Oxidative stress, male infertility and the role of carnitines.

Oxidative stress has been shown to be a major cause of male infertility; a large proportion of infertile men have elevated levels of seminal reactive oxygen species (ROS). High concentrations of ROS cause sperm pathology such as ATP depletion leading to insufficient axonemal phosphorylation, lipid peroxidation and loss of motility and viability. L-carnitine, a naturally occurring enzymatic antioxidant, is a necessary factor in the utilization of long chain fatty acids to produce energy. Furthermore, it plays a pivotal role in the maturation of spermatozoa within the male reproductive tract. Epididymal plasma contains the highest levels of L-carnitine found in the human body, and initiation of sperm motility occurs in parallel to L-carnitine increase in the epididymal lumen. It is known that L-carnitine prevents the formation of ROS, scavenges free radicals and protects cells from peroxidative stress. Moreover, it plays a key role in sperm metabolism by providing readily available energy for use by spermatozoa, which positively affects sperm motility, maturation and the spermatogenic process. L-carnitine and its derivatives have been proposed recently for treatment of male infertility, and a number of controlled and uncontrolled human and animal studies have been conducted to indicate their possible application. As a result, antioxidant therapy with carnitines may represent a new nonhormonal option within a broader therapeutic strategy in men with ROS-mediated infertility.