Molecular and Cellular Biochemistry

, Volume 423, Issue 1–2, pp 53–65 | Cite as

Quercetin modulates toll-like receptor-mediated protein kinase signaling pathways in oxLDL-challenged human PBMCs and regulates TLR-activated atherosclerotic inflammation in hypercholesterolemic rats



Toll-like receptors (TLRs) are pattern recognition receptors that have a unique and essential function in innate immunity. The effect of quercetin on TLR-mediated downstream signaling mechanism and its effect on TLR-mediated MAP kinase and Akt pathways were studied in oxLDL-stimulated hPBMCs using specific inhibitors. The pretreatment of hPBMCs with specific TLR inhibitor, CLI-095, decreased the NF-κB nuclear translocation and TNF-α release by oxLDL. When the cells treated with inhibitor and quercetin together, the inhibition was more effective. The specific inhibitor for p38 MAPK, SB203580, reduced the phosphorylated p38 level and decreased the NF-κB activation and TNF-α release by oxLDL-challenged hPBMCs. This inhibitor showed enhanced inhibition when treated with quercetin together. The inhibitors for ERK1/2, PD98059, and for JNK, SP606125, also showed inhibitory effect on NF-κB activation and TNF-α release by oxLDL-simulated hPBMCs. Quercetin supplementation enhanced the inhibition of nuclear translocation of NF-κB and the release of cytokines. TLR4 inhibition study confirmed the downstream signaling mechanism mediated by NF-κB which is involved in the oxLDL-induced inflammatory response, and quercetin suppresses the cytokine, TNF-α release by modulating TLR–NF-κB signaling pathway. In addition to NF-κB signaling pathway, inflammation induced by oxLDL was also related to the activation of p38MAPK, ERK1/2 and JNK, and Akt pathways, and the protective effect of quercetin may be also related to the inhibition of activation of these pathways. Quercetin significantly downregulated the elevated mRNA expression of TLRs and cytokine TNF-α in HCD-fed atherosclerotic rats in vivo. As quercetin possesses inhibition on both TLR–NF-κB signaling pathway and TLR-mediated MAPK pathway, it is evident that it can be used as a therapeutic agent to ameliorate atherosclerotic inflammation. Since quercetin is the major flavonoid and forms the backbone of many other flavonoids and this study provides strong evidence that it has potent anti-inflammatory effect, quercetin may be a promising agent for the prevention and treatment of atherosclerosis and promote health by reducing harmful vascular inflammation.


TLR NF-κB Atherosclerosis MAPK Cytokines Inflammation 



The funding was provided by the Department of SC/ST Development, Govt of Kerala, India (Grant No. B3-9272/04). The authors express their sincere gratitude to Prof. Dr. P. R. Sudhakaran (former Head of the Department of Biochemistry, University of Kerala), Emeritus Scientist (KSCSTE), Department of Computational Biology and Bioinformatics, University of Kerala, for his valuable suggestions and guidance to do this work.


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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.Department of BiochemistryUniversity of KeralaThiruvananthapuramIndia

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