Enabling a robust scalable manufacturing process for therapeutic exosomes through oncogenic immortalization of human ESC-derived MSCs

Background

Exosomes or secreted bi-lipid vesicles from human ESC-derived mesenchymal stem cells (hESC-MSCs) have been shown to reduce myocardial ischemia/reperfusion injury in animal models. However, as hESC-MSCs are not infinitely expansible, large scale production of these exosomes would require replenishment of hESC-MSC through derivation from hESCs and incur recurring costs for testing and validation of each new batch. Our aim was therefore to investigate if MYC immortalization of hESC-MSC would circumvent this constraint without compromising the production of therapeutically efficacious exosomes.

Methods

The hESC-MSCs were transfected by lentivirus carrying a MYC gene. The transformed cells were analyzed for MYC transgene integration, transcript and protein levels, and surface markers, rate of cell cycling, telomerase activity, karyotype, genome-wide gene expression and differentiation potential. The exosomes were isolated by HPLC fractionation and tested in a mouse model of myocardial ischemia/reperfusion injury, and infarct sizes were further assessed by using Evans' blue dye injection and TTC staining.

Results

MYC-transformed MSCs largely resembled the parental hESC-MSCs with major differences being reduced plastic adherence, faster growth, failure to senesce, increased MYC protein expression, and loss of in vitro adipogenic potential that technically rendered the transformed cells as non-MSCs. Unexpectedly, exosomes from MYC-transformed MSCs were able to reduce relative infarct size in a mouse model of myocardial ischemia/reperfusion injury indicating that the capacity for producing therapeutic exosomes was preserved.

Conclusion

Our results demonstrated that MYC transformation is a practical strategy in ensuring an infinite supply of cells for the production of exosomes in the milligram range as either therapeutic agents or delivery vehicles. In addition, the increased proliferative rate by MYC transformation reduces the time for cell production and thereby reduces production costs.

Circulating leukocyte and carotid atherosclerotic plaque telomere length: interrelation, association with plaque characteristics, and restenosis after endarterectomy

OBJECTIVE

Shorter leukocyte telomeres are associated with atherosclerosis and predict future heart disease. The goal of the present study was to determine whether leukocyte telomere length is related to atherosclerotic plaque telomere length and whether it is associated with plaque characteristics or recurrence of disease.

METHODS AND RESULTS

Telomere length was measured by real-time quantitative polymerase chain reaction in atherosclerotic plaques and leukocytes in patients with carotid atherosclerosis undergoing carotid endarterectomy (n=684) and of leukocytes in age- and gender-balanced subjects without clinical atherosclerosis (n=780). Leukocyte telomere length was shorter in patients versus controls (0.99 [interquartile range (IQR): 0.79 to 1.26] versus 1.06 [0.80 to 1.39]; P=0.0007). Plaque telomeres were longer than leukocyte telomeres (1.42 [IQR: 1.21 to 1.77] versus 1.01 [IQR: 0.75 to 1.34]; P<1.00×10(-6)) and independent of age. Leukocyte and plaque telomere length were only weakly correlated (correlation coefficient r2=0.04, P=0.03). Patients, whose plaques showed marked macrophage infiltration and large lipid core, had longer plaque telomeres (1.61 [IQR: 1.32 to 2.04] versus 1.40 [IQR: 1.15 to 1.57]; P=0.006) and shorter leukocyte telomeres (0.88 [IQR: 0.75 to 1.20] versus 1.03 [IQR: 0.83 to 1.34]; P=0.02). Plaque telomere length was associated with restenosis 1 year after endarterectomy (OR 1.58±0.206; P=0.026 per SD decrease of plaque telomere length).

CONCLUSIONS

Leukocyte telomere length is associated with the presence of atherosclerotic carotid plaques but is not a proxy for local plaque telomere length. Plaque telomere length is related to plaque characteristics and development of restenosis following endarterectomy.

Human mesenchymal stem cell-conditioned medium improves cardiac function following myocardial infarction

Recent studies suggest that the therapeutic effects of stem cell transplantation following myocardial infarction (MI) are mediated by paracrine factors. One of the main goals in the treatment of ischemic heart disease is to stimulate vascular repair mechanisms. Here, we sought to explore the therapeutic angiogenic potential of mesenchymal stem cell (MSC) secretions. Human MSC secretions were collected as conditioned medium (MSC-CM) using a clinically compliant protocol. Based on proteomic and pathway analysis of MSC-CM, an in vitro assay of HUVEC spheroids was performed identifying the angiogenic properties of MSC-CM. Subsequently, pigs were subjected to surgical left circumflex coronary artery ligation and randomized to intravenous MSC-CM treatment or non-CM (NCM) treatment for 7 days. Three weeks after MI, myocardial capillary density was higher in pigs treated with MSC-CM (645 ± 114 vs 981 ± 55 capillaries/mm(2); P = 0.021), which was accompanied by reduced myocardial infarct size and preserved systolic and diastolic performance. Intravenous MSC-CM treatment after myocardial infarction increases capillary density and preserves cardiac function, probably by increasing myocardial perfusion.

Adipocyte fatty acid binding protein in atherosclerotic plaques is associated with local vulnerability and is predictive for the occurrence of adverse cardiovascular events

AIMS

There is an increasing need for translational studies identifying molecular targets contributing to atherosclerotic plaque destabilization. Local molecular plaque markers that are related to plaque vulnerability may hold predictive value to identify patients who are at increased risk to suffer from cardiovascular events. Animal studies revealed that adipocyte fatty acid binding protein (FABP4) is associated with the progression of atherosclerosis; however, FABP4 expression studies in human atherosclerotic plaques are lacking. We investigated FABP4 expression in carotid atherosclerotic lesions in relation to plaque composition and future cardiovascular events.

METHODS AND RESULTS

Atherosclerotic plaques were obtained from 561 patients undergoing carotid endarterectomy (CEA). Plaques were analysed for the presence of macrophages, lipid core, smooth-muscle cells, collagen, calcification, and intraplaque haemorrhage. Patients were followed for 3 years after CEA. The primary outcome was defined as the composite of vascular death, vascular event, and surgical or percutaneous vascular intervention. Fatty acid binding protein levels correlated with unstable plaque characteristics and symptomatic lesions. Patients with increased FABP4 plaque levels showed a two-fold increased risk [HR = 1.99, 95% confidence interval (95% CI) (1.30-3.04)] (P = 0.005) to reach the primary outcome during follow-up. Increased FABP4 levels related to primary outcome, independent from general cardiovascular risk factors [HR = 1.33, 95% CI (1.08-1.65)] (P = 0.008).

CONCLUSION

FABP4 levels in atherosclerotic lesions are associated with an unstable plaque phenotype and an increased risk for cardiovascular events during follow-up. Besides risk stratification for adverse future cardiovascular events, the outcome of the present study supports the relevance of exploring FABP4 antagonists as a potential pharmaceutical intervention to treat atherosclerotic disease progression.

Modulation of TGF-β/BMP-6 expression and increased levels of circulating smooth muscle progenitor cells in a type I diabetes mouse model

Background

Diabetic patients experience exaggerated intimal hyperplasia after endovascular procedures. Recently it has been shown that circulating smooth muscle progenitor cells (SPC) contribute to intimal hyperplasia. We hypothesized that SPC differentiation would be increased in diabetes and focused on modulation of TGF-β/BMP-6 signaling as potential underlying mechanism.

Methods

We isolated SPC from C57Bl/6 mice with streptozotocin-induced diabetes and controls. SPC differentiation was evaluated by immunofluorescent staining for αSMA and collagen Type I. SPC mRNA expression of TGF-β and BMP-6 was quantified using real-time PCR. Intima formation was assessed in cuffed femoral arteries. Homing of bone marrow derived cells to cuffed arterial segments was evaluated in animals transplanted with bone marrow from GFP-transgenic mice.

Results

We observed that SPC differentiation was accelerated and numeric outgrowth increased in diabetic animals (24.6 ± 8.8 vs 8.3 ± 1.9 per HPF after 10 days, p < 0.05). Quantitative real-time PCR showed increased expression of TGF-β and decreased expression of the BMP-6 in diabetic SPC. SPC were MAC-3 positive, indicative of monocytic lineage. Intima formation in cuffed arterial segments was increased in diabetic mice (intima/media ratio 0.68 ± 0.15 vs 0.29 ± 0.06, p < 0.05). In GFP-chimeric mice, bone marrow derived cells were observed in the neointima (4.4 ± 3.3 cells per section) and particularly in the adventitia (43.6 ± 9.3 cells per section). GFP-positive cells were in part MAC-3 positive, but rarely expressed α-SMA.

Conclusions

In conclusion, in a diabetic mouse model, SPC levels are increased and SPC TGF-β/BMP-6 expression is modulated. Altered TGF-β/BMP-6 expression is known to regulate smooth muscle cell differentiation and may facilitate SPC differentiation. This may contribute to exaggerated intimal hyperplasia in diabetes as bone marrow derived cells home to sites of neointima formation.

High myeloid-related protein: 8/14 levels are related to an increased risk of cardiovascular events after carotid endarterectomy

BACKGROUND AND PURPOSE

Myeloid-related protein (Mrp) 8/14 complex is the functional relevant form of Mrp-8 and Mrp-14. Mrp-8/14 complex is actively formed in the cytoplasm of circulating neutrophils and monocytes and then secreted. Plasma Mrp-8/14 complex is emerging as a new biomarker that may discriminate between patients with an acute coronary syndrome and those with stable coronary heart disease. Little is known about the predictive value of Mrp-8/14 plaque and plasma levels for cardiovascular events after atherectomy.

METHODS

Plasma and plaque Mrp-8/14 levels were determined by ELISA in 230 consecutive patients (mean age 73) who underwent carotid endarterectomy. Patients were followed for 3 years for recurrent cardiovascular events (vascular death, nonfatal vascular event, and peripheral intervention). During follow-up, 62 patients experienced an event. Baseline Mrp-8/14 levels were higher in patients who experienced an event than in event-free patients (plasma 0.78+/-0.63 versus 0.57+/-0.67 mg/L; P=0.030 and plaque 0.54+/-1.23 versus 0.08+/-1.51 mg/kg; P=0.027). In a Cox model, a 1 U increase in log Mrp-8/14 was associated with an increased risk of recurrent events (plasma, hazard ratio [HR], 1.51; 95% CI, 1.02 to 2.23, P=0.040; and plaque, HR, 1.23, 95% CI, 1.04 to 1.46, P=0.018). After multivariate adjustment for risk factors (both plasma and plaque Mrp-8/14) and plaque characteristics (only plaque Mrp-8/14), the HR remained the same for both plasma (HR, 1.50, 95% CI, 1.01 to 2.30; P=0.046) and plaque (HR, 1.20, 95% CI, 1.01 to 1.44; P=0.042).

CONCLUSIONS

High Mrp-8/14 plasma and plaque levels are related to an increased risk of adverse cardiovascular events after a carotid endarterectomy, independent of traditional cardiovascular risk factors.

Endogenous inflammatory molecules engage Toll-like receptors in cardiovascular disease

Innate immunity is important in the pathogenesis and progression of cardiovascular disease. Innate immune cells express various pattern-recognition receptors, among which also Toll-like receptors (TLRs). TLRs occur in atherosclerotic lesions where they are triggered by both exogenous (bacterial and viral pathogens) and endogenous (tissue damage-associated) molecules. Several endogenous TLR activators are described in relation to atherosclerotic disease or ischemia-induced cardiac injury. Experimental animal models have proved the role of TLR endogenous activators in disease initiation and further development. Nowadays, researchers aim to unravel the exact mechanisms involved in the endogenous ligand-dependent TLR signaling and to discover new potential activators, released during pathological conditions such as atherosclerosis and related ischemic manifestations. This review provides an overview of the currently known endogenous molecules which trigger innate immunity via TLRs in cardiovascular disease.

Exosome secreted by MSC reduces myocardial ischemia/reperfusion injury

Human ESC-derived mesenchymal stem cell (MSC)-conditioned medium (CM) was previously shown to mediate cardioprotection during myocardial ischemia/reperfusion injury through large complexes of 50-100 nm. Here we show that these MSCs secreted 50- to 100-nm particles. These particles could be visualized by electron microscopy and were shown to be phospholipid vesicles consisting of cholesterol, sphingomyelin, and phosphatidylcholine. They contained coimmunoprecipitating exosome-associated proteins, e.g., CD81, CD9, and Alix. These particles were purified as a homogeneous population of particles with a hydrodynamic radius of 55-65 nm by size-exclusion fractionation on a HPLC. Together these observations indicated that these particles are exosomes. These purified exosomes reduced infarct size in a mouse model of myocardial ischemia/reperfusion injury. Therefore, MSC mediated its cardioprotective paracrine effect by secreting exosomes. This novel role of exosomes highlights a new perspective into intercellular mediation of tissue injury and repair, and engenders novel approaches to the development of biologics for tissue repair.

Folic acid supplementation normalizes the endothelial progenitor cell transcriptome of patients with type 1 diabetes: a case-control pilot study

BACKGROUND

Endothelial progenitor cells play an important role in vascular wall repair. Patients with type 1 diabetes have reduced levels of endothelial progenitor cells of which their functional capacity is impaired. Reduced nitric oxide bioavailability and increased oxidative stress play a role in endothelial progenitor cell dysfunction in these patients. Folic acid, a B-vitamin with anti-oxidant properties, may be able to improve endothelial progenitor cell function. In this study, we investigated the gene expression profiles of endothelial progenitor cells from patients with type 1 diabetes compared to endothelial progenitor cells from healthy subjects. Furthermore, we studied the effect of folic acid on gene expression profiles of endothelial progenitor cells from patients with type 1 diabetes.

METHODS

We used microarray analysis to investigate the gene expression profiles of endothelial progenitor cells from type 1 diabetes patients before (n = 11) and after a four week period of folic acid supplementation (n = 10) compared to the gene expression profiles of endothelial progenitor cells from healthy subjects (n = 11). The probability of genes being differentially expressed among the classes was computed using a random-variance t-test. A multivariate permutation test was used to identify genes that were differentially expressed among the two classes. Functional classification of differentially expressed genes was performed using the biological process ontology in the Gene Ontology database.

RESULTS

Type 1 diabetes significantly modulated the expression of 1591 genes compared to healthy controls. These genes were found to be involved in processes regulating development, cell communication, cell adhesion and localization. After folic acid treatment, endothelial progenitor cell gene expression profiles from diabetic patients were similar to those from healthy controls. Genes that were normalized by folic acid played a prominent role in development, such as the transcription factors ID1 and MAFF. Few oxidative-stress related genes were affected by folic acid.

CONCLUSION

Folic acid normalizes endothelial progenitor cell gene expression profiles of patients with type 1 diabetes. Signaling pathways modulated by folic acid may be potential therapeutic targets to improve endothelial progenitor cell function.

Targeted deletion of nuclear factor kappaB p50 enhances cardiac remodeling and dysfunction following myocardial infarction

Myocardial infarction is commonly complicated by left ventricular remodeling, a process that leads to cardiac dilatation, congestive heart failure and death. The innate immune system plays a pivotal role in the remodeling process via nuclear factor (NF)-kappaB activation. The NF-kappaB transcription factor family includes several subunits (p50, p52, p65, c-Rel, and Rel B) that respond to myocardial ischemia. The function of NF-kappaB p50, however, is controversial in this process. To clarify the role of NF-kappaB p50 in postinfarct left ventricular remodeling, myocardial infarction was induced in wild-type 129Bl6 mice and NF-kappaB p50-deficient mice. Without affecting infarct size, deletion of NF-kappaB p50 markedly increased the extent of expansive remodeling (end-diastolic volume: 176+/-13 microL versus 107+/-11 microL; P=0.003) and aggravated systolic dysfunction (left ventricular ejection fraction: 16.1+/-1.5% versus 24.7+/-3.7%; P=0.029) in a 28-day time period. Interstitial fibrosis and hypertrophy in the noninfarcted myocardium was increased in NF-kappaB p50 knockout mice. In the infarct area, a lower collagen density was observed, which was accompanied by an increased number of macrophages, higher gelatinase activity and increased inflammatory cytokine expression. In conclusion, targeted deletion of NF-kappaB p50 results in enhanced cardiac remodeling and functional deterioration following myocardial infarction by increasing matrix remodeling and inflammation.

Biobanks and the search for predictive biomarkers of local and systemic outcome in atherosclerotic disease

Multiple risk factors have been associated with progression of atherosclerosis. To identify the individual patient who is at risk for disruption of a vulnerable plaque, leading to a cardiovascular event, remains a major challenge. Current screening methods, based on traditional risk factors, do not allow risk stratification on an individual level. The discovery of new biomarkers would aid in identifying specific patient groups at risk for adverse cardiovascular events due to atherosclerotic disease progression. The current definition of the vulnerable plaque, e.g. atheromatous inflammatory plaque with a thin fibrous cap, has been based on cross-sectional post-mortem studies. The predictive value of these histological characteristics of the vulnerable plaque is likely to be low, because they are also frequently observed at multiple locations in symptomatic and asymptomatic patients. The Athero-express study follows a new concept to search for the atherosclerotic patient who may suffer from adverse events. In this study, we investigate the predictive value of local plaque composition for adverse events in other vascular territories, regarding the plaque as a concentrated expression of this systemic disease. First results from this longitudinal biobank study show that the local plaque hides strong predictive value for cardiovascular events elsewhere in the vascular tree. Longitudinal biobank studies will facilitate the identification of novel local plaque markers. The search for the plaque protein signature that is predictive for adverse events might enable patient stratification that will allow individualized tailor made medicine and subsequently guide the choice for therapeutic interventions.

The Nuclear Factor-kappa B p50 subunit is involved in flow-induced outward arterial remodeling

AIMS

Outward arterial remodeling is a structural enlargement of the artery that is associated with unstable inflammatory atherosclerotic lesions. Toll-like receptor (Tlr) activation is known as a key pathway in outward arterial remodeling. Tlr activation results in nuclear translocation of the transcription factor Nuclear Factor-kappa B (NF-kappaB) that controls the transcription of many inflammatory genes. The NF-kappaB subunit p50 is generally considered to be an inhibitory subunit of the NF-kappaB complex. We therefore hypothesize that NF-kappaB p50 inhibits outward arterial remodeling.

METHODS AND RESULTS

Carotid artery ligation in mice, induced outward remodeling in contralateral arteries of NF-kappaB p50(-/-) (p50(-/-)) and wild type (WT) arteries. p50(-/-) arteries showed more outward arterial remodeling than WT arteries (19894.0+/-3136.7 microm(2) vs. 6120.7+/-2741.2 microm(2), respectively, P=0.006). In vitro, lipopolysaccharide induced higher cytokine expression levels in p50(-/-) cells compared to WT cells. In vivo, more outward remodeling in p50(-/-) arteries was associated with a decrease in collagen density and an increased influx of macrophages.

CONCLUSIONS

The NF-kappaB p50 subunit is involved in outward arterial remodeling. This is probably due to modulation of macrophage influx and adventitial collagen, leading to enhanced flow-induced outward arterial remodeling after targeted deletion of NF-kappaB subunit p50.

Histological characterization of restenotic carotid plaques in relation to recurrence interval and clinical presentation: a cohort study

Backgrounds and Purpose- Restenosis is an important complication after carotid endarterectomy, but little is known about plaque composition in early versus late restenosis and which plaque characteristics are associated with symptomatic clinical presentation of restenotic lesions.

METHODS

Endarterectomy specimens of 822 consecutive patients undergoing carotid endarterectomy (33 restenotic; 789 primary) were subjected to histological examination for the presence of macrophages, smooth muscle cells, collagen, calcifications, luminal thrombus, intraplaque bleeding and lipid core size.

RESULTS

Early restenotic plaques showed marked accumulation of smooth muscle cells and fibrous tissue, whereas late restenotic plaques demonstrated increased macrophage infiltration, calcification and lipid core (P trend <0.05), resembling primary plaques. Patients with symptomatic restenosis had plaques with higher macrophage infiltration (P=0.01) and a larger lipid core (P=0.02) than asymptomatic patients, independent of recurrence interval.

CONCLUSIONS

Restenosis occurring >5 years after primary carotid endarterectomy resembles primary plaques. Symptomatic presentation of restenotic lesions is independently associated with an unstable plaque phenotype.

Toll-like receptor 4 mediates maladaptive left ventricular remodeling and impairs cardiac function after myocardial infarction

Left ventricular (LV) remodeling leads to congestive heart failure and is a main determinant of morbidity and mortality following myocardial infarction. Therapeutic options to prevent LV remodeling are limited, which necessitates the exploration of alternative therapeutic targets. Toll-like receptors (TLRs) serve as pattern recognition receptors within the innate immune system. Activation of TLR4 results in an inflammatory response and is involved in extracellular matrix degradation, both key processes of LV remodeling following myocardial infarction. To establish the role of TLR4 in postinfarct LV remodeling, myocardial infarction was induced in wild-type BALB/c mice and TLR4-defective C3H-Tlr4(LPS-d) mice. Without affecting infarct size, TLR4 defectiveness reduced the extent of LV remodeling (end-diastolic volume: 103.7+/-6.8 microL versus 128.5+/-5.7 microL; P<0.01) and preserved systolic function (ejection fraction: 28.2+/-3.1% versus 16.6+/-1.3%; P<0.01), as assessed by MRI. In the noninfarcted area, interstitial fibrosis, and myocardial hypertrophy were reduced in C3H-Tlr4(LPS-d) mice. In the infarcted area, however, collagen density was increased, which was accompanied by fewer macrophages, reduced inflammation regulating cytokine expression levels (interleukin [IL]-1alpha, IL-2, IL-4, IL-5, IL-6, IL-10, IL-17, tumor necrosis factor-alpha, interferon-gamma, granulocyte/macrophage colony-stimulating factor), and reduced matrix metalloproteinase-2 (4684+/-515 versus 7573+/-611; P=0.002) and matrix metalloproteinase-9 activity (76.0+/-14.3 versus 168.0+/-36.2; P=0.027). These data provide direct evidence for a causal role of TLR4 in postinfarct maladaptive LV remodeling, probably via inflammatory cytokine production and matrix degradation. TLR4 may therefore constitute a novel target in the treatment of ischemic heart failure.

Microsomal Prostaglandin E2 Synthase: A Safer Target than Cyclooxygenases?

Non-steroidal anti-inflammatory drugs (NSAIDs) are inhibitors of the cyclo-oxygenase (COX)-1 and -2 activities of prostaglandin G/H synthase-1 and -2, respectively. They have been extensively used in the treatment of prostaglandin E(2)-mediated chronic inflammatory diseases. Selective COX-2 inhibitors (coxibs), which were developed to provide an alternative with reduced gastrointestinal risk for the traditional NSAIDs, have been associated with an increased incidence of major adverse cardiovascular events. Could the targeting of microsomal prostaglandin E(2) synthase (mPGES-1) lead to novel anti-inflammatory drugs with possibly reduced risks of gastrointestinal and cardiovascular side effects?

Elucidating the secretion proteome of human embryonic stem cell-derived mesenchymal stem cells

Transplantation of mesenchymal stem cells (MSCs) has been used to treat a wide range of diseases, and the mechanism of action is postulated to be mediated by either differentiation into functional reparative cells that replace injured tissues or secretion of paracrine factors that promote tissue repair. To complement earlier studies that identified some of the paracrine factors, we profiled the paracrine proteome to better assess the relevance of MSC paracrine factors to the wide spectrum of MSC-mediated therapeutic effects. To evaluate the therapeutic potential of the MSC paracrine proteome, a chemically defined serum-free culture medium was conditioned by MSCs derived from human embryonic stem cells using a clinically compliant protocol. The conditioned medium was analyzed by multidimensional protein identification technology and cytokine antibody array analysis and revealed the presence of 201 unique gene products. 86-88% of these gene products had detectable transcript levels by microarray or quantitative RT-PCR assays. Computational analysis predicted that these gene products will significantly drive three major groups of biological processes: metabolism, defense response, and tissue differentiation including vascularization, hematopoiesis, and skeletal development. It also predicted that the 201 gene products activate important signaling pathways in cardiovascular biology, bone development, and hematopoiesis such as Jak-STAT, MAPK, Toll-like receptor, transforming growth factor-beta, and mTOR (mammalian target of rapamycin) signaling pathways. This study identified a large number of MSC secretory products that have the potential to act as paracrine modulators of tissue repair and replacement in diseases of the cardiovascular, hematopoietic, and skeletal tissues. Moreover our results suggest that human embryonic stem cell-derived MSC-conditioned medium has the potency to treat a variety of diseases in humans without cell transplantation.

Low levels of Nogo-B in human carotid atherosclerotic plaques are associated with an atheromatous phenotype, restenosis, and stenosis severity

OBJECTIVE

Reticulon-4/Nogo (Nogo-B) protects mouse arteries from lumen loss by reducing smooth muscle cell (SMC) migration and intimal thickening. Our goal was to determine plaque and circulating levels of Nogo-B in atherosclerotic and control subjects. Therefore, we studied the relationships between local Nogo-B, plaque characteristics, and clinical data in patients undergoing carotid endarterectomy.

METHODS AND RESULTS

Western blot analysis showed that endarterectomy specimens from the femoral (n=19) and carotid arteries (n=145) contained significantly less Nogo-B than nonatherosclerotic mammary arteries (n=8; P<0.003) and aortas (n=15; P=0.03). Immunohistochemistry revealed that in atherosclerotic lesions, Nogo-B was expressed by macrophage/foam cells, SMC rich, and neo-vascularized areas. Atheromatous plaques (>40% fat content) showed a significant reduction in Nogo-B expression (P=0.002). Nogo-B expression levels were significantly lower in patients with more than 90% of carotid stenosis (P=0.04) or restenotic lesions after prior carotid intervention (duplex; P=0.01). In contrast, plasmatic levels of Nogo-B (soluble Nogo-B) did not differ between atherosclerotic subjects (n=68) and risk-factor matched controls (n=63; P=0.5).

CONCLUSION

Our findings suggest that local reduction of Nogo-B in atherosclerotic tissue might contribute to plaque formation and/or instability triggering luminal narrowing. In contrast, plasma Nogo-B levels are not associated with clinically manifested atherosclerotic disease.

Peptidoglycan increases firm adhesion of monocytes under flow conditions and primes monocyte chemotaxis

The Toll-like receptor (TLR) 2/nucleotide-binding oligomerization domain ligand peptidoglycan (PG) has been shown to be present in macrophage-rich regions within atherosclerotic lesions, and stimulation of TLR2 promotes atherosclerotic plaque and intima formation in in vivo mouse models. We determined the effect of a PG preparation and Pam(3)Cys-SK(4), a synthetic TLR2 activator, on (1) adhesion molecule expression by flow cytometry; (2) monocyte adhesion under flow conditions, and (3) monocyte migration. The total adhesion (rolling and firm adhesion) of the PG-preparation-stimulated monocytes to L cells, constitutively expressing ICAM-1 (intercellular adhesion molecule-1) and E-selectin, was decreased. This was most likely due to the L-selectin shedding, since monocyte incubation with a blocking L-selectin antibody resulted in a comparable number of adherent monocytes as PG-stimulated cells. The PG preparation induced an increased percentage of firmly adherent, polarized cells and a beta(2)-integrin-dependent binding to ICAM-1-coated beads. Interestingly, the PG preparation induced a priming of the monocytes for increased migration towards the chemoattractant C5a which was TLR2 and beta(2)-integrin dependent. Pam(3)Cys-SK(4) gave comparable results to the PG preparation in all assays tested. This study demonstrates that PG activation of monocytes results in an increase in adhesive and migratory capacities of these cells. This might be a mechanism by which PG promotes atherosclerotic disease in vivo.

Cyclooxygenase-2 Inhibition Increases Mortality, Enhances Left Ventricular Remodeling, and Impairs Systolic Function After Myocardial Infarction in the Pig

BACKGROUND

Cyclooxygenase (COX)-2 expression in the heart increases after myocardial infarction (MI). In murine models of MI, COX-2 inhibition preserves left ventricular dimensions and function. We studied the effect of selective COX-2 inhibition on left ventricular remodeling and function after MI in a pig model.

METHODS AND RESULTS

Twenty-two pigs were assigned to COX-2 inhibition with a COX-2 inhibitor (COX-2i; celecoxib 400 mg twice daily; n=14) or a control group (n=8). MI was induced by left circumflex coronary artery ligation, and the animals were euthanized 6 weeks later. Cardiac dimensions and function were assessed with echocardiography and conductance catheters. Infarct size and collagen density were analyzed with triphenyltetrazolium chloride staining and picrosirius red staining, respectively. COX-2 inhibition increased mortality compared with controls (50% versus 0%, P=0.022), whereas infarct size was similar (13.1+/-0.7% versus 14.1+/-0.1%, P=0.536). The decrease in thickness of the infarcted myocardial wall was more pronounced in the COX-2i group (60.6+/-9.6% versus 36.2+/-5.7%, P=0.001). End-diastolic volume was higher in the COX-2i group (133.9+/-33.5 versus 91.1+/-24.0 mL; P=0.021), as was the end-systolic volume at 100 mm Hg (81.7+/-27.8 versus 56.3+/-21.1 mL; P=0.037), which indicates that systolic function was more severely impaired. Infarct collagen density was lower after COX-2i treatment (25.3+/-3.9 versus 56.1+/-23.8 gray value/mm2; P=0.005).

CONCLUSIONS

In pigs, COX-2 inhibition after MI is associated with increased mortality, enhanced left ventricular remodeling, and impaired systolic function, probably due to decreased infarct collagen fiber density.

cNGR: A Novel Homing Sequence for CD13/APN Targeted Molecular Imaging of Murine Cardiac Angiogenesis In Vivo

Objective— Previously, the peptide sequence cNGR has been shown to home specifically to CD13/APN (aminopeptidase N) on tumor endothelium. Here, we investigated the feasibility of selective imaging of cardiac angiogenesis using the cNGR-CD13/APN system.

Methods and Results— CD13/APN induction and cNGR homing were studied in the murine myocardial infarction (MI) model. By real-time polymerase chain reaction (PCR) at 7 days after MI, CD13/APN expression was 10- to 20-fold higher in the angiogenic infarct border zone and the MI area than in non-MI areas. In vivo fluorescence microscopy confirmed specific homing of fluorophore-tagged cNGR to the border zone and MI territory at 4 and 7 days after MI with a local advantage of 2.3, but not at 1 or 14 days after MI. Tissue residence half-life was 9.1±0.3 hours, whereas the half-life in plasma was 15.4±3.4 minutes. Pulse chase experiments confirmed reversible binding of cNGR in the infarct area. Fluorescent labeled cNGR conjugates or antibodies were injected in vivo, and their distribution was studied ex vivo by 2-photon laser scanning microscopy (TPLSM). cNGR co-localized exclusively with CD13/APN and the endothelial marker CD31 on vessels.

Conclusions— In cardiac angiogenesis endothelial CD13/APN is upregulated. It can be targeted specifically with cNGR conjugates. In the heart cNGR binds its endothelial target only in angiogenic areas.

Statin Treatment Is Not Associated With Consistent Alterations in Inflammatory Status of Carotid Atherosclerotic Plaques

BACKGROUND AND PURPOSE

Anti-inflammatory qualities are held partially responsible for the reduction of cardiovascular events after statin treatment. We examined the phenotype of carotid atherosclerotic plaques harvested during carotid endarterectomy in relation to the previous use of different statins prescribed in clinical practice.

METHODS

Three hundred and seventy-eight patients were included. Atherosclerotic plaques were harvested, immunohistochemically stained and semiquantitively examined for the presence of macrophages (CD68), smooth muscle cells, collagen and fat. Adjacent atherosclerotic plaques were used to study protease activity and interleukin levels. Patients' demographics were recorded and blood samples were stored.

RESULTS

Serum cholesterol, low-density lipoprotein, apolipoprotein B, and C-reactive protein levels were lower in patients treated with statins compared with patients without statin treatment. Atheromatous plaques were less prevalent in patients receiving statins compared with patients without statin therapy (29% versus 42%, P=0.04). An increase of CD68 positive cells was observed in patients receiving statins compared with nonstatin treatment (P=0.05). This effect was specifically related to atorvastatin treatment. In patients treated with atorvastatin, the increased amount of CD68 positive cells were not associated with increased protease activity. In contrast, a dose-dependent decrease in protease activity was shown in the atorvastatin group. Interleukin 6 expression was lower in plaques obtained from patients treated with statins (P=0.04).

CONCLUSIONS

Statin use may exert pleiotropic effects on plaque phenotype. However, not the presence of macrophages but activation with subsequent protease and cytokine release may be attenuated by statin use.

Carotid atherosclerotic plaques in patients with transient ischemic attacks and stroke have unstable characteristics compared with plaques in asymptomatic and amaurosis fugax patients

INTRODUCTION

Atherosclerotic carotid artery disease is responsible for a variety of clinical presentations, ranging from asymptomatic to cerebral ischemic events. Considering the upcoming use of noninvasive imaging modalities, plaque characteristics could serve as a marker in the selection of patients eligible for carotid endarterectomy (CEA). This would be more likely if characteristics corresponded with clinical manifestations and were predictive of future events. In this study, we hypothesized that plaque characteristics correlate with the clinical presentation of carotid artery disease.

METHODS

We included 404 patients undergoing a carotid endarterectomy (CEA). Ipsilateral clinical symptoms and duplex measurements were recorded. Patients could be asymptomatic (23.5%) or symptomatic with stroke (26.5%), transient ischemic attack (TIA) (36.1%), or amaurosis fugax (AFX) (13.9%). Plaques were stained and semi-quantitatively analyzed for the presence of macrophages, smooth muscle cells, collagen, calcifications, and thrombus. Plaques were categorized in three phenotypes by their overall presentation and the amount of fat. In addition, plaque matrix metalloproteinase (MMP) activity and cytokines expressions were measured.

RESULTS

Fibrous, fibro-atheromatous, and atheromatous plaques were observed in 30.2%, 35.6%, and 34.2%, respectively. Atheromatous plaques were more prevalent in patients with stroke and TIA compared with asymptomatic patients or patients with AFX (P = .001). Collagen staining was less evident in patients with TIA and stroke compared with asymptomatic patients or patients with AFX (P < .001). Plaques of patients with TIA and stroke showed significantly higher activity levels of MMP-8 and MMP-9 and higher levels of interleukin-8 compared with asymptomatic and AFX patients.

CONCLUSION

Plaque phenotype of patients with TIA is comparable to that of patients with stroke; whereas, the plaque phenotype of patients with AFX resembles the plaque phenotype of asymptomatic patients. Follow-up studies should be encouraged to determine whether plaque characteristics visualized by imaging techniques might help to identify patients most likely to benefit from CEA.

Vascular remodeling and protease inhibition--bench to bedside

Physiological and pathological tissue remodeling needs an orderly degradation of the extracellular matrix. Matrix metalloproteinases (MMPs) are proteases capable of degrading different extracellular matrix components, including collagen and elastin. MMP expression is strongly enhanced in vascular pathologies such as stenosis following balloon dilation, in-stent restenosis, sustained flow changes, aneurysm formation, and atherosclerosis. Experimental studies have revealed that some biological actions of MMPs aggravate a pathological condition, whereas others may be beneficial for the patient suffering from atherosclerotic disease. Therefore, a better understanding of the biological consequence and regulation of MMP activity is critical for the design and potential application of specific MMP inhibitors in vascular disease. In this review, we will give an overview of preclinical experimental studies using MMP inhibitors with the objective to influence vascular occlusive diseases, and we will also highlight new targets that influence MMP expression and activity and that possess potential for therapeutic interventions.

Matrix Metalloproteinase 2 Is Associated With Stable and Matrix Metalloproteinases 8 and 9 With Vulnerable Carotid Atherosclerotic Lesions

Background and Purpose— We studied matrix metalloproteinases (MMP) 2, 8, and 9 and extracellular matrix metalloproteinase inducer (EMMPRIN) levels in relation to carotid atherosclerotic plaque characteristics.

Methods— Carotid atherosclerotic plaques (n=150) were stained and analyzed for the presence of collagen, smooth muscle cell (SMC), and macrophages. Adjacent segments were used to isolate total protein to assess MMP-2 and MMP-9 activities and gelatin breakdown, MMP-8 activity, and EMMPRIN levels.

Results— Macrophage-rich lesions revealed higher MMP-8 and MMP-9 activities, whereas SMC-rich lesions showed higher MMP-2 activity. The levels of less glycosylated EMMPRIN-45kD were higher in SMC-rich lesions and lower in macrophage-rich plaques. EMMPRIN-45kD was associated with MMP-2 levels, whereas EMMPRIN-58kD was related to MMP-9 levels.

Conclusions— MMP-2, MMP-8, and MMP-9 activities differed among carotid plaque phenotypes. Different EMMPRIN glycosylation forms are associated with either MMP-2 or MMP-9 activity, which suggests that EMMPRIN glycosylation may play a role in MMP regulation and plaque destabilization.

Involvement of furin-like proprotein convertases in the arterial response to injury

BACKGROUND

Furin-like proprotein convertases (PCs) are proteolytic activators of proproteins, like membrane type 1-matrix metalloproteinase (MT1-MMP) and transforming growth factor beta (TGF-beta), that are described in the arterial response to injury. However, the involvement of furin-like PCs in the arterial response to injury has not been studied yet. We studied furin, MT1-MMP, MMP levels and TGF-beta signaling after arterial injury. We also investigated the effect of an inhibitor of furin-like PCs, alpha1-antitrypsin Portland (alpha1-PDX), on arterial injury following balloon dilation.

METHODS AND RESULTS

NZW rabbit femoral and iliac arteries (N=42) were balloon dilated unilaterally and harvested after 2, 7, 14, 28 or 42 days. Furin mRNA levels were increased after 2 and 7 days. MMP-2 and MT1-MMP levels were increased after day 7 and TGF-beta signaling, by phosphorylating Smad 1/5 and 2/3, was increased at all time points. Inhibition of furin-like PCs, by adenoviral over-expression of alpha1-PDX, blocked proTGF-beta activation and Smad phosphorylation, and reduced MT1-MMP and MMP-2 activation (N=5). In vivo adventitial inhibition of furin-like PCs (N=9) resulted in a reduction of 13.1+/-5.2% in advential and 23.6+/-7.9% in intimal areas (P<0.05), but had no effect on lumen size due to decreased vessel areas.

CONCLUSIONS

This study demonstrates that furin-like PCs are involved in the arterial response to injury possibly through activation of the TGF-beta-Smad signaling pathway and identifies furin-like PCs as a possible target to inhibit intimal hyperplasia.