Title: Sperm DNA Damage as Measured by the Sperm Chromatin Structure Assay (SCSA) Does Not Predict Sperm Survival Rate
Abstract: The percentage of sperm with high levels of DNA damage, the DNA fragmentation index (% DFI), has been shown to correlate with abnormal semen parameters and reduced pregnancy outcome in IVF. Sperm survival rates, the percentage of sperm that maintain their motility after sperm processing and 24h incubation, have also been shown to be predictive of IVF outcome. Thus, we designed a study to evaluate the relationship between sperm survival test results and sperm DNA damage anticipating that they would be highly correlated. Retrospective analysis of data from 102 consecutive completed IVF cases in a private infertility center. Semen samples were collected after 2-7 days abstinence from male patients undergoing pre-IVF screening. A routine semen analysis and sperm processing by density gradient centrifugation was performed, with an aliquot of semen frozen for the SCSA within 1h of collection. The washed sperm pellet was resuspended in HTF + 5% HSA at 10-20 M/ml and motility of sperm assessed at 0h and following incubation at 37°C in 5% CO2 for 24h. Sperm survival percentage rates were expressed as the (24h motility/0h motility) x100. Coefficients of correlation were calculated using Spearman's rank correlation analysis. The study population consisted of 102 men (mean age 39.5 ± 6.0 years, range 20 to 53 years) of whom 39 had at least one abnormal semen analysis parameter, 13 had an elevated DFI (>30%), and 16 had abnormally low sperm survival rate < 75% (mean 85% ± 14.3). Sperm DNA damage correlated significantly positively with age (r = 0.39, p < 0.0001). Of the conventional semen parameters, morphology (r = -0.36, p < 0.0002) and motility (r = -0.45, p < 0.0001) had a statistically significant negative association with DFI . Motility after processing at 0h (r = -0.53, p < 0.0001) and 24 h (r = -0.4, p < 0.0001) also correlated significantly negatively with DFI. Unexpectedly, however, there was no significant correlation between DFI and sperm survival rate. The lack of association between DFI and sperm survival rate was unexpected because DNA fragmentation has been reported to correlate with oxidative stress, and sperm motility loss in vitro is believed to result in part from lipid peroxidation of the plasma membrane. One possible explanation for this finding is that sperm processing preferentially excludes sperm with high levels of DNA damage, thus the DFI values for semen were not predictive of the percentage of sperm with DNA damage in the sperm fraction used for the motility assay. This may also explain the inconsistent results seen in studies assessing the utility of SCSA to predict IVF and ICSI outcome. Another possible explanation is that factors other than oxidative damage may play a more critical role in determining the rate of motility loss.