Synergistic anti-inflammatory effects of luteolin and tangeretin on lipopolysaccharide-stimulated raw 264.7 cells

Different dietary components in combination may act synergistically and produce enhanced biological activities. In the present work, we investigated the anti-inflammatory effects of two dietary flavonoids i.e. luteolin and tangeretin in combination. Lipopolysaccharide (LPS)-stimulated Raw 264.7 macrophage cells were treated with noncytotoxic concentrations of luteolin, tangeretin, and their combinations. The results showed that luteolin and tangeretin in combination produced much stronger inhibitory effects on LPS-stimulated production of nitric oxide than luteolin or tangeretin alone. Isobologram analysis demonstrated that these enhanced inhibitory effects were highly synergistic. Western blot analysis showed that luteolin/tangeretin combination significantly decreased the expression levels of COX-2 and iNOS, and increased the expression levels of HO-1 (hemeoxygnase-1). Enzyme-linked immunosorbent assay demonstrated that luteolin and tangeretin in combination significantly suppressed the levels of IL-1 and IL-6. These anti-inflammatory effects of the combination treatments were stronger than those produced by luteolin or tangeretin alone. Overall, our results demonstrated for the first time that combination of luteolin and tangeretin produced synergistic anti-inflammatory effects in LPS-stimulated macrophage cells.