Activating Autoantibodies to the Beta-1 Adrenergic and M2 Muscarinic Receptors Facilitate Atrial Fibrillation in Patients With Graves' Hyperthyroidism
Stavros Stavrakis, MD*, ,
Xichun Yu, MD*,, ,
Eugene Patterson, PhD, ,
Shijun Huang, MD*,,,
Sean R. Hamlett, MD*,,
Laura Chalmers, MD*,,
Reji Pappy, MD*,
Madeleine W. Cunningham, PhD||,
Syed A. Morshed, PhD¶,
Terry F. Davies, MD¶,
Ralph Lazzara, MD*, and
David C. Kem, MD*,,,*
* Department of Medicine, University of Oklahoma Health Sciences Center and Veterans Affairs Medical Center, Oklahoma City, Oklahoma
Heart Rhythm Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
Harold Hamm Oklahoma Diabetes Center, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
|| Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
¶ Thyroid Research Unit, Mount Sinai School of Medicine, James J. Peters Veterans Affairs Medical Center, New York, New York
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Figure 1 Functional Effects of IgG From Patients With Graves' Disease and Control Subjects on Purkinje Fiber Contractility
(A) The mean effect (percent over baseline) of activating autoantibodies to beta-1 adrenergic receptor (AAβ1AR) from the 24 AAβ1AR-positive patients (Graves' AAβ1AR) and the absolute value of the mean inhibitory effect (percent change over baseline) of activating autoantibodies to M2 muscarinic receptor (AAM2R) in the 19 AAM2R-positive patients (Graves' AAM2R) are compared with control immunoglobulin (Ig)G. The antibody-negative Graves' values were not significantly different from the control subjects and therefore are not shown. Isoproterenol (ISO) (10 nmol/l) served as a positive control. Both AAβ1AR and AAM2R effects were significantly greater in patients than in control subjects. *p < 0.001. (B) The percentages of autoantibody-positive patients for AAβ1AR and AAM2R and their combination are shown. Autoantibodies were significantly more frequent in patients with atrial fibrillation (AF) compared with patients with normal sinus rhythm (NSR). *p < 0.001.
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Figure 2 Electrophysiologic Effects of IgG on Canine Pulmonary Vein Sleeves
(A) Action potentials are shown before (black) and after (red) IgG administration demonstrating hyperpolarization, increased action potential amplitude, and decreased action potential duration. (B) Enhanced early afterdepolarization formation produced by tachycardia (6 Hz)-pause (2 sec) pacing is shown post-IgG in electrical recordings from pulmonary vein sleeves. Numbers represent action potential duration at 90% of repolarization. (C) Pause-duration–dependent prolongation of the terminal action potential duration (change in action potential duration at 90% of repolarization [ APD90]) with tachycardia (20-beat train at 6 Hz)-pause pacing is shown with IgG compared with control (n = 14). *p < 0.01 for each pause duration. (D) Electrical recordings from pulmonary vein sleeves during local autonomic nerve stimulation (dark areas) show enhanced triggered firing after IgG versus before IgG administration. The numbers in the upper panel represent the action potential duration at 50% and 90% of repolarization. (E) Stimulus response curves (local autonomic nerve stimulation) are shown before and after IgG administration, demonstrating enhancement of triggered firing by IgG in canine pulmonary vein sleeves (significant movement of the stimulus voltage-response curve to the left) (n = 14). APD50 = action potential duration at 50% of repolarization; RMP = resting membrane potential; other abbreviations as in Figure 1.
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Figure 3 Binding of Patient Sera to CHO-TSHR Cells by Flow Cytometry
Fluorescence was measured after exposing these cells to 1:200 dilutions of purified IgG (before and after adsorption with TSHR) and fluorescein isothiocyanate-labeled anti-human IgG. A 50% decrease supports a significant loss of binding activity. Patients #1 and #2 had documented stimulating thyrotropin receptor antibodies and coexisting activating autoantibodies to AAβ1AR and AAM2R. Patients #3 and #4 were non-Graves' patients harboring AAβ1AR and AAM2R. Patient #5 was a control subject with nonactivating autoantibodies to β1AR and M2R by ELISA. There were significant adsorbable antibodies to the TSHR in the 2 Graves' patients. The other 3 had either no or small amounts of adsorbable activity. CHO-TSHR = Chinese hamster ovary cells expressing full-length thyrotropin receptor; ELISA = enzyme-linked immunosorbent assay; other abbreviations as in Figure 1.
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