Ventricular arrhythmias are related to the presence of autoantibodies with adrenergic activity in chronic chagasic patients with preserved left ventricular function

Chagas' cardiomyopathy and Lyme carditis: Lessons learned from two infectious diseases affecting the heart

Chagas' disease and Lyme disease are two endemic, vector-borne zoonotic infectious diseases that impact multiple organ systems, including the heart. Chagas' cardiomyopathy is a progressive process that can evolve into a dilated cardiomyopathy and heart failure several decades after the acute infection; in contrast, although early-disseminated Lyme carditis has been relatively well characterized, the sequelae of Lyme disease on the heart are less well-defined. A century of research on Chagas' cardiomyopathy has generated compelling data for pathophysiological models, evaluated the efficacy of therapy in large randomized controlled trials, and explored the social determinants of health impacting preventative measures. Recognizing the commonalities between Chagas' disease and Lyme disease, we speculate on whether some of the lessons learned from Chagas' cardiomyopathy may be applicable to Lyme carditis.

ROS and Trypanosoma cruzi: Fuel to infection, poison to the heart

The activation of macrophage respiratory burst in response to infection with Trypanosoma cruzi inflicts oxidative damage to the host’s tissues. For decades, the role of reactive oxygen species (ROS) in the elimination of T. cruzi was taken for granted, but recent evidence suggests parasite growth is stimulated in oxidative environments. It is still a matter of debate whether indeed oxidative environments provide ideal conditions (e.g., iron availability in macrophages) for T. cruzi growth and whether indeed ROS signals directly to stimulate growth. Nitric oxide (NO) and ROS combine to form peroxynitrite, participating in the killing of phagocytosed parasites by activated macrophages. In response to infection, mitochondrial ROS are produced by cardiomyocytes. They contribute to oxidative damage that persists at the chronic stage of infection and is involved in functional impairment of the heart. In this review, we discuss how oxidative stress helps parasite growth during the acute stage and how it participates in the development of cardiomyopathy at the chronic stage.

Autoantibodies with beta-adrenergic activity from chronic chagasic patients induce cardiac arrhythmias and early afterdepolarization in a drug-induced LQT2 rabbit hearts

BACKGROUND

Cardiac arrhythmias are one of the main causes of death in ChCP and other dilated cardiomyopathies. Previous studies demonstrated that ventricular arrhythmias are associated with the presence of autoantibodies with beta-adrenergic activity, Ab-β.

OBJECTIVES

The aim of this study was to investigate whether Ab-β, present in chronic chagasic patients (ChCP), induce cardiac arrhythmias in the pharmacological type-2 long QT syndrome model (LQTS-2).

METHODS/RESULTS

The LQTS2 was established by perfusion of Tyrode saline solution with a potassium channel blocker E-4031 (5μM) in isolated rabbit hearts or in rabbit cardiac strips, in order to record ECG or action potential, respectively. Autoantibodies from ChCP activating (Ab-β) or not (Ab-NR) cardiac beta 1-adrenergic receptors were used. Ab-β, but not Ab-NR, were able to significantly shorten QT, QTc and increase Tpeak-Tend interval in the LQTS-2. A positive correlation between higher QTc and Tpeak-Tend was found after Ab-β perfusion in the same model. In addition, in the LQTS-2 model, in almost 75% (11/15) of the hearts perfused with Ab-β, ventricular and atrio-ventricular electrical disturbances were observed. Atenolol abolished all Ab-β-induced arrhythmias. Ab-β, when perfused in a cellular LQTS-2, drastically reduced the action potential duration and evoked early afterdepolarization (EAD's), while Ab-NR did not modulate the AP properties in the LQTS-2.

CONCLUSION

The results indicate that Ab-β were able to induce cardiac arrhythmias and EAD's. This phenomenon can explain, at least in part, the cellular mechanism of Ab-β-induced arrhythmias. Furthermore, atenolol is effective for the treatment of Ab-β-induced arrhythmias.

β1 -Adrenoceptor autoantibodies increase the susceptibility to ventricular arrhythmias involving abnormal repolarization in guinea-pigs

NEW FINDINGS

What is the central question of this study? High titres of autoantibodies against the second extracellular loop of the β₁ -adrenergic receptor (β₁ -AAs) can be detected in the sera of patients with ventricular arrhythmias, but a causal relationship between β₁ -AAs and ventricular arrhythmias has not been established. What is the main finding and its importance? Monoclonal β₁ -AAs (β₁ -AR mAbs) were used in the experiments. We showed that β₁ -AR mAbs increased susceptibility to ventricular arrhythmias and induced repolarization abnormalities. Antibody adsorption of β₁ -AAs will be a potential new therapeutic strategy for ventricular arrhythmias in patients with high titres of β₁ -AAs. High titres of autoantibodies against the second extracellular loop of the β₁ -adrenergic receptor (β₁ -AAs) can be detected in sera from patients with ventricular arrhythmias, but a causal relationship between β₁ -AAs and ventricular arrhythmias has not been established. In this work, ECGs of guinea-pigs and isolated guinea-pig hearts were recorded. Ventricular tachycardia (VT) and ventricular fibrillation (VF) were evoked by programmed electrical stimulation of the left ventricular epicardium of isolated guinea-pig hearts. The monophasic action potential and effective refractory period of the left ventricle were recorded in paced isolated guinea-pig hearts. Furthermore, to increase the specificity, monoclonal autoantibodies against the second extracellular loop of the β₁ -adrenergic receptor (β₁ -AR mAbs) were used in all experiments. The results showed that β₁ -AR mAbs induced premature ventricular contractions in guinea-pigs and isolated guinea-pig hearts. In addition, β₁ -AR mAbs decreased the threshold of VT/VF and prolonged the duration of VT/VF. Furthermore, β₁ -AR mAbs shortened the corrected QT interval and effective refractory period, and prolonged late-phase repolarization of the monophasic action potential (MAPD_90-30 ). These changes in electrophysiological parameters might be attributed, at least in part, to the arrhythmogenicity of β₁ -AR mAbs.

Monoclonal anti-β1-adrenergic receptor antibodies activate G protein signaling in the absence of β-arrestin recruitment

Thermostabilized G protein-coupled receptors used as antigens for in vivo immunization have resulted in the generation of functional agonistic anti-β1-adrenergic (β1AR) receptor monoclonal antibodies (mAbs). The focus of this study was to examine the pharmacology of these antibodies to evaluate their mechanistic activity at β1AR. Immunization with the β1AR stabilized receptor yielded five stable hybridoma clones, four of which expressed functional IgG, as determined in cell-based assays used to evaluate cAMP stimulation. The antibodies bind diverse epitopes associated with low nanomolar agonist activity at β1AR, and they appeared to show some degree of biased signaling as they were inactive in an assay measuring signaling through β-arrestin. In vitro characterization also verified different antibody receptor interactions reflecting the different epitopes on the extracellular surface of β1AR to which the mAbs bind. The anti-β1AR mAbs only demonstrated agonist activity when in dimeric antibody format, but not as the monomeric Fab format, suggesting that agonist activation may be mediated through promoting receptor dimerization. Finally, we have also shown that at least one of these antibodies exhibits in vivo functional activity at a therapeutically-relevant dose producing an increase in heart rate consistent with β1AR agonism.