The effects of cysteine and L-carnitine on the DNA integrity of post-thaw sperm of frozen buck semen

BACKGROUND: The addition of antioxidants to semen extenders is fundamental to limit oxidative changes resulting from cryopreservation. AIMS: This experiment was designed to clarify the effects of cysteine and L-carnitine (LC) on post-thaw sperm criteria. METHODS: Semen samples were collected once weekly from five mature Zaraibi bucks for 10 successive weeks. Fresh semen samples were evaluated for basic semen characteristics, and the accepted samples were pooled and divided into seven aliquots: control (Tris egg yolk extender), cysteine (2.5, 5 and 10 mM) and LC (2.5, 5 and 7.5 mM). Aliquots were diluted and subjected to cryopreservation procedures. After thawing, sperm criteria were evaluated regarding motility, viability, plasma membrane (hypo-osmotic swelling test, HOST) and acrosome integrity, total antioxidant capacity (TAC), level of malondialdehyde (MDA), and DNA comet assay. RESULTS: Addition of both 10 mM cysteine and 7.5 mM LC significantly increased post-thaw sperm motility, viability, HOST, and acrosome integrity. Comet assay revealed significant decreases in DNA damage with best results at 2.5 mM cysteine and 7.5 mM LC. Besides, 10 mM cysteine and 7.5 mM LC exhibited significant diminish in MDA levels. Cysteine was positively correlated with sperm viability, acrosome integrity, and comet, but negatively correlated with MDA and tail length. Positive correlations were declared between LC and progressive motility, viability, HOST and TAC, while negative correlations were found with MDA, comet, tail DNA, tail moment, and olive tail moment. CONCLUSION: Supplementing cysteine and LC to frozen buck semen improved sperm criteria and decreased DNA damage, possibly due to their effectiveness in the suppression of MDA formation.