Does advanced paternal age affect global DNA methylation of human spermatozoa and intracytoplasmic sperm injection outcome?

OBJECTIVE: This study was performed to (I) evaluate the potential effect of advanced paternal age on global DNA methylation in spermatozoa, and (II) to investigate the association between the outcome of intracytoplasmic sperm injection (ICSI), semen parameters, and advanced paternal age. MATERIAL AND METHODS: This study comprised 230 semen samples collected from males with a mean age of 38.2±8.5 years. Medical records were used to gather clinical information related to the female partner. The participants were divided into three groups depending on age: age <30 years; age 30-40 years; and age >40 years. The DNA was extracted from purified spermatozoa. Then the sperm global DNA methylation, sperm DNA fragmentation, and chromatin decondensation were evaluated by an ELISA, TUNEL, and Chromomycin A3 staining, respectively. RESULTS: The sample counts were n=50 (21.8%), n=90 (39.1%) and n=90 (39.1%) for the <30, 30-40 and >40 year age-groups, respectively. A significant variation was found in the age of males included in this study (p<0.001). There was a significant reduction in sperm count, total motility, and non-progressive motility in the older group compared to the younger group (p<0.001). There was also a significant elevation in chromatin decondensation, DNA fragmentation, and global DNA methylation of spermatozoa in the older age group (p<0.001). Finally, there was a significant positive correlation between the percentage of non-motile sperm, sperm chromatin decondensation, DNA fragmentation, global DNA methylation status, and paternal age (p<0.001). CONCLUSION: These results suggest that advanced paternal age increased the DNA fragmentation, chromatin decondensation, and global DNA methylation level in human spermatozoa, which negatively affects the ICSI outcomes in couples undergoing ICSI cycles.