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Anti-Inflammatory Effect of Piper attenuatum Methanol Extract in LPS-Stimulated Inflammatory Response 时间:2017-07-29 14:06 来源:未知作者:admin 点击: 次 Abstract:Piper attenuatum is used as a traditional medicinal plant in India. One of the substances in P. attenuatum has been suggested to have anti-inflammatory effects. However, there is insufficient research about the anti-inflammatory mechanisms of action of P. attenuatum. The effects of P. attenuatum methanol extract (Pa-ME) on the production of inflammatory mediators nitric oxide (NO) and prostaglandin E2 (PGE2), the expression of proinflammatory genes, the translocation level of transcription factors, and intracellular signaling activities were investigated using macrophages. Pa-ME suppressed the production of NO and PGE2 in lipopolysaccharide- (LPS-), pam3CSK4-, and poly(I:C)-stimulated RAW264.7 cells without displaying cytotoxicity. The mRNA expression levels of inducible NO synthase (iNOS) and cyclooxygenase 2 (COX-2) were decreased by Pa-ME. P-ME reduced the translocation of p50/NF-κB and AP-1 (c-Jun and c-Fos), as well as the activity of their upstream enzymes Src, Syk, and TAK1. Immunoprecipitation analysis showed failure of binding between their substrates, phospho- (p-) p85 and p-MKK3/6. p-p85 and p-MKK3/6, which were induced by overexpression of Src, Syk, and TAK1, were also reduced by Pa-ME. Therefore, these results suggest that Pa-ME exerts its anti-inflammatory effects by targeting Src and Syk in the NF-κB signaling pathway and TAK1 in the AP-1 signaling pathway.
1. Introduction
Inflammation is a kind of innate immunity that provides a defense against pathogens, damaged cells, and other dangerous molecules. Inflammatory cells, such as macrophages and neutrophils, let leukocytes and plasma components come to sites where infection or injury has occurred during inflammation to eliminate dangers [1, 2]. Although inflammation is important to the immune system, excessive activity of inflammatory cells can cause cancer, rheumatoid arthritis, multiple sclerosis, chronic asthma, psoriasis, and other diseases [1, 3, 4]. To treat those inflammation-driven diseases, inflammatory responses should be controlled. Nuclear factor- (NF-) κB and activator protein- (AP-) 1 are two main transcription factors that initiate inflammation by activation of a series of intracellular signals composed of inhibitor of κB kinase (IKKα/β), AKT (protein kinase B), Src, and Syk for NF-κB and extracellular signal-regulated kinase (ERK), p38, c-Jun N-terminal kinase (JNK), interleukin-1 receptor-associated kinase 1 (IRAK1), IRAK4, transforming growth factor beta-kinase 1 (TAK1), mitogen-activated protein kinase kinase 3 (MKK3), and MKK6 for AP-1 [5–8]. These molecules are usually considered targets for suppression of the NF-κB or AP-1 pathways to obtain anti-inflammatory outcomes.
Piper attenuatum is a plant in the Piperaceae family that inhabits the eastern tropical Himalayas, Assam, Khasi Hills, and the Nilgiris in India. The whole plant is used to cure headache and muscular pain [9]. Piper attenuatum has antibacterial [10] and antioxidant effects [11], and neolignans in P. attenuatum fruit are candidate free radical scavengers [12]. In addition, many substances such as cepharanone B, piperolactam A, piperolactam D, and cepharadione A have been isolated from P. attenuatum [13]. Cepharanone and piperolactam exhibit anti-inflammatory effects [13]. However, there is no detailed research regarding the anti-inflammatory mechanism of P. attenuatum. In this study, we aimed to explore the molecular mechanism of P. attenuatum with its methanol extract (Pa-ME) with respect to the NF-κB and AP-1 signaling pathways.