La fragmentation de l'ADN du spermatozoïde : impact en Assistance médicale à la procréation

Oxidative Stress, Testicular Inflammatory Pathways, and Male Reproduction

Inflammation is among the core causatives of male infertility. Despite male infertility being a serious global issue, "bits and pieces" of its complex etiopathology still remain missing. During inflammation, levels of proinflammatory mediators in the male reproductive tract are greater than usual. According to epidemiological research, in numerous cases of male infertility, patients suffer from acute or chronic inflammation of the genitourinary tract which typically occurs without symptoms. Inflammatory responses in the male genital system are inextricably linked to oxidative stress (OS). OS is detrimental to male fertility parameters as it causes oxidative damage to reproductive cells and intracellular components. Multifarious male infertility causative factors pave the way for impairing male reproductive functions via the common mechanisms of OS and inflammation, both of which are interlinked pathophysiological processes, and the occurrence of any one of them induces the other. Both processes may be simultaneously found in the pathogenesis of male infertility. Thus, the present article aims to explain the role of inflammation and OS in male infertility in detail, as well as to show the mechanistic pathways that link causative factors of male reproductive tract inflammation, OS induction, and oxidant-sensitive cellular cascades leading to male infertility.

JG. The effects of male age on sperm DNA damage: an evaluation of 2,178 semen samples

OBJECTIVE

This study aimed to evaluate the effects of male age on sperm DNA damage.

METHODS

This cross-sectional study included semen samples collected from 2,178 men seen at an infertility clinic. For DNA integrity analysis, the proportions of spermatozoa showing DNA fragmentation (TUNEL assay), abnormal chromatin packaging/underprotamination (chromomycin A3), abnormal mitochondrial membrane potential (MMP/MitoTracker Green), and apoptosis (annexin V) were recorded. For group comparisons, enrolled subjects were divided into three groups based on their ages: ≤35 years; 36-44 years; and ≥45 years. The associations between age and sperm parameters were assessed using Spearman's rank correlation coefficient.

RESULTS

Although aging did not affect sperm apoptosis (p>.05), sperm DNA fragmentation and MMP deteriorated significantly with age (p<.05). Chromatin packaging/protamination improved significantly with age (p<.05).

CONCLUSION

Sperm DNA fragmentation worsened with age and was apparently associated with mitochondrial damage. The age-related increase in sperm DNA damage suggests that delaying childbearing, not only in women but also in men, might jeopardize a couple's reproductive capacity. The increase seen in chromatin packaging might represent a protective feature for DNA. However, additional studies must be performed to confirm the results concerning chromatin packaging/protamination.

A systematic review and meta-analysis to determine the effect of sperm DNA damage on in vitro fertilization and intracytoplasmic sperm injection outcome

Sperm DNA damage is prevalent among infertile men and is known to influence natural reproduction. However, the impact of sperm DNA damage on assisted reproduction outcomes remains controversial. Here, we conducted a meta-analysis of studies on sperm DNA damage (assessed by SCSA, TUNEL, SCD, or Comet assay) and clinical pregnancy after IVF and/or ICSI treatment from MEDLINE, EMBASE, and PUBMED database searches for this analysis. We identified 41 articles (with a total of 56 studies) including 16 IVF studies, 24 ICSI studies, and 16 mixed (IVF + ICSI) studies. These studies measured DNA damage (by one of four assays: 23 SCSA, 18 TUNEL, 8 SCD, and 7 Comet) and included a total of 8068 treatment cycles (3734 IVF, 2282 ICSI, and 2052 mixed IVF + ICSI). The combined OR of 1.68 (95% CI: 1.49–1.89; P < 0.0001) indicates that sperm DNA damage affects clinical pregnancy following IVF and/or ICSI treatment. In addition, the combined OR estimates of IVF (16 estimates, OR = 1.65; 95% CI: 1.34–2.04; P < 0.0001), ICSI (24 estimates, OR = 1.31; 95% CI: 1.08–1.59; P = 0.0068), and mixed IVF + ICSI studies (16 estimates, OR = 2.37; 95% CI: 1.89–2.97; P < 0.0001) were also statistically significant. There is sufficient evidence in the existing literature suggesting that sperm DNA damage has a negative effect on clinical pregnancy following IVF and/or ICSI treatment.

Sperm quality and paternal age: effect on blastocyst formation and pregnancy rates

BACKGROUND

Several studies suggest a decrease in sperm quality in men in the last decades. Therefore, the aim of this work was to assess the influence of male factors (sperm quality and paternal age) on the outcomes of conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI).

METHODS

This retrospective study included all couples who underwent IVF or ICSI at Montpellier University Hospital, France, between 1 January 2010 and 31 December 2015. Exclusion criteria were cycles using surgically retrieved sperm or frozen sperm, with pre-implantation genetic diagnosis or using frozen oocytes. The primary outcomes were the blastulation rate (number of blastocysts obtained at day 5 or day 6/number of embryos in prolonged culture at day 3) and the clinical pregnancy rate. The secondary outcomes were the fertilization and early miscarriage rates.

RESULTS

In total, 859 IVF and 1632 ICSI cycles were included in this study. The fertilization rate after ICSI was affected by oligospermia. Moreover, in ICSI, severe oligospermia (lower than 0.2 million/ml) led to a reduction of the blastulation rate. Reduced rapid progressive motility affected particularly IVF, with a decrease of the fertilization rate and number of embryos at day 2 when progressive motility was lower than 32%. Paternal age also had a negative effect. Although it was difficult to eliminate the bias linked to the woman's age, pregnancy rate was reduced in IVF and ICSI when the father was older than 51 and the mother older than 37 years.

CONCLUSIONS

These results allow adjusting our strategies of fertilization technique and embryo transfer. In the case of severe oligospermia, transfer should be carried out at the cleaved embryo stage (day 2-3) due to the very low blastulation rate. When the man is older than 51 years, couples should be aware of the reduced success rate, especially if the woman is older than 37 years. Finally, promising research avenues should be explored, such as the quantification of free sperm DNA, to optimize the selection of male gametes.

Measuring Sperm DNA Fragmentation and Clinical Outcomes of Medically Assisted Reproduction: A Systematic Review and Meta-Analysis

Sperm DNA fragmentation has been associated with reduced fertilization rates, embryo quality, pregnancy rates and increased miscarriage rates. Various methods exist to test sperm DNA fragmentation such as the sperm chromatin structure assay (SCSA), the sperm chromatin dispersion (SCD) test, the terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labelling (TUNEL) assay and the single cell gel electrophoresis (Comet) assay. We performed a systematic review and meta-analysis to assess the value of measuring sperm DNA fragmentation in predicting chance of ongoing pregnancy with IVF or ICSI. Out of 658 unique studies, 30 had extractable data and were thus included in the meta-analysis. Overall, the sperm DNA fragmentation tests had a reasonable to good sensitivity. A wide variety of other factors may also affect the IVF/ICSI outcome, reflected by limited to very low specificity. The constructed hierarchical summary receiver operating characteristic (HSROC) curve indicated a fair discriminatory capacity of the TUNEL assay (area under the curve (AUC) of 0.71; 95% CI 0.66 to 0.74) and Comet assay (AUC of 0.73; 95% CI 0.19 to 0.97). The SCSA and the SCD test had poor predictive capacity. Importantly, for the TUNEL assay, SCD test and Comet assay, meta-regression showed no differences in predictive value between IVF and ICSI. For the SCSA meta-regression indicated the predictive values for IVF and ICSI were different. The present review suggests that current sperm DNA fragmentation tests have limited capacity to predict the chance of pregnancy in the context of MAR. Furthermore, sperm DNA fragmentation tests have little or no difference in predictive value between IVF and ICSI. At this moment, there is insufficient evidence to recommend the routine use of sperm DNA fragmentation tests in couples undergoing MAR both for the prediction of pregnancy and for the choice of treatment. Given the significant limitations of the evidence and the methodological weakness and design of the included studies, we do urge for further research on the predictive value of sperm DNA fragmentation for the chance of pregnancy after MAR, also in comparison with other predictors of pregnancy after MAR.

DNA fragmentation status in patients with necrozoospermia

The aim of this study was to determine if a relationship exists between the levels of sperm DNA fragmentation and necrospermia in infertile men. Semen samples obtained from 70 men consulting for infertility evaluation were analyzed according to World Health Organization (WHO) guidelines. Patients were subdivided into three groups according to the percentage of necrotic spermatozoa: normozoospermia (<30%; n = 20), moderate necrozoospermia (50-80%; n = 30), and severe necrozoospermia (>80%; n = 20). DNA fragmentation was detected by the terminal desoxynucleotidyl transferase-mediated deoxyuridine triphosphate biotin nick-end labeling (TUNEL) assay. The sperm DNA fragmentation index (DFI) was 9.28 ± 2.98% in patients with a normal level of necrotic spermatozoa, 20.25 ± 3.21% in patients with moderate necrozoospermia, and 35.31 ± 5.25% in patients with severe necrozoospermia. There was a statistically significant increase of DNA fragmentation in the necrozoospermic group (P < 0.01). A strong correlation was found between the degree of necrozoospermia and sperm DNA fragmentation. We concluded that patients with necrozoospermia showed a high level of DNA fragmentation compared to normozoospermic men. Severe necrozoospermia (>80%) is a predictive factor for increased sperm DNA damage.

Detection of DNA fragmentation and meiotic segregation in human with isolated teratozoospermia

PURPOSE

To evaluate levels of DNA fragmentation and chromosomal abnormalities in ejaculated sperm of males with isolated teratozoospermia and to determine if specific sperm morphological types occur simultaneously with these nuclear defects.

METHODS

Sperm obtained from isolated teratozoospermic men (n = 70) and fertile men (n = 30) were analysed using fluorescence in situ hybridization and TUNEL assay.

RESULTS

Teratozoospermic men, compared to fertile men, showed significantly higher rates of sex chromosomes disomy, and diploidy. Significant correlations were found between amorphous head, microcephalic head, short tail, and sex chromosomes disomy. Level of sperm DNA fragmentation was significantly higher in teratozoospermic men than in controls and positively correlated to the incidence of macrocephalic heads, amorphous heads, and short flagella.

CONCLUSIONS

Patients with isolated teratozoospermia have increased levels of DNA fragmentation and chromosomal aneuploidy. Some specific morphological abnormalities were shown to be predictive of chromosomal abnormalities and DNA alteration.

Malonaldehyde formation and DNA fragmentation: two independent sperm decays linked to reactive oxygen species

Malondialdehyde (MDA), a product involved in membrane lipid peroxidation, was dosed in the sperm of 163 patients who had consulted the clinic regarding hypofertility. We attempted to determine if there was correlation between MDA content, sperm World Health Organization parameters and DNA fragmentation that results mainly from reactive oxygen species assaults. We found that no correlation could be established; however MDA and sperm decondensation were shown to be significantly linked. The impact of membrane polyunsaturated fatty acids and the role of phospholipid hydroperoxide glutathione peroxidase are discussed.

Effect of maternal and paternal age on pregnancy and miscarriage rates after intrauterine insemination

More than 17,000 intrauterine insemination (lUI) cycles were analysed retrospectively with respect to outcome according to differing aetiologies of infertility. The quantity and motility of spermatozoa in the final preparation used for insemination had a positive effect on the outcome, as classically observed in the past. It was found that advanced maternal age had a negative effect on the pregnancy rate and was associated with increased miscarriage rate. More interestingly, an exactly parallel effect was found for paternal age. The impact of increased age on necrospermia and sperm DNA structure is discussed as a probable direct cause of this paternal effect.

DNA fragmentation and meiotic segregation in sperm of carriers of a chromosomal structural abnormality

OBJECTIVE

To determine the meiotic segregation and DNA fragmentation in spermatozoa of carriers of a chromosomal structural abnormality.

DESIGN

Case series.

SETTING

University hospital.

PATIENT(S)

Thirty-seven male carriers of a chromosomal structural abnormality (21 with a balanced reciprocal translocation, 7 with a robertsonian translocation, 9 with a pericentric inversion).

INTERVENTION(S)

Meiotic segregation was analyzed by the human sperm-hamster oocyte fusion technique or by fluorescent in situ hybridization, and DNA fragmentation was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay.

MAIN OUTCOME MEASURE(S)

Relationships between abnormal sperm parameters, DNA fragmentation, and meiotic mechanisms.

RESULT(S)

The average rates of chromosomally unbalanced spermatozoa were 55.22%, 14.09%, and 18.43% for reciprocal translocation, robertsonian translocation, and pericentric inversion carriers, respectively. The rates of DNA fragmentation were significantly higher in the whole group of carriers of a chromosomal structural abnormality and in each specific group than in the control group. No correlations between sperm DNA fragmentation and parameters of spermogram, age, or percentage of unbalanced chromosomal gametes were found.

CONCLUSION(S)

The DNA fragmentation rate depends solely on the presence of a chromosomal structural abnormality, and, therefore, a chromosomal structural abnormality predicts DNA fragmentation. Both meiotic segregation and DNA fragmentation studies should be integrated in the genetic exploration of male carriers of a chromosomal structural abnormality.

[Could apoptotic markers help the exploration of male infertility?]

Apoptosis is a cell death program involved in different steps of spermatogenesis, first at puberty, at the beginning of spermatogenesis, then in adult testicles by controlling normal spermatogenesis. As a result, apoptosis deregulation can affect spermatogenesis. Many studies have provided evidence that apoptosis deregulation in germinal cells resulted in male infertility. In addition, apoptosis detection in ejaculated spermatozoa arouses a growing interest in research as a reliable marker of spermatozoon quality. The aim of this review is to summarize our knowledge on physiological apoptosis during spermatogenesis, and then analyse the possibility of using apoptotic markers as selective markers of spermatozoon quality to optimize the rate of success of in vitro fertilization.

Expression profile of genes coding for DNA repair in human oocytes using pangenomic microarrays, with a special focus on ROS linked decays

PURPOSE

To determine the level of expression for mRNAs that regulate DNA repair activity in oocytes at the germinal vesicle (GV) stage. Reactive oxygen species (ROS) have been shown to play a major role in the appearance of deleterious DNA decays, and this study focuses on the repair of damage linked to decay caused by the action of ROS. The oocyte needs a mechanism for repairing DNA decays in the early preimplantation embryo before the onset of genomic activation, since in the absence of repair, residual DNA damage would lead to either apoptosis or tolerance. Tolerance of DNA damage is a source of potential mutations.

METHOD

GV oocytes were selected for this study, both for the ethical reason that they are unsuitable for patient treatment, and because no transcription takes place during the period from GV to MII and then prior to genomic activation. The GV oocyte is therefore a good model for looking at DNA during the first cleavages of early preimplantation development. Six cohorts of GV oocytes were pooled for extraction of mRNA; the DNA was analysed using Affimetrix HG-UG133 Plus 2, containing 54,675 probe sets; spike and housekeeping genes were also added as internal controls.

RESULTS

In GV oocytes, DNA repair pathways for oxidized bases are redundant. One step repair procedure (OSR), BER (base excision repair), MMR (mismatch repair) and NER (Nucleotide excision repair) are present. All the recognition proteins are also present. The chromatin assembly factors necessary for the maintenance of genomic stability are highly expressed.

CONCLUSION

Gene expression analysis shows that the oocyte does not allow a high level of tolerance for DNA decays. This regulatory mechanism should avoid transmitting mutations into the next generation.

Prise en charge en Assistance médicale à la procréation des femmes de 38 ans et plus: résultats d'une enquête à propos de 84 couples

OBJECTIVE

More and more young women are delaying childbearing until the fourth decade of life: thus, Assisted Reproductive Techniques centres receive more and more requests from ageing women. The aim of the study is to analyse the purpose of these requests, the biological and clinical features of these patients and the results in our infertility centre.

PATIENTS AND METHODS

A retrospective study was carried out at the CHU of Saint-Etienne from 01.01.01 to 31.12.04. We analysed the social, clinical and biological features of 84 couples when the woman's age was equal or superior to 38 years, representing 218 cycles. A questionnaire was used to collect social data.

RESULTS

Several factors can explain the increasing number of ageing women consulting for infertility: extend university time and professional career, professional stability, contraception and late meeting of the partner, false reassuring information concerning progress in ART, second child desire after a late first pregnancy, but also second marital unions and child desire in the redefined couple. In our study, above 40 years old, the pregnancy (19.4 versus 10.5%) and delivery rates (16.7 versus 5.8%) clearly decreased in IUI. Thus, most of the clinicians propose, in first choice, an IVF cycle to a 40 year-old woman. The ultrasound measurement of antral follicle count can accurately evaluate the prognosis in terms of pregnancy (P<0.01) and delivery rate (P=0.03). For patients with unfavourable prognosis, oocyte donation, embryo donation, or adoption can be considered.

DISCUSSION AND CONCLUSION

ART cannot compensate for the natural decrease in pregnancy rates and the increase in early miscarriages in ageing women. Therefore, it is essential to inform young women of the negative effects of age on their potential fertility.

[How to improve assisted reproductive techniques results? Biological aspects]

In spite of recent improvements in IVF, pregnancy rates remained dramatically low. Better criteria are therefore necessary to establish the viability of a transferable top quality embryo. Observation of both pronuclei patterns at the zygote stage and early cleavage appears to offer an additional prognostic tool, correlating with chromosomal status and IVF outcome. Developmental ability and morphological evaluation of the embryo on days 2-3 remains the most used and valid method of selection, even though it is not sufficient to select embryos with the higher implantation potential. Blastocyst culture is another possible strategy for selecting the ideal embryo with theoretical, reduced risk of aneuploidies, though not all major chromosomal aberrations are excluded by prolonged in-vitro-culture. Concerning micro-manipulation of embryo such as hatching or cleaning or cytoplasm transfer, only controversial data are still available. In the field of ART, recent meta-analysis could not conclude to a positive effect concerning hatching, blastocyst culture or systematic PGD-AS (preimplantation genetic diagnosis with aneuploidy screening). Beside the technological aspect, Quality Management System is of great importance. Staff development and monitoring of staff performance in the IVF laboratory has to be considered in the next future.

Paternal and maternal factors in preimplantation embryogenesis: interaction with the biochemical environment

Paternal effect on embryonic development occurs as early as fertilization. Incorrect formation of the spermatozoon due to centrosome defects and abnormal concentrations of any components involved in the activation process lead to failure immediately or in the subsequent cell cycles. Sperm chromosomal abnormalities result in early embryo developmental arrests. Generally poor spermatozoa lead to poor blastocyst formation. Sperm DNA fragmentation may impair even late post-implantation development. The DNA repair capacity of the oocytes is of major importance. Early preimplantation development, i.e. until maternal to zygotic transition, is maternally driven. Maternal mRNAs and proteins are of major importance, as there is an unavoidable turnover of these reserves. Polyadenylation of these mRNAs is precisely controlled, in order to avoid too early or too late transcription and translation of the housekeeping genes. An important set of maternal regulations, such as DNA stability, transcriptional regulation and protection against oxidative stress, are impaired by age. The embryo biochemical endogenous pool is very important and may depend upon the environment, i.e. the culture medium. Paternal, maternal and environmental factors are unavoidable parameters; they become evident when age impairs oocyte quality.

The influence of cigarette smoking on human sperm quality and DNA fragmentation

The aim of the present study was to evaluate consequences of cigarette smoking on male gametes. In this prospective study, sperm parameters such as sperm density, motility, viability and normal morphology were measured according to the WHO criteria. In addition to these standard parameters, we analysed the degree of DNA fragmentation in spermatozoa using the TUNEL-assay with flow cytometry detection in 57 non-smokers and 51 smokers seeking for infertility counselling. The smoking intoxication was assessed by questionnaire and measured with the CO-Tester. We show that smokers' spermatozoa have a significantly higher DNA fragmentation than non-smokers (32% versus 25.9%, p<0.01). In contrast there is no significant difference in conventional parameters between smokers and non-smokers. The degree of sperm DNA fragmentation is not significantly correlated with any of the conventional parameters. These findings suggest that cigarette smoking may have deleterious effects on sperm nuclear quality and that sperm DNA fragmentation can therefore be considered as an independent parameter with diagnostic, prognostic, and strategic value in the treatment of infertility.