Vascular B1 Kinin Receptors in Patients With Congestive Heart Failure

Unraveling the Pivotal Role of Bradykinin in ACE Inhibitor Activity

Historically, the first described effect of an angiotensin converting enzyme (ACE) inhibitor was an increased activity of bradykinin, one of the substrates of ACE. However, in the subsequent years, molecular models describing the mechanism of action of ACE inhibitors in decreasing blood pressure and cardiovascular risk have focused mostly on the renin-angiotensin system. Nonetheless, over the last 20 years, the importance of bradykinin in regulating vasodilation, natriuresis, oxidative stress, fibrinolysis, inflammation, and apoptosis has become clearer. The affinity of ACE appears to be higher for bradykinin than for angiotensin I, thereby suggesting that ACE inhibitors may be more effective inhibitors of bradykinin degradation than of angiotensin II production. Data describing the effect of ACE inhibition on bradykinin signaling support the hypothesis that the most cardioprotective benefits attributed to ACE inhibition may be due to increased bradykinin signaling rather than to decreased angiotensin II signaling, especially when high dosages of ACE inhibitors are considered. In particular, modulation of bradykinin in the endothelium appears to be a major target of ACE inhibition. These new mechanistic concepts may lead to further development of strategies enhancing the bradykinin signaling.

Expression of the genes encoding kinin receptors are increased in human carotid atherosclerotic plaques

There is increasing evidence showing that inflammation occurs in atherosclerosis and contributes to the formation of atherosclerotic plaques. As important inflammatory peptides, kinins are increased in inflammation, eliciting vasodilation, increasing vascular permeability and recruiting inflammatory cells to the injury sites by activating specific receptors, B1 and B2. The two receptors have been reported to increase in inflammation, but their expressions remain to be defined in human carotid atherosclerotic plaques (CAP). In order to assess the gene expression of kinin receptors in human CAP, 47 CAP specimens were collected from patients undergoing endarterectomy and classified into stable and unstable plaque groups, respectively, with 10 mesenteric arteries used as controls. Total mRNA of B1R and B2R was extracted from CAPs and their levels were determined using reverse transcription-polymerase chain reaction. The expression of B1R and B2R mRNA was significantly upregulated in human CAPs compared to the control arteries. In the unstable plaques, the ratios of B1R to the β-actin mRNA level were significantly increased relative to the stable plaques. However, no notable differences were observed in the ratios of B2R to β-actin in mRNA expression between the stable and unstable plaques. The present study suggests that kinin-mediated inflammation involves the formation of atherosclerotic plaque and B1R plays an important role in plaque instability, indicating that kinin receptors can be used as potential targets for future therapeutic interventions.

β-blockade abolishes the augmented cardiac tPA release induced by transactivation of heterodimerised bradykinin receptor-2 and β2-adrenergic receptor in vivo

Bradykinin (BK) receptor-2 (B2R) and β2-adrenergic receptor (β2AR) have been shown to form heterodimers in vitro. However, in vivo proofs of the functional effects of B2R-β2AR heterodimerisation are missing. Both BK and adrenergic stimulation are known inducers of tPA release. Our goal was to demonstrate the existence of B2R-β2AR heterodimerisation in myocardium and to define its functional effect on cardiac release of tPA in vivo. We further investigated the effects of a non-selective β-blocker on this receptor interplay. To investigate functional effects of B2R-β2AR heterodimerisation (i. e. BK transactivation of β2AR) in vivo, we induced serial electrical stimulation of cardiac sympathetic nerves (SS) in normal pigs that underwent concomitant BK infusion. Both SS and BK alone induced increases in cardiac tPA release. Importantly, despite B2R desensitisation, simultaneous BK infusion and SS (BK+SS) was characterised by 2.3 ± 0.3-fold enhanced tPA release compared to SS alone. When β-blockade (propranolol) was introduced prior to BK+SS, tPA release was inhibited. A persistent B2R-β2AR heterodimer was confirmed in BK-stimulated and non-stimulated left ventricular myocardium by immunoprecipitation studies and under non-reducing gel conditions. All together, these results strongly suggest BK transactivation of β2AR leading to enhanced β2AR-mediated release of tPA. Importantly, non-selective β-blockade inhibits both SS-induced release of tPA and the functional effects of B2R-β2AR heterodimerisation in vivo, which may have important clinical implications.

The effect of Des-Arg9-bradykinin and bradykinin-potentiating peptide C on isolated rat hearts

OBJECTIVES

Des-Arg9-bradykinin and bradykinin-potentiating peptide C (BPPC) may contribute to the regulation of cardiovascular function. Therefore, we studied effects of these peptides on coronary perfusion pressure (CPP), heart rate, left ventricular developed pressure (LVDP) and maximum rate of increase of left ventricular pressure (+dP/dtmax).

METHODS

The isolated rat hearts were perfused with modified Krebs-Henseleit solution.

RESULTS

Infusion of 10, 100 and 1000 nM Des-Arg9-bradykinin decreased CPP (-13.6, -14.8 and -19.0%), LVDP (-16.5, -21.0 and -30.7%) and +dP/dtmax (-11.8, -17.8 and -23.7%), respectively (p < 0.001). Ten or 100 nM Des-Arg9-bradykinin did not alter heart rate, but 1000 nM increased it (+11.3%, p < 0.01). One, 10 and 100 nM BBPC reduced CPP (-16.3, -28.5 and -47.5%), LVDP (-12.6, -19.6 and -21.3%) and +dP/dtmax (-8.7, -18.6 and -20.3%), respectively (p < 0.001). BPPC increased heart rate at 1 nM (+9.6%, p < 0.05 ) and at 10 nM (+14.2%, p < 0.01), however 100 nM decreased it (-15.3%, p < 0.001).

CONCLUSIONS

This study evidences that Des-Arg9-bradykinin and BPPC possess vasodilatory effect with modest negative inotropic action. Furthermore, high-dose of Des-Arg9-bradykinin and low-dose of BPPC may produce a tachycardic action, but high dose of BBPC may cause a bradycardic action.

Vascular effects of urocortins 2 and 3 in healthy volunteers

BACKGROUND

Urocortin 2 and urocortin 3 are endogenous peptides with an emerging role in cardiovascular pathophysiology. We assessed their pharmacodynamic profile and examined the role of the endothelium in mediating their vasomotor effects in vivo in man.

METHODS AND RESULTS

Eighteen healthy male volunteers (23±4 years) were recruited into a series of double-blind, randomized crossover studies using bilateral forearm venous occlusion plethysmography during intra-arterial urocortin 2 (3.6 to 120 pmol/min), urocortin 3 (1.2 to 36 nmol/min), and substance P (2 to 8 pmol/min) in the presence or absence of inhibitors of cyclooxygenase (aspirin), cytochrome P450 metabolites of arachidonic acid (fluconazole), and nitric oxide synthase (L-NMMA). Urocortins 2 and 3 evoked arterial vasodilatation (P<0.0001) without tachyphylaxis but with a slow onset and offset of action. Inhibition of nitric oxide synthase with L-NMMA reduced vasodilatation to substance P and urocortin 2 (P≤0.001 for both) but had little effect on urocortin 3 (P>0.05). Neither aspirin nor fluconazole affected vasodilatation induced by any of the infusions (P>0.05 for all). In the presence of all 3 inhibitors, urocortin 2- and urocortin 3-induced vasodilatation was attenuated (P<0.001 for all) to a greater extent than with L-NMMA alone (P≤0.005).

CONCLUSIONS

Urocortins 2 and 3 cause potent and prolonged arterial vasodilatation without tachyphylaxis. These vasomotor responses are at least partly mediated by endothelial nitric oxide and cytochrome P450 metabolites of arachidonic acid. The role of urocortins 2 and 3 remains to be explored in the setting of human heart failure, but they have the potential to have major therapeutic benefits.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov//. Unique identifier: NCT01096706 and NCT01296607.