Induction of the CXC chemokine interferon-gamma-inducible protein 10 regulates the reparative response following myocardial infarction.

RATIONALE: Interferon-gamma-inducible protein (IP)-10/CXCL10, an angiostatic and antifibrotic chemokine with an important role in T-cell trafficking, is markedly induced in myocardial infarcts, and may regulate the reparative response. OBJECTIVE: To study the role of IP-10 in cardiac repair and remodeling. METHODS AND RESULTS: We studied cardiac repair in IP-10-null and wild-type (WT) mice undergoing reperfused infarction protocols and examined the effects of IP-10 on cardiac fibroblast function. IP-10-deficient and WT animals had comparable acute infarct size. However, the absence of IP-10 resulted in a hypercellular early reparative response and delayed contraction of the scar. Infarcted IP-10(-/-) hearts exhibited accentuated early dilation, followed by rapid wall thinning during infarct maturation associated with systolic dysfunction. Although IP-10-null and WT mice had comparable cytokine expression, the absence of IP-10 was associated with marked alterations in the cellular content of the infarct. IP-10(-/-) infarcts had more intense infiltration with CD45(+) leukocytes, Mac-2(+) macrophages, and alpha-smooth muscle actin (alpha-SMA)(+) myofibroblasts than WT infarcts but exhibited reduced recruitment of the subpopulations of leukocytes, T lymphocytes and alpha-SMA(+) cells that expressed CXCR3, the IP-10 receptor. IP-10 did not modulate cardiac fibroblast proliferation and apoptosis but significantly inhibited basic fibroblast growth factor-induced fibroblast migration. In addition, IP-10 enhanced growth factor-mediated wound contraction in fibroblast-populated collagen lattices. CONCLUSIONS: Endogenous IP-10 is an essential inhibitory signal that regulates the cellular composition of the healing infarct and promotes wound contraction, attenuating adverse remodeling. IP-10-mediated actions may be due, at least in part, to direct effects on fibroblast migration and function.

Increased myocardial susceptibility to repetitive ischemia with high-fat diet-induced obesity.

Obesity and diabetes are frequently associated with cardiovascular disease. When a normal heart is subjected to brief/sublethal repetitive ischemia and reperfusion (I/R), adaptive responses are activated to preserve cardiac structure and function. These responses include but are not limited to alterations in cardiac metabolism, reduced calcium responsiveness, and induction of antioxidant enzymes. In a model of ischemic cardiomyopathy inducible by brief repetitive I/R, we hypothesized that dysregulation of these adaptive responses in diet-induced obese (DIO) mice would contribute to enhanced myocardial injury. DIO C57BL/6J mice were subjected to 15 min of daily repetitive I/R while under short-acting anesthesia, a protocol that results in the development of fibrotic cardiomyopathy. Cardiac lipids and candidate gene expression were analyzed at 3 days, and histology at 5 days of repetitive I/R. Total free fatty acids (FFAs) in the cardiac extracts of DIO mice were significantly elevated, reflecting primarily the dietary fatty acid (FA) composition. Compared with lean controls, cardiac FA oxidation (FAO) capacity of DIO mice was significantly higher, concurrent with increased expression of FA metabolism gene transcripts. Following 15 min of daily repetitive I/R for 3 or 5 days, DIO mice exhibited increased susceptibility to I/R and, in contrast to lean mice, developed microinfarction, which was associated with an exaggerated inflammatory response. Repetitive I/R in DIO mice was associated with more profound significant downregulation of FA metabolism gene transcripts and elevated FFAs and triglycerides. Maladaptive metabolic changes of FA metabolism contribute to enhanced myocardial injury in diet-induced obesity.

CD44 is critically involved in infarct healing by regulating the inflammatory and fibrotic response.

Infarct healing is dependent on an inflammatory reaction that results in leukocyte infiltration and clearance of the wound from dead cells and matrix debris. However, optimal infarct healing requires timely activation of "stop signals" that suppress inflammatory mediator synthesis and mediate resolution of the inflammatory infiltrate, promoting formation of a scar. A growing body of evidence suggests that interactions involving the transmembrane receptor CD44 may play an important role in resolution of inflammation and migration of fibroblasts in injured tissues. We examined the role of CD44 signaling in infarct healing and cardiac remodeling using a mouse model of reperfused infarction. CD44 expression was markedly induced in the infarcted myocardium and was localized on infiltrating leukocytes, wound myofibroblasts, and vascular cells. In comparison with wild-type mice, CD44(-/-) animals showed enhanced and prolonged neutrophil and macrophage infiltration and increased expression of proinflammatory cytokines following myocardial infarction. In CD44(null) infarcts, the enhanced inflammatory phase was followed by decreased fibroblast infiltration, reduced collagen deposition, and diminished proliferative activity. Isolated CD44(null) cardiac fibroblasts had reduced proliferation upon stimulation with serum and decreased collagen synthesis in response to TGF-beta in comparison to wild-type fibroblasts. The healing defects in CD44(-/-) mice were associated with enhanced dilative remodeling of the infarcted ventricle, without affecting the size of the infarct. Our findings suggest that CD44-mediated interactions are critically involved in infarct healing. CD44 signaling is important for resolution of the postinfarction inflammatory reaction and regulates fibroblast function.

Interleukin-10 is not a critical regulator of infarct healing and left ventricular remodeling.

OBJECTIVE: Interleukin-10 (IL-10) exerts potent anti-inflammatory actions and modulates matrix metalloproteinase expression. We hypothesized that endogenous IL-10 may regulate infarct healing and left ventricular remodeling by promoting resolution of the post-infarction inflammatory response and by modulating extracellular matrix metabolism. METHODS: IL-10 null and wildtype (WT) mice underwent reperfused infarction protocols. We compared the healing response and remodeling-associated parameters between IL-10-/-and WT infarcts. In addition, we studied the effects of IL-10 on inflammatory gene synthesis by stimulated murine cardiac fibroblasts. RESULTS: Infarcted IL-10-/-mice exhibited comparable mortality rates with WT animals. Although IL-10-/-mice had higher peak tumor necrosis factor (TNF)-alpha and monocyte chemoattractant protein (MCP)-1/CCL2 mRNA levels in the infarcted heart than WT mice, both groups demonstrated timely repression of pro-inflammatory cytokine and chemokine mRNA synthesis after 24 h of reperfusion and exhibited a similar time course of resolution of the neutrophil infiltrate. IL-10 gene disruption did not alter fibrous tissue deposition and dilative remodeling of the infarcted heart. Pre-incubation with IL-10 did not modulate the pro-inflammatory phenotype of TNF-alpha-stimulated cardiac fibroblasts, failing to inhibit chemokine mRNA synthesis. In contrast, transforming growth factor (TGF)-beta1 pre-incubation suppressed interferon-gamma-inducible protein (IP)-10/CXCL10 synthesis by cardiac fibroblasts exposed to TNF-alpha. CONCLUSIONS: IL-10 signaling plays a non-critical role in suppression of inflammatory mediators, resolution of the inflammatory response, and fibrous tissue deposition following myocardial infarction. This may be due to the relative selectivity of IL-10-mediated anti-inflammatory actions, with respect to cell type and stimulus. Resolution of post-infarction inflammation is likely to involve multiple overlapping regulatory mechanisms controlling various pro-inflammatory pathways activated in the infarcted myocardium.

The role of platelet-derived growth factor signaling in healing myocardial infarcts.

OBJECTIVES: This study sought to examine the role of platelet-derived growth factor (PDGF) signaling in healing myocardial infarcts. BACKGROUND: Platelet-derived growth factor isoforms exert potent fibrogenic effects through interactions with PDGF receptor (PDGFR)-alpha and PDGFR-beta. In addition, PDGFR-beta signaling mediates coating of developing vessels with mural cells, leading to the formation of a mature vasculature. We hypothesized that PDGFR activation may regulate fibrosis and vascular maturation in healing myocardial infarcts. METHODS: Mice undergoing reperfused infarction protocols were injected daily with a neutralizing anti-PDGFR-beta antibody (APB5), an anti-PDGFR-alpha antibody (APA5), or control immunoglobulin G, and were killed after 7 days of reperfusion. RESULTS: The PDGF-B, PDGFR-alpha, and PDGFR-beta mRNA expression was induced in reperfused mouse infarcts. Perivascular cells expressing phosphorylated PDGFR-beta were identified in the infarct after 7 days of reperfusion, indicating activation of the PDGF-BB/PDGFR-beta pathway. The PDGFR-beta blockade resulted in impaired maturation of the infarct vasculature, enhanced capillary density, and formation of dilated uncoated vessels. Defective vascular maturation in antibody-treated mice was associated with increased and prolonged extravasation of red blood cells and monocyte/macrophages, suggesting increased permeability. These defects resulted in decreased collagen content in the healing infarct. In contrast, PDGFR-alpha inhibition did not affect vascular maturation, but significantly decreased collagen deposition in the infarct. CONCLUSIONS: Platelet-derived growth factor signaling critically regulates postinfarction repair. Both PDGFR-beta- and PDGFR-alpha-mediated pathways promote collagen deposition in the infarct. Activation of PDGF-B/PDGFR-beta is also involved in recruitment of mural cells by neovessels, regulating maturation of the infarct vasculature. Acquisition of a mural coat and maturation of the vasculature promotes resolution of inflammation and stabilization of the scar.

Critical role of endogenous thrombospondin-1 in preventing expansion of healing myocardial infarcts.

BACKGROUND: Matricellular proteins are extracellular matrix proteins that do not contribute directly to tissue integrity but are capable of modulating cell function. We hypothesized that the matricellular protein thrombospondin (TSP)-1, a potent inhibitor of angiogenesis and activator of transforming growth factor (TGF-beta), is induced in healing myocardial infarcts and plays a role in suppressing the postinfarction inflammatory response, inhibiting local angiogenesis, and limiting expansion of granulation tissue into the noninfarcted area. METHODS AND RESULTS: We used a canine and a murine model of reperfused infarction. TSP-1 mRNA was induced in canine infarcts after 1 hour of ischemia and 3 to 7 days of reperfusion. TSP-1 protein showed a strikingly selective localization in the extracellular matrix, microvascular endothelium, and a subset of mononuclear cells of the infarct border zone after 5 to 28 days of reperfusion. Isolated canine venous endothelial cells showed low-level constitutive expression of TSP-1 mRNA, which was markedly induced by TGF-beta, and basic fibroblast growth factor. Murine infarcts also had marked TSP-1 deposition in the border zone. Infarcted TSP-1-/- mice exhibited sustained upregulation of the chemokines monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, and interferon-gamma-inducible protein-10/CXCL10 and the cytokines interleukin-1beta, interleukin-6, and TGF-beta, suggesting an enhanced and prolonged postinfarction inflammatory response. In addition, TSP-1-/- mice had markedly increased macrophage and myofibroblast density in infarcts and in remodeling noninfarcted myocardial areas neighboring the myocardial scar, suggesting expansion of granulation tissue formation into the noninfarcted territory. TSP-1-/- animals had more extensive postinfarction remodeling than wild-type mice, although infarct size was similar in both groups. CONCLUSIONS: The infarct border zone may be capable of modulating the healing process through its unique extracellular matrix content. The selective endogenous expression of TSP-1 in the infarct border zone may serve as a "barrier," limiting expansion of granulation tissue and protecting the noninfarcted myocardium from fibrotic remodeling.

CCL2/Monocyte Chemoattractant Protein-1 regulates inflammatory responses critical to healing myocardial infarcts.

The CC chemokine Monocyte Chemoattractant Protein (MCP)-1/CCL2 has potent mononuclear cell chemo-attractant properties, modulates fibroblast and endothelial cell phenotype and may play an important role in wound healing. In order to examine whether MCP-1 critically regulates myocardial infarct healing, we studied the effects of MCP-1 gene disruption and antibody neutralization in a closed-chest model of reperfused murine myocardial infarction. MCP-1-/- mice had decreased and delayed macrophage infiltration in the healing infarct and demonstrated delayed replacement of injured cardiomyocytes with granulation tissue. In contrast, the time course and density of neutrophil infiltration was similar in MCP-1 null and wild-type animals. MCP-1-/- infarcts had decreased mRNA expression of the cytokines TNF-alpha, IL-1beta, TGF-beta2, -beta3, and IL-10 and demonstrated defective macrophage differentiation evidenced by decreased Osteopontin-1 expression. MCP-1 deficiency diminished myofibroblast accumulation but did not significantly affect infarct angiogenesis. Despite showing delayed phagocytotic removal of dead cardiomyocytes, MCP-1-/- mice had attenuated left ventricular remodeling, but similar infarct size when compared with wild-type animals. MCP-1 antibody inhibition resulted in defects comparable with the pathological findings noted in infarcted MCP-1-/- animals without an effect on macrophage recruitment. MCP-1 has important effects on macrophage recruitment and activation, cytokine synthesis and myofibroblast accumulation in healing infarcts. Absence of MCP-1 results in attenuated post-infarction left ventricular remodeling, at the expense of a prolonged inflammatory phase and delayed replacement of injured cardiomyocytes with granulation tissue.

Outcomes of patients presenting with acute coronary syndromes and negative Troponin-T.

UNLABELLED: The aim of the study was to compare need for revascularization and clinical course between troponin-positive and troponin-negative patients with unstable angina pectoris defined as class IIIB according to Braunwald classification. METHODS: The study group consisting of 104 patients was divided into troponin-positive (28 patients) and troponin-negative (76 patients) subgroups. Per study design all patients underwent coronary angiography. The subgroups were compared in regard to angiographic status and consequently the need for revascularization. Additionally, major adverse cardiac events (MACE) consisting of death, myocardial infarction, in-hospital revascularization during 30-days follow-up were assessed in subgroups. RESULTS: In 58 (76%) patients with negative troponin test, the angiographically significant coronary artery stenosis was shown. Major adverse cardiac events were similar in both groups. Regardless of the initial TnT status, in both groups revascularizations (percutaneous or surgical) were performed with high frequency (89 versus 72%, P=NS). CONCLUSION: In patients with unstable angina in class IIIB according to Braunwald classification, the negative cardiac troponin test did not exclude severe coronary artery disease, which in the majority of patients required revascularization without any additional non-invasive testing for ischemia. Therefore, we postulate that patients with clinically evident unstable angina (IIIB) should be referred to early invasive assessment despite negative troponin T screening.

Contemporary coronary intervention in bifurcation lesions--two-year follow-up in an unselected cohort.

BACKGROUND: Optimization of coronary angioplasty in bifurcation lesions remains a major challenge for percutaneous revascularization techniques. MATERIAL/METHODS: We evaluated procedural success, major in-hospital complications, target vessel revascularization, and 2-year clinical outcomes in 45 patients who underwent PTCA of a bifurcation lesion using currently available techniques and rigorous criteria for optimal immediate RESULTS: Angiographic success occurred in 100% of the parent vessels and in 84.4% of both vessels. Within the first 24 hours, there were no deaths or Q-wave myocardial infarction. Three non-Q-wave myocardial infarctions occurred (6.6%) and one emergency PTCA was necessary (2.2%). Therefore, clinical success was achieved in 91.2% of these patients. At 2-year follow-up, 3 cardiac deaths had occurred, the target revascularization rate was 20%, and the total frequency of major adverse cardiac events (MACE) was 37.8%. CONCLUSIONS: Optimization of coronary angioplasty in bifurcation lesions is possible and results in a high angiographic success rate, low risk of acute complications and acceptable long-term clinical outcomes. However, the fairly high incidence of MACE at 2 years suggests that bifurcation lesions remain a challenge in everyday practice despite contemporary intervention methods and the use of GPIIb/IIIa inhibitors.

Intracoronary brachytherapy.

Patients presenting with in-stent restenosis have an increased risk of need for repeat intervention. Intracoronary brachytherapy is indicated for these patients to prevent recurrent in-stent restenosis. Three intravascular brachytherapy systems are currently FDA-approved for use in patients: one utilizing gamma-radiation (Cordis) and two using beta-radiation (Novoste and Guidant). Current evidence and labeling do not support using intracoronary brachytherapy for prevention of restenosis in de novo lesions. Brachytherapy is absolutely contraindicated in patients unable to take prolonged combination antiplatelet drugs. Aspirin and a thienopyridine should be taken for 6 months if no new stent is placed and 12 months if a new stent is placed. If possible, new stent implementation should be avoided.