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 × 10(6) 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.

Human sperm DNA oxidation, motility and viability in the presence of L-carnitine during in vitro incubation and centrifugation.

In vitro incubation and centrifugation is known to decrease human sperm quality. In the human body, besides its antioxidant effects, L-carnitine (LC) facilitates the transport of activated fatty acids from the cytosol to the mitochondrial matrix. In this study, we investigated the effect of LC on human sperm motility, viability and DNA oxidation after incubation and centrifugation, following the sperm preparation protocols of assisted reproduction. Normozoospermic semen samples (n = 55) were analysed according to the World Health Organization (WHO) guidelines. LC concentrations that are not toxic to spermatozoa as determined by sperm motility and viability were standardised after 2 and 4 h of incubation at 37 °C. Semen samples to which the optimal LC concentrations were added were also centrifuged for 20 min at 300 g and analysed for sperm motility, viability and DNA oxidation. Sperm motility was improved at 0.5 mg ml(-1) LC after incubation and centrifugation with 5 × 10(6) sperm ml(-1). Higher concentration of LC (50 mg ml(-1)) significantly decreased sperm motility and viability. LC did not alter the baseline of sperm DNA oxidation during both incubation and centrifugation. In conclusion, LC may enhance sperm motility following incubation and centrifugation, while it might not affect sperm viability and DNA oxidation.

Catalytic two-electron reductions of N2O and N3- by myoglobin in surfactant films.

Myoglobin (Mb), in films of dimethyldidodecylammonium bromide (ddab) on graphite electrodes, is used as a catalyst to mediate the electrochemical reduction of nitrous oxide (N2O) as well as the isoelectronic ion azide (N3-) in aqueous solutions. The electrocatalytic reductions are characterized by a rate-dependent irreversibility in cyclic voltammograms of Mb/ddab in the presence of the substrates. Bulk electrolysis shows that the reduction of 15N15NO by Mb/ddab yields 15N15N as shown by GC/MS. The catalytic reduction of azide results in almost quantitative formation of ammonia. These electrocatalytic processes are rationalized as two-electron reductions, with the catalyst cycling between the Fe(I) and Fe(III) states of Mb. To our knowledge, this is the first characterization of N2O reduction by an Fe porphyrin or heme protein.