PET Assessment of Immune Cell Activity and Therapeutic Monitoring Following Myocardial Infarction.

PURPOSE OF REVIEW: Local inflammation after myocardial infarction (MI) plays a role in subsequent ventricular remodeling, influences cardiac outcome, and has emerged as a therapeutic target. Preclinical and clinical PET imaging studies have employed a variety of radiotracers to target inflammatory leukocytes in the early stages after MI. RECENT FINDINGS: Imaging of enhanced metabolism in activated macrophages with 18F-FDG is feasible and has been associated with cardiac outcome in a small prospective study. Novel targeted PET agents show higher specificity for inflammatory leukocytes and can identify therapeutic response with limited background. While PET imaging of acute inflammation after MI has grown in recent years, significant challenges remain to widespread clinical application, including the complex cellular composition of the imaging signal and unclear association with functional outcome. Future studies must address the prognostic value of post-MI inflammation imaging and the ability to discern response to targeted, expensive, and personalized therapies.

Assessment of TSPO in a Rat Experimental Autoimmune Myocarditis Model: A Comparison Study between [18F]Fluoromethyl-PBR28 and [18F]CB251.

Overexpression of the 18-kDa translocator protein (TSPO) is closely linked to inflammatory responses in the heart, including myocarditis, which can lead to myocardial necrosis. In vivo assessment of inflammatory responses has enabled the precise diagnosis of myocarditis to improve clinical outcomes. Here, we evaluated TSPO overexpression in a rat model of experimental autoimmune myocarditis (EAM) compared to healthy rats using two TSPO radiotracers, [18F]fluoromethyl-PBR28 ([18F]1) and [18F]CB251 ([18F]2). All radiolabeling methods were successfully applied to an automated module for the reproducible preparation of TSPO radiotracers. Both radiotracers were directly compared in an EAM rat model, as well as in healthy rats to determine whether either radiotracer provides a more promising assessment of in vivo TSPO overexpression. [18F]2 provided more specific TSPO-uptake in the heart of the EAM rats (1.32-fold that of the heart-to-lung uptake ratio versus healthy controls), while [18F]1 did not show a significant difference between the two groups. Histopathological characterization revealed that a prominent positron emission tomography (PET) signal of [18F]2 in the EAM rats corresponded to the presence of a higher density of TSPO compared to the healthy controls. These results suggest that the imidazole[1,2-a]pyridine-based radiotracer [18F]2 is a sensitive tool for noninvasively diagnosing myocarditis related to inflammation of the heart muscle by assessing abnormal TSPO expression.

[Assessment of clinical-instrumental, morphological data and expression of coxsackie adenovirus receptor in patients with inflammatory cardiac pathology].

In 22 patients with heart failure and/or ventricular arrhythmias presumably of inflammatory etiology the results of clinical and instrumental investigation were analyzed and compared to the endomyocardial biopsy data. In the subgroup of patients with left bundle branch block (LBBB) we revealed features indicative of lesser contribution of inflammatory destruction in pathogenesis of cardiomyopathy. The only virus, detected in biopsy samples, was parvovirus B19. Its persistence in myocardium was not related to activity of inflammation and severity of clinical course. Increased expression of Coxsackie adenovirus receptor (CAR) was found in 20 patients. It was not related to inflammatory cells infiltration and virus persistence in myocardium. Patients with most prominent CAR expression were characteried by right heart dilatation, more severe heart failure and absence of LBBB. Enhancement of CAR expression could reflect the attempt of organism to repair intercellular communications between cardiomyocites and to protect cells from the products of necrotic lysis during long standing inflammation.

Non-invasive assessment of experimental autoimmune myocarditis in rats using a 3 T clinical MRI scanner.

AIMS: The aim of this study was to assess the use of a 3 T clinical cardiac magnetic resonance (CMR) scanner to detect injury to the heart in experimental autoimmune myocarditis (EAM). METHODS AND RESULTS: The use of 3 T CMR for the detection of cardiac injury was assessed in EAM (n = 55) and control (n = 10) male Lewis rats. Animals were evaluated with serial CMR imaging studies, using a 3 T scanner, and with 2D echocardiography before, and at 2 and 5 weeks after EAM induction. By CMR, regional wall motion abnormalities were noted in seven out of eight rats with myocarditis 5 weeks after induction. Subsequently, the rats developed significant left ventricular (LV) dilatation, wall thickening, and pericardial effusion. Average LV systolic and diastolic volumes increased from 131 ± 10 to 257 ± 20 µL (P = 0.0008), and from 309 ± 14 to 412 ± 24 µL (P < 0.0001), and ejection fraction markedly deteriorated (from 58 ± 2 to 37 ± 5%; P = 0.0003). Areas of fibrosis were located by late gadolinium enhancement (LGE) CMR at the subepicardium, mainly within the anterior, lateral, and inferior walls. The extent and location of LGE were highly correlated (r = 0.94; P < 0.0001) with areas of myocardial fibrosis by histopathology, with 85% sensitivity and 86% specificity. CONCLUSION: A clinical 3 T CMR scanner enables accurate detection, quantification, and monitoring of experimental myocarditis in rats, and could be used for translational research to study the pathophysiology of the disease and evaluate novel therapies.

Sex and gender differences in myocarditis and dilated cardiomyopathy.

Heart failure due to nonischemic dilated cardiomyopathy (DCM) contributes significantly to the global burden of cardiovascular disease. Myocarditis is, in turn, a major cause of acute DCM in both men and women. However, recent clinical and experimental evidence suggests that the pathogenesis and prognosis of DCM differ between the sexes. This seminar provides a contemporary perspective on the immune mediators of myocarditis, including interdependent elements of the innate and adaptive immune response. The heart's acute response to injury is influenced by sex hormones that appear to determine the subsequent risk of chronic DCM. Preliminary data suggest additional genetic variations may account for some of the differences in epidemiology, left ventricular recovery, and survival between men and women. We highlight the gaps in our knowledge regarding the management of women with acute DCM and discuss emerging therapies, including bromocriptine for the treatment of peripartum cardiomyopathy.

Noninvasive assessment of myocardial inflammation by cardiovascular magnetic resonance in a rat model of experimental autoimmune myocarditis.

BACKGROUND: Limited availability of noninvasive and biologically precise diagnostic tools poses a challenge for the evaluation and management of patients with myocarditis. METHODS AND RESULTS: The feasibility of cardiovascular magnetic resonance (CMR) imaging with magneto-fluorescent nanoparticles (MNPs) for detection of myocarditis and its effectiveness in discriminating inflammation grades were assessed in experimental autoimmune myocarditis (EAM) (n=65) and control (n=10) rats. After undergoing CMR, rats were administered with MNPs, followed by a second CMR 24 hours later. Head-to-head comparison of MNP-CMR with T(2)-weighted, early and late gadolinium enhancement CMR was performed in additional EAM (n=10) and control (n=5) rats. Contrast-to-noise ratios were measured and compared between groups. Flow cytometry and microscopy demonstrated that infiltrating inflammatory cells engulfed MNPs, resulting in altered myocardial T(2)* effect. Changes in contrast-to-noise ratio between pre- and post-MNP CMR were significantly greater in EAM rats (1.08 ± 0.10 versus 0.48 ± 0.20; P<0.001). In addition, contrast-to-noise ratio measurement in MNP-CMR clearly detected the extent of inflammation (P<0.001) except for mild inflammation. Compared with conventional CMR, MNP-CMR provided better image contrast (CNR change 8% versus 46%, P<0.001) and detectability of focal myocardial inflammation. Notably, MNP-CMR successfully tracked the evolution of myocardial inflammation in the same EAM rats. CONCLUSIONS: Magneto-fluorescent nanoparticle CMR permitted effective visualization of myocardial inflammatory cellular infiltrates and distinction of the extent of inflammation compared with conventional CMR in a preclinical model of EAM. Magneto-fluorescent nanoparticle CMR performs best in EAM rats with at least moderate inflammatory response.

Assessment of the inflammatory process by endomyocardial biopsy in patients with dilated cardiomyopathy based on pathological and immunohistochemical methods.

INTRODUCTION: Myocarditis may lead to dilated cardiomyopathy (DCM) in immunogenetically predisposed individuals. The diagnosis of myocardial inflammation is currently based on histopathological and immunohistochemical methods. Previous studies indicate that inflammatory cardiomyopathy occurs in approximately 50% of patients with DCM. AIM: The goal of the study was to assess the inflammatory process in patients with DCM by endomyocardial biopsy using histopathological and immunohistochemical methods. METHODS: Endomyocardial biopsy specimens was examined using routine histopathological methods and immunochemical staining for T lymphocytes (CD3(+), n=84), major histocompatibility complex I (HLA ABC, n=48) and II (HLA DPQR, n=84) antigens and the adhesion molecules ICAM-1 (n=51) and VCAM-1 (n=48) in 84 patients (69 male, 15 female; mean age 35.0+/-10.5 years) with angiographically-confirmed DCM. Familial disease occurrence was noted in 14 (16.7%) patients. Cardiac samples obtained from 18 patients who died of non-cardiovascular causes were used as a control group. RESULTS: Myocarditis was diagnosed, according to the Dallas criteria, in 8 (9.5%) patients. The frequency of inflammatory cardiomyopathy, defined as the presence of >2 CD3(+) T lymphocytes per high-power field (hpf) in myocardial biopsy, was 14.3%. When broader criteria were applied (presence of >2.0 CD3(+) lymphocytes/hpf and/or 1.5 CD3(+) lymphocytes/hpf in multiple foci and increased expression of class I/II HLA), inflammatory cardiomyopathy was diagnosed in 32.1% of patients. Inflammatory activation of the endothelium, indicated by increased expression of at least three adhesion molecules (class I and II HLA, ICAM-1, VCAM-1), was present in 22 (45.8%) patients. The expression of HLA DPQR, HLA ABC and ICAM-1 was observed on the endothelium of capillaries and larger vessels, interstitial cells, and the surface of activated lymphocytes; immunohistochemical reactions were diffuse. In patients with markedly elevated expression of the aforementioned adhesion molecules, the expression was also present on cardiomyocyte cell membranes. VCAM-1 was restricted to the endothelium of individual small veins. The control group did not demonstrate any signs of myocarditis, inflammatory cardiomyopathy or inflammatory endothelial activation. CONCLUSIONS: The application of immunohistochemical methods to myocardial biopsy in order to identify the inflammatory cell phenotype and the presence of adhesion molecules permits the diagnosis of inflammatory cardiomyopathy in 14% or 32% of patients, depending on the criteria used, while conventional pathology allows for this diagnosis in 9% of patients. The observed frequency of inflammatory cardiomyopathy, defined as the presence of >2 CD3(+) T lymphocytes/hpf in the myocardium, was lower (14%) than in previous studies, while the frequency of inflammatory endothelial activation was similar (45%).

Host gene regulation during coxsackievirus B3 infection in mice: assessment by microarrays.

Host genetic responses that characterize enteroviral myocarditis have not yet been determined. The injurious and inflammatory process in heart muscle may reflect host responses of benefit to the virus and ultimately result in congestive heart failure and dilated cardiomyopathy. On the other hand, host responses within the myocardium may secure the host against acute or protracted damage. To investigate the nature of modified gene expression in comparison with normal tissue, mRNA species were assessed in myocardium using cDNA microarray technology at days 3, 9, and 30 after infection. Of 7000 clones initially screened, 169 known genes had a level of expression significantly different at 1 or more postinfection time points as compared with baseline. The known regulated genes were sorted according to their functional groups and normalized expression patterns and, subsequently, interpreted in the context of viremic, inflammatory, and healing phases of the myocarditic process.

Studies of peripheral blood T lymphocytes in assessment of disease activity in rheumatic fever.

The study included three groups of children: (a) 38 with active rheumatic fever (ARF) and active carditis; 21 seen during their first attack and 17 during recurrence of activity, (b) 47 with inactive rheumatic fever (IARF); the period since activity was less than 3 years in 31 cases and more than 3 years in 16 cases. Using monoclonal antibodies and T lymphocyte blast transformation induced by PHA, we found: (1) low total T lymphocytes, helper-inducer cells and helper-inducer/suppressor-cytotoxic ratio which persisted for years; and (2) reduced lymphoblast transformation in active disease.

Assessment of cell-mediated immunity against coxsackievirus B3-induced myocarditis in a primate model (Papio papio).

Delayed hypersensitivity and myocarditis were induced in five baboons (Papio papio) after inoculation with myocarditic murine coxsackievirus B3 (CVB3m). By means of the [3H]thymidine incorporation assay and the agarose droplet cell migration inhibition assay, specific cell-mediated immunity was detected in all five animals against viral antigens and/or KCl-extractable soluble antigens extracted from the heart of a CVB3m-inoculated baboon. KCl-extracted antigens from normal baboon heart tissues, as well as KCl-extracted antigens from spleen or liver tissues from a CVB3m-inoculated baboon, failed to stimulate baboon peripheral blood lymphocytes or inhibit the migration of baboon peritoneal exudate cells. The appearance of dissimilar antigen(s) in extracts of heart tissues from CVB3m-inoculated baboons which did not contain infectious CVB3m parallels the appearance of novel KCl-extractable antigen(s) induced by CVB3m in murine heart tissues (Paque et al., J. Immunol. 120:1672-1678). The animal model described represents the first systematic evaluation of cell-mediated immunity in CVB3m-induced myocarditis in primates and suggests that a similar phenomenon may occur in humans.

Assessment of antibody mediated cytolysis of adult cardiocytes isolated by centrifugation in a continuous gradient of Percoll in patients with acute myocarditis.

Principal objections to conventional cytotoxicity assays in cardiac disease with myocytes as target cells are the use of fetal or neonatal myocardium, the cell-membrane of which does not express all antigenic determinants, and the use of trypsin as enzyme for isolation of the cells, since this alters the myolemmal membrane considerably. An improved and rapid procedure for the isolation of intact adult cardiocytes with collaggenase was developed. by means of a performed continuous self-generating silica sol and gradient centrifugation average enrichment of 81% vital myocytes was achieved by a single isopycnic procedure. The yield was improved to 94 +/- 3% vital cells by identical second centrifugation. Cardiocytes isolated by this method were used as target cells in an assay measuring the cytolytic activity of antibodies in the presence of complement: sera of patients suffering from acute viral myocarditis (Coxsackie B- and influenza-virus) with complement fixing antisacrolemmal antibodies (ASA) of the IgG- and IgM-type showed significant cardiocytolysis. ASA are postulated to play a role in the pathogenesis of acute Coxsackie B- and influenza-virus myocarditis.

Assessment of coxsackievirus B3 ts mutants for induction of myocarditis in a murine model.

Ten temperature-sensitive (ts) mutants isolated from a myocarditis-inducing wild-type (WT) coxsackievirus B3 parent did not induce myocarditis in adolescent CD-1 mice. An avirulent prototype ts mutant from one of the three complementation groups adsorbed to murine cardiac tissue, as did WT virus. Heart tissues from mice inoculated with WT virus contained 100- to 1,000-fold more virus than heart tissues from mice inoculated with any of the three prototype ts mutants. WT virus exhibited a greater capsid stability and a higher efficiency of replication at 37 degrees C than any of the three prototype ts mutants. All three prototype ts mutants induced less interferon in vivo than WT virus. Cell-mediated immune responses, assessed by the cell migration inhibition assay, were different in mice inoculated with WT virus when compared to ts 5 mutant virus. Peritoneal exudate cells from mice inoculated with WT but not ts 5 virus reacted specifically against antigens in WT virus HeLa cell lysates and antigens extracted with KCl from cardiac tissues of mice inoculated with WT virus. Cardiac tissues of mice inoculated with WT but not ts 5 virus contained KCl-extractable antigens which were able to specifically inhibit the migration of peritoneal exudate cells taken from mice immunized with WT virus. Therefore, ts 5 neither elicited a measurable cell-mediated immune response nor induced antigens in cardiac tissues which were immunoreactive with sensitized-(WT virus)-peritoneal exudate cells. Of 9 revertant viruses isolated from the 10 ts mutants, 5 showed covariance in ability to replicate at 39.5 degrees C and capacity for induction of myocarditis. Some revertants exhibited a reduced capsid thermostability compared to WT virus but yet retained the capacity for induction of myocarditis. The data suggest that induction of myocarditis by coxsackievirus B3 variants depends on a combination of several variables, including capsid stability, capacity for replication at 37 degrees C, and expression of the three identified genes. All three prototype ts mutants served as vaccine viruses in preventing myocarditis in adolescent mice subsequently challenged with WT virus. However, all three prototype ts mutants and their revertant variants retained partial to complete lethality in CD-1 neonates.