Toll-like receptor 4 mediates endothelial cell activation through NF-κB but is not associated with endothelial dysfunction in patients with rheumatoid arthritis

OBJECTIVE: To investigate the effects of TLR4 antagonism on human endothelial\r\ncells activation and cytokine expression, and whether the Asp299Gly TLR4\r\npolymorphism is associated with better endothelial function in patients with\r\nrheumatoid arthritis (RA).\r\nMETHODS: Human aortic endothelial cells (HAECs) were treated with\r\nlipopolysaccharide (LPS), OxPAPC, and free fatty acids (FFA) at baseline and\r\nafter incubation with the TLR4 antagonist eritoran (E5564). Cytokine expression\r\nwas assessed by quantitative real-time PCR. In vivo endothelial function was\r\nassessed as brachial artery flow-mediated dilation (FMD) in RA patients with the \r\nwild type gene (aa) and with the Asp299Gly TLR4 polymorphic variant (ag).\r\nRESULTS: In HAEC, TLR4 antagonism with eritoran inhibited LPS-induced mRNA\r\nexpression of IL-6, IL-8, TNFα, CCL-2, VCAM and ICAM (P<0.05 for all) and\r\ninhibited Ox-PAPC-induced mRNA expression of IL-8 (P<0.05) and IL-6, albeit not\r\nto a statistically significant level (p = 0.07). In contrast, eritoran did not\r\naffect FFA-induced mRNA expression of IL-6 (P>0.05). In 30 patients with RA (15\r\nwith the ag allele) undergoing measurement of FMD, no differences in FMD and\r\nplasma levels of IL-6, IL-8, VCAM, and ICAM were found between the aa and the ag \r\nphenotype (P>0.05 for all).\r\nCONCLUSIONS: TLR4 signaling in endothelial cells may be triggered by LPS and\r\noxidized phospholipids, leading to endothelial activation and inflammation, which\r\nare inhibited by eritoran. Our in vivo investigation, however, does not support\r\nan association between the Asp299Gly TLR4 polymorphism and improved\r\nendothelium-dependent vasodilator function in patients with RA. Further study is \r\nneeded to better understand the potential role of TLR4 on endothelial dysfunction\r\nin this and other patient populations.