Oxidative Stress and Male Infertility

Infertility has affected approximately 10–15% of the population worldwide and has shown an increasing trend from the last decade. The Reactive Oxygen and Nitrogen Species (ROS/RNS) are involved in the aetiology of infertility, especially in male infertility. Various strategies were designed to remove or decrease the production of ROS and RNS in spermatozoa, in particular during in vitro fertilization. However, research has shown that spermatozoa naturally produced a variety of ROS/RNS recently, which included superoxide anion radical (O2·−), hydrogen peroxide and NO. These reactive species, in particular NO, are essential in regulating sperm capacitation and the acrosome reaction, and need to be acquired by sperm to achieve fertilization potential. In addition, the mitochondrial function is positively correlated with sperm fertilization potential and quality, and the NO and NO precursors increase the sperm motility by increasing energy production in mitochondria. Therefore, the potential implementation of new redox-active substances that modulate the content of NO in spermatozoa should be focused to increase fertility. A free radical is a molecule or element with an unpaired electron which is extremely reactive to become electronically stable. Reactive Oxygen Species (ROS) in infertility include: peroxyl (^•ROO⁻) and hydroxyl (^•OH) radicals, superoxide (^•O₂⁻) anion, and H₂O₂., nitric oxide (NO) and peroxynitrite anion (ONOO⁻). Oxidative stress describes an imbalance system of oxidation and reduction reactions, leading to generation of excess oxidants or molecules that accept an electron from another reactant. This leads to potential cellular and DNA damage when ROS are greater than the antioxidant carrying capacity.