Effects of sphondin, isolated from Heracleum laciniatum, on IL-1β-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.