Cardiovascular disease remains a leading global cause of mortality, with elevated blood cholesterol levels being a major contributor to its development. Excess plasma cholesterol accumulates within macrophages embedded in arterial walls, triggering inflammatory responses that initiate the formation of atherosclerotic plaques. While statin therapy effectively lowers low-density lipoprotein (LDL) cholesterol and reduces cardiovascular morbidity and mortality, residual risk persists among patients undergoing LDL-lowering treatments, prompting exploration of alternative therapeutic strategies. Epidemiological data suggest an inverse relationship between high-density lipoprotein (HDL) cholesterol levels and cardiovascular risk, indicating potential benefits from raising HDL. However, recent clinical trials involving cholesteryl ester transfer protein (CETP) inhibitors and niacin have failed to demonstrate significant clinical advantages despite increases in HDL cholesterol. These findings have led to the hypothesis that HDL functionality—rather than mere mass—may be a more accurate predictor of cardiovascular risk.
One of HDL’s earliest recognized functions is its ability to promote cholesterol efflux from macrophage foam cells within atherosclerotic lesions. This process has been shown to enhance macrophage egress and reduce plaque burden in animal models of cardiovascular disease. Measuring the dynamic rate of cholesterol efflux from macrophages may thus serve as a superior indicator of the anti-atherogenic potential of novel HDL-targeted therapies. The movement of cholesterol from peripheral cells like macrophages to HDL marks the initial step in reverse cholesterol transport (RCT), a pathway whereby cholesterol is transported to the liver for catabolism or excretion into bile. Recent studies have also identified hepatic-independent routes for cholesterol secretion.
Animal model research indicates that RCT measurements strongly correlate with the impact of genetic and pharmacological interventions on atherosclerosis. In humans, the ability of patient sera to accept cholesterol from macrophages in vitro inversely correlates with carotid intima-media thickness, making cholesterol acceptor capacity a robust predictor of coronary disease status. Despite these promising associations, the utility of in vitro plasma cholesterol acceptor activity as a clinical biomarker and the specific proteins or particles responsible remain controversial.
Central to the regulation of RCT are the liver X receptors (LXRs), LXRα and LXRβ, which belong to the nuclear hormone receptor superfamily of ligand-activated transcription factors.4-Methoxy-N-(4-methoxyphenyl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline References Genetic knockout and synthetic agonist studies have established critical roles for LXRs in cholesterol homeostasis and fatty acid metabolism.Tolebrutinib manufacturer Treatment with LXR agonists induces gene expression changes that promote cholesterol efflux from peripheral cells such as macrophages, stimulate cholesterol secretion from the liver, and inhibit intestinal cholesterol absorption.PMID:34929561 Endogenous ligands for LXRs are oxidized cholesterol derivatives (oxysterols), whose levels rise in parallel with intracellular cholesterol, enabling LXRs to function as cellular cholesterol sensors.
At the molecular level, LXRs regulate macrophage cholesterol efflux by modulating the expression of genes encoding ATP-binding cassette (ABC) transporters ABCA1 and ABCG1, as well as apolipoprotein E (APOE). Upregulation of ABCA1 and ABCG1 enhances the transfer of intracellular cholesterol to HDL particles. Genome-wide association studies link both transporters to HDL cholesterol levels in humans. Mutations in the human ABCA1 gene cause Tangier disease, characterized by near absence of HDL, massive cholesterol accumulation in lymphoid tissues, and heightened atherosclerosis risk.
LXRs also regulate ABCG5 and ABCG8, two half-transporters that form a functional complex involved in cholesterol excretion (liver) and absorption limitation (intestine). Expression of ABCG5/ABCG8 is largely confined to the liver and intestine, where they play key roles in maintaining systemic cholesterol balance. Genetic deletion of ABCG5/G8 or LXR in the liver abolishes the ability of LXR agonists to stimulate fecal cholesterol excretion. Thus, activation of LXRs promotes net cholesterol removal from the periphery.
Not surprisingly, LXR agonists reduce atherosclerosis in animal models and increase plasma HDL cholesterol, suggesting dual mechanisms of action: cell-autonomous control of cholesterol mobilization via transporter regulation, and non-autonomous enhancement of plasma cholesterol acceptor capacity. Interestingly, the HDL-raising effect of LXR agonists is primarily mediated by intestinal ABCA1 induction. An intestinal-specific LXR agonist has been shown to increase RCT, underscoring the importance of gut-mediated pathways.
Despite evidence pointing to macrophage LXR activity as central to the anti-atherogenic effects of LXR agonists, this study reveals a surprising disconnect. Using tissue-specific LXR deletions combined with in vivo and in vitro assays, we demonstrate that macrophage LXR activity is neither necessary nor sufficient for LXR agonist-stimulated RCT. Instead, the primary driver of increased RCT appears to be the ability of LXR agonists to enhance HDL mass and function through intestinal activation. Our findings indicate that macrophage cholesterol efflux in vivo is not regulated in a cell-autonomous manner but is instead determined predominantly by the quantity and functional quality of circulating HDL.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com