Receptors for bradykinin and related kinins: a critical analysis

A Comprehensive Review of Bradykinin-Induced Angioedema Versus Histamine-Induced Angioedema in the Emergency Department

Angioedema (AE) is a condition that is frequently encountered in the emergency department (ED). It is a rare condition with localized, asymmetrical swelling of the skin and/or mucosa that is frequently nonpruritic and primarily affects locations with loose connective tissue. Physicians must have a thorough understanding of this condition since it can cause fatal airway compromise, which might be the presenting symptom. Histamine-mediated AE is the most common type of AE seen in EDs. However, ED physicians must be on the lookout for the less common bradykinin-mediated types of AE as these do not respond to the same therapy as histamine-mediated AE. Hospitals may lack specialized drugs or protocols, and many ED staff may be unable to identify or treat bradykinin-mediated AE. It is crucial to understand the pathophysiology of the various kinds of AE in order to optimize treatment. The goal of this review paper is to provide an overview of the pathophysiology, clinical manifestations, and treatment options for bradykinin and histamine-induced AE in the ED.

Hypothalamic kinin B1 receptor mediates orexin system hyperactivity in neurogenic hypertension

Brain orexin system hyperactivity contributes to neurogenic hypertension. We previously reported upregulated neuronal kinin B1 receptor (B1R) expression in hypertension. However, the role of central B1R activation on the orexin system in neurogenic hypertension has not been examined. We hypothesized that kinin B1R contributes to hypertension via upregulation of brain orexin-arginine vasopressin signaling. We utilized deoxycorticosterone acetate (DOCA)-salt hypertension model in wild-type (WT) and B1R knockout (B1RKO) mice. In WT mice, DOCA-salt-treatment increased gene and protein expression of orexin A, orexin receptor 1, and orexin receptor 2 in the hypothalamic paraventricular nucleus and these effects were attenuated in B1RKO mice. Furthermore, DOCA-salt- treatment increased plasma arginine vasopressin levels in WT mice, but not in B1RKO mice. Cultured primary hypothalamic neurons expressed orexin A and orexin receptor 1. B1R specific agonist (LDABK) stimulation of primary neurons increased B1R protein expression, which was abrogated by B1R selective antagonist R715 but not by the dual orexin receptor antagonist, ACT 462206, suggesting that B1R is upstream of the orexin system. These data provide novel evidence that B1R blockade blunts orexin hyperactivity and constitutes a potential therapeutic target for the treatment of salt-sensitive hypertension.

Role of Kinins in Hypertension and Heart Failure

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

Bradykinin stimulates prostaglandin E2 release in human skeletal muscular fibroblasts

Local mediator prostaglandins and bradykinin are involved in inflammation and pain. We explored bradykinin effects on prostaglandin E2 (PGE2) release from fibroblasts derived from human skeletal muscular biopsies. Bradykinin induced PGE₂ release through bradykinin B2 receptors, since PGE₂ release was blocked by the bradykinin B2 receptor selective antagonist FR173657 and B2 receptor agonist (Hyp³)-bradykinin showed effects comparable to bradykinin. Consistently, bradykinin induced both mRNA cyclooxygenase 2 (COX-2) and protein. Bradykinin also induced ERK1/2 and p38 phosphorylation and provoked the translocation from the cytosol to the nucleus of p65/NF-kB. The release of PGE₂ by bradykinin could be blocked inhibiting COX-2 and p65/NF-kB, ERK1/2 or p38 activation. Both ERK1/2 and p38 were upstream to NF-kB inasmuch siRNAs significantly blocked the p65/NF-kB activation induced by bradykinin. Thus, bradykinin, acting via B2 receptors, induced PGE₂ release through ERK1/2 and p38-dependent pathways and consequent p65/NF-kB translocation to nucleus. p65/NF-kB induced COX-2 transcription. The release of PGE₂ provide a possible explanation for the role of bradykinin in inflammatory diseases.

Plasma bradykinin concentrations during septic shock determined by a novel LC-MS/MS assay

BACKGROUND

Bradykinin is an important mediator of inflammation and vascular permeability and could have an important role in the development of septic shock. Measurement of bradykinin by immunological methods may suffer from interference and lack of specificity. We developed and validated a liquid chromatography mass spectrometry assay (LC-MS/MS) for plasma bradykinin.

METHODS

We used plasma samples from healthy volunteers (n = 19) and patients with septic shock (n = 47). Stable isotope bradykinin internal standard was added to samples before solid-phase extraction and quantification by LC-MS/MS. Stability of bradykinin was studied for 12 months.

RESULTS

Our assay has good sensitivity (0.1 nmol/l) and a wide linear range (0.1-1000 nmol/l). Bradykinin added to plasma was stable for 12 months at -20 °C when a mixture of protease inhibitors was added at sampling but degraded during repeated freezing and thawing. Bradykinin concentration in plasma from septic shock patients (<0.1-0.6 nmol/l) did not change significantly during shock and recovery but differed slightly from that in healthy individuals (0.5-1.1 nmol/l).

CONCLUSIONS

Our bradykinin assay was successfully used to determine bradykinin concentrations in plasma samples. Intensive care unit patients with septic shock had low concentrations of plasma bradykinin during both shock and recovery phases.

Novel signaling of dynorphin at κ-opioid receptor/bradykinin B2 receptor heterodimers

The κ-opioid receptor (KOR) and bradykinin B2 receptor (B2R) are involved in a variety of important physiological processes and share many similar characteristics in terms of their distribution and functions in the nervous system. We first demonstrated the endogenous expression of KOR and B2R in human SH-SY5Y cells and their co-localization on the membrane of human embryonic kidney 293 (HEK293) cells. Bioluminescence and fluorescence resonance energy transfer and the proximity ligation assay were exploited to demonstrate the formation of functional KOR and B2R heteromers in transfected cells. KOR/B2R heteromers triggered dynorphin A (1-13)-induced Gαs/protein kinase A signaling pathway activity, including upregulation of intracellular cAMP levels and cAMP-response element luciferase reporter activity, resulting in increased cAMP-response element-binding protein (CREB) phosphorylation, which could be dampened by the protein kinase A (PKA) inhibitor H89. This indicated that the co-existence of KOR and B2R is critical for CREB phosphorylation. In addition, dynorphin A (1-13) induced a significantly higher rate of proliferation in HEK293-KOR/B2R and human SH-SY5Y cells than in the control group. These results indicate that KOR can form a heterodimer with B2R and this leads to increased protein kinase A activity by the CREB signaling pathway, leading to a significant increase in cell proliferation. The nature of this signaling pathway has significant implications for the role of dynorphin in the regulation of neuroprotective effects.

Bowman-Birk protease inhibitor from Vigna unguiculata seeds enhances the action of bradykinin-related peptides

The hydrolysis of bradykinin (Bk) by different classes of proteases in plasma and tissues leads to a decrease in its half-life. Here, Bk actions on smooth muscle and in vivo cardiovascular assays in association with a protease inhibitor, Black eyed-pea trypsin and chymotrypsin inhibitor (BTCI) and also under the effect of trypsin and chymotrypsin were evaluated. Two synthetic Bk-related peptides, Bk₁ and Bk₂, were used to investigate the importance of additional C-terminal amino acid residues on serine protease activity. BTCI forms complexes with Bk and analogues at pH 5.0, 7.4 and 9.0, presenting binding constants ranging from 10³ to 10⁴ M⁻¹. Formation of BTCI-Bk complexes is probably driven by hydrophobic forces, coupled with slight conformational changes in BTCI. In vitro assays using guinea pig (Cavia porcellus) ileum showed that Bk retains the ability to induce smooth muscle contraction in the presence of BTCI. Moreover, no alteration in the inhibitory activity of BTCI in complex with Bk and analogous was observed. When the BTCI and BTCI-Bk complexes were tested in vivo, a decrease of vascular resistance and consequent hypotension and potentiating renal and aortic vasodilatation induced by Bk and Bk₂ infusions was observed. These results indicate that BTCI-Bk complexes may be a reliable strategy to act as a carrier and protective approach for Bk-related peptides against plasma serine proteases cleavage, leading to an increase in their half-life. These findings also indicate that BTCI could remain stable in some tissues to inhibit chymotrypsin or trypsin-like enzymes that cleave and inactivate bradykinin in situ.

Ornithokinin (avian bradykinin) from the skin of the Chinese bamboo odorous frog, Odorrana versabilis

One of the most widespread and abundant families of pharmacologically active peptides in amphibian defensive skin secretions is the bradykinins and related peptides. Despite retaining certain primary structural attributes that assign them to this peptide family, bradykinins and related peptides are unique among amphibian skin peptides in that they exhibit a wide range of primary structural variations, post-translational modifications and/or N-terminal or C-terminal extensions. Initially it was believed that their high degree of primary structural heterogeneity was reflective of random gene mutations within species, but latterly, there is an increasing body of evidence that the spectrum of structural modifications found within this peptide family is reflective of the vertebrate predator spectrum of individual species. Here we report the discovery of ornithokinin (avian bradykinin - Thr(6) , Leu(8) -bradykinin) in the skin secretion of the Chinese bamboo odorous frog, Odorrana versabilis. Molecular cloning of its biosynthetic precursor-encoding cDNA from a skin secretion-derived cDNA library revealed a deduced open-reading frame of 86 amino acid residues, encoding a single copy of ornithokinin towards its C-terminus. The domain architecture of this ornithokinin precursor protein was consistent with that of a typical amphibian skin peptide and quite different to that of the ornithokininogen from chicken plasma. Ornithokinin was reported to induce hypotension in the chicken and to contract the chicken oviduct but to have no obvious effect on the rat uterus. However, in this study, synthetic ornithokinin was found to contract the rat ileum (EC50  = 539 nM) and to increase contraction frequency in the rat uterus (EC50  = 1.87 μM).

Activation of kinin B1 receptor evokes hyperthermia through a vagal sensory mechanism in the rat

Background

Kinins are mediators of pain and inflammation. Their role in thermoregulation is, however, unknown despite the fact the B1 receptor (B1R) was found implicated in lipopolysaccharide (LPS)-induced fever. The aim of this study was to investigate the mechanism by which peripheral B1R affects body core temperature in a rat model known to show up-regulated levels of B1R.

Methods

Male Sprague–Dawley rats received streptozotocin (STZ, 65 mg/kg; i.p.) to enhance B1R expression. Control rats received the vehicle only. One week later, rectal temperature was measured in awake rats after i.p. injection of increasing doses (0.01 to 5 mg/kg) of des-Arg⁹-Bradykinin (BK) and Sar-[D-Phe⁸]des-Arg⁹-BK (B1R agonists) or BK (B2R agonist). The mechanism of B1R-induced hyperthermia was addressed using specific inhibitors and in rats subjected to subdiaphragmatic vagal nerve ligation. B1R mRNA level was measured by quantitative Real Time-polymerase chain reaction (qRT-PCR) and B1R was localized by confocal microscopy.

Results

B1R agonists (0.1 to 5 mg/kg) showed transient (5- to 30-minute) and dose-dependent increases of rectal temperature (+1.5°C) in STZ-treated rats, but not in control rats. BK caused no effect in STZ and control rats. In STZ-treated rats, B1R agonist-induced hyperthermia was blocked by antagonists/inhibitors of B1R (SSR240612), cyclooxygenase-2 (COX-2) (niflumic acid) and nitric oxide synthase (NOS) (L-NAME), and after vagal nerve ligation. In contrast, COX-1 inhibition (indomethacin) had no effect on B1R agonist-induced hyperthermia. In STZ-treated rats, B1R mRNA was significantly increased in the hypothalamus and the vagus nerve where it was co-localized with calcitonin-gene-related peptide in sensory C-fibers.

Conclusion

B1R, which is induced in inflammatory diseases, could contribute to hyperthermia through a vagal sensory mechanism involving prostaglandins (via COX-2) and nitric oxide.

Bradykinin type-2 receptor expression correlates with age and is subjected to transcriptional regulation

Accumulating work in experimental animals suggests that bradykinin (BK) exerts cardioprotective effects via bradykinin type-2 receptors (BK-2Rs). In human end-stage heart failure, BK-2Rs are significantly downregulated by mechanisms that have remained elusive. Heart tissues from idiopathic dilated cardiomyopathy (IDC; n = 7), coronary heart disease (CHD; n = 6), and normal patients (n = 6) were analyzed by RT-PCR, SSCP, and Western blotting. In normal and IDC hearts, BK-2R expression increased with age, with a lower relative increase in IDC hearts. BK-2R mRNA and protein levels showed a positive linear correlation, suggesting transcriptional regulation. Two known BK-2R promoter polymorphisms, −58T/C and −9/+9, were found to be present in the study population. The allelic frequencies for the C-allele in −58T/C were 0.58 in normal and CHD hearts and 0.81 in IDC hearts. Furthermore, the allelic frequencies for the −9 and +9 alleles were 0.42 and 0.58 in normal hearts and 0.64 and 0.36 in IDC hearts, respectively. All analyzed CHD hearts were homozygous for the −9 allele. Thus, the expression of cardioprotective BK-2Rs in human hearts is increased with age in normal and IDC hearts and may be regulated on the transcriptional level. Moreover, comparison of normal subjects and patients with failing hearts revealed different allelic frequencies in each of two known BK-2R gene polymorphisms.

Peptidomic dissection of the skin secretion of Phasmahyla jandaia (Bokermann and Sazima, 1978) (Anura, Hylidae, Phyllomedusinae)

The systematic investigation of the peptidic composition of the skin secretion of Phasmahyla jandaia, a phyllomedusine anuran endemic to the southern region of the Espinhaço range in Brazil, is herein reported. By means of de novo interpretation of tandem mass spectrometric data, Edman N-terminal sequencing and similarity searches, 57 peptides - including phylloseptins, dermaseptins stricto sensu, dermatoxins, hyposins, tryptophyllins, caerulein-related, bradykinin-related, bradykinin potentiating, tyrosine-rich, and opioid peptides - were sequenced. Moreover, five peptide families without significant similarity to other known molecules were verified. Differently from most Phyllomedusinae genera, the molecular diversity in the skin of representatives of Phasmahyla remained unprospected until now. Therefore, besides disclosing novel natural variants of number of bioactive peptides, the present study contributes to the understanding of the evolution of biochemical characters of the phyllomedusines.

Differential regulation of inducible and endothelial nitric oxide synthase by kinin B1 and B2 receptors

Kinins are vasoactive peptides that play important roles in cardiovascular homeostasis, pain and inflammation. After release from their precursor kininogens, kinins or their C-terminal des-Arg metabolites activate two distinct G protein-coupled receptors (GPCR), called B2 (B2R) or B1 (B1R). The B2R is expressed constitutively with a wide tissue distribution. In contrast, the B1R is not expressed under normal conditions but is upregulated by tissue insult or inflammatory mediators. The B2R is considered to mediate many of the acute effects of kinins while the B1R is more responsible for chronic responses in inflammation. Both receptors can couple to Galphai and Galphaq families of G proteins to release mediators such as nitric oxide (NO), arachidonic acid, prostaglandins, leukotrienes and endothelium-derived hyperpolarizing factor and can induce the release of other inflammatory agents. The focus of this review is on the different transduction events that take place upon B2R and B1R activation in human endothelial cells that leads to generation of NO via activation of different NOS isoforms. Importantly, B2R-mediated eNOS activation leads to a transient ( approximately 5min) output of NO in control endothelial cells whereas in cytokine-treated endothelial cells, B1R activation leads to very high and prolonged ( approximately 90min) NO production that is mediated by a novel signal transduction pathway leading to post-translational activation of iNOS.

Structure-activity relationships of novel peptide agonists of the human bradykinin B2 receptor

The nonapeptide bradykinin (BK) is involved in the genesis of inflammation, edema and in pain mediation. As such, much effort has gone into the development of peptide/non-peptide antagonists to counteract these processes. However, there is an increasing awareness of the potential value of chemically stable BK agonists in the treatment of diabetes and cardiovascular diseases. In this study, a structure-activity relationship study of BK was performed to develop potent and stable peptide mimetics active at the human B2 receptors (hB2R). Twenty-three analogues were produced with substitutions at positions 1, 3, 5, 7, 8 and/or 9 of BK. In vitro binding (on transiently transfected HEK-293T cells) and biological activities (vasomotricity tests on human umbilical veins, MAPK assays on HEK-293T cells) of novel BK peptide derivatives at hB2R were determined alongside with previously reported synthetic agonists (e.g. RMP-7, JMV1609, FR190997). Some peptides were also tested in vivo in rats and rabbits using blood pressure assays. Two compounds, [Hyp(3), Thi(5), Cha(8)]-BK and [Hyp(3), Thi(5), (N)Chg(7), Thi(8)]-BK, exhibited equivalent (or even greater) in vitro affinities and potencies to BK at the naturally expressed and recombinant hB2R. Their potency and duration of action in vivo were highly superior to BK, thus inferring that they can withstand intravascular proteolysis. These novel compounds show promise as candidates for investigating the pharmacology of BK receptors and developing potential therapeutical applications.

Mode of action of cytokines on nociceptive neurons

Cytokines are pluripotent soluble proteins secreted by immune and glial cells and are key elements in the induction and maintenance of pain. They are categorized as pro-inflammatory cytokines, which are mostly algesic, and anti-inflammatory cytokines, which have analgesic properties. Progress has been made in understanding the mechanisms underlying the action of cytokines in pain. To date, several direct and indirect pathways are known that link cytokines with nociception or hyperalgesia. Cytokines may act via specific cytokine receptors inducing downstream signal transduction cascades, which then modulate the function of other receptors like the ionotropic glutamate receptor, the transient vanilloid receptors, or sodium channels. This receptor activation, either through amplification of the inflammatory reaction, or through direct modulation of ion channel currents, then results in pain sensation. Following up on results from animal experiments, cytokine profiles have recently been investigated in human pain states. An imbalance of pro- and anti-inflammatory cytokine expression may be of importance for individual pain susceptibility. Individual cytokine profiles may be of diagnostic importance in chronic pain states, and, in the future, might guide the choice of treatment.

Role of kinin B1 and B2 receptors in a rat model of neuropathic pain

Kinin B1 and B2 receptor (R) gene expression (mRNA) is increased in the sensory system after peripheral nerve injury. This study measured the densities of B1R and B2R binding sites in the spinal cord and dorsal root ganglia (DRG) by quantitative autoradiography, and evaluated the effects of two selective non-peptide antagonists at B1R (LF22-0542) and B2R (LF16-0687) on pain behavior after partial ligation of the left sciatic nerve. Increases of B1R binding sites were seen in superficial laminae of the ipsi- and contralateral spinal cord at 2 and 14 days while B2R binding sites were increased on the ipsilateral side at 2 days and on both sides at 14 days. In DRG, B1R and B2R binding sites were significantly increased at 2 days (ipsilateral) and 14 days on both sides. Whereas tactile allodynia started to develop progressively from 2 to 25 days post-ligation, the occurrence of cold allodynia and thermal hyperalgesia became significant from day 8 and day 14 post-ligation, respectively. At day 21 after sciatic nerve ligation, thermal hyperalgesia was blocked by LF22-0542 (10 mg/kg, s.c.) and LF16-0687 (3 mg/kg, s.c.), yet both antagonists had no effect on tactile and cold allodynia. Data highlight the implication of both kinin receptors in thermal hyperalgesia but not in tactile and cold allodynia associated with peripheral nerve injury. Hence LF22-0542 and LF16-0687 present therapeutic potential for the treatment of some aspects of neuropathic pain.

Lovastatin induces the expression of bradykinin type 2 receptors in cultured human coronary artery endothelial cells

Cardioprotective bradykinin type-2 receptors (BK-2Rs) are downregulated in the myocardial endothelium of both human and rat failing hearts. Statins are cardioprotective drugs that reduce the level of plasma cholesterol but also exert cholesterol-independent pleiotropic effects. Here we examined the effect of lovastatin on BK-2R expression in cultured human coronary artery endothelial cells. The effect of lovastatin on the expression of BK receptors in human coronary artery endothelial cells (HCAECs) was examined by real-time PCR, Western blot analysis and immunocytochemistry. Lovastatin induced a time- and concentration-dependent increase in both BK-2R and BK-1R mRNA expression in the cultured HCAECs. Also, the number of functional BK-2Rs capable of inducing BK-mediated NO production and cGMP signaling was increased in the lovastatin-treated HCAECs. Mevalonate, the direct metabolite of HMG-CoA reductase, reversed the effect of lovastatin. Furthermore, lovastatin inhibited Rho activation and a selective inhibitor of Rho-associated kinases, Y-27632, induced a similar increase in BK-2R expression as lovastatin. In contrast, a specific inhibitor of COX-2, NS398, significantly inhibited the lovastatin-induced expression of BK-2Rs. Here we show for the first time that lovastatin induces the expression of BK-2Rs in cultured human coronary artery endothelial cells through a novel cholesterol-independent pleiotropic mechanism that involves RhoA kinase inhibition and COX-2 activation. Thus, reported beneficial effects of statins in cardiovascular diseases may be partly mediated by an increased expression of cardioprotective BK-2Rs in the endothelial cells of the coronary tree. Moreover, the use of COX-2 inhibitors may affect the level of endothelial BK-2Rs in a negative fashion.

TNF-alpha and IL-1beta mediate inflammatory hypernociception in mice triggered by B1 but not B2 kinin receptor

Kinin receptors are involved in the genesis of inflammatory pain. However, there is controversy concerning the mechanism by which B(1) and B(2) kinin receptors mediate inflammatory hypernociception. In the present study, the role of these receptors on inflammatory hypernociception in mice was addressed. Mechanical hypernociception was detected with an electronic pressure meter paw test in mice and cytokines were measured by ELISA. It was observed that in naïve mice a B(2) (d-Arg-Hyp(3), d-Phe(7)-bradykinin) but not a B(1) kinin receptor antagonist (des-Arg(9)-[Leu(8)]-bradykinin, DALBK) inhibited bradykinin- and carrageenin-induced hypernociception. Bradykinin-induced hypernociception was inhibited by indomethacin (5 mg/kg) and guanethidine (30 mg/kg), while not affected by IL-1ra (10 mg/kg) or antibody against keratinocyte-derived chemokine (KC/CXCL-1, 500 ng/paw) or in TNFR1 knockout mice. By contrast, in previously lipopolysaccharide (LPS)-primed mouse paw, B(1) but not B(2) kinin receptor antagonist inhibited bradykinin hypernociception. Furthermore, B(1) kinin receptor agonist induced mechanical hypernociception in LPS-primed mice, which was inhibited by indomethacin, guanethidine, antiserum against TNF-alpha or IL-1ra. This was corroborated by the induction of TNF-alpha and IL-1beta release by B(1) kinin receptor agonist in LPS-primed mouse paws. Moreover, B(1) but not B(2) kinin receptor antagonist inhibited carrageenin-induced hypernociception, and TNF-alpha and IL-1beta release as well, in LPS-primed mice. These results suggest that in naïve mice the B(2) kinin receptor mediates inflammatory hypernociception dependent on prostanoids and sympathetic amines, through a cytokine-independent mechanism. On the other hand, in LPS-primed mice, the B(1) kinin receptor mediates hypernociception by a mechanism dependent on TNF-alpha and IL-1beta, which could stimulate prostanoid and sympathetic amine production.

Kallikrein-kinin system activation by Lonomia obliqua caterpillar bristles: involvement in edema and hypotension responses to envenomation

Lonomia obliqua envenomation induces an intense burning sensation at the site of contact and severe hemorrhage followed by edema and hypotension, and after few days death can occur usually due to acute renal failure. In order to understand more about the envenomation syndrome, the present study investigates the role played by kallikrein-kinin system (KKS) in edematogenic and hypotensive responses to the envenomation by L. obliqua. The incubation of L. obliqua caterpillar bristles extract (LOCBE) with plasma results in kallikrein activation, measured by cromogenic assay using the kallikrein synthetic substrate S-2302 (H-D-Pro-Phe-Arg-pNA). It was also showed that LOCBE was able to release kinins from low-molecular weight kininogen (LMWK). Moreover, it was demonstrated that previous administration of a kallikrein inhibitor (aprotinin) or bradykinin B2 receptor antagonist (HOE-140) significantly reduces the edema and hypotension in response to LOCBE, using mouse paw edema bioassay and mean arterial blood pressure analysis, respectively. The results demonstrate a direct involvement of the KKS in the edema formation and in the fall of arterial pressure that occur in the L. obliqua envenomation syndrome.

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.

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.

Role of cystatins in tumor neovascularization

Cystatins form a large superfamily of proteins with diverse biologic activities. All members of the cystatin superfamily share the presence of one, two or three cystatin domains. Cystatins were initially believed to act mainly as inhibitors of lysosomal cysteine proteases. In recent years, however, there has been increased awareness of additional or alternate biologic functions for these proteins. In this review, the authors will discuss the most recent findings and hypotheses that suggest that some members of the cystatin superfamily may play important roles during tumor progression. Special emphasis is given to their potential role as novel anti-angiogenic agents.

Increased expression of bradykinin type-1 receptors in endothelium of intramyocardial coronary vessels in human failing hearts

In experimental animals, bradykinin type-1 receptors (BK-1Rs) are induced during inflammation and ischemia, and, by exerting either cardioprotective or cardiotoxic effects, they may contribute to the pathogenesis of heart failure. Nothing is known about the expression of BK-1Rs in human heart failure. Human heart tissue was obtained from excised hearts of patients undergoing cardiac transplantation (n = 13), due to idiopathic dilated cardiomyopathy (IDC; n = 7) or to coronary heart disease (CHD; n = 6), and from normal hearts (n = 6). The expression of BK-1Rs was analyzed by means of competitive RT-PCR, Western blot analysis, and immunohistochemistry. Expression of BK-1R mRNA was increased in both IDC (2.8-fold) and CHD (2.1-fold) hearts compared with normal hearts. The observed changes were verified at the protein level. Expression of BK-1Rs in failing hearts localized to the endothelium of intramyocardial coronary vessels and correlated with an increased expression of TNF-alpha in the vessel wall. Treatment of human coronary artery endothelial cells with TNF-alpha increases their BK-1R expression. These novel results show that BK-1Rs are induced in the endothelium of intramyocardial coronary vessels in failing human hearts and so may participate in the pathogenesis of heart failure.

Characterisation of local inflammatory response induced by Thalassophryne nattereri fish venom in a mouse model of tissue injury

The Thalassophryne nattereri fish venom induces a severe burning pain, oedema, and necrosis observed both clinically and experimentally. The present study was carried out in order to describe the pattern of local acute inflammatory response after T. nattereri venom injection. Our findings show that the edematogenic response induced by T. nattereri venom in footpad of mice was dose- and time dependent, and remained significantly elevated over 48 h after injection. Analysis of footpad homogenates were tested for the presence of TNF-alpha, IL-1beta and IL-6, and demonstrated augmented levels of these cytokines. Our results showed that the injection of venom developed an inadequate cellular inflammatory response evidenced by poor infiltration of mononuclear cells, preceded by decreased number of these cells in peripheral blood. In contrast, we observed an early intense recruitment of neutrophil to peritoneal cavity, accompanied by a significant decrease in the number of mononuclear cells. A drastic increase in the total amount of cells, mainly in neutrophils, followed by mononuclear cell recruitment was observed 24 h. In addition, we also demonstrated that T. nattereri venom affects the viability of mononuclear cells (J774A1) in culture. We conclude that the scarcity of inflammatory cellular influx into local lesions (intraplantar) induced by T. nattereri venom could be a consequence of an impaired blood flow in venules at injured tissue and cytotoxic effect of the venom on inflammatory cells can contribute to this impairment.

Mechanism of kinin release during experimental acute pancreatitis in rats: evidence for pro- as well as anti-inflammatory roles of oedema formation

1 Kinin B(2) receptor antagonists or tissue kallikrein (t-KK) inhibitors prevent oedema formation and associated sequelae in caerulein-induced pancreatitis in the rat. We have now further investigated the mechanism of kinin generation in the pancreas. 2 Kinins were elevated in the pancreatic tissue already before oedema formation became manifest. Peak values (421+/-59 pmol g(-1) dry wt) were reached at 45 min and remained elevated for at least 2 h; a second increase was observed at 24 h. Pretreatment with the B(2) receptor antagonist icatibant abolished kinin formation, while post-treatment was ineffective. 3 Total kininogen levels were very low in the pancreas of controls, but increased 75-fold during acute pancreatitis. This increase was absent in rats that were pretreated with icatibant. 4 During pancreatitis, t-KK-like and plasma kallikrein (p-KK)-like activity in the pancreas, as well as trypsinogen activation peptide (TAP) increased significantly. Icatibant pretreatment further augmented t-KK about 100-fold, while p-KK was significantly attenuated; TAP levels remained unaffected. 5 Endogenous protease inhibitors (alpha(1)-antitrypsin, alpha(2)-macroglobulin) were low in normal tissues, but increased 45- and four-fold, respectively, during pancreatitis. This increase was abolished when oedema formation was prevented by icatibant. 6 In summary, oedema formation is initiated by t-KK; the ensuing plasma protein extravasation supplies further kininogen and active p-KK to the tissue. Concomitantly, endogenous protease inhibitors in the oedema fluid inhibit up to 99% of active t-KK. Our data thus suggest a complex interaction between kinin action and kinin generation involving positive and negative feedback actions of the inflammatory oedema.

Bradykinin receptors as a therapeutic target

Biologically-active kinins, including bradykinin (BK) and Lys(0)-BK (kallidin), are short-lived peptide mediators predominantly generated by the enzymatic action of kallikreins on kininogen precursors. A diverse spectrum of physiological and pathological actions attributed to local kinin production is a consequence of the activation of G-protein-coupled receptors (GPCRs). Currently, two major subtypes of kinin receptor, designated B(1) and B(2), are recognised, although there is much evidence for pharmacological heterogeneity, particularly within the B(2) receptors. Considering these facts and the widespread distribution of kinin receptors in many human tissues, it is no surprise that the therapeutic potential of kinins and kinin receptor antagonists remains the focus of numerous investigations. Studies in animals and animal tissues, instrumental in elucidating the biological roles of kinins, are well-documented in numerous excellent reviews. Unfortunately, and despite the enormous potential illustrated by animal studies, attempts to develop kinin analogues as therapeutic agents to combat human disease have largely proven disappointing. Consequently, this review selectively focuses upon studies that are directly relevant to the targeting of human BK receptors as a therapeutic intervention. In addition to providing a succinct review of well-documented pathological conditions to which kinin receptors contribute, the authors have also included more recent data that illustrate new avenues for the therapeutic application of kinin analogues.

Structure and signalling pathways of kinin receptors

Kinins are peptide hormones that transmit their biological effects via G protein-coupled receptors. They are generated by kallikrein-mediated proteolysis of their precursors, the kininogens. Kinins have been implicated in the regulation of blood pressure, pain sensation and cell growth. Interestingly, all components of the kallikrein-kinin system have also been localized in testis. Effects of kallikrein and bradykinin on pre-spermatogonial cell proliferation and on sperm motility suggest a regulatory function of kinins and their cognate receptors in the male reproductive system. This review is dedicated to summarize the current knowledge about structure, signal transduction and regulation of kinin receptors. Particular emphasis will be given to the kinin-induced activation of the mitogen-activated protein kinase cascade which might represent an important signalling pathway involved in regulation of spermatogenesis and sperm function.

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).

MAP kinase signaling cascade dysfunction specific to Alzheimer's disease in fibroblasts

Mitogen-activated protein kinases (such as Erk1/2) regulate phosphorylation of the microtubule-associated protein tau and processing of the amyloid protein beta, both events critical to the pathophysiology of Alzheimer's disease (AD). Here we report that enhanced and prolonged Erk1/2 phosphorylation in response to bradykinin (BK) was detected in fibroblasts of both familial and sporadic AD, but not age-matched controls (AC). The AD-associated abnormality in Erk1/2 phosphorylation was not seen in fibroblasts from Huntington's disease patients with dementia. The elevation of Erk1/2 phosphorylation occurred immediately after BK stimulation and required an IP3-sensitive Ca(2+) release as well as activation of PKC and c-src as upstream events. Treatment of cells with the PI-3 kinase blocker LY924002 partially inhibited the BK-stimulated Erk1/2 phosphorylation in AC, but had no effect in AD cells, suggesting that the BK-induced Erk1/2 phosphorylation in AD cells is independent of PI-3 kinase. Activation of the cAMP-responsive element binding protein (CREB) monitored as an increase in phosphorylation at Ser-133 was also observed after BK stimulation. Unlike the AD-specific differences for Erk1/2, however, the BK-stimulated CREB phosphorylation was not different between AC and AD cells. Abnormal Erk1/2 activities may alter downstream cellular processes such as gene transcription, amyloid precursor protein processing, and tau protein phosphorylation, which contribute to the pathogenesis of AD. Moreover, detection of AD-specific differences in MAP kinase in peripheral tissues may provide an efficient means for early diagnosis of AD as well as help us to identify therapeutic targets for drug discovery.

Mechanism involved in bradykinin-induced efferent arteriole dilation

BACKGROUND

There is evidence that kinins play a role in the regulation of renal hemodynamics. The balance of vascular resistance in afferent and efferent arterioles (Af-Art and Ef-Art) is a crucial factor in controlling glomerular filtration. We have previously reported that bradykinin has a biphasic effect on the Af-Art and that dilation and constriction are due to cyclooxygenase products, not nitric oxide (NO). The present study was designed to examine (1) the direct effect of bradykinin on the Ef-Art and (2) the mechanisms that mediate bradykinin-induced Ef-Art dilation.

METHODS

Isolated Ef-Arts were microperfused retrograde while maintaining the Ef-Art pressure at 30 mm Hg. Isolated Ef-Arts were preconstricted with norepinephrine.

RESULTS

Perfusing the Ef-Art lumen with bradykinin caused dose-dependent vasodilation, increasing diameter from 6.9 +/- 0.7 to 8.0 +/- 0.8 (0.01 nmol/L), 8.3 +/- 0.7* (0.1 nmol/L), 10.3 +/- 0.7* (1 nmol/L) and 11.5 +/- 0.8* microm (10 nmol/L; N = 8; *P < 0.05 vs. NE). Neither L-NAME nor indomethacin blocked the vasodilator effect of bradykinin; the diameter increased from 8.1 +/- 0.9 to 12.9 +/- 0.6 microm (10 nmol/L; P < 0.05 vs. control; N = 6) in the L-NAME-treated group and from 7.4 +/- 0.9 to 11.0 +/- 1.0 microm (10 nmol/L; P < 0.05 vs. control; N = 6) in the indomethacin-treated group. However, 25 micromol/L 17-ODYA, a cytochrome cP450 inhibitor, blocked the vasodilator effect of 10-8 mol/L bradykinin, leaving diameter unchanged (from 7.9 +/- 0.8 to 7.7 +/- 0.7 microm; N = 6). Finally, 0.1 micromol/L icatibant, a B2 receptor antagonist, completely blocked the vasodilation induced by bradykinin, and the diameter went from 7.8 +/- 0.7 to 8.3 +/- 0.8 microm (10 nmol/L).

CONCLUSIONS

Bradykinin dilates Ef-Arts, but in contrast to Af-Arts its effect is not biphasic. The vasodilator effect of bradykinin in Ef-Arts via B2 receptors is mediated by cP450 metabolites (probably EETs), but not by NO or cyclooxygenase products.

Studies on the angiotensin-converting enzyme and the kinin B2 receptor in the rabbit jugular vein: modulation of contractile response to bradykinin

The rabbit jugular vein (rbJV) was used as a bioassay system to validate some early and new hypothetical interactions between the angiotensin-converting enzyme (ACE) and the B2 receptor, which may be influenced by ACE inhibitors (ACE-I). These involve the potentiation of the contractile effect of bradykinin (BK) and BK analogues, which are inactivated by ACE (e.g., [Hyp3, Tyr(Me8)]-BK (R556)), the prevention of BK-induced B2 receptor desensitisation, and the restoration of receptor sensitivity in tissues desensitised with B2 receptor agonists. Enzymatic degradation studies performed in vitro and in vivo revealed that BK and R556 are readily degraded by rabbit ACE whereas [Phe8psi(CH2-NH)Arg9]-BK (R379) is totally resistant. BK, R556, and R379 contracted endothelium-denuded veins with similar potencies (pEC50 range 8.10-8.50). Tissues pretreated with ACE-I showed an increase in pEC50 values for BK and R556 but not for R379. ACE-I (captopril, enalaprilat) were unable to prevent B2 receptor desensitisation induced by BK (1 microM). ACE-I partially restored B2 receptor-mediated contraction in tissues initially exposed to BK but not to R379. These effects were antagonised by HOE 140 (0.1 microM) but were unaffected by AcLys[Dbeta-Nal7, Ile8]-desArg9BK (R715) (1 microM) or by Losartan (1 microM). In conclusion, the potentiation of BK and its analogues relates exclusively on prevention of their metabolism, B2 receptor desensitisation is not affected by ACE-I, and restoration of tissue responsiveness to BK by ACE-I may be attributed to changes in BK concentrations in the vicinity of the B2 receptor.

Species differences in bradykinin receptor-mediated responses of the airways

1. Bradykinin (BK) is a nine amino acid peptide (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) formed from the plasma precursor kininogen during inflammation and tissue injury. The actions of BK are mediated by G protein-coupled cell surface receptors, designated B1 and B2. 2. BK has a plethora of effects in the airways including bronchoconstriction, bronchodilation, stimulation of cholinergic and sensory nerves, mucus secretion, cough and oedema resulting from promotion of microvascular leakage. These airway effects are mediated in the main by the B2 receptor subtype. 3. BK acts mainly indirectly, primarily through airway nerve activation, but also by the release of prostanoids, thromboxanes and nitric oxide (NO). 4. Airway responses to BK have been studied in detail in guinea-pigs, mice, sheep and rats. This review describes the effects of BK in these species and draws comparison with its effects in normal humans and patients with respiratory diseases. 5. Despite its many and varied effects in the airways of animals and man, the exact contribution of BK to airways disease remains unclear.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Bradykinin increases Na(+)-K(+) pump activity in cultured guinea-pig tracheal smooth muscle cells

1. The effect of bradykinin on the Na+-K+ pump of airway smooth muscle was investigated by measuring ouabain-sensitive (86)Rb(+) uptake in cultured guinea-pig tracheal smooth muscle cells. 2. Bradykinin induced a concentration-dependent increase in ouabain-sensitive (86)Rb(+) uptake, with an EC(50) of 3 nM (pD(2) = 8.50+/-0.10). Stimulation was not affected by indomethacin (1 microM) suggesting that it is not mediated by cycloxygenase products of arachidonic acid. 3. The B(1) receptor agonists Lys-des-Arg(9)-bradykinin and des-Arg(9)-bradykinin had no effect on ouabain-sensitive (86)Rb(+) uptake. In contrast, the B(1) and B(2) receptor agonist Lys-bradykinin induced a concentration-dependent increase in ouabain-sensitive (86)Rb(+) uptake with an EC(50) of 6 nM (pD(2) = 8.21 +/- 0.20). 4. The B(1) receptor antagonist des-Arg(10)-HOE 140 (1 microM) had no effect on bradykinin-stimulated ouabain-sensitive (86)Rb(+) uptake. The B(2) receptor antagonists HOE 140 and WIN 64338 antagonized bradykinin-stimulated ouabain-sensitive (86)Rb(+) uptake with pK(B) values (-log M) of 8.20 +/- 0.08 and 8.11 +/- 0.20 respectively. 5. Reducing extracellular Na+ from 146 mM to 11 mM caused a 53.5% decrease in basal ouabain-sensitive (86)Rb+ uptake and abolished bradykinin-induced uptake. Two inhibitors of the Na(+)-H(+) exchanger, methylisobutyl-amiloride (MIA; 1 - 100 microM) and ethylisopropyl-amiloride (EIPA; 0.1 - 10 microM), inhibited bradykinin-stimulated ouabain-sensitive (86)Rb(+) uptake without affecting basal uptake. 6. These results suggest that bradykinin increases Na+-K+ pump activity of guinea-pig tracheal smooth muscle via stimulation of B(2) receptors and activation of the Na+-H+ exchanger.

Bradykinin augments fibroblast-mediated contraction of released collagen gels

Bradykinin is a multifunctional mediator of inflammation believed to have a role in asthma, a disorder associated with remodeling of extracellular connective tissue. Using contraction of collagen gels as an in vitro model of wound contraction, we assessed the effects of bradykinin tissue on remodeling. Human fetal lung fibroblasts were embedded in type I collagen gels and cultured for 5 days. After release, the floating gels were cultured in the presence of bradykinin. Bradykinin significantly stimulated contraction in a concentration- and time-dependent manner. Coincubation with phosphoramidon augmented the effect of 10(-9) and 10(-8) M bradykinin. A B2 receptor antagonist attenuated the effect of bradykinin, whereas a B1 receptor antagonist had no effect, suggesting that the effect is mediated by the B2 receptor. An inhibitor of intracellular Ca2+ mobilization abolished the response; addition of EGTA to the culture medium attenuated the contraction of control gels but did not modulate the response to bradykinin. In contrast, the phospholipase C inhibitor U-73122 and the protein kinase C inhibitors staurosporine and GF-109203X attenuated the responses. These data suggest that by augmenting the contractility of fibroblasts, bradykinin may have an important role in remodeling of extracellular matrix that may result in tissue dysfunction in chronic inflammatory diseases, such as asthma.

G protein-coupled receptor-mediated mitogen-activated protein kinase activation through cooperation of Galpha(q) and Galpha(i) signals

G protein-coupled receptors (GPCRs) have been shown to stimulate extracellular regulated kinases (ERKs) through a number of linear pathways that are initiated by G(q/11) or G(i) proteins. We studied signaling to the ERK cascade by receptors that simultaneously activate both G protein subfamilies. In HEK293T cells, bradykinin B(2) receptor (B(2)R)-induced stimulation of ERK2 and transcriptional activity of Elk1 are dependent on Galpha(q)-mediated protein kinase C (PKC) and on Galpha(i)-induced Ras activation, while they are independent of Gbetagamma subunits, phosphatidylinositol 3-kinase, and tyrosine kinases. Similar results were obtained with m(1) and m(3) muscarinic receptors in HEK293T cells and with the B(2)R in human and mouse fibroblasts, indicating a general mechanism in signaling toward the ERK cascade. Furthermore, the bradykinin-induced activation of ERK is strongly reduced in Galpha(q/11)-deficient fibroblasts. In addition, we found that constitutively active mutants of Galpha(q/11) or Galpha(i) proteins alone poorly stimulate ERK2, whereas a combination of both led to synergistic effects. We conclude that dually coupled GPCRs require a cooperation of Galpha(i)- and G(q/11)-mediated pathways for efficient stimulation of the ERK cascade. Cooperative signaling by multiple G proteins thus might represent a novel concept implicated in the regulation of cellular responses by GPCRs.

Hoe 140 and pseudo-irreversible antagonism in the rat vas deferens in vitro

The effects of bradykinin and the bradykinin B(2) receptor antagonists D-Arg-[Hyp(3),Thi(5,8),D-Phe(7)]-bradykinin (NPC 349) and D-Arg-[Hyp(3),Thi(5),D-Tic(7),Oic(8)]-bradykinin (Hoe 140) were examined in the electrically-stimulated rat vas deferens. Cumulative additions of bradykinin (1-3000 nM) produced two distinct responses: an enhancement in the magnitude of the basal electrically-induced twitch response (neurogenic response) and an increase in the baseline tension (musculotropic response). NPC 349 (10-100 microM) produced concentration-dependent surmountable rightward shifts of both the bradykinin neurogenic and musculotropic response curves. In contrast, while Hoe 140 (10-100 nM) caused an apparently surmountable antagonism of the bradykinin neurogenic response, it caused an apparent insurmountable antagonism of the bradykinin musculotropic response. Interestingly, co-incubation of Hoe 140 (30 nM) with NPC 349 (30 and 100 microM) resulted in a concentration-related upwards displacement of the Hoe 140-suppressed bradykinin musculotropic response curve. Thus, Hoe 140 can be described as a pseudo-irreversible antagonist against the bradykinin musculotropic response. No time-dependent changes were observed in the maximum bradykinin musculotropic response attainable when NPC 349 (100 microM) additions were made for the final 2 or 18 min of the Hoe 140 incubation (20 min). These findings indicate that slow reversibility of Hoe 140 from the bradykinin B(2) receptor is unlikely to be the mechanism responsible for the pseudo-irreversible antagonism of the bradykinin-induced musculotropic response. Instead, we propose an alternative explanation involving a third, unstable and inactive form of the bradykinin B(2) receptor.

Regulation of inducible bradykinin B1 receptor gene expression through absence of internalization and resensitization

Rapid induction and down-regulation of bradykinin B1 receptor (BKB1R) gene expression is tightly regulated at the transcriptional and mRNA levels (Zhou et al. [1998] Biochem. J. 330:361-366; Zhou et al. [1999] Mol. Cell Biol. Res. Commun. 1:29-35). Here we explore regulation of BKB1R expression at the protein level. To make this inducible gene express constitutively, we utilized a bicistronic mammalian expression vector (pCMin) for stable transfection of the BKB1R gene into human lung fibroblasts, IMR90SV40. The BKB1R displayed a high affinity and specificity (K(d) = 0.5 nM) for desArg(10)-kallidin. The receptor mediated such signaling events as arachidonic acid (ARA) release, phosphoinositide (PI) turnover and Ca(2+)-flux. The receptor function proved differentially desensitized. For example, after initial exposure to desArg(10)-kallidin, a second stimulation with desArg(10)-kallidin did not induce further Ca(2+)-flux or ARA-release while PI-turnover continued unabated. Unlike most of the G-protein coupled receptors, the BKB1R did not internalize within 60 min of exposure to 10 nM desArg(10)-kallidin. It also did not resensitize. Thus, the duration and signal capacity of the BKB1R at the protein level is regulated through lack of internalization, an absence of resensitization and a lack of desensitization for certain events such as PI turnover. In fact, the absence of BKB1R resensitization is likely a very important contributor to the rapid disappearance of this inducible receptor.

Effect of antagonists for NK(2)and B(2) receptors on antigen-induced airway responses in allergic rabbits

The effects of the tachykinin NK(2)receptor antagonist, MEN 11420 (300 nmol/kg) and the bradykinin B(2)receptor antagonist, CP 0597 (17.2 and 172 nmol/kg) were studied in a rabbit model of antigen-induced airway responses. Antigen inhalation induced acute bronchoconstriction, airway hyperresponsiveness to histamine, and pulmonary eosinophil infiltration in 3-month-old rabbits immunized with Alternaria tenuis antigen within 24 h of birth. Treatment with MEN 11420 significantly reduced the acute bronchoconstriction induced by antigen, in terms of lung resistance. Antigen-induced changes in dynamic compliance were unaffected. CP 0597 had no effect on antigen-induced changes in lung function. Neither MEN 11420 nor CP 0597 had a significant effect on the antigen-induced increase in airway responsiveness to inhaled histamine or the pulmonary eosinophil infiltration 24 h after antigen challenge. We conclude that blockade of the NK(2)receptor can alter acute airway responses to antigen, but not antigen-induced eosinophilia or hyperresponsiveness to histamine. We also conclude that bradykinin B(2)receptor-mediated responses do not play a role in airway responses to antigen.

Virus- and bradykinin-induced airway hyperresponsiveness in guinea pigs

The involvement of bradykinin in virus-induced airway hyperresponsiveness (AHR) in guinea pig airways in vivo was determined with the B(2)-receptor antagonist Hoe 140. The efficacy of Hoe 140 treatment was assessed through its effect on the bradykinin-induced (up to 2.5 microgram/100 g B.W. administered intravenously) decrease in blood pressure (BP). Hoe 140 (0.1 micromol/kg), administered subcutaneously twice a day for 5 d almost completely blocked bradykinin-induced changes in BP. Four days after parainfluenza-3 (PI-3) virus infection, guinea pigs showed AHR; excessive airway contraction was found with histamine-receptor stimulation. This hyperresponsiveness was completely inhibited by pretreatment with Hoe 140 (0.1 micromol/kg) administered subcutaneously twice a day for five consecutive days, starting 1 d before virus inoculation. Interestingly, nebulized delivery of bradykinin itself to captopril-treated animals induced an AHR comparable to that observed in virus-treated guinea pigs. Viral infection also caused influx of bronchoalveolar cells into the lungs. Both histologic examinations and lung lavage experiments showed that this cell influx could not be inhibited by pretreatment with Hoe 140. In summary, the results of the study show that bradykinin is involved in a cascade of events leading to AHR after a viral infection in guinea pigs, without affecting bronchoalveolar cell influx.

Inactivation of bradykinin by angiotensin-converting enzyme and by carboxypeptidase N in human plasma

Because bradykinin (BK) appears to have cardioprotective effects ranging from improved hemodynamics to antiproliferative effects, inhibition of BK-degrading enzymes should potentiate such actions. The purpose of this study was to find out which enzymes are responsible for the degradation of BK in human plasma. Human plasma from healthy donors (n = 10) was incubated with BK in the presence or absence of specific enzyme inhibitors. At high (micromolar) concentrations, BK was mostly (>90%) degraded by carboxypeptidase N (CPN)-like activity. In contrast, at low (nanomolar) substrate concentrations, at which the velocity of the catalytic reaction is equivalent to that under physiological conditions, BK was mostly (>90%) converted into an inactive metabolite, BK-(1-7), by angiotensin-converting enzyme (ACE). BK-(1-7) was further converted by ACE into BK-(1-5), with accumulation of this active peptide. A minor fraction (<10%) of the BK was converted into another active metabolite, BK-(1-8), by CPN-like activity. The present study shows that the most critical step in plasma kinin metabolism, i.e., inactivation of BK, is mediated by ACE. Thus inhibition of plasma ACE activity would be cardioprotective by elevating the concentration of BK in the circulation.

Renal haemodynamic and excretory responses to bradykinin in anaesthetized dogs

1. Effects of bradykinin (BK) on renal haemodynamics and urine formation were examined in anaesthetized dogs. 2. Renal arterial infusion of BK at doses of 5 or 50 ng/kg per min produced dose-dependent increases in renal blood flow (RBF), without affecting systemic arterial pressure or glomerular filtration rate. There were also significant and dose-dependent increases in urine flow (UF), urinary excretion of sodium (UNaV) and fractional excretion of sodium (FENa) and decreases in urine osmolality during BK infusion. 3. Renal haemodynamic and excretory responses to the BK infusion were completely abolished by the simultaneous administration of Hoe 140 (icatibant, 100 ng/kg per min intrarenally), a selective BK B2-receptor antagonist. 4. In the presence of NG-nitro-L-arginine (NOARG; 40 micrograms/kg per min intrarenally), a nitric oxide (NO) synthase inhibitor, BK-induced renal vasodilative and natriuretic effects were markedly attenuated, although responses of UF and urine osmolality to BK remained unchanged. The water diuretic effect of BK was abolished in dogs given both NOARG and ibuprofen (12.5 mg/kg bolus injection plus 12.5 mg/kg per h of sustained infusion intravenously), a cyclooxygenase inhibitor. 5. These results clearly indicate that renal haemodynamic and excretory responses to BK were mediated exclusively by the B2-receptor. Renal vasodilative and natriuretic responses are mainly linked to NO generation, while both NO and prostaglandin biosynthesis are involved in the BK-induced water diuresis.

Activation of mitogen-activated protein kinase by the bradykinin B2 receptor is independent of receptor phosphorylation and phosphorylation-triggered internalization

Recent evidence suggests that serine/threonine phosphorylation and internalization of beta2-adrenergic receptors play critical roles in signalling to the mitogen-activated protein kinase cascade. To investigate whether this represents a general mechanism employed by G protein-coupled receptors, we studied the requirement of these processes in the activation of mitogen-activated protein kinase by G alpha(q)-coupled bradykinin B2 receptors. Mutant B2 receptors impaired in receptor phosphorylation and internalization are fully capable to activate mitogen-activated protein kinase. Bradykinin-induced long-term effects on mitogenic signalling monitored by measuring the transcriptional activity of Elk1 were identical in cells expressing the wild-type or mutant B2 receptors. Therefore, G protein-coupled bradykinin receptors activate the mitogen-activated protein kinase pathway independently of receptor phosphorylation and internalization.

Bradykinin inhibits ceramide production and activates phospholipase D in rabbit cortical collecting duct cells

Recent reports suggest that inflammatory cytokines, growth factors, and vasoconstrictor peptides induce sphingomyelinase (SMase) activity. This results in the hydrolysis of sphingomyelin (SM) into ceramide, which is implicated in various cellular functions. Although ceramide regulates phospholipase D (PLD) activity, there is controversy about this relationship. Thus we investigated whether the effect of bradykinin (BK), a proinflammatory factor and vasodilator, was mediated by ceramide signal transduction and by PLD. In rabbit cortical collecting duct (RCCD) cells, BK increased SM levels and decreased ceramide levels in a time-dependent manner. Thus SMase activity was inhibited by BK. Also, the production of ceramide was regulated in a concentration-dependent manner. The BK-B1 antagonist [Lys-des-Arg9,Leu8]BK did not affect ceramide signal transduction but the BK-B2 antagonist (Hoe-140) blocked the effect of BK on SMase, suggesting that the BK-B2 receptor mediates BK-induced inhibition of ceramide generation. Our results show that exogenous SMase significantly hydrolyzed endogenous SM to form ceramide and weakly activated PLD. In contrast, BK induced a significant activation of PLD. However, additive effects of BK and ceramide on PLD activity were not observed. We concluded that in RCCD cells, the BK-induced second messengers ceramide and phosphatidic acid were generated by distinct signal transduction mechanisms, namely the SMase and PLD pathways.

Kinin B1 receptor antagonists containing alpha-methyl-L-phenylalanine: in vitro and in vivo antagonistic activities

-To protect from metabolism and to improve potency of the AcLys-[D-betaNal7,Ile8]desArg9-bradykinin (BK) (R 715), we prepared and tested 3 analogues containing alpha-methyl-L-Phe ([alphaMe]Phe) in position 5: these are the AcLys-[(alphaMe)Phe5,D-betaNal7, Ile8]desArg9BK (R 892), Lys-Lys-[(alphaMe)Phe5,D-betaNal7, Ile8]desArg9BK (R 913), and AcLys-Lys-[(alphaMe)Phe5,D-betaNal7, Ile8]desArg9BK (R 914). The new compounds were tested against the contractile effect induced by desArg9BK on 2 B1 receptor bioassays, the human umbilical vein, and the rabbit aorta. Their antagonistic activities were compared with those of the early prototypes (Lys-[Leu8]desArg9BK and [Leu8]desArg9BK) and with other recently described peptide antagonists. The 3 (alphaMe)Phe analogues showed high antagonistic potencies (pA2) at both the human (8.8, 7.7, and 8. 7, respectively) and rabbit (8.6, 7.8, and 8.6, respectively) B1 receptors. No antagonistic effects (pA2<5) were observed on the B2 receptors that mediate the contractile effects of BK on the human umbilical vein, the rabbit jugular vein, and the guinea pig ileum. Moreover, these new B1 antagonists were found to be resistant to in vitro degradation by purified angiotensin-converting enzyme from rabbit lung. The Nalpha-acetylated forms, R 892 and R 914, were resistant to aminopeptidases from human plasma. In vivo antagonistic potencies (ID50) of B1 receptor antagonists were evaluated in anesthetized lipopolysaccharide-treated (for B1 receptor) and nontreated (for B2 receptor) rabbits against the hypotensive effects of exogenous desArg9BK and BK. R 892 efficiently inhibited (ID50 2.8 nmol/kg IV) hypotension induced by desArg9BK without affecting that evoked by BK (ID50 >600 nmol/kg IV). Conversely, the peptide antagonists Lys-Lys-[Hyp3,Igl5,D-Igl7,Oic8]desArg9BK (B 9858) and DArg-[Hyp3,Thi5,D-Tic7,Oic8] desArg9BK (S 0765) showed dual B1/B2 receptor antagonism in vitro and in vivo. It is concluded that R 892 and congeners provide selective, highly potent, and metabolically stable B1 kinin receptor antagonists that can be useful for the assessment of the physiological and pathological roles of kinin B1 receptors.

Inflammation-induced changes in peripheral glutamate receptor populations

The ionotropic glutamate receptors N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate (KA) have been localized on subpopulations of unmyelinated and myelinated sensory axons in normal skin. Behavioral studies indicate that activation of these receptors results in nociceptive behaviors and contributes to inflammatory pain. The goal of the present study was to determine if these glutamate receptors might contribute to the peripheral hypersensitivity observed in inflammation. The major findings were that 48 h following complete Freund's adjuvant (CFA)-induced inflammation, the proportions of unmyelinated axons labeled for NMDA, AMPA or KA receptors were 61%, 43% and 48%, respectively, in cutaneous nerves in the inflamed paw compared to 48%, 22% and 27%, respectively, in the non-inflamed paw. The proportions of myelinated axons labeled for NMDA, AMPA or KA receptors were 61%, 61% and 43%, respectively, compared to 43%, 42% and 28%, respectively, in the non-inflamed hindpaw. These increases were all significant. These data indicate that the number of sensory axons containing ionotropic glutamate receptors increases during inflammation, and this may be a contributing factor to peripheral sensitization in inflammation.