Prolonged ethanol treatment enhances lipopolysaccharide/phorbol myristate acetate-induced tumor necrosis factor-alpha production in human monocytic cells

Background: Ethanol (EtOH) is known to alter host immune responses and cyto kine production. Acute EtOH exposure can suppress tumor necrosis factor (TN F)-alpha production, which attenuates pulmonary defense against infection. Previous studies in our laboratory show that acute EtOH inhibited TNF-alpha production by a posttranscriptional process, namely suppression of TNF-alp ha -converting, enzyme-mediated, ectodomain shedding. However. chronic EtOH has been shown to augment TNF-alpha production, and this has been associat ed with EtOH-induced liver injury. To further characterize this paradoxical effect of EtOH on TNF-alpha production, we developed an in vitro model by using Mono Mac 6 cells, a human monocytic cell line. Methods: Mono Mac 6 cells were treated with EtOH (0-75 mM) for 1 to 7 days. TNF-alpha production was induced by lipopolysaccharide and phorbol myrista te acetate and quantitated by enzyme-linked immunosorbent assay. Generation of reactive oxygen species (ROS) was assayed by using a specific flurogeni c reagent. Results: Acute EtOH initially inhibited lipopolysaccharide/phorbol myristat e acetate-induced TNF-alpha production in Mono Mac 6 cells. However, during chronic EtOH exposure, this inhibition was reversed gradually over time. B y day 6 after EtOH treatment, Mono Mac 6 cells demonstrated significant upr egulation of TNF-alpha production. Moreover, chronic EtOH induced the gener ation of ROS in these Mono Mac 6 cells. Scavenging ROS by Mn(III)tetrakis(1 -methyl-4pyridyl)porphyrin pentachloride and N-aceryl-L-cysteine attenuated chronic EtOH-enhanced TNF-alpha production. Conclusion: These results suggest that ROS induction is involved in EtOH-en hanced TNF-alpha production by monocytes. This study also provides insight into the mechanisms of alteration of TNF-alpha production in different EtOH exposure settings.