Cryoprotective effect of l‐carnitine on motility,vitality and DNA oxidation of human spermatozoa

Successful cryopreservation for human spermatozoa markedly influences the reproductive outcomes of assisted reproductive technologies. But in spite of its usefulness, cryopreservation significantly decreases sperm quality. l ‐carnitine has been found to improve the quality of spermatozoa in selected cases with male infertility. Here, we examined the efficacy of l ‐carnitine in improving sperm motility and vitality and reducing sperm DNA oxidation during cryopreservation. Semen samples from infertile patients (n = 22) were collected and analysed. Cryopreservation medium supplemented with l ‐carnitine was mixed with the semen at a ratio of 1 : 1 (v/v). The final l ‐carnitine concentration in each cryovial was 0.5 mg ml^?1 per 5 × 10⁶ cell ml^?1. Controls were cryopreserved without addition of l ‐carnitine. After 24 h of cryopreservation, thawed sperm samples were analysed for motility, vitality and DNA oxidation. Sperm vitality was assessed by the eosin–nigrosin test, while sperm DNA oxidation was measured by flow cytometry. Addition of l ‐carnitine significantly improved sperm motility and vitality (P < 0.05) compared with the control. The flow cytometry experiment showed no statistical difference (P > 0.05) in the levels of DNA oxidation between samples and controls. In conclusion, l ‐carnitine improves human sperm motility and vitality, but has no effect on sperm DNA oxidation after cryopreservation.