Polarization of THP-1-Derived Human M0 to M1 Macrophages Exposed to Flavored E-Liquids

Electronic cigarettes (ECIGs) are widely used but their effects on the immune system need to be further investigated. Macrophages are white blood cells central to the immune response. Using THP-1-derived M0 macrophages, this study aims to determine the effects of ECIG liquids (E-liquids) on the polarization of M0 to the pro-inflammatory M1 macrophage subtype. THP-1 cells were cultured and differentiated to M0 macrophages using RPMI media. E-liquids ± cinnamon, menthol, strawberry and tobacco flavors were added to cell cultures at 1% (v/v) during polarization with lipopolysaccharides and interferon γ for 24 to 72 h. Morphology, viability, gene expression and cytokine production were measured using light microscopy, the LDH cytotoxicity assay, qPCR and ELISA, respectively. The results show that cells present little to no LDH activity under any treatments. In addition, cinnamon-flavored E-liquid severely affects morphology (i.e., abolishing pseudopodia formation), gene expression of all genes tested, and cytokine production. Other E-liquid flavors also affect some of these parameters, but to a lesser extent. Our data suggest that E-liquids can affect the polarization from M0 to M1, thus affecting the immune response in ECIG-exposed tissues such as the mucosa in the oral cavity and airways, ultimately mitigating the health status.