Biological Relevance of Free Radicals in the Process of Physiological Capacitation and Cryocapacitation

Abstract

Before fertilization, spermatozoa must undergo a process called capacitation in order to fulfill their fertilization potential. This includes a series of structural, biochemical, and functional changes before a subsequent acrosome reaction and fusion with the oocyte. However, low temperatures during cryopreservation may induce a premature activation of capacitation-like changes, also known as cryocapacitation, immediately after thawing, which may lead to a decreased viability, motility, and fertilization ability of cryopreserved spermatozoa. Furthermore, cryopreservation is responsible for the overgeneration of reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radicals, which may result in the development of oxidative stress, cell membrane damage, and lipid peroxidation. Despite that, both capacitation and cryocapacitation are considered to be oxidative events; however, potential beneficial or detrimental effects of ROS depend on a wide array of circumstances. This review summarizes the available information on the role of free radicals in the process of capacitation and cryocapacitation of spermatozoa.