Enhanced Levels of Oxidized Low-Density Lipoprotein Prime Monocytes to Cytokine Overproduction via Upregulation of CD14 and Toll-Like Receptor 4 in Unstable Angina

Abstract

Objectives-The purpose of this study was to establish whether oxidized low-density lipoprotein (oxLDL) contributes to cytokine overproduction via upregulation of CD14 and toll-like receptor-4 (TLR-4) expression on circulating monocytes of unstable angina (UA) patients. Methods and Results-Expression of CD14 and TLR-4 on circulating monocytes, and the concentration of plasma oxLDL, (interleukin [IL])-6, IL-1 beta, IL-8, tumor necrosis factor (TNF)-alpha, monocyte chemoattractant protein-1 (MCP-1) were measured in 27 control (C) subjects, 29 patients with stable angina (SA), and 27 with UA. CD14 and TLR-4 expression on monocytes and circulating IL-6, IL-1 beta, and oxLDL were higher in UA than in SA and C subjects (PϽ0.001). In in vitro experiments, oxLDL increased CD14 and TLR-4 expression (PϽ0.001) in control monocytes as well as IL-6, IL-1 beta, and at a lower extent TNF-␣ and MCP-1 levels in the supernatant (P from Ͻ0.05 to Ͻ0.001).The preincubation of sera derived from UA patients but with control monocytes also induced a significant increase of CD14 and TLR-4 expression (PϽ0.001) and of IL-6 and IL-1 beta production (PϽ0.001) in the supernatant. Conclusions-In UA patients oxLDL may contribute to monocyte overproduction of some cytokines by upregulating

TLR4/NF-κB signaling pathway-mediated and oxLDL-induced up-regulation of LOX-1, MCP-1, and VCAM-1 expressions in human umbilical vein endothelial cells

“…Moreover, compared with the control group, mice with both myeloid differentiation factor 88 (MyD88), which is the downstream gene of TLR4, and ApoE knocked out showed a 60% reduction of the plaque area. Another study (Pasini et al, 2007) found that MCP-1 and other inflammatory cytokines that were excessively expressed in patients with unstable angina might be related to the oxLDL-induced up-regulation of TLR4. RNA interference technology was used to block TLR4 to investigate the function and mechanism of TLR4 in the oxLDL-induced up-regulation of LOX-1, MCP-1, and VCAM-1 expressions in HUVECs.…”

PKCδ-IRAK1 axis regulates oxidized LDL-induced IL-1β production in monocytes

“…TLR2, TLR4, or TLR6 can also heterodimerize and interact with CD36 in a ligand-specifi c manner ( 54 ). Ox-LDL can also prime monocytes and peripheral blood mononuclear cell for cytokine overproduction by upregulating TLR2 and TLR4 ( 4,55,56 ).…”

“…Standard curve was prepared for each assay run using calibrators and control supplied along with the assay kit. Cu 2+ -modifi ed LDL (50-500 ng/ml) was used as standard solution ( 4 ) to quantify the circulating plasma Ox-LDL in micrograms per milliliter for the treatment in primary monocytes isolated from healthy volunteers.…”

“…Ox-LDL itself serves as a pro-infl ammatory molecule and contributes to the generation of various infl ammatory cytokines ( 3,4 ). Elevated Ox-LDL and infl ammatory response were observed in extremely obese pediatric subjects ( 5 ).…”

The Innate Immune Response Mediated by TLRs in Atherosclerosis

“…Subsequently, it was determined that mmLDL is capable of binding to CD14 and that, through the TLR4/MD2 complex, mmLDL causes actin polymerization and membrane spreading in macrophages (Miller et al, 2002). However, it has been shown that mmLDL induces secretion of pro-inflammatory cytokines, such as IL-1 , IL-6, and TNF-, in human monocytes and macrophages through CD14 (Chávez-Sánchez et al, 2010a, Chávez-Sánchez et al, 2010b, which is corroborated by the fact that the blockade of CD14 with anti-CD14 antibodies significantly reduces the concentration of pro-inflammatory cytokines, including IL-1 and IL-6, produced by macrophages in response to oxLDL (Pasini et al, 2007). The stimulation of human monocytes and macrophages with mmLDL induces the secretion of IL-1 , IL-6, and TNFthrough a TLR4-dependent mechanism (Chávez-Sánchez et al, 2010a, Chávez-Sánchez et al, 2010b, which is similar to the mechanism by which end products of LDL glycosylation lead to the production of TNF- (Hodgkinson et al, 2008a).…”