DNA fragmentation and male infertility
In order for a spermatozoon to be fertile, the chromatin must decondense correctly after fertilization. Nuclear alterations, such as an abnormal chromatin structure, micro-deletions in the chromosome, or DNA fragmentation, will all reduce the sperm cell’s ability to produce a viable embryo.
Sperm DNA Fragmentation (SDF) is inversely related to the sperm cell’s ability to fertilize. Thus, when the percentage of cells with SDF is high, the less likely it will be that a spermatozoon from that semen sample successfully fertilizes an egg. Numerous scientific publications have demonstrated that an SDF value that exceeds 30% suggests sub-par sperm quality.
There exist numerous causes for Sperm DNA Fragmentation including: increased testicular temperature due to tight clothing, bouts of fever or varicocele; the presence of reactive oxygen species in the semen; the metabolic effects of overweight such as high insulin levels; smoking; certain drugs such as certain serotonin re-uptake inhibitors; and age.
Approximately 25% of infertile males present elevated SDF values. Approximately 10% of infertile patients presenting spermiograms that are considered normal have an SDF value that is considered pathological. Thus, Sperm DNA Fragmentation is considered an independent and complementary parameter in the assessment of semen quality to concentration, morphology and motility.
Measuring sperm DNA fragmentation confers clinicians and scientists the power to make more informed decisions in their daily practice and take action based on quantitative results:
- To distinguish which couples are suitable for treatment by intra-uterine insemination Sperm DNA fragmentation (SDF) is correlated with pregnancy outcome in intra-uterine insemination (IUI). When SDF levels are above 30%, the probability of delivery is significantly reduced from 19.0% to 1.5% (Table 1).
On the other hand, using in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) there is no such statistical correlation. This is probably because the selection of gametes and embryos in these techniques mitigates any effect that DNA damage in sperm cells may have over pregnancy outcome.
Thus, the measurement of SDF may serve to evaluate the most appropriate assisted reproduction technique. Couples presenting values of SDF above the 30% threshold should undergo IVF or ICSI in their first cycle, avoiding unnecessary IUI cycles.
The results obtained from Bungum et al., 2007 demonstrate that there is a greater number of deliveries when measuring SDF to determine the type of assisted reproduction technique. By selecting IVF or ICSI for couples presenting SDF values over 30%, there is a significant increase from 62 to 78 deliveries; that is, a 25.8% increase in the efficacy of the first cycle of assisted reproduction (Table 2).
Table 1 Deliveries per started cycle (%)
SDF<30% SDF>30% IUI 19,0% 1,5%* IVF Not significant ICSI Not significant * Odds Ratio (95% Confidence Interval) = 0.07 (0.01 – 0.48)
Table 2 Number of deliveries after the first cycle, taking into account SDF in the choice of assisted reproduction technique
WITHOUT MEASURING SDF WITH MEASURING SDF Total deliveries= 62
Total deliveries= 78
- To assess the quality of semen samples or donors for suitability Traditional WHO and Kruger criteria for the assessment of semen quality present several limitations:
(a) Traditional parameters are based on subjective observations and are prone to variability (Keel, 1990)
(b) A cut-off based on traditional parameters creates overlap between fertile and infertile populations and is thus of little predictive value (Aziz and Agarwal, 2008)
(c) A traditional analysis does not take into account the diverse array of biological properties of a spermatozoon - the most important of which being its ability to transmit an intact genome for the initiation of a viable pregnancy (Fernandez et al., 2005)
(d) Traditional parameters do not provide a diagnosis of the cause of male infertility (Agarwal and Allamaneni, 2005, Nallella et al., 2006)
A call has therefore been made by the international community to look beyond these criteria to improve seminal analysis (Aziz and Agarwal, 2008). In light of the available technology, SDF analysis provides the obvious answer for clinicians to assess in a rigorous manner the quality of semen samples from a donors or patients undergoing ART. - To assess the efficacy of medical interventions or treatments of infectious diseases (A)Varicocele
Infertile men with varicocele show a high proportion of sperm cells with intense nuclear DNA damage levels (Enciso et al., 2006). Varicocelectomy interventions have been demonstrated to significantly reduce SDF levels (Werthman et al., 2008). Studies are currently in progress showing that SDF levels decrease only transiently following varicocelectomy (Suresh et al. personal communication). Measurement of SDF values following varicocelectomy provide a much more quantifiable parameter than morphology in order to assess the efficacy of such an intervention. Measuring SDF allows the clinician to follow the progress of his patient and select the best semen sample from different time intervals following varicocelectomy for ART.
(B)Chlamydia trachomatis and Mycoplasma infections
The percentage of spermatozoa with fragmented DNA is significantly higher in patients with Chlamydia trachomatis and Mycoplasma infections (Gallegos et al., 2008). Antibiotic therapy in these patients was demonstrated to significantly reduce SDF levels(Gallegos et al., 2008). As opposed to other seminal parameters that are unaffected by these genitourinary tract infections, measurement of SDF levels allows clinicians to check the efficacy of antibiotic treatments and select the best semen samples for ART following treatment. - To provide answers to cases of unexplained infertility, ART failure or repeated abortions
High SDF levels have been shown to influence fertilization rate (Muriel et al., 2006a, Muriel et al., 2006b) and embryo quality (Velez de la Calle et al., 2008), leading to repeated pregnancy loss (Carrell et al., 2003) and low ART outcome (Henkel et al., 2004, Sakkas et al., 2004, Virro et al., 2004). Failures may therefore be due to poor sperm DNA quality. When facing an SDF value exceeding 30%, a clinician should consider factors that may influence sperm DNA fragmentation such as: medications, toxic compounds, fever, smoking, drugs, infectious diseases, varicocele, age and long abstinence. Importantly, high SDF values have been shown to be reversible using 1 g vitamin C and 1 g vitamin E daily for 2 months (Akmal et al., 2006, Greco et al., 2005)or Menevit (antioxidant)-one capsule per day for three months before ART (Tremellen et al., 2007) - To provide a quality control in improving semen handling or cryopreservation protocols
Numerous clinics are improving their standard operating procedures by evaluating how their semen handling procedures or cryopreservation protocols may be inducing iatrogenic damage to their semen samples.
