Lin Zuo

Long-term active immunization with a synthetic peptide corresponding to the second extracellular loop of β1-adrenoceptor induces both morphological and functional cardiomyopathic changes in rats

BACKGROUND β1-adrenoceptors (β1-ARs) are the predominant receptors in regulating heart functions. β1-ARs contain 7-transmembrane domains (7TM), 3 extracellular loops and 3 intracellular loops. Among these loops, the second extracellular loop of β1-AR (β1-AR-ECII) plays an important role in the pathogenesis of heart failure. METHODS (1) Select the sera-negative rats for antibodies against β1-AR-ECII. (2) Detect the level of antibodies against β1-AR-ECII in the process of active immunization with artificial synthetic peptides according to the sequence of human β1-AR-ECII. (3) Observe its long-term role on cardiac structure and function in vivo by immunizing rats. (4) Detect the changes of T lymphocytes subsets in the process of active immunization. RESULTS The peptides induced the production of specific autoantibody against β1-AR-ECII. Furthermore, immunization with β1-AR-ECII peptide induced both morphological and functional alterations in the hearts of rats, which potentially results in heart failure. In addition, induction of the autoantibodies against β1-AR-ECII increased the CD4+/CD8+ ratio in the peripheral blood of rats. DISCUSSION In this study, we determined the effect of anti-β1-AR-ECII autoantibody on morphological and functional cardiomyopathic alterations by immunization of rats with a synthetic peptide corresponding to the β1-AR-ECII for 18 months. These results provide further evidence that autoantibody against β1-AR-ECII is involved in the pathogenesis of heart failure. But the underlying mechanisms need further study.

Inhibition of iNOS protects endothelial-dependent vasodilation in aged rats

AbstractAim:To examine whether iNOS contributes to endothelial dysfunction in aged rats.Methods:Male Sprague Dawley rats were divided into three groups: young rats, aged rats treated with vehicle and aged rats treated with N-[3-(Aminomethyl) benzyl] acetamidine (1400W, 1 mg/kg, ip). Vasorelaxation was measured in isolated thoracic aorta. iNOS expression of thoracic aortic arteries was detected using immunohistochemistry and Western blot. Nitrotyrosine (a marker for peroxynitrite formation) content and expression in thoracic aortic tissue were determined using enzyme linked immunosorbent assay and immunohistochemistry.Results:Maximal relaxation induced by acetylcholine (10-9 to 10-5 mol/L) in the aged rats treated with vehicle was significantly decreased (70%±15%, P<0.01), as compared with the young rats (95%±8%). However, the maximal relaxation induced by acidified NaNO2 (an endothelium-independent vasodilator) had no significant difference between the two groups. Moreover, iNOS and nitrotyrosine expression increased in the vessels of the aged rats. In the aged rats treated with 1400W (a highly selective iNOS inhibitor) nitrotyrosine expression was reduced and acetylcholine-induced vasorelaxation was markedly improved (maximal relaxation was increased to 87%±8%, P<0.05), but the acidified NaNO2-induced vasorelaxation had no significant change.Conclusion:Our study demonstrated that inhibition of iNOS by 1400W increased endothelium-dependent vasodilation in aged rats. The mechanism was related with attenuation of peroxynitrite formation.

Pro-arrhythmic action of autoantibodies against the second extracellular loop of β1-adrenoceptor and its underlying molecular mechanisms.

OBJECTIVES The incidence of arrhythmia is associated with autoantibodies against the second extracellular loop of β1-adrenergic receptor (β1-AAbs). The current study was designed to determine the mechanisms by which arrhythmia experimentally might be induced by β1-AAbs. METHODS Blood samples were collected from patients with varied arrhythmias or coronary heart disease (CHD) and healthy subjects. The titer of β1-AAbs was assessed. Passive immunization rat models with β1-AAbs were established to determine whether β1-AAbs induced arrhythmia. Conventional intracellular microelectrode technique and whole cell patch clamp were employed to record action potential duration (APD), resting potential (RP), L-type calcium current (ICa-L), sodium-calcium exchange current (INCX), transient outward potassium current (Ito), inward rectifier potassium current (Ik1) and delayed rectifier potassium current (Ik). RESULTS High levels of β1-AAbs were found in the sera of heart disease patients, especially in ventricular arrhythmia (VA). Transfusion with β1-AAbs could induce arrhythmias in normal rats in vivo. β1-AAbs purified from the sera of active immunized rats induced triggered activity (TA), delayed after depolarization (DAD), and prolonged APD in the papillary muscles of rats. β1-AAbs prolonged QT interval, increased ICa-L and decreased IK1, Ito and INa-Ca in rat ventricular myocytes in vitro. All these effects can be inhibited by β1-AR blocker metoprolol. CONCLUSIONS These results demonstrate for the first time that β1-AAbs could directly induce ventricular arrhythmia by prolonging QT interval.