Des-Arg9-bradykinin metabolism in patients who presented hypersensitivity reactions during hemodialysis: role of serum ACE and aminopeptidase P

Bradykinin Metabolism and Drug-Induced Angioedema

Bradykinin (BK) metabolism and its receptors play a central role in drug-induced angioedema (AE) without urticaria through increased vascular permeability. Many cardiovascular and diabetic drugs may cause BK-mediated AE. Angiotensin-converting enzyme inhibitors (ACEIs) and neprilysin inhibitors impair BK catabolism. Dipeptidyl peptidase-IV (DPP-IV) inhibitors reduce the breakdown of BK and substance P (SP). Moreover, angiotensin receptor blockers, thrombolytic agents, and statins may also induce BK-mediated AE. Understanding pathophysiological mechanisms is crucial for preventing and treating drug-induced AE.

Kinins and Their Receptors as Potential Therapeutic Targets in Retinal Pathologies

The kallikrein-kinin system (KKS) contributes to retinal inflammation and neovascularization, notably in diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Bradykinin type 1 (B1R) and type 2 (B2R) receptors are G-protein-coupled receptors that sense and mediate the effects of kinins. While B2R is constitutively expressed and regulates a plethora of physiological processes, B1R is almost undetectable under physiological conditions and contributes to pathological inflammation. Several KKS components (kininogens, tissue and plasma kallikreins, and kinin receptors) are overexpressed in human and animal models of retinal diseases, and their inhibition, particularly B1R, reduces inflammation and pathological neovascularization. In this review, we provide an overview of the KKS with emphasis on kinin receptors in the healthy retina and their detrimental roles in DR and AMD. We highlight the crosstalk between the KKS and the renin–angiotensin system (RAS), which is known to be detrimental in ocular pathologies. Targeting the KKS, particularly the B1R, is a promising therapy in retinal diseases, and B1R may represent an effector of the detrimental effects of RAS (Ang II-AT1R).

Neprilysin Inhibitors and Bradykinin

Bradykinin has important physiological actions related to the regulation of blood vessel tone and renal function, and protection from ischemia reperfusion injury. However, bradykinin also contributes to pathological states such as angioedema and inflammation. Bradykinin is metabolized by many different peptidases that play a major role in the control of bradykinin levels. Peptidase inhibitor therapies such as angiotensin converting enzyme (ACE) and neprilysin inhibitors increase bradykinin levels, and the challenge for such therapies is to achieve the beneficial cardiovascular and renal effects without the adverse consequences such as angioedema that may result from increased bradykinin levels. Neprilysin also metabolizes natriuretic peptides. However, despite the potential therapeutic benefit of increased natriuretic peptide and bradykinin levels, neprilysin inhibitor therapy has only modest efficacy in essential hypertension and heart failure. Initial attempts to combine neprilysin inhibition with inhibition of the renin angiotensin system led to the development of omapatrilat, a drug that combines ACE and neprilysin inhibition. However, omapatrilat produced an unacceptably high incidence of angioedema in patients with hypertension (2.17%) in comparison with the ACE inhibitor enalapril (0.68%), although angioedema incidence was less in patients with heart failure with reduced ejection fraction (HFrEF) treated with omapatrilat (0.8%), and not different from that for enalapril therapy (0.5%). More recently, LCZ696, a drug that combines angiotensin receptor blockade and neprilysin inhibition, was approved for the treatment of HFrEF. The approval of LCZ696 therapy for HFrEF represents the first approval of long-term neprilysin inhibitor administration. While angioedema incidence was acceptably low in HFrEF patients receiving LCZ696 therapy (0.45%), it remains to be seen whether LCZ696 therapy for other conditions such as hypertension is also accompanied by an acceptable incidence of angioedema.

Incidence of hypotension and acute hypotensive transfusion reactions following platelet concentrate transfusions

BACKGROUND AND OBJECTIVES

Platelet concentrates (PCs) are associated with transfusion reactions involving hypotension, particularly bradykinin-mediated acute hypotensive transfusion reactions. This study aims to determine the incidence of hypotensive events and more specifically acute hypotensive transfusion reaction associated with PC transfusions. We also sought to ascertain whether these reactions are associated with elevated bradykinin levels.

MATERIALS AND METHODS

This is a prospective descriptive study of PCs administered at Sainte-Justine Hospital over 28 months. All PCs administered during this period were screened for hypotension through review of all transfusion-associated reaction reports (TARRs) sent to the blood bank. All residual PC bags were returned to the blood bank. TARRs associated with hypotension were reviewed by adjudicators that established the imputability of the PC transfusion to the reaction. Bradykinin levels were sampled in the first 168 PC bags returned to the blood bank. Levels were compared between PCs associated with hypotension and control PCs not associated with hypotension.

RESULTS

A total of 3672 PC bags were returned to the blood bank; 25 PCs were associated with hypotension. Adjudicators ascertained that five hypotensive events were imputable to PCs of which one was an acute hypotensive transfusion reaction (incidence: 0·03%). Bradykinin level in the latter PC was 10 pg/ml, whereas levels were 226·2 ± 1252 pg/ml in the 143 control PCs.

CONCLUSION

Our results show a low incidence of hypotension after PC transfusion. We identified only one acute hypotensive transfusion reaction. No correlation between bradykinin level and the occurrence of acute hypotensive reactions could be observed given that only one event was identified.

Fatal laryngeal angioedema: a case report and a workup of angioedema in a forensic setting

Angioedema is an episodic swelling of the deep dermis, subcutis, and/or submucosal tissue due to an increase in local vascular permeability. Swelling may involve skin, respiratory, and gastrointestinal tracts. The most commonly involved areas are the periorbital region and the lips. Here we report a case of a fatal laryngeal obstruction due to angioedema likely caused by an angiotensin-converting-enzyme inhibitor. The decedent, a 58-year-old man, was witnessed developing sudden facial swelling and acute respiratory difficulties quickly followed by unresponsiveness. His past medical history suggested that this was his second episode of angioedema without urticaria. Postmortem examination revealed a complete laryngeal obstruction in the absence of infection, neoplasm, or autoimmune disease. Postmortem computed tomography of the head and neck showed a complete obstruction of the upper airway. Based on the current understanding of the pathophysiology of different types of angioedema, we will suggest a workup of angioedema without urticaria in the forensic setting and offer readers resources they can use in their practice.

Genetic variants associated with angiotensin-converting enzyme inhibitor-associated angioedema

OBJECTIVE

The objective of this study was to identify genetic variants associated with angiotensin-converting enzyme (ACE) inhibitor-associated angioedema.

PARTICIPANTS AND METHODS

We carried out a genome-wide association study in 175 individuals with ACE inhibitor-associated angioedema and 489 ACE inhibitor-exposed controls from Nashville (Tennessee) and Marshfield (Wisconsin). We tested for replication in 19 cases and 57 controls who participated in Ongoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial (ONTARGET).

RESULTS

There were no genome-wide significant associations of any single-nucleotide polymorphism (SNP) with angioedema. Sixteen SNPs in African Americans and 41 SNPs in European Americans were associated moderately with angioedema (P<10) and evaluated for association in ONTARGET. The T allele of rs500766 in PRKCQ was associated with a reduced risk, whereas the G allele of rs2724635 in ETV6 was associated with an increased risk of ACE inhibitor-associated angioedema in the Nashville/Marshfield sample and ONTARGET. In a candidate gene analysis, rs989692 in the gene encoding neprilysin (MME), an enzyme that degrades bradykinin and substance P, was significantly associated with angioedema in ONTARGET and Nashville/Marshfield African Americans.

CONCLUSION

Unlike other serious adverse drug effects, ACE inhibitor-associated angioedema is not associated with a variant with a large effect size. Variants in MME and genes involved in immune regulation may be associated with ACE inhibitor-associated angioedema.

Many faces of angioedema: focus on the diagnosis and management of abdominal manifestations of hereditary angioedema

Angioedema of the intestinal tract is an infrequent but well-described cause of abdominal pain that can occur because of inherited, acquired, allergic, or drug-induced causes. Hereditary angioedema (HAE) is a genetic disorder that causes recurrent attacks of severe edema of various body parts, including the intestinal tract. Moderate to severe abdominal pain occurs in 43-93% of such attacks due to intestinal edema. Laryngeal edema is a potentially life-threatening manifestation. Failure to recognize and diagnose HAE or other causes of intestinal angioedema can lead to years of delay in diagnosis, and in the case of HAE, often to unnecessary abdominal surgeries. Recognizing the typical history of recurrent attacks of abdominal pain, oropharyngeal/laryngeal angioedema or cutaneous angioedema, family history of similar symptoms, association of attacks with stress or menses, and exacerbation of attacks after administration of estrogens or angiotensin-converting enzyme inhibitors will increase diagnostic accuracy. Interdisciplinary treatment is often necessary after the diagnosis of HAE, first with acute management in the emergency room or the intensive care unit, followed by either drug prophylaxis against future attacks using a C1-esterase inhibitor concentrate or attenuated androgens and discontinuation of medications known to trigger attacks. Newer drugs approved for treatment of acute attacks may have future roles in the prevention of attacks if further studies support their efficacy. Gastroenterologists in particular should maintain a high index of suspicion for the possibility of HAE or other causes of intestinal angioedema in patients with a history of recurrent abdominal pain.

A functional XPNPEP2 promoter haplotype leads to reduced plasma aminopeptidase P and increased risk of ACE inhibitor-induced angioedema

Angiotensin I-converting enzyme inhibitors (ACEi) are widely used antihypertensive agents that are associated with a potentially life-threatening reaction, ACEi-angioedema. Impaired metabolism of bradykinin and des-Arg(9) -bradykinin by aminopeptidase P (APP) is a key contributor to ACEi-angioedema. This study aimed to characterize the genetic regulation of the XPNPEP2 gene and identify the genetic factors contributing to variance in plasma APP activity and ACEi-angioedema. Additive genetic factors accounted for 47.3% of variance in plasma APP activity in healthy individuals. Nested deletion analysis identified the minimal promoter (-338 bp to -147 bp) and an enhancer region (-2,502 bp to -2,238 bp). Three polymorphisms (c.-2399C>A, c.-1612G>T, and c.-393G>A) were significantly associated with plasma APP activity. Haplotype ATG was significantly associated with reduced reporter gene activity and with reduced plasma APP activity. The c.-2399C>A polymorphism was located in an enhancer region and was predicted to differentially bind hepatic nuclear factor 4 (HNF4). Over expression of HNF4 increased the activation of haplotype ATG compared with haplotype CGG. In a case control study of subjects with a history of ACEi-angioedema, haplotype ATG was significantly associated with ACEi-angioedema (OR 4.87 [1.78-13.35] P = 0.002). The ATG haplotype is functional and contributes to ACEi-angioedema through a reduction in APP.

Bradykinin forming capacity of oversulfated chondroitin sulfate contaminated heparin in vitro

Oversulfated chondroitin sulfate (OSCS) contaminated heparin has been associated with severe anaphylactoid reaction (AR), mainly in dialysed patients. Although attributed to bradykinin (BK) released during contact system activation by OSCS, no definitive evidence exists until now for a BK release during incubation of contaminated heparin with human plasma. In this study, we investigated the kinin forming capacity of OSCS and OSCS contaminated heparin when incubated in vitro with a pool of human plasma. At 100 microg/mL, OSCS liberates BK in a profile similar but not identical to dextran sulfate, a well known activator of the plasma contact system. The results have highlighted that the quantity of BK accumulated during contact system activation depends not only on the concentration of OSCS but also on the plasma dilution and the presence of an angiotensin converting enzyme inhibitor. We demonstrate a highly significant correlation between the concentration of OSCS present in the contaminated heparin and BK released concentration. In conclusion, for the first time, we show that OSCS contaminated heparin incubated with human plasma has the capacity to liberate BK at a concentration that could explain the role of this inflammatory peptide in the pathophysiology of AR associated with OSCS contaminated heparin.

DISCLAIMER

The findings and conclusions in this article have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy.

Heparin-induced anaphylactic and anaphylactoid reactions: two distinct but overlapping syndromes

BACKGROUND

Heparin-induced anaphylactic and anaphylactoid reactions are of increasing clinical and scientific interest, particularly given the recent identification of a syndrome of heparin-induced anaphylaxis due to oversulfated chondroitin sulfate (OSCS), a contaminant in certain heparin preparations. However, heparin-induced anaphylactoid reactions also have been reported to be a consequence of immune-mediated heparin-induced thrombocytopenia (HIT).

OBJECTIVE

To summarize the clinical features and pathophysiology of two distinct disorders, HIT-associated anaphylactoid reactions as well as anaphylaxis resulting from OSCS-contaminated heparin.

METHODS

We review literature describing these two types of heparin-induced anaphylactic and anaphylactoid reactions, and seek potential pathophysiologic links between them.

RESULTS

Intravenous bolus heparin administered to patients with circulating 'HIT antibodies', usually as a result of recent heparin therapy, can produce anaphylactoid reactions, probably as a consequence of in vivo activation of platelets and, possibly, leukocytes. Affected patients often evince fever/chills, hypertension and/or acute respiratory compromise ('pseudo-pulmonary embolism'). In contrast, heparin-induced anaphylaxis is caused by activation of the contact system, with formation of vasoactive kinins (bradykinin, des-arg(9)-bradykinin). This latter syndrome has been linked in an epidemic form to administration of OSCS-contaminated heparin; these reactions feature prominent hypotension and laryngeal edema. Hemodialysis patients are at increased risk for both syndromes. There is evidence that OSCS-contaminated heparin itself increases the risk of HIT compared with non-contaminated heparin.

CONCLUSION

Two distinct syndromes of heparin-induced anaphylaxis and anaphylactoid reactions exist. These seem to share certain epidemiologic features, given that OSCS-contaminated heparin can produce anaphylaxis through contact system activation but also could increase risk of HIT and HIT-associated anaphylactoid reactions.

Metallopeptidase activities in hereditary angioedema: effect of androgen prophylaxis on plasma aminopeptidase P

BACKGROUND

Aminopeptidase P (APP) plays an important role in the catabolism of kinins in human plasma, mostly for des-Arg(9)-bradykinin. Impaired degradation of this active bradykinin metabolite was found to be associated with a decreased APP activity in hypertensive patients who experienced angioedema while being treated with angiotensin I-converting enzyme inhibitors. The pathophysiology of hereditary angioedema is presently attributed only to a quantitative/qualitative C1 inhibitor (CI-INH) defect with increased bradykinin release.

OBJECTIVES

In the context of androgen prophylaxis, increased CI-INH function cannot fully explain protection from angioedema attacks alone because of the limited reversion of the CI-INH defects. Therefore we hypothesized that androgen prophylaxis could enhance plasma APP activity.

METHODS

Patients with hereditary angioedema were investigated for plasma metallopeptidase activities responsible for kinin catabolism (APP, angiotensin I-converting enzyme, and carboxypeptidase N) and for CI-INH function in treated and untreated patients.

RESULTS

APP activity was asymmetrically distributed in untreated patients (n = 147): the mean value was significantly lower than the value in a reference healthy and unmedicated population (n = 116; P < or = .001). Prophylaxis with androgen induced a significant increase in APP activity (P < or = .001), whereas it did not affect the other metallopeptidase activities. In both patient groups, APP activity showed a significant inverse relationship to disease severity (P < or = .001).

CONCLUSION

In addition to the effect on circulating CI-INH levels, the increase in APP levels brought on by androgens could contribute to a more effective control of the kinin accumulation considered to be responsible for the symptoms of angioedema.

Generation of kinins during preparation and storage of whole blood?derived platelet concentrates

BACKGROUND

Leukoreduction of platelet (PLT) concentrates (PCs) may be associated with hypotension in recipients, and a role for bradykinin (BK)-related peptides has been proposed for this side effect.

STUDY DESIGN AND METHODS

The concentration of BK and one of its vasoactive metabolites, des-arginine(9)-BK (des-Arg(9)-BK), was measured in a large number of PCs as a function of leukoreduction and storage duration with specific enzyme immunoassays and complementary techniques.

RESULTS

On Day 0 of storage, kinins were detected in leukoreduced and unfiltered PCs at a concentration lower than 100 pg per mL. During storage, both kinin levels peaked on Day 5 of storage, with a concentration higher than 1 ng per mL in 22 percent of PCs whether filtered on Day 0 or not. Physicochemical and pharmacologic characterizations of immunoreactive kinins confirm their nature. In vitro activation of the contact system of the corresponding PLT-poor plasma showed that a high kinin concentration on Day 5 of the storage corresponded with a low kinin-forming capacity of plasma. On Day 7, BK was no longer elevated presumably due to its degradation and the depletion of kinin-forming capacity of the plasma in stored PCs. The activities of metallopeptidases that metabolize BK-related peptides in plasma from PCs were at levels similar to those recorded in the plasma of a normal reference population and were unaffected by storage.

CONCLUSION

Storage of PCs contributes to the hydrolysis of high-molecular-weight kininogen and generation of pharmacologically relevant BK levels that might pose a hazard in susceptible patients.

Neuropeptide Y (NPY) cleaving enzymes: structural and functional homologues of dipeptidyl peptidase 4

N-terminal truncation of NPY has important physiological consequences, because the truncated peptides lose their capability to activate the Y1-receptor. The sources of N-terminally truncated NPY and related peptides are unknown and several proline specific peptidases may be involved. First, we therefore provide an overview on the peptidases, belonging to structural and functional homologues of dipeptidyl peptidase 4 (DP4) as well as aminopeptidase P (APP) and thus, represent potential candidates of NPY cleavage in vivo. Second, applying selective inhibitors against DP4, DP8/9 and DP2, respectively, the enzymatic distribution was analyzed in brain extracts from wild type and DP4 deficient F344 rat substrains and human plasma samples in activity studies as well as by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry. Third, co-transfection of Cos-1 cells with Dpp4 and Npy followed by confocal lasermicroscopy illustrated that hNPY-dsRed1-N1 was transported in large dense core vesicles towards the membrane while rDP4-GFP-C1 was transported primarily in different vesicles thereby providing no clear evidence for co-localization of NPY and DP4. Nevertheless, the review and experimental results of activity and mass spectrometry studies support the notion that at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) are potentially involved in NPY cleavage while the serine protease DP4 (CD26) could be the principal peptidase involved in the N-terminal truncation of NPY. However, DP8 and DP9 are also capable of cleaving NPY, whereas no cleavage could be demonstrated for DP2.

Kinin-dependent hypersensitivity reactions in hemodialysis: metabolic and genetic factors

Although the association of angiotensin I-converting enzyme inhibitors (ACEis) with a negatively charged membrane is thought to be responsible for hypersensitivity reactions (HSRs) during hemodialysis, we hypothesize that these complications are due to changes in plasma aminopeptidase P (APP) activity and genotype. To test this hypothesis, we measured plasma APP activity in 14 patients who suffered HSR (HSR+) while dialyzed with an AN69 membrane and simultaneously treated with an ACEi. APP activity was also studied in a control group (n=39) dialyzed under the same conditions, but who did not suffer any side effect (HSR-). We found significantly decreased plasma APP activity (P=0.013) in HSR+ subjects as well as altered degradation of endogenous des-Arginine(9)-bradykinin, with a significantly lower beta value (P<0.001). The same analytical approach was taken in 171 relatives of HSR+ patients. Variance component analysis suggested that genetic differences may explain 61% of the phenotypic variability of plasma APP activity (P<0.001) and the kinetic parameters that characterized kinin degradation. We also showed that the C-2399A single-nucleotide polymorphism at the XPNPEP2 locus was a significant predictor of APP activity in the 39 HSR- controls (P=0.029). Furthermore, a recessive genetic model for the A allele disclosed a significant difference in mean APP activity by genotype (P<0.001). Finally, our study defined the nonspecific inhibition of recombinant APP by some ACEis. In conclusion, this paper highlights the complexity of HSR in hemodialysis, suggesting, as with angioedema, that these rare, but life-threatening adverse events are governed by several metabolic and genetic factors.

Aspect multifactoriel des effets secondaires aigus des inhibiteurs de l′enzyme de conversion de l′angiotensine

Angiotensin converting enzyme inhibitors are a class of drugs successfully used in the treatment of cardiovascular diseases. Despite their effectiveness, treatment with these drugs is characterized by chronic and acute side effects with variable expression depending on the clinical context. Angioedema occurs in patients with hypertension or heart failure. Anaphylactoid reaction is also reported in hemodialysis patients and severe hypotensive reaction in patients receiving transfused blood products and plasmapheresis. In this paper, we describe the role of kinins and metallopeptidases in the pathophysiology of these acute side effects. We also propose different experimental and clinical evidences which plead for an ecogenetic nature of these rare but life-threatening events.

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.

A variant in XPNPEP2 is associated with angioedema induced by angiotensin I-converting enzyme inhibitors

Angiotensin I-converting enzyme inhibitors (ACEi), which are used to treat common cardiovascular diseases, are associated with a potentially life-threatening adverse reaction known as angioedema (AE-ACEi). We have previously documented a significant association between AE-ACEi and low plasma aminopeptidase P (APP) activity. With eight large pedigrees, we hereby demonstrate that this quantitative trait is partially regulated by genetic factors. We tested APP activity using a variance-component QTL analysis of a 10-cM genomewide microsatellite scan enriched with seven markers over two candidate regions. We found significant linkage (LOD = 3.75) to a locus that includes the XPNPEP2 candidate gene encoding membrane-bound APP. Mutation screening of this QTL identified a large coding deletion segregating in one pedigree and an upstream single-nucleotide polymorphism (C-2399A SNP), which segregates in the remaining seven pedigrees. Measured genotype analysis strongly suggests that the linkage signal for APP activity at this locus is accounted for predominantly by the SNP association. In a separate case-control study (20 cases and 60 controls), we found significant association of this SNP to ACEi-induced AE (P=.0364). In conclusion, our findings provide supporting evidence that the C-2399A variant in XPNPEP2 is associated with reduced APP activity and a higher incidence of AE-ACEi.

Expression of Metallopeptidases and Kinin Receptors in Swine Oropharyngeal Tissues: Effects of Angiotensin I-Converting Enzyme Inhibition and Inflammation

Angiotensin I-converting enzyme inhibitors (ACEi) cause both chronic and acute side effects, including rare but potentially life-threatening angioedema (AE). The main hypothesis to be tested in this study was that metallopeptidases and kinin receptors are present in oropharyngeal tissues and that their expression is modulated by ACEi and inflammation. Novel real-time polymerase chain reaction analysis was developed and allowed the relative quantification of tissue's gene expression for neprilysin, membrane-bound aminopeptidase P (mAPP), and both B1 and B2 kinin receptor subtypes in tongue, parotid gland, and laryngeal tissue (areas especially involved in the gravest clinical forms of AE) and in kidney in a porcine model (single injection or 7-day ACEi oral treatments applied or lipopolysaccharide injected as a positive inflammatory control). The results provide evidence of the expression and activities of kininases in oropharyngeal tissues in the swine. ACEi treatment modulated the expression of neutral endopeptidase and mAPP mRNA, but the corresponding enzyme activities and that of angiotensin I-converting enzyme (ACE) were generally stable in tissues. The 7-day ACEi treatment up-regulated both kinin receptor mRNAs in the oropharynx and the B1 receptor mRNA in the lingual vascular endothelium (immunohistochemistry). The inhibition of ACE in plasma is responsible for an accumulation of bradykinin and des-arginine9-bradykinin generated during activation of the contact system with glass beads. The expression of critical components of the kallikrein-kinin system in the oropharyngeal tissues supports the role of kinins in ACEi-induced AE.

International union of pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences

Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development.

The cardioprotective effect of dual metallopeptidase inhibition: respective roles of endogenous kinins and natriuretic peptides

The objective of the present study was to assess the cardioprotective effect of dual NEP–ACE inhibition in relation to endogenous cardiac bradykinin (BK), its active metabolite des-Arg9-BK, endogenous brain natriuretic peptides (BNP), and cGMP. Rats were treated with the dual metallopeptidase inhibitor, omapatrilat, or the ACE inhibitor, ramipril, for 7 d (1 mg·kg–1·d–1). Hearts were then isolated and subjected to a zero-flow ischemia and reperfusion (except controls), in the absence or presence of either a B2-receptor antagonist (Hoe-140), a B1-receptor antagonist (Lys-Leu8-des-Arg9-BK), or the GC-A/GC-B-receptor antagonist (HS-142-1). Chronic omapatrilat and ramipril increased the amount of endogenous BK collected upon reperfusion, but only ramipril increased that of des-Arg9-BK. Only omapatrilat increased both peak BNP and peak cGMP upon reperfusion, those increases being blocked by Hoe-140. Chronic omapatrilat (but not ramipril) decreased the total noradrenaline and lactate dehydrogenase release during the reperfusion period. Importantly, only omapatrilat improved the functional recovery of the ischemic reperfused heart, with a reduced left ventricular end-diastolic pressure, and improved developed left ventricular pressure. All cardio protective effects of omapatrilat were blocked by Hoe-140 and by HS-142-1, but not by the B1-receptor antagonist. In conclusion, a chronic treatment with a dual metallopeptidase inhibitor demonstrated a cardioprotective action not observed with an ACE inhibitor in a context of severe ischemia in rat isolated hearts, which was mediated by both endogenous BK and BNP.Key words: ACE inhibitors, omapatrilat, bradykinin, natriuretic peptide, ischemia, reperfusion.

Human recombinant membrane-bound aminopeptidase P: production of a soluble form and characterization using novel, internally quenched fluorescent substrates

APP (aminopeptidase P) has the unique ability to cleave the N-terminal amino acid residue from peptides exhibiting a proline at P(1)'. Despite its putative involvement in the processing of bioactive peptides, among them the kinins, little is known about the physiological roles of both human forms of APP. The purpose of the present study is first to engineer and characterize a secreted form of hmAPP (human membrane-bound APP). Our biochemical analysis has shown that the expressed glycosylated protein is fully functional, and exhibits enzymic parameters similar to those described previously for mAPP purified from porcine or bovine lungs or expressed from a porcine clone. This soluble form of hmAPP cross-reacts with a polyclonal antiserum raised against a 469-amino-acid hmAPP fragment produced in Escherichia coli. Secondly, we synthesized three internally quenched fluorescent peptide substrates that exhibit a similar affinity for the enzyme than its natural substrates, the kinins, and a higher affinity compared with the tripeptide Arg-Pro-Pro used until now for the quantification of APP in biological samples. These new substrates represent a helpful analytical tool for rapid and reliable screening of patients susceptible to adverse reactions associated with angiotensin-converting enzyme inhibitors or novel vasopeptidase (mixed angiotensin-converting enzyme/neprilysin) inhibitors.

Drug therapy for hypertension in hemodialysis patients

The majority of end-stage renal disease (ESRD) patients are hypertensive. Drug therapy for hypertension in hemodialysis (HD) patients includes all classes of antihypertensive drugs, with the sole exception of diuretics. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers may decrease morbidity and mortality by reducing the mean arterial pressure (MAP), aortic pulse wave velocity, and aortic systolic pressure augmentation, as well as left ventricular hypertrophy (LVH) and probably reduction of C-reactive protein (CRP) and oxidant stress. Potential risk factors include hyperkalemia, anaphylactoid reaction with AN69 membranes (particularly ACE inhibitors), and aggravation of renal anemia. beta-blockers decrease not only mortality, blood pressure (BP), and ventricular arrhythmias, but also improve left ventricular function in ESRD patients. Nonselective beta-blockers can cause an increase in serum potassium (particularly during fasting or exercise). Lisinopril and atenolol have a predominant renal excretion and therefore a prolonged half life in ESRD patients. Thus thrice-weekly supervised administration of these drugs after HD can enhance BP control. The use of calcium channel blockers is also associated with lower total and cardiovascular-specific mortality in HD patients. Minoxidil is a very potent vasodilator that is generally reserved for dialysis patients with severe hypertension. Hypertensive dialysis patients who are noncompliant with their medications may benefit from transdermal clonidine therapy once a week. The majority of dialysis patients need a combination of several antihypertensive drugs for adequate BP control.

Hereditary and acquired angioedema: problems and progress: proceedings of the third C1 esterase inhibitor deficiency workshop and beyond

Hereditary angioedema (HAE), a rare but life-threatening condition, manifests as acute attacks of facial, laryngeal, genital, or peripheral swelling or abdominal pain secondary to intra-abdominal edema. Resulting from mutations affecting C1 esterase inhibitor (C1-INH), inhibitor of the first complement system component, attacks are not histamine-mediated and do not respond to antihistamines or corticosteroids. Low awareness and resemblance to other disorders often delay diagnosis; despite availability of C1-INH replacement in some countries, no approved, safe acute attack therapy exists in the United States. The biennial C1 Esterase Inhibitor Deficiency Workshops resulted from a European initiative for better knowledge and treatment of HAE and related diseases. This supplement contains work presented at the third workshop and expanded content toward a definitive picture of angioedema in the absence of allergy. Most notably, it includes cumulative genetic investigations; multinational laboratory diagnosis recommendations; current pathogenesis hypotheses; suggested prophylaxis and acute attack treatment, including home treatment; future treatment options; and analysis of patient subpopulations, including pediatric patients and patients whose angioedema worsened during pregnancy or hormone administration. Causes and management of acquired angioedema and a new type of angioedema with normal C1-INH are also discussed. Collaborative patient and physician efforts, crucial in rare diseases, are emphasized. This supplement seeks to raise awareness and aid diagnosis of HAE, optimize treatment for all patients, and provide a platform for further research in this rare, partially understood disorder.

Hypotensive transfusion reactions can occur with blood products that are leukoreduced before storage

BACKGROUND

Leukoreduction before storage, rather than bedside white blood cell filtration, is recommended to prevent hypotensive transfusion reactions.

STUDY DESIGN AND METHODS

Investigation of hypotensive transfusion reactions during radical prostatectomy in two patients on angiotensin-converting enzyme inhibitors. In Patient A, hypotension occurred during the transfusion of each of the following blood products: 2 units of autologous blood deposited and leukoreduced (LR) before storage; 3 units of allogeneic red cells LR before storage; and 2 units of non-LR acute normovolemic hemodilution (ANH) whole blood. When each of the transfusions was stopped, the blood pressure recovered. In Patient B, hypotension occurred during the transfusion of non-LR ANH whole blood. All implicated units were administered rapidly using a blood infuser at 37 degrees C. Bradykinin (BK) and des-Arg9-BK formation and degradation and the activity of kinin-degrading metallopeptidases were measured in plasma samples from both patients.

RESULTS

Degradation of des-Arg9-BK was severely impaired and the activity of aminopeptidase P severely reduced in Patient A, but not in Patient B. BK degradation was mildly impaired in both patients.

CONCLUSION

Hypotensive reactions can occur with blood products that are LR before storage and non-LR ANH. An inherent defect in the metabolism of kinins may be a risk factor for the development of hypotensive transfusion reactions.

The pharmacokinetics and pharmacodynamics of angiotensin-receptor blockers in end-stage renal disease

Angiotensin-converting enzyme (ACE) inhibitors and more recently angiotensin-receptor blockers (ARBs) have become popular therapies in the end-stage renal disease (ESRD) patient. The ability of either of these drug classes to reduce blood pressure in the ESRD patient is well accepted; however, there is considerably less information available to guide the clinician in the safe and effective use of these drugs in the ESRD patient with congestive heart failure and/or coronary artery disease. Head-to-head studies in the ESRD patient are lacking for both drug classes. Several pharmacokinetic factors can influence the selection of these drugs, including dialysability and the propensity for systemic accumulation. ACE inhibitors (ACE-Is) and ARBs are recognised as having a range of nonpressor effects that are pertinent to patients with ESRD. Such effects include their ability to decrease both thirst drive and erythropoiesis. These drug classes, though, are distinguishable by the unique adverse effect profile for ACE-Is. As is the case in patients without renal failure, ESRD patients can experience cough and, less frequently, angioneurotic oedema with ACE-Is. In the ESRD population, so-called anaphylactoid dialyser reactions can occur in conjunction with ACE-I use. The use of a drug from within the ARB class carries both less risk and permits a compound with a preferred pharmacokinetic profile limited dialysability and minimal systemic accumulation to be administered. These attributes would favour the increased use of ARBs in this population.

Hypotensive reaction during staphylococcal protein A column therapy in a patient with anomalous degradation of bradykinin and Des-Arg9-bradykinin after contact activation

BACKGROUND

Hypotensive reactions have occurred in patients taking angiotensin converting enzyme (ACE) inhibitors after infusion of blood previously in contact with negatively charged surfaces capable of generating kinins, which accumulate when ACE, a kininase, is inhibited. A patient with anomalous bradykinin (BK) metabolism who experienced hypotension during extracorporeal staphylococcal protein A (SPA) therapy while on an ACE inhibitor was studied.

CASE REPORT

A patient with mitomycin-associated hemolytic-uremic syndrome received SPA treatments after her ACE inhibitor, lisinopril, was held. Lisinopril was restarted before her 18th SPA treatment, and immediately after return of treated plasma she developed facial redness and hypotension, which resolved after the return stopped and recurred when restarted. To study formation and degradation of kinins, exposed her plasma to glass beads. We found a normal kinin formation rate but an abnormal degradation and accumulation of Des-Arg9-BK. The kinin degradation enzymes ACE, aminopeptidase P (APP), and carboxypeptidase N (CPN) were measured while on an ACE inhibitor, showing absence of ACE activity, low APP, but normal CPN.

CONCLUSION

This patient's vasodilation and hypotension during SPA therapy was associated with a pre- existing anomaly of BK metabolism. Her ACE inhibitor shifted degradation toward Des-Arg9-BK formation, and her low APP was associated with a prolonged t50 and accumulation of the vasoactive Des-Arg9-BK.

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.

Dipeptidyl peptidase IV activity in patients with ACE-inhibitor-associated angioedema

Bradykinin and substance P have been implicated as mediators in angiotensin-converting enzyme inhibitor (ACEI)-associated angioedema. Studies investigating the metabolism of bradykinin in sera from patients with a history of ACEI-associated angioedema and controls suggest that there is a defect in a non-ACE, non-kininase I pathway of bradykinin degradation, such as the aminopeptidase P (APP)/dipeptidyl peptidase IV (DPPIV) pathway. This study tested the hypothesis that serum APP or DPPIV activity is decreased in patients with ACEI-associated angioedema. APP and DPPIV activity were measured in sera collected from patients during ACEI-associated angioedema, from patients with a remote history of ACEI-associated angioedema, and from normotensive and untreated hypertensive controls. The effects of acute and chronic ACEI and corticosteroid treatment on serum DPPIV activity were also assessed. DPPIV activity was similar in normotensive volunteers (37.8 +/- 6.3 nmol/mL per min), in untreated hypertensive subjects who had been exposed previously to ACEI without angioedema (36.2 +/- 4.3 nmol/mL per min), in hypertensive patients with a remote history of angioedema (35.1 +/-8.5 nmol/mL per min), and in chronically ACEI-treated hypertensive subjects (36.1 +/- 5.6 nmol/mL per min). DPPIV activity decreased with increasing age (R(2)=0.10, P=0.016). Subject group significantly affected DPPIV activity (F=6.208, P=0.016) such that DPPIV activity was significantly lower in patients with ACEI-associated angioedema (26.9 +/- 4.1 nmol/mL per min) than in normotensive controls, in previously ACEI-exposed untreated hypertensive volunteers, or in ACEI-treated hypertensive volunteers, even after controlling for age. There was no effect of acute ACE inhibition or corticosteroids on DPPIV activity. With respect to APP activity, there was no difference between groups. These results suggest that DPPIV activity is depressed in individuals with hypertension during acute ACEI-associated angioedema.

Functional expression and characterization of the cytoplasmic aminopeptidase P of Caenorhabditis elegans

Aminopeptidase P (AP-P; X-Pro aminopeptidase; EC 3.4.11.9) cleaves the N-terminal X-Pro bond of peptides and occurs in mammals as both cytosolic and plasma membrane forms, encoded by separate genes. In mammals, the plasma membrane AP-P can function as a kininase, but little is known about the physiological role of the cytosolic enzyme. The C. elegans genome contains a single gene encoding AP-P (W03G9.4), analysis of which predicts regions displaying high levels of amino-acid sequence homology between the predicted gene product and mammalian cytoplasmic AP-P, with the absolute conservation of key catalytic residues. The sequence of an EST (yk91g4), comprising the open reading frame of W03G9.4, confirmed the predicted genomic structure of the gene and the prediction that W03G9.4 codes for a nonsecreted protein with a molecular mass of 68 kDa. Nematodes transformed with a promoter reporter construct, W03G9.4:GFP, showed high levels of fluorescence in the intestine of larvae and adult hermaphrodites, indicating that the intestine is a major site of W03G9.4 expression. yk91g4 tagged with a hexahistidine and DLYDDDDK peptide epitope was expressed in Escherichia coli to yield, after affinity purification, a recombinant protein with a molecular mass of 71 kDa. The recombinant W03G9.4 removed the N-terminal amino acid from bradykinin (RPPGFSPFR), a Caenorhabditis elegans neuropeptide (KPSFVRFamide) and Lem Trp 1 (APSGFLGVRamide), but did not display activity towards angiotensin I (NRVYIHPFHL), des-Arg bradykinin and AF1 (KNEFIRFamide). The activity towards bradykinin was inhibited by EDTA and 1, 10 phenanthroline, as expected for a metalloenzyme, and also by apstatin (IC50, 1 microM), a selective inhibitor of mammalian AP-P. A Km of 45 microM and an optimum pH of 7-8 was observed with bradykinin as the substrate. The activity of the nematode AP-P, like its mammalian counterparts, was strongly influenced by metal ions, with Co2+, Mn2+ and Zn2+ all inhibiting the hydrolysis of bradykinin. We conclude that W03G9.4 codes for a cytoplasmic AP-P with very similar enzymatic properties to those of mammalian AP-P, and we suggest that the enzyme has a physiological role in the intracellular hydrolysis of proline-containing peptides absorbed from the lumen of the intestine.

Bradykinin metabolism in the isolated perfused rabbit heart

BACKGROUND

Bradykinin is a potent cardioprotective hormone, the beneficial role of which in vivo appears to be limited by its rapid metabolism. Inhibitors of peptidases that degrade endogenously formed bradykinin are themselves cardioprotective, presumably by increasing local bradykinin concentrations. As bradykinin-degrading peptidases are potential therapeutic targets, it is important to identify these enzymes in different animal models of cardiac function.

OBJECTIVE

To determine the mechanism of bradykinin degradation in the coronary circulation of the rabbit, using an isolated perfused heart preparation.

DESIGN AND METHODS

[3H]Bradykinin (16 nmol/l) was perfused as a bolus through the isolated rabbit heart in the presence and absence of specific peptidase inhibitors. The effluent was collected and the radiolabeled metabolites of [3H]bradykinin were separated by high performance liquid chromatography, identified, and quantified.

RESULTS

[3H]Bradykinin was metabolized to the extent of 62 +/- 3% in a single passage through the rabbit coronary circulation at a physiological flow rate. The metabolites were identified as [3H]bradykinin(1-5) and [3H]bradykinin(1-7),accounting for 50 +/- 4 and 12 +/- 2% of the radioactivity, respectively. Co-perfusion with the angiotensin converting enzyme inhibitor, ramiprilat, completely blocked formation of these metabolites.

CONCLUSIONS

Angiotensin-converting enzyme fully accounts for the metabolism of [3H]bradykinin in the rabbit coronary circulation. This result contrasts with data obtained using rat heart, which demonstrated a prominent role for aminopeptidase P in bradykinin metabolism in this species.

Bradykinin and des-Arg(9)-bradykinin metabolic pathways and kinetics of activation of human plasma

In the serum of 116 healthy individuals, exogenous bradykinin (BK) half-life (27 +/- 10 s) was lower than that of des-Arg(9)-BK (643 +/- 436 s) and was statistically different in men compared with women. The potentiating effect of an angiotensin-converting enzyme (ACE) inhibitor was, however, more extensive for BK (9.0-fold) than for des-Arg(9)-BK (2.2- fold). The activities of ACE, aminopeptidase P (APP), and kininase I were respectively 44 +/- 12, 22 +/- 9, and 62 +/- 10 nmol x min(-1) x ml(-1). A mathematical model (y = kt(alpha)e(-beta t), t > 0), applied to the BK kinetically released from endogenous high-molecular-weight kininogen (HK) during plasma activation in the presence of an ACE inhibitor, revealed a significant difference in the rate of formation of BK between men and women. For des-Arg(9)-BK, the active metabolite of BK, the rate of degradation was higher in women compared with men, correlating significantly with serum APP activity (r(2) = 0.6485, P < 0.001). In conclusion, these results constitute a basis for future pathophysiological studies of inflammatory processes where activation of the contact system of plasma and the kinins is involved.

Effects of the vasopeptidase inhibitor omapatrilat on cardiac endogenous kinins in rats with acute myocardial infarction

The purposes of this study were to evaluate and to compare the effects of simultaneous angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) inhibition by the vasopeptidase inhibitor omapatrilat (1 mg. kg(-1). day(-1)) with those of the selective ACE inhibitor enalapril (1 mg. kg(-1). day(-1)) on survival, cardiac hemodynamics, and bradykinin (BK) and des-Arg(9)-BK levels in cardiac tissues 24 h after myocardial infarction (MI) in rats. The effect of the co-administration of both B(1) and B(2) kinin receptor antagonists (2.5 mg. kg(-1). day(-1) each) with metallopeptidase inhibitors was also evaluated. The pharmacological treatments were infused subcutaneously using micro-osmotic pumps for 5 days starting 4 days before the ligation of the left coronary artery. Immunoreactive kinins were quantified by highly sensitive and specific competitive enzyme immunoassays. The post-MI mortality of untreated rats with a large MI was high; 74% of rats dying prior to the hemodynamic study. Mortality in the other MI groups was not significantly different from that of the untreated MI rats. Cardiac BK levels were not significantly different in the MI vehicle-treated group compared with the sham-operated rats. Both omapatrilat and enalapril treatments of MI rats significantly increased cardiac BK concentrations compared with the sham-operated group (P < 0.05). However, cardiac BK levels were significantly increased only in the MI omapatrilat-treated rats compared with the MI vehicle-treated group (P < 0.01). Cardiac des-Arg(9)-BK concentrations were not significantly modified by MI, and MI with omapatrilat or enalapril treatment compared with the sham-operated group. The co-administration of both kinin receptor antagonists with MI omapatrilat- and enalapril-treated rats had no significant effect on cardiac BK and des-Arg(9)-BK levels. Thus, the significant increase of cardiac BK concentrations by omapatrilat could be related to a biochemical or a cardiac hemodynamic parameter on early (24 h) post-MI state.

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 and nitric oxide generation by dialysis membranes can be blunted by alkaline rinsing solutions

BACKGROUND

Bradykinin (BK) generation following the first contact of blood with the dialysis materials is thought to enhance hypersensitivity reactions (HSRs). Some of the effects of BK are mediated by nitric oxide (NO). We have recently reported that the pH of diluted blood modulates the kinin system. The present study was aimed to investigate the role of the pH of culture media and filter-washing solutions and BK and NO generation, either in vitro and ex vivo.

METHODS

BK was measured by a specific enzyme-linked immunosorbent assay (ELISA), and NO synthase (NOS) activity by 3H-citrulline production after incubation with 3H-arginine and nitrites by using the Griess reagent. In in vitro experiments, NOS activity was detected in endothelial cells (ECs) cultured with graded BK concentrations at various pH values. Blood from 30 patients in regular dialysis was ex vivo circulated in one single passage through minifilters prerinsed with pH 7 or pH 8 phosphate buffer (PB) solutions. The out-flowing blood was tested for BK and nitrite content and was incubated with cultured ECs to evaluate its capacity to modulate NOS activity.

RESULTS

BK induced in vitro a dose-dependent increase in NOS activity of ECs, which was mediated by tyrosine kinase phosphorylation. NO generation was enhanced at pH 7.2, which remained unchanged at pH 7.6. In ex vivo experiments, blood out-flowing after one passage on filters washed with pH 7 PB solutions had increased BK levels (P < 0.0001), increased nitrites (P < 0.05), and enhanced EC NOS activity (P < 0. 05) in comparison to data found when filters were washed with pH 8 PB. Only when the filters were rinsed with a solution at pH 7 did PAN DX and AN69 membranes show a distinct BK generation capability, and cuprophane a peculiar capability to enhance NOS. Such effects were prevented when dialyzers were prerinsed with pH 8 PB. Multiple regression analysis showed that the pH of the uremic blood was the driving factor for BK and NOS activation (r = 0.54, P < 0.02).

CONCLUSIONS

BK and NO generation are modulated by environmental pH. Rinsing the blood and dialysate compartments of filters with an alkaline solution prior to use may mitigate the activation of mediators likely to be involved in some HSRs.

Anomaly of the des-Arg9-bradykinin metabolism associated with severe hypotensive reactions during blood transfusions: a preliminary study

BACKGROUND

Severe hypotensive reactions have been described after the transfusion of platelets or red cells through negatively-charged bedside white cell-reduction filters. The possibility of a role for bradykinin (BK) in the genesis of these reactions has been raised.

STUDY DESIGN AND METHODS

To understand if an anomaly of BK metabolism is associated with these reactions, the metabolism of BK and des-Arg9-BK was studied in the sera of four patients who presented with a severe hypotensive transfusion reaction. Tests were performed in the absence and the presence of complete in vitro inhibition of angiotensin-converting enzyme (ACE) activity by enalaprilat.

RESULTS

In the presence of ACE inhibition (enalaprilat), the half-life (t1/2) of BK measured in the sera of patients who presented with a severe hypotensive transfusion reaction (361 +/- 90 sec) was not significantly different from that measured in the sera of normal controls (249 +/- 16 sec). In the presence of ACE inhibition (enalaprilat), the t1/2 of des-Arg9-BK was significantly greater in patients who presented with a severe hypotensive transfusion reaction (1549 +/- 319 sec) than in normal controls (661 +/- 38 sec) (p < 0.001).

CONCLUSION

A metabolic anomaly mainly affecting the degradation of des-Arg9-BK could be responsible for its accumulation in vivo. Des-Arg9-BK could be responsible, at least in part, for severe hypotensive transfusion reactions.

Serum metabolism of bradykinin and des-Arg9-bradykinin in patients with angiotensin-converting enzyme inhibitor-associated angioedema

Angioedema (AE) associated with angiotensin-converting enzyme inhibitors (ACEi) is a rare, but potentially life-threatening adverse reaction. Several studies have suggested that bradykinin (BK) is responsible for ACEi-induced AE, but the mechanism remains unclear. We investigated the metabolism of BK and des-Arg9-BK in the serum of 20 patients with a history of ACEi-associated AE and 21 control (C) subjects. Synthetic BK was incubated with the sera for various periods of time and residual BK and generated des-Arg9-BK were quantified by specific and sensitive enzyme immunoassays. No significant difference of half-life (t1/2) of both BK and des-Arg9-BK could be measured between C subjects and patients with AE (AE) in absence of ACEi. However, an analysis according to the prolonged (+) or not (-) t1/2 of des-Arg9-BK allowed a new stratification of C subjects and AE patients in four subgroups. The preincubation of sera with enalaprilat at a concentration inhibiting ACE significantly prevented the rapid degradation of BK and des-Arg9-BK in these four subgroups. In presence of ACEi, a subgroup (50%) of AE patients (AE + ) had a particularly significant rise of the t1/2 of des-Arg9-BK. Once ACE was inhibited, the concentration or the nature of the ACEi had no significant effect on the t1/2 of des-Arg9-BK. However, a test dilution of AE + sera with a control (C) serum showed that an enzyme defect rather than a circulating inhibitor could be responsible for the abnormal metabolism of des-Arg9-BK when ACE is inhibited. In conclusion, half of the patients with ACEi-associated AE present in serum had an enzyme defect involved in the des-Arg9-BK metabolism leading to its accumulation. The B1 agonist could be responsible, at least in part, for the local inflammatory reaction associated with the AE.