Abstract
Decreased potential of spermatozoa fertility is closely associated with the development of oxidative stress and dysfunction of ion-transporting ATPases. Oxidative stress may have negative impact on the activity of membrane-bound enzymes, such as Са 2+ ,Мg 2+ -АТPase that is involved in maintaining calcium homeostasis in sperm cells. The aim of present work was to evaluate the exogenous H 2 O 2 effect on the main kinetic parameters of ATP hydrolysis by plasma membrane Са 2+ ,Мg 2+ -АТPase of spermatozoa of fertile (normozoospermia) and infertility (asthenozoospermia) men. Since Са 2+ ,Mg 2+ -АТPase is one of the targets for the reactive oxygen species and is directly involved in oxidative stress, spermatozoa obtained from normo- and asthenozoospermic samples were subjected to oxidative stress in the form of exogenous H 2 O 2 . Then ATP hydrolysis by thapsigargin-resistant Ca 2+ ,Mg 2+ -ATPase in media with different Ca 2+ concentrations was measured. An effective inhibitory effect of H 2 O 2 on the activity of the thapsigargin-resistant component of Са 2+ ,Мg 2+ -АТPase of sperm cells was demonstrated. In order to elucidate possible mechanisms of change in Ca 2+ ,Mg 2+ -ATPase activity under H 2 O 2 -induced oxidative stress, the concentration curves were linearized using Hanes–Woolf plot {[S]/V; [S]}. The apparent activation constant for Ca 2+ (K Ca2+ ) in sperm cell obtained from men with proven fertility was not changed, whereas in the asthenozoospermic samples, it was decreased almost twice under H 2 O 2 -induced oxidative stress. These results indicate that in normozoospermic samples H 2 O 2 implements its inhibitory action through the mechanism of uncompetitive inhibition of plasma membrane Ca 2+ ,Mg 2+ -ATPase activity. According to formal features of kinetics in the asthenozoospermic samples a mixed type of enzyme inhibition occurs under the oxidative stress induced by H 2 O 2 . Strategies to protect against a loss in Cа 2+ ,Mg 2+ -ATPase activity may be useful to prevent the harmful biochemical cascades leading to Ca 2+ overload and dysfunction of spermatozoa as a result of the oxidative stress.
Highlights
Oxidative stress is a major factor in development of male infertility
The depressed ATPase activity in the infertile men could be due to a reduction in the intracellular adenosine triphosphate and damage of spermal membranes caused by lipid peroxidation products [11]
A decrease in PMCA activity might derive from the nitration of tyrosine residues that may affect the catalytic activity of enzymes [16]
Summary
Oxidative stress is a major factor in development of male infertility. It is triggered by oxygen and oxygen-derived free radicals known as the reactive oxygen species (ROS). It was shown that low concentrations of H2O2 activate the antioxidant defense system in human sperm cells. Oxidative stress is the most apparent in sperm membranes. It triggers a loss of membrane integrity, changes in membrane permeability, enzyme inactivation etc. It may have a negative impact on the activity of membrane-bound enzymes, such as Са2+, Мg2+АТPase involved in maintaining calcium homeostasis in sperm cells. Ion-transporting ATPses are very sensitive to oxidation and inhibition of Ca2+,Mg2+-ATPase may occur through a different mechanism [13, 18]
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