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.

Sperm telomere length in motile sperm selection techniques: A qFISH approach.

Several studies have associated telomere shortening with alterations in reproductive function. The objective of the present study was to determine telomere length (TL) in spermatozoa selected by either density-gradient centrifugation (DGC) or swim-up. The analysis of TL was performed using quantitative fluorescent in situ hybridisation (qFISH) using PNA probes in combination with a chromatin decompaction protocol in sperm cells. Results of TL were 24.64 ± 5.00 Kb and 24.95 ± 4.60 Kb before and after DGC, respectively, and 19.59 ± 8.02 Kb and 20.22 ± 5.18 Kb before and after swim-up respectively. Sperm selected by DGC or swim-up did not show any significant differences in TL as compared to nonselected sperm (p > .05). Negative correlations between TL and sperm motility (r = -.308; p = .049) and concentration (r = -.353; p = .028) were found. Furthermore, exposure of sperm to increasing concentrations of hydrogen peroxide during incubation resulted in a reduction in TL. These data indicate that oxidative stress may be one of the main factors involved in the reduction of TL in sperm. Preliminary clinical results from patients included in this study indicate that TL was shorter in spermatozoa from couples who never achieved a pregnancy compared to couples who did achieve at least one natural pregnancy (p < .05); however, the clinical utility of this biomarker still needs to be confirmed in further studies.

Nuclear degraded sperm subpopulation is affected by poor chromatin compaction and nuclease activity.

There is an interest in the nuclear degraded sperm subpopulation because, although it is present in a low percentage in all semen samples, patient groups such as varicocele and rearranged genome carriers show high levels of these degraded spermatozoa. This study is designed with two objectives in mind: first, incubations of H2 O2 and nuclease on DTT-treated and untreated samples to show the aetiology of this subpopulation and second, assessment of the correlation between the protamine ratio and nuclear degraded spermatozoa. A very high increase in the nuclear degraded subpopulation has been found with nuclease incubation, and it is even higher when it has been merged with nuclear decompaction using DTT. Alternatively, incubation with H2 O2 with and without DTT did not show such a significant increase in nuclear degraded spermatozoa. The protamine ratio correlated with this subpopulation, showing, in patients, that poor nuclear compaction would turn the sperm susceptible to degradation. Then, the assessment of nuclear degraded spermatozoa might not be only a measure of DNA degradation but also an indicator of chromatin compaction in the spermatozoa. Different patient groups would fit this model for sperm nuclear degradation, such as varicocele patients, who show a high percentage of immature spermatozoa and nuclear degraded spermatozoa, and reorganised genome carriers, where reorganisation might also cause poor chromatin compaction on the sperm nucleus.

Human semen cryopreservation: a sperm DNA fragmentation study with alkaline and neutral Comet assay.

Sperm cryopreservation is widely used for both research and reproduction purposes, but its effect on sperm DNA damage remains controversial. Sperm DNA fragmentation (SDF) has become an important biomarker to assess male infertility. In particular, the differentiation between single- and double-stranded DNA fragmentation (ssSDF and dsSDF) has clinical implications for male infertility where ssSDF is associated with reduced fertility, whereas dsSDF is associated with increased risk of miscarriage. In this study, semen samples from 30 human males have been analysed in both fresh and cryopreserved using the alkaline and neutral Comet assays. Results show an increase of about 10% of ssSDF, assessed by the alkaline Comet assay, regardless of the male fertility status. Neutral Comet analysis of dsSDF does not show any statistical increase when comparing fresh and cryopreserved samples in any of the patient groups. Results support previous reports that oxidative stress is the major effector in DNA damage during sample cryopreservation, as, on one hand, ssSDF has previously been related to oxidative damage and, on the other hand, we have not found any effect on dsSDF. Therefore, there might be a slight risk of decreased fertility after using a freezed sample, but no evidence for increased miscarriage risk from cryopreserved spermatozoa should be expected.

Double-stranded DNA breaks hidden in the neutral Comet assay suggest a role of the sperm nuclear matrix in DNA integrity maintenance.

We used a mouse model in which sperm DNA damage was induced to understand the relationship of double-stranded DNA (dsDNA) breaks to sperm chromatin structure and to the Comet assay. Sperm chromatin fragmentation (SCF) produces dsDNA breaks located on the matrix attachment regions, between protamine toroids. In this model, epididymal sperm induced to undergo SCF can religate dsDNA breaks while vas deferens sperm cannot. Here, we demonstrated that the conventional neutral Comet assay underestimates the epididymal SCF breaks because the broken DNA ends remain attached to the nuclear matrix, causing the DNA to remain associated with the dispersion halo, and the Comet tails to be weak. Therefore, we term these hidden dsDNA breaks. When the Comet assay was modified to include an additional incubation with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) after the conventional lysis, thereby solubilizing the nuclear matrix, the broken DNA was released from the matrix, which resulted in a reduction of the sperm head halo and an increase in the Comet tail length, exposing the hidden dsDNA breaks. Conversely, SCF-induced vas deferens sperm had small halos and long tails with the conventional neutral Comet assay, suggesting that the broken DNA ends were not tethered to the nuclear matrix. These results suggest that the attachment to the nuclear matrix is crucial for the religation of SCF-induced DNA breaks in sperm. Our data suggest that the neutral Comet assay identifies only dsDNA breaks that are released from the nuclear matrix and that the addition of an SDS treatment can reveal these hidden dsDNA breaks.

Comprehensive analysis of sperm DNA fragmentation by five different assays: TUNEL assay, SCSA, SCD test and alkaline and neutral Comet assay.

Sperm DNA fragmentation (SDF) is becoming an important test to assess male infertility. Several different tests are available, but no consensus has yet been reached as to which tests are most predictive of infertility. Few publications have reported a comprehensive analysis comparing these methods within the same population. The objective of this study was to analyze the differences between the five most common methodologies, to study their correlations and to establish their cut-off values, sensitivity and specificity in predicting male infertility. We found differences in SDF between fertile donors and infertile patients in TUNEL, SCSA, SCD and alkaline Comet assays, but none with the neutral Comet assay. The alkaline COMET assay was the best in predicting male infertility followed by TUNEL, SCD and SCSA, whereas the neutral COMET assay had no predictive power. For our patient population, threshold values for infertility were 20.05% for TUNEL assay, 18.90% for SCSA, 22.75% for the SCD test, 45.37% for alkaline Comet and 34.37% for neutral Comet. This work establishes in a comprehensive study that the all techniques except neutral Comet are useful to distinguish fertile and infertile men.

Alkaline and neutral Comet assay profiles of sperm DNA damage in clinical groups.

BACKGROUND: The analysis of sperm DNA fragmentation has become a new marker to predict male infertility, and many techniques have been developed. The sperm Comet assay offers the possibility of differentiating single- and double-stranded DNA (ssDNA and dsDNA) breaks, which could have different effects on fertility. The objective of this study was to perform a descriptive characterization of different groups of patients, such as those with asthenoteratozoospermic (ATZ) with or without varicocele, oligoasthenoteratozoospermic (OATZ) or balanced chromosome rearrangements, as compared with fertile donors. The Comet assay was used to investigate sperm samples for ssDNA and dsDNA breaks. METHODS AND RESULTS: The analysis of alkaline and neutral Comet assays in different groups of patients showed different sperm DNA damage profiles. Most fertile donors presented low values for ssDNA and dsDNA fragmentation (low-equivalent Comet profile), which would be the best prognosis for achieving a pregnancy. OATZ, ATZ and ATZ with varicocele presented high percentages of ssDNA and dsDNA fragmentation (high-equivalent Comet assay profile), ATZ with varicocele being associated with the worst prognosis, due to higher levels of DNA fragmentation. Rearranged chromosome carriers display a very high variability and, interestingly, two different profiles were seen: a high-equivalent Comet assay profile, which could be compatible with a bad prognosis, and a non-equivalent Comet assay profile, which has also been found in three fertile donors. CONCLUSIONS: Comet assay profiles, applied to different clinical groups, may be useful for determining prognosis in cases of male infertility.