Effects of long-term active immunization with the second extracellular loop of human β1- or β3-adrenoceptors in thoracic aorta and mesenteric arteries in Lewis rats

OBJECTIVE

To evaluate whether active immunization producing β₁- or β₃-antibodies (β₁-ABs and β₃-ABs) detected in sera of patients with dilated cardiomyopathies has deleterious effects on vascular reactivity in Lewis rat thoracic aorta (TA) and small mesenteric arteries (SMA).

DESIGN AND METHOD

Lewis rats were immunized for 6months with peptidic sequences corresponding to the second extracellular loop of β₁- and β₃-adrenoceptors (ARs). During the immunization, systolic blood pressure (SBP) was monitored using the tail cuff method. The vascular reactivity of immunized rats was assessed by ex vivo studies on SMA and TA using various β-AR agonists, phenylephrine and KCl.

RESULTS

The immunizations producing functional β₁-ABs and β₃-ABs did not affect the SBP. However, in TA from β₁-AR-immunized rats, the relaxations mediated by dobutamine and salbutamol were significantly impaired in comparison with adjuvant rats whereas nebivolol-induced relaxation was not modified. Moreover, phenylephrine and KCl-mediated contractions were enhanced in these rats. In contrast, immunization with β₃-AR peptide led to the increase of relaxations induced by dobutamine in TA but did not change those induced by salbutamol and nebivolol. Surprisingly, in SMA from both rats immunized with β₁- or β₃-peptides, relaxations induced by the various β-agonists were not changed whereas phenylephrine and KCl-mediated contractions were impaired.

CONCLUSIONS

Our study shows that β₁- and β₃-ABs can affect vascular reactivity. β₁-ABs would have a pathogenic action whereas β₃-ABs would have a beneficial effect on aorta reactivity.

[Cardiovascular effects of beta1 and beta3-adrenergic receptor autoantibodies in Lewis rat]

PURPOSE

To analyze vascular reactivity changes in response to immunization protocols with antigens corresponding to the second extracellular loop of -β3 and -β1 and 3 adrenergic receptors (AR).

METHODS

Lewis rats were immunized for 3months with peptidic sequences corresponding to the second extracellular loop of β3-AR or β1 and 3-AR. Specific β3-AR antibodies were characterized by Elisa and purified using "Proteus Protein G" kit. Their functionality were tested in rabbit isolated ventricular cardiomyocytes. Aortic and mesenteric artery rings isolated from control or immunized rats were mounted in organ baths and precontracted with phenylephrine. Then, relaxant curves were established.

RESULTS

SR58611A (10nM), a preferential β3-AR agonist and purified β3-AR antibodies (25μg/mL) induced a decrease of cell shortening (-39.56±4.4% [n=11] and -18.45±3.9% [n=10] respectively) in isolated cardiomyocytes. This decrease was significantly inhibited when the cardiomyocytes were pre-incubated with the L-748337 (1μM), a selective β3-AR antagonist (P<0.05). In contrast with what was observed in rats immunized against the β1-AR, vasorelaxations induced by acetylcholine and SR58611A in both aorta and mesenteric arteries were unaltered in rats immunized against the β3-AR and β1 and 3-AR.

CONCLUSION

These results show, for the first time, that β3-AR antibodies induced a β3-AR agonist-like activity. They would not have a vascular pathogenic action but would offset the endothelial dysfunction caused by β1-AR antibodies.

Recent structural advances of β1 and β2 adrenoceptors yield keys for ligand recognition and drug design

Because they represent attractive drug targets, adrenoceptors have been widely studied. Recent progress in structural data of β-adrenoceptors allows us to understand and predict key interactions in ligand recognition and receptor activation. Nevertheless, an important aspect of this process has only begun to be explored: the stabilization of a conformational state of these receptors upon contact with a ligand and the capacity of a ligand to influence receptor conformation through allosteric modulation, biased signaling, and selectivity. The aim of the present Perspective is to identify the well-defined orthosteric binding site and possible allosteric sites and to analyze the importance of the ligand-receptor interaction in the stabilization of certain receptor conformations. For this purpose, we have reviewed recent advances made through the use of X-ray data from ligand-β-adrenoceptor (including ADRB1 and ADRB2) crystal structures. Most importantly, implications in the medicinal chemistry field are explored in relation to drug design.

[Antibodies against the second extracellular loop of beta1-adrenergic receptor induce aortic endothelial dysfunction in Wistar rat]

PURPOSE

To evaluate the effect of active immunization with a peptide corresponding to the second extracellular loop of the human beta1-adrenoceptors (β(1)-AR) on the reactivity of Wistar rat isolated aorta.

METHODS

Nine-week-old Wistar rats were actively immunized for 3months with a peptide corresponding to the second extracellular loop of the human β(1)-AR. Specific immunoglobulins G (IgG) were characterized by Elisa and the bicinchonic acid protein assay and their functionality were tested in isolated ventricular cardiomyocytes (IVC) from control rats. Aortic rings isolated from control or immunized rats were mounted in organ baths. Then, contractile curves to phenylephrine (1nM to 300μM) and relaxant curves to acetylcholine (1nM to 100μM) and isoprenaline (1nM to 30μM) were established.

RESULTS

Cell shortening increased dose-dependently in rat IVC superfused with IgG containing β(1)-AR antibodies (10 or 25μg/mL). Isoprenaline-induced positive inotropy was strongly reduced in IgG containing β(1)-AR antibodies preincubated (3h) IVC. Phenylephrine-and acetylcholine-induced aortic responses were greatly inhibited in immunized rats compared to control ones. However, active immunization did not influence the isoprenaline-mediated relaxation.

CONCLUSIONS

The present work confirms that β(1)-AR antibodies directed against the second extracellular loop of β(1)-AR induce a positive inotropic effect in adult rat IVC. Moreover, we demonstrated, for the first time, that 3-month immunization with β(1)-AR peptide was associated with altered aortic endothelial function without change in the β-AR-mediated vasorelaxation.