Non-selectivity of new bradykinin antagonists for B1 receptors

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

Preclinical pharmacology, metabolic stability, pharmacokinetics and toxicology of the peptidic kinin B1 receptor antagonist R-954

We previously showed that R-954 (AcOrn[Oic(2),(αMe)Phe(5),dβNal(7),Ile(8)]desArg(9)-bradykinin) is a potent, selective and stable peptide antagonist of the inducible GPCR kinin B1 receptor. This compound shows potential applications for the treatment of several diseases, including cancer and neurological disturbances of diabetes. To enable clinical translation, more information regarding its pharmacological, pharmacokinetics (PK) and toxicological properties at preclinical stage is warranted. This was the principal objective of the present study. Herein, specificity of R-954 was characterized in binding studies on 133 human molecular targets to reveal minor cross-reactivities against the angiotensin AT2 and the bombesin receptors (110- and 330-fold lower affinity than for B1R, respectively). The pharmacokinetic of R-954 was studied in both normal and streptozotocin-diabetic anaesthetized rats providing half-lives of 1.9-2.7h. R-954 does not appear to be metabolized in the rat circulation and in several rat tissue homogenates, as the kidney, lung and liver. It appears to be excreted as parent drug in the bile (21%) and in urine. A preliminary toxicological profile of R-954 was obtained in rats under various administration routes. R-954 appears to be well tolerated. Overall, these results indicate that R-954 exhibits favorable preclinical pharmacological/PK characteristics and encouraging safety profiles, suitable for early studies in humans.

International union of pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences

Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development.

Vasoactive amine responses in murine cerebrovascular endothelial cells as measured by extracellular acidification rates

The Cytosensortrade mark microphysiometer device is capable detecting cellular responses to specific bioactive ligands by measuring the extracellular acidification rate (ECAR). Using microphysiometry, we were able to determine that cerebovascular endothelial cells derived from SJL/J mice were more sensitive to serotonin (maximal ECAR response at 100 nM), whereas BALB/c-derived cerebrovascular endothelial cells (CVE) were relatively insensitive (maximal ECAR response at 30 microM). Serotonin (5HT)(1) and 5HT(2) receptor antagonists inhibited the serotonin-mediated increases in ECAR. The cells' responses to histamine in both strains were similar (maximal ECAR required 100 microM of histamine). H(1) and H(3) receptor subtype antagonists specifically inhibited the histamine responses. Bradykinin also revealed sensitivity differences in that maximal ECAR changes for CVE from SJL/J mice could be observed with 1 microM, as compared to the ECAR responses from BALB/c mice CVE, which required 10 microM. Exposure to bradykinin antagonists revealed that the response was due to the stimulation of B(2) receptors. These microphysiometry results reveal that the cerebrovascular endothelial cells of SJL/J mice tend to be more sensitive to vasoactive substances than those of BALB/c mice.

Heat stress-induced B1 receptor synthesis in the rat: an ex vivo study

1. This ex vivo study was performed to characterize B1 receptor induction in rats submitted to heat stress. Changes in aortic isometric tension were recorded after a 90 min in vitro incubation with [des-Arg9]-bradykinin. B1 receptor mRNA were detected in aorta and heart using RT-PCR technique. 2. Aortic rings from sham rats did not respond to [des-Arg9]-bradykinin. In contrast, this agonist induced a concentration-dependent relaxation of aortic rings from rats submitted to lipopolysaccharide (LPS) treatment or to heat stress 24 h earlier. 3. The concentration-dependent relaxation induced by [des-Arg9]-bradykinin on aortic rings from heat-stressed rats was abolished by [des-Arg10]-HOE 140, a selective B1 receptor antagonist. 4. In endothelium denuded aortic rings from heat-stress rats, [des-Arg9]-bradykinin induced a concentration-dependent constriction. 5. Pretreatment of intact aortic rings from heat-stress rats with the cyclo-oxygenase inhibitor, diclofenac (1 microM) did not prevent the concentration-dependent relaxation in response to [des-Arg9]-bradykinin. In contrast. NO synthase inhibition with N(omega)-nitro-L-arginine methyl ester (30 microM) totally prevented the vasorelaxant response. 6. B1 receptor mRNA were not detected in aorta and heart from sham animals but were present in tissue from heat-stressed and LPS-treated rats. 7. In conclusion, our results suggest that heat stress induces a transcriptional activation of the B1 receptor gene. The induction of B1 receptors leads to an endothelium- and NO-dependent vasorelaxant response to [des-Arg9]-bradykinin.

In vivo evidence for B1-receptor synthesis induction by heat stress in the rat

A hypotensive effect of intravenously injected [des-Arg9]-bradykinin was found in Wistar rats following acute heat stress. This effect was similar to that of intravenously injected bradykinin and was observed 6, 18 and 24 h following an increase in rectal temperature at 42 degrees C for 20 min (H6, H18 and H24 groups, respectively). In contrast, [des-Arg9-bradykinin had no effect on blood pressure in control or sham conditions, early on (3 h) or later on (72 h) after heat stress (Ctl, H3 and H72 groups, respectively), while the response to bradykinin was maintained. The hypotension induced by [des-Arg9]-bradykinin in groups H6, H18 and H24 was comparable to that induced in rats pretreated with a small amount of endotoxin 24 h earlier (LPS group). The hypotensive response in group H24 was totally blunted by [des-Arg10]-Hoe 140 (a potent B1 receptor antagonist) infused at a rate of 10 microg min(-1). These results suggest that heat stress induces the synthesis of vascular B1 receptors in the rat.

Kinin B1 receptors: a review

The kinin B1 receptor has been initially defined as the one mediating the contractile effect of bradykinin (BK)-related peptides in the isolated rabbit aorta. The B1 receptor is selectively sensitive to kinin metabolites without the C-terminal arginine residue, e.g. des-Arg9-BK and Lys-des-Arg9-BK; it is apparently rapidly up-regulated in immunopathology under the influence of cytokines and is further regulated by growth factors. Progress in the understanding of this pharmacologic entity is reviewed, including the development of B1 receptor agonists and antagonists, binding assays, physiopathological applications and the recent cloning and sequencing of the receptor cDNA.

Agonistic and antagonistic properties of the bradykinin B2 receptor antagonist, Hoe 140, in isolated blood vessels from different species

1. Hoe 140, a recently described bradykinin B2 antagonist, and NPC 567 from an earlier generation of bradykinin B2 antagonists, were tested in rabbit and sheep isolated blood vessels. 2. In rabbit jugular vein, a bradykinin B2 preparation, NPC 567 was an antagonist (apparent pA2: 8.67 +/- 0.16) with marked residual agonistic activity (log[EC50]: -7.29 +/- 0.13). Hoe 140 was a potent non-competitive antagonist devoid of agonistic properties (slope of the Schild plot: 2.02; estimated pA2: 9.04). 3. In rabbit aorta, a bradykinin B1 preparation, NPC 567 was a competitive antagonist (pA2: 6.32 +/- 0.13) but Hoe 140 was ineffective. The two antagonists did not show any agonistic properties in this tissue. 4. In sheep femoral artery without endothelium, bradykinin and Hoe 140 induced contractions with identical efficacy and similar potency (log[EC50]: -8.05 +/- 0.12, -7.73 +/- 0.10; maximal contraction in % of KCl [60 mM]: 59.5 +/- 15.1, 62.0 +/- 13.1; for bradykinin and Hoe 140, respectively). In contrast NPC 567 was an extremely weak agonist. The contractile responses to bradykinin and Hoe 140 were inhibited by NPC 567 (apparent pKB: 6.89 +/- 0.22 and 6.58 +/- 0.08 versus bradykinin and Hoe 140, respectively) but not by a B1 bradykinin antagonist, suggesting that the receptor involved was a bradykinin B2 receptor. 5. In sheep femoral artery with endothelium, bradykinin induced a biphasic response: an endothelium-dependent relaxation and a contraction which were both inhibited by NPC 567 (apparent pKB: 7.10 +/- 0.15) and Hoe 140 (pA2: 8.38 +/- 0.12). As bradykinin B2 receptor antagonists, Hoe 140 and NPC 567 were less potent in the sheep femoral artery than in the rabbit jugular vein. Neither Hoe 140 nor NPC 567 were agonists for the endothelial receptor.6. This study demonstrates that Hoe 140, a new bradykinin B2 receptor antagonist, is more selective and more potent than NPC 567; however, it may possess, depending on the tissue studied, marked residual agonistic properties. Furthermore, bradykinin B2 receptors are subject to important species specificity. Finally, two different bradykinin B2 receptor subtypes may coexist in the sheep femoral artery with endothelium.

Bradykinin receptor types and B2 subtypes

Bradykinin, desArg9BK, some agonist analogues and several antagonists have been tested in isolated organs in order to identify bradykinin B2 receptor subtypes. The initial pharmacological characterization was made in the rabbit jugular vein and the guinea pig ileum, two widely used B2 preparations which have shown marked differences in their sensitivities to both agonists and antagonists. The study has then been extended to peripheral tissues (stomach, colon, urinary bladder) of four species (the rat, guinea pig, rabbit and man) and to isolated vessels (rabbit jugular vein, rabbit vena cava, guinea pig pulmonary artery, rat portal vein) in order to determine if pharmacologic receptor subtypes may be related to species. It has been shown that B2 receptors in rat and guinea pig tissues belong to a similar pharmacological entity, a receptor which is different from that mediating the responses of rabbit and human tissues. Agonists order of potency ([Hyp3]BK > BK > [Aib7]BK) obtained in the rabbit jugular vein is different from that found in the guinea pig ileum (BK < or = [Aib7]BK > [Hyp3]BK). Affinities of competitive antagonists (for instance DArg[Hyp3,DPhe7,Leu8]BK) in rabbit tissues are higher than in guinea pig and rat tissues by at least 2 log units, while the non peptidic compound WIN 64338 is more active (also by two log units) in guinea pig than in human and rabbit tissues. The non competitive long-acting antagonist HOE 140 is very potent and equally active in the four species. Some antagonists (peptides without unnatural residues, peptides with unnatural residues, non peptides) have been shown to be specific for kinin receptors and selective for the B2. Altogether, the present results a) confirm the existence of two B2 receptor subtypes, b) suggest that receptor subtypes may be species dependent and c) indicate that the B2 receptor subtype found in the rabbit is similar to that found in man.