Free cholesterol loading of macrophages is associated with widespread mitochondrial dysfunction and activation of the mitochondrial apoptosis pathway

Loss of embryonically-derived Kupffer cells during hypercholesterolemia accelerates atherosclerosis development

Hypercholesterolemia is a major risk factor for atherosclerosis and associated cardiovascular diseases. The liver plays a key role in the regulation of plasma cholesterol levels and hosts a large population of tissue-resident macrophages known as Kupffer cells (KCs). KCs are located in the hepatic sinusoids where they ensure key functions including blood immune surveillance. However, how KCs homeostasis is affected by the build-up of cholesterol-rich lipoproteins that occurs in the circulation during hypercholesterolemia remains unknown. Here, we show that embryo-derived KCs (EmKCs) accumulate large amounts of lipoprotein-derived cholesterol, in part through the scavenger receptor CD36, and massively expand early after the induction of hypercholesterolemia. After this rapid adaptive response, EmKCs exhibit mitochondrial oxidative stress and their numbers gradually diminish while monocyte-derived KCs (MoKCs) with reduced cholesterol-loading capacities seed the KC pool. Decreased proportion of EmKCs in the KC pool enhances liver cholesterol content and exacerbates hypercholesterolemia, leading to accelerated atherosclerotic plaque development. Together, our data reveal that KC homeostasis is perturbed during hypercholesterolemia, which in turn alters the control of plasma cholesterol levels and increases atherosclerosis.

Recent progress of endoplasmic reticulum stress in the mechanism of atherosclerosis

The research progress of endoplasmic reticulum (ER) stress in atherosclerosis (AS) is of great concern. The ER, a critical cellular organelle, plays a role in important biological processes including protein synthesis, folding, and modification. Various pathological factors may cause ER stress, and sustained or excessive ER stress triggers the unfolded protein response, ultimately resulting in apoptosis and disease. Recently, researchers have discovered the importance of ER stress in the onset and advancement of AS. ER stress contributes to the occurrence of AS through different pathways such as apoptosis, inflammatory response, oxidative stress, and autophagy. Therefore, this review focuses on the mechanisms of ER stress in the development of AS and related therapeutic targets, which will contribute to a deeper understanding of the disease's pathogenesis and provide novel strategies for preventing and treating AS.

Development, validation and visualization of a web-based nomogram for predicting risk of new-onset diabetes after percutaneous coronary intervention

Simple and practical tools for screening high-risk new-onset diabetes after percutaneous coronary intervention (PCI) (NODAP) are urgently needed to improve post-PCI prognosis. We aimed to evaluate the risk factors for NODAP and develop an online prediction tool using conventional variables based on a multicenter database. China evidence-based Chinese medicine database consisted of 249, 987 patients from 4 hospitals in mainland China. Patients ≥ 18 years with implanted coronary stents for acute coronary syndromes and did not have diabetes before PCI were enrolled in this study. According to the occurrence of new-onset diabetes mellitus after PCI, the patients were divided into NODAP and Non-NODAP. After least absolute shrinkage and selection operator regression and logistic regression, the model features were selected and then the nomogram was developed and plotted. Model performance was evaluated by the receiver operating characteristic curve, calibration curve, Hosmer-Lemeshow test and decision curve analysis. The nomogram was also externally validated at a different hospital. Subsequently, we developed an online visualization tool and a corresponding risk stratification system to predict the risk of developing NODAP after PCI based on the model. A total of 2698 patients after PCI (1255 NODAP and 1443 non-NODAP) were included in the final analysis based on the multicenter database. Five predictors were identified after screening: fasting plasma glucose, low-density lipoprotein cholesterol, hypertension, family history of diabetes and use of diuretics. And then we developed a web-based nomogram ( https://mr.cscps.com.cn/wscoringtool/index.html ) incorporating the above conventional factors for predicting patients at high risk for NODAP. The nomogram showed good discrimination, calibration and clinical utility and could accurately stratify patients into different NODAP risks. We developed a simple and practical web-based nomogram based on multicenter database to screen for NODAP risk, which can assist clinicians in accurately identifying patients at high risk of NODAP and developing post-PCI management strategies to improved patient prognosis.

TREM2 protects from atherosclerosis by limiting necrotic core formation

Atherosclerosis is a chronic disease of the vascular wall driven by lipid accumulation and inflammation in the intimal layer of arteries, and its main complications, myocardial infarction and stroke, are the leading cause of mortality worldwide [1], [2]. Recent studies have identified Triggering receptor expressed on myeloid cells 2 (TREM2), a lipid-sensing receptor regulating myeloid cell functions [3], to be highly expressed in macrophage foam cells in experimental and human atherosclerosis [4]. However, the role of TREM2 in atherosclerosis is not fully known. Here, we show that hematopoietic or global TREM2 deficiency increased, whereas TREM2 agonism decreased necrotic core formation in early atherosclerosis. We demonstrate that TREM2 is essential for the efferocytosis capacities of macrophages, and to the survival of lipid-laden macrophages, indicating a crucial role of TREM2 in maintaining the balance between foam cell death and clearance of dead cells in atherosclerotic lesions, thereby controlling plaque necrosis.

Macrophage-specific deletion of MIC26 (APOO) mitigates advanced atherosclerosis by increasing efferocytosis

BACKGROUND AND AIMS

Recent studies have suggested that MIC26 (apolipoprotein O, APOO), a novel mitochondrial inner membrane protein, is involved in inflammation. Thus, the role of macrophage MIC26 in acute inflammation and chronic inflammatory disease atherosclerosis was investigated.

METHODS

Macrophage-specific MIC26 knockout mice (MIC26LysM) were generated by crossing Apooflox/flox and LysMcre+/- mice. An endotoxemia mouse model was generated to explore the effects of macrophage MIC26 deficiency on acute inflammation, while an atherosclerosis mouse model was constructed by crossing MIC26LysM mice with Apoe-/- mice and challenged with a Western diet. Atherosclerotic plaques, primary macrophage function, and mitochondrial structure and function were analyzed.

RESULTS

MIC26 knockout did not affect the median survival time and post-injection serum interleukin 1β concentrations in mice with endotoxemia. Mice with MIC26 deficiency in an Apoe-/- background had smaller atherosclerotic lesions and necrotic core than the control group. In vitro studies found that the loss of MIC26 did not affect macrophage polarization, apoptosis, or lipid handling capacity, but increased efferocytosis (the ability to clear apoptotic cells). An in situ efferocytosis assay of plaques also showed that the ratio of macrophage-associated apoptotic cells to free apoptotic cells was higher in the MIC26-deficient group than in the control group, indicating increased efferocytosis. In addition, an in vivo thymus efferocytosis assay indicated that MIC26 deletion promoted efferocytosis. Mechanistically, the loss of MIC26 resulted in an abnormal mitochondrial inner membrane structure, increased mitochondrial fission, and decreased mitochondrial membrane potential. Loss of MIC26 reduced mitochondria optic atrophy type 1 (OPA1) protein, and OPA1 silencing in macrophages promoted efferocytosis. Overexpression of OPA1 abolished the increase in efferocytosis produced by MIC26 deficiency.

CONCLUSIONS

Macrophage MIC26 deletion alleviated advanced atherosclerosis and necrotic core expansion by promoting efferocytosis. This mechanism may be related to the increased mitochondrial fission caused by reduced mitochondrial OPA1.

Implications of High-Density Cholesterol Metabolism for Oocyte Biology and Female Fertility

Cholesterol is an essential component of animal cells. Different regulatory mechanisms converge to maintain adequate levels of this lipid because both its deficiency and excess are unfavorable. Low cell cholesterol content promotes its synthesis and uptake from circulating lipoproteins. In contrast, its excess induces the efflux to high-density lipoproteins (HDL) and their transport to the liver for excretion, a process known as reverse cholesterol transport. Different studies suggest that an abnormal HDL metabolism hinders female fertility. HDL are the only lipoproteins detected in substantial amounts in follicular fluid (FF), and their size and composition correlate with embryo quality. Oocytes obtain cholesterol from cumulus cells via gap junctions because they cannot synthesize cholesterol de novo and lack HDL receptors. Recent evidence has supported the possibility that FF HDL play a major role in taking up excess unesterified cholesterol (UC) from the oocyte. Indeed, genetically modified mouse models with disruptions in reverse cholesterol transport, some of which show excessive circulating UC levels, exhibit female infertility. Cholesterol accumulation can affect the egg´s viability, as reported in other cell types, and activate the plasma membrane structure and activity of membrane proteins. Indeed, in mice deficient for the HDL receptor Scavenger Class B Type I (SR-B1), excess circulating HDL cholesterol and UC accumulation in oocytes impairs meiosis arrest and hinders the developmental capacity of the egg. In other cells, the addition of cholesterol activates calcium channels and dysregulates cell death/survival signaling pathways, suggesting that these mechanisms may link altered HDL cholesterol metabolism and infertility. Although cholesterol, and lipids in general, are usually not evaluated in infertile patients, one study reported high circulating UC levels in women showing longer time to pregnancy as an outcome of fertility. Based on the evidence described above, we propose the existence of a well-regulated and largely unexplored system of cholesterol homeostasis controlling traffic between FF HDL and oocytes, with significant implications for female fertility.

Mitochondrial Dysfunction and Cardiovascular Disease: Pathophysiology and Emerging Therapies

Mitochondria ensure the supply of cellular energy through the production of ATP via oxidative phosphorylation. The alteration of this process, called mitochondrial dysfunction, leads to a reduction in ATP and an increase in the production of reactive oxygen species (ROS). Mitochondrial dysfunction can be caused by mitochondrial/nuclear DNA mutations, or it can be secondary to pathological conditions such as cardiovascular disease, aging, and environmental stress. The use of therapies aimed at the prevention/correction of mitochondrial dysfunction, in the context of the specific treatment of cardiovascular diseases, is a topic of growing interest. In this context, the data are conflicting since preclinical studies are numerous, but there are no large randomized studies.

Suppression of the ABCA1 Cholesterol Transporter Impairs the Growth and Migration of Epithelial Ovarian Cancer

Simple Summary

Epithelial ovarian cancer (EOC) is the most lethal gynaecological cancer. Over 80% of cases have already spread at diagnosis, and these patients face a five-year survival rate of 35%. EOC cells often spread to the greater omentum, an abdominal fat pad. Here, EOC cells take-up cholesterols. Excessive amounts of cholesterol are lethal; thus, we proposed that the ABCA1 cholesterol transporter exports cholesterol from serous EOC cells to maintain cholesterol balance. Indeed, we found that reducing the level of ABCA1 could suppress serous EOC growth in two-dimensional as well as three-dimensional cell culture and also hindered their migration, a key process required for cancer spread. We also identified drugs that impair EOC cell growth by inhibiting cholesterol export. Our data demonstrate that disrupting the cholesterol balance by targeting ABCA1 may be an effective treatment strategy for EOC patients.

Abstract

Background: Epithelial ovarian cancer (EOC) is the most lethal gynaecological malignancy with over 80% of cases already disseminated at diagnosis and facing a dismal five-year survival rate of 35%. EOC cells often spread to the greater omentum where they take-up cholesterol. Excessive amounts of cholesterol can be cytocidal, suggesting that cholesterol efflux through transporters may be important to maintain homeostasis, and this may explain the observation that high expression of the ATP-binding cassette A1 (ABCA1) cholesterol transporter has been associated with poor outcome in EOC patients. Methods: ABCA1 expression was silenced in EOC cells to investigate the effect of inhibiting cholesterol efflux on EOC biology through growth and migration assays, three-dimensional spheroid culture and cholesterol quantification. Results: ABCA1 suppression significantly reduced the growth, motility and colony formation of EOC cell lines as well as the size of EOC spheroids, whilst stimulating expression of ABCA1 reversed these effects. In serous EOC cells, ABCA1 suppression induced accumulation of cholesterol. Lowering cholesterol levels using methyl-B-cyclodextrin rescued the effect of ABCA1 suppression, restoring EOC growth. Furthermore, we identified FDA-approved agents that induced cholesterol accumulation and elicited cytocidal effects in EOC cells. Conclusions: Our data demonstrate the importance of ABCA1 in maintaining cholesterol balance and malignant properties in EOC cells, highlighting its potential as a therapeutic target for this disease.

Acyl-Coenzyme A: Cholesterol Acyltransferase (ACAT) in Cholesterol Metabolism: From Its Discovery to Clinical Trials and the Genomics Era

The purification and cloning of the acyl-coenzyme A: cholesterol acyltransferase (ACAT) enzymes and the sterol O-acyltransferase (SOAT) genes has opened new areas of interest in cholesterol metabolism given their profound effects on foam cell biology and intestinal lipid absorption. The generation of mouse models deficient in Soat1 or Soat2 confirmed the importance of their gene products on cholesterol esterification and lipoprotein physiology. Although these studies supported clinical trials which used non-selective ACAT inhibitors, these trials did not report benefits, and one showed an increased risk. Early genetic studies have implicated common variants in both genes with human traits, including lipoprotein levels, coronary artery disease, and Alzheimer’s disease; however, modern genome-wide association studies have not replicated these associations. In contrast, the common SOAT1 variants are most reproducibly associated with testosterone levels.

Lead (Pb) Accumulation in Human THP-1 Monocytes/Macrophages In Vitro and the Influence on Cell Apoptosis

In this study, we investigated the ability of THP-1 monocytes and macrophages to accumulate lead (Pb) in vitro, relative to Pb concentration and length of exposure. Moreover, we also evaluated the effect of Pb accumulation on cell viability and apoptosis. THP-1 monocytes and macrophages were cultured in the presence of Pb at 1.25 μg/dL, 2.5 μg/dL, 5 μg/dL, and 10 μg/dL. Pb accumulation was examined by inductively coupled plasma and confocal microscopy. The influence of Pb on cell viability, apoptosis, and necrosis was assessed using flow cytometry. The results showed that Pb was toxic to THP-1 monocytes/macrophages even at very low environmental concentrations. Despite the use of low concentrations, both monocytes and macrophages showed dose-dependent and time-dependent decreases in viability, with a simultaneous increase in the percentage of early and late apoptotic cells. Macrophages reacted more strongly to Pb than monocytes. When exposed to the same Pb concentrations, they showed lower viability and a higher percentage of necrotic cells. The incubation time positively correlated with Pb accumulation in a dose-dependent manner. The obtained results indicate that environmental exposure to low Pb concentrations may significantly impair the function of macrophages, with the increased number of apoptotic cells potentially contributing to the development of many pathologies in the brain and whole body.

Novel insights: Dynamic foam cells derived from the macrophage in atherosclerosis

Atherosclerosis can be regarded as a chronic disease derived from the interaction between disordered lipoproteins and an unsuitable immune response. The evolution of foam cells is not only a significant pathological change in the early stage of atherosclerosis but also a key stage in the occurrence and development of atherosclerosis. The formation of foam cells is mainly caused by the imbalance among lipids uptake, lipids treatment, and reverse cholesterol transport. Although a large number of studies have summarized the source of foam cells and the mechanism of foam cells formation, we propose a new idea about foam cells in atherosclerosis. Rather than an isolated microenvironment, the macrophage multiple lipid uptake pathways, lipid internalization, lysosome, mitochondria, endoplasmic reticulum, neutral cholesterol ester hydrolase (NCEH), acyl-coenzyme A-cholesterol acyltransferase (ACAT), and reverse cholesterol transport are mutually influential, and form a dynamic process under multi-factor regulation. The macrophage takes on different uptake lipid statuses depending on multiple uptake pathways and intracellular lipids, lipid metabolites versus pro-inflammatory factors. Except for NCEH and ACAT, the lipid internalization of macrophages also depends on multicellular organelles including the lysosome, mitochondria, and endoplasmic reticulum, which are associated with each other. A dynamic balance between esterification and hydrolysis of cholesterol for macrophages is essential for physiology and pathology. Therefore, we propose that the foam cell in the process of atherosclerosis may be dynamic under multi-factor regulation, and collate this study to provide a holistic and dynamic idea of the foam cell.

Gene Expression Profiling of Apoptotic Proteins in Circulating Peripheral Blood Mononuclear Cells in Type II Diabetes Mellitus and Modulation by Metformin

INTRODUCTION

Insulin resistance in obesity and type 2 diabetes mellitus (T2DM) is associated with cardiovascular complications such as atherosclerosis. On the other hand, the reduction of apoptosis in macrophages has been linked with accelerated atherosclerosis. Apoptosis is controlled by a different family of proteins including Bcl-2 and caspases.

METHODS

To examine apoptosis in insulin resistance, we assessed the mRNA expression by qRT-PCR of several Bcl-2 family members, as well as caspase-3, -7, -8, and -9 in peripheral blood mononuclear cells (PBMCs) isolated from lean, obese, diabetic, and diabetic on metformin individuals.

RESULTS

PBMCs of diabetic individuals exhibited reduced expression of caspase-7 and increased expression of Bcl-10, Bad, Bax, Bid, and caspase-3. T2DM on metformin group had significantly higher Bad, Bax, and caspase-7 expression.

DISCUSSION

The moderate up-regulation of pro-apoptotic Bcl-10, Bax, Bad, Bid, and the effector caspase-3 coupled with inhibition of caspase-7 in circulating PBMCs of T2DM could be the result of increased inflammation in T2DM. Metformin treatment significantly inhibited the expression of Bcl-10, Bid, and caspase-3 and upregulated Bad/Bax/caspase-7 pathway suggesting the activation of Bad/Bax/caspase-7 apoptotic pathway. Further studies are warranted to elicit the underlying apoptotic pathways of PBMCs in T2DM and following metformin treatment.

Cardiometabolic risk factors are associated with immune cell mitochondrial respiration in humans

Modifiable cardiometabolic risk factors induce the release of proinflammatory cytokines and reactive oxygen species from circulating peripheral blood mononuclear cells (PBMCs), resulting in increased cardiovascular disease risk and compromised immune health. These changes may be driven by metabolic reprogramming of PBMCs, resulting in reduced mitochondrial respiration; however, this has not been fully tested. We aimed to determine the independent associations between cardiometabolic risk factors including BMI, blood pressure, fasting glucose, and plasma lipids with mitochondrial respiration in PBMCs isolated from generally healthy individuals (n = 21) across the adult lifespan (12 men/9 women; age, 56 ± 21 yr; age range, 22-78 yr; body mass index, 27.9 ± 5.7 kg/m²; blood pressure, 123 ± 16/72 ± 10 mmHg; glucose, 90 ± 14 mg/dL; low-density lipoprotein cholesterol (LDL-C), 111 ± 22 mg/dL; and high-density lipoprotein cholesterol (HDL-C), 62 ± 16 mg/dL). PBMCs were isolated from whole blood by density-dependent centrifugation and used to assess mitochondrial function by respirometry. Primary outcomes included basal and maximal oxygen consumption rate (OCR), which were subsequently used to determine spare respiratory capacity and OCR metabolic potential. After we corrected for systolic blood pressure (SBP), diastolic blood pressure (DBP), and blood glucose, LDL-C was negatively associated with maximal respiration (r = -0.56, P = 0.016), spare respiratory capacity (r = -0.58, P = 0.012), and OCR metabolic potential (r = -0.71, P = 0.0011). In addition, SBP was negatively associated with OCR metabolic potential (r = -0.62, P = 0.0056) after we corrected for DBP, blood glucose, and LDL-C. These data suggest a link between blood cholesterol, SBP, and mitochondrial health that may provide insight into how cardiometabolic risk factors contribute to impaired immune cell function.NEW & NOTEWORTHY Independent of other cardiometabolic risk factors, low-density lipoprotein cholesterol, and systolic blood pressure were found to be negatively associated with several parameters of mitochondrial respiration in peripheral blood mononuclear cells of healthy adults. These data suggest that low-density lipoprotein cholesterol and systolic blood pressure may induce metabolic reprogramming of immune cells, contributing to increased cardiovascular disease risk and impaired immune health.

Cardiac apoptosis caused by elevated cholesterol level in experimental autoimmune myocarditis

It has been reported that cholesterol-lowing agents can ameliorate severity of myocarditis. However, the beneficial effect of the agents has been claimed to be independent of cholesterol reduction as there is no significant change in the plasma cholesterol level in myocarditis. In the present study, using experimental autoimmune myocarditis (EAM) rats as an animal model, we demonstrated that EAM induced elevation of cholesterol level and impaired cholesterol efflux capacity in the cardiac tissue. Moreover, serum high-density lipoprotein (HDL) content was reduced and HDL function associated protein Paraoxonase 1 (PON1) activity was decreased. Besides, the major structural protein within HDL, Apolipoprotein A1 (ApoA1) expression in the cardiac tissues was significantly reduced while the level of serum ApoA1 was not significantly altered. Importantly, cholesterol depleting agent methyl-β-cyclodextrin (MβCD) alleviated the development of EAM, as monitored by decreased ratio of heart weight to body weight (HW/BW), decreased infiltration of inflammatory cells and collagen deposition, improved cardiac function, reduced expression of apoptosis-related protein Bax, Fas, FasL and caspase-3 and increased level of anti-apoptotic protein Bcl-2. These results suggest that reduction of cholesterol level in cardiac tissue could suppress EAM-induced cardiac apoptosis through both intrinsic and extrinsic apoptotic pathways.

The Role of Mitochondria in Cardiovascular Diseases

The role of mitochondria in cardiovascular diseases is receiving ever growing attention. As a central player in the regulation of cellular metabolism and a powerful controller of cellular fate, mitochondria appear to comprise an interesting potential therapeutic target. With the development of DNA sequencing methods, mutations in mitochondrial DNA (mtDNA) became a subject of intensive study, since many directly lead to mitochondrial dysfunction, oxidative stress, deficient energy production and, as a result, cell dysfunction and death. Many mtDNA mutations were found to be associated with chronic human diseases, including cardiovascular disorders. In particular, 17 mtDNA mutations were reported to be associated with ischemic heart disease in humans. In this review, we discuss the involvement of mitochondrial dysfunction in the pathogenesis of atherosclerosis and describe the mtDNA mutations identified so far that are associated with atherosclerosis and its risk factors.

MicroRNA-205-5p Promotes Unstable Atherosclerotic Plaque Formation In Vivo

PURPOSE

Atherosclerosis is a narrowing of the arteries caused by plaque buildup. MicroRNAs (miRNAs) have been proposed to participate in the pathogenesis of atherosclerosis. Here, we aimed to investigate miR-205-5p's role in promoting atherosclerotic progression.

METHODS

Knock-in (KI) mice with human/murine miR-205-5p within the murine host gene for miR-205 (MIR205HG) were crossed with apolipoprotein E knockout (Apoe^-/-) mice. This miR-205KI Apoe^-/- murine model was employed to study the impact of miR-205-5p in Apoe^-/- mice susceptible to atherosclerotic plaque formation.

RESULTS

miR-205KI Apoe^-/-mice developed larger, more unstable plaques relative to their Apoe^-/- counterparts (0.45 vs. 0.26 mm², P < 0.001). miR-205KI Apoe^-/- mice exhibited lower serum levels of high-density lipoprotein cholesterol (HDL-C) (5.18 vs. 19.31 mg/dL, P < 0.001) and triglycerides (32.79 vs. 156.76 mg/dL, P < 0.001) with system-wide reversal of cholesterol transport. Macrophages derived from miR-205KI Apoe^-/- mice exhibited ~ 20% lowered cholesterol efflux capability with enhanced pro-inflammatory gene expression through lipid raft formation. Bone marrow transplantation demonstrated that bone marrow (BM) donor cells with miR-205-5pKI simulated plaque formation independent of the recipients' miR-205-5p status.

CONCLUSIONS

miR-205-5p encourages unstable atherogenesis in vivo. miR-205-5p also adversely influences lipid metabolism and promotes a pro-inflammatory macrophage phenotype. Our findings advocate miR-205-5p as a potential therapeutic target for combating unstable atherogenesis.

Mitochondrial bioenergetics and redox dysfunctions in hypercholesterolemia and atherosclerosis

In the first part of this review, we summarize basic mitochondrial bioenergetics concepts showing that mitochondria are critical regulators of cell life and death. Until a few decades ago, mitochondria were considered to play essential roles only in respiration, ATP formation, non-shivering thermogenesis and a variety of metabolic pathways. However, the concept presented by Peter Mitchell regarding coupling between electron flow and ATP synthesis through the intermediary of a H⁺ electrochemical potential leads to the recognition that the proton-motive force also regulates a series of relevant cell signalling processes, such as superoxide generation, redox balance and Ca²⁺ handling. Alterations in these processes lead to cell death and disease states. In the second part of this review, we discuss the role of mitochondrial dysfunctions in the specific context of hypercholesterolemia-induced atherosclerosis. We provide a literature analysis that indicates a decisive role of mitochondrial redox dysfunction in the development of atherosclerosis and discuss the underlying molecular mechanisms. Finally, we highlight the potential mitochondrial-targeted therapeutic strategies that are relevant for atherosclerosis.

Hepatocyte Deletion of Triglyceride-Synthesis Enzyme Acyl CoA: Diacylglycerol Acyltransferase 2 Reduces Steatosis Without Increasing Inflammation or Fibrosis in Mice

Nonalcoholic fatty liver disease (NAFLD) is characterized by excess lipid accumulation in hepatocytes and represents a huge public health problem owing to its propensity to progress to nonalcoholic steatohepatitis, fibrosis, and liver failure. The lipids stored in hepatic steatosis (HS) are primarily triglycerides (TGs) synthesized by two acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes. Either DGAT1 or DGAT2 catalyzes this reaction, and these enzymes have been suggested to differentially utilize exogenous or endogenously synthesized fatty acids, respectively. DGAT2 has been linked to storage of fatty acids from de novo lipogenesis, a process increased in NAFLD. However, whether DGAT2 is more responsible for lipid accumulation in NAFLD and progression to fibrosis is currently unknown. Also, it is unresolved whether DGAT2 can be safely inhibited as a therapy for NAFLD. Here, we induced NAFLD-like disease in mice by feeding a diet rich in fructose, saturated fat, and cholesterol and found that hepatocyte-specific Dgat2 deficiency reduced expression of de novo lipogenesis genes and lowered liver TGs by ~70%. Importantly, the reduction in steatosis was not accompanied by increased inflammation or fibrosis, and insulin and glucose metabolism were unchanged. Conclusion: This study suggests that hepatic DGAT2 deficiency successfully reduces diet-induced HS and supports development of DGAT2 inhibitors as a therapeutic strategy for treating NAFLD and preventing downstream consequences.

Macrophage autophagy regulates mitochondria-mediated apoptosis and inhibits necrotic core formation in vulnerable plaques

The vulnerable plaque is a key distinguishing feature of atherosclerotic lesions that can cause acute atherothrombotic vascular disease. This study was designed to explore the effect of autophagy on mitochondria-mediated macrophage apoptosis and vulnerable plaques. Here, we generated the mouse model of vulnerable carotid plaque in ApoE^-/- mice. Application of ApoE^-/- mice with rapamycin (an autophagy inducer) inhibited necrotic core formation in vulnerable plaques by decreasing macrophage apoptosis. However, 3-methyladenine (an autophagy inhibitor) promoted plaque vulnerability through deteriorating these indexes. To further explore the mechanism of autophagy on macrophage apoptosis, we used macrophage apoptosis model in vitro and found that 7-ketocholesterol (7-KC, one of the primary oxysterols in oxLDL) caused macrophage apoptosis with concomitant impairment of mitochondria, characterized by the impairment of mitochondrial ultrastructure, cytochrome c release, mitochondrial potential dissipation, mitochondrial fragmentation, excessive ROS generation and both caspase-9 and caspase-3 activation. Interestingly, such mitochondrial apoptotic responses were ameliorated by autophagy activator, but exacerbated by autophagy inhibitor. Finally, we found that MAPK-NF-κB signalling pathway was involved in autophagy modulation of 7-KC-induced macrophage apoptosis. So, we provide strong evidence for the potential therapeutic benefit of macrophage autophagy in regulating mitochondria-mediated apoptosis and inhibiting necrotic core formation in vulnerable plaques.

SREBF1/MicroRNA-33b Axis Exhibits Potent Effect on Unstable Atherosclerotic Plaque Formation In Vivo

Objective- Atherosclerosis is a common disease caused by a variety of metabolic and inflammatory disturbances. MicroRNA (miR)-33a within SREBF2 (sterol regulatory element-binding factor 2) is a potent target for treatment of atherosclerosis through regulating both aspects; however, the involvement of miR-33b within SREBF1 remains largely unknown. Although their host genes difference could lead to functional divergence of miR-33a/b, we cannot dissect the roles of miR-33a/b in vivo because of lack of miR-33b sequences in mice, unlike human. Approach and Results- Here, we analyzed the development of atherosclerosis using miR-33b knock-in humanized mice under apolipoprotein E-deficient background. MiR-33b is prominent both in human and mice on atheroprone condition. MiR-33b reduced serum high-density lipoprotein cholesterol levels and systemic reverse cholesterol transport. MiR-33b knock-in macrophages showed less cholesterol efflux capacity and higher inflammatory state via regulating lipid rafts. Thus, miR-33b promotes vulnerable atherosclerotic plaque formation. Furthermore, bone marrow transplantation experiments strengthen proatherogenic roles of macrophage miR-33b. Conclusions- Our data demonstrated critical roles of SREBF1-miR-33b axis on both lipid profiles and macrophage phenotype remodeling and indicate that miR-33b is a promising target for treating atherosclerosis.

Cholesterol Acceptors Regulate the Lipidome of Macrophage Foam Cells

Arterial foam cells are central players of atherogenesis. Cholesterol acceptors, apolipoprotein A-I (apoA-I) and high-density lipoprotein (HDL), take up cholesterol and phospholipids effluxed from foam cells into the circulation. Due to the high abundance of cholesterol in foam cells, most previous studies focused on apoA-I/HDL-mediated free cholesterol (FC) transport. However, recent lipidomics of human atherosclerotic plaques also identified that oxidized sterols (oxysterols) and non-sterol lipid species accumulate as atherogenesis progresses. While it is known that these lipids regulate expression of pro-inflammatory genes linked to plaque instability, how cholesterol acceptors impact the foam cell lipidome, particularly oxysterols and non-sterol lipids, remains unexplored. Using lipidomics analyses, we found cholesterol acceptors remodel foam cell lipidomes. Lipid subclass analyses revealed various oxysterols, sphingomyelins, and ceramides, species uniquely enriched in human plaques were significantly reduced by cholesterol acceptors, especially by apoA-I. These results indicate that the function of lipid-poor apoA-I is not limited to the efflux of cholesterol and phospholipids but suggest that apoA-I serves as a major regulator of the foam cell lipidome and might play an important role in reducing multiple lipid species involved in the pathogenesis of atherosclerosis.

ABCA1 and metabolic syndrome; a review of the ABCA1 role in HDL-VLDL production, insulin-glucose homeostasis, inflammation and obesity

ATP-binding cassette transporter A1 (ABCA1) is an integral cell-membrane protein that mediates the rate-limiting step of high density lipoprotein (HDL) biogenesis and suppression of inflammation by triggering a number of signaling pathways via interacting with an apolipoprotein acceptor. The hepatic ABCA1 is involved in regulation of very low density lipoprotein (VLDL) production by affecting the apolipoprotein B trafficking and lipidation of VLDL particles. This protein is involved in protecting the function of pancreatic β-cells and insulin secretion by cholesterol homeostasis. Adipose tissue lipolysis is associated with ABCA1 activity. This transporter is involved in controlling obesity and insulin sensitivity by regulating triglyceride (TG) lipolysis and influencing on adiponectin, visfatin, leptin, and GLUT4 genes expression. The ABCA1 of skeletal muscle cells play a role in increasing the glucose uptake by enhancing the Akt phosphorylation and transferring GLUT4 to the plasma membrane. Abnormal status of ABCA1-regulated phenotypes is observed in metabolic syndrome. This syndrome is associated with the occurrence of many diseases. This review is a summary of the role of ABCA1 in HDL and VLDL production, homeostasis of insulin and glucose, suppression of inflammation and obesity controlling to provide a better insight into the association of this protein with metabolic syndrome.

Probucol prevents blood-brain barrier dysfunction and cognitive decline in mice maintained on pro-diabetic diet

An emerging body of evidence consistently suggests that compromised blood-brain barrier integrity may be causally associated with cognitive decline induced by type-2 diabetes. Our previous studies demonstrated that selected anti-inflammatory/anti-oxidative agents can preserve the integrity of blood-brain barrier and prevent neuroinflammation in mouse models of dysfunctional blood-brain barrier. Therefore, we have tested whether the previously proven blood-brain barrier protective agent, probucol, can prevent blood-brain barrier breakdown and cognitive decline in a dietary-induced murine model of diabetic insulin resistance. After 6-month chronic ingestion of a diet high in fat and fructose, the mice became insulin resistant. The high-fat and high-fructose-fed mice showed significant cognitive decline assessed by Morris water maze, concomitant with significant elevations in cortical and hippocampal glial acidic fibrillary protein and Fluoro Jade-C staining, indicating heightened neuroinflammation and neurodegeneration, respectively. The integrity of blood-brain barrier in high-fat and high-fructose-fed mice was substantially compromised, and this showed a significant association with heightened neurodegeneration. Co-provision of probucol with high-fat and high-fructose diet completely prevented the cognitive decline and blood-brain barrier dysfunction. Similarly, metformin was able to restore the cognitive function in high-fat and high-fructose-fed mice, while its blood-brain barrier protective effects were modest. These data suggest that probucol may prevent cognitive decline induced by insulin resistance by preserving the integrity of blood-brain barrier, whereas metformin's neuroprotective effects may be mediated through a separate pathway.

Dysregulation of cardiac lipid parameters in high-fat high-cholesterol diet-induced rat model

Background

Lipid dysregulation is a classical risk factor for cardiovascular disease (CVD), yet scanty evidence existed regarding cardiac lipid metabolism that is directly related to heart damage. Recently, the relationship between dyslipidemia and pro-inflammatory insults has led to further understanding on the CVD-predisposing effects of dyslipidemia. The aims of the present study were to investigate whether high-fat high-cholesterol (HFHC) diet-induced hyperlipidemia would cause heart damage and to study the potential role of local cardiac lipid dysregulation in the occurrence of cellular injury.

Methods

Male Sprague–Dawley rats were divided into normal chow or HFHC diet groups, and sacrificed after 2 or 4 weeks, respectively. Lipid peroxidation marker level was measured. Lipid parameters in the rat hearts were detected. Cardiac damage was evaluated.

Results

HFHC diet increased serum levels of cholesterol and free fatty acids (FFAs) and led to systemic oxidative stress and pro-inflammatory status. Cardiac lipid dysregulation, which was characterized by elevated levels of cholesterol and adipocyte (A)- and heart (H)-fatty acid binding proteins (FABPs), occurred after HFHC diet for 4 weeks. Cardiac damage was further evident with elevated circulating H-FABP levels, increased cardiac interstitial fibrosis and the loss of troponin I.

Conclusion

Our data demonstrated that HFHC diet led to systemic and cardiac lipid dysregulation, accompanied by systemic oxidative and pro-inflammatory stresses, and these may finally cooperate to cause a series of pathological changes of the heart tissue. Our findings suggest that maintenance of lipid regulation may be essential in the prevention of heart damage.

Effect of carnosine supplementation on the plasma lipidome in overweight and obese adults: a pilot randomised controlled trial

Carnosine has been shown to reduce oxidation and glycation of low density lipoprotein hence improving dyslipidaemia in rodents. The effect of carnosine on human plasma lipidome has thus far not been investigated. We aimed to determine whether carnosine supplementation improves the plasma lipidome in overweight and obese individuals. Lipid analysis was performed by liquid chromatography mass spectrometry in 24 overweight and obese adults: 13 were randomly assigned to 2 g carnosine daily and 11 to placebo, and treated for 12 weeks. Carnosine supplementation maintained trihexosylceramide (0.01 ± 0.19 vs -0.28 ± 0.34 nmol/ml, p = 0.04), phosphatidylcholine (77 ± 167 vs -81 ± 196 nmol/ml, p = 0.01) and free cholesterol (20 ± 80 vs -69 ± 80 nmol/ml, p = 0.006) levels compared to placebo. Trihexosylceramide was inversely related with fasting insulin (r = -0.6, p = 0.002), insulin resistance (r = -0.6, p = 0.003), insulin secretion (r = -0.4, p = 0.05) and serum carnosinase 1 activity (r = -0.3, p = 0.05). Both phosphatidylcholine and free cholesterol did not correlate with any cardiometabolic parameters. Our data suggest that carnosine may have beneficial effects on the plasma lipidome. Future larger clinical trials are needed to confirm this.

High-sucrose-induced maternal obesity disrupts ovarian function and decreases fertility in Drosophila melanogaster

As the obesity epidemic worsens, the prevalence of maternal obesity is expected to rise. Both high-fat and high-sucrose diets are known to promote maternal obesity and several studies have elucidated the molecular influence of high-fat feeding on female reproduction. However, to date, the molecular impact of a high-sucrose diet on maternal obesity remains to be investigated. Using our previously reported Drosophila high-sucrose maternal obesity model, we sought to determine how excess dietary sucrose impacted the ovary. High-sucrose diet (HSD) fed adult females developed systemic insulin resistance and exhibited an ovarian phenotype characterized by excess accumulation of lipids and cholesterol in the ovary, decreased ovary size, and impaired egg maturation. We also observed decreased expression of antioxidant genes and increased protein carbonylation in the ovaries of HSD females. HSD females laid fewer eggs; however, the overall survival of offspring was unchanged relative to lean control females. Ovaries of HSD females had increased mitochondrial DNA copy number and decreased expression of key mitochondrial regulators, suggestive of an ineffective compensatory response to mitochondrial dysfunction. Mitochondrial alterations were also observed in male offspring of obese females. This study demonstrates that high-sucrose-induced maternal obesity promotes insulin resistance, while disrupting ovarian metabolism and function.

Mouse models of atherosclerosis: a historical perspective and recent advances

Atherosclerosis represents a significant cause of morbidity and mortality in both the developed and developing countries. Animal models of atherosclerosis have served as valuable tools for providing insights on its aetiology, pathophysiology and complications. They can be used for invasive interrogation of physiological function and provide a platform for testing the efficacy and safety of different pharmacological therapies. Compared to studies using human subjects, animal models have the advantages of being easier to manage, with controllable diet and environmental risk factors. Moreover, pathophysiological changes can be induced either genetically or pharmacologically to study the harmful effects of these interventions. There is no single ideal animal model, as different systems are suitable for different research objectives. A good understanding of the similarities and differences to humans enables effective extrapolation of data for translational application. In this article, we will examine the different mouse models for the study and elucidation of the pathophysiological mechanisms underlying atherosclerosis. We also review recent advances in the field, such as the role of oxidative stress in promoting endoplasmic reticulum stress, mitochondrial dysfunction and mitochondrial DNA damage, which can result in vascular inflammation and atherosclerosis. Finally, novel therapeutic approaches to reduce vascular damage caused by chronic inflammation using microRNA and nano-medicine technology, are discussed.

Protein Thiol Redox Signaling in Monocytes and Macrophages

SIGNIFICANCE

Monocyte and macrophage dysfunction plays a critical role in a wide range of inflammatory disease processes, including obesity, impaired wound healing diabetic complications, and atherosclerosis. Emerging evidence suggests that the earliest events in monocyte or macrophage dysregulation include elevated reactive oxygen species production, thiol modifications, and disruption of redox-sensitive signaling pathways. This review focuses on the current state of research in thiol redox signaling in monocytes and macrophages, including (i) the molecular mechanisms by which reversible protein-S-glutathionylation occurs, (ii) the identification of bona fide S-glutathionylated proteins that occur under physiological conditions, and (iii) how disruptions of thiol redox signaling affect monocyte and macrophage functions and contribute to atherosclerosis. Recent Advances: Recent advances in redox biochemistry and biology as well as redox proteomic techniques have led to the identification of many new thiol redox-regulated proteins and pathways. In addition, major advances have been made in expanding the list of S-glutathionylated proteins and assessing the role that protein-S-glutathionylation and S-glutathionylation-regulating enzymes play in monocyte and macrophage functions, including monocyte transmigration, macrophage polarization, foam cell formation, and macrophage cell death.

CRITICAL ISSUES

Protein-S-glutathionylation/deglutathionylation in monocytes and macrophages has emerged as a new and important signaling paradigm, which provides a molecular basis for the well-established relationship between metabolic disorders, oxidative stress, and cardiovascular diseases.

FUTURE DIRECTIONS

The identification of specific S-glutathionylated proteins as well as the mechanisms that control this post-translational protein modification in monocytes and macrophages will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis and other metabolic diseases. Antioxid. Redox Signal. 25, 816-835.

ATR-101, a Selective and Potent Inhibitor of Acyl-CoA Acyltransferase 1, Induces Apoptosis in H295R Adrenocortical Cells and in the Adrenal Cortex of Dogs

ATR-101 is a novel, oral drug candidate currently in development for the treatment of adrenocortical cancer. ATR-101 is a selective and potent inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase 1 (ACAT1), an enzyme located in the endoplasmic reticulum (ER) membrane that catalyzes esterification of intracellular free cholesterol (FC). We aimed to identify mechanisms by which ATR-101 induces adrenocortical cell death. In H295R human adrenocortical carcinoma cells, ATR-101 decreases the formation of cholesteryl esters and increases FC levels, demonstrating potent inhibition of ACAT1 activity. Caspase-3/7 levels and terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeled-positive cells are increased by ATR-101 treatment, indicating activation of apoptosis. Exogenous cholesterol markedly potentiates the activity of ATR-101, suggesting that excess FC that cannot be adequately esterified increases caspase-3/7 activation and subsequent cell death. Inhibition of calcium release from the ER or the subsequent uptake of calcium by mitochondria reverses apoptosis induced by ATR-101. ATR-101 also activates multiple components of the unfolded protein response, an indicator of ER stress. Targeted knockdown of ACAT1 in an adrenocortical cell line mimicked the effects of ATR-101, suggesting that ACAT1 mediates the cytotoxic effects of ATR-101. Finally, in vivo treatment of dogs with ATR-101 decreased adrenocortical steroid production and induced cellular apoptosis that was restricted to the adrenal cortex. Together, these studies demonstrate that inhibition of ACAT1 by ATR-101 increases FC, resulting in dysregulation of ER calcium stores that result in ER stress, the unfolded protein response, and ultimately apoptosis.

The effect of cholesteryl ester transfer protein on pancreatic beta cell dysfunction in mice

BACKGROUND

Cholesterol accumulation causes pancreatic beta cell lipotoxicity and dysfunction. Cholesteryl ester transfer protein (CETP) plays an important role in blood lipid homeostasis. However, its role in tissue lipid metabolism remains unclear. We hypothesized that plasma CETP impact cholesterol homeostasis in the beta cells, thus damaging their functions.

METHODS

The adipose tissue-specific CETP expression transgenic (aP2-CETPTg) mice, characterized by high CETP levels in the circulation, were used in this study. Pancreatic islet cholesterol and beta cell function were assessed in mice. We further measured mRNA levels of the genes involved in beta cell proliferation and differentiation, inflammation and cholesterol metabolism. TUNEL assay was applied to investigate beta cell apoptosis in islets.

RESULTS

The aP2-CETPTg mice exhibited glucose intolerance, lower plasma insulin concentrations but increased insulin sensitivity compared with wild type mice. In addition, glucose-stimulated insulin secretion from isolated pancreatic islets significantly decreased, and free cholesterol significantly increased. Moreover, the number and size of islets from aP2-CETPTg mice were significantly decreased. Genes involved in beta cell proliferation, such as Pdx1 and BETA2, were down-regulated; genes involved in inflammation and ER stress, such as IL-1β, CHOP, and Xbp1 were up-regulated, in line with an increase of beta cell apoptosis.

CONCLUSIONS

Plasma CETP causes free cholesterol accumulation in islets which could contribute to beta cell dysfunction. Thus, CETP inhibition could be a novel protective strategy for dyslipidemia related to diabetes and obese.

Susceptibility of monocytes to activation correlates with atherogenic mitochondrial DNA mutations

We have recently evaluated the susceptibility of circulating monocytes to pro- and anti-inflammatory activation comparing samples from healthy individuals and patients with asymptomatic carotid atherosclerosis. Surprisingly, we found a dramatic individual difference in susceptibility to activation between monocytes isolated from the blood of different subjects, regardless of the presence or absence of atherosclerosis. In the present study the monocyte susceptibility to pro-inflammatory activation was evaluated in comparison with mitochondrial DNA mutations that have previously been shown to correlate with the degree of carotid atherosclerosis assessed by intima-media thickness. Among the mutations associated with atherosclerosis were both homoplasmic (absence or presence of the mutation) or heteroplasmic (different proportions of mutant allele). It was found that two homoplasmic mutations, A1811G and G9477A, tended to correlate with the degree of monocyte susceptibility to activation. At the same time, the mutation G9477A inversely correlated with the degree of monocyte activability, that is, the mutation was more prevalent in monocytes with a low degree of activability. We have found that at least three heteroplasmic mutations of mtDNA (G14459A, A1555G, G12315A) earlier known to be associated with human atherosclerosis, also correlate with proinflammatory activation of circulating human monocytes. We suggest that some mutations can cause mitochondrial dysfunction, which in turn may lead to changes of macrophage activities in atherosclerosis.

Correlation between Mitochondrial Reactive Oxygen and Severity of Atherosclerosis

Atherosclerosis has been associated with mitochondria dysfunction and damage. Our group demonstrated previously that hypercholesterolemic mice present increased mitochondrial reactive oxygen (mtROS) generation in several tissues and low NADPH/NADP+ ratio. Here, we investigated whether spontaneous atherosclerosis in these mice could be modulated by treatments that replenish or spare mitochondrial NADPH, named citrate supplementation, cholesterol synthesis inhibition, or both treatments simultaneously. Robust statistical analyses in pooled group data were performed in order to explain the variation of atherosclerosis lesion areas as related to the classic atherosclerosis risk factors such as plasma lipids, obesity, and oxidative stress, including liver mtROS. Using three distinct statistical tools (univariate correlation, adjusted correlation, and multiple regression) with increasing levels of stringency, we identified a novel significant association and a model that reliably predicts the extent of atherosclerosis due to variations in mtROS. Thus, results show that atherosclerosis lesion area is positively and independently correlated with liver mtROS production rates. Based on these findings, we propose that modulation of mitochondrial redox state influences the atherosclerosis extent.

Evaluation of in vitro anti-inflammatory effects of crude ginger and rosemary extracts obtained through supercritical CO2 extraction on macrophage and tumor cell line: the influence of vehicle type

BACKGROUND

Numerous plants from have been investigated due to their anti-inflammatory activity and, among then, extracts or components of ginger (Zingiber officinale Roscoe) and rosemary (Rosmarinus officinalis L.), sources of polyphenolic compounds. 6-gingerol from ginger rhizome and carnosic acid and carnosol from rosemary leaves present anti-tumor, anti-inflammatory and antioxidant activities. However, the evaluation of the mechanisms of action of these and other plant extracts is limited due to their high hydrophobicity. Dimethylsulfoxide (DMSO) is commonly used as a vehicle of liposoluble materials to mammalian cells in vitro, presenting enhanced cell penetration. Liposomes are also able to efficiently deliver agents to mammalian cells, being capable to incorporate in their structure not only hydrophobic molecules, but also hydrophilic and amphiphilic compounds. Another strategy is based on the use of Pluronic F-68, a biocompatible low-foaming, non-ionic surfactant, to disperse hydrophobic components. Here, these three delivery approaches were compared to analyze their influence on the in vitro anti-inflammatory effects of ginger and rosemary extracts, at different concentrations, on primary mammalian cells and on a tumor cell line.

METHODS

Ginger and rosemary extracts free of organic solvents were obtained by supercritical fluid extraction and dispersed in DMSO, Pluronic F-68 or liposomes, in variable concentrations. Cell viability, production of inflammatory mediators and nitric oxide (NO) release were measured in vitro on J774 cell line and murine macrophages primary culture stimulated with bacterial lipopolysaccharide and interferon-γ after being exposed or not to these extracts.

RESULTS

Ginger and rosemary extracts obtained by supercritical CO2 extraction inhibited the production of pro-inflammatory cytokines and the release of NO by peritoneal macrophages and J774 cells. The delivery vehicles influenced the anti-inflammatory effects. Comparatively, the ginger extract showed the highest anti-inflammatory activity on the tumor cell line. Controversially, rosemary extract dispersed on DMSO induced a more significant IL-1 and TNF-α reduction than ginger extract in primary macrophages.

CONCLUSIONS

Amongst the tested delivery vehicles, DMSO was the most suitable, presenting reduced cytotoxicity, followed by Pluronic F-68 and liposomes, provably due to differences in their form of absorption, distribution and cellular metabolism. Co-administration of liposomes and plant extracts may cause death of macrophages cells and induction of NO production. It can be concluded that some of the beneficial effects attributed to extracts of ginger and rosemary may be associated with the inhibition of inflammatory mediators due to their high antioxidant activity. However, these effects were influenced by the type of delivery vehicle.

Cholesterol homeostasis in cardiovascular disease and recent advances in measuring cholesterol signatures

Despite the biochemical importance of cholesterol, its abnormal metabolism has serious cellular consequences that lead to endocrine disorders such as cardiovascular disease (CVD). Nevertheless, the impact of blood cholesterol as a CVD risk factor is still debated, and treatment with cholesterol-lowering drugs remains controversial, particularly in older patients. Although, the prevalence of CVD increases with age, the underlying mechanisms for this phenomenon are not well understood, and metabolic changes have not been confirmed as predisposing factors of atherogenesis. The quantification of circulating biomarkers for cholesterol homeostasis is therefore warranted, and reference values for cholesterol absorption and synthesis should be determined in order to establish CVD risk factors. The traditional lipid profile is often derived rather than directly measured and lacks a universal standard to interpret the results. In contrast, mass spectrometry-based cholesterol profiling can accurately measure free cholesterol as a biologically active component. This approach allows to detect alterations in various metabolic pathways that control cholesterol homeostasis, by quantitative analysis of cholesterol and its precursors/metabolites as well as dietary sterols. An overview of the mechanism of cholesterol homeostasis under different physiological conditions may help to identify predictive biomarkers of concomitant atherosclerosis and conventional CVD risk factors.

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.

PON3 knockout mice are susceptible to obesity, gallstone formation, and atherosclerosis

We report the engineering and characterization of paraoxonase-3 knockout mice (Pon3KO). The mice were generally healthy but exhibited quantitative alterations in bile acid metabolism and a 37% increased body weight compared to the wild-type mice on a high fat diet. PON3 was enriched in the mitochondria-associated membrane fraction of hepatocytes. PON3 deficiency resulted in impaired mitochondrial respiration, increased mitochondrial superoxide levels, and increased hepatic expression of inflammatory genes. PON3 deficiency did not influence atherosclerosis development on an apolipoprotein E null hyperlipidemic background, but it did lead to a significant 60% increase in atherosclerotic lesion size in Pon3KO mice on the C57BL/6J background when fed a cholate-cholesterol diet. On the diet, the Pon3KO had significantly increased plasma intermediate-density lipoprotein/LDL cholesterol and bile acid levels. They also exhibited significantly elevated levels of hepatotoxicity markers in circulation, a 58% increase in gallstone weight, a 40% increase in hepatic cholesterol level, and increased mortality. Furthermore, Pon3KO mice exhibited decreased hepatic bile acid synthesis and decreased bile acid levels in the small intestine compared with wild-type mice. Our study suggests a role for PON3 in the metabolism of lipid and bile acid as well as protection against atherosclerosis, gallstone disease, and obesity.

Excess cholesterol induces mouse egg activation and may cause female infertility

The HDL receptor scavenger receptor, class B type I (SR-BI) controls the structure and fate of plasma HDL. Female SR-BI KO mice are infertile, apparently because of their abnormal cholesterol-enriched HDL particles. We examined the growth and meiotic progression of SR-BI KO oocytes and found that they underwent normal germinal vesicle breakdown; however, SR-BI KO eggs, which had accumulated excess cholesterol in vivo, spontaneously activated, and they escaped metaphase II (MII) arrest and progressed to pronuclear, MIII, and anaphase/telophase III stages. Eggs from fertile WT mice were activated when loaded in vitro with excess cholesterol by a cholesterol/methyl-β-cyclodextrin complex, phenocopying SR-BI KO oocytes. In vitro cholesterol loading of eggs induced reduction in maturation promoting factor and MAPK activities, elevation of intracellular calcium, extrusion of a second polar body, and progression to meiotic stages beyond MII. These results suggest that the infertility of SR-BI KO females is caused, at least in part, by excess cholesterol in eggs inducing premature activation and that cholesterol can activate WT mouse eggs to escape from MII arrest. Analysis of SR-BI KO female infertility raises the possibility that abnormalities in cholesterol metabolism might underlie some cases of human female infertility of unknown etiology.

Lipoprotein subclass metabolism in nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is associated with increased synthesis of triglycerides and cholesterol coupled with increased VLDL synthesis in the liver. In addition, increased cholesterol content in the liver associates with NASH. Here we study the association of lipoprotein subclass metabolism with NASH. To this aim, liver biopsies from 116 morbidly obese individuals [age 47.3 ± 8.7 (mean ± SD) years, BMI 45.1 ± 6.1 kg/m², 39 men and 77 women] were used for histological assessment. Proton NMR spectroscopy was used to measure lipid concentrations of 14 lipoprotein subclasses in native serum samples at baseline and after obesity surgery. We observed that total lipid concentration of VLDL and LDL subclasses, but not HDL subclasses, associated with NASH [false discovery rate (FDR) < 0.1]. More specifically, total lipid and cholesterol concentration of VLDL and LDL subclasses associated with inflammation, fibrosis, and cell injury (FDR < 0.1), independent of steatosis. Cholesterol concentration of all VLDL subclasses also correlated with total and free cholesterol content in the liver. All NASH-related changes in lipoprotein subclasses were reversed by obesity surgery. High total lipid and cholesterol concentration of serum VLDL and LDL subclasses are linked to cholesterol accumulation in the liver and to liver cell injury in NASH.

Ac‑hE‑18A‑NH2, a novel dual‑domain apolipoprotein mimetic peptide, inhibits apoptosis in macrophages by promoting cholesterol efflux

A novel synthetic dual-domain apolipoprotein (apo)-mimetic peptide, Ac-hE-18A-NH2, has been proposed to possess several apo A-I- and apo E-mimetic properties. This study investigated the protective effect of this peptide on oxidized low-density lipoprotein (ox-LDL)-induced apoptosis in RAW264.7 cells. For this purpose, RAW264.7 cells were exposed to 50 µg/ml ox-LDL for 48 h, and then incubated with the peptide Ac-hE-18A-NH2 at various concentrations. Apoptosis was detected using annexin V-fluorescein isothiocyanate staining and flow cytometric analysis. The study revealed that the peptide Ac-hE-18A-NH2 (1, 10 and 50 µg/ml) inhibited ox-LDL-mediated apoptosis, and this was accompanied by an increased rate of intracellular cholesterol efflux, and decreased total cholesterol levels in the cells in a concentration-dependent manner. The peptide also decreased caspase-3 activity and increased B-cell lymphoma 2 protein (Bcl-2) expression in macrophages in a dose-dependent manner. Moreover, blockage of cholesterol efflux by brefeldin A decreased the protective effect of Ac-hE-18A-NH2 against ox-LDL induced apoptosis, while increasing the cholesterol efflux by β-cyclodextrin administration led to a marked decrease in the rate of apoptosis of the cells. These findings demonstrate that the apo-mimetic peptide Ac-hE-18A-NH2 exerts a protective effect against apoptosis by reducing the accumulation of cholesterol.

Cholesterol induces autophagic and apoptotic death in gastric carcinoma cells

Despite conflicting results, there is evidence to suggest an inverse link between total body cholesterol levels and the risk of certain malignancies. Based on previous reports, this phenomenon appears to vary with cancer site, and, in particular, more consistent data on inverse relations was reported in the risk of gastric cancer. In the current study, the effect of cholesterol on gastric cancer cell viability was examined using an in vitro cell culture system. Addition of cholesterol in culture medium resulted in reduced viability and clonogenicity of SNU601, SNU638 and SNU216 gastric cancer cells by induction of both autophagic and apoptotic death. Transient inactivation of ERK1/2 was linked to reduction of cholesterol-mediated cell viability, and tumor necrosis factor‑related apoptosis-inducing ligand receptor 2 (TRAIL‑R2/DR5) was also involved in cell death signaling. In conclusion, these results imply that cholesterol can act as a signal regulator to modulate cell viability and that proper cellular cholesterol levels may be advantageous to suppress growth of gastric carcinomas.

MicroRNA-27a/b regulates cellular cholesterol efflux, influx and esterification/hydrolysis in THP-1 macrophages

RATIONALE

Macrophage cholesterol homeostasis maintenance is the result of a balance between influx, endogenous synthesis, esterification/hydrolysis and efflux. Excessive accumulation of cholesterol leads to foam cell formation, which is the major pathology of atherosclerosis. Previous studies have shown that miR-27 (miR-27a and miR-27b) may play a key role in the progression of atherosclerosis.

OBJECTIVE

We set out to investigate the molecular mechanisms of miR-27a/b in intracellular cholesterol homeostasis.

METHODS AND RESULTS

In the present study, our results have shown that the miR-27 family is highly conserved during evolution, present in mammals and directly targets the 3' UTR of ABCA1, LPL, and ACAT1. apoA1, ABCG1 and SR-B1 lacking miR-27 bind sites should not be influenced by miR-27 directly. miR-27a and miR-27b directly regulated the expression of endogenous ABCA1 in different cells. Treatment with miR-27a and miR-27b mimics reduced apoA1-mediated cholesterol efflux by 33.08% and 44.61% in THP-1 cells, respectively. miR-27a/b also regulated HDL-mediated cholesterol efflux in THP-1 macrophages and affected the expression of apoA1 in HepG2 cells. However, miR-27a/b had no effect on total cellular cholesterol accumulation, but regulated the levels of cellular free cholesterol and cholesterol ester. We further found that miR-27a/b regulated the expression of LPL and CD36, and then affected the ability of THP-1 macrophages to uptake Dil-oxLDL. Finally, we identified that miR-27a/b regulated cholesterol ester formation by targeting ACAT1 in THP-1 macrophages.

CONCLUSION

These findings indicate that miR-27a/b affects the efflux, influx, esterification and hydrolysis of cellular cholesterol by regulating the expression of ABCA1, apoA1, LPL, CD36 and ACAT1.

Metabolism, energetics, and lipid biology in the podocyte - cellular cholesterol-mediated glomerular injury

Chronic kidney disease (CKD) is associated with a high risk of death. Dyslipidemia is commonly observed in patients with CKD and is accompanied by a decrease in plasma high-density lipoprotein, and an increase in plasma triglyceride-rich lipoproteins and oxidized lipids. The observation that statins may decrease albuminuria but do not stop the progression of CKD indicates that pathways other than the cholesterol synthesis contribute to cholesterol accumulation in the kidneys of patients with CKD. Recently, it has become clear that increased lipid influx and impaired reverse cholesterol transport can promote glomerulosclerosis, and tubulointerstitial damage. Lipid-rafts are cholesterol-rich membrane domains with important functions in regulating membrane fluidity, membrane protein trafficking, and in the assembly of signaling molecules. In podocytes, which are specialized cells of the glomerulus, they contribute to the spatial organization of the slit diaphragm (SD) under physiological and pathological conditions. The discovery that podocyte-specific proteins such as podocin can bind and recruit cholesterol contributing to the formation of the SD underlines the importance of cholesterol homeostasis in podocytes and suggests cholesterol as an important regulator in the development of proteinuric kidney disease. Cellular cholesterol accumulation due to increased synthesis, influx, or decreased efflux is an emerging concept in podocyte biology. This review will focus on the role of cellular cholesterol accumulation in the pathogenesis of kidney diseases with a focus on glomerular diseases.

Liposomal cholesterol delivery activates the macrophage innate immune arm to facilitate intracellular Leishmania donovani killing

Leishmania donovani causes visceral leishmaniasis (VL) by infecting the monocyte/macrophage lineage and residing inside specialized structures known as parasitophorous vacuoles. The protozoan parasite has adopted several means of escaping the host immune response, with one of the major methods being deactivation of host macrophages. Previous reports highlight dampened macrophage signaling, defective antigen presentation due to increased membrane fluidity, and the downregulation of several genes associated with L. donovani infection. We have reported previously that the defective antigen presentation in infected hamsters could be corrected by a single injection of a cholesterol-containing liposome. Here we show that cholesterol in the form of a liposomal formulation can stimulate the innate immune arm and reactivate macrophage function. Augmented levels of reactive oxygen species (ROS) and reactive nitrogen intermediates (RNI), along with proinflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6), corroborate intracellular parasite killing. Cholesterol incorporation kinetics is favored in infected macrophages more than in normal macrophages. Such an enhanced cholesterol uptake is associated with preferential apoptosis of infected macrophages in an endoplasmic reticulum (ER) stress-dependent manner. All these events are coupled with mitogen-activated protein (MAP) kinase activation, while inhibition of such pathways resulted in increased parasite loads. Hence, liposomal cholesterol is a potential facilitator of the macrophage effector function in favor of the host, independently of the T-cell arm.

Probucol prevents blood-brain barrier dysfunction in wild-type mice induced by saturated fat or cholesterol feeding

Dysfunction of the blood-brain barrier (BBB) is an early pathological feature of vascular dementia and Alzheimer's disease (AD) and is triggered by inflammatory stimuli. Probucol is a lipid-lowering agent with potent anti-oxidant properties once commonly used for the treatment of cardiovascular disease. Probucol therapy was found to stabilize cognitive symptoms in elderly AD patients, whereas in amyloid transgenic mice probucol was shown to attenuate amyloidosis. However, the mechanisms underlying the effects of probucol have note been determined. In the present study we investigated whether probucol can prevent BBB disturbances induced by chronic ingestion of proinflammatory diets enriched with either 20% (w/w) saturated fats (SFA) or 1% (w/w) cholesterol. Mice were fed the diets for 12 weeks before they were killed and BBB integrity was measured. Mice maintained on either the SFA- or cholesterol-supplemented diets were found to have a 30- and sevenfold greater likelihood of BBB dysfunction, respectively, as determined by the parenchymal extravasation of plasma-derived immunoglobulins and endogenous lipoprotein enrichment with β-amyloid. In contrast, mice fed the SFA- or cholesterol-enriched diets that also contained 1% (w/w) probucol showed no evidence of BBB disturbance. The parenchymal expression of glial fibrillary acidic protein, a marker of cerebrovascular inflammation, was significantly greater in mice fed the SFA-enriched diet. Plasma lipid, β-amyloid and apolipoprotein B levels were not increased by feeding of the SFA- or cholesterol-enriched diets. However, mice fed the SFA- or cholesterol-enriched diets did exhibit increased plasma non-esterified fatty acid levels that were not reduced by probucol. The data suggest that probucol prevents disturbances of BBB induced by chronic ingestion of diets enriched in SFA or cholesterol by suppressing inflammatory pathways rather than by modulating plasma lipid homeostasis.

Nutraceutical agents with anti-inflammatory properties prevent dietary saturated-fat induced disturbances in blood-brain barrier function in wild-type mice

Background

Emerging evidence suggests that disturbances in the blood–brain barrier (BBB) may be pivotal to the pathogenesis and pathology of vascular-based neurodegenerative disorders. Studies suggest that heightened systemic and central inflammations are associated with BBB dysfunction. This study investigated the effect of the anti-inflammatory nutraceuticals garlic extract-aged (GEA), alpha lipoic acid (ALA), niacin, and nicotinamide (NA) in a murine dietary-induced model of BBB dysfunction.

Methods

C57BL/6 mice were fed a diet enriched in saturated fatty acids (SFA, 40% fat of total energy) for nine months to induce systemic inflammation and BBB disturbances. Nutraceutical treatment groups included the provision of either GEA, ALA, niacin or NA in the positive control SFA-group and in low-fat fed controls. Brain parenchymal extravasation of plasma derived immunoglobulin G (IgG) and large macromolecules (apolipoprotein (apo) B lipoproteins) measured by quantitative immunofluorescent microscopy, were used as markers of disturbed BBB integrity. Parenchymal glial fibrillar acidic protein (GFAP) and cyclooxygenase-2 (COX-2) were considered in the context of surrogate markers of neurovascular inflammation and oxidative stress. Total anti-oxidant status and glutathione reductase activity were determined in plasma.

Results

Brain parenchymal abundance of IgG and apoB lipoproteins was markedly exaggerated in mice maintained on the SFA diet concomitant with significantly increased GFAP and COX-2, and reduced systemic anti-oxidative status. The nutraceutical GEA, ALA, niacin, and NA completely prevented the SFA-induced disturbances of BBB and normalized the measures of neurovascular inflammation and oxidative stress.

Conclusions

The anti-inflammatory nutraceutical agents GEA, ALA, niacin, or NA are potent inhibitors of dietary fat-induced disturbances of BBB induced by systemic inflammations.