Bicarbonate enhances the inflammatory response by activating JAK/STAT signaling in LPS+IFN-γ-stimulated macrophages.

Macrophages, which develop by changing their functions according to various environmental conditions and stimuli, defend against the pathogens and play roles in homeostasis and disease states. Bicarbonate (HCO3-) is important in the maintenance of intracellular and extracellular pH in the body. However, the effects of bicarbonate on macrophage function have not been examined. In this study, we investigated the effects of bicarbonate on macrophage activation in lipopolysaccharide (LPS) and interferon (IFN)-gamma (LPS+IFN-gamma)-stimulated murine macrophage-like RAW264.7 cells. The expression of the interleukin (IL)-6, inducible nitric oxide (NO) synthase, and cyclooxygenase-2 genes was enhanced by NaHCO3 in a concentration-dependent manner in LPS+IFN-gamma-stimulated RAW264.7 cells. Production of IL-6, NO2-, and prostaglandin E2 was also increased by treatment with NaHCO3 in these cells. Moreover, NaHCO3-mediated elevation of inflammatory gene expression was abrogated by solute carrier (SLC) transporter inhibitors. Furthermore, its NaHCO3-mediated activation was negated by a JAK inhibitor, tofacitinib. NaHCO3 enhanced phosphorylation of STAT1, and its enhancement was abrogated by pre-treating with SLC transporter inhibitors in LPS+IFN-gamma-stimulated RAW264.7 cells. In addition, similar results were obtained in murine bone-marrow derived macrophages. These results indicate that bicarbonate enhanced the inflammatory response through the JAK/STAT signaling in LPS+IFN-gamma-stimulated macrophages.