Previous studies have shown that chronic ethanol (EtOH) ingestion results in impaired alveolar macrophage function, increased TGF-β1 production, and decreased antioxidant availability. Similarly, alternative activation (M2 activation) of alveolar macrophages also induces TGF-β1 production and impairs macrophage function. However, the potential links between EtOH-induced alveolar macrophage derangements, M2 activation, TGF-β1 production signaling, and oxidant stress have yet to be examined. We hypothesized that EtOH-induced oxidant stress and induction of TGF-β1 signaling result in alternative activation which subsequently impairs the phagocytic capacity of alveolar macrophages.
Primary rat alveolar macrophages and the alveolar macrophages cell line NR8383 were treated with 0.08% EtOH ± the antioxidant glutathione (GSH) or a TGF-β1 neutralizing antibody for 5 days. Outcome measures included TGF-β1 production, reactive oxygen species (ROS) production, phagocytic capacity, and expression of markers of M2 activation.
Chronic EtOH treatment greatly decreased alveolar macrophage phagocytic function, increased ROS production, increased TGF-β1, and increased expression of markers of M2 activation. GSH supplementation and inhibition of TGF-β1 signaling during EtOH treatment prevented these alterations.
EtOH treatment increased oxidant stress, TGF-β1 production, and alternative activation in NR8383 cells. However, GSH supplementation and ablation of TGF-β1 signaling prevented these effects. This suggested that the EtOH-induced switch to an M2 phenotype was a result of decreased antioxidant availability and increased TGF-β1 signaling. Preventing EtOH-induced induction of alternative activation may improve alveolar macrophage function in alcoholic subjects and decrease the risk of respiratory infections.
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