AMPLIFIED PROINFLAMMATORY CYTOKINE EXPRESSION AND TOXICITY IN MICE COEXPOSED TO LIPOPOLYSACCHARIDE AND THE TRICHOTHECENE VOMITOXIN (DEOXYNIVALENOL)

Abstract

A single oral exposure to the trichothecene vomitoxin (VT) has been previously shown in the mouse to increase splenic mRNA levels for several cytokines in as little as 2 h. Since one underlying mechanism for these effects likely involves superinduction of transiently expressed cytokine genes, VT may also potentially amplify cytokine responses to inflammatory stimuli. To test this possibility, the effects of oral VT exposure on tumor necrosis factor- (TNF- ), interleukin-6 (IL-6), and IL-1 expression were measured in mice that were intraperitoneally injected with lipopolysaccharide (LPS), a prototypic inflammatory agent. As anticipated, VT alone at 1, 5, and 25 mg/kg body weight increased splenic mRNA expression of all three cytokines after 3 h in a dose-response fashion. LPS injection at 1 and 5 mg/kg body weight also induced proinflammatory cytokine mRNA expression. There was a synergistic increase in TNF- splenic mRNA levels in mice treated with both VT and LPS as compared to mice treated with either toxin alone, whereas the effects were additive for IL-6 and IL-1 mRNA expression. When relative mRNA levels were examined over a 12-h period in mice given LPS (1 mg/kg) and/or VT (5 mg/kg), significant enhance ment was observed up to 6, 12, and 3 h for TNF- , IL-6, and IL-1 , respectively. When plasma cytokine concentrations were measured, TNF- was found to peak at 1 h and was significantly increased at 1, 3, and 6 h if mice were given LPS and VT, whereas LPS or VT alone caused much smaller increases in plasma TNF- . Plasma IL-6 peaked at 3 h in LPS, VT, and LPS/VT groups, with the combined toxin group exhibiting additive effects. Plasma IL-1 was not detectable. The potential for VT and LPS to enhance toxicity was examined in a subsequent study. Mortality was not observed up to 72 h in mice exposed to a single oral dose of VT at 25 mg/kg body weight or to an intraperitoneal dose of LPS at 1 or 5 mg/kg body weight; however, all mice receiving VT and either LPS dose became moribund in less than 40 h. The principal histologic lesions in the moribund mice treated with VT and LPS were marked cell death and loss in thymus, Peyer's patches, spleen, and bone marrow. In all of these lymphoid tissues, treatment-induced cell death had characteristic histologic features of apoptosis causing lymphoid atrophy. These results suggest that LPS exposure may markedly increase the toxicity of trichothecenes and that the immune system was a primary target of these interactive effects.