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The plasma contact system contributes to thrombosis in experimental models. Even though our standard blood coagulation tests are prolonged when plasma lacks contact factors, this enzyme system appears to have a minor (if any) role in hemostasis. In this review, we explore the clinical phenotype of C1 esterase inhibitor (C1-INH) deficiency. C1-INH is the key plasma inhibitor of the contact system enzymes, and its deficiency causes hereditary angioedema (HAE). This inflammatory disorder is characterized by recurrent aggressive attacks of tissue swelling that occur at unpredictable locations throughout the body. Bradykinin, which is considered to be a byproduct of the plasma contact system during in vitro coagulation, is the main disease mediator in HAE. Surprisingly, there is little evidence for thrombotic events in HAE patients, suggesting mechanistic uncoupling from the intrinsic pathway of coagulation. In addition, it is questionable whether a surface is responsible for contact system activation in HAE. In this review, we discuss the clinical phenotype, disease modifiers and diagnostic challenges of HAE. We subsequently describe the underlying biochemical mechanisms and contributing disease mediators. Furthermore, we review three types of HAE that are not caused by C1-INH inhibitor deficiency. Finally, we propose a central enzymatic axis that we hypothesize to be responsible for bradykinin production in health and disease., (© 2018 The Authors. Journal of Thrombosis and Haemostasis published by Wiley Periodicals, Inc. on behalf of International Society on Thrombosis and Haemostasis.)

Kinin B1 receptors are induced by various inflammatory mediators. The aim of the present study was to investigate the effect of the CXC chemokine IL-8 on kinin B1 receptor expression in IMR-90 cells, by performing binding studies and Northern blot analysis of B1 receptor mRNA levels. We demonstrated here that the density of the kinin B1 receptors could be increased by the chemokine IL-8 in a concentration- and time-dependent manner. IL-8 also increased the kinin B1 receptor mRNA level in IMR-90 cells. IL-8-induced B1 receptor expression could be totally abolished by pretreatment with the metabolic inhibitors. Furthermore, expression was markedly reduced by antibodies to human IL-1alpha. In conclusion, IL-8 increased the expression of kinin B1 receptors in IMR-90 cells and this effect is likely to be secondary to the production of IL-1beta.

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

A kallidin-releasing enzyme with arginine ester hydrolytic activity was isolated from Bitis arietans venom by Sephadex G-75, DEAE-cellulose, and Sephadex G-100 column chromatography. This enzyme was shown to be homogeneous as demonstrated by a single band on polyacrylamide gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and NH2-terminal sequence analysis. The molecular weight was determined to be 58,000 Da with an isoelectric point of 4.4. Kallidin-releasing enzyme possesses proteolytic activity demonstrated by the hydrolysis of Gly(8)-Ser(9), Ala(14)-Leu(15), Tyr(16)-Leu(17), and Phe(25)-Tyr(26) bonds of oxidized insulin B chain. This enzyme did not convert fibrinogen to fibrin, yet it did hydrolyze the A alpha, B beta, and gamma chains of fibrinogen. The enzyme was shown to cleave a kininogen analog with the release of kallidin. Arginine ester hydrolytic activity of the preparation was inhibited by diisopropyl fluorophosphate and benzamidine hydrochloride, suggesting that serine and glutamic acid or aspartic acid are involved in this activity. This protein was stable to heat and over the pH range of 3-12.

Angiotensin I converting enzyme (ACE) and kininase activities were measured in various segments of the rabbit nephron. ACE was determined with tritiated hippuryl-glycylglycine as substrate. Lysyl-bradykinin (LBK) hydrolysis (kininase activity) was measured by radioimmunoassay. ACE was only found in the glomerulus and in the two parts of proximal tubule: the convoluted proximal tubule and the pars recta (PR). It was distributed along a concentration gradient which increased from the glomerulus to PR. Kininase activity was found in both proximal and distal parts of the nephron. Besides intense LBK-hydrolyzing activity in the proximal tubule, a kininase activity was also found in the medullary collecting tubule (MCT). Kininase activity in the glomerulus and the proximal tubule was completely inhibited by chelating agents. Captopril inhibited this activity only in the PR and at high concentrations (above 10(-7) M). These results indicate that several types of enzymes other than ACE hydrolyze kinins in the glomerulus and in the proximal tubule. The contribution of ACE to kinin hydrolysis appears only minimal. The kininase activity found in MCT was different from ACE and other proximal tubule kininases because it was not inhibited by chelating agents. This kininase may play a physiological role in inactivating the kinins formed by kallikrein at or beyond the connecting tubule.

Human neutrophil cathepsin G and human skin chymase can inactivate bradykinin by cleavage at the carboxy terminal phenylalanyl-arginyl peptide bond of this polypeptide. The mast cell enzyme is far more effective than cathepsin G, the rates of hydrolysis being comparable to that found for angiotensin I to angiotensin II conversion (C.F. Reilly, D. Tewksbury, N. Schechter, and J. Travis, J. Biological Chemistry 257:8619-8622). This ability to both inactivate bradykinin and accelerate the production of angiotensin II may be of significance in the development of biochemical events associated with inflammation.

A group of 15 biologically active peptides were studied with respect to their susceptibility to chain shortening by human pancreas alanine aminopeptidase. Those susceptible were somatostatin, melanocyte stimulating hormone, fibrinopeptide A, eosinophilotactictetrapeptide, lysyl-bradykinin, and methionyl-lysyl-bradykinin. The latter two were selected for further study. Direct identification and determination of the reaction products, lysine and/or methionine, were undertaken to establish unequivocally the kinin-converting activity of human pancreas alanine aminopeptidase, which exhibited a pH optimum at pH 7.9. The Km and kcat values for this enzyme for lysyl-bradykinin were 57 mumol/l and 3000 min-1, respectively. The corresponding values for this enzyme for methionyl-lysyl-bradykinin were calculated to be 49 mumol/l and 16000 min-1, respectively. Bradykinin itself is extremely resistant to hydrolysis by this pancreatic enzyme.