Inhibition of acyl-coenzyme A:cholesterol acyltransferase stimulates cholesterol efflux from macrophages and stimulates farnesoid X receptor in hepatocytes

Inhibition of ACAT as a Therapeutic Target for Alzheimer's Disease Is Independent of ApoE4 Lipidation

APOE4, encoding apolipoprotein E4 (apoE4), is the greatest genetic risk factor for Alzheimer's disease (AD), compared to the common APOE3. While the mechanism(s) underlying APOE4-induced AD risk remains unclear, increasing the lipidation of apoE4 is an important therapeutic target as apoE4-lipoproteins are poorly lipidated compared to apoE3-lipoproteins. ACAT (acyl-CoA: cholesterol-acyltransferase) catalyzes the formation of intracellular cholesteryl-ester droplets, reducing the intracellular free cholesterol (FC) pool. Thus, inhibiting ACAT increases the FC pool and facilitates lipid secretion to extracellular apoE-containing lipoproteins. Previous studies using commercial ACAT inhibitors, including avasimibe (AVAS), as well as ACAT-knock out (KO) mice, exhibit reduced AD-like pathology and amyloid precursor protein (APP) processing in familial AD (FAD)-transgenic (Tg) mice. However, the effects of AVAS with human apoE4 remain unknown. In vitro, AVAS induced apoE efflux at concentrations of AVAS measured in the brains of treated mice. AVAS treatment of male E4FAD-Tg mice (5xFAD+/-APOE4+/+) at 6-8 months had no effect on plasma cholesterol levels or distribution, the original mechanism for AVAS treatment of CVD. In the CNS, AVAS reduced intracellular lipid droplets, indirectly demonstrating target engagement. Surrogate efficacy was demonstrated by an increase in Morris water maze measures of memory and postsynaptic protein levels. Amyloid-beta peptide (Aβ) solubility/deposition and neuroinflammation were reduced, critical components of APOE4-modulated pathology. However, there was no increase in apoE4 levels or apoE4 lipidation, while amyloidogenic and non-amyloidogenic processing of APP were significantly reduced. This suggests that the AVAS-induced reduction in Aβ via reduced APP processing was sufficient to reduce AD pathology, as apoE4-lipoproteins remained poorly lipidated.

TNFα-Induced LDL Cholesterol Accumulation Involve Elevated LDLR Cell Surface Levels and SR-B1 Downregulation in Human Arterial Endothelial Cells

Excess lipid droplets are frequently observed in arterial endothelial cells at sites of advanced atherosclerotic plaques. Here, the role of tumor necrosis factor alpha (TNFα) in modulating the low-density lipoprotein (LDL) content in confluent primary human aortic endothelial cells (pHAECs) was investigated. TNFα promoted an up to 2 folds increase in cellular cholesterol, which was resistant to ACAT inhibition. The cholesterol increase was associated with increased ¹²⁵I-LDL surface binding. Using the non-hydrolysable label, Dil, TNFα could induce a massive increase in Dil-LDL by over 200 folds. The elevated intracellular Dil-LDL was blocked with excess unlabeled LDL and PCSK9, but not oxidized LDL (oxLDL), or apolipoprotein (apoE) depletion. Moreover, the TNFα-induced increase of LDL-derived lipids was elevated through lysosome inhibition. Using specific LDLR antibody, the Dil-LDL accumulation was reduced by over 99%. The effects of TNFα included an LDLR cell surface increase of 138%, and very large increases in ICAM-1 total and surface proteins, respectively. In contrast, that of scavenger receptor B1 (SR-B1) was reduced. Additionally, LDLR antibody bound rapidly in TNFα-treated cells by about 30 folds, inducing a migrating shift in the LDLR protein. The effect of TNFα on Dil-LDL accumulation was inhibited by the antioxidant tetramethythiourea (TMTU) dose-dependently, but not by inhibitors against NF-κB, stress kinases, ASK1, JNK, p38, or apoptosis caspases. Grown on Transwell inserts, TNFα did not enhance apical to basolateral LDL cholesterol or Dil release. It is concluded that TNFα promotes LDLR functions through combined increase at the cell surface and SR-B1 downregulation.

Unconjugated p-cresol activates macrophage macropinocytosis leading to increased LDL uptake

Patients with chronic kidney disease (CKD) and end-stage renal disease suffer from increased cardiovascular events and cardiac mortality. Prior studies have demonstrated that a portion of this enhanced risk can be attributed to the accumulation of microbiota-derived toxic metabolites, with most studies focusing on the sulfonated form of p-cresol (PCS). However, unconjugated p-cresol (uPC) itself was never assessed due to rapid and extensive first-pass metabolism that results in negligible serum concentrations of uPC. These reports thus failed to consider the host exposure to uPC prior to hepatic metabolism. In the current study, not only did we measure the effect of altering the intestinal microbiota on lipid accumulation in coronary arteries, but we also examined macrophage lipid uptake and handling pathways in response to uPC. We found that atherosclerosis-prone mice fed a high-fat diet exhibited significantly higher coronary artery lipid deposits upon receiving fecal material from CKD mice. Furthermore, treatment with uPC increased total cholesterol, triglycerides, and hepatic and aortic fatty deposits in non-CKD mice. Studies employing an in vitro macrophage model demonstrated that uPC exposure increased apoptosis whereas PCS did not. Additionally, uPC exhibited higher potency than PCS to stimulate LDL uptake and only uPC induced endocytosis- and pinocytosis-related genes. Pharmacological inhibition of varying cholesterol influx and efflux systems indicated that uPC increased macrophage LDL uptake by activating macropinocytosis. Overall, these findings indicate that uPC itself had a distinct effect on macrophage biology that might have contributed to increased cardiovascular risk in patients with CKD.

Changing Perspectives on HDL: From Simple Quantity Measurements to Functional Quality Assessment

High-density lipoprotein (HDL) comprises a heterogeneous group of particles differing in size, density, and composition. HDL cholesterol (HDL-C) levels have long been suggested to indicate cardiovascular risk, inferred from multiple epidemiological studies. The failure of HDL-C targeted interventions and genetic studies has raised doubts on the atheroprotective role of HDL-C. The current consensus is that HDL-C is neither a biomarker nor a causative agent of cardiovascular disorders. With better understanding of the complex nature of HDL which comprises a large number of proteins and lipids with unique functions, recent focus has shifted from HDL quantity to HDL quality in terms of atheroprotective functions. The current research is focused on developing laboratory assays to assess HDL functions for cardiovascular risk prediction. Also, HDL mimetics designed based on the key determinants of HDL functions are being investigated to modify cardiovascular risk. Improving HDL functions by altering its composition is the key area of future research in HDL biology to reduce cardiovascular risk.

Effect of Spent Mushroom (Cordyceps militaris) on Growth Performance, Immunity, and Intestinal Microflora in Weaning Pigs

There are limited published reports regarding the optimal dosage of spent mushroom. This study investigated the effect of various levels of spent mushroom derived from C. militaris as an alternative growth promoter to an in-feed antibiotic on the growth performance, blood profiles, immunoglobulin, inflammation, and microbial count of weaning pigs. A total of 120 pigs (6.63 ± 0.13 kg initial body weight) were blocked by weight and sex in a randomized complete block design. Each treatment had six replicates of four pigs each. The pigs were allotted into five treatments: (1) positive control (PC) with 150 mg/kg colistin; (2) negative control (NC) without antibiotic inclusion; and (3-5) negative control groups with 0.5, 1.0, and 1.5 g/kg of C. militariss pent mushroom (SM), respectively. Blood samples were collected at day 35 for determination of blood-related lipid metabolism and immunity. Fresh fecal samples were collected to examine microbial counts on day 35 postweaning. The results showed that SM at 1.5 g/kg improved the body weight, average daily weight gain, and average daily feed intake of weaning pigs in the overall period (p < 0.05). Moreover, the highest dosage of SM caused improvements in the concentrations of high-density lipoprotein, and immunoglobulin A, along with suppressions of total cholesterol, interleukin-1, tumor necrosis factor-α, and E. coli (p < 0.05). Therefore, the weaned pigs fed a 1.5 g/kg SM diet showed improved growth performance and displayed greater immunoglobulin secretion and lower inflammation, pathogenic population, and cholesterol concentration.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

In vitro exploration of ACAT contributions to lipid droplet formation during adipogenesis

As adipose tissue is the major cholesterol storage organ and most of the intracellular cholesterol is distributed to lipid droplets (LDs), cholesterol homeostasis may have a role in the regulation of adipocyte size and function. ACATs catalyze the formation of cholesteryl ester (CE) from free cholesterol to modulate the cholesterol balance. Despite the well-documented role of ACATs in hypercholesterolemia, their role in LD development during adipogenesis remains elusive. Here, we identify ACATs as regulators of de novo lipogenesis and LD formation in murine 3T3-L1 adipocytes. Pharmacological inhibition of ACAT activity suppressed intracellular cholesterol and CE levels, and reduced expression of genes involved in cholesterol uptake and efflux. ACAT inhibition resulted in decreased de novo lipogenesis, as demonstrated by reduced maturation of SREBP1 and SREBP1-downstream lipogenic gene expression. Consistent with this observation, knockdown of either ACAT isoform reduced total adipocyte lipid content by approximately 40%. These results demonstrate that ACATs are required for storage ability of lipids and cholesterol in adipocytes.

The complex interplay among hepatocytes and immune cells at the crossroad between inflammation and cholesterol metabolism in hyperglycemia

An intriguing piece of evidence for the inflammatory story of type 2 diabetes has come to the light. A recent study by Okin and colleagues adds new clues to the interplay between cholesterol metabolism and immunity and how it impacts glucose homeostasis in inflammatory conditions. But some questions are a still unsolved conundrum. Here we suggest to better dissect the regulatory mechanism of Mevalonate pathway and to underpin a new causative link between immunometabolic dysregulation and diabetes.

ATR-101 inhibits cholesterol efflux and cortisol secretion by ATP-binding cassette transporters, causing cytotoxic cholesterol accumulation in adrenocortical carcinoma cells

BACKGROUND AND PURPOSE

To further the development of new agents for the treatment of adrenocortical carcinoma (ACC), we characterized the molecular and cellular mechanisms of cytotoxicity by the adrenalytic compound ATR-101 (PD132301-02).

EXPERIMENTAL APPROACH

We compared the effects of ATR-101, PD129337, and ABC transporter inhibitors on cholesterol accumulation and efflux, on cortisol secretion, on ATP levels, and on caspase activation in ACC-derived cell lines. We examined the effects of these compounds in combination with methyl-β-cyclodextrin or exogenous cholesterol to determine the roles of altered cholesterol levels in the effects of these compounds.

KEY RESULTS

ATR-101 caused cholesterol accumulation, ATP depletion, and caspase activation within 30 minutes after addition to ACC-derived cells, whereas PD129337 did not. Suppression of cholesterol accumulation by methyl-β-cyclodextrin or exogenous cholesterol, prevented ATP depletion and caspase activation by ATR-101. ATR-101 blocked cholesterol efflux and cortisol secretion, suggesting that it inhibited ABCA1, ABCG1, and MDR1 transporters. Combinations of ABCA1, ABCG1, and MDR1 inhibitors were also cytotoxic. Combinations of ATR-101 with inhibitors of ABCG1, MDR1, or mitochondrial functions had increased cytotoxicity. Inhibitors of steroidogenesis reduced ATP depletion by ATR-101, whereas U18666A enhanced cholesterol accumulation and ATP depletion together with ATR-101. ATR-101 repressed ABCA1, ABCG1, and IDOL transcription by mechanisms that were distinct from the mechanisms that caused cholesterol accumulation.

CONCLUSIONS AND IMPLICATIONS

Inhibition of multiple ABC transporters and the consequent accumulation of cholesterol mediated the cytotoxicity of ATR-101. Compounds that replicate these effects in tumours are likely to be useful in the treatment of ACC.

HDL-mediated mechanisms of protection in cardiovascular disease

Low plasma levels of HDL-cholesterol (HDL-C) represent a strong and independent risk factor for cardiovascular disease. HDL particles display a wide spectrum of atheroprotective activities, which include effluxing cellular cholesterol, diminishing cellular death, decreasing vascular constriction, reducing inflammatory response, protecting from pathological oxidation, combating bacterial infection, lessening platelet activation, regulating gene expression by virtue of microRNAs, and improving glucose metabolism. It remains presently indeterminate as to whether some biological activities of HDL are more relevant for the protection of the endothelium from atherogenesis when compared with others. The multitude of such activities raises the question of a proper assay to assess HDL functionality ex vivo. Together with clear understanding of molecular mechanisms underlying atheroprotective properties of HDL, such assay will provide a basis to resolve the ultimate question of the HDL field to allow the development of efficient HDL-targeting therapies.

Lipoprotein-associated phospholipase A2 regulates macrophage apoptosis via the Akt and caspase-7 pathways

AIM

Mutations in lipoprotein-associated phospholipase A2 (Lp-PLA2) are related to atherosclerosis. However, the molecular effects of Lp-PLA2 on atherosclerosis have not been fully investigated. Therefore, this study attempted to elucidate this issue.

METHODS

Monocytes were isolated from randomly selected healthy male volunteers according to each Lp-PLA2 genotype (wild-type Lp-PLA2 [Lp-PLA2 (V/V)], the heterozygous V279F mutation [LpPLA2 (V/F)] and the homozygous V279F mutation [Lp-PLA2 (F/F)]) and differentiated into macrophages. The level of apoptosis in the macrophages following incubation without serum was measured using the annexin V/propidium iodide double staining method, and the underlying mechanisms were further examined using a culture cell line.

RESULTS

The average plasma Lp-PLA2 concentration [Lp-PLA2 (V/V): 129.4 ng/mL, Lp-PLA2 (V/F): 70.7 ng/mL, Lp-PLA2 (F/F): 0.4 ng/mL] and activity [Lp-PLA2 (V/V): 164.3 nmol/min/mL, LpPLA2 (V/F): 100.9 nmol/min/mL, Lp-PLA2 (F/F): 11.6 nmol/min/mL] were significantly different between each genotype, although the basic clinical characteristics were similar. The percentage of apoptotic cells was significantly higher among the Lp-PLA2 (F/F) macrophages compared with that observed in the Lp-PLA2 (V/V) macrophages. This induction of apoptosis was independent of the actions of acetylated low-density lipoproteins. In addition, the transfection of the expression plasmid of V279F mutant Lp-PLA2 into Cos-7 cells or monocyte/macrophage-like U937 cells promoted apoptosis. The knockdown of Lp-PLA2 also increased the number of apoptotic cells. Among the cells expressing mutant Lp-PLA2, the caspase-7 activity was increased, while the activated Akt level was decreased.

CONCLUSIONS

The V279F mutation of Lp-PLA2 positively regulates the induction of apoptosis in macrophages and Cos-7 cells. An increase in the caspase-7 activity and a reduction in the activated Akt level are likely to be involved in this phenomenon.

Atherosclerosis and Alzheimer--diseases with a common cause? Inflammation, oxysterols, vasculature

BACKGROUND

Aging is accompanied by increasing vulnerability to pathologies such as atherosclerosis (ATH) and Alzheimer disease (AD). Are these different pathologies, or different presentations with a similar underlying pathoetiology?

DISCUSSION

Both ATH and AD involve inflammation, macrophage infiltration, and occlusion of the vasculature. Allelic variants in common genes including APOE predispose to both diseases. In both there is strong evidence of disease association with viral and bacterial pathogens including herpes simplex and Chlamydophila. Furthermore, ablation of components of the immune system (or of bone marrow-derived macrophages alone) in animal models restricts disease development in both cases, arguing that both are accentuated by inflammatory/immune pathways. We discuss that amyloid β, a distinguishing feature of AD, also plays a key role in ATH. Several drugs, at least in mouse models, are effective in preventing the development of both ATH and AD. Given similar age-dependence, genetic underpinnings, involvement of the vasculature, association with infection, Aβ involvement, the central role of macrophages, and drug overlap, we conclude that the two conditions reflect different manifestations of a common pathoetiology.

MECHANISM

Infection and inflammation selectively induce the expression of cholesterol 25-hydroxylase (CH25H). Acutely, the production of 'immunosterol' 25-hydroxycholesterol (25OHC) defends against enveloped viruses. We present evidence that chronic macrophage CH25H upregulation leads to catalyzed esterification of sterols via 25OHC-driven allosteric activation of ACAT (acyl-CoA cholesterol acyltransferase/SOAT), intracellular accumulation of cholesteryl esters and lipid droplets, vascular occlusion, and overt disease.

SUMMARY

We postulate that AD and ATH are both caused by chronic immunologic challenge that induces CH25H expression and protection against particular infectious agents, but at the expense of longer-term pathology.

The complex interplay between cholesterol and prostate malignancy

Research into the role of cholesterol and prostate disease has been ongoing for many years, but our mechanistic and translational understanding is still poor. Recent evidence indicates that cholesterol-lowering drugs reduce the risk of aggressive prostate cancer. This article reviews the literature on the relationship between circulating cholesterol and prostate cancer. The data strongly point to hypercholesterolemia as a risk factor for prostate cancer progression and suggest clinical opportunities for the use of cholesterol-lowering therapies to alter disease course.

Rimonabant is a dual inhibitor of acyl CoA:cholesterol acyltransferases 1 and 2

Acyl coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the intracellular synthesis of cholesteryl esters (CE). Both ACAT isoforms, ACAT1 and ACAT2, play key roles in the pathophysiology of atherosclerosis and ACAT inhibition retards atherosclerosis in animal models. Rimonabant, a type 1 cannabinoid receptor (CB1) antagonist, produces anti-atherosclerotic effects in humans and animals by mechanisms which are not completely understood. Rimonabant is structurally similar to two other cannabinoid receptor antagonists, AM251 and SR144528, recently identified as potent inhibitors of ACAT. Therefore, we examined the effects of Rimonabant on ACAT using both in vivo cell-based assays and in vitro cell-free assays. Rimonabant dose-dependently reduced ACAT activity in Raw 264.7 macrophages (IC(50)=2.9+/-0.38 microM) and isolated peritoneal macrophages. Rimonabant inhibited ACAT activity in intact CHO-ACAT1 and CHO-ACAT2 cells and in cell-free assays with approximately equal efficiency (IC(50)=1.5+/-1.2 microM and 2.2+/-1.1 microM for CHO-ACAT1 and CHO-ACAT2, respectively). Consistent with ACAT inhibition, Rimonabant treatment blocked ACAT-dependent processes in macrophages, oxysterol-induced apoptosis and acetylated-LDL induced foam cell formation. From these results we conclude that Rimonabant is an ACAT1/2 dual inhibitor and suggest that some of the atherosclerotic beneficial effects of Rimonabant are, at least partly, due to inhibition of ACAT.

Lipids-induced apoptosis is aggravated by acyl-coenzyme A: cholesterol acyltransferase inhibitor

OBJECTIVE

To investigate the role of acyl-coenzyme A: cholesterol acyltransferase inhibitor (ACATI) in apoptosis induced by lipids and whether lipids-induced apoptosis is accompanied by increase of free cholesterol in endoplasmic reticulum (ER), in order to further understand the mechanism of lipids-induced apoptosis in advanced atherosclerosis.

METHODS

Human vascular smooth muscle cells (VSMCs) and phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 macrophages were used. Tritiated thymidine incorporation was applied to detect cell proliferation. Cytotoxicity was assessed by lactate dehydrogenase (LDH) release. 4',6-diamidino-2-phenylindole (DAPI) staining, caspase-3, -7 assay, and Annexin-V/propidium iodide (PI) staining were used to detect apoptosis. High performance liquid chromatography was used in intracellular free cholesterol and cholesterol ester assay. ER free cholesterol was quantified.

RESULTS

Different lipids had different effects on proliferation and cytotoxicity of VSMCs. 25-hydroxycholesterol (25OHC) had biphasic effects on the proliferation of VSMCs. At low concentration, it stimulated cell proliferation, but turned to proliferation inhibition as concentration reached 15 mug/mL. 25OHC and acetylated low density lipoprotein (AcLDL) could respectively induce apoptosis in human VSMCs and PMA differentiated THP-1 macrophages, which was aggravated by ACATI, accompanied by increase of intracellular free cholesterol content. There was also an increase of cholesterol content in ER with AcLDL-induced apoptosis in THP-1 macrophages.

CONCLUSIONS

Lipids could induce apoptosis, accompanied by increase of intracellular free cholesterol content, which could be augmented by ACATI, suggesting that insults resulting in ER free cholesterol rise might be the initiator of apoptosis.