Effects of sphondin, isolated from Heracleum laciniatum, on IL-1beta-induced cyclooxygenase-2 expression in human pulmonary epithelial cells

Recently, under large-scale screening experiments, we found that sphondin, a furanocoumarin derivative isolated from Heracleum laciniatum, possessed an inhibitory effect on IL–1β-induced increase in the level of COX–2 protein and PGE2 release in A549 cells. Accordingly, we examined in the present study the action mechanism of sphondin on the inhibition of IL–1β-induced COX–2 protein expression and PGE2 release in a human pulmonary epithelial cell line (A549). Pretreatment of cells with sphondin (10–50 μM) concentration-dependently attenuated IL–1β-induced COX–2 protein expression and PGE2 release. The IL–1β-induced increase in COX–2 mRNA expression was also attenuated by sphondin (50 μM). The selective COX–2 inhibitor, NS–398 (0.01–1 μM), inhibited the activity of the COX–2 enzyme in a concentration-dependent manner, while sphondin (10–50 μM) had no effect. Sphondin (50 μM) did not affect the IL–1β-induced activations of p44/42 MAPK, p38 MAPK, and JNK. Treatment of cells with sphondin (50 μM) or the NF-κB inhibitor, PDTC (50 μM) partially inhibited IL–1β-induced degradation of IκB-α in the cytosol and translocation of p65 NF-κB from the cytosol to the nucleus. Furthermore, IL–1β-induced NF-κB-specific DNA-protein complex formation in the nucleus was partially inhibited by sphondin (50 μM) or PDTC (50 μM). Taken together, we demonstrate that sphondin inhibits IL–1β-induced PGE2 release in A549 cells; this inhibition is mediated by suppressing of COX–2 expression, rather than by inhibiting COX–2 enzyme activity. The inhibitory mechanism of sphondin on IL–1β-induced COX–2 expression may be, at least in part, through suppression of NF-κB activity. We conclude that sphondin may have the therapeutic potential as an anti-inflammatory drug on airway inflammation.