Santamarin, a sesquiterpene lactone isolated from Saussurea lappa, represses LPS-induced inflammatory responses via expression of heme oxygenase-1 in murine macrophage cells

Saussurea lappa C.B. Clarke (Compositae) is indigenous to India and Pakistan. The dried root of S. lappa has been traditionally used for alleviating pain in abdominal distention and tenesmus, indigestion with anorexia, dysentery, nausea, and vomiting. Santamarin is a sesquiterpene lactone isolated from S. lappa. In the present study, santamarin inhibited inducible nitric oxide synthase (iNOS) protein, reduced iNOS-derived nitric oxide (NO), suppressed COX-2 protein and reduced COX-derived PGE(2) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells and murine peritoneal macrophages. Similarly, santamarin reduced tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) production. In addition, santamarin suppressed the phosphorylation and degradation of IκB-α as well as the nuclear translocation of p65 in response to LPS in RAW264.7 cells. Furthermore, santamarin induced heme oxygenase (HO)-1 expression mRNA and protein level that plays a cytoprotective role against inflammation. The induction of HO-1 is primarily regulated at the transcriptional level, and its induction by various agents is mediated by the nuclear transcription factor E2-related factor 2 (Nrf2), master regulator of antioxidant responses. Unbound Nrf2 translocates into the nucleus and binds to the antioxidant response element (ARE) in the upstream promoter region of many antioxidative genes, where it initiates their transcription. The effects of santamarin on LPS-induced NO, PGE(2), TNF-α, and IL-1β production were partially reversed by the HO-1 inhibitor, tin protoporphyrin (SnPP). Therefore, our data suggest that the anti-inflammatory effect of santamarin in macrophages may be exerted through a novel mechanism that involves HO-1 expression.