Abstract
Research question: Does regular smoking affect semen quality and the levels of DNA methylation in mature human spermatozoa?
Design: Spermatozoa from 109 men were evaluated (55 smokers and 54 non-smokers). DNA was extracted from purified spermatozoa, and DNA methylation was quantified by enzyme-linked immunosorbent assay (ELISA).
Results: Global DNA methylation of non-smokers is significantly lower (P < 0.001) than that of smokers (4.85 +/- 2.72 and 7.08 +/- 1.77 ng/mu l, respectively). Moreover, the mean global DNA methylation levels were significantly correlated (r = 0.22; P = 0.02) with non-condensed chromatin in the spermatozoa. Levels of non-condensed chromatin were significantly higher (P < 0.001) in smokers (29.75 +/- 9.38%) compared with non-smokers (20.96 +/- 11.31%). Furthermore, global sperm DNA methylation was negatively correlated with high significance (P < 0.010) with sperm: count (r = -0.27), motility (r = -0.30) and vitality (r = -0.26).
Conclusion: Smoking interferes with DNA methylation. Also, DNA methylation is significantly correlated with sperm parameters and sperm non-condensed chromatin. These data emphasize another detrimental effect of smoking on male fertility. DNA methylation may, therefore, be considered as a fertility marker in men.