Pharmacotherapy of coronary atherosclerosis

TREML4 Promotes Inflammatory Programs in Human and Murine Macrophages and Alters Atherosclerosis Lesion Composition in the Apolipoprotein E Deficient Mouse

The Triggering Receptor Expressed on Myeloid cells-like 4 (TREML4) is a member of the TREM receptor family, known modulators of inflammatory responses. We have previously found that TREML4 expression positively correlates with human coronary arterial calcification (CAC). However, the role of TREML4 in the pathogenesis of cardiovascular disease remains incompletely defined. Since macrophages play a key role in inflammatory conditions, we investigated if activated macrophages selectively expressed TREML4 and found that carriage of either one of the eQTL SNP's previously associated with increased TREML4 expression conferred higher expression in human inflammatory macrophages (M1) compared to alternatively activated macrophages (M2). Furthermore, we found that TREML4 expression in human M1 dysregulated several inflammatory pathways related to leukocyte activation, apoptosis and extracellular matrix degradation. Similarly, murine M1 expressed substantial levels of Treml4, as did oxLDL treated macrophages. Transcriptome analysis confirmed that murine Treml4 controls the expression of genes related to inflammation and lipid regulation pathways, suggesting a possible role in atherosclerosis. Analysis of Apoe-/-/Treml4-/- mice showed reduced plaque burden and lesion complexity as indicated by decreased stage scores, macrophage content and collagen deposition. Finally, transcriptome analysis of oxLDL-loaded murine macrophages showed that Treml4 represses a specific set of genes related to carbohydrate, ion and amino acid membrane transport. Metabolomic analysis confirmed that Treml4 deficiency may promote a beneficial relationship between iron homeostasis and glucose metabolism. Together, our results suggest that Treml4 plays a role in the development of cardiovascular disease, as indicated by Treml4-dependent dysregulation of macrophage inflammatory pathways, macrophage metabolism and promotion of vulnerability features in advanced lesions.

Long non‑coding RNA MALAT1 regulates cholesterol accumulation in ox‑LDL‑induced macrophages via the microRNA‑17‑5p/ABCA1 axis

Atherosclerosis (AS), a major cause of cardiovascular disease, has developed into a serious challenge to the health system. The long non-coding RNA (lncRNA) metastasis associated lung adenocarcinoma transcript 1 (MALAT1) is associated with the pathogenesis of AS. However, whether MALAT1 can affect cholesterol accumulation in macrophages during AS progression, and the potential molecular mechanism involved in this progression have not been elucidated. In the present study, the mRNA expression level of MALAT1 was measured using reverse transcription-quantitative PCR (RT-qPCR) and the protein expression level was detected via western blot analysis. Oil Red O staining was used for detecting lipid accumulation in macrophages. Bioinformatics, dual-luciferase reporter and RT-qPCR assays were used to investigate the relationship between MALAT1 and the microRNA (miR)-17-5p/ATP-binding cassette transporter A1 (ABCA1) axis. The present results suggested that the MALAT1 expression level was significantly decreased in patients with AS and in oxidized low-density lipoprotein (ox-LDL)-stimulated macrophages. Knockdown of MALAT1 increased ox-LDL uptake, lipid accumulation and the total cholesterol (T-CHO) level in ox-LDL-induced macrophages. In addition, MALAT1 inhibition significantly decreased the mRNA and protein expression levels of scavenger receptor (SR) class B member 1, apolipoprotein E (ApoE) and ABCA1. However, MALAT1 increased the expression level of SR class A. Subsequently, the present study investigated whether MALAT1 could target miR-17-5p to regulate the expression level of ABCA1, which is involved in cholesterol efflux from macrophages. The present results suggested that inhibition of miR-17-5p reversed the effects of MALAT1 knockdown on T-CHO content, and protein expression levels of ApoE and ABCA1 in ox-LDL-stimulated macrophages. In summary, knockdown of MALAT1 may promote cholesterol accumulation by regulating the miR-17-5p/ABCA1 axis in ox-LDL-induced THP-1 macrophages.

Bone-targeted delivery of simvastatin-loaded PEG-PLGA micelles conjugated with tetracycline for osteoporosis treatment

This study aimed to investigate the improved therapeutic efficacy and pharmacokinetic profiles of simvastatin (SIM) with imparted bone targeting potential using tetracycline-mediated PEG-PLGA (TC-PEG-PLGA) micelles in osteoporotic rats. The SIM-loaded TC-PEG-PLGA (TC-PEG-PLGA/SIM) micelles were evaluated for particle size, morphology, stability, loading efficiency, cell viability, bone mineral binding ability in vitro, mineralization, pharmacokinetics, and pharmacodynamics. TC-PEG-PLGA conjugates were successfully and could self-assembly form micelles in aqueous medium with a 19.4 μg/mL critical micelle concentration. Then, TC-PEG-PLGA/SIM micelles were prepared with solvent diffusion method, and the obtained micelles (56.21 ± 7.39 nm average size; 81.8 ± 3.1% encapsulation efficiency; and 7.56 ± 0.27% drug loading) led to the prolonged release of SIM from micelles. Cellular uptake test indicated that TC had no effects on micellar internalization and micellar internalization was mainly involved with clathrin-mediated endocytic pathway. In vivo pharmacokinetic results indicated that TC-PEG-PLGA/SIM micelles exhibited a significantly prolonged time in systemic circulation and were preferentially accumulated in bone tissue. TC-PEG-PLGA/SIM micelles showed better therapeutic effects, as reflected by the improved bone mineral density, bone mineral content, and bone mechanical strength. Overall, these results suggested that TC-PEG-PLGA/SIM micelles provide several advantages, including prolonged systemic circulation, enhanced bone tissue distribution, and improved therapeutic outcomes in osteoporotic rats.

Assessment of vulnerable and unstable carotid atherosclerotic plaques on endarterectomy specimens

The types of lesion instability responsible for the majority of acute coronary events frequently include plaque disruption and plaque erosion with superimposed thrombosis. The term 'vulnerable plaque is used to describe atherosclerotic (ATS) plaques that are particularly prone to rupture and susceptible to thrombus formation, such as the thin-cap fibroatheroma (TCFA). The aim of the present study was to assess the morphological and histological differences between plaques that are unstable and those that are vulnerable to instability. Carotid artery endarterectomy specimens were obtained from 26 patients with carotid artery stenosis, consisting of 20 men and 6 women (age range, 35-80 years). Histological and morphometric methods were used to visualize and characterize the ATS plaques. Among the 26 carotid ATS plaques, 23% were stable, 23% were unstable and 54% were vulnerable. With regard to morphometric characteristics, the following mean values were obtained for the TCFA and unstable plaques, respectively: Fibrous cap thickness, 21.91 and 11.66 µM; proportion of necrotic core area in the total plaque area, 25.90 and 22.03%; and the proportion of inflammatory area in the total plaque area, 8.41 and 3.04%. No plaque calcification was observed in any of them. Since ATS coronary artery disease is considerably widespread and fatal, it is crucial to further study ATS lesions to obtain an improved understanding of the nature of vulnerable and unstable plaques. The methods used to detect plaque size, necrotic core area and fibrous cap thickness are considered to be particularly useful for identifying vulnerable and unstable plaques.

Poly(ADP-ribose) polymerase 1 (PARP1) in atherosclerosis: from molecular mechanisms to therapeutic implications

Poly(ADP-ribosyl)ation reactions, carried out by poly(ADP-ribose) polymerases (PARPs/ARTDs), are reversible posttranslational modifications impacting on numerous cellular processes (e.g., DNA repair, transcription, metabolism, or immune functions). PARP1 (EC 2.4.2.30), the founding member of PARPs, is particularly important for drug development for its role in DNA repair, cell death, and transcription of proinflammatory genes. Recent studies have established a novel concept that PARP1 is critically involved in the formation and destabilization of atherosclerotic plaques in experimental animal models and in humans. Reduction of PARP1 activity by pharmacological or molecular approaches attenuates atherosclerotic plaque development and enhances plaque stability as well as promotes the regression of pre-established atherosclerotic plaques. Mechanistically, PARP1 inhibition significantly reduces monocyte differentiation, macrophage recruitment, Sirtuin 1 (SIRT1) inactivation, endothelial dysfunction, neointima formation, foam cell death, and inflammatory responses within plaques, all of which are central to the pathogenesis of atherosclerosis. This article presents an overview of the multiple roles and underlying mechanisms of PARP1 activation (poly(ADP-ribose) accumulation) in atherosclerosis and emphasizes the therapeutic potential of PARP1 inhibition in preventing or reversing atherosclerosis and its cardiovascular clinical sequalae.

(S)-[6]-Gingerol inhibits TGF-β-stimulated biglycan synthesis but not glycosaminoglycan hyperelongation in human vascular smooth muscle cells

Objectives

(S)-[6]-Gingerol is under investigation for a variety of therapeutic uses. Transforming growth factor (TGF)-β stimulates proteoglycan synthesis, leading to increased binding of low-density lipoproteins, which is the initiating step in atherosclerosis. We evaluated the effects of (S)-[6]-gingerol on these TGF-β-mediated proteoglycan changes to explore its potential as an anti-atherosclerotic agent.

Methods

Purified (S)-[6]-gingerol was assessed for its effects on proteoglycan synthesis by [35S]-sulfate incorporation into glycosaminoglycan chains and [35S]-Met/Cys incorporation into proteoglycans and total proteins in human vascular smooth muscle cells. Biglycan level was assessed by real-time quantitative polymerase chain reactions and the effects of (S)-[6]-gingerol on TGF-β signalling by assessment of the phosphorylation of Smads and Akt by western blotting.

Key findings

(S)-[6]-Gingerol concentration-dependently inhibited TGF-β-stimulated proteoglycan core protein synthesis, and this was not secondary to inhibition of total protein synthesis. (S)-[6]-Gingerol inhibited biglycan mRNA expression. (S)-[6]-Gingerol did not inhibit TGF-β-stimulated glycosaminoglycan hyperelongation or phosphorylation of Smad 2, in either the carboxy terminal or linker region, or Akt phosphorylation.

Conclusions

The activity of (S)-[6]-gingerol to inhibit TGF-β-stimulated biglycan synthesis suggests a potential role for ginger in the prevention of atherosclerosis or other lipid-binding diseases. The signalling studies indicate a novel site of action of (S)-[6]-gingerol in inhibiting TGF-β responses.

Effect of Si-Miao-Yong-An on the stability of atherosclerotic plaque in a diet-induced rabbit model

ETHNOPHARMACOLOGICAL RELEVANCE

Si-Miao-Yong-An (Trade name: Mai-Luo-Ning), a Chinese herbal formulation comprising Flos Lonicerae Japonicae, Radix Scrophulariae Ningpoensis, Radix Angelicae Sinensis and Radix Glycyrrhizae Uralensis, has been used in treating ischemic cardiovascular and cerebrovascular diseases for many years. Clinical and experimental studies have shown that Si-Miao-Yong-An can inhibit the inflammatory response and antagonize the blood clotting process.

AIM OF THE STUDY

To investigate the effect of Si-Miao-Yong-An on atherosclerotic plaque stability in rabbit model.

MATERIALS AND METHODS

Seventy male rabbits were divided into four groups. Rabbits in the normal group were fed with normal diet, while rabbits in model group and drug treatment groups were fed with high cholesterol diet, underwent BSA-induced immunologic injury and balloon-induced mechanical injury. After atherosclerotic rabbits were treated with simvastatin or Si-Miao-Yong-An for 16 weeks, blood and aorta in four groups were collected for analysis.

RESULTS

Si-Miao-Yong-An reduced the level of triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) in blood after treatment for 16 weeks. Compared with model group, Si-Miao-Yong-An decreased the content of many inflammatory cytokines in blood and plaque. Morphological analysis of abdominal aorta showed that Si-Miao-Yong-An increased fibrous cap thickness and smooth muscle cells, reduced lipid core area and macrophages, and contributed to inhibit matrix degradation and inflammatory response.

CONCLUSION

In this study, we provided evidence for that Si-Miao-Yong-An could promote the stability of atherosclerotic plaque in the rabbit model, indicating that this medicine was a reasonable drug treating cardiovascular diseases in clinical.

Molecular prediction for atherogenic risks across different cell types of leukocytes

Background

Diagnosing subclinical atherosclerosis is often difficult since patients are asymptomatic. In order to alleviate this limitation, we have developed a molecular prediction technique for predicting patients with atherogenic risks using multi-gene expression biomarkers on leukocytes.

Methods

We first discovered 356 expression biomarkers which showed significant differential expression between genome-wide microarray data of monocytes from patients with familial hyperlipidemia and increased risk of atherosclerosis compared to normal controls. These biomarkers were further triaged with 56 biomarkers known to be directly related to atherogenic risks. We also applied a COXEN algorithm to identify concordantly expressed biomarkers between monocytes and each of three different cell types of leukocytes. We then developed a multi-gene predictor using all or three subsets of these 56 biomarkers on the monocyte patient data. These predictors were then applied to multiple independent patient sets from three cell types of leukocytes (macrophages, circulating T cells, or whole white blood cells) to predict patients with atherogenic risks.

Results

When the 56 predictor was applied to the three patient sets from different cell types of leukocytes, all significantly stratified patients with atherogenic risks from healthy people in these independent cohorts. Concordantly expressed biomarkers identified by the COXEN algorithm provided slightly better prediction results.

Conclusion

These results demonstrated the potential of molecular prediction of atherogenic risks across different cell types of leukocytes.

Pharmacological suppression of hepcidin increases macrophage cholesterol efflux and reduces foam cell formation and atherosclerosis

OBJECTIVE

We recently reported that lowering of macrophage free intracellular iron increases expression of cholesterol efflux transporters ABCA1 and ABCG1 by reducing generation of reactive oxygen species. In this study, we explored whether reducing macrophage intracellular iron levels via pharmacological suppression of hepcidin can increase macrophage-specific expression of cholesterol efflux transporters and reduce atherosclerosis.

METHODS AND RESULTS

To suppress hepcidin, increase expression of the iron exporter ferroportin, and reduce macrophage intracellular iron, we used a small molecule inhibitor of bone morphogenetic protein (BMP) signaling, LDN 193189 (LDN). LDN (10 mg/kg IP b.i.d.) was administered to mice, and its effects on atherosclerosis, intracellular iron, oxidative stress, lipid efflux, and foam cell formation were measured in plaques and peritoneal macrophages. Long-term LDN administration to apolipoprotein E-/- mice increased ABCA1 immunoreactivity within intraplaque macrophages by 3.7-fold (n=8; P=0.03), reduced Oil Red O-positive lipid area by 50% (n=8; P=0.02), and decreased total plaque area by 43% (n=8; P=0.001). LDN suppressed liver hepcidin transcription and increased macrophage ferroportin, lowering intracellular iron and hydrogen peroxide production. LDN treatment increased macrophage ABCA1 and ABCG1 expression, significantly raised cholesterol efflux to ApoA-1, and decreased foam cell formation. All preceding LDN-induced effects on cholesterol efflux were reversed by exogenous hepcidin administration, suggesting modulation of intracellular iron levels within macrophages as the mechanism by which LDN triggers these effects.

CONCLUSIONS

These data suggest that pharmacological manipulation of iron homeostasis may be a promising target to increase macrophage reverse cholesterol transport and limit atherosclerosis.

Zinc and cardiovascular disease

Zinc is a vital element in maintaining the normal structure and physiology of cells. The fact that it has an important role in states of cardiovascular diseases has been studied and described by several research groups. It appears to have protective effects in coronary artery disease and cardiomyopathy. Intracellular zinc plays a critical role in the redox signaling pathway, whereby certain triggers such as ischemia and infarction lead to release of zinc from proteins and cause myocardial damage. In such states, replenishing with zinc has been shown to improve cardiac function and prevent further damage. Thus, the area of zinc homeostasis is emerging in cardiovascular disease research. The goal of this report is to review the current knowledge and suggest further avenues of research.

Smad linker region phosphorylation in the regulation of extracellular matrix synthesis

The canonical TGF-β signalling pathway involves Smad transcription factors through direct serine phosphorylation of the carboxy termini, nuclear translocation and regulation of transcription by receptor-regulated (R)-Smad complexes. Smads can also be phosphorylated in the linker region most prominently by the action of mitogen-activated protein (MAP) kinases, which in turn have been activated by TGF-β or a multitude of other growth factors and hormones. Linker region phosphorylation can prevent nuclear translocation of Smads and inhibit TGF-β signalling, potentially leading to oncogenesis. However, some evidence has revealed that linker region phosphorylated Smads can be translocated to the nucleus where they regulate transcription particularly of the synthesis of extracellular matrix molecules. Matrix molecules such as collagen and proteoglycans are involved in diseases such a fibrosis and atherosclerosis, respectively, and the involvement of linker region phosphorylation may represent a new therapeutic target.

Transforming growth factor-β regulation of proteoglycan synthesis in vascular smooth muscle: contribution to lipid binding and accelerated atherosclerosis in diabetes

Atherosclerosis is accelerated in the setting of diabetes, but the factors driving this phenomenon remain elusive. Hyperglycemia leads to elevated levels of transforming growth factor (TGF)-β and TGF-β has been implicated as a factor in atherosclerosis. Given the established association between hyperglycemia and elevated TGF-β, it is plausible that elevated TGF-β levels in diabetes play a pathogenic role in the development of accelerated atherosclerosis. TGF-β is a potent regulator of extracellular matrix synthesis, including many actions on proteoglycan synthesis that lead to increased binding to low-density lipoprotein and therefore potentially increased lipid retention in the vessel wall and accelerated atherosclerosis. TGF-β signals through the canonical TGF-β receptor I-mediated phosphorylation of Smad transcription factors and TGF-β signaling is also known to involve, positively and negatively, interactions with the mitogen-activated protein kinase pathways. The focus of the present review is on the effects of TGF-β on proteoglycan synthesis in vascular smooth muscle and particularly the signaling pathways through which TGF-β exerts its effects, because those pathways may be therapeutic targets for the prevention of pathological modifications in the proteoglycan component of the vessel wall in the vascular diseases of diabetes.

Concept of Vulnerable/Unstable Plaque

Today’s concept of vulnerable plaque has evolved primarily from the early pioneering work uncovering the pivotal role of plaque rupture and coronary thrombosis as the major cause of acute myocardial infarction and sudden cardiac death. Since the first historical description of plaque rupture in 1844, several key studies by leading researchers and clinicians have lead to the current accepted views on lesion instability. Important to the complex paradigm of plaque destabilization and thrombosis are many discoveries beginning with the earliest descriptions of advanced plaques, reminiscent of abscesses encapsulated by fibrous tissue capable of rupture. It was not until the late 1980s that studies of remodeling provided keen insight into the growth of advanced plaques, beyond the simple accumulation of lipid. The emphasis in the next decade, however, was on a focused shift toward the mechanisms of lesion vulnerability based on the contribution of tissue proteolysis by matrix metalloproteinases as an essential factor responsible for thinning and rupture of the fibrous cap. In an attempt to unify the understanding of what constitutes a vulnerable plaque, morphological studies, mostly from autopsy, suggest the importance of necrotic core size, inflammation, and fibrous cap thickness. Definitive proof of the vulnerable plaque, however, remains elusive because animal or human data supporting a cause-and-effect relationship are lacking. Although emerging imagining technologies involving optical coherence tomography, high-resolution MRI, molecular biomarkers, and other techniques have far surpassed the limits of the early days of angiography, advancing the field will require establishing relevant translational animal models that produce vulnerable plaques at risk for rupture and further testing of these modalities in large prospective clinical trials.

TGF-beta stimulates biglycan synthesis via p38 and ERK phosphorylation of the linker region of Smad2

Transforming growth factor (TGF)-beta treatment of human vascular smooth-muscle cells increases the expression of biglycan and causes marked elongation of its glycosaminoglycan (GAG) chains. We investigated the role of MAP kinases and Smad transcription factors in this response. TGF-beta-stimulated phosphorylation of p38, ERK, and JNK as well as Smad2 at both its carboxy terminal (phospho-Smad2C) and in the linker region (phospho-Smad2L). Pharmacological inhibition of ERK and p38 blocked TGF-beta-mediated GAG elongation and expression of biglycan whereas inhibition of JNK had no effect. Inhibition of ERK and p38 but not JNK attenuated the effect of TGF-beta to increase phospho-Smad2L. High levels of phospho-Smad2L were detected in a nuclear fraction of TGF-beta treated cells. Thus, MAP kinase signaling through ERK and p38 and via phosphorylation of the linker region of Smad2 mediates the effects of TGF-beta on biglycan synthesis in vascular smooth-muscle cells.

Imatinib inhibits vascular smooth muscle proteoglycan synthesis and reduces LDL binding in vitro and aortic lipid deposition in vivo

The ‘response to retention’ hypothesis of atherogenesis proposes that proteoglycans bind and retain low-density lipoproteins (LDL) in the vessel wall. Platelet-derived growth factor (PDGF) is strongly implicated in atherosclerosis and stimulates proteoglycan synthesis. Here we investigated the action of the PDGF receptor inhibitor imatinib on PDGF-mediated proteoglycan biosynthesis in vitro, lipid deposition in the aortic wall in vivo and the carotid artery ex vivo. In human vSMCs, imatinib inhibited PDGF mediated ³⁵S-SO₄ incorporation into proteoglycans by 31% (P < 0.01) and inhibited PDGF-mediated size increases in both chemically cleaved and xyloside associated glycosaminoglycan (GAG) chains by 19%, P < 0.05 and 27%, P < 0.05, respectively. Imatinib decreased PDGF stimulation of the 6:4 position sulphation ratio of disaccharides. The half maximal saturation value for LDL binding for proteoglycans from PDGF stimulated cells in the presence of imatinib was approximately 2.5-fold higher than for PDGF treatment alone. In high fat fed ApoE^−/– mice, imatinib reduced total lipid staining area by ∼31% (P < 0.05). Carotid artery lipid accumulation in imatinib treated mice was also reduced. Furthermore, we demonstrate that imatinib inhibits phosphorylation of tyrosine 857, the autophosphorylation site of the PDGF receptor, in vSMCs. Thus imatinib inhibits GAG synthesis on vascular proteoglycans and reduces LDL binding in vitro and in vivo and this effect is mediated via the PDGF receptor. These findings validate a novel mechanism to prevent cardiac disease.