The status of global DNA methylation in the spermatozoa of smokers and non-smokers

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/μl, 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.

Keywords: Dna methylation; Elisa; Protamines; Smoking; Sperm parameters.