Sterol O-acyltransferase (SOAT/ACAT) activity is required to form cholesterol crystals in hepatocyte lipid droplets

OBJECTIVE

Excess cholesterol storage can induce the formation of cholesterol crystals in hepatocyte lipid droplets. Such crystals distinguish metabolic dysfunction associated steatohepatitis (MASH) from simple steatosis and may underlie its pathogenesis by causing cell damage that triggers liver inflammation. The mechanism linking cholesterol excess to its crystallization in lipid droplets is unclear. As cholesteryl esters localize to and accumulate in lipid droplets more readily than unesterified free cholesterol, we investigated whether cholesterol esterification by sterol O-acyltransferase (SOAT), also known as acyl co-A cholesterol acyltransferase (ACAT), is required for hepatocyte lipid droplet crystal formation.

METHOD

Cholesterol crystals were measured in cholesterol loaded Hep3B hepatocytes, RAW264.7 macrophages, and mouse liver using polarizing light microscopy. We examined the effect of blocking SOAT activity on crystal formation and compared these results to features of cholesterol metabolism and the progression to intracellular crystal deposits.

RESULTS

Cholesterol loading of Hep3B cells caused robust levels of lipid droplet localized crystal formation in a dose- and time-dependent manner. Co-treatment with SOAT inhibitors and genetic ablation of SOAT1 blocked crystal formation. SOAT inhibitor also blocked crystal formation in low density lipoprotein (LDL) treated Hep3B cells, acetylated LDL treated RAW 264.7 macrophages, and in the liver of mice genetically predisposed to hepatic cholesterol overload and in mice with cholesterol enriched diet-induced MASH.

CONCLUSION

SOAT1-mediated esterification may underlie cholesterol crystals associated with MASH by concentrating it in lipid droplets. These findings imply that inhibiting hepatocyte SOAT1 may be able to alleviate cholesterol associated MASH. Moreover, that either a lipid droplet localized cholesteryl ester hydrolase is required for cholesterol crystal formation, or the crystals are composed of cholesteryl ester.

VHL mutation drives human clear cell renal cell carcinoma progression through PI3K/AKT-dependent cholesteryl ester accumulation

BACKGROUND

Cholesteryl ester (CE) accumulation in intracellular lipid droplets (LDs) is an essential signature of clear cell renal cell carcinoma (ccRCC), but its molecular mechanism and pathological significance remain elusive.

METHODS

Enabled by the label-free Raman spectromicroscopy, which integrated stimulated Raman scattering microscopy with confocal Raman spectroscopy on the same platform, we quantitatively analyzed LD distribution and composition at the single cell level in intact ccRCC cell and tissue specimens in situ without any processing or exogenous labeling. Since we found that commonly used ccRCC cell lines actually did not show the CE-rich signature, primary cancer cells were isolated from human tissues to retain the lipid signature of ccRCC with CE level as high as the original tissue, which offers a preferable cell model for the study of cholesterol metabolism in ccRCC. Moreover, we established a patient-derived xenograft (PDX) mouse model that retained the CE-rich phenotype of human ccRCC.

FINDINGS

Surprisingly, our results revealed that CE accumulation was induced by tumor suppressor VHL mutation, the most common mutation of ccRCC. Moreover, VHL mutation was found to promote CE accumulation by upregulating HIFα and subsequent PI3K/AKT/mTOR/SREBPs pathway. Inspiringly, inhibition of cholesterol esterification remarkably suppressed ccRCC aggressiveness in vitro and in vivo with negligible toxicity, through the reduced membrane cholesterol-mediated downregulations of integrin and MAPK signaling pathways.

INTERPRETATION

Collectively, our study improves current understanding of the role of CE accumulation in ccRCC and opens up new opportunities for treatment.

FUNDING

This work was supported by National Natural Science Foundation of China (No. U23B2046 and No. 62027824), National Key R&D Program of China (No. 2023YFC2415500), Fundamental Research Funds for the Central Universities (No. YWF-22-L-547), PKU-Baidu Fund (No. 2020BD033), Peking University First Hospital Scientific and Technological Achievement Transformation Incubation Guidance Fund (No. 2022CX02), and Beijing Municipal Health Commission (No. 2020-2Z-40713).

Soat2 inhibitor avasimibe alleviates acute pancreatitis by suppressing acinar cell ferroptosis

Ferroptosis, characterized by lipid peroxidation, plays a significant role in the pathogenesis of acute pancreatitis (AP). While sterol O-acyltransferase 2 (Soat2) is known for its crucial regulatory role in cholesterol homeostasis, its involvement in the development of AP remains unreported. We conducted this study to identify the pivotal role of Soat2 in AP using transcriptomic databases. Subsequently, we confirmed its alterations through both in vitro and in vivo experimental models. Furthermore, we performed intervention with the Soat2 inhibitor avasimibe to evaluate pancreatic tissue pathology and serum enzymatic levels and observe inflammatory cell infiltration through immunohistochemistry. Additionally, changes in indicators related to ferroptosis were also observed. The results showed that in the AP mouse model, the protein and mRNA levels of Soat2 were significantly increased. Following avasimibe administration, there was a decrease in serum amylase levels, reduction in pancreatic tissue pathological damage, and attenuation of inflammatory cell infiltration. Furthermore, avasimibe administration resulted in downregulation of ferroptosis-related indicators. In conclusion, our findings suggest that the Soat2 inhibitor avasimibe protects against AP in mice through inhibition of the ferroptosis.

Reversible translocation of acyl-CoA:cholesterol acyltransferase (ACAT) between the endoplasmic reticulum and vesicular structures

The enzyme acyl-CoA:cholesterol acyltransferase (ACAT) is normally localized in the endoplasmic reticulum (ER) where it can esterify cholesterol for storage in lipid droplets and/or the formation of lipoproteins. Here, we report that ACAT can translocate from the ER into vesicular structures in response to different ACAT inhibitors. The translocation was fast (within minutes), reversible and occurred in different cell types. Interestingly, oleic acid was able to fasten the re-translocation from vesicles back into the reticular ER network. The process of ACAT translocation could also be induced by cyclodextrins, cholesterol, lanosterol (but not 4-cholestene-3 one), 25-hydroxycholesterol, and by certain stress stimuli such as hyperosmolarity (sucrose treatment), temperature change, or high-density cultivation. In vitro esterification showed that ACAT remains fully active after it has been translocated to vesicles in response to hyperosmotic sucrose treatment of the cells. The translocation process was not accompanied by changes in the electrophoretic mobility of ACAT, even after chemical crosslinking. Interestingly, the protein synthesis inhibitor cycloheximide showed a stimulating effect on ACAT activity and prevented the translocation of ACAT from the ER into vesicles.

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.

An ACAT inhibitor suppresses SARS-CoV-2 replication and boosts antiviral T cell activity

The severity of disease following infection with SARS-CoV-2 is determined by viral replication kinetics and host immunity, with early T cell responses and/or suppression of viraemia driving a favourable outcome. Recent studies uncovered a role for cholesterol metabolism in the SARS-CoV-2 life cycle and in T cell function. Here we show that blockade of the enzyme Acyl-CoA:cholesterol acyltransferase (ACAT) with Avasimibe inhibits SARS-CoV-2 pseudoparticle infection and disrupts the association of ACE2 and GM1 lipid rafts on the cell membrane, perturbing viral attachment. Imaging SARS-CoV-2 RNAs at the single cell level using a viral replicon model identifies the capacity of Avasimibe to limit the establishment of replication complexes required for RNA replication. Genetic studies to transiently silence or overexpress ACAT isoforms confirmed a role for ACAT in SARS-CoV-2 infection. Furthermore, Avasimibe boosts the expansion of functional SARS-CoV-2-specific T cells from the blood of patients sampled during the acute phase of infection. Thus, re-purposing of ACAT inhibitors provides a compelling therapeutic strategy for the treatment of COVID-19 to achieve both antiviral and immunomodulatory effects. Trial registration: NCT04318314.

Targeting Sterol O-Acyltransferase/Acyl-CoA:Cholesterol Acyltransferase (ACAT): A Perspective on Small-Molecule Inhibitors and Their Therapeutic Potential

Sterol O-acyltransferase (SOAT) is a membrane-bound enzyme that aids the esterification of cholesterol and fatty acids to cholesterol esters. SOAT has been studied extensively as a potential drug target, since its inhibition can serve as an alternative to statin therapy. Two SOAT isozymes that have discrete functions in the human body, namely, SOAT1 and SOAT2, have been characterized. Over three decades of research has focused on candidate SOAT1 inhibitors with unsatisfactory results in clinical trials. Recent research has focused on targeting SOAT2 selectively. In this perspective, we summarize the literature covering various SOAT inhibitory agents and discuss the design, structural requirements, and mode of action of SOAT inhibitors.

Progress of potential drugs targeted in lipid metabolism research

Lipids are a class of complex hydrophobic molecules derived from fatty acids that not only form the structural basis of biological membranes but also regulate metabolism and maintain energy balance. The role of lipids in obesity and other metabolic diseases has recently received much attention, making lipid metabolism one of the attractive research areas. Several metabolic diseases are linked to lipid metabolism, including diabetes, obesity, and atherosclerosis. Additionally, lipid metabolism contributes to the rapid growth of cancer cells as abnormal lipid synthesis or uptake enhances the growth of cancer cells. This review introduces the potential drug targets in lipid metabolism and summarizes the important potential drug targets with recent research progress on the corresponding small molecule inhibitor drugs. The significance of this review is to provide a reference for the clinical treatment of metabolic diseases related to lipid metabolism and the treatment of tumors, hoping to deepen the understanding of lipid metabolism and health.

Pregnane X Receptor Activation in Liver Perfusion

BACKGROUND

Liver normothermic machine perfusion (NMP) is being adopted as a method of optimizing livers before transplantation. However, there is further potential to use the NMP model as a platform for drug delivery. Pregnane X receptor (PXR) activation upregulates CYP3A expression and has been shown to be protective against ischemia-reperfusion in rodents. We introduced a PXR activator during NMP and assessed activation of its downstream targets.

METHODS AND MATERIALS

Organs were perfused on a NMP circuit using an oxygenated red cell-based perfusate. A series of livers were allocated to PXR treatment and compared with a control group. Biopsies were taken at the start and end of the perfusion process to quantify CYP3A expression. Perfusion samples were taken throughout the perfusion process and used to measure biochemical variables (lactate and alanine transaminase).

RESULTS

Quantification polymerase chain reaction using the delta computed tomography method on 5 livers which received Avasimibe demonstrated successful upregulation of CYP3A43 and CYP3A4 over the course of perfusion by 3.8-fold and 2.2-fold, respectively (P = .026 and P = .098, respectively; Student t test). The 4 control livers had no significant change in expression of CYP3A43 or CYP3A over the course of perfusion.

CONCLUSIONS

We have demonstrated that NMP can be successfully used as a platform for drug delivery with reliable transcription activation of downstream targets. Although it remains to be seen whether PXR therapy is beneficial in humans, the model suggests that perfusion could be used clinically in the future to further optimize grafts by acting as a drug delivery system.

Facile method to incorporate high-affinity ACAT/SOAT1 inhibitor F12511 into stealth liposome-based nanoparticle and demonstration of its efficacy in blocking cholesteryl ester biosynthesis without overt toxicity in neuronal cell culture

BACKGROUND

Acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors have been considered as potential therapeutic agents to treat several diseases, including Alzheimer's disease, atherosclerosis, and cancer. While many ACAT inhibitors are readily available, methods to encapsulate them as nanoparticles have not been reported.

NEW METHOD

We report a simple method to encapsulate ACAT inhibitors, using the potent hydrophobic ACAT inhibitor F12511 as an example. By mixing DSPE-PEG_2000, egg phosphatidylcholine (PC), and F12511 in ethanol, followed by drying, resuspension and sonication in buffer, we show that F12511 can be encapsulated as stealth liposomes at high concentration.

RESULTS

We successfully incorporated F12511 into nanoparticles and found that increasing PC in the nanoparticles markedly increased the amount of F12511 incorporated in stealth liposomes. The nanoparticles containing F12511 (Nanoparticle F) exhibit average size of approximately 200 nm and are stable at 4 ºC for at least 6 months. Nanoparticle F is very effective at inhibiting ACAT in human and mouse neuronal and microglial cell lines. Toxicity tests using mouse primary neuronal cells show that F12511 alone or Nanoparticle F added at concentrations from 2 to 10 µM for 24-, 48-, and 72-hours produces minimal, if any, toxicity.

COMPARISON WITH EXISTING METHOD(S)

Unlike existing methods, the current method is simple, cost effective, and can be expanded to produce tagged liposomes to increase specificity of delivery. This also offers opportunity to embrace water soluble agent(s) within the aqueous compartment of the nanoparticles for potential combinatorial therapy.

CONCLUSIONS

This method shows promise for delivery of hydrophobic ACAT inhibitors at high concentration in vivo.

ACAT-1-Regulated Cholesteryl Ester Accumulation Modulates Gemcitabine Resistance in Biliary Tract Cancer

BACKGROUND

Biliary tract cancer (BTC) has few choices of chemotherapy, including gemcitabine, therefore exploring the mechanisms of gemcitabine resistance is important. We focused on lipid metabolism because biliary tract epithelial cells are essential in cholesterol and bile acid metabolism and the messenger RNA (mRNA) microarray analysis showed high acyl coenzyme A: cholesterol acyltransferase 1 (ACAT-1) expression in BTC gemcitabine-resistant (GR) cell lines. We hypothesized that aberrant accumulation of cholesteryl ester (CE) regulated by ACAT-1 could modulate GR in BTC.

METHODS

CE accumulations were measured in human BTC cell lines, and the relationships between CE levels, ACAT-1 expressions, and gemcitabine sensitivity were analyzed. We performed a small-interfering RNA (siRNA)-mediated knockdown and biochemical inhibition of ACAT-1 in BTC cell lines and alterations of gemcitabine sensitivity were evaluated. To evaluate the clinical significance of ACAT-1 in regard to GR, immunohistochemistry was performed and ACAT-1 expressions were analyzed in resected BTC specimens.

RESULTS

CE levels were correlated with ACAT-1 expressions and GR in four human BTC cell lines. siRNA-mediated knockdown of ACAT-1 in two independent GR cell clones as well as ACAT-1 inhibitor treatment significantly increased gemcitabine sensitivity; knockdown of ACAT-1: 5.63- and 8.02-fold; ACAT-1 inhibitor: 8.75- and 9.13-fold, respectively. ACAT-1 expression in resected BTC specimens revealed that the disease-free survival of the ACAT-1 low-intensity group (median 2.3 years) had a significantly better outcome than that of the ACAT-1 high-intensity group (median 1.1 years) under gemcitabine treatment after surgery (*p < 0.05).

CONCLUSIONS

Our findings suggest that CE and ACAT-1 might be a novel therapeutic target for GR in BTC.

Sphingomyelin synthase 1 mediates hepatocyte pyroptosis to trigger non-alcoholic steatohepatitis

OBJECTIVE

Lipotoxic hepatocyte injury is a primary event in non-alcoholic steatohepatitis (NASH), but the mechanisms of lipotoxicity are not fully defined. Sphingolipids and free cholesterol (FC) mediate hepatocyte injury, but their link in NASH has not been explored. We examined the role of free cholesterol and sphingomyelin synthases (SMSs) that generate sphingomyelin (SM) and diacylglycerol (DAG) in hepatocyte pyroptosis, a specific form of programmed cell death associated with inflammasome activation, and NASH.

DESIGN

Wild-type C57BL/6J mice were fed a high fat and high cholesterol diet (HFHCD) to induce NASH. Hepatic SMS1 and SMS2 expressions were examined in various mouse models including HFHCD-fed mice and patients with NASH. Pyroptosis was estimated by the generation of the gasdermin-D N-terminal fragment. NASH susceptibility and pyroptosis were examined following knockdown of SMS1, protein kinase Cδ (PKCδ), or the NLR family CARD domain-containing protein 4 (NLRC4).

RESULTS

HFHCD increased the hepatic levels of SM and DAG while decreasing the level of phosphatidylcholine. Hepatic expression of Sms1 but not Sms2 was higher in mouse models and patients with NASH. FC in hepatocytes induced Sms1 expression, and Sms1 knockdown prevented HFHCD-induced NASH. DAG produced by SMS1 activated PKCδ and NLRC4 inflammasome to induce hepatocyte pyroptosis. Depletion of Nlrc4 prevented hepatocyte pyroptosis and the development of NASH. Conditioned media from pyroptotic hepatocytes activated the NOD-like receptor family pyrin domain containing 3 inflammasome (NLRP3) in Kupffer cells, but Nlrp3 knockout mice were not protected against HFHCD-induced hepatocyte pyroptosis.

CONCLUSION

SMS1 mediates hepatocyte pyroptosis through a novel DAG-PKCδ-NLRC4 axis and holds promise as a therapeutic target for NASH.

Pharmacological inhibition of acyl-coenzyme A:cholesterol acyltransferase alleviates obesity and insulin resistance in diet-induced obese mice by regulating food intake

BACKGROUND/OBJECTIVES

Acyl-coenzyme A:cholesterol acyltransferases (ACATs) catalyze the formation of cholesteryl ester (CE) from free cholesterol to regulate intracellular cholesterol homeostasis. Despite the well-documented role of ACATs in hypercholesterolemia and their emerging role in cancer and Alzheimer's disease, the role of ACATs in adipose lipid metabolism and obesity is poorly understood. Herein, we investigated the therapeutic potential of pharmacological inhibition of ACATs in obesity.

METHODS

We administrated avasimibe, an ACAT inhibitor, or vehicle to high-fat diet-induced obese (DIO) mice via intraperitoneal injection and evaluated adiposity, food intake, energy expenditure, and glucose homeostasis. Moreover, we examined the effect of avasimibe on the expressions of the genes in adipogenesis, lipogenesis, inflammation and adipose pathology in adipose tissue by real-time PCR. We also performed a pair feeding study to determine the mechanism for body weight lowering effect of avasimibe.

RESULTS

Avasimibe treatment markedly decreased body weight, body fat content and food intake with increased energy expenditure in DIO mice. Avasimibe treatment significantly lowered blood levels of glucose and insulin, and improved glucose tolerance in obese mice. The beneficial effects of avasimibe were associated with lower levels of adipocyte-specific genes in adipose tissue and the suppression of food intake. Using a pair-feeding study, we further demonstrated that avasimibe-promoted weight loss is attributed mainly to the reduction of food intake.

CONCLUSIONS

These results indicate that avasimibe ameliorates obesity and its-related insulin resistance in DIO mice through, at least in part, suppression of food intake.

Interfering with cholesterol metabolism impairs tick embryo development and turns eggs susceptible to bacterial colonization

Cholesterol is a known precursor of arthropod molecules such as the hormone 20-hydroxyecdysone and the antimicrobial boophiline, a component of tick egg wax coat. Because the cholesterol biosynthetic pathway is absent in ticks, it is necessarily obtained from the blood meal, in a still poorly understood process. In contrast, dietary cholesterol absorption is better studied in insects, and many proteins are involved in its metabolism, including Niemann-Pick C (NPC) transporter and acyl-CoA:cholesterol acyltransferase (ACAT), as well as enzymes to convert between free cholesterol and esterified cholesterol. The present work addresses the hypothesis that tick viability can be impaired by interfering with cholesterol metabolism, proposing this route as a target for novel tick control methods. Two drugs, ezetimibe (NPC inhibitor) and avasimibe (ACAT inhibitor) were added to calf blood and used to artificially feed Rhipicephalus microplus females. Results show that, after ingesting avasimibe, tick reproductive ability and egg development are impaired. Also, eggs laid by females fed with avasimibe did not hatch and were susceptible to Pseudomonas aeruginosa adhesion and biofilm formation in their surfaces. The immunoprotective potential of ACAT against ticks was also accessed using two selected ACAT peptides. Antibodies against these peptides were used to artificially feed female ticks, but no deleterious effects were observed. Taken together, data presented here support the hypothesis that enzymes and other proteins involved in cholesterol metabolism are suitable as targets for tick control methods.

Combination of metabolic intervention and T cell therapy enhances solid tumor immunotherapy

Treatment of solid tumors with T cell therapy has yielded limited therapeutic benefits to date. Although T cell therapy in combination with proinflammatory cytokines or immune checkpoints inhibitors has demonstrated preclinical and clinical successes in a subset of solid tumors, unsatisfactory results and severe toxicities necessitate the development of effective and safe combinatorial strategies. Here, the liposomal avasimibe (a metabolism-modulating drug) was clicked onto the T cell surface by lipid insertion without disturbing the physiological functions of the T cell. Avasimibe could be restrained on the T cell surface during circulation and extravasation and locally released to increase the concentration of cholesterol in the T cell membrane, which induced rapid T cell receptor clustering and sustained T cell activation. Treatment with surface anchor-engineered T cells, including mouse T cell receptor transgenic CD8⁺ T cells or human chimeric antigen receptor T cells, resulted in superior antitumor efficacy in mouse models of melanoma and glioblastoma. Glioblastoma was completely eradicated in three of the five mice receiving surface anchor-engineered chimeric antigen receptor T cells, whereas mice in other treatment groups survived no more than 64 days. Moreover, the administration of engineered T cells showed no obvious systemic side effects. These cell-surface anchor-engineered T cells hold translational potential because of their simple generation and their safety profile.

Cholesteryl Ester Promotes Mammary Tumor Growth in MMTV-PyMT Mice and Activates Akt-mTOR Pathway in Tumor Cells

The association between intratumoral cholesteryl ester (CE) and tumor progression has been reported previously. The objective of our study was to investigate a causal effect of CE on mammary tumor progression. Using MMTV-PyMT (MMTV-polyoma virus middle T) transgenic mice and breast tumor cell MCF-7, we show that both exogenous and endogenous CE can increase mammary tumor growth, that CE upregulates the AKT/mTOR pathway, and that CE synthesis blockade suppresses this signaling pathway. Our data suggest that SOAT1, a sterol O-acyltransferase, may be a potential target for the treatment of breast cancer.

Avasimibe Dampens Cholangiocarcinoma Progression by Inhibiting FoxM1-AKR1C1 Signaling

Avasimibe is a bioavailable acetyl-CoA acetyltransferase (ACAT) inhibitor and shows a good antitumor effect in various human solid tumors, but its therapeutic value in cholangiocarcinoma (CCA) and underlying mechanisms are largely unknown. In the study, we proved that avasimibe retard cell proliferation and tumor growth of CCAs and identified FoxM1/AKR1C1 axis as the potential novel targets of avasimibe. Aldo-keto reductase 1 family member C1 (AKR1C1) is gradually increased along with the disease progression and highly expressed in human CCAs. From survival analysis, AKR1C1 could be a vital predictor of tumor recurrence and prognostic factor. Enforced Forkhead box protein M1 (FoxM1) expression results in the upregulation of AKR1C1, whereas silencing FoxM1 do the opposite. FoxM1 directly binds to promoter of AKR1C1 and triggers its transcription, while FoxM1-binding site mutation decreases AKR1C1 promoter activity. Moreover, over-expressing exogenous FoxM1 reverses the growth retardation of CCA cells induced by avasimibe administration, while silencing AKR1C1 in FoxM1-overexpressing again retard cell growth. Furthermore, FoxM1 expression significantly correlates with the AKR1C1 expression in human CCA specimens. Our study demonstrates a novel positive regulatory between FoxM1 and AKR1C1 contributing cell growth and tumor progression of CCA and avasimibe may be an alternative therapeutic option for CCA by targeting this FoxM1/AKR1C1 signaling pathway.

Targeting human Acyl-CoA:cholesterol acyltransferase as a dual viral and T cell metabolic checkpoint

Determining divergent metabolic requirements of T cells, and the viruses and tumours they fail to combat, could provide new therapeutic checkpoints. Inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) has direct anti-carcinogenic activity. Here, we show that ACAT inhibition has antiviral activity against hepatitis B (HBV), as well as boosting protective anti-HBV and anti-hepatocellular carcinoma (HCC) T cells. ACAT inhibition reduces CD8+ T cell neutral lipid droplets and promotes lipid microdomains, enhancing TCR signalling and TCR-independent bioenergetics. Dysfunctional HBV- and HCC-specific T cells are rescued by ACAT inhibitors directly ex vivo from human liver and tumour tissue respectively, including tissue-resident responses. ACAT inhibition enhances in vitro responsiveness of HBV-specific CD8+ T cells to PD-1 blockade and increases the functional avidity of TCR-gene-modified T cells. Finally, ACAT regulates HBV particle genesis in vitro, with inhibitors reducing both virions and subviral particles. Thus, ACAT inhibition provides a paradigm of a metabolic checkpoint able to constrain tumours and viruses but rescue exhausted T cells, rendering it an attractive therapeutic target for the functional cure of HBV and HBV-related HCC.

NPC1L1-dependent transport of 27-alkyne cholesterol in intestinal epithelial cells

Niemann-Pick C1 Like-1 (NPC1L1) mediates the uptake of micellar cholesterol by intestinal epithelial cells and is the molecular target of the cholesterol-lowering drug ezetimibe (EZE). The detailed mechanisms responsible for intracellular shuttling of micellar cholesterol are not fully understood due to the lack of a suitable NPC1L1 substrate that can be traced by fluorescence imaging and biochemical methods. 27-Alkyne cholesterol has been previously shown to serve as a substrate for different cellular processes similar to native cholesterol. However, it is not known whether alkyne cholesterol is absorbed via an NPC1L1-dependent pathway. We aimed to determine whether alkyne cholesterol is a substrate for NPC1L1 in intestinal cells. Human intestinal epithelial Caco2 cells were incubated with micelles containing alkyne cholesterol in the presence or absence of EZE. Small intestinal closed loops in C57BL/6J mice were injected with micelles containing alkyne cholesterol with or without EZE. Alkyne cholesterol esterification in Caco2 cells was significantly inhibited by EZE and by inhibitor of clathrin-mediated endocytosis Pitstop 2. The esterification was similarly reduced by inhibitors of the acyl-CoA cholesterol acyltransferase (ACAT). Alkyne cholesterol efficiently labeled the apical membrane of Caco2 cells and the amount retained on the membrane was significantly increased by EZE as judged by accessibility to exogenous cholesterol oxidase. In mouse small intestine, the presence of EZE reduced total alkyne cholesterol uptake by ∼75%. These data show that alkyne cholesterol acts as a substrate for NPC1L1 and may serve as a nonradioactive tracer to measure cholesterol absorption in both in vitro and in vivo models.

Targeting Cholesterol Metabolism as Efficient Antiviral Strategy Against the Hepatitis E Virus

BACKGROUND AND AIMS

The Hepatitis E virus hijacks the endosomal system for its release. These structures are highly dependent on cholesterol. Hence, this study investigates the impact of HEV on cholesterol-metabolism, the effect of intracellular cholesterol content on HEV-release and the potential of cholesterol-modulators to serve as antivirals.

METHODS

Intracellular cholesterol-content of cells was modulated and impacts on HEV were monitored using qPCR, Western blot, microscopy, virus-titration and density-gradient centrifugation. Blood-lipids and HEV-RNA were routinely quantified in chronically infected patients during follow-up visits.

RESULTS

In HEV-infected cells, decreased levels of cholesterol are found. In patients, HEV infection decreases serum-lipid concentrations. Importantly, statin treatment herein increases viral titers. Similarly, reduction of intracellular cholesterol via simvastatin treatment increases viral release in vitro. On the contrary, elevating intracellular cholesterol via LDL or 25-hydroxycholesterol strongly reduces viral release due to enhanced lysosomal degradation of HEV. Drug-induced elevation of intracellular cholesterol via fenofibrate or PSC833 impairs HEV release via the same mechanism.

CONCLUSIONS

This study analyses the crosstalk between HEV and intracellular cholesterol. The results highlight the importance of an intact cholesterol homeostasis for HEV-release and thereby identify a potential target for antiviral strategies. Especially fenofibrate is considered a promising novel antiviral against HEV. Beyond this, the study may help clinicians evaluating co-treatments of HEV-infected patients with statins, as this may be counter indicated.

Long-term autophagy is sustained by activation of CCTβ3 on lipid droplets

Macroautophagy initiates by formation of isolation membranes, but the source of phospholipids for the membrane biogenesis remains elusive. Here, we show that autophagic membranes incorporate newly synthesized phosphatidylcholine, and that CTP:phosphocholine cytidylyltransferase β3 (CCTβ3), an isoform of the rate-limiting enzyme in the Kennedy pathway, plays an essential role. In starved mouse embryo fibroblasts, CCTβ3 is initially recruited to autophagic membranes, but upon prolonged starvation, it concentrates on lipid droplets that are generated from autophagic degradation products. Omegasomes and isolation membranes emanate from around those lipid droplets. Autophagy in prolonged starvation is suppressed by knockdown of CCTβ3 and is enhanced by its overexpression. This CCTβ3-dependent mechanism is also present in U2OS, an osteosarcoma cell line, and autophagy and cell survival in starvation are decreased by CCTβ3 depletion. The results demonstrate that phosphatidylcholine synthesis through CCTβ3 activation on lipid droplets is crucial for sustaining autophagy and long-term cell survival.

Commentary on: Combination of Metabolic Intervention and T Cell Therapy Enhances Solid Tumor Immunotherapy

Metabolism is a common cellular feature. Cancer creates a suppressive microenvironment resulting in inactivation of antigen-specific T cells by metabolic reprogramming. Development of approaches that enhance and sustain physiologic properties of T cell metabolism to prevent T cell inactivation and promote effector function in the tumor microenvironment is an urgent need for improvement of cell-based cancer immunotherapies.

Combined effects of avasimibe immunotherapy, doxorubicin chemotherapy, and metal-organic frameworks nanoparticles on breast cancer

CD8⁺ T cells play a vital role in cancer immunotherapy and can be shaped by metabolism. Avasimibe is an acyl coenzyme A-cholesterol acyltransferase (ACAT) inhibitor, which has been clinically verified safe in other phase Ⅲ clinical trials. It can potentiate the killing function of CD8⁺ T cells by modulating cholesterol metabolism. Doxorubicin (DOX) is an anticancer drug widely used in many cancers to induce tumor cell apoptosis. Unfortunately, DOX also can induce toxic and side effects in many organs, compromising its usage and efficacy. Herein, we report the combinational usage of avasimibe and a safe pH sensitive nano-drug delivery system composing of DOX and metal-organic frameworks nanoparticles (MNPs). Our findings demonstrated that DOX-MNPs treatment inhibited tumor growth with good safety profile and avasimibe treatment combined DOX-MNPs treatment exhibited a better efficacy than monotherapies in 4T1 breast cancer therapy.

Lipid trafficking in cardiovascular disease

The reduction of plasma apolipoprotein B (apoB) containing lipoproteins has long been pursued as the main modifiable risk factor for the development of cardiovascular disease (CVD). This has led to an intense search for strategies aiming at reducing plasma apoB-lipoproteins, culminating in reduction of overall CV risk. Despite 3 decades of progress, CVD remains the leading cause of morbidity and mortality worldwide and, as such, new therapeutic targets are still warranted. Clinical and preclinical research has moved forward from the original concept, under which some lipids must be accumulated and other removed to achieve the ideal condition in disease prevention, into the concept that mechanisms that orchestrate lipid movement between lipoproteins, cells and organelles is equally involved in CVD. As such, this review scrutinizes potentially atherogenic changes in lipid trafficking and assesses the molecular mechanisms behind it. New developments in risk assessment and new targets for the mitigation of residual CVD risk are also addressed.

Nonglucuronidated Ezetimibe Disrupts CD13- and CD64-Coassembly in Membrane Microdomains and Decreases Cellular Cholesterol Content in Human Monocytes/Macrophages

Ezetimibe (EZE) and glucuronidated EZE (EZE-Glu) differentially target Niemann-Pick C1-like 1 (NPC1L1) and CD13 (aminopeptidase-N) to inhibit intestinal cholesterol absorption and cholesterol processing in other cells, although the precise molecular mechanisms are not fully elucidated. Cellular effects of EZE, EZE-Glu, and the low-absorbable EZE-analogue S6130 were investigated on human monocyte-derived macrophages upon loading with atherogenic lipoproteins. EZE and S6130, but not EZE-Glu disturbed the colocalization of CD13 and its coreceptor CD64 (Fcγ receptor I) in membrane microdomains, and decreased the presence of both receptors in detergent-resistant membrane fractions. Biotinylated cholesterol absorption inhibitor C-5 (i.e., derivative of EZE) was rapidly internalized to perinuclear tubular structures of cells, resembling endoplasmic reticulum (ER), but CD13 was detected on extracellular sites of the plasma membrane and endolysosomal vesicles. Administration of EZE, but not of EZE-Glu or S6130, was associated with decreased cellular cholesteryl ester content, indicating the sterol-O acyltransferase 1 (SOAT1)-inhibition by EZE. Furthermore, EZE decreased the expression of molecules involved in cholesterol uptake and synthesis, in parallel with increased apolipoprotein A-I-mediated cholesterol efflux and upregulation of efflux-effectors. However, NPC1L1 the other claimed molecular target of EZE, was not detected in macrophages, thereby excluding this protein as target for EZE in macrophages. Thus, EZE is very likely a CD13-linked microdomain-disruptor and SOAT1-inhibitor in macrophages leading to in vitro anti-atherosclerotic effects through a decrease of net cellular cholesterol content. © 2019 International Society for Advancement of Cytometry.

Vicinal diaryl azole-based urea derivatives as potential cholesterol lowering agents acting through inhibition of SOAT enzymes

A novel series of vicinal diaryl azole-urea derivatives were synthesized and evaluated for their potential to inhibit SOAT enzyme. Among the reported compounds, compound (12d) emerged as the most potent compound with an IC₅₀ value of 2.43 μM. In polaxamer-407 induced lipoprotein lipase inhibition model, compound (12d) reduced triglyceride turnover in vivo. Compound (12d) also showed dose-dependent prevention of serum total cholesterol and prevention of LDL-C elevation at a dose of 30 mg/kg. Furthermore, compound (12d) showed potential to stop falling levels of serum HDL-C dose-dependently and improved the atherogenic index. Effect of 12d on body weight, plaque formation and development of atherogenic lesions were studied. Toxicological study of compound (12d) indicated that at a dose of 2000 mg/kg, 12d was devoid of any signs of toxicity or mortality.

Corn silk extract improves cholesterol metabolism in C57BL/6J mouse fed high-fat diets

BACKGROUND/OBJECTIVES

Corn silk (CS) extract contains large amounts of maysin, which is a major flavonoid in CS. However, studies regarding the effect of CS extract on cholesterol metabolism is limited. Therefore, the purpose of this study was to determine the effect of CS extract on cholesterol metabolism in C57BL/6J mouse fed high-fat diets.

MATERIALS/METHODS

Normal-fat group fed 7% fat diet, high-fat (HF) group fed 25% fat diet, and high-fat with corn silk (HFCS) group were orally administered CS extract (100 mg/kg body weight) daily. Serum and hepatic levels of total lipids, triglycerides, and total cholesterol as well as serum free fatty acid, glucose, and insulin levels were determined. The mRNA expression levels of acyl-CoA: cholesterol acyltransferase (ACAT), cholesterol 7-alpha hydroxylase (CYP7A1), farnesoid X receptor (FXR), lecithin cholesterol acyltransferase (LCAT), low-density lipoprotein receptor, 3-hyroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase), adiponectin, leptin, and tumor necrosis factor α were determined.

RESULTS

Oral administration of CS extract with HF improved serum glucose and insulin levels as well as attenuated HF-induced fatty liver. CS extracts significantly elevated mRNA expression levels of adipocytokines and reduced mRNA expression levels of HMG-CoA reductase, ACAT, and FXR. The mRNA expression levels of CYP7A1 and LCAT between the HF group and HFCS group were not statistically different.

CONCLUSIONS

CS extract supplementation with a high-fat diet improves levels of adipocytokine secretion and glucose homeostasis. CS extract is also effective in decreasing the regulatory pool of hepatic cholesterol, in line with decreased blood and hepatic levels of cholesterol though modulation of mRNA expression levels of HMG-CoA reductase, ACAT, and FXR.

Abrogating cholesterol esterification suppresses growth and metastasis of pancreatic cancer

Cancer cells are known to execute reprogramed metabolism of glucose, amino acids and lipids. Here, we report a significant role of cholesterol metabolism in cancer metastasis. By using label-free Raman spectromicroscopy, we found an aberrant accumulation of cholesteryl ester in human pancreatic cancer specimens and cell lines, mediated by acyl-CoA cholesterol acyltransferase-1 (ACAT-1) enzyme. Expression of ACAT-1 showed a correlation with poor patient survival. Abrogation of cholesterol esterification, either by an ACAT-1 inhibitor or by shRNA knockdown, significantly suppressed tumor growth and metastasis in an orthotopic mouse model of pancreatic cancer. Mechanically, ACAT-1 inhibition increased intracellular free cholesterol level, which was associated with elevated endoplasmic reticulum stress and caused apoptosis. Collectively, our results demonstrate a new strategy for treating metastatic pancreatic cancer by inhibiting cholesterol esterification.

ACAT1/SOAT1 as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia with no cure at present. Cholesterol metabolism is closely associated with AD at several stages. ACAT1 converts free cholesterol to cholesteryl esters, and plays important roles in cellular cholesterol homeostasis. Recent studies show that in a mouse model, blocking ACAT1 provides multiple beneficial effects on AD. Here we review the current evidence that implicates ACAT1 as a therapeutic target for AD. We also discuss the potential usage of various ACAT inhibitors currently available to treat AD.

Discovery and Development of the Aryl O-Sulfamate Pharmacophore for Oncology and Women's Health

In 1994, following work from this laboratory, it was reported that estrone-3-O-sulfamate irreversibly inhibits a new potential hormone-dependent cancer target steroid sulfatase (STS). Subsequent drug discovery projects were initiated to develop the core aryl O-sulfamate pharmacophore that, over some 20 years, have led to steroidal and nonsteroidal drugs in numerous preclinical and clinical trials, with promising results in oncology and women's health, including endometriosis. Drugs have been designed to inhibit STS, e.g., Irosustat, as innovative dual-targeting aromatase-steroid sulfatase inhibitors (DASIs) and as multitargeting agents for hormone-independent tumors, such as the steroidal STX140 and nonsteroidal counterparts, acting inter alia through microtubule disruption. The aryl sulfamate pharmacophore is highly versatile, operating via three distinct mechanisms of action, and imbues attractive pharmaceutical properties. This Perspective gives a personal view of the work leading both to the therapeutic concepts and these drugs, their current status, and how they might develop in the future.

Acyl-coenzyme A:cholesterol acyltransferase 1 blockage enhances autophagy in the neurons of triple transgenic Alzheimer's disease mouse and reduces human P301L-tau content at the presymptomatic stage

Patients with Alzheimer's disease (AD) display amyloidopathy and tauopathy. In mouse models of AD, pharmacological inhibition using small molecule enzyme inhibitors or genetic inactivation of acyl-coenzyme A (Acyl-CoA):cholesterol acyltransferase 1 (ACAT1) diminished amyloidopathy and restored cognitive deficits. In microglia, ACAT1 blockage increases autophagosome formation and stimulates amyloid β peptide1-42 degradation. Here, we hypothesize that in neurons ACAT1 blockage augments autophagy and increases autophagy-mediated degradation of P301L-tau protein. We tested this possibility in murine neuroblastoma cells ectopically expressing human tau and in primary neurons isolated from triple transgenic AD mice that express mutant forms of amyloid precursor protein, presenilin-1, and human tau. The results show that ACAT1 blockage increases autophagosome formation and decreases P301L-tau protein content without affecting endogenous mouse tau protein content. In vivo, lacking Acat1 decreases P301L-tau protein content in the brains of young triple transgenic AD mice but not in those of old mice, where extensive hyperphosphorylations and aggregation of P301L-tau take place. These results suggest that, in addition to ameliorating amyloidopathy in both young and old AD mice, ACAT1 blockage may benefit AD by reducing tauopathy at early stage.

Avasimibe encapsulated in human serum albumin blocks cholesterol esterification for selective cancer treatment

Undesirable side effects remain a significant challenge in cancer chemotherapy. Here we report a strategy for cancer-selective chemotherapy by blocking acyl-CoA cholesterol acyltransferase-1 (ACAT-1)-mediated cholesterol esterification. To efficiently block cholesterol esterification in cancer in vivo, we developed a systemically injectable nanoformulation of avasimibe (a potent ACAT-1 inhibitor), called avasimin. In cell lines of human prostate, pancreatic, lung, and colon cancer, avasimin significantly reduced cholesteryl ester storage in lipid droplets and elevated intracellular free cholesterol levels, which led to apoptosis and suppression of proliferation. In xenograft models of prostate cancer and colon cancer, intravenous administration of avasimin caused the concentration of avasimibe in tumors to be 4-fold higher than the IC50 value. Systemic treatment of avasimin notably suppressed tumor growth in mice and extended the length of survival time. No adverse effects of avasimin to normal cells and organs were observed. Together, this study provides an effective approach for selective cancer chemotherapy by targeting altered cholesterol metabolism of cancer cells.

Cholesteryl ester accumulation induced by PTEN loss and PI3K/AKT activation underlies human prostate cancer aggressiveness

Altered lipid metabolism is increasingly recognized as a signature of cancer cells. Enabled by label-free Raman spectromicroscopy, we performed quantitative analysis of lipogenesis at single-cell level in human patient cancerous tissues. Our imaging data revealed an unexpected, aberrant accumulation of esterified cholesterol in lipid droplets of high-grade prostate cancer and metastases. Biochemical study showed that such cholesteryl ester accumulation was a consequence of loss of tumor suppressor PTEN and subsequent activation of PI3K/AKT pathway in prostate cancer cells. Furthermore, we found that such accumulation arose from significantly enhanced uptake of exogenous lipoproteins and required cholesterol esterification. Depletion of cholesteryl ester storage significantly reduced cancer proliferation, impaired cancer invasion capability, and suppressed tumor growth in mouse xenograft models with negligible toxicity. These findings open opportunities for diagnosing and treating prostate cancer by targeting the altered cholesterol metabolism.

Effects of NS Lactobacillus strains on lipid metabolism of rats fed a high-cholesterol diet

BACKGROUND

Elevated serum cholesterol level is generally considered to be a risk factor for the development of cardiovascular diseases which seriously threaten human health. The cholesterol-lowering effects of lactic acid bacteria have recently become an area of great interest and controversy for many researchers. In this study, we investigated the effects of two NS lactobacillus strains, Lactobacillus plantarum NS5 and Lactobacillus delbrueckii subsp. bulgaricus NS12, on lipid metabolism of rats fed a high cholesterol diet.

METHODS

Thirty-two SD rats were assigned to four groups and fed either a normal or a high-cholesterol diet. The NS lactobacillus treated groups received the high-cholesterol diet supplemented with Lactobacillus plantarum NS5 or Lactobacillus delbrueckii subsp. bulgaricus NS12 in drinking water. The rats were sacrificed after a 6-week feeding period. Body weights, visceral organ and fat weights, serum and liver cholesterol and lipid levels, intestinal microbiota and liver mRNA expression levels related to cholesterol metabolism were analyzed. Liver lipid deposition and adipocyte size were evaluated histologically.

RESULTS

Compared with rats fed a high cholesterol diet, serum total cholesterol, low-density lipoprotein cholesterol, apolipoprotein B and free fatty acids levels were decreased and apolipoprotein A-I level was increased in NS5 or NS12 strain treated rats, and with no significant change in high-density lipoprotein cholesterol level. Liver cholesterol and triglyceride levels were also significantly decreased in NS lactobacillus strains treated groups. Meanwhile, the NS lactobacillus strains obviously alleviated hepatic injuries, decreased liver lipid deposition and reduced adipocyte size of high cholesterol diet fed rats. NS lactobacillus strains restored the changes in intestinal microbiota compositions, such as the increase in Bacteroides and the decrease in Clostridium. NS lactobacillus strains also regulated the mRNA expression levels of liver enzymes related to cholesterol metabolism, including the down regulation of acyl-CoA:cholesterol acyltransferase (ACAT) and the upregulation of cholesterol 7α-hydroxylase (CYP7A1).

CONCLUSION

This study suggested that the two NS lactobacillus strains may affect lipid metabolism and have cholesterol-lowering effects in rats fed a high cholesterol diet.

Effects of compound X, a novel potent inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase, on the adrenal gland of rats

To investigate the adrenal toxicity of a novel inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase, compound X (CX), histopathological examinations, fat staining, adrenal cholesterol measurement, blood biochemistry, plasma corticosterone and ACTH measurement, ACTH-stimulation assay, and adrenal gene-expression analyses were done in rats in repeated-dose studies (experiment 1: 0, 3, 10, 30 and 150mg/kg for 4, 8, 15 and 28 days; experiment 2: 0, 3, 10,30 and 150mg/kg for 28 days; experiment 3: 0, 10, 30, 100 and 300mg/kg for 28 days). CX induced morphologic changes such as vacuolation and hypertrophy in the zona fasciculata (ZF) at ≥10mg/kg, and eosinophilic changes in the ZF at 150mg/kg. Vacuolation decreased in a dose-dependent manner and was replaced by eosinophilic changes. Inflammatory and fibrous changes were observed at ≥30mg/kg. These changes were expressed at early stages of dosing and were not exacerbated by extension of the administration period. Oil-red-O/Filipin staining showed depletion of cholesterol ester in dose-dependent manner and enabled adrenal cholesterol measurement. Filipin staining also revealed vacuoles to be composed of cholesterol esters. No significant changes were observed during the dosing period of CX for plasma corticosterone and ACTH levels. Gene-expression analyses showed up-regulation of Star and Abca1 mRNA levels at 300mg/kg. In conclusion, CX induced adrenal toxicity, but CX did not influence adrenocortical functions, and exacerbation of adrenal toxicities by extension of the administration period was not observed. Up-regulation of genes related to the transport of FC, such as Star and Abca1, were observed in CX groups, and these genes may be involved in the maintenance of adrenal structure and function in rats given CX.

The acyl-coenzyme A: cholesterol acyltransferase inhibitor CI-1011 reverses diffuse brain amyloid pathology in aged amyloid precursor protein transgenic mice

Cerebral accumulation of amyloid-beta (Abeta) is characteristic of Alzheimer disease and of amyloid precursor protein (APP) transgenic mice. Here, we assessed the efficacy of CI-1011, an inhibitor of acyl-coenzyme A:cholesterol acyltransferase, which is suitable for clinical use, in reducing amyloid pathology in both young (6.5 months old) and aged (16 months old) human APP transgenic mice. Treatment of young animals with CI-1011 decreased amyloid plaque load in the cortex and hippocampus and reduced the levels of insoluble Abeta40 and Abeta42 and C-terminal fragments of APP in brain extracts. In aged mice, CI-1011 specifically reduced diffuse amyloid plaques with a minor effect on thioflavin S-positive dense-core plaques. Reduced diffusible amyloid was accompanied by suppression of astrogliosis and enhanced microglial activation. Collectively, these data suggest that CI-1011 treatment reduces amyloid burden in human APP mice by limiting generation and increasing clearance of diffusible Abeta.

Acyl-coenzyme A:cholesterol acyltransferases

The enzymes acyl-coenzyme A (CoA):cholesterol acyltransferases (ACATs) are membrane-bound proteins that utilize long-chain fatty acyl-CoA and cholesterol as substrates to form cholesteryl esters. In mammals, two isoenzymes, ACAT1 and ACAT2, encoded by two different genes, exist. ACATs play important roles in cellular cholesterol homeostasis in various tissues. This chapter summarizes the current knowledge on ACAT-related research in two areas: 1) ACAT genes and proteins and 2) ACAT enzymes as drug targets for atherosclerosis and for Alzheimer's disease.

Mechanisms for cellular cholesterol transport: defects and human disease

This review summarizes the mechanisms of cellular cholesterol transport and monogenic human diseases caused by defects in intracellular cholesterol processing. In addition, selected mouse models of disturbed cholesterol trafficking are discussed. Current pharmacological strategies to prevent atherosclerosis are largely based on altering cellular cholesterol balance and are introduced in this context. Finally, because of the organizing potential of cholesterol in membranes, disturbances in cellular cholesterol transport have implications for a wide variety of human diseases, of which selected examples are given.

Potential role of acyl-coenzyme A:cholesterol transferase (ACAT) Inhibitors as hypolipidemic and antiatherosclerosis drugs

Acyl-coenzyme A:cholesterol transferase (ACAT) is an integral membrane protein localized in the endoplasmic reticulum. ACAT catalyzes the formation of cholesteryl esters from cholesterol and fatty acyl coenzyme A. The cholesteryl esters are stored as cytoplasmic lipid droplets inside the cell. This process is very important to the organism as high cholesterol levels have been associated with cardiovascular disease. In mammals, two ACAT genes have been identified, ACAT1 and ACAT2. ACAT1 is ubiquitous and is responsible for cholesteryl ester formation in brain, adrenal glands, macrophages, and kidneys. ACAT2 is expressed in the liver and intestine. The inhibition of ACAT activity has been associated with decreased plasma cholesterol levels by suppressing cholesterol absorption and by diminishing the assembly and secretion of apolipoprotein B-containing lipoproteins such as very low density lipoprotein (VLDL). ACAT inhibition also prevents the conversion of macrophages into foam cells in the arterial walls, a critical event in the development of atherosclerosis. This review paper will focus on the role of ACAT in cholesterol metabolism, in particular as a target to develop novel therapeutic agents to control hypercholesterolemia, atherosclerosis, and Alzheimer's disease.

Margarine phytosterols decrease the secretion of atherogenic lipoproteins from HepG2 liver and Caco2 intestinal cells

Several studies in humans have demonstrated the hypocholesterolemic effect of plant sterol consumption. It is unclear whether plant sterols regulate lipoprotein metabolism in the liver and intestines, thereby decreasing the levels of circulating atherogenic lipoproteins. We investigated the effect of the three main phytosterols: stigmasterol, campesterol, and beta-sitosterol on lipoprotein production in HepG2 human liver cells and Caco2 human intestinal cells and the mechanisms involved. Cells were incubated for 24h with 50 micromol/L of the different phytosterols or 10 micromol/L of atorvastatin. Very low-density lipoprotein levels (measured by apolipoprotein (apo) B100) in HepG2 cells and chylomicron levels (measured by apoB48) in Caco2 cells were measured using western blotting. Intracellular cholesterol levels were measured using gas chromatography. Analysis was carried out using Student's t-test and ANOVA. Secretion levels of apoB100 significantly decreased by approximately 30% after incubation with all phytosterols compared to control. In addition, cholesterol ester (CE) concentrations significantly decreased when HepG2 cells were incubated with the phytosterols compared to control cells. Secretion of apoB48 from intestinal cells significantly decreased by 15% with stigmasterol, 16% with campesterol and 19% beta-sitosterol compared to control. Collectively the data suggests that plant sterols limit lipid (CE) availability in cells. Decreases in circulating levels of LDL and chylomicron remnants seen in humans with the consumption of margarine phytosterols are possibly due to their effect on lipid production in cells and would therefore reduce the risk of developing cardiovascular disease.

New drugs for the treatment of hypercholesterolaemia

Endogenous and exogenous pathways determine plasma levels of cholesterol and lipoproteins. Plasma cholesterol levels and coronary heart disease risk can be reduced pharmacologically by decreasing cholesterol synthesis, increasing its elimination and/or reducing its absorption from the intestine. The more profound knowledge about cholesterol homeostasis has allowed the development of several lipid-lowering drugs with different mechanisms of action, with the purpose of reducing both morbidity and mortality associated with coronary heart disease. Two new and more potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), also called superstatins (rosuvastatin and pitavastatin), are being studied for their ability to improve lipid profiles. Rosuvastatin is a potent, hepato-selective and relatively hydrophilic statin with a low propensity for muscle toxicity and drug interactions. Pitavastatin is another statin with a high oral bioavailability and minimal propensity for cytochrome p450-mediated drug interactions. Rosuvastatin seems to be more potent than other available statins while pitavastatin presents with a similar potency to that of atorvastatin. Another promising approach for lowering total and low-density lipoprotein cholesterol levels is inhibition of cholesterol absorption. A wide variety of new agents with the capacity for inhibiting the intestinal cholesterol absorption is currently being investigated. Ezetimibe is a selective cholesterol absorption inhibitor whose clinical efficacy has been recently demonstrated both in monotherapy and in combination with other lipid-lowering drugs. Colesevelam, a new bile acid sequestrant, has shown a clinical efficacy similar to that of other resins, with minimal gastrointestinal side effects, improving tolerability and patient compliance. Other lipid-lowering drugs with the ability to act at the enterocyte level, such as avasimibe and implitapide, are currently being investigated in humans.