Exposure of cigarette smoke condensate activates NLRP3 inflammasome in THP-1 cells in a stage-specific manner: An underlying role of innate immunity in atherosclerosis.

Smoking is known to affect all the phases of atherosclerosis, thus is considered as an independent and major risk factor. The underlying mechanism responsible for the atherogenic effects of smoking is still uncertain and a major concern. Recent evidence implicates NLRP3 inflammasome, an innate immunity component in the pathogenesis of atherosclerosis. Therefore, we hypothesized that NLRP3 inflammasome may be an associated pathway between smoking and atherosclerosis. Differentiation in monocytes, macrophages and foam cells are the key stages in atherosclerotic plaque development, best mimicked by THP-1 cells. Therefore, to determine whether cigarette smoke condensate (CSC) could induce differentiation of THP-1 monocytes into macrophages, morphological changes and the expression levels of the inflammatory surface markers, i.e. CD11b, CD14 and CD36 were analyzed. The results showed that CD14 and CD36 levels were significantly increased in CSC-treated THP-1 monocytes. Further, we investigated the effect of CSC exposure on the status of NLRP3 inflammasome markers, i.e. NLRP3, pro-caspase-1, caspase-1, pro-IL-18, pro-IL-1β, IL-1β and IL-18 in a stage-specific manner. For this, THP-1 monocytes, PMA-differentiated macrophages and oxidized-low density lipoprotein (ox-LDL)-induced macrophage foam cells were exposed to 10 μg/ml of CSC for 6 h. CSC exposure significantly upregulated the expression of NLRP3 inflammasome in CSC-treated cells at both transcriptional and translational levels. Moreover, downstream pro-cytokines, i.e. IL-1β and IL-18 levels were also significantly increased in culture supernatants of CSC-exposed cells. These observations suggest that CSC exposure may activate NLRP3 inflammasome in a stage-specific manner and may promote initiation and progression of atherosclerosis.