Autoimmune giant cell myocarditis: clinical characteristics, experimental models and future treatments

Programmed death of cardiomyocytes in cardiovascular disease and new therapeutic approaches

Cardiovascular diseases (CVDs) have a complex pathogenesis and pose a major threat to human health. Cardiomyocytes have a low regenerative capacity, and their death is a key factor in the morbidity and mortality of many CVDs. Cardiomyocyte death can be regulated by specific signaling pathways known as programmed cell death (PCD), including apoptosis, necroptosis, autophagy, pyroptosis, and ferroptosis, etc. Abnormalities in PCD can lead to the development of a variety of cardiovascular diseases, and there are also molecular-level interconnections between different PCD pathways under the same cardiovascular disease model. Currently, the link between programmed cell death in cardiomyocytes and cardiovascular disease is not fully understood. This review describes the molecular mechanisms of programmed death and the impact of cardiomyocyte death on cardiovascular disease development. Emphasis is placed on a summary of drugs and potential therapeutic approaches that can be used to treat cardiovascular disease by targeting and blocking programmed cell death in cardiomyocytes.

New insights gained from cellular landscape changes in myocarditis and inflammatory cardiomyopathy

Advances in the etiological classification of myocarditis and inflammatory cardiomyopathy (ICM) have reached a consensus. However, the mechanism of myocarditis/ICM remains unclear, which affects the development of treatment and the improvement of outcome. Cellular transcription and metabolic reprogramming, and the interactions between cardiomyocytes and non-cardiomyocytes, such as the immune cells, contribute to the process of myocarditis/ICM. Recent efforts have been made by multi-omics techniques, particularly in single-cell RNA sequencing, to gain a better understanding of the cellular landscape alteration occurring in disease during the progression. This article aims to provide a comprehensive overview of the latest studies in myocarditis/ICM, particularly as revealed by single-cell sequencing.

STING-Targeted PET Imaging for Specific Detection and Therapeutic Monitoring of Myocarditis

Imaging strategies for the specific detection and therapeutic monitoring of myocarditis are still lacking. Stimulator of interferon genes (STING) is a signal transduction molecule involved in an innate immune response. Here, we evaluated the feasibility of the recently developed STING-targeted radiotracer [18F]FBTA for positron emission tomography (PET) imaging to detect myocardial inflammation and monitor treatment in myocarditis mice. [18F]FBTA-PET imaging was performed in myocarditis mice and normal mice to verify the specificity of [18F]FBTA for the diagnosis of myocarditis. We also performed PET imaging in mice with myocarditis treated to verify the ability of [18F]FBTA in therapeutic monitoring. The expression of STING and inflammatory cell types was confirmed by flow cytometry and immunohistochemistry. [18F]FDG-PET imaging of myocarditis was used as a contrast. [18F]FBTA-PET imaging showed that the average radioactive uptake was significantly higher in the hearts of the myocarditis group than in the control group. STING was highly overexpressed in cardiac inflammatory cells, including macrophages, dendritic cells (DCs), and T cells. However, there was no significant difference in cardiac radiotracer uptake of [18F]FDG between the myocarditis group and the control group. Moreover, cardiac uptake of [18F]FBTA was significantly reduced in cyclosporin A-treated myocarditis mice and myocardial STING expression was also significantly reduced after the treatment. Overall, we showed that a STING-targeted PET tracer [18F]FBTA can be used to monitor changes in the inflammatory microenvironment in myocarditis. Besides, [18F]FBTA-PET is also suitable for real-time monitoring of myocarditis treatment, representing a promising diagnostic and therapeutic monitoring approach for myocarditis.

Empagliflozin alleviates the development of autoimmune myocarditis via inhibiting NF-κB-dependent cardiomyocyte pyroptosis

Autoimmune myocarditis, which falls within the broad spectrum of myocarditis, is characterized by an excessive inflammatory response in the heart, and can progress into dilated cardiomyopathy and irreversible heart failure in all possibility. However, effective clinical therapeutics are limited due to its complex inflammatory reactions. Empagliflozin (EMPA) has been previously demonstrated to possess anti-inflammatory properties. This study aimed to determine the improvement effects of EMPA on cardiac dysfunction under the condition of autoimmune myocarditis, and to further investigate the potential mechanisms. In vivo, all male Balb/c mice were randomly divided into four groups: control, experimental autoimmune myocarditis (EAM), EAM+EMPA and EMPA. In vitro, the effects of EMPA on IL-18-stimulated H9C2 cells were explored and the underlying molecular mechanisms were further determined. EMPA treatment significantly inhibited the development of autoimmune myocarditis, and mice treated with EMPA exhibited improved cardiac function compared with that in the EAM group, potentially through modulating pyroptosis of myocardium. Specifically, the NF-κB pathway was activated in the hearts of the EAM mice, which further activated NLRP3 inflammasome-dependent pyroptosis. EMPA treatment significantly inhibited such activation, thus alleviating inflammatory reactions in the context of EAM. Moreover, in vitro, we also observed that EMPA significantly inhibited pyroptosis of IL-18-stimulated H9C2 cells, and reduced nuclear translocation of NF-κB and degradation of activated IκBα. This work provides the first direct evidence that EMPA can inhibit myocardial inflammation and improve cardiac function in EAM mice, partly attributed to the drug-induced suppression of cardiomyocyte pyroptosis via disrupting the NF-κB pathway.

Inhibition of NETosis via PAD4 alleviated inflammation in giant cell myocarditis

Giant cell myocarditis (GCM) is a rare, usually rapidly progressive, and potentially fatal disease. Detailed inflammatory responses remain unknown, in particular the formation of multinucleate giant cells. We performed single-cell RNA sequencing analysis on 15,714 Cd45+ cells extracted from the hearts of GCM rats and normal rats. NETosis has been found to contribute to the GCM process. An inhibitor of NETosis, GSK484, alleviated GCM inflammation in vivo. MPO (a marker of neutrophils) and H3cit (a marker of NETosis) were expressed at higher levels in patients with GCM than in patients with DCM and healthy controls. Imaging mass cytometry analysis revealed that immune cell types within multinucleate giant cells included CD4+ T cells, CD8+ T cells, neutrophils, and macrophages but not B cells. We elucidated the role of NETosis in GCM pathogenesis, which may serve as a potential therapeutic target in the clinic.

Aggravation of TGFβ1-Smad Pathway and Autoimmune Myocarditis by Fungicide (Tebuconazole) Exposure

Myocarditis is an inflammatory cardiac disorder and the primary cause of heart failure in young adults. Its origins can be attributed to various factors, including bacterial or viral infections, exposure to toxins or drugs, endocrine disruptors (EDs), and autoimmune processes. Tebuconazole (TEB), which is a member of the triazole fungicide family, is utilized to safeguard agricultural crop plants against fungal pathogens. Although TEB poses serious threats to mammal health, the information about how it induces toxic effects through various pathways, particularly in autoimmune diseases, are still limited. Thus, the aim of this paper was to evaluate the effect of TEB exposure in autoimmune myocarditis (AM). To induce AM, rats were immunized with porcine cardiac myosin and exposed to TEB for 21 days. Thereafter, animals were sacrificed, and histological, biochemical, and molecular analyses were performed. TEB exposure increased heart weight, systolic blood pressure and heart rate already augmented by AM. Additionally, it significantly increased creatine phosphokinase heart (CK-MB), creatine phosphokinase (CPK), cardiac troponin T (cTnT), and cardiac troponin I (cTnI), as compared to the control. From the histological perspective, TEB exacerbates the histological damage induced by AM (necrosis, inflammation and cell infiltration) and increased fibrosis and collagen deposition. TEB exposure strongly increased pro-inflammatory cytokines and prooxidant levels (O2^-, H₂O₂, NO₂^-, lipid peroxidation) and reduced antioxidant enzyme levels, which were already dysregulated by AM. Additionally, TEB increased NOX-4 expression and the TGFβ1-Smads pathway already activated by AM. Overall, our results showed that TEB exposure strongly aggravated the cardiotoxicity induced by AM.

Melissa officinalis L. Supplementation Provides Cardioprotection in a Rat Model of Experimental Autoimmune Myocarditis

Due to existing evidence regarding antioxidant and anti-inflammatory effects of Melissa officinalis extracts (MOEs), this study was aimed at investigating the potential of ethanolic MOE to prevent the development of myocarditis and its ability to ameliorate the severity of experimental autoimmune myocarditis (EAM) by investigating MOE effects on in vivo cardiac function, structure, morphology, and oxidative stress parameters. A total of 50 7-week-old male Dark Agouti rats were enrolled in the study and randomly allocated into the following groups: CTRL, nontreated healthy rats; EAM, nontreated rats with EAM; MOE50, MOE100, and MOE200, rats with EAM treated with either 50, 100, or 200 mg/kg of MOE for 3 weeks per os. Myocarditis was induced by immunization of the rats with porcine myocardial myosin (0.5 mg) emulsion on day 0. Cardiac function and dimensions of the left ventricle (LV) were assessed via echocardiography. Additionally, the blood pressure and heart rate were measured. On day 21, rats were sacrificed and the hearts were isolated for further histopathological analyses (H/E and Picrosirius red staining). The blood samples were collected to determine oxidative stress parameters. The EAM group characteristically showed greater LV wall thickness and lower ejection fraction (50.33 ± 7.94% vs. 84.81 ± 7.74%) and fractional shortening compared to CTRL (p < 0.05). MOE significantly improved echocardiographic parameters (EF in MOE200 81.44 ± 5.51%) and also reduced inflammatory infiltrate (by 88.46%; p < 0.001) and collagen content (by 76.39%; p < 0.001) in the heart tissues, especially in the MOE200 group compared to the EAM group. In addition, MOEs induced a significant decrease of prooxidants production (O₂⁻, H₂O₂, and TBARS) and improved antioxidant defense system via increase in GSH, SOD, and CAT compared to EAM, with medium and high dose being more effective than low dose (p < 0.05). The present study suggests that ethanolic MOEs, especially in a 200 mg/kg dose, improve cardiac function and myocardial architecture, possibly via oxidative stress mitigation, thus preventing heart remodeling, development of dilated cardiomyopathy, and subsequent heart failure connected with EAM. MOEs might be considered as a potentially helpful adjuvant therapy in patients with autoimmune myocarditis.

Clinical Identification and Characteristic Analysis of Giant Cell Myocarditis in 12 Cases

Aims: Giant cell myocarditis (GCM) is a rare, rapidly progressing cardiomyopathy with high mortality, if not diagnosed and treated in time. We analyzed the progression and clinical manifestations of patients with definitive diagnosis of GCM.

Methods and Result: We enrolled 12 patients diagnosed with GCM in the explanted heart during heart transplantation (HTx) or by endomyocardial biopsy (EMB) and collected information on demographic data, cardiac structure and function, arrhythmias, preliminary diagnosis, and delay of the diagnosis. Seven cases were diagnosed from biopsy samples during HTx, and five cases were diagnosed through EMB. Before the diagnosis of GCM based on pathological analysis, these patients had been incorrectly diagnosed with arrhythmogenic right ventricular cardiomyopathy (n = 5), dilated cardiomyopathy (n = 2), ventricular tachycardia (n = 2), viral myocarditis (n = 1), cardiac amyloidosis (n = 1), and ischemic cardiomyopathy (n = 1) based on clues such as symptoms, arrhythmia, and cardiac imaging. Patients diagnosed with GCM through EMB had a shorter symptom-onset-to-diagnosis time (6.6 ± 2.7 months) and milder heart damage (left ventricular ejection fraction, 47.2 ± 8.8%) than those diagnosed during HTx (11.0 ± 3.3 months, P = 0.034; 31.4 ± 10.9%, P = 0.024).

Conclusion: GCM is easily misdiagnosed as other types of myocarditis and cardiomyopathy. Pathological examination of the myocardium is the most reliable diagnostic method for GCM. Endocardial biopsy can identify patients with GCM at an earlier stage.

11C-Methionine PET of Myocardial Inflammation in a Rat Model of Experimental Autoimmune Myocarditis

Myocarditis represents a major cause of dilated cardiomyopathy and sudden cardiac death in younger adults. Currently, definitive diagnosis of myocarditis requires endomyocardial biopsy, which is highly invasive and has the drawback of variable sensitivity due to inherent sampling error. Therefore, reliable noninvasive methods to detect and monitor cardiac inflammation are clinically relevant. In this study, we explored the potential of radiolabeled methionine to assess myocardial inflammatory activity in a rat model of experimental autoimmune myocarditis (EAM).

METHODS

Autoimmune myocarditis was induced by immunizing Lewis rats twice with porcine cardiac myosin and Freund complete adjuvant. Control animals were treated with adjuvant alone. Dual-tracer autoradiography was performed to assess ¹⁴C-methionine uptake and to compare the distributions of ¹⁴C-methionine versus ¹⁸F-FDG. Hematoxylin and eosin staining and anti-CD68 macrophage staining were performed for histologic analysis. Additionally, cardiac ¹¹C-methionine PET was performed to evaluate the feasibility of in vivo imaging. ¹⁸F-FDG PET was also conducted to compare the in vivo uptake of ¹¹C-methionine and ¹⁸F-FDG.

RESULTS

Multiple focal cardiac inflammatory lesions were histologically identified in myosin-immunized rats, whereas no cardiac lesions were observed in the controls. Autoradiographic images clearly showed a high-density accumulation of ¹⁴C-methionine in inflammatory lesions of EAM rats, whereas no significant uptake was observed in the control animals. ¹⁴C-methionine uptake was significantly higher in inflammatory lesions than in remote noninflammatory areas and control rat hearts. The distribution of ¹⁴C-methionine correlated well with that of ¹⁸F-FDG and with macrophage density. The contrast between inflammatory and noninflammatory areas was higher for ¹⁸F-FDG than for ¹⁴C-methionine (3.45 ± 0.68 vs. 2.07 ± 0.21, respectively; P < 0.05). In the PET imaging study, the regional ¹¹C-methionine uptake (percentage injected dose per cubic centimeter) observed in EAM rats was significantly higher than the values obtained for control animals (0.64 ± 0.09 vs. 0.28 ± 0.02, respectively; P < 0.001). A good positive correlation between ¹¹C-methionine and ¹⁸F-FDG uptake was found.

CONCLUSION

In a rat model of autoimmune myocarditis, we demonstrated the colocalization of radiolabeled methionine accumulation with ¹⁸F-FDG uptake in histologically proven inflammatory lesions. These data suggest that ¹¹C-methionine might represent a promising candidate for the noninvasive detection and monitoring of myocarditis.

Fulminant heart failure due to giant cell myocarditis affecting the left ventricle

A 56-year-old woman, previously healthy, was hospitalized after an episode of ventricular tachycardia in the course of infection. In view of the fulminant course of heart failure the patient was connected to an extracorporeal membrane oxygenation (ECMO) system. After 3 weeks of treatment with ECMO the patient received a heart transplant. A histopathological examination of the tissues of the explanted heart revealed giant cell myocarditis. The patient was treated with immunosuppression based on induction therapy followed by a standard regimen with steroids. Currently, the patient remains in good general condition with an left ventricular ejection fraction of 60%.

A P2X7 receptor antagonist attenuates experimental autoimmune myocarditis via suppressed myocardial CD4+ T and macrophage infiltration and NADPH oxidase 2/4 expression in mice

Myocarditis is a clinically serious disease; however, no effective treatment has been elucidated. The P2X7 receptor is related to the pathophysiology of inflammation in many cardiovascular diseases. The P2X7 receptor antagonist is promising as an immunosuppressive treatment; however, its role in myocarditis is still to be established. To clarify the role of the P2X7 receptor, we used a murine experimental autoimmune myocarditis (EAM) model. Mice were immunized on day 0 and 7 with synthetic cardiac myosin peptide to establish EAM. The mice with induced EAM were treated with A740003, the P2X7 receptor antagonist (n = 10), or not treated (n = 11); hearts were harvested on day 21. The P2X7 receptor antagonist improved myocardial contraction of the EAM hearts via suppressed infiltration of CD4+ T cells and macrophages. Similarly, mRNA expression of interleukin 1 beta, the P2X7 receptor and NADPH oxidase 2/4 was lower in the heart of the P2X7 receptor antagonist-treated group compared to the non-treat group. The P2X7 receptor antagonist suppressed EAM development; thus, this inhibition is promising for treating clinical myocarditis.