DIFFERENTIAL MODULATION OF SMOOTH MUSCLE CELL PHENOTYPE BY NEXT-GENERATION NICOTINE PRODUCTS AND TRADITIONAL CIGARETTE

Cigarette smoke is one of the most important modifiable risk factors for cardiovascular diseases (CVDs) since smoking is responsible for 20% of deaths from coronary heart disease. Cigarette smoke contains 7.000 different components, many of which are known to be cytotoxic, mutagenic or carcinogenic. In the effort to reduce the harm associated with conventional cigarettes caused by the toxicants in the cigarette smoke produced by the burning of tobacco, alternative next generation nicotine products (NGPs, such as E-cigarettes (E-CIG) designed to deliver nicotine through an aerosol state), have been developed. Our research group has previously demonstrated that cigarette smoke condensate affects the plasticity of smooth muscle cells (SMCs). The aim of my project was to evaluate the effects of cigarette smoke aqueous extracts (AEs) on SMC phenotypic switch potential, a key step in the atherogenic process, and to get more information on the potentially toxic effects of the new NGPs. The in vitro studies in human aortic SMCs, showed that AEs, obtained from a traditional (TC) and E-CIG, stimulated the expression of extracellular matrix genes (ECM) and at the same time, E-CIG showed a potent and faster induction of SMC proliferation and migratory activity, while TC slowed down these processes compared to control and E-CIG. Moreover, we observed that the stimulatory effects exert by E-CIG are probably due to its nicotine content. In addition, α-BTX a potent and selective antagonist of alpha7 nicotinic acetylcholine receptor (α7nAChR) activation counteracted nicotine-induced cell migration and proliferation. Furthermore, the incubation with TC and E-CIG AEs also affected cell morphology, with the extension of lamellipodia, and increased F-actin and RAC1 levels. Interestingly, E-CIG showed a suppressive effect on inflammatory markers that was reversed by blocking α7nAChR with α-BTX. Overall, these results suggested that E-CIG promotes a phenotypic modulation in SMCs. In fact, E-CIG extract induces changes in cytoskeleton organization enhancing a proliferative and promigratory behavior. Moreover, we can speculate that these effects are mediated by nicotine through α7nAChR activation. On the contrary, TC increases ECM gene expression and induces changes in cell morphology but it might probably contain some other chemical compounds that overwhelmed the stimulatory effects exerted by nicotine on proliferation and migration activity. In addition, we demonstrated that TC is the most effective in promoting an inflammatory response by inducing the expression of several cytokines and matrix remodeling genes. In conclusion, these results demonstrated that E-CIG induce SMC phenotypic modulation by promoting SMC proliferation and migration activity and by inducing an alteration in cytoskeletal organization. E-CIG also exerts a negative modulation of the inflammatory pathway reducing cytokines expression. Further, the inhibitory effect is due to nicotine, one of the major components of cigarette smoke, through the activation of α7nAChR. TC is less effective in inducing a proper phenotypic modulation of SMCs while it is the most effective in increasing markers of inflammation and matrix-degrading metalloproteinases thus, promoting vascular inflammation and the atherogenic process.