Bikunin Inhibits Lipopolysaccharide-Induced Tumor Necrosis Factor Alpha Induction in Macrophages

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Abstract
Bikunin, a Kunitz-type protease inhibitor, exhibits anti-inflammatory activity in protection against cancer and inflammation. To investigate the molecular mechanism of this inhibition, we analyzed the effect of bikunin on tumor necrosis factor alpha (TNF-α) production in human peripheral mononuclear cells stimulated by lipopolysaccharide (LPS), an inflammatory inducer. Here, we show the following results. (i) LPS induced TNF-α expression in time- and dose-dependent manners through phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase pathways. (ii) Bikunin inhibits LPS-induced up-regulation of TNF-α protein expression in a dose-dependent manner, reaching 60% inhibition at the highest doses of bikunin tested (5.0 μM). (iii) Inhibition by bikunin of TNF-α induction correlates with the suppressive capacity of ERK1/2, JNK, and p38 signaling pathways, implicating repressions of at least three different signals in the inhibition. (iv) Bikunin blocks the induction of TNF-α target molecules interleukin-1β (IL-1β) and IL-6 proteins. (v) Bikunin is functional in vivo, and this glycoprotein blocks systemic TNF-α release in mice challenged with LPS. (vi) Finally, bikunin can prevent LPS-induced lethality. In conclusion, bikunin significantly inhibits LPS-induced TNF-α production, suggesting a mechanism of anti-inflammation by bikunin through control of cytokine induction during inflammation. Bikunin might be a candidate for the treatment of inflammation, including septic shock.