Luteolin inhibits extracellular signal-regulated kinase pathway through protease-activated receptors (-2 and -4) and their agonist activity

Luteolin is a major flavonoid of Lonicera japonica and has anti-inflammatory effect. The activation of proteinase-activated receptor (PAR)-2 and -4 by trypsin appears to play a role in inflammation. In the present study, we examined the inhibitory effects of luteolin on activation of trypsin-induced human leukemic mast cells (HMC-1). HMC-1 cells were stimulated with trypsin, PAR-2 and PAR-4 agonist, in the presence or absence of luteolin. The level of TNF-α secretion was measured by enzyme-linked immunosorbent assay (ELISA). The expression of tryptase and phosphorylated-extracellular signal-regulated kinase (ERK) were assessed by Western blot analysis. Moreover, trypsin activity was measured by the substrate Bz-DL-Arg-p-nitroanilide (BAPNA). TNF-α secretion and tryptase expression in trypsin-stimulated HMC-1 cells were markedly inhibited by pretreatment of luteolin. Furthermore, the pretreatment of luteolin resulted in the reduction of ERK phosphorylation and trypsin activity. These results suggest that luteolin might has the inhibitory effects on the PAR-2 and -4-dependent inflammation.