Familial carboxypeptidase N deficiency

Hereditary angioedema with normal C1 inhibitor associated with carboxypeptidase N deficiency

Background

Hereditary angioedema (HAE) is a potentially life-threatening disorder characterized by recurrent episodes of subcutaneous or submucosal swelling. HAE with normal C1 inhibitor (HAE-nC1-INH) is an underdiagnosed condition. Although the association with genetic variants has been identified for some families, the genetic causes in many patients with HAE-nC1-INH remain unknown. The role of genes associated with bradykinin catabolism is not fully understood.

Objective

We sought to investigate the biological parameters and the genes related to kallikrein-kinin system in families with a clinical phenotype of HAE-nC1-INH and presenting with a carboxypeptidase N (CPN) deficiency.

Methods

This study includes 4 families presenting with HAE-nC1-INH and CPN deficiency. Patients' clinical records were examined, biological parameters of kallikrein-kinin system were measured, and genetics was analyzed by next-generation sequencing and Sanger sequencing. Predictive algorithms (Human Splicing Finder, Sorting Intolerant From Tolerant, Polymorphism Phenotyping v2, MutationTaster, and ClinPred) were used to classify variants as affecting splicing, as benign to deleterious, or as disease-causing.

Results

Patients presented with angioedema and urticaria, mainly on face/lips, but also with abdominal pain or laryngeal symptoms. Affected patients displayed low CPN activity-30% to 50% of median value in plasma. We identified 3 variants of the CPN1 gene encoding the catalytic 55-kDa subunit of CPN: c.533G>A, c.582A>G, and c.734C>T. CPN deficiency associated with genetic variants segregated with HAE-nC1-INH symptoms in affected family members.

Conclusions

CPN1 gene variants are associated with CPN deficiency and HAE-nC1-INH symptoms in 4 unrelated families. Genetic CPN deficiency may contribute to bradykinin and anaphylatoxin accumulation, with synergistic effects in angioedema and urticarial symptoms.

Searching for Genetic Biomarkers for Hereditary Angioedema Due to C1-Inhibitor Deficiency (C1-INH-HAE)

Existing evidence indicates that modifier genes could change the phenotypic outcome of the causal SERPING1 variant and thus explain the expression variability of hereditary angioedema due to C1-inhibitor deficiency (C1-INH-HAE). To further examine this hypothesis, we investigated the presence or absence of 18 functional variants of genes encoding proteins involved in the metabolism and function of bradykinin, the main mediator of C1-INH-HAE attacks, in relation to three distinct phenotypic traits of patients with C1-INH-HAE, i.e., the age at disease onset, the need for long-term prophylaxis (LTP), and the severity of the disease. Genetic analyses were performed by a validated next-generation sequencing platform. In total, 233 patients with C1-INH-HAE from 144 unrelated families from five European countries were enrolled in the study. Already described correlations between five common functional variants [F12-rs1801020, KLKB1-rs3733402, CPN1-rs61751507, and two in SERPING1 (rs4926 and rs28362944)] and C1-INH-HAE severity were confirmed. Furthermore, significant correlations were found between either the age at disease onset, the LTP, or the severity score of the disease and a series of other functional variants (F13B-rs6003, PLAU-rs2227564, SERPINA1-rs28929474, SERPINA1-rs17580, KLK1-rs5515, SERPINE1-rs6092, and F2-rs1799963). Interestingly, correlations uncovered in the entire cohort of patients were different from those discovered in the cohort of patients carrying missense causal SERPING1 variants. Our findings indicate that variants other than the SERPING1 causal variants act as independent modifiers of C1-INH-HAE severity and could be tested as possible prognostic biomarkers.

Identification and characterization of a carboxypeptidase N1 from red lip mullet (Liza haematocheila); revealing its immune relevance

Complement system orchestrates the innate and adaptive immunity via the activation, recruitment, and regulation of immune molecules to destroy pathogens. However, regulation of the complement is essential to avoid injuries to the autologous tissues. The present study unveils the characteristic features of an important complement component, anaphylatoxin inactivator from red lip mullet at its molecular and functional level. Mullet carboxypeptidase N1 (MuCPN1) cDNA sequence possessed an open reading frame of 1347 bp, which encoded a protein of 449 amino acids with a predicted molecular weight of 51 kDa. In silico analysis discovered two domains of PM14-Zn carboxypeptidase and a C-terminal domain of M14 N/E carboxypeptidase, two zinc-binding signature motifs, and an N-glycosylation site in the MuCPN1 sequence. Homology analysis revealed that most of the residues in the sequence are conserved among the other selected homologs. Phylogeny analysis showed that MuCPN1 closely cladded with the Maylandia zebra CPN1 and clustered together with the teleostean counterparts. A challenge experiment showed modulated expression of MuCPN1 upon polyinosinic:polycytidylic acid and Lactococcus garviae in head kidney, spleen, gill, and liver tissues. The highest upregulation of MuCPN1 was observed 24 h post infection against poly I:C in each tissue. Moreover, the highest relative expressions upon L. garviae challenge were observed at 24 h post infection in head kidney tissue and 48 h post infection in spleen, gill, and liver tissues. MuCPN1 transfected cells triggered a 2.2-fold increase of nitric oxide (NO) production upon LPS stimulation compared to the un-transfected controls suggesting that MuCPN1 is an active protease which releases arginine from complement C3a, C4a, and C5a. These results have driven certain way towards enhancing the understanding of immune role of MuCPN1 in the complement defense mechanism of red lip mullet.

Carboxypeptidase B2 and carboxypeptidase N in the crosstalk between coagulation, thrombosis, inflammation, and innate immunity

Two basic carboxypeptidases, carboxypeptidase B2 (CPB2) and carboxypeptidase N (CPN) are present in plasma. CPN is constitutively active, whereas CPB2 circulates as a precursor, procarboxypeptidase B2 (proCPB2), that needs to be activated by the thrombin-thrombomodulin complex or plasmin bound to glycosaminoglycans. The substrate specificities of CPB2 and CPN are similar; they both remove C-terminal basic amino acids from bioactive peptides and proteins, thereby inactivating them. The complement cascade is a cascade of proteases and cofactors activated by pathogens or dead cells, divided into two phases, with the second phase only being triggered if sufficient C3b is present. Complement activation generates anaphylatoxins: C3a, which stimulates macrophages; and C5a, which is an activator and attractant for neutrophils. Pharmacological intervention with inhibitors has shown that CPB2 delays fibrinolysis, whereas CPN is responsible for systemic inactivation of C3a and C5a. Among mice genetically deficient in either CPB2 or CPN, in a model of hemolytic-uremic syndrome, Cpb2-/- mice had the worst disease, followed by Cpn-/- mice, with wild-type (WT) mice being the most protected. This model is driven by C5a, and shows that CPB2 is important in inactivating C5a. In contrast, when mice were challenged acutely with cobra venom factor, the reverse phenotype was observed; Cpn-/- mice had markedly worse disease than Cpb2-/- mice, and WT mice were resistant. These observations need to be confirmed in humans. Therefore, CPB2 and CPN have different roles. CPN inactivates C3a and C5a generated spontaneously, whereas proCPB2 is activated at specific sites, where it inactivates bioactive peptides that would overwhelm CPN.

[Basic carboxypeptidases of blood: significance for coagulology]

This review considers the basic metallocarboxypeptidases of human blood and their role in coagulologic disorders. In includes information on the history of the discovery and biological characteristics of potential enzymes-regulators of the fibrinolytic process: carboxypeptidase U and carboxypeptidase N. Certain attention is paid to the biochemical mechanisms and the main modern concepts of the antifibrinolytic effects of these enzymes.

Carboxypeptidase N-deficient mice present with polymorphic disease phenotypes on induction of experimental autoimmune encephalomyelitis

Carboxypeptidase N (CPN) is a member of the carboxypeptidase family of enzymes that cleave carboxy-terminal lysine and arginine residues from a large number of biologically active peptides and proteins. These enzymes are best known for their roles in modulating the activity of kinins, complement anaphylatoxins and coagulation proteins. Although CPN makes important contributions to acute inflammatory events, little is known about its role in autoimmune disease. In this study we used CPN(-/-) mice in experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. Unexpectedly, we observed several EAE disease phenotypes in CPN(-/-) mice compared to wild type mice. The majority of CPN(-/-) mice died within five to seven days after disease induction, before displaying clinical signs of disease. The remaining mice presented with either mild EAE or did not develop EAE. In addition, CPN(-/-) mice injected with complete or incomplete Freund's adjuvant died within the same time frame and in similar numbers as those induced for EAE. Overall, the course of EAE in CPN(-/-) mice was significantly delayed and attenuated compared to wild type mice. Spinal cord histopathology in CPN(-/-) mice revealed meningeal, but not parenchymal leukocyte infiltration, and minimal demyelination. Our results indicate that CPN plays an important role in EAE development and progression and suggests that multiple CPN ligands contribute to the disease phenotypes we observed.

Angioedema

Angioedema can be caused by either mast cell degranulation or activation of the kallikrein-kinin cascade. In the former case, angioedema can be caused by allergic reactions caused by immunoglobulin E (IgE)-mediated hypersensitivity to foods or drugs that can also result in acute urticaria or a more generalized anaphylactic reaction. Nonsteroidal anti-inflammatory drugs (cyclooxygenase 1 inhibitors, in particular) may cause angioedema with or without urticaria, and leukotrienes may have a particular role as a mediator of the swelling. Reactions to contrast agents resemble allergy with basophil and mast cell degranulation in the absence of specific IgE antibody and can be generalized, that is, anaphylactoid. Angioedema accompanies chronic urticaria in 40% of patients, and approximately half have an autoimmune mechanism in which there is IgG antibody directed to the subunit of the IgE receptor (40%) or to IgE itself (5%-10%). Bradykinin is the mediator of angioedema in hereditary angioedema types I and II (C1 inhibitor [INH] deficiency) and the newly described type III disorder some of which are caused bya mutation involving factor XII. Acquired C1 INH deficiency presents in a similar fashion to the hereditary disorder and is due either toC1 INH depletion by circulating immune complexes or to an IgG antibody directed to C1 INH. Although each of these causes excessive bradykinin formation because of activation of the plasma bradykinin-forming pathway, the angioedema due to angiotensin-converting enzyme inhibitors is caused by excessive bradykinin levels due to inhibition of bradykinin degradation. Idiopathic angioedema (ie, pathogenesis unknown) may be histaminergic, that is, caused by mast cell degranulation with histamine release, or nonhistaminergic. The mediator pathways in the latter case are yet to be defined. A minority may be associated with the same autoantibodies associated with chronic urticaria. Angioedema that is likely to be life threatening (laryngeal edema or tongue/pharyngeal edema that obstructs the airway) is seen in anaphylactic/anaphylactoid reactions and the disorders mediated by bradykinin.

Cobra venom factor: Structure, function, and humanization for therapeutic complement depletion

Cobra venom factor (CVF) is the complement-activating protein in cobra venom. This manuscript reviews the structure and function of CVF, how it interacts with the complement system, the structural and functional homology to complement component C3, and the use of CVF as an experimental tool to decomplement laboratory animals to study the functions of complement in host defense and immune response as well as in the pathogenesis of diseases. This manuscript also reviews the recent progress in using the homology between CVF and C3 to study C3 structure and function, and to develop human C3 derivatives with the complement-depleting function of CVF. These human C3 derivatives represent humanized CVF, and are a conceptually different concept for pharmacological intervention of the complement system, therapeutic complement depletion. The use of humanized CVF for therapeutic complement depletion in several pre-clinical models of human diseases is also reviewed.

Plasmin alters the activity and quaternary structure of human plasma carboxypeptidase N

Human CPN (carboxypeptidase N) is a tetrameric plasma enzyme containing two glycosylated 83 kDa non-catalytic/regulatory subunits that carry and protect two active catalytic subunits. Because CPN can regulate the level of plasminogen binding to cell surface proteins, we investigated how plasmin cleaves CPN and the consequences. The products of hydrolysis were analysed by activity assays, Western blotting, gel filtration and sequencing. When incubated with intact CPN tetramer, plasmin rapidly cleaved the 83 kDa subunit at the Arg457-Ser458 bond near the C-terminus to produce fragments of 72 and 13 kDa, thereby releasing an active 142 kDa heterodimer, and also cleaved the active subunit, decreasing its size from 55 kDa to 48 kDa. Further evidence for the heterodimeric form of CPN was obtained by re-complexing the non-catalytic 72 kDa fragment with recombinant catalytic subunit or by immunoprecipitation of the catalytic subunit after plasmin treatment of CPN using an antibody specific for the 83 kDa subunit. Upon longer incubation, plasmin cleaved the catalytic subunit at Arg218-Arg219 to generate fragments of 27 kDa and 21 kDa, held together by non-covalent bonds, that were more active than the native enzyme. These data show that plasmin can alter CPN structure and activity, and that the C-terminal 13 kDa fragment of the CPN 83 kDa subunit is a docking peptide that is necessary to maintain the stable active tetrameric form of human CPN in plasma.

Targeted disruption of the gene encoding the murine small subunit of carboxypeptidase N (CPN1) causes susceptibility to C5a anaphylatoxin-mediated shock

Carboxypeptidase N (CPN) is a plasma zinc metalloprotease, which consists of two enzymatically active small subunits (CPN1) and two large subunits (CPN2) that protect the protein from degradation. Historically, CPN has been implicated as a major regulator of inflammation by its enzymatic cleavage of functionally important arginine and lysine amino acids from potent phlogistic molecules, such as the complement anaphylatoxins C3a and C5a. Because of no known complete CPN deficiencies, the biological impact of CPN in vivo has been difficult to evaluate. Here, we report the generation of a mouse with complete CPN deficiency by targeted disruption of the CPN1 gene. CPN1(-/-) mice were hypersensitive to lethal anaphylactic shock due to acute complement activation by cobra venom factor. This hypersensitivity was completely resolved in CPN1(-/-)/C5aR(-/-) but not in CPN1(-/-)/C3aR(-/-) mice. Moreover, CPN1(-/-) mice given C5a i.v., but not C3a, experienced 100% mortality. This C5a-induced mortality was reduced to 20% when CPN1(-/-) mice were treated with an antihistamine before C5a challenge. These studies describe for the first time a complete deficiency of CPN and demonstrate 1) that CPN plays a requisite role in regulating the lethal effects of anaphylatoxin-mediated shock, 2) that these lethal effects are mediated predominantly by C5a-induced histamine release, and 3) that C3a does not contribute significantly to shock following acute complement activation.

Proteolytic cleavage of carboxypeptidase N markedly increases its antifibrinolytic activity

BACKGROUND

Carboxypeptidase N (CPN) is a constitutively active basic carboxypeptidase sharing specificity with activated thrombin-activable fibrinolysis inhibitor (TAFIa). Generally, CPN is regarded as being non-antifibrinolytic. However, this assumption has not been thoroughly investigated, particularly with respect to long-term antifibrinolysis. In addition, a recent report has shown that plasmin cleavage increases the catalytic activity of CPN. Therefore, we investigated the antifibrinolytic properties of CPN and plasmin-cleaved CPN (CPNc).

METHODS

CPN was incubated with plasmin for various periods of time and the prolongation of clot lysis at various concentrations of CPN/CPNc mixture was investigated in TAFI-depleted plasma. CPN cleavage was analyzed by electrophoresis and catalytic activity was determined by monitoring cleavage of the small substrate, FA-Ala-Lys.

RESULTS

CPN exhibited antifibrinolytic properties in plasma clot lysis assays when present at supraphysiological concentrations. Depletion of CPN from plasma decreased the lysis time of clots formed from minimally diluted plasma at low tissue-type plasminogen activator (t-PA) concentrations. Plasmin cleavage of CPN markedly increased the antifibrinolytic properties. CPN and CPNc prolonged lysis in a non-saturable, dose-dependent, and t-PA-dependent manner. At sufficient concentration, CPN and CPNc prolonged lysis at least forty-fivefold. CPNc was 700% more antifibrinolytic than CPN but only 7% more active toward FA-Ala-Lys. The active site inhibitor GEMSA eliminated the antifibrinolytic effects of CPN and CPNc. Antifibrinolytic activity correlated with cleavage of active and/or regulatory subunits, presumably generating heterodimeric CPNc.

CONCLUSIONS

Limited proteolysis of CPN by plasmin generates an enzyme with greatly increased antifibrinolytic properties. We speculate that (patho)physiological proteolysis of CPN may generate a long-term antifibrinolytic enzyme.

Structure and function of human plasma carboxypeptidase N, the anaphylatoxin inactivator

Human carboxypeptidase N (CPN) was discovered in the early 1960s as a plasma enzyme that inactivates bradykinin and was identified 8 years later as the major "anaphylatoxin inactivator" of blood. CPN plays an important role in protecting the body from excessive buildup of potentially deleterious peptides that normally act as local autocrine or paracrine hormones. This review summarizes the structure, enzymatic properties and function of this important human enzyme, including insights gained by the recent elucidation of the crystal structure of the CPN catalytic subunit and structural modeling of the non-catalytic regulatory 83 kDa subunit. We also discuss its physiological role in cleaving substrates such as kinins, anaphylatoxins, creatine kinase, plasminogen receptors, hemoglobin and stromal cell-derived factor-1alpha (SDF-1alpha).

Angio-œdèmes iatrogènes: rôle des inhibiteurs de l'enzyme de conversion et des antagonistes des récepteurs à l'angiotensine II (sartans)

Nephrologists should be aware the fact that the angioedema is a common side effect not only under angiotensin-converting enzyme (ACE) inhibitors treatment but also under sartans therapy. The frequency of angioedema under ACE inhibitors is estimated at 1 to 7 per thousand. The physiopathology of ACE angioedema implicates the lack of degradation of kinines due to the inhibition of multiple enzymes activity including ACE. Angioedema under sartans seems less frequent than this observed under ACE inhibitors. Its mechanism remains poorly defined, but implicates the increase of kinine production via the stimulation of angiotensin receptor type II, and/or the lack of degradation of kinines via multiple enzymes other than ACE. The frequency of the apparition of angioedema under sartans in patients who had have angioedema under ACE inhibitors is inconsistent and varied from 7.7% to 50%. Reports indicated that angioedema under ACE or sartans could have a spontaneous regression. However, the relapse of angioedema under these drugs should lead to the diagnosis of iatrogenic etiology, and to the drugs withdrawal. ACE inhibitors/Sartans-associated angioedema episodes need to be reported to the French Adverse Event Reporting System database to evaluate their frequency and to avoid severe consequences.

A rapid and sensitive assay for the quantitation of carboxypeptidase N, an important regulator of inflammation

BACKGROUND

Carboxypeptidase N is a plasma zinc metallocarboxypeptidase which is constitutively expressed in the liver and was identified as the enzyme responsible for inactivating bradykinin and kallidin by removing the C-terminal arginine. Because CPN can cleave the C-terminal arginine of C3a, C4a and C5a it is often referred to as anaphylatoxin inactivator. Markedly reduced levels of circulating CPN are associated with recurrent angioedema and abnormal cutaneous polymorphonuclear cell infiltration.

METHODS

In this paper we describe a fast kinetic coupled enzymatic assay for the sensitive measurement of carboxypeptidase N activities in serum samples. The assay makes use of the excellent CPN substrate Benzoyl-L-Alanyl-L-Arginine.

RESULTS

This novel assay is very fast, easy to perform and combines good reliability and reproducibility with excellent correlation with the HPLC-assisted assay (r=0.927; n=140).

CONCLUSION

The presented assay can be used for high throughput screening of this important regulator of inflammation in clinical plasma or serum samples.

Genetic test indications and interpretations in patients with hereditary angioedema

Patients with hereditary angioedema (HAE) present with recurrent, circumscribed, and self-limiting episodes of tissue or mucous membrane swelling caused by C1-inhibitor (CI-INH) deficiency. The estimated frequency of HAE is 1:50,000 persons. Distinguishing HAE from acquired angioedema (AAE) facilitates therapeutic interventions and family planning or testing. Patients with HAE benefit from treatment with attenuated androgen, antifibrinolytic agents, and C1-INH concentrate replacement during acute attacks. HAE is currently recognized as a genetic disorder with autosomal dominant transmission. Other forms of inherited angioedema that are not associated with genetic mutations have also been identified. Readily available tests are complement studies, including C4 and C1-esterase inhibitor, both antigenic and functional C1-INH. These are the most commonly used tests in the diagnosis of HAE. Analysis of C1q can help differentiate between HAE and AAE caused by C1-INH deficiency. Genetic tests would be particularly helpful in patients with no family history of angioedema, which occurs in about half of affected patients, and in patients whose C1q level is borderline and does not differentiate between HAE and AAE. Measuring autoantibodies against C1-INH also would be helpful, but the test is available in research laboratories only. Simple complement determinations are appropriate for screening and diagnosis of the disorder.

Angioedema

Although first described more than 130 years ago, the pathophysiology, origin, and management of the several types of angioedema are poorly understood by most dermatologists. Although clinically similar, angioedema can be caused by either mast cell degranulation or activation of kinin formation. In the former category, allergic and nonsteroidal anti-inflammatory drug-induced angioedema are frequently accompanied by urticaria. Idiopathic chronic angioedema is also usually accompanied by urticaria, but can occur without hives. In either case, an autoimmune process leading to dermal mast cell degranulation occurs in some patients. In these patients, histamine-releasing IgG anti-FcepsilonR1 autoantibodies are believed to be the cause of the disease, removal or suppression by immunomodulation being followed by remission. Angiotensin-converting enzyme inhibitor-induced angioedema is unaccompanied by hives, and is caused by the inhibition of enzymatic degradation of tissue bradykinin. Hereditary angioedema, caused by unchecked tissue bradykinin formation, is recognized biochemically by a low plasma C'4 and low quantitative or functional C'1 inhibitor. Progress has now been made in understanding the molecular genetic basis of the two isoforms of this dominantly inherited disease. Recently, a third type of hereditary angioedema has been defined by several groups. Occurring exclusively in women, it is not associated with detectable abnormalities of the complement system. Angioedema caused by a C'1 esterase inhibitor deficiency can also be acquired in several clinical settings, including lymphoma and autoimmune connective tissue disease. It can also occur as a consequence of specific anti-C'1 esterase autoantibodies in some patients. We have reviewed the clinical features, diagnosis, and management of these different subtypes of angioedema.

LEARNING OBJECTIVE

After completing this learning activity, participants should be aware of the classification, causes, and differential diagnosis of angioedema, the molecular basis of hereditary and non-hereditary forms of angioedema, and be able to formulate a pathophysiology-based treatment strategy for each of the subtypes of angioedema.

Identification of carboxypeptidase N as an enzyme responsible for C-terminal cleavage of stromal cell-derived factor-1alpha in the circulation

The chemokine stromal-derived factor-1alpha (SDF-1alpha) is an essential regulator of hematopoiesis, lymphocyte homing, pre-B-cell growth, and angiogenesis. As SDF-1alpha is constitutively expressed in many tissues, chemokine function is mostly regulated by proteolytic degradation. Human serum cleaves the 68-amino acid chemokine, SDF-1alpha, at both termini. The enzyme or enzymes responsible for the removal of the carboxy-terminal lysine from SDF-1alpha, leading to significant reduction in biologic activity, have not been identified. Using a new biochemical assay for measuring the carboxy-terminal cleavage activity, we purified from serum and plasma a peptidase that specifically removes the carboxy-terminal lysine from SDF-1alpha and identified it as carboxypeptidase N (CPN, also known as kininase I, arginine carboxypeptidase, and anaphylotoxin inactivator). We demonstrate that SDF-1alpha in serum and plasma lacks the carboxy terminal lysine, and depletion of CPN from serum and plasma significantly reduces the SDF-1alpha carboxypeptidase activity. Purified CPN effectively and specifically removes the carboxy-terminal lysine from SDF-1alpha and significantly reduces the chemokine's biologic activity as a pre-B-cell growth factor and chemoattractant. Thus, in addition to its role as a regulator of the biologic activity of kinins and anaphylatoxins, CPN is an important regulator of the biologic activity of SDF-1alpha by reducing the chemokine-specific activity.

Imidazole acetic acid TAFIa inhibitors: SAR studies centered around the basic P(1)(') group

Structural modifications of the aminopyridine P(1)(') group of imidazole acetic acid based TAFIa inhibitors led to the discovery of the aminocyclopentyl analog 28, a 1 nM TAFIa inhibitor with CLT(50) functional activity of 14 nM but without selectivity against CPB. While not as active, aminobutyl derivative 27 provided an improved 6.7-fold selectivity for TAFIa versus CPB.

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.

Carboxypeptidase N: a pleiotropic regulator of inflammation

Carboxypeptidase N (CPN) is a plasma zinc metalloprotease, which consists of two enzymatically active small subunits (CPN1) and two large subunits (CPN2) that protect the protein from degradation. CPN cleaves carboxy-terminal arginines and lysines from peptides found in the bloodstream such as complement anaphylatoxins, kinins, and creatine kinase MM (CK-MM). By removing only one amino acid, CPN has the ability to change peptide activity and receptor binding. CPN is a member of a larger family of carboxypeptidases, many of which also cleave arginine and lysine. Because of the highly conserved active sites and the possible redundant functions of carboxypeptidases, it has been difficult to elucidate the role of CPN in disease processes. The future use of gene ablation technology may be the most appropriate way to understand the function of CPN in vivo.

Synthesis and evaluation of imidazole acetic acid inhibitors of activated thrombin-activatable fibrinolysis inhibitor as novel antithrombotics

Thrombin-activatable fibrinolysis inhibitor (TAFI) is an important regulator of fibrinolysis, and inhibitors of this enzyme have potential use in antithrombotic and thrombolytic therapy. Appropriately substituted imidazole acetic acids such as 10j were found to be potent inhibitors of activated TAFI and selective versus the related carboxypeptidases CPA, CPN, and CPM but not CPB. Further, 10j accelerated clot lysis in vitro and was shown to be efficacious in a primate model of thrombosis.

Can angiotensin receptor antagonists be used safely in patients with previous ACE inhibitor-induced angioedema?

Angioedema is an uncommon but potentially life-threatening adverse event associated with ACE inhibitor therapy which is believed to be due to potentiation of the vascular effects of bradykinin. Angiotensin receptor antagonists were not expected to produce angioedema, as they do not inhibit the catabolism of bradykinin. However, it is now apparent that angioedema is occasionally associated with angiotensin receptor antagonist therapy and may be more likely to occur in patients who have previously experienced angioedema while receiving ACE inhibitors. Angiotensin receptor antagonists cannot be considered to be a safe alternative therapy in patients who have previously experienced ACE inhibitor-associated angioedema.

[Non-allergic angioedema: update]

PURPOSE

Nonallergic isolated angioedema is an uncommon clinical syndrome raising difficult diagnosis and therapeutic problems. Occurrences linked to a C1Inh are the predominant ones and have to be examined as a priority, taking into account the specificity of the associated follow-up.

CURRENT KNOWLEDGE AND KEY POINTS

Diseases with a clinical profile close to hereditary angioneurotic edema, but without C1Inh anomaly, have been described recently. It is in fact family cases, concerning only women, where estrogens seem to play a dominant role. Angioedema's secondary aspects are gathering various pathologies (vasculitis, Gleich's syndrome, angioedema initiated by physical agents). The role played by some drugs must not be forgotten, mainly angiotensin converting enzyme inhibitors, which are at the origin of angiodema in nearly 0.5% of users.

FUTURE PROSPECT AND PROJECTS

Uncontrolled activation of the contact system seems to play a major role in the main part of these angiodemas. The efficiency of the tranexaminic acid (which modulates its activation) is to be taken as evident. The key to the future seems to be the development of plasmin and bradykinin inhibitors.

Ophidian envenomation strategies and the role of purines

Snake envenomation employs three well integrated strategies: prey immobilization via hypotension, prey immobilization via paralysis, and prey digestion. Purines (adenosine, guanosine and inosine) evidently play a central role in the envenomation strategies of most advanced snakes. Purines constitute the perfect multifunctional toxins, participating simultaneously in all three envenomation strategies. Because they are endogenous regulatory compounds in all vertebrates, it is impossible for any prey organism to develop resistance to them. Purine generation from endogenous precursors in the prey explains the presence of many hitherto unexplained enzyme activities in snake venoms: 5'-nucleotidase, endonucleases (including ribonuclease), phosphodiesterase, ATPase, ADPase, phosphomonoesterase, and NADase. Phospholipases A(2), cytotoxins, myotoxins, and heparinase also participate in purine liberation, in addition to their better known functions. Adenosine contributes to prey immobilization by activation of neuronal adenosine A(1) receptors, suppressing acetylcholine release from motor neurons and excitatory neurotransmitters from central sites. It also exacerbates venom-induced hypotension by activating A(2) receptors in the vasculature. Adenosine and inosine both activate mast cell A(3) receptors, liberating vasoactive substances and increasing vascular permeability. Guanosine probably contributes to hypotension, by augmenting vascular endothelial cGMP levels via an unknown mechanism. Novel functions are suggested for toxins that act upon blood coagulation factors, including nitric oxide production, using the prey's carboxypeptidases. Leucine aminopeptidase may link venom hemorrhagic metalloproteases and endogenous chymotrypsin-like proteases with venom L-amino acid oxidase (LAO), accelerating the latter. The primary function of LAO is probably to promote prey hypotension by activating soluble guanylate cyclase in the presence of superoxide dismutase. LAO's apoptotic activity, too slow to be relevant to prey capture, is undoubtedly secondary and probably serves principally a digestive function. It is concluded that the principal function of L-type Ca(2+) channel antagonists and muscarinic toxins, in Dendroaspis venoms, and acetylcholinesterase in other elapid venoms, is to promote hypotension. Venom dipeptidyl peptidase IV-like enzymes probably also contribute to hypotension by destroying vasoconstrictive peptides such as Peptide YY, neuropeptide Y and substance P. Purines apparently bind to other toxins which then serve as molecular chaperones to deposit the bound purines at specific subsets of purine receptors. The assignment of pharmacological activities such as transient neurotransmitter suppression, histamine release and antinociception, to a variety of proteinaceous toxins, is probably erroneous. Such effects are probably due instead to purines bound to these toxins, and/or to free venom purines.

Thrombin-activatable fibrinolysis inhibitor (TAFI, plasma procarboxypeptidase B, procarboxypeptidase R, procarboxypeptidase U)

Recently, a new inhibitor of fibrinolysis was described. This inhibitor downregulated fibrinolysis after it was activated by thrombin, and was therefore named TAFI (thrombin-activatable fibrinolysis inhibitor; EC 3.4.17.20). TAFI turned out to be identical to previously described proteins, procarboxypeptidase U, procarboxypeptidase R, and plasma procarboxypeptidase B. In this overview, the protein will be referred to as TAFI. TAFI is a procarboxypeptidase and a member of the family of metallocarboxypeptidases. These enzymes are circulating in plasma and are present in several tissues such as pancreas. In this review, we will describe the properties of basic carboxypeptidases with the emphasis on the role of TAFI in coagulation and fibrinolysis. It cannot be ruled out, however, that TAFI has other, yet undefined, functions in biology.

Pro-carboxypeptidase R is an acute phase protein in the mouse, whereas carboxypeptidase N is not

Carboxypeptidase R (EC 3.4.17.20; CPR) and carboxypeptidase N (EC 3. 4.17.3; CPN) cleave carboxyl-terminal arginine and lysine residues from biologically active peptides such as kinins and anaphylatoxins, resulting in regulation of their biological activity. Human proCPR, also known as thrombin-activatable fibrinolysis inhibitor, plasma pro-carboxypeptidase B, and pro-carboxypeptidase U, is a plasma zymogen activated during coagulation. CPN, however, previously termed kininase I and anaphylatoxin inactivator, is present in a stable active form in plasma. We report here the isolation of mouse proCPR and CPN cDNA clones that can induce their respective enzymatic activities in culture supernatants of transiently transfected cells. Potato carboxypeptidase inhibitor can inhibit carboxypeptidase activity in culture medium of mouse proCPR-transfected cells. The expression of proCPR mRNA in murine liver is greatly enhanced following LPS injection, whereas CPN mRNA expression remains unaffected. Furthermore, the CPR activity in plasma increased 2-fold at 24 h after LPS treatment. Therefore, proCPR can be considered a type of acute phase protein, whereas CPN is not. An increase in CPR activity may facilitate rapid inactivation of inflammatory mediators generated at the site of Gram-negative bacterial infection and may consequently prevent septic shock. In view of the ability of proCPR to also inhibit fibrinolysis, an excess of proCPR induced by LPS may contribute to hypofibrinolysis in patients suffering from disseminated intravascular coagulation caused by sepsis.

Chromosomal localization of the genes for human carboxypeptidase D (CPD) and the active 50-kilodalton subunit of human carboxypeptidase N (CPN1)

Human carboxypeptidase N is a 280-kDa tetrameric enzyme consisting of two 83-kDa regulatory subunits and two catalytic 50-kDa subunits. The 83-kDa subunit is a member of the leucine-rich repeat family of proteins and has been localized to chromosome 8p22-p23. The 50-kDa subunit is a member of the regulatory B-type carboxypeptidase family, which includes carboxypeptidases M, E/H, AEBP1, and a newly described member, carboxypeptidase D, which has three tandem active site domains. The human genes for carboxypeptidase D (HGMW-approved symbol CPD) and the 50-kDa subunit of carboxypeptidase N (HGMW-approved symbol CPN1) were localized to chromosomes 17 and 10, respectively, using the polymerase chain reaction with gene-specific primers and DNAs derived from somatic cell hybrids. The carboxypeptidase D gene was further localized to the centromeric region 17p11.1-q11.1/11.2 by use of a regional mapping panel derived from somatic cell hybrids containing different portions of chromosome 17.

ACE inhibitor-induced angioedema. Incidence, prevention and management

Available information from 1980 to 1997 on angiotensin converting enzyme (ACE) inhibitor-induced angioedema and its underlying mechanisms are summarised and discussed. The incidence of angioedema is low (0.1 to 0.2%) but can be considered as a potentially life-threatening adverse effect of ACE inhibitor therapy. This adverse effect of ACE inhibitors, irrespective of the chemical structure, can occur early in treatment as well as after prolonged exposure for up to several years. The estimate incidence is quite underestimated. The actual incidence can be far higher because of poorly recognised presentation of angioedema as a consequence of its late onset in combination with usually long term therapy. Also, a spontaneous reporting bias can contribute to an actual higher incidence of this phenomenon. The incidence can be even higher (up to 3-fold) in certain risk groups, for instance Black Americans. Treatment includes immediate withdrawal of the ACE inhibitor and acute symptomatic supportive therapy followed by immediate (and long term) alternative therapy with other classes of drugs to manage hypertension and/or heart failure. Preclinical and clinical studies for the elucidation of the underlying mechanism(s) of ACE inhibitor-associated angioedema have not generated definite conclusions. It is suggested that immunological processes and several mediator systems (bradykinin, histamine, substance P and prostaglandins) are involved in the pathogenesis of angioedema. A great part of all reviewed reports suggest a relationship between ACE inhibitor-induced angioedema and increased levels of (tissue) bradykinin. However, no conclusive evidence of the role of bradykinin in angioedema has been found and an exclusive role of bradykinin seems unlikely. So far, no clear-cut evidence for an immune-mediated pathogenesis has been found. In addition, ACE gene polymorphism and some enzyme deficiencies are proposed to be involved in ACE inhibitor-induced angioedema. Progress in pharmacogenetic and molecular biological research should throw more light on a possible genetic component in the pathogenesis of ACE inhibitor-associated angioedema.

Metabolism of Bradykinin by Peptidases in Health and Disease

This chapter provides an overview of the metabolism of bradykinin (BK) by peptidases in health and disease. The enzymatic breakdown of kinins affects the duration of their biological actions as the plasma half-life of intravenously injected BK is in the range of seconds. Kinins are cleaved in vitro and in vivo by enzymes that belong to families, such as zinc-metallopeptidases, astacin-like metallopeptidases, and catheptic enzymes. Vane noted the importance of the pulmonary circulation in the metabolism of vasoactive substances, such as BK as well as angiotensin 1 and 5- hydroxytryptamine. It is clear after decades of research that angiotensin 1-converting enzyme (ACE) on the vascular endothelial cell surface is the most important inactivator of blood-borne BK. BK may act primarily in an autocrine and paracrine fashion, establishing the importance of local regulation of its activity by enzymes on cell surfaces. Thus, the assortment of other enzymes that can inactivate BK is important in a variety of physiological and pathological situations. Most physiological systems have redundant pathways of metabolism so that the abolishment of one pathway is compensated for by the presence of others. This is demonstrated by the pharmacological inhibition of ACE in hypertension.

A case report of angioedema during long-term (66 months) angiotensin converting enzyme inhibition therapy with enalapril

We describe a rare case of ACE inhibitor-induced angioedema during long-term therapy in a 51-year-old male patient with essential hypertension; and this is the third case reported of this adverse reaction in Japan. The patient received enalapril for 66 months, and complained of a dry cough which was mild and tolerable. Recently, he noted tenderness of his mouth, face, swelling of lips and tongue for 3 to 4 h after taking his morning dose of enalapril. These symptoms abated spontaneously, so he continued taking the drugs. He again noted similar episodes of angioedema 29 days after the first experience. He had no further episodes of angioedema or dry cough after cessation of enalapril. This case of angioedema developed during long-term therapy with enalapril administered as 19,930 mg of enalapril maleate. We emphasize that angioedema may occur at any time during the use of enalapril.

Bradykinin is a mediator of anaphylactoid reactions during hemodialysis with AN69 membranes

Anaphylactoid reactions (AR) are the most feared complications of hemodialysis. Recently, a high incidence of AR has been reported during dialysis with AN69 membranes in patients treated with ACE inhibitors. Plasma levels of C3a, histamine and bradykinin were measured in 12 patients at the onset of AR during dialysis with AN69. We also investigated bradykinin generation in 10 symptom-free patients dialyzed with four different membranes. None of the 12 patients studied during AR displayed excessive complement activation or histamine release. In contrast, high bradykinin plasma levels (2392 +/- 53 fmol/ml; mean +/- SEM) were observed in all nine patients of whom bradykinin was measured. One patient developed two consecutive episodes of hypersensitivity on AN69 membranes even without taking ACE inhibitors. Bradykinin levels were high in both episodes (5280 and 10467.7 fmol/ml). Furthermore, this patient showed no symptoms and normal bradykinin levels (123.4 fmol/ml) when dialyzed with other membranes. The role of the membrane type in the AR is further substantiated by the observation that AN69 also provoked a significantly higher bradykinin generation (327.6 +/- 18 fmol/ml; mean +/- SEM) during symptom-free sessions compared to other membranes like CuprophanR (5.1 +/- 7.3), HemophanR (17.2 +/- 6.3) and PolysulfoneR (39.7 +/- 6.6). Our findings strongly suggest that bradykinin is the principal mediator of AR during hemodialysis with AN69 membranes. To our knowledge it is the first time that data support the hypothesis of a more general role of bradykinin in shock-like symptoms. Furthermore, bradykinin generation must be regarded as a new marker of biocompatibility of extracorporeal treatments.

Angioedema associated with lisinopril

Angioedema has been reported to occur in association with all angiotensin-converting enzyme inhibitors used in the United States. We reviewed nine cases of angioedema associated with lisinopril use seen in the emergency department at our hospital among 1,970 patients that had been prescribed lisinopril from March 1989 to May 1990. Cases were considered as probably (six cases) or possibly (three cases) drug related, depending on the temporal relationship of the initiation of therapy and the onset of angioedema. All of the cases had edema of the lips, buccal mucosa, and or face. None presented with laryngeal edema or stridor. The angioedema resolved within 1 to 2 days with diphenhydramine treatment and discontinuation of lisinopril. Our data suggest that the incidence of angioedema associated with lisinopril is greater than that associated with captopril or enalapril.

Peripheral edema due to increased vascular permeability: a clinical appraisal

The release of vasoactive substances produces reversible changes of endothelial permeability with consequent edematous syndromes. We present 899 patients referred to our clinic for "non-hydrostatic non-hyponcotic" recurrent edema problems. Personal and family histories were recorded and a complete physical examination was carried out for each patient. In chronic situations laboratory tests [blood cell count, cryoglobulins, thyroid hormones, complement components (C3, C4, C1 inhibitor), total IgE, skin testing] were performed. Four subgroups of angioedema are identified for relevant clinical and etiopathogenetic differences. Seventy-three percent of patients had an urticaria-angioedema syndrome responding to antihistamine and/or corticosteroid treatment (histamine-dependent angioedema). Twenty-three percent had an angioedema related to a deficiency in C1 esterase inhibitor (complement-dependent angioedema). In a minority of patients, angioedema was due to the pharmacological effect of a drug (pharmacological angioedema) or was of a totally unknown origin (idiopathic angioedema). A generalized increase in vascular permeability was reported in 3 patients (systemic capillary leak syndrome). A brief survey of the literature is given with the review of our patients.

Purification and characterization of a new arginine carboxypeptidase in human serum

A carboxypeptidase capable of cleaving basic amino acids from synthetic peptide substrates is present in fresh human serum, and not in human heparinized plasma. Its activity is generated during the process of coagulation. Because of its unstability at room temperature and at 37 degrees C, we named it unstable carboxypeptidase (carboxypeptidase U). Carboxypeptidase U was partially purified from fresh human serum by chromatography on DEAE-cellulose and Mono-Q sepharose and was found to be a 435 kDa protein. We compared this enzyme with carboxypeptidase N, purified from human serum by a two-step affinity chromatography on arginine-Sepharose 4B, followed by ion-exchange chromatography on Mono-Q sepharose. Carboxypeptidase U cleaves hippuryl-L-arginine and hippuryl-L-lysine, but at a different relative rate than carboxypeptidase N, and has no esterase activity on hippuryl-L-argininic acid. Its activity was inhibited by o-phenanthroline, DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid, CoCl2, 2-mercaptoethanol, dithiothreitol and 4-chloromercuribenzoic acid. These characteristics differentiate carboxypeptidase U from carboxypeptidase N and other known carboxypeptidases.

Enalapril induced angioedema

A report of three patients who developed angiodema while receiving enalapril. Patient 1 came in with an 8-hour history of facial swelling after enalapril had been started 2 days earlier. The second patient came in with severe angiodema of the tongue, larynx, and glottis requiring emergency tracheostomy, hydroxyzine, and steroids. He had been treated with enalapril for 1 year. The third patient developed facial swelling within a few hours of the first dose of enalapril. Angiodema with enalapril can occur early or late in the course of therapy. A possible mechanism for this drug reaction is the potentiation of bradykinin with resultant kinin system activation.

The effects of intradermal bradykinin are potentiated by angiotensin converting enzyme inhibitors in hypertensive patients

1. To test the hypothesis that angiotensin converting enzyme (ACE) inhibitors potentiate the tissue effects of bradykinin, the thickness of weals produced by intradermal injections of bradykinin was measured in 17 hypertensive subjects whose antihypertensive regimen included an ACE inhibitor, and in 12 whose treatment did not. 2. Weal thickness increased linearly with the logarithm of the bradykinin dose in both groups (P less than 0.0001). 3. The patients receiving ACE inhibitors showed a mean response of 1.18 +/- 0.08 mm (mean +/- s.e. mean), compared with a mean response of 0.75 +/- 0.08 mm for patients not receiving an ACE inhibitor (P = 0.002). Mean weal response (1.08 +/- 0.9 mm) was not significantly different in patients taking captopril (n = 11) compared with that (1.29 +/- 0.12 mm) in patients taking enalapril (n = 9). 4. Facial flushing during the experiment occurred in six patients taking ACE inhibitors but none who were not. 5. Dermal responses to bradykinin are enhanced in patients taking ACE inhibitors as routine antihypertensive therapy. This study supports the hypothesis that bradykinin may be responsible for some of the adverse effects of these drugs.

Carboxypeptidase N: colorimetric assay using a new substrate

A method has been developed for determining carboxypeptidase N (EC 3.4.17.3) activity by a hippuricase (EC 3.5.1.14)-assisted colorimetric assay. The method is based on the absorbance at 506 nm of a quinoneimine dye, produced by the action of carboxypeptidase N on the new substrates p-hydroxybenzoylglycine-L-Arg and p-hydroxybenzoylglycine-L-Lys. The enzyme acts on the substrates producing p-hydroxybenzoylglycine and L-Arg or L-Lys. The former is then hydrolyzed by hippuricase into p-hydroxybenzoic acid and Gly. Subsequently, oxidative coupling of p-hydroxybenzoic acid with 4-aminoantipyrine by sodium periodate forms a quinoneimine dye. The mean value of carboxypeptidase N activities in sera of 50 normal individuals was 30.8 (SD 5.9) nmol of p-hydroxybenzoylglycine released per milliliter of serum for the p-hydroxybenzoylglycine-L-Arg substrate and 137.8 (SD 28.1) for the p-hydroxybenzoylglycine-L-Lys substrate. The sensitivity of the assay is such that as little as 20 microliters of serum provides reliable and precise results (RSD% ranging from 1.8 to 4.9).