Roles of acyl-coenzyme A:cholesterol acyltransferase-1 and -2

Sterol O-Acyltransferase 2 Contributes to the Yolk Cholesterol Trafficking during Zebrafish Embryogenesis

To elucidate whether Sterol O-acyltransferase (Soat) mediates the absorption and transportation of yolk lipids to the developing embryo, zebrafish soat1 and soat2 were cloned and studied. In the adult zebrafish, soat1 was detected ubiquitously while soat2 mRNA was detected specifically in the liver, intestine, brain and testis. Whole mount in situ hybridization demonstrated that both soat1 and soat2 expressed in the yolk syncytial layer, hatching gland and developing cardiovascular as well as digestive systems, suggesting that Soats may play important roles in the lipid trafficking and utilization during embryonic development. The enzymatic activity of zebrafish Soat2 was confirmed by Oil Red O staining in the HEK293 cells overexpressing this gene, and could be quenched by Soat2 inhibitor Pyripyropene A (PPPA). The zebrafish embryos injected with PPPA or morpholino oligo against soat2 in the yolk showed significantly larger yolk when compared with wild-type embryos, especially at 72 hpf, indicating a slower rate of yolk consumption. Our result indicated that zebrafish Soat2 is catalytically active in synthesizing cholesteryl esters and contributes to the yolk cholesterol trafficking during zebrafish embryogenesis.

Low-level expression of human ACAT2 gene in monocytic cells is regulated by the C/EBP transcription factors

Acyl-coenzyme A:cholesterol acyltransferases (ACATs) are the exclusive intracellular enzymes that catalyze the formation of cholesteryl/steryl esters (CE/SE). In our previous work, we found that the high-level expression of human ACAT2 gene with the CpG hypomethylation of its whole promoter was synergistically regulated by two transcription factors Cdx2 and HNF1α in the intestine and fetal liver. Here, we first observed that the specific CpG-hypomethylated promoter was correlated with the low expression of human ACAT2 gene in monocytic cell line THP-1. Then, two CCAAT/enhancer binding protein (C/EBP) elements within the activation domain in the specific CpG-hypomethylation promoter region were identified, and the expression of ACAT2 in THP-1 cells was evidently decreased when the C/EBP transcription factors were knock-downed using RNAi technology. Furthermore, ChIP assay confirmed that C/EBPs directly bind to their elements for low-level expression of human ACAT2 gene in THP-1 cells. Significantly, the increased expressions of ACAT2 and C/EBPs were also found in macrophages differentiated from both ATRA-treated THP-1 cells and cultured human blood monocytes. These results demonstrate that the low-level expression of human ACAT2 gene with specific CpG-hypomethylated promoter is regulated by the C/EBP transcription factors in monocytic cells, and imply that the lowly expressed ACAT2 catalyzes the synthesis of certain CE/SE that are assembled into lipoproteins for the secretion.

The ACAT2 expression of human leukocytes is responsible for the excretion of lipoproteins containing cholesteryl/steryl esters

Acyl-coenzymeA:cholesterol acyltransferase 2 (ACAT2) is abundantly expressed in intestine and fetal liver of healthy human. Our previous studies have shown that in monocytic cells the low-level expression of human ACAT2 gene with specific CpG-hypomethylated promoter is regulated by the CCAAT/enhancer binding protein (C/EBP) transcription factors. In this study, we further report that the ACAT2 gene expression is attributable to the C/EBPs in the human leukocytes and correlated with the excretion of fluorescent lipoproteins containing the ACAT2-catalyzed NBD22-steryl esters. Moreover, this lipoprotein excretion can be inhibited by the ACAT2 isoform-selective inhibitor pyripyropene A (PPPA) in a dose-dependent manner, and employed to determine the half maximum inhibitory concentration (IC50) values of PPPA. Significantly, it is found that the differentiation-inducing factor all-trans retinoic acid, but not the proinflammatory cytokine tumor necrosis factor-α, enhances this ACAT2-dependent lipoprotein excretion. These data demonstrate that the ACAT2 expression of human leukocytes is responsible for the excretion of lipoproteins containing cholesteryl/steryl esters (CE/SE), and suggest that the excretion of lipoproteins containing the ACAT2-catalyzed CS/SE may avoid cytotoxicity through decreasing the excess intracellular cholesterols/sterols (especially various oxysterols), which is essential for the action of the human leukocytes.

Intermittent hypoxia induces murine macrophage foam cell formation by IKK-β-dependent NF-κB pathway activation

Obstructive sleep apnea (OSA) is a common sleep disorder characterized by intermittent hypoxia (IH). Clinical studies have previously shown that OSA is an independent risk factor for atherosclerosis. Atherogenicity in OSA patients has been assumed to be associated with the NF-κB pathways. Although foam cells are considered to be a hallmark of atherosclerosis, how IH as in OSA affects their development has not been fully understood. Therefore, we hypothesized that IH induces macrophage foam cell formation through NF-κB pathway activation. To test this hypothesis, peritoneal macrophages collected from myeloid-restricted IKK-β-deleted mice were incubated with native LDL and exposed to either IH or normoxia. After exposure, NF-κB pathway activity and intracellular cholesterol were measured. In control macrophages, IH significantly increased NF-κB pathway activity by 93% compared with normoxia (P < 0.05). However, such response to IH was diminished by IKK-β deletion (increased by +31% compared with normoxia; P = 0.64), suggesting that IKK-β is critical for IH-induced NF-κB pathway activation. Likewise, in control macrophages, total cholesterol was increased in IH compared with normoxia (65.7 ± 3.8 μg/mg cellular protein and 53.2 ± 1.2, respectively; P < 0.05). However, this IH-induced foam cell formation was disappeared when IKK-β was deleted (52.2 ± 1.2 μg/mg cellular protein for IH and 46.3 ± 1.7 for normoxia; P = 0.55). This IH-mediated effect still existed in macrophages without LDL receptor. Taken together, our findings show that IH activates the IKK-β-dependent NF-κB pathway and that this, in turn, induces foam cell formation in murine macrophages.

Inhibition of SOAT1 Suppresses Glioblastoma Growth via Blocking SREBP-1-Mediated Lipogenesis

PURPOSE

Elevated lipogenesis regulated by sterol regulatory element-binding protein-1 (SREBP-1), a transcription factor playing a central role in lipid metabolism, is a novel characteristic of glioblastoma (GBM). The aim of this study was to identify effective approaches to suppress GBM growth by inhibition of SREBP-1. As SREBP activation is negatively regulated by endoplasmic reticulum (ER) cholesterol, we sought to determine whether suppression of sterol O-acyltransferase (SOAT), a key enzyme converting ER cholesterol to cholesterol esters (CE) to store in lipid droplets (LDs), effectively suppressed SREBP-1 and blocked GBM growth.

EXPERIMENTAL DESIGN

The presence of LDs in glioma patient tumor tissues was analyzed using immunofluorescence, immunohistochemistry, and electronic microscopy. Western blotting and real-time PCR were performed to analyze protein levels and gene expression of GBM cells, respectively. Intracranial GBM xenografts were used to determine the effects of genetically silencing SOAT1 and SREBP-1 on tumor growth.

RESULTS

Our study unraveled that cholesterol esterification and LD formation are signature of GBM, and human patients with glioma possess elevated LDs that correlate with GBM progression and poor survival. We revealed that SOAT1 is highly expressed in GBM and functions as a key player in controlling the cholesterol esterification and storage in GBM. Targeting SOAT1 suppresses GBM growth and prolongs survival in xenograft models via inhibition of SREBP-1-regulated lipid synthesis.

CONCLUSIONS

Cholesterol esterification and storage in LDs are novel characteristics of GBM, and inhibiting SOAT1 to block cholesterol esterification is a promising therapeutic strategy to treat GBM by suppressing SREBP-1. Clin Cancer Res; 22(21); 5337-48. ©2016 AACR.

Serralongamines B-D, three new Lycopodium alkaloids from Lycopodium serratum var. longipetiolatum, and their inhibitory effects on foam cell formation in macrophages

Three new Lycopodium alkaloids, serralongamines B-D (1-3), have been isolated from the club moss Lycopodium serratum var. longipetiolatum, and the structures were elucidated on the basis of spectroscopic data and chemical transformation. 1 and 3 significantly exhibited the inhibitory activity against foam cell formation in human macrophages, one of characteristic features of early atherosclerotic lesions.

Cholesteryl esters stabilize human CD1c conformations for recognition by self-reactive T cells

Cluster of differentiation 1c (CD1c)-dependent self-reactive T cells are abundant in human blood, but self-antigens presented by CD1c to the T-cell receptors of these cells are poorly understood. Here we present a crystal structure of CD1c determined at 2.4 Å revealing an extended ligand binding potential of the antigen groove and a substantially different conformation compared with known CD1c structures. Computational simulations exploring different occupancy states of the groove reenacted these different CD1c conformations and suggested cholesteryl esters (CE) and acylated steryl glycosides (ASG) as new ligand classes for CD1c. Confirming this, we show that binding of CE and ASG to CD1c enables the binding of human CD1c self-reactive T-cell receptors. Hence, human CD1c adopts different conformations dependent on ligand occupancy of its groove, with CE and ASG stabilizing CD1c conformations that provide a footprint for binding of CD1c self-reactive T-cell receptors.

ACAT1 regulates the dynamics of free cholesterols in plasma membrane which leads to the APP-α-processing alteration

Acyl-CoA:cholesterol acyltransferase 1 (ACAT1) is a key enzyme exclusively using free cholesterols as the substrates in cell and is involved in the cellular cholesterol homeostasis. In this study, we used human neuroblastoma cell line SK-N-SH as a model and first observed that inhibiting ACAT1 can decrease the amyloid precursor protein (APP)-α-processing. Meanwhile, the transfection experiments using the small interfering RNA and expression plasmid of ACAT1 indicated that ACAT1 can dependently affect the APP-α-processing. Furthermore, inhibiting ACAT1 was found to increase the free cholesterols in plasma membrane (PM-FC), and the increased PM-FC caused by inhibiting ACAT1 can lead to the decrease of the APP-α-processing, indicating that ACAT1 regulates the dynamics of PM-FC, which leads to the alteration of the APP-α-processing. More importantly, further results showed that under the ACAT1 inhibition, the alterations of the PM-FC and the subsequent APP-α-processing are not dependent on the cellular total cholesterol level, confirming that ACAT1 regulates the dynamics of PM-FC. Finally, we revealed that even when the Niemann-Pick-Type C-dependent pathway is blocked, the ACAT1 inhibition still obviously results in the PM-FC increase, suggesting that the ACAT1-dependent pathway is responsible for the shuttling of PM-FC to the intracellular pool. Our data provide a novel insight that ACAT1 which enzymatically regulates the dynamics of PM-FC may play important roles in the human neuronal cells.

Host cell phosphatidylcholine is a key mediator of malaria parasite survival during liver stage infection

During invasion, Plasmodium, the causative agent of malaria, wraps itself in a parasitophorous vacuole membrane (PVM), which constitutes a critical interface between the parasite and its host cell. Within hepatocytes, each Plasmodium sporozoite generates thousands of new parasites, creating high demand for lipids to support this replication and enlarge the PVM. Here, a global analysis of the total lipid repertoire of Plasmodium-infected hepatocytes reveals an enrichment of neutral lipids and the major membrane phospholipid, phosphatidylcholine (PC). While infection is unaffected in mice deficient in key enzymes involved in neutral lipid synthesis and lipolysis, ablation of rate-limiting enzymes in hepatic PC biosynthetic pathways significantly decreases parasite numbers. Host PC is taken up by both P. berghei and P. falciparum and is necessary for correct localization of parasite proteins to the PVM, which is essential for parasite survival. Thus, Plasmodium relies on the abundance of these lipids within hepatocytes to support infection.

Bastadins, brominated-tyrosine derivatives, suppress accumulation of cholesterol ester in macrophages

The formation of foam cells in macrophages has been suggested to play an essential role in the progression of early atherosclerotic lesions in vivo and, thus, its suppression is considered to be one of the major approaches for the treatment of atherosclerosis. We isolated eight brominated-tyrosine derivatives, bastadins, from the EtOH extract of the marine sponge Ianthella vasta as inhibitors of the formation of foam cells induced by acetylated low-density lipoproteins in human monocyte-derived macrophages. Bastadin 6 was the strongest inhibitor of foam cell formation due to its suppression of acyl-coenzyme A:cholesterol acyltransferase.

Concentration-Dependent Diversifcation Effects of Free Cholesterol Loading on Macrophage Viability and Polarization

BACKGROUND/AIMS

The accumulation of free cholesterol in atherosclerotic lesions has been well documented in both animals and humans. In studying the relevance of free cholesterol buildup in atherosclerosis, contradictory results have been generated, indicating that free cholesterol produces both pro- and anti-atherosclerosis effects in macrophages. This inconsistency might stem from the examination of only select concentrations of free cholesterol. In the present study, we sought to investigate the implication of excess free cholesterol loading in the pathophysiology of atherosclerosis across a broad concentration range from (in µg/ml) 0 to 60.

METHODS

Macrophage viability was determined by measuring formazan formation and flow cytometry viable cell counting. The polarization of M1 and M2 macrophages was differentiated by FACS (Fluorescence-Activated Cell Sorting) assay. The secretion of IL-1β in macrophage culture medium was measured by ELISA kit. Macrophage apoptosis was detected by flow cytometry using a TUNEL kit.

RESULTS

Macrophage viability was increased at the treatment of lower concentrations of free cholesterol from (in µg/ml) 0 to 20, but gradually decreased at higher concentrations from 20 to 60. Lower free cholesterol loading induced anti-inflammatory M2 macrophage polarization. The activation of the PPARx03B3; (Peroxisome Proliferator-Activated Receptor gamma) nuclear factor underscored the stimulation of this M2 phenotype. Nevertheless, higher levels of free cholesterol resulted in pro-inflammatory M1 activation. Moreover, with the application of higher free cholesterol concentrations, macrophage apoptosis and secretion of the inflammatory cytokine IL-1β increased significantly.

CONCLUSION

These results for the first time demonstrate that free cholesterol could render concentration-dependent diversification effects on macrophage viability, polarization, apoptosis and inflammatory cytokine secretions, thereby reconciling the pros and cons of free cholesterol buildup in macrophages to the pathophysiology of atherosclerosis.

Long non-coding RNAs expression profile in HepG2 cells reveals the potential role of long non-coding RNAs in the cholesterol metabolism

BACKGROUND

Green tea has been shown to improve cholesterol metabolism in animal studies, but the molecular mechanisms underlying this function have not been fully understood. Long non-coding RNAs (lncRNAs) have recently emerged as a major class of regulatory molecules involved in a broad range of biological processes and complex diseases. Our aim was to identify important lncRNAs that might play an important role in contributing to the benefits of epigallocatechin-3-gallate (EGCG) on cholesterol metabolism.

METHODS

Microarrays was used to reveal the lncRNA and mRNA profiles in green tea polyphenol(-)-epigallocatechin gallate in cultured human liver (HepG2) hepatocytes treated with EGCG and bioinformatic analyses of the predicted target genes were performed to identify lncRNA-mRNA targeting relationships. RNA interference was used to investigate the role of lncRNAs in cholesterol metabolism.

RESULTS

The expression levels of 15 genes related to cholesterol metabolism and 285 lncRNAs were changed by EGCG treatment. Bioinformatic analysis found five matched lncRNA-mRNA pairs for five differentially expressed lncRNAs and four differentially expressed mRNA. In particular, the lncRNA AT102202 and its potential targets mRNA-3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) were identified. Using a real-time polymerase chain reaction technique, we confirmed that EGCG down-regulated mRNA expression level of the HMGCR and up-regulated expression of AT102202. After AT102202 knockdown in HepG2, we observed that the level of HMGCR expression was significantly increased relative to the scrambled small interfering RNA control (P < 0.05).

CONCLUSIONS

Our results indicated that EGCG improved cholesterol metabolism and meanwhile changed the lncRNAs expression profile in HepG2 cells. LncRNAs may play an important role in the cholesterol metabolism.

Fish oil and krill oil differentially modify the liver and brain lipidome when fed to mice

BACKGROUND

Marine food is an important source of omega-3 fatty acids with beneficial health effects. Oils from marine organisms have different fatty acid composition and differ in their molecular composition. Fish oil (FO) has a high content of eicosapentaenoic and docosahexaenoic acids mainly esterified to triacylglycerols, while in krill oil (KO) these fatty acids are mainly esterified to phospholipids. The aim was to study the effects of these oils on the lipid content and fatty acid distribution in the various lipid classes in liver and brain of mice.

METHODS

Mice were fed either a high-fat diet (HF), a HF diet supplemented with FO or with KO (n = 6). After six weeks of feeding, liver and brain lipid extracts were analysed using a shotgun and TAG lipidomics approach. Student t-test was performed after log-transformation to compare differences between study groups.

RESULTS

Six weeks of feeding resulted in significant changes in the relative abundance of many lipid classes compared to control mice. In both FO and KO fed mice, the triacylglycerol content in the liver was more than doubled. The fatty acid distribution was affected by the oils in both liver and brain with a decrease in the abundance of 18:2 and 20:4, and an increase in 20:5 and 22:6 in both study groups. 18:2 decreased in all lipid classes in the FO group but with only minor changes in the KO group. Differences between the feeding groups were particularly evident in some of the minor lipid classes that are associated with inflammation and insulin resistance. Ceramides and diacylglycerols were decreased and cholesteryl esters increased in the liver of the KO group, while plasmalogens were decreased in the FO group. In the brain, diacylglycerols were decreased, more by KO than FO, while ceramides and lactosylceramides were increased, more by FO than KO.

CONCLUSION

The changes in the hepatic sphingolipids and 20:4 fatty acid levels were greater in the KO compared to the FO fed mice, and are consistent with a hypothesis that krill oil will have a stronger anti-inflammatory action and enhances insulin sensitivity more potently than fish oil.

Inhibitors for cholesterol ester accumulation in macrophages from Chinese cabbage

The cholesterol ester accumulates in macrophages in the early stage of atherosclerotic lesions, leading to the formation of foam cells. We examined the inhibitory effects of the crude extracts of 22 edible plants on foam cell formation and isolated nine chlorophyll derivatives as potent inhibitors from Chinese cabbage. The results of the present study suggest that the chlorophyll derivatives contained in edible plants may be useful for the prevention and treatment of atherosclerosis.

Potential approaches to ameliorate hepatic fat accumulation seen with MTP inhibition

Microsomal triglyceride transfer protein (MTP) is one of the promising targets for the therapy of dyslipidemia and MTP inhibition can lead to robust plasma low-density lipoprotein cholesterol (LDL-C) reduction. Lomitapide, a small-molecule MTP inhibitor, was recently approved by the US FDA as an additional treatment for homozygous familial hypercholesterolemia (hoFH). However, liver-related side effects, including hepatic fat accumulation and transaminase elevations, are the main safety concerns associated with MTP inhibitors. Here, we review recent knowledge on the mechanisms underlying liver toxicity of MTP inhibitors. The contribution of altered levels of intracellular triglycerides, cholesteryl esters, and free cholesterols toward cellular dysfunction is specifically addressed. On this basis, therapies targeted to attenuate cellular lipid accumulation, to reduce risk factors for non-alcoholic fatty liver disease (NAFLD) (i.e., insulin resistance and oxidative stress) and to specifically inhibit intestinal MTP may be useful for ameliorating liver damage induced by MTP inhibitors. In particular, weight loss through lifestyle interventions is expected to be the most effective and safest way to minimize the undesirable side effects. Specific dietary supplementation might also have protective effects against hepatosteatosis. Despite that, to date, few clinical data support these therapeutic options in MTP inhibition-related liver damage, such proposed approaches may be further explored in the future for their use in preventing unwanted effects of MTP inhibitors.

Lipidome of atherosclerotic plaques from hypercholesterolemic rabbits

The cellular, macromolecular and neutral lipid composition of the atherosclerotic plaque has been extensively characterized. However, a comprehensive lipidomic analysis of the major lipid classes within atherosclerotic lesions has not been reported. The objective of this study was to produce a detailed framework of the lipids that comprise the atherosclerotic lesion of a widely used pre-clinical model of plaque progression. Male New Zealand White rabbits were administered regular chow supplemented with 0.5% cholesterol (HC) for 12 weeks to induce hypercholesterolemia and atherosclerosis. Our lipidomic analyses of plaques isolated from rabbits fed the HC diet, using ultra-performance liquid chromatography (UPLC) and high-resolution mass spectrometry, detected most of the major lipid classes including: Cholesteryl esters, triacylglycerols, phosphatidylcholines, sphingomyelins, diacylglycerols, fatty acids, phosphatidylserines, lysophosphatidylcholines, ceramides, phosphatidylglycerols, phosphatidylinositols and phosphatidylethanolamines. Given that cholesteryl esters, triacylglycerols and phosphatidylcholines comprise greater than 75% of total plasma lipids, we directed particular attention towards the qualitative and quantitative assessment of the fatty acid composition of these lipids. We additionally found that sphingomyelins were relatively abundant lipid class within lesions, and compared the abundance of sphingomyelins to their precursor phosphatidylcholines. The studies presented here are the first approach to a comprehensive characterization of the atherosclerotic plaque lipidome.

Assessment of epithelial innate antimicrobial factors in sinus tissue from patients with and without chronic rhinosinusitis

BACKGROUND

Airway secretions contain endogenous antimicrobial factors (AMFs) that contribute to the innate host defense of the respiratory tract. Antibacterial peptides as well as host-derived lipids including cholesteryl esters have been detected in maxillary lavage fluid. Sterol O-acyltransferase 1 (SOAT1) is a key enzyme in cholesteryl ester production. The purpose of this study is to determine if such intrinsic microbicidal molecules are acutely expressed within sinus tissue and to compare levels of expression between patients with and without chronic rhinosinusitis (CRS).

METHODS

Sinus tissue was obtained from subjects with (24) and without (9) a history of CRS. Six CRS patients had nasal polyposis (CRSwNP). Immunofluorescence staining for human neutrophil peptide (HNP) was done as a marker for inflammation. Real-time polymerase chain reaction (RT-PCR) following RNA extraction was used to quantify the expression of SOAT-1, the epithelial beta-defensins (HBD2 and HBD3), and the cathelicidin LL37 with ribosomal protein, large, P0 (RPLP0) as the housekeeping gene.

RESULTS

Immunofluorescence showed significant increase in HNP staining in CRS patients without nasal polyposis (CRSsNP) vs non-CRS specimens (p = 0.010), in agreement with clinical inflammation status. SOAT1 messenger RNA (mRNA) expression was also upregulated in CRSsNP compared to non-CRS (p = 0.041) and CRSwNP (p = 0.005) patients, whereas increases for HBD2 and HBD3 were less prominent. LL37 was either absent or expressed at very low levels in all samples.

CONCLUSION

Increased biosynthesis of SOAT1, a key enzyme for antimicrobial cholesteryl ester production, was observed in the sinus tissue of CRSsNP patients but not in CRSwNP patients. This further supports the novel concept of lipid-mediated innate mucosal defense and delineates CRS with and without nasal polyposis as distinct subtypes.

Intestine-specific MTP and global ACAT2 deficiency lowers acute cholesterol absorption with chylomicrons and HDLs

Intestinal cholesterol absorption involves the chylomicron and HDL pathways and is dependent on microsomal triglyceride transfer protein (MTP) and ABCA1, respectively. Chylomicrons transport free and esterified cholesterol, whereas HDLs transport free cholesterol. ACAT2 esterifies cholesterol for secretion with chylomicrons. We hypothesized that free cholesterol accumulated during ACAT2 deficiency may be secreted with HDLs when chylomicron assembly is blocked. To test this, we studied cholesterol absorption in mice deficient in intestinal MTP, global ACAT2, and both intestinal MTP and global ACAT2. Intestinal MTP ablation significantly increased intestinal triglyceride and cholesterol levels and reduced their transport with chylomicrons. In contrast, global ACAT2 deficiency had no effect on triglyceride absorption but significantly reduced cholesterol absorption with chylomicrons and increased cellular free cholesterol. Their combined deficiency reduced cholesterol secretion with both chylomicrons and HDLs. Thus, contrary to our hypothesis, free cholesterol accumulated in the absence of MTP and ACAT2 is unavailable for secretion with HDLs. Global ACAT2 deficiency causes mild hypertriglyceridemia and reduces hepatosteatosis in mice fed high cholesterol diets by increasing hepatic lipoprotein production by unknown mechanisms. We show that this phenotype is preserved in the absence of intestinal MTP in global ACAT2-deficient mice fed a Western diet. Further, we observed increases in hepatic MTP activity in these mice. Thus, ACAT2 deficiency might increase MTP expression to avoid hepatosteatosis in cholesterol-fed animals. Therefore, ACAT2 inhibition might avert hepatosteatosis associated with high cholesterol diets by increasing hepatic MTP expression and lipoprotein production.

Cholesterol transport and regulation in the mammary gland

The milk-producing alveolar epithelial cells secrete milk that remains after birth the principal source of nutrients for neonates. Milk secretion and composition are highly regulated processes via integrated actions of hormones and local factors which involve specific receptors and downstream signal transduction pathways. Overall milk composition is similar among mammalian species, although the content of individual constituents such as lipids may significantly differ from one species to another. The milk lipid fraction is essentially composed of triglycerides, which represent more than 95 % of the total lipids in human and commercialized bovine milk. Though sterols, including cholesterol, which is the major milk sterol, represent less than 0.5 % of the total milk lipid fraction, they are of key importance for several biological processes. Cholesterol is required for the formation of biological membranes especially in rapidly growing organisms, and for the synthesis of sterol-based compounds. Cholesterol found in milk originates predominantly from blood uptake and, to a certain extent, from local synthesis in the mammary tissue. The present review summarizes current knowledge on cellular mechanisms and regulatory processes determining intra- and transcellular cholesterol transport in the mammary gland. Cholesterol exchanges between the blood, the mammary alveolar cells and the milk, and the likely role of active cholesterol transporters in these processes are discussed. In this context, the hormonal regulation and signal transduction pathways promoting active cholesterol transport as well as potential regulatory crosstalks are highlighted.

Lipid absorption defects in intestine-specific microsomal triglyceride transfer protein and ATP-binding cassette transporter A1-deficient mice

We have previously described apolipoprotein B (apoB)-dependent and -independent cholesterol absorption pathways and the role of microsomal triglyceride transfer protein (MTP) and ATP-binding cassette transporter A1 (ABCA1) in these pathways. To assess the contribution of these pathways to cholesterol absorption and to determine whether there are other pathways, we generated mice that lack MTP and ABCA1, individually and in combination, in the intestine. Intestinal deletions of Mttp and Abca1 decreased plasma cholesterol concentrations by 45 and 24%, respectively, whereas their combined deletion reduced it by 59%. Acute cholesterol absorption was reduced by 28% in the absence of ABCA1, and it was reduced by 92-95% when MTP was deleted in the intestine alone or together with ABCA1. MTP deficiency significantly reduced triglyceride absorption, although ABCA1 deficiency had no effect. ABCA1 deficiency did not affect cellular lipids, but Mttp deficiency significantly increased intestinal levels of triglycerides and free fatty acids. Accumulation of intestinal free fatty acids, but not triglycerides, in Mttp-deficient intestines was prevented when mice were also deficient in intestinal ABCA1. Combined deficiency of these genes increased intestinal fatty acid oxidation as a consequence of increased expression of peroxisome proliferator-activated receptor-γ (PPARγ) and carnitine palmitoyltransferase 1α (CPT1α). These studies show that intestinal MTP and ABCA1 are critical for lipid absorption and are the main determinants of plasma and intestinal lipid levels. Reducing their activities might lower plasma lipid concentrations.

Manzamine A, a marine-derived alkaloid, inhibits accumulation of cholesterol ester in macrophages and suppresses hyperlipidemia and atherosclerosis in vivo

The formation of foam cells in macrophages plays an essential role in the progression of early atherosclerotic lesions and therefore its prevention is considered to be a promising target for the treatment of atherosclerosis. We found that an extract of the marine sponge Acanthostrongylophora ingens inhibited the foam cell formation induced by acetylated low-density lipoprotein (AcLDL) in human monocyte-derived macrophages, as measured based on the accumulation of cholesterol ester (CE). Bioassay-guided purification of inhibitors from the extract afforded manzamines. Manzamine A was the most potent inhibitor of foam cell formation, and also suppressed CE formation in Chinese hamster ovary cells overexpressing acyl-CoA:cholesterol acyl-transferase (ACAT)-1 or ACAT-2. In addition, manzamine A inhibited ACAT activity. Next, we orally administered manzamine A to apolipoprotein E (apoE)-deficient mice for 80 days, and found that total cholesterol, free cholesterol, LDL-cholesterol, and triglyceride levels in serum were significantly reduced and the area of atherosclerotic lesions in the aortic sinus was also substantially diminished. These findings clearly suggest that manzamine A suppresses hyperlipidemia and atherosclerosis in apoE-deficient mice by inhibiting ACAT and is therefore a promising lead compound in the prevention or treatment of atherosclerosis. Although manzamine A has been reported to show several biological activities, this is the first report of a suppressive effect of manzamine A on atherosclerosis in vivo.

Making, baking, and breaking: the synthesis, storage, and hydrolysis of neutral lipids

The esterification of amphiphilic alcohols with fatty acids is a ubiquitous strategy implemented by eukaryotes and some prokaryotes to conserve energy and membrane progenitors and simultaneously detoxify fatty acids and other lipids. This key reaction is performed by at least four evolutionarily unrelated multigene families. The synthesis of this "neutral lipid" leads to the formation of a lipid droplet, which despite the clear selective advantage it confers is also a harbinger of cellular and organismal malaise. Neutral lipid deposition as a cytoplasmic lipid droplet may be thermodynamically favored but nevertheless is elaborately regulated. Optimal utilization of these resources by lipolysis is similarly multigenic in determination and regulation. We present here a perspective on these processes that originates from studies in model organisms, and we include our thoughts on interventions that target reductions in neutral lipids as therapeutics for human diseases such as obesity and diabetes.

Homocysteine-mediated cholesterol efflux via ABCA1 and ACAT1 DNA methylation in THP-1 monocyte-derived foam cells

Homocysteine (Hcy) has been recognized as a prevalent risk factor for cardiovascular events. Cholesterol-loaded foam cells are a central component of atherosclerotic lesions. ATP-binding cassette transporter A1 (ABCA1), which mediates the efflux of cellular cholesterol and phospholipids, is the rate-limiting step in lipid metabolism. Acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT1) promotes accumulation of cholesterol ester in macrophages, thereby resulting in the foam cell formation, a hallmark of early stage in atherosclerosis. In this study, cultured monocyte-derived foam cells were incubated with clinical relevant concentrations of Hcy for 24 h. Both increased number of foam cells and accumulation of cholesterol were found, and the mRNA and protein expression levels of ABCA1 were decreased, while ACAT1 expression was increased in the presence of Hcy. Furthermore, the DNA methylation level of ABCA1 gene was increased whereas ACAT1 DNA methylation was decreased by using different concentrations of Hcy. Moreover, our results showed that DNA methyltransferase (DNMT) activity and DNA methyltransferase 1 (DNMT1) mRNA expression were increased by Hcy. It is indicated that DNA methylation has the function to regulate the expression of ABCA1 and ACAT1 via DNMT. In conclusion, these results suggest that ABCA1 and ACAT1 DNA methylation induced by Hcy may play a potential role in ABCA1 and ACAT1 expression and the accumulation of cholesterol in monocyte-derived foam cells.

Cholesterol homeostasis: a key to prevent or slow down neurodegeneration

Neurodegeneration, a common feature for many brain disorders, has severe consequences on the mental and physical health of an individual. Typically human neurodegenerative diseases are devastating illnesses that predominantly affect elderly people, progress slowly, and lead to disability and premature death; however they may occur at all ages. Despite extensive research and investments, current therapeutic interventions against these disorders treat solely the symptoms. Therefore, since the underlying mechanisms of damage to neurons are similar, in spite of etiology and background heterogeneous, it will be of interest to identify possible trigger point of neurodegeneration enabling development of drugs and/or prevention strategies that target many disorders simultaneously. Among the factors that have been identified so far to cause neurodegeneration, failures in cholesterol homeostasis are indubitably the best investigated. The aim of this review is to critically discuss some of the main results reported in the recent years in this field mainly focusing on the mechanisms that, by recovering perturbations of cholesterol homeostasis in neuronal cells, may correct clinically relevant features occurring in different neurodegenerative disorders and, in this regard, also debate the current potential therapeutic interventions.

Eugenosedin-A prevents high-fat diet increased adhesion molecules through inhibition of MAPK- and p65-mediated NF-κB pathway in rat model

Objectives

Previous studies have shown eugenosedin-A, a 5-HT1B/2A and α1/α2/β1-adrenergic blocker, is able to decrease cholesterol levels, hyperglycaemia and inflammation in hyperlipidaemic mice induced by high-fat diet (HFD). The aim of this study is to examine the effects of eugenosedin-A on the inhibition of adhesion molecules of platelets, the aorta and acyl-coenzymeA:cholesterol acyltransferase-1 (ACAT-1) of macrophages in a hyperlipidaemic rat model.

Methods

Six-week-old Sprague–Dawley rats were randomly divided into two control and treatment groups. The control rats received either a regular diet or HFD and the treatment groups were fed HFD with either 5 mg/kg eugenosedin-A or atorvastatin for a 10-week period.

Key findings

Compared with the two control groups, the HFD group had lower levels of high-density lipoprotein, higher concentrations of triglycerides, total cholesterol, low-density lipoprotein and insulin. The expression of adhesion molecules in platelets, aorta and monocyte-macrophage were enhanced by HFD. HFD also increased upstream proteins and their phosphorylated form in the aorta. In treatment groups, eugenosedin-A and atorvastatin improved HFD-induced hyperlipidaemia and levels of insulin. Eugenosedin-A reduced the upregulation of P-selectin, ICAM-1, ICAM-2, ICAM-3, VCAM, PECAM in platelets and inhibited E-selectin, ICAM-1, ICAM-2, ICAM-3, VCAM and PECAM protein levels in the aorta. Eugenosedin-A reduced the ACAT-1 protein expression of monocyte-macrophages. The expression of PKCα, MAPKs, IKKα and p65 and their phosphorylated form were reduced in treatment groups.

Conclusions

Taken together, hyperlipidaemia enhances the expression of adhesion molecules and ACAT-1 protein, and eugenosedin-A ameliorates those increases. Through inhibition of MAPK- and p-65-mediated NF-κB pathway, eugenosedin-A decreases the quantity of adhesion molecules.

Ezetimibe blocks the internalization of NPC1L1 and cholesterol in mouse small intestine

The multiple transmembrane protein Niemann-Pick C1 like1 (NPC1L1) is essential for intestinal cholesterol absorption. Ezetimibe binds to NPC1L1 and is a clinically used cholesterol absorption inhibitor. Recent studies in cultured cells have shown that NPC1L1 mediates cholesterol uptake through vesicular endocytosis that can be blocked by ezetimibe. However, how NPC1L1 and ezetimibe work in the small intestine is unknown. In this study, we found that NPC1L1 distributed in enterocytes of villi and transit-amplifying cells of crypts. Acyl-CoA cholesterol acyltransferase 2 (ACAT2), another important protein for cholesterol absorption by providing cholesteryl esters to chylomicrons, was mainly presented in the apical cytoplasm of enterocytes. NPC1L1 and ACAT2 were highly expressed in jejunum and ileum. ACAT1 presented in the Paneth cells of crypts and mesenchymal cells of villi. In the absence of cholesterol, NPC1L1 was localized on the brush border of enterocytes. Dietary cholesterol induced the internalization of NPC1L1 to the subapical layer beneath the brush border and became partially colocalized with the endosome marker Rab11. Ezetimibe blocked the internalization of NPC1L1 and cholesterol and caused their retention in the plasma membrane. This study demonstrates that NPC1L1 mediates cholesterol entering enterocytes through vesicular endocytosis and that ezetimibe blocks this step in vivo.

Characterization of lipid and lipoprotein metabolism in primary human hepatocytes

Primary rodent hepatocytes and hepatoma cell lines are commonly used as model systems to elucidate and study potential drug targets for metabolic diseases such as obesity and atherosclerosis. However, if therapies are to be developed, it is essential that our knowledge gained from these systems is translatable to that of human. Here, we have characterized lipid and lipoprotein metabolism in primary human hepatocytes for comparison to rodent primary hepatocytes and human hepatoma cell lines. Primary human hepatocytes were maintained in collagen coated dishes in confluent monolayers for up to 3 days. We found primary human hepatocytes were viable, underwent lipid synthesis, and were able to secret lipoproteins up to 3 days in culture. Furthermore, the lipoprotein profile secreted by primary human hepatocytes was comparable to that found in human plasma; this contrasts with primary rodent hepatocytes and human hepatoma cells. We also investigated the pharmacological effects of nicotinic acid (niacin, NA), a potent dyslipidemic drug, on hepatic lipid synthesis and lipoprotein secretion. We found NA increased the expression of ATP-binding cassette transporter A1 in primary human hepatocytes, which may potentially explain how NA increases plasma high-density lipoproteins in humans. In conclusion, primary human hepatocytes are a more relevant model to study lipid synthesis and lipoprotein secretion than hepatoma cells or rodent primary hepatocyte models. Further research needs to be done to maintain liver specific functions of primary human hepatocytes in prolonged cultures for these cells to be a viable model.

Discovery of a potent and orally available acyl-CoA: cholesterol acyltransferase inhibitor as an anti-atherosclerotic agent: (4-phenylcoumarin)acetanilide derivatives

Acyl-CoA: cholesterol acyltransferase (ACAT) is an intracellular enzyme that catalyzes cholesterol esterification. ACAT inhibitors are expected to be potent therapeutic agents for the treatment of atherosclerosis. A series of potent ACAT inhibitors based on an (4-phenylcoumarin)acetanilide scaffold was identified. Evaluation of the structure-activity relationships of a substituent on this scaffold, with an emphasis on improving the pharmacokinetic profile led to the discovery of 2-[7-chloro-4-(3-chlorophenyl)-6-methyl-2-oxo-2H-chromen-3-yl]-N-[4-chloro-2-(trifluoromethyl)phenyl]acetamide (23), which exhibited potent ACAT inhibitory activity (IC50=12 nM) and good pharmacokinetic profile in mice. Compound 23 also showed regressive effects on atherosclerotic plaques in apolipoprotein (apo)E knock out (KO) mice at a dose of 0.3 mg/kg per os (p.o.).

Tomatidine, a tomato sapogenol, ameliorates hyperlipidemia and atherosclerosis in apoE-deficient mice by inhibiting acyl-CoA:cholesterol acyl-transferase (ACAT)

It was previously revealed that esculeoside A, a new glycoalkaloid, and esculeogenin A, a new aglycon of esculeoside A, contained in ripe tomato ameliorate atherosclerosis in apoE-deficent mice. This study examined whether tomatidine, the aglycone of tomatine, which is a major tomato glycoalkaloid, also shows similar inhibitory effects on cholesterol ester (CE) accumulation in human monocyte-derived macrophages (HMDM) and atherogenesis in apoE-deficient mice. Tomatidine significantly inhibited the CE accumulation induced by acetylated LDL in HMDM in a dose-dependent manner. Tomatidine also inhibited CE formation in Chinese hamster ovary cells overexpressing acyl-CoA:cholesterol acyl-transferase (ACAT)-1 or ACAT-2, suggesting that tomatidine suppresses both ACAT-1 and ACAT-2 activities. Furthermore, the oral administration of tomatidine to apoE-deficient mice significantly reduced levels of serum cholesterol, LDL-cholesterol, and areas of atherosclerotic lesions. The study provides the first evidence that tomatidine significantly suppresses the activity of ACAT and leads to reduction of atherogenesis.

Discovery of a novel acyl-CoA: cholesterol acyltransferase inhibitor: the synthesis, biological evaluation, and reduced adrenal toxicity of (4-phenylcoumarin)acetanilide derivatives with a carboxylic acid moiety

As a part of our research for novel potent and orally available acyl-CoA: cholesterol acyltransferase (ACAT) inhibitors that can be used as anti-atherosclerotic agents, we recently reported the discovery of the (4-phenylcoumarine)acetanilide derivative 1. However, compound 1 showed adrenal toxicity in animal models. In order to search for safer ACAT inhibitors that do not have adrenal toxicity, we examined the inhibitory activity of ACAT in human macrophage and adrenal cells. The introduction of a carboxylic acid moiety on the pendant phenyl ring and the adjustment of the lipophilicity led to the discovery of (2E)-3-[7-chloro-3-[2-[[4-fluoro-2-(trifluoromethyl)phenyl]amino]-2-oxoethyl]-6-methyl-2-oxo-2H-chromen-4-yl]phenyl]acrylic acid (21e), which showed potent ACAT inhibitory activity in macrophages and a selectivity of around 30-fold over adrenal cells. In addition, compound 21e showed high adrenal safety in guinea pigs.

Multiple functions of microsomal triglyceride transfer protein

Microsomal triglyceride transfer protein (MTP) was first identified as a major cellular protein capable of transferring neutral lipids between membrane vesicles. Its role as an essential chaperone for the biosynthesis of apolipoprotein B (apoB)-containing triglyceride-rich lipoproteins was established after the realization that abetalipoproteinemia patients carry mutations in the MTTP gene resulting in the loss of its lipid transfer activity. Now it is known that it also plays a role in the biosynthesis of CD1, glycolipid presenting molecules, as well as in the regulation of cholesterol ester biosynthesis. In this review, we will provide a historical perspective about the identification, purification and characterization of MTP, describe methods used to measure its lipid transfer activity, and discuss tissue expression and function. Finally, we will review the role MTP plays in the assembly of apoB-lipoprotein, the regulation of cholesterol ester synthesis, biosynthesis of CD1 proteins and propagation of hepatitis C virus. We will also provide a brief overview about the clinical potentials of MTP inhibition.

Two novel cis-elements involved in hepatocyte nuclear factor 4α regulation of acyl-coenzyme A:cholesterol acyltransferase 2 expression

Acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) is important for cholesterol ester synthesis and secretion. A previous study revealed that ACAT2 gene promoter activity was upregulated by hepatocyte nuclear factor 4α (HNF4α) through two sites around -247 and -311 of ACAT2 gene promoter. Here, we identified two novel cis-elements, site I (-1006 to -898) and site II (-38 to -29), which are important for HNF4α effect. In HepG2 cells, mutation of site I decreased ACAT2 gene promoter activity to one-fifth of that of the wild type, while mutation of site II reduced promoter activity to less than one-tenth of that of the wild type. In 293T cells, mutation of these two cis-elements profoundly impaired the HNF4α induction effect. When either of these two elements was inserted into pGL3-promoter, HNF4α induced promoter activity through the inserted element, while mutation of the element impaired HNF4α induction effect. In electrophoretic mobility shift assay and chromatin immunoprecipitation experiment, HNF4α bound to these two elements. Thus, the two cis-elements are important for HNF4α effect on ACAT2 gene transcription. We also showed that HNF4α positively regulates ACAT2 gene expression at mRNA level. Overexpression of HNF4α increased ACAT2 expression, whereas knockdown of HNF4α decreased ACAT2 expression. Peroxisome proliferator-activated receptor gamma coactivator 1α (PCG1α), a coactivator of HNF4α, increased ACAT2 expression, while small heterodimer partner (SHP), a corepressor of HNF4α, decreased ACAT2 expression. These results provide more insights into transcriptional regulation of ACAT2 expression.

Atherosclerosis, caveolae and caveolin-1

Atherosclerosis is a disease of the blood vessel characterized by the development of an arterial occlusion containing lipid and cellular deposits. Caveolae are 50-100 nm cell surface plasma membrane invaginations that are believed to play an important role in the regulation of cellular signaling and transport of molecules among others. These organelles are enriched in sphingolipids and cholesterol and are characterized by the presence of the protein caveolin-1. Caveolin-1 and caveolae are present in most of the cells involved in the development of atherosclerosis. The current literature suggests a rather complex role for caveolin-1 in this disease, with evidence of either pro- or anti-atherogenic functions depending on the cell type examined. In the present chapter, the various roles of caveolae and caveolin-1 in the development of atherosclerosis are examined.

Plasma lipid profiling across species for the identification of optimal animal models of human dyslipidemia

In an attempt to understand the applicability of various animal models to dyslipidemia in humans and to identify improved preclinical models for target discovery and validation for dyslipidemia, we measured comprehensive plasma lipid profiles in 24 models. These included five mouse strains, six other nonprimate species, and four nonhuman primate (NHP) species, and both healthy animals and animals with metabolic disorders. Dyslipidemic humans were assessed by the same measures. Plasma lipoprotein profiles, eight major plasma lipid fractions, and FA compositions within these lipid fractions were compared both qualitatively and quantitatively across the species. Given the importance of statins in decreasing plasma low-density lipoprotein cholesterol for treatment of dyslipidemia in humans, the responses of these measures to simvastatin treatment were also assessed for each species and compared with dyslipidemic humans. NHPs, followed by dog, were the models that demonstrated closest overall match to dyslipidemic humans. For the subset of the dyslipidemic population with high plasma triglyceride levels, the data also pointed to hamster and db/db mouse as representative models for practical use in target validation. Most traditional models, including rabbit, Zucker diabetic fatty rat, and the majority of mouse models, did not demonstrate overall similarity to dyslipidemic humans in this study.

Cytokines, macrophage lipid metabolism and foam cells: implications for cardiovascular disease therapy

Cardiovascular disease is the biggest killer globally and the principal contributing factor to the pathology is atherosclerosis; a chronic, inflammatory disorder characterized by lipid and cholesterol accumulation and the development of fibrotic plaques within the walls of large and medium arteries. Macrophages are fundamental to the immune response directed to the site of inflammation and their normal, protective function is harnessed, detrimentally, in atherosclerosis. Macrophages contribute to plaque development by internalizing native and modified lipoproteins to convert them into cholesterol-rich foam cells. Foam cells not only help to bridge the innate and adaptive immune response to atherosclerosis but also accumulate to create fatty streaks, which help shape the architecture of advanced plaques. Foam cell formation involves the disruption of normal macrophage cholesterol metabolism, which is governed by a homeostatic mechanism that controls the uptake, intracellular metabolism, and efflux of cholesterol. It has emerged over the last 20 years that an array of cytokines, including interferon-γ, transforming growth factor-β1, interleukin-1β, and interleukin-10, are able to manipulate these processes. Foam cell targeting, anti-inflammatory therapies, such as agonists of nuclear receptors and statins, are known to regulate the actions of pro- and anti-atherogenic cytokines indirectly of their primary pharmacological function. A clear understanding of macrophage foam cell biology will hopefully enable novel foam cell targeting therapies to be developed for use in the clinical intervention of atherosclerosis.

Triterpenoids isolated from Zizyphus jujuba inhibit foam cell formation in macrophages

Because foam cell formation in macrophages is believed to play an essential role in the progression of early atherosclerotic lesions in vivo, prevention of foam cell formation is considered to be one of the major targets for the treatment of atherosclerosis. The present study examined the inhibitory effect of 50 crude plant extracts on foam cell formation. Among those crude extracts, Zizyphi Fructus (ZF) and Zizyphi Semen (ZS) extracts significantly inhibited the foam cell formation induced by acetylated LDL. Furthermore, triterpenoids such as oleanonic acid, pomolic acid, and pomonic acid were the major active compounds, and triterpenoids containing a carboxylic acid at C-28 play an important role in the inhibitory effect on foam cell formation in human macrophages. These data suggest that triterpenoids in Zizyphus jujuba , the plant source of ZF and ZS, may therefore be useful for the prevention of atherosclerosis.

Changes in esculeoside A content in different regions of the tomato fruit during maturation and heat processing

We previously demonstrated that esculeogenin A, a new aglycone of the tomato sapogenol esculeoside A, inhibits both acyl coenzyme A:cholesterol acyl-transferase (ACAT)-1 and -2 and ameliorates the pathogenesis of atherosclerosis in apoE deficient mice. Although we believe that daily intake of esculeoside A from tomato products can play a beneficial role in preventing the pathogenesis of atherosclerosis, the compound is not being used for preventive medicine due to the lack of information on methods for quantitative analysis and the content and stability of the compound in tomato products. In the present study, we report the development of a high-performance liquid chromatography (HPLC) method using an instrument equipped with a refractive index (RI) detector for esculeoside A quantification. We used this method to measure the changes in esculeoside A content during maturation, its distribution in the fruit body, and its stability during the heating process. The contents of esculeoside A in cherry tomatoes and Momotaro tomatoes were 21- and 9-fold, respectively, higher than that of lycopene, which is the most well-known compound in tomatoes. Furthermore, the esculeoside A content in pericarp wall was higher than in the whole tomato fruit and increased in a time-dependent manner during maturation. Although the melting point of purified esculeoside A was 225 °C, the esculeoside A in crude tomato extract decreased in a temperature-dependent manner. Degradation due to the heating process was inhibited under a pH of 9. These results demonstrated that the esculeoside A content differs in the various types of tomatoes, during maturation, and during the heating process used for preservation.

Effect of the ethanolic extract from Fagara tessmannii on testicular function, sex reproductive organs and hormone level in adult male rats

The effect of ethanolic extract of Fagara tessmannii, wide medicinal plants used on reproductive function in South Cameroon, was investigated in male rats. Twenty male sexually experienced rats (four groups) were orally treated with vehicle, 0.01, 0.1, 1 g kg(-1) BW per day of F. tessmannii (equivalent to 16.67 g, 33.33 g, 50 g, 66.66 g kg(-1) dry raw material) for 14 days, the upper limit dose without any clinical sign of toxicity was 2 g kg(-1). Fagara tessmannii extract negatively affected weight of accessory organs and significantly affected body weight gain at dose 1 g kg(-1) (P < 0.05) in treated rats. The weight of epididymis and seminal vesicle significantly decreased at low doses (0.01 g kg(-1)) while the prostate weight decreased at all doses (P < 0.05). The transit of spermatozoa in cauda epididymidis significantly increased at lower dose of 0.01 g kg(-1) (P < 0.05). In addition, F. tessmannii extract affected neither daily sperm production (DSP) and DSP per g nor sperm count in vas deferens and epididymis. The length of stages IX-I of the seminiferous tubule and serum testosterone level increased dose-dependently following 14 days of treatment (P < 0.05). The results suggest that F. tessmannii, 14 days after treatment, may improve spermatogenesis, testosterone level and sperm transit in cauda epididymidis but negatively impair reproductive organ activities.

HIV-1 and the macrophage

Macrophages and CD4+ T cells are natural target cells for HIV-1, and both cell types contribute to the establishment of the viral reservoir that is responsible for continuous residual virus replication during antiretroviral therapy and viral load rebound upon treatment interruption. Scientific findings that support a critical role for the infected monocyte/macrophage in HIV-1-associated diseases, such as neurological disorders and cardiovascular disease, are accumulating. To prevent or treat these HIV-1-related diseases, we need to halt HIV-1 replication in the macrophage reservoir. This article describes our current knowledge of how monocytes and certain macrophage subsets are able to restrict HIV-1 infection, in addition to what makes macrophages respond less well to current antiretroviral drugs as compared with CD4+ T cells. These insights will help to find novel approaches that can be used to meet this challenge.

Potential mechanisms of hypocholesterolaemic effect of Thai spices/dietary extracts

Several Thai spices/dietary ingredients were previously shown to have hypocholesterolaemic effects. These studies were mostly conducted in animal models in which the mechanisms of action were not yet well-established. Therefore, this study aimed to investigate the potential mechanism of hypocholesterolaemic action of 12 selected plants, namely Hibiscus sabdariffa L., Moringa oleifera Lam., Cucurbita moschata Duchesne, Ananas comosus (L.) Merr., Zingiber officinale, Morus alba L., Camellia sinensis (L.) Kuntze, Piper nigrum L., Alpinia galanga (L.) Willd., Curcuma zedoaria Rose, Bacopa monnieri (L.) Wettst. and Piper retrofractum Vahl., widely used as spices and ingredients in various types of Thai food. The extract of P. nigrum at 100 µg mL(-1) was found to be the most effective cholesterol uptake inhibitor whereas those of A. galanga and C. sinensis effectively inhibited pancreatic lipase activity with IC50 values of 8.99±3.41 and 12.36±1.23 µg mL(-1), respectively. The potency of extracts from H. sabdariffa, M. oleifera and C. moschata at 100 µg mL(-1) were found to be similar to 0.4 µg mL(-1) pravastatin in inhibiting HMG-CoA reductase and possibly reduced cholesterol biosynthesis. This study also demonstrated that several of the tested plants possessed multiple sites of action that were possibly responsible for their cholesterol-lowering effect in the in vivo model.

Regulation of acyl-coenzyme A: cholesterol acyltransferase 2 expression by saturated fatty acids

OBJECTIVE

To verify the regulation of acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT 2), which is associated with cholesterol metabolism, by saturated fatty acids (SFAs).

METHODS

Palmitic acid (PA), the most abundant saturated fatty acid in plasma, and oleic acid (OA), a widely distributed unsaturated fatty acid, were used to treat hepatic cells HepG2, HuH7, and mouse primary hepatocytes. In addition, PA at different concentrations and PA treatment at different durations were applied in HepG2 cells. In in vivo experiment, three-month male C57/BL6 mice were fed with control diet and SFA diet containing hydrogenated coconut oil rich of SFAs. The mRNA level of ACAT2 in those hepatic cells and the mouse livers was detected with real-time polymerase chain reaction (PCR).

RESULTS

In the three types of hepatic cells treated with PA, that SFA induced significant increase of ACAT2 expression (Pü0.01), whereas treatment with OA showed no significant effect. That effect of PA was noticed gradually rising along with the increase of PA concentration and the extension of PA treatment duration (both Pü0.05). SFA diet feeding in mice resulted in a short-term and transient increase of ACAT2 expression in vivo, with a peak level appearing in the mice fed with SFA diet for two days (Pü0.05).

CONCLUSION

SFA may regulate ACAT2 expression in human and mouse hepatic cells and in mouse livers.

The tomato saponin, esculeoside A

Esculeoside A (2), a spirosolane steroidal glycoside, is a major constituent isolated from Solanum lycopersicum, a commercial strain of mini tomatoes. The content variability of esculeoside A (2) was examined in mini, midi, and Momotaro tomatoes and various processed tomato products. In the green immature tomato fruit, tomatine (1) is oxidized at C-23 and C-27 to produce esculeoside A (2) in the ripe fruit. Further, esculeoside A (2) is partly converted to 3β-hydroxy-5α-pregn-16-en-20-one 3-O-β-lycotetraoside (6), a pregnane glycoside, in the overripe fruit. Esculeogenin A (3), the sapogenol of 2, is easily converted into 3β,16β-dihydroxy-5α-pregn-20-one (17). Metabolic studies showed excretion of androstane derivatives in the urine of human volunteer subjects after tomato consumption. Esculeogenin A (3) inhibited the accumulation of cholesterol esters in macrophages through its effects on acyl-CoA:cholesterol acyl transferase (ACAT). Oral administration of esculeoside A (2) to apoE-deficient mice significantly reduced serum levels of cholesterol, triglycerides, and LDL-cholesterol and ameliorated the severity of atherosclerotic lesions.

Sequential depletion of rat testicular lipids with long-chain and very long-chain polyenoic fatty acids after X-ray-induced interruption of spermatogenesis

When a single dose of X-rays is applied to the adult rat testis, stem spermatogonia are damaged, and spermatogenesis is interrupted. Supported by Sertoli cells, spermatogenic cells that endure irradiation complete their differentiation and gradually leave the testis as spermatozoa. In this study, the in vivo changes taking place a number of weeks after irradiation revealed cell-specific features of testicular lipid classes. A linear drop, taking about six weeks, in testis weight, nonlipid materials, free cholesterol, and 22:5n-6-rich glycerophospholipids took place with germ cell depletion. Sphingomyelins and ceramides with nonhydroxy very long-chain polyenoic fatty acids (n-VLCPUFA) disappeared in four weeks, together with the last spermatocytes, whereas species with 2-hydroxy VLCPUFA lasted for six weeks, disappearing with the last spermatids and spermatozoa. The amount per testis of 22:5n-6-rich triacylglycerols, unchanged for four weeks, fell between weeks 4 and 6, associating these lipids with spermatids and their residual bodies, detected as small, bright lipid droplets. In contrast, 22:5n-6-rich species of cholesterol esters and large lipid droplets increased in seminiferous tubules up to week 6, revealing they are Sertoli cell products. At week 30, the lipid and fatty acid profiles reflected the resulting permanent testicular involution. Our data highlight the importance of Sertoli cells in maintaining lipid homeostasis during normal spermatogenesis.

ACAT inhibition and amyloid beta reduction

Alzheimer's disease (AD) is a devastating neurodegenerative disorder. Accumulation and deposition of the beta-amyloid (Abeta) peptide generated from its larger amyloid precursor protein (APP) is one of the pathophysiological hallmarks of AD. Intracellular cholesterol was shown to regulate Abeta production. Recent genetic and biochemical studies indicate that not only the amount, but also the distribution of intracellular cholesterol is critical to regulate Abeta generation. Acyl-coenzyme A: cholesterol acyl-transferase (ACAT) is a family of enzymes that regulates the cellular distribution of cholesterol by converting membrane cholesterol into hydrophobic cholesteryl esters for cholesterol storage and transport. Using pharmacological inhibitors and transgenic animal models, we and others have identified ACAT1 as a potential therapeutic target to lower Abeta generation and accumulation. Here we discuss data focusing on ACAT inhibition as an effective strategy for the prevention and treatment of AD.