Inducible cardiac arrhythmias caused by enhanced β₁-adrenergic autoantibody expression in the rabbit

Abstract

Previous studies demonstrated burst pacing and intravenous infusion of ACh induced sustained atrial tachycardia when rabbits were immunized to produce ␤2-adrenergic receptor (␤2AR)-activating autoantibodies. The objective of this study was to examine the arrhythmogenic effect of ␤1-adrenergic receptor (␤1AR)-activating autoantibodies in the rabbit. Eight New Zealand white rabbits were immunized with a ␤1AR second extracellular loop peptide to raise ␤1AR antibody titers. A catheter-based electrophysiological study was performed on anesthetized rabbits before and after immunization. Arrhythmia occurrence was determined in response to burst pacing before and after ACh infusion in incremental concentrations of 10 M, 100 M, and 1 mM. The baseline sinus heart rate before and after immunization averaged 149 Ϯ 17 per min and 169 Ϯ 16 per min, respectively (P Ͻ 0.05). In the preimmune studies, there were five sustained (Ն10 s) arrhythmias in 32 induction attempts, which occurred in only four of eight rabbits. In the postimmune studies, there were 22 sustained arrhythmias in 32 induction attempts, which occurred in all eight rabbits (P Ͻ 0.0001 for the independent effect of immunization). Of the 22 sustained arrhythmias postimmunization, 15 were sinus tachycardia compared with only two before immunization (P Ͻ 0.01 for the independent effect of immunization). Postimmune (but not preimmune) rabbit sera demonstrated specific binding to ␤1AR and induced significant ␤1AR activation in transfected cells in vitro. No cross-reactivity with ␤2AR was observed. In conclusion, in contrast with rabbits with ␤2AR-activating autoantibodies that demonstrate predominantly atrial tachycardias, enhanced autoantibody activation of ␤1AR in the rabbit leads to tachyarrhythmias mainly in the form of sustained sinus tachycardia.

A peptidomimetic inhibitor suppresses the inducibility of β1-adrenergic autoantibody-mediated cardiac arrhythmias in the rabbit

“…Six New Zealand white rabbits (2.5–3 kg) were immunized with 1 mg of the β1AR ECL2 peptide (HWWRAESDEARRCYNDPKCCDFVTNR) [15] in 0.5 ml of complete Freund’s adjuvant. The animals were boosted with the same peptide plus incomplete Freund’s adjuvant (1 mg/0.5 ml) at 2 and 4 weeks.…”

“…Therefore, each rabbit served as its own control. The various types of arrhythmias induced in the rabbit heart have been detailed previously [14, 15] and are defined as follows. These are based on the Lambeth Conventions for arrhythmia classification [21].…”

“…Antibodies produced in the sera were detected by ELISA [15]. Briefly, microtiter plates were coated with the β1AR ECL2 peptide at 10 μg/ml in coating buffer.…”

“…Rabbit sera were tested for β1AR activation using the cAMP Hunter eXpress GPCR Assay kit (DiscoveRx, Fremont, CA) [15]. Briefly, 30,000 β1AR-transfected Chinese hamster ovary cells were dispensed into each well of 96-well culture plate and incubated overnight.…”

“…We then demonstrated that burst pacing in conjunction with intravenous infusion of acetylcholine (ACh), at dosages which were insufficient by themselves to induce sustained tachyarrhythmias, subsequently produced sustained atrial tachycardia in β2AR-immunized animals [14]. The atrial tachyarrhythmias induced in similarly studied β1AR-immunized animals were predominantly sustained sinus tachycardia [15]. These data support the concept that autoantibody activation of β1AR in the sinus node and β2AR in the atrial myocardium selectively predisposes the rabbit heart to increased induction of distinct atrial tachyarrhythmias [16].…”