Objective: To study the effects of L-carnitine (LC) on cryopreserved human sperm.
Methods: Ten semen samples were collected from normal sperm donors, each divided into six groups, fresh ejaculate (FE), non-LC cryopreservation (non-LC), and cryopreservation with LC at 1 mmol/L (LC-1), 2.5 mmol/L (LC-2), 5 mmol/L (LC-3) and 10 mmol/L (LC-4), respectively. The optimal concentration of LC was identified based on the motility and motion parameters of the post-thaw sperm. The plasma membrane integrity (PMI) of the sperm was assessed by eosin-nigrosin staining, their mitochondrial membrane potential (MMP) monitored by JC-1 assay, and the level of sperm ROS measured by the fluorescent probe DCFH-DA, followed by analysis of the mechanisms of LC protecting sperm against cryopreservation injury.
Results: Compared with the sperm in the FE group, the post-thaw sperm in the non-LC and LC groups showed significantly decreased progressive motility, average path velocity (VAP), straight line velocity (VSP) and curvilinear velocity (VCP) (P < 0.05). In comparison with the non-LC group, the LC-3 group exhibited a remarkably higher percentage of progressively motile sperm (［41.9 ± 4.6］ vs ［47.0 ± 4.3］%, P = 0.0261) and VAP (［34.9 ± 2.6］ vs ［38.9 ± 4.2］ μm/s, P = 0.0152), indicating that the optimal concentration of LC was 5 mmol/L. Both PMI and MMP were significantly lower in the non-LC than in the FE group (［52.7 ± 5.7］ vs ［75.5 ± 5.4］%, P < 0.01 and ［44.5 ± 3.5］ vs ［57.3 ± 4.4］%, P < 0.01), but higher in the LC groups (［70.1 ± 8.2］% and ［50.3 ± 3.4］%) than in the non-LC group (P < 0.01 and P < 0.05). The level of sperm ROS, however, was markedly higher in the non-LC than in the FE group (［12.5 ± 3.9］ vs ［6.8 ± 2.4］, P < 0.01) but lower in the LC groups (［8.4 ± 5.3］%) than in the non-LC group (P = 0.05).
Conclusions: L-carnitine can improve the motility and motion parameters of cryopreserved human sperm by reducing sperm ROS, enhancing sperm mitochondrial membrane potential and protecting the sperm plasma membrane.
Keywords: fertility preservation; mitochondrial membrane potential; reactive oxygen species; sperm cryopreservation; L-carnitine.