Although DNA damage in human spermatozoa is associated with adverse health effects, its origin is not fully understood. Therefore, we assessed biomarkers in ejaculates that retrospectively reflect processes that occurred in the epididymis or testis. Smoking increased the amount of DNA strand breaks (P<0.01), and enhanced the presence of vitamin C radicals in seminal plasma. In vitro, vitamin C protected mature spermatozoa against DNA damage, but this protection appeared to be insufficient in vivo. CAT and DDIT4 expression in spermatozoa were higher in smokers than in nonsmokers, but were not related to DNA damage. CAT and DDIT4 expression were inversely related with sperm count (P=0.039 and 0.024 resp.), but no effect was observed for SOD2 expression. These data indicate that spermatozoa of smokers encounter higher levels of oxidative stress. Expression of antioxidant enzymes and seminal vitamin C were insufficient to provide full protection of spermatozoa against DNA damage.
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