Bradykinin receptors: characterization, distribution and mechanisms of signal transduction

Bradykinin B1 Receptor Affects Tumor-Associated Macrophage Activity and Glioblastoma Progression

Bradykinin is a small active peptide and is considered an inflammatory mediator in several pathological conditions. Bradykinin exerts its effects by coupling to its receptors, including bradykinin B1 (B1R) and bradykinin B2. B1R has been implicated in the development of various cancers. Our previous study reported that B1R promoted glioblastoma (GBM) development by supporting the migration and invasion of GBM cells. However, the mechanisms underlying the effects of B1R on tumor-associated macrophages (TAMs) and GBM progression remain unknown. Accordingly, to explore the regulatory effects of B1R overexpression (OE) in GBM on tumor-associated immune cells and tumor progression, we constructed a B1R wild-type plasmid and developed a B1R OE model. The results reveal that B1R OE in GBM promoted the expression of ICAM-1 and VCAM-1-cell adhesion molecules-in GBM. Moreover, B1R OE enhanced GBM cell migration ability and monocyte attachment. B1R also regulated the production of the protumorigenic cytokines and chemokines IL-6, IL-8, CXCL11, and CCL5 in GBM, which contributed to tumor progression. We additionally noted that B1R OE in GBM increased the expression of CD68 in TAMs. Furthermore, B1R OE reduced the level of reactive oxygen species in GBM cells by upregulating heme oxygenase-1, an endogenous antioxidant protein, thereby protecting GBM cells from oxidative stress. Notably, B1R OE upregulated the expression of programmed death-ligand 1 in both GBM cells and macrophages, thus providing resistance against T-cell response. B1R OE in GBM also promoted tumor growth and reduced survival rates in an intracranial xenograft mouse model. These results indicate that B1R expression in GBM promotes TAM activity and modulates GBM progression. Therefore, B1R could be an effective target for therapeutic methods in GBM.

The acute anti-inflammatory action of xylopic acid isolated from Xylopia aethiopica

Background Our earlier studies had given evidence of the traditional application of Xylopia aethiopica in the management of inflammation. The principal constituent obtained from its bio-fractionation is xylopic acid. It is a crystalline diterpene that belongs to the class of kauranes. This work sets out to investigate the anti-inflammatory potential of the xylopic acid isolated from the dried fruit of X. aethiopica. Methods A preliminary anti-inflammatory study, using the protein denaturation model, and in vivo anti-inflammatory assay were employed in the investigation of acute inflammation. The modulation of the effect of the pro-inflammatory markers histamine, serotonin, bradykinin, and prostaglandin E2 by xylopic acid was investigated by in vivo mice paw oedema models. Results Xylopic acid showed a concentration-dependent inhibition of albumen denaturation with an IC50 of 15.55 μg mL-1. Xylopic acid (10, 30, 100 mg kg-1) inhibited the maximal oedema and the average paw thickness (oedema) over the period of each study considerably for all phlogistic agents employed (i.e. carrageenan, histamine, serotonin, bradykinin, and prostaglandin E2) in the inflammation induction for both prophylactic and therapeutic protocols. Conclusion This study establishes that xylopic acid has anti-inflammatory action in acute inflammation.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

The Angiotensin-Converting-Enzyme-Induced Angioedema

The bradykinin B2 receptor antagonist icatibant is effective in angiotensin-converting enzyme inhibitor-induced angioedema. The drug is not approved officially for this indication and has to be administered in an emergency situation off-label. Corticosteroids or antihistamines do not seem to work in this condition. The effectiveness of C1-esterase-inhibitor in angiotensin-converting enzyme-induced angioedema must be verified in a double-blind study.

Evidence and evidence gaps of medical treatment of non-tumorous diseases of the head and neck

Unfortunately, the treatment of numerous otolaryngological diseases often lacks of evidence base because appropriate studies are missing.

Whereas sufficient high-quality trials exist for the specific immunotherapy of allergic rhinitis and in a limited measure also for the angiotensin-converting enzyme inhibitor induced angioedema, the evidence for Menière’s disease or for pharmacotherapy of postoperative laryngeal edema is rather poor. This contribution will discuss the trial situation and evidence of the respective diseases.

The role of kinin receptors in cancer and therapeutic opportunities

Kinins are generated within inflammatory tissue microenvironments, where they exert diverse functions, including cell proliferation, leukocyte activation, cell migration, endothelial cell activation and nociception. These pleiotropic functions depend on signaling through two cross talking receptors, the constitutively expressed kinin receptor 2 (B2R) and the inducible kinin receptor 1 (B1R). We have reviewed evidence, which supports the concept that kinin receptors, especially kinin receptor 1, are promising targets for cancer therapy, since (1) many tumor cells express aberrantly high levels of these receptors; (2) some cancers produce kinins and use them as autocrine factors to stimulate their growth; (3) activation of kinin receptors leads to activation of macrophages, dendritic cells and other cells from the tumor microenvironment; (4) kinins have pro-angiogenic properties; (5) kinin receptors have been implicated in cancer migration, invasion and metastasis; and (6) selective antagonists for either B1R or B2R have shown anti-proliferative, anti-inflammatory, anti-angiogenic and anti-migratory properties. The multiple cross talks between kinin receptors and renin-angiotensin system (RAS) as well as its implications for targeting KKS or RAS for the treatment of malignancies are also discussed. It is expected that B1R antagonists would interfere less with housekeeping functions and therefore would be attractive compounds to treat selected types of cancer. Reliable clinical studies are needed to establish the translatability of these data to human settings and the usefulness of kinin receptor antagonists.

Nonallergic angioedema: role of bradykinin

Angioedema is an underestimated clinical problem. Many cases are nonallergic reactions, e.g. bradykinin-induced angioedema caused by genetic defects and angiotensin-converting enzyme (ACE) inhibitors. This difference is crucial for successful therapy, in particular when complete emergency care is not available. Five important forms of nonallergic angioedema can be distinguished: hereditary (HAE), acquired (AAE), renin-angiotensin-aldosterone system (RAAS)-blocker-induced (RAE), pseudoallergic angioedema (PAE) and idiopathic angioedema (IAE). Some angioedema are present in the larynx and may cause death. A vast majority of nonallergic angioedema are RAE, particularly those caused by ACE inhibitors. It appears important to emphasize that in patients with complete intolerance to RAAS-blockers, cessation of RAAS-blockers is likely to be associated with increased cardiovascular risk. Currently, there is no published algorithm for diagnosis and treatment. Angioedema is usually treated by a conservative clinical approach using artificial ventilation, glucocorticoids and antihistamines. Today, a plasma pool C1-esterase inhibitor (C1-INH) concentrate is the therapy of choice in HAE. The current pharmacotherapy of nonallergic angioedema is not satisfactory, thus requiring the identification of effective agents in clinical trials. Recently, several new drugs were developed: a recombinant C1-INH, a kallikrein inhibitor (ecallantide) and a specific bradykinin-B2-receptor antagonist (icatibant). According to currently available reports, these drugs may improve the treatment of kinin-induced angioedema.

Upregulation of tissue kallikrein, kinin B1 receptor, and kinin B2 receptor in mast and giant cells infiltrating oesophageal squamous cell carcinoma

BACKGROUND

The mitogenic kinin peptides formed by the serine protease, tissue kallikrein (TK1), stimulate the proliferation of tumour cells and, by increasing vascular permeability, enhance metastasis. Oesophageal mucosal epithelial cells are derived from the epithelial cell germ layer, which expresses the kallikrein-kinin cascade.

AIM

To determine the cellular distribution of active TK1, prokallikrein, and the kinin B(1) and B(2) receptors in oesophageal carcinoma by immunocytochemistry and in situ hybridisation (ISH).

METHODS

Fifty oesophageal specimens (33 biopsies and 17 resections) and 10 control specimens adjacent to tumour or normal oesophageal biopsies were studied. Specific antibodies were used to determine the cellular localisation of TK1, prokallikrein, and the kinin B(1) and B(2) receptors in normal and oesophageal specimens by standard immunohistochemical techniques. The intensity of immunolabelling was quantified by image analysis. Antisense probes for TK1 and the kinin B(1) and B(2) receptors were also used to localise mRNA.

RESULTS

TK1 (active and prokallikrein) was expressed in the mucosa of normal and tumour oesophageal epithelium. In general, expression was highest in activated mast cells, followed by giant tumour cells. Immunolabelling results were confirmed by ISH experiments.

CONCLUSIONS

This is the first demonstration that TK1 and kinin B(1) and B(2) receptors are expressed in oesophageal carcinoma. Because TK1 released from tumour cells enzymatically generates mitogenic kinins from its endogenous substrate, kininogen, it is possible that third generation kinin receptor antagonists, which have been shown to be cytotoxic to cancer cells, may be useful therapeutic agents in this disease.

Kinin receptors in cultured rat microglia

Kinins are produced and act at the site of injury and inflammation in various tissues. They are likely to initiate a particular cascade of inflammatory events, which evokes physiological and pathophysiological responses including an increase in blood flow and plasma leakage. In the central nervous system (CNS), kinins are potent stimulators of the production and release of pro-inflammatory mediators represented by prostanoids and cytotoxins. They are known to induce neural tissue damage. Many of the cytotoxins such as cytokines and free radicals and prostanoids are released from glial cells. Among glial cells, astrocytes and oligodendrocytes are known to possess bradykinin (BK) B(2) receptors that phosphoinositide (PI) turnover and raise intracellular Ca(2+) concentration. The presence of bradykinin receptors in microglia has been of great significance. We recently showed that rat primary microglia express kinin receptors. In resting microglia, B(2) receptors but not B(1) receptors are expressed. When the microglia are activated by bradykinin, B(1) receptors are up-regulated, while B(2) receptors are down-regulated. As observed in other glial cells, electrophysiological measurements suggest that B(2) receptors in phosphoinositide turnover and intracellular Ca(2+) concentration in microglia. Release of cytotoxins is likely consequent upon the activation of BK receptors. Our study provides the first evidence that microglia express functional kinin receptors and suggests that microglia play an important role in CNS inflammatory responses.

The renal kallikrein-kinin system: its role as a safety valve for excess sodium intake, and its attenuation as a possible etiologic factor in salt-sensitive hypertension

The distal tubules of the kidney express the full set of the components of the kallikrein-kinin system, which works independently from the plasma kallikrein-kinin system. Studies on the role of the renal kallikrein-kinin system, using congenitally kininogen-deficient Brown-Norway Katholiek rats and also bradykinin B2 receptor knockout mice, revealed that this system starts to function and to induce natriuresis and diuresis when sodium accumulates in the body as a result of excess sodium intake or aldosterone release, for example, by angiotensin II. Thus, it can be hypothesized that the system works as a safety valve for sodium accumulation. The large numbers of studies on hypertensive animal models and on essential hypertensive patients, particularly those with salt sensitivity, indicate a tendency toward the reduced excretion of urinary kallikrein, although this reduction is modified by potassium intake and impaired renal function. We hypothesize that the reduced excretion of the renal kallikrein may be attributable to a genetic defect of factor(s) in renal kallikrein secretion process and may cause salt-sensitive hypertension after salt intake.

Transcriptional regulation of the rat bradykinin B2 receptor gene: identification of a silencer element

Kinins are involved in a variety of physiological and pathophysiological processes related to cardiovascular homeostasis, inflammation, blood flow, and nociception. Under physiological conditions, the bradykinin B2 (BKB2) receptor is constitutively expressed and mediates most of kinins' actions. However, the mechanisms regulating BKB2 receptor gene expression are still poorly understood. In this study, 4.6 kilobases of the 5'-flanking region from the rat BKB2 receptor gene were sequenced, and computer analysis revealed several sites for transcriptional factors. Nine promoter mutants were cloned in luciferase reporter gene vectors and transfected in NG108-15 cells and rat aorta vascular smooth muscle cells (VSMCs), showing several positive and negative regulatory elements. A classical silencer with 56 base pairs (bp) caused a decrease in reporter gene activity in NG108-15 cells and VSMCs and was able to inhibit the thymidine kinase promoter. Using electrophoretic mobility shift assay and surface plasmon resonance assay, protein-DNA interactions in the silencer region were determined and specific sets of protein-silencer complexes were detected in both cell types. More intense complexes were observed in the central 21 bp of the silencer and mutation in a putative SRE-1 site strongly impaired the protein-DNA binding. Down-regulation of the BKB2 receptor population in NG108-15 cells promoted by N(6), 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate was paralleled by an increase in the amount of nuclear proteins bound to the silencer sequence showing an inverse relationship between protein-silencer complexes and the transcription of the BKB2 receptor gene. In summary, these data highlight the cell-specific regulation of the BKB2 receptor and the importance of a silencer element present in the regulatory region of the gene.

Mechanisms regulating the expression, self-maintenance, and signaling-function of the bradykinin B2 and B1 receptors

Bradykinin (BK) is a potent short-lived effector belonging to a class of peptides known as kinins. It participates in inflammatory and vascular regulation and processes including angioedema, tissue permeability, vascular dilation, and smooth muscle contraction. BK exerts its biological effects through the activation of the bradykinin B2 receptor (BKB2R) which is G-protein-coupled and is generally constitutively expressed. Upon binding, the receptor is activated and transduces signal cascades which have become paradigms for the actions of the Galphai and Galphaq G-protein subunits. Following activation the receptor is then desensitized, endocytosed, and resensitized. The bradykinin B1 (BKB1R) is a closely related receptor. It is activated by desArg(10)-kallidin or desArg(9)-BK, metabolites of kallidin and BK, respectively. This receptor is induced following tissue injury or after treatment with bacterial endotoxins such as lipopolysacharide or cytokines such as interleukin-1 or tumor necrosis factor-alpha. In this review we will summarize the BKB2R and BKB1R mediated signal transduction pathways. We will then emphasize the relevance of key residues and domains of the intracellular regions of the BKB2R as they relate to modulating its function (signal transduction) and self-maintenance (desensitization, endocytosis, and resensitization). We will examine the features of the BKB1R gene promoter and its mRNA as these operate in the expression and self-maintenance of this inducible receptor. This communication will not cover areas discussed in earlier reviews pertaining to the actions of peptide analogs. For these we refer you to earlier reviews (Regoli and Barabé, 1980, Pharmacol Rev 32:1-46; Regoli et al., 1990, J Cardiovasc Pharmacol 15(Suppl 6):S30-S38; Regoli et al., 1993, Can J Physiol Pharmacol 71:556-557; Marceau, 1995, Immunopharmacology 30:1-26; Regoli et al., 1998, Eur J Pharmacol 348:1-10).

Functional studies of bradykinin receptors in Chinese hamster ovary cells stably expressing the human B2 bradykinin receptor

Bradykinin B1 and B2 receptors, members of the G-protein coupled receptor superfamily, are involved in inflammation and pain. Chinese hamster ovary (CHO) cells stably expressing the human B2 bradykinin receptor (CHO-B2) were used to characterize the signal transduction pathways associated with this receptor and its regulation. The selective B2 antagonist [3H]NPC17731 but not the selective B1 antagonist [3,4-prolyl-3,4-(3)H(N)]-[des-Arg10,Leu9]kallidin ([3H]DALKD) bound to CHO-B2 cell membranes with a Kd of 0.77 nM and a Bmax of 1087 fmol/mg protein. [3H]NPC17731 binding was inhibited by bradykinin ligands in the order: NPC17731 > bradykinin > kallidin >> DALKD > [des-Arg10] kallidin (DAKD), consistent with the pharmacological profile of B2 bradykinin receptors. The B2 agonist bradykinin and the B1/B2 agonist kallidin, but not the B1 agonist DAKD, increased [35S]GTP gamma S binding to the CHO-B2 cell membranes. The B2 bradykinin receptors were co-immunoprecipitated with G alpha q/11. In response to bradykinin stimulation, coupling of the B2 receptors to G alpha q/11 was increased by 10-fold. Bradykinin and kallidin, but not DAKD, induced intracellular calcium release in CHO-B2 cells, which was blocked by NPC17731 but not by DALKD. These results demonstrate that B2 bradykinin receptors directly coupled to G alpha q/11 to regulate intracellular calcium release. CHO-B2 cell is a useful system that can be applied to study the effect of potential agents that may influence the B2 receptor function.

Des-Arg(10)-kallidin engagement of the B1 receptor stimulates type I collagen synthesis via stabilization of connective tissue growth factor mRNA

Expression of the kinin B1 receptor is up-regulated in chronic inflammatory and fibrotic disorders; however, little is known about its role in fibrogenesis. We examined human embryonic lung fibroblasts that constitutively express the B1 receptor and report that engagement of the B1 receptor by des-Arg(10)-kallidin stabilized connective tissue growth factor (CTGF) mRNA, stimulated an increase in alpha1(I) collagen mRNA, and stimulated type I collagen production. These events were not observed in B2 receptor-activated fibroblasts. In addition, B1 receptor activation by des-Arg(10)-kallidin induced a rise in cytosolic Ca(2+) that is consistent with B1 receptor pharmacology. Our results show that the des-Arg(10)-kallidin-stimulated increase in alpha1(I) collagen mRNA was time- and dose-dependent, with a peak response observed at 20 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was also time- and dose-dependent, with a peak response observed at 4 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was blocked by the B1 receptor antagonist des-Arg(10),Leu(9)-kallidin. Inhibition of protein synthesis by cycloheximide did not block the des-Arg(10)-kallidin-induced increase in CTGF mRNA. These results suggest that engagement of the kinin B1 receptor contributes to fibrogenesis through increased expression of CTGF.

Suppressive effect of distinct bradykinin B2 receptor antagonist on allergen-evoked exudation and leukocyte infiltration in sensitized rats

1. Bradykinin is suggested to play a role in the pathophysiology of several acute and chronic diseases, including allergic disorders such as asthma. In the present study, we have investigated the importance of bradykinin in mediating allergic inflammation in rats. 2. To this end we have tested the effects of the B2 receptor antagonists Hoe 140, FR173657 or FR172357 on the pleural inflammatory response triggered by intrapleural (i.pl.) injection of allergen (ovalbumin, 12 microg cavity(-1)) in 14 day-actively sensitized Wistar rats. Analysis of the pleural fluid effluent revealed a sequence of mast cell-dependent inflammatory events, including early protein exudation and neutrophilia and late pleural eosinophil influx. 3. Local treatment with Hoe 140 (0.1 and 1 microg cavity(-1)), FR173657 (1 and 10 microg cavity(-1)) or FR172357 (1 and 10 microg cavity(-1)) inhibited dose-dependently allergen-induced mast cell activation with impairment of pleural plasma leakage, neutrophil accumulation and late eosinophil influx. 4. Moreover, the B2 receptor antagonists also dose-dependently inhibited the allergic like inflammatory pleurisy triggered by bradykinin (50 microg cavity(-1)), which is characterized by acute mast cell degranulation, protein leakage and pleural eosinophil infiltration. 5. Taken together, our findings provide substantial evidence to suggest that bradykinin acting on its B2 receptors play a critical role in mediating allergic mast cell-dependent inflammation in rats, and suggest that B2 receptor antagonists may be useful therapeutically to control allergic dysfunction.

Phenotypic transformation of normal rat kidney fibroblasts by endothelin-1. Different mode of action from lysophosphatidic acid, bradykinin, and prostaglandin f2alpha

In the present study, we compared the effects of endothelin (ET)-1 on cell proliferation and second messenger induction in normal rat kidney (NRK) fibroblasts, with those of other activators of G-protein-coupled receptors such as prostaglandin (PG)-F2alpha, bradykinin (BK), and lysophosphatidic acid (LPA). LPA is mitogenic by itself, while the other factors require the presence of EGF. In density-arrested NRK cells, ET-1 and LPA induce phenotypic transformation rapidly, with similar kinetics as retinoic acid (RA) and transforming growth factor (TGF)-beta, while BK and PGF2alpha only do so with delayed kinetics. ET-1 and PGF2alpha are strong inducers of anchorage-independent growth, with a similar level of induction as TGFbeta, in contrast to LPA and BK. When investigating the second messenger generation, we found that ET-1 is the strongest activator of arachidonic acid release and phosphatidylinositol diphosphate hydrolysis. Only in the case of ET-1 the cell depolarization is not reversible upon removal of the factor. Similarly, only the ET-1-induced transient enhancement of intracellular calcium concentration is paralleled by both homologous and heterologous desensitization. In conclusion, these data show that ET-1 is a potent inducer of second messengers and phenotypic transformation in NRK cells, with characteristics that clearly differ from those of other activators of G-protein-coupled receptors, most likely as a result of prolonged receptor activation.

Molecular biology of the kallikrein-kinin system: from structure to function

The participation of the kallikrein-kinin system, comprising the serine proteases kallikreins, the protein substrates kininogens and the effective peptides kinins, in some pathological processes like hypertension and cardiovascular diseases is still a matter of controversy. The use of different experimental set-ups in concert with the development of potent and specific inhibitors and antagonists for the system has highlighted its importance but the results still lack conclusivity. Over the last few years, transgenic and gene-targeting technologies associated with molecular biology tools have provided specific information about the elusive role of the kallikrein-kinin system in the control of blood pressure and electrolyte homeostasis. cDNA and genomic sequences for kinin receptors B2 and B1 from different species were isolated and shown to encode G-protein-coupled receptors and the structure and pharmacology of the receptors were characterized. Transgenic animals expressing an overactive kallikrein-kinin system were established to study the cardiovascular effects of these alterations and the results of these investigations further corroborate the importance of this system in the maintenance of normal blood pressure. Knockout animals for B2 and B1 receptors are available and their analysis also points to the role of these receptors in cardiovascular regulation and inflammatory processes. In this paper the most recent and relevant genetic animal models developed for the study of the kallikrein-kinin system are reviewed, and the advances they brought to the understanding of the biological role of this system are discussed.

Characterization of bradykinin receptors in human lung fibroblasts using the binding of 3[H][Des-Arg10,Leu9]kallidin and [3H]NPC17731

Bradykinin (BK) receptors are involved in pain and inflammation. Two BK receptor subtypes, B1 and B2, have been defined based on their pharmacological properties. Both B1 and B2 receptors are G-protein coupled membrane receptors. B1 receptors are present in smooth muscle tissue, whereas B2 receptors are found in both smooth muscle tissue and neurons. [Des-Arg10,Leu9]kallidin (DALKD) is a selective B1 receptor antagonist, and NPC17731 is a selective B2 receptor antagonist. To develop binding assays for the two known BK receptor subtypes, [3H]DALKD and [3H]NPC17731 were used as selective ligands for B1 and B2 receptors respectively. Both ligands bound to the CCD-16 human lung fibroblast membranes reaching equilibrium at 25 degrees C within 30 min. Binding was stable for at least 60 min. The Kd of [3H]DALKD was 0.33 nM and Bmax was 52 fmol/mg membrane protein. The Kd of [3H]NPC17731 was 0.39 nM and Bmax was 700 fmol/mg membrane protein. Competition for [3H]DALKD binding with BK receptor agonists was in the order: [des-Arg10]KD (DAKD) > KD >> [des-Arg9]BK (DABK) > BK, and competition for [3H]DALKD binding with BK receptor antagonists was in the order: DALKD > [des-Arg10]Hoe 140 (DAHoe 140) > [des-Arg9,Leu8]BK (DALBK) > NPC17731 > Hoe 140 > DNMFBK, suggesting that [3H]DALKD bound selectively to B1 receptors. By contrast, competition for [3H]NPC17731 binding by BK agonists was in the order: BK > KD >> DAKD > DABK, and competition for [3H]NPC17731 binding by BK antagonists was in the order: NPC17731 = Hoe 140 >> DNMFBK > DAHoe 140 > DALBK > DALKD, indicating that [3H]NPC17731 labeled B2 receptors selectively. These results demonstrate that [3H]DALKD and [3H]NPC17731 can be used with CCD-16 human lung fibroblast membranes to provide a pair of binding assays for the simultaneous evaluation of B1 and B2 BK receptor subtypes.

Glucose-dependency of bradykinin-induced insulin secretion from the perfused rat pancreas

In order to investigate the glucose dependency of bradykinin (BK)-induced insulin secretion, rat pancreata were perfused in situ with BK (1 microM) for 30 min in the presence of glucose concentrations of 0 - 20 mM. Glucose (6 mM) alone maintained a steady baseline insulin secretion which was 6.7 %/- 0.5 ng/min (n = 4). The rate of insulin secretion in the presence of 0 and 1 mM glucose was approximately 70 - 80% and approximately 60-70% less, respectively, than in the presence of 6 mM glucose. The perfusate glucose concentrations of 10 and 20 mM induced a biphasic and dose-dependent insulin secretion, characterized by a transient increase followed by a sustained phase; the sustained phase was higher than the transient increase. BK failed to change insulin secretion in the absence of extracellular glucose. When BK was administered in 1 mM glucose, it induced a transient insulin release peak which was 2.8-fold of the insulin secretion induced by 6 mM glucose, then the insulin concentrations of the effluents decreased gradually to the levels that were slightly higher than that induced by the 1 mM glucose alone, but lower than that induced by 6 mM glucose. After BK was administered in 6 mM glucose, it induced a transient insulin release peak that was 3.6-fold of the baseline level, and followed by a sustained insulin secretion phase which was approximately 50% higher than that of the 6 mM glucose control group. When BK was perfused with 10 or 20mM glucose, it induced a similar insulin secretion pattern as in the glucose alone groups. However, the combination of glucose (10 or 20 mM) and BK induced a higher transient insulin release peak, which was 7.8- and 12-fold of the baseline level, respectively. Also, the BK-glucose-induced sustained phase was higher than the transient peak. BK caused a greater potentiation of insulin secretion in 20 mM glucose than in 10 mM glucose. Taken together, our findings suggest that 1) BK requires the presence of glucose to stimulate insulin secretion and 2) BK induces insulin secretion in a glucose concentration-dependent manner; the higher the glucose concentration, the greater the potentiation in BK-induced insulin secretion.

Cloning and functional characterization of the ornithokinin receptor. Recognition of the major kinin receptor antagonist, HOE140, as a full agonist

Kinins are proinflammatory peptides that dilate vessels, increase vascular permeability, contract smooth muscles, and provoke pain. The known mammalian kinin receptors are classified as two subtypes, i.e. the B1 receptor triggered by [des-Arg9]bradykinin and inhibited by [des-Arg9,Leu8]bradykinin, and the B2 receptor stimulated by bradykinin and antagonized by HOE140. Here we report the cloning of a non-mammalian kinin receptor gene amplified from genomic chicken DNA. The protein predicted from the open reading frame shows 31 and 49% sequence identity to the human B1 and B2 receptors, respectively, suggesting that it represents a G protein-coupled receptor of the kinin receptor family. The recombinantly expressed chicken receptor had IC50 values of 4.7 nM for the authentic ligand, ornithokinin ([Thr6,Leu8]bradykinin), 3.8 nM for HOE140, and >/=10 microM for bradykinin, [des-Arg9]bradykinin, and [des-Arg9,Leu8]bradykinin. Ornithokinin and HOE140 at nanomolar concentrations stimulated intracellular inositol phosphate accumulation and induced a significant transient rise in intracelluar free Ca2+, whereas bradykinin was ineffective even at 100 nM. Hence the principal B2 receptor antagonist HOE140 is a potent agonist of the chicken kinin receptor. This unique pharmacological profile classifies the ornithokinin receptor as a novel subtype among kinin receptors and will facilitate further molecular studies on ligand binding and receptor activation.

Membrane depolarization in NRK fibroblasts by bradykinin is mediated by a calcium-dependent chloride conductance

The effects of the phosphoinositide-mobilizing agonist bradykinin (BK) on membrane potential and intracellular calcium in monolayers of normal rat kidney (NRK) fibroblasts were investigated. BK induced a rapid transient depolarization in these cells, which was mimicked by other phosphoinositide-mobilizing factors such as prostaglandin F2alpha (PGF2alpha), lysophosphatidic acid (LPA), platelet-derived growth factor (PDGF-BB), and serum. Depolarization by BK was independent of extracellular Ca2+ or Na+. It was shown using extracellular Cl- substitutions that the depolarization was caused by an increased Cl- conductance. Depolarization was inhibited by 5-nitro-2-3-phenylpropyl(amino)benzoic acid (NPPB), niflumic acid, and flufenamic acid, inhibitors of calcium-dependent chloride channels. The depolarization provoked by BK could be mimicked by raising intracellular calcium with ionomycin or thapsigargin and could be blocked with geneticin, a blocker of phospholipase C. When intracellular calcium was buffered by loading the cells with 1,2-bis(2-aminophenoxy)ethane-NNN'N'-tetra-acetic acid (BAPTA), depolarization was prevented. We conclude that in NRK fibroblasts extracellular stimuli that increase intracellular calcium, depolarize the cells via the activation of a calcium-dependent chloride conductance. In addition to an increase in intracellular calcium, depolarization may be an important effector pathway in response to extracellular stimuli in fibroblasts. It is hypothesized that, in electrically coupled cells such as NRK fibroblasts, intercellular transmission of these depolarizations may represent a mechanism to coordinate uniform multicellular responses to Ca2+-mobilizing agonists.

Mechanism of contraction induced by bradykinin in the rabbit saphenous vein

1. By using fura-PE3 fluorometry and receptor-coupled permeabilization by alpha-toxin, the mechanism of the bradykinin (BK)-induced contraction was determined in the rabbit saphenous vein (RSV). The receptor subtype responsible for the BK-induced contraction of RSV was determined by means of a pharmacological blocker study and reverse transcription polymerase chain reaction (RT-PCR). 2. In the presence of extracellular Ca2+ (1.25 mM), BK (10(-11)-3 x 10(-7) M) induced increases in both the cytosolic Ca2+ concentration ([Ca2+]i) and force, in a concentration-dependent manner. Both the release of Ca2+ from the store site and the influx of extracellular Ca2+ contribute to an increase in [Ca2+]i induced by BK. 3. In the absence of extracellular Ca2+, the application of 10(-7) M BK induced transient elevations of [Ca2+]i and force, both of which thereafter declined to the levels observed before the application of BK. When extracellular Ca2+ was replenished (1.25 mM), [Ca2+]i and force increased to form a peak, followed by a sustained elevation in the presence of BK. When an RSV strip was pretreated with 10(-5) M thapsigargin for 20 min, the BK-induced transient increases in both [Ca2+]i and force were markedly inhibited. 4. These responses induced by BK were inhibited by Hoe 140 (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8] bradykinin), a highly specific bradykinin B2 receptor antagonist, in a concentration-dependent manner. In RT-PCR, B2-receptor mRNA was expressed in the smooth muscle of RSV. 5. The [Ca2+]i-force relationships, which were determined by cumulative applications of extracellular Ca2+ (0-5 mM) during 118 mM K(+)-depolarization, shifted to the upper left in the presence of BK, thus indicating that BK induced a greater force than 118 mM K(+)-depolarization for a given level of [Ca2+]i. 6. In alpha-toxin-permeabilized preparations of RSV, application of 10(-7) M BK after a steady state contraction had been induced by a mixture of 5 x 10(-7) M Ca2+, 10(-6) M GTP and 10(-6) M captopril caused an additional force development at a constant [Ca2+]i. However, treatment with 1 mM guanosine-5'-O-(beta-thiodiphosphate) (GDP beta S) for 5 min before and during the application of BK (10(-7) M), abolished this BK-induced additional contraction. 7. These results indicated that in RSV: (1) BK elicits vasoconstriction by increasing the Ca2+ influx from the extracellular space, Ca2+ release from intracellular thapsigargin-sensitive storage sites and increasing the Ca2+ sensitivity of the contractile apparatus, (2) the BK-induced increase in Ca2+ sensitivity is mediated by G-protein, (3) the BK-induced contractions are mediated via B2-receptors and (4) the smooth muscle cells express B2-receptor mRNA.

Bradykinin receptors

1. The last decade has witnessed a phenomenal increase in our understanding of the pharmacology of bradykinin receptors, and has led to an appreciation of a key role for the peptide kinins as proinflammatory mediators. This short review summarises the major changes that have taken place in the expanding area of bradykinin receptor pharmacology, and highlights important advances that we hope to anticipate in the future. 2. Bradykinin receptors are cell surface, G-protein coupled receptors of the seven-transmembrane domained family. The existence of two subtypes of bradykinin receptor, B1 and B2, has been confirmed through the use of high affinity peptide and nonpeptide receptor antagonists, radioligand binding studies and, recently, receptor cloning and expression studies. 3. Differences in the affinities of B2 receptor antagonists, including those of the [D-Phe7]-bradykinin series, D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]-bradykinin (Hoe140, Icatibant) and the non-peptide, WIN64338, have led to proposals of the possible existence of further subtypes of bradykinin receptor (including a tracheal B3 receptor), and/or of species homologues of the B2 receptor. 4. Molecular cloning techniques have identified the gene encoding B1 receptors in the rabbit, human and mouse, and B2 receptors in the rat, human and mouse. B1 and B2 receptor show little (36%) overall sequence homology. Cloning studies reveal the potential for the existence of species homologues of receptors. 5. The use of bradykinin receptor antagonists in vivo has led to an appreciation of the involvement of bradykinin receptors in inflammation. Evidence suggests a role for B2 receptors in more classical acute inflammatory events, such as oedema and inflammatory pain, whereas B1 receptors appear to be involved in chronic inflammatory responses, including certain forms of persistent hyperalgesia. 6. The continuing advances in our knowledge of the characteristics of bradykinin receptors through the further development of selective receptor antagonists and molecular biology techniques will aid in the rational design of drugs effective in the therapeutic manipulation of inflammatory processes and in the control of inflammatory disease.

Cardiovascular effects produced by bradykinin microinjection into the nucleus tractus solitarii of anesthetized rats

In this study, we characterized the cardiovascular effects produced by microinjection of doses in the femtomole range of bradykinin (BK) into the nucleus tractus solitarii of male Wistar rats (230-280 g, n = 120) anesthetized with urethane (1.2 g/kg, i.p.). Microinjections of BK (1, 10, 100 fmol, and 1 and 10 pmol, in 50 nl) or vehicle (NaCl, 0.9%) were made by using a triple-barreled glass micropipette into the medial nTS (0.4 mm anterior, 0.3 mm lateral to the obex and 0.3 mm deep from the dorsal surface). Microinjection of BK produced a shallow dose-dependent decrease in mean arterial pressure and heart rate reaching -18 +/- 6 mmHg and -21 +/- 5 beats/min, with the dose of 10 pmol. The peripheral mechanism of these effects, tested in animals treated with methylatropine (2 mg/kg, i.v.), or propranolol (2 mg/kg, i.v.) or prazosin (30 micrograms/kg, i.v.), was shown to be mainly dependent on an increase in vagal efferent activity for bradycardia and a decrease in sympathetic activity for hypotension. In order to investigate the receptor subtype involved in these effects, BK was microinjected into the nTS before and after the injection of the B1 receptor antagonist, Des-Arg9-Leu8-BK (DALBK) (11.5 pmol) or before and after the B2 receptor antagonist, HOE-140 (7.7 pmol). The cardiovascular effects of BK were significantly attenuated by the microinjection of HOE-140 and DALBK into the nTS. The effect of BK microinjected into the nTS on the baroreflex modulation was also investigated. While BK produced a significant facilitation of the baroreflex, HOE-140 and DALBK produced a significant attenuation of the baroreceptor control of heart rate. Taken together, the data presented in this study indicate the nTS as a site, in the central nervous system, for the modulatory effect of BK on the central cardiovascular control.

A comparative study of endothelium-derived relaxing factor-mediated relaxation and smooth muscle cell function in arterial and venous vein bypass grafts

The development of intimal hyperplasia in reversed vein grafts is associated with altered endothelial and vasomotor function. This study examines the effect of surgery on the morphology and vasomotor function of experimental arterial and venous vein bypass grafts. Twelve reversed vein grafts, 12 in situ vein grafts and 12 venovenous grafts were placed in 24 New Zealand White rabbits. All grafts remained patent and were harvested after 28 days. Isometric contraction to norepinephrine, histamine, bradykinin, serotonin and relaxation to acetylcholine and sodium nitroprusside following pre-contraction with prostaglandin F(2 alpha) were determined on the grafts and on contralateral jugular veins. Compared to the contralateral jugular veins, norepinephrine supersensitivity was induced in the reversed vein grafts, and venovenous vein grafts but not in the in situ vein grafts. Decrease in histamine sensitivity occurred in all grafted vessels. Bradykinin responses were significantly reduced in the in situ vein grafts and reversed vein grafts. Contractile responses to serotonin developed in the in situ vein grafts and reversed vein grafts only. Acetylcholine-induced endothelium-derived relaxing factor-mediated relaxation of the contralateral jugular veins was preserved in both venovenous grafts and in situ vein grafts but was lost in reversed vein grafts. All tissues relaxed to sodium nitroprusside in dose-dependent manner. The data suggest that norepinephrine supersensitivity in reversed vein grafts results from excision of the vessel. Attenuation of bradykinin responses and the enhanced contractile responses to serotonin appear predominantly to result from arterialization. Decreases in histamine sensitivity appear related both to excision and to arterialization. Neither the excision of the vein nor arterialization individually influences the alterations in endothelium-derived relaxing factor-mediated relaxation. However, a combination of excision and arterialization results in the altered endothelium-derived relaxing factor-mediated relaxation. This study suggests that the surgical preparation of the vein and the surgical procedure used have significantly different effects on endothelium-derived relaxing factor-mediated relaxation and smooth muscle contractility in vein grafts.

Bradykinin induces tyrosine phosphorylation in human foreskin fibroblasts and 293 cells transfected with rat B2 kinin receptor

The intracellular effects of bradykinin are mediated through the recently cloned B2 kinin receptor which belongs to the superfamily of receptors with seven transmembrane domains. The molecular events which transduce the bradykinin signal on the post-receptor level are not understood in detail. We studied whether in human foreskin fibroblasts bradykinin treatment induces tyrosine phosphorylation of cellular proteins. Using phosphotyrosine antibodies we detected a bradykinin-dependent phosphorylation of a group of proteins of about 130 kDa and an additional signal around 70kDa after starvation of cells. The effect evoked by 10 nM bradykinin was rapid (2 min) and it was partially reduced by the B2-kinin-receptor antagonist Hoe 140 which was shown to be a weak inducer of tyrosine phosphorylation. The bradykinin-mediated tyrosine phosphorylation events were reproduced in human embryonal kidney 293 fibroblasts which were transiently transfected with the rat B2 kinin receptor, but they were not observed in untransfected 293 control cells. These data suggest that the B2 kinin-receptor subtype is involved. Upon fractionation of cells the 130kDa protein group was recovered both in the membrane and the cytosolic protein fraction. To assess the specificity of this bradykinin effect we stimulated human foreskin fibroblasts with epidermal growth factor (EGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF-I) and insulin. While IGF-I, insulin and EGF were almost ineffective, PDGF stimulated the tyrosine phosphorylation of 130-kDa bands with a similar pattern to that produced by bradykinin. Immunoprecipitation experiments with specific antibodies against potential candidate proteins in the molecular-mass range around 130kDa revealed positive results for the focal adhesion kinase FAK and the p130 Src substrate while negative results were obtained for the GTPase-activating protein GAP, the phospholipase C-gamma1, the Janus kinase JAK-1 and vinculin. The data suggest that the tyrosine phosphorylation of FAK and the pl30 Src substrate might be involved in the B2-kinin-receptor signalling cascade.

Pharmacology and structure--activity relationships of the nonpeptide bradykinin receptor antagonist WIN 64338

A series of competitive, nonpeptide bradykinin receptor antagonists based on an alpha-amino acid scaffold have been developed and biologically characterized. The lead compound in the series, WIN 64338, demonstrates competitive inhibition of bradykinin-mediated functional responses through B2 receptors in a variety of tissues and species. WIN64338 is a specific for the bradykinin B2 receptor; it is inactive at both the B1 and B2 kinin receptors. In conscious guinea pigs, WIN 64338 inhibits kinin-mediated bronchoconstriction but does not attenuate a similar response to acetylcholine. A series of WIN 64338 analogues display a well-defined structure-activity relationship, strongly suggesting binding in a specific manner to the B2 receptor. Structure-activity data suggest that a hydrophobic binding pocket that prefers large aromatic groups in a specific conformational orientation exists in the receptor ligand binding domain. This class of nonpeptide bradykinin receptor antagonists may lead to the design of other compounds with enhanced receptor affinity and optimal in vivo biological activity.

A bradykinin-potentiating peptide (peptide K12) isolated from the venom of Egyptian scorpion Buthus occitanus

A nontoxic peptide with bradykinin-potentiating activity was isolated from the dialyzed venom of the scorpion Buthus occitanus by reverse-phase high performance liquid chromatography (RP-HPLC). The pharmacological activity of the peptide was bioassayed by its ability to potentiate added bradykinin (BK) on the isolated guinea pig ileum as well as the isolated rat uterus for contraction. Moreover, the peptide potentiates in vivo the depressor effect of BK on arterial blood pressure in the normotensive anesthetized rat. Chemical characterization of the peptide was also performed. The amino acid composition of the peptide showed 21 amino acid residues per molecule including three proline residues. The amino acid sequence of the purified peptide was confirmed by mass spectrometry. Either N- or C-terminal ends were free. The sequence does not show a homology with bradykinin-potentiating peptides isolated from either scorpion or snake venoms. Furthermore, we did not find a significant sequence homology between the sequence of the isolated peptide and any of proteins or peptides in GenPro or NBRF data banks. The peptide also inhibited angiotensin-converting enzyme (ACE), and could not serve as substrate for the enzyme. It could be concluded that the mechanism of bradykinin-potentiating peptide (BPP) activity may be due to ACE inhibition.

Lysophosphatidic acid and bradykinin have opposite effects on phenotypic transformation of normal rat kidney cells

The bioactive lipid lysophosphatidic acid is besides a strong mitogen for quiescent fibroblasts, a potent inducer of phenotypic transformation of normal rat kidney cells. The lysophosphatidic acid induced loss of density-arrest is strongly inhibited by bradykinin. Although their effects on normal rat kidney cell proliferation are opposite, bradykinin mimics many of the intracellular effects induced upon lysophosphatidic acid receptor activation, including phosphoinositide turnover, Ca(2+)-mobilization and arachidonic acid release. Bradykinin does not counteract the lysophosphatidic acid induced reduction of cAMP levels in normal rat kidney cells. However, bradykinin inhibits the lysophosphatidic acid and other growth factor induced phenotypic transformation through the induction of a so far uncharacterized prostaglandin G/H synthase product. The growth inhibitory effect of bradykinin is limited to density-arrested cells, while upon prolonged treatment bradykinin itself is capable to induce the loss of density-dependent growth control. It is concluded that bradykinin is a bifunctional regulator of normal rat kidney cell proliferation and that its inhibitory effects are mediated via the induction of a prostaglandin derivative.

Bradykinin receptor modulation in vein grafts

Following vein grafting, bradykinin B2 receptor-mediated responses in the vein graft are decreased and B1 receptor-mediated responses are increased. It is not known whether these changes in bradykinin receptor responses are due to nonspecific changes, local inflammation, or arterial hemodynamics. Four experimental tissue models were studied to discriminate among these possibilities. Twelve New Zealand White rabbits underwent excision of native vein (n = 4), external jugular veno-venous bypass (n = 4), or common carotid veno-arterial bypass (n = 4). Grafts and unoperated contralateral jugular veins (n = 4) were harvested at 28 days postoperatively. Isometric tension studies were performed on four rings from each vein and vein graft. The responses to bradykinin, a B2 agonist (BK: 10(-12) to 10(-5) M) and des-Arg9-bradykinin, a B1 agonist (DABK; 10(-12) to 10(-5) M) were recorded. Compared to native veins, the results show a progressive attenuation in BK sensitivity in contralateral veins, veno-venous grafts, and veno-arterial grafts, and the development of DABK sensitivity in the contralateral veins and both vein graft models. The alterations in B2 receptor-mediated responses appear therefore to be induced by a combination of the surgical procedure and arterialization, while changes in B1 receptor-mediated responses appear to be related solely to nonspecific sensitization of the cardiovascular tissue following the operative procedure. Thus, it appears from this study that there are two distinct mechanisms involved in the modulation of bradykinin receptors in vein grafts after implantation into the arterial circulation.

Bradykinin induces translocation of the protein kinase C isoforms alpha, epsilon, and zeta

Bradykinin exerts a broad spectrum of cellular effects on different tissues. It is believed that these effects are predominantly mediated by the recently cloned B2 receptor. The mechanism of post-receptor signal transduction is not known in detail. Involvement of protein kinase C (PKC) was suggested and activation of the classical PKC isoforms alpha and beta was recently demonstrated. The aim of the present study was to investigate whether the B2 receptor also activates new (delta, epsilon) and atypical (zeta) PKC isoforms. To investigate this, chinese hamster ovary (CHO) cells, stably transfected with human B2 receptor, were used. In these cells the PKC isoforms alpha, delta, epsilon and zeta were detected by immunoblotting with specific antibodies. To monitor hormone-induced PKC translocation plasma membranes were prepared. Stimulation of the cells with bradykinin resulted in a rapid (30-60 s) translocation of the PKC isoforms alpha, epsilon, and zeta. Translocation of PKC delta was not detected. The effect of bradykinin was reduced by simultaneous addition of the receptor antagonist HOE 140, a bradykinin-related decapeptide. The data show that the B2 receptor in this cell model is able to activate, in addition to the classical PKC isoform alpha, the new PKC isoform epsilon and the atypical PKC isoform zeta. To test whether these effects are as well observed in a non-transfected cell, the experiments were repeated in human foreskin fibroblasts which naturally express high levels of B2 receptors. In this cell system similar results on PKC alpha, epsilon, and zeta were observed, suggesting that all three PKC isoforms are involved in signal transduction of the B2 receptor.

Relaxation of porcine coronary artery to bradykinin. Role of arachidonic acid

Bradykinin-induced relaxation of precontracted, porcine coronary artery (PCA) rings is mediated by distinctly different endothelium-derived relaxing factors depending on the contractile agent used. Thus when contracted with KCl, bradykinin-induced relaxation of PCA rings is mediated solely by nitric oxide (NO), whereas when contracted with the thromboxane mimetic U46619, a small component of the relaxation is attributable to NO and a large component is attributable to a non-NO mechanism that is independent of cyclooxygenase activity. We hypothesized that the non-NO component was mediated by arachidonic acid (AA) or by a non-cyclooxygenase product of AA metabolism. Bradykinin-induced relaxations of PCA rings precontracted with U46619 in the presence of indomethacin (10 mumol/L) were moderately attenuated by the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 100 mumol/L), whereas when precontracted with KCl, L-NAME abolished the relaxations. AA produced endothelium-dependent relaxations of rings precontracted with U46619 that were unaffected by L-NAME, whereas AA did not relax rings precontracted with KCl. In rings precontracted with U46619, in the presence of L-NAME and indomethacin the phospholipase inhibitors quinacrine (50 mumol/L) and 4-bromophenacyl bromide (10 mumol/L) attenuated bradykinin- but not AA-induced relaxations. Inhibitors of both lipoxygenase (BW 755c [100 mumol/L] and nafazatrom [20 mumol/L]) and cytochrome P-450 (proadifen [10 mumol/L] and clotrimazole [10 mumol/L]) pathways did not eliminate bradykinin- or AA-induced relaxations, although clotrimazole partially attenuated AA-induced relaxations. These findings suggest that bradykinin-induced relaxation of PCA rings is mediated by AA through a mechanism that is not dependent on cyclooxygenase, lipoxygenase, or cytochrome P-450 pathways.

The nonpeptide WIN 64338 is a bradykinin B2 receptor antagonist

We report the synthesis and in vitro biological activity of the nonpeptide bradykinin receptor antagonist WIN 64338, [[4-[[2-[[bis(cyclohexylamino)methylene]amino]-3-(2- naphthyl)-1-oxopropyl]amino]phenyl]methyl]tributylphosphonium chloride monohydrochloride. WIN 64338 inhibits [3H]-bradykinin binding to the bradykinin B2 receptor on human IMR-90 cells with a binding inhibition constant (Ki) of 64 +/- 8 nM and demonstrates competitive inhibition of bradykinin-stimulated 45Ca2+ efflux from IMR-90 cells (pA2 = 7.1). The antagonist inhibits bradykinin-mediated guinea pig ileum contractility (pA2 = 8.2) and has significantly weaker activity against acetylcholine-induced contractility in the same preparation. WIN 64338 is not active in a rabbit aorta bradykinin B1 receptor assay, demonstrating that it is a selective bradykinin B2 receptor antagonist. The compound inhibits [3H]quinuclidinyl benzilate binding to the rat brain muscarinic receptor (Ki = 350 nM) but is 25- to 100-fold more selective for the bradykinin receptor compared with other receptors against which it has been tested. Synthesis of WIN 64338 has provided a nonpeptide competitive bradykinin B2 antagonist active in both bradykinin radioligand binding and functional assays.

Bradykinin-induced growth inhibition of normal rat kidney (NRK) cells is paralleled by a decrease in epidermal-growth-factor receptor expression

Normal rat kidney fibroblasts, grown to density arrest in the presence of epidermal growth factor (EGF), can be induced to undergo phenotypic transformation by treatment with transforming growth factor beta or retinoic acid. Here we show that bradykinin blocks this growth-stimulus-induced loss of density-dependent growth arrest by a specific receptor-mediated mechanism. The effects of bradykinin are specific, and are not mimicked by other phosphoinositide-mobilizing agents such as prostaglandin F2 alpha. Northern-blot analysis and receptor-binding studies demonstrate that bradykinin also inhibits the retinoic acid-induced increase in EGF receptor levels in these cells. These studies provide additional evidence that EGF receptor levels modulate EGF-induced expression of the transformed phenotype in these cells.

[D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P inhibits the growth of human small cell lung cancer xenografts in vivo

We report the effect of substance P analogue, [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P (D-Phe5SP), on the growth of human small cell lung cancer (SCLC) xenografts HC12 and ICR-SC112. Daily intraperitoneal (ip) administration (500 micrograms/day for 3 weeks) had no effect on HC12 growth rate. When administered by continuous 14-day subcutaneous (sc) infusion by osmotic minipump implanted adjacent to the tumour, D-Phe5SP 2.1 micrograms/day, caused significant inhibition (P < 0.05) of the growth of HC12 and ICR-SC112 on day 7 and day 14 compared with phosphate buffered saline (PBS)-treated controls. HC12 and ICR-SC112 tumour volume remained at 53-67% of control for 14-21 days postinfusion. D-Phe5SP 1 mg/day did not inhibit tumour growth, but dense fibrous capsules developed at the minipump outlet. Animals treated by sc infusion (but not ip) of PBS or D-Phe5SP failed to gain weight, and some groups lost weight. D-Phe5SP-treated animals had lower white blood counts than controls (not significant). These data suggest a potential clinical role for D-Phe5SP in the treatment of SCLC.

Characterization of bradykinin B2 receptors on human IMR-90 lung fibroblasts: stimulation of 45Ca2+ efflux by D-Phe substituted bradykinin analogues

[3H]Bradykinin binds to intact human IMR-90 fetal lung fibroblasts in a time and dose-dependent manner. Binding equilibrium was attained by 120 minutes at 4 degrees C. [3H]Bradykinin binding was saturable; Scatchard analysis of saturation binding data demonstrated a single binding site having a KD = 1.8 +/- 0.2 nM and a receptor concentration of 17.4 +/- 4.0 fmol/10(5) cells. The calculated value for KD(k-1/k1) from the association (k1 = 4.71 x 10(6) mol-1 min-1) and dissociation (k-1 = 1.13 x 10(-2) min-1) rate constants was 2.4 nM. The rank order of potency observed for bradykinin peptide agonists, bradykinin > Lys-bradykinin > Met,Lys-bradykinin > Ile,Ser-bradykinin >> des-Arg9-bradykinin, is consistent with that of a bradykinin B2 receptor. Bradykinin stimulated efflux of 45Ca2+ from IMR-90 cells dose dependently with an EC50 = 331 +/- 50 pM. 45Ca2+ efflux was also demonstrated with Lys-bradykinin and Met-Lys-bradykinin but not by des-Arg10-kallidin (100 nM) or NKA (1 microM). Hoe-140 inhibited bradykinin-induced 45Ca2+ efflux (IC50 = 3 +/- 2 nM). D-Phe7-substituted bradykinin analogues stimulated 45Ca2+ efflux dose dependently and this stimulation of 45Ca2+ efflux was inhibited by Hoe-140. These results suggest that D-Phe7 substituted bradykinin analogues are agonists at the bradykinin B2 receptor in IMR-90 cells.

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.

Functional expression of the bradykinin-B2 receptor cDNA in Chinese hamster lung CCL39 fibroblasts

The bradykinin (BK) B2 receptor cDNA was synthesized by rt-PCR and transfected into the Chinese hamster lung fibroblasts, CCL39. The CCL39 do not contain the mRNA for this receptor and do not bind BK. Clones of transfected cells were screened for BK receptor mRNA, binding of BK, and for [Ca2+]i response to BK. The clones showed various levels of receptor mRNA. Scatchard analysis of three clones, B6, B5 and B1, each gave a Kd of approximately 1.0nM while the Bmax for each clone differed at 320, 38.7, and 5.39 fmoles per 10(6) cells respectively. The [Ca2+]i response of the three clones to BK decreased with the receptor number/cell. Thus, levels of mRNA, BK binding and [Ca2+]i response proved proportionally related in the transfected clones. The actions of BK and alpha-thrombin, which has an endogenous receptor in these cells, were assessed in clone B6. BK proved active but also distinct from thrombin. BK at 10nM and thrombin at 2units/ml both effectively increased cytosolic [Ca2+]i. BK at 10nM stimulated PGE2 production three fold over basal, while thrombin only marginally elevated PGE2 levels. Alone, BK stimulated a small increase in 3H-thymidine incorporation into DNA. However, in combination with insulin, BK stimulated DNA synthesis to 76% of thrombin, a potent mitogen in these cells. These results illustrate that the BK-B2 receptor cDNA can be stably transfected into a mammalian cell and can activate transmembrane signalling pathways.

The structure of neuropeptide receptors

Recently, the primary structures of 17 different receptors for neuropeptides and small peptide hormones have been elucidated by molecular cloning. All but one belong to the superfamily of G-protein coupled receptors which share a topography consisting of seven transmembrane domains. Comparison of primary structures shows that two classes of peptide receptors exist. One referred to as the 'neurokinin-type receptors', possesses many of the typical, conserved amino acid sequence motifs of the aminergic transmitter receptors (e.g. beta-adrenoceptor). The other, referred to the 'secretin-type receptors', displays unrelated and distinctly different sequence motifs which are conserved between the three presently known members of this class. These are the secretin, calcitonin and parathyroid hormone/parathyroid hormone-like polypeptide receptors. One may speculate that many other peptides with a core of biological activity in the N-terminal or middle region may have receptors of the secretin-type.

The effect of TNFa on bradykinin receptor binding, phosphatidylinositol turnover and cell growth in human A431 epidermoid carcinoma cells

In this study, we examined the effect of TNFa on bradykinin (BK) B2 receptor binding and function in human A431 epidermoid carcinoma cells. [3H]BK binds to a single class of receptors on A431 cells in a saturable and reversible manner. A binding affinity (KD) of 3.0 +/- 0.3 nM (n = 4) and a Bmax of 151 +/- 14 fmols/10(6) cells, representing approximately 90,000 BK receptors per cell, was observed. The rank order of potency for BK agonist peptides indicates that the A431 BK receptor appears to be of the B2 subtype. When A431 cells were incubated with TNFa (10 ng/ml) for 48 h prior to BK binding, a significant decrease in the number of BK receptors compared to control was observed. TNFa did not influence the affinity of BK binding to A431 cells and direct addition of TNFa to the binding assay did not effect BK binding. BK-stimulated IP1 formation appeared to be increased in TNFa treated cells compared to control whereas histamine-stimulated IP1 formation was not influenced. Both control and TNFa treated cells were greater than 95% viable. However, TNFa treated cells were blocked in the G1 phase of the cell cycle resulting in a decrease in DNA synthesis. This may be one mechanism for the TNFa-induced decrease in BK receptors in A431 cells.

Recent developments in the understanding of bradykinin receptors

The dramatic activities of bradykinin and related peptides as mediators of pain, inflammation and hypotension have been intensely studied for several decades. More recently, the involvement of bradykinin in regulation of ion transport by epithelia, hormone release from endocrine organs, energy metabolism, tissue growth, and leukocyte activation have become topics of study. Kininogen precursors, synthetic kallikreins, and degradative kininases have been characterized in detail with regard to catalytic mechanisms, physical structure and gene regulation; however, the actual receptors for bradykinin are still only poorly understood. This situation is caused by the lack of availability of potent, specific receptor antagonists. However, specific bradykinin receptor antagonists became available in 1985, and several very potent classes of agents are now available; also, the first bradykinin receptor has been cloned.

Role of bradykinin in inflammatory arthritis: identification and functional analysis of bradykinin receptors on human synovial fibroblasts

Receptor type and function of bradykinin (BK) receptors on human synovial fibroblasts (HSF) was determined. Scatchard analysis of [3H]BK saturation binding to intact synovial cells revealed a single binding site, with a Kd of 3.8 +/- 0.6 nM. HSF express approximately 50,000 BK sites/cell. Specificity of [3H]BK binding was confirmed by the ability of several BK peptide agonists and antagonists to inhibit binding in a dose dependent manner. The rank order of potency for agonist inhibition of [3H]BK and the inability of selective antagonists of the B1-type to displace binding suggest that the BK receptor on HSF is a B2 subtype receptor. The addition of BK to HSF caused a time and concentration dependent increase in PGE2 production. This BK induced PGE2 production was blocked by specific B2 type BK antagonists and not by B1 antagonists. The results of this study identify B2 type BK receptors on synovial fibroblasts and suggest that BK may be a primary mediator in inflammatory arthritis.

Expression cloning of a rat B2 bradykinin receptor

A cDNA encoding a functional bradykinin receptor was isolated from a rat uterus library by a clonal selection strategy using Xenopus laevis oocytes to assay for expression of bradykinin responses. The predicted protein is homologous to the seven transmembrane G protein-coupled superfamily of receptors. Bradykinin and its analogs stimulate a Cl- current oocytes expressing the receptor with the rank order of potency: bradykinin approximately Lys-bradykinin greater than [Tyr8]-bradykinin much greater than [Phe6]bradykinin. This is the rank order of potency observed for these compounds in competitive binding assays on soluble receptor from rat uterus. Des-Arg9-bradykinin (10 microM) elicits no response when applied to oocytes expressing the receptor; thus, the cDNA encodes a B2 type bradykinin receptor. [Thi5,8,DPhe7]bradykinin, where Thi is beta-(2-thienyl)-alanine, is a very weak partial agonist and inhibits the bradykinin-mediated ion flux, suggesting the cDNA encodes a smooth muscle, rather than a neuronal, B2 receptor subtype. Receptor message has a distribution consistent with previous reports of bradykinin function and/or binding in several tissues and is found in rat uterus, vas deferens, kidney, lung, heart, ileum, testis, and brain. Receptor subtypes are a possibility because several tissues contain two or three message species (4.0, 5.7, and 6.5 kilobases). Southern blot high-stringency analysis demonstrated that the rat, guinea pig, and human genomes contain a single gene. As bradykinin is a key mediator of pain, knowledge of the primary structure of this receptor will allow a molecular understanding of the receptor and aid the design of antagonists for pain relief.

Bradykinin receptors undergo ligand-induced desensitization

Bradykinin binds to specific cell surface receptors on Rat13 fibroblasts with a high affinity (2.1 nM). Prolonged exposure of cells to the ligand causes a concentration-dependent decline in surface levels of the 2.1 nM receptor from 40,000 receptors per cell to undetectable levels with a t1/2 of approximately 2 h. The decline occurs in parallel with the appearance of an equal number of lower affinity binding sites (40 nM), suggesting that ligand exposure causes desensitization by an alteration in receptor affinity. The affinity change is characterized by a faster rate of ligand dissociation while the rate of association remains unaltered. The observed desensitization is dependent on the presence of active cellular metabolism since (i) it does not occur in whole cells maintained at 4 degrees C and (ii) membranes prepared from Rat13 cells retain their high-affinity sites at 37 degrees C despite extensive ligand exposure.