Targeting chronic cardiac remodeling with cardiac progenitor cells in a murine model of ischemia/reperfusion injury

BACKGROUND

Translational failure for cardiovascular disease is a substantial problem involving both high research costs and an ongoing lack of novel treatment modalities. Despite the progress already made, cell therapy for chronic heart failure in the clinical setting is still hampered by poor translation. We used a murine model of chronic ischemia/reperfusion injury to examine the effect of minimally invasive application of cardiac progenitor cells (CPC) in cardiac remodeling and to improve clinical translation.

METHODS

28 days after the induction of I/R injury, mice were randomized to receive either CPC (0.5 million) or vehicle by echo-guided intra-myocardial injection. To determine retention, CPC were localized in vivo by bioluminescence imaging (BLI) two days after injection. Cardiac function was assessed by 3D echocardiography and speckle tracking analysis to quantify left ventricular geometry and regional myocardial deformation.

RESULTS

BLI demonstrated successful injection of CPC (18/23), which were mainly located along the needle track in the anterior/septal wall. Although CPC treatment did not result in overall restoration of cardiac function, a relative preservation of the left ventricular end-diastolic volume was observed at 4 weeks follow-up compared to vehicle control (+5.3 ± 2.1 μl vs. +10.8 ± 1.5 μl). This difference was reflected in an increased strain rate (+16%) in CPC treated mice.

CONCLUSIONS

CPC transplantation can be adequately studied in chronic cardiac remodeling using this study set-up and by that provide a translatable murine model facilitating advances in research for new therapeutic approaches to ultimately improve therapy for chronic heart failure.

Abstract 55: The Natural Course of Myocardial Infarction in Large Animal Models; a Systematic Review and Meta-analysis

Background: Large animal models of myocardial infarction (MI) are essential for the development of novel therapeutic strategies. However, it is unclear which experimental factors are independent determinants of disease progression outcomes and the fidelity with which these models resemble MI in humans. The aim of this study was to investigate systematically what independently influences the outcome after MI in large animal models and determine which methodological factors influence primary endpoints and disease progression.

Methods: We used control animal data from two meta-analyses of large animal models of MI. We performed univariable and multivariable meta-regression to analyze if potential relevant variables were influencing outcomes; infarct size as a ratio of the area at risk (IS/AAR), as a ratio of the left ventricle (IS/LV) and ejection fraction (EF). Pre-defined independent variables were species, sex, weight, ischemia model (open vs closed), occlusion type (temporary vs permanent), occluded vessel, follow-up duration, use of co-medication, use of immunosuppression and study quality. Outcomes and variables were complemented per dataset if needed.

Results: Our analyses yielded 246 relevant studies, reporting 1500, 1221 and 775 control animals for IS/AAR, IS/LV and EF respectively. Multivariable meta-regression showed IS/AAR was influenced by species (p<0.001), sex (p=0.03), co-medication (p=0.01), occlusion type (p<0.001), occluded vessel (p=0.002) and follow-up (p=0.001). For IS/LV occlusion type (p=0.03), occluded vessel (p=0.03) and study quality (p=0.03) showed significant effects. EF measurements revealed that species (p=0.04), sex (p=0.04) and occluded vessel (p=0.05) were independent predictors. Using these variables, we can partially predict these outcomes for certain study setups.

Conclusion: Many methodological variations exist in the design of large animal MI studies. This should be taken into account when selecting a model to study therapy efficacy. We provide evidence that disease manifestation and progression greatly depend on certain biological characteristics, e.g. location of MI and sex of the patient. It is therefore possible that therapies have a different effect in specific patient populations.

Assessment of coronary microvascular resistance in the chronic infarcted pig heart

Pre-clinical studies aimed at treating ischemic heart disease (i.e. stem cell- and growth factor therapy) often consider restoration of the impaired microvascular circulation as an important treatment goal. However, serial in vivo measurement hereof is often lacking. The purpose of this study was to evaluate the applicability of intracoronary pressure and flow velocity as a measure of microvascular resistance in a large animal model of chronic myocardial infarction (MI). Myocardial infarction was induced in Dalland Landrace pigs (n = 13; 68.9 ± 4.1 kg) by a 75-min. balloon occlusion of the left circumflex artery (LCX). Intracoronary pressure and flow velocity parameters were measured simultaneously at rest and during adenosine-induced hyperemia, using the Combowire (Volcano) before and 4 weeks after MI. Various pressure- and/or flow-derived indices were evaluated. Hyperemic microvascular resistance (HMR) was significantly increased by 28% in the infarct-related artery, based on a significantly decreased peak average peak flow velocity (pAPV) by 20% at 4 weeks post-MI (P = 0.03). Capillary density in the infarct zone was decreased compared to the remote area (658 ± 207/mm²versus 1650 ± 304/mm², P = 0.017). In addition, arterioles in the infarct zone showed excessive thickening of the alpha smooth muscle actin (αSMA) positive cell layer compared to the remote area (33.55 ± 4.25 μm versus 14.64 ± 1.39 μm, P = 0.002). Intracoronary measurement of HMR successfully detected increased microvascular resistance that might be caused by the loss of capillaries and arteriolar remodelling in the chronic infarcted pig heart. Thus, HMR may serve as a novel outcome measure in pre-clinical studies for serial assessment of microvascular circulation.

Abstract 003: Progenitor Cells Suppress T-Lymphocyte Proliferation Via a Paracrine Mechanism

PURPOSE: Limited treatment options are available for heart failure patients. Stem cell therapy has recently become a potential new way of repairing injured cardiac tissue. Different progenitor cell sources have been investigated, but most promising for cardiac therapy are mesenchymal stem cells (MSC) and cardiomyocyte progenitor cells (CMPC). Cardiac stem cell therapy using MSC or CMPC improved cardiac function, despite low engraftment of the cells. Paracrine factors, produced by the injected cells, presumably cause these improvements. Many studies are performed on the paracrine effects, yet modulation of the immune response in cardiac stem cell therapy, especially the strong influence of T-lymphocytes on adverse remodeling, has not been explored extensively.

Methods: Human fetal MSC and CMPC were characterized and tested for multipotency. The immunosuppressive properties of both cell types were tested in co-culture with allogeneic peripheral blood mononuclear cells (PBMC) or T-lymphocytes stimulated with IL-2 and PMA. Proliferation was measured by CFSE-analysis using flow cytometry.

Results: Proliferation of PBMC and T-lymphocytes was significantly reduced in the presence of MSC (65 ± 8%) or CMPC (97 ± 0.6%). In addition, production of inflammatory cytokines IFN-gamma and TNF-alpha was strongly downregulated. This effect was observed in both direct cell contact as well as in transwell co-culture systems (MSC: 58 ± 10%; CMPC: 62 ± 9%). Transfer of conditioned medium from these co-cultures to unrelated, activated PBMC or T-lymphocytes abrogated proliferation in these cells to a similar extent as the original co-culture (MSC: 51 ± 8%; CMPC: 97 ± 0.7%). Interestingly, exosomes isolated from the conditioned medium of MSC and CMPC prevented T-lymphocyte proliferation in a dose-dependent fashion. At a concentration of 1.5μg, T-lymphocyte proliferation was significantly suppressed (MSC-exosomes: 73 ± 12%; CMPC-exosomes: 77 ± 10%).

Conclusion: Both MSC and CMPC have a strong capacity for in vitro immunosuppression, which is mediated by paracrine factors. One potent immunosuppressive factor secreted by both MSC and CMPC are exosomes, which prevented T-lymphocyte proliferation in a dose-dependent fashion.

Lack of haptoglobin results in unbalanced VEGFα/angiopoietin-1 expression, intramural hemorrhage and impaired wound healing after myocardial infarction

Decreased haptoglobin (Hp) functionality due to allelic variations is associated with worsened outcome in patients after myocardial infarction (MI). However, mechanisms through which haptoglobin deficiency impairs cardiac repair remain to be elucidated. In the present study, we identified novel molecular alterations mediated by Hp involved in early and late cardiac repair responses after left coronary artery ligation in Hp(-/-) and wild-type (WT) mice. We observed a higher mortality rate in Hp(-/-) mice despite similar infarct size between groups. Deaths were commonly caused by cardiac rupture in Hp(-/-) animals. Histological analysis of 3 and 7days old non-ruptured infarcted hearts revealed more frequent and more severe intramural hemorrhage and increased leukocyte infiltration in Hp(-/-) mice. Analyses of non-ruptured hearts revealed increased oxidative stress, reduced PAI-1 activity and enhanced VEGFα transcription in Hp(-/-) mice. In line with these observations, we found increased microvascular permeability in Hp(-/-) hearts 3days after infarction. In vitro, haptoglobin prevented hemoglobin-induced oxidative stress and restored VEGF/Ang-1 balance in endothelial cell cultures. During long-term follow-up of the surviving animals, we observed altered matrix turnover, impaired scar formation and worsened cardiac function and geometry in Hp(-/-)mice. In conclusion, haptoglobin deficiency severely deteriorates tissue repair and cardiac performance after experimental MI. Haptoglobin plays a crucial role in both short- and long-term cardiac repair responses by reducing oxidative stress, maintaining microvascular integrity, myocardial architecture and proper scar formation.

Molecular MRI of murine atherosclerotic plaque targeting NGAL: a protein associated with unstable human plaque characteristics

AIMS

Neutrophil gelatinase-associated lipocalin (NGAL) is an effector molecule of the innate immune system. One of its actions is the prolongation of matrix metalloproteinase-9 (MMP-9) activity by the formation of a degradation-resistant NGAL/MMP-9 complex. We studied NGAL in human atherosclerotic lesions and we examined whether NGAL could act as a target for molecular imaging of atherosclerotic plaques.

METHODS AND RESULTS

Increased levels of NGAL and the NGAL/MMP-9 complex were associated with high lipid content, high number of macrophages, high interleukin-6 (IL-6) and IL-8 levels, and low smooth muscle cell content in human atherosclerotic lesions obtained during carotid endarterectomy (n= 122). Moreover, plaque levels of NGAL tended to be higher when intra-plaque haemorrhage (IPH) or luminal thrombus was present (n= 77) than without the presence of IPH or thrombus (n= 30). MMP-9 and -8 activities were strongly related to NGAL levels. The enhancement on magnetic resonance (MR) images of the abdominal aorta of ApoE(-/-)/eNOS(-/-) mice was observed at 72 h after injection of NGAL/24p3-targeted micelles. The specificity of these results was validated by histology, and co-localization of micelles, macrophages, and NGAL/24p3 was observed.

CONCLUSION

NGAL is highly expressed in atheromatous human plaques and associated with increased MMP-9 activity. NGAL can be detected in murine atherosclerotic arteries using targeted high-resolution MR imaging. Therefore, we conclude that NGAL might serve as a novel imaging target for the detection of high-risk plaques.

Furin and membrane type-1 metalloproteinase mRNA levels and activation of metalloproteinase-2 are associated with arterial remodeling

Matrix metalloproteinase (MMP) activation is an essential feature of pathological and physiological arterial enlargement or shrinkage. Recently, furin-activated membrane type-1 MMP (MT1-MMP) was identified as the in vivo activator of MMP2 in mice. Although arterial enlargement and shrinkage are important in several pathological processes, this proprotein convertase-MT1-MMP axis has not been described during arterial remodeling. In rabbit femoral and carotid arteries, we report an increase in furin and MT1-MMP mRNA levels before and at the onset of arterial remodeling followed by an increase in activated MMP2. This reveals the presence of the proprotein convertase-MT1-MMP axis in flow-induced arterial remodeling and identifies furin as a possible target for local intervention in pathological arterial remodeling.