Aloe-emodin from rhubarb (Rheum rhabarbarum) inhibits lipopolysaccharide-induced inflammatory responses in RAW264.7 macrophages

Ethnopharmacological relevance: Rheum rhabarbarum (rhubarb) has long been used for the treatment of inflammation in China and other Asian countries. However, the mechanism underlying the antiinflammatory activity of this medicinal plant is not fully understood. The present study was designed to investigate the anti-inflammatory effects of anthraquinones, the major constituents in rhubarb, and the molecular mechanism involved in their anti-inflammatory effects. Materials and methods: RAW264.7 cells were stimulated by lipopolysaccharide (LPS) in the presence or absence of the compounds examined. The proliferation of RAW264.7 cells was assayed by the AlamarBlue method. The quantity of nitric oxide (NO) was determined by Griess assay. The expression of proinflammatory cytokines was determined by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time PCR. Inducible nitric oxide synthase (iNOS), inhibitor of nuclear factor kappa B alpha (l kappa B alpha), extracellular signal-regulated kinase (ERR), p38 mitogen-activated protein kinase (MAPK), c-Jun NH2-terminal kinase (INK), and Akt/phosphoinositide 3-kinase (PI3K) protein expression levels were determined by Western blotting. Results: Aloe-emodin markedly suppressed the production of NO, interleukin-6 (IL-6), and interleukin1 beta (IL-1 beta) in LPS-stimulated RAW264.7 cells with no apparent cytotoxicity. The mRNA expression levels of iNOS, IL-6, and IL-1 beta genes were also significantly inhibited by aloe-emodin. Western blot analysis showed that aloe-emodin suppressed LPS-induced iNOS protein expression, IkB alpha degradation, and the phosphorylation of ERK, p38, JNK, and Akt Conclusions: These results demonstrate that aloe-emodin is the bioactive component of rhubarb that confers an anti-inflammatory effect through a likely mechanism involving a decrease in proinflammatory cytokine production in LPS-induced RAW264.7 macrophages via inhibition of NF-kappa B, MAPK, and PI3K pathways. (c) 2014 Elsevier Ireland Ltd. All rights reserved.