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.

[Effects of exhaustive exercise on contractile responses mediated by beta-adrenoceptor in rat cardiac myocytes]

OBJECTIVE

To investigate the effects of exhaustive exercise on contraction mediated by beta-adrenoceptor (beta-AR) in rat cardiac myocytes and to analyze the mechanism by which cardiac systolic dysfunction is caused after exhaustive exercise.

METHODS

Sixteen SD rats were divided randomly into sedentary group and trained group. Cardiac myocytes were isolated from sedentary group and trained group after five times of exhaustive exercise in one week. Shortening response to norepinephrine (NE), time-to-peak contraction (TTP) and time-to-95% relaxation (R95) were measured after alpha1-AR were blocked. Also shortening responses to different levels of NE were observed.

RESULTS

Shortening amplitudes in trained rat cardiomyocytes were lower than that in sedentary group. Compared with sedentary group, shortening amplitudes induced by beta-AR stimulation were significantly decreased, meanwhile TTPs and R95 were prolonged when beta-AR were activated in trained rat cardiomyocytes. beta-AR responsiveness to NE was weakened in trained group compared with that in sedentary group.

CONCLUSION

Decreased shortening cardiomyocyte systolic function stimulating by beta-AR could result in cardiac systolic dysfunction after exhaustive exercise.

[The immune-enzyme analysis based on chimeric molecule and oligopeptide fragmentations to detect autoantibodies to beta-adrenergic receptor in patients with dilation cardiomyopathy]

The article deals with specification of technique of immune-enzyme analysis to detect autoantibodies to beta-adrenergic receptors (beta1-AP) using compound of oligopeptids representing the fragmentations of extracellular sites beta1-AP and chimeric molecule of extracellular section of receptor This technique significantly exceeds the analogues defined in publications by its sensitivity and correlation with diagnosis.

[Ser49gly polymorphism as predictor of development of hereditary sick sinus node syndrome]

We demonstrated for the first time on clinico-genetic material an association of hereditary sick sinus node syndrome (SSNS) with polymorphism of beta-adrenorecetor gene. We found that heterozygous variant of Ser49gly of beta-adrenoreceptor gene was significantly more often met in patients with SSNS and their healthy relatives than in subjects of control group. In the group of patients with SSNS contrary to control group we noted statistically significant preponderance of carriers of mutant Gly49 allele of.

[Genetic aspects of individual sensitivity to betaxolol in patients with arterial hypertension]

Association of polymorphism of b1-adrenoreceptors gene and cytochrome 2D6 gene with efficacy of b-adrenoblocker betaxolol was studied in 81 patients with I and II degree arterial hypertension. Betaxolol (10-20 mg/day) was given for 4 weeks, its efficacy was assessed by office blood pressure (BP) measurements, 24-hour BP and ECG monitoring and standard exercise test. At the end of the study significant lowering of systolic and diastolic BP was noted by 11,8 +/- 2,47 (p=0,001) and 7,8 +/- 1,68 mm Hg (p=0,001), respectively. Heart rate (HR) at rest lowered by 19,8 +/- 1,96 beats/min (p=0,0001). At analysis of individual reaction of patients to treatment with betaxolol it turned out that decrease of BP and HR was variable, but their distribution in the group did not differ significantly from normal. Hypotensive activity and influence on HR were confirmed by results of all instrumental investigations. No significant differences were revealed in dynamics of systolic and diastolic BP both at rest and at effort between patients with different genotypes of polymorphic marker Gly389Arg of ADRB1 gene. Compared with carriers of genotype Ser/Ser carriers of genotype Ser/Pro of polymorphic marker Pro34Ser of Cyp2D6 gene had significantly more pronounced decrease of HR at the background of treatment with betaxolol: - 32,6 +/- 4,77 and - 18,4 +/- 2,01 beats/min (p=0,023) at rest and - 30,1 +/- 3,05 and - 24,0 +/- 2,59 beats/min (p=0,043) at maximal exercise, respectively. These patients had also more pronounced lowering of diastolic BP at maximal work load and more pronounced increase of exercise duration at the background of treatment. Thus efficacy of betaxolol in patients with hypertension was associated solely with genotype of polymorphic marker Ser34Pro of CYP2D6 gene. In patients having in genotype Pro allele of polymorphic marker Pro34Ser of CYP2D6 gene therapy with betaxolol is more effective, than in homozygote carriers of Ser allele. This can be related to low rate of metabolism of the preparation in these patients.

Reduced oxidative stress in parallel to improved cardiac performance one year after selective removal of anti-beta 1-adrenoreceptor autoantibodies in patients with idiopathic dilated cardiomyopathy: data of a preliminary study

Patients with idiopathic dilated cardiomyopathy (IDC) were treated with selective immunoadsorption to remove anti-beta 1-adrenoreceptor autoantibodies (anti-beta1A-AB). After one year, the effect on cardiac performance and oxidative stress was tested. Extracorporeal immunoadsorption of the whole IgG class in IDC patients for the removal of anti-beta1A-AB reduced oxidative stress in parallel to an improvement of cardiac performance. However, the non-specificity of IgG adsorption means that these beneficial effects cannot be attributed exclusively to anti-beta1A-AB removal. In an open clinical pilot study enrolling 8 patients with IDC prior to and one year after selective immunoadsorption of anti-beta1A-AB, plasma markers for oxidative stress--thiobarbituric acid-reactive substances (TBARS), lipid peroxides (LPO) and anti-oxidized low-density lipoprotein autoantibodies (anti-oxLDL-AB)--were measured in parallel to evaluation of the left ventricular function using conventional echocardiography and wall motion analysis by tissue Doppler imaging. After one year, TBARS (Wilcoxon test with bootstrapping simulation for paired data: 95% confidence interval of the P value 0.020 to 0.029) and anti-oxLDL-AB (P = 0.025 to 0.035) were decreased in parallel to an improvement of the peak systolic wall motion velocity (P = 0.006 to 0.01) and left ventricular ejection fraction (P = 0.002 to 0.02). For changes over the study period, a direct correlation with borderline significance (P = 0.076) was calculated for TBARS to the left ventricular diameter in the diastole. One year after selective immunoadsorption for anti-beta1A-AB removal, patients with ICD show a reduction in oxidative stress and a parallel improvement in cardiac performance.

Transfer of Rabbit Autoimmune Cardiomyopathy into Severe Combined Immunodeficiency Mice

Growing evidence suggests that the autoimmune mechanism plays an important role in the pathogenesis of dilated cardiomyopathy. The purpose of this study was to evaluate the effect on the cardiac structure and function by the transfer of immunoglobulin G (IgG) and/or lymphocytes from rabbits immunized with a synthetic peptide corresponding to the sequence of the second extracellular loop of beta1-adrenoceptor (beta peptide) into severe combined immunodeficiency (SCID) mice. CB-17 SCID mice were injected intraperitoneally with 2 mg of IgG and/or 1 x 10(7) peripheral blood lymphocytes (PBL) from either rabbits immunized with both beta1 peptide and adjuvant (beta group), and adjuvant or rabbits with adjuvant only (N group). Thirty-five SCID mice were divided into seven groups: (1) N-IgG group; (2) N-PBL group; (3) N-IgG+PBL group; (4) beta-IgG group; (5) beta-PBL group; (6) beta-IgG+PBL group; and (7) control group. Morphological, serological and endocrinological studies were performed 70 days after the transfer. Results showed that heart weight and heart weight/body weight ratio in the beta-IgG+PBL group tended to be increased as compared with those in other groups. All mice in the beta-IgG group, two in the beta-PBL group and four in the beta-IgG+PBL group showed high titer of rabbit anti-beta1-adrenoceptor antibodies. Brain natriuretic peptide in the beta-IgG+PBL group showed a significant increase as compared with those in the control group and N-IgG+PBL. Pathohistologically, focal infiltration of inflammatory cells in the myocardium was observed in one mouse of the beta-IgG+PBL group. Rabbit CD3-positive T-lymphocytes in the myocardium were observed in two mice of the beta group. In conclusion, transfer of IgG and PBL from rabbits immunized with beta1 peptide was able to induce the early stages of myocardial damage in SCID mice. These data provide direct evidence that the autoimmune mechanism is important in the pathogenesis of dilated cardiomyopathy.

Canine dilated cardiomyopathy: lymphocyte and cardiac alpha(1)- and beta-adrenoceptor concentrations in normal and affected great danes

Serum catecholamine levels and myocardial and lymphocyte adrenergic receptor (AR) concentrations were measured in adult great danes affected by canine dilated cardiomyopathy (DCM) and compared to those of healthy animals. A non-homogeneous population of beta -AR, consisting of beta(1)-AR and beta(2)-AR, was observed in healthy (41 and 59%, respectively) and affected (17 and 83%, respectively) dog lymphocytes. Binding assays revealed that total beta -AR, beta(1)-AR and alpha(1)-AR were significantly downregulated (P<0.05;P<0.01;P<0. 001), both in lymphocyte and myocardial cell membranes of affected dogs. beta(2)-Adrenergic receptor concentrations were significantly reduced only in lymphocyte and right atrium cell membranes (P<0.05). Downregulation was not associated with alterations in receptor binding characteristics, as no significant differences in K(d)values were found. Mean plasma catecholamine levels were significantly higher (P<0.01) in DCM dogs (939+/-41) than in normal subjects (348+/-32), thus suggesting a sympathetic activation. The present study indicates a condition similar to that observed in human patients affected by DCM and that adrenergic receptors in canine lymphocytes reflect the fluctuation of adrenergic receptor concentrations in the myocardium.

Lymphocyte beta -adrenoceptor downregulation in great danes with occult dilated cardiomyopathy (DCM) and with DCM and heart failure

The importance of the adrenergic nervous system in supporting the failing heart has long been known. The adrenergic drive on cardiac structure and function has however some adverse effects, which include myocardial beta-adrenoceptor (beta-AR) downregulation and decreased beta-adrenergic responsiveness to cathecolamines. In dog lymphocytes, beta(1)-AR and beta(2)-AR populations are almost equally represented (with a slight prevalence of beta(2)) and a significant correlation between cardiac and lymphocytic adrenoceptors has been found. The aim of the present study was to investigate possible differences between the concentration of lymphocytic beta-AR in healthy dogs, dogs with dilated cardiomyopathy (DCM) and dogs with occult DCM. Three groups of great danes were considered: a control group (n =10), dogs with DCM (n =9) and dogs with occult DCM (n =4). Lymphocytic beta-AR populations were determined in all dogs. A substantial and significant decrease (P<0.05) in total-AR, beta(1)-AR and beta(2)-AR concentrations in the lymphocytes of dogs with symptomatic DCM and occult DCM compared to the control group was found. Although the mean value of the lymphocyte beta(1)-AR number in the asymptomatic group was double compared to the DCM group, this difference was not statistically significant. We conclude that in dogs beta-AR downregulation occurs early in the course of dilated cardiomyopathy. This finding may suggest the value of early use of a beta-blocker in the therapeutic regimen. Moreover, the continuous monitoring of lymphocytic beta-AR may represent a useful tool for the development of a more effective individual therapy.

Weaning from mechanical cardiac support in patients with idiopathic dilated cardiomyopathy

BACKGROUND

Implantation of mechanical cardiac support systems (MCSS) in patients with idiopathic dilated cardiomyopathy (IDC) may improve cardiac function and allow explantation of the device. We report of long-term effects of ventricular unloading on cardiac function, humoral anti-beta1-adrenoceptor autoantibodies (A-beta1-AABs), and myocardial fibrosis.

METHODS AND RESULTS

Seventeen patients in New York Heart Association functional class IV with nonischemic IDC received MCSS. All had a cardiac index of < 1.6 L x min(-1) x m(-2) of body surface area, a left ventricular ejection fraction (LVEF) of <16%, and a left ventricular internal diameter in diastole (LVIDd) of >68 mm and tested positive for A-beta1-AABs. Echocardiographic evaluation, serum tests for A-beta1-AABs, and histological assessment of myocardial fibrosis were performed before and after MCSS implantation. The mean support duration was 230+/-201 days. Six patients died, four were transplanted, and two are still on MCSS. Five patients with significant cardiac recovery (mean LVIDd, 54+/-2.3 mm; LVEF, 47+/-3.7%) were weaned after 160 to 794 days and are now device free for 51 to 592 days. A-beta1-AABs disappeared gradually during MCSS without increase after weaning; cardiac function and volume density of fibrosis remained normal. Nine patients' cardiac function hardly improved during ventricular unloading.

CONCLUSIONS

Cardiac function can be normalized in selected patients with end-stage IDC by MCSS. The degree of preoperative myocardial fibrosis may be an indicator for outcome; A-beta1-AABs can be used to monitor myocyte recovery. Weaning from MCSS offers an alternative to cardiac transplantation in certain patients.