Suppression of inducible cyclooxygenase and inducible nitric oxide synthase by apigenin and related flavonoids in mouse macrophages

Abstract

Prostaglandins biosynthesis and nitric oxide production have been implicated in the process of carcinogenesis and inflammation. In this study, we investigated the effect of various flavonoids and (-)-epigallocatechin-3-gallate on the activities of inducible cyclooxygenase (COX-2) and inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. Apigenin, genistein and kaempferol were markedly active inhibitors of transcriptional activation of COX-2, with IC(50) < 15 microM. In addition, apigenin and kaempferol were also markedly active inhibitors of transcriptional activation of iNOS, with IC(50) < 15 microM. Of those compounds tested, apigenin was the most potent inhibitor of transcriptional activation of both COX-2 and iNOS. Western and northern blot analyses demonstrated that apigenin significantly blocked protein and mRNA expression of COX-2 and iNOS in LPS-activated macrophages. Transient transfection experiments showed that LPS caused an approximately 4-fold increase in both COX-2 and iNOS promoter activities, these increments were suppressed by apigenin. Moreover, electrophoretic mobility shift assay (EMSA) experiments indicated that apigenin blocked the LPS-induced activation of nuclear factor-kB (NF-kB). The inhibition of NF-kB activation occurs through the prevention of inhibitor kB (IkB) degradation. Transient transfection experiments also showed that apigenin inhibited NF-kB-dependent transcriptional activity. Finally, we showed that apigenin could inhibit the IkB kinase activity induced by LPS or interferon-gamma. The results of further studies suggest that suppression of transcriptional activation of COX-2 and iNOS by apigenin might mainly be mediated through inhibition of IkB kinase activity. This study suggests that modulation of COX-2 and iNOS by apigenin and related flavonoids may be important in the prevention of carcinogenesis and inflammation.

Anti–inflammatory and analgesic activities of Melanthera scandens

“…Flavonoids also have anti-inflammatory effects through its inhibition of the cyclooxygenase pathway [33] . That the extract inhibited neurogenic and non-neurogenic pains as well as narcotic pains may in part explain the mechanisms of its action and these effects are due to the presence of phytochemical components in the extract.…”

Apigenin and cancer chemoprevention: Progress, potential and promise (Review)

“…The anti-inflammatory properties of apigenin are evident in studies that have shown suppression of LPS-induced cyclooxygenase-2 and nitric oxide synthase-2 activity and expression in mouse macrophages (40). In a separate study, apigenin treatment resulted in suppression of the constitutive and tumor necrosis factor (TNF) ·-induced nuclear factor (NF)-κB activation in human umbilical vein endothelial cells (41).…”

The roles of polyphenols in cancer chemoprevention

“…Genistein effectively suppresses the COX-2 promoter activity with and without tumor growth factor-α-stimulation in DLD-1 colon cancer cells [73]. Genistein strongly represses the transcriptional activation of COX-2 in macrophages [67], and consistently inhibits COX-2 expression by blocking the LPS-mediated tyrosine kinase signal transduction pathway [92]. Using a β-galactosidase reporter gene system in human colon cancer cells, Mutoh et al [73] showed that genistein suppresses the COX-2 promoter activity in the presence or absence of tumor necrosis factor-α stimulation.…”