Acetazolamide treatment prevents in vitro endotoxin-stimulated tumor necrosis factor release in mouse macrophages

We previously showed that incubation in carbon dioxide (CO₂), but not air or helium (He), markedly decreased macrophage intracellular pH (pH_i) and resulted in reversible inhibition of lipopolysaccharide- (LPS) stimulated tumor necrosis factor (TNF) and interleukin-1 release. We sought to determine whether carbonic anhydrase inhibition with acetazolamide would prevent CO₂-mediated inhibition of LPS-stimulated TNF release. Murine peritoneal macrophages were treated with acetazolamide for 1 h under control atmosphere (95% air/5% CO₂) and then switched to incubator modules containing: 1) 80% CO₂/20% O₂, 2) 80% He/20% O₂, or 3) 100% air. Before transfer to experimental atmospheric conditions the macrophages were stimulated with O or 1 μg/mL of LPS (Escherichia coli 0111B4). Supernatant TNF was measured 4 h later by bioassay. In parallel experiments LPS-stimulated cytokine mRNA was estimated using reverse transcriptase polymerase chain reaction (RT-PCR) 2 h after LPS stimulation. Viability was determined using dye uptake. Incubation in CO₂ or helium had no effect on TNF production in the absence of LPS. In the absence of acetazolamide CO₂ produced marked inhibition of LPS-stimulated TNF release, but this was not blocked by the presence of acetazolamide. This CO₂-mediated inhibition of TNF was associated with normal levels of TNF mRNA. In acetazolamide-treated macrophages, LPS resulted in a dose-dependent inhibition of TNF release when the cells were incubated in air or helium. Maintenance of normal intracellular pH is required for TNF release, but not TNF mRNA induction by LPS. Factors that alter intracellular pH regulation may modulate LPS-stimulated cytokine production.