Quercetin Attenuates Adhesion Molecule Expression in Intestinal Microvascular Endothelial Cells by Modulating Multiple Pathways.

BACKGROUND: In inflammatory bowel disease, activation of microvascular endothelial cells and adhesion of immune cells are required for the initiation and maintenance of inflammation. We evaluated the effects and mechanisms of quercetin, a flavone identified in a wide variety of dietary sources, in LPS-induced rat intestinal microvascular endothelial cells (RIMVECs).
METHODS: RIMVECs were pretreated with quercetin of various concentrations (20, 40 and 80 μM) followed by LPS (10 μg/ml) stimulation. ELISA was used to examine protein levels of intercellular adhesion molecules-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in the supernatant. Protein levels of Toll-like receptor 4 (TLR4), nuclear transcription factor kappa B (NF-κB) p65, inhibitors of NF-κB (IκB-α), extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), mitogen-activated protein kinase (MAPK) p38 and signal transducer and activator of transcription (STAT) in cells were measured by Western blot.
RESULTS: Quercetin significantly suppressed protein levels of ICAM-1 and VCAM-1 induced by LPS. Quercetin also inhibited TLR4 expression, NF-κB p65, ERK, JNK and STAT phosphorylation and decreased IκB-α degradation. Moreover, the MAPK p38 signal does not contribute to the anti-inflammatory effects on RIMVECs, although LPS significantly increases its phosphorylation.
CONCLUSIONS: These results indicate that quercetin may have an anti-inflammatory effect by inhibiting expression of ICAM-1 and VCAM-1 in RIMVECs by suppressing TLR4, NF-κB, ERK, JNK and STAT but not the p38 signaling pathway.