Cardiac delivery of modified mRNA using lipid nanoparticles: Cellular targets and biodistribution after intramyocardial administration.

Despite research efforts being made towards preserving (or even regenerating) heart tissue after an ischemic event, there is a lack of resources in current clinical treatment modalities for patients with acute myocardial infarction that specifically address cardiac tissue impairment. Modified messenger RNA (modRNA) presents compelling properties that could allow new therapeutic strategies to tackle the underlying molecular pathways that ultimately lead to development of chronic heart failure. However, clinical application of modRNA for the heart is challenged by the lack of effective and safe delivery systems. Lipid nanoparticles (LNPs) represent a well characterized class of RNA delivery systems, which were recently approved for clinical usage in mRNA-based COVID-19 vaccines. In this study, we evaluated the potential of LNPs for cardiac delivery of modRNA. We tested how variations in C12-200 modRNA-LNP composition affect transfection levels and biodistribution after intramyocardial administration in both healthy and myocardial-infarcted mice, and determined the targeted cardiac cell types. Our data revealed that LNP-mediated modRNA delivery outperforms the current state of the art (modRNA in citrate buffer) upon intramyocardial administration in mice, with only minor differences among the formulations tested. Furthermore, we determined both in vitro and in vivo that the cardiac cells targeted by modRNA-LNPs include fibroblasts, endothelial cells and epicardial cells, suggesting that these cell types could represent targets for therapeutic interference with these LNP formulations. These outcomes may serve as a starting point for LNP development specifically for therapeutic mRNA cardiac delivery applications.

Increased frequency of proangiogenic tunica intima endothelial kinase 2 (Tie2) expressing monocytes in individuals with type 2 diabetes mellitus.

BACKGROUND: Individuals with type 2 diabetes mellitus (T2DM) have an increased risk for developing macrovascular disease (MVD) manifested by atherosclerosis. Phenotypically and functionally different monocyte subsets (classical; CD14++CD16-, non-classical; CD14+CD16++, and intermediate; CD14++CD16+) including pro-angiogenic monocytes expressing Tie2 (TEMs) can be identified. Here we investigated monocyte heterogeneity and its association with T2DM and MVD. METHODS: Individuals with (N = 51) and without (N = 56) T2DM were recruited and allocated to "non-MVD" or "with MVD" (i.e., peripheral or coronary artery disease) subgroups. Blood monocyte subsets were quantified based on CD14, CD16 and Tie2 expression levels. Plasma levels of Tie2-ligands angiopoietin-1 and angiopoietin-2 were determined using ELISA. Carotid endarterectomy samples from individuals with (N = 24) and without (N = 22) T2DM were stained for intraplaque CD68+ macrophages (inflammation) and CD34+ (angiogenesis), as plaque vulnerability markers. RESULTS: Monocyte counts were similar between individuals with T2DM and healthy controls (non-diabetic, non-MVD). Non-classical monocytes were reduced (p < 0.05) in T2DM, whereas the percentage of TEMs within the intermediate subset was increased (p < 0.05). T2DM was associated with increased angiopoietin-1 (p < 0.05) and angiopoietin-2 (p = 0.0001) levels. Angiopoietin-2 levels were higher in T2DM individuals with MVD compared with non-MVD (p < 0.01). Endarterectomized plaques showed no differences in macrophage influx and microvessel number between individuals with and without T2DM. CONCLUSIONS: Monocyte subset distribution is altered in T2DM with reduced non-classical monocytes and increased TEM percentage in the intermediate monocyte subset. Increased angiopoietin-2 levels together with increased frequency of TEMs might promote plaque vulnerability in T2DM which could however not be confirmed at tissue level in advanced atherosclerotic lesions.

The morphological and molecular mechanisms of epithelial/endothelial-to-mesenchymal transition and its involvement in atherosclerosis.

Cell transdifferentiation occurs during cardiovascular development or remodeling either as a pathologic feature in the progression of disease or as a response to injury. Endothelial-to-Mesenchymal Transition (EndMT) is a process that is classified as a specialized form of Epithelial-to-Mesenchymal Transition (EMT), in which epithelial cells lose their epithelial characteristics and gain a mesenchymal phenotype. During transdifferentiation, cells lose both cell-cell contacts and their attachment to the basement membrane. Subsequently, the shape of the cells changes from a cuboidal to an elongated shape. A rearrangement of actin filaments facilitates the cells to become motile and prime their migration into the underlying tissue. EMT is a key process during embryonic development, wound healing and tissue regeneration, but has also been implicated in pathophysiological processes, such organ fibrosis and tumor metastases. EndMT has been associated with additional pathophysiological processes in cardiovascular related diseases, including atherosclerosis. Recent studies prove a significant role for EndMT in the progression and destabilization of atherosclerotic plaques, as a consequence of EndMT-derived fibroblast infiltration and the increased secretion of matrix metalloproteinase respectively. In this review we will discuss the essential molecular and morphological mechanisms of EMT and EndMT, along with their common denominators and key differences. Finally, we will discuss the role of EMT/EndMT in developmental and pathophysiological processes, focusing on the potential role of EndMT in atherosclerosis in more depth.

Heat-killed Staphylococcus aureus reduces atherosclerosis by inducing anti-inflammatory macrophages.

BACKGROUND: Staphylococcus aureus cell wall components can induce IL-10 responses by immune cells, which may be atheroprotective. Therefore, in this study, we investigated whether heat-killed S. aureus (HK-SA) could inhibit the development of atherosclerosis. METHODS: Atherosclerosis-susceptible LDL receptor-deficient mice were administered intraperitoneal HK-SA twice weekly and fed a Western-type diet for 6 weeks. RESULTS: HK-SA administration resulted in a 1.6-fold increase in IL-10 production by peritoneal macrophages and splenocytes, and a 12-fold increase in serum IL-10 levels. Moreover, aortic plaque ICAM-1, VCAM-1 and CCL2 expression levels were significantly downregulated by on average 40%. HK-SA-treated mice had reduced numbers of inflammatory Ly-6C(hi) monocytes as well as Th1 and Th17 cells in the circulation and spleen, respectively. Attenuated leucocyte recruitment resulted in a significant inhibition of macrophage and T cell infiltration in atherosclerotic plaques, culminating in a significant 34% reduction in the development of atherosclerosis. To determine the effects of intraperitoneal HK-SA treatment, we stimulated macrophages with HK-SA in vitro. This resulted in a significant toll-like receptor 2 (TLR2)-dependent increase in IL-10, arginase-1, iNOS, TNF-α, PD-L1, CCL22 and indoleamine 2,3-dioxygenase expression. It was found that phosphoinositide 3-kinase crucially determined the balance of pro- and anti-inflammatory gene expression. The HK-SA-induced macrophage phenotype resembled M2b-like immunoregulatory macrophages. CONCLUSIONS: We have shown that HK-SA treatment induces strong anti-inflammatory IL-10 responses by macrophages, which are largely dependent on TLR2 and PI3K, and protects against the development of atherosclerosis. Commensalism with S. aureus could thus reduce cardiovascular events.

Elevated mean neutrophil volume represents altered neutrophil composition and reflects damage after myocardial infarction.

Myocardial infarction (MI) induces an inflammatory response in which neutrophils fulfill a prominent role. Mean neutrophil volume (MNV) represents the average size of the circulating neutrophil population. Our goal was to determine the effect of MI on MNV and investigate the mechanisms behind MNV elevation. MNV of 84 MI patients was compared with the MNV of 209 stable angina patients and correlated to simultaneously measured CK levels. Fourteen pigs were subjected to temporary coronary balloon occlusion and blood was sampled at multiple time points to measure MNV. Echocardiography was performed followed by ex vivo infarct size assessment after 72 h. MNV was higher in MI patients compared to stable angina patients (602 SD26 AU vs. 580 SD20 AU, p < 0.0001) and correlated with simultaneously measured CK levels (R = 0.357, p < 0.0001). In pigs, MNV was elevated post-MI (451 SD11 AU vs. 469 SD12 AU), p < 0.0001). MNV correlated with infarct size (R = 0.705, p = 0.007) and inversely correlated with left ventricular ejection fraction (R = -0.718, p = 0.009). Cell sorting revealed an increased presence of banded neutrophils after MI, which have a higher MNV compared to mature neutrophils post-MI (495 SD14 AU vs. 478 SD11 AU, p = 0.012). MNV from coronary sinus blood was higher than MNV of neutrophils from simultaneously sampled arterial blood (463 SD7.6 AU vs. 461 SD8.6 AU, p = 0.013) post-MI. The current study shows MNV is elevated and reflects cardiac damage post-MI. MNV increases due to altered neutrophil composition and systemic neutrophil activation. MNV may be an interesting parameter for prognostic assessment in MI and provide new insights into pathological innate immune responses evoked by ischemia-reperfusion.

Exendin-4 decreases liver inflammation and atherosclerosis development simultaneously by reducing macrophage infiltration.

BACKGROUND AND PURPOSE: The aetiology of inflammation in the liver and vessel wall, leading to non-alcoholic steatohepatitis (NASH) and atherosclerosis, respectively, shares common mechanisms including macrophage infiltration. To treat both disorders simultaneously, it is highly important to tackle the inflammatory status. Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, reduces hepatic steatosis and has been suggested to reduce atherosclerosis; however, its effects on liver inflammation are underexplored. Here, we tested the hypothesis that exendin-4 reduces inflammation in both the liver and vessel wall, and investigated the common underlying mechanism. EXPERIMENTAL APPROACH: Female APOE*3-Leiden.CETP mice, a model with human-like lipoprotein metabolism, were fed a cholesterol-containing Western-type diet for 5 weeks to induce atherosclerosis and subsequently treated for 4 weeks with exendin-4. KEY RESULTS: Exendin-4 modestly improved dyslipidaemia, but markedly decreased atherosclerotic lesion severity and area (-33%), accompanied by a reduction in monocyte adhesion to the vessel wall (-42%) and macrophage content in the plaque (-44%). Furthermore, exendin-4 reduced hepatic lipid content and inflammation as well as hepatic CD68⁺ (-18%) and F4/80⁺ (-25%) macrophage content. This was accompanied by less monocyte recruitment from the circulation as the Mac-1⁺ macrophage content was decreased (-36%). Finally, exendin-4 reduced hepatic chemokine expression in vivo and suppressed oxidized low-density lipoprotein accumulation in peritoneal macrophages in vitro, effects dependent on the GLP-1 receptor. CONCLUSIONS AND IMPLICATIONS: Exendin-4 reduces inflammation in both the liver and vessel wall by reducing macrophage recruitment and activation. These data suggest that exendin-4 could be a valuable strategy to treat NASH and atherosclerosis simultaneously.

An unexpected intriguing effect of Toll-like receptor regulator RP105 (CD180) on atherosclerosis formation with alterations on B-cell activation.

OBJECTIVE: In atherosclerosis, Toll-like receptors (TLRs) are traditionally linked to effects on tissue macrophages or foam cells. RP105, a structural TLR4 homolog, is an important regulator of TLR signaling. The effects of RP105 on TLR signaling vary for different leukocyte subsets known to be involved in atherosclerosis, making it unique in its role of either suppressing (in myeloid cells) or enhancing (in B cells) TLR-regulated inflammation in different cell types. We aimed to identify a role of TLR accessory molecule RP105 on circulating cells in atherosclerotic plaque formation. APPROACH AND RESULTS: Irradiated low density lipoprotein receptor deficient mice received RP105(-/-) or wild-type bone marrow. RP105(-/-) chimeras displayed a 57% reduced plaque burden. Interestingly, total and activated B-cell numbers were significantly reduced in RP105(-/-) chimeras. Activation of B1 B cells was unaltered, suggesting that RP105 deficiency only affected inflammatory B2 B cells. IgM levels were unaltered, but anti-oxidized low-density lipoprotein and anti-malondialdehyde-modified low-density lipoprotein IgG2c antibody levels were significantly lower in RP105(-/-) chimeras, confirming effects on B2 B cells rather than B1 B cells. Moreover, B-cell activating factor expression was reduced in spleens of RP105(-/-) chimeras. CONCLUSIONS: RP105 deficiency on circulating cells results in an intriguing unexpected TLR-associated mechanisms that decrease atherosclerotic lesion formation with alterations on proinflammatory B2 B cells.

Mesenchymal stem cell therapy for cardiac inflammation: immunomodulatory properties and the influence of toll-like receptors.

BACKGROUND: After myocardial infarction (MI), the inflammatory response is indispensable for initiating reparatory processes. However, the intensity and duration of the inflammation cause additional damage to the already injured myocardium. Treatment with mesenchymal stem cells (MSC) upon MI positively affects cardiac function. This happens likely via a paracrine mechanism. As MSC are potent modulators of the immune system, this could influence this postinfarct immune response. Since MSC express toll-like receptors (TLR), danger signal (DAMP) produced after MI could influence their immunomodulatory properties. SCOPE OF REVIEW: Not much is known about the direct immunomodulatory efficiency of MSC when injected in a strong inflammatory environment. This review focuses first on the interactions between MSC and the immune system. Subsequently, an overview is provided of the effects of DAMP-associated TLR activation on MSC and their immunomodulative properties after myocardial infarction. MAJOR CONCLUSIONS: MSC can strongly influence most cell types of the immune system. TLR signaling can increase and decrease this immunomodulatory potential, depending on the available ligands. Although reports are inconsistent, TLR3 activation may boost immunomodulation by MSC, while TLR4 activation suppresses it. GENERAL SIGNIFICANCE: Elucidating the effects of TLR activation on MSC could identify new preconditioning strategies which might improve their immunomodulative properties.

Vaccination strategies in atherosclerosis.

The treatment of atherosclerosis is currently based on lipid lowering in combination with anti-inflammatory therapies that slow the progression of atherosclerosis. Still, we are not able to fully inhibit the formation or progression of atherosclerotic lesions. A very effective strategy in other disease pathologies is vaccination, in which the body is challenged with the culprit protein or micro-organism in order to create a highly specific humoral immune-response. Immunisation can typically be divided into active or passive immunisation. Active immunisation occurs naturally when the body is exposed to certain microbes or antigens, but also artificially in the case of vaccination. Exposure to a microbe or antigen will result in the production of (antigen specific) antibodies. Passive immunisation is defined as the transfer of humoral immunity (as a result of antibody transfer). Another mechanism to ensure immune-protection is tolerance induction. Immune tolerance occurs naturally to prevent immune responses to 'self-antigens', but can also be induced to non-self antigens. Acquired tolerance to foreign antigens is accompanied by suppression of cellular and/or humoral immune response to the introduced antigen. In its most effective way, vaccination can result in a lifelong protection against the targeted pathology, and therefore the development of an atherosclerosis-specific vaccination is of high importance in the future prevention of atherosclerosis. One of the difficulties in developing effective vaccination strategies for atherosclerosis is the selection of a specific antigen to target. So far vaccination strategies have been based on targeting of lipid-antigens, inflammation-derived antigens, and recently cell-based vaccination strategies have been employed; but also the cardiovascular 'side-effects' of infection-based vaccines are worthy of our attention. This review describes the current status-quo on classical antibody associated vaccination strategies but also includes promising immune-modulation approaches that may lead to a clinical application.

Reduced leucocyte cholesteryl ester transfer protein expression in acute coronary syndromes.

OBJECTIVE: Cholesterol ester transfer protein (CETP) plays an important role in HDL cholesterol metabolism. Leucocytes, including monocyte-derived macrophages in the arterial wall synthesize and secrete CETP, but its role in atherosclerosis is unclear. The aim of the current study was to investigate the effect of acute coronary syndromes (ACS) on leucocyte CETP expression. RESEARCH DESIGN: Peripheral blood mononuclear cells (PBMCs) were freshly isolated from hospitalized ACS patients displaying Braunwald class IIIB unstable angina pectoris (UAP) on admission (t = 0) and at 180 days post inclusion (t = 180) for analysis of CETP expression. In addition, to prove the potential correlation between leucocyte CETP and ACS the effect of acute myocardial infarction on leucocyte CETP expression was studied in CETP transgenic mice. RESULTS: Upon admission, UAP patients displayed approximately 3-6 fold (P < 0.01) lower CETP mRNA and nearly absent CETP protein expression in PBMCs, as compared to healthy age-/sex-matched controls. Interestingly, CETP mRNA and protein levels were significantly elevated in PBMCs isolated from UAP patients (both stabilized and refractory) at t = 180 as compared to t = 0 (P < 0.01), which was correlated with a reduced inflammatory status after medical treatment. In agreement with the data obtained in UAP patients, markedly down-regulated leucocyte CETP mRNA expression was observed after coronary artery ligation in CETP transgenic mice, which also correlated with increased serum amyloid A levels. CONCLUSIONS: We are the first to report that episodes of UAP in humans and myocardial infarction in CETP transgenic mice are associated with reduced leucocyte CETP expression. We propose that the impairment in leucocyte CETP production is associated with an enhanced inflammatory status, which could be clinically relevant for the pathogenesis of ACS.

CC chemokine ligand-5 (CCL5/RANTES) and CC chemokine ligand-18 (CCL18/PARC) are specific markers of refractory unstable angina pectoris and are transiently raised during severe ischemic symptoms.

BACKGROUND: Chemokines play an important role in atherogenesis and in ischemic injury and repair; however, prospective data on individual chemokines in unstable angina pectoris (UAP) are scarce. Therefore, we assessed chemokine patterns in a prospective cohort of patients with UAP. METHODS AND RESULTS: Plasma samples of 54 patients with Braunwald class IIIB UAP were examined at baseline for 11 chemokines and 5 inflammatory mediators via multiplex analysis. Levels of CC chemokine ligand (CCL)-5 (also known as RANTES [regulated on activation, normally T-cell expressed, and secreted]; 32.7 versus 23.1 ng/mL, P=0.018) and CCL18 (also known as PARC [pulmonary and activation-regulated chemokine]; 104.4 versus 53.7 ng/mL, P=0.011) were significantly elevated in patients with refractory ischemic symptoms versus stabilized patients. Temporal monitoring by ELISA of CCL5, CCL18, and soluble CD40 ligand (sCD40) levels revealed a drop in CCL5 and sCD40L levels in all UAP patients from day 2 onward (CCL5 12.1 ng/mL, P<0.001; sCD40L 1.35 ng/mL, P<0.05), whereas elevated CCL18 levels were sustained for at least 2 days, then were decreased at 180 days after inclusion (34.5 ng/mL, P<0.001). Peripheral blood mononuclear cells showed increased protein expression of chemokine receptors CCR3 and CCR5 in CD3+ and CD14+ cells at baseline compared with 180 days after inclusion, whereas mRNA levels were downregulated, which was attributable in part to a postischemic release of human neutrophil peptide-3-positive neutrophils and in part to negative feedback. Finally, elevated CCL5 and CCL18 levels predicted future cardiovascular adverse events, whereas C-reactive protein and sCD40L levels did not. CONCLUSIONS: We are the first to report that CCL18 and CCL5 are transiently raised during episodes of UAP, and peak levels of both chemokines are indicative of refractory symptoms. Because levels of both chemokines, as well as of cognate receptor expression by circulating peripheral blood mononuclear cells, are increased during cardiac ischemia, this may point to an involvement of CCL5/CCL18 in the pathophysiology of UAP and/or post-UAP responses.

Chemokines and atherosclerotic plaque progression: towards therapeutic targeting?

Atherosclerosis is currently viewed as an inflammatory disease in which the initiation and progression of the atherosclerotic plaque towards a rupture prone, unstable plaque is driven by leukocyte recruitment mediated by various inflammatory mediators. Recently, interest in chemotactic cytokines or chemokines with regard to atherosclerosis has been growing as chemokines mediate the influx of leukocytes that is typical of atherothrombosis. The activity of the majority of chemokines is overlapping and chemokines are not only produced by the various cellular constituents of the atherosclerotic plaque but also by activated platelets. Consequently, the direct influence of individual chemokines on plaque destabilisation and rupture is widespread and rather unclear. Experimental research has already established the role of a number of chemokines in advanced atherosclerosis. Nevertheless, given the complexity and size of the chemokine family, further screening of cardiovascular disease for chemokine level and genetic polymorphisms for chemokines will be warranted as the search for viable biomarkers of plaque destabilization as well as novel therapeutic targets for specific atheroregressive therapeutic compounds is ongoing. With regard to the latter, clinical trials with specific chemokine inhibitory strategies, like chemokine receptor antagonists, are already underway in other inflammatory disorders. Summarizing, chemokine inhibition likely constitutes an important therapeutic option next to already established drugs in the management of cardiovascular disease.

Hypersensitivity reactions in mouse airways after a single and a repeated hapten challenge.

OBJECTIVE AND DESIGN: In this study, we examined the effect of a single and a repeated hapten-challenge on inflammatory processes in the airways of mice undergoing a hapten-induced non-IgE mediated hypersensitivity reaction. METHODS: BALB/c mice were skin-sensitized with the hapten dinitroflourobenzene (DNFB) and intra-airway challenged with dinitrobenzene sulphonic acid (DNS). Mucosal exudation, tracheal vascular permeability, cellular accumulation, and serum murine mast cell protease (MMCP) were investigated at different time points after the first DNS-challenge and 30 min after a repeated DNS-challenge. RESULTS: MMCP levels in serum were increased at all time points after single challenge and repeated challenge. Increased vascular permeability as determined by Monastral blue staining, was found in the trachea of DNFB-sensitized mice after single DNS-challenge. A second exposure to DNS profoundly enhanced the Monastral blue labeling of the tracheal blood vessels of DNFB-sensitized mice. Furthermore, increased mucosal exudation and polymorphonuclear cell (PMN) accumulation were present in DNFB-sensitized mice compared to vehicle-sensitized animals after the first DNS challenge. CONCLUSIONS: Increased mucosal exudation, vascular permeability, and PMN accumulation are prominent inflammatory features of the DNFB-induced hypersensitivity reaction in the airways. Furthermore, mast cell activation is associated with this hapten-induced hypersensitivity reaction.