LXRs are finally being adequately targeted in atherosclerosis

Liver X Receptor: a potential target in the treatment of atherosclerosis

INTRODUCTION

Liver X receptors (LXRs) are master regulators of atherogenesis. Their anti-atherogenic potential has been attributed to their role in the inhibition of macrophage-mediated inflammation and promotion of reverse cholesterol transport. Owing to the significance of their anti-atherogenic potential, it is essential to develop and test new generation LXR agonists, both synthetic and natural, to identify potential LXR-targeted therapeutics for the future.

AREAS COVERED

This review describes the role of LXRs in atherosclerotic development, provides a summary of LXR agonists and future directions for atherosclerosis research. We searched PubMed, Scopus and Google Scholar for relevant reports, from last 10 years, using atherosclerosis, liver X receptor, and LXR agonist as keywords.

EXPERT OPINION

LXRα has gained widespread recognition as a regulator of cholesterol homeostasis and expression of inflammatory genes. Further research using models of cell type-specific knockout and specific agonist-targeted LXR isoforms is warranted. Enthusiasm for therapeutic value of LXR agonists has been tempered due to LXRα-mediated induction of hepatic lipogenesis. LXRα agonism and LXRβ targeting, gut-specific inverse LXR agonists, investigations combining LXR agonists with other lipogenesis mitigating agents, like IDOL antagonists and synthetic HDL, and targeting ABCA1, M2 macrophages and LXRα phosphorylation, remain as promising possibilities.

Screening for liver X receptor modulators: Where are we and for what use?

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are canonically activated by oxidized derivatives of cholesterol. Since the mid-90s, numerous groups have identified LXRs as endocrine receptors that are involved in the regulation of various physiological functions. As a result, when their expression is genetically modified in mice, phenotypic analyses reveal endocrine disorders ranging from infertility to diabetes and obesity, nervous system pathologies such Alzheimer's or Parkinson's disease, immunological disturbances, inflammatory response, and enhancement of tumour development. Based on such findings, it appears that LXRs could constitute good pharmacological targets to prevent and/or to treat these diseases. This review discusses the various aspects of LXR drug discovery, from the tools available for the screening of potential LXR modulators to the current situational analysis of the drugs in development. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

The atheroprotective roles of heart-protecting musk pills against atherosclerosis development in apolipoprotein E-deficient mice

Background

Heart-protecting musk pill (HMP), derived from Chinese herbal medicines, has been found to possess protective roles against atherosclerosis-related cardiovascular diseases (CVDs), however, the anti-atherosclerotic mechanisms of HMP are still unclear. Here, we investigated the effects of HMP on alleviating atherosclerotic lesion severity in mice and explored the molecular mechanisms.

Methods

Apolipoprotein E-deficient mice were fed western-type diet supplemented with HMP (25 mg/kg/day) or normal saline gavage for 20 weeks. Then histopathological staining was performed to assess the atheromatous plaque burden. Biochemical kits were used to detect levels of lipid profiles. Moreover, effector factors associated with lipid metabolism in liver and intestinal tissues were investigated by western blot and real-time PCR assays. Levels of signal molecules participating in the mitochondrial-mediated apoptosis pathway were detected by Western blot.

Results

We found that HMP notably reduced atherosclerotic lesion size (P<0.05) and improved plaque stability (P<0.05). HMP treatment decreased circulating TC (P<0.01), LDL-C (P<0.01) and TG (P<0.05) levels and increased HDL-C (P<0.05) content. HMP was found to suppress SREBP2, HMGCR and PCSK9 expressions (P<0.05), yet promote LDLR expression (P<0.05) in hepatocytes. Moreover, HMP was discovered to activate PPARα/CPT-1A cascade (P<0.05) and inhibit contents of SREBP1c and the lipogenic genes FAS and ACCα (P<0.05). The LBK1/AMPK cascade was also activated after HMP administration (P<0.05). Additionally, HMP was found to facilitate transintestinal cholesterol excretion by increasing ABCG5 and ABCG8 levels and reducing NPC1L1 content (P<0.05). In terms of vasoprotective activities, we observed that HMP decreased cleaved caspase-3 content (P<0.05) in the vascular intima, which might be due to inhibition of mitochondrial-related signaling pathway.

Conclusions

Altogether, our study indicates that HMP plays anti-atherosclerotic roles via regulating lipid metabolism and improving vascular intimal injury.