Combination of curcumin and luteolin synergistically inhibits TNF-α-induced vascular inflammation in human vascular cells and mice

Emerging evidence shows that phytochemicals, the secondary plant metabolites present in a large variety of foods, have the potential ability in reducing the risk of cardiovascular diseases. However, the dosages of phytochemicals in the cellular and animal studies are too high to reach in humans by relevant foods or dietary supplement intake. The aims of this study were to investigate whether and how combined curcumin and luteolin synergistically inhibit tumor necrosis factor-alpha (TNF-α)-induced monocytes adhesion endothelium, a crucial step of the development of endothelial dysfunction, both in human vascular cells and mouse aortic endothelium. Our results show that combined curcumin (1 μM) and luteolin (0.5 μM) synergistically (combination index is 0.60) inhibited TNF-α-induced monocytes adhesion to human EA.hy926 endothelial cells while the individual chemicals did not have such effect at the selected concentrations. We also found that TNF-α-enhanced protein expressions of vascular cell adhesion molecule 1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1) and nuclear factor (NF)-κB translocation were synergistically reduced by the combined curcumin and luteolin in EA.hy 926 cells while the individual chemical did not have this inhibitory effect. Consistently, 2 weeks dietary intake of combined curcumin (500 mg/kg) and luteolin (500 mg/kg) in C57BL/6 mice synergistically prevented TNF-α-stimulated adhesion of mouse monocytes to aortic endothelium ex vivo as well as the TNF-α-increased aortic protein expression of MCP-1 and VCAM-1. Therefore, combined curcumin and luteolin at physiological concentrations synergistically inhibits TNF-α-induced monocytes adhesion to endothelial cells and expressions of MCP-1 and VCAM-1 via suppressing NF-κB translocation into the nucleus.