Antiinflammatory activity of methanol extract isolated from stem bark of Magnolia kobus

The present study reports the antiinflammatory activity of a methanol extract isolated from the stem bark of Magnolia kobus (MK). MK potently inhibited lipopolysaccharide (LPS)-induced production of nitric oxide and interleukin-1β (IL-1β) in RAW 264.7 cells, a murine macrophage-like cell line. The secretion of tumor necrosis factor-α (TNF-α) was also suppressed in LPS-stimulated RAW 264.7 cells although the magnitude of inhibition was weaker than that of nitric oxide and IL-1β. The mRNA expressions of inducible nitric oxide synthase (iNOS), IL-1β and TNF-α were also suppressed by MK in LPS-stimulated RAW 264.7 cells. Further study demonstrated that LPS-induced DNA binding of AP-1 and phosphorylation of c-jun TV-terminal kinase (JNK) were inhibited by MK treatment in RAW 264.7 cells, whereas phosphorylation of p38 mitogen-activated protein kinase was unaffected. Moreover, topical application of MK suppressed ear swelling in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin inflammation model. Collectively, these results suggest that MK exerts antiinflammatory effects in vitro and in vivo and this might be mediated, at least in part, by blocking AP-1 and JNK activation.