Tocopherol: uses in male reproduction

SATORRE MM; BREININGER E; BECONI MT

Tocopherol: Sources, Uses and Health Benefits

Nova Publishers

Año: 2012; p. 183 - 192

Oxidative stress is associated with increased rates of cell damage induced by molecules commonly called reactive oxygen species (ROS). ROS are highly oxidant agents which belong to free radicals molecules. Commonly reactive oxygen species, which have potential implications in reproductive biology, included hydrogen peroxide, peroxyl radicals and the very reactive hydroxyl radical. The ROS balance could be called “the creation and destruction balance”. In normal circumstances, there is an appropriate balance between pro- and antioxidants compounds, but when ROS production overcomes its destruction, we are encountered in an oxidative stress situation. It has been widely demonstrated that cryopreservation increases ROS generation and it is associated with oxidative stress. Reactive oxygen species alters cellular functions by mechanism that includes: peroxidation of fatty acid of the sperm plasma membrane, increase of DNA fragmentation, cytoskeleton modifications, alterations of the sperm axoneme development, and inhibition of spermatozoa- oocyte fusion. Lipid peroxidation is a harmful process that leads to loss of motility and decrease in fertilizing ability in spermatozoa of many species, including human. Lipid peroxidation is a non-controlled chain reaction that is initiated by a free radical attack on a double bond of a polyunsaturated fatty acid, resulting in the removal of hydrogen from a metilene group. The molecular rearrangement of this unstable carbon radical results in more stable configuration, a conjugated diene, which quickly reacts with oxygen to form a peroxyl radical. This radical could remove hydrogen from an adjacent polyunsaturated fatty acid to produce hydroperoxide and another lipid radical, leading to chain propagation of the lipid peroxidation. Spermatozoa are especially sensitive to peroxidative damage due to their content of polyunsaturated fatty acids in their plasma membrane. A complex antioxidant system is present in spermatozoa and seminal plasma to remove ROS and prevent its deleterious actions in physiological conditions. However, this antioxidant system does not enough powerful to completely prevent lipid peroxidation, especially during in vitro procedures, like cryopreservation, when ROS generation is increased as a result of the metabolic changes that occurs during these processes. The addition to dilution extenders of lipid or water-soluble antioxidants could minimize the toxic effect of lipid peroxidation. Alpha-tocopherol, a member of the vitamin E group, is a well known lipid peroxidation inhibitor in biological membranes. It is a primary antioxidant, which terminate the free radical chain reaction by donating hydrogen or electrons to free radicals, and converting them to more stable products. The addition of alpha-tocopherol to the freezing extender exerts a protective effect on the plasma membrane of cryopreserved bovine and boar spermatozoa. Even more, alpha-tocopherol improves post-thaw motility and acrosome integrity and decreases the level of capacitation-like changes and tyrosine phosphorylation, confirming that alpha-tocopherol protects sperm membrane from the cryopreservation effects.