Addition of l-carnitine to the freezing extender improves post-thaw sperm quality of Okinawan native Agu pig

Abstract

The objective of the present study was to establish whether the addition of l-carnitine (LC), which exhibits antioxidant activity, to the freezing extender improves the quality of cryopreserved Okinawan native Agu pig sperm. Ejaculated sperm frozen in an extender supplemented with 0, 1, 2.5, or 5 mM LC was thawed, and the integrities of mitochondria and the plasmalemma and other sperm characteristics were evaluated. The treatment with different concentrations of LC effectively improved sperm motility, mitochondrial and plasmalemmal integrities, and the proteolytic activity of acrosomal contents after freeze-thawing (P < 0.05). The proportion of post-thaw sperm possessing intact mitochondria and plasmalemma and higher proteolytic activity of acrosomal contents was markedly higher among sperm frozen in the presence of 2.5 mM LC than among sperm frozen in the extender without LC (P < 0.05). Furthermore, although the addition of LC to the freezing extender had no effect on disturbance of DNA damage and caspase activity, sperm treated with 2.5 mM LC during freezing exhibited significantly higher penetrability into matured oocytes in vitro than untreated sperm. Collectively, these results indicate that the addition of LC to the freezing extender effectively improved the post-thaw quality of Agu pig sperm by preventing mitochondrial dysfunction caused by oxidative stress during cryopreservation.