ALTERATIONS OF AMBIENT OXYGEN-TENSION MODULATE THE EXPRESSION OF TUMOR-NECROSIS-FACTOR AND MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA FROM MURINE ALVEOLAR MACROPHAGES

Tissue injury that occurs as a result of ischemia and subsequent reper fusion is characterized by endothelial cell injury, edema formation, a nd the influx of inflammatory leukocytes. Two macrophage-derived proin flammatory cytokines which may play a critical role in cellular injury and leukocyte recruitment/activation that occurs in the setting of is chemia-reperfusion injury are tumor necrosis factor alpha (TNF) and ma crophage inflammatory protein-1 alpha (MIP-1 alpha). To determine if m odulation of ambient oxygen tensions in vitro alters the expression of proinflammatory cytokines from activated macrophages, murine alveolar macrophages (AMO) were cultured in various combinations of ambient ox ygen concentrations, then the supernatant fluid and cell pellet assaye d for the presence of TNF and MIP-la messenger RNA (mRNA) and protein, We demonstrated that conditions of anoxia (95% nitrogen/5% CO2) or hy peroxia (95% oxygen/5% CO2) independently resulted in the increased ex pression of both TNF and MIP-1 alpha mRNA and protein from lipopolysac charide (LPS)-stimulated AMO, as compared with cells cultured in room air, The specific culture condition of anoxia (x 6 h) followed by hype roxia (x 18 h) produced the greatest increases in both TNF and MIP-1 a lpha, suggesting that when following a period of anoxic priming, oxyge n stress results in exaggerated cytokine production. A period of at le ast 4.5 to 6 h of anoxia prior to hyperoxic exposure was found to be t he minimal time required for anoxic priming. Furthermore, the coincuba tion of LPS-treated AMO with dimethyl sulfoxide (DMSO) attenuated the anoxia-hyperoxia-induced increases in TNF and MIP-1 alpha mRNA by 23% and 34%, respectively. These findings suggested that alterations in am bient oxygen tension can regulate the expression of TNF and MIP-1 alph a from activated AMO, and that oxidant-related cytokine production may represent an important mechanism by which inflammation occurs in the clinical settings of ischemia-reperfusion injury and hyperoxia.