Influence of ROS on Ovarian Functions

High level of ROS (Reactive Oxygen Species), due to an increased production of oxidant species and/or a decreased efficacy of antioxidant system, can lead to oxidative stress (OS) an emerging health risk factor involved in the aging and in many diseases, either in humans or in animals. ROS are a double-edged sword – they serve as key signal molecules in physiological processes, but also have a role in pathological processes involving the female reproductive tract.ROS affect multiple physiological processes in reproduction and fertility, from oocyte maturation to fertilization, embryo development and pregnancy. Several studies indicate that follicular atresia in mammalian species due to the accumulation of toxic metabolites often results from oxidative stress. It has been suggested that ROS under moderate concentrations play a role in signal transduction processes involved in growth and protection from apoptosis. Conversely, increase of ROS levels is primarily responsible for the alteration of macromolecules, such as lipids, proteins and nucleic acids, that lead to significant damage of cell structures and thereby cause oxidative stress. To prevent damage due to ROS, cells possess a number of non-enzymatic and enzymatic antioxidants. Non-enzymatic antioxidants include vitamin C, glutathione and vitamin E. Enzymatic antioxidants consist of superoxide dismutases (MnSOD and Cu/ZnSOD) that convert superoxide into hydrogen peroxide; glutathione peroxidase (GPX) and catalase (CAT) which neutralize hydrogen peroxide. Intracellular homeostasis is ensured by the complex interaction between pro-oxidants and antioxidants.This chapter describes gathering evidence that oxidative stress is involved in ovarian physio-pathology caused by diverse stimuli. There is strong evidence that ROS are involved in initiation of apoptosis in antral follicles caused by several chemical and physical agents, in the fluid follicular environment, influencing the folliculogenesis and the steroidogenesis. Although less attention has been focused on the roles of ROS in primordial and primary follicle death, several studies have shown protective effects of antioxidants and/or evidence of oxidative damage, suggesting that ROS may play a role in these smaller follicles as well. Oxidative damage to lipids in the oocyte has been implicated as a cause of persistently poor oocyte quality. Developing germ cells in the fetal ovary have also been shown to be sensitive to toxicants and ionizing radiation, which induce oxidative stress. Recent studies have begun to elucidate the mechanisms by which ROS mediate ovarian toxicity. It has been investigated the role of antioxidant enzymes, such as catalase, glutathione peroxidase and the SOD isoforms in maintaining low levels of oxidative stress.The literature provides some evidence of oxidative stress influencing the entire reproductive cycle. OS plays a role in multiple physiological processes from oocyte maturation to fertilization and embryo development. An increasing number of published studies have pointed towards increased importance of the role of OS in female reproduction. Of course, there is much to learn about this topic, whereby it cannot be underestimated