The Role of Inducible Nitric Oxide Synthase in Assessing the Functional Level of Coronary Artery Lesions in Chronic Coronary Syndrome

Chronic coronary syndrome (CCS) is a long-term manifestation of coronary artery disease, marked by stable but recurring chest pain and myocardial ischemia due to the gradual buildup of atherosclerotic plaques in the coronary arteries. It is a metabolic disorder of coronary arteries characterized by oxidative stress, endothelial dysfunction, inflammation, and hyperlipidemia. The imbalance in oxidative-anti- oxidative status contributes to stable ischemic heart disease. Oxidative stress involves reactive oxygen and nitrogen species, leading to low-density lipoprotein (LDL) oxidation. Endothelial dysfunction, marked by reduced nitric oxide (NO) bioavailability, is an early onset of CCS, affecting vasodilation, cell proliferation, and inflammatory responses. Enzyme myeloperoxidase (MPO), traditionally considered protective, plays a dual role in initiating and progressing inflammatory diseases. MPO interacts with NO, modulating its catalytic activity. Elevated NO levels inhibit MPO through a reversible complex formation, preventing NO-induced inhibition by inducible nitric oxide synthase (iNOS). MPO also inactivates endothelial nitric oxide synthase (eNOS) and reacts with L-arginine, hindering NO synthesis. The interplay between MPO and NO significantly influences inflammation sites, impacting peroxidation rates and oxidation reactions. Peroxynitrite, a reactive species, contributes to nitration of tyrosine residues and lipid peroxidation. Mechanistic pathways suggest MPO enhances iNOS catalytic activity, influencing CCS development. iNOS, implicated in inflammation and atherosclerosis, is connected to NO regulation. This review analyzes the complex interplay of MPO, iNOS, and NO that affects plaque morphology, oxidative stress, and inflammation, contributing to atherosclerosis progression. Therefore, it is possible that the phenotypes of atherosclerotic plaques, focal and diffuse coronary artery disease, could be defined by the relationship between MPO and iNOS.