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.

Equine digital veins are more sensitive to superoxide anions than digital arteries

This work was designed to investigate (i) the effect of superoxide dismutase (SOD) inhibition on endothelial function and (ii) the free radical-induced endothelial dysfunction in equine digital veins (EDVs) and equine digital arteries (EDAs) isolated from healthy horses. EDV and EDA rings were suspended in a 5 ml organ bath containing Krebs solution. After a 60 min equilibration period, EDV and EDA rings were contracted with phenylephrine. Then, cumulative concentration-response curves (CCRCs) to acetylcholine were performed. In both EDVs and EDAs, acetylcholine (1 nM to 10 µM) produced concentration-dependent relaxation. We investigated the influence of SOD inhibition by diethyldithiocarbamate (DETC; 100 µM), a CuZnSOD inhibitor, on EDAs and EDVs relaxant responses to acetylcholine. Acetylcholine -mediated relaxation was impaired by DETC only in EDVs. SOD activity assayed by a xanthine-xanthine oxidase method was higher in EDAs compared with EDVs (P<0.05). CCRCs to acetylcholine established in the presence of pyrogallol (30 µM) or homocysteine (20 µM), two superoxide anions generating systems showed that in both EDVs and EDAs, the acetylcholine-mediated relaxation was significantly impaired by pyrogallol and homocysteine. This impairment was more pronounced in EDVs than in EDAs. Moreover, the pyrogallol-induced impairment of acetylcholine-mediated relaxation was potentiated by DETC to a greater extent in EDVs. We concluded that due to the lower activity of SOD, EDVs are more sensitive to superoxide anions than EDAs. So, any alteration of superoxide anions metabolism is likely to have a more important impact on venous rather than arterial relaxation.

[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.

Vasorelaxant effect of propentofylline in isolated equine digital veins

We evaluated the vasorelaxant effect of propentofylline (PPF), a methylxanthine derivative, and its mechanism of action in equine digital veins (EDVs). Cumulative concentration-response curves to PPF (1 nM-300 µM) were recorded in phenylephrine-precontracted EDV rings under different experimental conditions. PPF-induced relaxation was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (an adenosine receptor antagonist; 3 µM). PPF-induced relaxation was partially inhibited in the presence of L-NAME (a nitric oxide (NO) synthase inhibitor; 100 µM), ODQ (an inhibitor of soluble guanylyl cyclase; 30 µM) or Rp-8-Br-PET-cGMP-S (a protein kinase G inhibitor; 3 µM). It was not modified by indomethacin (a non-selective cyclooxygenase (COX) inhibitor; 10 µM), and was slightly potentiated by H-89 (a protein kinase A inhibitor; 2 µM). In endothelium-intact EDVs, PPF-induced relaxation was associated with a 2.4- and 24.1-fold increase in the tissue cGMP and cAMP content respectively. PPF (100 μM) did not shift the concentration-response curve to phenylephrine (1 nM-300 µM) but reduced the maximal effect. To investigate whether PPF can affect cAMP- and cGMP-induced relaxations, relaxation curves to forskolin (an activator of adenylate cyclase) and to sodium nitroprusside (SNP, a NO donor) were recorded in EDV rings pretreated with PPF (100 µM). PPF only slightly potentiated the forskolin-induced relaxation without affecting the SNP-induced relaxation. We demonstrated that PPF-induced relaxation in EDVs is partially endothelium-dependent. The PPF-induced relaxation partially occurred via NO release and both cAMP and cGMP generation, through COX-independent mechanisms but could also result from the inhibition of cAMP-phosphodiesterase activity for the highest concentrations.

Celiprolol induces β(3)-adrenoceptors-dependent relaxation in isolated porcine coronary arteries

In porcine coronary arteries (PCAs), celiprolol, a selective β(1)-adrenoceptors antagonist, induces vasodilatation by an endothelium- and nitric oxide (NO)-dependent pathway. However, the mechanisms of that vascular effect have not been precisely established. β(3)-Adrenoceptors have been shown to be involved in the relaxation per se of various vascular beds, including coronary vessels. Thus, we evaluated (i) the presence of β(3)-adrenoceptors in the PCA and (ii) their role in celiprolol-induced vasodilatation. PCA rings were placed in organ baths and preconstricted with KCl. All experiments were performed in the presence of nadolol (a β(1)/β(2)-adrenoceptor antagonist). Cumulative concentration-response curves to SR 58611A and ICI 215001 (2 β(3)-adrenoceptor agonists) and to celiprolol were constructed. We also used semiquantitative reverse transcription - polymerase chain reaction, which clearly showed the presence of β(3)-adrenoceptor transcripts. SR 58611A, ICI 215001, and celiprolol induced concentration-dependent relaxations in PCA rings. SR 58611A-induced relaxation was almost abolished after removal of endothelium or pretreatment with L-NAME (a NO synthase inhibitor). The vasorelaxations induced by SR 58611A and celiprolol were inhibited in the presence of SR 59230A and L-748337 (2 selective β(3)-adrenoceptor antagonists). We showed (i) that PCAs possess functional β(3)-adrenoceptors mediating endothelium- and NO-dependent relaxation, and (ii) that celiprolol exerts a β(3)-adrenoceptor agonistic activity in this vascular bed.

[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.

Autoantibodies against cardiac β1-adrenoceptor do not affect the low-affinity state β1-adrenoceptor-mediated inotropy in rat cardiomyocytes

Circulating autoantibodies directed against the 2nd extracellular loop (EL-2) of β1-adrenoceptors (β1-AABs) have been detected in the serum of patients with various cardiovascular pathologies. β1-AABs induce agonistic, positive inotropic effects via β1-adrenoceptors (β1ARs). In the mammalian heart, β1-AR can exist in 2 distinct activated configurations (the so-called high- and low-affinity states). The aim of the present study was to investigate whether the action of β1-AAB is dependent on the affinity state of β1AR in isolated ventricular cardiomyocytes of adult Wistar rats. Immunoglobulin G (IgG) containing β1-AAB obtained from animals immunized with a peptide corresponding to the EL-2 of human β1-AR, caused a dose-dependent increase in cell shortening. Isoproterenol-induced inotropy was significantly reduced in cardiomyocytes that had been preincubated with IgG containing β1-AAB and in cardiomyocytes isolated from immunized rats. The negative effects of preincubation with IgG containing β1-AAB on the response to isoproterenol was inhibited in the presence of bisoprolol. CGP 12177A and pindolol-induced inotropy was not affected by IgG preincubation or immunization. No detectable inotropic effect of cell shortening was obtained with IgG containing β1-AAB in the presence of propranolol and 3-isobutyl-1-methylxanthine. The present study demonstrates that β1-AABs have no agonist/antagonist-like effects upon low-affinity state β1-ARs. This result indicates that β1-AABs recognize and stabilize the high-affinity state, but are unable to stabilize and (or) induce the low-affinity state receptor.

Vasodilatory effect of pentoxifylline in isolated equine digital veins

The direct vasodilatory action of pentoxifylline (1-(5-oxohexyl)-3,7-dimethylxanthine) and its signalling pathway was evaluated in equine digital veins. Cumulative concentration-response curves to pentoxifylline (1 nM to 300 μM) were recorded in phenylephrine-precontracted equine digital vein rings under different experimental conditions. Relaxation to pentoxifylline was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (a non-xanthine adenosine receptor antagonist; 3 μM). Nitric oxide synthase (NOS), soluble guanylate cyclase and cyclooxygenase (COX) inhibitors (Nω-nitro-L-arginine methyl ester (100 μM), ODQ (30 μM) and indomethacin (10 μM), respectively) significantly reduced the maximum relaxation induced by pentoxifylline. Moreover, pentoxifylline-induced relaxation was strongly reduced by Rp-8-Br-PET-cyclic guanosine monophosphate-S (a protein kinase G inhibitor; 3 μM), but remained unaffected by H-89 (a protein kinase A inhibitor; 2 μM). Pentoxifylline-induced relaxation was associated with a 3.4-fold increase in tissue cGMP content. To investigate whether pentoxifylline can affect cAMP- and cGMP-mediated relaxations, curves to forskolin, to sodium nitroprusside (SNP) and 8-bromo-cGMP were also recorded in endothelium-denuded equine digital vein rings pretreated with pentoxifylline (10 and 100 μM). Pentoxifylline only potentiated the SNP-mediated relaxation at the highest concentration (100 μM). Thus, pentoxifylline relaxed equine digital veins via endothelium-dependent and endothelium-independent components. The effect was mediated through both the NOS and COX pathways and could also result from inhibition of cGMP specific-phosphodiesterase activity at the highest concentrations used.

Nonlinear mixed effects models applied to cumulative concentration–response curves

Objectives

In experimental pharmacology, drug effect studies currently establish and analyse cumulative concentration–response curves (CCRC) under repeated measurements designs. Usually the CCRC parameters are estimated using the Hill's function in a nonlinear regression for independent data. The two-way analysis of variance is generally used to identify a statistical difference between the responses for two treatments but that analysis does not take into account the nonlinearity of the model and the heteroscedasticity (uneven distribution) of the data. We presently tested the possibility of finding a statistical solution for the nonlinear response in repeated measurements data using the nonlinear mixed effects (nlme) models.

Methods

Experimental data sets, originating from studies on β-adrenoceptor-induced relaxation in rat thoracic aorta ring, were analysed using the nlme methods.

Key findings

Comparison with classical methods showed the superiority of the nlme models approach. For each pharmacological parameter (Em, n, pD2), a point estimate, a standard error and a confidence interval are returned by the nlme procedures respecting the assumption of independency and normality of the residuals.

Conclusions

Using the method presently described, it is now possible to detect significant differences for each pharmacological parameter estimated in different situations, even for designs with small samples size (i.e. at least six complete curves).

Low-affinity state beta1-adrenoceptor-induced vasodilation in SHR

Low-affinity state beta1-adrenoceptor (beta1-AR) was functionally expressed in some blood vessels and was different from beta1, beta2 and beta3-AR. In rat aorta, low-affinity state beta1-AR activation produced an endothelium-independent relaxation which was impaired in spontaneously hypertensive rats (SHRs). In the present work, we investigated whether renin-angiotensin system was involved in this alteration by evaluating the effects of enalapril, an angiotensin converting enzyme (ACE) inhibitor or losartan, an AT1 angiotensin receptor antagonist. Cumulative concentration-response curves to low-affinity state beta1-AR agonists (CGP 12177, cyanopindolol or alprenolol) and to NS 1619, a large conductance Ca2+-activated K+ channels (BK) agonist were performed in denuded aortic rings isolated from control or treated Wistar Kyoto (WKY) rats or SHRs in different experimental conditions. The low-affinity state beta1-AR-mediated aortic vasodilation was impaired in 5 and 12 weeks old SHRs when compared to age-matched WKY. Twelve days enalapril (5 mg/kg/day) or losartan (15 mg/kg/day) treatments reduced systolic blood pressure (SBP) only in 12 weeks old SHRs whereas no significant change was observed in other groups. These treatments improved low-affinity state beta1-AR effect only in SHRs groups. In 12 weeks old WKY rats, CGP 12177-induced relaxation was insensitive to glibenclamide, a K(ATP)+ channel blocker, but was reduced by TEA or iberiotoxin, two large conductance Ca2+-activated K+ channel (BK) blockers. The impairment of NS 1619-induced vasodilation in both 5 and 12 weeks old SHRs was restored by enalapril or losartan. These results suggested that improvement of the low-affinity state beta1-AR-mediated vasodilation in 5 and 12 weeks old SHRs could be attributed to enhanced BK channels-induced hyperpolarization in SHRs independently of lowering of SBP.

Impairment of the low-affinity state beta1-adrenoceptor-induced relaxation in spontaneously hypertensive rats

1 In hypertension, a decrease of the vascular beta-adrenergic relaxation has been described. However, the specific involvement of each beta-adrenoceptor (beta-AR) subtype, in particular the low-affinity state of beta1-AR, has not yet been evaluated. We investigated whether the low-affinity state of beta1-AR-induced relaxation was impaired in Spontaneously Hypertensive Rats (SHR). 2 The relaxant responses to CGP 12177 and cyanopindolol, low-affinity state beta1-AR agonists (with beta1-/beta2-AR antagonistic and partial beta3-AR agonistic properties) were evaluated on thoracic aortic rings isolated from 12-weeks-old Wistar Kyoto rats (WKY) and SHR. 3 In WKY, CGP 12177 and cyanopindolol produced an endothelium and nitric oxide (NO)-independent relaxation. CGP 12177-induced endothelium-independent relaxation was not modified either by beta1-, beta2-AR (nadolol) or beta3-AR (L-748337 or SR 59230A) antagonists but was significantly reduced by high concentrations of CGP 20712A (P<0.05). This relaxation was also reduced by adenylyl cyclase inhibitors, SQ 22536 or MDL 12330A. 4 In SHR, CGP 12177 produced mainly an endothelium and NO-dependent relaxation. This effect was not modified by nadolol, but was strongly reduced by beta3-AR blockade. Endothelium-independent relaxation to CGP 12177 was not altered by adenylyl cyclase inhibition, but was amplified in preparations from pertussis toxin-pretreated SHR. 5 The immunohistochemical analysis revealed an upregulation of beta3-AR in the endothelial layer of SHR aorta, whereas the beta3-AR-induced relaxation was not modified. 6 In conclusion, we demonstrated an impaired low-affinity state of the beta1-AR-induced relaxation and an upregulation of the beta3-AR in hypertension. Some clinical implications of those findings are discussed.