Sperm Function Test
The intracellular enzyme creatine kinase (CK) can more accurately predict whether a given individual's sperm have good fertilizing capacity. Cells that require a lot of energy, such as male gametes, have high CK activity which is considered a key enzyme in the generation, transport and use of energy. For the sperm, CK works as a fuel for it to move actively, as it facilitates the maintenance of levels of important substances for energy generation. To understand how it works, we need to understand how sperm is formed.
OXYGEN FREE RADICALS
Toxicity arising from excess exposure to oxygen (O2) is an inherent challenge to aerobic life. The harmful effects of O2 are attributed to its reduced form (superoxide radical: O2-) or its by-products combined with other highly unstable molecules (hydrogen peroxide: H2O2; hydroxyl radical: HO-). These substances, called oxygen free radicals (from English Reactive Oxygen Species; ROS) have harmful effects in cascade with the surrounding cells in an almost instantaneous way. Cell survival in the face of free radical attack depends, therefore, on the balance between the processes of production and elimination of ROS.
Any circumstance that unbalances these two processes can induce the installation of a condition called oxidative stress, in which the formation of free radicals (oxidizing agents) to antioxidants prevails.
ACROMOSOMIC REACTION
The acrosome is the region of the head of the sperm that is membrane-coated and composed of enzymes. These enzymes have the biological function of breaking down the cell layers that surround the oocyte (Cumulus oophorus and zona pellucida), thus allowing sperm penetration and fertilization. The release of these enzymes is called an acrosome reaction.
LIPID PEROXIDATION
The sperm membrane is composed of polyunsaturated and target fatty acids (PUFAs) that guarantee the necessary fluidity for its movement during the fertilization process. Due to their chemical composition, PUFAs are targets of oxygen free radicals (ROS), small molecules from sperm metabolism and from external sources such as leukocytes present in genitourinary tract infections, drug abuse, or varicocele. Under normal conditions, ROS are countered by a defense system made up of antioxidants, however, several medical conditions can reduce the antioxidant capacity or increase the production of ROS. When the antioxidant capacity is ineffective, ROS initiate an attack on the sperm membrane and initiate a cascade of cellular changes that compromise their fertilization potential. Therefore, membrane changes are early markers of sperm changes.
References:
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Huszar G, Corrales M, and Vigue L: Correlation between creatine phosphokinase sperm activity and sperm concentration in normospermic and oligospermic men. Gamete Res 19: 67–75, 1988.
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Huszar G, Vigue L, and Corrales M: Sperm creatine kinase activity in fertile and infertile men. J Androl 11: 40–46, 1990.
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Huszar G, and Vigue L: Correlation between the rate of lipid peroxidation and cellular maturity as measured by creatine kinase activity in human spermatozoa. J Androl 15: 71–77, 1994.
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Aitken RJ, Krausz C, and Buckingham D: Relationships between biochemical markers for residual sperm cytoplasm, reactive oxygen species generation, and the presence of leukocytes and precursor germ cells in human sperm suspensions. Mol Reprod Dev 39: 268–279, 1994
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Sidhu RS, Hallak J, Sharma RK, et al: Relationship between creatine kinase levels and clinical diagnosis of infertility. J Assist Reprod Genet 15: 188–192, 1998.
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Hallak J, Sharma RK, Pasqualotto FF, Ranganathan P, Thomas AJ Jr, Agarwal A. Creatine kinase as an indicator of sperm quality and maturity in men with oligospermia. Urology. 2001 Sep;58(3):446-51.