Contribution of plasma protease inhibitors to the inactivation of kallikrein in plasma

A mechanistic model of in vitro plasma activation to evaluate therapeutic kallikrein-kinin system inhibitors

BACKGROUND

The kallikrein-kinin system (KKS) is a complex biochemical pathway that plays a crucial role in regulating several physiological processes, including inflammation, coagulation, and blood pressure. Dysregulation of the KKS has been associated with several pathological conditions such as hereditary angioedema (HAE), hypertension, and stroke. Developing an accurate quantitative model of the KKS may provide a better understanding of its role in health and disease and facilitate the rapid and targeted development of effective therapies for KKS-related disorders.

OBJECTIVES

Here, we present a novel, detailed mechanistic model of the plasma KKS, elucidating the processes of Factor XII (FXII) activation, the kallikrein feedback loop, cleavage of high molecular weight kininogen leading to bradykinin (BK) production, and the impact of inhibitors.

METHODS

The model incorporates both surface and solution-phase reactions of all proteins in the KKS, describing how binding site concentration affects the rate of surface reactions. The model was calibrated and validated using a variety of published and in-house experimental datasets, which encompass a range of dextran sulphate (DXS) concentrations to initiate contact activation and various KKS inhibitors to block bradykinin production.

RESULTS

Our mathematical model showed that a trace amount of activated FXII is required for subsequent FXII activation. The model also reveals a bell-shaped curve relationship between the activation of the KKS and the number of DXS surface binding sites. Simulations of BK generation in healthy and HAE plasma demonstrated the impact of C1 esterase inhibitor (C1inh) deficiency via increased peak BK levels and accelerated formation in HAE plasma. The efficacy of KKS inhibitors, such as CSL312, ecallantide, and C1inh, was also evaluated, with CSL312 showing the most potent inhibition of BK generation.

CONCLUSIONS

The present model represents a valuable framework for studying the intricate interactions within the plasma KKS and provides a better understanding of the mechanism of action of various KKS-targeted therapies.

Genital Attacks in Hereditary Angioedema and Their Effects on Sexual Life

Background and Objectives: Hereditary angioedema (HAE) is characterized by unpredictable skin and mucosal angioedema attacks. We aimed to find the frequency of sexual-activity-triggered attacks (STAs) and understand how the sexual life of HAE with C1-inhibitor deficiency (HAE-C1INH) patients is affected. Materials and Methods: Adult HAE-C1INH patients were included in this cross-sectional study, which started in March 2020. Demographic information, marriage properties, gender-specific sexual life characteristics, and the HAE-specific histories of the patients were collected. The Hospital Anxiety and Depression Scale (HADS) and the Turkish version of the New Sexual Satisfaction Scale (NSSS) were applied to all participants. Results: Among 42 symptomatic HAE patients, 33 (78.57%) had genital attacks and 17 (42.5%) had STAs. Ten (58.8%) had genital pain, tenderness, or swelling, and five (29.4%) had isolated abdominal and groin pain. Eight (47.1%) patients with STAs experienced a HAE attack during their first time engaging in sexual intercourse. Anxiety/depression scales, NSSS scores, and distribution of other HAE attack localizations were similar in patients with and without STAs, and no gender differences were observed. Compared to the patients without STAs, the ratio of patients who stated that their sexual lives were negatively affected and that they lost their sexual desire was higher in patients with STAs. Conclusions: Genital or abdominal attacks triggered by sexual activity may be more common than thought. Sexual activity should also be questioned for evaluating attack triggers. There is a possibility of triggering an attack with the first and ongoing sexual intercourse, and patients should be informed to keep their attack treatment medications ready in advance.

Extension of the circulatory half-life of recombinant ecallantide via albumin fusion without loss of anti-kallikrein activity

Ecallantide comprises Kunitz Domain 1 of Tissue Factor Pathway Inhibitor, mutated at seven amino acid positions to inhibit plasma kallikrein (PK). It is used to treat acute hereditary angioedema (HAE). We appended hexahistidine tags to the N- or C-terminus of recombinant Ecallantide (rEcall) and expressed and purified the resulting proteins, with or without fusion to human serum albumin (HSA), using Pichia pastoris. The inhibitory constant (Ki) of rEcall-H6 or H6-rEcall for PK was not increased by albumin fusion. When 125I-labelled rEcall proteins were injected intravenously into mice, the area under the clearance curve (AUC) was significantly increased, 3.4- and 3.6-fold, for fusion proteins H6-rEcall-HSA and HSA-rEcall-H6 versus their unfused counterparts but remained 2- to 3-fold less than that of HSA-H6. The terminal half-life of H6-rEcall-HSA and HSA-H6 did not differ, although that of HSA-rEcall-H6 was significantly shorter than either other protein. Receptor Associated Protein (RAP), a Low-density lipoprotein Receptor-related Protein (LRP1) antagonist, competed H6-rEcall-HSA clearance more effectively than intravenous immunoglobulin (IVIg), a neonatal Fc receptor (FcRn) antagonist. HSA fusion decreases rEcall clearance in vivo, but LRP1-mediated clearance remains more important than FcRn-mediated recycling for rEcall fusion proteins. The properties of H6-rEcall-HSA warrant investigation in a murine model of HAE.

Increased thromboinflammatory load in hereditary angioedema

C1 inhibitor (C1Inh) is a serine protease inhibitor involved in the kallikrein-kinin system, the complement system, the coagulation system, and the fibrinolytic system. In addition to the plasma leakage observed in hereditary angioedema (HAE), C1Inh deficiency may also affect these systems, which are important for thrombosis and inflammation. The aim of this study was to investigate the thromboinflammatory load in C1Inh deficiency. We measured 27 cytokines including interleukins, chemokines, interferons, growth factors, and regulators using multiplex technology. Complement activation (C4d, C3bc, and sC5b-C9/TCC), haemostatic markers (β-thromboglobulin (β-TG), thrombin-antithrombin complexes (TAT), prothrombin fragment 1 + 2 (F1 + 2), active plasminogen activator inhibitor-1 (PAI-1), and the neutrophil activation marker myeloperoxidase (MPO) were measured by enzyme immunoassays. Plasma and serum samples were collected from 20 patients with HAE type 1 or 2 in clinical remission and compared with 20 healthy age- and sex-matched controls. Compared to healthy controls, HAE patients had significantly higher levels of tumour necrosis factor (TNF), interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-7, IL-9, IL-12, and IL-17A, chemokine ligand (CXCL) 8, chemokine ligand (CCL) 3, CCL4, IL-1 receptor antagonist (IL-1RA), granulocyte-macrophage colony-stimulating factor (GM-CSF), fibroblast growth factor (FGF) 2 and platelet-derived growth factor (PDGF)-BB. HAE patients also had higher levels of TAT and F1 + 2. Although granulocyte colony-stimulating factor (G-CSF), β-TG and PAI-1 were higher in HAE patients, the differences did not reach statistical significance after correction for multiple testing. In conclusion, C1Inh deficiency is associated with an increased baseline thromboinflammatory load. These findings may reflect that HAE patients are in a subclinical attack state outside of clinically apparent oedema attacks.

C1 inhibitor and prolylcarboxypeptidase modulate prekallikrein activation on endothelial cells

BACKGROUND

We examined how prekallikrein (PK) activation on human microvascular endothelial cells (HMVECs) is regulated by the ambient concentration of C1 inhibitor (C1INH) and prolylcarboxypeptidase (PRCP).

OBJECTIVE

We sought to examine the specificity of PK activation on HMVECs by PRCP and the role of C1INH to regulate it, high-molecular-weight kininogen (HK) cleavage, and bradykinin (BK) liberation.

METHODS

Investigations were performed on cultured HMVECs. Immunofluorescence, enzymatic activity assays, immunoblots, small interfering RNA knockdowns, and cell transfections were used to perform these studies.

RESULTS

Cultured HMVECs constitutively coexpressed PK, HK, C1INH, and PRCP. PK activation on HMVECs was modulated by the ambient C1INH concentration. In the absence of C1INH, forming PKa on HMVECs cleaved 120-kDa HK completely to a 65-kDa H-chain and a 46-kDa L-chain in 60 minutes. In the presence of 2 μM C1INH, only 50% of the HK became cleaved. C1INH concentrations (0.0-2.5 μM) decreased but did not abolish BK liberated from HK by activated PK. Factor XII did not activate when incubated with HMVECs alone for 1 hour. However, if incubated in the presence of HK and PK, factor XII became activated. The specificity of PK activation on HMVECs by PRCP was shown by several inhibitors to each enzyme. Furthermore, PRCP small interfering RNA knockdowns magnified C1INH inhibitory activity on PK activation, and PRCP transfections reduced C1INH inhibition at any given concentration.

CONCLUSIONS

These combined studies indicated that on HMVECs, PK activation and HK cleavage to liberate BK were modulated by the local concentrations of C1INH and PRCP.

Human plasma kallikrein: roles in coagulation, fibrinolysis, inflammation pathways, and beyond

Human plasma kallikrein (PKa) is obtained by activating its precursor, prekallikrein (PK), historically named the Fletcher factor. Human PKa and tissue kallikreins are serine proteases from the same family, having high- and low-molecular weight kininogens (HKs and LKs) as substrates, releasing bradykinin (Bk) and Lys-bradykinin (Lys-Bk), respectively. This review presents a brief history of human PKa with details and recent observations of its evolution among the vertebrate coagulation proteins, including the relations with Factor XI. We explored the role of Factor XII in activating the plasma kallikrein-kinin system (KKS), the mechanism of activity and control in the KKS, and the function of HK on contact activation proteins on cell membranes. The role of human PKa in cell biology regarding the contact system and KSS, particularly the endothelial cells, and neutrophils, in inflammatory processes and infectious diseases, was also approached. We examined the natural plasma protein inhibitors, including a detailed survey of human PKa inhibitors' development and their potential market.

C1 inhibitor deficiency enhances contact pathway-mediated activation of coagulation and venous thrombosis

C1 inhibitor (C1INH) is a multifunctional serine protease inhibitor that functions as a major negative regulator of several biological pathways, including the contact pathway of blood coagulation. In humans, congenital C1INH deficiency results in a rare episodic bradykinin-mediated swelling disorder called hereditary angioedema (HAE). Patients with C1INH deficiency-associated HAE (C1INH-HAE) have increased circulating markers of activation of coagulation. Furthermore, we recently reported that patients with C1INH-HAE had a moderate but significant increased risk of venous thromboembolism. To further investigate the impact of C1INH deficiency on activation of coagulation and thrombosis, we conducted studies using patient samples and mouse models. Plasmas from patients with C1INH-HAE had significantly increased contact pathway-mediated thrombin generation. C1INH-deficient mice, which have been used as a model of C1INH-HAE, had significantly increased baseline circulating levels of prothrombin fragment 1+2 and thrombin-antithrombin complexes. In addition, whole blood from C1INH-deficient mice supported significantly increased contact pathway-mediated thrombin generation. Importantly, C1INH-deficient mice exhibited significantly enhanced venous, but not arterial, thrombus formation. Furthermore, purified human C1INH normalized contact pathway-mediated thrombin generation and venous thrombosis in C1INH-deficient mice. These findings highlight a key role for endogenous C1INH as a negative regulator of contact pathway-mediated coagulation in humans and mice. Further, this work identifies endogenous C1INH as an important negative regulator of venous thrombus formation in mice, complementing the phenotype associated with C1INH-HAE.

Biochemistry, molecular genetics, and clinical aspects of hereditary angioedema with and without C1 inhibitor deficiency

Hereditary angioedema (HAE) is a rare disorder characterized by cutaneous and submucosal swelling caused mostly by excessive local bradykinin production. Bradykinin is a vasoactive peptide generated by the limited proteolysis of high molecular weight kininogen (HMWK) by plasma kallikrein via the contact activation system. The contact activation system occurs not only in solution but also on the cell surface. Factor XII (FXII), prekallikrein, and HMWK are assembled on the endothelial cell surface via several proteins, including a trimer of a receptor for globular C1q domain in a Zn²⁺-dependent manner, and the reciprocal activation on the cell surface is believed to be physiologically important in vivo. Thus, the contact activation system leads to the activation of coagulation, complement, inflammation, and fibrinolysis. C1-inhibitor (C1-INH) is a plasma protease inhibitor that is a member of the serpin family. It mainly inhibits activated FXII (FXIIa), plasma kallikrein, and C1s. C1-INH hereditary deficiency induces HAE (HAE-C1-INH) due to excessive bradykinin production via the incomplete inhibition of plasma kallikrein and FXIIa through the low C1-INH level. HAE is also observed in patients with normal C1-INH (HAEnCI) who carry pathogenic variants in genes of factor XII, plasminogen, angiopoietin 1, kininogen, myoferlin, and heparan sulfate 3-O-sulfotransferase 6, which are associated with bradykinin production and/or vascular permeability. HAE-causing pathways triggered by pathogenic variants in patients with HAE-C1-INH and HAEnCI are reviewed and discussed.

Interplay between C1-inhibitor and group IIA secreted phospholipase A2 impairs their respective function

High levels of human group IIA secreted phospholipase A₂ (hGIIA) have been associated with various inflammatory disease conditions. We have recently shown that hGIIA activity and concentration are increased in the plasma of patients with hereditary angioedema due to C1-inhibitor deficiency (C1-INH-HAE) and negatively correlate with C1-INH plasma activity. In this study, we analyzed whether the presence of both hGIIA and C1-INH impairs their respective function on immune cells. hGIIA, but not recombinant and plasma-derived C1-INH, stimulates the production of IL-6, CXCL8, and TNF-α from peripheral blood mononuclear cells (PBMCs). PBMC activation mediated by hGIIA is blocked by RO032107A, a specific hGIIA inhibitor. Interestingly, C1-INH inhibits the hGIIA-induced production of IL-6, TNF-α, and CXCL8, while it does not affect hGIIA enzymatic activity. On the other hand, hGIIA reduces the capacity of C1-INH at inhibiting C1-esterase activity. Spectroscopic and molecular docking studies suggest a possible interaction between hGIIA and C1-INH but further experiments are needed to confirm this hypothesis. Together, these results provide evidence for a new interplay between hGIIA and C1-INH, which may be important in the pathophysiology of hereditary angioedema.

Factor VII activating protease (FSAP) is not essential in the pathophysiology of angioedema in patients with C1 inhibitor deficiency

BACKGROUND

Excessive bradykinin (BK) generation from high molecular weight kininogen (HK) by plasma kallikrein (PK) due to lack of protease inhibition is central to the pathophysiology of hereditary angioedema (HAE). Inadequate protease inhibition may contribute to HAE through a number of plasma proteases including factor VII activating protease (FSAP) that can also cleave HK.

OBJECTIVE

To investigate the interaction between FSAP and C1 inhibitor (C1Inh) and evaluate the potential role of FSAP in HAE with C1Inh deficiency.

MATERIALS AND METHODS

Plasma samples from 20 persons with HAE types 1 or 2 in remission were studied and compared to healthy controls. We measured and compared antigenic FSAP levels, spontaneous FSAP activity, FSAP generation potential, activation of plasma pre-kallikrein (PPK) by FSAP, and the formation of FSAP-C1Inh and FSAP-alpha2-antiplasmin (FSAP-α2AP) complexes. Furthermore, we measured HK cleavage and PK activation after activation of endogenous pro-FSAP and after addition of exogenous FSAP.

RESULTS

In plasma from HAE patients, there is increased basal FSAP activity compared to healthy volunteers. HAE plasma exhibits decreased formation of FSAP-C1Inh complexes and increased formation of FSAP-α2AP complexes in histone-activated plasma. Although exogenous FSAP can cleave HK in plasma, this was not seen when endogenous plasma pro-FSAP was activated with histones in either group. PK was also not activated by FSAP in plasma.

CONCLUSION

In this study, we established that FSAP activity is increased and the pattern of FSAP-inhibitor complexes is altered in HAE patients. However, we did not find evidence suggesting that FSAP contributes directly to HAE attacks.

A Review of Neutrophil Extracellular Traps (NETs) in Disease: Potential Anti-NETs Therapeutics

Activated neutrophils release neutrophil extracellular traps (NETs) in response to a variety of stimuli. NETosis is driven by protein-arginine deiminase type 4, with the release of intracellular granule components that function by capturing and destroying microbes, including viral, fungal, bacterial, and protozoal pathogens. The positive effects of pathogen control are countered by pro-inflammatory effects as demonstrated in a variety of diseases. Components of NETS are non-specific, and other than controlling microbes, they cause injury to surrounding tissue by themselves or by increasing the pro-inflammatory response. NETs can play a role in enhancement of the inflammation seen in autoimmune diseases including psoriasis, rheumatoid arthritis, and systemic lupus erythematosis. In addition, autoinflammatory diseases such as gout have been associated with NETosis. Inhibition of NETs may decrease the severity of many diseases improving survival. Herein, we describe NETosis in different diseases focusing on the detrimental effect of NETs and outline possible therapeutics that can be used to mitigate netosis. There is a need for more studies and clinical trials on these and other compounds that could prevent or destroy NETs, thereby decreasing damage to patients.

C1-Inhibitor: Structure, Functional Diversity and Therapeutic Development

Human C1-Inhibitor (C1INH), also known as C1-esterase inhibitor, is an important multifunctional plasma glycoprotein that is uniquely involved in a regulatory network of complement, contact, coagulation, and fibrinolytic systems. C1INH belongs to a superfamily of serine proteinase inhibitor (serpins) and exhibits its inhibitory activities towards several target proteases of plasmatic cascades, operating as a major anti-inflammatory protein in the circulation. In addition to its inhibitory activities, C1INH is also involved in non-inhibitory interactions with some endogenous proteins, polyanions, cells and infectious agents. While C1INH is essential for multiple physiological processes, it is better known for its deficiency with regards to Hereditary Angioedema (HAE), a rare autosomal dominant disease clinically manifested by recurrent acute attacks of increased vascular permeability and edema. Since the link was first established between functional C1INH deficiency in plasma and HAE in the 1960s, tremendous progress has been made in the biochemical characterization of C1INH and its therapeutic development for replacement therapies in patients with C1INH-dependent HAE. Various C1INH biological activities, recent advances in the HAE-targeted therapies, and availability of C1INH commercial products have prompted intensive investigation of the C1INH potential for treatment of clinical conditions other than HAE. This article provides an updated overview of the structure and biological activities of C1INH, its role in HAE pathogenesis, and recent advances in the research and therapeutic development of C1INH; it also considers some trends for using C1INH therapeutic preparations for applications other than angioedema, from sepsis and endotoxin shock to severe thrombotic complications in COVID-19 patients.

Heat-Inactivation of Human Serum Destroys C1 Inhibitor, Pro-motes Immune Complex Formation, and Improves Human T Cell Function

Heat-inactivation of sera is used to reduce possible disturbing effects of complement factors in cell-culture experiments, but it is controversially discussed whether this procedure is appropriate or could be neglected. Here, we report a strong impact of heat-inactivation of human sera on the activation and effector functions of human CD4+ T cells. While T cells cultured with native sera were characterized by a higher proliferation rate and higher expression of CD28, heat-inactivated sera shaped T cells towards on-blast formation, higher cytokine secretion (interferon γ, tumor necrosis factor, and interleukin-17), stronger CD69 and PD-1 expression, and increased metabolic activity. Heat-inactivated sera contained reduced amounts of complement factors and regulators like C1 inhibitor, but increased concentrations of circulating immune complexes. Substitution of C1 inhibitor reduced the beneficial effect of heat-inactivation in terms of cytokine release, whereas surface-molecule expression was affected by the addition of complex forming anti-C1q antibody. Our data clearly demonstrate a beneficial effect of heat-inactivation of human sera for T cell experiments but indicate that beside complement regulators and immune complexes other components might be relevant. Beyond that, this study further underpins the strong impact of the complement system on T cell function.

A Robust Bioassay of the Human Bradykinin B2 Receptor that Extends Molecular and Cellular Studies: The Isolated Umbilical Vein

Bradykinin (BK) has various physiological and pathological roles. Medicinal chemistry efforts targeted toward the widely expressed BK B₂ receptor (B₂R), a G-protein-coupled receptor, were primarily aimed at developing antagonists. The only B₂R antagonist in clinical use is the peptide icatibant, approved to abort attacks of hereditary angioedema. However, the anti-inflammatory applications of B₂R antagonists are potentially wider. Furthermore, the B₂R antagonists notoriously exhibit species-specific pharmacological profiles. Classical smooth muscle contractility assays are exploited over a time scale of several hours and support determining potency, competitiveness, residual agonist activity, specificity, and reversibility of pharmacological agents. The contractility assay based on the isolated human umbilical vein, expressing B₂R at physiological density, was introduced when investigating the first non-peptide B₂R antagonist (WIN 64338). Small ligand molecules characterized using the assay include the exquisitely potent competitive antagonist, Pharvaris Compound 3 or the partial agonist Fujisawa Compound 47a. The umbilical vein assay is also useful to verify pharmacologic properties of special peptide B₂R ligands, such as the carboxypeptidase-activated latent agonists and fluorescent probes. Furthermore, the proposed agonist effect of tissue kallikrein on the B₂R has been disproved using the vein. This assay stands in between cellular and molecular pharmacology and in vivo studies.

Deep Intronic Mutation in SERPING1 Caused Hereditary Angioedema Through Pseudoexon Activation

PURPOSE

Hereditary angioedema (HAE) is a rare autosomal dominant life-threatening disease characterized by low levels of C1 inhibitor (type I HAE) or normal levels of ineffective C1 inhibitor (type II HAE), typically occurring as a consequence of a SERPING1 mutation. In some cases, a causal mutation remains undetected after using a standard molecular genetic analysis.

RESULTS

Here we show a long methodological way to the final discovery of c.1029 + 384A > G, a novel deep intronic mutation in intron 6 which is responsible for HAE type I in a large family and has not been identified by a conventional diagnostic approach. This mutation results in de novo donor splice site creation and subsequent pseudoexon inclusion, the mechanism firstly described to occur in SERPING1 in this study. We additionally discovered that the proximal part of intron 6 is a region potentially prone to pseudoexon-activating mutations, since natural alternative exons and additional cryptic sites occur therein. Indeed, we confirmed the existence of at least two different alternative exons in this region not described previously.

CONCLUSIONS

In conclusion, our results suggest that detecting aberrant transcripts, which are often low abundant because of nonsense-mediated decay, requires a modified methodological approach. We suggest SERPING1 intron 6 sequencing and/or tailored mRNA analysis to be routinely used in HAE patients with no mutation identified in the coding sequence.

Bradykinin-Mediated Angioedema: An Update of the Genetic Causes and the Impact of Genomics

Recurrent episodes of bradykinin-mediated angioedema (Bk-AE) can associate with acquired or hereditary conditions, the former most commonly developing secondarily to a pharmacological treatment. Despite successful genomic advances that have led to the identification of a large number of disease genes irrespective of disease prevalence, their application to Bk-AE has barely occurred. As a consequence, the genetic causes of Bk-AE remain poorly understood, obstructing the identification of patient subtypes and the development of precision medicine strategies. This review provides an update of the genetic studies completed to date on the acquired forms, which have almost exclusively focused on Bk-AE secondarily to the angiotensin-converting enzyme inhibitor treatment, and the blooming subdivision of the hereditary forms established by the identification of novel causal genes with next-generation sequencing (NGS) technology-based exome studies in genetically undiagnosed patients. Finally, based on the diverse benefits that are offered by the technology, we present arguments favoring the use of holistic NGS approaches as first-tier genetic tests as a promise to reduce the diagnostic odyssey of patients with suspected hereditary forms of Bk-AE.

Knockdown of circulating C1 inhibitor induces neurovascular impairment, glial cell activation, neuroinflammation, and behavioral deficits

The cross-talk between blood proteins, immune cells, and brain function involves complex mechanisms. Plasma protein C1 inhibitor (C1INH) is an inhibitor of vascular inflammation that is induced by activation of the kallikrein-kinin system (KKS) and the complement system. Knockout of C1INH was previously correlated with peripheral vascular permeability via the bradykinin pathway, yet there was no evidence of its correlation with blood-brain barrier (BBB) integrity and brain function. In order to understand the effect of plasma C1INH on brain pathology via the vascular system, we knocked down circulating C1INH in wild-type (WT) mice using an antisense oligonucleotide (ASO), without affecting C1INH expression in peripheral immune cells or the brain, and examined brain pathology. Long-term elimination of endogenous C1INH in the plasma induced the activation of the KKS and peritoneal macrophages but did not activate the complement system. Bradykinin pathway proteins were elevated in the periphery and the brain, resulting in hypotension. BBB permeability, extravasation of plasma proteins into the brain parenchyma, activation of glial cells, and elevation of pro-inflammatory response mediators were detected. Furthermore, infiltrating innate immune cells were observed entering the brain through the lateral ventricle walls and the neurovascular unit. Mice showed normal locomotion function, yet cognition was impaired and depressive-like behavior was evident. In conclusion, our results highlight the important role of regulated plasma C1INH as it acts as a gatekeeper to the brain via the neurovascular system. Thus, manipulation of C1INH in neurovascular disorders might be therapeutically beneficial.

SERPINs-From Trap to Treatment

Excessive enzyme activity often has pathological consequences. This for example is the case in thrombosis and hereditary angioedema, where serine proteases of the coagulation system and kallikrein-kinin system are excessively active. Serine proteases are controlled by SERPINs (serine protease inhibitors). We here describe the basic biochemical mechanisms behind SERPIN activity and identify key determinants that influence their function. We explore the clinical phenotypes of several SERPIN deficiencies and review studies where SERPINs are being used beyond replacement therapy. Excitingly, rare human SERPIN mutations have led us and others to believe that it is possible to refine SERPINs toward desired behavior for the treatment of enzyme-driven pathology.

SERPING1 exon 3 splicing variants using alternative acceptor splice sites

Mutations in the C1 inhibitor (C1INH) encoding gene, SERPING1, are associated with hereditary angioedema (HAE) which manifests as recurrent submucosal and subcutaneous edema episodes. The major C1INH function is the complement system inhibition, preventing its spontaneous activation. The presented study is focused on SERPING1 exon 3, an alternative and extraordinarily long exon (499 bp). Endogenous expression analysis performed in the HepG2, human liver, and human peripheral blood cells revealed several exon 3 splicing variants alongside exon inclusion: a highly prevalent exon skipping variant and less frequent +38 and -15 variants with alternative 3' splice sites (ss) located 38 and 15 nucleotides downstream and upstream from the authentic 3' ss, respectively. An exon skipping variant introducing a premature stop codon, represented nearly one third of all splicing variants and surprisingly appeared not to be degraded by NMD. The alternative -15 3' ss was used to a small extent, although predicted to be extremely weak. Its use was shown to be independent of its strength and highly sensitive to any changes in the surrounding sequence. -15 3' ss seems to be co-regulated with the authentic 3' ss, whose use is dependent mainly on its strength and less on the presence of intronic regulatory motifs. Subtle SERPING1 exon 3 splicing regulation can contribute to overall C1INH plasma levels and HAE pathogenesis.

N-terminal domain of EcC1INH in Epinephelus coioides can antagonize the LPS-stimulated inflammatory response

Complement 1 inhibitor (C1INH) serving as a multifunctional factor can participate in the regulation of complement cascades and attenuate the activation of various proteases. In this study, we obtained EcC1INH cDNA and the tissue-specific analysis indicate that the highest expression level of EcC1INH mRNA was detected in liver. Moreover, Vibrio alginolyticus challenge can significantly increase EcC1INH mRNA expression in liver and kidney. N-terminal domain of EcC1INH could decrease LPS binding activity to cell surface, while loss of positively charged residues (PCRs) Arg21, His22, Lys50, Arg61 in N-terminal domain of EcC1INH can significantly reduce its interaction with LPS. Furthermore, LPS injection experiment indicated that the binding of EcC1INH N-terminal domain to LPS can antagonize LPS-induced inflammatory signaling pathway and attenuate the production of proinflammatory cytokines in vivo, indicating that EcC1INH was involved in negative regulation of inflammatory response.

Hereditary angioedema: the plasma contact system out of control

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.

Peptidoglycan induces disseminated intravascular coagulation in baboons through activation of both coagulation pathways

Anthrax infections exhibit progressive coagulopathies that may contribute to the sepsis pathophysiology observed in fulminant disease. The hemostatic imbalance is recapitulated in primate models of late-stage disease but is uncommon in toxemic models, suggesting contribution of other bacterial pathogen-associated molecular patterns (PAMPs). Peptidoglycan (PGN) is a bacterial PAMP that engages cellular components at the cross talk between innate immunity and hemostasis. We hypothesized that PGN is critical for anthrax-induced coagulopathies and investigated the activation of blood coagulation in response to a sterile PGN infusion in primates. The PGN challenge, like the vegetative bacteria, induced a sepsis-like pathophysiology characterized by systemic inflammation, disseminated intravascular coagulation (DIC), organ dysfunction, and impaired survival. Importantly, the hemostatic impairment occurred early and in parallel with the inflammatory response, suggesting direct engagement of coagulation pathways. PGN infusion in baboons promoted early activation of contact factors evidenced by elevated protease-serpin complexes. Despite binding to contact factors, PGN did not directly activate either factor XII (FXII) or prekallikrein. PGN supported contact coagulation by enhancing enzymatic function of active FXII (FXIIa) and depressing its inhibition by antithrombin. In parallel, PGN induced de novo monocyte tissue factor expression in vitro and in vivo, promoting extrinsic clotting reactions at later stages. Activation of platelets further amplified the procoagulant state during PGN challenge, leading to DIC and subsequent ischemic damage of peripheral tissues. These data indicate that PGN may be a major cause for the pathophysiologic progression of Bacillus anthracis sepsis and is the primary PAMP behind the pathogen-induced coagulopathy in late-stage anthrax.

Plasma Prekallikrein: Its Role in Hereditary Angioedema and Health and Disease

Plasma prekallikrein (PK) has a critical role in acute attacks of hereditary angioedema (HAE). Unlike C1 inhibitor, its levels fall during HAE attacks with resultant cleaved high-molecular-weight kininogen. Cleavage of high-molecular-weight kininogen liberates bradykinin, the major biologic peptide that promotes the edema. How prekallikrein initially becomes activated in acute attacks of HAE is not known. PK itself is negatively associated with cardiovascular disease. High prekallikrein is associated with accelerated vascular disease in diabetes and polymorphisms of prekallikrein that reduce high-molecular-weight kininogen binding are associated with protection from cardiovascular events. Prekallikrein-deficient mice have reduced thrombosis risk and plasma kallikrein (PKa) inhibition is associated with reduced experimental gastroenterocolitis and arthritis in rodents. In sum, prekallikrein and its enzyme PKa are major targets in HAE providing much opportunity to improve the acute and chronic management of HAE. PKa inhibition also may be a target to ameliorate cardiovascular disease, thrombosis risk, and inflammation as in enterocolitis and arthritis.

Reduction of thrombus size in murine models of thrombosis following administration of recombinant α1-proteinase inhibitor mutant proteins

The variant serpin α1-PI M358R inhibits thrombin and other proteases such as activated protein C (APC) and factor XIa. We previously described recombinant proteins HAPI M358R (α1-PI M358R containing an N-terminal extension corresponding to residues 1–75 of heparin cofactor II) and HAPI RCL5 (HAPI M358R with F352-I356 and I360 substituted for the corresponding residues of antithrombin), with enhanced selectivity for thrombin over APC inhibition. We tested the hypotheses that these recombinant proteins would limit thrombosis in three mouse models, and that the HAPI chimeric proteins would be more effective than α1-PI M358R. Recombinant serpins were purified from Escherichia coli by nickel chelate and ion exchange affinity chromatography, and administered to mice intravenously. HAPI RCL5 reduced incorporation of radiolabelled fibrin(ogen) into thrombi in the ferric chloride-injured vena cava in a dose-dependent manner; HAPI M358R was less effective and α1-PI M358R was without effect. In a model of murine endotoxaemia, HAPI RCL5 was more effective than α1-PI M358R in reducing radiolabelled fibrin(ogen) deposition in heart and kidneys; immunohis-tochemistry of tissue sections showed lesser staining with anti-fibrin(ogen) antibodies with both treatments. In the ferric chloride-injured murine carotid artery, administration of both recombinant serpins was equally effective in lengthening the vessel’s time to occlusion. Our results show that the antithrombotic efficacy of the recombinant serpins correlates with their potency as thrombin inhibitors, since HAPI RCL5 inhibits thrombin, but not factors Xa, XIa, XIIa, or neutrophil elastase, more rapidly than α1-PI M358R.

Analysis of Milk from Mothers Who Delivered Prematurely Reveals Few Changes in Proteases and Protease Inhibitors across Gestational Age at Birth and Infant Postnatal Age

Background: Peptidomics research has demonstrated that protease activity is higher in breast milk from preterm-delivering mothers than from term-delivering mothers. However, to our knowledge, the effect of the degree of prematurity and postnatal age on proteases and protease inhibitors in human milk remains unknown.Objective: We aimed to determine the change of proteases and protease inhibitors in milk from mothers who delivered prematurely across gestational age (GA) and postnatal age.Methods: Milk samples were collected from 18 mothers aged 26-40 y who delivered preterm infants and who lacked mastitis. For analysis, samples were separated into 2 groups: 9 from early GA (EGA) (24-26 wk GA)-delivering mothers and 9 from late GA (LGA) (27-32 wk GA)-delivering mothers. Within the 9 samples in each group, the collection time ranged from postnatal days 2 to 47. The activity and predicted activity of proteases in preterm milk were determined with the use of fluorometric and spectrophotometric assays and peptidomics, respectively. Protease and protease inhibitor concentrations were determined with the use of ELISA. Linear mixed models were applied to compare enzymes across GA and postnatal age.Results: Carboxypeptidase B2, kallikrein, plasmin, elastase, thrombin, and cytosol aminopeptidase were present and active in the milk of preterm-delivering mothers. Most milk protease and antiprotease concentrations did not change with GA or postnatal age. However, the concentration and activity of kallikrein, the most abundant and active protease in preterm milk, increased by 25.4 ng · mL-1 · d-1 and 0.454 μg · mL-1 · d-1 postnatally, respectively, in EGA milk samples while remaining stable in LGA milk samples.Conclusions: This research demonstrates that proteases are active in human milk and begin to degrade milk protein within the mammary gland before consumption by infants. Proteases and protease inhibitors in milk from mothers of premature infants mostly did not vary substantially across GA and postnatal age.

Plasma Kallikrein Inhibitors in Cardiovascular Disease: An Innovative Therapeutic Approach

Plasma prekallikrein is the liver-derived precursor of the trypsin-like serine protease plasma kallikrein, and circulates in plasma bound to high molecular weight kininogen. Plasma prekallikrein is activated to plasma kallikrein by activated factor XII or prolylcarboxypeptidase. Plasma kallikrein regulates the activity of multiple proteolytic cascades in the cardiovascular system such as the intrinsic pathway of coagulation, the kallikrein-kinin system, the fibrinolytic system, the renin-angiotensin system, and the complement pathways. As such, plasma kallikrein plays a central role in the pathogenesis of thrombosis, inflammation, and blood pressure regulation. Under physiological conditions, plasma kallikrein serves as a cardioprotective enzyme. However, its increased plasma concentration or hyperactivity perpetuates cardiovascular disease (CVD). In this article, we review the biochemistry and cell biology of plasma kallikrein and summarize data from preclinical and clinical studies that have established important functions of this serine protease in CVD states. Finally, we propose plasma kallikrein inhibitors as a novel class of drugs with potential therapeutic applications in the treatment of CVDs.

Recombinant human C1 esterase inhibitor in the management of hereditary angioedema

Hereditary angioedema (HAE), a rare autosomal dominant genetic disorder, is caused by a deficiency in functional C1 esterase inhibitor (C1-INH). This potentially life-threatening condition manifests as recurrent attacks of subcutaneous and submucosal swelling of the skin, gastrointestinal tract and larynx. The management of HAE includes treatment of acute episodes, short-term prophylaxis in preparation for exposure to known triggers and long-term prophylaxis to decrease the incidence and severity of HAE attacks. Four products are approved in the USA for the treatment of acute attacks of HAE, including one human plasma-derived C1-INH therapy, a recombinant human C1-INH product (rhC1-INH), a plasma kallikrein inhibitor and a bradykinin B2 receptor antagonist. In addition, one human plasma-derived C1-INH therapy and danazol are approved for prophylaxis of HAE attacks. rhC1-INH, extracted from the milk of transgenic rabbits, is a glycoprotein of 478 amino acids with an identical amino acid sequence to the endogenous human C1-INH protein. Population pharmacokinetic analysis of rhC1-INH supports an intravenous dosing strategy of 50 U/kg (maximum 4200 U). The safety and efficacy of rhC1-INH in the treatment of acute attacks in patients with HAE were demonstrated in three randomized, double-blind, placebo-controlled studies and two open-label extension studies. In a pilot prophylaxis study, weekly administration of rhC1-INH 50 U/kg for 8 weeks reduced the incidence of HAE attacks and was well tolerated. Administration of rhC1-INH has not been associated with the development of anti-drug antibodies or antibodies to anti-host-related impurities.

Polyphosphate is a novel cofactor for regulation of complement by a serpin, C1 inhibitor

The complement system plays a key role in innate immunity, inflammation, and coagulation. The system is delicately balanced by negative regulatory mechanisms that modulate the host response to pathogen invasion and injury. The serpin, C1-esterase inhibitor (C1-INH), is the only known plasma inhibitor of C1s, the initiating serine protease of the classical pathway of complement. Like other serpin-protease partners, C1-INH interaction with C1s is accelerated by polyanions such as heparin. Polyphosphate (polyP) is a naturally occurring polyanion with effects on coagulation and complement. We recently found that polyP binds to C1-INH, prompting us to consider whether polyP acts as a cofactor for C1-INH interactions with its target proteases. We show that polyP dampens C1s-mediated activation of the classical pathway in a polymer length- and concentration-dependent manner by accelerating C1-INH neutralization of C1s cleavage of C4 and C2. PolyP significantly increases the rate of interaction between C1s and C1-INH, to an extent comparable to heparin, with an exosite on the serine protease domain of the enzyme playing a major role in this interaction. In a serum-based cell culture system, polyP significantly suppressed C4d deposition on endothelial cells, generated via the classical and lectin pathways. Moreover, polyP and C1-INH colocalize in activated platelets, suggesting that their interactions are physiologically relevant. In summary, like heparin, polyP is a naturally occurring cofactor for the C1s:C1-INH interaction and thus an important regulator of complement activation. The findings may provide novel insights into mechanisms underlying inflammatory diseases and the development of new therapies.

Proteolytic Systems in Milk: Perspectives on the Evolutionary Function within the Mammary Gland and the Infant

Milk contains elements of numerous proteolytic systems (zymogens, active proteases, protease inhibitors and protease activators) produced in part from blood, in part by mammary epithelial cells and in part by immune cell secretion. Researchers have examined milk proteases for decades, as they can cause major defects in milk quality and cheese production. Most previous research has examined these proteases with the aim to eliminate or control their actions. However, our recent peptidomics research demonstrates that these milk proteases produce specific peptides in healthy milk and continue to function within the infant's gastrointestinal tract. These findings suggest that milk proteases have an evolutionary function in aiding the infant's digestion or releasing functional peptides. In other words, the mother provides the infant with not only dietary proteins but also the means to digest them. However, proteolysis in the milk is controlled by a balance of protease inhibitors and protease activators so that only a small portion of milk proteins are digested within the mammary gland. This regulation presents a question: If proteolysis is beneficial to the infant, what benefits are gained by preventing complete proteolysis through the presence of protease inhibitors? In addition to summarizing what is known about milk proteolytic systems, we explore possible evolutionary explanations for this proteolytic balance.

C1 inhibitor function using contact-phase proteases as target: evaluation of an innovative assay

BACKGROUND

Controlling prekallikrein activation by C1 inhibitor (C1Inh) represents the most essential mechanism for angioedema patient protection. C1Inh function in the plasma is usually measured based on the residual activity of the C1s protease not involved in the pathological process. We have hereby proposed an alternative enzymatic measurement of C1Inh function based on contact-phase activation and correlation with angioedema diagnostic requirements.

METHODS

The contact phase was reconstituted using the purified components, with C1Inh standard or plasma sample. The kinetics of the amidase activity were monitored using Pro-Phe-Arg-pNA, independently of alpha2-macroglobulin. We prevented any interference from a possible high plasma kininogenase activity by preincubating the samples with protease inhibitor. Receiver operating characteristics (ROC) were used to calculate the assay's diagnostic performance.

RESULTS

The calibration curve was built using C1Inh standard (threshold limit 0.10 × 10(-3) U, i.e., 0.2 pmol), and C1Inh function was quantified in the sample, with a reference interval established based on healthy individuals (n = 281; men: 0.61-1.10 U/ml, median: 0.85 U/ml; women: 0.42-1.08 U/ml, median: 0.74 U/ml). The median values of female donors were lower than those of the others due to estrogen, yet C1Inh function remained within the reference interval. The ROC curve calculation provided the following optimum diagnostic cutoff values: women 0.36 U/ml (area under curve [AUC]: 0.99; sensitivity: 93.48%; specificity: 99.37%); and men 0.61 U/ml (AUC: 1; sensitivity: 100.0%; specificity: 100.0%).

CONCLUSION

The performance outcome provided features suitable for angioedema diagnostic or follow-up. Established by means of the kinin formation process, this assay should be preferred over the method based on a C1s protease target.

Recombinant C1-inhibitor: effects on coagulation and fibrinolysis in patients with hereditary angioedema

BACKGROUND

Recombinant human C1-inhibitor (rhC1INH; Ruconest®) has been developed for treatment of acute angioedema attacks in patients with hereditary angioedema (HAE) due to heterozygous deficiency of C1INH. Previous reports suggest that administration of plasma-derived C1INH products may be associated with an increased risk for thromboembolic complications.

OBJECTIVES

Our aim is to evaluate the effects of rhC1INH on coagulation and fibrinolysis in symptomatic HAE patients.

METHODS

Levels of various coagulation and fibrinolytic parameters were determined in pre- and post-exposure plasma samples from HAE patients included in a randomized clinical trial. Patients were treated with either saline, or 50 or 100 U/kg rhC1INH for an acute angioedema attack.

RESULTS

Prior to rhC1INH treatment, the majority of patients had low to normal activated partial thromboplastin times (aPTT) and increased levels of prothrombin fragment 1+2, thrombin-antithrombin complexes, D-dimers and plasmin-antiplasmin complexes, all of which indicate activation of both coagulation and fibrinolysis. Infusion of rhC1INH at doses up to 100 U/kg did not affect these parameters except for a dose-dependent prolongation of aPTT, confirming that rhC1INH is an inhibitor of the contact system, and that F1+2 levels decreased.

CONCLUSION

Coagulation and fibrinolytic systems are activated in HAE patients suffering from an acute angioedema attack. Treatment with rhC1INH at 50 or 100 U/kg had no effect on parameters reflecting activation of these systems except for a significant effect on aPTT, which likely reflects a pharmacodynamic effect of rhC1INH, and a reduction on plasma levels of the prothrombin activation fragment F1+2. We conclude that these results argue against a prothrombotic effect of treatment with this rhC1INH product in HAE patients.

Biochemical characterization of a novel high-affinity and specific plasma kallikrein inhibitor

BACKGROUND AND PURPOSE

Kallikrein acts on high molecular weight kininogen (HK) to generate HKa (cleaved HK) and bradykinin (BK). BK exerts its effects by binding to B(2) receptors. The activation of B(2) receptors leads to the formation of tissue plasminogen activator, nitric oxide (NO) and prostacyclin (PGI(2) ). An elevated kallikrein-dependent pathway has been linked to cardiovascular disease risk. The aim of this study was to investigate whether our novel plasma kallikrein inhibitor abolishes kallikrein-mediated generation of BK from HK and subsequent BK-induced NO and PGI(2) formation, thereby influencing endothelial pathophysiology during chronic inflammatory diseases.

EXPERIMENTAL APPROACH

Kinetic analysis was initially used to determine the potency of PF-04886847. Biochemical ligand binding assays, immunological methods and calcium flux studies were used to determine the selectivity of the kallikrein inhibitor. In addition, the effect of PF-04886847 on BK-induced relaxation of the rat aortic ring was determined in a model of lipopolysaccharide-induced tissue inflammation.

KEY RESULTS

Evidence was obtained in vitro and in situ, indicating that PF-04886847 is a potent and specific inhibitor of plasma kallikrein. PF-04886847 efficiently blocked calcium influx as well as NO and PGI(2) formation mediated through the BK-stimulated B(2) receptor signalling pathway. PF-04886847 blocked kallikrein-induced endothelial-dependent relaxation of isolated rat aortic rings pre-contracted with phenylephrine.

CONCLUSIONS AND IMPLICATIONS

PF-04886847 was shown to be the most potent small molecule inhibitor of plasma kallikrein yet described; it inhibited kallikrein in isolated aortic rings and cultured endothelial cells. Overall, our results indicate that PF-04886847 would be useful for the treatment of kallikrein-mediated inflammatory disorders.

Ecallantide for the treatment of hereditary angiodema in adults

Hereditary angioedema (HAE) is a clinical disorder characterized by a deficiency of C1 esterase inhibitor (C1-INH). HAE has traditionally been divided into two subtypes. Unique among the inherited deficiencies of the complement system, HAE Types I and II are inherited as an autosomal dominant disorder. The generation of an HAE attack is caused by the depletion and/or consumption of C1-inhibitor manifested as subcutaneous or submucosal edema of the upper airway, face, extremities, or gastrointestinal tract mediated by bradykinin. Attacks can be severe and potentially life-threatening, particularly with laryngeal involvement and treatment of acute attacks in the United States has been severely limited. In December 2009 the FDA approved ecallantide for the treatment of acute HAE attacks. Ecallantide is a small recombinant protein acting as a potent, specific and reversible inhibitor of plasma kallikrein which binds to plasma kallikrein blocking its binding site, directly inhibiting the conversion of high molecular weight kininogen to bradykinin. Administered subcutaneously, ecallantide was demonstrated in two clinical trials, EDEMA3 and EDEMA4, to decrease the length and severity of acute HAE attacks. Although there is a small risk for anaphylaxis, which limits home administration, ecallantide is a novel, safe, effective and alternative treatment for acute HAE attacks.

Interaction of high-molecular-weight kininogen with endothelial cell binding proteins suPAR, gC1qR and cytokeratin 1 determined by surface plasmon resonance (BiaCore)

The physiologic activation of the plasma kallikrein-kinin system requires the assembly of its constituents on a cell membrane. High- molecular-weight kininogen (HK) and cleaved HK (HKa) both interact with at least three endothelial cell binding proteins: urokinase plasminogen activator receptor (uPAR), globular C1q receptor (gC1qR,) and cytokeratin 1 (CK1). The affinity of HK and HKa for endothelial cells are KD=7-52 nM. The contribution of each protein is unknown. We examined the direct binding of HK and HKa to the soluble extracellular form of uPAR (suPAR), gC1qR and CK1 using surface plasmon resonance. Each binding protein linked to a CM-5 chip and the association, dissociation and KD (equilibrium constant) were measured. The interaction of HK and HKa with each binding protein was zinc-dependent. The affinity for HK and HKa was gC1qR>CK1>suPAR, indicating that gC1qR is dominant for binding. The affinity for HKa compared to HK was the same for gC1qR, 2.6-fold tighter for CK1 but 53-fold tighter for suPAR. Complex between binding proteins was only observed between gC1qR and CK1 indicating that a binary CK1-gC1qR complex can form independently of kininogen. Although suPAR has the weakest affinity of the three binding proteins, it is the only one that distinguished between HK and HKa. This finding indicates that uPAR may be a key membrane binding protein for differential binding and signalling between the cleaved and uncleaved forms of kininogen. The role of CK1 and gC1qR may be to initially bind HK to the membrane surface before productive cleavage to HKa.

Cinryze as the first approved C1 inhibitor in the USA for the treatment of hereditary angioedema: approval, efficacy and safety

Hereditary angioedema (HAE) is a clinical disorder characterized by a deficiency of C1 esterase inhibitor (C1-INH). HAE has traditionally been divided into two subtypes. Unique among the inherited deficiencies of the complement system, HAE Types I and II are inherited as an autosomal dominant disorder. The generation of an HAE attack is caused by the depletion and/or consumption of C1-inhibitor manifested as subcutaneous or submucosal edema of the upper airway, face, extremities, or gastrointestinal tract. Attacks can be severe and potentially life-threatening, particularly with laryngeal involvement. Despite the availability of C1-INH for the treatment of HAE since the 1980s in Europe and other countries, HAE treatment in the United States was limited to androgen therapy. The human plasma-derived C1 esterase inhibitor (Cinryze™), distributed by Lev Pharmaceuticals, was approved in October 2008 for the prevention of HAE attacks based on the results of a phase III clinical trial. This review aims to describe the history of C1-INH replacement in HAE as well as the pharmacology, efficacy and safety of C1-INH, concentrating on Cinryze as the first approved chronic replacement treatment for the prophylaxis of HAE attacks.

Human plasma kallikrein-kinin system: physiological and biochemical parameters

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

C1 inhibitor: just a serine protease inhibitor? New and old considerations on therapeutic applications of C1 inhibitor

C1 inhibitor is a potent anti-inflammatory protein as it is the major inhibitor of proteases of the contact and the complement systems. C1-inhibitor administration is an effective therapy in the treatment of patients with hereditary angioedema (HAE) who are genetically deficient in C1 inhibitor. Owing to its ability to modulate the contact and complement systems and the convincing safety profile, plasma-derived C1 inhibitor is an attractive therapeutic protein to treat inflammatory diseases other than HAE. In the present review we give an overview of the biology of C1 inhibitor and its use in HAE. Furthermore, we discuss C1 inhibitor as an experimental therapy in diseases such as sepsis and myocardial infarction.

New treatments addressing the pathophysiology of hereditary angioedema

Hereditary angioedema is a serious medical condition caused by a deficiency of C1-inhibitor. The condition is the result of a defect in the gene controlling the synthesis of C1-inhibitor, which regulates the activity of a number of plasma cascade systems. Although the prevalence of hereditary angioedema is low – between 1:10,000 to 1:50,000 – the condition can result in considerable pain, debilitation, reduced quality of life, and even death in those afflicted. Hereditary angioedema presents clinically as cutaneous swelling of the extremities, face, genitals, and trunk, or painful swelling of the gastrointestinal mucosa. Angioedema of the upper airways is extremely serious and has resulted in death by asphyxiation.

Subnormal levels of C1-inhibitor are associated with the inappropriate activation of a number of pathways – including, in particular, the complement and contact systems, and to some extent, the fibrinolysis and coagulation systems.

Current findings indicate bradykinin, a product of contact system activation, as the primary mediator of angioedema in patients with C1-inhibitor deficiency. However, other systems may play a role in bradykinin's rapid and excessive generation by depleting available levels of C1-inhibitor.

There are currently no effective therapies in the United States to treat acute attacks of hereditary angioedema, and currently available agents used to treat hereditary angioedema prophylactically are suboptimal. Five new agents are, however, in Phase III development. Three of these agents replace C1-inhibitor, directly addressing the underlying cause of hereditary angioedema and re-establishing regulatory control of all pathways and proteases involved in its pathogenesis. These agents include a nano-filtered C1-inhibitor replacement therapy, a pasteurized C1-inhibitor, and a recombinant C1-inhibitor isolated from the milk of transgenic rabbits. All C1-inhibitors are being investigated for acute angioedema attacks; the nano-filtered C1-inhibitor is also being investigated for prophylaxis of attacks. The other two agents, a kallikrein inhibitor and a bradykinin receptor-2 antagonist, target contact system components that are mediators of vascular permeability. These mediators are formed by contact system activation as a result of C1-inhibitor consumption.

The plasma kallikrein-kinin system and risk of cardiovascular disease in men

BACKGROUND

The plasma kallikrein-kinin system (PKKS) has been implicated in cardiovascular disease, but activation of the PKKS has not been directly probed in individuals at risk of coronary heart disease (CHD) or stroke.

OBJECTIVE

To determine the involvement of the PKKS, including factor XI, in cardiovascular disease occurring in a nested case-control study from the Second Northwick Park Heart Study (NPHS-II).

METHODS AND RESULTS

After a median follow-up of 10.7 years, 287 cases of CHD and stroke had been recorded and 542 age-matched controls were selected. When FXIIa-C1 esterase inhibitor (C1-inhibitor) concentrations were divided into tertiles (lowest tertile as reference), the odds ratios (ORs) at 95% CIs for CHD were 0.52 (0.34-0.80) in the middle tertile and 0.73 (0.49-1.09) in the highest tertile (P = 0.01 for the overall difference; P = 0.01 for CHD and stroke combined). For kallikrein-C1-inhibitor complexes, the ORs for stroke were 0.29 (0.12-0.72) and 0.67 (0.30-1.52) in the middle and high tertiles, respectively (P = 0.02). FXIIa-C1-inhibitor and kallikrein-C1-inhibitor complexes were negatively related to smoking and fibrinogen (P < 0.005). FXIa-inhibitor complexes correlated strongly with FXIIa-inhibitor complexes.

CONCLUSIONS

Lower levels of inhibitory complexes of the PKKS enzymes and particularly of FXIIa contribute to the risk of CHD and stroke in middle-aged men. This observation supports the involvement of the PKKS in atherothrombosis.

Suppression of complement regulatory protein C1 inhibitor in vascular endothelial activation by inhibiting vascular cell adhesion molecule-1 action

Increased expression of adhesion molecules by activated endothelium is a critical feature of vascular inflammation associated with the several diseases such as endotoxin shock and sepsis/septic shock. Our data demonstrated complement regulatory protein C1 inhibitor (C1INH) prevents endothelial cell injury. We hypothesized that C1INH has the ability of an anti-endothelial activation associated with suppression of expression of adhesion molecule(s). C1INH blocked leukocyte adhesion to endothelial cell monolayer in both static assay and flow conditions. In inflammatory condition, C1INH reduced vascular cell adhesion molecule (VCAM-1) expression associated with its cytoplasmic mRNA destabilization and nuclear transcription level. Studies exploring the underlying mechanism of C1INH-mediated suppression in VCAM-1 expression were related to reduction of NF-kappaB activation and nuclear translocation in an IkappaBalpha-dependent manner. The inhibitory effects were associated with reduction of inhibitor IkappaB kinase activity and stabilization of the NF-kappaB inhibitor IkappaB. These findings indicate a novel role for C1INH in inhibition of vascular endothelial activation. These observations could provide the basis for new therapeutic application of C1INH to target inflammatory processes in different pathologic situations.

Complement factor 1 inhibitor improves cardiopulmonary function in neonatal cardiopulmonary bypass

BACKGROUND

The inflammatory insult associated with cardiopulmonary bypass (CPB) continues to result in morbidity for neonates undergoing complex repair of congenital cardiac defects. Complement and contact activation are important mediating processes involved in this injury. Complement factor 1 esterase inhibitor (C1-inh), a natural inhibitor of complement, kallikrein, and coagulation pathways, may be decreased in children undergoing cardiac operations requiring CPB. We tested the hypothesis that C1-inh supplementation will ameliorate the cardiac and pulmonary dysfunction in a model of neonatal CPB.

METHODS

Fifty-two neonatal pigs were randomly assigned to receive 0 IU (n = 22), 500 IU (n = 15), 1,000 IU (n = 8), or 1,500 IU (n = 7) of C1-inh. Doses were delivered 5 minutes before starting 90 minutes of normothermic CPB. Pulmonary and cardiovascular measures were taken before and 5, 30, and 60 minutes after CPB.

RESULTS

Five animals did not survive CPB. The C1-inh concentration post-CPB increased monotonically with increasing dose (p < 0.001). Weight gain was significantly less in the 1,500 IU group (0.24 +/- 0.10 kg versus 0.38 +/- 0.09 kg, p = 0.001). Dynamic compliance increased with C1-inh dose from 0 to 500 IU by 23% +/- 4% (p < 0.001), but the increase leveled off at the higher doses. Alveolar-arterial O2 gradient decreased with C1-inh dose (p = 0.009). Time derivative of left ventricular pressure (dP/dt(max)) increased significantly with increasing dose (p = 0.016). At the highest dose of C1-inh, the time constant of isovolumic relaxation was increased (p = 0.018).

CONCLUSIONS

The C1-inh supplementation results in improved pulmonary and systolic cardiac function in a model of neonatal CPB. The negative effect on diastolic function requires further investigation.

The therapeutic potential of a kallikrein inhibitor for treating hereditary angioedema

Hereditary angioedema (HAE) manifests as intermittent, painful attacks of submucosal oedema affecting the larynx, gastrointestinal tract or limbs. Currently, acute treatment is available in Europe but not USA, and requires intravenous administration of a pooled blood product. HAE is most likely caused by dysinhibition of the contact cascade, resulting in overproduction of bradykinin. DX-88 (ecallantide, Dyax Corp.) is a highly specific recombinant plasma kallikrein inhibitor that halts the production of bradykinin and can be dosed subcutaneously. In a placebo-controlled Phase II trial in patients with HAE, DX-88 resulted in significant improvement in symptoms compared with placebo. A Phase III trial is ongoing. This review explains the pathophysiology of HAE and the mechanism by which DX-88, a non-intravenous, nonplasma-derived therapy, might improve the disease, and discusses the clinical course of HAE and available treatments. Finally, it explores the potential value and efficacy of DX-88 in treating HAE.

Mechanism of angioedema in first complement component inhibitor deficiency

Since shortly after the discovery that hereditary angioedema resulted from deficiency of first complement component (C1) inhibitor, the characterization of the mediator of angioedema has been a major goal. However, because C1 inhibitor regulates activation of both the contract and complement systems, identification of the mediator was not immediately accomplished. For a number of years, some studies appeared to indicate involvement of one system, whereas other studies suggested involvement of the other. However, the vast majority of the evidence accumulated over the past years indicates quite clearly that the major mediator is bradykinin. Therefore, unregulated contact system activation is the defect that leads directly to the development of angioedema.

Structure and Function of C1-Inhibitor

C1-INH belongs to the family of serpins. Structural studies have yielded a clear understanding of the biochemical principle underlying the functional activities of these proteins. Although the crystal structure of C1-INH has yet to be revealed, homology modeling has provided a three-dimensional model of the serpin part of C1-INH. This model has helped us understand the biochemical consequences of mutations of the C1-INH gene as they occur in patients who have HAE. The structure of the N-terminal domain of C1-INH remains unknown; however, this part of the molecule is unlikely to be important in the inhibitory activity of C1-INH toward its target proteases. Mutations in this part have not been described in patients who have HAE, except for a deletion containing two cysteine residues involved in the stabilization of the serpin domain. Recent studies suggest some anti-inflammatory functions for this N-terminal part, possibly explaining the effects of C1-INH in diseases other than HAE.

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.