidelines were reviewed by 46 independent international reviewers. A total of 272 comments were received and incorporated where relevant.

MAIN RESULTS AND THE ROLE OF CHANCE

The multidisciplinary working group formulated 42 recommendations in three sections; diagnosis and diagnostic tests, laboratory tests and interventions, and clinical management.

LIMITATIONS, REASONS FOR CAUTION

Of the 42 recommendations, none could be based on high-quality evidence and only four could be based on moderate-quality evidence, implicating that 95% of the recommendations are supported only by low-quality randomized controlled trials, observational data, professional experience, or consensus of the development group.

WIDER IMPLICATIONS OF THE FINDINGS

These guidelines offer valuable direction for healthcare professionals who are responsible for the care of patients undergoing ART treatment for infertility. Their purpose is to promote safe and effective ART treatment, enabling patients to make informed decisions based on realistic expectations. The guidelines aim to ensure that patients are fully informed about the various treatment options available to them and the likelihood of any additional treatment or test to improve the chance of achieving a live birth.

STUDY FUNDING/COMPETING INTEREST(S)

All costs relating to the development process were covered from ESHRE funds. There was no external funding of the development process or manuscript production. K.L. reports speakers fees from Merck and was part of a research study by Vitrolife (unpaid). T.E. reports consulting fees from Gynemed, speakers fees from Gynemed and is part of the scientific advisory board of Hamilton Thorne. N.P.P. reports grants from Merck Serono, Ferring Pharmaceutical, Theramex, Gedeon Richter, Organon, Roche, IBSA and Besins Healthcare, speakers fees from Merck Serono, Ferring Pharmaceutical, Theramex, Gedeon Richter, Organon, Roche, IBSA and Besins Healthcare. S.R.H. declares being managing director of Fertility Europe, a not-for-profit organization receiving financial support from ESHRE. I.S. is a scientific advisor for and has stock options from Alife Health, is co-founder of IVFvision LTD (unpaid) and received speakers' fee from the 2023 ART Young Leader Prestige workshop in China. A.P. reports grants from Gedeon Richter, Ferring Pharmaceuticals and Merck A/S, consulting fees from Preglem, Novo Nordisk, Ferring Pharmaceuticals, Gedeon Richter, Cryos and Merck A/S, speakers fees from Gedeon Richter, Ferring Pharmaceuticals, Merck A/S, Theramex and Organon, travel fees from Gedeon Richter. The other authors disclosed no conflicts of interest.

DISCLAIMER

This Good Practice Recommendations (GPRs) document represents the views of ESHRE, which are the result of consensus between the relevant ESHRE stakeholders and are based on the scientific evidence available at the time of preparation.ESHRE GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or bedeemedinclusive of all proper methods of care, or be exclusive of other methods of care reasonably directed to obtaining the same results.Theydo not replace the need for application of clinical judgement to each individual presentation, or variations based on locality and facility type.Furthermore, ESHRE GPRs do not constitute or imply the endorsement, or favouring, of any of the included technologies by ESHRE.

Surgically retrieved spermatozoa for ICSI cycles in non-azoospermic males with high sperm DNA fragmentation in semen

Intracytoplasmic sperm injection (ICSI) using surgically retrieved spermatozoa outside the classic context of azoospermia has been increasingly used to overcome infertility. The primary indications include high levels of sperm DNA damage in ejaculated spermatozoa and severe oligozoospermia or cryptozoospermia, particularly in couples with ICSI failure for no apparent reason. Current evidence suggests that surgically retrieved spermatozoa for ICSI in the above context improves  outcomes, mainly concerning pregnancy and miscarriage rates. The reasons are not fully understood but may be related to the lower levels of DNA damage in spermatozoa retrieved from the testis compared with ejaculated counterparts. These findings are consistent with the notion that excessive sperm DNA damage  can be a limiting factor responsible for the failure to conceive. Using testicular in preference of low-quality ejaculated spermatozoa bypasses post-testicular sperm DNA damage caused primarily by oxidative stress, thus increasing the likelihood of oocyte fertilization by genomically intact spermatozoa. Despite the overall favorable results, data remain limited, and mainly concern males with confirmed sperm DNA damage in the ejaculate. Additionally, information regarding the health of ICSI offspring resulting from the use of surgically retrieved spermatoa of non-azoospermic males is still lacking. Efforts should be made to improve the male partner's reproductive health for safer ICSI utilization. A comprehensive andrological evaluation aiming to identify and treat the underlying male infertility factor contributing to sperm DNA damage is essential for achieving this goal.

Unraveling the Impact of Sperm DNA Fragmentation on Reproductive Outcomes

In recent years, there has been a growing interest in identifying subcellular causes of male infertility, and sperm DNA fragmentation (SDF) research has been at the forefront of this focus. DNA damage can occur during spermatogenesis due to faulty chromatin compaction or excessive abortive apoptosis. It can also happen as sperm transit through the genital tract, often induced by oxidative stress. There are several methods for SDF testing, with the sperm chromatin structure assay, terminal deoxynucleotidyl transferase d-UTI nick end labeling (TUNEL) assay, comet assay, and sperm chromatin dispersion test being the most commonly used. Numerous studies strongly support the negative impact of SDF on male fertility potential. DNA damage has been linked to various morphological and functional sperm abnormalities, ultimately affecting natural conception and assisted reproductive technology outcomes. This evidence-based review aims to explore how SDF influences male reproduction and provide insights into available therapeutic options to minimize its detrimental impact.

DNA strand displacement and TdT-Mediated DNA extension for swift, convenient, and quantitative evaluation of sperm DNA integrity and its clinical implications

DNA integrity is crucial for the clinical pregnancy outcome and offspring health, while detection methods currently used (comet assay, TUNNEL assay, SCSA, etc.) can only provide the ratio of positive sperms at the cellular level and are unable to quantitatively detect the breakpoints at the DNA molecular level. Herein, we developed a detection system based on terminal deoxynucleotidyl transferase and DNA strand displacement fluorescent probe, which could efficiently and conveniently measure the number of 3'-OH (equivalent to the number of breakpoints). We further investigated the use of this technique in assisted reproduction after completing the principle verification, system optimization, and research on analytical performance. The detection system was shown to have a good linear range from 0.01 nM to 4 nM, using single-stranded DNA with 3'-OH end as the calibrator. The system underwent thorough optimization for stability and accuracy. In comparison to the widely accepted index DFI detected by SCSA, the new system demonstrated reasonable correlation and better prediction efficiency. Its applicability was also proven through its use in assisted reproductive technology procedures.

Can a sperm selection technique improve embryo ploidy?

BACKGROUND

Spermatozoa with the highest motility retain a superior genomic integrity, and elevated sperm chromatin fragmentation (SCF) has been linked to a lower ability of the conceptus to develop and implant. Therefore, the utilization of a sperm selection method, such as microfluidic sperm selection (MFSS), is capable of reducing the SCF by yielding the most motile fraction of spermatozoa with the highest embryo developmental competence. What remains unclear, however, is the causal mechanism that links SCF to an impaired embryo development.

OBJECTIVES

To identify a relationship between SCF and an unexpectedly high proportion of embryo aneuploidy, while addressing treatment options.

MATERIALS AND METHODS

We identified couples with a high incidence of embryo aneuploidy in a previous intracytoplasmic sperm injection (ICSI) cycle with pre-implantation genetic testing for aneuploidy (PGT-A), utilizing spermatozoa selected by density gradient (DG). Terminal deoxynucleotidyl dUTP transferase nick-end labeling (TUNEL) and neutral Comet assays were carried out on the semen specimens to assess total SCF and double-stranded DNA (dsDNA) fragmentation, respectively. These couples underwent subsequent ICSI/PGT-A cycles with MFSS. Total SCF and dsDNA fragmentation were compared between the two sperm selection methods. Embryo aneuploidy, implantation, clinical pregnancy, delivery, and pregnancy loss rates were compared between the couples' historical DG and subsequent MFSS cycles.

RESULTS

In 57 couples undergoing 71 ICSI/PGT-A cycles, where DG sperm selection was carried out, a high incidence of aneuploid embryos (74.7%) resulted in poor implantation and no viable pregnancies. Testing for SCF, inclusive of dsDNA breaks, evidenced a SCF of 26.2% and dsDNA break of 3.6% in the raw specimen, that decreased to 18.0% (p < 0.001) and 3.1%, respectively, in the DG processed specimen. Following MFSS, total SCF and dsDNA fragmentation decreased to 1.9% and 0.3%, respectively (p < 0.001). The embryo euploidy rate remarkable improved from 25.3% in the DG cycles to 42.9% in the MFSS cycles (p < 0.001). The 6.7% implantation rate in the DG cycles increased to 65.5% in the MFSS cycles (p < 0.001). Similarly, the clinical pregnancy rate rose from 10.5% (DG) to 64.6% (MFSS), resulting in a 62.5% delivery rate (p < 0.001).

DISCUSSION AND CONCLUSIONS

In couples with a relatively young female partner with a negative infertility workup, and a male partner with semen parameters adequate for ICSI, presenting with a high rate of embryo aneuploidy, an additional subtle male factor component may be the culprit. Thus, it is crucial to assess the SCF and test for the dsDNA breaks, which can eventually contribute to embryo chromosomal abnormalities. Given the inverse relationship between SCF and motility, a selection of the most motile gamete by MFSS enhanced the proportion of spermatozoa with an intact genome, contributing to the generation of more euploid embryos that are capable of implanting and yielding increased term pregnancies.

Sperm centriolar factors and genetic defects that can predict pregnancy

The human sperm centrosome, comprising the two morphologically distinct centrioles and associated pericentriolar materials, plays a crucial role in fertilization and early embryonic development after fertilization. Once inside the oocyte, the sperm centrosome serves as a microtubule-organizing center, orchestrating mitotic spindle formation, chromosome segregation, and syngamy. Abnormalities of the sperm centrosome can lead to abnormal embryonic development and embryonic chromosomal instability, and are associated with pregnancy loss. Recent research has shed light on the molecular composition, regulation, and function of this vital organelle. Understanding the intricacies of the sperm centrosome is crucial for elucidating the mechanisms underlying successful fertilization and early embryonic development, as well as addressing infertility and developmental disorders associated with centrosomal defects.

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.

Assessment of Ante- and Postnatal Development of the Offspring of Male Rats Crossed in Delayed Periods after Treatment with Methotrexate in Low Doses

We studied ante- and postnatal development of the offspring of intact female rats crossed with males injected with low doses of methotrexate 3 and 6 months before mating. The time of crossing corresponded to the manifestation of the cytostatic effect on spermatogonial stem cells. The offspring of methotrexate-treated males was characterized by increased preimplantation losses and fetal growth restriction in the antenatal period and inhibition of physical development, delayed formation of sensory-motor reflexes, and impaired learning abilities in the postnatal period.

The influence and mechanistic action of sperm DNA fragmentation index on the outcomes of assisted reproduction technology

We investigated the influence of DNA fragmentation index (DFI) on in vitro fertilization (IVF), embryo transfer (ET), and intracytoplasmic sperm injection (ICSI). We analyzed the semen parameters of 61 cycles in infertile couples undergoing IVF-ET and ICSI and determined DFI by sperm chromatin dispersion testing. Based on DFI, the patients were differentiated into a control group (DFI < 25%, n = 35) and a test group (DFI ≥ 25%, n = 26). Flow cytometry and immunofluorescence were used to investigate the extent of sperm reactive oxygen species (ROS) and apoptosis. We also investigated the effect of DFI on pregnancy outcomes of IVF-ET/ICSI. DFI was negatively related to sperm motility and positively correlated with ROS and apoptosis (P < 0.05). Abnormally elevated DFI reduced the rate of transplantable, high-quality embryos, implantation, clinical pregnancy, delivery, and live birth after IVF-ET, and increased the chance of early abortion per transfer cycle (P < 0.05). However, there was no significant correlation between DFI and fertilization rate, cleavage rate, transplantable rate, high-quality embryo rate, implantation rate, clinical pregnancy rate, early abortion rate, delivery rate and live birth rate when assisted by ICSI (P > 0.05). Sperm DNA integrity is crucial for fertilization and the development of healthy offspring. ROS may increase the level of DFI by inducing apoptosis in sperm.

An Algorithm to Predict the Lack of Pregnancy after Intrauterine Insemination in Infertile Patients

Increasing intrauterine insemination (IUI) success rates is essential to improve the quality of care for infertile couples. Additionally, straight referral of couples with less probability of achieving a pregnancy through IUI to more complex methods such as in vitro fertilization is important to reduce costs and the time to pregnancy. The aim of the present study is to prospectively evaluate the threshold values for different parameters related to success in intrauterine insemination in order to provide better reproductive counseling to infertile couples, moreover, to generate an algorithm based on male and female parameters to predict whether the couple is suitable for achieving pregnancy using IUI. For that, one hundred ninety-seven infertile couples undergoing 409 consecutive cycles of intrauterine insemination during a two-year period were included. The first year served as a definition of the parameters and thresholds related to pregnancy achievement, while the second year was used to validate the consistency of these parameters. Subsequently, those parameters that remained consistent throughout two years were included in a generalized estimating equation model (GEE) to determine their significance in predicting pregnancy achievement. Parameters significantly associated with the lack of pregnancy through IUI and included in the GEE were (p < 0.05): (i) male age > 41 years; (ii) ejaculate sperm count < 51.79 x 10⁶ sperm; (iii) swim-up alkaline Comet > 59%; (iv) female body mass index > 45 kg/m²; (v) duration of infertility (>84 months), and (vi) basal LH levels > 27.28 mUI/mL. The application of these limits could provide a pregnancy prognosis to couples before undergoing intrauterine insemination, therefore avoiding it in couples with low chances of success. The retrospective application of these parameters to the same cohort of patients would have increased the pregnancy rate by up to 30%.

Diluent pH affects sperm motility via GSK3 α/β-hexokinase pathway for the efficient enrichment of X-sperm to increase the female kids rate of dairy goats

Dairy goats are the goats bred with the ability to produce large quantities of milk, and the increase of the female kid rate of breeding dairy goats is beneficial for milk production and economic benefits of dairy goat farms. Our previous study revealed that regulating the pH of dairy goat semen diluent to 6.2 or 7.4 respectively, the proportion of X chromosome bearing sperm (X-sperm) in the up and down layers of the tube after incubation was significantly higher than that of Y chromosome bearing sperm (Y-sperm) i.e. enriched X-sperm. In this study, fresh dairy goat semen collected in different seasons was diluted in different pH solutions to calculate the number and rate of X-sperm and to measure the functional parameters of enriched sperm. The artificial insemination experiments were performed with enriched X-sperm. The mechanisms of regulating the pH of diluent affecting sperm enrichment were further studied. The results showed that the proportion of enriched X-sperm in pH 6.2 and 7.4 diluents of sperm collected in different seasons showed no significantly different, but were significantly higher than that of the control group (pH 6.8). The in vitro functional parameters of X-sperm enriched in pH 6.2 and 7.4 diluent solution were not significantly different from those of the control group (P > 0.05). After artificial insemination with X-sperm enriched in pH7.4 diluent, the proportion of female offspring was significantly higher than that of the control group. It was found that the regulating pH of the diluent affected sperm mitochondrial activity and glucose uptake capacity via phosphorylating NF-κB and GSK3α/β proteins. The motility activity of X-sperm was enhanced under acidic conditions and weakened under alkaline conditions, which was conducive to the effective enrichment of X-sperm. This study demonstrated that the number and proportion of X-sperm enriched using pH 7.4 diluent were elevated, and the proportion of female kids was increased. This technology can be used for the reproduction and production of dairy goats in farms at large scales.

In vitro exposure to environmentally relevant concentrations of norgestrel affects sperm physiology and reproductive success of the Pacific oyster Crassostrea gigas

Progestins in aquatic environments are of increasing concern, as shown by the results of toxicological studies on adult invertebrates with external fertilization. However, their potential effects on the gametes and reproductive success of such animals remain largely unknown. Thus, the current study assessed the effect of in vitro exposure of environmentally relevant concentrations (10 ng/L and 1000 ng/L) of norgestrel (NGT) on the sperm of Pacific oyster Crassostrea gigas, analyzing sperm motility, ultrastructure, mitochondrial function, ATP status, characteristic enzyme activities, and DNA integrity underlying fertilization and hatching success. The results showed that NGT increased the percentage of motile sperm by elevating intracellular Ca²⁺ levels, Ca²⁺-ATPase activity, creatine kinase activity, and ATP content. Although superoxide dismutase activity was enhanced to eliminate reactive oxygen species generated by NGT, oxidative stress occurred, as indicated by the increase in malonaldehyde content and damage to plasma membranes and DNA. As a consequence, fertilization rates decreased. However, hatching rates did not alter significantly, possibly as a result of DNA repair processes. This study demonstrates oyster sperm as a useful, sensitive tool for toxicological research of progestins and provides ecologically relevant information on reproductive disturbance in oysters resulting from exposure to NGT.

Condensation and protamination of sperm chromatin affect ICSI outcomes when gametes from healthy individuals are used

STUDY QUESTION

Do defects in sperm chromatin protamination and condensation have an impact on ICSI outcomes?

SUMMARY ANSWER

Sperm protamination is related to fertilization rates in healthy donors, and the in vitro capacity of sperm to condense their chromatin is linked to blastocyst rates, both associations being more apparent in women <33 years of age.

WHAT IS KNOWN ALREADY

Previous data on how sperm chromatin damage affects ICSI outcomes are inconsistent. Revealing which sperm factors influence embryo development is necessary to understand the male contribution to ICSI success and to develop novel sperm selection techniques or male-based treatments. Sperm chromatin is mainly condensed in protamines, which are cross-linked through disulphide bridges. This study aimed to determine whether sperm protamination and the integrity of disulphide bonds (condensation) are related to embryo development after ICSI.

STUDY DESIGN, SIZE, DURATION

The design was a retrospective study with a blind analysis of sperm chromatin. Gametes were divided into two groups: double donation (DD) cohort and single donation (SD) cohort. Samples from 45 semen donors used in 55 ICSI cycles with oocyte donors (age range 19-33 years), generating 491 embryos, were included in the DD cohort. The SD cohort consisted of samples from 34 semen donors used in 41 ICSI cycles with oocytes from healthy females (single-parent families or lesbian couples, age range 20-44 years), generating a total of 378 embryos.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Donor sperm samples from DD and SD cohorts were used for standard ICSI, and embryo development was observed by time-lapse imaging. The incidence of thiol reduction (dibromobimane, DBB) and the degree of chromatin protamination (chromomycin A3, CMA3, indicating non-protaminated regions) in sperm were determined by flow cytometry at 0 and 4 h post-thawing.

MAIN RESULTS AND THE ROLE OF CHANCE

Percentages ± standard deviation of CMA3 were 21.08 ± 9.09 and 35.01 ± 14.68 at 0 and 4 h post-thawing, respectively, in the DD cohort and 22.57 ± 9.48 and 35.79 ± 12.58, at 0 and 4 h post-thawing, respectively, in the SD cohort. Percentages of DBB+ were 16.57 ± 11.10 and 10.51 ± 8.40 at 0 and 4 h post-thawing (P < 0.0001), respectively, in the DD cohort and 17.98 ± 10.19 and 12.72 ± 8.76 at 0 and 4 h post-thawing (P < 0.0001), respectively, in the SD cohort. Female age correlated with fertilization rates, and the relation between sperm chromatin and embryo development was determined through multiple linear regression. While CMA3 was associated with fertilization rates, with no influence of female age, in the DD cohort (β1 = -1.036, P < 0.001 for CMA3; β2 = 0.667, P = 0.304 for female age), this was not observed in the SD cohort, where female age had a significant effect, masking the effects of CMA3 (β1 = -0.066, P = 0.804 for CMA3; β 2 = -1.451, P = 0.003 for female age). The in vitro capacity of sperm to condense their chromatin after 4 h of incubation was associated with blastocyst rates, independent of female age (DD cohort: β1 = -0.238, P = 0.008 for %DBB+ variation; β2 = 0.404, P = 0.638 for female age; SD cohort: β1 = -0.278, P = 0.010 for %DBB+ variation; β2 = -0.292, P = 0.594 for female age). The in vitro capacity of sperm to condense their chromatin was also related to the time required for the embryo to reach blastocyst stage in the DD cohort (P = 0.007). Finally, multiple logistic regression showed that both chromatin protamination and condensation, together with the age of the oocyte donors and the embryo recipients, had an impact on pregnancy achievement (P < 0.01) and on live birth rates (P < 0.01).

LIMITATIONS, REASONS FOR CAUTION

The main limitation was the restrictive selection of couples, which led to a relatively small sample size and could influence the observed outcomes. For this reason, and to reduce Type I error, the level of significance was set at P ≤ 0.01. On the other hand, the use of cryopreserved samples could also be a limitation.

WIDER IMPLICATIONS OF THE FINDINGS

This research demonstrated that protamination and condensation of sperm chromatin are related to embryo development after ICSI, but female age could be a confounding factor when oocytes from older females are used.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the European Union's Horizon 2020 Research and Innovation scheme under the Marie Skłodowska-Curie grant agreement No 801342 (Tecniospring INDUSTRY; TECSPR-19-1-0003); La Marató de TV3 Foundation (214/857-202039); the Ministry of Science and Innovation, Spain (IJC2019-039615-I); the Catalan Agency for Management of University and Research Grants, Regional Government of Catalonia, Spain (2017-SGR-1229); and the Catalan Institution for Research and Advanced Studies, Spain (ICREA). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Comprehensive Analysis of the Effect of Maternal and Paternal Demographics and Lifestyle Factors on the Embryo Quality and In Vitro Fertilization Outcomes: A Retrospective Study in North Eastern India

Background Lifestyle habits and demographic characteristics are strongly associated with sperm and oocyte quality and are important co-variates in fertility. However, their effect on the pre-implantation embryo quality in in vitro fertilization (IVF) has not been explored widely. The present retrospective study aimed to explore the effect of maternal and paternal demographic and lifestyle factors on the pre-implantation embryo quality in IVF. Methodology Women in the age group of 21 to 40 years undergoing IVF (n=105) in the Department of Reproductive Medicine, Indira Gandhi Institute of Medical Sciences, Patna, Bihar, and their partners were recruited in the study. Maternal and paternal charts were reviewed, and the demographic, lifestyle habit related data, and data related to oocyte retrieval, oocyte quality, and embryo quality were retrieved in a predesigned spreadsheet. Appropriate statistical analysis was conducted using SPSS Version 21 to evaluate the association of the studied maternal and paternal factors with oocyte and embryo quality. P-values less than 0.05 were considered to be significant. Results Maternal factors such as tubal blockage (p=0.02) and residence in an industrial locality (p=0.001) were found to be significantly associated with the quality of oocytes. None of the maternal factors studied were associated with embryo quality; however, day 3 and day 5 embryo quality was significantly associated with educational status of the male partners (p=0.02), smoking (p=0.05), and chewing tobacco (p=0.01). Day 5 embryo quality was also associated with residence in an industrial locality of the male partners (p=0.04). Conclusions Paternal lifestyle habits such as smoking, chewing tobacco, and demographic characteristics such as education and proximity to an industrial area were all related to poor embryo quality. Maternal factors such as tubal blockage and residence of industrial locality were found to be significantly associated with the quality of oocytes.

Oxidative versus reductive stress: a delicate balance for sperm integrity

Despite the long-standing notion of "oxidative stress," as the main mediator of many diseases including male infertility induced by increased reactive oxygen species (ROS), recent evidence suggests that ROS levels are also increased by "reductive stress," due to over-accumulation of reductants. Damaging mechanisms, like guanidine oxidation followed by DNA fragmentation, could be observed following reductive stress. Excessive accumulation of the reductants may arise from excess dietary supplementation over driving the one-carbon cycle and transsulfuration pathway, overproduction of NADPH through the pentose phosphate pathway (PPP), elevated levels of GSH leading to impaired mitochondrial oxidation, or as a result NADH accumulation. In addition, lower availability of oxidized reductants like NAD⁺, oxidized glutathione (GSSG), and oxidized thioredoxins (Trx-S2) induce electron leakage leading to the formation of hydrogen peroxide (H₂O₂). In addition, a lower level of NAD⁺ impairs poly (ADP-ribose) polymerase (PARP)-regulated DNA repair essential for proper chromatin integrity of sperm. Because of the limited studies regarding the possible involvement of reductive stress, antioxidant therapy remains a central approach in the treatment of male infertility. This review put forward the concept of reductive stress and highlights the potential role played by reductive vs oxidative stress at pre-and post-testicular levels and considering dietary supplementation.

What Does Intracytoplasmic Sperm Injection Change in Embryonic Development? The Spermatozoon Contribution

The intracytoplasmic sperm injection (ICSI) technique was invented to solve severe male infertility due to altered sperm parameters. Nowadays, it is applied worldwide for the treatment of couple infertility. ICSI is performed with any available spermatozoon from surgery or ejaculated samples, whatever are the sperm motility, morphology or quantity. The aim of the present review was to study if embryo development and kinetics would be modified by (1) ICSI under the technical aspects, (2) the micro-injected spermatozoa in connection with male infertility. From published data, it can be seen that ICSI anticipates the zygote kinetics Furthermore, because fertilization rate is higher in ICSI compared to conventional in vitro fertilization (IVF), more blastocysts are obtained for clinical use in ICSI. Sperm and spermatozoa characteristics, such as sperm parameters, morphology and vitality, DNA content (levels of sperm DNA fragmentation, microdeletions, and chromosomal abnormalities), RNA content, epigenetics, and sperm recovery site (testicular, epididymis, and ejaculated), have an impact on fertilization and blastocyst rates and embryo kinetics in different ways. Even though ICSI is the most common solution to solve couples' infertility, the causes of male infertility are crucial in building a competent spermatozoa that will contribute to normal embryonic development and healthy offspring.

Microfluidic sperm sorting improves ICSI outcomes in patients with increased values of Double-Strand Breaks in sperm DNA

BACKGROUND

Delays in embryo kinetics, implantation failures in ICSI treatments and recurrent miscarriages have been associated with high values of Double-Strand Breaks (DSB) in sperm DNA. While conventional methods for semen preparation have been shown to be inefficient reducing DSB values, Microfluidic Sperm Sorting (MSS) devices are promising tools to reduce this damage.

OBJECTIVE

To study the clinical utility of an MSS device in ICSI treatments when the male partner presents increased DSB values, as compared to the use of conventional methods based on sperm motility.

METHODS

This retrospective cohort study included 28 infertile couples undergoing ICSI treatments. Only couples where the male partner presented increased values of DSB were included. DSB values were evaluated in semen samples by the Neutral Comet assay. Couples performed a first ICSI cycle using conventional methods for semen preparation (Density Gradients and Swim-up) and a second ICSI cycle using the ZyMōt™ICSI (formerly named FertileChip®) microfluidic device. Embryology and clinical outcomes were compared between ICSI cycles.

RESULTS

Semen parameters and the number of obtained and fertilized oocytes did not show differences between ICSI rounds. Clinical outcomes were statistically better when MSS was used: the biochemical pregnancy rate increased 28.31%; the clinical pregnancy rate increased 35.56% and the number of live births increased 35.29%, as compared to the first ICSI cycle in this group of patients.

CONCLUSIONS

The ZyMōt™ICSI microfluidic device improved the reproductive outcomes in couples where the male partner presented increased DSB values, when compared to the use of conventional semen preparation techniques.

A comprehensive investigation of human endogenous retroviral syncytin proteins and their receptors in men with normozoospermia and impaired semen quality

PURPOSE

The study aims to investigate first the presence of Syncytin 2 and its receptor, MFSD2, in human sperm, and second whether the expressions of Syncytin 1, Syncytin 2, and their receptors, SLC1A5 and MFSD2, differ between normozoospermic, asthenozoospermic, oligozoospermic, and oligoasthenozoospermic human sperm samples.

METHODS

The localization patterns and expression levels of syncytins and their receptors were evaluated in normozoospermic (concentration = 88.9 ± 5.5 × 10⁶, motility = 79.2 ± 3.15%, n = 30), asthenozoospermic (concentration = 51.7 ± 7.18 × 10⁶, motility = 24.0 ± 3.12%, n = 15), mild oligozoospermic (concentration = 13.5 ± 2.17 × 10⁶, motility = 72.1 ± 6.5%, n = 15), moderate oligozoospermic (concentration = 8.4 ± 3.21 × 10⁶, motility = 65.1 ± 8.9%, n = 15), severe oligozoospermic (concentration = 2.1 ± 1.01 × 10⁶, motility = 67.5 ± 3.2%, n = 15), and oligoasthenozoospermic (concentration = 5.5 ± 3.21 × 10⁶, motility = 18.5 ± 1.2%, n = 15) samples by immunofluorescence staining and western blot.

RESULTS

Syncytins and their receptors visualized by immunofluorescence showed similar staining patterns with slight staining of the tail in all spermatozoa regardless of normozoospermia, asthenozoospermia, oligozoospermia, or oligoasthenozoospermia. The localization patterns were categorized as equatorial segment, midpiece region, acrosome, and post-acrosomal areas. The combined staining patterns were also detected as acrosomal cap plus post acrosomal region, the midpiece plus equatorial segment, and midpiece plus acrosomal region. However, some sperm cells were categorized as non-stained. Both syncytin proteins were most intensely localized in the midpiece region, while their receptors were predominantly present in the midpiece plus acrosomal region. Conspicuously, syncytins and their receptors showed decreased expression in asthenozospermic, oligozoospermic, and oligoasthenozoospermic samples compared to normozoospermic samples.

CONCLUSION

The expression patterns of HERV-derived syncytins and their receptors were identical regardless of the spermatozoa in men with normozoospermia versus impaired semen quality. Further, asthenozoospermia, oligozoospermia, and oligoasthenozoospermia as male fertility issues are associated with decreased expression of both syncytins and their receptors.

Sperm DNA integrity does play a crucial role for embryo development after ICSI, notably when good-quality oocytes from young donors are used

Based on the inconsistent literature published thus far involving infertile patients, whether intracytoplasmic sperm injection (ICSI) allows overcoming total fertilization failure due to sperm DNA fragmentation is still unclear. Related to this, female factors, which may have a significant impact on assisted reproduction outcomes, can mask male infertility. In this scenario, evaluating ICSI outcomes following cycles using healthy donor gametes could shed light on this realm, as it would avoid the influence of (un)known confounding factors present in infertile individuals. The present work, therefore, aimed to address whether single- and double-stranded sperm DNA fragmentation leads to impaired ICSI outcomes in double gamete donation cycles. The study also compared these double-gamete donation cycles to cycles in which only sperm were donated and oocytes were obtained from infertile patients. Two cohorts were included: (a) the Donor-Donor (DD) cohort, which included 27 semen donor samples used in 49 ICSI cycles with young healthy oocyte donors; and (b) the Donor-Infertile (DI) cohort, which involved 34 semen donor samples used in 57 ICSI cycles with oocytes from patients. Single- and double-stranded sperm DNA breaks were determined with alkaline and neutral Comet assays, respectively; ICSI was conducted following standard protocols and embryos were monitored through time-lapse microscopy. In the DD cohort, the percentage of sperm with high overall DNA damage correlated with fertilization rates (Rs = - 0.666; P < 0.001) and with the percentage of blastocysts per injected oocyte (Rs = - 0.414; P = 0.040). In addition, sperm DNA damage delayed the first embryo division (Rs = 0.421; P = 0.036), and development from the 8-cell to the morula stage (Rs = 0.424; P = 0.034). In contrast, double-stranded DNA breaks had no effect in this cohort. As far as the DI cohort is concerned, while overall sperm DNA damage was not found to be correlated to fertilization or blastocyst rates, pronuclei formation following ICSI was delayed when the incidence of double-stranded DNA breaks was high (Rs = 0.485; P = 0.005). In conclusion, this study, which is the first involving double donation cycles (i.e., a donor-donor cohort), supports that sperm DNA damage has a detrimental impact on fertilization rates after ICSI, and delays embryo development. Moreover, the use of oocytes from infertile individuals is suggested to hide the male-factor effect.

Antioxidant Intervention against Male Infertility: Time to Design Novel Strategies

Infertility is a highly prevalent condition, affecting 9-20% of couples worldwide. Among the identifiable causes, the male factor stands out in about half of infertile couples, representing a growing problem. Accordingly, there has been a decline in both global fertility rates and sperm counts in recent years. Remarkably, nearly 80% of cases of male infertility (MI) have no clinically identifiable aetiology. Among the mechanisms likely plausible to account for idiopathic cases, oxidative stress (OS) has currently been increasingly recognized as a key factor in MI, through phenomena such as mitochondrial dysfunction, lipid peroxidation, DNA damage and fragmentation and finally, sperm apoptosis. In addition, elevated reactive oxygen species (ROS) levels in semen are associated with worse reproductive outcomes. However, despite an increasing understanding on the role of OS in the pathophysiology of MI, therapeutic interventions based on antioxidants have not yet provided a consistent benefit for MI, and there is currently no clear consensus on the optimal antioxidant constituents or regimen. Therefore, there is currently no applicable antioxidant treatment against this problem. This review presents an approach aimed at designing an antioxidant strategy based on the particular biological properties of sperm and their relationships with OS.

Determination of double- and single-stranded DNA breaks in bovine sperm is predictive of their fertilizing capacity

BACKGROUND

The analysis of chromatin integrity has become an important determinant of sperm quality. In frozen-thawed bovine sperm, neither the sequence of post-thaw injury events nor the dynamics of different types of sperm DNA breaks are well understood. The aim of the present work was to describe such sperm degradation aftermath focusing on DNA damage dynamics, and to assess if this parameter can predict pregnancy rates in cattle.

RESULTS

A total of 75 cryopreserved ejaculates from 25 Holstein bulls were evaluated at two post-thawing periods (0-2 h and 2-4 h), analyzing global and double-stranded DNA damage through alkaline and neutral Comet assays, chromatin deprotamination and decondensation, sperm motility, viability, acrosomal status, and intracellular levels of total ROS, superoxides and calcium. Insemination of 59,605 females was conducted using sperm from the same bulls, thus obtaining the non-return to estrus rates after 90 d (NRR). Results showed an increased rate of double-stranded breaks in the first period (0-2 h: 1.29 ± 1.01%/h vs. 2-4 h: 0.13 ± 1.37%/h; P <  0.01), whereas the rate of sperm with moderate + high single-stranded breaks was higher in the second period (0-2 h: 3.52 ± 7.77 %/h vs. 2-4h: 21.06 ± 11.69 %/h; P < 0.0001). Regarding sperm physiology, viability decrease rate was different between the two periods (0-2 h: - 4.49 ± 1.79%/h vs. 2-4 h: - 2.50 ± 3.39%/h; P = 0.032), but the progressive motility decrease rate was constant throughout post-thawing incubation (0-2 h: - 4.70 ± 3.42%/h vs. 2-4 h: - 1.89 ± 2.97%/h; P > 0.05). Finally, whereas no correlations between bull fertility and any dynamic parameter were found, there were correlations between the NRR and the basal percentage of highly-damaged sperm assessed with the alkaline Comet (Rs = - 0.563, P = 0.003), between NRR and basal progressive motility (Rs = 0.511, P = 0.009), and between NRR and sperm with high ROS at 4 h post-thaw (Rs = 0.564, P = 0.003).

CONCLUSION

The statistically significant correlations found between intracellular ROS, sperm viability, sperm motility, DNA damage and chromatin deprotamination suggested a sequence of events all driven by oxidative stress, where viability and motility would be affected first and sperm chromatin would be altered at a later stage, thus suggesting that bovine sperm should be used for fertilization within 2 h post-thaw. Fertility correlations supported that the assessment of global DNA damage through the Comet assay may help predict bull fertility.

TMT-Based Proteomic Analysis of Human Spermatozoa from Unexplained Recurrent Miscarriage Patients before and after Oral Antioxidant Treatment

Recently, sperm quality and the presence of double-stranded breaks (DSB) has been pointed out as a possible cause of recurrent miscarriage, and the use of antioxidants has expanded as a treatment for male infertility. The aim of the present study was to analyze the proteomic effects of antioxidants on sperm from RM patients with high incidence of DSB. Proteomic analysis was performed using a tandem mass tag labeling technique, and subsequently compared with the PANTHER database for DEPs, and the STRING database for protein–protein interactions (PPI). Differentially expressed proteins (DEPs) both before and after antioxidant oral treatment were identified. PPI involving DEPs clustered into networks related to cell metabolism, cytoskeleton, and DNA damage. Results show that the sperm proteomic profiles before and after antioxidant treatment do not significantly differ from each other. However, some DEPs found after the antioxidant treatment shifted towards a DEPs profile typical of fertile donors. This indirect measurement suggests an improvement caused by antioxidants on the expression of several proteins. Among them were proteins involved in sperm DNA remodeling (LMO7, MMP28, BNC2, H2B, and PRDM2). The results presented here represent the first approach in the analysis and repair of the proteomic change caused by antioxidants in recurrent miscarriage patients, elucidating biomarkers that may be useful for the diagnosis and further sperm selection in this type of patient. Further studies should be conducted to validate the usefulness of these biomarkers in larger study groups.

A Review of the Impact of Microfluidics Technology on Sperm Selection Technique

Sperm sorting procedures depend on centrifugation processes. These processes produce oxidative stress and cell damage that are undesirable for in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) outcomes because they affect fertilization and implantation chances. The microfluidic sperm selection technique has shown promise in this area. It can create a platform for isolating and manipulating good-quality sperm cells using diverse triggers such as mechanical factors, chemical agents, and temperature gradients. Furthermore, microfluidic platforms can direct sperm cells for IVF or sperm sorting by utilizing an approach that is passive or active. In this review, we explain the use of microfluidics technologies for sorting and arranging sperm cells for different purposes. We also discuss the use of microfluidics technology in selecting and assessing sperm parameters and how it affects male infertility.

Seminal Microbiota of Idiopathic Infertile Patients and Its Relationship With Sperm DNA Integrity

The development of new biomarkers for human male infertility is crucial to improve the diagnosis and the prognosis of this disease. Recently, seminal microbiota was shown to be related to sperm quality parameters, suggesting an effect in human fertility and postulating it as a biomarker candidate. However, its relationship to sperm DNA integrity has not been studied yet. The aim of the present study is to characterize the seminal microbiota of a western Mediterranean population and to evaluate its relationship to sperm chromatin integrity parameters, and oxidative stress. For that purpose, 14 samples from sperm donors and 42 samples from infertile idiopathic patients were obtained and were analyzed to assess the composition of the microbiota through full-length 16S rRNA gene sequencing (Illumina MiSeq platform). Microbial diversity and relative abundances were compared to classic sperm quality parameters (macroscopic semen parameters, motility, morphology and concentration), chromatin integrity (global DNA damage, double-stranded DNA breaks and DNA protamination status) and oxidative stress levels (oxidation-reduction potential). The seminal microbiota observed of these samples belonged to the phyla Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes. The most abundant genera were Finegoldia, Peptoniphilus, Anaerococcus, Campylobacter, Streptococcus, Staphylococcus, Moraxella, Prevotella, Ezakiella, Corynebacterium and Lactobacillus. To our knowledge, this is the first detection of Ezakiella genus in seminal samples. Two clusters of microbial profiles were built based on a clustering analysis, and specific genera were found with different frequencies in relation to seminal quality defects. The abundances of several bacteria negatively correlate with the sperm global DNA fragmentation, most notably Moraxella, Brevundimonas and Flavobacterium. The latter two were also associated with higher sperm motility and Brevundimonas additionally with lower oxidative-reduction potential. Actinomycetaceae, Ralstonia and Paenibacillus correlated with reduced chromatin protamination status and increased double-stranded DNA fragmentation. These effects on DNA integrity coincide in many cases with the metabolism or enzymatic activities of these genera. Significant differences between fertile and infertile men were found in the relative presence of the Propionibacteriaceae family and the Cutibacterium, Rhodopseudomonas and Oligotropha genera, which supports its possible involvement in male fertility. Our findings sustain the hypothesis that the seminal microbiome has an effect on male fertility.

Microplastics May Be a Significant Cause of Male Infertility

Due to the problematic degradation properties of plastics, the decomposition of plastic results in the formation of numerous microplastics (MPs), less than 5 mm in diameter. These MPs enter the soil and the ocean, eventually passing through the air, water, or food chain back to the human body and harming human health. In the last 80 years, male semen analysis parameters have shown a significant decline for unknown reasons, speculated to be caused by pollutants. No studies examined the relationship between human MP exposure and male infertility. In this article, we reviewed the relevant animal experimental research literature in recent years and calculated that the minimum human equivalent dose of MPs leading to abnormal male semen quality is 0.016 mg/kg/d. The literature comparison found that MP exposure in Japan and South Korea was close to this value. These results suggest that MPs can affect male semen quality and that MPs may significantly impact male fertility.

Sperm DNA damage compromises embryo development, but not oocyte fertilisation in pigs

Background

The assessment of sperm DNA integrity has been proposed as a complementary test to conventional mammalian semen analysis. In this sense, single-strand (SSB) and double-strand (DSB) DNA breaks, the two types of sperm DNA fragmentation (SDF), have been reported to have different aetiologies and to be associated to different fertility outcomes in bovine and humans. Considering that no studies in porcine have addressed how SDF may affect sperm quality and fertility outcomes, the present work aimed to determine the impact of global DNA damage, SSB and DSB on sperm quality and in vitro fertilising ability. To this end, 24 ejaculates (one per boar) were split into three aliquots: the first was used to assess sperm quality parameters through a computer-assisted sperm analysis (CASA) system and flow cytometry; the second was used to perform in vitro fertilisation, and the third, to evaluate sperm DNA integrity using alkaline and neutral Comet assays.

Results

The results showed that global DNA damage negatively correlates (P < 0.05) with normal sperm morphology (R = − 0.460) and progressive motility (R = − 0.419), and positively with the percentage of non-viable sperm (R = 0.507). Multiple regression analyses showed that non-viable sperm were related to SSB (β = − 0.754). In addition, while fertilisation did not seem to be affected by sperm DNA integrity, global DNA damage, DSB and SSB were found to be correlated to embryo development outcomes. Specifically, whereas global DNA damage and DSB negatively affected (P < 0.05) the later preimplantation embryo stages (percentage of early blastocyst/blastocyst D6: for global DNA damage, R = − 0.458, and for DSB, R = − 0.551; and percentage of hatching/hatched blastocyst D6: for global DNA damage, R = − 0.505, and for DSB, R = − 0.447), global DNA damage and SSB had a negative impact (P < 0.05) on the developmental competency of fertilised embryos (R = − 0.532 and R = − 0.515, respectively). Remarkably, multiple regression analyses supported the associations found in correlation analyses. Finally, the present work also found that the inclusion of Comet assays to the conventional sperm quality tests improves the prediction of blastocyst formation (AUC = 0.9021, P < 0.05), but not fertilisation rates (P > 0.05).

Conclusion

Considering all these findings, this work sets a useful model to study how SDF negatively influences fertility.

Nursing Exposure to Bisphenols as a Cause of Male Idiopathic Infertility

Idiopathic infertility is a serious problem, which can be caused and explained by exposure to endocrine disruptors, such as bisphenols. In our study, we studied transactional exposure to bisphenol and its effects on newborn male mice throughout their reproductive life. Newborn male mice were exposed to bisphenol S and bisphenol F through maternal milk from post-natal day 0 to post-natal day 15 at concentrations of 0.1 ng.g/bw/day and 10 ng.g/bw/day, respectively. Although there were minimal differences between the control and experimental groups in testicular tissue quality and spermatozoa quality, we discovered an interesting influence on early embryonic development. Moderate doses of bisphenol negatively affected cleavage of the early embryo and subsequently, the blastocyst rate, as well as the number of blastomeres per blastocyst. In our study, we focused on correlations between particular stages from spermatogenesis to blastocyst development. We followed epigenetic changes such as dimethylation of histone H3 and phosphorylation of histone H2 from germ cells to blastocysts; we discovered the transfer of DNA double-strand breaks through the paternal pronucleus from spermatozoa to blastomeres in the blastocyst. We elucidated the impact of sperm DNA damage on early embryonic development, and our results indicate that idiopathic infertility in adulthood may have causes related to the perinatal period.

Functional Aspects of Sperm Chromatin Organization

Sperm nuclei present a highly organized and condensed chromatin due to the interchange of histones by protamines during spermiogenesis. This high DNA condensation leads to almost inert chromatin, with the impossibility of conducting gene transcription as in most other somatic cells. The major chromosomal structure responsible for DNA condensation is the formation of protamine-DNA toroids containing 25-50 kilobases of DNA. These toroids are connected by toroid linker regions (TLR), which attach them to the nuclear matrix, as matrix attachment regions (MAR) do in somatic cells. Despite this high degree of condensation, evidence shows that sperm chromatin contains vulnerable elements that can be degraded even in fully condensed chromatin, which may correspond to chromatin regions that transfer functionality to the zygote at fertilization. This chapter covers an updated review of our model for sperm chromatin structure and its potential functional elements that affect embryo development.

DNA repair and response to sperm DNA damage in oocytes and embryos, and the potential consequences in ART: a systematic review

Sperm DNA damage is considered a predictive factor for the clinical outcomes of patients undergoing ART. Laboratory evidence suggests that zygotes and developing embryos have adopted specific response and repair mechanisms to repair DNA damage of paternal origin. We have conducted a systematic review in accordance with guidelines from Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to identify and review the maternal mechanisms used to respond and repair sperm DNA damage during early embryonic development, how these mechanisms operate and their potential clinical implications. The literature search was conducted in Ovid MEDLINE and Embase databases until May 2021. Out of 6297 articles initially identified, 36 studies were found to be relevant through cross referencing and were fully extracted. The collective evidence in human and animal models indicate that the early embryo has the capacity to repair DNA damage within sperm by activating maternally driven mechanisms throughout embryonic development. However, this capacity is limited and likely declines with age. The link between age and decreased DNA repair capacity could explain decreased oocyte quality in older women, poor reproductive outcomes in idiopathic cases, and patients who present high sperm DNA damage. Ultimately, further understanding mechanisms underlying the maternal repair of sperm DNA damage could lead to the development of targeted therapies to decrease sperm DNA damage, improved oocyte quality to combat incoming DNA insults or lead to development of methodologies to identify individual spermatozoa without DNA damage.

Direct but Not Indirect Methods Correlate the Percentages of Sperm With Altered Chromatin to the Intensity of Chromatin Damage

Although sperm chromatin damage, understood as damage to DNA or affectations in sperm protamination, has been proposed as a biomarker for sperm quality in both humans and livestock, the low incidence found in some animals raises concerns about its potential value. In this context, as separate methods measure different facets of chromatin damage, their comparison is of vital importance. This work aims at analyzing eight techniques assessing chromatin damage in pig sperm. With this purpose, cryopreserved sperm samples from 16 boars were evaluated through the following assays: TUNEL, TUNEL with decondensation, SCSA, alkaline and neutral sperm chromatin dispersion (SCD) tests, alkaline and neutral Comet assays, and chromomycin A3 test (CMA3). In all cases, the extent of chromatin damage and the percentage of sperm with fragmented DNA were determined. The degree of chromatin damage and the percentage of sperm with fragmented DNA were significantly correlated (p < 0.05) in direct methods (TUNEL, TUNEL with decondensation, and alkaline and neutral Comet) and CMA3, but not in the indirect ones (SCD and SCSA). Percentages of sperm with fragmented DNA determined by alkaline Comet were significantly (p < 0.05) correlated with TUNEL following decondensation and CMA3; those determined by neutral Comet were correlated with the percentage of High DNA Stainability (SCSA); those determined by SCSA were correlated with neutral and alkaline SCD; and those determined by neutral SCD were correlated with alkaline SCD. While, in pigs, percentages of sperm with fragmented DNA are directly related to the extent of chromatin damage when direct methods are used, this is not the case for indirect techniques. Thus, the results obtained herein differ from those reported for humans in which TUNEL, SCSA, alkaline SCD, and alkaline Comet were found to be correlated. These findings may shed some light on the interpretation of these tests and provide some clues for the standardization of chromatin damage methods.

Morphokinetic parameter comparison between embryos from couples with high or low sperm DNA fragmentation index

OBJECTIVE

To study whether time-lapse imaging can identify morphokinetic events impacted by a high sperm DNA fragmentation index (DFI).

DESIGN

Historical cohort study.

SETTING

Private university-affiliated in vitro fertilization center.

PATIENT(S)

A total of 978 zygotes cultured until day 5 in a time-lapse imaging incubator between March 2019 and August 2020, derived from 118 patients undergoing intracytoplasmic sperm injection as a result of idiopathic male factor infertility.

INTERVENTION(S)

Kinetic markers from the point of insemination were recorded. Generalized linear mixed models adjusted for potential confounders followed by the Bonferroni post hoc test were used to compare the timing of specific events in patients with a low (<30%) or high (≥30%) sperm DFI. The recorded kinetic markers were the following: timing to pronuclei appearance and fading; timing to 2, 3, 4, 5, 6, 7, and 8 cells; and timing to start blastulation and blastulation.

MAIN OUTCOME MEASURE(S)

Timing to blastulation.

RESULT(S)

Embryos derived from sperm samples with ≥30% DFI showed significantly slower divisions compared with those with <30% DFI (mean differences of 0.7 hours in timing to pronuclei appearance, 1.2 hours in timing to pronuclei fading, 1.5 hours in timing to 2 cells, 2.5 hours in timing to 3 cells, 1.8 hours in timing to 4 cells, 3.3 hours in timing to 5 cells, 3.1 hours in timing to 6 cells, 3.2 hours in timing to 7 cells, 2.7 hours in timing to 8 cells, 8.4 hours in timing to start blastulation, and 3.8 hours in timing to blastulation). The incidences of reverse or direct cleavages (9.3% vs. 4.4%; odds ratio [OR], 2.24; 95% confidence interval [CI], 1.32-3.77) and multinucleation at 2-cell (18.9% vs. 12.0%; OR, 1.70; 95% CI, 1.12-2.58) and 4-cell (14.2% vs. 6.4%; OR, 2.42; 95% CI, 1.57-3.74) stages were significantly higher in embryos deriving from ≥30% DFI than from <30% DFI. The KIDScore ranked significantly different between embryos derived from samples with <30% and ≥30% DFI. Continuous DFI was positively correlated with all timings of specific events and with the incidences of abnormal cleavage patterns (OR, 1.042; 95% CI, 1.025-1.059) and multinucleation at 2-cell stage (OR, 1.053; 95% CI, 1.030-1.076) and inversely correlated with the KIDScore rank (B, -0.218; 95% CI, -0.044 to -0.007). No significant differences were observed in clinical outcomes between the groups.

CONCLUSION(S)

Embryo morphokinetic parameters are negatively impacted by high sperm DFI, resulting in delayed cell cleavage and blastulation.

Sperm DNA Fragmentation

Sperm DNA fragmentation refers to the accumulation of adducts as well as single- or double-strand DNA breaks and reflects the sperm DNA quality. Current data suggest that there are differences in sperm DNA quality among individuals with high or low fertility, and this observation has led to the idea that testing sperm DNA fragmentation could be a useful test of male fertility. However, sperm DNA fragmentation has become one of the most frequently debated topics in reproductive medicine, as there is no agreement about the optimal way to test for DNA fragmentation, the clinically significant level of sperm DNA fragmentation, as well as the best therapeutic options for infertile men. This article presents current evidence related to sperm DNA fragmentation and its role in managing male infertility.

Effects of Diluent pH on Enrichment and Performance of Dairy Goat X/Y Sperm

In this paper, on the basis of the differences in the hydrogen ion concentration (pH) of the diluent dairy goat semen on X/Y sperm motility, an X/Y sperm enrichment study was conducted to establish a simple and effective method for gender control in dairy goats. Dairy goat semen was diluted using different pH dilutions and was incubated. Then, the X/Y sperm ratio in the isolated upper sperm was determined using the double TaqMan qPCR method. The internal pH change pattern of sperm cells at different pH dilutions was measured using BCECF-AM probe, and the functional parameters of the isolated sperm were tested with the corresponding kit. Next, an in vitro fertilization test was conducted using isolated spermatozoa and oocytes to determine their fertilization rates, the percentages of female embryos, and the expression of genes related to developing potentially fertilized embryos. Results showed that the percentages of the X sperm cells in the upper sperm layer were 67.24% ± 2.61% at sperm dilution pH of 6.2 and 30.45% ± 1.03% at sperm dilution pH of 7.4, which was significantly different from 52.35% ± 1.72% of the control group (pH 6.8) (P < 0.01). Results also showed that there is a relationship between the external pHo and internal pHi of sperm cells. Furthermore, the percentages of female embryos after the in vitro fertilization of the isolated upper sperm with mature oocytes at pH 6.2 and 7.4 were 66.67% ± 0.05 and 29.73% ± 0.04%, respectively, compared with 48.57% ± 0.02% in the control group (pH 6.8). Highly significant differences occurred between groups (P < 0.01). Additionally, no significant difference was observed during the expression of genes related to embryonic development between the blastocysts formed from sperm isolated by changing the pH of the diluent and the control sperm (P > 0.05). Therefore, this study successfully established a simple and effective method for enriched X/Y sperms from dairy goats, which is important for regulating the desired sex progeny during dairy goat breeding and for guiding dairy goat production.

The TUNEL assay underestimates the incidence of DNA damage in pig sperm due to chromatin condensation

Inconsistencies in the relationship between sperm DNA fragmentation and reproductive outcomes as well as the low incidence in farm animals raise concerns on its actual value as a sperm quality parameter. Previous studies suggested that the different sensitivity of techniques evaluating DNA fragmentation could explain variations in the correlation with reproductive outcomes. While the TUNEL assay is one of the most standardized methods to detect DNA damage and cell death, the steric impediment for the terminal nucleotidyl transferase enzyme to access the highly condensed sperm nucleus may decrease the ability of this test to detect internal DNA breaks. In the present study, we sought to determine whether increasing chromatin decondensation makes the TUNEL assay more sensitive to detect DNA damage in pig sperm. We compared three chromatin decondensation treatments (2 mM DTT for 45 min; 5 mM DTT for 8 min and further 45 min; and 5 mM DTT+ 1 M NaCl for 8 min) through the Chromomycin A3 test (CMA3). While incubation with DTT increased the percentages of sperm with decondensed chromatin, regardless of concentration and time of incubation (P < 0.05), the extent of that decondensation was higher when 5 mM DTT was combined with 1 M NaCl. In addition, the TUNEL assay detected a higher number of DNA breaks in sperm with decondensed chromatin (1.89% ± 1.63% vs 8.74% ± 6.05%; P = 0.003). This study shows, for the first time, that previous chromatin decondensation increases the sensitivity of the TUNEL assay to detect DNA damage in pig sperm. These findings also support that larger chromatin decondensation is needed in order for DNA damage to be evaluated properly in species containing protamine P1 only.

A microfluidic sperm-sorting device reduces the proportion of sperm with double-stranded DNA fragmentation

Sperm DNA fragmentation can be produced in one (ssSDF) or both (dsSDF) DNA strands, linked to difficulties in naturally achieving a pregnancy and recurrent miscarriages, respectively. The techniques more frequently used to select sperm require centrifugation, which may induce sperm DNA fragmentation (SDF). The objective of this study was to assess whether the microfluidic-based device FertileChip® (now ZyMot®ICSI) can diminish the proportion of sperm with dsSDF. First, in a blinded split pilot study, the semen of nine patients diagnosed with ≥60% dsSDF, was divided into three aliquots: not processed, processed with FertileChip®, and processed with swim up. The three aliquots were all analyzed using neutral COMET for the detection of dsSDF, resulting in a reduction of 46% (P < 0.001) with FertileChip® (dsSDF: 34.9%) compared with the ejaculate and the swim up (dsSDF: 65%). Thereafter, the FertileChip® was introduced into clinical practice and a cohort of 163 consecutive ICSI cycles of patients diagnosed with ≥60% dsSDF was analyzed. Fertilization rate was 75.41%. Pregnancy rates after the first embryo transfer were 53.2% (biochemical), 37.8% (clinical), 34% (ongoing) and the live birth rate was 28.8%. Cumulative pregnancy rates after one (65.4% of patients), two (27.6% of patients) or three (6.4% of patients) transfers were 66% (biochemical), 56.4% (clinical), 53.4% (ongoing) and the live birth rate was 42%. The selection of spermatozoa using Fertile Chip® significantly diminishes the percentage of dsSDF, compared with either the fresh ejaculate or after swim up. Its applicability in ICSI cycles of patients with high dsSDF resulted in good laboratory and clinical outcomes.

Quantitative selection of single human sperm with high DNA integrity for intracytoplasmic sperm injection

OBJECTIVE

To study at the single-cell level whether a sperm's motility and morphology parameters reflect its DNA integrity, and to establish a set of quantitative criteria for selecting single sperm with high DNA integrity.

DESIGN

Prospective study.

SETTING

In vitro fertilization center and university laboratories.

PATIENT(S)

Male patients undergoing infertility treatments.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The motility and morphology parameters of each sperm were measured with the use of computer vision algorithms. The sperm was then aspirated and transferred for DNA fragmentation measurement by single-cell gel electrophoresis (comet assay).

RESULT(S)

We adapted the World Health Organization criteria, which were originally defined for semen analysis, and established a set of quantitative criteria for single-sperm selection in intracytoplasmic sperm injection. Sperm satisfying the criteria had significantly lower DNA fragmentation levels than the sample population. Both normal motility and normal morphology were required for a sperm to have low DNA fragmentation. The quantitative criteria were integrated into a software program for sperm selection. In blind tests in which our software and three embryologists selected sperm from the same patient samples, our software outperformed the embryologists and selected sperm with the highest DNA integrity.

CONCLUSION(S)

At the single-cell level, a sperm's motility and morphology parameters reflect its DNA integrity. The developed technique and criteria hold the potential to mitigate the risk factor of sperm DNA fragmentation in intracytoplasmic sperm injection.

Application of the comet assay for the evaluation of DNA damage in mature sperm

DNA integrity is considered an important parameter of semen quality and is of significant value as a predictor of male fertility. Currently, there are several methods that can assess sperm DNA integrity. One such assay is the comet assay, or single-cell gel electrophoresis, which is a simple, sensitive, reliable, quick and low-cost technique that is used for measuring DNA strand breaks and repair at the level of individual cells. Although the comet assay is usually performed with somatic cells from different organs, the assay has the ability to detect genotoxicity in germ cells at different stages of spermatogenesis. Since the ability of sperm to remove DNA damage differs between the stages, interpretation of the results is dependent on the cells used. In this paper we give an overview on the use and applications of the comet assay on mature sperm and its ability to detect sperm DNA damage in both animals and humans. Overall, it can be concluded that the presence in sperm of significantly damaged DNA, assessed by the comet assay, is related to male infertility and seems to reduce live births. Although there is some evidence that sperm DNA damage also has a long-term impact on offspring's health, this aspect of DNA damage in sperm is understudied and deserves further attention. In summary, the comet assay can be applied as a useful tool to study effects of genotoxic exposures on sperm DNA integrity in animals and humans.

Selection of high-quality sperm with thousands of parallel channels

Sperm selection is essential for successful fertilization and embryo development. Current clinical sperm selection methods are labor-intensive and lack the selectivity required to isolate high-quality sperm. Microfluidic sperm selection approaches have shown promise but present a trade-off between the quality and quantity of selected sperm - clinicians demand both. The structure of the female reproductive tract helps to isolate a sufficient quantity of high-quality sperm for fertilization with densely folded epithelium that provides a multitude of longitudinally oriented pathways that guide sperm toward the fertilization site. Here, a three-dimensionally structured sperm selection device is presented that levers this highly parallelized in vivo mechanism for in vitro sperm selection. The device is inserted in a test tube atop 1 mL of raw semen and provides 6500 channels that isolate ∼100 000 high-DNA-integrity sperm for assisted reproduction. In side-by-side clinical testing, the developed approach outperforms the best current clinical methods by improving the DNA integrity of the selected sperm subpopulation up to 95%. Also, the device streamlines clinical workflow, reducing the time required for sperm preparation 3-fold. This single-tube, single-step sperm preparation approach promises to improve both the economics and outcomes of assisted reproduction practices, especially in cases with significant male-factors.