Impact of glucocorticoids on damage-associated molecular patterns (DAMPs) release by human macrophages exposed to cigarette smoke and lipopolysaccharide

Glucocorticoids are poorly effective in treating chronic inflammation in smokers. Cigarette smoke (CS) inhibits the TLR4/MyD88 pathway in human macrophages, blocking the inflammatory and cytoprotective transcriptional response to bacterial lipopolysaccharide (LPS). This is accompanied by the activation of the TLR4/TRIF/caspase-8 axis, which promotes cleavage of the pore-forming proteins gasdermins and lytic cell death. Herein we hypothesized that the TLR4/TRIF/caspase-8 pathway represents a steroid-resistant inflammatory axis that propagates inflammation through the release of damage associated-molecular patterns (DAMPs). Human monocyte-derived macrophages (hMDMs) were exposed to CS Extract (CSE) or to the MyD88 inhibitor Pepinh-MYD followed by LPS treatment (with/without fluticasone propionate and dexamethasone). After 24h, cell death, caspase activation, gasdermin cleavage and S100A8/A9 release were evaluated. Conditioned medium (CM) was used to stimulate freshly differentiated hMDMs in order to evaluate IL-6 and TNF release. When CSE- and PephinMYD-treated hMDMs were exposed to LPS, a similar pattern of lytic cell death was observed, with caspase-8 activation, gasdermin E cleavage and S100A8/A9 release. This suggests that MyD88 inhibition followed by LPS exposure recapitulates the features of LPS/CSE-induced cell death. Steroids failed to inhibit S100A8/A9 release in both stimulation models. CM from LPS/CSE treated macrophages triggered IL-6 and TNF release in hMDMs. Our data suggest that caspase-8-dependent cell death and DAMP release represent a new axis to target for the treatment of steroid-resistant inflammation in smokers.