EFFECT OF HYPOXIA ON RELEASE OF IL-1 AND TNF BY HUMAN ALVEOLAR MACROPHAGES

Our previous work demonstrated that hypoxia decreases transcription of the human prostaglandin H synthase-2 (PGHS-2) gene during exposure to lipopolysaccharide (LPS), resulting in decreased prostaglandin E(2) ( PGE(2)) synthesis (J. Biol. Chem. 269:32979-32984, 1994). Because PGE( 2) is reported to inhibit interleukin 1 (IL-1) and tumor necrosis fact or (TNF), it is likely that hypoxia, through changes in PGE(2), will a lter IL-1 and TNF release from the human alveolar macrophage. In addit ion, like PGHS-2, the TNF and IL-1 promoters contain oxidant-sensitive elements which might be altered by hypoxia, Therefore, we hypothesize d that LPS-induced release of TNF and IL-1 would be altered by hypoxia , To test this, human alveolar macrophages were cultured for 24 h with 0 to 1 mu g/ml LPS in a room-air incubator with 5% CO2 or a hypoxia i ncubator continuously perfused with 5% CO2/95% N-2 (O-2 < 0.05%). With room air, LPS increased IL-1 beta mRNA and increased IL-1 beta protei n release into the culture medium in a dose-dependent manner. Hypoxia increased the LPS-stimulated release of IL-1 beta 30% above that of ro om-air controls. However, immunoblots showed that hypoxia caused no ch ange in intracellular IL-1 beta compared with room-air controls. There was also no change in LPS-induced IL-1 beta message with hypoxia. The inhibitor of IL-1, IL-1RA, was apparently decreased by hypoxia, but t his decrease was not statistically significant, TNF-alpha mRNA and rel ease of protein also increased during LPS exposure in room air, Hypoxi a markedly increased LPS-induced TNF-alpha message and release of TNF- alpha compared with LPS-exposed room-air controls. Consistent with our prior observations, hypoxia decreased LPS-induced PGHS-2 message and protein, and also the PGHS-2 product, PGE(2). Because PGE(2) is report ed to inhibit the expression of IL-1 and TNF genes, we inhibited PGE(2 ) synthesis with indomethacin during culture in room air; the result w as an increase in the release of IL-1 and TNF. In additional studies, adding PGE(2) inhibited TNF release from the hypoxia cells to values n ear those of room-air controls. In summary, hypoxia increases the rele ase of the cytokines IL-1 beta and TNF-alpha. This increase may be due to decreased PGE(2) synthesis during hypoxia, These results demonstra te that the response of the human alveolar macrophage to hypoxia is co mplex. Hypoxia increases the LPS-stimulated release of the inflammator y cytokines IL-1 and TNF, whereas synthesis of PGHS-2, which generates the anti-inflammatory prostaglandin PGE(2) is decreased.