Oxidative Stress in Sperm Biology- a Review

Dairy Cattle Physiology Division, National Dairy Research Institute, Karnal 132 001, India Received: 30-07-2011 Accepted: 18-08-2011 ABSTRACT Oxidative stress occurs when the production of potentially destructive reactive oxygen species (ROS) exceeds the bodies own natural antioxidant defenses, resulting in cellular damage. ROS, defined as including oxygen ions, free radicals and peroxides, are generated by sperm and seminal leukocytes within semen and produce infertility by two key mechanisms. First, they damage the sperm membrane, decreasing sperm motility and its ability to fuse with the oocyte. Second, ROS can alter the sperm DNA, resulting in the passage of defective paternal DNA on to the conceptus. Spermatozoa, like all cells living in aerobic conditions face the oxygen (O2) paradox: O2 is required to support life, but its metabolites such as ROS can modify sperm cell functions, endanger sperm cell survival. ROS in small amount is necessary to maintain normal spermatozoa function. It is not surprising that a battery of different antioxidants is available to protect spermatozoa against oxidants. Spermatozoa are particularly susceptible to oxidative stress induced damage because their plasma membranes contain large quantities of polyunsaturated fatty acids (PUFA) and their cytoplasm contains low concentrations of scavenging enzymes. In addition, the intracellular antioxidant enzymes cannot protect the plasma membrane that surrounds the acrosome and the tail, forcing spermatozoa to supplement their limited intrinsic antioxidant defenses by depending on the protection afforded by the seminal plasma. Oxidative stress attacks not only the fluidity of the sperm plasma membrane, but also the integrity of DNA in the sperm nucleus. High content of polyunsaturated fatty acids in the plasma membrane and a low level of antioxidant in the sperm cytoplasm make them susceptible to oxidative stress and peroxidative attack during preservation. Defective and dead spermatozoa, major source of ROS during cryopreservation Cryoprotective media with antioxidants to overcome cryodamage.