They are not only the smallest but also the most polarized cells in the body that fulfill their functions even outside the body in a different individual, the female genital tract. To maintain this extreme polarization, spermatozoa exhibit a specially composed plasma membrane containing an extraordinary amount of polyunsaturated fatty acids (PUFA). This high PUFA content is essential for normal sperm function, as it is the foundation for the sperm plasma membrane´s high fluidity. In turn, membrane fluidity is directly related to normal sperm functions which can actually be regarded as membrane functions.
Furthermore, spermatozoa are characterized by their very special morphological features, which comprise not only the extreme polarization but also the dramatic loss of most of the cytoplasm during spermatogenesis. As a result, the male germ cells exhibit an inevitable lack of intrinsic antioxidative protection by ROS scavengers such as catalase, glutathione peroxidase (GPx) or superoxide dismutase (SOD) as well as non-enzymatic molecules such as vitamin C, vitamin E and gluthathione. Both these factors, the intrinsic lack of antioxidant protection together with the extraordinary high content of PUFA in the plasma membrane, make the male germ cell extremely vulnerable to oxidative stress. Since developing spermatozoa have very limited ability to DNA repair, replenishment and regeneration of glutathione, this oxidative stress does lead not only to disturbed sperm functions but also to damaged DNA.