Effects of electronegative VLDL on endothelium damage in metabolic syndrome

Metabolic Syndrome and Cardiac Vessel Remodeling Associated with Vessel Rarefaction: A Possible Underlying Mechanism May Result from a Poor Angiogenic Response to Altered VEGF Signaling Pathways

BACKGROUND

Elevated mortality rates in patients with metabolic syndrome (MetS) are partly due to adverse remodeling of multiple organs, which may lead to cardiovascular disease, nonalcoholic fatty liver disease, kidney failure, or other conditions. MetS symptoms, such as obesity, hypertension, hyperglycemia, dyslipidemia, associated with insulin and leptin resistance, are recognized as major cardiovascular risk factors that adversely affect the heart.

SUMMARY

Pathological cardiac remodeling is accompanied by endothelial cell dysfunction which may result in diminished coronary flow, dysregulated oxygen demand/supply balance, as well as vessel rarefaction. The reduced number of vessels and delayed or inhibited formation of collaterals after myocardial infarction in MetS heart may be due to unfavorable changes in endothelial cell metabolism but also to altered expression of vascular endothelial growth factor molecules, their receptors, and changes in signal transduction from the cell membrane, which severely affect angiogenesis.

KEY MESSAGES

Given the established role of cardiac vessel endothelial cells in maintaining tissue homeostasis, defining the molecular background underlying vessel dysfunction associated with impaired angiogenesis is of great importance for future therapeutic purposes. Therefore, the aim of this paper was to present current information regarding vascular endothelial growth factor signaling in the myocardium of MetS individuals.

Up-regulated small-conductance calcium-activated potassium currents contribute to atrial arrhythmogenesis in high-fat feeding mice

AIMS

Metabolic syndrome (MetS) is associated with arrhythmias and cardiovascular mortality. Arrhythmogenesis in MetS results from atrial structural and electrical remodelling. The small-conductance Ca2+-activated K+ (SK) currents modulate atrial repolarization and may influence atrial arrhythmogenicity. This study investigated the regulation of SK current perturbed by a high-fat diet (HFD) to mimic MetS.

METHODS AND RESULTS

Thirty mice were divided into two groups that were fed with normal chow (CTL) and HFD for 4 months. Electrocardiography and echocardiography were used to detect cardiac electrical and structure remodelling. Atrial action potential duration (APD) and calcium transient duration (CaTD) were measured by optical mapping of Langendorff-perfused mice hearts. Atrial fibrillation (AF) inducibility and duration were assessed by burst pacing. Whole-cell patch clamp was performed in primarily isolated atrial myocytes for SK current density. The SK current density is higher in atrial myocytes from HFD than in CTL mice (P ≤ 0.037). The RNA and protein expression of SK channels are increased in HFD mice (P ≤ 0.041 and P ≤ 0.011, respectively). Action potential duration is shortened in HFD compared with CTL (P ≤ 0.015). The shortening of the atrial APD in HFD is reversed by the application of 100 nM apamin (P ≤ 0.043). Compared with CTL, CaTD is greater in HFD atria (P ≤ 0.029). Calcium transient decay (Tau) is significantly higher in HFD than in CTL (P = 0.001). Both APD and CaTD alternans thresholds were higher in HFD (P ≤ 0.043), along with higher inducibility and longer duration of AF in HFD (P ≤ 0.023).

CONCLUSION

Up-regulation of apamin-sensitive SK currents plays a partial role in the atrial arrhythmogenicity of HFD mice.

Oxidative Stress, Atherogenic Dyslipidemia, and Cardiovascular Risk

Oxidative stress is the consequence of an overproduction of reactive oxygen species (ROS) that exceeds the antioxidant defense mechanisms. Increased levels of ROS contribute to the development of cardiovascular disorders through oxidative damage to macromolecules, particularly by oxidation of plasma lipoproteins. One of the most prominent features of atherogenic dyslipidemia is plasma accumulation of small dense LDL (sdLDL) particles, characterized by an increased susceptibility to oxidation. Indeed, a considerable and diverse body of evidence from animal models and epidemiological studies was generated supporting oxidative modification of sdLDL particles as the earliest event in atherogenesis. Lipid peroxidation of LDL particles results in the formation of various bioactive species that contribute to the atherosclerotic process through different pathophysiological mechanisms, including foam cell formation, direct detrimental effects, and receptor-mediated activation of pro-inflammatory signaling pathways. In this paper, we will discuss recent data on the pathophysiological role of oxidative stress and atherogenic dyslipidemia and their interplay in the development of atherosclerosis. In addition, a special focus will be placed on the clinical applicability of novel, promising biomarkers of these processes.

A novel regulatory facet for hypertriglyceridemia: The role of microRNAs in the regulation of triglyceride-rich lipoprotein biosynthesis

Atherosclerotic cardiovascular disease (ASCVD) is one of the major leading global causes of death. Genetic and epidemiological studies strongly support the causal association between triacylglycerol-rich lipoproteins (TAGRL) and atherogenesis, even in statin-treated patients. Recent genetic evidence has clarified that variants in several key genes implicated in TAGRL metabolism are strongly linked to the increased ASCVD risk. There are several triacylglycerol-lowering agents; however, new therapeutic options are in development, among which are miRNA-based therapeutic approaches. MicroRNAs (miRNAs) are small non-coding RNAs (18-25 nucleotides) that negatively modulate gene expression through translational repression or degradation of target mRNAs, thereby reducing the levels of functional genes. MiRNAs play a crucial role in the development of hypertriglyceridemia as several miRNAs are dysregulated in both synthesis and clearance of TAGRL particles. MiRNA-based therapies in ASCVD have not yet been applied in human trials but are attractive. This review provides a concise overview of current interventions for hypertriglyceridemia and the development of novel miRNA and siRNA-based drugs. We summarize the miRNAs involved in the regulation of key genes in the TAGRLs synthesis pathway, which has gained attention as a novel target for therapeutic applications in CVD.

Design of Smart Aggregates: Toward Rapid Clinical Diagnosis of Hyperlipidemia in Human Blood

Molecular aggregates with environmental responsive properties are desired for their wide practical applications such as bioprobes. Here, a series of smart near-infrared (NIR) luminogens for hyperlipidemia (HLP) diagnosis is reported. The aggregates of these molecules exhibit a twisted intramolecular charge-transfer effect in aqueous media, but aggregation-induced emission in highly viscous media due to the restriction of the intramolecular motion. These aggregates, which can autonomously respond to different environments via switching the aggregation state without changing their chemical structures are described, as "smart aggregates". Intriguingly, these luminogens demonstrate NIR-II and NIR-III luminescence with ultralarge Stokes shifts (>950 nm). Both in vitro detection and in vivo imaging of HLP can be realized in a mouse model. Linear relationships exist between the emission intensity and multiple pathological parameters in blood samples of HLP patients. Thus, the design of smart aggregate facilitates rapid and accurate detection of HLP and provides a promising attempt in aggregate science.

Spotlight on very-low-density lipoprotein as a driver of cardiometabolic disorders: Implications for disease progression and mechanistic insights

Very-low-density lipoprotein (VLDL) is the only lipoprotein containing apolipoprotein B that is secreted from the liver, where VLDL is assembled from apolipoproteins, cholesterol, and triglycerides. The primary function of VLDL is to transport cholesterol and other lipids to organs and cells for utilization. Apart from its role in normal biologic processes, VLDL is also known to contribute to the development of atherosclerotic cardiovascular disease. Large VLDL particles, which are subclassified according to their size by nuclear magnetic resonance spectrometry, are significantly correlated not only with atherosclerosis, but also with insulin resistance and diabetes incidence. VLDL can also be subclassified according to surface electrical charge by using anion-exchange chromatography. The most electronegative VLDL subclass is highly cytotoxic to endothelial cells and may contribute to coronary heart disease. In addition, electronegative VLDL contributes to the development of atrial remodeling, especially in patients with metabolic syndrome, which is an established risk factor for atrial fibrillation. In this review, we focus on the VLDL subclasses that are associated with apolipoprotein alterations and are involved in cardiometabolic disease. The postprandial enhancement of VLDL’s pathogenicity is a critical medical issue, especially in patients with metabolic syndrome. Therefore, the significance of the postprandial modification of VLDL’s chemical and functional properties is extensively discussed.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

Lipid nutrition: "In silico" studies and undeveloped experiments

This review examines lipids and lipid-binding sites on proteins in relation to cardiovascular disease. Lipid nutrition involves food energy from ingested fatty acids plus fatty acids formed from excess ingested carbohydrate and protein. Non-esterified fatty acids (NEFA) and lipoproteins have many detailed attributes not evident in their names. Recognizing attributes of lipid-protein interactions decreases unexpected outcomes. Details of double bond position and configuration interacting with protein binding sites have unexpected consequences in acyltransferase and cell replication events. Highly unsaturated fatty acids (HUFA) have n-3 and n-6 motifs with documented differences in intensity of destabilizing positive feedback loops amplifying pathophysiology. However, actions of NEFA have been neglected relative to cholesterol, which is co-produced from excess food. Native low-density lipoproteins (LDL) bind to a high-affinity cell surface receptor which poorly recognizes biologically modified LDLs. NEFA increase negative charge of LDL and decrease its processing by "normal" receptors while increasing processing by "scavenger" receptors. A positive feedback loop in the recruitment of monocytes and macrophages amplifies chronic inflammatory pathophysiology. Computer tools combine multiple components in lipid nutrition and predict balance of energy and n-3:n-6 HUFA. The tools help design and execute precise clinical nutrition monitoring that either supports or disproves expectations.

Autoimmune Rheumatic Diseases: An Update on the Role of Atherogenic Electronegative LDL and Potential Therapeutic Strategies

Atherosclerosis has been linked with an increased risk of atherosclerotic cardiovascular disease (ASCVD). Autoimmune rheumatic diseases (AIRDs) are associated with accelerated atherosclerosis and ASCVD. However, the mechanisms underlying the high ASCVD burden in patients with AIRDs cannot be explained only by conventional risk factors despite disease-specific factors and chronic inflammation. Nevertheless, the normal levels of plasma low-density lipoprotein (LDL) cholesterol observed in most patients with AIRDs do not exclude the possibility of increased LDL atherogenicity. By using anion-exchange chromatography, human LDL can be divided into five increasingly electronegative subfractions, L1 to L5, or into electropositive and electronegative counterparts, LDL (+) and LDL (-). Electronegative L5 and LDL (-) have similar chemical compositions and can induce adverse inflammatory reactions in vascular cells. Notably, the percentage of L5 or LDL (-) in total LDL is increased in normolipidemic patients with AIRDs. Electronegative L5 and LDL (-) are not recognized by the normal LDL receptor but instead signal through the lectin-like oxidized LDL receptor 1 (LOX-1) to activate inflammasomes involving interleukin 1β (IL-1β). Here, we describe the detailed mechanisms of AIRD-related ASCVD mediated by L5 or LDL (-) and discuss the potential targeting of LOX-1 or IL-1β signaling as new therapeutic modalities for these diseases.

Electronegative very-low-density lipoprotein induces brain inflammation and cognitive dysfunction in mice

Epidemiologic studies have indicated that dyslipidemia may facilitate the progression of cognitive dysfunction. We previously showed that patients with metabolic syndrome (MetS) had significantly higher plasma levels of electronegative very-low-density lipoprotein (VLDL) than did healthy controls. However, the effects of electronegative-VLDL on the brain and cognitive function remain unclear. In this study, VLDL isolated from healthy volunteers (nVLDL) or patients with MetS (metVLDL) was administered to mice by means of tail vein injection. Cognitive function was assessed by using the Y maze test, and plasma and brain tissues were analyzed. We found that mice injected with metVLDL but not nVLDL exhibited significant hippocampus CA3 neuronal cell loss and cognitive dysfunction. In mice injected with nVLDL, we observed mild glial cell activation in the medial prefrontal cortex (mPFC) and hippocampus CA3. However, in mice injected with metVLDL, plasma and brain TNF-α and Aβ-42 levels and glial cell activation in the mPFC and whole hippocampus were higher than those in control mice. In conclusion, long-term exposure to metVLDL induced levels of TNF-α, Aβ-42, and glial cells in the brain, contributing to the progression of cognitive dysfunction. Our findings suggest that electronegative-VLDL levels may represent a new therapeutic target for cognitive dysfunction.

An Increased Plasma Level of ApoCIII-Rich Electronegative High-Density Lipoprotein May Contribute to Cognitive Impairment in Alzheimer's Disease

High-density lipoprotein (HDL) plays a vital role in lipid metabolism and anti-inflammatory activities; a dysfunctional HDL impairs cholesterol efflux pathways. To understand HDL's role in patients with Alzheimer's disease (AD), we analyzed the chemical properties and function. HDL from AD patients (AD-HDL) was separated into five subfractions, H1-H5, using fast-protein liquid chromatography equipped with an anion-exchange column. Subfraction H5, defined as the most electronegative HDL, was increased 5.5-fold in AD-HDL (23.48 ± 17.83%) in comparison with the control HDL (4.24 ± 3.22%). By liquid chromatography mass spectrometry (LC/MS^E), AD-HDL showed that the level of apolipoprotein (apo)CIII was elevated but sphingosine-1-phosphate (S1P)-associated apoM and anti-oxidative paraoxonase 1 (PON1) were reduced. AD-HDL showed a lower cholesterol efflux capacity that was associated with the post-translational oxidation of apoAI. Exposure of murine macrophage cell line, RAW 264.7, to AD-HDL induced a vibrant expression of ganglioside GM1 in colocalization with apoCIII on lipid rafts alongside a concomitant increase of tumor necrosis factor-α (TNF-α) detectable in the cultured medium. In conclusion, AD-HDL had a higher proportion of H5, an apoCIII-rich electronegative HDL subfraction. The associated increase in pro-inflammatory (apoCIII, TNF-α) components might favor Amyloid β assembly and neural inflammation. A compromised cholesterol efflux capacity of AD-HDL may also contribute to cognitive impairment.

The role of postprandial very-low-density lipoprotein in the development of atrial remodeling in metabolic syndrome

Background

Negatively charged very-low-density lipoprotein (VLDL-χ) in metabolic syndrome (MetS) patients exerts cytotoxic effects on endothelial cells and atrial myocytes. Atrial cardiomyopathy, manifested by atrial remodeling with a dilated diameter, contributes to atrial fibrillation pathogenesis and predicts atrial fibrillation development. The correlation of VLDL-χ with atrial remodeling is unknown. This study investigated the association between VLDL-χ and remodeling of left atrium.

Methods

Consecutively, 87 MetS and 80 non-MetS individuals between 23 and 74 years old (50.6% men) without overt cardiovascular diseases were included in the prospective cohort study. Blood samples were collected while fasting and postprandially (at 0.5, 1, 2, and 4 h after a unified meal). VLDL was isolated by ultracentrifugation; the percentile concentration of VLDL-χ (%) was determined by ultra-performance liquid chromatography. The correlations of left atrium diameter (LAD) with variables including VLDL-χ, LDL-C, HDL-C, triglycerides, glucose, and blood pressure, were analyzed by multiple linear regression models. A hierarchical linear model was conducted to test the independencies of each variable’s correlation with LAD.

Results

The mean LAD was 3.4 ± 0.5 cm in non-MetS subjects and 3.9 ± 0.5 cm in MetS patients (P < 0.01). None of the fasting lipid profiles were associated with LAD. VLDL-χ, BMI, waist circumference, hip circumference, and blood pressure were positively correlated with LAD (all P < 0.05) after adjustment for age and sex. Significant interactions between VLDL-χ and blood pressure, waist circumference, and hip circumference were observed. When adjusted for obesity- and blood pressure-related variables, 2-h postprandial VLDL-χ (mean 1.30 ± 0.61%) showed a positive correlation with LAD in MetS patients. Each 1% VLDL-χ increase was estimated to increase LAD by 0.23 cm.

Conclusions

Postprandial VLDL-χ is associated with atrial remodeling particularly in the MetS group. VLDL-χ is a novel biomarker and may be a therapeutic target for atrial cardiomyopathy in MetS patients.

Trial registration

ISRCTN 69295295. Retrospectively registered 9 June 2020.

Effects of Lipids and Lipoproteins on Mesenchymal Stem Cells Used in Cardiac Tissue Regeneration

Mesenchymal stem cells (MSCs) have two characteristics of interest for this paper: the ability to self-renew, and the potential for multiple-lineage differentiation into various cells. MSCs have been used in cardiac tissue regeneration for over a decade. Adult cardiac tissue regeneration ability is quite low; it cannot repair itself after injury, as the heart cells are replaced by fibroblasts and lose function. It is therefore important to search for a feasible way to repair and restore heart function through stem cell therapy. Stem cells can differentiate and provide a source of progenitor cells for cardiomyocytes, endothelial cells, and supporting cells. Studies have shown that the concentrations of blood lipids and lipoproteins affect cardiovascular diseases, such as atherosclerosis, hypertension, and obesity. Furthermore, the MSC lipid profiles, such as the triglyceride and cholesterol content, have been revealed by lipidomics, as well as their correlation with MSC differentiation. Abnormal blood lipids can cause serious damage to internal organs, especially heart tissue. In the past decade, the accumulated literature has indicated that lipids/lipoproteins affect stem cell behavior and biological functions, including their multiple lineage capability, and in turn affect the outcome of regenerative medicine. This review will focus on the effect of lipids/lipoproteins on MSC cardiac regenerative medicine, as well as the effect of lipid-lowering drugs in promoting cardiomyogenesis-associated MSC differentiation.

Increased APOE glycosylation plays a key role in the atherogenicity of L5 low-density lipoprotein

Low-density lipoprotein (LDL) is heterogeneous, composed of particles with variable atherogenicity. Electronegative L5 LDL exhibits atherogenic properties in vitro and in vivo, and its levels are elevated in patients with increased cardiovascular risk. Apolipoprotein E (APOE) content is increased in L5, but what role APOE plays in L5 function remains unclear. Here, we characterized the contributions of APOE posttranslational modification to L5's atherogenicity. Using two-dimensional electrophoresis and liquid chromatography-mass spectrometry, we studied APOE's posttranslational modification in L5 from human plasma. APOE structures with various glycan residues were predicted. Molecular docking and molecular dynamics simulation were performed to examine the functional changes of APOE resulting from glycosylation. We also examined the effects of L5 deglycosylation on endothelial cell apoptosis. The glycan sequence N-acetylgalactosamine, galactose, and sialic acid was consistently expressed on serine 94, threonine 194, and threonine 289 of APOE in L5 and was predicted to contribute to L5's negative surface charge and hydrophilicity. The electrostatic force between the negatively charged sialic acid-containing glycan residue of APOE and positively charged amino acids at the receptor-binding area suggested that glycosylation interferes with APOE's attraction to receptors, lipid-binding ability, and lipid transportation and metabolism functions. Importantly, L5 containing glycosylated APOE induced apoptosis in cultured endothelial cells through lectin-like oxidized LDL receptor-1 (LOX-1) signaling, and glycosylation removal from L5 attenuated L5-induced apoptosis. APOE glycosylation may contribute to the atherogenicity of L5 and be a useful biomarker for rapidly quantifying L5.

The Pathogenic Role of Very Low Density Lipoprotein on Atrial Remodeling in the Metabolic Syndrome

Atrial fibrillation (AF) is the most common persistent arrhythmia, and can lead to systemic thromboembolism and heart failure. Aging and metabolic syndrome (MetS) are major risks for AF. One of the most important manifestations of MetS is dyslipidemia, but its correlation with AF is ambiguous in clinical observational studies. Although there is a paradoxical relationship between fasting cholesterol and AF incidence, the benefit from lipid lowering therapy in reduction of AF is significant. Here, we reviewed the health burden from AF and MetS, the association between two disease entities, and the metabolism of triglyceride, which is elevated in MetS. We also reviewed scientific evidence for the mechanistic links between very low density lipoproteins (VLDL), which primarily carry circulatory triglyceride, to atrial cardiomyopathy and development of AF. The effects of VLDL to atria suggesting pathogenic to atrial cardiomyopathy and AF include excess lipid accumulation, direct cytotoxicity, abbreviated action potentials, disturbed calcium regulation, delayed conduction velocities, modulated gap junctions, and sarcomere protein derangements. The electrical remodeling and structural changes in concert promote development of atrial cardiomyopathy in MetS and ultimately lead to vulnerability to AF. As VLDL plays a major role in lipid metabolism after meals (rather than fasting state), further human studies that focus on the effects/correlation of postprandial lipids to atrial remodeling are required to determine whether VLDL-targeted therapy can reduce MetS-related AF. On the basis of our scientific evidence, we propose a pivotal role of VLDL in MetS-related atrial cardiomyopathy and vulnerability to AF.

Combined LDL and VLDL Electronegativity Correlates with Coronary Heart Disease Risk in Asymptomatic Individuals

The most electronegative constituents of human plasma LDL (i.e., L5) and VLDL (i.e., V5) are highly atherogenic. We determined whether the combined electronegativity of L5 and V5 (i.e., L5 + V5) plays a role in coronary heart disease (CHD). In 33 asymptomatic individuals (ages 32–64), 10-year hard CHD risk correlated with age (r = 0.42, p = 0.01). However, in age-adjusted analyses, 10-year hard CHD risk correlated with L5 + V5 plasma concentration (r = 0.43, p = 0.01) but not age (p = 0.74). L5 + V5 plasma concentration was significantly greater in the group with high CHD risk (39.4 ± 22.0 mg/dL; n = 17) than in the group with low CHD risk (16.9 ± 14.8 mg/dL; n = 16; p = 0.01). In cultured human aortic endothelial cells, L5 + V5 treatment induced significantly more senescence-associated–β-Gal activity than did equal concentrations of L1 + V1 (n = 4, p < 0.001). To evaluate the in vivo relevance of these findings, we fed ApoE^−/− and wild-type mice with a high-fat diet and found that plasma LDL, VLDL, and LDL + VLDL from ApoE^−/− mice exhibited significantly greater electrophoretic mobility than did wild-type counterparts (n = 6, p < 0.01). The increased electronegativity of LDL and VLDL in ApoE^−/− mice was accompanied by increased aortic lipid accumulation and cellular senescence (n = 6, p < 0.05). Clinical trials are warranted to test the predictive value of L5 + V5 concentration in patients with CHD.

Immunoregulatory effects of very low density lipoprotein from healthy individuals and metabolic syndrome patients on glial cells

Epidemiological studies have reported that elderly patients with metabolic syndrome (MetS) are significantly more likely to develop neuronal degenerative diseases than those without MetS. Our previous study showed that patients with MetS had significantly higher levels of negatively charged very low density lipoproteins (VLDLs) in the plasma than healthy controls. Highly electronegative VLDL is a key risk factor for endothelial dysfunction and atrial fibrillation. However, the impact of negatively charged VLDL in brain immunity remains unclear. In this study, VLDLs were isolated from normal healthy (nVLDL) individuals or patients with MetS (metVLDL). Primary astroglia and microglia mixed cell cultures as well as microglial-enriched cultures were used to test the effects of VLDLs. Microglia/astroglia activation as evidenced by their morphological changes and production of pro-inflammatory factors, such as tumor necrosis factor-α (TNF-α) and prostaglandin E2 (PGE2), were assessed by immunofluorescence staining and ELISA, respectively. Our results showed that metVLDLs mainly act on the microglia, and not the astroglia, with low concentration (0.05-0.5 μg/mL) inducing cell morphological changes and decreased cellular processes in the microglia. However, nVLDL treatment at these concentrations had no effects on microglia and astroglia. Most importantly, TNF-α and PGE2 levels significantly increased in the microglia treated with metVLDL via a dose-dependent manner. Together, our data indicate that metVLDLs can contribute to MetS-associated brain disorders through microglia activation and neuroinflammation.

Very Low-Density Lipoproteins of Metabolic Syndrome Modulates STIM1, Suppresses Store-Operated Calcium Entry, and Deranges Myofilament Proteins in Atrial Myocytes

Individuals with metabolic syndrome (MetS) are at high risk for atrial myopathy and atrial fibrillation. Very low-density lipoproteins (VLDLs) of MetS (MetS-VLDLs) are cytotoxic to atrial myocytes in vivo and in vitro. The calcineurin-nuclear factor of activated T-cells (NFAT) pathway, which is regulated by stromal interaction molecule 1 (STIM1)/ calcium release-activated calcium channel protein 1 (Orai1)-mediated store-operated Ca²⁺ entry (SOCE), is a pivotal mediator of adaptive cardiac hypertrophy. We hypothesized that MetS-VLDLs could affect SOCE and the calcineurin-NFAT pathway. Normal-VLDL and MetS-VLDL samples were isolated from the peripheral blood of healthy volunteers and individuals with MetS. VLDLs were applied to HL-1 atrial myocytes for 18 h and were also injected into wild-type C57BL/6 male mouse tails three times per week for six weeks. After the sarcoplasmic reticulum (SR) Ca²⁺ store was depleted, SOCE was triggered upon reperfusion with 1.8 mM of Ca²⁺. SOCE was attenuated by MetS-VLDLs, along with reduced transcriptional and membranous expression of STIM1 (P = 0.025), and enhanced modification of O-GlcNAcylation on STIM1 protein, while Orai1 was unaltered. The nuclear translocation and activity of calcineurin were both reduced (P < 0.05), along with the alteration of myofilament proteins in atrial tissues. These changes were absent in normal-VLDL-treated cells. Our results demonstrated that MetS-VLDLs suppressed SOCE by modulating STIM1 at the transcriptional, translational, and post-translational levels, resulting in the inhibition of the calcineurin-NFAT pathway, which resulted in the alteration of myofilament protein expression and sarcomere derangement in atrial tissues. These findings may help explain atrial myopathy in MetS. We suggest a therapeutic target on VLDLs to prevent atrial fibrillation, especially for individuals with MetS.

Very-Low-Density Lipoprotein of Metabolic Syndrome Modulates Gap Junctions and Slows Cardiac Conduction

Very-low-density lipoproteins (VLDL) is a hallmark of metabolic syndrome (MetS) and each manifestation of MetS is related to atrial fibrillation (AF) risks. Slowed atrial conduction is a mechanism of AF in MetS. We hypothesized that VLDL can modulate and reduce atrial gap junctions. VLDLs were separated from normal (Normal-VLDL) and MetS (MetS-VLDL) individuals. VLDLs (15 µg/g) and equivalent volumes of saline (CTL) were injected respectively to C57BL/6 mice for 6 weeks. Electrocardiograms demonstrated that MetS-VLDL induced prolongation of P wave (P = 0.041), PR intervals (P = 0.014), QRS duration and QTc interval (both P = 0.003), but Normal-VLDL did not. Optical mapping of perfused hearts confirmed slowed conduction on atria and ventricles of MetS-VLDL mice. Slowed cardiac conduction was associated with significant atrial and ventricular remodeling, along with systolic dysfunction and comparable intra-cardiac fibrosis. MetS-VLDL induced downregulation of Cx40 and Cx43 at transcriptional, translational and tissue levels, and it also enhanced O-GlcNAcylation of Cx40 and Cx43. Protein structure analyses predicted O-GlcNAcylation at serine 18 of Cx40 and Cx43 which may impair stability of gap junctions. In conclusion, MetS-VLDL modulates gap junctions and delays both atrial and ventricular conduction. VLDL may contribute to the pathophysiology of atrial fibrillation and ventricular arrhythmias in MetS.

Association of very Low-density Lipoprotein Cholesterol with All-cause and Cardiovascular Mortality in Peritoneal Dialysis

BACKGROUND/AIMS

Cardiovascular disease (CVD) is the leading cause of death in dialysis patients. Little is known about the relationship between very low-density lipoprotein cholesterol (VLDL-C) and cardiovascular mortality in these patients.

METHODS

A total of 1324 incident patients who began continuous ambulatory peritoneal dialysis (CAPD) therapy at our hospital between January 1, 2005, and September 30, 2014, with baseline serum VLDL-C values were investigated. The associations of the VLDL-C levels with all-cause and cardiovascular mortality were assessed.

RESULTS

The mean age of the cohort was 50.2 ± 14.8 years, and the mean VLDL-C level was 33.6 ± 18.0 mg/dl. One hundred sixty-five (12.5%) patients died during the study period. Multivariable models revealed that the high VLDL-C group was associated with significantly higher all-cause (HR, 2.08, 95% CI, 1.13 to 3.29, P = 0.002) and cardiovascular mortality (HR, 1.92, 95% CI, 1.18 to 4.29, P = 0.013) compared with the low VLDL-C group even after adjusting for various covariates. Using the VLDL-C level as a continuous variable, the hazard ratios (HRs) of all-cause and cardiovascular mortality associated with a 10-mg/dl increase in VLDL-C level were 1.12 (95% CI, 1.02 to 1.26, P = 0.025) and 1.11 (95% CI, 1.02 to 1.22, P = 0.029), respectively. VLDL-C was associated more strongly to all-cause (e.g., Akaike information criteria of 1990.205 vs. 1994.451) and cardiovascular (e.g., Akaike information criteria of 984.146 vs. 985.634) mortality than triglyceride (TG) levels.

CONCLUSIONS

An elevated VLDL-C level is an independent risk factor for all-cause and cardiovascular mortality in peritoneal dialysis (PD) patients.

VLDL and LDL, but not HDL, promote breast cancer cell proliferation, metastasis and angiogenesis

Abnormal lipoprotein profiles are associated with breast cancer progression. However, the mechanisms linking abnormal lipoprotein levels to breast cancer progression, especially metastasis, remain unclear. Herein, we found that L1 and L5 subfractions of LDL and VLDL, but not HDL, enhanced breast cancer cell viability. L1, L5, and VLDL also increased the in vitro tumorigenesis of breast cancer cells in anchorage-independent soft agar assay. In addition, L1, L5, and VLDL, but not HDL, increased the levels of mesenchymal markers Slug, Vimentin, and β-Catenin, and promoted breast cancer cell migration and invasion. L1, L5, and VLDL increased Akt Ser473 phosphorylation and promoted cell migration, which were reversed by the PI3K/Akt inhibitor wortmannin. Further in vitro angiogenesis assay and cytokine array analysis demonstrated that L1, L5, and VLDL enhanced secretion of angiogenic factors in breast cancer cells and promoted angiogenic activity. However, only VLDL reduced anchorage-dependent cell death and promoted lung metastasis in nude mice. In summary, our data suggest that L1, L5, and especially VLDL promote breast cancer progression and metastasis through Akt-induced EMT and angiogenesis, and provide a novel mechanism of how dyslipoproteinemia promotes breast cancer progression.

Double Filtration Plasma Apheresis Shortens Hospital Admission Duration of Patients With Severe Hypertriglyceridemia-Associated Acute Pancreatitis

OBJECTIVES

The treatment effectiveness of double filtration plasma apheresis (DFPP) on severe hypertriglyceridemia-associated acute pancreatitis (STAP) has been questioned because the currently defined serum triglyceride level--1000 mg/dL--is too low for STAP. Given this, we aimed to investigate DFPP effectiveness when we elevated STAP definition to 5000 mg/dL serum triglyceride.

METHODS

We performed nested case-control studies for STAP patients and divided them into groups "with" or "without" DFPP. We further recruited outpatient asymptomatic hypertriglyceridemia patients with STAP history, then divided them into groups "with" or "without" prophylactic DFPP once every 3 to 6 months for 2 years. We observed hospitalization duration and STAP recurrence between patients with and patients without DFPP.

RESULTS

Twelve STAP patients receiving DFPP had a median hospitalization of 5 days, whereas 24 patients without DFPP had 10 days (P = 0.009). Six outpatient referrals with STAP history receiving prophylactic DFPP showed no STAP recurrences whereas 6 without DFPP showed 3 recurrences (P = 0.046). For the 25 patients whose serum triglyceride exceeded 5000 mg/dL, 11 receiving DFPP had median hospitalization of 5 days while 14 without DFPP had 11 days (P = 0.012).

CONCLUSIONS

When applied to serum triglyceride in excess of 5000 mg/dL, DFPP removes oxidized and inflammatory lipoproteins, shortens hospitalization duration, and minimizes STAP recurrence.

VLDL from Metabolic Syndrome Individuals Enhanced Lipid Accumulation in Atria with Association of Susceptibility to Atrial Fibrillation

Metabolic syndrome (MetS) represents a cluster of metabolic derangements. Dyslipidemia is an important factor in MetS and is related to atrial fibrillation (AF). We hypothesized that very low density lipoproteins (VLDL) in MetS (MetS-VLDL) may induce atrial dilatation and vulnerability to AF. VLDL was therefore separated from normal (normal-VLDL) and MetS individuals. Wild type C57BL/6 male mice were divided into control, normal-VLDL (nVLDL), and MetS-VLDL (msVLDL) groups. VLDL (15 µg/g) and equivalent volumes of saline were injected via tail vein three times a week for six consecutive weeks. Cardiac chamber size and function were measured by echocardiography. MetS-VLDL significantly caused left atrial dilation (control, n = 10, 1.64 ± 0.23 mm; nVLDL, n = 7, 1.84 ± 0.13 mm; msVLDL, n = 10, 2.18 ± 0.24 mm; p < 0.0001) at week 6, associated with decreased ejection fraction (control, n = 10, 62.5% ± 7.7%, vs. msVLDL, n = 10, 52.9% ± 9.6%; p < 0.05). Isoproterenol-challenge experiment resulted in AF in young msVLDL mice. Unprovoked AF occurred only in elderly msVLDL mice. Immunohistochemistry showed excess lipid accumulation and apoptosis in msVLDL mice atria. These findings suggest a pivotal role of VLDL in AF pathogenesis for MetS individuals.

Aggravated restenosis and atherogenesis in ApoCIII transgenic mice but lack of protection in ApoCIII knockouts: the effect of authentic triglyceride-rich lipoproteins with and without ApoCIII

AIM

Previously, our group and others have demonstrated a causative relationship between severe hypertriglyceridaemia and atherogenesis in mice. Furthermore, clinical investigations have shown high levels of plasma Apolipoprotein C-III (ApoCIII) associated with hypertriglyceridaemia and even cardiovascular disease. However, it remains unclear whether ApoCIII affects restenosis in vivo, and whether such an effect is mediated by ApoCIII alone, or in combination with hypertriglyceridaemia. We sought to investigate ApoCIII in restenosis and clarify how smooth muscle cells (SMCs) respond to authentic triglyceride-rich lipoproteins (TRLs) with or without ApoCIII (TRLs ± ApoCIII).

METHODS AND RESULTS

ApoCIII transgenic (ApoCIIItg) and knockout (ApoCIII-/-) mice underwent endothelial denudation to model restenosis. Here, ApoCIIItg mice displayed severe hypertriglyceridaemia and increased neointimal formation compared with wild-type (WT) or ApoCIII-/- mice. Furthermore, increased proliferating cell nuclear antigen (PCNA)-positive cells, Mac-3, and vascular cell adhesion protein-1 (VCAM-1) expression, and 4-hydroxynonenal (4HNE) production were found in lesion sites. ApoCIIItg and ApoCIII-/- mice were then crossed to low-density lipoprotein receptor-deficient (Ldlr-/-) mice and fed an atherogenic diet. ApoCIIItg/Ldlr-/- mice had significantly increased atherosclerotic lesions. However, there was no statistical difference in restenosis between ApoCIII-/- and WT mice, and in atherosclerosis between ApoCIII/Ldlr double knockout and Ldlr-/- mice. SMCs were then incubated in vitro with authentic TRLs ± ApoCIII isolated from extreme hypertriglyceridaemia glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1-deficient (GPIHBP1-/-) mice crossed with ApoCIIItg or ApoCIII-/- mice. It was shown that TRLs + ApoCIII promoted SMC proliferation, VCAM-1 expression, and reactive oxygen species (ROS) production, and activated the Akt pathway. Scavenging ROS significantly reduced SMC activation caused by TRLs + ApoCIII.

CONCLUSIONS

Severe hypertriglyceridaemia resulting from ApoCIII overexpression promotes restenosis and atherosclerosis. Furthermore, we demonstrated that TRLs + ApoCIII promotes SMC proliferation.

Atherogenic subfractions of lipoproteins in the treatment of metabolic syndrome by physical activity and diet - the RESOLVE trial

Background

We aimed to comprehensively evaluate lipoprotein profile including lipid particle size following a lifestyle intervention in metabolic syndrome (MetS) volunteers and to assess the associations between lipoprotein subfractions and carotid-intima-media-thickness (CIMT) – a surrogate indicator of atherogenesis.

Methods

100 participants (50–70 years) from the RESOLVE trial, underwent a one-year follow-up beginning with a three-week residential program combining high exercise volume (15-20 h/week), restrictive diet (-500 kcal/day), and education. For baseline references, 40 aged-matched healthy controls were recruited. Independent associations between subfractions of lipoproteins and CIMT were evaluated using a generalized estimating equations model accounting for variation in correlations between repeated measures. The lipoprotein subfractions profile was assessed using Lipoprint® electrophoresis allowing to separate: the very low-density lipoprotein (VLDL) fraction, then the intermediate-density lipoprotein (IDL) C, B and A, the low-density lipoprotein (LDL) with subfractions 1 and 2 as large LDL and subfractions 3 to 7 as small dense LDL (sdLDL), and the high density lipoprotein (HDL) subfractions categorized into large, intermediate, and small HDL. Apolipoproteins A1 and B were also measured.

Results

78 participants completed the program. At baseline, apolipoproteins B/A1, VLDL, sdLDL and small HDL were higher in MetS than in healthy controls; IDL, LDL size, large and intermediate HDL were lower. Despite time-related regains during the follow-up, lipoprotein subfractions traditionally involved in cardiovascular risk, such as sdLDL, improved immediately after the residential program with values closest to those of healthy controls. CIMT improved throughout the lifestyle intervention. Using a generalized estimating equations model, none of the subfractions of lipoproteins nor apolipoproteins were linked to CIMT.

Conclusions

Lipoprotein subfractions traditionally involved in CVR, decreased after the 3-week residential program. During a 12 month follow-up, the time-related regains remained closer to the values of healthy controls than they were at baseline. CIMT improved throughout the lifestyle intervention. However, we failed to demonstrate a link between some lipoprotein subfractions and the atherogenicity directly measured from the wall thickness of arteries (CIMT). Further investigations are required to explore the atherogenicity of lipoprotein subfractions.

Trial registration

NCT00917917

Gender disparity in LDL-induced cardiovascular damage and the protective role of estrogens against electronegative LDL

Background

Increased levels of the most electronegative type of LDL, L5, have been observed in the plasma of patients with metabolic syndrome (MetS) and ST-segment elevation myocardial infarction and can induce endothelial dysfunction. Because men have a higher predisposition to developing coronary artery disease than do premenopausal women, we hypothesized that LDL electronegativity is increased in men and promotes endothelial damage.

Methods

L5 levels were compared between middle-aged men and age-matched, premenopausal women with or without MetS. We further studied the effects of gender-influenced LDL electronegativity on aortic cellular senescence and DNA damage in leptin receptor–deficient (db/db) mice by using senescence-associated–β-galactosidase and γH2AX staining, respectively. We also studied the protective effects of 17β-estradiol and genistein against electronegative LDL–induced senescence in cultured bovine aortic endothelial cells (BAECs).

Results

L5 levels were higher in MetS patients than in healthy subjects (P < 0.001), particularly in men (P = 0.001). LDL isolated from male db/db mice was more electronegative than that from male or female wild-type mice. In addition, LDL from male db/db mice contained abundantly more apolipoprotein CIII and induced more BAEC senescence than did female db/db or wild-type LDL. In the aortas of db/db mice but not wild-type mice, we observed cellular senescence and DNA damage, and the effect was more significant in male than in female db/db mice. Pretreatment with 17β-estradiol or genistein inhibited BAEC senescence induced by male or female db/db LDL and downregulated the expression of lectin-like oxidized LDL receptor-1 and tumor necrosis factor-alpha protein.

Conclusion

The gender dichotomy of LDL-induced cardiovascular damage may underlie the increased propensity to coronary artery disease in men.

Electronegative low-density lipoprotein induces cardiomyocyte apoptosis indirectly through endothelial cell-released chemokines

Cardiomyocyte apoptosis has a critical role in the pathogenesis of heart failure. L5, the most negatively charged subfraction of human plasma low-density lipoprotein (LDL), induces several atherogenic responses in endothelial cells (ECs), including apoptosis. We hypothesized that L5 also contributes to cardiomyocyte apoptosis and studied whether it does so indirectly by inducing the secretion of factors from ECs. We examined apoptosis of rat cardiomyocytes treated with culture-conditioned medium (CCM) of rat ECs that were exposed to L5 or L1 (the least negatively charged LDL subfraction). Apoptosis at early and late time points was twofold greater in cardiomyocytes treated with L5 CCM than in those treated with L1 CCM. The indirect effect of L5 on cardiomyocyte apoptosis was significantly reduced by pretreating ECs with inhibitors of phosphatidylinositol 3-kinase (PI3K) or CXC receptor 2 (CXCR2). Studies with cytokine protein arrays revealed that L5 CCM, but not L1 CCM, contained high levels of ELR(+) CXC chemokines, including lipopolysaccharide-induced chemokine (LIX) and interleukin (IL)-8. The L5-induced release of these chemokines from ECs was abolished by inhibiting the lectin-like oxidized LDL receptor-1 (LOX-1). Addition of recombinant LIX or IL-8 to CCM-free cardiomyocyte cultures increased apoptosis and enhanced production of tumor necrosis factor (TNF)-α and IL-1β by increasing the translocation of NF-κB into the nucleus; these effects were attenuated by inhibiting PI3K and CXCR2. In conclusion, L5 may indirectly induce cardiomyocyte apoptosis by enhancing secretion of ELR(+) CXC chemokines from ECs, which in turn activate CXCR2/PI3K/NF-κB signaling to increase the release of TNF-α and IL-1β.

Aspirin protects human coronary artery endothelial cells against atherogenic electronegative LDL via an epigenetic mechanism: a novel cytoprotective role of aspirin in acute myocardial infarction

AIMS

L5 is the most negatively charged subfraction of human low-density lipoprotein (LDL) and is the only subfraction of LDL capable of inducing apoptosis in cultured vascular endothelial cells (ECs) by inhibiting fibroblast growth factor-2 (FGF2) transcription. We examined whether plasma L5 levels are elevated in patients with ST-segment elevation myocardial infarction (STEMI) and whether aspirin provides epigenetic protection of human coronary artery ECs (HCAECs) exposed to L5.

METHODS AND RESULTS

Plasma L5 levels were compared between patients with STEMI (n = 10) and control subjects with chest pain syndrome but a normal coronary arteriogram (n = 5). L5 was isolated from the plasma of STEMI patients and control subjects, and apoptosis, FGF2 expression, and FGF2 promoter methylation were examined in HCAECs treated with L5 and aspirin. Plasma L5 levels were significantly higher in STEMI patients than in control subjects (P < 0.001). Treatment of HCAECs with L5 resulted in reduced survival and FGF2 expression and increased CpG methylation of the FGF2 promoter. Co-treatment of HCAECs with L5 and a physiologically relevant, low concentration of aspirin (0.2 mM) attenuated the adverse effects of L5 on HCAEC survival, FGF2 expression, and FGF2 promoter methylation. In contrast, high concentrations of aspirin (≥1.0 mM) accentuated the effects of L5.

CONCLUSIONS

Our results show that L5 levels are significantly increased in STEMI patients. Furthermore, L5 impairs HCAEC function through CpG methylation of the FGF2 promoter, which is suppressed in the presence of low-concentration aspirin. Our results provide evidence of a novel mechanism of aspirin in the prevention of MI.