Oxidative stress (OS) has been considered a major contributory factor to the infertility. Oxidative stress is the result of imbalance between the reactive oxygen species (ROS) and antioxidants in the body which can lead to sperm damage, deformity, and eventually male infertility. Although high concentrations of the ROS cause sperm pathology (ATP depletion) leading to insufficient axonemal phosphorylation, lipid peroxidation, and loss of motility and viability but, many evidences demonstrate that low and controlled concentrations of these ROS play an important role in sperm physiological processes such as capacitation, acrosome reaction, and signaling processes to ensure fertilization. The supplementation of a cryopreservation extender with antioxidant has been shown to provide a cryoprotective effect on mammalian sperm quality. This paper reviews the impacts of oxidative stress and reactive oxygen species on spermatozoa functions, causes of ROS generation, and antioxidative strategies to reduce OS. In addition, we also highlight the emerging concept of utilizing OS as a tool of contraception.

Numerous factors influence male fertility, one of these being the oxidative stress, which has elicited enormous interest recently. In sperm, induction of oxidation decreases motility and viability but increases lipid peroxidation (LPO). The optimum dose of ferrous ascorbate (FeAA: FeSO 4 1 ascorbic acid) for inducing oxidative stress by affecting motility, viability and LPO has been ascertained in local crossbred cattle bull spermatozoa. The fractions of spermatozoa suspended in 2.9% sodium citrate were subjected to three doses of FeAA (100 : 500, 150 : 750, 200 : 1000; mmol/l FeSO 4 : mmol/l ascorbic acid). These fractions were assessed for various parameters. Increase in the incubation period and promoter concentration induced a decrease in motility and viability, but an increase in LPO. Among three doses of FeAA, 150 : 750 mmol/l ascorbic acid is suggested to be the optimum/best dose as it induces the oxidative stress/LPO to a significant extent and also maintains better motility and viability as compared with the other two doses, and such conditions may enhance the fertilising potential of bull spermatozoa.

Reactive oxygen species (ROS) are generated by sperm metabolism. While, ROS are required for maturation, capacitation and acrosome reaction, they also modify many peroxidable cellular compounds. There is production of ROS during cryopreservation and frozen spermatozoa are highly sensitive to lipid peroxidation (LPO). Antioxidants exert a protective effect on the plasma membrane of frozen bovine sperm preserving both metabolic activity and cellular viability. Manganese (Mn++) is proved to be a chain breaking antioxidant in biological system. Therefore, we examined the role of (Mn++) during cryopreservation of cattle bull semen. Semen was divided into four parts and cryopreserved in egg-yolk-citrate extender + glycerol (EYC-G), EYC-G + 100 µM of Mn++, EYC-G + 150 µM of Mn++ and EYC-G + 200 µM of Mn++. After four hours of cooling and 24 hrs of freezing, the spermatozoa were examined for percentage motility, Hypo-osmotic swelling (HOS), LPO and protein leakage. Addition of manganese to the semen during cryopreservation showed a protective effect and accounted for an increase in semen quality parameters [percentage motility, HOS percent and decrease in malondialdehyde (MDA) production and protein leakage]. The effect of manganese on motility and HOS was non-significant (p < 0.05) in cooled spermatozoa but significant with 150 µM of Mn++ in frozen-thawed spermatozoa. MDA production and protein leakage decreased to a significant and maximum level (p < 0.05) on addition of 200 µM of manganese. The addition of manganese to EYC-G dilutor will improve the quality/fertility of semen, which will result in improvement of in vitro fertilization and artificial insemination success rate.

Summary. The

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