We investigated a molecular mechanism underlying quercetinmediated amelioration of colonic mucosal injury and analyzed chemical structure contributing to the quercetin's effect. Quercetin up-regulated vascular endothelial growth factor (VEGF), an ulcer healing factor, not only in colon epithelial cell lines but also in the inflamed colonic tissue. VEGF derived from quercetin-treated colon epithelial cells promoted tube formation. The VEGF induction was dependent on quercetin-mediated hypoxia-inducible factor-1 (HIF-1) activation. Quercetin delayed HIF-1␣ protein disappearance, which occurred by inhibiting HIF-prolyl hydroxylase (HPH), the key enzyme for HIF-1␣ hydroxylation and subsequent von Hippel Lindau-dependent HIF-1␣ degradation. HPH inhibition by quercetin was neutralized significantly by an elevated dose of iron. Consistent with this, cellular induction of HIF-1␣ by quercetin was abolished by pretreatment with iron. Two iron-chelating moieties in quercetin, -OH at position 3 of the C ring and/or -OH at positions 3Ј and 4Ј of the B ring, enabled the flavonoid to inhibit HPH and subsequently induce HIF-1␣. Our data suggest that the clinical effect of quercetin may be partly attributed to the activation of an angiogenic pathway HIF-1-VEGF via inhibiting HPH and the chelating moieties of quercetin were required for inhibiting HPH.

In previous reports, a novel colon-specific prodrug, 5-aminosalicyltaurine (5-ASA-Tau) administered orally, is successfully delivered to and liberates 5-aminosalicylic acid (5-ASA) and taurine in the inflamed large intestine of rats. Furthermore, the prodrug ameliorates the 2,4,6-trinitrobenzene-sulfonic acid-induced colitis, and taurine acts not only as a carrier but also as an active therapeutic agent. In this study, we investigated the anti-inflammatory properties of the prodrug at a molecular level. After rectal administration of taurine, formation of taurine chloramine (TauCl) in the inflamed colonic tissue was examined using high-performance liquid chromatography. In human colon epithelial cell lines, nuclear factor-B (NF-B) activity was accessed using an NF-B-dependent luciferase reporter gene. Protein levels were monitored by Western blotting. DNA binding activity of the NF-B subunit p65 was determined using a DNA binding assay kit. A millimolar level of TauCl was formed in the inflamed tissue. TauCl inhibited tumor necrosis factor (TNF)-dependent NF-B activation by modifying thiol(s) on p65 and blocking DNA binding. In addition, 5-ASA inhibited phosphorylation of p65 at serine 536, which is critical for transcriptional activity of NF-B. Furthermore, combined TauCl/5-ASA treatment additively inhibited TNF-dependent NF-B activation. Together, our data suggest that the colon-specific carrier taurine contributes to the clinical effect of the prodrug by potentiating the inhibitory effect of the active ingredient 5-ASA on a major proinflammatory signal, TNF-dependent NF-B activation in the inflamed large intestine.

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