Sesquiterpene lactones are potent inhibitors of interleukin 8 gene expression in cultured human respiratory epithelium.

Sesquiterpene lactones, derived from Mexican-Indian medicinal plants, are known to have potent anti-inflammatory properties but the mechanisms of this effect are not completely understood. Recent data demonstrated that sesquiterpene lactones were potent inhibitors of the pro-inflammatory transcription factor NF-kappaB. Because activation of NF-kappaB is involved in the regulation of the chemokine interleukin 8 (IL-8), we hypothesized that the sesquiterpene lactones, isohelenin and parthenolide, would inhibit IL-8 gene expression in cultured human respiratory epithelium. Incubating A549 cells with tumour necrosis factor alpha (TNF-alpha) induced IL-8 mRNA expression and secretion of immunoreactive IL-8. Pretreatment with either isohelenin or parthenolide inhibited TNF-alpha-mediated IL-8 gene expression in a concentration-dependent manner. Pretreatment with either compound inhibited TNF-alpha mediated activation of the IL-8 promoter and TNF-alpha-mediated nuclear translocation of NF-kappaB. In addition, pretreatment with isohelenin or parthenolide inhibited TNF-alpha-mediated degradation of the NF-kappaB inhibitory protein, I-kappaBalpha. We conclude that sesquiterpene lactones are potent in vitro inhibitors of IL-8 gene expression in cultured human respiratory epithelium. The most proximal mechanism of inhibition appears to involve inhibition of I-kappaBalpha degradation. Stabilization of cytoplasmic I-kappaBalpha leads to inhibition of NF-kappaB nuclear translocation and of subsequent IL-8 promoter activation. The ability of sesquiterpene lactones to modulate IL-8 gene expression may explain, in part, their anti-inflammatory effects.

Hyperoxia synergistically increases TNF-alpha-induced interleukin-8 gene expression in A549 cells.

Interleukin (IL)-8 is an important mediator of acute lung injury. Hyperoxia induces IL-8 production in some cell types, but its effect on IL-8 gene expression in respiratory epithelium is not well described. In addition, IL-8 gene expression resulting from the combined effects of hyperoxia and proinflammatory cytokines has not been well characterized. We treated cultured respiratory epithelial-like cells (A549 cells) with hyperoxia alone, tumor necrosis factor (TNF)-alpha alone, or the combination of TNF-alpha and hyperoxia and evaluated IL-8 gene expression. Hyperoxia alone had a minimal effect on IL-8 gene expression, and TNF-alpha alone increased IL-8 gene expression in a time-dependent manner. In contrast, the combination of TNF-alpha and hyperoxia synergistically increased IL-8 gene expression as measured by ELISA (TNF-alpha alone for 24 h = 769 +/- 89 pg/ml vs. hyperoxia + TNF-alpha for 24 h = 1, 189 +/- 89 pg/ml) and Northern blot analyses. Experiments involving IL-8 promoter-reporter assays, electromobility shift assays, and Western blot analyses demonstrated that hyperoxia augmented TNF-alpha-mediated activation of the IL-8 promoter by a nuclear factor (NF)-kappaB-dependent mechanism and increased the duration of NF-kappaB nuclear translocation after concomitant treatment with TNF-alpha. Additional reporter gene assays demonstrated, however, that increased activation of NF-kappaB does not fully account for the synergistic effect of hyperoxia and that the NF-IL-6 site in the IL-8 promoter is also required for the synergistic effect of hyperoxia. We conclude that hyperoxia alone has a minimal effect on IL-8 gene expression but synergistically increases IL-8 gene expression in the presence of TNF-alpha by a mechanism involving cooperative interaction between the transcription factors NF-kappaB and NF-IL-6.