Regulation of macrophage foam cell formation by alphaVbeta3 integrin: potential role in human atherosclerosis

Novel tracers to assess myocardial inflammation with radionuclide imaging

Myocardial inflammation plays a central role in the pathophysiology of various cardiac diseases. While FDG-PET is currently the primary method for molecular imaging of myocardial inflammation, its effectiveness is hindered by physiological myocardial uptake as well as its propensity for uptake by multiple disease-specific mechanisms. Novel radiotracers targeting diverse inflammatory immune cells and molecular pathways may provide unique insight through the visualization of underlying mechanisms central to the pathogenesis of inflammatory cardiac diseases, offering opportunities for increased understanding of immunocardiology. Moreover, the potentially enhanced specificity may lead to better quantification of disease activity, aiding in the guidance and monitoring of immunomodulatory therapy. This review aims to provide an update on advancements in non-FDG radiotracers for imaging myocardial inflammatory diseases, with a focus on cardiac sarcoidosis, myocarditis, and acute myocardial infarction.

Natural History of Myocardial αvβ3 Integrin Expression After Acute Myocardial Infarction: Correlation with Changes in Myocardial Blood Flow

Angiogenesis is an essential part of the cardiac repair process after myocardial infarction, but its spatiotemporal dynamics remain to be fully deciphered.68Ga-NODAGA-Arg-Gly-Asp (RGD) is a PET tracer targeting αvβ3 integrin expression, which is a marker of angiogenesis. Methods: In this prospective single-center trial, we aimed to monitor angiogenesis through myocardial integrin αvβ3 expression in 20 patients with ST-segment elevation myocardial infarction (STEMI). In addition, the correlations between the expression levels of myocardial αvβ3 integrin and the subsequent changes in 82Rb PET/CT parameters, including rest and stress myocardial blood flow (MBF), myocardial flow reserve (MFR), and wall motion abnormalities, were assessed. The patients underwent 68Ga-NODAGA-RGD PET/CT and rest and stress 82Rb-PET/CT at 1 wk, 1 mo, and 3 mo after STEMI. To assess 68Ga-NODAGA-RGD uptake, the summed rest 82Rb and 68Ga-NODAGA-RGD images were coregistered, and segmental SUVs were calculated (RGD SUV). Results: At 1 wk after STEMI, 19 participants (95%) presented increased 68Ga-NODAGA-RGD uptake in the infarcted myocardium. Seventeen participants completed the full imaging series. The values of the RGD SUV in the infarcted myocardium were stable 1 mo after STEMI (1 wk vs. 1 mo, 1.47 g/mL [interquartile range (IQR), 1.37-1.64 g/mL] vs. 1.47 g/mL [IQR, 1.30-1.66 g/mL]; P = 0.9), followed by a significant partial decrease at 3 mo (1.32 g/mL [IQR, 1.12-1.71 g/mL]; P = 0.011 vs. 1 wk and 0.018 vs. 1 mo). In segment-based analysis, positive correlations were found between RGD SUV at 1 wk and the subsequent changes in stress MBF (Spearman ρ: r = 0.17, P = 0.0033) and MFR (Spearman ρ: r = 0.31, P < 0.0001) at 1 mo. A negative correlation was found between RGD SUV at 1 wk and the subsequent changes in wall motion abnormalities at 3 mo (Spearman ρ: r = -0.12, P = 0.035). Conclusion: The present study found that αvβ3 integrin expression is significantly increased in the infarcted myocardium 1 wk after STEMI. This expression remains stable after 1 mo and partially decreases after 3 mo. Initial αvβ3 integrin expression at 1 wk is significantly weakly correlated with subsequent improvements in stress MBF, MFR, and wall motion analysis.

Tumor integrin targeted theranostic iron oxide nanoparticles for delivery of caffeic acid phenethyl ester: preparation, characterization, and anti-myeloma activities

Multiple myeloma (MM) is characterized by the accumulation of malignant plasma cells preferentially in the bone marrow. Currently, emerging chemotherapy drugs with improved biosafety profiles, such as immunomodulatory agents and protease inhibitors, have been used in clinics to treat MM in both initial therapy or maintenance therapy post autologous hematopoietic stem cell transplantation (ASCT). We previously discovered that caffeic acid phenethyl ester (CAPE), a water-insoluble natural compound, inhibited the growth of MM cells by inducing oxidative stress. As part of our continuous effort to pursue a less toxic yet more effective therapeutic approach for MM, the objective of this study is to investigate the potential of CAPE for in vivo applications by using magnetic resonance imaging (MRI)-capable superparamagnetic iron oxide nanoparticles (IONP) as carriers. Cyclo (Arg-Gly-Asp-D-Phe-Cys) (RGD) is conjugated to IONP (RGD-IONP/CAPE) to target the overexpressed αvβ3 integrin on MM cells for receptor-mediated internalization and intracellular delivery of CAPE. A stable loading of CAPE on IONP can be achieved with a loading efficiency of 48.7% ± 3.3% (wt%). The drug-release studies indicate RGD-IONP/CAPE is stable at physiological (pH 7.4) and basic pH (pH 9.5) and subject to release of CAPE at acidic pH (pH 5.5) mimicking the tumor and lysosomal condition. RGD-IONP/CAPE causes cytotoxicity specific to human MM RPMI8226, U266, and NCI-H929 cells, but not to normal peripheral blood mononuclear cells (PBMCs), with IC50s of 7.97 ± 1.39, 16.75 ± 1.62, and 24.38 ± 1.71 μM after 72-h treatment, respectively. Apoptosis assays indicate RGD-IONP/CAPE induces apoptosis of RPMI8226 cells through a caspase-9 mediated intrinsic pathway, the same as applying CAPE alone. The apoptogenic effect of RGD-IONP/CAPE was also confirmed on the RPMI8226 cells co-cultured with human bone marrow stromal cells HS-5 in a Transwell model to mimic the MM microenvironment in the bone marrow. In conclusion, we demonstrate that water-insoluble CAPE can be loaded to RGD-IONP to greatly improve the biocompatibility and significantly inhibit the growth of MM cells in vitro through the induction of apoptosis. This study paves the way for investigating the MRI-trackable delivery of CAPE for MM treatment in animal models in the future.

CD61 identifies a superior population of aged murine HSCs and is required to preserve quiescence and self-renewal

ABSTRACT

Aging leads to a decline in function of hematopoietic stem cells (HSCs) and increases susceptibility to hematological disease. We found CD61 to be highly expressed in aged murine HSCs. Here, we investigate the role of CD61 in identifying distinct subpopulations of aged HSCs and assess how expression of CD61 affects stem cell function. We show that HSCs with high expression of CD61 are functionality superior and retain self-renewal capacity in serial transplantations. In primary transplantations, aged CD61High HSCs function similarly to young HSCs. CD61High HSCs are more quiescent than their CD61Low counterparts. We also show that in aged bone marrow, CD61High and CD61Low HSCs are transcriptomically distinct populations. Collectively, our research identifies CD61 as a key player in maintaining stem cell quiescence, ensuring the preservation of their functional integrity and potential during aging. Moreover, CD61 emerges as a marker to prospectively isolate a superior, highly dormant population of young and aged HSCs, making it a valuable tool both in fundamental and clinical research.

Myocardial Fibrosis: Emerging Target for Cardiac Molecular Imaging and Opportunity for Image-Guided Therapy

Myocardial fibrosis is a major contributor to the development and progression of heart failure. Significant progress in the understanding of its pathobiology has led to the introduction and preclinical testing of multiple highly specific antifibrotic therapies. Because the mechanisms of fibrosis are highly dynamic, and because the involved cell populations are heterogeneous and plastic, there is increasing emphasis that any therapy directed specifically against myocardial fibrosis will require personalization and guidance by equally specific diagnostic testing for successful clinical translation. Noninvasive imaging techniques have undergone significant progress and provide increasingly specific information about the quantity, quality, and activity of myocardial fibrosis. Cardiac MRI can precisely map the extracellular space of the myocardium, whereas nuclear imaging characterizes activated fibroblasts and immune cells as the cellular components contributing to fibrosis. Existing techniques may be used in complementarity to provide the imaging biomarkers needed for the success of novel targeted therapies. This review provides a road map on how progress in basic fibrosis research, antifibrotic drug development, and high-end noninvasive imaging may come together to facilitate the success of fibrosis-directed cardiovascular medicine.

Differential Expression of Subsets of Genes Related to HDL Metabolism and Atherogenesis in the Peripheral Blood in Coronary Artery Disease

Differential expression of genes (DEGs) in coronary artery disease (CAD) and the association between transcript level and high-density lipoprotein cholesterol (HDL-C) were studied with 76 male patients with CAD and 63 control patients. The transcript level of genes related to HDL metabolism (24 genes) and atherosclerosis-prone (41 genes) in RNA isolated from peripheral blood mononuclear cells was measured by real-time RT-PCR. Twenty-eight DEGs were identified. The expression of cholesterol transporters, ALB, APOA1, and LCAT was down-regulated, while the expression of AMN, APOE, LDLR, LPL, PLTP, PRKACA, and CETP was up-regulated. The systemic inflammation in CAD is evidenced by the up-regulation of IL1B, TLR8, CXCL5, and TNFRSF1A. For the controls, TLR8 and SOAT1 were negative predictors of the HDL-C level. For CAD patients, PRKACG, PRKCQ, and SREBF1 were positive predictors, while PRKACB, LCAT, and S100A8 were negative predictors. For CAD patients, the efficiency of reverse cholesterol transport is 73-79%, and intracellular free cholesterol seems to accumulate at hyperalphalipoproteinemia. Both atheroprotective (via S100A8) and proatherogenic (via SREBF1, LCAT, PRKACG, PRKACB, and PRKCQ) associations of gene expression with HDL-C determine HDL functionality in CAD patients. The selected key genes and involved pathways may represent HDL-specific targets for the diagnosis and treatment of CAD and atherosclerosis.

Epsin Nanotherapy Regulates Cholesterol Transport to Fortify Atheroma Regression

BACKGROUND

Excess cholesterol accumulation in lesional macrophages elicits complex responses in atherosclerosis. Epsins, a family of endocytic adaptors, fuel the progression of atherosclerosis; however, the underlying mechanism and therapeutic potential of targeting Epsins remains unknown. In this study, we determined the role of Epsins in macrophage-mediated metabolic regulation. We then developed an innovative method to therapeutically target macrophage Epsins with specially designed S2P-conjugated lipid nanoparticles, which encapsulate small-interfering RNAs to suppress Epsins.

METHODS

We used single-cell RNA sequencing with our newly developed algorithm MEBOCOST (Metabolite-mediated Cell Communication Modeling by Single Cell Transcriptome) to study cell-cell communications mediated by metabolites from sender cells and sensor proteins on receiver cells. Biomedical, cellular, and molecular approaches were utilized to investigate the role of macrophage Epsins in regulating lipid metabolism and transport. We performed this study using myeloid-specific Epsin double knockout (LysM-DKO) mice and mice with a genetic reduction of ABCG1 (ATP-binding cassette subfamily G member 1; LysM-DKO-ABCG1fl/+). The nanoparticles targeting lesional macrophages were developed to encapsulate interfering RNAs to treat atherosclerosis.

RESULTS

We revealed that Epsins regulate lipid metabolism and transport in atherosclerotic macrophages. Inhibiting Epsins by nanotherapy halts inflammation and accelerates atheroma resolution. Harnessing lesional macrophage-specific nanoparticle delivery of Epsin small-interfering RNAs, we showed that silencing of macrophage Epsins diminished atherosclerotic plaque size and promoted plaque regression. Mechanistically, we demonstrated that Epsins bound to CD36 to facilitate lipid uptake by enhancing CD36 endocytosis and recycling. Conversely, Epsins promoted ABCG1 degradation via lysosomes and hampered ABCG1-mediated cholesterol efflux and reverse cholesterol transport. In a LysM-DKO-ABCG1fl/+ mouse model, enhanced cholesterol efflux and reverse transport due to Epsin deficiency was suppressed by the reduction of ABCG1.

CONCLUSIONS

Our findings suggest that targeting Epsins in lesional macrophages may offer therapeutic benefits for advanced atherosclerosis by reducing CD36-mediated lipid uptake and increasing ABCG1-mediated cholesterol efflux.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Increased soluble urokinase plasminogen activator levels modulate monocyte function to promote atherosclerosis

People with kidney disease are disproportionately affected by atherosclerosis for unclear reasons. Soluble urokinase plasminogen activator receptor (suPAR) is an immune-derived mediator of kidney disease, levels of which are strongly associated with cardiovascular outcomes. We assessed suPAR's pathogenic involvement in atherosclerosis using epidemiologic, genetic, and experimental approaches. We found serum suPAR levels to be predictive of coronary artery calcification and cardiovascular events in 5,406 participants without known coronary disease. In a genome-wide association meta-analysis including over 25,000 individuals, we identified a missense variant in the plasminogen activator, urokinase receptor (PLAUR) gene (rs4760), confirmed experimentally to lead to higher suPAR levels. Mendelian randomization analysis in the UK Biobank using rs4760 indicated a causal association between genetically predicted suPAR levels and atherosclerotic phenotypes. In an experimental model of atherosclerosis, proprotein convertase subtilisin/kexin-9 (Pcsk9) transfection in mice overexpressing suPAR (suPARTg) led to substantially increased atherosclerotic plaques with necrotic cores and macrophage infiltration compared with those in WT mice, despite similar cholesterol levels. Prior to induction of atherosclerosis, aortas of suPARTg mice excreted higher levels of CCL2 and had higher monocyte counts compared with WT aortas. Aortic and circulating suPARTg monocytes exhibited a proinflammatory profile and enhanced chemotaxis. These findings characterize suPAR as a pathogenic factor for atherosclerosis acting at least partially through modulation of monocyte function.

Preliminary Clinical Application of RGD-Containing Peptides as PET Radiotracers for Imaging Tumors

Angiogenesis is a common feature of many physiological processes and pathological conditions. RGD-containing peptides can strongly bind to integrin αvβ3 expressed on endothelial cells in neovessels and several tumor cells with high specificity, making them promising molecular agents for imaging angiogenesis. Although studies of RGD-containing peptides combined with radionuclides, namely, 18F, 64Cu, and 68Ga for positron emission tomography (PET) imaging have shown high spatial resolution and accurate quantification of tracer uptake, only a few of these radiotracers have been successfully translated into clinical use. This review summarizes the RGD-based tracers in terms of accumulation in tumors and adjacent tissues, and comparison with traditional 18F-fluorodeoxyglucose (FDG) imaging. The value of RGD-based tracers for diagnosis, differential diagnosis, tumor subvolume delineation, and therapeutic response prediction is mainly discussed. Very low RGD accumulation, in contrast to high FDG metabolism, was found in normal brain tissue, indicating that RGD-based imaging provides an excellent tumor-to-background ratio for improved brain tumor imaging. However, the intensity of the RGD-based tracers is much higher than FDG in normal liver tissue, which could lead to underestimation of primary or metastatic lesions in liver. In multiple studies, RGD-based imaging successfully realized the diagnosis and differential diagnosis of solid tumors and also the prediction of chemoradiotherapy response, providing complementary rather than similar information relative to FDG imaging. Of most interest, baseline RGD uptake values can not only be used to predict the tumor efficacy of antiangiogenic therapy, but also to monitor the occurrence of adverse events in normal organs. This unique dual predictive value in antiangiogenic therapy may be better than that of FDG-based imaging.

Nuclear Molecular Imaging of Cardiac Remodeling after Myocardial Infarction

The role of molecular imaging technologies in detecting, evaluating, and monitoring cardiovascular disease and their treatment is expanding rapidly. Gradually replacing the conventional anatomical or physiological approaches, molecular imaging strategies using biologically targeted markers provide unique insight into pathobiological processes at molecular and cellular levels and allow for cardiovascular disease evaluation and individualized therapy. This review paper will discuss currently available and developing molecular-based single-photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging strategies to evaluate post-infarction cardiac remodeling. These approaches include potential targeted methods of evaluating critical biological processes, such as inflammation, angiogenesis, and scar formation.

Evaluation of [68Ga]Ga-NODAGA-RGD for PET Imaging of Rat Autoimmune Myocarditis

The ⁶⁸Gallium-labeled 1,4,7-triazacyclononane-1-glutaric acid-4,7-diacetic acid conjugated radiolabelled arginine-glycine-aspartic acid peptide ([⁶⁸Ga]Ga-NODAGA-RGD) is a positron emission tomography (PET) tracer binding to cell surface receptor α_vβ₃ integrin that is upregulated during angiogenesis and inflammation. We studied whether α_vβ₃ targeting PET imaging can detect myocardial inflammation in a rat model of autoimmune myocarditis. To induce myocarditis, rats (n = 8) were immunized with porcine cardiac myosin in complete Freund's adjuvant on days 0 and 7. Control rats (n = 8) received Freund's adjuvant alone. On day 21, in vivo PET/CT imaging with [⁶⁸Ga]Ga-NODAGA-RGD followed by ex vivo autoradiography and immunohistochemistry were carried out. Inflammatory lesions were detected histologically in the myocardium of 7 out of 8 immunized rats. In vivo PET images showed higher [⁶⁸Ga]Ga-NODAGA-RGD accumulation in the myocardium of rats with inflammation than the non-inflamed myocardium of control rats (SUV_mean 0.4 ± 0.1 vs. 0.1 ± 0.02; P = 0.00006). Ex vivo autoradiography and histology confirmed that [⁶⁸Ga]Ga-NODAGA-RGD uptake co-localized with inflammatory lesions containing α_vβ₃ integrin-positive capillary-like structures. A non-specific [⁶⁸Ga]Ga-DOTA-(RGE)₂ tracer showed 76% lower uptake than [⁶⁸Ga]Ga-NODAGA-RGD in the inflamed myocardium. Our results indicate that α_vβ₃ integrin-targeting [⁶⁸Ga]Ga-NODAGA-RGD is a potential PET tracer for the specific detection of active inflammatory lesions in autoimmune myocarditis.

Identification of genes associated with susceptibility to persistent breeding-induced endometritis by RNA-sequencing of uterine cytobrush samples

This study aimed to investigate the susceptibility to persistent breeding-induced endometritis (PBIE). Cytobrush samples were collected from 81 broodmares 1-3 days before artificial insemination (AI). Susceptibility to PBIE was evaluated by the presence of ≥ 2 cm of intrauterine fluid 24 h after AI, besides the fertility was determined by a sonographic pregnancy diagnosis 2 weeks after ovulation. RNA expressions were compared between susceptible non-pregnant (SNP) mares (n=9) and resistant pregnant (RP) mares (n=9) as well as between susceptible pregnant (SP) mares (n=9) and susceptible non-pregnant (SNP) mares. 66 differentially expressed genes (DEGs) were identified between SNP and RP mares and 60 DEGs between SP and SNP mares. In SNP compared to RP mares, transcript levels of genes regulating steroid hormone metabolism and neutrophil chemotaxis were lower, while higher for genes participating in uterine inflammation.Transcripts of genes related to extracellular matrix degradation, tissue adhesions, and fibrosis were lower in SP mares than in SNP mares, while higher for genes related to uterine cell proliferation, differentiation, and angiogenesis in SP mares than SNP mares. In conclusion, increased transcript levels of apolipoprotein E (APOE) and roundabout 2 (ROBO2), cluster domain 44 (CD44), integrin beta 3 (ITGB3), and epidermal growth factor (EGF) are possible biomarkers for susceptibility to PBIE. While higher expression of fibroblast growth factor 9 (FGF9), kinase domain receptor (KDR), and C-X-C motif chemokine ligand (CXCL) 16, collagen type V alpha 2 (COL5A2) and fibronectin (FN1) are suggested indicators of fertility in susceptible mares if they receive proper breeding management.

Feasibility of 125I-RGD uptake as a marker of angiogenesis after myocardial infarction

OBJECTIVE

Angiogenesis is an important process facilitating the healing process after myocardial infarction. ¹²⁵I-RGD imaging may be a promising candidate to image angiogenesis but may also detect inflammation.

METHODS

Left coronary artery was occluded for 30 min, followed by reperfusion in a rat model (n = 31). One, 3, 7 and 14 days, 1 and 2 months later, Triple-tracer autoradiography was performed. ¹²⁵I-RGD (1.5 MBq) and ²⁰¹Tl (15 MBq) were injected at 80 and 10 min before sacrifice. Left coronary artery was reoccluded and ^99mTc-MIBI (150-180 MBq) was injected 1 min before sacrifice to verify the area at risk. Angiogenesis and macrophage infiltration were evaluated by immunohistochemical analysis with anti-alpha-smooth muscle actin and anti-CD68, respectively.

RESULTS

¹²⁵I-RGD uptake ratio in the area at risk was weak at day 3 (1.23 ± 0.23 but increased markedly and peaked at day 7 (2.27 ± 0.37) followed by a gradual reduction until 1 and 2 months later (1.93 ± 0.16 at 1 month, 1.58 ± 0.15 at 2 month). In the immunohistochemical analysis, copious staining of anti-CD68 cells was observed, with anti-SMA cells stained only minimally at day 3. The number of anti-CD68 cells was decreased significantly at day 7 but largely absent at 1 month. Anti-SMA positive cells peaked at day 7 and reduced gradually until 1 month.

CONCLUSIONS

Myocardial ¹²⁵I-RGD uptake reflects angiogenesis rather than inflammation after myocardial infarction.

Omentin-1 Modulates Macrophage Function via Integrin Receptors αvβ3 and αvβ5 and Reverses Plaque Vulnerability in Animal Models of Atherosclerosis

Backgrounds: Omentin-1 is a novel cytokine that is primarily released by the epicardial adipose tissue. Molecular structure analysis revealed that it contained a fibrinogen-like domain. Clinical studies have demonstrated that the expression of omentin-1 is tightly associated with the development of cardiovascular diseases, but the receptor by which omentin-1 modulates macrophage function has not been identified yet. Objective: This study sought to investigate the effect of omentin-1 on already-established atherosclerosis (AS) lesions in both ApoE-/- and Ldlr^-/- mice and further, study its underlying mechanisms. Methods and Results: We investigated the effect of omentin-1 on the plaque phenotype by implanting a minipump in ApoE-/- and Ldlr^-/- mice. In vivo studies showed that the infusion of omentin-1 increased the collagen content and mitigated the formation of the necrotic core in both animal models. Immunohistochemistry and immunofluorescence analysis revealed that omentin-1 suppressed inflammatory cytokines expression, macrophage infiltration, and apoptosis within the plaque. An immunoprecipitation experiment and confocal microscopy analysis confirmed the binding of omentin-1 to the integrin receptors αvβ3 and αvβ5. The cell studies demonstrated that omentin-1 suppressed the apoptosis and inflammatory cytokines expression induced by the oxidized low-density lipoprotein in the macrophage. In addition, omentin-1 promoted the phosphorylation of the integrin-relevant signaling pathway as well as the Akt and AMPK in the macrophage. The addition of the inhibitor of the integrin receptor or interfering with the expression of the integrin subunit αv (ITGAV) both significantly abrogated the bioeffects induced by omentin-1. A flow cytometry analysis indicated that the antibodies against αvβ3 and αvβ5 had a competitive effect on the omentin-1 binding to the cell membrane. Conclusions: The administration of adipokine omentin-1 can inhibit the necrotic cores formation and pro-inflammatory cytokines expression within the AS lesion. The mechanisms may include the suppression of apoptosis and pro-inflammatory cytokines expression in the macrophage by binding to the integrin receptors αvβ3 and αvβ5.

Integrin αv and Vitronectin Prime Macrophage-Related Inflammation and Contribute the Development of Dry Eye Disease

Cell signaling mediated by the αv integrin plays a pivotal role in macrophage activation in various inflammatory processes, but its involvement in the pathogenesis of dry eye disease (DED) remains unclear. In a murine model of DED, we found increased αv integrin expression in ocular surface macrophages. The αv integrins inhibitor c(RGDfK) ameliorated the corneal damage caused by DED, suggesting a pathogenic role for αv integrin. Because tear hyperosmolarity induces ocular inflammation in DED, a hyperosmolar culture of murine bone marrow-derived macrophages (BMDMs) is used to reproduce inflammation in vitro. However, the expression of proinflammatory cytokine mRNA was minimal, even though αv integrin was induced. In searching for components that are involved in αv integrin-mediated inflammation but that are missing from the culture model, we showed that the levels of vitronectin (VTN), a binding ligand of αv integrins, were increased in the tear fluid and conjunctival stroma of DED animals. The addition of VTN prominently enhanced hyperosmolarity-induced inflammation in BMDMs. Mechanistically, we showed that VTN/αv integrins mediated NF-κB activation to induce inflammatory gene expression in the BMDMs. Our findings indicate that interaction the of VTN with αv integrins is a crucial step in the inflammatory process in DED and suggests a novel therapeutic target.

The association of atherosclerotic cardiovascular disease and statin use with inflammation and treatment outcomes in tuberculosis

Tuberculosis (TB) and atherosclerotic cardiovascular disease (ASCVD) have a close epidemiological and pathogenetic overlap. Thus, it becomes essential to understand the relationship between ASCVD and TB outcomes. From our retrospective cohort on drug-susceptible TB patients at the National Taiwan University Hospital, we assessed the association of pre-existing ASCVD (coronary artery disease (CAD) and atherothrombotic stroke (ATS)) with 9-month all-cause and infection-related mortality and the extent of mediation by systemic inflammatory markers. We determined the effect of pre-existing ASCVD on 2-month sputum microbiological status. Among ASCVD patients, we assessed the association of statin use on mortality. Nine-month all-cause mortality was higher in CAD patients with prior acute myocardial infarction (CAD⁺AMI⁺) (adjusted HR 2.01, 95%CI 1.38–3.00) and ATS patients (aHR 2.79, 95%CI 1.92–4.07) and similarly, for infection-related mortality was higher in CAD⁺AMI⁺ (aHR 1.95, 95%CI 1.17–3.24) and ATS (aHR 2.04, 95%CI 1.19–3.46) after adjusting for confounding factors. Pre-existing CAD (AMI^- or AMI⁺) or ATS did not change sputum culture conversion or sputum smear AFB positivity at 2 months. The CAD⁺AMI⁺ group had significantly higher levels of CRP at TB diagnosis in the multivariable linear regression analysis (Adjusted B(SE) 1.24(0.62)). CRP mediated 66% (P = 0.048) and 25% (P = 0.033) of the association all-cause mortality with CAD⁺AMI⁻ and CAD⁺AMI⁺, respectively. In summary, patients with ASCVD have higher hazards of 9-month all-cause and infection-related mortality, with elevated serum inflammation mediating one to three-quarters of this association when adjusted for confounders. Statin use was associated with lower all-cause mortality among patients with ASCVD.

Molecular Imaging Using Cardiac PET/CT: Opportunities to Harmonize Diagnosis and Therapy

PURPOSE OF REVIEW

Current therapeutic strategies to mitigate heart failure progression after myocardial infarction involve support of endogenous repair through molecular targets. The capacity for repair varies greatly between individuals. In this review, we will assess how cardiac PET/CT enables precise characterization of early pathogenetic processes which govern ventricle remodeling and progression to heart failure.

RECENT FINDINGS

Inflammation in the first days after myocardial infarction predicts subsequent functional decline and can influence therapy decisions. The expansion of anti-inflammatory approaches to improve outcomes after myocardial infarction may benefit from noninvasive characterization using imaging. Novel probes also allow visualization of fibroblast transdifferentiation and activation, as a precursor to ventricle remodeling. The expanding arsenal of molecular imaging agents in parallel with new treatment options provides opportunity to harmonize diagnostic imaging with precision therapy.

Cell adhesion molecule-mediated therapeutic strategies in atherosclerosis: From a biological basis and molecular mechanism to drug delivery nanosystems

Atherosclerosis (AS), characterized by pathological constriction of blood vessels due to chronic low-grade inflammation and lipid deposition, is a leading cause of human morbidity and mortality worldwide. Cell adhesion molecules (CAMs) have the ability to regulate the inflammatory response and endothelial function, as well as potentially driving plaque rupture, which all contribute to the progression of AS. Moreover, recent advances in the development of clinical agents in the cardiovascular field are based on CAMs, which show promising results in the fight against AS. Here, we review the current literature on mechanisms by which CAMs regulate atherosclerotic progression from the earliest induction of inflammation to plaques formation. In particular, we focused on therapeutic strategies based on CAMs inhibitors that prevent leukocyte from migrating to endothelium, including high-affinity antibodies and antagonists, nonspecific traditional medicinal formulas and lipid lowering drugs. The CAMs-based drug delivery nanosystem and the available data on the more reasonable and effective clinical application of CAMs inhibitors have been emphasized, raising hope for further progress in the field of AS therapy.

Lebecetin, a snake venom C-type lectin protein, modulates LPS-induced inflammatory cytokine production in human THP-1-derived macrophages

The excessive production of inflammatory mediators results in an overactive immune response leading to the worsening of various human diseases. Thus, there is a still need to identify molecules able to regulate the inflammatory response. Lebecetin, a C-type lectin protein isolated from Macrovipera lebetina snake venom, was previously characterized as a platelet aggregation inhibitor and antitumor active biomolecule. In the present work, we investigated its effect on the production of some cytokines linked to inflammatory response and the underlying mechanisms in lipopolysaccharide (LPS)-induced THP1 macrophages. Interestingly, we found that lebecetin reduced the levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-8 while it partially increased LPS-induced secretion of the immunomodulatory cytokine IL-10. Furthermore, this modulatory effect was accompanied by decreased activation of ERK1/2, p38, AKT kinases and NF-κB along with reduced expression of αvβ3 integrin. Thus, this study highlights the promising role of lebecetin as a natural biomolecule that could manage the inflammatory response involved in the development and progression of inflammatory diseases.

Inflammasomes: a preclinical assessment of targeting in atherosclerosis

INTRODUCTION

Inflammasomes are central to atherosclerotic vascular dysfunction with regulatory effects on inflammation, immune modulation, and lipid metabolism. The NLRP3 inflammasome is a critical catalyst for atherogenesis thus highlighting its importance in understanding the pathophysiology of atherosclerosis and for the identification of novel therapeutic targets and biomarkers for the treatment of cardiovascular disease.

AREAS COVERED

This review includes an overview of macrophage lipid metabolism and the role of NLRP3 inflammasome activity in cardiovascular inflammation and atherosclerosis. We highlight key activators, signal transducers and major regulatory components that are being considered as putative therapeutic targets for inhibition of NLRP3-mediated cardiovascular inflammation and atherosclerosis.

EXPERT OPINION

NLRP3 inflammasome activity lies at the nexus between inflammation and cholesterol metabolism; it offers unique opportunities for understanding atherosclerotic pathophysiology and identifying novel modes of treatment. As such, a host of NLRP3 signaling cascade components have been identified as putative targets for drug development. We catalog these current discoveries in therapeutic targeting of the NLRP3 inflammasome and, utilizing the CANTOS trial as the translational (bench-to-bedside) archetype, we examine the complexities, challenges, and ultimate goals facing the field of atherosclerosis research.

The Development of Hyaluronan/Fucoidan-Based Nanoparticles as Macrophages Targeting an Epigallocatechin-3-Gallate Delivery System

The aim of this study was to develop a macrophage-targeted nanoparticle composed of hyaluronan/fucoidan complexes with polyethylene glycol-gelatin to encapsulate and deliver epigallocatechin-3-gallate (EGCG), a compound that can regulate macrophage activation and pro-inflammatory mediator production. We show that our nanoparticles can successfully bond to macrophages and deliver more EGCG than an EGCG solution treatment, confirming the anti-inflammatory effects of these nanoparticles in lipopolysaccharide-stimulated macrophages. The prepared nanoparticles were established with a small mean particle size (217.00 ± 14.00 nm), an acceptable polydispersity index (0.28 ± 0.07), an acceptable zeta potential value (-33.60 ± 1.30 mV), and a high EGCG loading efficiency (52.08% ± 5.37%). The targeting abilities of CD44 binding were increased as the hyaluronan concentration increased and decreased by adding a competitor CD44 antibody. Moreover, we found that fucoidan treatment significantly reduced macrophage migration after lipopolysaccharide treatment in a dose-responsive manner. In summary, we successfully created macrophage-targeted nanoparticles for effective targeted delivery of EGCG, which should aid in the development of future anti-inflammatory drugs against macrophage-related diseases.

Frontiers in positron emission tomography imaging of the vulnerable atherosclerotic plaque

Rupture of vulnerable atherosclerotic plaques leading to an atherothrombotic event is the primary driver of myocardial infarction and stroke. The ability to detect non-invasively the presence and evolution of vulnerable plaques could have a huge impact on the future identification and management of atherosclerotic cardiovascular disease. Positron emission tomography (PET) imaging with an appropriate radiotracer has the potential to achieve this goal. This review will discuss the biological hallmarks of plaque vulnerability before going on to evaluate and to present PET imaging approaches which target these processes. The focus of this review will be on techniques beyond [18F]FDG imaging, some of which are clinically advanced, and others which are on the horizon. As inflammation is the primary driving force behind atherosclerotic plaque development, we will predominantly focus on approaches which either directly, or indirectly, target this process.

Infection and Inflammation Imaging: Beyond FDG

This review discusses nuclear imaging of inflammation using molecular probes beyond fluoro-d-glucose, is structured by cellular targets, and focuses on those tracers that have been successfully applied clinically.

Molecular Imaging of Fibroblast Activity After Myocardial Infarction Using a 68Ga-Labeled Fibroblast Activation Protein Inhibitor, FAPI-04

Heart failure remains a major source of late morbidity and mortality after myocardial infarction (MI). The temporospatial presence of activated fibroblasts in the injured myocardium predicts the quality of cardiac remodeling after MI. Therefore, monitoring of activated fibroblasts is of great interest for studying cardiac remodeling after MI. Fibroblast activation protein (FAP) expression is upregulated in activated fibroblasts. This study investigated the feasibility of imaging activated fibroblasts with a new ⁶⁸Ga-labeled FAP inhibitor (⁶⁸Ga-FAPI-04) for PET imaging of fibroblast activation in a preclinical model of MI. Methods: MI and sham-operated rats were scanned with ⁶⁸Ga-FAPI-04 PET/CT (1, 3, 6, 14, 23, and 30 d after MI) and with ¹⁸F-FDG (3 d after MI). Dynamic ⁶⁸Ga-FAPI-04 PET and blocking studies were performed on MI rats 7 d after coronary ligation. After in vivo scans, the animals were euthanized and their hearts harvested for ex vivo analyses. Cryosections were prepared for autoradiography, hematoxylin and eosin (H&E), and immunofluorescence staining. Results: ⁶⁸Ga-FAPI-04 uptake in the injured myocardium peaked on day 6 after coronary ligation. The tracer accumulated intensely in the MI territory, as identified by decreased ¹⁸F-FDG uptake and confirmed by PET/MR and H&E staining. Autoradiography and H&E staining of cross-sections revealed that ⁶⁸Ga-FAPI-04 accumulated mainly at the border zone of the infarcted myocardium. In contrast, there was only minimal uptake in the infarct of the blocked rats, comparable to the uptake in the remote noninfarcted myocardium (PET image-derived ratio of infarct uptake to remote uptake: 6 ± 2). Immunofluorescence staining confirmed the presence of FAP-positive myofibroblasts in the injured myocardium. Morphometric analysis of the whole-heart sections demonstrated 3- and 8-fold higher FAP-positive fibroblast density in the border zone than in the infarct center and remote area, respectively. Conclusion: ⁶⁸Ga-FAPI-04 represents a promising radiotracer for in vivo imaging of post-MI fibroblast activation. Noninvasive imaging of activated fibroblasts may have significant diagnostic and prognostic value, which could aid clinical management of patients after MI.

Lipid Metabolism Disorder and Renal Fibrosis

Since the lipid nephrotoxicity hypothesis was proposed in 1982, increasing evidence has supported the hypothesis that lipid abnormalities contributed to the progression of glomerulosclerosis. In this chapter, we will discuss the general promises of the original hypothesis, focusing especially on the role of lipids and metabolic inflammation accompanying CKD in renal fibrosis and potential new strategies of prevention.

Abrogation of GH action in Kupffer cells results in increased hepatic CD36 expression and exaggerated nonalcoholic fatty liver disease

OBJECTIVE

To investigate the effects of GH signaling on Kupffer cells and the resulting changes in lipid homeostasis and their underlying mechanism(s) in the livers of diet-induced obese (DIO) mice.

DESIGN

Male macrophage specific-growth hormone receptor knockout mice (MacGHR KO) and their litter mate controls were fed a high fat diet containing 60% calories from fat for 26 weeks. Lipid content and lipid profiles in the liver and circulation were analyzed. Expression levels of CD36 in the liver were quantified by RT-PCR and Western Blot.

RESULTS

Increased hepatic lipid content and abundance of long-chain unsaturated fatty acids were observed in the liver of MacGHR KO mice. These findings were associated with increased steady state levels of CD36 mRNA and protein in MacGHR KO mice when compared with their litter mate controls.

CONCLUSION

GH action in Kupffer cells is required for maintaining hepatic lipid homeostasis, in part via regulation of hepatic CD36 expression.

Peroxisome proliferator-activated receptor γ (PPARγ) induces the gene expression of integrin αVβ5 to promote macrophage M2 polarization

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear receptor superfamily and polarizes the macrophages into an anti-inflammatory M2 state. Integrins are transmembrane receptors that drive various cellular functions, including monocyte adhesion and foam cell formation. In this study, we first reported that the expression of integrins α_V and β₅ was up-regulated by PPARγ activation in RAW264.7 cells and human peripheral blood monocytes. Luciferase reporter and ChIP assay revealed that PPARγ directly bound to the potential PPAR-responsive elements sites in the 5'-flanking regions of both murine and human integrin α_V and β₅ genes, respectively. In addition, we showed that PPARγ augmented the ligation of integrins α_V and β₅ Knockdown of integrin α_Vβ₅ by siRNA strategy or treatment with cilengitide, a potent inhibitor of integrin α_Vβ₅, attenuated PPARγ-induced expression of Ym1 (chitinase-like protein 3), Arg1 (Arginase1), Fizz1 (resistin-like molecule RELMα), and other M2 marker genes, suggesting that the heterodimers of integrin α_Vβ₅ were involved in PPARγ-induced M2 polarization. In conclusion, these results provided novel evidence that PPARγ-mediated gene expression and the ensuing ligation of integrins α_V and β₅ are implicated in macrophage M2 polarization.

Angiopoietin-Like 3 (ANGPTL3) and Atherosclerosis: Lipid and Non-Lipid Related Effects

Genetic and clinical studies have demonstrated that loss-of-function variants in the angiopoietin-like 3 (ANGPTL3) gene are associated with decreased plasma levels of triglycerides (TGs), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C), which leads to a significant reduction in cardiovascular risk. For this reason, ANGPTL3 is considered an important new pharmacological target for the treatment of cardiovascular diseases (CVDs) together with more conventional lipid lowering therapies, such as statins and anti proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibodies. Experimental evidence demonstrates that anti-ANGPTL3 therapies have an important anti-atherosclerotic effect. Results from phase I clinical trials with a monoclonal anti-ANGPTL3 antibody (evinacumab) and anti-sense oligonucleotide (ASO) clearly show a significant lipid lowering effect. In addition, from the analysis of the protein structure of ANGPTL3, it has been hypothesized that, beyond its inhibitory activity on lipoprotein and endothelial lipases, this molecule may have a pro-inflammatory, pro-angiogenic effect and a negative effect on cholesterol efflux, implying additional pro-atherosclerotic properties. In the future, data from phase II clinical trials and additional experimental evidence will help to define the efficacy and the additional anti-atherosclerotic properties of anti-ANGPTL3 therapies beyond the already available lipid lowering therapies.

Comparing the Differential Diagnostic Values of 18F-Alfatide II PET/CT between Tuberculosis and Lung Cancer Patients

Purpose

To compare the differential diagnostic values of ¹⁸F-Alfatide II PET/CT between tuberculosis and lung cancer patients and in patients with sarcoidosis and common inflammation.

Methods

Nine inflammation patients (4 tuberculosis, 3 sarcoidosis, and 2 common inflammation) and 11 lung cancer patients were included in this study. All patients underwent ¹⁸F-FDG and ¹⁸F-Alfatide II PET/CT within 2 weeks, followed by biopsy and surgery. The maximized standard uptake value (SUVmax) and the mean standard uptake value (SUVmean) were evaluated.

Results

The active tuberculosis lesions showed a high accumulation of ¹⁸F-FDG, but varying degrees of accumulation of ¹⁸F-Alfatide II, including negative results. The SUVmax of ¹⁸F-Alfatide II in malignant lesions was significantly higher than that in tuberculosis (4.08 ± 1.51 versus 2.63 ± 1.34, P = 0.0078). Three patients with sarcoidosis showed negative results in ¹⁸F-Alfatide II PET/CT.

Conclusions

The expression of α_Vβ₃ is much lower in tuberculosis as compared to that in lung cancer, and accumulation of ¹⁸F-Alfatide II varied even in lesions of the same patient. The negative results of sarcoidosis patients led to the speculation that α_Vβ₃ was not expressed in those lesions.

The Upregulation of Integrin αDβ2 (CD11d/CD18) on Inflammatory Macrophages Promotes Macrophage Retention in Vascular Lesions and Development of Atherosclerosis

Macrophage accumulation is a critical step during development of chronic inflammation, initiating progression of many devastating diseases. Leukocyte-specific integrin α_Dβ₂ (CD11d/CD18) is dramatically upregulated on macrophages at inflammatory sites. Previously we found that CD11d overexpression on cell surfaces inhibits in vitro cell migration due to excessive adhesion. In this study, we have investigated how inflammation-mediated CD11d upregulation contributes to macrophage retention at inflammatory sites during atherogenesis. Atherosclerosis was evaluated in CD11d^-/-/ApoE^-/- mice after 16 wk on a Western diet. CD11d deficiency led to a marked reduction in lipid deposition in aortas and isolated macrophages. Macrophage numbers in aortic sinuses of CD11d^-/- mice were reduced without affecting their apoptosis and proliferation. Adoptive transfer of fluorescently labeled wild-type and CD11d^-/- monocytes into ApoE^-/- mice demonstrated similar recruitment from circulation, but reduced accumulation of CD11d^-/- macrophages within the aortas. Furthermore, CD11d expression was significantly upregulated on macrophages in atherosclerotic lesions and M1 macrophages in vitro. Interestingly, expression of the related ligand-sharing integrin CD11b was not altered. This difference defines their distinct roles in the regulation of macrophage migration. CD11d-deficient M1 macrophages demonstrated improved migration in a three-dimensional fibrin matrix and during resolution of peritoneal inflammation, whereas migration of CD11b^-/- M1 macrophages was not affected. These results prove the contribution of high densities of CD11d to macrophage arrest during atherogenesis. Because high expression of CD11d was detected in several inflammation-dependent diseases, we suggest that CD11d/CD18 upregulation on proinflammatory macrophages may represent a common mechanism for macrophage retention at inflammatory sites, thereby promoting chronic inflammation and disease development.

Integrin signaling in atherosclerosis

Atherosclerosis, a chronic lipid-driven inflammatory disease affecting large arteries, represents the primary cause of cardiovascular disease in the world. The local remodeling of the vessel intima during atherosclerosis involves the modulation of vascular cell phenotype, alteration of cell migration and proliferation, and propagation of local extracellular matrix remodeling. All of these responses represent targets of the integrin family of cell adhesion receptors. As such, alterations in integrin signaling affect multiple aspects of atherosclerosis, from the earliest induction of inflammation to the development of advanced fibrotic plaques. Integrin signaling has been shown to regulate endothelial phenotype, facilitate leukocyte homing, affect leukocyte function, and drive smooth muscle fibroproliferative remodeling. In addition, integrin signaling in platelets contributes to the thrombotic complications that typically drive the clinical manifestation of cardiovascular disease. In this review, we examine the current literature on integrin regulation of atherosclerotic plaque development and the suitability of integrins as potential therapeutic targets to limit cardiovascular disease and its complications.

Molecular Imaging of Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) represent a vascular disease with severe complications. AAAs are currently the overall 10th leading cause of death in western countries and their incidence is rising. Although different diagnostic techniques are currently available in clinical practice, including ultrasound (US), magnetic resonance imaging (MRI), and computed tomography (CT), imaging-based prediction of life-threatening complications such as aneurysm-rupture remains challenging. Molecular imaging provides a novel diagnostic approach for in vivo visualization of biological processes and pathological alterations at a cellular and molecular level. Its overall aim is to improve our understanding of disease pathogenesis and to facilitate novel diagnostic pathways. This review outlines recent preclinical and clinical developments in molecular MRI, positron emission tomography (PET), and single-photon emission computed tomography (SPECT) for imaging of AAAs.

Preclinical validations of [18F]FPyPEGCBT-c(RGDfK): a 18F-labelled RGD peptide prepared by ligation of 2-cyanobenzothiazole and 1,2-aminothiol to image angiogenesis

Background

α_Vβ₃, α_Vβ₅ and α₅β₁ integrins are known to be involved in carcinogenesis and are overexpressed in many types of tumours compared to healthy tissues; thereby they have been selected as promising therapeutic targets. Positron emission tomography (PET) is providing a unique non-invasive screening assay to discriminate which patient is more prone to benefit from antiangiogenic therapies, and extensive research has been carried out to develop a clinical radiopharmaceutical that binds specifically to integrin receptors. We recently reported the synthesis of a new ¹⁸F-labelled RGD peptide prepared by 2-cyanobenzothiazole (CBT)/1,2-aminothiol conjugation. This study aims at characterising the preclinical biologic properties of this new tumour-targeting ligand, named [¹⁸F]FPyPEGCBT-c(RGDfK).

The in vitro binding properties of [¹⁸F]FPyPEGCBT-c(RGDfK) were analysed by standard binding assay in U-87 MG and SKOV-3 cancer models and its selectivity towards integrins by siRNA depletions. Its preclinical potential was studied in mice bearing subcutaneous tumours by ex vivo biodistribution studies and in vivo microPET/CT imaging.

Results

In vitro, FPyPEGCBT-c(RGDfK) efficiently bound RGD-recognising integrins as compared to a control c(RGDfV) peptide (IC₅₀ = 30.8 × 10⁻⁷ M vs. 6.0 × 10⁻⁷ M). [¹⁸F]FPyPEGCBT-c(RGDfK) cell uptake was mediated by an active transport through binding to α_V, β₃ and β₅ but not to β₁ subunits. In vivo, this new tracer demonstrated specific tumour uptake with %ID/g of 2.9 and 2.4 in U-87 MG and SKOV-3 tumours 1 h post injection. Tumour-to-muscle ratios of 4 were obtained 1 h after intravenous administration of the tracer allowing good visualisation of the tumours. However, unfavourable background accumulation and high hepatobiliary excretion were observed.

Conclusion

[¹⁸F]FPyPEGCBT-c(RGDfK) specifically detects tumours expressing RGD-recognising integrin receptors in preclinical studies. Further optimisation of this radioligand may yield candidates with improved imaging properties and would warrant the further use of this efficient labelling technique for alternative targeting vectors.

Electronic supplementary material

The online version of this article (doi:10.1186/s41181-016-0019-z) contains supplementary material, which is available to authorized users.

Talin and vinculin are downregulated in atherosclerotic plaque; Tampere Vascular Study

BACKGROUND AND AIMS

Focal adhesions (FA) play an important role in the tissue remodeling and in the maintenance of tissue integrity and homeostasis. Talin and vinculin proteins are among the major constituents of FAs contributing to cellular well-being and intercellular communication.

METHODS

Microarray analysis (MA) and qRT-PCR low-density array were implemented to analyze talin-1, talin-2, meta-vinculin and vinculin gene expression in circulating blood and arterial plaque.

RESULTS

All analyzed genes were significantly and consistently downregulated in plaques (carotid, abdominal aortic and femoral regions) compared to left internal thoracic artery (LITA) control. The use of LITA samples as controls for arterial plaque samples was validated using immunohistochemistry by comparing LITA samples with healthy arterial samples from a cadaver. Even though the differences in expression levels between stable and unstable plaques were not statistically significant, we observed further negative tendency in the expression in unstable atherosclerotic plaques. The confocal tissue imaging revealed gradient of talin-1 expression in plaque with reduction close to the vessel lumen. Similar gradient was observed for talin-2 expression in LITA controls but was not detected in plaques. This suggests that impaired tissue mechanostability affects the tissue remodeling and healing capabilities leading to development of unstable plaques.

CONCLUSIONS

The central role of talin and vinculin in cell adhesions suggests that the disintegration of the tissue in atherosclerosis could be partially driven by downregulation of these genes, leading to loosening of cell-ECM interactions and remodeling of the tissue.

Inhibition of transglutaminase 2 reduces efferocytosis in human macrophages: Role of CD14 and SR-AI receptors

BACKGROUND AND AIMS

Transglutaminase 2 (TGM2), a member of the transglutaminase family of enzymes, is a multifunctional protein involved in numerous events spanning from cell differentiation, to signal transduction, apoptosis, and wound healing. It is expressed in a variety of cells, macrophages included. Macrophage TGM2 promotes the clearance of apoptotic cells (efferocytosis) and emerging evidence suggests that defective efferocytosis contributes to the consequences of inflammation-associated diseases, including atherosclerotic lesion progression and its sequelae. Of interest, active TGM2 identified in human atherosclerotic lesions plays critical roles in plaque stability through effects on matrix cross-linking and TGFβ activity. This study explores the mechanisms by which TGM2 controls efferocytosis in human macrophages.

METHODS AND RESULTS

Herein we show that TGM2 increases progressively during monocyte differentiation towards macrophages and controls their efferocytic potential as well as morphology and viability. Two experimental approaches that took advantage of the inhibition of TGM2 activity and protein silencing give proof that TGM2 reduction significantly impairs macrophage efferocytosis. Among the mechanisms involved we highlighted a role of the receptors CD14 and SR-AI whose levels were markedly reduced by TGM2 inhibition. Conversely, CD36 receptor and αvβ3 integrin levels were not influenced. Of note, lipid accumulation and IL-10 secretion were reduced in macrophages displaying defective efferocytosis.

CONCLUSION

Overall, our data define a crucial role of TGM2 activity during macrophage differentiation via mechanisms involving CD14 and SR-AI receptors and show that TGM2 inhibition triggers a pro-inflammatory phenotype.

Molecular Imaging of Vulnerable Atherosclerotic Plaques in Animal Models

Atherosclerosis is characterized by intimal plaques of the arterial vessels that develop slowly and, in some cases, may undergo spontaneous rupture with subsequent heart attack or stroke. Currently, noninvasive diagnostic tools are inadequate to screen atherosclerotic lesions at high risk of acute complications. Therefore, the attention of the scientific community has been focused on the use of molecular imaging for identifying vulnerable plaques. Genetically engineered murine models such as ApoE^−/− and ApoE^−/−Fbn1C1039G^+/− mice have been shown to be useful for testing new probes targeting biomarkers of relevant molecular processes for the characterization of vulnerable plaques, such as vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, intercellular adhesion molecule (ICAM)-1, P-selectin, and integrins, and for the potential development of translational tools to identify high-risk patients who could benefit from early therapeutic interventions. This review summarizes the main animal models of vulnerable plaques, with an emphasis on genetically altered mice, and the state-of-the-art preclinical molecular imaging strategies.

Quantification of Endothelial αvβ3 Expression with High-Frequency Ultrasound and Targeted Microbubbles: In Vitro and In Vivo Studies

Angiogenesis is a critical feature of plaque development in atherosclerosis and might play a key role in both the initiation and later rupture of plaques. The precursory molecular or cellular pro-angiogenic events that initiate plaque growth and that ultimately contribute to plaque instability, however, cannot be detected directly with any current diagnostic modality. This study was designed to investigate the feasibility of ultrasound molecular imaging of endothelial αvβ3 expression in vitro and in vivo using αvβ3-targeted ultrasound contrast agents (UCAs). In the in vitro study, αvβ3 expression was confirmed by immunofluorescence in a murine endothelial cell line and detected using the targeted UCA and ultrasound imaging at 18-MHz transmit frequency. In the in vivo study, expression of endothelial αvβ3 integrin in murine carotid artery vessels and microvessels of the salivary gland was quantified using targeted UCA and high-frequency ultrasound in seven animals. Our results indicated that endothelial αvβ3 expression was significantly higher in the carotid arterial wall containing atherosclerotic lesions than in arterial segments without any lesions. We also found that the salivary gland can be used as an internal positive control for successful binding of targeted UCA to αvβ3 integrin. In conclusion, αvβ3-targeted UCA allows non-invasive assessment of the expression levels of αvβ3 on the vascular endothelium and may provide potential insights into early atherosclerotic plaque detection and treatment monitoring.

WISP1-αvβ3 integrin signaling positively regulates TLR-triggered inflammation response in sepsis induced lung injury

We recently noted that the matricellular protein WISP1 contributes to sepsis induced acute lung injury (ALI) via integrin β6. In the current study, we pursued further aspects of WISP1 modulation of TLR signaling in lungs of mice after sepsis and TLR4 mediated release of TNF-α in macrophages. After confirming that TLR4 and CD14 are critical in transducing sepsis mediated ALI, we now demonstrate that intrapulmonary αvβ3 is increased by polymicrobrial sepsis in a TLR4, CD14 dependent fashion. Comparison of cultured macrophages revealed that WISP1 increased release of TNF-α from RAW264.7 cells with baseline expression of αvβ3, but primary cultures of peritoneal macrophages (PMø) required activation of TLR4 to induce de novo synthesis of αvβ3 enabling WISP1 to stimulate release of TNF-α. The specific requirement for β3 integrin was apparent when the effect of WISP1 was lost in PMø isolated from β3(-/-) mice. WISP1 enhanced TLR4 mediated ERK signaling and U0126 (an ERK inhibitor) blocked LPS induced β3 integrin expression and WISP1 enhanced TNF-α release. Collectively these data suggest that WISP1-αvβ3 integrin signaling is involved in TLR4 pathways in macrophages and may be an important contributor to TLR4/CD14 mediated inflammation in sepsis induced lung injury.

Dual-Modality Activity-Based Probes as Molecular Imaging Agents for Vascular Inflammation

Macrophages are cellular mediators of vascular inflammation and are involved in the formation of atherosclerotic plaques. These immune cells secrete proteases such as matrix metalloproteinases and cathepsins that contribute to disease formation and progression. Here, we demonstrate that activity-based probes (ABPs) targeting cysteine cathepsins can be used in murine models of atherosclerosis to noninvasively image activated macrophage populations using both optical and PET/CT methods. The probes can also be used to topically label human carotid plaques demonstrating similar specific labeling of activated macrophage populations.

METHODS

Macrophage-rich carotid lesions were induced in FVB mice fed on a high-fat diet by streptozotocin injection followed by ligation of the left common carotid artery. Mice with carotid atherosclerotic plaques were injected with the optical or dual-modality probes BMV109 and BMV101, respectively, via the tail vein and noninvasively imaged by optical and small-animal PET/CT at different time points. After noninvasive imaging, the murine carotid arteries were imaged in situ and ex vivo, followed by immunofluorescence staining to confirm target labeling. Additionally, human carotid plaques were topically labeled with the probe and analyzed by both sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunofluorescence staining to confirm the primary targets of the probe.

RESULTS

Quantitative analysis of the signal intensity from both optical and PET/CT imaging showed significantly higher levels of accumulation of BMV109 and BMV101 (P < 0.005 and P < 0.05, respectively) in the ligated left carotid arteries than the right carotid or healthy arteries. Immunofluorescence staining for macrophages in cross-sectional slices of the murine artery demonstrated substantial infiltration of macrophages in the neointima and adventitia of the ligated left carotid arteries compared with the right. Analysis of the human plaque tissues by sodium dodecyl sulfate polyacrylamide gel electrophoresis confirmed that the primary targets of the probe were cathepsins X, B, S, and L. Immunofluorescence labeling of the human tissue with the probe demonstrated colocalization of the probe with CD68, elastin, and cathepsin S, similar to that observed in the experimental carotid inflammation murine model.

CONCLUSION

We demonstrate that ABPs targeting the cysteine cathepsins can be used in murine models of atherosclerosis to noninvasively image activated macrophage populations using both optical and PET/CT methods. The probes could also be used to topically label human carotid plaques demonstrating similar specific labeling of activated macrophage populations. Therefore, ABPs targeting the cysteine cathepsins are potentially valuable new reagents for rapid and noninvasive imaging of atherosclerotic disease progression and plaque vulnerability.

Recent Advances in the Development of PET/SPECT Probes for Atherosclerosis Imaging

The rupture of vulnerable atherosclerotic plaques and subsequent thrombus formation are the major causes of myocardial and cerebral infarction. Accordingly, the detection of vulnerable plaques is important for risk stratification and to provide appropriate treatment. Inflammation imaging using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) has been most extensively studied for detecting vulnerable atherosclerotic plaques. It is of great importance to develop PET/SPECT probes capable of specifically visualizing the biological molecules involved in atherosclerotic plaque formation and/or progression. In this article, we review recent advances in the development of PET/SPECT probes for visualizing atherosclerotic plaques and their application to therapy monitoring, mainly focusing on experimental studies.

αVβ3 integrin-targeted microSPECT/CT imaging of inflamed atherosclerotic plaques in mice

Background

α_Vβ₃-integrin is expressed by activated endothelial cells and macrophages in atherosclerotic plaques and may represent a valuable marker of high-risk plaques. We evaluated ^99mTc-maraciclatide, an integrin-specific tracer, for imaging vascular inflammation in atherosclerotic lesions in mice.

Methods

Apolipoprotein E-negative (ApoE^−/−) mice on a Western diet (n = 10) and normally fed adult C57BL/6 control mice (n = 4) were injected with ^99mTc-maraciclatide (51.8 ± 3.7 MBq). A blocking peptide was infused in three ApoE^−/− mice; this condition served as another control. After 90 min, the animals were imaged via single-photon emission computed tomography (SPECT). While maintained in the same position, the mice were transferred to computed tomography (CT) to obtain contrast-enhanced images of the aortic arch. Images from both modalities were fused, and signal was quantified in the aortic arch and in the vena cava for subtraction of blood-pool activity. The aorta was carefully dissected after imaging for gamma counting, autoradiography, and histology.

Results

Tracer uptake was significantly higher in ApoE^−/− mice than in both groups of control mice (1.56 ± 0.33 vs. 0.82 ± 0.24 vs. 0.98 ± 0.11, respectively; P = 0.006). Furthermore, higher tracer activity was detected via gamma counting in the aorta of hypercholesterolemic mice than in both groups of control mice (1.52 ± 0.43 vs. 0.78 ± 0.19 vs. 0.47 ± 0.31 ^99mTc-maraciclatide %ID/g, respectively; P = 0.018). Autoradiography showed significantly higher tracer uptake in the atherosclerotic aorta than in the control aorta (P = 0.026). Finally, in the atherosclerotic aorta, immunostaining indicated that the integrin signal came predominantly from macrophages and was correlated with the macrophage CD68 immunomarker (r = 0.73).

Conclusions

^99mTc-maraciclatide allows in vivo detection of inflamed atherosclerotic plaques in mice and may represent a non-invasive approach for identifying high-risk plaques in patients.

Optical imaging biomarkers of drug-induced vascular injury

Drug-induced vascular injury (DIVI), defined as arterial medial degeneration/necrosis usually associated with perivascular inflammation, is frequently observed in the mesenteric arteries of rats but the relevance to humans remains a hurdle for drug development. Here, we describe the evaluation of commercially available optical imaging biomarkers using a rat DIVI model. Male Sprague Dawley rats were administered 10 mg/kg/day of a proprietary soluble guanylate cyclase activator (sGCa). Optical agents, AngioSense for the detection of vessel permeability, MMPSense for the detection of activated matrix metalloproteinases (MMPs), and IntegriSense for the detection of αvβ3 integrin, were injected via tail vein 24 hours before fluorescence (FL) ex vivo imaging. Imaging found a statistically significant difference in FL from all optical agents between treated and vehicle groups (p < .05). Mesenteric arteries were further analyzed by histopathology, flow cytometry, and immunohistochemistry. Histopathology confirmed perivascular inflammation and/or arterial medial degeneration in the sGCa-treated animals. Flow cytometry of digested arteries revealed myeloid cells as a main source of MMPSense signal. Immunohistochemical analysis further identified elevated MMP-9 expression within arterial walls and surrounding tissue of treated animals. Together, these data demonstrate that MMPSense and AngioSense are sensitive optical imaging biomarkers for the quantification of DIVI in rat mesenteric arteries.

Radiolabeled Cyclic RGD Peptide Bioconjugates as Radiotracers Targeting Multiple Integrins

Angiogenesis is a requirement for tumor growth and metastasis. The angiogenic process depends on vascular endothelial cell migration and invasion, and is regulated by various cell adhesion receptors. Integrins are such a family of receptors that facilitate the cellular adhesion to and migration on extracellular matrix proteins in the intercellular spaces and basement membranes. Among 24 members of the integrin family, αvβ3 is studied most extensively for its role in tumor angiogenesis and metastasis. The αvβ3 is expressed at relatively low levels on epithelial cells and mature endothelial cells, but it is highly expressed on the activated endothelial cells of tumor neovasculature and some tumor cells. This restricted expression makes αvβ3 an excellent target to develop antiangiogenic drugs and diagnostic molecular imaging probes. Since αvβ3 is a receptor for extracellular matrix proteins with one or more RGD tripeptide sequence, many radiolabeled cyclic RGD peptides have been evaluated as "αvβ3-targeted" radiotracers for tumor imaging over the past decade. This article will use the dimeric and tetrameric cyclic RGD peptides developed in our laboratories as examples to illustrate basic principles for development of αvβ3-targeted radiotracers. It will focus on different approaches to maximize the radiotracer tumor uptake and tumor/background ratios. This article will also discuss some important assays for preclinical evaluations of integrin-targeted radiotracers. In general, multimerization of cyclic RGD peptides increases their integrin binding affinity and the tumor uptake and retention times of their radiotracers. Regardless of their multiplicity, the capability of cyclic RGD peptides to bind other integrins (namely, αvβ5, α5β1, α6β4, α4β1, and αvβ6) is expected to enhance the radiotracer tumor uptake due to the increased integrin population. The results from preclinical and clinical studies clearly show that radiolabeled cyclic RGD peptides (such as (99m)Tc-3P-RGD2, (18)F-Alfatide-I, and (18)F-Alfatide-II) are useful as the molecular imaging probes for early cancer detection and noninvasive monitoring of the tumor response to antiangiogenic therapy.

Tenascin-C may accelerate cardiac fibrosis by activating macrophages via the integrin αVβ3/nuclear factor-κB/interleukin-6 axis

Tenascin-C (TN-C) is an extracellular matrix protein not detected in normal adult heart, but expressed in several heart diseases closely associated with inflammation. Accumulating data suggest that TN-C may play a significant role in progression of ventricular remodeling. In this study, we aimed to elucidate the role of TN-C in hypertensive cardiac fibrosis and underlying molecular mechanisms. Angiotensin II was administered to wild-type and TN-C knockout mice for 4 weeks. In wild-type mice, the treatment induced increase of collagen fibers and accumulation of macrophages in perivascular areas associated with deposition of TN-C and upregulated the expression levels of interleukin-6 and monocyte chemoattractant protein-1 as compared with wild-type/control mice. These changes were significantly reduced in TN-C knockout/angiotensin II mice. In vitro, TN-C accelerated macrophage migration and induced accumulation of integrin αVβ3 in focal adhesions, with phosphorylation of focal adhesion kinase (FAK) and Src. TN-C treatment also induced nuclear translocation of phospho-NF-κB and upregulated interleukin-6 expression of macrophages in an NF-κB-dependent manner; this being suppressed by inhibitors for integrin αVβ3 and Src. Furthermore, interleukin-6 upregulated expression of collagen I by cardiac fibroblasts. TN-C may enhance inflammatory responses by accelerating macrophage migration and synthesis of proinflammatory/profibrotic cytokines via integrin αVβ3/FAK-Src/NF-κB, resulting in increased fibrosis.

αvβ3 Integrins Mediate Flow-Induced NF-κB Activation, Proinflammatory Gene Expression, and Early Atherogenic Inflammation

Endothelial cell interactions with transitional matrix proteins, such as fibronectin, occur early during atherogenesis and regulate shear stress-induced endothelial cell activation. Multiple endothelial cell integrins bind transitional matrix proteins, including α5β1, αvβ3, and αvβ5. However, the role these integrins play in mediating shear stress-induced endothelial cell activation remains unclear. Therefore, we sought to elucidate which integrin heterodimers mediate shear stress-induced endothelial cell activation and early atherogenesis. We now show that inhibiting αvβ3 integrins (S247, siRNA), but not α5β1 or αvβ5, blunts shear stress-induced proinflammatory signaling (NF-κB, p21-activated kinase) and gene expression (ICAM1, VCAM1). Importantly, inhibiting αvβ3 did not affect cytokine-induced proinflammatory responses or inhibit all shear stress-induced signaling, because Akt, endothelial nitric oxide synthase, and extracellular regulated kinase activation remained intact. Furthermore, inhibiting αv integrins (S247), but not α5 (ATN-161), in atherosclerosis-prone apolipoprotein E knockout mice significantly reduced vascular remodeling after acute induction of disturbed flow. S247 treatment similarly reduced early diet-induced atherosclerotic plaque formation associated with both diminished inflammation (expression of vascular cell adhesion molecule 1, plaque macrophage content) and reduced smooth muscle incorporation. Inducible, endothelial cell-specific αv integrin deletion similarly blunted inflammation in models of disturbed flow and diet-induced atherogenesis but did not affect smooth muscle incorporation. Our studies identify αvβ3 as the primary integrin heterodimer mediating shear stress-induced proinflammatory responses and as a key contributor to early atherogenic inflammation.

Role of mast cells in atherosclerosis: a classical inflammatory disease

Atherosclerosis is an inflammatory disease and hyperlipidaemia is one of the main risk factors for aging, hypertension and diabetes. Variance in plasma LDL cholesterol concentration may be associated with differences in cardiovascular disease risk and high levels of lipids are associated with increased risk of developing atherosclerosis. Macrophages, which generate pro-inflammatory cytokines, mainly interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-alpha), are deeply involved in atherosclerosis, as well as mast cells which generate several cytokines, including IL-6 and IFN-gamma, and chemokines such as eotaxin, MCP-1 and RANTES involved in monocyte recruitment and differentiation in the arterial wall. In addition, mast cells participate in lipid retention and vascular cell remodeling, and are mediators of innate and adaptive immunity during atherosclerosis. Mast cells which accumulate in the human arterial intima and adventitia during atherosclerotic plaque progression, release vasoactive and angiogenic compounds, and pro-inflammatory mediators, such as arachidonic acid metabolites, histamine, cytokines/chemokines, platelet activating factor (PAF) and proteolytic enzymes. Mast cells can be activated by pro-inflammatory stimuli, including cytokines, hypercholesterolemia, and hyperglycemia, and trigger the endothelial expression of adhesion molecules such as P-selection, vascular cell adhesion molecule-1 (VCAM-1) and chemokines which mediate the recruitment and adhesion of leukocytes. The participation of mast cells in atherosclerosis is still an enigma and it may be of therapeutic interest to clarify this process.

Under-expression of α8 integrin aggravates experimental atherosclerosis

Integrins play an important role in vascular biology. The α8 integrin chain attenuates smooth muscle cell migration but its functional role in the development of atherosclerosis is unclear. Therefore, we studied the contribution of α8 integrin to atherosclerosis and vascular remodelling. We hypothesized that α8 integrin expression is reduced in atherosclerotic lesions, and that its under-expression leads to a more severe course of atherosclerosis. α8 Integrin was detected by immunohistochemistry and qPCR and α8 integrin-deficient mice were used to induce two models of atherosclerotic lesions. First, ligation of the carotid artery led to medial thickening and neointima formation, which was quantified in carotid cross-sections. Second, after crossing into ApoE-deficient mice, the formation of advanced vascular lesions with atherosclerotic plaques was quantified in aortic en face preparations stained with Sudan IV. Parameters of renal physiology and histopathology were assessed: α8 integrin was detected in the media of human and murine vascular tissue and was down-regulated in arteries with advanced atherosclerotic lesions. In α8 integrin-deficient mice (α8(-/-) ) as well as α8(+/-) and α8(+/+) littermates, carotid artery ligation increased media:lumen ratios in all genotypes, with higher values in ligated α8(-/-) and α8(+/-) compared to ligated α8(+/+) animals. Carotid artery ligation increased smooth muscle cell number in the media of α8(+/+) mice and, more prominently, of α8(-/-) or α8(+/-) mice. On an ApoE(-/-) background, α8(+/-) and α8(-/-) mice developed more atherosclerotic plaques than α8(+/+) mice. α8 Integrin expression was reduced in α8(+/-) animals. Renal damage with increased serum creatinine and glomerulosclerosis was detected in α8(-/-) mice only. Thus, under-expression of α8 integrin aggravates vascular lesions, while a complete loss of α8 integrin results in reduced renal mass and additional renal disease in the presence of generalized atherosclerosis. Our data support the hypothesis that integrin α8β1 has a protective role in arterial remodelling and atherosclerosis.