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1. Introduction
Cigarette use is one of the most important causes of early and preventable death and a significant public health concern worldwide [1]. The smoke contains more than 4000 harmful chemical compounds, of which 200 are very toxic, with 1017 free radicals/oxidants present in each puff [2,3]. These compounds are responsible for the recruitment of inflammatory agents and cells and the formation of oxidants, thus inducing oxidative stress and the oxidation of proteins and thiol groups [4].
Smoking is a widespread behavior among adolescents and a major subject of discussion all around the world. It has been reported that up to 15% of all smokers and up to 26% of heavy smokers develop Chronic Obstructive Pulmonary Disease (COPD), typically characterized by persistent airflow obstruction and chronic inflammation of the airways [5,6,7,8]. However, the changes leading to serious disorders (increase of reactive oxygen species, increase of alveolar cellularity, with a higher proportion of neutrophils and a smaller proportion of lymphocytes) may start after only a short period of smoking [2,9,10].
Oxidative stress is defined as a disturbance in the balance between the production of free radicals such as reactive oxygen species (ROS) and antioxidant defenses [11,12]. It has a negative effect on cellular proteins (modify redox-sensitive amino acids in a variety of proteins, including phosphatases, ion channels, and transcription factors, oxidation of proteins may lead to the formation of insoluble protein aggregates, it can cause oxidation of the protein backbone resulting in the protein fragmentation, and formation of protein-protein cross-linkages), despite the existence of protective systems and reductive pathways. The accumulation of oxidized protein products impairs the function of cells and may even lead to cell death. During oxidative stress, oxidation of cellular thiol (-SH) groups is observed through the direct effect of reactive oxygen species (ROS). Oxidative damage causes a rapid loss of biological activity of the protein, leads to disorders in the proper functioning of many transporters and enzymes and disrupts the calcium homeostasis [13,14].
One of the main sources of reactive oxygen species (ROS) in cells is NADPH oxidase [15]. Cigarette smoke is known to enhance the expression of the gp91phox gene, which is one of the components of the NADPH oxidase complex. Apocynin can effectively inhibit NADPH oxidase activity and thus...