Abstract
OBJECTIVES: This study sought to develop a rapid method for the detection
of activating autoantibodies directed against the beta1-adrenoceptor
(anti-beta1-Abs) in patients with heart failure. BACKGROUND: The
anti-beta1-Abs are supposed to play a pathophysiological role in
heart failure. However, there is no reliable method for their detection.
With a complex screening strategy (enzyme-linked immunosorbent assay,
immunofluorescence, cyclic adenosine monophosphate cAMP-radioimmunoassay)
we have previously identified antibodies targeting the second extracellular
beta1-receptor loop (anti-beta1-EC(II)) in 13% of patients with ischemic
cardiomyopathy (ICM) and in 26% with dilated cardiomyopathy (DCM).
METHODS: To detect anti-beta1-Abs, we measured beta1-receptor-mediated
increases in intracellular cAMP by fluorescence resonance energy
transfer using a highly sensitive cAMP sensor (Epac1-based fluorescent
cAMP sensor). RESULTS: The immunoglobulin G (IgG) prepared from 77
previously antibody-typed patients (22 ICM/55 DCM) and 50 matched
control patients was analyzed. The IgG from all 22 previously anti-beta1-EC(II)-positive
patients (5 ICM/17 DCM) induced a marked cAMP increase, indicating
receptor activation (49.8 +/- 4.2% of maximal isoproterenol-induced
signal). The IgG from control patients and 32 previously anti-beta1-EC(II)-negative
patients (17 ICM/15 DCM) did not significantly affect cAMP. Surprisingly,
our technology detected anti-beta1-Abs in 23 DCM patients formerly
judged antibody-negative, but their cAMP signals were generally lower
(31.3 +/- 6.8%) than in the previous group. "Low"-activator anti-beta1-Abs
were blocked preferentially by peptides corresponding to the first,
and "high"-activator anti-beta1-Abs by peptides corresponding to
the second beta1-extracellular loop. Beta-blockers alone failed to
fully prevent anti-beta1-EC(II)-induced receptor activation, which
could be achieved, however, by the addition of beta1-EC(II) peptides.
CONCLUSIONS: Our novel method of detecting anti-beta1-Abs proved
to be fast and highly sensitive. It also revealed an insufficient
ability of beta-blockers to prevent anti-beta1-EC(II)-induced receptor
activation, which opens new venues for the research on anti-beta1-Abs
and eventual treatment options in heart failure.
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