Factor XII Contact Activation.

Contact activation is the surface-induced conversion of factor XII (FXII) zymogen to the serine protease FXIIa. Blood-circulating FXII binds to negatively charged surfaces and this contact to surfaces triggers a conformational change in the zymogen inducing autoactivation. Several surfaces that have the capacity for initiating FXII contact activation have been identified, including misfolded protein aggregates, collagen, nucleic acids, and platelet and microbial polyphosphate. Activated FXII initiates the proinflammatory kallikrein-kinin system and the intrinsic coagulation pathway, leading to formation of bradykinin and thrombin, respectively. FXII contact activation is well characterized in vitro and provides the mechanistic basis for the diagnostic clotting assay, activated partial thromboplastin time. However, only in the past decade has the critical role of FXII contact activation in pathological thrombosis been appreciated. While defective FXII contact activation provides thromboprotection, excess activation underlies the swelling disorder hereditary angioedema type III. This review provides an overview of the molecular basis of FXII contact activation and FXII contact activation-associated disease states.

Defective glycosylation of coagulation factor XII underlies hereditary angioedema type III.

Hereditary angioedema type III (HAEIII) is a rare inherited swelling disorder that is associated with point mutations in the gene encoding the plasma protease factor XII (FXII). Here, we demonstrate that HAEIII-associated mutant FXII, derived either from HAEIII patients or recombinantly produced, is defective in mucin-type Thr309-linked glycosylation. Loss of glycosylation led to increased contact-mediated autoactivation of zymogen FXII, resulting in excessive activation of the bradykinin-forming kallikrein-kinin pathway. In contrast, both FXII-driven coagulation and the ability of C1-esterase inhibitor to bind and inhibit activated FXII were not affected by the mutation. Intravital laser-scanning microscopy revealed that, compared with control animals, both F12-/- mice reconstituted with recombinant mutant forms of FXII and humanized HAEIII mouse models with inducible liver-specific expression of Thr309Lys-mutated FXII exhibited increased contact-driven microvascular leakage. An FXII-neutralizing antibody abolished bradykinin generation in HAEIII patient plasma and blunted edema in HAEIII mice. Together, the results of this study characterize the mechanism of HAEIII and establish FXII inhibition as a potential therapeutic strategy to interfere with excessive vascular leakage in HAEIII and potentially alleviate edema due to other causes.

Current pharmacotherapy of bradykinin-mediated angioedema.

INTRODUCTION: Bradykinin-mediated angioedema is characterized by subcutaneous and/or submucosal edema formation without wheals and pruritus. It is linked to bradykinin-enhanced vascular permeability and, therefore, it does not respond to conventional measures, but requires specific therapy. AREAS COVERED: This summary briefly reviews the different types of bradykinin-mediated angioedema and its remedies. Therapy focuses on relieving edema, as well as on decreasing its incidence and severity. The modes of the actions of attenuated androgens and antifibrinolytics are not precisely known - these agents have been introduced on an empirical basis. Contemporary treatments, by contrast, have been purposely developed to inhibit bradykinin. Most experience pertains to angioedema resulting from C1-inhibitor deficiency, and the controlled studies have focused on the hereditary form of this disease type (HAE). The pathomechanisms of HAE with normal C1-inhibitor activity, as well as of angiotensin-converting enzyme inhibitor-releated, and of non-histaminergic idiopathic sporadic angioedemas are largely unknown. Appropriate laboratory methods for the diagnosis, or specific interventions for the therapy of these conditions are not available or only available off-label. EXPERT OPINION: In this case, diagnosis and management are challenging. The range of targeted therapeutic options has increased in recent years and includes measures to handle emergencies, prevent edematous episodes and manage additional types of bradykinin-mediated angioedema.

HAE update: special considerations in the female patient with hereditary angioedema.

This review on hereditary angioedema (HAE) focuses on special topics regarding HAE in female patients. HAE is a bradykinin-mediated disorder, and the role of hormonal regulation of disease expression will be discussed focusing on the effect of estrogen on disease mechanism. The impact of exogenous estrogen on symptom exacerbation leads to special consideration regarding choice of contraceptives and safety of hormone replacement therapy. The effects of pregnancy and childbirth will be examined on the course of disease control. Unique considerations regarding therapeutic management for female HAE patients will be addressed, including the role of C1 inhibitor (C1-INH), ecallantide, and icatibant. Finally, this review will provide an overview of the more recently characterized HAE with normal C1-INH (HAE type III) that predominantly affects women and is in some cases associated with factor XII gene mutations.

Hereditary angioedema with normal C1-INH (HAE type III).

Hereditary angioedema (HAE) with normal C1 inhibitor (C1-INH), also known as HAE type III, is a familial condition only clinically recognized within the past three decades. Similar to HAE from C1-INH deficiency (HAE types I and II), affected individuals experience unpredictable angioedema episodes of the skin, gastrointestinal tract, and airway. Unique clinical features of HAE with normal C1-INH include the predominance of affected women, frequent exacerbation by estrogen, and a prominence of angioedema that involves the face and oropharynx. The underlying pathophysiology of HAE with normal C1-INH is poorly understood, but indirect evidence points to contact pathway dysregulation with bradykinin-mediated angioedema. Currently, evaluation is complicated by a lack of confirmatory laboratory testing such that clinical criteria must often be used to make the diagnosis of HAE with normal C1-INH. Factor XII mutations have been identified in only a minority of persons affected by HAE with normal C1-INH, limiting the utility of such analysis. To date, no controlled clinical studies have examined the efficacy of therapeutic agents for HAE with normal C1-INH, although published evidence supports frequent clinical benefit with medications shown effective in HAE due to C1-INH deficiency.

Clinical, biochemical, and genetic characterization of type III hereditary angioedema in 13 Northwest Spanish families.

BACKGROUND: A new variant of hereditary angioedema has been reported during the last decade. Three main characteristics distinguish it from classic hereditary angioedema: normal C1 inhibitor activity, predominance in women, and different genetic alterations. OBJECTIVE: To assess the symptoms, laboratory findings, and treatment of a population with type III hereditary angioedema from Northwest Spain. METHODS: We studied 29 patients (26 female and 3 male) from 13 different families. RESULTS: The 26 female patients showed a similar clinical pattern to the classic forms of hereditary angioedema, and 22 of these patients had the estrogen-dependent phenotype. Three patients had a negative family history, and 1 of the parents was confirmed as an asymptomatic carrier in 2 of them. All had functional C1 inhibitor activity within the normal range in periods without high estrogen levels, but during attacks (in female patients) and pregnancy, activity decreased to below 50%. One male patient had normal C1 inhibitor activity during attacks, and he was initially diagnosed as having idiopathic angioedema. The C4 and antigenic C1 inhibitor levels were always normal. All studied patients had the c.1032C>A, Thr309Lys mutation in the factor XII gene. The mutation was also found in asymptomatic relatives: 5 of 6 men studied and 1 of 8 women studied. CONCLUSION: Positive family history is a diagnosis criterion, but it could be lacking because there may be asymptomatic relatives, primarily males.