[Mechanism of the dysfunction of the bull spermatozoa treated with cadmium]

Heavy metals such as cadmium (Cd) are widely distributed in the environment as industrial pollutants and characterized by their ability to affect the male reproductive system. The objective of the present study was to test the effect of Cd in the concentration range from 10 to 1000 micromol/L, in vitro, on the membrane and DNA integrity, motility, and ability of sperm to undergo acrosomal exocytosis in Holstein bull spermatozoa.

Bull semen samples were processed for sperm analyses using semen-diluting fluid, PBS. Membrane integrity of the processed bull sperm was evaluated by lipoperoxidation (LPO) test. Gelatin digestion test was performed to determine the ability of bull spermatozoa to undergo acrosomal exocytosis. Single cell gel electrophoresis (SCGE) assay was performed to detect the DNA strand breaks and alkali labile damages in the individual cell.

We found a significant increase in the lipoperoxidation (LPO) indicating the deleterious effect of Cd on the sperm membrane integrity. This effect was prominent at the concentration of 1000 micromol/L Cd. There was a negative correlation between LPO rate and the percentage of motile spermatozoa (r = -0.94, P < 0.001). The gelatin digestion test indicated that Cd caused a decline in the percentage of acrosomal exocytosis of bull spermatozoa. A reverse correlation was also found between LPO rate and the percentage of halos (r = -0.97, P < 0.001). Data obtained from the comet assay revealed that Cd was capable of inducing DNA breaks in the sperm nuclei. Almost 93% of DNA damages were double-stranded breaks. The correlation between LPO rate and the percentage of DNA breaks was found to be 0.95 (P < 0.001).

Collectively, Cd induced membrane impairments, lowered motility, DNA breaks and a decreased rate in the acrosome reaction of bull spermatozoa, leading to sperm dysfunction. Entering Cd in the male gonads and seminal plasma may exert deleterious effects on the animal sperm cells.