Nitric oxide inhibits dystrophin proteolysis by coxsackieviral protease 2A through S-nitrosylation: A protective mechanism against enteroviral cardiomyopathy

Nitric oxide: does it play a role in the heart of the critically ill?

Nitric oxide regulates many aspects of myocardial function, not only in the normal heart but also in ischemic and nonischemic heart failure, septic cardiomyopathy, cardiac allograft rejection, and myocarditis. Accumulating evidence implicates the endogenous production of nitric oxide in the regulation of myocardial contractility, distensibility, heart rate, coronary vasodilation, myocardial oxygen consumption, mitochondrial respiration, and apoptosis. The effects of nitric oxide promote left ventricular mechanical efficiency, ie, appropriate matching between cardiac work and myocardial oxygen consumption. Most of these beneficial effects are attributed to the low physiologic concentrations generated by the constitutive endothelial or neuronal nitric oxide synthase. By contrast, inducible nitric oxide synthase generates larger concentrations of nitric oxide over longer periods of time, leading to mostly detrimental effects. In addition, the recently identified beta3-adrenoceptor mediates a negative inotropic effect through coupling to endothelial nitric oxide synthase and is overexpressed in heart failure. An imbalance between beta 1 and beta2-adrenoceptor and beta3-adrenoceptor, with a prevailing influence of beta3-adrenoceptor, may play a causal role in the pathogenesis of cardiac diseases such as terminal heart failure. Likewise, changes in the expression of endothelial nitric oxide synthase or inducible nitric oxide synthase within the myocardium may alter the delicate balance between the effects of nitric oxide produced by either of these isoforms. New treatments such as selective inducible nitric oxide synthase blockade, endothelial nitric oxide synthase promoting therapies, and selective beta3-adrenoceptor modulators may offer promising new therapeutic approaches to optimize the care of critically ill patients according to their stage and specific underlying disease process.

*NO, RSNO, ONOO-, NO+, *NOO, NOx--dynamic regulation of oxidant scavenging, nitric oxide stores, and cyclic GMP-independent cell signaling

Following its release from nitric oxide synthase, nitric oxide seldom perfuses the cytosol; rather this reactive mediator quickly interacts with available target molecules proximate to its site of release. Within the cell, virtually every component, low-molecular-weight oxidants and reductants, proteins, lipids, sugars, and nucleic acids can be modified by nitrogen oxides thus acting as potential targets for reactive nitrogen oxides. Adducts formed by nitrogen oxides often modulate the cellular activities of the target molecules, and these modified molecules may be differentially metabolized or localized. The formation of nitrogen oxide adducts can be a reversible process, and the reactive nitrogen species released may be specifically oxidized or reduced during the process. Recently, numerous studies have demonstrated that reversible nitration of cellular proteins acts to transduce molecular signals regulating such diverse processes as muscle contraction, neurotransmission, protein metabolism, and apoptosis. The vast numbers of molecules that undergo biologically relevant interactions with nitrogen oxides imply that the cellular concentration of nitrosated and nitrated species may effectively comprise a reserve or cellular store. Potentially, these nitroso reserves function as critical components of the overall redox status of the intracellular environs. Understanding the dynamic regulation of nitric oxide/nitrogen oxides release from these stores is likely to provide clues important in resolving the complex pathophysiology of poorly understood multifactorial disorders, including neurodegeneration, multiorgan failure, cardiomyopathy, and septic shock.