Luteolin Protects HUVECs from TNF-α-induced Oxidative Stress and Inflammation via its Effects on the Nox4/ROS-NF-κB and MAPK Pathways

Aim: Inflammation and oxidative stress are now recognized to be two important contributing factors to the development of atherosclerosis (AS). NADPH oxidase-4 (Nox4)-derived reactive oxygen species (ROS), NF-kappa B and MAPK play crucial roles in these processes. Luteolin, a flavone rich in many plants, can interrupt the molecular expression and inhibit the progression of inflammation and oxidative stress. The present study was designed to test whether luteolin inhibits TNF-alpha-induced inflammation and oxidative stress in human umbilical vein endothelial cells (HUVECs) and identify some of the mechanisms underlying these effects. Methods: HUVECs were treated with luteolin in the presence/absence of TNF-alpha. The mechanism of luteolin against TNF-alpha-induced cell injury was evaluated using Western blotting, real-time RT-PCR and flow cytometry analyses. Results: Luteolin suppressed the TNF-alpha-activated ROS generation, as well as the Nox4, p22phox, and ICAM-1 and VCAM-1 expression. Luteolin also enhanced the Bcl-2 and reduced caspase-3, -9 expression in the TNF-alpha-treated HUVECs. Finally, luteolin inhibited the TNF-alpha-induced transcriptional activity of NF-kappa B and p38 in addition to ERK1/2 phosphorylation. The inhibitors and siRNA of Nox4 and NF-kappa B not only reduced ROS generation, p38, ERK1/2 phosphorylation and the ICAM-1 and VCAM-1 expression, but also enhanced Bcl-2 expression. The inhibitor of p38 had the same effect on the expression of ICAM-1, VCAM-1 and Bcl-2, while the inhibitor of ERK1/2 increased the Bcl-2 expression rather than reducing the ICAM-1 and VCAM-1 expression. Conclusions: Luteolin attenuates TNF-alpha-induced oxidative stress and inflammation via its effects on the Nox4/ROS-NF-kappa B and MAPK pathways. These results suggest that luteolin may provide a beneficial effect in treating vascular diseases associated with oxidative stress and inflammation.