In the last ten years significant progress has been made in understanding of role of neutrophil granulocytes and their enzyme myeloperoxidase in the evolution and complications of atherosclerosis. Myeloperoxidase plays the role in the development of vulnerable plaque associated with the development of acute coronary syndrome. There is much evidence that suggests the role of myeloperoxidase in the development of vulnerable plaque. We investigate the value of myeloperoxidase as marker of the presence of vulnerable plaques in patients with acute coronary syndrome. Myeloperoxidase activity was significantly high in serum of the patients with the diagnosis of acute coronary syndrome as reflection of the presence of vulnerable plaques. Increase in myeloperoxidase activity in serum of patients with the diagnosis of acute coronary syndrome precedes to myocardial damage.

Reactive products of oxygen are among the most potent and omnipresent threats faced by the living organism. Intracellular accumulation of reactive oxygen species such as superoxide anion, hydrogen peroxide, hydroxyl radical, and peroxy radical, can arise from toxic insults or normal metabolic processes. These species may perturb the cell's natural antioxidant defence systems, resulting in damage to all of the major classes of biological macromolecules, including nuclear acids, proteins, carbohydrates and lipids. Oxidative stress has been defined as a disturbance in the prooxidant-antioxidant balance, resulting in potential cell damage. It has been implicated in several biological and pathological processes like ageing, inflammation, carcinogenesis, ischemia-reperfusion and in diseases including diabetes mellitus, atherosclerosis, and/or neurodegenerative diseases

Cells continuously produce free radicals and reactive oxygen species as part of metabolic processes. These free radicals are neutralized by antioxidant defense system consisting of enzymes such as catalase, superoxide dismutase, glutathione peroxidase, and numerous non-enzymatic antioxidants, including vitamins A, E and C, glutathione, ubiquinone, and flavonoids. Antioxidants include both water and lipid soluble varieties. The lipid soluble antioxidants are located in the cellular membranes and lipoproteins, whereas the water soluble antioxidants are present in the aqueous environments, such as fluids inside cells and in the blood.