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 (pHi) 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 0 or 1 microg/mL of LPS (Escherichia coli 0111 B4). 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.

Inhibition of amiloride-sensitive sodium-channel activity in distal lung epithelial cells by nitric oxide

Distal lung epithelial cells (DLECs) play an active role in fluid clearance from the alveolus by virtue of their ability to actively transport Na+ from the alveolus to the interstitial space. The present study evaluated the ability of activated macrophages to modulate the bioelectric properties of DLECs. Low numbers of lipopolysaccharide (LPS)-treated macrophages were able to significantly reduce amiloride-sensitive short-circuit current (Isc) without affecting total Isc or monolayer resistance. This was associated with a rise in the flufenamic acid-sensitive component of the Isc. The effect was reversed by the addition of N-monomethyl-L-arginine to the medium, implying a role for nitric oxide. We hypothesized that macrophages exerted their effect by expressing inducible nitric oxide synthase (iNOS) in DLECs. The products of LPS-treated macrophages increased the levels of iNOS protein and mRNA transcripts in DLECs as well as causing a rise in iNOS activity. Immunofluorescence microscopy of LPS-stimulated macrophage-DLEC cocultures with anti-nitrotyrosine antibodies provided evidence for the generation of peroxynitrite in macrophages but not in DLECs. These data indicate that activated macrophages in the lung may contribute to impaired resolution of acute respiratory distress syndrome and suggest a novel mechanism whereby nitric oxide might alter cell function by altering its ion-transporting phenotype.

Granulocytic differentiation of HL-60 cells results in spontaneous apoptosis mediated by increased caspase expression

HL-60 cells differentiating into neutrophil-like cells die an apoptotic death in vitro. Susceptibility to apoptosis is associated with decreased Bcl-2 protein and mRNA expression; however, the effect of differentiation on the expression of pro-apoptotic caspases is unknown. Spontaneous apoptosis occurred 6 days after retinoic acid treatment. Western blotting showed loss of Bcl-2 by day 7, and new expression of ICE (caspase 1) and CPP32 (caspase 3) protein by day 2. Northern analysis demonstrated loss of Bcl-2 mRNA and increases in ICE mRNA by day 2; CPP32 mRNA was unchanged. Differential Bcl-2 and ICE mRNA expression was also found when granulocytic differentiation was stimulated by DMSO. Differentiated HL-60 cell lysates exhibited functional ICE proteolytic activity. De novo caspase expression was responsible for the development of spontaneous apoptosis, since specific inhibitors of ICE (YVAD-CMK) and CPP32 (DEVD-CHO), inhibited retinoic acid induced spontaneous apoptosis. Functional maturation and susceptibility to apoptosis are both inducible and linked in this granulocyte precursor cell line.