I-3: Reactive Oxygen Species: A Dilemma for

Spermatozoa are very special cells and constantly exposed to the interphase between oxidative stress through high amounts of reactive oxygen species (ROS) and leukocytes, and reduction by means of scavengers and antioxidants. Considering the very special functions of spermatozoa as being the only cells with such high polarization and exerting their functions outside the body, even in a different individual, the female genital tract, the membranes of these cells are chemically composed of an extraordinary high amount of polyunsaturated fatty acids of about 50%, of which docosahexaenoic acid (C22: 6), an ω3 fatty acid, amounts to 43%. This high presence of double bonds renders the male germ cell very susceptible to oxidative stress. Oxidative stress is defined as an imbalance between oxidation and reduction towards the oxidative status. As a result, ROS deriving from both leukocytes and the male germ cells themselves not only initiate a process called ‘lipid peroxidation’, but also causes other damages to the sperm cell like direct oxidative damage of the DNA. On the other hand, a certain limited amount of ROS is required by the sperm cell in order to trigger vital physiological reactions in cells. These physiological processes include capacitation or the acrosome reaction as central points at the interphase of gamete interaction. A number of studies revealed that spermatozoa from patients treated with antioxidants showed lower DNA fragmentation and a higher fertilizing capacity, while others did not see any effect or even a negative effect. Thus, the treatment of patients with antioxidants to compensate the oxidative stress is still highly debated and one cannot deny that an uncontrolled treatment with antioxidants might result in a paradoxical situation where the system might derail towards the reduced status, which is also unphysiological and can even induce cancer. This paradox is called the ‘antioxidant paradox’. Therefore, a proper andrological diagnostic work-up, including the evaluation of ROS levels and the antioxidant capacity of the semen has to be carried out in advance. Essentially, the equilibrium between oxidation and scavenging of vital amounts of ROS must be kept in fine balance in order for spermatozoa to function properly.