Piperine, a main component of Piper longum Linn. and Piper nigrum Linn., is a plant alkaloid with a long history of medical use. Piperine exhibits anti-inflammatory activity; however, the underlying mechanism remains unknown. We examined the effects of piperine on lipopolysaccharide (LPS)-induced inflammatory responses. Administration of piperine inhibited LPS-induced endotoxin shock, leukocyte accumulation and the production of tumor necrosis factor-alpha (TNF-alpha), but not of interleukin (IL)-1beta and IL-6. In peritoneal macrophages, piperine inhibited LPS/poly (I:C)/CpG-ODN-induced TNF-alpha production. Piperine also inhibited LPS-induced endotoxin shock in TNF-alpha knockout (KO) mice. To clarify the inhibitory mechanism of LPS-induced endotoxin shock, type 1 interferon (IFN) mRNA expression was determined. Piperine inhibited LPS-induced expression of type 1 IFN mRNA. Piperine inhibited the levels of interferon regulatory factor (IRF)-1 and IRF-7 mRNA, and the phosphorylation and nuclear translocation of IRF-3. Piperine also reduced activation of signal transducer and activator of transcription (STAT)-1. In addition, activation of STAT-1 was inhibited in IFN-alpha/beta-treated cells by piperine. These results suggest that piperine inhibits LPS-induced endotoxin shock through inhibition of type 1 IFN production.
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