Atherogenic lipids and lipoproteins trigger CD36-TLR2-dependent apoptosis in macrophages undergoing endoplasmic reticulum stress

The Evolving Understanding and Approach to Residual Cardiovascular Risk Management

Despite unprecedented advances in treatment of atherosclerotic cardiovascular disease, it remains the leading cause of death and disability worldwide. Treatment of major traditional risk factors, including low-density lipoprotein-cholesterol, serves as the foundation of atherosclerotic risk reduction. However, there remains a significant residual risk of cardiovascular events despite optimal risk factor management. Beyond traditional risk factors, other drivers of residual risk have come to the forefront, including inflammatory, pro-thrombotic, and metabolic pathways that contribute to recurrent events and are often unrecognized and not addressed in clinical practice. This review will explore the evidence linking these pathways to atherosclerotic cardiovascular disease and potential future therapeutic options to attenuate residual cardiovascular risk conferred by these pathways.

Metabolic effects of PCSK9 inhibition with Evolocumab in subjects with elevated Lp(a)

Background

Epidemiological studies substantiated that subjects with elevated lipoprotein(a) [Lp(a)] have a markedly increased cardiovascular risk. Inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) lowers both LDL cholesterol (LDL-C) as well as Lp(a), albeit modestly. Effects of PCSK9 inhibition on circulating metabolites such as lipoprotein subclasses, amino acids and fatty acids remain to be characterized.

Methods

We performed nuclear magnetic resonance (NMR) metabolomics on plasma samples derived from 30 individuals with elevated Lp(a) (> 150 mg/dL). The 30 participants were randomly assigned into two groups, placebo (N = 14) and evolocumab (N = 16). We assessed the effect of 16 weeks of evolocumab 420 mg Q4W treatment on circulating metabolites by running lognormal regression analyses, and compared this to placebo. Subsequently, we assessed the interrelationship between Lp(a) and 14 lipoprotein subclasses in response to treatment with evolocumab, by running multilevel multivariate regression analyses.

Results

On average, evolocumab treatment for 16 weeks resulted in a 17% (95% credible interval: 8 to 26%, P < 0.001) reduction of circulating Lp(a), coupled with substantial reduction of VLDL, IDL and LDL particles as well as their lipid contents. Interestingly, increasing concentrations of baseline Lp(a) were associated with larger reduction in triglyceride-rich VLDL particles after evolocumab treatment.

Conclusions

Inhibition of PCSK9 with evolocumab markedly reduced VLDL particle concentrations in addition to lowering LDL-C. The extent of reduction in VLDL particles depended on the baseline level of Lp(a). Our findings suggest a marked effect of evolocumab on VLDL metabolism in subjects with elevated Lp(a).

Trial registration

Clinical trial registration information is registered at ClinicalTrials.gov on April 14, 2016 with the registration number NCT02729025.

Profiling APOL1 Nephropathy Risk Variants in Genome-Edited Kidney Organoids with Single-Cell Transcriptomics

BACKGROUND

DNA variants in APOL1 associate with kidney disease, but the pathophysiologic mechanisms remain incompletely understood. Model organisms lack the APOL1 gene, limiting the degree to which disease states can be recapitulated. Here we present single-cell RNA sequencing (scRNA-seq) of genome-edited human kidney organoids as a platform for profiling effects of APOL1 risk variants in diverse nephron cell types.

METHODS

We performed footprint-free CRISPR-Cas9 genome editing of human induced pluripotent stem cells (iPSCs) to knock in APOL1 high-risk G1 variants at the native genomic locus. iPSCs were differentiated into kidney organoids, treated with vehicle, IFN-γ, or the combination of IFN-γ and tunicamycin, and analyzed with scRNA-seq to profile cell-specific changes in differential gene expression patterns, compared with isogenic G0 controls.

RESULTS

Both G0 and G1 iPSCs differentiated into kidney organoids containing nephron-like structures with glomerular epithelial cells, proximal tubules, distal tubules, and endothelial cells. Organoids expressed detectable APOL1 only after exposure to IFN-γ. scRNA-seq revealed cell type-specific differences in G1 organoid response to APOL1 induction. Additional stress of tunicamycin exposure led to increased glomerular epithelial cell dedifferentiation in G1 organoids.

CONCLUSIONS

Single-cell transcriptomic profiling of human genome-edited kidney organoids expressing APOL1 risk variants provides a novel platform for studying the pathophysiology of APOL1-mediated kidney disease.

TLRs and RAGE are elevated in carotid plaques from patients with moderate-to-severe obstructive sleep apnea syndrome

Background

There is growing evidence that obstructive sleep apnea (OSA) promotes vascular endothelial dysfunction and atherogenesis. Pathways that mediate this pathology may include Toll-like receptors (TLRs) and receptor for advanced glycation end products (RAGE) which play a significant role in proinflammatory processes. The aim of this study was to measure the expression of the above-mentioned receptors in relation to OSA severity in carotid plaques obtained during open endarterectomy.

Methods

This prospective study included patients with a sleep study prior to surgery and a plaque specimen obtained during standard open endarterectomy. Immunohistochemistry of TLR2, TLR4, TLR7, TLR9, RAGE, HMGB1, and NF-κB was performed on atherosclerotic plaques from carotid arteries of patients with and without OSA.

Results

There were 46 patients (22 women, mean age 73.2 ± 1.3 years): 14 control patients, 13 with mild, 11 with moderate, and 8 with severe OSA. The expression of all TLRs and RAGE increased proportionately with increasing OSA severity. The largest differences between patients with severe OSA and no OSA were found for TLR2 (2.88 ± 0.35 vs. 1.27 ± 0.47, p < 0.001), TLR4 (2.88 ± 0.35 vs. 1.64 ± 0.5, p < 0.001), TLR9 (2.38 ± 0.52 vs. 1.45 ± 0.52, p < 0.01), and RAGE (2.5 ± 0.53 vs. 1.82 ± 0.6, p < 0.05).

Conclusion

TLR2, TLR4, TLR9, and RAGE expression was significantly increased in carotid plaques of patients with moderate-to-severe OSA when compared with control patients with no OSA and those with mild OSA. TLR and RAGE-mediated pathways may play a significant role in OSA-dependent atherogenesis.

Lipoprotein(a) the Insurgent: A New Insight into the Structure, Function, Metabolism, Pathogenicity, and Medications Affecting Lipoprotein(a) Molecule

Lipoprotein(a) [Lp(a)], aka "Lp little a", was discovered in the 1960s in the lab of the Norwegian physician Kåre Berg. Since then, we have greatly improved our knowledge of lipids and cardiovascular disease (CVD). Lp(a) is an enigmatic class of lipoprotein that is exclusively formed in the liver and comprises two main components, a single copy of apolipoprotein (apo) B-100 (apo-B100) tethered to a single copy of a protein denoted as apolipoprotein(a) apo(a). Plasma levels of Lp(a) increase soon after birth to a steady concentration within a few months of life. In adults, Lp(a) levels range widely from <2 to 2500 mg/L. Evidence that elevated Lp(a) levels >300 mg/L contribute to CVD is significant. The improvement of isoform-independent assays, together with the insight from epidemiologic studies, meta-analyses, genome-wide association studies, and Mendelian randomization studies, has established Lp(a) as the single most common independent genetically inherited causal risk factor for CVD. This breakthrough elevated Lp(a) from a biomarker of atherosclerotic risk to a target of therapy. With the emergence of promising second-generation antisense therapy, we hope that we can answer the question of whether Lp(a) is ready for prime-time clinic use. In this review, we present an update on the metabolism, pathophysiology, and current/future medical interventions for high levels of Lp(a).

Efficacy of Curcumin on Aortic Atherosclerosis: A Systematic Review and Meta-Analysis in Mouse Studies and Insights into Possible Mechanisms

Since the first report in 2005, accumulating interests have been focused on the effect of curcumin in atherosclerosis with discrepancies. Therefore, we conducted a systematic review and meta-analysis to comprehensively estimate its effect against atherosclerosis. Literature search was performed on the database of PubMed, EMBASE, and Cochrane Library to identify relevant studies which estimated the effect of curcumin in atherosclerosis. Reporting effects on aortic lesion area was the primary outcome while effects on serum lipid profiles and circulating inflammatory markers were the secondary outcome. A total of 10 studies including 14 independent pairwise experiments were included in our analysis. We clarified that curcumin could significantly reduce aortic atherosclerotic lesion area (SMD = -0.89, 95% CI: -1.36 to -0.41, P = 0.0003), decrease serum lipid profiles (Tc, MD = -1.005, 95% CI: -1.885 to -0.124, P = 0.025; TG, MD = -0.045, 95% CI: -0.088 to -0.002, P = 0.042; LDL-c, MD = -0.523, 95% CI: -0.896 to -0.149, P = 0.006) as well as plasma inflammatory indicators (TNF-α, MD = -56.641, 95% CI: -86.848 to -26.433, P < 0.001; IL-1β, MD = -5.089, 95% CI: -8.559 to -1.619, P = 0.004). Dose-response meta-analysis predicted effective dosage of curcumin between 0 and 347 mg/kg BW per day, which was safe and nontoxic according to the existing publications. The underlying mechanisms were also discussed and might be associated with the modulation of lipid transport and inflammation in cells within artery walls as well as indirect modulations in other tissues. Clinical evidence from nonatherosclerosis populations revealed that curcumin would lower the lipid profiles and inflammatory responses as it has in a mouse model. However, standard preclinical animal trial designs are still needed; further studies focusing on the optimal dose of curcumin against atherosclerosis and RCTs directly in atherosclerosis patients are also warranted.

Neutralization of Oxidized Phospholipids Ameliorates Non-alcoholic Steatohepatitis

Oxidized phospholipids (OxPLs), which arise due to oxidative stress, are proinflammatory and proatherogenic, but their roles in non-alcoholic steatohepatitis (NASH) are unknown. Here, we show that OxPLs accumulate in human and mouse NASH. Using a transgenic mouse that expresses a functional single-chain variable fragment of E06, a natural antibody that neutralizes OxPLs, we demonstrate the causal role of OxPLs in NASH. Targeting OxPLs in hyperlipidemic Ldlr^-/- mice improved multiple aspects of NASH, including steatosis, inflammation, fibrosis, hepatocyte death, and progression to hepatocellular carcinoma. Mechanistically, we found that OxPLs promote ROS accumulation to induce mitochondrial dysfunction in hepatocytes. Neutralizing OxPLs in AMLN-diet-fed Ldlr^-/- mice reduced oxidative stress, improved hepatic and adipose-tissue mitochondrial function, and fatty-acid oxidation. These results suggest targeting OxPLs may be an effective therapeutic strategy for NASH.

Amount of Mononuclear Phagocyte Infiltrate Does Not Predict Area of Experimental Choroidal Neovascularization (CNV)

Purpose: Mononuclear phagocytes (MNPs) are present in neovascular age-related macular degeneration (nv AMD) which is also called choroidal neovascularization (CNV). The number and phenotype of the MNPs depend upon the local environment in the CNV and effect of nv AMD therapy. We investigated ocular cell infiltration and conditions that modulate angiogenesis in a laser-induced mouse CNV model.

Methods: We developed assays to quantify MNPs in our established mouse CNV model. One MNP assay quantified the number of subretinal cells peripheral to the CNV lesions. A second assay semiquantitatively assesses the number of MNPs localized to the CNV lesion. We used these assays to measure the effect of toll-like receptor-2 (TLR-2) activation, anti-vascular endothelial growth factor (VEGF) therapy, and chemokine (C-C motif) ligand 2 (Ccl2) genetic deletion on MNP infiltration after laser injury.

Results: Laser injury induced blood vessel growth and infiltration of MNPs. Systemic administration of a TLR-2 activating peptide increased laser-induced CNV area, MNP cell numbers, and MNP density over the CNV lesions. Systemic administration of a VEGF antibody reduced CNV area, while Ccl2 genetic deletion increased CNV area. Despite the change in amount of angiogenesis, MNP infiltration was, surprisingly, unchanged in these 2 conditions.

Conclusions: MNP quantification provides biological insights for candidate AMD therapies. The number of infiltrating MNP cells does not correlate with the amount of laser-induced CNV area.

Proprotein convertase subtilisin/kexin type 9 inhibitors and lipoprotein(a)-mediated risk of atherosclerotic cardiovascular disease: more than meets the eye?

PURPOSE OF REVIEW

Evidence continues to mount for elevated lipoprotein(a) [Lp(a)] as a prevalent, independent, and causal risk factor for atherosclerotic cardiovascular disease. However, the effects of existing lipid-lowering therapies on Lp(a) are comparatively modest and are not specific to Lp(a). Consequently, evidence that Lp(a)-lowering confers a cardiovascular benefit is lacking. Large-scale cardiovascular outcome trials (CVOTs) of inhibitory mAbs targeting proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) may address this issue.

RECENT FINDINGS

Although the ability of PCSK9i to lower Lp(a) by 15-30% is now clear, the mechanisms involved continue to be debated, with in-vitro and in-vivo studies showing effects on Lp(a) clearance (through the LDL receptor or other receptors) and Lp(a)/apolipoprotein(a) biosynthesis in hepatocytes. The FOURIER CVOT showed that patients with higher baseline levels of Lp(a) derived greater benefit from evolocumab and those with the lowest combined achieved Lp(a) and LDL-cholesterol (LDL-C) had the lowest event rate. Meta-analysis of ten phase 3 trials of alirocumab came to qualitatively similar conclusions concerning achieved Lp(a) levels, although an effect independent of LDL-C lowering could not be demonstrated.

SUMMARY

Although it is not possible to conclude that PCSK9i specifically lower Lp(a)-attributable risk, patients with elevated Lp(a) could derive incremental benefit from PCSK9i therapy.

An update on lipid oxidation and inflammation in cardiovascular diseases

Cardiovascular diseases (CVD), including ischemic heart diseases and cerebrovascular diseases, are the leading causes of morbidity and mortality worldwide. Atherosclerosis is the major underlying factor for most CVD. It is well-established that oxidative stress and inflammation are two major mechanisms leading to atherosclerosis. Under oxidative stress, polyunsaturated fatty acids (PUFA)-containing phospholipids and cholesterol esters in cellular membrane and lipoproteins can be readily oxidized through a free radical-induced lipid peroxidation (LPO) process to form a complex mixture of oxidation products. Overwhelming evidence demonstrates that these oxidized lipids are actively involved in the inflammatory responses in atherosclerosis by interacting with immune cells (such as macrophages) and endothelial cells. In addition to lipid lowering in the prevention and treatment of atherosclerotic CVD, targeting chronic inflammation has been entering the medical realm. Clinical trials are under way to lower the lipoprotein (a) (Lp(a)) and its associated oxidized phospholipids, which will provide clinical evidence that targeting inflammation caused by oxidized lipids is a viable approach for CVD. In this review, we aim to give an update on our understanding of the free radical oxidation of LPO, analytical technique to analyze the oxidation products, especially the oxidized phospholipids and cholesterol esters in low density lipoproteins (LDL), and focusing on the experimental and clinical evidence on the role of lipid oxidation in the inflammatory responses associated with CVD, including myocardial infarction and calcific aortic valve stenosis. The challenges and future directions in understanding the role of LPO in CVD will also be discussed.

Mitochondrial Metabolic Reprogramming by CD36 Signaling Drives Macrophage Inflammatory Responses

RATIONALE

A hallmark of chronic inflammatory disorders is persistence of proinflammatory macrophages in diseased tissues. In atherosclerosis, this is associated with dyslipidemia and oxidative stress, but mechanisms linking these phenomena to macrophage activation remain incompletely understood.

OBJECTIVE

To investigate mechanisms linking dyslipidemia, oxidative stress, and macrophage activation through modulation of immunometabolism and to explore therapeutic potential targeting specific metabolic pathways.

METHODS AND RESULTS

Using a combination of biochemical, immunologic, and ex vivo cell metabolic studies, we report that CD36 mediates a mitochondrial metabolic switch from oxidative phosphorylation to superoxide production in response to its ligand, oxidized LDL (low-density lipoprotein). Mitochondrial-specific inhibition of superoxide inhibited oxidized LDL-induced NF-κB (nuclear factor-κB) activation and inflammatory cytokine generation. RNA sequencing, flow cytometry, 3H-labeled palmitic acid uptake, lipidomic analysis, confocal and electron microscopy imaging, and functional energetics revealed that oxidized LDL upregulated effectors of long-chain fatty acid uptake and mitochondrial import, while downregulating fatty acid oxidation and inhibiting ATP5A (ATP synthase F1 subunit alpha)-an electron transport chain component. The combined effect is long-chain fatty acid accumulation, alteration of mitochondrial structure and function, repurposing of the electron transport chain to superoxide production, and NF-κB activation. Apoe null mice challenged with high-fat diet showed similar metabolic changes in circulating Ly6C⁺ monocytes and peritoneal macrophages, along with increased CD36 expression. Moreover, mitochondrial reactive oxygen species were positively correlated with CD36 expression in aortic lesional macrophages.

CONCLUSIONS

These findings reveal that oxidized LDL/CD36 signaling in macrophages links dysregulated fatty acid metabolism to oxidative stress from the mitochondria, which drives chronic inflammation. Thus, targeting to CD36 and its downstream effectors may serve as potential new strategies against chronic inflammatory diseases such as atherosclerosis.

Tanshinone IIA Promotes Macrophage Cholesterol Efflux and Attenuates Atherosclerosis of apoE-/- Mice by Omentin-1/ABCA1 Pathway

BACKGROUND

Tanshinone IIA (Tan IIA) and Omentin-1 have a protective role in the cardiovascular system. However, if and how Tan IIA and Omentin-1 regulate cholesterol metabolism in macrophages has not been fully elucidated.

OBJECTIVE

To investigate the possible mechanisms of Tan IIA and Omentin-1 on preventing macrophage cholesterol accumulation and atherosclerosis development.

METHODS

The effect of Tan IIA on the protein and mRNA levels of Omentin-1 and ATP-binding cassette transporter A1 (ABCA1) in macrophages was examined by Western blot and qRT-PCR assay, respectively. Cholesterol efflux was assessed by liquid scintillation counting (LSC). Cellular lipid droplet was measured by Oil Red O staining, and intracellular lipid content was detected by high performance liquid chromatography (HPLC). In addition, the serum lipid profile of apoE-/- mice was measured by enzymatic method. The size of atherosclerotic lesion areas and content of lipids and collagen in the aortic of apoE-/- mice were examined by Sudan IV, Oil-red O, and Masson staining, respectively.

RESULTS

Tan IIA up-regulated expression of Omentin-1 and ABCA1 in THP-1 macrophages, promoting ABCA1-mediated cholesterol efflux and consequently decreasing cellular lipid content. Consistently, Tan IIA increased reverse cholesterol transport in apoE-/- mice. Plasma levels of high-density lipoprotein cholesterol (HDL-C), ABCA1 expression and atherosclerotic plaque collagen content were increased while plasma levels of low-density lipoprotein cholesterol (LDL-C) and atherosclerotic plaque sizes were reduced in Tan IIA-treated apoE-/- mice. These beneficial effects were, however, essentially blocked by knockdown of Omentin-1.

CONCLUSION

Our results revealed that Tan IIA promotes cholesterol efflux and ameliorates lipid accumulation in macrophages most likely via the Omentin-1/ABCA1 pathway, reducing the development of aortic atherosclerosis.

Intravascular optical coherence tomography method for automated detection of macrophage infiltration within atherosclerotic coronary plaques

BACKGROUND AND AIMS

Significant macrophages infiltration in advanced atherosclerotic plaques promotes acute coronary events. Hence, the clinical imaging of macrophage content in coronary atherosclerotic plaques could potentially aid in identifying patients most at risk of future acute coronary events. The aim of this study was to introduce and validate a simple intravascular optical coherence tomography (IV-OCT) image processing method for automated, accurate and fast detection of macrophage infiltration within coronary atherosclerotic plaques.

METHODS

This method calculates the ratio of the normalized-intensity standard deviation (NSD) values estimated over two axially-adjacent regions of interest in an IV-OCT cross-sectional image (B-scan). When applied to entire IV-OCT B-scans, this method highlights plaque areas with high NSD ratio values (NSDRatio), which was demonstrated to be correlated with the degree of coronary plaque macrophage infiltration.

RESULTS

Using an optimized NSDRatio threshold value, coronary plaque macrophage infiltration could be detected with ~88% sensitivity and specificity in a database of 28 IV-OCT scans from postmortem coronary segments. For comparison, using an optimized NSD threshold value, considered the standard IV-OCT signature for macrophages, coronary plaque macrophage infiltration could be detected with only ~55% sensitivity and specificity.

CONCLUSIONS

The proposed NSDRatio method significantly increases the sensitivity and specificity for the detection of coronary plaque macrophage infiltration compared to the standard NSD method. This computationally efficient method can be seamlessly implemented within standard IV-OCT imaging systems for in-vivo real-time imaging of macrophage content in coronary plaques, which could potentially aid in identifying patients most at risk of future acute coronary events.

Macrophage Trafficking, Inflammatory Resolution, and Genomics in Atherosclerosis: JACC Macrophage in CVD Series (Part 2)

Atherosclerosis is characterized by the retention of modified lipoproteins in the arterial wall. These modified lipoproteins activate resident macrophages and the recruitment of monocyte-derived cells, which differentiate into mononuclear phagocytes that ingest the deposited lipoproteins to become "foam cells": a hallmark of this disease. In this Part 2 of a 4-part review series covering the macrophage in cardiovascular disease, we critically review the contributions and relevant pathobiology of monocytes, macrophages, and foam cells as relevant to atherosclerosis. We also review evidence that via various pathways, a failure of the resolution of inflammation is an additional key aspect of this disease process. Finally, we consider the likely role played by genomics and biological networks in controlling the macrophage phenotype in atherosclerosis. Collectively, these data provide substantial insights on the atherosclerotic process, while concurrently offering numerous molecular and genomic candidates that appear to hold great promise for selective targeting as clinical therapies.

Immunometabolic modulation of retinal inflammation by CD36 ligand

In subretinal inflammation, activated mononuclear phagocytes (MP) play a key role in the progression of retinopathies. Little is known about the mechanism involved in the loss of photoreceptors leading to vision impairment. Studying retinal damage induced by photo-oxidative stress, we observed that cluster of differentiation 36 (CD36)-deficient mice featured less subretinal MP accumulation and attenuated photoreceptor degeneration. Moreover, treatment with a CD36-selective azapeptide ligand (MPE-001) reduced subretinal activated MP accumulation in wild type mice and preserved photoreceptor layers and function as assessed by electroretinography in a CD36-dependent manner. The azapeptide modulated the transcriptome of subretinal activated MP by reducing pro-inflammatory markers. In isolated MP, MPE-001 induced dissociation of the CD36-Toll-like receptor 2 (TLR2) oligomeric complex, decreasing nuclear factor-kappa B (NF-κB) and NLR family pyrin domain containing 3 (NLRP3) inflammasome activation. In addition, MPE-001 caused an aerobic metabolic shift in activated MP, involving peroxisome proliferator-activated receptor-γ (PPAR-γ) activation, which in turn mitigated inflammation. Accordingly, PPAR-γ inhibition blocked the cytoprotective effect of MPE-001 on photoreceptor apoptosis elicited by activated MP. By altering activated MP metabolism, MPE-001 decreased immune responses to alleviate subsequent inflammation-dependent neuronal injury characteristic of various vision-threatening retinal disorders.

Efferocytosis and Atherosclerosis: Regulation of Phagocyte Function by MicroRNAs

There is evidence of the critical role of efferocytosis, the clearance of apoptotic cells (ACs) by phagocytes, in vascular cell homeostasis and protection against atherosclerosis. Specific microRNAs (miRs) can regulate atherogenesis by controlling the accumulation of professional phagocytes (e.g., macrophages) and nonprofessional phagocytes (i.e., neighboring tissue cells with the ability to acquire a macrophage-like phenotype) within the arterial wall, the differentiation of phagocytes into foam cells, the efferocytosis of apoptotic foam cells by phagocytes, and the phagocyte-mediated inflammatory response. A better understanding of the mechanisms involved in miR-regulated phagocyte function might lead to novel therapeutic antiatherosclerotic strategies. In this review, we try to shed light on the relationship between miRs and cellular players in the process of efferocytosis in the context of atherosclerotic plaque and their potential as molecular targets for novel antiatherosclerotic therapies.

Oxidative and endoplasmic reticulum stress in tuberculous meningitis related seizures

BACKGROUND AND PURPOSE

High oxygen consumption and high polyunsaturated fatty acid content in the brain may render it vulnerable to oxidative stress and endoplasmic reticulum (ER) stress. We report the role of these parameters in tuberculous meningitis (TBM) patients with seizures and correlate these with clinical radiological, and laboratory findings.

METHODS

Serum oxidative stress markers ; Catalase, Superoxide dismutase (SOD), Glutathione (GSH), Protein-carbonyl, Malonaldehyde (MDA) were measured using spectrophotometer and ER stress markers-ATF4, CHOP, XBP1 and GRP-78 using RT-PCR in TBM patients, 29 with seizures, 20 without seizures and 20 matched controls. In 10 patients, sequential estimation of oxidative stress and ER stress markers was also measured.

RESULTS

In comparison to controls, TBM patients had significant difference in the expression of oxidative stress and ER stress markers. Serum MDA (P=0.02), protein-carbonyl (P < 0.01) were significantly higher and SOD (P=0.02) and GSH (P < 0.01) significantly lower in the patients with seizures compared to those without seizures. The ER stress markers were insignificantly elevated in TBM patients with seizures. On sequential evaluation, oxidative stress and ER stress markers increased following seizures and returned to baseline at the time of discharge.

CONCLUSION

The results suggest some role of oxidative stress and ER stress in TBM, but do not predict its outcome.

Macrophages and T cells in atherosclerosis: a translational perspective

Atherosclerosis is now considered a chronic maladaptive inflammatory disease. The hallmark feature in both human and murine disease is atherosclerotic plaques. Macrophages and various T-cell lineages play a crucial role in atherosclerotic plaque establishment and disease progression. Humans and mice share many of the same processes that occur within atherogenesis. The various similarities enable considerable insight into disease mechanisms and those which contribute to cardiovascular complications. The apolipoprotein E-null and low-density lipoprotein receptor-null mice have served as the foundation for further immunological pathway manipulation to identify pro- and antiatherogenic pathways in attempt to reveal more novel therapeutic targets. In this review, we provide a translational perspective and discuss the roles of macrophages and various T-cell lineages in contrasting proatherosclerotic and atheroprotective settings.

Implications of Necroptosis for Cardiovascular Diseases

Necroptosis is a non-apoptotic programmed cell death pathway, which causes necrosis-like morphologic changes and triggers inflammation in the surrounding tissues. Accumulating evidence has demonstrated that necroptosis is involved in a number of pathological processes that lead to cardiovascular diseases. However, the exact molecular pathways linking them remain unknown. Herein, this review summarizes the necroptosis-related pathways involved in the development of various cardiovascular diseases, including atherosclerosis, cardiac ischemia-reperfusion injury, cardiac hypertrophy, dilated cardiomyopathy and myocardial infarction, and may shed light on the diagnosis and treatment of these diseases.

The Role of Distinctive Sphingolipids in the Inflammatory and Apoptotic Effects of Electronegative LDL on Monocytes

Electronegative low-density lipoprotein (LDL(-)) is a minor LDL subfraction that is present in blood with inflammatory and apoptotic effects. We aimed to evaluate the role of sphingolipids ceramide (Cer), sphingosine (Sph), and sphingosine-1-phosphate (S1P) in the LDL(-)-induced effect on monocytes. Total LDL was subfractioned into native LDL and LDL(-) by anion-exchange chromatography and their sphingolipid content evaluated by mass spectrometry. LDL subfractions were incubated with monocytes in the presence or absence of enzyme inhibitors: chlorpromazine (CPZ), d-erythro-2-(N-myristoyl amino)-1-phenyl-1-propanol (MAPP), and N,N-dimethylsphingosine (DMS), which inhibit Cer, Sph, and S1P generation, respectively. After incubation, we evaluated cytokine release by enzyme-linked immunosorbent assay (ELISA) and apoptosis by flow cytometry. LDL(-) had an increased content in Cer and Sph compared to LDL(+). LDL(-)-induced cytokine release from cultured monocytes was inhibited by CPZ and MAPP, whereas DMS had no effect. LDL(-) promoted monocyte apoptosis, which was inhibited by CPZ, but increased with the addition of DMS. LDL enriched with Sph increased cytokine release in monocytes, and when enriched with Cer, reproduced both the apoptotic and inflammatory effects of LDL(-). These observations indicate that Cer content contributes to the inflammatory and apoptotic effects of LDL(-) on monocytes, whereas Sph plays a more important role in LDL(-)-induced inflammation, and S1P counteracts apoptosis.

NHLBI Working Group Recommendations to Reduce Lipoprotein(a)-Mediated Risk of Cardiovascular Disease and Aortic Stenosis

Pathophysiological, epidemiological, and genetic studies provide strong evidence that lipoprotein(a) [Lp(a)] is a causal mediator of cardiovascular disease (CVD) and calcific aortic valve disease (CAVD). Specific therapies to address Lp(a)-mediated CVD and CAVD are in clinical development. Due to knowledge gaps, the National Heart, Lung, and Blood Institute organized a working group that identified challenges in fully understanding the role of Lp(a) in CVD/CAVD. These included the lack of research funding, inadequate experimental models, lack of globally standardized Lp(a) assays, and inadequate understanding of the mechanisms underlying current drug therapies on Lp(a) levels. Specific recommendations were provided to facilitate basic, mechanistic, preclinical, and clinical research on Lp(a); foster collaborative research and resource sharing; leverage expertise of different groups and centers with complementary skills; and use existing National Heart, Lung, and Blood Institute resources. Concerted efforts to understand Lp(a) pathophysiology, together with diagnostic and therapeutic advances, are required to reduce Lp(a)-mediated risk of CVD and CAVD.

CD36 tango in cancer: signaling pathways and functions

CD36, a scavenger receptor expressed in multiple cell types, mediates lipid uptake, immunological recognition, inflammation, molecular adhesion, and apoptosis. CD36 is a transmembrane glycoprotein that contains several posttranslational modification sites and binds to diverse ligands, including apoptotic cells, thrombospondin-1 (TSP-1), and fatty acids (FAs). Beyond fueling tumor metastasis and therapy resistance by enhancing lipid uptake and FA oxidation, CD36 attenuates angiogenesis by binding to TSP-1 and thereby inducing apoptosis or blocking the vascular endothelial growth factor receptor 2 pathway in tumor microvascular endothelial cells. Moreover, CD36-driven lipid metabolic reprogramming and functions in tumor-associated immune cells lead to tumor immune tolerance and cancer development. Notable advances have been made in demonstrating the regulatory networks that govern distinct physiological properties of CD36, and this has identified targeting CD36 as a potential strategy for cancer treatment. Here, we provide an overview on the structure, regulation, ligands, functions, and clinical trials of CD36 in cancer.

CD36 signaling in vascular redox stress

Scavenger receptor CD36 is a multifunctional membrane protein that promotes thrombosis in conditions of oxidative stress such as metabolic disorders including dyslipidemia, diabetes mellitus, and chronic inflammation. In these conditions, specific reactive oxidant species are generated that are context and cell dependent. In the vasculature, CD36 signaling in smooth muscle cells and endothelial cells promotes generation of reactive oxygen species, genetic downregulation of antioxidant genes, and impaired smooth muscle and endothelial function. In hematopoietic cells, CD36 signaling enhances platelet dysfunction thus decreasing the threshold for platelet activation and accelerating arterial thrombosis, whereas in macrophages, CD36 promotes lipid-laden foam cell formation and atherosclerosis. These clinically significant processes are mediated through complex redox regulated signaling mechanisms that include Src-family kinases, MAP kinases and other downstream effectors. We provide an overview of CD36 signaling in vascular redox stress highlighting the role in oxidant generation in vascular and hematopoietic cells, but with special emphasis on platelets and dyslipidemia.

Automated detection of superficial macrophages in atherosclerotic plaques using autofluorescence lifetime imaging

BACKGROUND AND AIMS

Macrophages play an important role in the development and destabilization of advanced atherosclerotic plaques. Hence, the clinical imaging of macrophage content in advanced plaques could potentially aid in identifying patients most at risk of future clinical events. The lifetime of the autofluorescence emission from atherosclerotic plaques has been correlated with lipids and macrophage accumulation in ex vivo human coronary arteries, suggesting the potential of intravascular endogenous fluorescence or autofluorescence lifetime imaging (FLIM) for macrophage imaging. The aim of this study was to quantify the accuracy of the coronary intima autofluorescence lifetime to detect superficial macrophage accumulation in atherosclerotic plaques.

METHODS

Endogenous FLIM imaging was performed on 80 fresh postmortem coronary segments from 23 subjects. The plaque autofluorescence lifetime at an emission spectral band of 494 ± 20.5 nm was used as a discriminatory feature to detect superficial macrophage accumulation in atherosclerotic plaques. Detection of superficial macrophage accumulation in the imaged coronary segments based on immunohistochemistry (CD68 staining) evaluation was taken as the gold standard. Receiver Operating Characteristic (ROC) curve analysis was applied to select an autofluorescence lifetime threshold value to detect superficial macrophages accumulation.

RESULTS

A threshold of 6 ns in the plaque autofluorescence lifetime at the emission spectral band of 494 ± 20.5 nm was applied to detect plaque superficial macrophages accumulation, resulting in ∼91.5% accuracy.

CONCLUSIONS

This study demonstrates the capability of endogenous FLIM imaging to accurately identify superficial macrophages accumulation in human atherosclerotic plaques, a key biomarker of atherosclerotic plaque vulnerability.

Oxidized low-density lipoprotein (oxLDL) supports Mycobacterium tuberculosis survival in macrophages by inducing lysosomal dysfunction

Type 2 diabetes mellitus (DM) is a major risk factor for developing tuberculosis (TB). TB-DM comorbidity is expected to pose a serious future health problem due to the alarming rise in global DM incidence. At present, the causal underlying mechanisms linking DM and TB remain unclear. DM is associated with elevated levels of oxidized low-density lipoprotein (oxLDL), a pathologically modified lipoprotein which plays a key role during atherosclerosis development through the formation of lipid-loaded foamy macrophages, an event which also occurs during progression of the TB granuloma. We therefore hypothesized that oxLDL could be a common factor connecting DM to TB. To study this, we measured oxLDL levels in plasma samples of healthy controls, TB, DM and TB-DM patients, and subsequently investigated the effect of oxLDL treatment on human macrophage infection with Mycobacterium tuberculosis (Mtb). Plasma oxLDL levels were significantly elevated in DM patients and associated with high triglyceride levels in TB-DM. Strikingly, incubation with oxLDL strongly increased macrophage Mtb load compared to native or acetylated LDL (acLDL). Mechanistically, oxLDL -but not acLDL- treatment induced macrophage lysosomal cholesterol accumulation and increased protein levels of lysosomal and autophagy markers, while reducing Mtb colocalization with lysosomes. Importantly, combined treatment of acLDL and intracellular cholesterol transport inhibitor (U18666A) mimicked the oxLDL-induced lysosomal phenotype and impaired macrophage Mtb control, illustrating that the localization of lipid accumulation is critical. Collectively, these results demonstrate that oxLDL could be an important DM-associated TB-risk factor by causing lysosomal dysfunction and impaired control of Mtb infection in human macrophages.

Tuberculosis (TB) is an infectious disease of the lungs caused by a bacterium, Mycobacterium tuberculosis (Mtb), and is responsible for over a million deaths per year worldwide. Population studies have demonstrated that type 2 diabetes mellitus (DM) is a risk factor for TB as it triples the risk of developing the disease. DM is a metabolic disorder which is generally associated with obesity, and is characterized by resistance to the pancreatic hormone insulin and high blood glucose and lipid levels. As the global incidence of DM is rising at an alarming rate, especially in regions where TB is common, it is important to understand precisely how DM increases the risk of developing TB. Both TB and DM are associated with the development of foamy macrophages, lipid-loaded white blood cells, which can be the result of a specific lipoprotein particle called oxidized low-density lipoprotein (oxLDL). Here, we demonstrated that DM patients have high blood levels of oxLDL, and generating foamy macrophages with oxLDL supported Mtb survival after infection as a result of faulty intracellular cholesterol accumulation. Our results propose a proof of concept for oxLDL as a risk factor for TB development, encouraging future studies on lipid-lowering therapies for TB-DM.

Tumor-derived nanovesicles promote lung distribution of the therapeutic nanovector through repression of Kupffer cell-mediated phagocytosis

Tumor-derived nanovesicles have been widely used as a biomarker or therapeutic target in various tumor types. However, these nanovesicles have limited use in therapy due to the risk of advancing tumor development. Methods: Exosome-like nanovesicles (ENVs) were developed from metastatic breast cancer 4T1 cells-derived exosomes. The distribution of ENVs and their impact on macrophage-mediated phagocytosis were evaluated. The effect of ENVs pretreatment on anti-lung metastasis therapeutic effects of chemotherapeutic drugs delivered by DOTAP/DOPE liposomes in breast cancer-bearing mice was also examined. Results: We demonstrated that, following intravenous injection in mice, ENVs were preferentially uptaken by Kupffer cells and repressed phagocytosis. The decreased uptake appeared to be due to the translocation of membrane nucleolin from the inner face of the plasma membrane to the cell surface and intercellular Ca2+ fluxes, leading to altered expression of genes involved in phagocytosis by macrophages. Mice pretreated with 4T1-derived ENVs led to the decreased uptake of DOTAP: DOPE liposomes (DDL) in the liver. Consequently, doxorubicin-loaded DDL transported to the lungs instead of the liver, effectively inhibiting breast cancer lung metastasis. Importantly, 4T1 cells exosome-derived ENVs had no detectable toxicity in vivo and low-risk to promote tumor growth and metastasis compared to 4T1 cells exosomes. Conclusion: Our results suggested that pretreatment with 4T1 ENVs represents a strategy to escape Kupffer cell-mediated phagocytosis effectively targeting drug delivery vehicles to tumor metastasis, reducing the IC50 of the chemotherapeutic drugs, and avoiding adverse side effects.

To test, or not to test: that is the question for the future of lipoprotein(a)

INTRODUCTION

Lipoprotein(a) [Lp(a)] is a potent, highly heritable and common risk factor for atherosclerotic cardiovascular disease (ASCVD). Evidence for a causal association between elevated Lp(a) and ASCVD has been provided by large epidemiological investigations that have demonstrated a curvilinear association with increased risk, as well as from genetic examinations and cellular and transgenic animal studies. Although there are several therapies available for lowering Lp(a), none are selective for Lp(a) and there is no clinical trial data that has specifically shown that lowering Lp(a) reduces the risk of ASCVD. Hence, screening for elevated Lp(a) is not routinely incorporated into clinical practice. Areas covered: This paper reviews the current evidence supporting the causal role of Lp(a) in the primary and secondary prevention of ASCVD, screening approaches for high Lp(a), current guidelines on testing Lp(a), and barriers to the routine screening of elevated Lp(a) in clinical practice. Expert opinion: At present, there is a moderate level of evidence supporting the routine screening of elevated Lp(a). Current guidelines recommend testing for elevated Lp(a) in individuals at intermediate or high risk of ASCVD.

Cardiomyopathy in obesity, insulin resistance and diabetes

The prevalence of obesity, insulin resistance and diabetes is increasing rapidly. Most patients with these disorders have hypertriglyceridaemia and increased plasma levels of fatty acids, which are taken up and stored in lipid droplets in the heart. Intramyocardial lipids that exceed the capacity for storage and oxidation can be lipotoxic and induce non-ischaemic and non-hypertensive cardiomyopathy, termed diabetic or lipotoxic cardiomyopathy. The clinical features of diabetic cardiomyopathy are cardiac hypertrophy and diastolic dysfunction, which lead to heart failure, especially heart failure with preserved ejection fraction. Although the pathogenesis of the cardiomyopathy is multifactorial, diabetic dyslipidaemia and intramyocardial lipid accumulation are the key pathological features, triggering cellular signalling and modifications of proteins and lipids via generation of toxic metabolic intermediates. Most clinical studies have shown no beneficial effect of anti-diabetic agents and statins on outcomes in heart failure patients without atherosclerotic diseases, indicating the importance of identifying underlying mechanisms and early interventions for diabetic cardiomyopathy. Here, we summarize the molecular mechanisms of diabetic cardiomyopathy, with a special emphasis on cardiac lipotoxicity, and discuss the role of peroxisome proliferator-activated receptor α and dysregulated fatty acid metabolism as potential therapeutic targets.

Oxidized low-density lipoprotein promotes vascular endothelial cell dysfunction by stimulating miR-496 expression and inhibiting the Hippo pathway effector YAP

Oxidized low‐density lipoprotein (ox‐LDL) can damage vascular endothelial cells and cause atherosclerosis, but its epigenetic regulatory mechanism has not been fully elucidated. We show that ox‐LDL induced significant apoptosis and loss of function in human umbilical vascular endothelial cells (HUVECs). At the same time, ox‐LDL significantly decreased the expression of Hippo–YAP/ZAP (Yes‐associated protein/YLP motif–containing 1) pathway proteins as compared to that of the control. The luciferase reporter system confirmed that microRNA (miR)‐496 silenced YAP gene expression by binding to its 3′ untranslated region (3′ UTR). Ox‐LDL–treated miR‐496 overexpression HUVECs had a higher apoptosis rate and more severe dysfunction compared to the control cells. This in‐depth study shows that ox‐LDL inhibits YAP protein expression by inducing miR‐496 expression, leading to its inability to enter the nucleus, thereby losing its function as a transcriptional cofactor for activating the downstream genes. Our findings reveal that, through epigenetic modification, ox‐LDL can inhibit the normal expression of Hippo–YAP/ZAP pathway proteins via miR‐496 expression and induce vascular endothelial cell dysfunction.

Oxidized LDL upregulates macrophage DPP4 expression via TLR4/TRIF/CD36 pathways

Background

We and others have shown that dipeptidyl peptidase-IV (DPP4) expression is increased in obesity/atherosclerosis and is positively correlated with atherosclerotic burden. However, the mechanism by which DPP4 expression is regulated in obesity remains unclear. In this study, we investigated the pathways regulating the expression of DPP4 on macrophages.

Methods

Flowsight® Imaging Flow Cytometry was employed for the detection of DPP4 and immunophenotyping. DPP4 enzymatic activity was measured by a DPPIV-Glo™ Protease Assay kit.

Findings

Human monocytes expressed a moderate level of membrane-bound DPP4. Obese patients with body mass index (BMI) ≥ 30 had a higher level of monocyte DPP4 expression, in parallel with higher levels of HOMA-IR, blood glucose, triglycerides, and non-HDL cholesterol, compared to those in the non-obese (BMI < 30) patients. Oxidized low-density lipoprotein (oxLDL), but not native LDL, up-regulated DPP4 expression on macrophages with a preferential increase in CD36⁺ cells. OxLDL mediated DPP4 up-regulation was considerably diminished by Toll-like receptor-4 (TLR4) knockdown and CD36 deficiency. TRIF deficiency, but not MyD88 deficiency, attenuated oxLDL-induced DPP4 increase.

Interpretation

Our study suggests a key role for oxLDL and downstream CD36/TLR4/TRIF in regulating DPP4 expression. Increased DPP4 in response to oxidized lipids may represent an integrated mechanism linking post-prandial glucose metabolism to lipoprotein abnormality-potentiated atherosclerosis.

New Frontiers in Lp(a)-Targeted Therapies

Interest in lipoprotein (a) [Lp(a)] has exploded over the past decade with the emergence of genetic and epidemiological studies pinpointing elevated levels of this unique lipoprotein as a causal risk factor for atherosclerotic cardiovascular disease (ASCVD) and calcific aortic valve disease (CAVD). This review summarizes the most recent discoveries regarding therapeutic approaches to lower Lp(a) and presents these findings in the context of an emerging, although far from complete, understanding of the biosynthesis and catabolism of Lp(a). Application of Lp(a)-specific lowering agents to outcome trials will be the key to opening this new frontier in the battle against CVD.

Reduction of myocardial ischaemia-reperfusion injury by inactivating oxidized phospholipids

Aims

Myocardial ischaemia followed by reperfusion (IR) causes an oxidative burst resulting in cellular dysfunction. Little is known about the impact of oxidative stress on cardiomyocyte lipids and their role in cardiac cell death. Our goal was to identify oxidized phosphatidylcholine-containing phospholipids (OxPL) generated during IR, and to determine their impact on cell viability and myocardial infarct size.

Methods and results

OxPL were quantitated in isolated rat cardiomyocytes using mass spectrophotometry following 24 h of IR. Cardiomyocyte cell death was quantitated following exogenously added OxPL and in the absence or presence of E06, a 'natural' murine monoclonal antibody that binds to the PC headgroup of OxPL. The impact of OxPL on mitochondria in cardiomyocytes was also determined using cell fractionation and Bnip expression. Transgenic Ldlr-/- mice, overexpressing a single-chain variable fragment of E06 (Ldlr-/--E06-scFv-Tg) were used to assess the effect of inactivating endogenously generated OxPL in vivo on myocardial infarct size. Following IR in vitro, isolated rat cardiomyocytes showed a significant increase in the specific OxPLs PONPC, POVPC, PAzPC, and PGPC (P < 0.05 to P < 0.001 for all). Exogenously added OxPLs resulted in significant death of rat cardiomyocytes, an effect inhibited by E06 (percent cell death with added POVPC was 22.6 ± 4.14% and with PONPC was 25.3 ± 3.4% compared to 8.0 ± 1.6% and 6.4 ± 1.0%, respectively, with the addition of E06, P < 0.05 for both). IR increased mitochondrial content of OxPL in rat cardiomyocytes and also increased expression of Bcl-2 death protein 3 (Bnip3), which was inhibited in presence of E06. Notably cardiomyocytes with Bnip3 knock-down were protected against cytotoxic effects of OxPL. In mice exposed to myocardial IR in vivo, compared to Ldlr-/- mice, Ldlr-/--E06-scFv-Tg mice had significantly smaller myocardial infarct size normalized to area at risk (72.4 ± 21.9% vs. 47.7 ± 17.6%, P = 0.023).

Conclusions

OxPL are generated within cardiomyocytes during IR and have detrimental effects on cardiomyocyte viability. Inactivation of OxPL in vivo results in a reduction of infarct size.

Lipoprotein(a) catabolism: a case of multiple receptors

Lipoprotein(a) [Lp(a)] is an apolipoprotein B (apoB)-containing plasma lipoprotein similar in structure to low-density lipoprotein (LDL). Lp(a) is more complex than LDL due to the presence of apolipoprotein(a) [apo(a)], a large glycoprotein sharing extensive homology with plasminogen, which confers some unique properties onto Lp(a) particles. ApoB and apo(a) are essential for the assembly and catabolism of Lp(a); however, other proteins associated with the particle may modify its metabolism. Lp(a) specifically carries a cargo of oxidised phospholipids (OxPL) bound to apo(a) which stimulates many proinflammatory pathways in cells of the arterial wall, a key property underlying its pathogenicity and association with cardiovascular disease (CVD). While the liver and kidney are the major tissues implicated in Lp(a) clearance, the pathways for Lp(a) uptake appear to be complex and are still under investigation. Biochemical studies have revealed an exceptional array of receptors that associate with Lp(a) either via its apoB, apo(a), or OxPL components. These receptors fall into five main categories, namely 'classical' lipoprotein receptors, toll-like and scavenger receptors, lectins, and plasminogen receptors. The roles of these receptors have largely been dissected by genetic manipulation in cells or mice, although their relative physiological importance for removal of Lp(a) from the circulation remains unclear. The LPA gene encoding apo(a) has an overwhelming effect on Lp(a) levels which precludes any clear associations between potential Lp(a) receptor genes and Lp(a) levels in population studies. Targeted approaches and the selection of unique Lp(a) phenotypes within populations has nevertheless allowed for some associations to be made. Few of the proposed Lp(a) receptors can specifically be manipulated with current drugs and, as such, it is not currently clear whether any of these receptors could provide relevant targets for therapeutic manipulation of Lp(a) levels. This review summarises the current status of knowledge about receptor-mediated pathways for Lp(a) catabolism.

The Complex Interplay between Lipids, Immune System and Interleukins in Cardio-Metabolic Diseases

Lipids and inflammation regulate each other. Early studies on this topic focused on the systemic effects that the acute inflammatory response-and interleukins-had on lipid metabolism. Today, in the era of the obesity epidemic, whose primary complications are cardio-metabolic diseases, attention has moved to the effects that the nutritional environment and lipid derangements have on peripheral tissues, where lipotoxicity leads to organ damage through an imbalance of chronic inflammatory responses. After an overview of the effects that acute inflammation has on the systemic lipid metabolism, this review will describe the lipid-induced immune responses that take place in peripheral tissues and lead to chronic cardio-metabolic diseases. Moreover, the anti-inflammatory effects of lipid lowering drugs, as well as the possibility of using anti-inflammatory agents against cardio-metabolic diseases, will be discussed.

The atheroprotective role of lipoxin A4 prevents oxLDL-induced apoptotic signaling in macrophages via JNK pathway

BACKGROUND AND AIMS

We examined whether the inflammation resolution mediator lipoxin A₄ (LXA₄) inhibits foam cell formation and oxidized low-density lipoprotein (oxLDL)-induced apoptotic signaling in macrophages and the role of circulating/local LXA₄ biosynthesis in atherogenesis.

METHODS

LXA₄ levels were measured by enzyme-linked immunosorbent assay. Dil-oxLDL and Dil-acLDL binding to and uptake by macrophages were evaluated by flow cytometry. Apoptosis was evaluated by TUNEL and Annexin V/PI assays.

RESULTS

Circulating LXA₄ levels in patients with coronary artery disease were much higher than those in respective controls. Local LXA₄ levels were much lower in rabbit atherosclerotic vessel walls. Interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α) were elevated in atherosclerotic vessels. After the inflammatory stimulus (IFN-γ, TNF-α, and C-reactive protein), LXA₄ synthesis decreased significantly in foam cells. LXA₄ dose-dependently suppressed the expression of the cholesterol uptake genes CD36 and SR-A in macrophages, which was blocked by the LXA₄ receptor antagonist BOC-2. LXA₄ also inhibited oxLDL-induced CD36 upregulation, Dil-oxLDL uptake, and foam cell formation. Furthermore, LXA₄ inhibited the oxLDL-activated c-Jun N-terminal kinase pathway and reduced oxLDL-induced macrophage apoptosis by inhibiting caspase-3 activation and restoring the mitochondrial membrane potential.

CONCLUSIONS

We found that LXA₄ inhibited foam cell formation, oxLDL-induced inflammation, and apoptotic signaling in macrophages. Insufficient levels of the anti-inflammatory pro-resolution molecule LXA₄ were found in rabbit atherosclerotic arteries, which might contribute to preventing inflammation resolution during atherogenesis.

RAGE and TLRs as Key Targets for Antiatherosclerotic Therapy

Receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLRs) are the key factors indicating a danger to the organism. They recognize the microbial origin pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). The primary response induced by PAMPs or DAMPs is inflammation. Excessive stimulation of the innate immune system occurs in arterial wall with the participation of effector cells. Persistent adaptive responses can also cause tissue damage and disease. However, inflammation mediated by the molecules innate responses is an important way in which the adaptive immune system protects us from infection. The specific detection of PAMPs and DAMPs by host receptors drives a cascade of signaling that converges at nuclear factor-κB (NF-κB) and interferon regulatory factors (IRFs) and induces the secretion of proinflammatory cytokines, type I interferon (IFN), and chemokines, which promote direct killing of the pathogen. Therefore, signaling of these receptors' pathways also appear to present new avenue for the modulation of inflammatory responses and to serve as potential novel therapeutic targets for antiatherosclerotic therapy.

tert-Butylhydroperoxide induces apoptosis in RAW264.7 macrophages via a mitochondria-mediated signaling pathway

Macrophage apoptosis occurs throughout all stages of atherosclerosis, mainly induced by oxidized low density lipoproteins (Ox LDLs), leading to the formation of necrotic cores. Nevertheless, the mechanism of macrophage apoptosis induced by Ox LDLs is not yet clearly understood. In this study, a model of RAW264.7 macrophages exposed to an Ox LDL analogue, i.e. tert-butylhydroperoxide (t-BHP), was established. We thoroughly evaluated the viability and apoptosis of RAW264.7 cells treated with t-BHP at different time intervals. t-BHP treatment decreases the viability of RAW264.7 cells in a dose- and time-dependent manner (IC₅₀: 400 μM) and also induces a loss of the mitochondrial membrane potential (MMP) in RAW264.7 cells. Moreover, the activation of Bid, up-regulation of Bcl-2, and down-regulation of Bax, as well as the proteolysis of pro-caspase 3 and cleavage of PARP, were all also observed in t-BHP treated RAW264.7 cells. Finally, we concluded that t-BHP induces the apoptosis of macrophages via a mitochondria-mediated signaling pathway.

Metabolically Activated Adipose Tissue Macrophages Perform Detrimental and Beneficial Functions during Diet-Induced Obesity

During obesity, adipose tissue macrophages (ATMs) adopt a metabolically activated (MMe) phenotype. However, the functions of MMe macrophages are poorly understood. Here, we combine proteomic and functional methods to demonstrate that, in addition to potentiating inflammation, MMe macrophages promote dead adipocyte clearance through lysosomal exocytosis. We identify NADPH oxidase 2 (NOX2) as a driver of the inflammatory and adipocyte-clearing properties of MMe macrophages and show that, compared to wild-type, Nox2^-/- mice exhibit a time-dependent metabolic phenotype during diet-induced obesity. After 8 weeks of high-fat feeding, Nox2^-/- mice exhibit attenuated ATM inflammation and mildly improved glucose tolerance. After 16 weeks of high-fat feeding, Nox2^-/- mice develop severe insulin resistance, hepatosteatosis, and visceral lipoatrophy characterized by dead adipocyte accumulation and defective ATM lysosomal exocytosis, a phenotype reproduced in myeloid cell-specific Nox2^-/- mice. Collectively, our findings suggest that MMe macrophages perform detrimental and beneficial functions whose contribution to metabolic phenotypes during obesity is determined by disease progression.

Endoplasmic Reticulum Stress in Metabolic Disorders

Metabolic disorders have become among the most serious threats to human health, leading to severe chronic diseases such as obesity, type 2 diabetes, and non-alcoholic fatty liver disease, as well as cardiovascular diseases. Interestingly, despite the fact that each of these diseases has different physiological and clinical symptoms, they appear to share certain pathological traits such as intracellular stress and inflammation induced by metabolic disturbance stemmed from over nutrition frequently aggravated by a modern, sedentary life style. These modern ways of living inundate cells and organs with saturating levels of sugar and fat, leading to glycotoxicity and lipotoxicity that induce intracellular stress signaling ranging from oxidative to ER stress response to cope with the metabolic insults (Mukherjee, et al., 2015). In this review, we discuss the roles played by cellular stress and its responses in shaping metabolic disorders. We have summarized here current mechanistic insights explaining the pathogenesis of these disorders. These are followed by a discussion of the latest therapies targeting the stress response pathways.

Oxidized phospholipids are proinflammatory and proatherogenic in hypercholesterolaemic mice

Oxidized phospholipids (OxPL) are ubiquitous, are formed in many inflammatory tissues, including atherosclerotic lesions, and frequently mediate proinflammatory changes 1 . Because OxPL are mostly the products of non-enzymatic lipid peroxidation, mechanisms to specifically neutralize them are unavailable and their roles in vivo are largely unknown. We previously cloned the IgM natural antibody E06, which binds to the phosphocholine headgroup of OxPL, and blocks the uptake of oxidized low-density lipoprotein (OxLDL) by macrophages and inhibits the proinflammatory properties of OxPL2-4. Here, to determine the role of OxPL in vivo in the context of atherogenesis, we generated transgenic mice in the Ldlr-/- background that expressed a single-chain variable fragment of E06 (E06-scFv) using the Apoe promoter. E06-scFv was secreted into the plasma from the liver and macrophages, and achieved sufficient plasma levels to inhibit in vivo macrophage uptake of OxLDL and to prevent OxPL-induced inflammatory signalling. Compared to Ldlr-/- mice, Ldlr -/- E06-scFv mice had 57-28% less atherosclerosis after 4, 7 and even 12 months of 1% high-cholesterol diet. Echocardiographic and histologic evaluation of the aortic valves demonstrated that E06-scFv ameliorated the development of aortic valve gradients and decreased aortic valve calcification. Both cholesterol accumulation and in vivo uptake of OxLDL were decreased in peritoneal macrophages, and both peritoneal and aortic macrophages had a decreased inflammatory phenotype. Serum amyloid A was decreased by 32%, indicating decreased systemic inflammation, and hepatic steatosis and inflammation were also decreased. Finally, the E06-scFv prolonged life as measured over 15 months. Because the E06-scFv lacks the functional effects of an intact antibody other than the ability to bind OxPL and inhibit OxLDL uptake in macrophages, these data support a major proatherogenic role of OxLDL and demonstrate that OxPL are proinflammatory and proatherogenic, which E06 counteracts in vivo. These studies suggest that therapies inactivating OxPL may be beneficial for reducing generalized inflammation, including the progression of atherosclerosis, aortic stenosis and hepatic steatosis.

The journey towards understanding lipoprotein(a) and cardiovascular disease risk: are we there yet?

PURPOSE OF REVIEW

Evidence continues to mount for an important role for elevated plasma concentrations of lipoprotein(a) [Lp(a)] in mediating risk of atherothrombotic and calcific aortic valve diseases. However, there continues to be great uncertainty regarding some basic aspects of Lp(a) biology including its biosynthesis and catabolism, its mechanisms of action in health and disease, and the significance of its isoform size heterogeneity. Moreover, the precise utility of Lp(a) in the clinic remains undefined.

RECENT FINDINGS

The contribution of elevated Lp(a) to cardiovascular risk continues to be more precisely defined by larger studies. In particular, the emerging role of Lp(a) as a potent risk factor for calcific aortic valve disease has received much scrutiny. Mechanistic studies have identified commonalities underlying the impact of Lp(a) on atherosclerosis and aortic valve disease, most notably related to Lp(a)-associated oxidized phospholipids. The mechanisms governing Lp(a) concentrations remain a source of considerable dispute.

SUMMARY

This article highlights some key remaining challenges in understanding Lp(a) actions and clinical significance. Most important in this regard is demonstration of a beneficial effect of lowering Lp(a), a development that is on the horizon as effective Lp(a)-lowering therapies are being tested in the clinic.

CD36 and lipid metabolism in the evolution of atherosclerosis

BACKGROUND

CD36 is a multi-functional class B scavenger receptor, which acts as an important modulator of lipid homeostasis and immune responses.

SOURCES OF DATA

This review uses academic articles.

AREAS OF AGREEMENT

CD36 is closely related to the development and progression of atherosclerosis.

AREAS OF CONTROVERSY

Both persistent up-regulation of CD36 and deficiency of CD36 increase the risk for atherosclerosis. Abnormally up-regulated CD36 promotes inflammation, foam cell formation, endothelial apoptosis, macrophage trapping and thrombosis. However, CD36 deficiency also causes dyslipidemia, subclinical inflammation and metabolic disorders, which are established risk factors for atherosclerosis.

GROWING POINTS

There may be an 'optimal protective window' of CD36 expression.

AREAS TIMELY FOR DEVELOPING RESEARCH

In addition to traditionally modulating protein functions using gene overexpression or deficiency, the modulation of CD36 function at post-translational levels has recently been suggested to be a potential therapeutic strategy.