Tamar Ben-Mordechai

Macrophage subpopulations are essential for infarct repair with and without stem cell therapy.

OBJECTIVES This study sought to investigate the hypothesis that the favorable effects of mesenchymal stromal cells (MSCs) on infarct repair are mediated by macrophages. BACKGROUND The favorable effects of MSC therapy in myocardial infarction (MI) are complex and not fully understood. METHODS We induced MI in mice and allocated them to bone marrow MSCs, mononuclear cells, or saline injection into the infarct, with and without early (4 h before MI) and late (3 days after MI) macrophage depletion. We then analyzed macrophage phenotype in the infarcted heart by flow cytometry and macrophage secretome in vitro. Left ventricular remodeling and global and regional function were assessed by echocardiography and speckle-tracking based strain imaging. RESULTS The MSC therapy significantly increased the percentage of reparative M2 macrophages (F4/80(+)CD206(+)) in the infarcted myocardium, compared with mononuclear- and saline-treated hearts, 3 and 4 days after MI. Macrophage cytokine secretion, relevant to infarct healing and repair, was significantly increased after MSC therapy, or incubation with MSCs or MSC supernatant. Significantly, with and without MSC therapy, transient macrophage depletion increased mortality 30 days after MI. Furthermore, early macrophage depletion produced the greatest negative effect on infarct size and left ventricular remodeling and function, as well as a significant incidence of left ventricular thrombus formation. These deleterious effects were attenuated with macrophage restoration and MSC therapy. CONCLUSIONS Some of the protective effects of MSCs on infarct repair are mediated by macrophages, which are essential for early healing and repair. Thus, targeting macrophages could be a novel strategy to improve infarct healing and repair.

Targeting Macrophage Subsets for Infarct Repair

Macrophages are involved in every cardiovascular disease and are an attractive therapeutic target. Macrophage activation is complex and can be either beneficial or deleterious, depending upon its mode of action, its timing, and its duration. An important macrophage characteristic is its plasticity, which enables it to switch from one subset to another. Macrophages, which regulate healing and repair after myocardial infarction, have become a major target for both treatment and diagnosis (theranostic). The aim of the present review is to describe the recent discoveries related to targeting and modulating of macrophage function to improve infarct repair. We will briefly review macrophage polarization, plasticity, heterogeneity, their role in infarct repair, regeneration, and cross talk with mesenchymal cells. Particularly, we will focus on the potential of macrophage targeting in situ by liposomes. The ability to modulate macrophage function could delineate pathways to reactivate the endogenous programs of myocardial regeneration. This will eventually lead to development of small molecules or biologics to enhance the endogenous programs of regeneration and repair.

Experimental myocardial infarction induces altered regulatory T cell hemostasis, and adoptive transfer attenuates subsequent remodeling.

Background Ischemic cardiac damage is associated with upregulation of cardiac pro-inflammatory cytokines, as well as invasion of lymphocytes into the heart. Regulatory T cells (Tregs) are known to exert a suppressive effect on several immune cell types. We sought to determine whether the Treg pool is influenced by myocardial damage and whether Tregs transfer and deletion affect cardiac remodeling. Methods and Results The number and functional suppressive activity of Tregs were assayed in mice subjected to experimental myocardial infarction. The numbers of splenocyte-derived Tregs in the ischemic mice were significantly higher after the injury than in the controls, and their suppressive properties were significantly compromised. Compared with PBS, adoptive Treg transfer to mice with experimental infarction reduced infarct size and improved LV remodeling and functional performance by echocardiography. Treg deletion with blocking anti-CD25 antibodies did not influence infarct size or echocardiographic features of cardiac remodeling. Conclusion Treg numbers are increased whereas their function is compromised in mice with that underwent experimental infarction. Transfer of exogeneous Tregs results in attenuation of myocardial remodeling whereas their ablation has no effect. Thus, Tregs may serve as interesting potential interventional targets for attenuating left ventricular remodeling.

Targeting and modulating infarct macrophages with hemin formulated in designed lipid-based particles improves cardiac remodeling and function.

ABSTRACT Uncontrolled activation of pro‐inflammatory macrophages after myocardial infarction (MI) accelerates adverse left ventricular (LV) remodeling and dysfunction. Hemin, an iron‐containing porphyrin, activates heme oxygenase‐1 (HO‐1), an enzyme with anti‐inflammatory and cytoprotective properties. We sought to determine the effects of hemin formulated in a macrophage‐targeted lipid‐based carrier (denoted HA‐LP) on LV remodeling and function after MI. Hemin encapsulation efficiency was ˜ 100% at therapeutic dose levels. In vitro, hemin/HA‐LP abolished TNF‐&agr; secretion from macrophages, whereas the same doses of free hemin and drug free HA‐LP had no effect. Hemin/HA‐LP polarized peritoneal and splenic macrophages toward M2 anti‐inflammatory phenotype. We next induced MI in mice and allocated them to IV treatment with hemin/HA‐LP (10 mg/kg), drug free HA‐LP, free hemin (10 mg/kg) or saline, one day after MI. Active in vivo targeting to infarct macrophages was confirmed with HA‐LP doped with PE‐rhodamine. LV remodeling and function were assessed by echocardiography before, 7, and 30 days after treatment. Significantly, hemin/HA‐LP effectively and specifically targets infarct macrophages, switches infarct macrophages toward M2 anti‐inflammatory phenotype, improves angiogenesis, reduces scar expansion and improves infarct‐related regional function. In conclusion, macrophage‐targeted lipid‐based drug carriers with hemin switch macrophages into an anti‐inflammatory phenotype, and improve infarct healing and repair. Our approach presents a novel strategy to modulate inflammation and improve infarct repair.

Experimental myocarditis in rat can be detected and monitored by cardiac magnetic resonance imaging performed on a clinical 3.0 T scanner

Methods and results Male Lewis rats (n=11) were subjected to myosin immunization and developed autoimmune myocarditis. Approximately 3 weeks later, rats with myocarditis underwent CMR scan and subsequently, histopathological evaluation. Rats with myocarditis showed pericardial thickening, effusion, and LV wall motion abnormalities with septal hypokinesis. Short axis views showed patchy delayed enhancement of epicardial segments, with distribution mainly located within the inferolateral LV wall including the septum. This increased signal/hyperenhancement defines focal areas of myocardial fibrosis/ edema and/or necrosis, highly suggestive of inflammation. Additionally, the presence of large pericardial effusion provides supportive evidence for the existence of perimyocarditis. Indeed, high correlation was found