The ABC transporters in lipid flux and atherosclerosis

Plasma from type 1 diabetes patients promotes pro-atherogenic cholesterol transport in human macrophages

Hyperglycemia, one of the major risk factors for atherosclerosis, leads to the accumulation of advanced glycation end products (AGEs), contributing to cardiovascular complications. Such accumulation may accelerate the progression of vascular disease in patients with diabetes. Reverse cholesterol transport (RCT) protein, ATP-binding membrane cassette transporters A1 and G1 (ABCA1 and ABCG1) and cholesterol 27-hydroxylase facilitate cholesterol removal from macrophages. AGE inhibits RCT by reducing the expression of ABCA1 and ABCG1. This study aimed to evaluate whether plasma from poorly controlled adolescents with type 1 diabetes (T1D) disrupts cholesterol homeostasis in human monocytes/macrophages. Twenty healthy controls (HCs) and 20 patients with type 1 diabetes mellitus (T1DM), 10-19 years old, were enrolled. Naïve THP-1 macrophages were exposed to plasma from each HC and patient with T1D. Following incubation, mRNA for cholesterol efflux (ABCA1, ABCG1, and 27-hydroxylase) and cholesterol uptake (CD36, ScR-A1, lectin oxidized low-density lipoprotein (LOX)-1, and CXCL16) were isolated. Foam cell formation was quantified to confirm the pro-atherogenic effects of T1D plasma on macrophages. Results showed that T1D plasma had an elevated level of N-(carboxymethyl)-lysine-modified proteins and upregulated CXCL16 and, to a lesser degree, ScR-A1. This change in gene expression in the presence of T1D plasma is associated with increased lipid accumulation and foam cell formation by THP-1 macrophages. In our study, these cells' uptake of an AGE product occurred mainly through the SR-A1 and CXCL16 receptors, leading to increased intracellular oxidized low-density lipoprotein. We conclude that AGEs may contribute to accelerated atherosclerosis in diabetes through effects on both forward and reverse cholesterol movement.

Cholesterol deficiency as a mechanism for autism: A valproic acid model

Dysregulated cholesterol metabolism represents an increasingly recognized feature of autism spectrum disorder (ASD). Children with fetal valproate syndrome caused by prenatal exposure to valproic acid (VPA), an anti-epileptic and mood-stabilizing drug, have a higher incidence of developing ASD. However, the role of VPA in cholesterol homeostasis in neurons and microglial cells remains unclear. Therefore, we examined the effect of VPA exposure on regulation of cholesterol homeostasis in the human microglial clone 3 (HMC3) cell line and the human neuroblastoma cell line SH-SY5Y. HMC3 and SH-SY5Y cells were each incubated in increasing concentrations of VPA, followed by quantification of mRNA and protein expression of cholesterol transporters and cholesterol metabolizing enzymes. Cholesterol efflux was evaluated using colorimetric assays. We found that VPA treatment in HMC3 cells significantly reduced ABCA1 mRNA, but increased ABCG1 and CD36 mRNA levels in a dose-dependent manner. However, ABCA1 and ABCG1 protein levels were reduced by VPA in HMC3. Furthermore, similar experiments in SH-SY5Y cells showed increased mRNA levels for ABCA1, ABCG1, CD36, and 27-hydroxylase with VPA treatment. VPA exposure significantly reduced protein levels of ABCA1 in a dose-dependent manner, but increased the ABCG1 protein level at the highest dose in SH-SY5Y cells. In addition, VPA treatment significantly increased cholesterol efflux in SH-SY5Y, but had no impact on efflux in HMC3. VPA differentially controls the expression of ABCA1 and ABCG1, but regulation at the transcriptional and translational levels are not consistent and changes in the expression of these genes do not correlate with cholesterol efflux in vitro.

Impact of Oat (Avena sativa L.) on Metabolic Syndrome and Potential Physiological Mechanisms of Action: A Current Review

Oat (Avena sativa L.), an annual herbaceous plant belonging to the Gramineae family, is widely grown in various regions including EU, Canada, America, Australia, etc. Due to the nutritional and pharmacological values, oats have been developed into various functional food including fermented beverage, noodle, cookie, etc. Meanwhile, numerous studies have demonstrated that oats may effectively improve metabolic syndrome, such as dyslipidemia, hyperglycemia, atherosclerosis, hypertension, and obesity. However, the systematic pharmacological mechanisms of oats on metabolic syndrome have not been fully revealed. Therefore, in order to fully explore the benefits of oat in food industry and clinic, this review aims to provide up-to-date information on oat and its constituents, focusing on the effects on metabolic syndrome.

Insoluble Dietary Fiber from Okara Combined with Intermittent Fasting Treatment Synergistically Confers Antiobesity Effects by Regulating Gut Microbiota and Its Metabolites

Insoluble dietary fiber (IDF) was recently revealed to have an antiobesity impact. However, the impact and potential mechanism of high-purity IDF derived from okara (HPSIDF) on obesity caused by a high-fat diet (HFD) remain unclear. Except for dietary supplementation, intermittent fasting (IF) has attracted extensive interest as a new dietary strategy against obesity. Thus, we hypothesize that HPSIDF combined with IF treatment may be more effective in preventing obesity. In this study, HPSIDF combined with IF treatment synergistically alleviated HFD-induced dyslipidemia, impaired glucose homeostasis, systemic inflammation, and fat accumulation. Furthermore, gut microbiota dysbiosis and lowered short-chain fatty acid synthesis were recovered by HPSIDF combined with IF treatment. Meanwhile, metabolomic analysis of feces revealed that HPSIDF combined with IF treatment obviously reversed the alterations of metabolic pathways and differential metabolites induced by HFD, which were linked to the modulations of the gut microbiota. Collectively, our findings indicated that HPSIDF combined with IF treatment has great potential to substantially enhance antiobesity efficacy by modulating the gut microbiota and its metabolites.

Methotrexate and cardiovascular prevention: an appraisal of the current evidence

New evidence continues to accumulate regarding a significant association between excessive inflammation and dysregulated immunity (local and systemic) and the risk of cardiovascular events in different patient cohorts. Whilst research has sought to identify novel atheroprotective therapies targeting inflammation and immunity, several marketed drugs for rheumatological conditions may serve a similar purpose. One such drug, methotrexate, has been used since 1948 for treating cancer and, more recently, for a wide range of dysimmune conditions. Over the last 30 years, epidemiological and experimental studies have shown that methotrexate is independently associated with a reduced risk of cardiovascular disease, particularly in rheumatological patients, and exerts several beneficial effects on vascular homeostasis and blood pressure control. This review article discusses the current challenges with managing cardiovascular risk and the new frontiers offered by drug discovery and drug repurposing targeting inflammation and immunity with a focus on methotrexate. Specifically, the article critically appraises the results of observational, cross-sectional and intervention studies investigating the effects of methotrexate on overall cardiovascular risk and individual risk factors. It also discusses the putative molecular mechanisms underpinning the atheroprotective effects of methotrexate and the practical advantages of using methotrexate in cardiovascular prevention, and highlights future research directions in this area.

Special Issue on "Advances in Cholesterol and Lipid Metabolism"

Cholesterol and lipid metabolism is a broad topic that encompasses multiple aspects of cellular function in every organ [...].

Advanced Glycation End Products: key player of the pathogenesis of atherosclerosis

Atherosclerosis is the most common type of cardiovascular disease, and it causes intima thickening, plaque development, and ultimate blockage of the artery lumen. Advanced glycation end products (AGEs) are thought to have a role in the development and progression of atherosclerosis. there is developing an enthusiasm for AGEs as a potential remedial target. AGES mainly induce arterial damage and exacerbate the development of atherosclerotic plaques by triggering cell receptor-dependent signalling. The interplay of AGEs with RAGE, a transmembrane signalling receptor present across all cells important to atherosclerosis, changes cell activity, boosts expression of genes, and increases the outflow of inflammatory compounds, resulting in arterial wall injury and plaque formation. Here in this review, function of AGEs in the genesis, progression, and instability of atherosclerosis is discussed. In endothelial and smooth muscle cells, as well as platelets, the interaction of AGEs with their transmembrane cell receptor, RAGE, triggers intracellular signalling, resulting in endothelial damage, vascular smooth muscle cell function modification, and changed platelet activity.

Healthy Immunity on Preventive Medicine for Combating COVID-19

Immunomodulation is influenced by the consumption of nutrients, and healthy immunity is pivotal to defending an individual from a variety of pathogens. The immune system is a network of intricately regulated biological processes that is comprised of many organs, cellular structures, and signaling molecules. A balanced diet, rich in vitamins, minerals, and antioxidants, is key to a strengthened immune system and, thus, crucial to proper functioning of various physiological activities. Conversely, deficiencies of these micronutrients, involving impaired immunity, are linked to numerous health complications, along with a host of pathologies. Coronavirus disease 2019 (COVID-19) is a dangerous infectious disease caused by a β-form of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its genomic variants, which enter host cells upon binding to the angiotensin converting enzyme 2 receptors, and is associated with substantial morbidities and mortalities globally. Patients afflicted with COVID-19 display asymptomatic to severe symptoms, occurrences of which are multifactorial and include diverse immune responses, sex and gender differences, aging, and underlying medical conditions. Geriatric populations, especially men in comparison to women, regardless of their states, are most vulnerable to severe COVID-19-associated infections and complications, with fatal outcomes. Advances in genomic and proteomic technologies help one understand molecular events, including host–pathogen interactions and pathogenesis of COVID-19 and, subsequently, have developed a variety of preventive measures urgently, ranging from mask wearing to vaccination to medication. Despite these approaches, no unique strategy is available today that can effectively prevent and/or treat this hostile disease. As a consequence, the maintenance of a boosted immune system could be considered a high priority of preventive medicine for combating COVID-19. Herein, we discuss the current level of understanding underlining the contribution of healthy immunity and its relevance to COVID-19 molecular pathogenesis, and potential therapeutic strategies, in the management of this devastating disease.

Effects of SNVs in ABCA1, ABCG1, ABCG5, ABCG8, and SCARB1 Genes on Plasma Lipids, Lipoproteins, and Adiposity Markers in a Brazilian Population

Several proteins are involved in cholesterol homeostasis, as scavenger receptor class B type I and ATP-binding cassette (ABC) transporters including ABCA1, ABCG1, ABCG5, and ABCG8. This study aimed to determine the effects of single nucleotide variants (SNVs) rs2275543 (ABCA1), rs1893590 (ABCG1), rs6720173 (ABCG5), rs6544718 (ABCG8), and rs5888 (SCARB1) on plasma lipids, lipoproteins, and adiposity markers in an asymptomatic population and its sex-specific effects. Volunteers (n = 590) were selected and plasma lipids, lipoproteins, and adiposity markers (waist-to-hip and waist-to-height ratios, lipid accumulation product and body adiposity index) were measured. Genomic DNA was isolated from peripheral blood cells according to the method adapted from Gross-Bellard. SNVs were detected in the TaqMan® OpenArray® Real-Time polymerase chain reaction platform and data analyses were performed using the TaqMan® Genotyper Software. The rs2275543*C point to an increase of high-density lipoprotein size in females while in males very-low-density lipoprotein, cholesterol, and triglycerides were statistically lower (P value < 0.05). The rs1893590*C was statistically associated with lower apolipoprotein A-I levels and higher activities of paraoxonase-1 and cholesteryl ester transfer protein (P value < 0.05). The rs6720173 was statistically associated with an increase in cholesterol and low-density lipoprotein cholesterol in males; moreover, rs6544718*T reduced adiposity markers in females (P value < 0.05). Regarding the rs5888, a decreased adiposity marker in the total population and in females occurred (P value < 0.05). Multivariate analysis of variance showed that SNVs could influence components of high-density lipoprotein metabolism, mainly through ABCG1 (P value < 0.05). The ABCA1 and ABCG5 variants showed sex-specific effects on lipids and lipoproteins, while SCARB1 and ABCG8 variants might influence adiposity markers in females. Our data indicate a possible role of ABCG1 on HDL metabolism.

Serum albumin modified by carbamoylation impairs macrophage cholesterol efflux in diabetic kidney disease

BACKGROUND AND AIMS

Abnormalities in lipid metabolism, accumulation of uremic toxins and advanced glycation end products may contribute to worsening atherosclerosis. This study characterized the glycation and carbamoylation profile of serum albumin isolated from individuals with diabetic kidney disease and its influence on cholesterol efflux.

MATERIAL AND METHODS

49 patients with type 2 diabetes (T2DM) and different eGFR evaluated glycation and carbamoylation profile by measurement of carboxymethyl lysine (CML) and carbamoylated proteins (CBL) in plasma by ELISA, homocitrulline (HCit) in plasma by colorimetry. In the isolated albumins, we quantified CBL (ELISA) and total AGE and pentosidine by fluorescence. Macrophages were treated with albumin isolated, and ¹⁴C-Cholesterol efflux mediated by HDL₂ or HDL₃ was measured. Kruskal-Wallis test, Jonckheere-Terpstra test and Brunner's posttest were used for comparisons among groups.

RESULTS

Determination of CML, HCit, CBL in plasma, as total AGE and pentosidine in albumins, did not differ between groups; however, CBL in the isolated albumins was higher in the more advanced stages of CKD (p=0.0414). There was reduction in the ¹⁴C-cholesterol efflux after treatment for 18h with albumin isolated from patients with eGFR<60mL/min/1.73m² compared with control group mediated by HDL₂ (p=0.0288) and HDL₃ (p<0.0001), as well as when compared with eGFR ≥60mL/min/1.73m² per HDL₂ (p=0.0001) and HDL₃ (p<0.0001). Treatment for 48h showed that eGFR<15mL/min/1.73m² had a lower percentage of ¹⁴C-cholesterol efflux mediated by HDL₂ compared to control and other CKD groups (p=0.0274).

CONCLUSIONS

Albumins isolated from individuals with T2DM and eGFR<60mL/min/1.73m² suffer greater carbamoylation, and they impair the cholesterol efflux mediated by HDL₂ and HDL₃. In turn, this could promote lipids accumulation in macrophages and disorders in reverse cholesterol transport.

Apple Polyphenol Extract Improves High-Fat Diet-Induced Hepatic Steatosis by Regulating Bile Acid Synthesis and Gut Microbiota in C57BL/6 Male Mice

Our previous study showed that apple polyphenol extract (APE) ameliorated high-fat diet-induced hepatic steatosis in C57BL/6 mice by targeting the LKB1/AMPK pathway; to investigate whether other mechanisms are involved in APE induction of improved hepatic steatosis, especially the roles of bile acid (BA) metabolism and gut microbiota, we conducted this study. Thirty-three C57BL/6 male mice were fed with high-fat diet for 12 weeks and concomitantly treated with sterilized water (CON) or 125 or 500 mg/(kg·bw·day) APE (low-dose APE, LAP; high-dose APE, HAP) by intragastric administration. APE treatment decreased total fecal BA contents, especially fecal primary BA levels, mainly including cholic acid, chenodeoxycholic acid, and muricholic acid. An upregulated hepatic Farnesoid X receptor (FXR) protein level and downregulated protein levels of cholesterol 7α-hydroxylase (CYP7A1) and cholesterol 7α-hydroxylase (CYP27A1) were observed after APE treatment, which resulted in the suppressed BA synthesis. Meanwhile, APE had no significant effects on mucosal injury and FXR expression in the jejunum. APE regulated the diversity of gut microbiota and microbiota composition, characterized by significantly increased relative abundance of Akkermansia and decreased relative abundance of Lactobacillus. Furthermore, APE might affect the reverse cholesterol transport in the ileum, evidenced by the changed mRNA levels of NPC1-like intracellular cholesterol transporter 1 (Npc1l1), liver X receptor (Lxr), ATP binding cassette subfamily A member 1 (Abca1), and ATP binding cassette subfamily G member 1 (Abcg1). However, APE did not affect the dihydroxylation and taurine metabolism of BA. The correlation analysis deduced no obvious interactions between BA and gut microbiota. In summary, APE, especially a high dose of APE, could alleviate hepatic steatosis, and the mechanisms were associated with inhibiting BA synthesis and modulating gut microbiota.

Modulation of LXR signaling altered the dynamic activity of human colon adenocarcinoma cancer stem cells in vitro

BACKGROUND

The expansion and metastasis of colorectal cancers are closely associated with the dynamic growth of cancer stem cells (CSCs). This study aimed to explore the possible effect of LXR (a regulator of glycolysis and lipid hemostasis) in the tumorgenicity of human colorectal CD133 cells.

METHODS

Human HT-29 CD133⁺ cells were enriched by MACS and incubated with LXR agonist (T0901317) and antagonist (SR9243) for 72 h. Cell survival was evaluated using MTT assay and flow cytometric analysis of Annexin-V. The proliferation rate was measured by monitoring Ki-67 positive cells using IF imaging. The modulation of LXR was studied by monitoring the activity of all factors related to ABC transporters using real-time PCR assay and western blotting. Protein levels of metabolic enzymes such as PFKFB3, GSK3β, FASN, and SCD were also investigated upon treatment of CSCs with LXR modulators. The migration of CSCs was monitored after being exposed to LXR agonist using scratch and Transwell insert assays. The efflux capacity was measured using hypo-osmotic conditions. The intracellular content of reactive oxygen species was studied by DCFH-DA staining.

RESULTS

Data showed incubation of CSCs with T0901317 and SR9243 reduced the viability of CD133 cells in a dose-dependent manner compared to the control group. The activation of LXR up-regulated the expression and protein levels of ABC transporters (ABCA1, ABCG5, and ABCG8) compared to the non-treated cells (p < 0.05). Despite these effects, LXR activation suppressed the proliferation, clonogenicity, and migration of CD133 cells, and increased hypo-osmotic fragility (p < 0.05). We also showed that SR9243 inhibited the proliferation and clonogenicity of CD133 cells through down-regulating metabolic enzymes PFKFB3, GSK3β, FASN, and SCD as compared with the control cells (p < 0.05). Intracellular ROS levels were increased after the inhibition of LXR by SR9243 (p < 0.05). Calling attention, both T0901317 and SR9243 compounds induced apoptotic changes in cancer stem cells (p < 0.05).

CONCLUSIONS

The regulation of LXR activity can be considered as a selective targeting of survival, metabolism, and migration in CSCs to control the tumorigenesis and metastasis in patients with advanced colorectal cancers.

DNA methylation and lipid metabolism: an EWAS of 226 metabolic measures

BACKGROUND

The discovery of robust and trans-ethnically replicated DNA methylation markers of metabolic phenotypes, has hinted at a potential role of epigenetic mechanisms in lipid metabolism. However, DNA methylation and the lipid compositions and lipid concentrations of lipoprotein sizes have been scarcely studied. Here, we present an epigenome-wide association study (EWAS) (N = 5414 total) of mostly lipid-related metabolic measures, including a fine profiling of lipoproteins. As lipoproteins are the main players in the different stages of lipid metabolism, examination of epigenetic markers of detailed lipoprotein features might improve the diagnosis, prognosis, and treatment of metabolic disturbances.

RESULTS

We conducted an EWAS of leukocyte DNA methylation and 226 metabolic measurements determined by nuclear magnetic resonance spectroscopy in the population-based KORA F4 study (N = 1662) and replicated the results in the LOLIPOP, NFBC1966, and YFS cohorts (N = 3752). Follow-up analyses in the discovery cohort included investigations into gene transcripts, metabolic-measure ratios for pathway analysis, and disease endpoints. We identified 161 associations (p value < 4.7 × 10-10), covering 16 CpG sites at 11 loci and 57 metabolic measures. Identified metabolic measures were primarily medium and small lipoproteins, and fatty acids. For apolipoprotein B-containing lipoproteins, the associations mainly involved triglyceride composition and concentrations of cholesterol esters, triglycerides, free cholesterol, and phospholipids. All associations for HDL lipoproteins involved triglyceride measures only. Associated metabolic measure ratios, proxies of enzymatic activity, highlight amino acid, glucose, and lipid pathways as being potentially epigenetically implicated. Five CpG sites in four genes were associated with differential expression of transcripts in blood or adipose tissue. CpG sites in ABCG1 and PHGDH showed associations with metabolic measures, gene transcription, and metabolic measure ratios and were additionally linked to obesity or previous myocardial infarction, extending previously reported observations.

CONCLUSION

Our study provides evidence of a link between DNA methylation and the lipid compositions and lipid concentrations of different lipoprotein size subclasses, thus offering in-depth insights into well-known associations of DNA methylation with total serum lipids. The results support detailed profiling of lipid metabolism to improve the molecular understanding of dyslipidemia and related disease mechanisms.

Expression levels of miR-27a, miR-329, ABCA1, and ABCG1 genes in peripheral blood mononuclear cells and their correlation with serum levels of oxidative stress and hs-CRP in the patients with coronary artery disease

Atherosclerosis is a chronic inflammatory disease with high mortality worldwide. The reverse cholesterol transport pathway in macrophage plays an important role in the pathogenesis of coronary artery disease (CAD) and is strongly controlled by regulatory factors. The microRNAs can promote or prevent the formation of atherosclerotic lesions by post-transcriptional regulation of vital genes in this pathway. Therefore, this study was conducted to investigate the relationship between the expression levels of miR-27a, miR-329, ABCA1, and ABCG1 genes and serum levels of hs-CRP, ox-LDL, and indices of oxidative stress in the patients with established CAD and controls. A total of 84 subjects (42 patients with CAD and 42 controls) were included in this study. Expression levels of miR-27a-3p, miR-329-3p, ABCA1, and ABCG1 genes in the peripheral blood mononuclear cells (PBMCs) and serum concentration of hs-CRP and ox-LDL were measured by real time-PCR and ELISA, respectively. Also, oxidative stress parameters in the serum were evaluated by ferric-reducing antioxidant power (FRAP) and malondialdehyde (MDA) assays. ABCA1 and ABCG1 gene expression in PBMC and serum concentration of FRAP were significantly lower in the CAD group compared to the control group. Expression levels of miR-27a and miR-329 and serum levels of hs-CRP, ox-LDL, and MDA were significantly higher in the CAD group compared to the control group. Serum levels of hs-CRP, ox-LDL, and expression level of miR-27a have inversely related to ABCA1 and ABCG1 gene expression in all the subjects. An increase in the expression levels of miR-27a and miR-329 may lead to the progression of atherosclerosis plaque by downregulating the expression of ABCA1 and ABCG1 genes.

Lactobacillus Strains Alleviated Hyperlipidemia and Liver Steatosis in Aging Rats via Activation of AMPK

In this study, we hypothesized that different strains of Lactobacillus can alleviate hyperlipidemia and liver steatosis via activation of 5′ adenosine monophosphate-activated protein kinase (AMPK), an enzyme that is involved in cellular energy homeostasis, in aged rats. Male rats were fed with a high-fat diet (HFD) and injected with D-galactose daily over 12 weeks to induce aging. Treatments included (n = 6) (i) normal diet (ND), (ii) HFD, (iii) HFD-statin (lovastatin 2 mg/kg/day), (iv) HFD-Lactobacillus fermentum DR9 (10 log CFU/day), (v) HFD-Lactobacillus plantarum DR7 (10 log CFU/day), and (vi) HFD-Lactobacillus reuteri 8513d (10 log CFU/day). Rats administered with statin, DR9, and 8513d reduced serum total cholesterol levels after eight weeks (p < 0.05), while the administration of DR7 reduced serum triglycerides level after 12 weeks (p < 0.05) as compared to the HFD control. A more prominent effect was observed from the administration of DR7, where positive effects were observed, ranging from hepatic gene expressions to liver histology as compared to the control (p < 0.05); downregulation of hepatic lipid synthesis and β-oxidation gene stearoyl-CoA desaturase 1 (SCD1), upregulation of hepatic sterol excretion genes of ATP-binding cassette subfamily G member 5 and 8 (ABCG5 and ABCG8), lesser degree of liver steatosis, and upregulation of hepatic energy metabolisms genes AMPKα1 and AMPKα2. Taken altogether, this study illustrated that the administration of selected Lactobacillus strains led to improved lipid profiles via activation of energy and lipid metabolisms, suggesting the potentials of Lactobacillus as a promising natural intervention for alleviation of cardiovascular and liver diseases.

The role of interferon-γ in cardiovascular disease: an update

PURPOSE

Cardiovascular disease (CVD) is the leading cause of death, globally, and its prevalence is only expected to rise due to the increasing incidence of co-morbidities such as obesity and diabetes. Medical treatment of CVD is directed primarily at slowing or reversing the underlying atherosclerotic process by managing circulating lipids with an emphasis on control of low-density lipoprotein (LDL) cholesterol. However, over the past several decades, there has been increasing recognition that chronic inflammation and immune system activation are important contributors to atherosclerosis. This shift in focus has led to the elucidation of the complex interplay between cholesterol and cellular secretion of cytokines involved in CVD pathogenesis. Of the vast array of cytokine promoting atherosclerosis, interferon (IFN)-γ is highly implicated and, therefore, of great interest.

METHODS

Literature review was performed to further understand the effect of IFN-γ on the development of atherosclerotic CVD.

RESULTS

IFN-γ, the sole member of the type II IFN family, is produced by T cells and macrophages, and has been found to induce production of other cytokines and to have multiple effects on all stages of atherogenesis. IFN-γ activates a variety of signaling pathways, most commonly the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, to induce oxidative stress, promote foam cell accumulation, stimulate smooth muscle cell proliferation and migration into the arterial intima, enhance platelet-derived growth factor expression, and destabilize plaque. These are just a few of the contributions of IFN-γ to the initiation and progression of atherosclerotic CVD.

CONCLUSION

Given the pivotal role of IFN-γ in the advancement of CVD, activation of its signaling pathways is being explored as a driver of atherosclerosis. Manipulation of this key cytokine may lead to novel therapeutic avenues for CVD prevention and treatment. A number of therapies are being explored with IFN-γ as the potential target.

Butyrate protects against high-fat diet-induced atherosclerosis via up-regulating ABCA1 expression in apolipoprotein E-deficiency mice

BACKGROUND AND PURPOSE

The gut microbial metabolite butyrate is linked to the modulation of metabolic disease. The mechanism by which butyrate effects in atherosclerosis is unknown. Hence, the present investigation into effects of butyrate on high-fat diet-fed ApoE-/- mice after 16 weeks' administration.

EXPERIMENTAL APPROACH

Gut microbiota composition was analysed via 16S rRNA gene sequencing of caecal contents. The effects of butyrate on atherosclerosis were evaluated in vivo using the ApoE-/- mice model. Serum lipids and glucose were analysed for physiological changes and differentially expressed genes in liver samples were identified by hepatic transcriptome profiling. The proteins involved in reverse cholesterol transport were quantified by Western blot and immunohistochemical staining. Finally, the up-regulatory effects of butyrate on ATP-binding cassette sub-family A member 1 (ABCA1) were further evaluated in RAW 264.7 cells along with role of specificity protein 1 by inhibition and silencing.

KEY RESULTS

Oral gavage of butyrate altered microbiota composition and enhanced gut microbial diversity that was decreased by high fat diet (HFD). Butyrate treatment significantly inhibited the HFD-induced atherosclerosis as well as hepatic steatosis without changing body weight gain in ApoE-/- mice. Butyrate had metabolic effects on the liver by regulation of gene expression involved in lipid/glucose metabolism. Furthermore, ABCA1 was significantly induced by butyrate in vivo, ex vivo and in vitro and Sp1 pathway was identified as a potential mechanism.

CONCLUSION AND IMPLICATIONS

Butyrate ameliorates HFD-induced atherosclerosis in ApoE-/- mice via ABCA1-mediated cholesterol efflux in macrophages, which suggesting a promising therapeutic strategy for protecting against atherosclerosis.

Adenosine and the Cardiovascular System

Adenosine is an endogenous nucleoside with a short half-life that regulates many physiological functions involving the heart and cardiovascular system. Among the cardioprotective properties of adenosine are its ability to improve cholesterol homeostasis, impact platelet aggregation and inhibit the inflammatory response. Through modulation of forward and reverse cholesterol transport pathways, adenosine can improve cholesterol balance and thereby protect macrophages from lipid overload and foam cell transformation. The function of adenosine is controlled through four G-protein coupled receptors: A₁, A_2A, A_2B and A₃. Of these four, it is the A_2A receptor that is in a large part responsible for the anti-inflammatory effects of adenosine as well as defense against excess cholesterol accumulation. A_2A receptor agonists are the focus of efforts by the pharmaceutical industry to develop new cardiovascular therapies, and pharmacological actions of the atheroprotective and anti-inflammatory drug methotrexate are mediated via release of adenosine and activation of the A_2A receptor. Also relevant are anti-platelet agents that decrease platelet activation and adhesion and reduce thrombotic occlusion of atherosclerotic arteries by antagonizing adenosine diphosphate-mediated effects on the P2Y12 receptor. The purpose of this review is to discuss the effects of adenosine on cell types found in the arterial wall that are involved in atherosclerosis, to describe use of adenosine and its receptor ligands to limit excess cholesterol accumulation and to explore clinically applied anti-platelet effects. Its impact on electrophysiology and use as a clinical treatment for myocardial preservation during infarct will also be covered. Results of cell culture studies, animal experiments and human clinical trials are presented. Finally, we highlight future directions of research in the application of adenosine as an approach to improving outcomes in persons with cardiovascular disease.

Lipid management in patients with chronic kidney disease

An increased risk of cardiovascular disease, independent of conventional risk factors, is present even at minor levels of renal impairment and is highest in patients with end-stage renal disease (ESRD) requiring dialysis. Renal dysfunction changes the level, composition and quality of blood lipids in favour of a more atherogenic profile. Patients with advanced chronic kidney disease (CKD) or ESRD have a characteristic lipid pattern of hypertriglyceridaemia and low HDL cholesterol levels but normal LDL cholesterol levels. In the general population, a clear relationship exists between LDL cholesterol and major atherosclerotic events. However, in patients with ESRD, LDL cholesterol shows a negative association with these outcomes at below average LDL cholesterol levels and a flat or weakly positive association with mortality at higher LDL cholesterol levels. Overall, the available data suggest that lowering of LDL cholesterol is beneficial for prevention of major atherosclerotic events in patients with CKD and in kidney transplant recipients but is not beneficial in patients requiring dialysis. The 2013 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for Lipid Management in CKD provides simple recommendations for the management of dyslipidaemia in patients with CKD and ESRD. However, emerging data and novel lipid-lowering therapies warrant some reappraisal of these recommendations.

Human Lupus Plasma Pro-Atherogenic Effects on Cultured Macrophages Are Not Mitigated by Statin Therapy: A Mechanistic LAPS Substudy

Background and Objectives: Atherosclerotic cardiovascular disease (CVD) remains a major cause of morbidity and mortality in persons with systemic lupus erythematosus (SLE, lupus). Atherosclerosis, which involves interplay between cholesterol metabolism and cellular inflammatory pathways, is primarily treated with statins since statins have lipid-lowering and anti-inflammatory properties. The Lupus Atherosclerosis Prevention Study (LAPS) was designed to investigate the efficacy of statins against CVD in SLE patients. LAPS demonstrated that 2 years of atorvastatin administration did not reduce atherosclerosis progression in lupus patients. In this LAPs substudy, we use cultured macrophages to explore the atherogenic properties of plasma from LAPS subjects to explain the mechanistic rationale for the inability of statins to reduce CVD in lupus. Materials and Methods: THP-1 differentiated macrophages were treated for 18 h with 10% SLE patient plasma obtained pre- and post-atorvastatin therapy or placebo. Gene expression of the following cholesterol transport genes was measured by qRT-PCR. For efflux—ATP binding cassette transporter (ABC)A1 and ABCG1, 27-hydroxylase, peroxisome proliferator-activated receptor (PPAR)γ, and liver X receptor (LXR)α; and for influx—cluster of differentiation 36 (CD36) and scavenger receptor (ScR)A1. Results: Macrophages exposed to plasma from both statin-treated and placebo-treated groups showed a significant decrease in cholesterol efflux proteins ATP binding cassette (ABC) transporters A1 and ABCG1, an increase in 27-hydroxylase, an increase in the LDL receptor and a decrease in intracellular free cholesterol. No change in influx receptors ScRA1 and CD36, nor nuclear proteins LXRα and PPARγ was observed. Conclusions: Statins do not normalize pro-atherogenic changes induced by lupus and these changes continue to worsen over time. This study provides mechanistic insight into LAPS findings by demonstrating that statins are overall ineffective in altering the balance of cholesterol transport gene expression in human macrophages. Furthermore, our study suggests that statins as a CVD treatment may not be useful in attenuating lipid overload in the SLE environment.

Cholesterol efflux alterations in adolescent obesity: role of adipose-derived extracellular vesical microRNAs

BACKGROUND

Macrophage cholesterol efflux capacity has been identified as a predictor for cardiovascular disease. We assessed the relationship between adipocyte-derived extracellular vesicle microRNAs and macrophage cholesterol efflux capacity.

METHODS

We assessed an adolescent cohort (n = 93, Age, median (IQR) = 17 (3) year, Female = 71, Male = 22) throughout the BMI continuum (BMI = 45.2 (13.2) kg/m²) for: (1) cholesterol efflux capacity and lipoprotein profiles; (2) adipocyte-derived extracellular vesicle microRNAs in serum; (3) the role of visceral adipose tissue extracellular vesicle in regulation of cholesterol efflux and cholesterol efflux gene expression in THP-1 macrophages in vitro.

RESULTS

Efflux capacity was significantly associated with HDL (r = 0.30, p = 0.01) and LDL (r = 0.33, p = 0.005) particle size. Multivariate-analysis identified six microRNAs associated (p < 0.05) with cholesterol efflux capacity: miR-3129-5p (Beta = 0.695), miR-20b (0.430), miR9-5p (0.111), miR-320d (- 0.190), miR301a-5p (0.042), miR-155-5p (0.004). In response to increasing concentrations (1 μg/mL vs. 3 μg/mL) of VAT extracellular vesicle, cholesterol efflux (66% ± 10% vs. 49% ± 2%; p < 0.01) and expression of ABCA1 (FC = 1.9 ± 0.8 vs 0.5 ± 0.2; p < 0.001), CD36 (0.7 ± 0.4 vs. 2.1 ± 0.8, p = 0.02), CYP27A1 (1.4 ± 0.4 vs. 0.9 ± 0.5; p < 0.05), and LXRA (1.8 ± 1.1 vs. 0.5 ± 0.2; p < 0.05) was altered in THP-1 cells in vitro.

CONCLUSION

Adipocyte-derived extracellular vesicle microRNAs may, in part, be involved macrophage cholesterol efflux regulation.

Accelerated Atherosclerosis in Rheumatoid Arthritis: Mechanisms and Treatment

Background:

Rheumatoid arthritis (RA) is a chronic systemic autoimmune inflammatory disorder that increases the risk of developing cardiovascular disease. There is accumulating evidence that the RA disease state accelerates the formation of atherosclerotic plaques. Treatments for RA improve joint symptomatology and may reduce inflammation, but consideration of their effects on the cardiovascular system is generally low priority.

Objective:

Since cardiovascular disease is the leading cause of mortality in RA patients, the impact of RA therapies on atherosclerosis is an area in need of attention and the focus of this review.

Results:

The drugs used to treat RA may be analgesics, conventional disease-modifying anti-rheumatic drugs, and/or biologics, including antibodies against the cytokine tumor necrosis factor-α. Pain relievers such as nonselective non-steroidal anti-inflammatory drugs and cyclooxygenase inhibitors may adversely affect lipid metabolism and cyclooxygenase inhibitors have been associated with increased adverse cardiovascular events, such as myocardial infarction and stroke. Methotrexate, the anchor disease-modifying anti-rheumatic drug in RA treatment has multiple atheroprotective advantages and is often combined with other therapies. Biologic inhibitors of tumor necrosis factor-α may be beneficial in preventing cardiovascular disease because tumor necrosis factor-α promotes the initiation and progression of atherosclerosis. However, some studies show a worsening of the lipid profile in RA with blockade of this cytokine, leading to higher total cholesterol and triglycerides.

Conclusion:

Greater understanding of the pharmacologic activity of RA treatments on the atherosclerotic process may lead to improved care, addressing both damages to the joints and heart.

Macrophage lipid accumulation in the presence of immunosuppressive drugs mycophenolate mofetil and cyclosporin A

OBJECTIVE

Mycophenolate (MPA) and cyclosporin A (CsA) are two immunosuppressive agents currently used for the treatment of autoimmune diseases. However, reports regarding their effects on inflammation and lipid handling are controversial. Here, we compare the effect of these two drugs on the expression of proteins involved in cholesterol handling and lipid accumulation in a macrophage cell system utilizing M0, M1 and M2 human macrophages and in murine bone marrow-derived macrophages (BMDM).

METHODS

Differentiated M0, M1 and M2 subsets of THP-1 human macrophages were subjected to various concentrations of either MPA or CsA. Expression of proteins involved in reverse cholesterol transport (ABCA1 and 27-hydroxylase) and scavenger receptors, responsible for uptake of modified lipids (CD36, ScR-A1, CXCL16 and LOX-1), were evaluated by real-time PCR and confirmed with Western blot. DiI-oxidized LDL internalization assay was used to assess foam cell formation. The influence of MPA was also evaluated in BMDM obtained from atherosclerosis-prone transgenic mice, ApoE^-/- and ApoE^-/-Fas^-/-.

RESULTS

In M0 macrophages, MPA increased expression of ABCA1 and CXCL16 in a concentration-dependent manner. In M1 THP-1 macrophages, MPA caused a significant increase of 27-hydroxylase mRNA and CD36 and SR-A1 receptor mRNAs. Exposure of M2 macrophages to MPA also stimulated expression of 27-hydroxylase, while downregulating all evaluated scavenger receptors. In contrast, CsA had no impact on cholesterol efflux in M0 and M1 macrophages, but significantly augmented expression of ABCA1 and 27-hydroxylase in M2 macrophages. CsA significantly increased expression of the LOX1 receptor in naïve macrophages, downregulated expression of CD36 and SR-A1 in the M1 subpopulation and upregulated expression of all evaluated scavenger receptors. However, CsA enhanced foam cell transformation in M0 and M2 macrophages, while MPA had no effect on foam cell formation unless used at a high concentration in the M2 subtype.

CONCLUSIONS

Our results clearly underline the importance of further evaluation of the effects of these drugs when used in atherosclerosis-prone patients with autoimmune or renal disease.

Cardiovascular disease models: A game changing paradigm in drug discovery and screening

Cardiovascular disease is the leading cause of death worldwide. Although investment in drug discovery and development has been sky-rocketing, the number of approved drugs has been declining. Cardiovascular toxicity due to therapeutic drug use claims the highest incidence and severity of adverse drug reactions in late-stage clinical development. Therefore, to address this issue, new, additional, replacement and combinatorial approaches are needed to fill the gap in effective drug discovery and screening. The motivation for developing accurate, predictive models is twofold: first, to study and discover new treatments for cardiac pathologies which are leading in worldwide morbidity and mortality rates; and second, to screen for adverse drug reactions on the heart, a primary risk in drug development. In addition to in vivo animal models, in vitro and in silico models have been recently proposed to mimic the physiological conditions of heart and vasculature. Here, we describe current in vitro, in vivo, and in silico platforms for modelling healthy and pathological cardiac tissues and their advantages and disadvantages for drug screening and discovery applications. We review the pathophysiology and the underlying pathways of different cardiac diseases, as well as the new tools being developed to facilitate their study. We finally suggest a roadmap for employing these non-animal platforms in assessing drug cardiotoxicity and safety.

Cereal fiber improves blood cholesterol profiles and modulates intestinal cholesterol metabolism in C57BL/6 mice fed a high-fat, high-cholesterol diet

Background

Dietary intake of cereal fiber has been reported to benefit lipid metabolism through multiple mechanisms. The present study aimed to discover the potential mechanisms by which cereal fiber could modify the intestinal cholesterol metabolism.

Design

Male C57BL/6 mice were fed a reference chow (RC) diet; high-fat, high-cholesterol (HFC) diet; HFC plus oat fiber diet; or HFC plus wheat bran fiber diet for 24 weeks. Serum lipids were measured by enzymatic methods. Western blot was used to determine the protein expressions involved in intestinal cholesterol metabolism.

Results

Our results showed that HFC-induced elevations of serum triglycerides, total cholesterol, and low-density lipoprotein cholesterol were normalized in both groups that received cereal fiber. At the protein level, compared with the HFC diet group, the two cereal fibers, especially the oat fiber, significantly increased the protein expression of peroxisome proliferator-activated receptor alpha, liver X receptor alpha, sterol regulatory element-binding protein (SREBP) 2, low-density lipoprotein receptor, adenosine triphosphate (ATP)-binding cassette A1, and ATP-binding cassette G1, while decreasing the protein expression of Niemann-Pick C1-like protein 1, SREBP-1, fatty acid synthase, and acetyl-coenzyme A carboxylase, which were involved in intestinal cholesterol metabolism.

Conclusion

Taken together, increased intake of cereal fiber improved blood cholesterol profiles and increased the intestinal cholesterol efflux and cholesterol clearance in C57BL/6 mice fed a HFC diet. Oat fiber had a stronger effect than wheat bran fiber on cholesterol metabolism by modulating the PPARα, LXRα, and SREBP signaling pathways.

Cardiovascular Protective Effects and Clinical Applications of Resveratrol

Resveratrol is a naturally occurring phenol that is generated by plant species following injury or attack by bacterial and fungal pathogens. This compound was first described as the French Paradox in 1992. Later in 2003, resveratrol was reported to activate sirtuins in yeast cells. Recent experimental studies have found that resveratrol offers a variety of benefits that include both anticarcinogenic and anti-inflammatory effects in addition to the ability to reverse obesity, attenuate hyperglycemia and hyperinsulinemia, protect heart and endothelial function, and increase the life span. Multiple molecular targets are associated with the cardioprotective capabilities of resveratrol, and therefore, resveratrol has potential for a wide range of new therapeutic strategies for atherosclerosis, ischemia/reperfusion, metabolic syndrome, cardiac failure, and inflammatory alterations during aging. Expectations for application in human patients, however, suffer from a lack of sufficient clinical evidence in support of these beneficial effects. This article reviews recently reported basic research results that describe the beneficial effects of resveratrol in an attempt to condense the evidence observed in clinical trials and provide support for the future development of novel clinical therapeutics in patients with cardiovascular diseases.

COX-2-dependent and independent effects of COX-2 inhibitors and NSAIDs on proatherogenic changes in human monocytes/macrophages

It is the second decade of controversy regarding the cardiovascular effects of cyclo-oxygenase-2 (COX-2) inhibitors. At this time, celecoxib is the only available COX-2-specific inhibitor for treatment of pain and inflammation. Therefore, the present study was designed primarily to determine the impact of celecoxib on cholesterol handling (uptake via scavenger receptors and efflux from the cells) and foam cell formation in human THP-1 macrophages, followed by comparison to rofecoxib and other non-steroidal anti-inflammatory drugs (NSAIDs). THP-1 human macrophages and peripheral blood mononuclear cells were incubated with: celecoxib, rofecoxib, naproxen (at 5, 10, 25 µM) and acetaminophen (0.5 mM, 1 mM)±oxidized low-density lipoprotein (oxLDL, 25 µg/mL). Scavenger receptors: CD36, LOX-1, SR-A1, and CXCL16 and cholesterol efflux proteins: ATP-binding cassette transporter (ABC) A1 and G1, and 27-hydroxylase were detected. The adhesion of monocytes to cultured endothelial cells with/ without COX-2 inhibitors/NSAIDs was also analyzed. The presence of celecoxib and rofecoxib (at high concentrations) significantly decreased expression of 27-hydroxylase and ABCA1, interfering with normal cholesterol outflow from macrophages. Acetaminophen and the non-specific COX inhibitor naproxen had no significant effect on these proteins. Only celecoxib had a profound effect on the class B scavenger receptor CD36 and the class E receptor LOX1. We demonstrate that in contrast to celecoxib, rofecoxib and naproxen increased adhesive properties of monocytes to endothelial cells. This work might contribute to our understanding of multiple mechanisms underlying elevated cardiovascular risk upon the use of COX-2 inhibitors and uncover new possibilities to enhance the safety profile of existing COX-2 inhibitors.

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

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

Resveratrol counters systemic lupus erythematosus-associated atherogenicity by normalizing cholesterol efflux

Resveratrol is a bioactive molecule used in dietary supplements and herbal medicines and consumed worldwide. Numerous investigations by our group and others have indicated cardioprotective and anti-inflammatory properties of resveratrol. The present study explored potential atheroprotective actions of resveratrol on cholesterol efflux in cultured human macrophages exposed to plasma from systemic lupus erythematosus (SLE) patients. These results were confirmed in ApoE(-/-)Fas(-/-) double knockout mice, displaying a lupus profile with accelerated atherosclerosis. Resveratrol treatment attenuated atherosclerosis in these mice. THP-1 human macrophages were exposed to 10% pooled or individual plasma from patients who met diagnostic criteria for SLE. Expression of multiple proteins involved in reverse cholesterol transport (ABCA1, ABCG1, SR-B1, and cytochrome P450 27-hydroxylase) was assessed using QRT-PCR and Western blotting techniques. Ten-week-old ApoE(-/-)Fas(-/-) double knockout mice (n = 30) were randomly divided into two equal groups of 15, one of which received 0.01% resveratrol for 10 consecutive weeks. Atherosclerosis progression was evaluated in murine aortas. Bone marrow-derived macrophages (BMDM) were cultured and expression of cholesterol efflux proteins was analyzed in each group of mice. Our data indicate that inhibition of cholesterol efflux by lupus plasma in THP-1 human macrophages is rescued by resveratrol. Similarly, administration of resveratrol in a lupus-like murine model reduces plaque formation in vivo and augments cholesterol efflux in BMDM. This study presents evidence for a beneficial role of resveratrol in atherosclerosis in the specific setting of SLE. Therefore, resveratrol may merit investigation as an additional resource available to reduce lipid deposition and atherosclerosis in humans, especially in such vulnerable populations as lupus patients.

Cholesterol Metabolism in CKD

Patients with chronic kidney disease (CKD) have a substantial risk of developing coronary artery disease. Traditional cardiovascular disease (CVD) risk factors such as hypertension and hyperlipidemia do not adequately explain the high prevalence of CVD in CKD. Both CVD and CKD are inflammatory states and inflammation adversely affects lipid balance. Dyslipidemia in CKD is characterized by elevated triglyceride levels and high-density lipoprotein levels that are both decreased and dysfunctional. This dysfunctional high-density lipoprotein becomes proinflammatory and loses its atheroprotective ability to promote cholesterol efflux from cells, including lipid-overloaded macrophages in the arterial wall. Elevated triglyceride levels result primarily from defective clearance. The weak association between low-density lipoprotein cholesterol level and coronary risk in CKD has led to controversy over the usefulness of statin therapy. This review examines disrupted cholesterol transport in CKD, presenting both clinical and preclinical evidence of the effect of the uremic environment on vascular lipid accumulation. Preventative and treatment strategies are explored.

Regulation of retinoid mediated cholesterol efflux involves liver X receptor activation in mouse macrophages

Removal of cholesterol from macrophage-derived foam cells is a critical step to the prevention of atherosclerotic lesions. We have recently demonstrated the functional importance of retinoids in the regulation of the steroidogenic acute regulatory (StAR) protein that predominantly mediates the intramitochondrial transport of cholesterol in target tissues. In the present study, treatment of mouse macrophages with retinoids, particularly all-trans retinoic acid (atRA) and 9-cis RA, resulted in increases in cholesterol efflux to apolipoprotein AI (Apo-A1). Activation of the PKA pathway by a cAMP analog, (Bu)2cAMP, markedly augmented retinoid mediated cholesterol efflux. Macrophages overexpressing hormone-sensitive lipase increased the hydrolysis of cholesteryl esters and concomitantly enhanced the efficacy of retinoic acid receptor and liver X receptor (LXR) ligands on StAR and ATP-binding cassette transporter A1 (ABCA1) protein levels. RAs elevated StAR promoter activity in macrophages, and an increase in StAR levels augmented cholesterol efflux to Apo-A1, suggesting retinoid-mediated efflux of cholesterol involves enhanced oxysterol production. Further studies revealed that retinoids activate the LXR regulated genes, sterol receptor-element binding protein-1c and ABCA1. These findings provide insights into the regulatory events in which retinoid signaling effectively enhances macrophage cholesterol efflux and indicate that retinoid therapy may have important implications in limiting and/or regressing atherosclerotic cardiovascular disease.

Oxidized cholesterol as the driving force behind the development of Alzheimer's disease

Alzheimer’s disease (AD), the most common neurodegenerative disorder associated with dementia, is typified by the pathological accumulation of amyloid Aβ peptides and neurofibrillary tangles (NFT) within the brain. Considerable evidence indicates that many events contribute to AD progression, including oxidative stress, inflammation, and altered cholesterol metabolism. The brain’s high lipid content makes it particularly vulnerable to oxidative species, with the consequent enhancement of lipid peroxidation and cholesterol oxidation, and the subsequent formation of end products, mainly 4-hydroxynonenal and oxysterols, respectively from the two processes. The chronic inflammatory events observed in the AD brain include activation of microglia and astrocytes, together with enhancement of inflammatory molecule and free radical release. Along with glial cells, neurons themselves have been found to contribute to neuroinflammation in the AD brain, by serving as sources of inflammatory mediators. Oxidative stress is intimately associated with neuroinflammation, and a vicious circle has been found to connect oxidative stress and inflammation in AD. Alongside oxidative stress and inflammation, altered cholesterol metabolism and hypercholesterolemia also significantly contribute to neuronal damage and to progression of AD. Increasing evidence is now consolidating the hypothesis that oxidized cholesterol is the driving force behind the development of AD, and that oxysterols are the link connecting the disease to altered cholesterol metabolism in the brain and hypercholesterolemia; this is because of the ability of oxysterols, unlike cholesterol, to cross the blood brain barrier (BBB). The key role of oxysterols in AD pathogenesis has been strongly supported by research pointing to their involvement in modulating neuroinflammation, Aβ accumulation, and cell death. This review highlights the key role played by cholesterol and oxysterols in the brain in AD pathogenesis.

Ezetimibe and simvastatin modulate gut microbiota and expression of genes related to cholesterol metabolism

AIMS

Hypolipidemic drugs are prescribed in the most of cases for the treatment of cardiovascular diseases. Several studies have showed that the gut microbiota is able to regulate the host cholesterol metabolism. This study aimed to investigate the potential impact of hypolipidemic drugs on the gut microbiota in mice, and to correlate it to the regulation of cholesterol metabolism.

MAIN METHODS

Male C57Bl/6J mice were divided into four groups fed either a control diet alone (CT), or supplemented with simvastatin (0.1% w/w, Zocor®, MSD), or ezetimibe (0.021% w/w, Ezetrol®, MSD) or a combination of simvastatin and ezetimibe (0.1% and 0.021%, respectively) for one week.

KEY FINDINGS

The combination of ezetimibe and simvastatin is required to observe a drop in cholesterolemia, linked to a huge activation of hepatic SREBP-2 and the consequent increased expression of genes involved in LDL cholesterol uptake and cholesterol synthesis. The gut microbiota analysis revealed no change in total bacteria, and in major Gram positive and Gram negative bacteria, but a selective significant increase in Lactobacillus spp. in mice treated with the ezetimibe and a decrease by the combination. The changes in lactobacilli level observed in ezetimibe or combination treated-mice are negatively correlated to expression of genes related to cholesterol metabolism.

SIGNIFICANCE

The present study showed that ezetimibe taken alone is able to modify the composition of gut microbiota in favor of Lactobacillus spp. These results suggest that members of the genus Lactobacillus play an important role in cholesterol metabolism, even in normocholesterolemic mouse model.

ABCC6- a new player in cellular cholesterol and lipoprotein metabolism?

BACKGROUND

Dysregulations in cholesterol and lipid metabolism have been linked to human diseases like hypercholesterolemia, atherosclerosis or the metabolic syndrome. Many ABC transporters are involved in trafficking of metabolites derived from these pathways. Pseudoxanthoma elasticum (PXE), an autosomal-recessive disease caused by ABCC6 mutations, is characterized by atherogenesis and soft tissue calcification.

METHODS

In this study we investigated the regulation of cholesterol biosynthesis in human dermal fibroblasts from PXE patients and healthy controls.

RESULTS

Gene expression analysis of 84 targets indicated dysregulations in cholesterol metabolism in PXE fibroblasts. Transcript levels of ABCC6 were strongly increased in lipoprotein-deficient serum (LPDS) and under serum starvation in healthy controls. For the first time, increased HMG CoA reductase activities were found in PXE fibroblasts. We further observed strongly elevated transcript and protein levels for the proprotein convertase subtilisin/kexin type 9 (PCSK9), as well as a significant reduction in APOE mRNA expression in PXE.

CONCLUSION

Increased cholesterol biosynthesis, elevated PCSK9 levels and reduced APOE mRNA expression newly found in PXE fibroblasts could enforce atherogenesis and cardiovascular risk in PXE patients. Moreover, the increase in ABCC6 expression accompanied by the induction of cholesterol biosynthesis supposes a functional role for ABCC6 in human lipoprotein and cholesterol homeostasis.

Mitofusin 2 decreases intracellular lipids in macrophages by regulating peroxisome proliferator-activated receptor-γ

Mitofusin 2 (Mfn2) inhibits atherosclerotic plaque formation, but the underlying mechanism remains elusive. This study aims to reveal how Mfn2 functions in the atherosclerosis. Mfn2 expression was found to be significantly reduced in arterial atherosclerotic lesions of both mice and human compared with healthy counterparts. Here, we observed that Mfn2 increased cellular cholesterol transporter expression in macrophages by upregulating peroxisome proliferator-activated receptor-γ, an effect achieved at least partially by inhibiting extracellular signal-regulated kinase1/2 (ERK1/2) and p38 mitogen-activated protein kinases (MAPKs) pathway. These findings provide insights into potential mechanisms of Mfn2-mediated alterations in cholesterol transporter expression, which may have significant implications for the treatment of atherosclerotic heart disease.

ABCA7 in Alzheimer's Disease

ATP-binding cassette A7 (ABCA7) gene has recently been identified as a strong genetic locus associated with late-onset Alzheimer's disease (LOAD) through genome-wide association studies (GWASs). ABCA7 is a member of the ATP-binding cassette (ABC) transporter gene superfamily, which codes for 49 ABC proteins, divided into 7 subfamilies (coded A-G). As a multispan transmembrane protein, ABCA7 is most abundantly expressed in the microglial cells in the brain. The levels of ABCA7 have been detected to be increased in the Alzheimer's disease (AD) brain, which positively correlated with amyloid plaque burden and disease severity. Emerging data suggests that ABCA7 could be associated with AD via various pathways, possibly including amyloid-β (Aβ) accumulation, lipid metabolism, and phagocytosis. In this review, we summarize the known functions of ABCA7 and discuss the single-nucleotide polymorphisms (SNPs) related to LOAD, as well as their potential physiological effects. Finally, given the contributions of ABCA7 to AD pathogenesis, targeting ABCA7 might provide novel opportunities for AD therapy.

Deficiency of ATP-binding cassette transporter B6 in megakaryocyte progenitors accelerates atherosclerosis in mice

OBJECTIVE

The ATP-binding cassette (ABC) transporter B6 (ABCB6) is highly expressed in megakaryocyte progenitors, but its role in platelet production and disease has not been elucidated.

APPROACH AND RESULTS

Among various ABC transporters, ABCB6 was highly expressed in megakaryocyte progenitors, exhibiting the same pattern of expression of genes involved in heme synthesis pathway. Transplantation of Abcb6 deficient (Abcb6(-/-)) bone marrow into low density lipoprotein receptor deficient recipient mice resulted in expansion and proliferation of megakaryocyte progenitors, attributable to increased reactive oxygen species production in response to porphyrin loading. The enhanced megakaryopoiesis in Abcb6(-/-) bone marrow-transplanted mice was further illustrated by increased platelet counts, mean platelet volume, and platelet activity. Platelets from Abcb6(-/-) bone marrow-transplanted mice had higher levels of chemokine (C-C motif) ligand 5, which was associated with increased plasma chemokine (C-C motif) ligand 5 levels. There were also increased platelet-leukocyte aggregates, which resulted in leukocyte activation. Abcb6(-/-) bone marrow-transplanted mice had accelerated atherosclerosis which was associated with deposition of the chemotactic agent, chemokine (C-C motif) ligand 5 in atherosclerotic plaques, resulting in increased macrophage accumulation.

CONCLUSIONS

Our findings identify a new role of ABCB6 in preventing atherosclerosis development by dampening platelet production, reactivity, and chemokine (C-C motif) ligand 5 deposition in atherosclerotic lesions.

Infliximab reverses suppression of cholesterol efflux proteins by TNF-α: a possible mechanism for modulation of atherogenesis

Tumor necrosis factor- (TNF-) α is a proinflammatory proatherogenic cytokine. Infliximab, an anti-TNF-α monoclonal antibody, is effective in treating rheumatoid arthritis. However, its impact on cardiovascular burden and lipid transport is unclear. The present study investigates the effect of TNF-α and infliximab on reverse cholesterol transport (RCT) proteins. Uptake of modified lipoproteins by macrophages in the vasculature leads to atherogenic foam cell formation. RCT is mediated by proteins including ATP binding cassette transporters A1 (ABCA1), G1 (ABCG1), liver X receptor- (LXR-) α, and 27-hydroxylase. RCT counteracts lipid overload by ridding cells of excess cholesterol. THP-1 human monocytes were incubated with either TNF-α alone or TNF-α with infliximab. Expression of proteins involved in cholesterol efflux was analyzed. TNF-α significantly reduced both ABCA1 and LXR-α mRNA (to 68.5 ± 1.59%, P < 0.05, and 41.2 ± 0.25%, P < 0.01, versus control set as 100%, resp.). Infliximab nullified the TNF-α effect. Results were confirmed by Western blot. Infliximab abolished the increase in foam cells induced by TNF-α. TNF-α treatment significantly reduces ABCA1 and LXR-α expression in monocytes, thus bringing about a proatherogenic state. The anti-TNF drug infliximab, commonly used in rheumatology, restored RCT proteins. This is the first report of an atheroprotective effect of infliximab on RCT in monocytes.

The ATP-binding cassette transporter-2 (ABCA2) regulates esterification of plasma membrane cholesterol by modulation of sphingolipid metabolism

The ATP-binding cassette transporters are a large family (~48 genes divided into seven families A-G) of proteins that utilize the energy of ATP-hydrolysis to pump substrates across lipid bilayers against a concentration gradient. The ABC "A" subfamily is comprised of 13 members and transport sterols, phospholipids and bile acids. ABCA2 is the most abundant ABC transporter in human and rodent brain with highest expression in oligodendrocytes, although it is also expressed in neurons. Several groups have studied a possible connection between ABCA2 and Alzheimer's disease as well as early atherosclerosis. ABCA2 expression levels have been associated with changes in cholesterol and sphingolipid metabolism. In this paper, we hypothesized that ABCA2 expression level may regulate esterification of plasma membrane-derived cholesterol by modulation of sphingolipid metabolism. ABCA2 overexpression in N2a neuroblastoma cells was associated with an altered bilayer distribution of the sphingolipid ceramide that inhibited acylCoA:cholesterol acyltransferase (ACAT) activity and cholesterol esterification. In contrast, depletion of endogenous ABCA2 in the rat schwannoma cell line D6P2T increased esterification of plasma membrane cholesterol following treatment with exogenous bacterial sphingomyelinase. These findings suggest that control of ABCA2 expression level may be a key locus of regulation for esterification of plasma membrane-derived cholesterol through modulation of sphingolipid metabolism.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.