Nitric Oxide-Derived Oxidants with a Focus on Peroxynitrite: Molecular Targets, Cellular Responses and Therapeutic Implications

Nitric oxide participates in a wide array of physiological processes, ranging from neurotransmission to precursor of cytotoxic effector molecules of the immune system. Although nitric oxide is a mildly reactive intermediary, it can act as a precursor of strong oxidants under pathological conditions associated with oxidative stress including cardiovascular, inflammatory and neurodegenerative disorders. Peroxynitrite, the reaction product of nitric oxide with superoxide radicals, emerges as one of the principal players of nitric oxide-derived toxicity due to its facile formation and ability to react with several critical cellular targets including, thiols, proteins, lipids and DNA. The extent of "nitroxidative stress" is determined by several factors, including the concentration and exposure time to this reactive species or its derived radicals and by the ability of the cell to face the oxidative challenge by means of its antioxidant defenses. The inflicted biomolecular damage can result on minimal and reversible changes to cell and tissue physiology, to alteration in bioenergetics, disruption of DNA integrity, mitochondrial dysfunction and even cell death. Although dissecting the free radical chemistry pathways responsible of cell/tissue disturbance of oxidative signaling and promotion of oxidative damage arising from nitric oxide-derived oxidants in a biological context is a vast endeavor, is an ineludible task in order to generate a rational therapeutic approach to modulate nitroxidative stress. Several redox-based pharmacological strategies with a collection of compounds with varying mechanisms of action have been tested at the cellular, preclinical and even clinical levels, and some novel and promising developments are underway. This review deals with key kinetic and biochemical aspects of nitric oxide-derived oxidant formation and reactions in biological systems, emphasizing the current evidence at the biochemical, cell/tissue and animal/human levels that support a pathophysiological role for peroxynitrite and related species in human pathology. In addition, a selection of available pharmacological tools will be discussed as an effort to rationalize antioxidant and/or redox-based therapeutic interventions in disease models.