Enzymatic assays for the diagnosis of bradykinin-dependent angioedema

Contact System Activation and Bradykinin Generation in Angioedema: Laboratory Assessment and Biomarker Utilization

The role of contact system activation has been clearly established in the pathogenesis of hereditary angioedema due to C1 inhibitor deficiency (HAE-C1INH). C1 inhibitor (C1INH)-protease complexes, levels of functional C1INH, plasma kallikrein activation, and cleavage of high-molecular-weight kininogen have each been associated with disease activity. More recently, HAE with normal levels of C1INH (HAE-nl-C1INH) has been recognized. Six genetic mutations have been identified which are linked to HAE-nl-C1INH phenotypes. The majority of individuals with HAE-nl-C1INH fall into the unknown category. There is substantial evidence that bradykinin generation underlies the recurrent attacks of swelling in some of these cohorts.

Hereditary angioedema with normal C1 esterase inhibitor: Current paradigms and clinical dilemmas

Background: A diagnosis of hereditary angioedema (HAE) with normal C1 esterase inhibitor (HAE-nl-C1-INH) can be challenging and pharmacologic management is not well defined. Objective: The objective was to discuss practical considerations in the clinical management of HAE-nl-C1-INH by using illustrative clinical vignettes to highlight and/or address select challenges. Methods: This was a narrative review. Results: Symptoms of HAE-nl-C1-INH overlap with HAE types I and II; the heterogeneity of presentation and symptom burden are diagnostic challenges. A patient history, with particular attention to whether urticaria or other symptoms of mast cell mediator release are present, is important because such symptoms would strongly suggest a mast cell-mediated pathway. A family history of angioedema is informative but a lack thereof does not rule out diagnosis. Expected laboratory findings would be normal for C4, C1-INH level and function, and Complement 1q; a genetic mutational analysis may be helpful, but current assays do not include all known mutations; most cases are categorized as unknown. To align with guideline-directed treatment approaches, the following stepwise approach is suggested for suspected HAE-nl-C1-INH: (1) thoroughly investigate the possibility of response to histaminergic and/or mast cell-targeting treatments; (2) if patients with normal C4, C1-INH level and/or function fail adequate trials with histamine/mast cell-directed therapy or have a mutation that suggests bradykinin pathway involvement, follow HAE type I and II treatment guidelines. Response to medications approved for HAE types I/II provides compelling support for a high clinical suspicion of HAE-nl-C1-INH. De-labeling an HAE-nl-C1-INH diagnosis may be appropriate if the initial diagnosis was made without adequate evaluation or if new information and/or testing indicates that the patient does not actually have HAE. Conclusion: Key unmet needs in HAE-nl-C1-INH include lack of confirmatory biomarker(s) for diagnosis and lack of prospective controlled clinical studies of pharmacologic products in this patient population.

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.

A phase 2 open-label extension study of prekallikrein inhibition with donidalorsen for hereditary angioedema

BACKGROUND

Hereditary angioedema (HAE) is a potentially fatal disease characterized by unpredictable, recurrent, often disabling swelling attacks. In a randomized phase 2 study, donidalorsen reduced HAE attack frequency and improved patient quality-of-life (ISIS721744-CS2, NCT04030598). We report the 2-year interim analysis of the phase 2 open-label extension (OLE) study (ISIS 721744-CS3, NCT04307381).

METHODS

In the OLE, the on-treatment study period consisted of fixed (weeks 1-13, donidalorsen 80 mg subcutaneously every 4 weeks [Q4W]) and flexible (weeks 17-105, donidalorsen 80 mg Q4W, 80 mg every 8 weeks [Q8W], or 100 mg Q4W) dosing periods. The primary outcome was incidence and severity of treatment-emergent adverse events (TEAEs). The secondary outcomes included efficacy, pharmacodynamic, and quality-of-life assessments.

RESULTS

Seventeen patients continued in the OLE study. No serious TEAEs or TEAEs leading to treatment discontinuation were reported. Mean monthly HAE attack rate was 96% lower than the study run-in baseline rate (mean, 0.06/month; 95% confidence interval [CI], 0.02-0.10; median, 0.04 on-treatment vs. mean, 2.70/month; 95% CI, 1.94-3.46; median, 2.29 at baseline). Mean monthly attack rate for Q8W dosing (n = 8) was 0.29 (range, 0.0-1.7; 95% CI, -0.21 to 0.79; median, 0.00). Mean plasma prekallikrein and D-dimer concentrations decreased, and Angioedema Quality of Life Questionnaire total score improved from baseline to week 105 with donidalorsen.

CONCLUSION

The 2-year interim results of this phase 2 OLE study of donidalorsen in patients with HAE demonstrated no new safety signals; donidalorsen was well tolerated. There was durable efficacy with a 96% reduction in HAE attacks.

Editorial: Kinin 2022 Meeting, Annecy, France

The Kinin 2022 meeting took place at the Imperial Palace, Annecy, France, from 5-8 June 2022 [...].

Picomolar Sensitivity Analysis of Multiple Bradykinin-Related Peptides in the Blood Plasma of Patients With Hereditary Angioedema in Remission: A Pilot Study

Background

Hereditary angioedema (HAE) is a rare autosomal dominant disease; the most well understood forms concern the haplodeficiency of C1 esterase inhibitor (C1INH) and a gain of function mutation of factor XII (FXII). The acute forms of these conditions are mediated by an excessive bradykinin (BK) formation by plasma kallikrein.

Methods

A validated LC-MS/MS platform of picomolar sensitivity developed for the analysis of eleven bradykinin-related peptides was applied to the plasma of HAE-C1INH and HAE-FXII sampled during remission.

Results

In HAE-C1INH plasma, the concentrations of the relatively stable BK1−5 fragment (mean ± S.E.M.: 12.0 ± 4.2 pmol/L), of BK2−9 (0.7 ± 0.2 pmol/L) and of the sums of BK and its tested fragments (18.0 ± 6.4 pmol/L) are significantly greater than those recorded in the plasma of healthy volunteers (1.9 ± 0.6, 0.03 ± 0.03 and 4.3 ± 0.8 pmol/L, respectively), consistent with the previous evidence of permanent plasma kallikrein activity in this disease. Kinin levels in the plasma of HAE-FXII patients did not differ from controls, suggesting that triggering factors for contact system activation are not active during remission.

Conclusion

BK1−5, BK2−9 and the sum of BK and its fragments determined by the sensitive LC-MS/MS technique are proposed as potential biomarkers of HAE-C1INH in remission while this was not applicable to HAE-FXII patients.

Guidelines for management of hereditary angioedema: What is new? What is missing?

Background: Hereditary angioedema is an autosomal dominant disease that presents with recurrent episodic swelling of the submucosal and/or subcutaneous tissues of the cutaneous, gastrointestinal, and respiratory systems. Evaluation and treatment guidelines have been published nationally and internationally to aid the treating provider. Methods: A review of the most cited and most recent updated guidelines was undertaken to review key points and to explore real-world feasibility of incorporating them into clinical practice. The International World Allergy Organization/European Academy of Allergy and Clinical Immunology (WAO/EAACI) Guideline for the Management of Angioedema - The 2017 Revision and Update, and the consensus reports from the Hereditary Angioedema International Working Group, the Joint Task Force on Practice Parameters focused practice parameter update, and the most recently updated US HAEA Medical Advisory Board 2020 Guidelines for the Management of Hereditary Angioedema were reviewed and summarized. Results: Key points that have been consistent throughout the guidelines include recommendations for evaluation and classification of hereditary angioedema as well as evidence-based guidelines for treatment. Further attention is required on the evaluation and continuous assessment of the burden of illness and quality of life (QoL). Conclusion: The guidelines for management of hereditary angioedema provide a framework for the clinician. However, the physician-patient dialog with regard to the patient disease experience, which includes attack frequency, severity, and Qol, must be continually assessed.

Angioedema Without Wheals: Challenges in Laboratorial Diagnosis

Angioedema is a prevailing symptom in different diseases, frequently occurring in the presence of urticaria. Recurrent angioedema without urticaria (AE) can be hereditary (HAE) and acquired (AAE), and several subtypes can be distinguished, although clinical presentation is quite similar in some of them. They present with subcutaneous and mucosal swellings, affecting extremities, face, genitals, bowels, and upper airways. AE is commonly misdiagnosed due to restricted access and availability of appropriate laboratorial tests. HAE with C1 inhibitor defect is associated with quantitative and/or functional deficiency. Although bradykinin-mediated disease results mainly from disturbance in the kallikrein–kinin system, traditionally complement evaluation has been used for diagnosis. Diagnosis is established by nephelometry, turbidimetry, or radial immunodiffusion for quantitative measurement of C1 inhibitor, and chromogenic assay or ELISA has been used for functional C1-INH analysis. Wrong handling of the samples can lead to misdiagnosis and, consequently, mistaken inappropriate approaches. Dried blood spot (DBS) tests have been used for decades in newborn screening for certain metabolic diseases, and there has been growing interest in their use for other congenital conditions. Recently, DBS is now proposed as an efficient tool to diagnose HAE with C1 inhibitor deficiency, and its use would improve the access to outbound areas and family members. Regarding HAE with normal C1 inhibitor, complement assays’ results are normal and the genetic sequencing of target genes, such as exon 9 of F12 and PLG, is the only available method. New methods to measure cleaved high-molecular-weight kininogen and activated plasma kallikrein have emerged as potential biochemical tests to identify bradykinin-mediated angioedema. Validated biomarkers of kallikrein–kinin system activation could be helpful in differentiating mechanisms of angioedema. Our aim is to focus on the capability to differentiate histaminergic AE from bradykinin-mediated AE. In addition, we will describe the challenges developing specific tests like direct bradykinin measurements. The need for quality tests to improve the diagnosis is well represented by the variability of results in functional assays.

Biomarkers in Hereditary Angioedema

A biomarker is a defined characteristic measured as an indicator of normal, biologic, pathogenic processes, or biological responses to an exposure or intervention. Diagnostic biomarkers are used to detect a disease or a subtype of a disease; monitoring biomarkers are measured serially to assess a medical condition; response biomarkers are used to check biologic response following a medical intervention; predictive biomarkers are used to identify patients who are more likely to respond to a medical intervention; and prognostic biomarkers are used to assess the future likelihood of a clinical event. Although biomarkers have been extensively investigated and validated in many diseases and pathologies, very few are currently useful for the diagnosis, evaluation of disease activity, and treatment of hereditary angioedema (HAE). Pathophysiologic pathways involved in HAE reveal a plethora of molecules from the complement, coagulation, and fibrinolysis systems or from the vascular endothelium, which may serve as biomarkers. The most promising candidates, together with their laboratory readout systems, should be evaluated with regard to their analytical and clinical validity and utility. To be highly specific, such biomarkers should be linked to the pathomechanisms of HAE, particularly the bradykinin-generating cascade. Additionally, major advances in high-throughput omics-based technologies may facilitate the discovery of new candidate biomarkers in the future. This review will cover the existing as well as future potential biomarkers that will support the diagnosis, monitor disease activity, and can be used to assess the efficacy of new avenues of therapy of HAE and other forms of angioedema.

The FXII c.-4T>C Polymorphism as a Disease Modifier in Patients With Hereditary Angioedema Due to the FXII p.Thr328Lys Variant

Background

Hereditary angioedema due to the Thr328Lys variant in the coagulation factor XII (HAE-FXII) affects mainly women in whom the symptomatology is dependent on high estrogen levels. Clinical variability and incomplete penetrance are challenging features that hinder the diagnosis and management of HAE-FXII. The c.-4T>C Kozak polymorphism is the only common variation accounting for FXII plasma levels and was previously shown to modify the course of HAE due to C1-Inhibitor deficiency.

Objectives

To assess the influence of the c.-4T>C polymorphism on disease expression in 39 Spanish HAE-FXII index patients.

Methods

The c.-4T>C polymorphism was sequenced by the standard Sanger method, and HAE severity was calculated according to the score by Cumming et al. (2003) The activation of the contact system was quantified by the kallikrein-like activity of plasma in chromogenic assays upon activation with high-molecular-weight dextran sulfate.

Results

The c.-4CC genotype was overrepresented in the studied cohort: 82% were CC-homozygous (expected frequency = 59%) and 18% were CT-heterozygous (expected frequency = 39%) (p = 0.001). Patients with a c.-4CC genotype exhibited higher kallikrein-like activity (0.9659 ± 0.1136) than those with a c.-4TC genotype (0.7645 ± 0.1235) (p = 0.024) or healthy donors. Moreover, the polymorphism influenced HAE-FXII severity score (c.-4CC = 4.43 ± 2.28 vs c.-4TC = 2.0 ± 1.15; p = 0.006) but not the degree of estrogen dependence or time until remission.

Conclusion

The c.-4T>C polymorphism is overrepresented in a Spanish HAE-FXII cohort and significantly influences the degree of contact system activation and the clinical severity of the disease.

Biological therapy in hereditary angioedema: transformation of a rare disease

Introduction: Hereditary angioedema, a disabling condition, with high mortality when untreated, is caused by C1 inhibitor deficiency and other regulatory disorders of bradykinin production or metabolism. This review covers the remarkable progress made in biological therapies for this rare disorder.Areas covered: Over the past 10 years, several evidence-based parenteral treatments have been licensed, including two plasma-derived C1 inhibitor replacement therapies and one recombinant C1 inhibitor replacement for acute treatment of angioedema attacks and synthetic peptides for inhibition of kallikrein or bradykinin B2 receptors, with oral small molecule treatments currently in clinical trial. Moreover, recent advances in prophylaxis by subcutaneous C1 inhibitor to restore near-normal plasma function or by humanized antibody inhibition of kallikrein have resulted in freedom from symptoms for a high proportion of those treated.Expert opinion: This plethora of treatment possibilities has come about as a result of recent scientific advances. Collaboration between patient groups, basic and clinical scientists, physicians, nurses, and the pharmaceutical industry has underpinned this translation of basic science into treatments and protocols. These in their turn have brought huge improvements in prognosis, quality of life and economic productivity to patients, their families, and the societies in which they live.

IONIS-PKKRx a Novel Antisense Inhibitor of Prekallikrein and Bradykinin Production

Kallikrein is the key contact system mediator responsible for the conversion of high-molecular-weight kininogen into the inflammatory vasodilator peptide bradykinin, a process regulated by C1-esterase inhibitor (C1-INH). In hereditary angioedema (HAE), genetic mutations result in deficient or dysfunctional C1-INH and dysregulation of the contact system leading to recurrent, sometimes fatal, angioedema attacks. IONIS-PKK_Rx is a second-generation 2'-O-(2-methoxyethyl)-modified chimeric antisense oligonucleotide, designed to bind and selectively reduce prekallikrein (PKK) mRNA in the liver. IONIS-PKK_Rx demonstrated dose-dependent reduction of human prekallikrein hepatic mRNA and plasma protein in transgenic mice and dose- and time-dependent reductions of plasma PKK in Cynomolgus monkeys. Similar dose-dependent reductions of plasma PKK levels were observed in healthy human volunteers accompanied by decreases in bradykinin generation capacity with an acceptable safety and tolerability profile. These results highlight a novel and specific approach to target PKK for the treatment of HAE and other diseases involving contact system activation and overproduction of bradykinin.

The diagnosis of hereditary angioedema with C1 inhibitor deficiency: a survey of Canadian physicians and laboratories

Background

Hereditary angioedema due to C1 inhibitor deficiency (C1-INH-HAE) is an autosomal dominant disease resulting in random and unpredictable attacks of swelling. The swelling in C1-INH-HAE is a result of impaired regulation of bradykinin production. The fact that the array of tests needed to diagnose HAE is not always available to the treating physicians is challenging for them and their patients.

Methods

The data for this article were extracted from two distinct surveys. The first survey was conducted among HAE treating physicians and aimed to determine the availability and utilization of the various assays performed to help the diagnosis of C1-INH-HAE. The second survey was conducted with the various laboratories across Canada that performs the assays used in the diagnosis of HAE. The aim of this survey was to determine the availability and profile of the various assays used in the diagnosis of C1-INH-HAE in Canada, thereby ultimately bringing a rational basis for the biological testing.

Results

C1-INH functional assay was widely available in Canada (93%), but was only offered by a small numbers of hospitals meaning that there could be longer delays in the analysis of these samples that may explain why the physicians expressed a lower level of confidence in this assay (59%). Antigenic C1-INH was available to the vast majority of the physicians treating C1-INH-HAE (93%) and was considered reliable by 96% of the respondents. Antigenic C4 was found available to all Canadian physicians and, although with limited specificity, was considered very reliable by all the participants. This study revealed that 81% of physicians were able to order the antigenic C1q and the confidence in this assay was moderate (70%). Concerning genetic testing, the survey revealed that most of the CHAEN members never had to or couldn't order this test.

Conclusion

This study highlights the need for improved education and knowledge exchange, about biological assays available to Canadian physicians and their performance in proper diagnosis of C1-INH-HAE to improve confidence and access to relevant tests.

Factor XII-Driven Inflammatory Reactions with Implications for Anaphylaxis

Anaphylaxis is a life-threatening allergic reaction. It is triggered by the release of pro-inflammatory cytokines and mediators from mast cells and basophils in response to immunologic or non-immunologic mechanisms. Mediators that are released upon mast cell activation include the highly sulfated polysaccharide and inorganic polymer heparin and polyphosphate (polyP), respectively. Heparin and polyP supply a negative surface for factor XII (FXII) activation, a serine protease that drives contact system-mediated coagulation and inflammation. Activation of the FXII substrate plasma kallikrein leads to further activation of zymogen FXII and triggers the pro-inflammatory kallikrein-kinin system that results in the release of the mediator bradykinin (BK). The severity of anaphylaxis is correlated with the intensity of contact system activation, the magnitude of mast cell activation, and BK formation. The main inhibitor of the complement system, C1 esterase inhibitor, potently interferes with FXII activity, indicating a meaningful cross-link between complement and kallikrein-kinin systems. Deficiency in a functional C1 esterase inhibitor leads to a severe swelling disorder called hereditary angioedema (HAE). The significance of FXII in these disorders highlights the importance of studying how these processes are integrated and can be therapeutically targeted. In this review, we focus on how FXII integrates with inflammation and the complement system to cause anaphylaxis and HAE as well as highlight current diagnosis and treatments of BK-related diseases.

Associations of the Polymorphisms in DHRS4, SERPING1, and APOR Genes with Postmortem pH in Berkshire Pigs

Postmortem pH is a main factor influencing the meat quality in pigs. This study investigated the association of postmortem pH with single-nucleotide polymorphisms (SNPs) in the fourth member of the short-chain dehydrogenase/reductase family (DHRS4), the first member of serpin peptidase inhibitor, clade G (complement inhibitor) (SERPING1), and the apolipoprotein R precursor (APOR) genes in Berkshire pigs. The study included 437 pigs, and genotyping was conducted using the GoldenGate Assay (Illumina, San Diego, CA, USA). DHRS4, SERPING1, and APOR polymorphisms were significantly associated with pH₄₅ or pH₂₄ (p < 0.05). SERPING1 was also statistically significantly associated with water holding capacity (p < 0.05), which is closely associated with postmortem pH. These results suggest that SNPs in the DHRS4, SERPING1, and APOR genes have potential for use as genetic markers for the meat quality in pigs.

Hereditary C1 inhibitor deficiency is associated with high spontaneous amidase activity

BACKGROUND

Angioedema diagnosis classically targets the complement system (via C1 inhibitor (C1Inh) function and antigenic C4 level) and contact phase activation (via amidase activity). Bradykinin is responsible for angioedema attacks and is produced from contact phase activation secondary to failed C1Inh control.

OBJECTIVE

We aimed to compare the diagnostic performances of spontaneous amidase activity and antigenic C4 level in C1Inh hereditary angioedema (C1Inh-HAE) patients.

METHODS

Samples from 185 C1Inh-HAE patients (81 men, 104 women; confirmed by SERPING1 gene mutations) and from 99 blood donors (50 men, 49 women) were tested for C1Inh function, antigenic C4 level and spontaneous amidase activity.

RESULTS

In the C1Inh-HAE group, antigenic C4 level was decreased (n=135) and amidase activity was increased (n=181). Receiver operating characteristic analyses showed higher diagnostic performance values for the spontaneous amidase assay compared to those of antigenic C4.

CONCLUSION

The spontaneous amidase activity assay should replace antigenic C4 level testing and should be tested alongside the C1Inh function for both AE screening and follow up of HAE patients.

HAE Pathophysiology and Underlying Mechanisms

Remarkable progress in understanding the pathophysiology and underlying mechanisms of hereditary angioedema has led to the development of effective treatment for this disorder. Progress in three separate areas has catalyzed our understanding of hereditary angioedema. The first is the recognition that HAE type I and type II result from a deficiency in the plasma level of functional C1 inhibitor. This observation has led to a detailed understanding of the SERPING1 mutations responsible for this deficiency as well as the molecular regulation of C1 inhibitor expression and function. The second is that the fundamental cause of swelling is enhanced contact system activation leading to increased generation of bradykinin. Substantial progress has been made in defining the parameters regulating bradykinin generation and catabolism as well as the receptors that transduce the biologic effects of kinins. The third is the understanding that tissue swelling in hereditary angioedema primarily involves the function of endothelial cell adherens junctions. This knowledge is driving increased attention to the role of endothelial biology in determining disease activity in hereditary angioedema. While there has been considerable progress made, large gaps still remain in our knowledge. Important areas that remain poorly understood include the factors that lead to very low plasma functional C1 inhibitor levels, the triggers of contact system activation in hereditary angioedema, and the role of the bradykinin B1 receptor. The phenotypic variability of hereditary angioedema has been extensively documented but never understood. The mechanisms discussed in this chapter likely contribute to this variability. Future progress in understanding these mechanisms should provide new means to improve the diagnosis and treatment of hereditary angioedema.

Angioedema Phenotypes: Disease Expression and Classification

Due to marked heterogeneity of clinical presentations, comprehensive knowledge of angioedema phenotypes is crucial for correct diagnosis and choosing the appropriate therapeutic approach. One of the ways to a meaningful clinical distinction can be made between forms of angioedema occurring "with or without wheals." Angioedema with wheals (rash) is a hallmark of urticaria, either acute or chronic, spontaneous or inducible. Angioedema without wheals may still be manifested in about 10 % of patients with urticaria, but it may also occur as a separate entity. Several classifications of angioedema as part of urticaria were published over time, while a latest one, released in 2014 (HAWK group consensus, see below), provided a classification of all forms of "angioedema without wheals" distinct from urticaria, which will be the focus of the present review. At this time, the HAWK consensus classification is the best in terms of covering the pathophysiology, mediators involved, angioedema triggers, and clinical expression. According to this classification, three types of hereditary angioedema (genetic C1-INH deficiency, normal C1-INH with factor XII mutations, and unknown origin) and four types of acquired angioedema (C1-INH deficiency, related to ACE inhibitors intake, idiopathic histaminergic, and idiopathic non-histaminergic) are presented. We will review the distinctive clinical features of each phenotype in details.

"Nuts and Bolts" of Laboratory Evaluation of Angioedema

Angioedema, as a distinct disease entity, often becomes a clinical challenge for physicians, because it may cause a life-threatening condition, whereas prompt and accurate laboratory diagnostics may not be available. Although the bedside diagnosis needs to be established based on clinical symptoms and signs, family history, and the therapeutic response, later, laboratory tests are available. Currently, only for five out of the nine different types of angioedema can be diagnosed by laboratory testing, and these occur only in a minority of the patient population. Hereditary angioedema with C1-inhibitor (C1-INH) deficiency type I can be diagnosed by the low C1-INH function and concentration, whereas in type II, C1-INH function is low, but its concentration is normal or even elevated. C1q concentration is normal in both forms. Acquired angioedema with C1-INH deficiency type I is characterized by the low C1-INH function and concentration; however, C1q concentration is also low, and autoantibodies against C1-INH cannot be detected. Complement profile of acquired angioedema with C1-INH deficiency type II is similar to that of type I, but in this form, autoantibodies against C1-INH are present. Hereditary angioedema due to a mutation of the coagulation factor XII can be diagnosed exclusively by mutation analysis of FXII gene. Diagnostic metrics are not available for idiopathic histaminergic acquired angioedema, idiopathic non-histaminergic acquired angioedema, acquired angioedema related to angiotensin-converting enzyme inhibitor, and hereditary angioedema of unknown origin; these angioedemas can be diagnosed by medical and family history, clinical symptoms, and therapeutic response and by excluding the forms previously described. Several potential biomarkers of angioedema are used to date only in research. In the future, they could be utilized into the clinical practice to improve the differential diagnosis, therapy, as well as the prognosis of angioedema.

Kininogen Cleavage Assay: Diagnostic Assistance for Kinin-Mediated Angioedema Conditions

Background

Angioedema without wheals (AE) is a symptom characterised by localised episodes of oedema presumably caused by kinin release from kininogen cleavage. It can result from a hereditary deficiency in C1 Inhibitor (C1Inh), but it can present with normal level of C1Inh. These forms are typically difficult to diagnose although enhanced kinin production is suspected or demonstrated in some cases.

Objectives

We wanted to investigate bradykinin overproduction in all AE condition with normal C1Inh, excluding cases with enhanced kinin catabolism, and to propose this parameter as a disease biomarker.

Methods

We retrospectively investigated high molecular weight kininogen (HK) cleavage pattern, using gel electrophoresis and immunorevelation. Plasma samples were drawn using the same standardised procedure from blood donors or AE patients with normal C1Inh conditions, normal kinin catabolism, and without prophylaxis.

Results

Circulating native HK plasma concentrations were similar in the healthy men (interquartile range: 98–175μg/mL, n = 51) and in healthy women (90–176μg/mL, n = 74), while HK cleavage was lower (p<0.001) in men (0–5%) than women (3–9%). Patients exhibited lower native HK concentration (p<10⁻⁴; 21–117μg/mL, n = 31 for men; 0–84μg/mL, n = 41 for women) and higher HK cleavage (p<10⁻⁴; 10–30% and 14–89%, respectively) than healthy donors. Pathological thresholds were set at: <72μg/mL native HK, >14.4% HK cleavage for men; <38μg/mL; native HK, >33.0% HK cleavage for women, with >98% specificity achieved for all parameters. In plasma from patients undergoing recovery two months after oestrogen/progestin combination withdrawal (n = 13) or two weeks after AE attack (n = 2), HK cleavage was not fully restored, suggesting its use as a post-attack assay.

Conclusion

As a diagnostic tool, HK cleavage can offer physicians supportive arguments for kinin production in suspected AE cases and improve patient follow-up in clinical trials or prophylactic management.

Hereditary and acquired C1-inhibitor-dependent angioedema: from pathophysiology to treatment

Uncontrolled generation of bradykinin (BK) due to insufficient levels of protease inhibitors controlling contact phase (CP) activation, increased activity of CP proteins, and/or inadequate degradation of BK into inactive peptides increases vascular permeability via BK-receptor 2 (BKR2) and results in subcutaneous and submucosal edema formation. Hereditary and acquired angioedema due to C1-inhibitor deficiency (C1-INH-HAE and -AAE) are diseases characterized by serious and potentially fatal attacks of subcutaneous and submucosal edemas of upper airways, facial structures, abdomen, and extremities, due to inadequate control of BK generation. A decreased activity of C1-inhibitor is the hallmark of C1-INH-HAE (types 1 and 2) due to a mutation in the C1-inhibitor gene, whereas the deficiency in C1-inhibitor in C1-INH-AAE is the result of autoimmune phenomena. In HAE with normal C1-inhibitor, a significant percentage of patients have an increased activity of factor XIIa due to a FXII mutation (FXII-HAE). Treatment of C1-inhibitor-dependent angioedema focuses on restoring control of BK generation by inhibition of CP proteases by correcting the balance between CP inhibitors and BK breakdown or by inhibition of BK-mediated effects at the BKR2 on endothelial cells. This review will address the pathophysiology, clinical picture, diagnosis and available treatment in C1-inhibitor-dependent angioedema focusing on BK-release and its regulation. Key Messages Inadequate control of bradykinin formation results in the formation of characteristic subcutaneous and submucosal edemas of the skin, upper airways, facial structures, abdomen and extremities as seen in hereditary and acquired C1-inhibitor-dependent angioedema. Diagnosis of hereditary and acquired C1-inhibitor-dependent angioedema may be troublesome as illustrated by the fact that there is a significant delay in diagnosis; a certain grade of suspicion is therefore crucial for quick diagnosis. Submucosal edema formation in hereditary and acquired C1-inhibitor-dependent angioedema is potentially life threatening and can occur at any age. To date effective therapies for acute and prophylactic treatment are available.

Presentation, diagnosis and treatment of angioedema without wheals: a retrospective analysis of a cohort of 1058 patients

BACKGROUND

The first classification of angioedema without wheals was recently reported and comprises different forms of the disease distinguished by aetiology, mediator of oedema and inheritance.

METHODS

In total, 1725 consecutive patients with angioedema without wheals were examined at our centre between 1993 and 2012. We excluded from the analysis 667 patients because of incomplete data or because angioedema was related to a specific factor.

RESULTS

According to the new classification of angioedema, the 1058 patients included in this analysis were diagnosed with hereditary (HAE; n = 377) or acquired angioedema (AAE; n = 681). The former group included HAE with C1-inhibitor (C1-INH) deficiency (C1-INH-HAE; n = 353) and HAE with normal C1-INH levels (n = 24), of which six had a factor XII mutation (FXII-HAE) and 18 had disease of unknown origin (U-HAE). The AAE group included disease with C1-INH deficiency (C1-INH-AAE; n = 49), AAE related to angiotensin-converting enzyme inhibitor treatment (n = 183), idiopathic histaminergic (IH-AAE; n = 379) and idiopathic nonhistaminergic angioedema (InH-AAE; n = 70). We compared hereditary and AAE with uncertain aetiopathogenesis: the FXII-HAE and U-HAE groups pooled (FXII/U-HAE) versus InH-AAE. The median age at onset of FXII/U-HAE and InH-AAE was 26 and 38 years, respectively. In addition, 56% of patients with FXII/U-HAE and 81% of those with InH-AAE reported more than five attacks per year (median duration of 48 h). The location of angioedema in patients with FXII/U-HAE versus those with InH-AAE was the following: face, 70% versus 86%; tongue, oral cavity or larynx, 55% versus 68%; limbs, 70% versus 56%; and gastrointestinal mucosa, 50% versus 20%. Prophylaxis with tranexamic acid was effective in all six patients with U-HAE and in 37 of 38 with InH-AAE who were started on this treatment.

CONCLUSION

Our findings in this cohort of patients with angioedema provide new information on the clinical characteristics, diagnosis and treatment of this disease.

Characterization of patients with angioedema without wheals: the importance of F12 gene screening

Sporadic and familiar forms of non-histaminergic angioedema and normal C1 inhibitor encompass a group of disorders possibly caused by bradikinin. We aimed to study the subgroups of hereditary angioedema with FXII mutation (FXII-HAE), unknown genetic defect (U-HAE) and idiopathic non-histaminergic acquired angioedema (InH-AAE). We screened the F12 locus in our cohort and delineated the clinical, laboratory and genetic features. Four families carried the p.Thr309Lys mutation in F12 gene. Haplotyping confirmed the hypothesis of a common founder. Six families were affected by U-HAE and 13 patients by sporadic InH-AAE. C4 levels were significantly lower in FXII-HAE than in InH-AAE. In the FXII-HAE group, none had attacks exclusively in high estrogenic states; acute attacks were treated with icatibant. Prophylaxis with tranexamic acid reduced the attack frequency in most patients. Our study provides new data on the diagnosis, clinical features and treatment of non-histaminergic angioedema, underlying the role of the screening for F12 mutations.

Distinct conditions support a novel classification for bradykinin-mediated angio-oedema

BACKGROUND

Angio-oedema (AO) can be attributable to bradykinin (BK) accumulation, as is the case for prototypical hereditary AO (HAO) due to C1 inhibitor (C1-INH) deficiency. However, our clinical experience in a reference centre has shown that some patients display a clinical history suggestive of HAO, but exhibit normal C1-INH function, have no mutation in the causative genes associated with HAO (SERPING1, F12), and report no intake of drugs known to promote AO.

OBJECTIVE

We sought to determine the frequency and distribution of different AO subtypes suspected to be BK-mediated AO (BK-AO) and defined by clinical, history and biological criteria (enzyme activities implicated in BK formation and catabolism).

METHODS

The files of all patients referred to our centre for suspected BK-AO were retrospectively analysed.

RESULTS

The distribution of patients (n = 162) was 16 and 4% with a hereditary deficiency of C1-INH or a gain of factor XII function, respectively, 29% with iatrogenic BK-AO, 21% with non-iatrogenic defective kininase activity and 30% with idiopathic increased kinin formation.

CONCLUSION

BK-AO may be caused by multiple inherited or acquired factors triggering BK accumulation. Therefore, we propose a novel typology for BK-AO based on the imbalance of production/catabolism of BK.

[Biological investigation of kinin-mediated angioedema]

Kinin-mediated angioedema results from accumulation of kinins, vasoactive and vasopermeant peptides, on the vascular endothelium. The disease is characterized by sudden episodes of swelling in the subcutaneous and submucosal tissues; the edema may occur spontaneously or it may be precipitated by triggering factors such as physical or emotional stress, or certain medicines. The characterization of kinin formation and catabolism systems helps improve knowledge of the aetiopathogenic mechanisms involved and provides the basis for classification of kinin-mediated angioedema conditions; thus, we may distinguish between angioedema with C1 inhibitor deficiency, whether inherited or acquired, and angioedema with normal C1 inhibitor activity, associated with increased kinin-forming activity or deficiency in kinin catabolism enzymes. In support of the clinical diagnosis, the physician may request laboratory investigation for a functional and molecular definition of the disease. Laboratory diagnosis is based on the characterization of: (1) kinin production control by C1 inhibitor investigation (function, antigen levels and circulating species); (2) kinin production (kininogenase activity, kininogen cleavage species); and (3) kinin catabolism enzymes (aminopeptidase P, carboxypeptidase N, angiotensin-I converting enzyme and dipeptidyl peptidase IV). An abnormal biological phenotype is supported by examination of susceptibility genes (SERPING1, F12 and XPNPEP2) and mutation segregation in the families.

[Hereditary angioedema biological diagnosis]

C1 inhibitor (C1 Inh) activity is an essential parameter for kinins angioedema (AE) diagnosis either hereditary or acquired or sporadic, it is analysed on plasma exclusively. Hereditary AE with C1 Inh functional deficiency is associated with alterations of the SERPING1 gene. Hereditary AE with normal C1 Inh (HAE nC1 Inh) is combined with F12 gene mutations, it is coding for Factor XII whose activity is controlled by C1 Inh, they are found in about 5% of HAE nC1 Inh cases. Every loss of C1 Inh activity must be taken as anormal by clinicians even for women with oral oestroprogestatives, it would be confirmed by the presence of cleaved C1 Inh. The kinins (primarily bradykinin) are the mediators responsible for local increase of vascular permeability. Bradykinin is released from high MW kininogen (HK) during the contact system activation. Plasma proteases mainly support this proteolytic activity controlled by C1 Inh. Family of a patient diagnosed with HAE must be studied, symptomatic as asymptomatic members indeed clinical symptoms regularly emerge very late in the life.

Hereditary angioedema with F12 mutation: factors modifying the clinical phenotype

BACKGROUND

Hereditary angioedema (HAE) with normal C1 inhibitor (C1Inh) associated with the c.983C>A and c.983C>G mutations of the F12 gene (FXII-HAE) is a rare condition, and presents with highly variable clinical expression. On the basis of data gathered from a large carrier cohort, we assessed the modifiers affecting the clinical phenotype.

METHODS

We analyzed clinical and biological data recorded from 118 mutation carriers (80 symptomatic and 38 asymptomatic), 58 noncarrier relatives from 40 families, and 200 healthy donors. Disease severity was scored in relation to frequency and location of edema, as well as age at disease onset. To predict FXII-HAE disease severity, we analyzed the biological phenotype [C1Inh, C4, spontaneous amidase, angiotensin-I-converting enzyme (ACE), aminopeptidase P (APP), and carboxypeptidase N/M (CPN)] by means of logistic regression (Akaike information criterion) and odds ratio (OR).

RESULTS

Meaningful variables contributed to FXII-HAE, with the kinin catabolism enzymes ACE and CPN exhibiting a significant inverse relationship with disease severity (OR = 0.36, 95% CI 0.23-0.59, P < 0.001; OR = 0.58, 95% CI 0.36-0.91, P < 0.05, respectively). CPN activities were 37.5 (28.5-41.3) nmol/ml/min and 38.5 (32.8-45.6) for FXII-HAE asymptomatic and symptomatic carriers, respectively, and 37.9 (30.5-43.7) nmol/ml/min for noncarriers. Angiotensin-I-converting enzyme activities were 58 (44-76) and 49 (35-59) nmol/ml/min for FXII-HAE asymptomatic and symptomatic carriers, respectively, and 56 (49-66) nmol/ml/min for noncarriers.

CONCLUSIONS

The FXII-HAE is associated with modifiers, for example kinin catabolism enzymes, ACE and CPN, different from those recognized in HAE with C1Inh deficiency.

Management of angioedema without urticaria in the emergency department

Angioedema refers to a localized, transient swelling of the deep skin layers or the upper respiratory or gastrointestinal mucosa. It develops as a result of mainly two different vasoactive peptides, histamine or bradykinin. Pathophysiology, as well as treatment, is different in each case; nevertheless, the resulting signs and symptoms may be similar and difficult to distinguish. Angioedema may occur at any location. When the affected area involves the upper respiratory tract, both forms of angioedema can lead to an imminent upper airway obstruction and a life-threatening emergency. Emergency physicians must have a basic understanding of the pathophysiology underlying this process. Angioedema evaluation in the emergency department (ED) should aim to distinguish between histamine- and bradykinin-induced angioedema, in order to provide appropriate treatment to patients. However, diagnostic methods are not available at the ED setting, neither to confirm one mechanism or the other, nor to identify a cause. For this reason, the management of angioedema should rely on clinical data depending on the particular features of the episode and the patient in each case. The history-taking should be addressed to identify a possible etiology or triggering agent, recording complete information for an ulterior diagnostic study in the outpatient clinic. It is mandatory quickly to recognize and treat a potential life-threatening upper airway obstruction or anaphylaxis. This review focuses on the underlying mechanisms and management of histamine- and bradykinin-induced angioedema at the emergency department and provides an update on the currently available treatments.