Anti - Inflammatory Activity of Quercetin and Kaempferol Is Limited to Tlr4 Stimulation in Monocytes

Abstract

Flavonoids are known to exert anti-inflammatory activity but their mechanism at receptor level and their comparative potencies are less studied. Objective of the study is to evaluate, rank order few flavonoids for their cytokine inhibitory activity in monocytes (THP-1) and explore the inhibitory signature among toll-like receptors (TLRs). We tested flavonoids for their potential to inhibit LPS induced cytokines IL-6, TNF alpha in human monocyte cell line THP-1 and mouse macrophage cell line using Enzyme linked immunosorbent assay (ELISA) assays. Quercetin and Kaempferol reduced LPS induced cytokine secretion in monocyte and macrophage cell lines. Quercetin and Kaempferol demonstrated dose dependent inhibition of cytokines IL-6 and TNF alpha. Quercetin demonstrated IC50 of 6.9µM whereas Kaempferol demonstrated IC50 of 14.3µM in cytokine reduction. In THP-1, NF-kB activity is measured using secreted embryonic alkaline phosphatase (SEAP) reporter with different toll-like receptor activation. TLR4 stimulated NF-kB activity was inhibited by Quercetin and Kaempferol in THP-1 cell line, while these flavonoids did not impact signaling of other TLR ligands Pam3CSK4 (TLR1/2) FLS (TLR2/6), Flagellin (TLR5) and R848 (TLR7/8). I. Quercetin and Kaempferol modulate NF-kB activity when stimulated with TLR4, but not with TLR1/2, TLR2/6, TLR5 and TLR7/8 in Monocytes. Understanding the inhibition profile of flavonoids against Toll receptors will help in design better inhibitor which can alleviate inflammatory diseases