Autoantibodies and Cardiomyopathy: Focus on Beta-1 Adrenergic Receptor Autoantibodies

Frequency of autoantibodies and their associated clinical characteristics and outcomes in patients with dilated cardiomyopathy: A systematic review and meta-analysis

BACKGROUND

Dilated cardiomyopathy (DCM) is a prevalent myocardial disorder characterized by impaired cardiac function affecting either the left ventricle or both ventricles. Accumulating evidence suggests that autoimmunity represents a key mechanism implicated in its pathogenesis, as several abundant autoantibodies have been identified in patients with the condition. However, the prevalence of these antibodies (Abs) in patients with DCM compared to that in both healthy controls (HCs) and those with ischemic cardiomyopathy (ICM), as well as their potential association with DCM, remains unclear. This study aimed to elucidate the prevalence of certain autoantibodies in patients with DCM compared to that in HCs and patients with ICM, as well as to evaluate their correlation with clinical characteristics and outcomes.

METHODS

A comprehensive literature search of the PubMed, Web of Science, EMBASE, the Cochrane Library, and Scopus was conducted up to March 26, 2024, and any article that fulfilled our inclusion criteria was reviewed. A meta-analysis was then conducted, using both random- and fixed-effects models.

RESULTS

A total of 38 studies met the inclusion criteria and were pulled for this analysis. Significantly higher prevalence rates of autoantibodies targeting the anti-β1 adrenergic receptor (β1-AR; odds ratio [OR] = 4.96, p = 0.000), M2 muscarinic receptor (M2-R; OR = 4.07, p = 0.000), adenine nucleotide translocator (ANT; OR = 21.18, p = 0.001) and myosin (OR = 12.26, p = 0.000) were observed in patients with DCM compared to HCs. Moreover, patients with DCM exhibited a significantly higher frequency of positive ANT Abs (OR = 34.52, p = 0.005) compared to those with ICM. Regarding clinical characteristics and outcomes, seropositivity for β1-AR Abs was found to be significantly correlated with New York Heart Association (NYHA) classification (standardized mean difference [SMD] = 0.78, p = 0.006), left ventricular ejection fraction (LVEF) (SMD = -1.38, p = 0.001), and heart rate (HR) (SMD = 1.505, p = 0.022). Seropositivity for anti‑calcium channel Abs was significantly associated with sudden cardiac death (SCD; OR = 3.17, p = 0.000) and all-cause mortality (OR = 2.06, p = 0.008), while anti-troponin I (TnI) Abs were associated with atrial fibrillation (OR = 0.21, p = 0.042). In terms of Ab prevalence rates, significant heterogeneity in the frequency of anti-β1-AR Abs between studies investigating DCM and ICM may be partially explained by the detection methods used and the mean ages of the patients. Meta-regression analysis suggested that the patients' ages may partially explain the observed heterogeneity between studies regarding β1-AR Ab seropositivity and HR. However, the heterogeneity observed in the studies comparing the prevalences of Abs in patients with DCM vs HCs and ICM, as well as their associated clinical characteristics, could not be explained by subgroup analyses or demographic factors such as age and sex-nor by cardiac function.

CONCLUSIONS

Patients with DCM are more likely to have elevated levels of anti- β1-AR, M2-R, ANT and myosin autoantibodies compared to HCs, as well as higher levels of ANT Abs compared to patients with ICM. Anti-β1-AR, calcium channel, and TnI Abs may play an essential role in DCM severity and poor prognosis. This study represents the first comprehensive meta-analysis regarding autoantibody prevalence and DCM and may thus potentially guide the clinical management of such patients. However, further research is warranted to evaluate the accuracy of this presumed role of autoantibodies in DCM, owing to the small number of the studies included and their high degree of heterogeneity.

Autoimmunity in Cardiomyopathy-Induced Heart Failure and Cardiac Autoantibody Removal by Immunoadsorption

There is increasing evidence that β1-adrenoreceptor autoantibody (β1AR-AAb) elimination can break the vicious circle induced by certain pathological conditions associated with alteration of the physiological self-tolerance, followed by generation of such AAbs and activation of cell-mediated immune processes directed against the myocardium. Concerning this, the present narrative review article provides an updated overview of the state of knowledge about the role of auto-immunity in the etiopathogenesis of cardiomyopathies, with a particular focus on immunoadsorption (IA) therapy for β1AR-AAb-positive adult patients with a dilated cardiomyopathy (DCM)-associated refractory heart failure (HF). Among many relevant findings, the increasing prevalence (up to 97%) of β1AR-AAb-positive patients related to the aggravation of HF, the high prevalence (between 84% and 91%) of HF patients in which IA can reduce to a minimum any increased β1AR-AAb level, as well as the high prevalence (about 80%) of responders to the IA-induced normalization of β1AR-AAb levels by long-term improvement in LV ejection fraction with increase in LV stroke volume and cardiac output, are of particular relevance. Given that after the elimination of β1AR-AAbs in potential candidates for heart transplantation (HTx), the post-IA 3- and 5-year HTx-/mechanical support-free survival probability reached 80% and 63-69%, respectively, the good tolerability of IA and the possibility to repeat that therapy also in elderly persons strongly suggest that in appropriately selected patients, this therapy deserves much more attention in the future.

Relationship between β1-AA and AT1-AA and Cardiac Function in Patients with Hypertension Complicated with Left Ventricular Diastolic Function Limitation

Objective

To investigate the association between β1 adrenergic receptor autoantibodies (β1-AA) and angiotensin II type-1 receptor autoantibodies (AT1-AA) and cardiac function in patients with hypertension complicated with left ventricular diastolic function limitation.

Methods

A total of 120 patients with essential hypertension who were not taking drug treatment and were hospitalised in the Department of Cardiology at the authors' hospital from April 2018 to December 2018 were enrolled in this study and divided into a diastolic dysfunction group (65 cases) and a normal diastolic group (55 cases) according to their left ventricular diastolic function. The levels of cardiac parameters, β1-AA, AT1-AA, and other indicators were compared. Logistic regression analysis was used to analyse the related factors affecting left ventricular diastolic dysfunction (LVDD). The diagnostic efficacy of related factors in the diagnosis of diastolic dysfunction was evaluated.

Results

Univariate analysis demonstrated that the left ventricular posterior wall diameter (10.29 ± 1.23 vs. 9.12 ± 1.53), left ventricular systolic dysfunction (10.56 ± 1.37 vs. 9.43 ± 1.44), systolic blood pressure (152.37 ± 10.24 vs. 140.33 ± 5.99), diastolic blood pressure (95.66 ± 6.34 vs. 87.33 ± 7.28), β1-AA (33 vs. 9 cases), and AT1-AA (35 cases vs. 12 cases) were higher in the dysfunction group than in the control group (all P < 0.05). Multivariate regression analysis showed that β1-AA (odds ratio (OR) = 1.96, 95% confidence interval (CI): 1.369-4.345) and AT1-AA (OR = 2.02, 95% CI: 1.332-6.720) were independent risk factors for cardiac diastolic dysfunction (P < 0.05). Both autoimmune antibodies had a certain predictive value, and the combined prediction value of the two was the highest, with an area under the curve of 0.942 (95% CI: 0.881~0.985).

Conclusion

The positive rate of β1-AA and AT1-AA in essential hypertension patients with LVDD was higher than that in the normal group. Both β1-AA and AT1-AA could be used as early markers of LVDD in essential hypertension patients.

The Role of Autoantibodies in Companion Animal Cardiac Disease

Clinical studies exploring the role of autoimmune diseases in cardiac dysfunction have become increasingly common in both human and veterinary literature. Autoantibodies (AABs) specific to cardiac receptors have been found in human and canine dilated cardiomyopathy, and circulating autoantibodies have been suggested as a sensitive biomarker for arrhythmogenic right ventricular cardiomyopathy in people and Boxer dogs. In this article, we will summarize recent literature on AABs and their role in cardiac diseases of small animals. Despite the potential for new discoveries in veterinary cardiology, current data in veterinary medicine are limited and further studies are needed.

Cardiological Challenges Related to Long-Term Mechanical Circulatory Support for Advanced Heart Failure in Patients with Chronic Non-Ischemic Cardiomyopathy

Long-term mechanical circulatory support by a left ventricular assist device (LVAD), with or without an additional temporary or long-term right ventricular (RV) support, is a life-saving therapy for advanced heart failure (HF) refractory to pharmacological treatment, as well as for both device and surgical optimization therapies. In patients with chronic non-ischemic cardiomyopathy (NICM), timely prediction of HF's transition into its end stage, necessitating life-saving heart transplantation or long-term VAD support (as a bridge-to-transplantation or destination therapy), remains particularly challenging, given the wide range of possible etiologies, pathophysiological features, and clinical presentations of NICM. Decision-making between the necessity of an LVAD or a biventricular assist device (BVAD) is crucial because both unnecessary use of a BVAD and irreversible right ventricular (RV) failure after LVAD implantation can seriously impair patient outcomes. The pre-operative or, at the latest, intraoperative prediction of RV function after LVAD implantation is reliably possible, but necessitates integrative evaluations of many different echocardiographic, hemodynamic, clinical, and laboratory parameters. VADs create favorable conditions for the reversal of structural and functional cardiac alterations not only in acute forms of HF, but also in chronic HF. Although full cardiac recovery is rather unusual in VAD recipients with pre-implant chronic HF, the search for myocardial reverse remodelling and functional improvement is worthwhile because, for sufficiently recovered patients, weaning from VADs has proved to be feasible and capable of providing survival benefits and better quality of life even if recovery remains incomplete. This review article aimed to provide an updated theoretical and practical background for those engaged in this highly demanding and still current topic due to the continuous technical progress in the optimization of long-term VADs, as well as due to the new challenges which have emerged in conjunction with the proof of a possible myocardial recovery during long-term ventricular support up to levels which allow successful device explantation.

Allosteric Regulation of G-Protein-Coupled Receptors: From Diversity of Molecular Mechanisms to Multiple Allosteric Sites and Their Ligands

Allosteric regulation is critical for the functioning of G protein-coupled receptors (GPCRs) and their signaling pathways. Endogenous allosteric regulators of GPCRs are simple ions, various biomolecules, and protein components of GPCR signaling (G proteins and β-arrestins). The stability and functional activity of GPCR complexes is also due to multicenter allosteric interactions between protomers. The complexity of allosteric effects caused by numerous regulators differing in structure, availability, and mechanisms of action predetermines the multiplicity and different topology of allosteric sites in GPCRs. These sites can be localized in extracellular loops; inside the transmembrane tunnel and in its upper and lower vestibules; in cytoplasmic loops; and on the outer, membrane-contacting surface of the transmembrane domain. They are involved in the regulation of basal and orthosteric agonist-stimulated receptor activity, biased agonism, GPCR-complex formation, and endocytosis. They are targets for a large number of synthetic allosteric regulators and modulators, including those constructed using molecular docking. The review is devoted to the principles and mechanisms of GPCRs allosteric regulation, the multiplicity of allosteric sites and their topology, and the endogenous and synthetic allosteric regulators, including autoantibodies and pepducins. The allosteric regulation of chemokine receptors, proteinase-activated receptors, thyroid-stimulating and luteinizing hormone receptors, and beta-adrenergic receptors are described in more detail.