Bradykinin formation. Plasma and tissue pathways and cellular interactions

Bradykinin actions in the central nervous system: historical overview and psychiatric implications

Bradykinin (BK), a well-studied mediator of physiological and pathological processes in the peripheral system, has garnered less attention regarding its function in the central nervous system, particularly in behavioural regulation. This review delves into the historical progression of research focused on the behavioural effects of BK and other drugs that act via similar mechanisms to provide new insights into the pathophysiology and pharmacotherapy of psychiatric disorders. Evidence from experiments with animal models indicates that BK modulates defensive reactions associated with panic symptoms and the response to acute stressors. The mechanisms are not entirely understood but point to complex interactions with other neurotransmitter systems, such as opioids, and intracellular signalling cascades. By addressing the existing research gaps in this field, we present new proposals for future research endeavours to foster a new era of investigation regarding BK's role in emotional regulation. Implications for psychiatry, chiefly for panic and depressive disorders are also discussed.

Recent advances in the discovery and development of drugs targeting the kallikrein-kinin system

BACKGROUND

The kallikrein-kinin system is a key regulatory cascade involved in blood pressure maintenance, hemostasis, inflammation and renal function. Currently, approved drugs remain limited to the rare disease hereditary angioedema. However, growing interest in this system is indicated by an increasing number of promising drug candidates for further indications.

METHODS

To provide an overview of current drug development, a two-stage literature search was conducted between March and December 2023 to identify drug candidates with targets in the kallikrein-kinin system. First, drug candidates were identified using PubMed and Clinicaltrials.gov. Second, the latest publications/results for these compounds were searched in PubMed, Clinicaltrials.gov and Google Scholar. The findings were categorized by target, stage of development, and intended indication.

RESULTS

The search identified 68 drugs, of which 10 are approved, 25 are in clinical development, and 33 in preclinical development. The three most studied indications included diabetic retinopathy, thromboprophylaxis and hereditary angioedema. The latter is still an indication for most of the drug candidates close to regulatory approval (3 out of 4). For the emerging indications, promising new drug candidates in clinical development are ixodes ricinus-contact phase inhibitor for thromboprophylaxis and RZ402 and THR-149 for the treatment of diabetic macular edema (all phase 2).

CONCLUSION

The therapeutic impact of targeting the kallikrein-kinin system is no longer limited to the treatment of hereditary angioedema. Ongoing research on other diseases demonstrates the potential of therapeutic interventions targeting the kallikrein-kinin system and will provide further treatment options for patients in the future.

Discovery of an effective anti-inflammatory agent for inhibiting the activation of NF-κB

In this study, based on the effect of compounds on the activation of NF-κB and NO release, compound 51 was discovered as the best one with NO release inhibition IC50 value was 3.1 ± 1.1 μM and NF-κB activity inhibition IC50 value was 172.2 ± 11.4 nM. Compound 51 could inhibit the activation of NF-κB through suppressing phosphorylation and nuclear translocation of NF-κB, and suppress LPS-induced inflammatory response in RAW264.7 cells, such as the over-expression of TNF-α and IL-6, which were target genes of NF-κB. This compound also showed preferable anti-inflammatory activity in vivo, including alleviating significantly gastric distention and splenomegaly caused by LPS stimulation, reducing the level of oxidative stress induced by LPS, and inhibiting the expression of IL-6 and TNF-α in serum. Thus, it's reasonable to consider that this compound is a promising small molecule with anti-inflammatory effect for inhibiting the NF-κB signalling pathway.

Anti-Inflammatory, Antinociceptive, and Antioxidant Properties of Anacardic Acid in Experimental Models

Anacardic acid (AA), a compound extracted from cashew nut liquid, exhibits numerous pharmacological activities. The aim of the current investigation was to assess the anti-inflammatory, antinociceptive, and antioxidant activities of AA in mouse models. For this, Swiss albino mice were pretreated with AA (10, 25, 50 mg/kg, intraperitoneally, ip) 30 min prior to the administration of carrageenan, as well as 25 mg/kg of prostaglandin E2, dextran, histamine, and compound 48/80. The antinociceptive activity was evaluated by formalin, abdominal, and hot plate tests, using antagonist of opioid receptors (naloxene, 3 mg/kg, ip) to identify antinociceptive mechanisms. Results from this study revealed that AA at 25 mg/kg inhibits carrageenan-induced edema. In addition, AA at 25 mg/kg reduced edema and leukocyte and neutrophilic migration to the intraperitoneal cavity, diminished myeloperoxidase activity and malondialdehyde concentration, and increased the levels of reduced glutathione. In nociceptive tests, it also decreased licking, abdominal writhing, and latency to thermal stimulation, possibly via interaction with opioid receptors. Taken together, these results indicate that AA exhibits anti-inflammatory and antinociceptive actions and also reduces oxidative stress in acute experimental models, suggesting AA as a promising compound in the pharmaceutical arena.

Host Pathways of Hemostasis that Regulate Group A Streptococcus pyogenes Pathogenicity

A hallmark feature of severe Group A Streptococcus pyogenes (GAS) infection is dysregulated hemostasis. Hemostasis is the primary pathway for regulating blood flow through events that contribute towards clot formation and its dissolution. However, a number of studies have identified components of hemostasis in regulating survival and dissemination of GAS. Several proteins have been identified on the surface of GAS and they serve to either facilitate invasion to host distal sites or regulate inflammatory responses to the pathogen. GAS M-protein, a surface-exposed virulence factor, appears to be a major target for interactions with host hemostasis proteins. These interactions mediate biochemical events both on the surface of GAS and in the solution when M-protein is released into the surrounding environment through shedding or regulated proteolytic processes that dictate the fate of this pathogen. A thorough understanding of the mechanisms associated with these interactions could lead to novel approaches for altering the course of GAS pathogenicity.

Plasma kallikrein cleaves and inactivates apelin-17: Palmitoyl- and PEG-extended apelin-17 analogs as metabolically stable blood pressure-lowering agents

Apelins are human peptide hormones with various physiological activities, including the moderation of cardiovascular, renal, metabolic and neurological function. Their potency is dependent on and limited by proteolytic degradation in the circulatory system. Here we identify human plasma kallikrein (KLKB1) as a protease that cleaves the first three N-terminal amino acids (KFR) of apelin-17. The cleavage kinetics are similar to neprilysin (NEP), which cleaves within the critical 'RPRL'-motif thereby inactivating apelin. The resulting C-terminal 14-mer after KLKB1 cleavage has much lower biological activity, and the presence of its N-terminal basic arginine seems to negate the blood pressure lowering effect. Based on C-terminally engineered apelin analogs (A2), resistant to angiotensin converting enzyme 2 (ACE2), attachment of an N-terminal C16 fatty acid chain (PALMitoylation) or polyethylene glycol chain (PEGylation) minimizes KLKB1 cleavage of the 17-mers, thereby extending plasma half-life while fully retaining biological activity. The N-terminally PEGylated apelin-17(A2) is a highly protease resistant analog, with excellent apelin receptor activation and pronounced blood pressure lowering effect.

Comparing Pathways of Bradykinin Formation in Whole Blood From Healthy Volunteers and Patients With Hereditary Angioedema Due to C1 Inhibitor Deficiency

Multiple pathways have been proposed to generate bradykinin (BK)-related peptides from blood. We applied various forms of activation to fresh blood obtained from 10 healthy subjects or 10 patients with hereditary angioedema (HAE-1 or −2 only) to investigate kinin formation. An enzyme immunoassay for BK was applied to extracts of citrated blood incubated at 37°C under gentle agitation for 0–2 h in the presence of activators and/or inhibitory agents. Biologically active kinins in extracts were corroborated by c-Fos accumulation in HEK 293a cells that express either recombinant human B₂ or B₁ receptors (B₂R, B₁R). Biological evidence of HAE diagnostic and blood cell activation was also obtained. The angiotensin converting enzyme inhibitor enalaprilat, without any effect per se, increased immunoreactive BK (iBK) concentration under active stimulation of blood. Tissue kallikrein (KLK-1) and Kontact-APTT, a particulate material that activates the contact system, rapidly (5 min) and intensely (>100 ng/mL) induced similar iBK generation in the blood of control or HAE subjects. Tissue plasminogen activator (tPA) slowly (≥1 h) induced iBK generation in control blood, but more rapidly and intensely so in that of HAE patients. Effects of biotechnological inhibitors indicate that tPA recruits factor XIIa (FXIIa) and plasma kallikrein to generate iBK. KLK-1, independent of the contact system, is the only stimulus leading to an inconsistent B₁R stimulation. Stimulating neutrophils or platelets did not generate iBK. In the HAE patients observed during remission, iBK formation capability coupled to B₂R stimulation appears largely intact. However, a selective hypersensitivity to tPA in the blood of HAE patients suggests a role of plasmin-activated FXIIa in the development of attacks. Proposed pathways of kinin formation dependent on blood cell activation were not corroborated.

Bifunctional ligands of the bradykinin B2 and B1 receptors: An exercise in peptide hormone plasticity

Kinins are the small and fragile hydrophilic peptides related to bradykinin (BK) and derived from circulating kininogens via the action of kallikreins. Kinins bind to the preformed and widely distributed B₂ receptor (B₂R) and to the inducible B₁ receptor (B₁R). B₂Rs and B₁Rs are related G protein coupled receptors that possess natural agonist ligands of nanomolar affinity (BK and Lys BK for B₂Rs, Lys-des-Arg⁹-BK for B₁R). Decades of structure-activity exploration have resulted in the production of peptide analogs that are antagonists, one of which is clinically used (the B₂R antagonist icatibant), and also non-peptide ligands for both receptor subtypes. The modification of kinin receptor ligands has made them resistant to extracellular or endosomal peptidases and/or produced bifunctional ligands, defined as agonist or antagonist peptide ligands conjugated with a chemical fluorophore (emitting in the whole spectrum, from the infrared to the ultraviolet), a drug-like moiety, an epitope, an isotope chelator/carrier, a cleavable sequence (thus forming a pro-drug) and even a fused protein. Dual molecular targets for specific modified peptides may be a source of side effects or of medically exploitable benefits. Biotechnological protein ligands for either receptor subtype have been produced: they are enhanced green fluorescent protein or the engineered peroxidase APEX2 fused to an agonist kinin sequence at their C-terminal terminus. Antibodies endowed with pharmacological actions (agonist, antagonist) at B₂R have been reported, though not monoclonal antibodies. These findings define classes of alternative ligands of the kinin receptor of potential therapeutic and diagnostic value.

Predictive value of serum bradykinin and desArg9-bradykinin levels for chemotherapeutic responses in active tuberculosis patients: A retrospective case series

BACKGROUND

There is an urgent need for methods that can rapidly and accurately assess therapeutic responses in patients with active tuberculosis (TB) in order to predict treatment outcomes. Exposure to bacterial pathogens can rapidly activate the plasma contact system, triggering the release of bradykinin (BK) and its metabolite desArg⁹-bradykinin (DABK) to induce inflammation and innate immune responses. We hypothesized that serum BK and DABK levels might act as sensitive immune response signatures for changes in Mycobacterium tuberculosis (Mtb) burden, and therefore examined how serum levels of these markers corresponded with anti-TB therapy in a small cohort of active TB cases.

METHODS

Nanotrap Mass-Spectrometry (MS) was used to analyze serial blood specimens from 13 HIV-negative adults with microbiologically confirmed active TB who were treated with first-line anti-TB chemotherapy. MS signal for BK (m/z 1060.5) and DABK (m/z 904.5) serum peptides were evaluated at multiple time-points (before, during, and after treatment) to evaluate how BK and DABK levels corresponded with disease status.

RESULTS

Serum BK levels declined from pretreatment baseline levels during the early stage anti-TB therapy (induction phase) and tended to remain below baseline levels during extended treatment (consolidation phase) and after therapy completion. BK levels were consistent with induction phase sputum culture conversions indicative of decreased Mtb burden reflecting good treatment responses. Serum DABK levels tended to increase during the induction phase and decrease at consolidation and post-therapy time points, which may indicate a shift from active disease to chronic inflammation to a disease free state. Elevated BK and DABK levels after treatment completion in one patient may be related to the subsequent recurrent TB disease.

CONCLUSIONS

Our pilot data suggests that changes in the circulating BK and DABK levels in adult TB patients can be used as potential surrogate markers of the host response both early and late in anti-TB treatment for both pulmonary and extrapulmonary TB patients. We will further exploit these host-response signatures in the future as biomarkers in combination with other clinical and microbiologic tools which may improve treatment efficacy and facilitate the development of host-directed therapy.

Cardiovascular Instability Preceded by Orolingual Angioedema after Alteplase Treatment

An 87-year-old man taking antihypertensive medications, including 10 mg enalapril, daily visited our hospital complaining of motor aphasia, dysarthria, and right hemiparesis. Magnetic resonance imaging revealed an ischemic lesion in the left frontal lobe including the insular cortex and severe stenosis of the left middle cerebral artery. After he received intravenous alteplase infusion, he developed orolingual angioedema followed by transient bradycardia with subsequent hypotension, resulting in the deterioration of his neurological signs and expansion of the ischemic lesion. Orolingual angioedema after intravenous alteplase infusion may follow cardiovascular instability and disease progression in stroke patients.

Bradykinin release avoids high molecular weight kininogen endocytosis

Human H-kininogen (120 kDa) plays a role in many pathophysiological processes and interacts with the cell surface through protein receptors and proteoglycans, which mediate H-kininogen endocytosis. In the present work we demonstrate that H-kininogen containing bradykinin domain is internalized and different endogenous kininogenases are present in CHO-K1 cells. We used CHO-K1 (wild type) and CHO-745 (mutant deficient in proteoglycans biosynthesis) cell lines. H-kininogen endocytosis was studied using confocal microscopy, and its hydrolysis by cell lysate fraction was determined by immunoblotting. Bradykinin release was also measured by radioimmunoassay. H-kininogen interaction with the cell surface of CHO-745 cells resulted in bradykinin release by serine proteases. In CHO-K1 cells, which produce heparan and chondroitin sulfate proteoglycans, internalization of H-kininogen through its bradykinin domain can occur on lipid raft domains/caveolae. Nevertheless bradykinin-free H-kininogen was not internalized by CHO-K1 cells. The H-kininogen present in acidic endosomal vesicles in CHO-K1 was approximately 10-fold higher than the levels in CHO-745. CHO-K1 lysate fractions were assayed at pH 5.5 and intact H-kininogen was totally hydrolyzed into a 62 kDa fragment. By contrast, at an assay pH 7.4, the remained fragments were 115 kDa, 83 kDa, 62 kDa and 48 kDa in size. The antipain-Sepharose chromatography separated endogenous kininogenases from CHO-K1 lysate fraction. No difference was detected in the assays at pH 5.5 or 7.4, but the proteins in the fraction bound to the resin released bradykinin from H-kininogen. However, the proteins in the unbound fraction cleaved intact H-kininogen at other sites but did not release bradykinin. H-kininogen can interact with extravascular cells, and is internalized dependent on its bradykinin domain and cell surface proteoglycans. After internalization, H-kininogen is proteolytically processed by intracellular kininogenases. The present data also demonstrates that serine or cysteine proteases in lipid raft domains/caveolae on the CHO cell can hydrolyze H-kininogen, thus releasing kinins.

Antiedematogenic effects of the polar fractions of Persea cordata Mez. (Lauraceae) on microvascular extravasation in rat skin

ETHNOPHARMACOLOGICAL RELEVANCE

Persea cordata Mez. (Lauraceae) is a medicinal plant used in veterinary ethnopharmacology, which is a popular medicine used as an anti-inflammatory and healing agent, mainly on animal skin diseases, characterized by cutaneous open wounds, in South Brazil.

AIM OF THIS STUDY

The purpose of this study was to investigate a possible antiedematogenic effect of ethyl acetate (EtAc) and butanol (BuOH) polar fractions of Persea cordata on Evans blue dye leakage induced by pro-inflammatory agents in rat skin.

MATERIALS AND METHODS

Male Wistar rats (180-200 g, n=5-6) were pretreated with a single intraperitoneal administration of EtAc or BuOH (1 to 600 mg kg(-1)) fractions followed by intravenous Evans blue dye injection (1%, 30 mg kg(-1), i.v.), 60 min before the injection of phlogistic agents. Animals received intradermal injections (0.05 ml) of carrageenan (CAR, 300 µg/site), 48/80 compound (C4880, 10 µg/site), histamine (HIS, 0.3 µg/site), serotonin (5-HT, 0.01 µg/site), dextran (DEX, 200 µg/site), bradykinin (BK, 0.003 µg/site), capsaicin (CPS, 400 µg/site), substance P (SP, 0.003 µg/site) or prostaglandin E2 (PGE2 10 nmol/site) and they were submitted to euthanasia after 60 min. Skin samples were obtained in the extravasation sites of Evans blue dye. Skin fragments were soaked in formamide at 37°C (during 24h) for Evans blue extraction. The amount of dye leakage in the tissue fragment was determined by a spectrophotometer (620 nm).

RESULTS

In a very similar manner in terms of potency and efficacy, systemic administration of EtAc and BuOH fractions caused dose-dependent inhibition of vascular Evans blue dye leakage induced by phlogistic agents in the rat skin. The results obtained (ID50 values in mgkg(-1) and maximal inhibition in %) with EtAc fraction, as follows were: CAR (34.42 and 63.0), 4880 (8.52 and 59.1), HIS (21.22 and 66.8), 5-HT (32.99 and 73.4), DEX (41.74 and 67.0), BK (34.03 and 68.0), CPS (100.7 and 77), SP (2.1 and 78.9) and PGE2 (133 and 71.0). BuOH fraction significantly inhibited CAR (25.9 and 70)-, 4880 (36.8 and 66)-, HIS (17.6 and 77)-, 5-HT (32.8 and 56)-, DEX (89.6 and 75)-, BK (28.0 and 66)-, CPS (136.37 and 71)-, SP (5.6 and 78)- and PGE2 (109.64 and 56)-induced VE, respectively.

CONCLUSION

Systemic administration of Persea cordata polar fractions exerts a non-specific inhibitory effect on microvascular leakage induced by pro-inflammatory agents in rat skin, probably to interfering with different biological systems involved in the development of the inflammatory process, reinforcing the popular use of Persea cordata as an anti-inflammatory and healing agent for skin.

Structure of plasma and tissue kallikreins

The kallikrein kinin system (KKS) consists of serine proteases involved in the production of peptides called kinins, principally bradykinin and Lys-bradykinin (kallidin). The KKS contributes to a variety of physiological processes including inflammation, blood pressure control and coagulation. Here we review the protein structural data available for these serine proteases and examine the molecular mechanisms of zymogen activation and substrate recognition focusing on plasma kallikrein (PK) and tissue kallikrein (KLK1) cleavage of kininogens. PK circulates as a zymogen bound to high-molecular-weight kininogen (HK). PK is activated by coagulation factor XIIa and then cleaves HK to generate bradykinin and factor XII to generate further XIIa.A structure has been described for the activated PK protease domain in complex with the inhibitor benzamidine. Kallikrein-related peptidases (KLKs) have a distinct domain structure and exist as a family of 15 genes which are differentially expressed in many tissues and the central nervous system.They cleave a wide variety of substrates including low-molecular-weight kininogen (LK) and matrix proteins. Crystal structures are available for KLK1, 3, 4, 5, 6 and 7 activated protease domains typically in complex with S1 pocket inhibitors. A substrate mimetic complex is described for KLK3 which provides insight into substrate recognition. A zymogen crystal structure determined for KLK6 reveals a closed S1 pocket and a novel mechanism of zymogen activation. Overall these structures have proved highly informative in understanding the molecular mechanisms of the KKS and provide templates to design inhibitors for treatment of a variety of diseases.

Icatibant , the bradykinin B2 receptor antagonist with target to the interconnected kinin systems

INTRODUCTION

HOE-140/ Icatibant is a selective, competitive antagonist to bradykinin (BK) against its binding to the kinin B2 receptor. Substitution of five non-proteogeneic amino acid analogues makes icatibant resistant to degradation by metalloproteases of kinin catabolism. Icatibant has clinical applications in inflammatory and vascular leakage conditions caused by an acute (non-controlled) production of kinins and their accumulation at the endothelium B2 receptor. The clinical manifestation of vascular leakage, called angioedema (AE), is characterized by edematous attacks of subcutaneous and submucosal tissues, which can cause painful intestinal consequences, and life-threatening complications if affecting the larynx. Icatibant is registered for the treatment of acute attacks of the hereditary BK-mediated AE, i.e., AE due to C1 inhibitor deficiency.

AREAS COVERED

This review discusses emerging knowledge on the kinin system: kinin pharmacological properties, biochemical characteristics of the contact phase and kinin catabolism proteases. It underlines the responsibility of the kinins in AE initiation and the potency of icatibant to inhibit AE formation by kinin-receptor interactions.

EXPERT OPINION

Icatibant antagonist properties protect BK-mediated AE patients against severe attacks, and could be developed for use in inflammatory conditions. More studies are required to confirm whether or not prolonged and frequent applications of icatibant could result in the impairment of the cardioprotective effect of BK.

Kallikrein-kinin system: a surgical perspective in post-aprotinin era

Kallikrein-kinin system (KKS) plays an important role in inflammation, ischemia-reperfusion (IR) injury, and development of neoplasia. There is evidence to suggest that KKS plays an important role in organ protection during preconditioning. Aprotinin is a nonspecific serine protease inhibitor, which has been extensively used in cardiac surgery for the control of post operative bleeding. The anti-inflammatory effects of aproprotin are due to its inhibitory effect on the kallikrein-kinin system (KKS). We herein review KKS and its role as applied to the practice of surgery.

Human plasma kallikrein-kinin system: physiological and biochemical parameters

The plasma kallikrein-kinin system (KKS) plays a critical role in human physiology. The KKS encompasses coagulation factor XII (FXII), the complex of prekallikrein (PK) and high molecular weight kininogen (HK). The conversion of plasma prekallikrein to kallikrein by the activated FXII and in response to numerous different stimuli leads to the generation of bradykinin (BK) and activated HK (HKa, an antiangiogenic peptide). BK is a proinflammatory peptide, a pain mediator and potent vasodilator, leading to robust accumulation of fluid in the interstitium. Systemic production of BK, HKa with the interplay between BK bound-BK receptors and the soluble form of HKa are key to angiogenesis and hemodynamics. KKS has been implicated in the pathogenesis of inflammation, hypertension, endotoxemia, and coagulopathy. In all these cases increased BK levels is the hallmark. In some cases, the persistent production of BK due to the deficiency of the blood protein C1-inhibitor, which controls FXII, is detrimental to the survival of the patients with hereditary angioedema (HAE). In others, the inability of angiotensin converting enzyme (ACE) to degrade BK leads to elevated BK levels and edema in patients on ACE inhibitors. Thus, the mechanisms that interfere with BK liberation or degradation would lead to blood pressure dysfunction. In contrast, anti-kallikrein treatment could have adverse effects in hemodynamic changes induced by vasoconstrictor agents. Genetic models of kallikrein deficiency are needed to evaluate the quantitative role of kallikrein and to validate whether strategies designed to activate or inhibit kallikrein may be important for regulating whole-body BK sensitivity.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

The kallikrein-kinin system: current and future pharmacological targets

The kallikrein-kinin system is an endogenous metabolic cascade, triggering of which results in the release of vasoactive kinins (bradykinin-related peptides). This complex system includes the precursors of kinins known as kininogens and mainly tissue and plasma kallikreins. The pharmacologically active kinins, which are often considered as either proinflammatory or cardioprotective, are implicated in many physiological and pathological processes. The interest of the various components of this multi-protein system is explained in part by the multiplicity of its pharmacological activities, mediated not only by kinins and their receptors, but also by their precursors and their activators and the metallopeptidases and the antiproteases that limit their activities. The regulation of this system by serpins and the wide distribution of the different constituents add to the complexity of this system, as well as its multiple relationships with other important metabolic pathways such as the renin-angiotensin, coagulation, or complement pathways. The purpose of this review is to summarize the main properties of this kallikrein-kinin system and to address the multiple pharmacological interventions that modulate the functions of this system, restraining its proinflammatory effects or potentiating its cardiovascular properties.

The syndrome of amniotic fluid embolism: a potential contribution of bradykinin

OBJECTIVE

Amniotic fluid embolism is a potentially fatal complication of pregnancy; although several hypotheses have been formulated, the pathophysiology of this condition is not well known. An exaggerated release of bradykinin, which is activated by products of the amniotic fluid that enter the maternal circulation, could explain the symptoms that are present in amniotic fluid embolism. The objective of this study was to assess whether bradykinin is involved in amniotic fluid embolism.

STUDY DESIGN

The plasma bradykinin-generating capacity was measured serially in a patient who experienced amniotic fluid embolism.

RESULTS

The plasma bradykinin-generating capacity was found to be very low at the time of the initial clinical manifestations, which were characterized by severe hypotension, cardiorespiratory arrest, and coagulopathy.

CONCLUSION

This study suggests a potential role for bradykinin release in the pathophysiology of amniotic fluid embolism.

K317, R319, and E320 within the proximal C-terminus of the bradykinin B2 receptor form a motif important for phospholipase C and phospholipase A2 but not connective tissue growth factor related signaling

We showed previously that large domain exchanges between the bradykinin B2 (BKB2) and angiotensin II type 1a (AT1a) receptors can result in functional hybrids. However, when we proceeded to exchange the entire bradykinin B2 receptor (BKB2R) C-terminal tail with the AT1aR C-terminus, the hybrid, while continuing to bind BK and be endocytosed as wild type (WT) BKB2R, lost much of its ability to activate phosphatidylinositol (PI) turnover or the release of arachidonic acid (ARA). In this study, we constructed chimeric receptors within the proximal C-terminus between the BKB2R and AT1aR or bradykinin B1 receptor (BKB1R). The mutant and WT receptor cDNAs were stably transfected into Rat-1 cells. Also, point mutations were generated to evaluate the role of the individual residues within this region. These chimeric studies revealed that the proximal portion of the BKB2R C-tail is crucial for G protein-linked BKB2R functions. This region could not be swapped with the AT1aR to obtain a BK activated PI turnover or ARA release. Further studies demonstrated that the distal portion (325-330) of this region is exchangeable; however, the middle portion (317-324) is not. Small motif exchanges within this section identified the KSR and EVY motifs as crucial for G(alphaq), G(alphai) related signaling of the BKB2R. Point mutations then showed that the charged amino acids K317, R319, and E320 are the residues critical for linking to PI turnover and ARA release. However, these proximal chimeras showed normal receptor uptake. Interestingly, while apparently not activating G protein-linked signaling, the proximal tail AT1aR exchange mutant and the entire C-terminus exchange hybrid continued to cause a substantial bradykinin effected increase in connective tissue growth factor (CTGF) mRNA level, as WT BKB2R.

Rapid increase in endothelial nitric oxide production by bradykinin is mediated by protein kinase A signaling pathway

Bradykinin (BK) acutely increases endothelial nitric oxide (NO) production by activating endothelial NO synthase (eNOS), and this increase is in part correlated with enhanced phosphorylation/dephosphorylation of eNOS by several protein kinases and phosphatases. However, the signaling mechanisms producing this increase are still controversial. In an attempt to delineate the acute effect of BK on endothelial NO production, confluent bovine aortic endothelial cells were incubated with BK, and NO production was measured by NO-specific chemiluminescence. Significant increase in NO levels was detected as early as 1 min after BK treatment, with concomitant increase in the phosphorylation of Ser(1179) (bovine sequence) site of eNOS (eNOS-Ser(1179)). This acute effect of BK on both increases was blocked only by treatment of protein kinase A inhibitor H-89, but not by the inhibitors of calmodulin-dependent kinase II and protein kinase B, suggesting that the rapid increase in NO production by BK is mediated by the PKA-dependent phosphorylation of eNOS-Ser(1179).

Tissue kallikrein actions at the rabbit natural or recombinant kinin B2 receptors

We have examined whether exogenous human tissue kallikrein exerts pharmacological actions via the bradykinin B2 receptor; specifically, whether the protease can bind to, cleave, internalize, and/or activate a fusion protein composed of the rabbit B2 receptor conjugated to the green fluorescent protein (B2R-GFP). The enzyme partially digested the fusion protein at 1 micromol/L, but not 100 nmol/L, and promoted B2R-GFP endocytosis in HEK 293 cells (> or =50 nmol/L). Trypsin and endoproteinase Lys-C, but not plasma kallikrein, also cleaved B2R-GFP. Phospholipase A2 was activated by 50 nmol/L tissue kallikrein in HEK 293 cells expressing B2R-GFP, and this was mediated by the receptor, as shown by the effect of a B2 receptor antagonist and by the lack of response in untransfected cells. However, 500 nmol/L kallikrein elicited a strong receptor-independent activation of phospholipase A2. Tissue kallikrein competed for [3H]bradykinin binding to B2R-GFP only at 1 micromol/L. A simulation involving kallikrein treatment of HEK 293 cells, pretreated or not with human plasma, evidenced the formation of immunoreactive bradykinin. The enzyme (50 nmol/L) contracted the rabbit isolated jugular vein via its endogenous B2 receptors, but the effect was tachyphylactic, and there was no cross-desensitization with bradykinin effects. Aprotinin prevented all pharmacological responses to tissue kallikrein, indicating that the enzyme activity is required for its effect. The local generation of kinins is a plausible mechanism for the pharmacological effects of lower concentrations of tissue kallikrein (50 to 100 nmol/L); higher levels (0.5 to 1 micromol/L) can not only initiate the degradation of rabbit B2 receptors but also exert nonreceptor-mediated effects.

Contraction-related factors affect the concentration of a kallidin-like peptide in rat muscle tissue

In order to study the effects of the manipulation of various factors related to muscular activity on the concentration of kinins in muscular tissue, a microdialysis probe was implanted in the adductor muscle of the hindlimb in anaesthetized rats. After collection of baseline samples, the perfusion fluid was changed to a Ringer solution containing sodium lactate (10 or 20 mM), adenosine (50 or 100 microM) or a lower pH (7.0 or 6.6). Whereas perfusion with lactate did not have any significant effect on the concentration of kinins in the dialysate, the perfusion with a lower pH or with adenosine dose-dependently increased the kinin content in the samples. In a second microdialysis experiment, by using specific radioimmunoassays (RIA) for bradykinin and kallidin, we observed that about 70 % of the total kinins dialysed from rat muscle are a kallidin-like peptide. Also, the simultaneous perfusion with 100 microM caffeine totally abolished the increase in kinin levels induced by the perfusion at pH 6.6. In a third experiment, soleus muscles from rat were stimulated in vitro during 30 min in the presence or absence of 77 microM caffeine. Electrically stimulated contraction, but not the addition of 10 mU ml(-1) insulin, induced an increase in the concentration of the kallidin-like peptide in the buffer. This effect was totally prevented by the addition of the adenosine antagonist caffeine. These results show that a kallidin-like peptide is released from rat muscle, and that its production is enhanced by muscle activity. Furthermore, the increase in kinin peptides during muscle contraction may be mediated by an increase in adenosine levels.

Angiotensin-converting enzyme inhibitor-associated angioedema is characterized by a slower degradation of des-arginine(9)-bradykinin

Angioedema (AE) is a rare but potentially life-threatening side effect of therapy with inhibitors of angiotensin-converting enzyme (ACE), the main bradykinin (BK)- inactivating metallopeptidase in humans. The pathogenesis of ACE inhibitor (ACEi)- associated AE (AE+) is presently unknown, although there is increasing evidence of a kinin role. We analyzed the metabolism of endogenous BK (B(2) receptor agonist) and its active metabolite, des-Arg(9)-BK (B(1) receptor agonist), in the presence of an ACEi during in vitro contact activation of plasma from hypertensive patients (n = 39) who presented AE+. Kinetic parameters were compared with those measured in a control group (AE-) of hypertensive patients (n = 39) who never manifested any acute or chronic side effects while treated with an ACEi. The different kinetic parameters were analyzed using a mathematical model (y = k t(alpha) e(-beta t)) previously applied to a normal, healthy population. The slope of BK degradation, but not its formation from high-molecular-weight kininogen, was lower in AE+ patients when compared with the AE- controls. des-Arg(9)-BK accumulation during the kinetic measurements was significantly higher in AE+ plasma. This accumulation of the B(1) agonist in AE+ patients paralleled its half-life of degradation. In conclusion, our results show, for the first time, that an abnormality of endogenous des-Arg(9)-BK degradation exists in the plasma of patients with ACEi-associated AE, suggesting that its pathogenetic mechanism lies in the catabolic site of kinin metabolism.

Zinc induces exposure of hydrophobic sites in the C-terminal domain of gC1q-R/p33

Endothelial cells and platelets are known to express gC1q-R on their surface. In addition to C1q, endothelial cell gC1q-R has been shown to bind high molecular weight kininogen (HK) and factor XII (FXII). However, unlike C1q, whose interaction with gC1q-R does not require divalent ions, the binding of HK to gC1q-R is absolutely dependent on the presence of zinc. However, the mechanism by which zinc modulates this interaction is not fully understood. To investigate the role of zinc, binding studies were done using the hydrophobic dye, bis-ANS. The fluorescence intensity of bis-ANS, greatly increases and the emission maximum is blue-shifted from 525 to 485nm upon binding to hydrophobic sites on proteins. In this report, we show that a blue-shift in emission maximum is also observed when bis-ANS binds to gC1q-R in the presence but not in the absence of zinc suggesting that zinc induces exposure of hydrophobic sites in the molecule. The binding of bis-ANS to gC1q-R is specific, dose-dependent, and reversible. In the presence of zinc, this binding is abrogated by monoclonal antibody 74.5.2 directed against gC1q-R residues 204-218. This segment of gC1q-R, which corresponds to the beta6 strand in the crystal structure, has been shown previously to be the binding site for HK. A similar trend in zinc-induced gC1q-R binding was also observed using the hydrophobic matrix octyl-Sepharose. Taken together, our data suggest that zinc can induce the exposure of hydrophobic sites in the C-terminal domain of gC1q-R involved in binding to HK/FXII.

Biochemical basis of angioedema associated with recombinant tissue plasminogen activator treatment: an in vitro experimental approach

BACKGROUND

Angioedema has been reported during recombinant tissue plasminogen activator (rtPA) treatment of acute ischemic stroke, often with concomitant use of angiotensin I-converting enzyme inhibitor treatment. Angioedema has been partly attributed to the nonapeptide bradykinin (BK), although its precise role has been poorly documented until now. The purposes of this report are 2-fold. First, we sought to define and characterize the in vitro kinin-forming capacity of rtPA when incubated with human plasma at a concentration within the therapeutic concentration range of rtPA attained in blood in vivo during fibrinolysis. Second, we sought to define the mechanism by which rtPA liberates BK from purified human single-chain high-molecular-weight kininogen, a key constituent of the contact system of plasma and the precursor of BK.

SUMMARY OF REPORT

When incubated with human plasma, in the presence of an angiotensin I-converting enzyme inhibitor, rtPA generates BK, which is further metabolized to des-Arg9-BK. The quantity of kinins generated by rtPA is similar to that observed during the activation of the contact system of plasma with a negatively charged surface, suggesting that it is physiologically relevant. The total amount of des-Arg9-BK liberated during the incubation period depends on the aminopeptidase P activity, its main degrading peptidase. Additionally, incubations using purified proteins of the fibrinolytic and the contact system pathways show that the rtPA kinin-forming capacity is mediated by plasmin.

CONCLUSIONS

We conclude that rtPA used in vitro at a therapeutic concentration has the capacity to generate significant quantities of kinins from human plasma. This kinin-forming activity depends on the activation of the fibrinolytic pathway. These data suggest that angioedema associated with rtPA treatment of ischemic stroke results directly from plasmin-mediated release of BK.

Pathways for bradykinin formation and inflammatory disease

Bradykinin is formed by the interaction of factor XII, prekallikrein, and high-molecular-weight kininogen on negatively charged inorganic surfaces (silicates, urate, and pyrophosphate) or macromolecular organic surfaces (heparin, other mucopolysaccharides, and sulfatides) or on assembly along the surface of cells. Catalysis along the cell surface requires zinc-dependent binding of factor XII and high-molecular-weight kininogen to proteins, such as the receptor for the globular heads of the C1q subcomponent of complement, cytokeratin 1, and urokinase plasminogen activator receptor. These 3 proteins complex together within the cell membrane, and initiation depends on autoactivation of factor XII on binding to gC1qR (the receptor for the globular heads of the C1q subcomponent of complement). There is also a factor XII-independent bypass mechanism requiring a cell-derived cofactor or protease that activates prekallikrein. Bradykinin is degraded by carboxypeptidase N and angiotensin-converting enzyme. Angioedema that is bradykinin dependent results from hereditary or acquired C1 inhibitor deficiencies or use of angiotensin-converting enzyme inhibitors to treat hypertension, heart failure, diabetes, or scleroderma. The role for bradykinin in allergic rhinitis, asthma, and anaphylaxis is to contribute to tissue hyperresponsiveness, local inflammation, and hypotension. Activation of the plasma cascade occurs as a result of heparin release and endothelial-cell activation and as a secondary event caused by other pathways of inflammation.

Cell damage excites nociceptors through release of cytosolic ATP

The release of cytosol from damaged cells has been proposed to be a chemical trigger for nociception. K(+), H(+), adenosine triphosphate (ATP), and glutamate are algogenic agents within cytosol that might contribute to such an effect. To examine which, if any, compounds in cytosol activate ion channels on nociceptors, we recorded currents in dissociated nociceptors when nearby skin cells were damaged. Skin cell damage caused action potential firing and inward currents in nociceptors. Extracts of fibroblast cytosol did the same. Virtually all response to extract and cell killing was eliminated by enzymatic degradation of ATP or desensitization or blockade of P2X receptors, ion channels that are activated by extracellular ATP. Thus, if cytosol provides a rapid nociceptive signal from damaged tissue, then ATP is a critical messenger and P2X receptors are its sensor.

Absence of ligand-induced regulation of kinin receptor expression in the rabbit

The induction of B(1) receptors (B(1)Rs) and desensitization or down-regulation of B(2) receptors (B(2)Rs) as a consequence of the production of endogenous kinins has been termed the autoregulation hypothesis. The latter was investigated using two models based on the rabbit: kinin stimulation of cultured vascular smooth muscle cells (SMCs) and in vivo contact system activation (dextran sulphate intravenous injection, 2 mg kg(-1), 5 h). Rabbit aortic SMCs express a baseline population of B(1)Rs that was up-regulated upon interleukin-1beta treatment ([(3)H]-Lys-des-Arg(9)-BK binding or mRNA concentration evaluated by RT - PCR; 4 or 3 h, respectively). Treatment with B(1)R or B(2)R agonists failed to alter B(1)R expression under the same conditions. Despite consuming endogenous kininogen (assessed using the kinetics of immunoreactive kinin formation in the plasma exposed to glass beads ex vivo) and producing hypotension mediated by B(2)Rs in anaesthetized rabbits, dextran sulphate treatment failed to induce B(1)Rs in conscious animals (RT - PCR in several organs, aortic contractility). By contrast, lipopolysaccharide (LPS, 50 microg kg(-1), 5 h) was an effective B(1)R inducer (kidney, duodenum, aorta) but did not reduce kininogen reserve. We tested the alternate hypothesis that endogenous kinin participate in LPS induction of B(1)Rs. Kinin receptor antagonists (icatibant combined to B-9858, 50 microg kg(-1) of each) failed to prevent or reduce the effect of LPS on B(1)R expression. Dextran sulphate or LPS treatments did not persistently down-regulate vascular B(2)Rs (jugular vein contractility assessed ex vivo). The kinin receptor autoregulation hypothesis is not applicable to primary cell cultures derived from a tissue known to express B(1)Rs in a regulated manner (aorta). The activation of the endogenous kallikrein-kinin system is ineffective to induce B(1)Rs in vivo in an experimental time frame sufficient for B(1)R induction by LPS.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Bradykinin-regulated interactions of the mitogen-activated protein kinase pathway with the endothelial nitric-oxide synthase

Activation of the bradykinin B2 receptor in endothelial cells initiates a complex array of cellular responses mediated by diverse signaling pathways, including stimulation of the mitogen-activated protein (MAP) kinase cascade and activation of the endothelial isoform of nitric-oxide synthase (eNOS). Several protein kinases have been implicated in eNOS regulation, but the role of MAP kinases remains less well understood. We explored the interactions between eNOS and components of the MAP kinase pathway in bovine aortic endothelial cells (BAEC). Using co-immunoprecipitation experiments, we isolated eNOS in a complex with the MAP kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2) as well as the protein kinases Raf-1 and Akt. Within minutes of adding bradykinin to BAEC, the eNOS-Raf-1-ERK-Akt heteromeric complex dissociated, and it subsequently reassociated following more prolonged agonist stimulation. Bradykinin treatment of BAEC led to the activation of ERK, associated with an increase in phosphorylation of eNOS; phosphorylation of eNOS by ERK in vitro significantly reduced eNOS enzyme activity. Evidence for the direct phosphorylation of eNOS by MAP kinase in BAEC came from "back-phosphorylation" experiments using [gamma-(32)P]ATP and ERK in vitro to phosphorylate eNOS isolated from cells previously treated with bradykinin or the MAP kinase inhibitor PD98059. The ERK-catalyzed in vitro (32)P phosphorylation of eNOS isolated from BAEC treated with bradykinin was significantly attenuated compared with untreated cells, indicating that bradykinin treatment led to the phosphorylation of ERK-sensitive sites in cells. Conversely, eNOS isolated from endothelial cells pretreated with the MAP kinase inhibitor PD98059 showed increased ERK-promoted phosphorylation in vitro. Taken together, our results suggest that bradykinin-induced activation of ERK leads to eNOS phosphorylation and enzyme inhibition, a process influenced by the reversible associations of members of the MAP kinase pathway with eNOS.