Myrrh mediates haem oxygenase-1 expression to suppress the lipopolysaccharide-induced inflammatory response in RAW264.7 macrophages

Objectives To elucidate a novel anti-inflammatory mechanism of myrrh against lipopolysaccharide (LPS)-induced inflammation. Methods RAW264.7 macrophages were cultured in DMEM and then cells were treated with LPS or LPS plus a myrrh methanol extract (MME) for 24 h. The culture medium was collected for determination of nitric oxide (NO), prostaglandin (PG)E ₂, interleukin (IL)-1β, and tumour necrosis factor (TNF)-α, and cells were harvested by lysis buffer for Western blot analysis. Key findings Our data showed that treatment with the MME (1∼100 μg/ml) did not cause cytotoxicity or activate haem oxygenase-1 (HO-1) protein synthesis in RAW264.7 macrophages. Furthermore, the MME inhibited LPS-stimulated NO, PGE ₂, IL-1β and TNF-α release and inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 protein expression. Zn(II) protoporphyrin IX, a specific inhibitor of HO-1, blocked the inhibition of iNOS and COX-2 expression by the MME. Conclusions These results suggest that among mechanisms of the anti-inflammatory response, the MME inhibited the production of NO, PGE ₂, IL-1β and TNF-α by downregulating iNOS and COX-2 gene expression in macrophages and worked through the action of HO-1.