Acidification of the intimal fluid: the perfect storm for atherogenesis

Investigating layer-by-layer chitosan-dextran sulfate-coated mesoporous silica as a pH-sensitive drug delivery system

Mesoporous silica nanoparticles (MSNPs) coated by chitosan (CS) were shown to be a proper candidate as a carrier for drug delivery purposes. However, choosing the suitable drug-containing complexes to be applied on MSNPs-CS is of much greater importance to evaluate the possible candidate for an efficient combination of cell viability, drug release kinetics, and atherosclerosis prevention. In this regard, this study concentrates on the synthesis and assessment of coated MSNPs-CS designed for drug delivery purposes. The MSNPs are coated with polyelectrolyte complexes (PEC) composed of CS and dextran sulfate (MSNPs-CS-DX), serving as a versatile drug carrier with favorable biological characteristics. CS-DX is applied to MSNPs without requiring complex or multi-step synthesis procedures. Rosuvastatin, a cholesterol-lowering medication, is chosen for its therapeutic relevance. Additionally, CS-DX is found to relatively impede the uptake of low-density lipoproteins (LDLs) by macrophages, enhancing their potential therapeutic utility. FTIR pattern, FESEM, and TEM images prove MSNPs-CS-DX formation. DLS measurement demonstrates the average particle size of 110 nm for MSNPs, with the combined thickness of CS and DX layers ranging from 10 to 15 nm. BET test is carried out to evaluate the pore size and porosity of structure, showing outstanding results that cause an entrapment efficiency of 57% for MSNPs-CS-DX. Furthermore, the findings demonstrate the pH sensitivity of MSNPs-CS-DX on drug release kinetics. Notably, the CS-DX layer exhibits a significant enhancement in cell viability of human umbilical vein endothelial cells (HUVEC) by approximately 24% within a 24 h timeframe compared to MSNPs lacking CS-DX.

Lactylation Modification in Cardiometabolic Disorders: Function and Mechanism

Cardiovascular disease (CVD) is recognized as the primary cause of mortality and morbidity on a global scale, and developing a clear treatment is an important tool for improving it. Cardiometabolic disorder (CMD) is a syndrome resulting from the combination of cardiovascular, endocrine, pro-thrombotic, and inflammatory health hazards. Due to their complex pathological mechanisms, there is a lack of effective diagnostic and treatment methods for cardiac metabolic disorders. Lactylation is a type of post-translational modification (PTM) that plays a regulatory role in various cellular physiological processes by inducing changes in the spatial conformation of proteins. Numerous studies have reported that lactylation modification plays a crucial role in post-translational modifications and is closely related to cardiac metabolic diseases. This article discusses the molecular biology of lactylation modifications and outlines the roles and mechanisms of lactylation modifications in cardiometabolic disorders, offering valuable insights for the diagnosis and treatment of such conditions.

A novel assay to measure low-density lipoproteins binding to proteoglycans

BACKGROUND

The binding of low-density lipoprotein (LDL) to proteoglycans (PGs) in the extracellular matrix (ECM) of the arterial intima is a key initial step in the development of atherosclerosis. Although many techniques have been developed to assess this binding, most of the methods are labor-intensive and technically challenging to standardize across research laboratories. Thus, sensitive, and reproducible assay to detect LDL binding to PGs is needed to screen clinical populations for atherosclerosis risk.

OBJECTIVES

The aim of this study was to develop a quantitative, and reproducible assay to evaluate the affinity of LDL towards PGs and to replicate previously published results on LDL-PG binding.

METHODS

Immunofluorescence microscopy was performed to visualize the binding of LDL to PGs using mouse vascular smooth muscle (MOVAS) cells. An in-cell ELISA (ICE) was also developed and optimized to quantitatively measure LDL-PG binding using fixed MOVAS cells cultured in a 96-well format.

RESULTS

We used the ICE assay to show that, despite equal APOB concentrations, LDL isolated from adults with cardiovascular disease bound to PG to a greater extent than LDL isolated from adults without cardiovascular disease (p<0.05).

CONCLUSION

We have developed an LDL-PG binding assay that is capable of detecting differences in PG binding affinities despite equal APOB concentrations. Future work will focus on candidate apolipoproteins that enhance or diminish this interaction.

Oxidative stress biomarker triggered multiplexed tool for auxiliary diagnosis of atherosclerosis

Oxidative stress is integral in the development of atherosclerosis, but knowledge of how oxidative stress affects atherosclerosis remains insufficient. Here, we design a multiplexed diagnostic tool that includes two functions (photoacoustic imaging and urinalysis), for assessing intraplaque and urinary malondialdehyde (MDA), a well-recognized end-product of oxidative stress. Molecular design is conducted to develop the first near-infrared MDA-responsive molecule (MRM). Acid-unlocked ratiometric photoacoustic nanoprobe is designed to report intraplaque MDA, enabling it to reflect plaque burden. Furthermore, MRM is tailored for urinary MDA detection with excellent specificity in a blind study. Moreover, we found a significant difference in urinary MDA between healthy adults and atherosclerotic patients (more than 600 participants). Combining these two functions, such a multiplexed diagnostic tool can dynamically report intraplaque and systemic oxidative stress levels during atherosclerosis progression, pneumonia infection, and drug treatment in atherosclerotic mice, which is promising for the auxiliary diagnosis of atherosclerosis.

Obesity-induced changes in cancer cells and their microenvironment: Mechanisms and therapeutic perspectives to manage dysregulated lipid metabolism

Obesity has been closely related to cancer progression, recurrence, metastasis, and treatment resistance. We aim to review recent progress in the knowledge on the obese macroenvironment and the generated adipose tumor microenvironment (TME) inducing lipid metabolic dysregulation and their influence on carcinogenic processes. Visceral white adipose tissue expansion during obesity exerts systemic or macroenvironmental effects on tumor initiation, growth, and invasion by promoting inflammation, hyperinsulinemia, growth-factor release, and dyslipidemia. The dynamic relationship between cancer and stromal cells of the obese adipose TME is critical for cancer cell survival and proliferation as well. Experimental evidence shows that secreted paracrine signals from cancer cells can induce lipolysis in cancer-associated adipocytes, causing them to release free fatty acids and acquire a fibroblast-like phenotype. Such adipocyte delipidation and phenotypic change is accompanied by an increased secretion of cytokines by cancer-associated adipocytes and tumor-associated macrophages in the TME. Mechanistically, the availability of adipose TME free fatty acids and tumorigenic cytokines concomitant with the activation of angiogenic processes creates an environment that favors a shift in the cancer cells toward an aggressive phenotype associated with increased invasiveness. We conclude that restoring the aberrant metabolic alterations in the host macroenvironment and in adipose TME of obese subjects would be a therapeutic option to prevent cancer development. Several dietary, lipid-based, and oral antidiabetic pharmacological therapies could potentially prevent tumorigenic processes associated with the dysregulated lipid metabolism closely linked to obesity.

Atherosclerosis treatment with nanoagent: potential targets, stimulus signals and drug delivery mechanisms

Cardiovascular disease (CVDs) is the first killer of human health, and it caused up at least 31% of global deaths. Atherosclerosis is one of the main reasons caused CVDs. Oral drug therapy with statins and other lipid-regulating drugs is the conventional treatment strategies for atherosclerosis. However, conventional therapeutic strategies are constrained by low drug utilization and non-target organ injury problems. Micro-nano materials, including particles, liposomes, micelles and bubbles, have been developed as the revolutionized tools for CVDs detection and drug delivery, specifically atherosclerotic targeting treatment. Furthermore, the micro-nano materials also could be designed to intelligently and responsive targeting drug delivering, and then become a promising tool to achieve atherosclerosis precision treatment. This work reviewed the advances in atherosclerosis nanotherapy, including the materials carriers, target sites, responsive model and treatment results. These nanoagents precisely delivery the therapeutic agents to the target atherosclerosis sites, and intelligent and precise release of drugs, which could minimize the potential adverse effects and be more effective in atherosclerosis lesion.

Scavenger receptor-AI targeted theranostic nanoparticles for regression of atherosclerotic plaques via ABCA1 modulation

ATP-binding cassette transporter A1 (ABCA1) plays a crucial role in atherosclerotic formation through mediated cholesterol efflux in macrophage-derived foam cells. In this study, a scavenger receptors AI (SR-AI) targeted theranostic nanoparticles was constructed for atherosclerosis regression via ABCA1 activation in foam cells. ABCA1-upregulator 5242331 and IR780 were encapsulated in PLGA-PEG micelles which were conjugated with SR-AI targeting peptide (PP1) to formulate the nanoparticles (SAU-NPs). Immunostaining revealed that SR-AI was highly expressed both in macrophage foam cells and in atherosclerotic plaque of ApoE^-/- mice. The SAU-NPs have shown more active targeting to plaque lesion with higher stability compared with non-SR-AI targeted nanoparticles. The transformation from macrophage to foam cells was inhibited by SAU-NPs carried 5242331. Cholesterol deposition was effectively reduced in foam cells by SAU-NPs through activating the LXRα-ABCA1/ABCG1/SR-BI pathway. In conclusion, theranostic SAU-NPs which carried ABCA1-upregulator 5242331 exert beneficial effects on atherosclerosis regression via LXRα activation.

Ligand-receptor interaction in the specific targeting of biomimetic peptide nanoparticles to lysophosphatidylcholine

As nanotechnology is applied clinical medicine, nanoparticle-based therapy is emerging as a novel approach for the treatment of atherosclerosis. Ligand-receptor interaction affects the effectiveness of nanoparticle targeting therapy. In this study, the biomimetic peptide (BP-KFFVLK-WYKDGD) ligand specifically targeting the lysophosphatidylcholine (LPC) receptor in atherosclerotic plaques was constructed. The corresponding ligand-receptor interaction under different pH values was investigated by molecular dynamics simulation and experimental measurements. Results show that the interaction force between the peptide and LPC is greater than that of the peptide and human umbilical vein endothelial cell, clearly demonstrating the specific targeting of the peptide ligand to the LPC receptor. The ligand-receptor binding of peptide and LPC dominantly depends on Coulomb and van der Waals interactions. The YKDG amino acids of the peptide are the main fragment that binds to LPC. Compared with neutral environment at pH 7.4, the interaction forces between the peptide and oxidized low-density lipoprotein (oxLDL) decreased by 18.22 % and 45.87 % under acidic environments at pH 6.5 and 5.5, respectively, because of the change in oxLDL secondary structure and the release of LPC from oxLDL. Nevertheless, the peptide still has a strong binding capacity with oxLDL for the treatment of atherosclerosis.

Redox-responsive polyurethane-polyurea nanoparticles targeting to aortic endothelium and atherosclerosis

Aortic endothelial cell dysfunction is an early trigger of atherosclerosis, the major cause of the cardiovascular disease (CVD). Nanomedicines targeting vascular endothelium and lesions hold great promise as therapeutic solutions to vascular disorders. This study investigates the vascular delivery efficacy of polyurethane-polyurea nanocapsules (Puua-NCs) with pH-synchronized shell cationization and redox-triggered release. Fluorescent lipophilic dye DiI was encapsulated into Puua-NCs of variable sizes and concentrations. In vitro cellular uptake studies with human aortic endothelial cells showed that these Puua-NCs were taken up by cells in a dose-dependent manner. In apolipoprotein E-deficient mice fed a Western diet, a model of atherosclerosis, circulating Puua-NCs were stable and accumulated in aortic endothelium and lesions within 24 hours after intravenous administration. Treatment with thiol-reducing and oxidizing reagents disrupted the disulfide bonds on the surface of internalized NCs, triggering disassembly and intracellular cargo release. Ultimately, Puua-NCs are a potential redox-controllable cardiovascular drug delivery system.

Effects of lysosomal low density lipoprotein oxidation by ferritin on macrophage function

We have previously demonstrated that low density lipoprotein (LDL) can be oxidised by iron in the lysosomes of macrophages. Some of the iron content of lysosomes might be delivered through autophagy of ferritin (the main iron-storage protein in the body). We have now investigated the effects of ferritin-mediated LDL oxidation on macrophage function. The addition of ferritin to human THP-1 cells and human monocyte-derived macrophages increased lysosomal lipid peroxidation, as shown by LPO-Foam, a fluorescent probe targetted to lysosomes. Incubating THP-1 cells with ferritin and native LDL or LDL aggregated by sphingomyelinase, to allow their endocytosis and delivery to lysosomes, led to the formation of lysosomal ceroid (an advanced lipid oxidation product), indicative of lysosomal LDL oxidation. Incubating THP-1 cells with ferritin and LDL caused metabolic activation of the cells, as shown by increased extracellular acidification and oxygen consumption measured by a Seahorse analyser. LDL oxidised by ferritin in lysosomes might be released from macrophages when the cells die and lyse and affect neighbouring cells in atherosclerotic lesions. Adding LDL oxidised by ferritin at lysosomal pH (pH 4.5) to macrophages increased their intracellular reactive oxygen species formation, shown using dihydroethidium, and increased apoptosis. Ferritin might therefore contribute to LDL oxidation in the lysosomes of macrophages and have atherogenic effects.

Advances in Glycolysis Metabolism of Atherosclerosis

Glycolysis is an important way for various cells such as vascular wall endothelial cells, smooth muscle cells, macrophages, and other cells to obtain energy. In pathological conditions, it can participate in the process of AS by regulating lipid deposition, calcification, angiogenesis in plaques, etc., together with its metabolite lactic acid. Recent studies have shown that lactate-related lactylation modifications are ubiquitous in the human proteome and are involved in the regulation of various inflammatory diseases. Combined with the distribution and metabolic characteristics of cells in the plaque in the process of AS, glycolysis-lactate-lactylation modification may be a new entry point for targeted intervention in atherosclerosis in the future. Therefore, this article intends to elaborate on the role and mechanism of glycolysis-lactate-lactylation modification in AS, as well as the opportunities and challenges in targeted therapy, hoping to bring some help to relevant scholars in this field. In atherosclerosis, glycolysis, lactate, and lactylation modification as a metabolic sequence affect the functions of macrophages, smooth muscle cells, endothelial cells, lymphocytes, and other cells and interfere with processes such as vascular calcification and intraplaque neovascularization to influence the progression of atherosclerosis.

Calcium-dependent reversible coaggregation activity of C-reactive protein and M-ficolin

C-reactive protein (CRP) and M-ficolin are the pattern recognition proteins of the innate immune system. In this report, a mixture of CRP and M-ficolin reversibly co-aggregated in a calcium-dependent manner. This coaggregation was enhanced at low pH (6.5) or low salt (35 mM NaCl) concentrations. The co-aggregate was dissolved by adding EDTA and reformed by adding calcium. The M-ficolin fibrinogen-like domain (FD1), the ligand-binding domain of M-ficolin, also showed calcium-dependent coaggregation with CRP, indicating that reversible coaggregation is caused by CRP interacting with FD1. Interestingly, adding phosphocholine (PC), the ligand of CRP, to a CRP-FD1 mixture abolished the reversible coaggregation activity. PC also inhibited the interaction between CRP and FD1. These results indicate that CRP retains PC-binding activity in the coaggregation state and that FD1 binds specifically to the PC-binding site on CRP but does not fully occupy the five PC-binding sites on a CRP pentamer as judged by SDS-PAGE analysis of precipitates. Coaggregation analysis using FD1 mutants showed that FD1 also retains ligand-binding activity in the coaggregation state and that coaggregation requires the trimeric form of FD1. It was also found that modifications to the ligand-binding site of FD1 affect coaggregation efficiency. Although the biological functions of the coaggregation activity of CRP and M-ficolin remain unresolved, the co-aggregates may function as bacteria-trapping particles with affinities for ligands of CRP and M-ficolin. In addition, coaggregation may be involved in CRP deposition in the lesions of several arterial diseases, such as atherosclerosis.

Targeting the Microenvironment of Vulnerable Atherosclerotic Plaques: An Emerging Diagnosis and Therapy Strategy for Atherosclerosis

Atherosclerosis is considered one of the primary causes of cardiovascular diseases (CVDs). Unpredictable rupture of the vulnerable atherosclerotic plaques triggers adverse cardiovascular events such as acute myocardial syndrome and even sudden cardiac death. Therefore, assessing the vulnerability of atherosclerotic plaques and early intervention are of significance in reducing CVD mortality. Nanomedicine possesses tremendous advantages in achieving the integration of the diagnosis and therapy of atherosclerotic plaques because of its magnetic, optical, thermal, and catalytic properties. Based on the pathological characteristics of vulnerable plaques, stimuli-responsive nanoplatforms and surface-functionalized nanoagents are designed and have drawn great attention for accomplishing the precise imaging and treatment of vulnerable atherosclerotic plaques due to their superior properties, such as high bioavailability, lesion-targeting specificity, on-demand cargo release, and low off-target damage. Here, the characteristics of vulnerable plaques are generalized, and some targeted strategies for boosting the accuracy of plaque vulnerability evaluation by imaging and the efficacy of plaque stabilization therapy (including antioxidant therapy, macrophage depletion therapy, regulation of lipid metabolism therapy, anti-inflammation therapy, etc.) are systematically summarized. In addition, existing challenges and prospects in this field are discussed, and it is believed to provide new thinking for the diagnosis and treatment of CVDs in the near future.

Different Pathways of Cellular Cholesterol Efflux

Cholesterol efflux is the first and rate-limiting step of reverse cholesterol transport (RCT) from peripheric cells to the liver. The involvement of high-density lipoprotein (HDL) in RCT determines the atheroprotective properties of HDL. Cholesterol efflux from different membrane pools includes both passive and energy-dependent processes. The first type of route consists of cholesterol desorption from the cell membrane into the unstirred layer adjacent to the cell surface and diffusion in the water phase. Moreover, the selective uptake and facilitated diffusion of cholesterol and cholesteryl ester molecules through the hydrophobic tunnel in the scavenger receptor BI molecule does not require energy consumption. The second type of route includes active cholesterol export by the ATP-binding cassette transporters A1 (ABCA1) and G1 (ABCG1). Several cholesterol acceptors specifically bind cholesterol and phospholipid molecules, and cholesterol binding to the albumin molecule, which acts as a shuttle, significantly increases cholesterol movement between acceptors and red blood cells, thus functioning as a sink for cholesterol. Cholesterol and phospholipid molecules effluxed from macrophages by ABCA1 are accepted exclusively by the lipid-free apolipoprotein apoA-I, which is the major protein moiety of HDL, whereas those effluxed by ABCG1 are accepted by HDL. ABCA1- and ABCG1-mediated cholesterol transport, together with cholesterol diffusion, largely determine cholesterol turnover at the physiological level of intracellular cholesterol. However, at cholesterol overload, ABCA1-mediated efflux prevails over other routes. The exchange of apoA-I between lipid-free and lipid-associated states and the synergism of nascent and mature HDL contribute to cholesterol efflux efficiency. Moreover, extracellular cholesterol deposits and microvesicles may be involved in RCT.

pH-Dependent Protonation of Histidine Residues Is Critical for Electrostatic LDL (Low-Density Lipoprotein) Binding to Human Coronary Arteries

BACKGROUND

The initiating step in atherogenesis is the electrostatic binding of LDL (low-density lipoprotein) to proteoglycan glycosaminoglycans in the arterial intima. However, although proteoglycans are widespread throughout the intima of most coronary artery segments, LDL is not evenly distributed, indicating that LDL retention is not merely dependent on the presence of proteoglycans. We aim to identify factors that promote the interaction between LDL and the vessel wall of human coronary arteries.

METHODS

We developed an ex vivo model to investigate binding of human-labeled LDL to human coronary artery sections without the interference of cellular processes.

RESULTS

By staining consecutive sections of human coronary arteries, we found strong staining of sulfated glycosaminoglycans throughout the arterial intima, whereas endogenous LDL deposits were focally distributed. Ex vivo binding of LDL was uniform in all intimal areas with sulfated glycosaminoglycans. However, lowering the pH from 7.4 to 6.5 triggered a 35-fold increase in LDL binding. The pH-dependent binding was abolished by pretreating LDL with diethyl-pyrocarbonate, which blocks the protonation of histidine residues, or cyclohexanedione, which inhibits the positive charge of site B on LDL. Thus, both histidine protonation and site B are required for strong electrostatic LDL binding to the intima.

CONCLUSIONS

This study identifies histidine protonation as an important component for electrostatic LDL binding to human coronary arteries. Our findings show that the local pH will have a profound impact on LDL's affinity for sulfated glycosaminoglycans, which may influence the retention and accumulation pattern of LDL in the arterial vasculature.

Modified Lipoproteins Induce Arterial Wall Inflammation During Atherogenesis

Circulating apolipoprotein B-containing lipoproteins, notably the low-density lipoproteins, enter the inner layer of the arterial wall, the intima, where a fraction of them is retained and modified by proteases, lipases, and oxidizing agents and enzymes. The modified lipoproteins and various modification products, such as fatty acids, ceramides, lysophospholipids, and oxidized lipids induce inflammatory reactions in the macrophages and the covering endothelial cells, initiating an increased leukocyte diapedesis. Lipolysis of the lipoproteins also induces the formation of cholesterol crystals with strong proinflammatory properties. Modified and aggregated lipoproteins, cholesterol crystals, and lipoproteins isolated from human atherosclerotic lesions, all can activate macrophages and thereby induce the secretion of proinflammatory cytokines, chemokines, and enzymes. The extent of lipoprotein retention, modification, and aggregation have been shown to depend largely on differences in the composition of the circulating lipoprotein particles. These properties can be modified by pharmacological means, and thereby provide opportunities for clinical interventions regarding the prevention and treatment of atherosclerotic vascular diseases.

Lipid-Laden Macrophages and Inflammation in Atherosclerosis and Cancer: An Integrative View

Atherosclerotic arterial plaques and malignant solid tumors contain macrophages, which participate in anaerobic metabolism, acidosis, and inflammatory processes inherent in the development of either disease. The tissue-resident macrophage populations originate from precursor cells derived from the yolk sac and from circulating bone marrow-derived monocytes. In the tissues, they differentiate into varying functional phenotypes in response to local microenvironmental stimulation. Broadly categorized, the macrophages are activated to polarize into proinflammatory M1 and anti-inflammatory M2 phenotypes; yet, noticeable plasticity allows them to dynamically shift between several distinct functional subtypes. In atherosclerosis, low-density lipoprotein (LDL)-derived cholesterol accumulates within macrophages as cytoplasmic lipid droplets thereby generating macrophage foam cells, which are involved in all steps of atherosclerosis. The conversion of macrophages into foam cells may suppress the expression of given proinflammatory genes and thereby initiate their transcriptional reprogramming toward an anti-inflammatory phenotype. In this particular sense, foam cell formation can be considered anti-atherogenic. The tumor-associated macrophages (TAMs) may become polarized into anti-tumoral M1 and pro-tumoral M2 phenotypes. Mechanistically, the TAMs can regulate the survival and proliferation of the surrounding cancer cells and participate in various aspects of tumor formation, progression, and metastasis. The TAMs may accumulate lipids, but their type and their specific roles in tumorigenesis are still poorly understood. Here, we discuss how the phenotypic and functional plasticity of macrophages allows their multifunctional response to the distinct microenvironments in developing atherosclerotic lesions and in developing malignant tumors. We also discuss how the inflammatory reactions of the macrophages may influence the development of atherosclerotic plaques and malignant tumors, and highlight the potential therapeutic effects of targeting lipid-laden macrophages in either disease.

Enhanced Anti-Atherosclerotic Efficacy of pH-Responsively Releasable Ganglioside GM3 Delivered by Reconstituted High-Density Lipoprotein

Recently, the atheroprotective role of endogenous GM3 and an atherogenesis-inhibiting effect of exogenous GM3 suggested a possibility of exogenous GM3 being recruited as an anti-atherosclerotic drug. This study seeks to endow exogenous GM3 with atherosclerotic targetability via reconstituted high-density lipoprotein (rHDL), an atherosclerotic targeting drug nanocarrier. Unloaded rHDL, rHDL loaded with exogenous GM3 at a low concentration (GM3_L-rHDL), and rHDL carrying GM3 at a relatively high concentration (GM3_H-rHDL) were prepared and characterized. The inhibitory effect of GM3-rHDL on lipid deposition in macrophages was confirmed, and GM3-rHDL did not affect the survival of red blood cells. In vivo experiments using ApoE^-/- mice fed a high fat diet further confirmed the anti-atherosclerotic efficacy of exogenous GM3 and demonstrated that GM3 packed in HDL nanoparticles (GM3-rHDL) has an enhanced anti-atherosclerotic efficacy and a reduced effective dose of GM3. Then, the macrophage- and atherosclerotic plaque-targeting abilities of GM3-rHD, most likely via the interaction of ApoA-I on GM3-rHDL with its receptors (e.g., SR-B1) on cells, were certified via a microsphere-based method and an aortic fragment-based method, respectively. Moreover, we found that solution acidification enhanced GM3 release from GM3-rHDL nanoparticles, implying the pH-responsive GM3 release when GM3-rHDL enters the acidic atherosclerotic plaques from the neutral blood. The rHDL-mediated atherosclerotic targetability and pH-responsive GM3 release of GM3-rHDL enhanced the anti-atherosclerotic efficacy of exogenous GM3. The development of the GM3-rHDL nanoparticle may help with the application of exogenous GM3 as a clinical drug. Moreover, the data imply that the GM3-rHDL nanoparticle has the potential of being recruited as a drug nanocarrier with atherosclerotic targetability and enhanced anti-atherosclerotic efficacy.

Overfeeding Saturated Fat Increases LDL (Low-Density Lipoprotein) Aggregation Susceptibility While Overfeeding Unsaturated Fat Decreases Proteoglycan-Binding of Lipoproteins

Supplemental Digital Content is available in the text.

Objective:

We recently showed that measurement of the susceptibility of LDL (low-density lipoprotein) to aggregation is an independent predictor of cardiovascular events. We now wished to compare effects of overfeeding different dietary macronutrients on LDL aggregation, proteoglycan-binding of plasma lipoproteins, and on the concentration of oxidized LDL in plasma, 3 in vitro parameters consistent with increased atherogenicity.

Approach and Results:

The participants (36 subjects; age, 48±10 years; body mass index, 30.9±6.2 kg/m²) were randomized to consume an extra 1000 kcal/day of either unsaturated fat, saturated fat, or simple sugars (CARB) for 3 weeks. We measured plasma proatherogenic properties (susceptibility of LDL to aggregation, proteoglycan-binding, oxidized LDL) and concentrations and composition of plasma lipoproteins using nuclear magnetic resonance spectroscopy, and in LDL using liquid chromatography mass spectrometry, before and after the overfeeding diets. LDL aggregation increased in the saturated fat but not the other groups. This change was associated with increased sphingolipid and saturated triacylglycerols in LDL and in plasma and reduction of clusterin on LDL particles. Proteoglycan binding of plasma lipoproteins decreased in the unsaturated fat group relative to the baseline diet. Lipoprotein properties remained unchanged in the CARB group.

Conclusions:

The type of fat during 3 weeks of overfeeding is an important determinant of the characteristics and functional properties of plasma lipoproteins in humans.

Registration:

URL: http://www.clinicaltrials.gov; Unique identifier NCT02133144.

AFM detects the effects of acidic condition on the size and biomechanical properties of native/oxidized low-density lipoprotein

Solution acidification exists under some physiological conditions (e.g. lysosomes in cells) and diseases (e.g. atherosclerosis, tumors, etc.). It is poorly understood whether and how acidification influences the size and biomechanical (stiffness and stickiness) properties of native Low-density lipoprotein (LDL) and its oxidized form (oxLDL) which plays a vital role in atherogenesis and tumorigenesis. Atomic force microscopy (AFM) evaluated that gradient acidification from pH 7.4 to pH 4.4 caused an expanding-first-and-then-shrinking decrease in size and a dramatic decrease in stiffness (but no statistically significant changes in stickiness) of LDL/oxLDL particles by influencing secondary/tertiary structures and lipid release detected by infrared spectral analysis and cholesterol detection, respectively. The smaller and softer characteristics of LDL/oxLDL at acidic conditions versus at the neutral pH partially explains the atherogenic role of acidification. The data may provide important information for a better understanding of LDL/oxLDL and some diseases (e.g. atherosclerosis and tumors).

Construction of a pH/TGase "Dual Key"-Responsive Gold Nano-radiosensitizer with Liver Tumor-Targeting Ability

The method of tumor microenvironment (TME)-responsive aggregation has become a promising approach to enhance treatment effect by improving the accumulation of nanoparticles in tumors. The enzymatic cross-linking strategy has widely attracted attention owing to its good aggregation stability and biocompatibility. However, the enzymes in nontumor tissue can also catalyze the cross-linking reaction and reduce accumulation of nanoparticles in tumor. In this work, a "dual key"-responsive strategy is utilized to construct a transglutaminase (TGase)/pH-responsive radiosensitizer (Au@TAcoGal) with specific aggregation behavior in hepatic tumor cells. Au@TAcoGal can retain its stability in blood circulation (pH 7.4) even in the presence of TGase in plasma. On reaching tumor sites, it can be endocytosed by hepatoma cells by the active targeting of phenylboronic acid (PBA) and aggregated under acidity and overexpression of TGase in cells. Due to its specific accumulation in hepatoma cells, radiotherapy can be operated under a lower dose of X-ray. The results show that the cellular accumulation of Au@TAcoGal increases by 30-70%, and the cell survival rate is less than 25% under X-ray irradiation. The antineoplastic results show that Au@TAcoGal exhibits a higher therapeutic effect, and the tumor inhibition rate can reach 84.21%.

Iron-binding cellular profile of transferrin using label-free Raman hyperspectral imaging and singular value decomposition (SVD)

Serum transferrin (Tf) is the essential iron transport protein in the body. Transferrin is responsible for the sequestration of free iron in serum and the delivery of iron throughout the body and into cells, where iron is released inside a mildly acidified endosome. Altered iron distributions are associated with diseases such as iron-overload, cancer, and cardiovascular disease. The presence of free iron is linked to deleterious redox reactions, inside and outside cells and organelles. As Tf iron release is pH dependent, any changes in intraorganelle and extracellular pH, often associated with disease progression, could inhibit normal iron delivery or accelerate iron release in the wrong compartment. However, imaging approaches to monitor changes in the iron-bound state of Tf are lacking. Recently, Raman spectroscopy has been shown to measure iron-bound forms of Tf in solution, intact cells and tissue samples. Here, a biochemical Raman assay has been developed to identify iron-release from Tf following modification of chemical environment. Quantitative singular value decomposition (SVD) method has been applied to discriminate between iron-bound Tf samples during endocytic trafficking in intact cancer cells subjected to Raman hyperspectral confocal imaging. We demonstrate the strength of the SVD method to monitor pH-induced Tf iron-release using Raman hyperspectral imaging, providing the redox biology field with a novel tool that facilitates subcellular investigation of the iron-binding profile of transferrin in various disease models.

Imaging and Targeting Coronary Artery Inflammation

Significance: Coronary artery disease (CAD) continues to be a leading cause of morbidity and mortality across the world despite significant progress in the prevention, diagnosis, and treatment of atherosclerotic disease. Recent Advances: The focus of the cardiovascular community has shifted toward seeking a better understanding of the inflammatory mechanisms driving residual CAD risk that is not modulated by current therapies. Significant progress has been achieved in revealing both proinflammatory and anti-inflammatory mechanisms, and how shift of the balance in favor of the former can drive the development of disease. Critical Issues: Advances in the noninvasive detection of coronary artery inflammation have been forthcoming. These advances include multiple imaging modalities, with novel applications of computed tomography both with and without positron emission tomography, and experimental ultrasound techniques. These advances will enable better selection of patients for anti-inflammatory treatments and assessment of treatment response. The rapid advancement in pharmaceutical design has enabled the production of specific antibodies against inflammatory pathways of atherosclerosis, with modest success to date. The pursuit of demonstrating the efficacy and safety of novel anti-inflammatory and/or proinflammatory resolution therapies for atherosclerotic CAD has become a major focus. Future Directions: This review seeks to provide an update of the latest evidence of all three of these highly related but disparate areas of inquiry: Our current understanding of the key mechanisms by which inflammation contributes to coronary artery atherosclerosis, the evidence for noninvasive assessment of coronary artery inflammation, and finally, the evidence for targeted therapies to treat coronary inflammation for the reduction of CAD risk. Antioxid. Redox Signal. 34, 1217-1243.

Aggregation Susceptibility of Low-Density Lipoproteins-A Novel Modifiable Biomarker of Cardiovascular Risk

Circulating low-density lipoprotein (LDL) particles enter the arterial intima where they bind to the extracellular matrix and become modified by lipases, proteases, and oxidizing enzymes and agents. The modified LDL particles aggregate and fuse into larger matrix-bound lipid droplets and, upon generation of unesterified cholesterol, cholesterol crystals are also formed. Uptake of the aggregated/fused particles and cholesterol crystals by macrophages and smooth muscle cells induces their inflammatory activation and conversion into foam cells. In this review, we summarize the causes and consequences of LDL aggregation and describe the development and applications of an assay capable of determining the susceptibility of isolated LDL particles to aggregate when exposed to human recombinant sphingomyelinase enzyme ex vivo. Significant person-to-person differences in the aggregation susceptibility of LDL particles were observed, and such individual differences largely depended on particle lipid composition. The presence of aggregation-prone LDL in the circulation predicted future cardiovascular events in patients with atherosclerotic cardiovascular disease. We also discuss means capable of reducing LDL particles' aggregation susceptibility that could potentially inhibit LDL aggregation in the arterial wall. Whether reductions in LDL aggregation susceptibility are associated with attenuated atherogenesis and a reduced risk of atherosclerotic cardiovascular diseases remains to be studied.

Interaction of lipid-free apolipoprotein A-I with cholesterol revealed by molecular modeling

We report the modeling of the interaction of differently self-associated lipid-free apoA-I with cholesterol monomer and tail-to-tail (TT) or face-to-face (FF) cholesterol dimer. Cholesterol dimerization is exploited to reconcile the existing experimental data on cholesterol binding to apoA-I with extremely low critical micelle concentration of cholesterol. Two crystal structures of 1-43 N-truncated apolipoprotein Δ(1-43)A-I tetramer (PDB ID: 1AV1, structure B), 185-243 C-truncated apolipoprotein Δ(185-243)A-I dimer (PDB ID: 3R2P, structure M) were analyzed. Cholesterol monomers bind to multiple binding sites in apoA-I monomer, dimer and tetramer with low, moderate and high energy (-10 to -28 kJ/mol with Schrödinger package), still insufficient to overcome the thermodynamic restriction by cholesterol micellization (-52.8 kJ/mol). The binding sites partially coincide with the putative cholesterol-binding motifs. However, apoA-I monomer and dimer existing in structure B, that contain nonoverlapping and non-interacting pairs of binding sites with high affinity for TT and FF cholesterol dimers, can bind in common 14 cholesterol molecules that correspond to existing values. ApoA-I monomer and dimer in structure M can bind in common 6 cholesterol molecules. The values of respective total energy of cholesterol binding up to 64.5 and 67.0 kJ/mol for both B and M structures exceed the free energy of cholesterol micellization. We hypothesize that cholesterol dimers may simultaneously interact with extracellular monomer and dimer of lipid-free apoA-I, that accumulate at acid pH in atheroma. The thermodynamically allowed apolipoprotein-cholesterol interaction outside the macrophage may represent a new mechanism of cholesterol transport by apoA-I from atheroma, in addition to ABCA1-mediated cholesterol efflux.

Targeting and clearance of senescent foamy macrophages and senescent endothelial cells by antibody-functionalized mesoporous silica nanoparticles for alleviating aorta atherosclerosis

Senescent cells drive atherosclerosis at all stages and contribute to cardiovascular disease. However, the markers in these senescent aortic plaques have not been well studied, creating a huge obstacle in the exploration of a precise and efficient system for atherosclerosis treatment. Recently, CD9 has been found to induce cellular senescence and aggravated atherosclerotic plaque formation in apolipoprotein E knockout (ApoE^-/-) mice. In the present study, this result has been leveraged to develop CD9 antibody-modified, hyaluronic acid-coated mesoporous silica nanoparticles with a hyaluronidase-responsive drug release profile. In invitro models of senescent foamy macrophages and senescent endothelial cells stimulated with oxidized high-density-lipoprotein, the CD9 antibody-modified mesoporous silica nanoparticles exhibit high cellular uptake; reduce the reactive oxygen species level, high-density lipoprotein oxidation, and production of TNF-α and IL-6; and attenuate the senescence process, contributing to improved cell viability. In vivo experiment demonstrated that these nanoparticles can successfully target the senescent lesion areas, deliver the anti-senescence drug rosuvastatin to the senescent atherosclerotic plaques (mainly endothelial cells and macrophages), and alleviate the progression of atherosclerosis in ApoE^-/- mice. By providing deep insight regarding the markers in senescent atherosclerotic plaque and developing a nano-system targeting this lesion area, the study proposes a novel and an accurate therapeutic approach for mitigating atherosclerosis through senescent cell clearance.

The hypoxia-sensor carbonic anhydrase IX affects macrophage metabolism, but is not a suitable biomarker for human cardiovascular disease

Hypoxia is prevalent in atherosclerotic plaques, promoting plaque aggravation and subsequent cardiovascular disease (CVD). Transmembrane protein carbonic anhydrase IX (CAIX) is hypoxia-induced and can be shed into the circulation as soluble CAIX (sCAIX). As plaque macrophages are hypoxic, we hypothesized a role for CAIX in macrophage function, and as biomarker of hypoxic plaque burden and CVD. As tumor patients with probable CVD are treated with CAIX inhibitors, this study will shed light on their safety profile. CAIX co-localized with macrophages (CD68) and hypoxia (pimonidazole), and correlated with lipid core size and pro-inflammatory iNOS+ macrophages in unstable human carotid artery plaques. Although elevated pH and reduced lactate levels in culture medium of CAIX knock-out (CAIXko) macrophages confirmed its role as pH-regulator, only spare respiratory capacity of CAIXko macrophages was reduced. Proliferation, apoptosis, lipid uptake and expression of pro- and anti-inflammatory genes were not altered. Plasma sCAIX levels and plaque-resident CAIX were below the detection threshold in 50 and 90% of asymptomatic and symptomatic cases, respectively, while detectable levels did not associate with primary or secondary events, or intraplaque hemorrhage. Initial findings show that CAIX deficiency interferes with macrophage metabolism. Despite a correlation with inflammatory macrophages, plaque-resident and sCAIX expression levels are too low to serve as biomarkers of future CVD.

Mitochondria orchestrate macrophage effector functions in atherosclerosis

Macrophages are pivotal in the initiation and development of atherosclerotic cardiovascular diseases. Recent studies have reinforced the importance of mitochondria in metabolic and signaling pathways to maintain macrophage effector functions. In this review, we discuss the past and emerging roles of macrophage mitochondria metabolic diversity in atherosclerosis and the potential avenue as biomarker. Beyond metabolic functions, mitochondria are also a signaling platform integrating epigenetic, redox, efferocytic and apoptotic regulations, which are exquisitely linked to their dynamics. Indeed, mitochondria functions depend on their density and shape perpetually controlled by mitochondria fusion/fission and biogenesis/mitophagy balances. Mitochondria can also communicate with other organelles such as the endoplasmic reticulum through mitochondria-associated membrane (MAM) or be secreted for paracrine actions. All these functions are perturbed in macrophages from mouse or human atherosclerotic plaques. A better understanding and integration of how these metabolic and signaling processes are integrated and dictate macrophage effector functions in atherosclerosis may ultimately help the development of novel therapeutic approaches.

Aldose Reductase Inhibitor Engeletin Suppresses Pelvic Inflammatory Disease by Blocking the Phospholipase C/Protein Kinase C-Dependent/NF-κB and MAPK Cascades

Pelvic inflammatory disease (PID) is a common inflammation in the upper reproductive tract in women and may cause serious and costly consequences without effective treatment. Engeletin is a flavanonol glycoside and a naturally derived aldose reductase (AR) inhibitor that is widely distributed in vegetables, fruits, and plant-based foods. The present study investigated the anti-PID activity of engeletin in a mucilage-induced rat model of PID and LPS-stimulated RAW 264.7 macrophages. Engeletin significantly reduced inflammation and ameliorated the typical uterine pathological changes in PID rats. Engeletin also inhibited AR-dependent PLC/PKC/NF-κB and MAPK inflammatory pathways, as indicated by the suppression of the phosphorylation levels of PLC, PKC, p38, ERK, and JNK and the nuclear translocation of NF-κB p65. In vitro studies demonstrated that engeletin significantly inhibited inflammatory mediator expression and enhanced the phagocytic ability of LPS-induced RAW 264.7 macrophages. RNA interference of AR prevented the engeletin-induced inhibition of inflammatory mediators. Engeletin also inhibited AR-dependent PLC/PKC/NF-κB and MAPK inflammatory pathways, which was consistent with the in vivo results. These findings support engeletin as a potential agent for prevention or treatment of PID.

Differential Effect of Extracellular Acidic Environment on IL-1β Released from Human and Mouse Phagocytes

Areas of locally decreased pH are characteristic for many chronic inflammatory diseases such as atherosclerosis and rheumatoid arthritis, acute pathologies such as ischemia reperfusion, and tumor microenvironment. The data on the effects of extracellular acidic pH on inflammation are conflicting with respect to interleukin 1 beta (IL-1β) as one of the most potent proinflammatory cytokines. In this study, we used various mouse- and human-derived cells in order to identify potential species-specific differences in IL-1β secretion pattern in response to extracellular acidification. We found that a short incubation in mild acidic medium caused significant IL-1β release from human macrophages, however, the same effect was not observed in mouse macrophages. Rather, a marked IL-1β suppression was observed when mouse cells were stimulated with a combination of various inflammasome instigators and low pH. Upon activation of cells under acidic conditions, the cytosolic pH was reduced while metabolic activity and the expression of the main inflammasome proteins were not affected by low pH. We show that IL-1β secretion in mouse macrophages is reversible upon restoration of physiological pH. pH sensitivity of NLRP3, NLRC4 and AIM2 inflammasomes appeared to be conferred by the processes upstream of the apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization and most likely contributed by the cell background rather than species-specific amino acid sequences of the sensor proteins.

Denaturation of human plasma high-density lipoproteins by urea studied by apolipoprotein A-I dissociation

We studied the mechanism of HDL denaturation with concomitant apoA-I dissociation with HDL preparations from 48 patients with a wide range of plasma HDL-C and evaluated the contribution of lipid-free apoA-I into cholesterol efflux from macrophage, in particular, mediated by cholesterol transporter ABCA1. We prepared HDL by precipitation of apoB-containing lipoproteins by polyethylene glycol and used the chaotropic agent urea to denature HDL preparations. Apo-I dissociation from urea-treated HDL was assessed by the increase of preβ-band fraction with agarose gel electrophoresis followed by electro transfer and immunodetection and by the increase of ABCA1-mediated efflux of fluorescent analogue BODIPY-Cholesterol from RAW 264.7 macrophages. The HDL denaturation is governed by a single transition to fully dissociated apoA-I and the transition cooperativity decreases with increasing HDL-C. The apoA-I release depends on phospholipid concentration of HDL preparation and HDL compositional and structural heterogeneity and is well described by apolipoprotein partition between aqueous and lipid phases. Dissociated apoA-I determines the increase of ABCA1-mediated efflux of BODIPY-Cholesterol from RAW 264.7 macrophages to patient HDL. The increase in apoA-I dissociation is associated with the increase of ABCA1 gene transcript in peripheral blood mononuclear cells from patients. The low level of plasma HDL particles may be compensated by their increased potency for apoA-I release, thus suggesting apoA-I dissociation as a new HDL functional property.

Acidic extracellular pH promotes accumulation of free cholesterol in human monocyte-derived macrophages via inhibition of ACAT1 activity

BACKGROUND AND AIMS

In focal areas of advanced human atherosclerotic lesions, the intimal fluid is acidic. An acidic medium impairs the ABCA1-mediated cholesterol efflux from macrophages, so tending to increase their content of free cholesterol, which is then available for esterification by the macrophage enzyme ACAT1. Here we investigated whether low extracellular pH would affect the activity of ACAT1.

METHODS

- Human monocyte-derived macrophages were first incubated with acetyl-LDL at neutral and acidic conditions (pH 7.5, 6.5, and 5.5) to generate foam cells, and then the foam cells were incubated with [³H]oleate-BSA complexes, and the formation of [³H]oleate-labeled cholesteryl esters was measured. ACAT1 activity was also measured in cell-free macrophage extracts.

RESULTS

- In acidic media, ACAT1-dependent cholesteryl [³H]oleate generation became compromised in the developing foam cells and their content of free cholesterol increased. In line with this finding, ACAT1 activity in the soluble cell-free fraction derived from macrophage foam cells peaked at pH 7, and gradually decreased under acidic pH with a rapid drop below pH 6.5. Incubation of macrophages under progressively more acidic conditions (until pH 5.5) lowered the cytosolic pH of macrophages (down to pH 6.0). Such intracellular acidification did not affect macrophage gene expression of ACAT1 or the neutral CEH.

CONCLUSIONS

Exposure of human macrophage foam cells to acidic conditions lowers their intracellular pH with simultaneous decrease in ACAT1 activity. This reduces cholesterol esterification and thus leads to accumulation of potentially toxic levels of free cholesterol, a contributing factor to macrophage foam cell death.

T-cell death-associated gene 8 accelerates atherosclerosis by promoting vascular smooth muscle cell proliferation and migration

BACKGROUND AND AIMS

Atherosclerosis is a serious cardiovascular disease, featuring inflammation, abnormal proliferation and migration of vascular smooth muscle cells (VSMCs). During atherosclerosis, inflammation may cause low pH. T-cell death-associated gene 8 (Tdag8) is a proton-sensing receptor, however, the role of Tdag8 in VSMCs remains unknown. This study aimed to investigate the potential effects of Tdag8 in VSMCs during atherosclerosis.

METHODS

We examined the expression of Tdag8 in an atherosclerotic model of high-fat-diet-fed ApoE^-/- mice, while the role and mechanism of Tdag8 in phenotype transformation, proliferation and migration of VSMCs were investigated in a series of in vivo and in vitro experiments.

RESULTS

We first found that Tdag8 expression at the mRNA and protein level was significantly increased in atherosclerotic ApoE^-/- mice. Immunofluorescence staining showed that Tdag8 was primarily distributed in PCNA-positive VSMCs and the phenotype of VSMCs switching from contractile phenotype to synthetic phenotype. Additionally, the protein level of Tdag8 was upregulated in FBS-treated VSMCs. VSMCs proliferation and migration were inhibited by Tdag8 silencing and increased by Tdag8 overexpression. Further mechanistic studies showed that cAMP level was increased in Tdag8-overexpressing VSMCs and ApoE^-/- mice. However, the PKA inhibitor H-89 reversed Tdag8-induced VSMC proliferation and migration.

CONCLUSIONS

The results demonstrate that Tdag8 mediated phenotype transformation, proliferation and migration of VSMCs via the cAMP/PKA signaling pathway, thus partially contributing to atherosclerosis.

Inflammation and its resolution in atherosclerosis: mediators and therapeutic opportunities

Atherosclerosis is a lipid-driven inflammatory disease of the arterial intima in which the balance of pro-inflammatory and inflammation-resolving mechanisms dictates the final clinical outcome. Intimal infiltration and modification of plasma-derived lipoproteins and their uptake mainly by macrophages, with ensuing formation of lipid-filled foam cells, initiate atherosclerotic lesion formation, and deficient efferocytotic removal of apoptotic cells and foam cells sustains lesion progression. Defective efferocytosis, as a sign of inadequate inflammation resolution, leads to accumulation of secondarily necrotic macrophages and foam cells and the formation of an advanced lesion with a necrotic lipid core, indicative of plaque vulnerability. Resolution of inflammation is mediated by specialized pro-resolving lipid mediators derived from omega-3 fatty acids or arachidonic acid and by relevant proteins and signalling gaseous molecules. One of the major effects of inflammation resolution mediators is phenotypic conversion of pro-inflammatory macrophages into macrophages that suppress inflammation and promote healing. In advanced atherosclerotic lesions, the ratio between specialized pro-resolving mediators and pro-inflammatory lipids (in particular leukotrienes) is strikingly low, providing a molecular explanation for the defective inflammation resolution features of these lesions. In this Review, we discuss the mechanisms of the formation of clinically dangerous atherosclerotic lesions and the potential of pro-resolving mediator therapy to inhibit this process.

Acid-sensing ion channels: Linking extracellular acidification with atherosclerosis

Extracellular acidification in atherosclerosis-prone regions of arterial walls is considered pro-atherosclerotic by exerting detrimental effect on macrophages, endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). Acid-sensing ion channels (ASICs), a family of extracellular H⁺ (proton)-gated cation channels, are present extensively in the nervous system and other tissues, implying physiologic as well as pathophysiologic importance. Aberrant activation of ASICs is thought to be associated in EC dysfunction, macrophage phenotypic switch, and VSMC migration and proliferation. Although in vitro evidence acknowledges the contribution of ASIC activation in atherosclerosis, no direct evidence confirms their pro-atherosclerotic roles in vivo. In this review, the effect of extracellular acidity on three major contributors, ECs, macrophages, and VSMCs, is discussed focusing on the potential roles of ASICs in atherosclerotic development and underlying pathology. A more comprehensive understanding of ASICs in these processes may provide promising new therapeutic targets for treatment and prevention of atherosclerotic diseases.

Na+-H+ exchanger 1 determines atherosclerotic lesion acidification and promotes atherogenesis

The pH in atherosclerotic lesions varies between individuals. IgE activates macrophage Na+-H+ exchanger (Nhe1) and induces extracellular acidification and cell apoptosis. Here, we show that the pH-sensitive pHrodo probe localizes the acidic regions in atherosclerotic lesions to macrophages, IgE, and cell apoptosis. In Apoe-/- mice, Nhe1-deficiency or anti-IgE antibody reduces atherosclerosis and blocks lesion acidification. Reduced atherosclerosis in Apoe-/- mice receiving bone marrow from Nhe1- or IgE receptor FcεR1-deficient mice, blunted foam cell formation and signaling in IgE-activated macrophages from Nhe1-deficient mice, immunocomplex formation of Nhe1 and FcεR1 in IgE-activated macrophages, and Nhe1-FcεR1 colocalization in atherosclerotic lesion macrophages support a role of IgE-mediated macrophage Nhe1 activation in atherosclerosis. Intravenous administration of a near-infrared fluorescent pH-sensitive probe LS662, followed by coregistered fluorescent molecular tomography-computed tomography imaging, identifies acidic regions in atherosclerotic lesions in live mice, ushering a non-invasive and radiation-free imaging approach to monitor atherosclerotic lesions in live subjects.

Suppression of Mouse AApoAII Amyloidosis Progression by Daily Supplementation with Oxidative Stress Inhibitors

Amyloidosis is a group of diseases characterized by protein misfolding and aggregation to form amyloid fibrils and subsequent deposition within various tissues. Previous studies have indicated that amyloidosis is often associated with oxidative stress. However, it is not clear whether oxidative stress is involved in the progression of amyloidosis. We administered the oxidative stress inhibitors tempol and apocynin via drinking water to the R1.P1-Apoa2^c mouse strain induced to develop mouse apolipoprotein A-II (AApoAII) amyloidosis and found that treatment with oxidative stress inhibitors led to reduction in AApoAII amyloidosis progression compared to an untreated group after 12 weeks, especially in the skin, stomach, and liver. There was no effect on ApoA-II plasma levels or expression of Apoa2 mRNA. Detection of the lipid peroxidation markers 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA) revealed that the antioxidative effects of the treatments were most obvious in the skin, stomach, and liver, which contained higher levels of basal oxidative stress. Moreover, the unfolded protein response was reduced in the liver and was associated with a decrease in oxidative stress and amyloid deposition. These results suggest that antioxidants can suppress the progression of AApoAII amyloid deposition in the improved microenvironment of tissues and that the effect may be related to the levels of oxidative stress in local tissues. This finding provides insights for antioxidative stress treatment strategies for amyloidosis.

Atherosclerosis Treatment with Stimuli-Responsive Nanoagents: Recent Advances and Future Perspectives

Atherosclerosis is the root of approximately one-third of global mortalities. Nanotechnology exhibits splendid prospects to combat atherosclerosis at the molecular level by engineering smart nanoagents with versatile functionalizations. Significant advances in nanoengineering enable nanoagents to autonomously navigate in the bloodstream, escape from biological barriers, and assemble with their nanocohort at the targeted lesion. The assembly of nanoagents with endogenous and exogenous stimuli breaks down their shells, facilitates intracellular delivery, releases their cargo to kill the corrupt cells, and gives imaging reports. All these improvements pave the way toward personalized medicine for atherosclerosis. This review systematically summarizes the recent advances in stimuli-responsive nanoagents for atherosclerosis management and its progress in clinical trials.

Pro-metastatic functions of lipoproteins and extracellular vesicles in the acidic tumor microenvironment

Although the overall mortality in cancer is steadily decreasing, major groups of patients still respond poorly to available treatments. The key clinical challenge discussed here relates to the inherent capacity of cancer cells to metabolically adapt to hypoxic and acidic stress, resulting in treatment resistance and a pro-metastatic behavior. Hence, a detailed understanding of stress adaptive responses is critical for the design of more rational therapeutic strategies for cancer. We will focus on the emerging role of extracellular vesicles (EVs) and lipoprotein particles in cancer cell metabolic stress adaptation and how these pathways may constitute potential Achilles' heels of the cancer cell machinery and alternative treatment targets of metastasis. In this context, common extracellular lipid uptake mechanisms, involving specific cell-surface receptors and endocytic pathways, may operate during remodeling of acidic atherosclerotic plaques as well as the tumor microenvironment. The role of endocytosis in regulating the cellular response to hypoxic and acidic stress through spatial coordination of receptor proteins may be exploited for therapeutic purposes. As a consequence, molecular mechanisms of endocytosis have attracted increasing attention as potential targets for tumor specific delivery of therapeutic substances, such as antibody-drug conjugates. The identification of internalizing surface proteins specific to the acidic tumor niche remains an unmet need of high clinical relevance. Among the currently explored, acidosis-related, internalizing target proteins, we will focus on the cell-surface proteoglycan carbonic anhydrase 9.

The role of Ca2+ in acid-sensing ion channel 1a-mediated chondrocyte pyroptosis in rat adjuvant arthritis

Rheumatoid arthritis is an autoimmune disease with a poor prognosis. Pyroptosis is a type of proinflammatory programmed cell death that is characterised by the activation of caspase-1 and secretion of the proinflammatory cytokines interleukin (IL)-1β/18. Previous reports have shown that pyroptosis is closely related to the development of some autoimmune diseases, such as rheumatoid arthritis. The decrease in the pH of joint fluid is a main pathogenic feature of RA and leads to excessive apoptosis in chondrocytes. Acid-sensitive ion channels (ASICs) are extracellular H⁺-activated cation channels that mainly influence Na⁺ and Ca²⁺ permeability. In this study, we investigated the role of Ca²⁺ in acid-sensing ion channel 1a-mediated chondrocyte pyroptosis in an adjuvant arthritis rat model. The expression of apoptosis-associated speck-like protein, NLRP3, caspase-1, ASIC 1a, IL-1β and IL-18 was upregulated in the joints of rats compared with that in normal rats, but the expression of Col2a in cartilage was decreased. However, these changes were reversed by amiloride, which is an inhibitor of ASIC1a. Extracellular acidosis significantly increased the expression of ASIC1a, IL-1β, IL-18, ASC, NLRP3 and caspase-1 and promoted the release of lactate dehydrogenase. Interestingly, Psalmotoxin-1 (Pctx-1) and BAPTA-AM inhibited these effects. These results indicate that ASIC1a mediates pyroptosis in chondrocytes from AA rats. The underlying mechanism may be associated with the ability of ASIC1a to promote [Ca²⁺]_i and upregulate the expression of the NLRP3 inflammasome.

A role for proteoglycans in vascular disease

The content of proteoglycans (PGs) is low in the extracellular matrix (ECM) of vascular tissue, but increases dramatically in all phases of vascular disease. Early studies demonstrated that glycosaminoglycans (GAGs) including chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) and heparan sulfate (HS) accumulate in vascular lesions in both humans and in animal models in areas of the vasculature that are susceptible to disease initiation (such as at branch points) and are frequently coincident with lipid deposits. Later studies showed the GAGs were covalently attached to specific types of core proteins that accumulate in vascular lesions. These molecules include versican (CSPG), biglycan and decorin (DS/CSPGs), lumican and fibromodulin (KSPGs) and perlecan (HSPG), although other types of PGs are present, but in lesser quantities. While the overall molecular design of these macromolecules is similar, there is tremendous structural diversity among the different PG families creating multiple forms that have selective roles in critical events that form the basis of vascular disease. PGs interact with a variety of different molecules involved in disease pathogenesis. For example, PGs bind and trap serum components that accumulate in vascular lesions such as lipoproteins, amyloid, calcium, and clotting factors. PGs interact with other ECM components and regulate, in part, ECM assembly and turnover. PGs interact with cells within the lesion and alter the phenotypes of both resident cells and cells that invade the lesion from the circulation. A number of therapeutic strategies have been developed to target specific PGs involved in key pathways that promote vascular disease. This review will provide a historical perspective of this field of research and then highlight some of the evidence that defines the involvement of PGs and their roles in the pathogenesis of vascular disease.

ApoB-100 Lipoprotein Complex Formation with Intima Proteoglycans as a Cause of Atherosclerosis and Its Possible Ex Vivo Evaluation as a Disease Biomarker

Experimental and clinical data indicate that the initiation and progress of atherosclerosis and its clinical manifestations are first caused by circulating apoB-100 lipoproteins that enter and are retained in the arterial intima. Extracellular sulfated proteoglycans (PGs) of the intima are the retention agents. The PGs also initiate physical and biochemical lipoprotein degradation with the production of bioactive, lipid products that trigger an inflammatory response that leads to atherosclerosis. There are many simple methods for measuring abnormalities of circulating lipoproteins and their relation to atherosclerotic cardiovascular disease (ACVD). However, limited research aims to evaluate procedures that could report quantitatively about the contribution of the interaction of apoB-100 lipoprotein-arterial intima PGs to clinical manifestation of ACVD. In the present review we discuss observations indicating that simple ex vivo evaluation of the affinity of apoB-100 lipoproteins for arterial PGs and glycosaminoglycans (GAGs) can give an indication of its association with clinical manifestations of atherosclerosis. In addition, we discuss molecular and cellular aspects of the apoB-100 lipoproteins association with arterial PGs that are related to atherogenesis and that support the experimental framework behind the current “Response-to-Retention” hypothesis of atherosclerosis.

Functional role of extracellular vesicles and lipoproteins in the tumour microenvironment

Cancer can be regarded as an invasive organ that exhibits unique plasticity provided by coordinated, cancer cell-stromal cell communication in the tumour microenvironment. Typical stress factors in the tumour niche, such as hypoxia and acidosis, are major drivers and modulators of these events. Recent findings reveal an important role of extracellular vesicles and lipoproteins in cancer cell adaption to exogenous stress. Adaptive mechanisms include stimulation of angiogenesis and increased metastasis. Here, we will discuss the similarities and distinct features of these endogenous nanoparticles and their roles as signalosomes and nutrient sources in cancer. We will focus on the accumulating evidence for a central role of cell-surface heparan sulphate proteoglycans in the uptake of extracellular vesicles and lipoproteins.This article is part of the discussion meeting issue 'Extracellular vesicles and the tumour microenvironment'.

Whole-Transcriptome Sequencing: a Powerful Tool for Vascular Tissue Engineering and Endothelial Mechanobiology

Among applicable high-throughput techniques in cardiovascular biology, whole-transcriptome sequencing is of particular use. By utilizing RNA that is isolated from virtually all cells and tissues, the entire transcriptome can be evaluated. In comparison with other high-throughput approaches, RNA sequencing is characterized by a relatively low-cost and large data output, which permits a comprehensive analysis of spatiotemporal variation in the gene expression profile. Both shear stress and cyclic strain exert hemodynamic force upon the arterial endothelium and are considered to be crucial determinants of endothelial physiology. Laminar blood flow results in a high shear stress that promotes atheroresistant endothelial phenotype, while a turbulent, oscillatory flow yields a pathologically low shear stress that disturbs endothelial homeostasis, making respective arterial segments prone to atherosclerosis. Severe atherosclerosis significantly impairs blood supply to the organs and frequently requires bypass surgery or an arterial replacement surgery that requires tissue-engineered vascular grafts. To provide insight into patterns of gene expression in endothelial cells in native or bioartificial arteries under different biomechanical conditions, this article discusses applications of whole-transcriptome sequencing in endothelial mechanobiology and vascular tissue engineering.

Coordinate effects of P2X7 and extracellular acidification in microglial cells

Extracellular adenosine 5′-triphosphate (ATP) is a damage-associated molecular pattern and contributes to inflammation associated diseases including cancer. Extracellular acidosis is a novel danger signal in the inflammatory sites, where it can modulate inflammation, immunity and tumor growth. Extracellular acidification was shown to inhibit P2X7-mediated channel currents, while it remains unknown how acidification and P2X7 together affect cellular responses. Here, we treated BV-2 microglial cells with ATP in a short period (<15 min) or a sustained acidified condition. For short acidification we compared the actions of neutralized ATP and acidic ATP in a condition with pH buffering. For sustained acidification, we treated cells with neutralized ATP in acidic medium or acidic ATP in medium without pH buffering. In the short acidified condition, neutralized ATP induced higher responses than acidic ATP to increase intracellular calcium and reactive oxygen species, decrease intracellular potassium and induce cell death. In contrast, these cellular responses and mitochondrial fission caused by neutralized ATP were enhanced by pH 6.0 and pH 4.5 media. P2X7 activation can also rapidly block mitochondrial ATP turnover and respiration capacity, both of which were mimicked by nigericin and enhanced by acidity. Taken together P2X7-mediated ionic fluxes and reactive oxygen species production are attenuated under short acidification, while sustained acidification itself can induce mitochondrial toxicity which deteriorates the mitochondrial function under P2X7 activation.

Methionine oxidized apolipoprotein A-I at the crossroads of HDL biogenesis and amyloid formation

Apolipoprotein A-I (apoA-I) shares with other exchangeable apolipoproteins a high level of structural plasticity. In the lipid-free state, the apolipoprotein amphipathic α-helices interact intra- and intermolecularly, providing structural stabilization by self-association. We have reported that lipid-free apoA-I becomes amyloidogenic upon physiologically relevant (myeloperoxidase-mediated) Met oxidation. In this study, we established that Met oxidation promotes amyloidogenesis by reducing the stability of apoA-I monomers and irreversibly disrupting self-association. The oxidized apoA-I monomers also exhibited increased cellular cholesterol release capacity and stronger association with macrophages, compared to nonoxidized apoA-I. Of physiologic relevance, preformed oxidized apoA-I amyloid fibrils induced amyloid formation in nonoxidized apoA-I. This process was enhanced when self-association of nonoxidized apoA-I was disrupted by thermal treatment. Solid state NMR analysis revealed that aggregates formed by seeded nonoxidized apoA-I were structurally similar to those formed by the oxidized protein, featuring a β-structure-rich amyloid fold alongside α-helices retained from the native state. In atherosclerotic lesions, the conditions that promote apoA-I amyloid formation are readily available: myeloperoxidase, active oxygen species, low pH, and high concentration of lipid-free apoA-I. Our results suggest that even partial Met oxidation of apoA-I can nucleate amyloidogenesis, thus sequestering and inactivating otherwise antiatherogenic and HDL-forming apoA-I.-Witkowski, A., Chan, G. K. L., Boatz, J. C., Li, N. J., Inoue, A. P., Wong, J. C., van der Wel, P. C. A., Cavigiolio, G. Methionine oxidized apolipoprotein A-I at the crossroads of HDL biogenesis and amyloid formation.