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Previous studies have demonstrated the essential role of TNF-induced reactive oxygen intermediates (ROI) in the necrosis of L929 cells. We investigated the molecular basis for the interaction of hyperthermia and TNF in these cells. Hyperthermia, both febrile (40.0-40.5 degrees C) and acute (41.5-41.8 degrees C), strongly potentiated TNF killing, and sensistization was significantly quenched by the antioxidant, BHA. The broad-spectrum caspase inhibitor, Z-VAD, has been shown to markedly increase the TNF sensitivity of L929 cells at 37 degrees C; we observed that hyperthermia would also enhance the sensitivity of L929 cells to TNF + Z- VAD and that BHA could significantly quench the response, as well. The basis for hyperthermic potentiation was unlikely thermally-increased sensitivity to ROI, as treatment with hydrogen peroxide for 24 h killed L929 cells essentially equivalently, whether incubated continuously at 37 degrees C or at 40.0-40.5 degrees C, or for 2 h at 41.5-41.8 degrees C. However, febrile and acute hyperthermia markedly increased TNF-induced production of ROI, with or without Z-VAD. Hyperthermia dramatically accelerated the onset of this production, as well as the onset of necrotic death, as determined by oxidation of dihydro-rhodamine and propidium iodide staining, respectively, both of which were significantly quenchable with BHA. We conclude that hyperthermia potentiates TNF-mediated killing in this cell model primarily by increasing the afferent, and not the efferent, phase of TNF-induced necrosis.

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