Role of the hepatic ABCA1 transporter in modulating intrahepatic cholesterol and plasma HDL cholesterol concentrations

Ellagic acid, a functional food component, ameliorates functionality of reverse cholesterol transport in murine model of atherosclerosis

BACKGROUND/OBJECTIVES

High levels of plasma low-density lipoprotein (LDL) cholesterol are an important determinant of atherosclerotic lesion formation. The disruption of cholesterol efflux or reverse cholesterol transport (RCT) in peripheral tissues and macrophages may promote atherogenesis. The aim of the current study was to examine whether bioactive ellagic acid, a functional food component, improved RCT functionality and high-density lipoprotein (HDL) function in diet-induced atherogenesis of apolipoproteins E (apoE) knockout (KO) mice.

MATERIALS/METHODS

Wild type mice and apoE KO mice were fed a high-cholesterol Paigen diet for 10 weeks to induce hypercholesterolemia and atherosclerosis, and concomitantly received 10 mg/kg ellagic acid via gavage.

RESULTS

Supplying ellagic acid enhanced induction of apoE and ATP-binding cassette (ABC) transporter G1 in oxidized LDL-exposed macrophages, facilitating cholesterol efflux associated with RCT. Oral administration of ellagic acid to apoE KO mice fed on Paigen diet improved hypercholesterolemia with reduced atherogenic index. This compound enhanced the expression of ABC transporters in peritoneal macrophages isolated from apoE KO mice fed on Paigen diet, indicating increased cholesterol efflux. Plasma levels of cholesterol ester transport protein and phospholipid transport protein involved in RCT were elevated in mice lack of apoE gene, which was substantially reduced by supplementing ellagic acid to Paigen diet-fed mice. In addition, ellagic acid attenuated hepatic lipid accumulation in apoE KO mice, evidenced by staining of hematoxylin and eosin and oil red O. Furthermore, the supplementation of 10 mg/kg ellagic acid favorably influenced the transcriptional levels of hepatic LDL receptor and scavenger receptor-B1 in Paigen diet-fed apoE KO mice.

CONCLUSION

Ellagic acid may be an athero-protective dietary compound encumbering diet-induced atherogenesis though improving the RCT functionality.

HDL and chronic kidney disease

Low HDL-cholesterol (HDL-C) concentrations are a typical trait of the dyslipidemia associated with chronic kidney disease (CKD). In this condition, plasma HDLs are characterized by alterations in structure and function, and these particles can lose their atheroprotective functions, e.g., the ability to promote cholesterol efflux from peripheral cells, anti-oxidant and anti-inflammatory proprieties and they can even become dysfunctional, i.e., exactly damaging. The reduction in plasma HDL-C levels appears to be the only lipid alteration clearly linked to the progression of renal disease in CKD patients. The association between the HDL system and CKD development and progression is also supported by the presence of genetic kidney alterations linked to HDL metabolism, including mutations in the APOA1, APOE, APOL and LCAT genes. Among these, renal disease associated with LCAT deficiency is well characterized and lipid abnormalities detected in LCAT deficiency carriers mirror the ones observed in CKD patients, being present also in acquired LCAT deficiency. This review summarizes the major alterations in HDL structure and function in CKD and how genetic alterations in HDL metabolism can be linked to kidney dysfunction. Finally, the possibility of targeting the HDL system as possible strategy to slow CKD progression is reviewed.

Hepatic nonvesicular cholesterol transport is critical for systemic lipid homeostasis

In cell models, changes in the 'accessible' pool of plasma membrane (PM) cholesterol are linked with the regulation of endoplasmic reticulum sterol synthesis and metabolism by the Aster family of nonvesicular transporters; however, the relevance of such nonvesicular transport mechanisms for lipid homeostasis in vivo has not been defined. Here we reveal two physiological contexts that generate accessible PM cholesterol and engage the Aster pathway in the liver: fasting and reverse cholesterol transport. During fasting, adipose-tissue-derived fatty acids activate hepatocyte sphingomyelinase to liberate sequestered PM cholesterol. Aster-dependent cholesterol transport during fasting facilitates cholesteryl ester formation, cholesterol movement into bile and very low-density lipoprotein production. During reverse cholesterol transport, high-density lipoprotein delivers excess cholesterol to the hepatocyte PM through scavenger receptor class B member 1. Loss of hepatic Asters impairs cholesterol movement into feces, raises plasma cholesterol levels and causes cholesterol accumulation in peripheral tissues. These results reveal fundamental mechanisms by which Aster cholesterol flux contributes to hepatic and systemic lipid homeostasis.

Air Pollution: Another Threat to HDL Function

Epidemiological studies have consistently demonstrated a positive association between exposure to air pollutants and the incidence of cardiovascular disease, with the strongest evidence for particles with a diameter < 2.5 μm (PM2.5). Therefore, air pollution has been included among the modifiable risk factor for cardiovascular outcomes as cardiovascular mortality, acute coronary syndrome, stroke, heart failure, and arrhythmias. Interestingly, the adverse effects of air pollution are more pronounced at higher levels of exposure but were also shown in countries with low levels of air pollution, indicating no apparent safe threshold. It is generally believed that exposure to air pollution in the long-term can accelerate atherosclerosis progression by promoting dyslipidemia, hypertension, and other metabolic disorders due to systemic inflammation and oxidative stress. Regarding high density lipoproteins (HDL), the impact of air pollution on plasma HDL-cholesterol levels is still debated, but there is accumulating evidence that HDL function can be impaired. In particular, the exposure to air pollution has been variably associated with a reduction in their cholesterol efflux capacity, antioxidant and anti-inflammatory potential, and ability to promote the release of nitric oxide. Further studies are needed to fully address the impact of various air pollutants on HDL functions and to elucidate the mechanisms responsible for HDL dysfunction.

The effects of brewers' spent grain on high-fat diet-induced fatty liver

Obesity drives nonalcoholic fatty liver disease (NAFLD). This study investigated the effects of dietary brewers' spent grain (BSG) supplementation on obesity-induced NAFLD. Mice fed a high-fat diet supplemented with 30% BSG (HFD30) had reduced body weight and decreased plasma total cholesterol (TC) concentrations compared with HFD-fed mice. Retroperitoneal white adipose tissue (RWAT) and liver weights were reduced. Consistent with reduced hepatic triacylglycerol, TC, and non-esterified fatty acid concentrations, HFD30-fed mice showed reduced hepatic steatosis. 3-hydroxy-3-methylglutaryl-CoA reductase and low-density lipoprotein receptor genes were increased, whereas carnitine palmitoyltransferase 1 alpha, ATP-binding cassette subfamily A member 1 (Abca1), and cholesterol 7 alpha-hydroxylase genes were upregulated in the liver of HFD30-fed mice. Abca1 gene expression was also increased in epididymal WAT and RWAT of HFD30-fed mice. BSG supplementation increased and decreased fecal fat and bile acid concentrations, respectively. Taken together, BSG supplementation reduced HFD-induced hepatic lipid accumulation by increasing fatty acid oxidation and bile acid synthesis in the liver as well as decreasing lipid absorption in the intestine.

Approaches to Visualising Endocytosis of LDL-Related Lipoproteins

Endocytosis is the process by which molecules are actively transported into cells. It can take on a variety of forms depending on the cellular machinery involved ranging from specific receptor-mediated endocytosis to the less selective and actin-driven macropinocytosis. The plasma lipoproteins, which deliver lipids and other cargo to cells, have been intensely studied with respect to their endocytic uptake. One of the first molecules to be visualised undergoing endocytosis via a receptor-mediated, clathrin-dependent pathway was low-density lipoprotein (LDL). The LDL molecule has subsequently been shown to be internalised through multiple endocytic pathways. Dissecting the pathways of lipoprotein endocytosis has been crucial to understanding the regulation of plasma lipid levels and how lipids enter cells in the arterial wall to promote atherosclerosis. It has also aided understanding of the dysregulation that occurs in plasma lipid levels when molecules involved in uptake are defective, as is the case in familial hypercholesterolemia (FH). The aim of this review is to outline the many endocytic pathways utilised for lipoprotein uptake. It explores the various experimental approaches that have been applied to visualise lipoprotein endocytosis with an emphasis on LDL and its more complex counterpart, lipoprotein(a) [Lp(a)]. Finally, we look at new developments in lipoprotein visualisation that hold promise for scrutinising endocytic pathways to finer detail in the future.

PPARγ/LXRα axis mediated phenotypic plasticity of lung fibroblasts in silica-induced experimental silicosis

Silicosis is a disease mainly caused by pulmonary interstitial fibrosis caused by long-term inhalation of dust with excessively high content of free SiO₂. Transdifferentiation of lung fibroblasts into myofibroblasts is an important cellular basis for silicosis, but the key transcription factors (TFs) involved in this process are still unclear. In order to explore the biological regulation of transcription factor PPARγ/LXRα in silica-induced pulmonary fibrosis, this study explored the molecular mechanism of PPARγ/LXRα involved in regulating transcription factors related to SiO₂-induced lung injury at the cellular level and in animal models. ChIP-qPCR detected that PPARγ directly regulated the transcriptional activity of the LXRα gene promoter, while the PPARγ agonist RSG increased the expression of LXRα. In addition, we demonstrated in the cell model that upregulation of LXRα can inhibit silica-mediated fibroblast transdifferentiation, accompanied by an increase in the expression of SREBF1, PLTP and ABCA1. The results of LXRα silencing experiment matched those of overexpression experiment. These studies explored the role of LXRα in plasticity and phenotypic transformation between lung fibroblasts and myofibroblasts. Therefore, inhibiting or reversing the transdifferentiation of lung fibroblasts to myofibroblasts by intervening PPARγ/LXRα may provide a new therapeutic target for the treatment of silicosis.

1H-NMR Plasma Lipoproteins Profile Analysis Reveals Lipid Metabolism Alterations in HER2-Positive Breast Cancer Patients

The lipid tumour demand may shape the host metabolism adapting the circulating lipids composition to its growth and progression needs. This study aims to exploit the straightforward 1H-NMR lipoproteins analysis to investigate the alterations of the circulating lipoproteins' fractions in HER2-positive breast cancer and their modulations induced by treatments. The baseline 1H-NMR plasma lipoproteins profiles were measured in 43 HER2-positive breast cancer patients and compared with those of 28 healthy women. In a subset of 32 patients, longitudinal measurements were also performed along neoadjuvant chemotherapy, after surgery, adjuvant treatment, and during the two-year follow-up. Differences between groups were assessed by multivariate PLS-DA and by univariate analyses. The diagnostic power of lipoproteins subfractions was assessed by ROC curve, while lipoproteins time changes along interventions were investigated by ANOVA analysis. The PLS-DA model distinguished HER2-positive breast cancer patients from the control group with a sensitivity of 96.4% and specificity of 90.7%, mainly due to the differential levels of VLDLs subfractions that were significantly higher in the patients' group. Neoadjuvant chemotherapy-induced a significant drop in the HDLs after the first three months of treatment and a specific decrease in the HDL-3 and HDL-4 subfractions were found significantly associated with the pathological complete response achievement. These results indicate that HER2-positive breast cancer is characterized by a significant host lipid mobilization that could be useful for diagnostic purposes. Moreover, the lipoproteins profiles alterations induced by the therapeutic interventions could predict the clinical outcome supporting the application of 1H-NMR lipoproteins profiles analysis for longitudinal monitoring of HER2-positive breast cancer in large clinical studies.

Rosmarinic Acid Exhibits a Lipid-Lowering Effect by Modulating the Expression of Reverse Cholesterol Transporters and Lipid Metabolism in High-Fat Diet-Fed Mice

Hyperlipidemia is a potent risk factor for the development of cardiovascular diseases. The reverse cholesterol transport (RCT) process has been shown to alleviate hyperlipidemia and protect against cardiovascular diseases. Recently, rosmarinic acid was reported to exhibit lipid-lowering effects. However, the underlying mechanism is still unclear. This study aims to investigate whether rosmarinic acid lowers lipids by modulating the RCT process in high-fat diet (HFD)-induced hyperlipidemic C57BL/6J mice. Our results indicated that rosmarinic acid treatment significantly decreased body weight, blood glucose, and plasma total cholesterol and triglyceride levels in HFD-fed mice. Rosmarinic acid increased the expression levels of cholesterol uptake-associated receptors in liver tissues, including scavenger receptor B type 1 (SR-B1) and low-density lipoprotein receptor (LDL-R). Furthermore, rosmarinic acid treatment notably increased the expression of cholesterol excretion molecules, ATP-binding cassette G5 (ABCG5) and G8 (ABCG8) transporters, and cholesterol 7 alpha-hydroxylase A1 (CYP7A1) as well as markedly reduced cholesterol and triglyceride levels in liver tissues. In addition, rosmarinic acid facilitated fatty acid oxidation through AMP-activated protein kinase (AMPK)-mediated carnitine palmitoyltransferase 1A (CPT1A) induction. In conclusion, rosmarinic acid exhibited a lipid-lowering effect by modulating the expression of RCT-related proteins and lipid metabolism-associated molecules, confirming its potential for the prevention or treatment of hyperlipidemia-derived diseases.

Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.

Efficacy of Polyphenols in the Management of Dyslipidemia: A Focus on Clinical Studies

Polyphenols (PLPs), phytochemicals found in a wide range of plant-based foods, have gained extensive attention in view of their antioxidant, anti-inflammatory, immunomodulatory and several additional beneficial activities. The health-promoting effects noted in animal models of various non-communicable diseases explain the growing interest in these molecules. In particular, in vitro and animal studies reported an attenuation of lipid disorders in response to PLPs. However, despite promising preclinical investigations, the effectiveness of PLPs in human dyslipidemia (DLP) is less clear and necessitates revision of available literature. Therefore, the present review analyzes the role of PLPs in managing clinical DLP, notably by dissecting their potential in ameliorating lipid/lipoprotein metabolism and alleviating hyperlipidemia, both postprandially and in long-term interventions. To this end, PubMed was used for article search. The search terms included polyphenols, lipids, triglycerides, cholesterol, LDL-cholesterol and /or HDL-cholesterol. The critical examination of the trials published to date illustrates certain benefits on blood lipids along with co-morbidities in participant’s health status. However, inconsistent results document significant research gaps, potentially owing to study heterogeneity and lack of rigor in establishing PLP bioavailability during supplementation. This underlines the need for further efforts in order to elucidate and support a potential role of PLPs in fighting DLP.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

Investigation of the Lipid-Lowering Mechanisms and Active Ingredients of Danhe Granule on Hyperlipidemia Based on Systems Pharmacology

Objective

Investigate the active ingredients and underlying hypolipidemic mechanisms of Danhe granule (DHG).

Methods

The lipid-lowering effect of DHG was evaluated in hyperlipidemic hamsters induced by a high-fat diet. The ingredients absorbed into the blood after oral administration of DHG in hamsters were identified by ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS). A systems pharmacology approach incorporating target prediction and network construction, gene ontology (GO) enrichment and pathway analysis was performed to predict the active compounds and map the compounds-targets-disease network. Real-time polymerase chain reaction (RT-PCR) and Western blot were utilized to analyze the mRNA and protein expression levels of predicted targets.

Results

DHG remarkably lowered the levels of serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), and arteriosclerosis index (AI), at the same time, elevated the levels of serum high-density lipoprotein cholesterol (HDL-c) and HDL-c/TC ratio in hyperlipidemic hamsters. Sixteen ingredients absorbed into blood after oral administration of DHG were identified as the possible components interacted with targets. Moreover, 65 potential targets were predicted after targets intersection and compounds–targets–disease network mapping. Then, compounds–targets–pathways network mapping revealed that six active compounds (emodin, naringenin, etc.) compounds could interact with 10 targets such as sterol regulatory element binding protein (SREBP) 1c, SREBP-2 and peroxisome proliferation-activated receptor (PPAR) α, regulate three lipid metabolism-related pathways including SREBP control of lipid synthesis pathway, PPAR signaling pathway and nuclear receptors in lipid metabolism and toxicity pathway, and further affect lipid metabolic processes including fatty acid biosynthesis, low-density lipoprotein receptor (LDLR)-mediated cholesterol uptake, bile acid biosynthesis, and cholesterol efflux. Experimental results indicated that DHG significantly increased SREBP-2, LDLR, PPARα, liver X receptor alpha (LXRα), cholesterol 7α-hydroxylase (CYP7A1), and ATP binding cassette subfamily A member 1 (ABCA1) mRNA and protein expressions while decreased SREBP-1c and fatty acid synthase (FAS) mRNA, and protein expressions.

Conclusion

DHG possessed a good hypolipidemic effect that may be through affecting the mRNA and protein expressions of SREBP-1c, FAS, SREBP-2, LDLR, PPARα, LXRα, CYP7A1, and ABCA1, involving in fatty acid synthesis, LDLR-mediated cholesterol uptake, bile acid biosynthesis, and cholesterol efflux. This study further provided experimental evidence about its practical application for treating hyperlipidemia and its complications.

Role of ATP-binding cassette transporter A1 in suppressing lipid accumulation by glucagon-like peptide-1 agonist in hepatocytes

Objective

Adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1) influences hepatic cholesterol transportation. Accumulation of hepatic cholesterol leads to fatty liver disease, which is improved by glucagon-like peptide 1 (GLP-1) in diabetes. Therefore, we analyzed the molecular mechanism in the regulation of hepatic ABCA1 by GLP-1 analogue exendin-4.

Methods

Hepatic ABCA1 expression and transcription were checked by western blotting, real-time polymerase chain reaction (PCR), and luciferase assay in HepG2 cells. Chromatin immunoprecipitation (ChIP) and site-directed mutagenesis were employed to determine transcriptional regulation of the ABCA1 gene. Prolactin regulatory element-binding (PREB)-transgenic mice were generated to access the effect of exendin-4 on improving lipid accumulation caused by a high-fat diet (HFD).

Results

Exendin-4 stimulated hepatic ABCA1 expression and transcription via the Ca²⁺/calmodulin (CaM)-dependent protein kinase kinase/CaM-dependent protein kinase IV (CaMKK/CaMKIV) pathway, whereas GLP-1 receptor antagonist exendin9-39 cancelled this effect. Therefore, exendin-4 decreased hepatic lipid content. ChIP showed that PREB could directly bind to the ABCA1 promoter, which was enhanced by exendin-4. Moreover, PREB stimulated ABCA1 promoter activity, and mutation of PREB-binding site in ABCA1 promoter cancelled exendin-4-enhanced ABCA1 promoter activity. Silencing of PREB attenuated the effect of exendin-4 and induced hepatic cholesterol accumulation. Blockade of CaMKK by STO-609 or siRNA cancelled the upregulation of ABCA1 and PREB induced by exendin-4. In vivo, exendin-4 or overexpression of PREB increased hepatic ABCA1 expression and decreased hepatic lipid accumulation and high plasma cholesterol caused by a HFD.

Conclusions

Our data shows that exendin-4 stimulates hepatic ABCA1 expression and decreases lipid accumulation by the CaMKK/CaMKIV/PREB pathway, suggesting that ABCA1 and PREB might be the therapeutic targets in fatty liver disease.

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The GLP-1R agonist exendin-4 suppressed lipid accumulation by upregulating ABCA1 expression in hepatocytes.

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Exendin-4 regulated the expression and transcription of hepatic ABCA1 via the CaMKK/CaMKIV/PREB pathway.

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Overexpression of PREB or exendin-4 protected mouse liver from fatty liver by upregulation of ABCA1.

The role of adiponectin in cholesterol efflux and HDL biogenesis and metabolism

Cholesterol efflux is the initial step in the reverse cholesterol transport pathway by which excess cholesterol in peripheral cells is exported and subsequently packaged into high-density lipoprotein (HDL) particles. Adiponectin is the most abundantly secreted adipokine that possesses anti-inflammatory and vasculoprotective properties via interaction with transmembrane receptors, AdipoR1 and AdipoR2. Evidence suggests that low levels of adiponectin may be a useful marker for atherosclerotic disease. A proposed anti-atherogenic mechanism of adiponectin involves its ability to promote cholesterol efflux. We performed a systematic review of the role of adiponectin in cholesterol efflux and HDL biogenesis, and of the proteins and receptors believed to be implicated in this process. Nineteen eligible studies (7 clinical, 11 fundamental, 1 clinical + fundamental) were identified through Ovid Medline, Ovid Embase, and Pubmed, that support the notion that adiponectin plays a key role in promoting ABCA1-dependent cholesterol efflux and in modulating HDL biogenesis via activation of the PPAR-γ/LXR-α signalling pathways in macrophages. AdipoR1 and AdipoR2 are suggested to also be implicated in this process, however the data are conflicting/insufficient to establish any firm conclusions. Once the exact mechanisms are unravelled, adiponectin may be critical in defining future treatment strategies directed towards increasing HDL functionality and ultimately reducing atherosclerotic disease.

Downregulation of ABCA1 and ABCG1 transporters by simvastatin in cholangiocarcinoma cells

Disturbances in cholesterol homeostasis of the bile duct epithelium, including transport interruption and the hyperaccumulation of intracellular cholesterol can lead to the initiation and progression of cholangiocarcinoma (CCA). Statins, which are lipid-lowering drugs, have been previously documented to exhibit anti-cancer properties. The role of statins in CCA cell cholesterol transport through the expression and function of ATP-binding cassette (ABC) A1 and ABCG1 was investigated in the current study. In four CCA cell lines, ABCA1 and ABCG1 expression was identified. However, neither ABCG5 nor ABCG8 expression was observed. Immunocytochemistry revealed that the expression of ABCA1 was localized in the proximity of the nucleus, while ABCG1 was more dispersed throughout the cytoplasm of KKU-100 cells. A cholesterol efflux assay was performed using bodipy cholesterol, and the translocation of cholesterol via ABCA1 and ABCG1 to Apo-A1 and high density lipoprotein was confirmed, respectively. Simvastatin and atorvastatin demonstrated the inhibitory effects on CCA cell viability. A reduction in intracellular lipid level and a lower expression of ABCA1 and ABCG1 were observed in KKU-100 cells under simvastatin treatment. The pre-exposure of KKU-100 cells to cholesterol diminished the statin effect. Furthermore, when KKU-100 cells were pre-loaded with cholesterol, ABCA1 and ABCG1-mediated exports were unaffected even though they were treated with simvastatin. The results of the current study indicated the limitations of the use of statin in CCA therapy, particularly under hypercholesterolemia conditions.

Carvedilol Ameliorates Experimental Atherosclerosis by Regulating Cholesterol Efflux and Exosome Functions

Carvedilol (Cav), a nonselective β-blocker with α1 adrenoceptor blocking effect, has been used as a standard therapy for coronary artery disease. This study investigated the effects of Cav on exosome expression and function, ATP-binding cassette transporter A1 (ABCA1) expression, and cholesterol efflux that are relevant to the process of atherosclerosis. Human monocytic (THP-1) cell line and human hepatic (Huh-7) cells were treated with Cav, and cholesterol efflux was measured. Exosomes from cell culture medium or mice serum were isolated using glycan-coated recognition beads. Low-density lipoprotein receptor knockout (ldlr^−/−) mice were fed with high-fat diet and treated with Cav. Cav accentuated cholesterol efflux and enhanced the expressions of ABCA1 protein and mRNA in both THP-1 and Huh-7 cells. In addition, Cav increased expression and function of exosomal ABCA1 in THP-1 macrophage exosomes. The mechanisms were associated with inhibition of nuclear factor-κB (NF-κB) and protein kinase B (Akt). In hypercholesterolemic ldlr^−/− mice, Cav enhanced serum exosomal ABCA1 expression and suppressed atherosclerosis by inhibiting lipid deposition and macrophage accumulation. Cav halts atherosclerosis by enhancing cholesterol efflux and increasing ABCA1 expression in macrophages and in exosomes, possibly through NF-κB and Akt signaling, which provides mechanistic insights regarding the beneficial effects of Cav on atherosclerotic cardiovascular disease.

Changes in lipid profiles during and after (neo)adjuvant chemotherapy in women with early-stage breast cancer: A retrospective study

Many different treatments may affect the serum lipid profiles of breast cancer patients. This study analyzed serum lipid levels at different periods during treatment to observe the changes in lipid profiles during and after chemotherapy and to compare the different effects of different chemotherapy regimens on serum lipid profiles. A total of 805 patients were included in this study. We measured the lipid profiles of patients who received surgery without chemotherapy prior to the operation and at 3, 6 and 12 months after operation. In addition, in patients who underwent chemotherapy, the lipid profiles were measured prior to chemotherapy, prior to the last cycle of chemotherapy and 6 months after chemotherapy. Lipid profile measurements included total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), homocysteine (HCY), and uric acid (UA). (Neo)Adjuvant chemotherapy exerted an adverse temporary effect on lipid levels (manifested as increased TG and LDL-C levels, and decreased HDL-C levels, particularly in the adjuvant chemotherapy group) during the chemotherapy periods. However, this influence was not sustained, as the lipid profiles levels were generally restored to baseline levels 6 months after chemotherapy completion. Different age groups showed different changes in lipid levels that were influenced by chemotherapy. The younger group (20-40 years old) showed a greater increase in TC and LDL-C levels during chemotherapy than the 41-65-year-old group. Chemotherapy exerts an adverse temporary effect, and the effects of different regimens on lipid levels are similar. Furthermore, lipid profiles in younger women may be more sensitive to chemotherapy.

Repression of hepatocyte nuclear factor 4 alpha by AP-1 underlies dyslipidemia associated with retinoic acid

All-trans retinoic acid (atRA) is used to treat certain cancers and dermatologic diseases. A common adverse effect of atRA is hypercholesterolemia; cytochrome P450 (CYP) 7A repression is suggested as a driver. However, the underlying molecular mechanisms remain unclear. We investigated CYP7A1 expression in the presence of atRA in human hepatocytes and hepatic cell lines. In HepaRG cells, atRA increased cholesterol levels dose-dependently alongside dramatic decreases in CYP7A1 expression. Lentiviral-mediated CYP7A1 overexpression reversed atRA-induced cholesterol accumulation, suggesting that CYP7A1 repression mediated cholesterol accumulation. In CYP7A1 promoter reporter assays and gene-knockdown studies, altered binding of hepatocyte nuclear factor 4 α (HNF4α) to the proximal promoter was essential for atRA-mediated CYP7A1 repression. Pharmacologic inhibition of c-Jun N-terminal kinase (JNK) and ERK pathways attenuated atRA-mediated CYP7A1 repression and cholesterol accumulation. Overexpression of AP-1 (c-Jun/c-Fos), a downstream target of JNK and ERK, repressed CYP7A1 expression. In DNA pull-down and chromatin immunoprecipitation assays, AP-1 exhibited sequence-specific binding to the proximal CYP7A1 promoter region overlapping the HNF4α binding site, and atRA increased AP-1 but decreased HNF4α recruitment to the promoter. Collectively, these results indicate that atRA activates JNK and ERK pathways and the downstream target AP-1 represses HNF4α transactivation of the CYP7A1 promoter, potentially responsible for hypercholesterolemia.

Role of Liver X Receptor in Mastitis Therapy and Regulation of Milk Fat Synthesis

Mastitis is important disease that causes huge economic losses in the dairy industry. In recent years, antibiotic therapy has become the primary treatment for mastitis, however, due to drug residue in milk and food safety factors, we lack safe and effective drugs for treating mastitis. Therefore, new targets and drugs are urgently needed to control mastitis. LXRα, one of the main members of the nuclear receptor superfamily, is reported to play important roles in metabolism, infection and immunity. Activation of LXRα could inhibit LPS-induced mastitis. Furthermore, LXRα is reported to enhance milk fat production, thus, LXRα may serve as a new target for mastitis therapy and regulation of milk fat synthesis. This review summarizes the effects of LXRα in regulating milk fat synthesis and treatment of mastitis and highlights the potential agonists involved in both issues.

Therapeutic FGF19 promotes HDL biogenesis and transhepatic cholesterol efflux to prevent atherosclerosis

Fibroblast growth factor (FGF)19, an endocrine hormone produced in the gut, acts in the liver to control bile acid synthesis. NGM282, an engineered FGF19 analog, is currently in clinical development for treating nonalcoholic steatohepatitis. However, the molecular mechanisms that integrate FGF19 with cholesterol metabolic pathways are incompletely understood. Here, we report that FGF19 and NGM282 promote HDL biogenesis and cholesterol efflux from the liver by selectively modulating LXR signaling while ameliorating hepatic steatosis. We further identify ABCA1 and FGF receptor 4 as mediators of this effect, and that administration of a HMG-CoA reductase inhibitor or a blocking antibody against proprotein convertase subtilisin/kexin type 9 abolished FGF19-associated elevations in total cholesterol, HDL cholesterol (HDL-C), and LDL cholesterol in db/db mice. Moreover, we show that a constitutively active MEK1, but not a constitutively active STAT3, mimics the effect of FGF19 and NGM282 on cholesterol change. In dyslipidemic Apoe ^-/- mice fed a Western diet, treatment with NGM282 dramatically reduced atherosclerotic lesion area in aortas. Administration of NGM282 to healthy volunteers for 7 days resulted in a 26% increase in HDL-C levels compared with placebo. These findings outline a previously unrecognized role for FGF19 in the homeostatic control of cholesterol and may have direct impact on the clinical development of FGF19 analogs.

trans-Chalcone prevents insulin resistance and hepatic inflammation and also promotes hepatic cholesterol efflux in high-fat diet-fed rats: modulation of miR-34a-, miR-451-, and miR-33a-related pathways

Insulin resistance and inflammation are strongly linked to non-alcoholic fatty liver disease (NAFLD) as a feature of the metabolic syndrome. Furthermore, the role of dysregulation of miR-34a, miR-451, and miR-33a in pathogenesis and progression of NAFLD has been identified. trans-Chalcone is a simple chalcone with anti-diabetic and anti-inflammatory activities. However, to the best of our knowledge, miRNA-dependent mechanisms of these protective effects under pathologic conditions are not understood. Thus, this study, for the first time, aimed to evaluate the effects of trans-Chalcone on miR-34a, miR-451, and miR-33a signaling pathways in the liver of high-fat (HF) emulsion-fed rats. To this aim, twenty-one rats were randomly and equally divided into three groups: control, which was gavaged with 10% tween 80; HF, which was gavaged with HF emulsion and 10% tween 80; and HF + trans-Chalcone (HF + TC), which was gavaged with HF emulsion and trans-Chalcone. Then, circulating levels of glucose and insulin were measured and used for the calculation of HOMA-IR. Hepatic expression levels of miR-34a, miR-451, miR-33a, SIRT1, and ABCA1 and also protein levels of ABCA1 and IL-8 were assayed. In this study, trans-chalcone increased hepatic cholesterol efflux and prevented insulin resistance and liver inflammation in HF emulsion-fed rats. These protective effects were modulated through the down-regulation of miR-34a and its associated elevation of SIRT1, the up-regulation of miR-451 which was associated with a reduction in IL-8, and the inhibition of miR-33a which was related to the elevation of ABCA1 in the liver of HF emulsion-fed rats. Therefore, trans-Chalcone exerts its beneficial effects by targeting hepatic miR-34a-, miR-451-, and miR-33a-related pathways.

Dietary supplementation of defatted kenaf (Hibiscus cannabinus L.) seed meal and its phenolics-saponins rich extract effectively attenuates diet-induced hypercholesterolemia in rats

Kenaf is one of the important commercial fiber crops worldwide and defatted kenaf seed meal (DKSM) is a secondary by-product from the kenaf industry. Thus, efforts to turn this low-cost agricultural waste into value-added functional food ingredients will definitely bring advantageous impacts to the community health, environment and economy. The present study was aimed to investigate the cardioprotective properties of DKSM and its phenolics-saponins rich extract (PSRE) in diet-induced hypercholesterolemic rat model. Hypercholesterolemia was induced in Sprague-Dawley rats via atherogenic diet feeding and dietary interventions were conducted by incorporating DKSM (15% and 30%) and equivalent levels of PSRE (2.3% and 4.6%, respectively, equivalent to the total content of phenolics and saponins in DKSM groups) into the atherogenic diets. After 10 weeks of DKSM and PSRE supplementation, the hepatosomatic index, hepatosteatosis, serum lipid profile, Castelli risk indexes as well as hepatic and renal functions of hypercholesterolemic rats were significantly improved (p < 0.05). Besides, the levels of hepatic Hmgcr and serum Pcsk9 were lowered, along with transcriptional upregulations of hepatic Cyp7a1, Abca1, Lcat, ApoA2 and ApoE (p < 0.05). The gene expression of hepatic Ldlr was marginally enhanced by DKSM supplementation (p > 0.05), but superiorly upregulated by PSRE (p < 0.05). The combined results showed that hypercholesterolemia and the atherogenic risk in rats were effectively attenuated by DKSM and PSRE supplementation, possibly via modulations of multiple vital processes in hepatic cholesterol metabolism. Furthermore, phenolics and saponins may be the bioactives conferring DKSM and PSRE with their anti-hypercholesterolemic properties. In conclusion, DKSM and PSRE are prospective cardioprotective functional food ingredients for hypercholesterolemic individuals.

RVX 208: A novel BET protein inhibitor, role as an inducer of apo A-I/HDL and beyond

Low-density cholesterol (LDL) has been the prime target of currently available lipid-lowering therapies although current research is expanding the focus beyond LDL lowering and has included high-density cholesterol (HDL) also as the target. Bromo and extra-terminal (BET) proteins are implicated in the regulation of transcription of several regulatory genes and regulation of proinflammatory pathways. As atherosclerosis is an inflammatory pathway and studies showed that BET inhibition has a role in inhibiting inflammation, the concept of BET inhibition came in the field of atherosclerosis. RVX 208 is a novel, orally active, BET protein inhibitor and the only BET inhibitor currently available in the field of atherosclerosis. RVX 208 acts primarily by increasing apo A-I (apolipoprotein A-I) and HDL levels. RVX 208 has a novel action of increasing larger, more cardio-protective HDL particles. Post hoc analysis of Phase II trials also showed that RVX 208 reduced major adverse cardiovascular events (MACE) in treated patients, over and above that of apo A-I/HDL increasing action. This MACE reducing actions of RVX 208 were largely due to its novel anti-inflammatory actions. Currently, a phase III trial, BETonMACE, is recruiting patients to look for the effects of RVX 208 in patients with increased risk of atherosclerotic cardiovascular disease. So BET inhibitors act in multiple ways to inhibit and modulate atherosclerosis and would be an emerging and potential option in the management of multifactorial disease like coronary artery disease by inhibiting a single substrate. But we need long-term phase III trial data's to look for effects on real-world patients.

Natural products as modulators of the nuclear receptors and metabolic sensors LXR, FXR and RXR

Nuclear receptors (NRs) represent attractive targets for the treatment of metabolic syndrome-related diseases. In addition, natural products are an interesting pool of potential ligands since they have been refined under evolutionary pressure to interact with proteins or other biological targets. This review aims to briefly summarize current basic knowledge regarding the liver X (LXR) and farnesoid X receptors (FXR) that form permissive heterodimers with retinoid X receptors (RXR). Natural product-based ligands for these receptors are summarized and the potential of LXR, FXR and RXR as targets in precision medicine is discussed.

Current and future therapies for addressing the effects of inflammation on HDL cholesterol metabolism

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Inflammatory processes arising from metabolic abnormalities are known to precipitate the development of CVD. Several metabolic and inflammatory markers have been proposed for predicting the progression of CVD, including high density lipoprotein cholesterol (HDL-C). For ~50 years, HDL-C has been considered as the atheroprotective 'good' cholesterol because of its strong inverse association with the progression of CVD. Thus, interventions to increase the concentration of HDL-C have been successfully tested in animals; however, clinical trials were unable to confirm the cardiovascular benefits of pharmaceutical interventions aimed at increasing HDL-C levels. Based on these data, the significance of HDL-C in the prevention of CVD has been called into question. Fundamental in vitro and animal studies suggest that HDL-C functionality, rather than HDL-C concentration, is important for the CVD-preventive qualities of HDL-C. Our current review of the literature positively demonstrates the negative impact of systemic and tissue (i.e. adipose tissue) inflammation in the healthy metabolism and function of HDL-C. Our survey indicates that HDL-C may be a good marker of adipose tissue health, independently of its atheroprotective associations. We summarize the current findings on the use of anti-inflammatory drugs to either prevent HDL-C clearance or improve the function and production of HDL-C particles. It is evident that the therapeutic agents currently available may not provide the optimal strategy for altering HDL-C metabolism and function, and thus, further research is required to supplement this mechanistic approach for preventing the progression of CVD.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Regulation of genes related to cholesterol metabolism in rainbow trout (Oncorhynchus mykiss) fed a plant-based diet

When compared with fish meal and fish oil, plant ingredients differ not only in their protein content and amino acid and fatty acid profiles but are also devoid of cholesterol, the major component of cell membrane and precursor of several bioactive compounds. Based on these nutritional characteristics, plant-based diets can affect fish physiology and cholesterol metabolism. To investigate the mechanisms underlying cholesterol homeostasis, rainbow trout were fed from 1 g body wt for 6 mo with a totally plant-based diet (V), a marine diet (M), and a marine-restricted diet (MR), with feed intake adjusted to that of the V group. The expression of genes involved in cholesterol synthesis, esterification, excretion, bile acid synthesis, and cholesterol efflux was measured in liver. Results showed that genes involved in cholesterol synthesis were upregulated in trout fed the V diet, whereas expression of genes related to bile acid synthesis ( cyp7a1) and cholesterol elimination ( abcg8) were reduced. Feeding trout the V diet also enhanced the expression of srebp-2 while reducing that of lxrα and miR-223. Overall, these data suggested that rainbow trout coped with the altered nutritional characteristics and absence of dietary cholesterol supply by increasing cholesterol synthesis and limiting cholesterol efflux through molecular mechanisms involving at least srebp-2, lxrα, and miR-223. However, plasma and body cholesterol levels in trout fed the V diet were lower than in fish fed the M diet, raising the question of the role of cholesterol in the negative effect of plant-based diet on growth.

Evidence for host genetic regulation of altered lipid metabolism in experimental toxoplasmosis supported with gene data mining results

Toxoplasma gondii is one of the most successful parasites on Earth, infecting a wide array of mammals including one third of the global human population. The obligate intracellular protozoon is not capable of synthesizing cholesterol (Chl), and thus depends on uptake of host Chl for its own development. To explore the genetic regulation of previously observed lipid metabolism alterations during acute murine T. gondii infection, we here assessed total Chl and its fractions in serum and selected tissues at the pathophysiological and molecular level, and integrated the observed gene expression of selected molecules relevant for Chl metabolism, including its biosynthetic and export KEGG pathways, with the results of published transcriptomes obtained in similar murine models of T. gondii infection. The serum lipid status as well as the transcript levels of relevant genes in the brain and the liver were assessed in experimental models of acute and chronic toxoplasmosis in wild-type mice. The results showed that acute infection was associated with a decrease in Chl content in both the liver and periphery (brain, peripheral lymphocytes), and a decrease in Chl reverse transport. In contrast, in chronic infection, a return to normal levels of Chl metabolism has been noted. These changes corresponded to the brain and liver gene expression results as well as to data obtained via mining. We propose that the observed changes in Chl metabolism are part of the host defense response. Further insight into the lipid metabolism in T. gondii infection may provide novel targets for therapeutic agents.

Bilirubin Decreases Macrophage Cholesterol Efflux and ATP-Binding Cassette Transporter A1 Protein Expression

BACKGROUND

Mild but chronically elevated circulating unconjugated bilirubin is associated with reduced total and low-density lipoprotein cholesterol concentration, which is associated with reduced cardiovascular disease risk. We aimed to investigate whether unconjugated bilirubin influences macrophage cholesterol efflux, as a potential mechanism for the altered circulating lipoprotein concentrations observed in hyperbilirubinemic individuals.

METHODS AND RESULTS

Cholesterol efflux from THP-1 macrophages was assessed using plasma obtained from normo- and hyperbilirubinemic (Gilbert syndrome) humans (n=60 per group) or (heterozygote/homozygote Gunn) rats (n=20 per group) as an acceptor. Hyperbilirubinemic plasma from patients with Gilbert syndrome and Gunn rats induced significantly reduced cholesterol efflux compared with normobilirubinemic plasma. Unconjugated bilirubin (3-17.1 μmol/L) exogenously added to plasma- or apolipoprotein A1-supplemented media also decreased macrophage cholesterol efflux in a concentration- and time-dependent manner. We also showed reduced protein expression of the ATP-binding cassette transporter A1 (ABCA1), a transmembrane cholesterol transporter involved in apolipoprotein A1-mediated cholesterol efflux, in THP-1 macrophages treated with unconjugated bilirubin and in peripheral blood mononuclear cells obtained from hyperbilirubinemic individuals. Furthermore, we demonstrated that bilirubin accelerates the degradation rate of the ABCA1 protein in THP-1 macrophages.

CONCLUSIONS

Cholesterol efflux from THP-1 macrophages is decreased in the presence of plasma obtained from humans and rats with mild hyperbilirubinemia. A direct effect of unconjugated bilirubin on cholesterol efflux was demonstrated and is associated with decreased ABCA1 protein expression. These data improve our knowledge concerning bilirubin's impact on cholesterol transport and represent an important advancement in our understanding of bilirubin's role in cardiovascular disease.

Exposure to High Glucose Concentration Decreases Cell Surface ABCA1 and HDL Biogenesis in Hepatocytes

Aim: To study atherosclerosis risk in diabetes, we investigated ATP-binding cassette transporter A1 (ABCA1) expression and high-density lipoprotein (HDL) biogenesis in the liver and hepatocytes under hyperglycemic conditions.

Methods and Results: In streptozotocin-induced diabetic mice, plasma HDL decreased while ABCA1 protein increased without changing its mRNA in the liver, only in the animals that responded to the treatment to show hypoinsulinemia and fasting hyperglycemia but not in the poor responders not showing those. To study the mechanism for this finding, hepatocytes were isolated from the control and diabetic mice, and they showed no difference in expression of ABCA1 protein, its mRNA, and HDL biogenesis in 1 g/l d-glucose but showed decreased HDL biogenesis in 4.5 g/l d-glucose although ABCA1 protein increased without change in its mRNA. Similar findings were confirmed in HepG2 cells with d-glucose but not with l-glucose. Thus, these cell models reproduced the in vivo findings in hyperglycemia. Labeling of cell surface protein revealed that surface ABCA1 decreased in high concentration of d-glucose in HepG2 cells despite the increase of cellular ABCA1 while not with l-glucose. Immunostaining of ABCA1 in HepG2 cells demonstrated the decrease of surface ABCA1 but increase of intracellular ABCA1 with high d-glucose. Clearance of ABCA1 was retarded both in primary hepatocytes and HepG2 cells exposed to high d-glucose but not to l-glucose, being consistent with the decrease of surface ABCA1.

Conclusions: It is suggested that localization of ABCA1 to the cell surface is decreased in hepatocytes in hyperglycemic condition to cause decrease of HDL biogenesis.

Testosterone differentially regulates targets of lipid and glucose metabolism in liver, muscle and adipose tissues of the testicular feminised mouse

Testosterone deficiency is commonly associated with obesity, metabolic syndrome, type 2 diabetes and their clinical consequences-hepatic steatosis and atherosclerosis. The testicular feminised mouse (non-functional androgen receptor and low testosterone) develops fatty liver and aortic lipid streaks on a high-fat diet, whereas androgen-replete XY littermate controls do not. Testosterone treatment ameliorates these effects, although the underlying mechanisms remain unknown. We compared the influence of testosterone on the expression of regulatory targets of glucose, cholesterol and lipid metabolism in muscle, liver, abdominal subcutaneous and visceral adipose tissue. Testicular feminised mice displayed significantly reduced GLUT4 in muscle and glycolytic enzymes in muscle, liver and abdominal subcutaneous but not visceral adipose tissue. Lipoprotein lipase required for fatty acid uptake was only reduced in subcutaneous adipose tissue; enzymes of fatty acid synthesis were increased in liver and subcutaneous tissue. Stearoyl-CoA desaturase-1 that catalyses oleic acid synthesis and is associated with insulin resistance was increased in visceral adipose tissue and cholesterol efflux components (ABCA1, apoE) were decreased in subcutaneous and liver tissue. Master regulator nuclear receptors involved in metabolism-Liver X receptor expression was suppressed in all tissues except visceral adipose tissue, whereas PPARγ was lower in abdominal subcutaneous and visceral adipose tissue and PPARα only in abdominal subcutaneous. Testosterone treatment improved the expression (androgen receptor independent) of some targets but not all. These exploratory data suggest that androgen deficiency may reduce the buffering capability for glucose uptake and utilisation in abdominal subcutaneous and muscle and fatty acids in abdominal subcutaneous. This would lead to an overspill and uptake of excess glucose and triglycerides into visceral adipose tissue, liver and arterial walls.

Hepatic miR-33a/miR-144 and their target gene ABCA1 are associated with steatohepatitis in morbidly obese subjects

BACKGROUND AND AIM

Abnormal cholesterol metabolism may contribute to the pathogenesis of non-alcoholic steatohepatitis (NASH) and fibrosis. miR-33 and miR-144 regulate adenosine triphosphate binding cassette transporter (ABCA1) and other target genes involved in cholesterol efflux, fatty acid oxidation and inflammation. We explored relationships between non-alcoholic fatty liver disease (NAFLD) and the hepatic expression of ABCA1/ABCG1, as well as other target genes regulated by miR-33 (carnitine O-octanoyltransferase, CROT and hydroxyacyl-CoA-dehydrogenase β-subunit, HADHB) and miR-144 (toll-like receptor-2, TLR2). Moreover, we evaluated whether the expression of these genes is correlated with miR-33a/b and miR-144 expression in Mexican individuals with morbid obesity.

METHODS

Eighty-four morbidly obese subjects undergoing bariatric surgery were included in this study. Liver biopsies were obtained to measure hepatic triglyceride and free cholesterol contents, as well as ABCA1, ABCG1, CROT, HADHB, TLR2, miR-33a/b and miR-144 expression.

RESULTS

Hepatic free cholesterol content was significantly increased in NASH as compared to non-NASH subjects, while ABCA1 and ABCG1 protein levels significantly decreased with NASH and fibrosis progression. The relative expression of miR-33a and miR-144 correlated inversely with ABCA1 but not with ABCG1 protein levels. Moreover, both miRNAs increased significantly in NASH individuals. miR-33 target genes CROT and HADHB correlated inversely with miR-33a. However, the expression of these genes was not associated with NASH.

CONCLUSIONS

miR-33a/144 and their target gene ABCA1 may contribute to the pathogenesis of NASH in morbidly obese subjects.

TSH increases synthesis of hepatic ATP-binding cassette subfamily A member 1 in hypercholesterolemia

Epidemiological evidence suggests that thyrotropin (TSH) levels are closely correlated with the severity of hypercholesterolemia. Reverse cholesterol transfer (RCT) plays an important role in regulating bloodcholesterol. However, the molecular mechanism of hypercholesterolemia in subclinical hypothyroidism (SCH) has not been fully clarified. The SCH mouse model, which is characterized by elevated serum TSH but not thyroid hormone levels, demonstrated a significant increase in plasma cholesterol compared with controls. Interestingly, Tshr KO mice, with normal thyroid hormone levels after thyroid hormone supplementation, showed lower plasma cholesterol levels compared with their wild-type littermates. ATP binding cassette subfamily A member 1(ABCA1) is a member of the ABC superfamily, which induces transfer of intracellular cholesterol to extracellular apolipoprotein. TSH upregulated hepatic ABCA1 to promote the efflux of intercellular cumulative cholesterol, resulting in increased plasma cholesterol. These data might partially explain the pathogenesis of hypercholesterolemia in SCH.

Hypoxanthine induces cholesterol accumulation and incites atherosclerosis in apolipoprotein E-deficient mice and cells

Reactive oxygen species (ROS) generation during purine metabolism is associated with xanthine oxidase and uric acid. However, the direct effect of hypoxanthine on ROS generation and atherosclerosis has not been evaluated. Smoking and heavy drinking are associated with elevated levels of hypoxanthine. In this study, we investigated the role of hypoxanthine on cholesterol synthesis and atherosclerosis development, particularly in apolipoprotein E (APOE)‐deficient mice. The effect of hypoxanthine on the regulation of cholesterol synthesis and atherosclerosis were evaluated in Apoe knockout (KO) mice and cultured HepG2 cells. Hypoxanthine markedly increased serum cholesterol levels and the atherosclerotic plaque area in ApoeKO mice. In HepG2 cells, hypoxanthine increased intracellular ROS production. Hypoxanthine increased cholesterol accumulation and decreased APOE and ATP‐binding cassette transporter A1 (ABCA1) mRNA and protein expression in HepG2 cells. Furthermore, H₂O₂ also increased cholesterol accumulation and decreased APOE and ABCA1 expression. This effect was partially reversible by treatment with the antioxidant N‐acetyl cysteine and allopurinol. Hypoxanthine and APOE knockdown using APOE‐siRNA synergistically induced cholesterol accumulation and reduced APOE and ABCA1 expression. Hypoxanthine induces cholesterol accumulation in hepatic cells through alterations in enzymes that control lipid transport and induces atherosclerosis in APOE‐deficient cells and mice. These effects are partially mediated through ROS produced in response to hypoxanthine.

Hydrogen Sulfide Up-Regulates the Expression of ATP-Binding Cassette Transporter A1 via Promoting Nuclear Translocation of PPARα

ATP binding cassette transporter A1 (ABCA1) plays a key role in atherogenesis. Hydrogen sulfide (H₂S), a gasotransmitter, has been reported to play an anti-atherosclerotic role. However, the underlying mechanisms are largely unknown. In this study we examined whether and how H₂S regulates ABCA1 expression. The effect of H₂S on ABCA1 expression and lipid metabolism were assessed in vitro by cultured human hepatoma cell line HepG2, and in vivo by ApoE^−/− mice with a high-cholesterol diet. NaHS (an exogenous H₂S donor) treatment significantly increased the expression of ABCA1, ApoA1, and ApoA2 and ameliorated intracellular lipid accumulation in HepG2 cells. Depletion of the endogenous H₂S generator cystathionine γ-lyase (CSE) by small RNA interference (siRNA) significantly decreased the expression of ABCA1 and resulted in the accumulation of lipids in HepG2 cells. In vivo NaHS treatment significantly reduced the serum levels of total cholesterol (TC), triglycerides (TG), and low-density lipoproteins (LDL), diminished atherosclerotic plaque size, and increased hepatic ABCA1 expression in fat-fed ApoE^−/− mice. Further study revealed that NaHS upregulated ABCA1 expression by promoting peroxisome proliferator-activated receptor α (PPARα) nuclear translocation. H₂S up-regulates the expression of ABCA1 by promoting the nuclear translocation of PPARα, providing a fundamental mechanism for the anti-atherogenic activity of H₂S. H₂S may be a promising potential drug candidate for the treatment of atherosclerosis.

Chemotherapy Agents Alter Plasma Lipids in Breast Cancer Patients and Show Differential Effects on Lipid Metabolism Genes in Liver Cells

Cardiovascular complications have emerged as a major concern for cancer patients. Many chemotherapy agents are cardiotoxic and some appear to also alter lipid profiles, although the mechanism for this is unknown. We studied plasma lipid levels in 12 breast cancer patients throughout their chemotherapy. Patients received either four cycles of doxorubicin and cyclophosphamide followed by weekly paclitaxel or three cycles of epirubicin, cyclophosphamide and 5’-fluorouracil followed by three cycles of docetaxel. Patients demonstrated a significant reduction (0.32 mmol/L) in high density lipoprotein cholesterol (HDL-C) and apolipoprotein A1 (apoA1) levels (0.18 g/L) and an elevation in apolipoprotein B (apoB) levels (0.15 g/L) after treatment. Investigation of the individual chemotherapy agents for their effect on genes involved in lipoprotein metabolism in liver cells showed that doxorubicin decreased ATP binding cassette transporter A1 (ABCA1) via a downregulation of the peroxisomal proliferator activated receptor γ (PPARγ) and liver X receptor α (LXRα) transcription factors. In contrast, ABCA1 levels were not affected by cyclophosphamide or paclitaxel. Likewise, apoA1 levels were reduced by doxorubicin and remained unaffected by cyclophosphamide and paclitaxel. Doxorubicin and paclitaxel both increased apoB protein levels and paclitaxel also decreased low density lipoprotein receptor (LDLR) protein levels. These findings correlate with the observed reduction in HDL-C and apoA1 and increase in apoB levels seen in these patients. The unfavourable lipid profiles produced by some chemotherapy agents may be detrimental in the longer term to cancer patients, especially those already at risk of cardiovascular disease (CVD). This knowledge may be useful in tailoring effective follow-up care plans for cancer survivors.

Lipidomic Profiling of Liver Tissue from Obesity-Prone and Obesity-Resistant Mice Fed a High Fat Diet

Obesity is a multifactorial health problem resulting from genetic, environmental, and behavioral factors. A particularly interesting aspect of obesity is the differences observed in response to the same high-fat diet (HFD). In this study, we performed lipidomic profiling on livers from HFD-fed C57BL/6J mice using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Mice were divided into three groups: normal diet (ND), HFD-obesity prone (HFD-OP), and HFD-obesity resistant (HFD-OR). Principal components analyses showed a difference between the HFD-OP and HFD-OR groups. Individuals in the HFD-OR group were closer to those in the ND group compared with those in the HFD-OP group. In particular, phosphocholine (PC) and triglyceride (TG) levels differed significantly depending on the length of the acyl chain and degree of unsaturation, respectively. PC species were either positively or negatively correlated with concentrations of glucose, insulin, leptin, and hepatic cholesterol according to the length of the acyl chain. Decreased expression of the scavenger receptor B1 and ATP-binding cassette A1 in HFD-OP mice indicated that the acyl chain length of PC species may be related to high-density lipoprotein cholesterol metabolism. This study demonstrates that lipidomic profiling is an effective approach to analyzing global lipid alterations as they pertain to obesity.

Selective oxidative stress and cholesterol metabolism in lipid-metabolizing cell classes: Distinct regulatory roles for pro-oxidants and antioxidants

Atherogenesis is associated with macrophage cholesterol and oxidized lipids accumulation and foam cell formation. However, two other major lipid-metabolizing cell classes, namely intestinal and liver cells, are also associated with atherogenesis. This study demonstrates that manipulations of cellular oxidative stress (by fatty acids, glucose, low-density lipoprotein, angiotensin II, polyphenolic antioxidants, or the glutathione/paraoxonase 1 systems) have some similar, but also some different effects on cholesterol metabolism in macrophages (J774A.1) versus intestinal cells (HT-29) versus liver cells (HuH7). Cellular oxidative stress was ≈3.5-folds higher in both intestinal and liver cells versus macrophages. In intestinal cells or liver cells versus macrophages, the cholesterol biosynthesis rate was increased by 9- or 15-fold, respectively. In both macrophages and intestinal cells C-18:1 and C-18:2 but not C-18:0, fatty acids significantly increased oxidative stress, whereas in liver cells oxidative stress was significantly decreased by all three fatty acids. In liver cells, trans C-18:1 versus cis C-18:1, unlike intestinal cells or macrophages, significantly increased cellular oxidative stress and cellular cholesterol biosynthesis rate. Pomegranate juice (PJ), red wine, or their phenolics gallic acids or quercetin significantly reduced cellular oxidation mostly in macrophages. Recombinant PON1 significantly decreased macrophage (but not the other cells) oxidative stress by ≈30%. We conclude that cellular atherogenesis research should look at atherogenicity, not only in macrophages but also in intestinal and liver cells, to advance our understanding of the complicated mechanisms behind atherogenesis. © 2015 BioFactors, 41(4):273-288, 2015.

Lipoprotein (a) upregulates ABCA1 in liver cells via scavenger receptor-B1 through its oxidized phospholipids

Elevated levels of lipoprotein (a) [Lp(a)] are a well-established risk factor for developing CVD. While Lp(a) levels are thought to be independent of other plasma lipoproteins, some trials have reported a positive association between Lp(a) and HDL. Whether Lp(a) has a direct effect on HDL is not known. Here we investigated to determine whether Lp(a) had any effect on the ABCA1 pathway of HDL production in liver cells. Incubation of HepG2 cells with Lp(a) upregulated the PPARγ protein by 1.7-fold and the liver X receptor α protein by 3-fold. This was accompanied by a 1.8-fold increase in ABCA1 protein and a 1.5-fold increase in cholesterol efflux onto apoA1. We showed that Lp(a) was internalized by HepG2 cells, however, the ABCA1 response to Lp(a) was mediated by the selective uptake of oxidized phospholipids (oxPLs) from Lp(a) via the scavenger receptor-B1 and not by Lp(a) internalization per se. We conclude that there is a biological connection between Lp(a) and HDL through the ability of Lp(a)’s oxPLs to upregulate HDL biosynthesis.

Low-density lipoprotein receptor affects the fertility of female mice

Low-density lipoprotein receptor (LDLR) has been demonstrated to play a central role in lipoprotein metabolism, with Ldlr-deficient (Ldlr–/–) mice developing severe dyslipidemia. In the present study we investigated whether Ldlr knockout could harm female reproduction and explored the mechanisms involved. The results indicate that although the number of litters born to Ldlr–/– mice did not differ significantly from that born to controls, the number of pups per litter was significantly lower in the former group. Interestingly, although Ldlr–/– mice were obese, the weight of their ovaries was lower than that in control mice. Serum cholesterol levels was significantly higher in Ldlr–/– mice than in their wild-type counterparts. In contrast, there were significant decreases in cholesterol, triglyceride and total lipid levels in ovaries of Ldlr–/– mice. Both ovarian lipid deposition, as detected by Oil red O staining, and lipid droplets, as evaluated by transmission electron microscopy, supported decreased lipid levels in ovaries from Ldlr–/– mice. In addition, Ldlr–/– mice had fewer ovarian follicles, more atretic follicles, lower oestrogen levels and spent significantly less time in oestrus than did the controls. Superovulation assays indicated immature Ldlr–/– mice ovulated fewer ova than controls. These results indicate that lack of Ldlr results in dyslipidaemia and poor fertility.

Genetic variants in ABCA1 promoter affect transcription activity and plasma HDL level in pigs

Excess accumulation of cholesterol in plasma may result in coronary artery disease. Numerous studies have demonstrated that ATP-binding cassette protein A1 (ABCA1) mediates the efflux of cholesterol and phospholipids to apolipoproteins, a process necessary for plasma high density lipoprotein (HDL) formation. Higher plasma levels of HDL are associated with lower risk for cardiovascular disease. Studies of human disease and animal models had shown that an increased hepatic ABCA1 activity relates to an enhanced plasma HDL level. In this study, we hypothesized that functional mutations in the ABCA1 promoter in pigs may affect gene transcription activity, and consequently the HDL level in plasma. The promoter region of ABCA1 was comparatively scanned by direct sequencing with pool DNA of high- and low-HDL groups (n=30 for each group). Two polymorphisms, c. - 608A>G and c. - 418T>A, were revealed with reverse allele distribution in the two groups. The two polymorphisms were completely linked and formed only G-A or A-T haplotypes when genotyped in a larger population (n=526). Furthermore, we found that the G-A/G-A genotype was associated with higher HDL and ABCA1 mRNA level than A-T/A-T genotype. Luciferase assay also revealed that G-A haplotype promoter had higher activity than A-T haplotype. Single-nucleotide mutant assay showed that c.-418T>A was the causal mutation for ABCA1 transcription activity alteration. Conclusively, we identified two completely linked SNPs in porcine ABCA1 promoter region which have influence on the plasma HDL level by altering ABCA1 gene transcriptional activity.

ABCA1 and nascent HDL biogenesis

ABCA1 mediates the secretion of cellular free cholesterol and phospholipids to an extracellular acceptor, apolipoprotein AI, to form nascent high-density lipoprotein (HDL). Thus, ABCA1 is a key molecule in cholesterol homeostasis. Functional studies of certain Tangier disease mutations demonstrate that ABCA1 has multiple activities, including plasma membrane remodeling and apoAI binding to cell surface, which participate in nascent HDL biogenesis. Recent advances in our understanding of ABCA1 have demonstrated that ABCA1also mediates unfolding the N terminus of apoAI on the cell surface, followed by lipidation of apoAI and release of nascent HDL. Although ABCA1-mediated cholesterol efflux to apoAI can occur on the plasma membrane, the role of apoAI retroendocytosis during cholesterol efflux may play a role in macrophage foam cells that store cholesterol esters in cytoplasmic lipid droplets.

Vitamin A-enriched diet modulates reverse cholesterol transport in hypercholesterolemic obese rats of the WNIN/Ob strain

AIM

Vitamin A plays a major role in lipid metabolism. Previously, we reported that chronic vitamin A feeding (129 mg/kg) for two months normalized the abnormally high plasma HDL-cholesterol (HDL-C) levels in hypercholesterolemic obese rats by upregulating the hepatic scavenger receptor class B type 1 (SR-BI) expression. In this report, we hypothesize that the administration of a dose less than 129 mg of vitamin A/kg would also be effective in lowering the plasma HDL-C levels in these rats.

METHODS

Changes in the activity and expression of proteins related to RCT were analyzed together with blood parameters in five-month-old male lean and obese rats supplemented with 2.6 (control group), 26, 52 and 129 mg of vitamin A/kg as retinyl palmitate for 20 weeks.

RESULTS

Vitamin A supplementation in the obese rats decreased the plasma HDL-C levels with a concomitant increase in the hepatic SR-BI expression and lipase activity compared to that observed in the control diet-fed obese rats treated with 2.6 mg of vitamin A/kg diet. Furthermore, vitamin A supplementation at doses of 52 and 129 mg/kg diet reduced the plasma lecithin cholesterol acyltransferase activity and increased the hepatic ATP-binding cassette transporter protein A1 expression in the obese rats. Interestingly, most of these changes were not observed in the lean rats fed a vitamin A-enriched diet.

CONCLUSIONS

Chronic feeding of a vitamin A-enriched diet in hypercholesterolemic obese rats normalizes the plasma HDL-C level and presumably improves RCT, with an effective dose of 52 mg/kg diet. Further studies should focus on the pharmacological potential of vitamin A supplementation to correct an abnormal human obesity-associated lipoprotein metabolism.

MicroRNA-33b knock-in mice for an intron of sterol regulatory element-binding factor 1 (Srebf1) exhibit reduced HDL-C in vivo

MicroRNAs (miRs) are small non-protein-coding RNAs that bind to specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports, including ours, indicated that miR-33a located within the intron of sterol regulatory element-binding protein (SREBP) 2 controls cholesterol homeostasis and can be a possible therapeutic target for treating atherosclerosis. Primates, but not rodents, express miR-33b from an intron of SREBF1. Therefore, humanized mice, in which a miR-33b transgene is inserted within a Srebf1 intron, are required to address its function in vivo. We successfully established miR-33b knock-in (KI) mice and found that protein levels of known miR-33a target genes, such as ABCA1, ABCG1, and SREBP-1, were reduced compared with those in wild-type mice. As a consequence, macrophages from the miR-33b KI mice had a reduced cholesterol efflux capacity via apoA-I and HDL-C. Moreover, HDL-C levels were reduced by almost 35% even in miR-33b KI hetero mice compared with the control mice. These results indicate that miR-33b may account for lower HDL-C levels in humans than those in mice and that miR-33b is possibly utilized for a feedback mechanism to regulate its host gene SREBF1. Our mice will also aid in elucidating the roles of miR-33a/b in different genetic disease models.

HIV protein Nef causes dyslipidemia and formation of foam cells in mouse models of atherosclerosis

Patients with HIV are at an increased risk of cardiovascular disease. In this study we investigated the effect of Nef, a secreted HIV protein responsible for the impairment of cholesterol efflux, on the development of atherosclerosis in two animal models. ApoE(-/-) mice fed a high-fat diet and C57BL/6 mice fed a high-fat, high-cholesterol diet were injected with recombinant Nef (40 ng/injection) or vehicle, and the effects of Nef on development of atherosclerosis, inflammation, and dyslipidemia were assessed. In apoE(-/-) mice, Nef significantly increased the size of atherosclerotic lesions and caused vessel remodeling. Nef caused elevation of total cholesterol and triglyceride levels in the plasma while reducing high-density lipoprotein cholesterol levels. These changes were accompanied by a reduction of ABCA1 abundance in the liver, but not in the vessels. In C57BL/6 mice, Nef caused a significant number of lipid-laden macrophages presented in adventitia of the vessels; these cells were absent from the vessels of control mice. Nef caused sharp elevations of plasma triglyceride levels and body weight. Taken together, our findings suggest that Nef causes dyslipidemia and accumulation of cholesterol in macrophages within the vessel wall, supporting the role of Nef in pathogenesis of atherosclerosis in HIV-infected patients.-Cui, H. L., Ditiatkovski, M., Kesani, R., Bobryshev, Y. V., Liu, Y., Geyer, M., Mukhamedova, N., Bukrinsky, M., Sviridov, D. HIV protein Nef causes dyslipidemia and formation of foam cells in mouse models of atherosclerosis.