Bradykinin antagonism: differentiation between peptide antagonists and antiinflammatory agents

Bradykinin B2-receptor-mediated positive chronotropic effect of bradykinin in isolated rat atria

The positive chronotropic effect of bradykinin was investigated in isolated spontaneously beating atria of the rat. Cumulative additions of bradykinin (0.3-100 nM) caused a concentration-dependent increase in the beating rate of the atria by maximally 35+/-4 beats/min, approximately 25% of the 1 microM isoprenaline-induced maximal responses. In contrast, the active metabolite of bradykinin and selective bradykinin B1-receptor agonist, Des-Arg9-bradykinin, did not influence the spontaneous frequency of beating. Propranolol (1 microM) combined with prazosin (1 microM) did not affect the positive chronotropic effect of bradykinin. A selective bradykinin B2-receptor antagonist, Hoe 140, concentration-dependently shifted the response curves for bradykinin to the right, whereas the bradykinin B1-receptor antagonist, Lys-[Leu8]Des-Arg9-bradykinin had no effect. The tachycardic responses to bradykinin were potentiated by ramipril, an angiotensin-converting enzyme/kininase II inhibitor, but not affected by Nomega-nitro-L-arginine methyl ester hydrochloride, a nitric oxide synthesis inhibitor. Indomethacin and meclofenamate, two cyclooxygenase inhibitors, abolished the bradykinin-induced chronotropic effect. These results indicate that exogenous bradykinin induces a positive chronotropic effect that occurs independent of adrenoceptors. The bradykinin-induced chronotropic effect is mediated by bradykinin B2 receptors, whereas B1 receptors do not play a role in mediating this effect. Prostaglandins but not nitric oxide appear to be involved in bradykinin-induced positive chronotropic effect.

The human bronchus model in vitro. Pharmacological approach of various components involved in the functional response

Studying the human bronchi in vitro, and therefore sheltered from the toxicity problems inherent in human experiments, makes it possible to conduct a monofactorial analysis, disregarding the perturbations engendered by reflex phenomena, hemodynamic changes, etc. Analysing the effects of mediators on tissues may be less simple that it looks, due to the multiplicity of the cell types that are present. For example, in studying the effects of bradykinin we have shown that bradykinin is a potent contractile agent of small-diameter isolated bronchi, whereas it has no significant contractile effect on larger bronchi. The bradykinin-induced contraction results from a contractile component due to stimulation of the TP receptor, and of a relaxant component due to relaxant prostanoids. The two components of the bradykinin effects are produced by stimulation of B2 receptors. In vitro stimulation of bronchi by LPS or interleukin-1 beta permits us to obtain hyperreactivity to bradykinin due to induction of thromboxane synthetase or isomerase rather than to induction of B2 receptors or cyclooxygenase. Involvement of the nervous system may persist in the in vitro bronchial model, and indeed we have shown, for example, that pentamidine, well known for its tussigenic effect, is an indirect parasympathomimetic compound. Thus, study of the isolated bronchus permits an approach to the mechanisms of action of medicinal drugs. Despite the simplification provided compared to the in vivo study, analysis of bronchoreactivity on the isolated bronchus must take into account numerous parameters which interfere with the proper effects of the substances.

Mechanisms involved in the relaxant response of bradykinin in epithelium intact strips of the guinea-pig trachea

Kinins caused graded relaxations in guinea-pig trachea with epithelium under spontaneous or carbachol-induced tone. The order of potency was: [Tyr8]bradykinin > lysyl-bradykinin > bradykinin > methionyl-lysyl- bradykinin. The bradykinin B1 receptor agonist des-Arg9-bradykinin (1 microM) was inactive. Relaxation in response to bradykinin (100 nM) was unaffected by tetrodotoxin (0.3 microM), nicardipine (1 microM), Ca(2+)-free solution without or plus ryanodine (10 microM), propranolol (1 microM), glibenclamide (1 microM), staurosporine (0.3 microM), nickel chloride (100 microM) or [D-p-Cl-Phe6,Leu17]VIP (a vasoactive intestinal peptide receptor antagonist, 0.03 microM), but was partially inhibited by apamin (0.3-1 microM). Both HOE 140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin) and NPC 17761 (D-Arg0[Hyp3,D-HypeE(trans-thiophenyl)7,Oic8]bra dykinin) (0.1-1000 nM) caused graded, reversible and selective inhibition of the bradykinin (100 nM) relaxation, with IC50 values of 1.4 and 19.1 nM, respectively. HOE 140 and NPC 17761 (0.1-10 nM) produced a graded shift to the right of the bradykinin concentration-response curves associated with a reduction of the maximum relaxation. The kinin B1 receptor antagonist, des-Arg9-[Leu8]bradykinin (1 microM), was inactive. Thus, bradykinin-induced relaxation in guinea-pig trachea results from activation of bradykinin B2 receptors and can be antagonized with high affinity in a selective and reversible manner, through noncompetitive mechanism, by both HOE 140 and NPC 17761. In addition, the bradykinin response does not involve neural pathways, extracellular Ca2+ influx or mobilization of intracellular Ca2+ stores sensitive to ryanodine, but is modulated by small conductance Ca(2+)-activated K+ channels.

Involvement of B2 receptors in the bradykinin-induced relaxation of guinea-pig isolated trachea

1. The aim of this study was to determine the receptor type and involvement of arachidonic acid metabolites in bradykinin-induced relaxation of the guinea-pig isolated trachea. 2. In the resting tracheal preparation, bradykinin (0.1 nM-30 microM induced a concentration-related contractile response (pD2 = 8.8 +/- 0.3). The maximal tension (1056 +/- 321 mg) was observed at 0.3 microM bradykinin. In contrast, when tracheal preparations were pre-contracted with histamine (30 microM leading to a half-maximum response), a concentration-related relaxation was observed with bradykinin. At the highest concentration of bradykinin used (3 microM), a reversal of 63 +/- 13% of the contractile response to histamine was observed. Both effects of bradykinin were inhibited by the cyclo-oxygenase inhibitor, indomethacin (1 microM). In concentration-response curves, melittin (10 nM-1 microM), a direct activator of phospholipase A2, mimicked both effects of bradykinin. The highest concentration of melittin used (1 microM), induced a tension of 813 +/- 120 mg and led to the reversal of 41 +/- 8% of the contractile response to histamine. The contractile effect of melittin was inhibited in the presence of both indomethacin (1 microM) and AA861 (1 microM), a 5-lipoxygenase inhibitor. 3. [Des Arg9]-bradykinin (1 nM-3 microM), a B1-receptor agonist, was unable to relax precontracted guinea-pig tracheal preparations. The relaxation induced by bradykinin was antagonized by the B2 receptor antagonists, Hoe 140 (D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin) and NPC 17761 (D-Arg0[Hyp3,D-HypE(trans-thiophenyl)7,Oic8]bradykinin ). Hoe 140 (0.1 microM to 0.6 microM) behaved as a non-competitive antagonist with an apparent pA2 = 7.2 +/- 0.4, whereas NPC 17761 (0.3 to 1 microM) competitively antagonized bradykinin-induced relaxation with a pKB = 7.3 +/- 0.2. The Schild regression slope did not differ from unity, 0.96 +/- 0.20, P<0.05.4. These data demonstrate that bradykinin-induced relaxation of guinea-pig trachea occurs via the activation of bradykinin B2-receptors. The stimulation of B2-bradykinin receptors induces the activation of the cyclo-oxygenase pathway, leading either to contraction or relaxation depending on the tone of the trachea.

Bradykinin receptors: pharmacological properties and biological roles

Kinins contribute to the acute inflammatory response and are implicated in the pathophysiology of inflammatory disease. The development of therapeutically viable agents that counteract the effects of kinins is, therefore, potentially very rewarding. Since kinin actions are generally mediated via an interaction with cell-surface receptors, one approach is the development of site-specific receptor antagonists. The emphasis in this review is to outline our current understanding of the properties of bradykinin receptors and the potential therapeutic applications for drugs acting at these sites. As a result of the recent introduction of potent bradykinin receptor antagonists and the cloning of bradykinin receptor genes, considerable advances in kinin research can now be confidently anticipated.

Bradykinin stimulates the production of prostaglandin E2 and interleukin-6 in human osteoblast-like cells

The effect of bradykinin (BK) on proteinase activity, prostaglandin synthesis, and the production of interleukin-6 (IL-6) was investigated in cultures of human osteoblast-like cells. Bradykinin had no effect on stromelysin activity and plasminogen activator activity produced by human osteoblast-like cells. However, BK stimulated the production of prostaglandin E2, an effect that was markedly enhanced by pre-incubation with recombinant interleukin-1 alpha (rhIL-1 alpha), but was apparently unaffected by BK receptor antagonists types 1 and 2. Bradykinin stimulated the intracellular accumulation of total inositol phosphates suggesting that its effects were mediated by stimulation of phosphoinositide metabolism. Bradykinin within the dose range of 10(-11)-10(-5) M also significantly stimulated the production of IL-6. Bradykinin may, therefore, mediate a variety of responses in bone under both physiological and pathological conditions.

Pharmacological characterization of a new highly potent B2 receptor antagonist (HOE 140: D-Arg-[Hyp3,Thi5,D-Tic7,Qic8]bradykinin)

HOE 140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin), a new B2 antagonist, was compared to R-493 (D-Arg[Hyp3-D-Phe7,Leu8]bradykinin) with respect to inhibition of the responses of seven isolated smooth muscle preparations to bradykinin. R-493 was found to exert: (a) high antagonistic activity on the rabbit jugular vein (pA2 of 8.86), (b) moderate activity on the rabbit aorta, guinea-pig ileum, hamster urinary bladder and human urinary bladder (pA2 of 5.76, 6.77, 7.16 and 7.15, respectively) and (c) a stimulatory effect on the guinea-pig trachea. On the other hand, HOE 140 showed identical apparent affinities (8.36-9.12) on all preparations except the rabbit aorta where it was inactive and the guinea-pig trachea where the compound was an antagonist (pA2: 7.42) without agonistic effect. HOE 140 is specific and selective for B2 receptors since it was inactive against angiotensin II, substance P, neurokinin A, desArg9-bradykinin, noradrenaline or acetylcholine in the various preparations. R-493 inhibited the contractile effects of bradykinin competitively, while HOE 140 was not competitive even at low concentrations (7.7 x 10(-9) M). These results demonstrate that HOE 140 is a potent B2 antagonist with high affinity, specific for kinin receptors and selective for the B2 receptor type, but is non-competitive. HOE 140 is the first bradykinin receptor antagonist that acts as such on the guinea-pig trachea without showing any agonistic activity.

Evidence for two high-affinity bradykinin binding sites in the guinea-pig lung

We examined the binding of [3H]bradykinin ([3H]BK) to the guinea-pig lung which was saturable. Scatchard analysis indicated the existence of two binding sites, one with a high affinity (KD = 15 pM) and one with a low one (KD = 570 pM) with maximum number of binding sites of 12 and 45 fmol/mg protein, respectively. Kinetic studies confirmed the presence of these two types of binding sites and their affinity ranges. Neither the B1 agonist des-Arg9-BK, nor the B1 antagonist des-Arg9-[Leu8]BK displaced [3H]BK, demonstrating the absence of B1 receptors in the guinea-pig lung. Current B2 antagonists fully displaced the [3H]BK binding. Their potencies differed slightly according to the concentration of [3H]BK, suggesting a specificity of current B2 antagonists for the lower affinity site as opposed to the higher one. Altogether, these results do not allow us to confirm the occurrence of putative B3 receptors in guinea-pig lung.

Evidence that cultured airway smooth muscle cells contain bradykinin B2 and B3 receptors

We examined bradykinin-induced 45Ca2+ efflux and prostaglandin synthesis in guinea pig tracheal smooth muscle cells maintained in tissue culture. We also studied the effects of a B1 receptor agonist and antagonist, a B2 receptor antagonist, and the cyclooxygenase inhibitor indomethacin. In cultured smooth muscle cells, bradykinin (0.1 nM to 10 microM) stimulated efflux of 45Ca2+ and induced the synthesis of prostaglandin E2 and the prostacyclin metabolite 6-keto-prostaglandin F1 alpha. DesArg9-bradykinin, a B1 receptor agonist, had no effect on 45Ca2+ efflux or prostaglandin synthesis, and no responses to bradykinin were unaffected by the B1 receptor antagonist desArg9-[Leu8]-bradykinin. Indomethacin (1 microM) abolished bradykinin-induced prostaglandin synthesis but was without effect on 45Ca2+ efflux. NPC 567 (DArg[Hyp3,DPhe7]-bradykinin), a B2 receptor antagonist, had no effect on bradykinin-induced 45Ca2+ efflux, but abolished prostaglandin synthesis. Unlike in membranes prepared freshly from guinea pig tracheal smooth muscle, the B2 receptor antagonist inhibited completely (Ki, 12 nM) binding of [3H]-bradykinin to membranes prepared from cultured tracheal smooth cells. These data suggest that tracheal smooth muscle cells, maintained in culture, express B2 receptors that mediate bradykinin-induced prostaglandin synthesis. The observation that bradykinin-induced efflux of calcium ions was unaffected by B1 or B2 antagonists provides further evidence that airway smooth muscle may contain a novel B3 receptor.

Structure-activity studies of bradykinin and related peptides. B2-receptor antagonists

Thirty-seven compounds were tested as antagonists of kinin B2- and B1-receptors to identify the chemical changes required to obtain antagonism, improve antagonist affinity, and eliminate residual agonistic activities. Apparent affinity of antagonists was evaluated in terms of pA2 on the rabbit jugular vein, the dog carotid and renal arteries, the hamster urinary bladder, the guinea pig ileum, the rat vas deferens, the guinea pig trachea, and the rabbit aorta, using bradykinin and desArg9-bradykinin as B2- and B1-receptor activators. Replacement of Pro7 of bradykinin with D-Phe leads to antagonism; substitution of Pro3 by Hyp and extension of the peptide chain at the N-terminal with a D-Arg residue improves the affinity of antagonists; acetylation of N-terminal amine function reduces residual agonistic activity; these changes, combined with the replacement of Phe8 by Leu as in Ac-D-Arg[Hyp3,D-Phe7,Leu8]-bradykinin, led to potent full B2-receptor antagonists. Affinity of antagonists differs markedly between highly sensitive (rabbit jugular vein, dog carotid and renal artery), moderately sensitive (hamster urinary bladder, guinea pig ileum, and rat vas deferens), and insensitive preparations (the guinea pig trachea) in which antagonists act as potent stimulants. High concentrations of antagonists block bradykinin completely in the rabbit jugular vein but not in the guinea pig ileum, suggesting that kinins stimulate the moderately sensitive tissues by two mechanisms, of which only one is blocked by antagonists. It thus appears that kinins act on various B2-receptor subtypes or by different action mechanisms.

Histamine secretion from mast cells stimulated with bradykinin

Bradykinin and a range of peptide analogues induced a dose-dependent release of histamine from rat peritoneal mast cells. The characteristics of the release were not consistent with the involvement of defined bradykinin receptors but indicated that the peptide acted through the putative mast cell polyamine receptor. Consistently, the effect of bradykinin was largely confined to serosal mast cells of the rat and hamster, while human histaminocytes were essentially unresponsive. These data do then not support a general role for kinin-induced activation of mast cells in human allergic disease.

New selective bradykinin receptor antagonists and bradykinin B2 receptor characterization

Substantial progress has been made recently in the field of kinin pharmacology with the identification of sensitive bioassay organs and the discovery of bradykinin B2 receptor antagonists. Data obtained with such compounds in various laboratories support the hypothesis that kinins act on multiple (at least two) receptor types. Domenico Regoli and colleagues review here the basic criteria of receptor characterization as they apply to kinins and present a critical analysis of the bioassay organs and B2 receptor antagonists currently used in kinin pharmacology.

Bradykinin receptor antagonists

Bradykinin and its active metabolites are produced at the sites of their actions by kallikreins. They potently elicit a variety of biological effects: hypotension, bronchoconstriction, gut and uterine contraction, epithelial secretion in airway, gut, and exocrine glands, vascular permeability, pain, connective tissue proliferation, and eicosanoid formation. These effects are mediated by at least two broad classes of receptors. The most common is the B2 subtype. The Stewart and Vavrek peptides characterized by a DPhe7 substitution have provided powerful tools for study of bradykinin's actions by competitively and specifically blocking bradykinin B2 receptors. The significance of kinins in certain human diseases is being explored using these new tools and potential therapeutic agents. At present, human clinical trials are underway to test the usefulness of bradykinin receptor antagonists in the symptoms of the common cold and in the pain associated with severe burns. Trials for use in asthma will be initiated in 1990.

Structure-activity studies on bradykinin and related peptides: agonists

1. Bradykinin, kallidin, T-kinin, [Hyp3]-bradykinin and several analogues were prepared by solid-phase synthesis and purified by high performance liquid chromatography. 2. The various peptides were tested for their abilities to relax the dog carotid and renal arteries, or to contract the rabbit jugular vein and aorta, in order to measure their activities on BK2 (the first three preparations) or BK1 (the rabbit aorta) receptors. The dog renal artery without endothelium was also used as a BK1 receptor system. 3. T-kinin was found to be less active than bradykinin, while the replacement of Pro3 with Hyp favoured BK2 receptor occupation. [Hyp3,Tyr(Me)8]-BK was found to be a selective BK2 receptor agonist. 4. Amidation or methylation of the C-terminal carboxyl decreased activity, while extension of the N-terminal with Sar or D-Arg increased affinity and selectivity for BK1 (Sar) and affinity for BK2 (D-Arg) receptors. Acetylation of N-terminal amide brought affinity down to 10% or less. 5. Replacement of the peptide bonds Phe8-Arg9 to protect from kininase I and II, decreased affinities slightly, but was incompatible with additional changes at the N-terminal or in the peptide bond Gly4-Phe5. 6. Substitution of C-terminal Phe in desArg9-BK (the BK1 receptor stimulant) with D-Phe increased potency and selectivity for BK1 receptors while protecting from carboxypeptidases. Sar[D-Phe8]desArg9-BK was found to be a potent and selective BK1 receptor agonist.

Multiple mechanisms in the motor responses of the guinea-pig isolated urinary bladder to bradykinin

1. Bradykinin (1 nm-1 microM) produced a contraction of bladder strips excised from the dome of the guinea-pig urinary bladder, an effect which was greatly enhanced by removal of the mucosal layer or by thiorphan (10 microM). All subsequent experiments were performed in mucosa-free strips and in the presence of thiorphan. 2. In carbachol (5 microM)-contracted strips, bradykinin produced a concentration (1 nm-1 microM)-dependent transient relaxation. 3. Kallidin was slightly more potent than bradykinin in producing a contraction and a relaxation of the carbachol-induced tone. By contrast, [des-Arg9]-bradykinin, a selective B1 receptor agonist was barely effective up to 1 microM. 4. The contractile response to bradykinin was: (a) unaffected by either tetrodotoxin (1 microM), in vitro capsaicin desensitization (10 microM for 30 min) or apamin (0.1 microM); (b) antagonized by indomethacin (5 microM), the prostaglandin receptor antagonist SC-19220 (100 microM) or the B2 receptor antagonist [D-Arg0, Hyp3, Thi5,8, Phe7]-bradykinin (10 micron) and (c) almost abolished by nifedipine (1 microM). 5. The antagonism of the contractile response to bradykinin produced by indomethacin and SC-19220 was non-additive while that produced by indomethacin and the B2 receptor antagonist was additive. 6. The relaxant response to bradykinin was unaffected by tetrodotoxin, in vitro capsaicin desensitization or indomethacin but antagonized in a competitive manner by the B2 receptor antagonist. Further, this response was abolished by apamin (0.1 microM) but unaffected by glibenclamide (1 microM). 7. Bradykinin (10 microM) produced a consistent release of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) but not substance P-LI from the guinea-pig bladder muscle. CGRP-LI release by bradykinin was greatly reduced in bladders exposed to indomethacin. [des-Arg9]-bradykinin (10 microM) was ineffective. 8. We conclude that: (a) bradykinin-induced contraction involves activation of both B2 receptors and prostanoid synthesis, via distinct mechanisms which act by inducing calcium influx via nifedipine-sensitive channels; (b) bradykinin-induced relaxation involves activation of B2 receptors and opening of apamin-sensitive potassium channels; (c) bradykinin stimulates sensory nerves in this tissue largely via prostanoid production.

Receptors for kinins in isolated arterial vessels of dogs

A variety of kinin peptides, agonists and antagonists were tested with dog carotid and renal arteries in order to characterize kinin receptor types and functions. The dog carotid artery responds to bradykinin with concentration-dependent relaxation only when the endothelium is intact but des-Arg9-bradykinin is practically inactive. The effect of bradykinin is blocked by B2 receptor antagonists, suggesting that the dog carotid artery has B2 receptors in the endothelium. These receptors mediate relaxation of the arterial smooth muscles by promoting the release of an endothelium-derived relaxing factor whose action is prevented by methylene blue. Kinins relax the dog renal artery with or without endothelium. Methylene blue prevents the effect of bradykinin only, suggesting that B2 receptors, promoting the release of endothelium-derived relaxing factor, are present in the endothelium of the dog renal artery. Moreover, the dog renal artery appears to have both B2 and B1 receptors mediating relaxation of the arterial smooth muscle. The presence of the two receptor types has been demonstrated by means of specific agonists and antagonists. Indomethacin blocks the effects of both bradykinin and des-Arg9-bradykinin on the dog renal artery without endothelium, suggesting that muscular B1 and B2 receptors act by promoting the release of prostaglandins. Captopril, a kininase II inhibitor, potentiates the effect of bradykinin on the dog carotid artery more than on the dog renal artery.