Abstract 11714: The Importance of Lipid Peroxidation in TLR4 Activation by Fatty Acids in Endothelial Cells
Background: Fatty acid (FA) is known as adipocytokine which enhances various functions like insulin resistance in skeletal muscle and glyconeogenesis in liver. We reported that acute systemic administration of FA causes endothelial dysfunction. But the details of the mechanism remained unclear. Based on recent reports that FA works as a ligand for Toll-like receptor 4 (TLR4), we examined FA's effect on the TLR4-NFκB pathway in endothelial cells (ECs) and found out that peroxidation of FA plays an essential role.
Methods: Phosphatidylcholine vesicles were used as carriers of FA (palmitic acid (PA), oleic acid (OA), docosahexaenoic acid (DHA), and 1:1 mixture of PA and OA). FA vesicles, no FA vesicles (control), and lipopolysaccharide (LPS, positive control) were loaded to cultured ECs for 1 hour. The effect of peroxidation was examined by repeating some experiments on the same sample after a certain interval of time. Peroxidation of lipid was evaluated by the concentration of malondialdehyde (MDA) in the vesicles. Activation of TLR4 was assessed by the shift of distribution in the plasma membrane to the caveolae/raft fraction. Downstream of TLR4 signalling including degradation of IκB-α was assessed in whole cell lysate by western blotting.
Results: Peroxidized FA as well as LPS activated TLR4 and enhanced degradation of IκB-α, whereas no FA or MDA-undetectable FA vesicles did not. Saturated FA of PA alone did not activate the TLR4-NFκB pathway whereas peroxidised unsaturated FAs showed activation. Dose dependency of DHA turned out that the pathway is activated by DHA with MDA concentration of more than 1 × 10-9 M.
Conclusion: In the acute action by FA that follows the same pathway as LPS, peroxidation of unsaturated FA is essential, suggesting the lipotoxicity on vascular function requires oxidative environment. Inactivation of nitric oxide by lipid-peroxide-related radicals and inflammatory reactions through the TLR4-NFκB pathway in ECs are considered to be involved in endothelial dysfunction by FA.
- © 2011 by American Heart Association, Inc.