Bimodal interplay of reactive oxygen and nitrogen species in physiology and pathophysiology of bovine sperm function

Abstract

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the mediators of redox activity and are known to perform concentration-specific bimodal roles. At lower concentrations, serves as a molecular messenger and signaling molecule while at higher concentrations induces stress which in turn alters the sperm's functional characteristics. Production of ROS and RNS cannot be prevented entirely and should not be followed as a pragmatic approach as they are involved in numerous sperm physiological functions. When the antioxidants defense armory is meager, excess generation of these species cross the physiological limits and inactivates essential metabolic enzymes and disrupts signal transduction altering normal sperm functions. As per the available literature, oxidants mostly arise as a result of pathological conditions or cryopreservation-induced injury. Dead and debilitated or abnormal spermatozoa and associated leukocytes release free radicals in an excess amount which elicits oxidative and nitrosative stressors that are potentially toxic to cryosurviving sperm. ROS plays a double edge sword effect on sperm function, as regulators of physiological mechanisms at low levels and as toxicants when produced at high concentrations. Recently nitric oxide (NO^.) has emerged as a potential regulator of sperm physiology, in addition, found to mediate homeostasis of the seminal plasma microenvironment when semen samples are incubated with optimal concentrations of NO^. compounds. The NO^. compounds can provide some resistance to future stresses which are not usually harnessed by using the defensive strategy of supplementing antioxidants. Therefore, through the optimized addition of NO^. donor and inhibitor in extender, the free radical-induced damage can be avoided without inhibiting their essential physiological effects on fertilization and subsequent embryo development. This article is intended to describe the role of reactive oxidants in the physiology and pathophysiology of spermatozoa and their relationship with various seminal attributes.

Keywords: Antioxidants; Cryopreservation; Nitrosative stress; Spermatozoa.