The identification of an orally active, nonpeptide bradykinin B2 receptor antagonist, FR173657

Function and structure of bradykinin receptor 2 for drug discovery

Type 2 bradykinin receptor (B2R) is an essential G protein-coupled receptor (GPCR) that regulates the cardiovascular system as a vasodepressor. Dysfunction of B2R is also closely related to cancers and hereditary angioedema (HAE). Although several B2R agonists and antagonists have been developed, icatibant is the only B2R antagonist clinically used for treating HAE. The recently determined structures of B2R have provided molecular insights into the functions and regulation of B2R, which shed light on structure-based drug design for the treatment of B2R-related diseases. In this review, we summarize the structure and function of B2R in relation to drug discovery and discuss future research directions to elucidate the remaining unknown functions of B2R dimerization.

Exploiting Knowledge on Structure-Activity Relationships for Designing Peptidomimetics of Endogenous Peptides

Endogenous peptides are important mediators in cell communication, being consequently involved in many physiological processes. Their use as therapeutic agents is limited due to their poor pharmacokinetic profile. To circumvent this drawback, alternative diverse molecules based on the stereochemical features that confer their activity can be synthesized, using them as guidance; from peptide surrogates provided with a better pharmacokinetic profile, to small molecule peptidomimetics, through cyclic peptides. The design process requires a competent use of the structure-activity results available on individual peptides. Specifically, it requires synthesis and analysis of the activity of diverse analogs, biophysical information and computational work. In the present work, we show a general framework of the process and show its application to two specific examples: the design of selective AT1 antagonists of angiotensin and the design of selective B2 antagonists of bradykinin.

Targeting intracellular B2 receptors using novel cell-penetrating antagonists to arrest growth and induce apoptosis in human triple-negative breast cancer

G protein-coupled receptors (GPCRs) are integral cell-surface proteins having a central role in tumor growth and metastasis. However, several GPCRs retain an atypical intracellular/nuclear location in various types of cancer. The pathological significance of this is currently unknown. Here we extend this observation by showing that the bradykinin B2R (BK-B2R) is nuclearly expressed in the human triple-negative breast cancer (TNBC) cell line MDA-MB-231 and in human clinical specimens of TNBC. We posited that these “nuclearized” receptors could be involved in oncogenic signaling linked to aberrant growth and survival maintenance of TNBC. We used cell-penetrating BK-B2R antagonists, including FR173657 and novel transducible, cell-permeable forms of the peptide B2R antagonist HOE 140 (NG68, NG134) to demonstrate their superior efficacy over impermeable ones (HOE 140), in blocking proliferation and promoting apoptosis of MDA-MB-231 cells. Some showed an even greater antineoplastic activity over conventional chemotherapeutic drugs in vitro. The cell-permeable B2R antagonists had less to no anticancer effects on B2R shRNA-knockdown or non-B2R expressing (COS-1) cells, indicating specificity in their action. Possible mechanisms of their anticancer effects may involve activation of p38kinase/p27^Kip1 pathways. Together, our data support the existence of a possible intracrine signaling pathway via internal/nuclear B2R, critical for the growth of TNBC cells, and identify new chemical entities that enable to target the corresponding intracellular GPCRs.

Inundation of asthma target research: Untangling asthma riddles

Asthma is an inveterate inflammatory disorder, delineated by the airway inflammation, bronchial hyperresponsiveness (BHR) and airway wall remodeling. Although, asthma is a vague term, and is recognized as heterogenous entity encompassing different phenotypes. Targeting single mediator or receptor did not prove much clinical significant, as asthma is complex disease involving myriad inflammatory mediators. Asthma may probably involve a large number of different types of molecular and cellular components interacting through complex pathophysiological pathways. This review covers the past, present, and future therapeutic approaches and pathophysiological mechanisms of asthma. Furthermore, review describe importance of targeting several mediators/modulators and receptor antagonists involved in the physiopathology of asthma. Novel targets for asthma research include Galectins, Immunological targets, K ⁺ Channels, Kinases and Transcription Factors, Toll-like receptors, Selectins and Transient receptor potential channels. But recent developments in asthma research are very promising, these include Bitter taste receptors (TAS2R) abated airway obstruction in mouse model of asthma and Calcium-sensing receptor obliterate inflammation and in bronchial hyperresponsiveness allergic asthma. All these progresses in asthma targets, and asthma phenotypes exploration are auspicious in untangling of asthma riddles.

Intratesticular Bradykinin Involvement in Rat Testicular Pain Models

OBJECTIVES

To clarify the role of bradykinin in urogenital pain, we investigated bradykinin involvement in rat models of testicular pain.

METHODS

Bradykinin (0.1, 0.3, 1, 3 and 10 mmol/L) or distilled water was injected into the testes of male Wistar rats, and induced pain behaviors in conscious rats were evaluated. The effect of pretreatment with bradykinin B2 receptor antagonist FK3657 on bradykinin-induced pain behavior was then examined. We also evaluated the analgesic effect of FK3657 in a rat acetic acid-induced testicular pain as well as changes in the intratesticular bradykinin concentration after testicular injection of acetic acid.

RESULTS

An injection of bradykinin into the testes of conscious rats induced pain behaviors that were dose-proportionally reduced by prior administration of FK3657. In addition, FK3657 dose-dependently inhibited the pain responses induced by testicular injection of 1% acetic acid. An increase in intratesticular bradykinin concentration was detected after the testicular injection of 1% acetic acid.

CONCLUSIONS

Here, we found that intratesticular bradykinin evokes pain behavior via stimulation of bradykinin B2 receptors and that intratesticular acetic acid injection induces intratesticular bradykinin synthesis, consequently leading to pain behavior. These findings suggest that the potential utility of bradykinin B2 receptor antagonists as a novel target for treating urogenital pain.

Effect of inflammatory mediators on ATP release of human urothelial RT4 cells

Inflammation is an important contributor to the aetiology of a number of bladder dysfunctions including interstitial cystitis, painful bladder syndrome, and overactive bladder. The aim of this study was to examine the effects of inflammatory mediators on urothelial ATP release. Human urothelial RT4 cells were exposed to normal buffer or varying concentrations of inflammatory mediators (bradykinin, histamine, and serotonin) in the presence or absence of hypotonic stretch stimuli (1 : 2 dilution of Krebs-Henseleit buffer). Others have demonstrated that bradykinin increased stretch-induced ATP release; however, we observed no change in control or stretch-induced ATP release with bradykinin. Pretreatment of RT4 cells with histamine or serotonin decreased stretch-induced ATP release (P = 0.037, P = 0.040, resp.). Previous studies have demonstrated increased ATP release in response to inflammation utilising whole bladder preparations in contrast to our simple model of cultured urothelial cells. The current study suggests that it is unlikely that there is a direct interaction between the release of inflammatory mediators and increased ATP release, but rather more complex interactions occurring in response to inflammation that lead to increased bladder sensation.

Comparative antagonist pharmacology at the native mouse bradykinin B2 receptor: radioligand binding and smooth muscle contractility studies

BACKGROUND AND PURPOSE

The aim was to characterize the recently discovered non-peptide antagonist MEN16132 at the mouse B2 receptor, relative to other antagonists.

EXPERIMENTAL APPROACH

[3H]-BK binding experiments used mouse lung and ileum tissue membranes and antagonist potency was measured in the isolated ileum contractility assay.

KEY RESULTS

Two BK binding sites resulted from saturation and homologous competition experiments. A role for the B1 receptor was excluded because of the poor affinity of B1 receptor ligands (pIC50<5). MEN16132, and the other reference antagonists, inhibited only one portion of BK specific binding, and the rank order of potency was (pIC50): Icatibant (lung 10.7; ileum 10.2)=MEN11270 (lung 10.4; ileum 9.9)=MEN16132 (lung 10.5; ileum 9.9).>LF16-0687 (lung 8.9; ileum 8.8)>FR173657 (lung 8.6; ileum 8.2). BK homologous curves performed with lung membranes after treatment with the antagonist MEN16132 or Icatibant (10 nM) displayed only the low affinity site. The functional antagonism by MEN16132 (pA2 9.4) and Icatibant (pA2 9.1), towards BK (control EC50 6.1 nM) induced ileum contractions, was concentration-dependent and surmountable, but the Schild plot slope was less than unity.

CONCLUSIONS AND IMPLICATIONS

In mouse tissue, radiolabelled BK recognizes two binding sites and B2 receptor antagonists can compete only for the higher affinity one. The pharmacological profile of the novel non-peptide antagonist MEN16132 indicates that it exhibits subnanomolar affinity and potency for the mouse B2 receptor and is suitable for further characterization in in vivo pathophysiological models.

Role of bradykinin B2 receptors in the modulation of the peristaltic reflex of the guinea pig isolated ileum

Bradykinin is well known to have a biphasic action to contract and relax gastrointestinal tissue. However, no studies have investigated the potential action of bradykinin to affect the peristaltic reflex. In the present study, serosally applied bradykinin (1-1000 nM) and the bradykinin B2 receptor agonist, kallidin (1-1000 nM), had inhibitory actions and increased the pressure threshold for peristalsis (maximum changes seen at 1000 nM were approximately 60 Pa), as did morphine (IC50=22.3+/-4.8 nM; maximum increase in the pressure threshold was approximately 130 Pa). Conversely, the B1 kinin receptor agonist, [des-Arg9]-bradykinin (1-1000 nM), had no effect (P>0.05). Two potent B2 receptor antagonists, FR173657 (1 and 100 nM) and icatibant (10 nM), significantly antagonized the inhibitory action of serosally applied bradykinin on peristalsis (P<0.01), whilst the B1 receptor antagonist, Lys-[des-Arg9, Leu8]-bradykinin (100 nM) was inactive (P>0.05). In comparison, 5-hydroxytryptamine (1-1000 nM) facilitated peristalsis (EC50=37.7+/-23.0 nM; maximum reduction of the pressure threshold for peristalsis was approximately 76 Pa), as did FR173657 at 100 nM (reducing the pressure threshold for peristalsis by approximately 15 Pa; P<0.05) but icatibant at 10 nM was inactive (P>0.05). The results indicate that bradykinin B2 receptors mediate an inhibition of peristalsis in the guinea pig isolated ileum.

MEN16132, a novel potent and selective nonpeptide antagonist for the human bradykinin B2 receptor. In vitro pharmacology and molecular characterization

The pharmacological characterization of the novel nonpeptide antagonist for the B2 receptor, namely MEN16132 (4-(S)-Amino-5-(4-{4-[2,4-dichloro-3-(2,4-dimethyl-8-quinolyloxymethyl)phenylsulfonamido]-tetrahydro-2H-4-pyranylcarbonyl}piperazino)-5-oxopentyl](trimethyl)ammonium chloride hydrochloride) is presented. The affinity of MEN16132 for the bradykinin B2 receptor has been investigated by means of competition studies at [3H]bradykinin binding to membranes prepared from Chinese Hamster Ovary (CHO) cells expressing the human bradykinin B2 receptor (pKi 10.5), human lung fibroblasts (pKi 10.5), guinea pig airways (pKi 10.0), guinea pig ileum longitudinal smooth muscle (pKi 10.2), or guinea pig cultured colonic myocytes (pKi 10.3). In all assays MEN16132 was as potent as the peptide antagonist Icatibant, and from 3- to 100-fold more potent than the reference nonpeptide antagonists FR173657 or LF16-0687. The selectivity for the bradykinin B2 receptor was checked at the human bradykinin B1 receptor (pKi<5), and at a panel of 26 different receptors and channels. The antagonist potency was measured in functional assays, i.e., in blocking the bradykinin induced inositolphosphates (IP) accumulation at the human (CHO: pKB 10.3) and guinea pig (colonic myocytes: pKB 10.3) B2 receptor, or in antagonizing the bradykinin induced contractile responses in human (detrusor smooth muscle: pKB 9.9) and guinea pig (ileum longitudinal smooth muscle: pKB 10.1) tissues. In both functional assay types MEN16132 exerted a different antagonist pattern, i.e., surmountable at the human and insurmountable at the guinea pig bradykinin B2 receptors. Moreover, the receptor determinants important for the high affinity interaction of MEN16132 with the human bradykinin B2 receptor were investigated by means of radioligand binding studies performed at 24 point-mutated receptors. The results obtained revealed that residues in transmembrane segment 2 (W86A), 3 (I110A), 6 (W256A), and 7 (Y295A, Y295F but not much Y295W), were crucial for the high affinity of MEN16132. In conclusion, MEN16132 is a new, potent, and selective nonpeptide bradykinin B2 receptor antagonist.

Antagonistic effects of novel non-peptide chlorobenzhydryl piperazine compounds on contractile response to bradykinin in the guinea-pig ileum

Two novel compounds, N-phenylacetyl-N'-(4-methoxybenzyl)-N''-1-(4-chlorobenzhydryl)piperazine iminodiacetic acid triamide (compound I) and N-phenylacetyl-N'-(4-methylbenzyl)-N''-1-(4-chlorobenzhydryl)piperazine iminodiacetic acid triamide (compound II), designed and synthesized as novel non-peptide bradykinin B2 receptor antagonists, were studied for their functional activities in isolated guinea-pig ileum smooth muscle. These compounds were compared with the conventional peptide bradykinin B2 receptor antagonist, icatibant (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-dTic-Oic-Arg-OH) for their in vitro functional activities. Compounds I and II showed highly potent, time-dependent insurmountable antagonism against contractile responses to bradykinin (pKB 8.80 and 8.57, respectively) with progressive reduction of maximum effect maintaining the concentration producing half maximal-response unchanged. Otherwise, icatibant, known as a non-competitive antagonist, showed a rightward displacement of cumulative concentration-response curves to bradykinin with decrease of its maximum effect (pKB 8.73). The IC50 values of compounds I and II were 3.56 x 10(-8) and 6.30 x 10(-8) M, respectively, while that of icatibant was 5.02 x 10(-8) M. The profile of action of compounds I and II varied when contact time was prolonged from 5 to 60 min, whereas that of icatibant did not. The inhibitory effects of the newly synthesized compounds and icatibant on the contractile response to bradykinin were differently reverted by washout (icatibant < 100 min, compounds I and II > 100 min). This class of compounds containing the chlorobenzhydryl piperazine moiety is expected to be a novel non-peptide bradykinin B2 receptor antagonists.

Tachykinins and kinins in airway allergy

Using models of airway diseases, our understanding of the role of tachykinins and kinins in airway pathophysiology has been greatly enhanced by the recent development of a large series of peptide, peptoid and non-peptide antagonists for tachykinin and kinin receptors. This article reviews the experimental findings of the contribution of kinins and tachykinins and their respective receptors, in models of airway inflammation in response to agents known to trigger or worsen asthma attacks, such as antigen and cold air. Some new antagonists, mostly of a non-peptide nature, exhibit excellent pharmacodynamic and pharmacokinetic profiles; a brief account of early clinical studies in which they have been used is also given.

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.

Bradykinin B2 receptor antagonist FR173657 ameliorates small bowel ischemia-reperfusion injury in dogs

Bradykinin mediates acute inflammation by increasing microvascular permeability, vasodilation, leukocyte migration and accumulation, and the production of arachidonic acid via phospholipase A2 activation. Arachidonic acid metabolites, or eicosanoids, are potent modulators of biological functions, particularly inflammation. Bradykinin exerts its inflammatory effects via the bradykinin B2 receptor. The aim of this study was to evaluate the effect of a bradykinin B2 receptor antagonist, FR173657 (FR), on intestinal ischemia-reperfusion (I/R) injury. Twenty-eight mongrel dogs were divided into four groups (n = 7 per group). Group I underwent I/R alone, Group II underwent I/R and received FR treatment, Group III was sham operated, and Group IV was sham operated and received FR treatment. The FR treatment consisted of FR continuously from 30 min prior to ischemia to 2 hr after reperfusion. In the I/R procedure, the superior mesenteric artery (SMA) and vein were clamped for 2 hr and then released to permit reperfusion for 12 hr. The intramucosal pH (pHi), SMA blood flow, and mucosal tissue blood flow were measured during the reperfusion period. The serum thromboxane B2 and 6-keto-prostaglandin F1alpha levels were determined, and tissue samples were examined histologically. Results showed that tissue blood flow, pHi, and SMA blood flow after reperfusion were maintained in Group II in comparison with Group I. Histopathological examination showed less severe mucosal damage after reperfusion in Group II than in Group I. The serum thromboxane B2 and 6-keto-prostagland in F1alpha levels were significantly lower in Group II than in Group I (P < 0.05). We conclude that FR treatment appears to have clear protective effects on small bowel I/R injury by inhibiting the release of eicosanoids.

Prostaglandin receptors EP2, EP3, and IP mediate exudate formation in carrageenin-induced mouse pleurisy

The roles of prostaglandins (PGs) as mediators of inflammation have been extensively studied, and production of PGI2 and PGE2 at inflammatory sites has been reported. However, it has not yet been clarified which type of PG receptors has a major role in inflammatory exudation. To examine in vivo role of PG receptors in inflammatory exudation, we induced pleurisy in PG receptors (IP, EP1, EP2, EP3, or EP4) knockout mice by intrapleural injection of carrageenin. Pleural exudate accumulation in wild-type (WT) mice at 1 to 5 h, but not at 24 h, was significantly attenuated by the pretreatment with indomethacin, indicating that PGs are responsible for exudate formation at the early phase of pleurisy. Pleural exudation at 1 to 5 h in IP, EP2, or EP3 knockout mice, but not in EP1 and EP4 knockout, was significantly reduced compared with in WT mice. In the exudates, 6-keto-PGF1alpha and PGE2 were detected as the major PGs, each with its peak concentration at 3 h. In addition, involvement of bradykinin in the phenomenon was suggested by the fact that captopril, a kininase inhibitor, enhanced the exudate formation and increased the amount of 6-keto-PGF1alpha and PGE2 and that a bradykinin B2-receptor antagonist inhibited the exudate formation. In contrast, leukocyte migration into pleural cavity was not influenced by indomethacin-treatment nor by these receptor deficiencies. These results demonstrate participation of EP2 and EP3 along with IP in pleural exudate formation but not in leukocyte migration in carrageenin-induced mouse pleurisy.

Perivascular nerves induce cardiorespiratory reflexes in response to algogens in anaesthetised rats

In the present study we measured cardiovascular and respiratory reflexes evoked by administration of bradykinin and capsaicin into the hindlimb vasculature of anaesthetised rats, whilst simultaneously recording activity of sensory afferents on the adventitial surface of femoral arteries and veins. Bradykinin (0.9 nmol) and capsaicin (0.3 nmol) caused a rapid reflex fall in mean arterial pressure (delta mmHg: -37 +/- 8 and -28 +/- 3, respectively; P < 0.01) and an increase in respiratory minute volume (delta ml min(-1): 180.0 +/- 39.2 and 156.1 +/- 24.5, respectively; P < 0.01), associated with an increase in neural discharge in arterial afferents (from basal 0.4 +/- 0.3 to 8.5 +/- 2.9 impulses s(-1) following intra-arterial administration of bradykinin, P < 0.05, n = 7; from basal 0.2 +/- 0.1 to 7.5 +/- 3.7 impulses s(-1) with capsaicin, P < 0.01, n = 18). The antagonists FR173657 and capsazepine confirmed bradykinin B2 and vanilloid VR1 receptors mediated the responses to bradykinin and capsaicin, respectively. Topical administration of algogen to the vessel surface, and electrical stimulation of the adventitia also evoked cardiovascular and respiratory responses. These data support the hypothesis that stimulation of sensory nerve endings within the hindlimb vasculature contributes to systemic cardiorespiratory reflexes in the rat.

Bradykinin receptor ligands: therapeutic perspectives

Kinins, which are produced by the action of kallikrein enzymes, are blood-derived local-acting peptides that have broad effects mediated by two related G-protein-coupled receptors termed the bradykinin receptors. The endogenous kallikrein-kinin system controls blood circulation and kidney function, and promotes inflammation and pain in pathological conditions, which has led to interest in developing modulators of bradykinin receptors as potential therapeutics. This review discusses recent progress in our understanding of the genetics, molecular biology and pathophysiology of kinins and their receptors, as well as developments in medicinal chemistry, which have brought us closer to therapeutic applications of kinin receptor ligands in various indications. The potential of kinin receptor antagonists as novel analgesic agents that do not result in tolerance or have a liability for abuse has attracted particular interest.

Effects of a bradykinin B(2) receptor antagonist on ischemia-reperfusion injury in a canine lung transplantation model

BACKGROUND

This study investigated the effects of a bradykinin B(2) receptor antagonist, FR173657 (FR), on ischemia-reperfusion (I/R) injury in a canine lung transplantation model.

METHODS

Eighteen pairs of weight-matched dogs were randomly divided into 3 groups. Six pairs were assigned to the FR(D+R) group, in which FR (100 nmol/kg/h) was administered to the transplant donor continuously beginning 30 minutes before ischemia until the onset of ischemia, and FR was administered to the transplant recipient beginning 30 minutes before reperfusion and continuing for 2 hours after reperfusion. Another 6 pairs of dogs were assigned to the FR(R) group, in which FR was administered only to the recipient in the same manner as in the FR(D+R) group. The other pairs were assigned to the control group, in which vehicle alone was administered. Orthotopic left lung transplantation was performed after 12-hour cold storage in Euro-Collins solution. Fifteen minutes after reperfusion, the right pulmonary artery and the right stem bronchus were ligated. The animals were measured for 4 hours after reperfusion for left pulmonary vascular resistance (L-PVR), cardiac output (CO), arterial oxygen pressure (PaO(2)) and alveolar-arterial oxygen pressure difference (A-aD(O(2))). Lung specimens were harvested for measurement of the wet-to-dry lung weight ratio (WDR), histopathologic studies and polymorphonuclear neutrophil (PMN) count.

RESULTS

Compared with the control group, PaO(2), A-aDO(2), L-PVR and CO were all significantly (p < 0.05) improved and WDR significantly (p < 0.05) lower in both the FR(D+R) and FR(R) groups. Moreover, in the FR-treated groups, histologic tissue edema was mild, and PMN infiltration was significantly (p < 0.05) reduced.

CONCLUSIONS

The bradykinin B(2) receptor antagonist, FR173657, ameliorates I/R injury in lung grafts, indicating that protection of lung grafts can be achieved by the administration of FR solely to the transplant recipient.

Host stromal bradykinin B2 receptor signaling facilitates tumor-associated angiogenesis and tumor growth

We evaluated the significance of the host kallikrein-kinin system in tumor angiogenesis and tumor growth using two rodent models genetically deficient in a kallikrein-kinin system. Inoculation of Walker 256 carcinoma cells into the s.c. tissues of the back of normal Brown Norway Kitasato rats (BN-Ki rats) resulted in the rapid development of solid tumors with marked angiogenesis. By contrast, in kininogen-deficient Brown Norway Katholiek rats (BN-Ka rats), which cannot generate intrinsic bradykinin (BK), the weights of the tumors and the extent of angiogenesis were significantly less than those in BN-Ki rats. Daily administration of B(2) receptor antagonists significantly reduced angiogenesis and tumor weights in BN-Ki rats to levels similar to those in BN-Ka rats but did not do so in BN-Ka rats. Angiogenesis and tumor growth were significantly suppressed in B(2) receptor knockout mice bearing sarcoma 180 compared with their wild-type counterparts. Immunoreactive vascular endothelial growth factor (VEGF) was localized in Walker tumor stroma more extensively in BN-Ki rats than in BN-Ka rats, although immunoreactive B(2) receptor also was detected in the stroma to the same extent in both types of rats. Cultured stromal fibroblasts isolated from BN-Ki rats and BN-Ka rats produced VEGF in response to BK (10(-8)-10(-6) m), and this stimulatory effect of BK was abolished with a B(2) receptor antagonist, Hoe140 (10(-5) m). These results suggest that BK generated from kininogens supplied from the host may facilitate tumor-associated angiogenesis and tumor growth by stimulating stromal B(2) signaling to up-regulate VEGF production mainly in fibroblasts.

The N-terminal of Icatibant and bradykinin interact with the same Asp residues in the human B2 receptor

The pharmacology of peptide and non-peptide bradykinin B2 receptor ligands was evaluated in the inositol phosphate (IP) production assay in CHO cells expressing the human bradykinin B2 receptor. The effect of single and double alanine mutation of D266 and D284 residues at the human bradykinin B2 receptor was evaluated on the agonist profile of bradykinin (H-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-OH) and the synthetic agonist FR190997 (8-[2,6-dichloro-3-[N-methylcarbamoyl)cinnamidoacetyl]-N-methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline). Bradykinin potency (EC50 0.5 nM at the wild-type receptor) was reduced by 16-fold at D266A and D284A mutants and by 2300-fold at the D266A/D284A double mutant. None of the mutants affected the potency or the efficacy of FR190997. Peptide antagonists, Icatibant (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-Dtic-Oic-Arg-OH) and MEN11270 (H-DArg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7gamma-10alpha)) (100 nM) similarly antagonized the concentration-response curve to bradykinin or FR190997 (pA2 values 8.5 and 8.4 versus bradykinin and 8.2 and 8.4 versus FR190997) at the wild-type receptor. Non-peptide antagonists FR173657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8-quinolinyl) oxymethyl]phenyl]-N-methylaminocarbonyl methyl]acrylamide) and LF16-0687 (1-[[2,4-dichloro-3-[(2,4-dimethylquinolin-8-yl)oxy] methyl]-phenyl]sulfonyl]-N-[3-[[4-(aminoiminomethyl)-phenyl]carbonylamino]propyl]-(S)-pyrrolidine carboxamide) (100 nM) showed an equivalent potency values in blocking the IP production induced by bradykinin or FR190997 (pA2 values 8.7 and 8.8 versus bradykinin and 8.8 and 8.6 versus FR190997). Whilst the antagonist potency of FR173657 and LF16-0687 was not affected by D266A/D284A double mutation (IP production induced by the synthetic agonist), that of Icatibant and MEN11270 was reduced by 50- and 200-fold. The antagonist potency of [Ala1]-Icatibant and [Ala2]-Icatibant (pA2 values at wild-type 7.7 and 6.4) was significantly less reduced (20-fold and 13-fold, respectively) by the D266A/D284A double mutation. Our results highlight a crucial role for two aspartic residues, D266 and D284, located at the top of transmembrane segments 6 and 7, in the high-affinity interaction of peptide antagonists with the human bradykinin B2 receptor. An interaction of these receptor residues with the N-terminal basic residues of Icatibant is hypothesized.

Site-directed mutagenesis at the human B2 receptor and molecular modelling to define the pharmacophore of non-peptide bradykinin receptor antagonists

Combining site-directed mutagenesis with information obtained from molecular modelling of the bradykinin (BK) human B2 receptor (hB2R) as derived from the bovine rhodopsin crystal structure [Science 289 (2000) 739], we previously defined a putative binding mode for the non-peptide B2 receptor antagonists, FR173657 and LF16-0687 [Can J Physiol Pharmacol 80 (2002) 303]. The present work is aimed to define the specific role of the quinoline moiety in the pharmacophore of these non-peptide antagonists. The effect of the mutations I110A, L114A (TM, transmembrane 3), W256A (TM6), F292A, Y295A and Y295F (TM7) was evaluated. None of the mutations affected the binding interaction of peptide ligands: the agonist BK and the peptide antagonist MEN 11270. The affinities in competing for [3H]-BK binding and in blocking the BK-induced IP production by the non-peptide antagonists LF16-0687 and FR173657 at the wild type and mutant receptors were analysed. While the affinities of LF16-0687 and FR173657 were crucially decreased at the I110A, Y295A, and Y295F mutants, the W256A mutation affected the affinity of the LF16-0687 only. The important contribution of the quinoline moiety was shown by the inability of an analogue of LF16-0687, lacking this moiety, to affect BK binding at the wild type receptor. On the other hand, the benzamidine group did not interact with mutated residues, since LF16-0687 analogues without this group or with an oxidated benzamidine displayed pairwise loss of affinity on wild type and mutated receptors. Further differences between FR173657 and LF16-0687 were highlighted at the I110 and Y295 mutants when comparing binding (pK(i)) and functional antagonist (pKB) affinity. First, the I110A mutation similarly impaired their binding affinity (250-fold), but at a less extent the antagonist potency of FR173657 only. Second, both the hydroxyl and the phenyl moieties of the Y295 residue had a specific role in the LF16-0687 interaction with the receptor, as demonstrated at the Y295F and Y295A mutants, respectively, but not in that of FR173657. Present data identify a receptor binding pocket comprised among TM3, 6, and 7, which concerns the interaction of the non-peptide antagonists FR173657 and LF16-0687, but not that of the peptide agonist or antagonist. Results indicate the quinoline group as the involved pharmacophoric element, and that the studied residues are differently involved in the interaction. The analysis performed by means of the GRID software led us to propose different spatial orientations of the quinoline moieties and partially overlapping binding pockets for the two ligands: that of LF16-0687 is located in the lipophilic environment amongst I110 (TM3), W256 (TM6), and Y295 (TM7) residues, whereas that of FR173657 lies essentially between I110 and Y295.

Role of the bradykinin B2 receptor for the local and systemic inflammatory response that follows severe reperfusion injury

1. Bradykinin (BK) appears to play an important role in the development and maintenance of inflammation. Here, we assessed the role of the BK B(2) receptor for the injuries that occur after ischemia and reperfusion (I/R) of the territory irrigated by the superior mesenteric artery. 2. Tissue (lung and duodenum) kallikrein activity increased after ischemia with greater enhancement after reperfusion. A selective inhibitor of tissue kallikrein, Phenylacetyl-Phe-Ser-Arg-N-(2,3-dinitrophenyl)-ethylenediamine (TKI, 0.001-10 mg ml(-1)), inhibited kallikrein activity in a concentration-dependent manner in vitro. In vivo, pretreatment with TKI (30 mg kg(-1)) prevented the extravasation of plasma and the recruitment of neutrophils. 3. Similarly, the bradykinin B(2) receptor antagonists, HOE 140 (0.01-1.0 mg kg(-1)) or FR173657 (10.0 mg kg(-1)), inhibited reperfusion-induced increases in vascular permeability and the recruitment of neutrophils in the intestine and lungs. 4. In a model of more severe I/R injury, HOE 140 (1.0 mg kg(-1)) inhibited the increase in vascular permeability, neutrophil recruitment, haemorrhage and tissue pathology. Furthermore, HOE 140 significantly inhibited the elevations of TNF-alpha in tissue and serum and partially prevented lethality. This was associated with an increase in the concentrations of IL-10 in tissue and serum. 5. Thus, our results demonstrate that, following intestinal I/R injury, there is an increase in tissue kallikrein activity and activation of BK B(2) receptors. B(2) receptor activation is essential for the development of inflammatory tissue injury and lethality. These results contrast with those of others showing that BK mostly exerts a protective role during I/R injury.

Effect of FK3657, a non-peptide bradykinin B2 receptor antagonist, on allergic airway disease models

Bradykinin has been suggested to be involved in allergic diseases. In this study, we tested the effect of FK3657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8-quinolinyl)-oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide), an orally active non-peptide bradykinin B(2) receptor antagonist, on allergic airway disease models in guinea pigs. FK3657 given orally inhibited bradykinin-induced or dextran sulfate (an activator of kinin-kallikrein cascade)-induced bronchoconstriction and plasma extravasation in the lower airways (trachea and main bronchi) and nasal mucosa of guinea pigs with ED(50) of 0.04-0.23 mg/kg. In the antigen-induced dual asthmatic response model of guinea pigs, FK3657 significantly attenuated the late phase asthmatic response, but not the immediate asthmatic response. FK3657 also significantly inhibited the 2,4-tolylene diisocyanate (TDI)-induced plasma extravasation in nasal mucosa of TDI-sensitized guinea pigs. These results suggest that oral FK3657 may be useful for asthma or allergic rhinitis as a therapeutic drug.

Topical and peripherally acting analgesics

Acute nociceptive, inflammatory, and neuropathic pain all depend to some degree on the peripheral activation of primary sensory afferent neurons. The localized peripheral administration of drugs, such as by topical application, can potentially optimize drug concentrations at the site of origin of the pain, while leading to lower systemic levels and fewer adverse systemic effects, fewer drug interactions, and no need to titrate doses into a therapeutic range compared with systemic administration. Primary sensory afferent neurons can be activated by a range of inflammatory mediators such as prostanoids, bradykinin, ATP, histamine, and serotonin, and inhibiting their actions represents a strategy for the development of analgesics. Peripheral nerve endings also express a variety of inhibitory neuroreceptors such as opioid, alpha-adrenergic, cholinergic, adenosine and cannabinoid receptors, and agonists for these receptors also represent viable targets for drug development. At present, topical and other forms of peripheral administration of nonsteroidal anti-inflammatory drugs, opioids, capsaicin, local anesthetics, and alpha-adrenoceptor agonists are being used in a variety of clinical states. There also are some clinical data on the use of topical antidepressants and glutamate receptor antagonists. There are preclinical data supporting the potential for development of local formulations of adenosine agonists, cannabinoid agonists, cholinergic ligands, cytokine antagonists, bradykinin antagonists, ATP antagonists, biogenic amine antagonists, neuropeptide antagonists, and agents that alter the availability of nerve growth factor. Given that activation of sensory neurons involves multiple mediators, combinations of agents targeting different mechanisms may be particularly useful. Topical analgesics represent a promising area for future drug development.

Role of kinin and prostaglandin in cutaneous thermal nociception

Involvements of kinin and prostaglandin and their interaction in noxious thermal stimuli were investigated in noninflamed and inflamed rats. The nociceptive response was evaluated from the escape latency of foot withdrawal to the thermal stimuli with a beam of light. The escape latency in kininogens-deficient Brown Norway (B/N-) Katholiek rats was significantly longer than that in the normal strain, B/N-Kitasato rats. The latency in B/N-Kitasato rat was prolonged by administration of a bradykinin (BK) B2 receptor antagonist, FR173657 (30 mg/kg, p.o.), whereas it was shortened by pretreatment with a kininase II inhibitor, captopril (10 mg/kg, i.p.). Both agents did not affect the latency in B/N-Katholiek rats. In normal Sprague-Dawley (SD) rat, administration of indomethacin did not change the escape latency against the thermal stimuli. In contrast, administration of indomethacin or a relatively cyclooxygenase-1-selective inhibitor, mofezolac (10 mg/kg, p.o.) significantly reduced numbers of writhing reaction in mice induced by acetic acid solution. Injection of lipopolysaccharide (1 mg/kg, i.v.) resulted in shortening escape latency at 8 h after the injection in B/N-Kitasato rats. This hyperalgesia could be reversed by pretreatment of the rats with indomethacin, a cyclooxygenase-2-selective inhibitor JTE-522 (10 mg/kg, p.o.), or FR173657, but not with mofezolac. The hyperalgesia was not seen in B/N-Katholiek rats. These results indicate that kinin has major participation in peripheral skin thermal nociception under noninflamed condition, although cyclooxygenases may have little participation. Prostaglandins produced by cyclooxygenase-2 could coordinate with BK to elicit hyperalgesia during inflammation induced by lipopolysaccharide.

Effects of a bradykinin B(2) receptor antagonist, FR173657, on pulmonary ischemia-reperfusion injury in dogs

BACKGROUND

This study investigated the effects of a bradykinin B(2) receptor antagonist, FR173657 (FR), on pulmonary ischemia-reperfusion (I/R) injury.

METHODS

Twenty-four mongrel dogs were divided into four groups (n = 6 each). In Groups I, II and III, FR doses of 33, 100 and 300 nmol/kg per hour, respectively, were administered continuously beginning 30 minutes before ischemia and continuing for 2 hours after reperfusion. In Group IV, vehicle alone was administered. Warm ischemia was induced for 3 hours by clamping the left pulmonary artery and veins. Simultaneously, the left stem bronchus was bisected and then anastomosed before reperfusion. Fifteen minutes after reperfusion, the right pulmonary artery and bronchus were ligated. Left pulmonary vascular resistance (L-PVR), cardiac output (CO), arterial oxygen pressure (PaO(2)) and the alveolar - arterial oxygen pressure difference (A-aDO2) were measured for 4 hours after reperfusion. Lung tissue was harvested for wet-to-dry weight ratio (WDR) measurements, histopathologic studies and polymorphonuclear neutrophil (PMN) counts. Serum thromboxane (TX) B(2), 6-keto-prostaglandin (PG) F(1alpha) and leukotriene (LT) B(4) levels were also measured.

RESULTS

PaO(2), A-aDO2, L-PVR and CO were significantly (p < 0.05) improved and WDR was significantly (p < 0.05) lower in Groups II and III than in Group IV. Histologic tissue edema was mild, and PMN infiltration was significantly (p < 0.05) reduced in Groups I, II and III compared with Group IV. TXB(2) levels were significantly (p < 0.05) lower in Group II than in Group IV, whereas 6-keto-PGF(1alpha) levels were not significantly different. LTB(4) levels were significantly (p < 0.05) lower in Groups II and III than in Group IV.

CONCLUSIONS

FR appears to have a protective effect on pulmonary I/R injury stemming from the inhibition of eicosanoid release.

Suppression of dextran sulfate sodium-induced colitis in kininogen-deficient rats and non-peptide B2 receptor antagonist-treated rats

Various proinflammatory mediators are believed to be involved in the processes and symptoms of ulcerative colitis (UC). To determine whether endogenous kinin enhances the severity of UC, we induced experimental colitis (EC) in kininogen-deficient mutant rats and tested the effect of a non-peptide B2 receptor antagonist. EC was induced in male kininogen-deficient Brown Norway-Katholiek rats (BN-Ka) and normal Brown Norway-Kitasato rats (BN-Ki) with 5% dextran sulfate sodium (DSS). Sprague-Dawley rats (SD) were also used. Colon length, body weight and hematocrit were determined for 7 days. Effects of FR173657, an orally active B2 antagonist, were tested. The colon length was shortened in BN-Ki with DSS treatment, but not in BN-Ka, and the difference between their lengths was significant. The hematocrit value was also reduced in BN-Ki, and the difference in hematocrit between BN-Ki and BN-Ka was significant. In SD, shortening of the colon and reduction in hematocrit were also observable, and both were blunted by FR173657. The survival rate in SD given DSS for 7 days was 68%, but FR173657 treatment restored it significantly to 100%. These results suggest that the endogenous kinins generated from the kallikrein-kinin system have a significant role in the development of EC.

The pharmacology of T-kinin and des-Arg(11)-T-kinin in primary cultures of rat bladder smooth muscle cells

T-kinin and its putative carboxypeptidase product des-Arg(11)-T-kinin are members of the kinin family that are unique to the rat. Primary cultures of rat bladder smooth muscle cells were used to investigate the pharmacology of these peptides. Calcium imaging experiments showed that rat bladder smooth muscle cells responded to both bradykinin and des-Arg(9)-bradykinin with an increase in [Ca(2+)](i) and responses to both agonists could be observed in the same cell. A more detailed pharmacological characterisation with a range of bradykinin receptor agonists and antagonists using 45Ca(2+) efflux confirmed the presence of both B(1) and B(2) bradykinin receptors. Using this cellular model, we confirm that T-kinin is a bradykinin B(2) receptor agonist and show for the first time that des-Arg(11)-T-kinin is a potent and selective bradykinin B(1) receptor agonist. In addition, using cells expressing the cloned rat and human bradykinin B(2) receptors plus the Ca(2+)-sensitive protein aequorin, T-kinin was shown to be selective for the rat over the human bradykinin B(2) receptor.

Beneficial effects of combined blockade of ACE and AT1 receptor on intimal hyperplasia in balloon-injured rat artery

OBJECTIVE

The present study was undertaken to elucidate the effect of the ACE inhibitor and the angiotensin II type 1 (AT1) receptor antagonist in combination on neointimal hyperplasia after balloon injury.

METHODS AND RESULTS

Temocapril (an ACE inhibitor), CS-866 (an AT1 receptor antagonist), or their combination was given orally to rats, and their effects were compared on vascular hyperplasia induced by balloon injury. The maximal preventive effect of temocapril and CS-866 alone on neointimal thickening after balloon injury was obtained at a dose of 20 and 10 mg/kg per day, respectively. However, compared with either agent alone, combined temocapril and CS-866 (20 and 10 mg/kg per day, respectively) prevented intimal thickening to a larger extent. Furthermore, compared with either agent alone, combined temocapril and CS-866 prevented vascular smooth muscle cell proliferation in the intima more potently. The increase in platelet-derived growth factor receptor tyrosyl phosphorylation was reduced more potently by the combination of both agents compared with either agent alone. The nonpeptide bradykinin B2 receptor antagonist or the NO synthase inhibitor reduced the prevention of intimal thickening by combined temocapril and CS-866.

CONCLUSIONS

Compared with either agent alone, the combination of an ACE inhibitor and an AT1 receptor antagonist is more effective in the prevention of vascular hyperplasia due to bradykinin or NO.

Suppressed angiogenesis in kininogen-deficiencies

We investigated whether the kinin-generating system enhanced angiogenesis in chronic and proliferative granuloma and in tumor-surrounding stroma. In rat sponge implants, angiogenesis was gradually developed in normal Brown Norway Kitasato rats (BN-Ki). The development of angiogenesis was significantly suppressed in kininogen-deficient Brown Norway Katholiek rats (BN-Ka). The angiogenesis enhanced by basic fibroblast growth factor was also significantly less marked in BN-Ka than in BN-Ki. Naturally occurring angiogenesis was significantly suppressed by B(1) or B(2) antagonist. mRNA of vascular endothelial growth factor was more highly expressed in the granulation tissues in BN-Ki than in BN-Ka. Daily topical injections of aprotinin, but not of soy bean trypsin inhibitor, suppressed angiogenesis. Daily topical injections of low-molecular weight kininogen enhanced angiogenesis in BN-Ka. Topical injections of serum from BN-Ki, but not from BN-Ka, also facilitated angiogenesis in BN-Ka. FR190997, a nonpeptide mimic of bradykinin, promoted angiogenesis markedly, with concomitant increases in vascular endothelial growth factor mRNA. Angiogenesis in the granulation tissues around the implanted Millipore chambers containing Walker-256 cells was markedly more suppressed in BN-Ka than in BN-Ki. Our results suggest that endogenous kinin generated from the tissue kallikrein-kinin system enhances angiogenesis in chronic and proliferative granuloma and in the stroma surrounding a tumor. Thus, the agents for the kinin-generating system and/or kinin receptor signaling may become useful tools for controlling angiogenesis.

Release of a new vascular permeability enhancing peptide from kininogens by human neutrophil elastase

Stimulated neutrophils produced vascular permeability enhancing (VPE) activity in the presence of high molecular weight kininogen (HMWK), which was inhibited mainly by a neutrophil elastase (NE) inhibitor or a bradykinin (BK) B(2)-receptor antagonist. NE (>3 nM) generated VPE activity from kininogens at normal plasma concentrations with the smaller protein being several fold more responsive than the larger protein, through releasing a new VPE peptide (E-kinin), SLMKRPPGFSPFRSSRI. Synthetic E-kinin, SLMKRPPGFSPFRSS and SLMKRPPGFSPFR had VPE and blood pressure lowering activities, which were comparable to the activities of BK and completely inhibited by B(2)-receptor antagonists. Interestingly, E-kinin and SLMKRPPGFSPFRSS did not induce smooth muscle contraction. These results suggest that E-kinin formed in vivo may be processed at the carboxy-terminus to give a peptide that can bind to the B(2)-receptor. The molecular mechanism for neutrophil-associated VPE may be explained by excision of E-kinin from kininogens by NE, followed by further processing of the peptide.

AT(2) receptor-dependent vasodilation is mediated by activation of vascular kinin generation under flow conditions

Physiological roles of angiotensin II type 2 receptor (AT(2)) are not well defined. This study was designed to investigate the mechanisms of AT(2)-dependent vascular relaxation by studying vasodilation in pressurized and perfused rat mesenteric arterial segments. Perfusion of angiotensin II in the presence of AT(1) antagonist elicited vascular relaxation, which was completely dependent on AT(2) receptors on endothelium. FR173657 (>1 microM), a bradykinin (BK) B(2)-specific antagonist, significantly suppressed AT(2)-dependent vasodilation (maximum inhibition: 68.5% at 10 microM). Kininogen-deficient Brown Norway Katholiek rats showed a significant reduction in AT(2)-mediated vasodilatory response compared with normal wild-type Brown Norway rats. Indomethacin (>1 microM), aprotinin (10 microM) and soybean trypsin inhibitor (10 microM) also reduced AT(2)-dependent vasodilation. Our results demonstrated that stimulation of AT(2) receptors caused a significant vasodilation through local production of BK in resistant arteries of rat mesentery in a flow-dependent manner. Such vasodilation counterbalances AT(1)-dependent vasoconstriction to regulate the vascular tone.

Preliminary mutational analysis of the human kinin B2 receptor for nonpeptide antagonist ligands recognition

FR173657, LF16,0335, and LF16,0687 are nonpeptide antagonists, endowed with high affinity and selectivity for the human kinin B2 receptor. The kinin B2 receptor belongs to the family of G-protein-coupled receptors with seven transmembrane (TM) helices. In the present study, we aimed, through computer-assisted modeling and mutagenesis, to identify residues in the human B2 receptor (hB2R) amino acid sequence that are involved in nonpeptide antagonist binding in order to build up experimental data as a first step towards a molecular model of nonpeptide ligands binding site. Fourteen amino acid residues within the TM segments were mutated to alanine. The wild type and mutant receptors were stably expressed in Chinese hamster ovary (dhfr-) cells and tested for their ability to bind agonist ([3H]bradykinin) and peptide antagonist ([3H]MENI 1270) radioligands. The affinity of nonpeptide ligands was determined by heterologous competition experiments using the above radioligands. We found that some mutations in TM2 (W86A) and TM7 (Y295A, N297A) impair the binding affinity of the three nonpeptide antagonists. On the other hand, some mutated residues in TM3 (S1 17A) and TM6 (W256A) reduce the affinity of LF16,0335 and LF16,0687 only. Results are discussed in order to build up a hypothesis for the likely different interactions of various nonpeptide ligands with the B2 receptor.

Pharmacological characterisation of novel kinin B2 receptor ligands

Peptide and nonpeptide compounds have been shown to interact specifically with B2 receptors of three different species, namely human, rabbit, and pig. Peptide agonists and nonpeptide antagonists show marked differences in potencies and suggest the existence of B2 receptor subtypes. This conclusion is based on data obtained with the modified agonist peptide LF 150943 whose potency (pEC50 9.4) is at least 100-fold higher in rabbit than in humans (7.4) and pig (6.7). The same conclusion can be drawn from data obtained with antagonists that are more potent in humans (LF 160687, pA2 9.2) than in rabbit (8.7) and pig (8.2) or with antagonists (S 1567) that show the opposite potency order, being much weaker in humans (pA2 6.9) than in rabbit (7.6) and pig (9.4). Two other compounds (FR 173657 and FR 172357) show similar pharmacological spectra as S 1567 and differ from LF 160687.

In vitro and in vivo activity of analogues of the kinin B2 receptor antagonist MEN1 1270

In this study, we describe the in vitro and in vivo activities of a series of cyclic peptide analogues of the selective kinin B2 receptor antagonist MEN11270 on Chinese hamster ovary cells expressing the human B2 receptor (hB2R), the human isolated umbilical vein (hUV), the isolated guinea pig ileum (gpI), and bradykinin (BK) induced bronchoconstriction (BC) and hypotension in anaesthetized guinea pigs. Substitutions in the backbone of MEN1 1270 (H-DArg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7gamma-10alpha)) aimed to increase the potency in inhibiting bronchospasm versus hypotension following the topical (intratracheal (i.t.)) or systemic (intravenous (i.v.)) application of these antagonists. A series of analogues were left unprotected from N-terminal cleavage by aminopeptidases (MEN12739, MEN13052, MEN13346, and MEN13371): these compounds maintained sizeable affinities for the hB2R (pKi = 9.4, 9.6, 9.7, and 8.6, respectively) and antagonist activities toward BK in the hUV (pA2 = 7.9, 8.3, 8.2, and 7.5) and gpI assays (pK(B) = 7.4, 7.8, 7.9, and 7.9), but the inhibition of BK-induced BC and hypotension in vivo was negligible following either i.v. or i.t. administration. Two analogues (MEN12388 and MEN13405) could be potential substrates of angiotensin-converting enzyme: these have good activity in the hB2R (pKi = 9.5 and 8.9, respectively), hUV (pA2 = 8.2 for MEN12388), and gpI assays (pK(B) = 8.4 and 8.0) but an in vivo activity 10- to 30-fold lower than the parent compound MEN1 1270 (pKi = 9.4, pA2 = 8.1, pKB = 8.3) when given by either the i.v. or the i.t. route. Other analogues were functionalized with a quaternary ammonium Lys derivative (MEN13031, MEN12374, and the previously mentioned MEN13052) or with an ethyl group on Arg (MEN13655 and the previously mentioned MEN13346 and MEN13405) in order to hinder or facilitate local absorption. MEN13346 and MEN13031 (pKi = 9.7and 9.5, pA2 = 8.2 and 7.9, pKB = 7.9 and 8.5, respectively) were 10- to 30-fold less active in vivo than MEN1 1270, without improving the discrimination between BK-induced BC and hypotension after either systemic or topical administration. It is concluded that the decreased in vivo activities of cyclic analogues of MEN11270 on BK-induced BC and hypotension following either their intratracheal or their intravenous routes of administration might be due in large part to metabolic degradation.

Roles of bradykinin in vascular permeability and angiogenesis in solid tumor

Bradykinin (BK) is involved in tumor angiogenesis. To elucidate the mechanism underlying BK-induced angiogenesis, we evaluated the roles of BK in tumor-associated vascular permeability and angiogenesis in the different phases of tumor development in mice bearing sarcoma 180 cells. The vascular permeability was significantly enhanced in the early growth phase (which peaked at day 5), and was thereafter markedly reduced. By contrast, tumor angiogenesis increased gradually over a 20-day experimental period. Oral administration of a B2 receptor antagonist, FR173657 (30 mg/kg/day), significantly suppressed the vascular permeability, but a B1 antagonist, desArg10-Hoe140 (1 mg/kg/day) did not. An immunohistochemical study revealed the presence of immunoreactive B2 receptor in the endothelial cells in the early phase, whereas B2 receptors were also observed in the stromal fibroblasts in the late phase. We also found that VEGF was detected exclusively in the stromal fibroblasts only in the late phase. Furthermore, VEGF immunoreactivity was attenuated by the treatment with FR173657. Tumor angiogenesis was significantly reduced by treating the tumor tissues with FR173657 both in the early phase (days 1-6, 30 mg/kg/day, oral administration) and in the late phase (days 7-12, 30 mg/kg/day, oral administration), whereas it was inhibited by neutralization with anti-VEGF antibody (1 microg/site/day, local injection) only in the late phase. These results suggest that BK would promote angiogenesis by increasing vascular permeability in the early phase via B2 receptor in the endothelial cells and by promoting up-regulation of VEGF via B2 receptor in the stromal fibroblasts in the late phase.

Pharmacological and functional characterization of the guinea-pig B2 bradykinin receptor stably expressed in CHO-K1 cell line

In the present study, pharmacological properties of a bradykinin B(2) receptor amplified either from guinea-pig ileum or lung and homologous to the previously reported sequence except two amino-acid changes L(124)-->P and N(227)-->Y in the receptor protein were characterized. Tritiated bradykinin ([(3)H]-BK) specifically bound to the cloned guinea-pig B(2) bradykinin receptor stably expressed in Chinese hamster ovary cells (CHO-K1) with a K(D) value of 0.29+/-0.07 nM. In competition experiments, bradykinin (BK) affinity constant value was 0.21+/-0.05 nM while the two specific kinin B(1) ligands, des-Arg(9)-bradykinin (DBK) and des-Arg(9)-Leu(8)-bradykinin (DLBK) were unable to compete with [(3)H]-BK. As the specific peptide antagonist D-Arg-[Hyp(3),Thi(5),D-Tic(7),Oic(8)]-bradykinin (HOE140), (E)-3-(6-acetamido-3-pyridil)-N-[-N-[2,4-dichloro-3-[(2-methyl-8-quinolinyl)oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide (FR173657) and 1-[[3-[2,4-dimethylquinolin-8-yl)oxymethyl] - 2,4 - dichloro - phenyl]sulfonyl] - 2(S) - [[4-[4-(aminoiminomethyl)-phenylcarbonyl]piperazin-1-yl]carbonyl]pyrrolidine (LF16-0335C) exhibited a high affinity for this receptor with K(i) values of 7.34+/-2.45 nM and 8.54+/-1.55 nM respectively. BK and kallidin (KD) increased inositol phosphates (IPs) levels with EC(50) values of 0.44+/-0.12 nM and 6.88+/-0.28 nM, respectively. Neither DLBK nor DBK (0.01 nM to 10 microM) stimulated or inhibited IPs turnover and as expected HOE140 did not raise IPs production. HOE140 (0.1 microM) and LF 16-0335c (1 microM) right shifted the BK response curve with pK(B) values of 9.2+/-0.4 and 8.4+/-0.3, respectively. The results indicate that this cloned guinea-pig receptor displayed typical pharmacological properties of a bradykinin B(2) receptor and support the existence of a single B(2) receptor in this species.

[Bradykinin antagonist: current status and perspective]

The kallikrein-kinin system plays an important role in many physiological and pathophysiological conditions such as homeostasis of circulation, inflammation/allergy, pain, shock, etc. Two types of kinin receptor are known, bradykinin (BK) B1 receptor and BK B2 receptor. B2 receptors are constitutively expressed and mediate most physiological actions of kinins, whereas B1 receptors are highly inducible upon inflammatory stimulation or tissue injury, suggesting that they are involved in inflammation and/or nociception. Only three peptide type B2 antagonists, NPC 567, CP-0127 and HOE-140, have been evaluated in clinical studies so far, and some beneficial effects of B2 antagonists have been shown for rhinitis, asthma, systemic inflammatory response syndrome/sepsis and brain injury. However, the results were less convincing than expected. Now several potent and orally active nonpeptide B2-receptor antagonists have been found, which are expected to overcome the weak point of the peptide type antagonists and clarify the therapeutic potential of the B2-receptor antagonist for novel indications as well as those mentioned above. As for B1 receptors, no antagonist has been tested in a clinical trial. The important role of B1 receptors is just being elucidated by use of peptide type antagonists or B1 receptor gene knockout mice. The further development of newer B1 antagonists and clinical evaluation is desired.

Blockade of bradykinin B(2) receptor suppresses acute pancreatitis induced by obstruction of the pancreaticobiliary duct in rats

1. The involvement of bradykinin (BK) B(2) receptor in acute pancreatitis induced by pancreaticobiliary duct ligation was investigated in rats. 2. The activities of amylase and lipase in the serum, the water content of the pancreas, and vacuolization of the acinar cells were significantly increased 2 h after obstruction of the duct in Sprague-Dawley rats. 3. Elevated serum amylase activity, increased pancreatic oedema, and damage of the pancreatic tissue were significantly less marked in plasma kininogen-deficient, B/N-Katholiek rats than in the normal strain, B/N-Kitasato rats 2 h after the ligation. 4. Obstruction of the pancreaticobiliary duct augmented the level of (1-5)-BK (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)), a stable BK metabolite, in the blood from 73.0+/-21.7 pg ml(-1) at 0 h to 149.8+/-38.0 pg ml(-1) at 2 h after the induction of pancreatitis in SD rats. 5. Administration of a BK B(2) receptor antagonist, FR173657 (100 mg kg(-1), p.o.) or Hoe140 (100 nmol kg(-1), s.c.), reduced the elevation of amylase and lipase activities in the serum and of pancreatic water content in a dose-dependent manner. The effective attenuation of oedema formation and vacuolization by the antagonists was also confirmed light-microscopically. In contrast, treatment with gabexate mesilate or indomethacin did not cause significant suppression of the pancreatitis. 6. These findings suggest a possible involvement of kinin B(2) receptor in the present pancreatitis model. Furthermore, they point to the potential usefulness of the B(2) receptor in clinical acute pancreatitis.

A potential role of bradykinin in angiogenesis and growth of S-180 mouse tumors

Angiogenesis is an important event in tumor growth. We evaluated the contribution of endogenous bradykinin to tumor-associated angiogenesis and tumor growth using pharmacological approaches in mice bearing sarcoma 180 cells. The weight of implanted tumors increased in parallel with increased hemoglobin contents (a parameter to evaluate angiogenesis) over a 20-day experimental period. Daily administration of bradykinin B2-receptor antagonists, Hoe140 (0.1 and 1 mg/kg per day, local injection) or FR173657 (30 mg/kg per day, p.o.), significantly suppressed the increment in angiogenesis and tumor weight, but a B1-receptor antagonist, desArg10-Hoe140 (1 mg/kgperday), did not. Administration of a plasma kallikrein inhibitor, soybean trypsin inhibitor (3 mg/site per day), significantly suppressed angiogenesis and tumor growth. In contrast, bradykinin-degrading enzyme inhibitors, captopril and phosphoramidon (500 microg/site per day), enhanced angiogenesis and increased tumor weight. Our results suggest that bradykinin, produced by plasma kallikrein or plasma kallikrein-like enzymes, promote tumor-associated angiogenesis and tumor growth in vivo.

Proinflammatory characteristics of a nonpeptide bradykinin mimic, FR190997, in vivo

1. Proinflammatory potency of the nonpeptide bradykinin (BK) B(2) receptor agonist FR190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacetyl]-N-methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline) was investigated. 2. Intradermal injection of FR190997 (0.03 - 3 nmol site(-1)) into dorsal skin of rats increased vascular permeability in a dose-dependent manner. The effect was less than that of BK, but it was long-acting and was inhibited by treatment with FR173657 (3 mg kg(-1), p.o.). Captopril (10 mg kg(-1), i.p.) did not enhance the plasma extravasation by FR190997 (0.3 nmol site(-1)) in the presence of soybean trypsin inhibitor (SBTI, 30 microg site(-1)). 3. Subcutaneous injection of FR190997 (3 nmol site(-1)) into the hindpaw of mice markedly induced paw swelling. The oedema lasted up to 3 h after the injection. Administration of indomethacin or NS-398 (10 mg kg(-1), i.p.) significantly reduced it at 3 h after the injection. 4. Simultaneous i.p. injection of prostaglandin (PG) E(2) (1 nmol site(-1)) or beraprost sodium (0.5 nmol site(-1)) with FR190997 (5 nmol site(-1)) greatly enhanced frequency of writhing reactions in mice. 5. FR190997 (0.3 - 30 nmol kg(-1), i.v.) showed less increase in airway opening pressure (Pao) in the guinea-pig after i.v. injection. Furthermore, FR190997 (0.03 - 30 nmol) resulted in a very weak contraction of tracheal ring strips and lung parenchymal sections in vitro. 6. In mice sponge implants, topical application of FR190997 increased angiogenesis and granulation with enhanced expressions of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) mRNAs. 7. These results indicate that FR190997 has proinflammatory long-lasting characteristics and it might be 'a stable tool' for studying the role of BK B(2) receptor in vivo.

Pharmacological characterization of bradykinin B1 and B2 receptors in IMR-90 and INT-407 human cell lines using a microphysiometer

1. In the present study, we used a microphysiometer to measure bradykinin-induced acidification responses in IMR-90, a human lung fibroblast cell line, and INT-407, a human colonic epithelial cell line. Furthermore, we investigated the effect of 24 h exposure of transforming growth factor (TGF)-alpha on the bradykinin response in INT-407 cells. 2. Bradykinin (0.1-100 nmol/L) was potent in producing acidification responses in IMR-90 cells (pEC50 8.79+/-0.13; Hill slope 0.96+/-0.04) and INT-407 cells (pEC50 8.90+/-0.04; Hill slope 1.00+/-0.07). These responses were competitively antagonized by the bradykinin B2 receptor antagonist icatibant in both IMR-90 cells (apparent pKB = 8.54+/-0.15; Hill slope = 1.09+/-0.13 and 1.66+/-0.26 in the absence and presence of 10 nmol/L icatibant, respectively) and INT-407 cells (pKB = 8.12+/-0.07 (3, 10 and 30 nmol/L icatibant); Hill slope = 1.06+/-0.04). However, the bradykinin B1 receptor antagonist des-Arg9Leu8-bradykinin (3 micromol/L) had no effect on the bradykinin responses. 3. The non-peptide bradykinin B2 receptor antagonist FR173657 selectively antagonized bradykinin-induced acidification responses in INT-407 cells in a competitive manner (pKB = 8.76+/-0.10; Hill slope = 0.92+/-0.05) at lower concentrations (1 and 3 nmol/L) but in an insurmountable manner at higher concentrations (10 nmol/L; Hill slope = 1.04+/-0.09). This compound, at concentrations of 10 and 100 nmol/L (Hill slope = 1.38+/-0.15), also proved to be an insurmountable antagonist in IMR-90 cells. 4. The bradykinin B1 receptor selective agonist Lys0des-Arg10-bradykinin (0.1 nmol/L to 0.1 micromol/L) failed to produce acidification responses in IMR-90 cells, even after 24 h pre-incubation with bacterial lipopolysaccharide (0.1 microg/mL). 5. A 24 h pre-incubation of INT-407 cells with TGF-alpha (1, 10 and 100 ng/mL) caused a significant concentration-dependent decrease in maximal bradykinin response without affecting the pEC50. 6. In addition to this study being the first to use a microphysiometer to characterize bradykinin B2 receptors in cultured IMR-90 human lung fibroblast cells and INT-407 human colonic epithelial cells, we also showed that pre-incubation of INT-407 cells with TGF-alpha caused a significant decrease in maximal acidification response mediated by bradykinin B2 receptors.

Evidence for bradykinin mediation of carrageenin-induced inflammatory pain: a study using kininogen-deficient Brown Norway Katholiek rats

Inflammatory pain was induced following an intradermal injection of carrageenin into rat paws, and the hyperalgesia was measured in terms of withdrawal time following thermal pain stimulation of the inflamed paw. This hyperalgesia was significantly less in kininogen-deficient Brown Norway (B/N)-Katholiek rats, which also showed less swelling in carrageenin-induced paw edema, than in normal B/N-Kitasato rats at 1 approximately 4 hr after the carrageenin injection (at the early phase). However, 24 hr after the injection, hyperalgesia and the swelling volume of the kininogen-deficient rats were almost the same as those in normal rats. The bradykinin B2 receptor antagonist FR173657, (E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8-quinolinyl)oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide, attenuated the carrageenin-induced swelling and hyperalgesia of the normal rats at the early phase to almost the levels of the B/N-Katholiek rats. Pretreatment with indomethacin, a cyclooxygenase inhibitor, also inhibited the carrageenin-induced responses significantly in normal rats. These results indicate that bradykinin, acting on the B2 receptor, is the main mediator at the early phase of inflammatory pain of carrageenin edema and that prostaglandins, produced by cyclooxygenase, potentiate the effects of bradykinin.

[Inflammation-allergy and prostanoids. (1). Prostanoids in experimental inflammatory reaction]

It is known that prostaglandins (PGs) modify the inflammatory reaction in concert with other biologically active mediators. However, characteristics of these interactions or modulating actions have not yet been clarified well. Recently, the production of mice with specific receptor deficiencies by using the gene targeting procedure for PG receptors has accelerated elucidation of the roles of PGs through correlation of their phenotypes and experimental features. Here I discuss roles of PGs in experimental paw edema, the writhing reaction of a pain model, and regulation of cytokine production, as determined using some PG-receptor-deficient mice. From the experiment of carrageenin-induced paw edema in IP receptor-deficient mice, with an indomethacin or bradykinin antagonist, we conclude that bradykinin initially induces paw swelling and then stimulates the release PGI2, which in turn enhances the swelling with bradykinin. By comparing the writhing responses in IP-deficient and wild-type mice, we found that PGI2 is a main mediator for this pain reaction. However, in the LPS-pretreated mice, not only PGI2 but also other PGs produced by COX-2 may be involved in pain induction. Production of TNF alpha and IL-10 was modified with PGI2 or PGE2; the production of TNF alpha was down-regulated by the stimulation via IP-, EP2- or EP4 receptor, but that of IL-10 was up-regulated by these receptors, resulting in an anti-inflammatory effect.

Change in tissue kallikrein level in nasal wash after the administration of oxatomide in patients with nasal allergy

The tissue kallikrein level in the nasal wash was measured before and after 4-week administration of oxatomide (30 mg per day) in 9 patients with perennial allergy. It was found that tissue kallikrein level in the nasal wash obtained following provocation tests significantly decreased from 6.05 +/- 4.43 (10(-10) mol/hour/L) to 1.84 +/- 0.93 (10(-10) mol/hour/L) after the administration of oxatomide. Improvement in subjective symptoms was also observed in all patients after the administration. These results would indicate that kinin in the system is actively involved in the pathogenesis of nasal allergy.

Classification of kinin receptors

This minireview is divided into three parts: the first part refers to the characterization and classification of kinin receptors using agonists and antagonists in isolated tissues (classical pharmacology). Two kinin receptors have been considered on the basis of their distinct pharmacology, namely the B1 receptor of the rabbit aorta (rank order of potency of agonists: LysdesArg9BK > desArg9BK > or = LysBK > BK; apparent affinities of antagonists Lys[Leu8]desArg9BK (pIC50 8.4) > [Leu8]desArg9BK (pIC50 7.4) >>> HOE 140, a B2 receptor antagonist, pIC50<5.0), and the B2 receptor of the rabbit jugular vein (potency of agonists: LysBK = BK >>> LysdesArg9BK = desArg9BK and HOE 140 (pIC50 9.0) >>> Lys[Leu8]desArg9BK, pIC50<5.0). The second part describes species-related B1 receptor subtypes, demonstrated by different pharmacological profiles of agonists and antagonists: human, rabbit and pig subtypes (LysdesArg9BK >> desArg9BK and Lys[Leu8]desArg9BK > [Leu8]desArg9BK) and dog, rat, mouse and hamster B1 receptors (desArg9BK = LysdesArg9BK and [Leus]desArg9BK = Lys[Leu8]desArg9BK). Affinities of agonists and antagonists in some species (man, rabbit, pig) are significantly increased (at least 10-fold) by the presence of a Lys at their N-terminus. The last part describes species-related B2 receptor subtypes supported by results obtained with non-peptide receptor agonists (FR 190997) and antagonists (FR 173657). While BK acts as a full agonist in man, rabbit and pig, FR 190997 behaves as a full agonist on human, as partial agonist on rabbit, and as pure antagonist on pig B2 receptors. Various hypotheses are considered to interpret these findings.

Peptide and non-peptide bradykinin B2 receptor agonists and antagonists: a reappraisal of their pharmacology in the guinea-pig ileum

We have compared the pharmacology of different antagonists, Icatibant (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH), MEN 11270 (H-DArg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7 gamma-10 alpha)), and FR173657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-[2, 4-dichloro-3-[(2-methyl-8-quinolinyl)oxymethyl]phenyl]-N-methyl aminocarbonylmethyl]acrylamide) at bradykinin B2 receptors expressed in the guinea-pig ileum by using bradykinin and the non-peptide FR190997 ((8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacety l]-N -methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline) as agonists. In organ bath experiments, Icatibant and FR173657 exerted a non-competitive antagonism (pKB 9.5 and 9.2, respectively) of the contractile response to bradykinin, whereas MEN 11270 showed competitive antagonism (pKB 8.3, slope -0.90). The profile of action and apparent affinities of the three antagonists did not change if contact time was prolonged. The inhibition by the three antagonists of the contractile response to bradykinin was differently reverted by washout (MEN 11270 <30 min, Icatibant <60 min, FR173657 >60 min). The non-peptide ligand FR190997 acted as partial agonist if applied cumulatively to the bath (pD2 8.06, Emax 43% of maximal contractility), but as a full agonist when a maximally effective concentration was added (Emax 83%). FR173657 produced non-competitive antagonism of the response to FR190997 with apparent affinity similar to that measured toward bradykinin. On the contrary, Icatibant and MEN 11270 (300 nM both) competitively antagonized the contractile activity exerted by FR190997 with lower apparent pA2 value (6.9 and 7.2, respectively). In radioligand binding experiments, MEN 11270 and Icatibant displaced the [3H]bradykinin binding with pKi of 10.2 and 10.5 (Hill slope not different from unity), respectively. The non-peptide ligands displaced the [3H]bradykinin binding with similar affinity, their pKi being 8.7 and 8.6 for FR173657 and FR190997, respectively (both Hill slopes <1). The present study indicates the difference in the antagonism type (competitive vs. non-competitive) by Icatibant, MEN 11270, and FR173657, as mainly ascribable to their different reversibility from the bradykinin B2 receptor, and affected by the kinetic of the response induced by the different agonists. Results are discussed in view of a different interaction of peptide and non-peptide agonist at the receptor.