Cigarette Smoking Blocks the Protective Expression of Nrf2/ARE Pathway in Peripheral Mononuclear Cells of Young Heavy Smokers Favouring Inflammation

Abstract

Cigarette smoking is an important risk factor for atherosclerosis, a chronic inflammatory disease. However the underlying factors of this effect are unclear. It has been hypothesized that water-soluble components of cigarette smoke can directly promote oxidative stress in vasculature and blood cells. Aim of this study was to study the relationship between oxidative stress and inflammation in a group of young smokers. To do this we evaluated: 1) the oxidation products of phospholipids (oxPAPC) in peripheral blood mononuclear cells (PBMC); 2) their role in causing PBMC reactive oxygen species (ROS) generation and changes in GSH; 3) the expression of the transcription factor NF-E2-related factor 2 (Nrf2) and of related antioxidant genes (ARE); 4) the activation of NF-kB and C-reactive protein (CRP) values. We studied 90 healthy volunteers: 32 non-smokers, 32 moderate smokers (5–10 cigarettes/day) and 26 heavy smokers (25–40 cigarettes/day). OxPAPC and p47phox expression, that reasonably reflects NADPH oxidase activity, were higher in moderate smokers and heavy smokers than in non-smokers (p<0.01), the highest values being in heavy smokers (p<0.01). In in vitro studies oxPAPC increased ROS generation via NADPH oxidase activation. GSH in PBMC and plasma was lower in moderate smokers and heavy smokers than in non-smokers (p<0.01), the lowest values being in heavy smokers (p<0.01). Nrf2 expression in PBMC was higher in moderate smokers than in non-smokers (p<0.01), but not in heavy smokers, who had the highest levels of NF-kB and CRP (p<0.01). In in vitro studies oxPAPC dose-dependently increased NF-kB activation, whereas at the highest concentrations Nrf2 expression was repressed. The small interference (si) RNA-mediated knockdown of NF-κB/p65 increased about three times the expression of Nrf2 stimulated with oxPAPC. Cigarette smoke promotes oxPAPC formation and oxidative stress in PBMC. This may cause the activation of NF-kB that in turn may participate in the negative regulation of Nrf2/ARE pathway favouring inflammation.

Involvement of CK2 in activation of electrophilic genes in endothelial cells by oxidized phospholipids

“…Previous studies have demonstrated that OxPLs induce NRF2 and electrophilic genes ( 3,18,19 ). However, the mechanisms of activation are only partially understood.…”

Role of Nrf2 in Oxidative Stress and Toxicity

“…Nrf2 KO mice have a tendency to develop age-dependent autoimmune and inflammatory lesions in multiple tissues (37,38). Inflammation is commonly observed in chemically induced pathology with Nrf2 deficiency (91)(92)(93)(94)(95)(96). Many ARE inducers are potent anti-inflammatory agents, and their potency for induction of ARE genes correlates well with their potency for inhibition of inflammation (97)(98)(99).…”

Smoking and Cardiovascular Disease

“…Free radicals and oxidants present in cigarette smoke, as well as endogenously produced oxidants and radicals (resulting from the smoke chemicalinduced alteration in the cellular redox system), cause a prooxidative environment. 20 This general shift is likely to contribute to lipid oxidation and to a general increase in oxidative modification (and inactivation) of biomolecules. Morrow et al 21 reported increased presence of lipid peroxidation products in the serum of smokers, and Salonen et al 22 found increased levels of circulating autoantibodies against oxidized LDL.…”