The bradykinin-forming cascade in anaphylaxis and ACE-inhibitor induced angioedema/airway obstruction

Anaphylaxis is a potentially life-threatening multi-system allergic reaction to a biological trigger resulting in the release of potent inflammatory mediators from mast cells and basophils and causing symptoms in at least two organ systems that generally include skin, lungs, heart, or gastrointestinal tract in any combination. One exception is profound hypotension as an isolated symptom. There are two types of triggers of anaphylaxis: immunologic and non-Immunologic. Immunologic anaphylaxis is initiated when a foreign antigen directly binds to IgE expressed on mast cells or basophils and induces the release of histamine and other inflammatory substances resulting in vasodilation, vascular leakage, decreased peripheral vascular resistance, and heart muscle depression. If left untreated, death by shock (profound hypotension) or asphyxiation (airway obstruction) can occur. The non-immunologic pathway, on the other hand, can be initiated in many ways. A foreign substance can directly bind to receptors of mast cells and basophils leading to degranulation. There can be immune complex activation of the classical complement cascade with the release of anaphylatoxins C3a and C5a with subsequent recruitment of mast cells and basophils. Finally, hyperosmolar contrast agents can cause blood cell lysis, enzyme release, and complement activation, resulting in anaphylactoid (anaphylactic-like) symptoms. In this report we emphasize the recruitment of the bradykinin-forming cascade in mast cell dependent anaphylactic reactions as a potential mediator of severe hypotension, or airway compromise (asthma, laryngeal edema). We also consider airway obstruction due to inhibition of angiotensin converting enzyme with a diminished rate of endogenous bradykinin metabolism, leading not only to laryngeal edema, but massive tongue swelling with aspiration of secretions.

A Comprehensive Management Approach in Pediatric and Adolescent Patients With Hereditary Angioedema

Hereditary angioedema (HAE) is a rare autosomal-dominant disorder; most cases are characterized by low plasma levels of C1 esterase inhibitor (C1-INH). Clinical manifestations of HAE due to C1-INH deficiency include unpredictable, acute, recurrent episodes of nonpruritic swelling that can affect the face, trunk, limbs, and the respiratory, gastrointestinal, and genitourinary tracts. Attacks can be disfiguring, disabling, painful, and even life-threatening if laryngeal swelling occurs. Symptoms of HAE generally manifest in childhood. Effective medications are available and approved to treat HAE in children. However, evidence informing use of these medications in pediatric clinical practice is limited. Hereditary angioedema management plans are critical to optimize outcomes and should address on-demand treatment for acute attacks and plans to prevent potentially fatal laryngeal attacks. The plan should also comprise a holistic approach to address nonclinical aspects of HAE, including quality of life (QoL) and psychological issues. This article provides an overview of HAE management principles that health care providers can apply to treat pediatric patients to improve their QoL.

The complex role of kininogens in hereditary angioedema

Human high molecular weight kininogen (HK) is the substrate from which bradykinin is released as a result of activation of the plasma “contact” system, a cascade that includes the intrinsic coagulation pathway, and a fibrinolytic pathway leading to the conversion of plasminogen to plasmin. Its distinction from low molecular weight kininogen (LK) was first made clear in studies of bovine plasma. While early studies did suggest two kininogens in human plasma also, their distinction became clear when plasma deficient in HK or both HK and LK were discovered. The light chain of HK is distinct and has the site of interaction with negatively charged surfaces (domain 5) plus a 6th domain that binds either prekallikrein or factor XI. HK is a cofactor for multiple enzymatic reactions that relate to the light chain binding properties. It augments the rate of conversion of prekallikrein to kallikrein and is essential for the activation of factor XI. It indirectly augments the “feedback” activation of factor XII by plasma kallikrein. Thus, HK deficiency has abnormalities of intrinsic coagulation and fibrinolysis akin to that of factor XII deficiency in addition to the inability to produce bradykinin by factor XII-dependent reactions. The contact cascade binds to vascular endothelial cells and HK is a critical binding factor with binding sites within domains 3 and 5. Prekallikrein (or factor XI) is attached to HK and is brought to the surface. The endothelial cell also secretes proteins that interact with the HK-prekallikrein complex resulting in kallikrein formation. These have been identified to be heat shock protein 90 (HSP 90) and prolylcarboxypeptidase. Cell release of urokinase plasminogen activator stimulates fibrinolysis. There are now 6 types of HAE with normal C1 inhibitors. One of them has a mutated kininogen but the mechanism for overproduction (presumed) of bradykinin has not yet been determined. A second has a mutation involving sulfation of proteoglycans which may lead to augmented bradykinin formation employing the cell surface reactions noted above.

The international WAO/EAACI guideline for the management of hereditary angioedema – The 2021 revision and update

Hereditary Angioedema (HAE) is a rare and disabling disease for which early diagnosis and effective therapy are critical. This revision and update of the global WAO/EAACI guideline on the diagnosis and management of HAE provides up-to-date guidance for the management of HAE. For this update and revision of the guideline, an international panel of experts reviewed the existing evidence, developed 28 recommendations, and established consensus by an online DELPHI process. The goal of these recommendations and guideline is to help physicians and their patients in making rational decisions in the management of HAE with deficient C1-inhibitor (type 1) and HAE with dysfunctional C1-inhibitor (type 2), by providing guidance on common and important clinical issues, such as: 1) How should HAE be diagnosed? 2) When should HAE patients receive prophylactic on top of on-demand treatment and what treatments should be used? 3) What are the goals of treatment? 4) Should HAE management be different for special HAE patient groups such as children or pregnant/breast feeding women? 5) How should HAE patients monitor their disease activity, impact, and control? It is also the intention of this guideline to help establish global standards for the management of HAE and to encourage and facilitate the use of recommended diagnostics and therapies for all patients.

SARS-CoV-2 Exacerbates COVID-19 Pathology Through Activation of the Complement and Kinin Systems

Infection with SARS-CoV-2 triggers the simultaneous activation of innate inflammatory pathways including the complement system and the kallikrein-kinin system (KKS) generating in the process potent vasoactive peptides that contribute to severe acute respiratory syndrome (SARS) and multi-organ failure. The genome of SARS-CoV-2 encodes four major structural proteins - the spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and the envelope (E) protein. However, the role of these proteins in either binding to or activation of the complement system and/or the KKS is still incompletely understood. In these studies, we used: solid phase ELISA, hemolytic assay and surface plasmon resonance (SPR) techniques to examine if recombinant proteins corresponding to S1, N, M and E: (a) bind to C1q, gC1qR, FXII and high molecular weight kininogen (HK), and (b) activate complement and/or the KKS. Our data show that the viral proteins: (a) bind C1q and activate the classical pathway of complement, (b) bind FXII and HK, and activate the KKS in normal human plasma to generate bradykinin and (c) bind to gC1qR, the receptor for the globular heads of C1q (gC1q) which in turn could serve as a platform for the activation of both the complement system and KKS. Collectively, our data indicate that the SARS-CoV-2 viral particle can independently activate major innate inflammatory pathways for maximal damage and efficiency. Therefore, if efficient therapeutic modalities for the treatment of COVID-19 are to be designed, a strategy that includes blockade of the four major structural proteins may provide the best option.

gC1qR Antibody Can Modulate Endothelial Cell Permeability in Angioedema

Angioedema is characterized by swelling of the skin or mucous membranes. Overproduction of the vasodilator bradykinin (BK) is an important contributor to the disease pathology, which causes rapid increase in vascular permeability. BK formation on endothelial cells results from high molecular weight kininogen (HK) interacting with gC1qR, the receptor for the globular heads of C1q, the first component of the classical pathway of complement. Endothelial cells are sensitive to blood-flow-induced shear stress and it has been shown that shear stress can modulate gC1qR expression. This study aimed to determine the following: (1) how BK or angioedema patients' (HAE) plasma affected endothelial cell permeability and gC1qR expression under shear stress, and (2) if monoclonal antibody (mAb) 74.5.2, which recognizes the HK binding site on gC1qR, had an inhibitory effect in HK binding to endothelial cells. Human dermal microvascular endothelial cells (HDMECs) grown on Transwell inserts were exposed to shear stress in the presence of HAE patients' plasma. Endothelial cell permeability was measured using FITC-conjugated bovine serum albumin. gC1qR expression and HK binding to endothelial cell surface was measured using solid-phase ELISA. Cell morphology was quantified using immunofluorescence microscopy. The results demonstrated that BK at 1 µg/mL, but not HAE patients' plasma and/or shear stress, caused significant increases in HDMEC permeability. The mAb 74.5.2 could effectively inhibit HK binding to recombinant gC1qR, and reduce HAE patients' plasma-induced HDMEC permeability change. These results suggested that monoclonal antibody to gC1qR, i.e., 74.5.2, could be potentially used as an effective therapeutic reagent to prevent angioedema.

Biologics for the Use in Chronic Spontaneous Urticaria: When and Which

Guidelines for the treatment of chronic spontaneous urticaria (CSU) recommend the use of the IgE-targeted biologic omalizumab in patients with antihistamine-refractory disease. The rationale for this is supported by the key role of IgE and its high-affinity receptor, FcεRI, in the degranulation of skin mast cells that drives the development of the signs and symptoms of CSU, itchy wheals, and angioedema. Here, we review the current understanding of the pathogenesis of CSU and its autoimmune endotypes. We describe the mechanisms of action of omalizumab, the only biologic currently approved for CSU, its efficacy and ways to improve it, biomarkers for treatment response, and strategies for its discontinuation. We provide information on the effects of the off-label use, in CSU, of biologics licensed for the treatment of other diseases, including dupilumab, benralizumab, mepolizumab, reslizumab, and secukinumab. Finally, we discuss targets for novel biologics and where we stand with their clinical development. These include IgE/ligelizumab, IgE/GI-310, thymic stromal lymphopoietin/tezepelumab, C5a receptor/avdoralimab, sialic acid-binding Ig-like lectin 8/lirentelimab, CD200R/LY3454738, and KIT/CDX-0159. Our aim is to provide updated information and guidance on the use of biologics in the treatment of patients with CSU, now and in the near future.

The Pathogenesis of Chronic Spontaneous Urticaria: The Role of Infiltrating Cells

Chronic spontaneous urticaria is characterized by a perivascular non-necrotizing cellular infiltrate around small venules of the skin. It consists primarily of CD4(+) lymphocytes, a prominence of the T helper (Th)2 subtype but also Th1 cells, with Th17 cell-derived cytokines elevated in plasma. There are also neutrophils, eosinophils, basophils, and monocytes. Chemokines derived from mast cells and activated endothelial cells drive the process. Although the role of the cellular infiltrate has not previously been addressed, each constituent can contribute to the overall pathogenesis. It is of interest that CSU responds to corticosteroid, yet, short-term steroids do not affect autoimmunity or degranulation of mast cells, and act on margination of cells along the endothelium and chemotaxis to enter the surrounding dermis. In this review, we address each cell's contribution to the overall inflammatory response, as it is currently understood, with a view toward development of therapeutic options that impede the function of critical cells and/or their secretory products.

Hereditary angioedema: Investigational therapies and future research

The future therapies for hereditary angioedema will likely involve the development of oral agents as alternatives to parenteral administration of drugs, specific targeting of proteins and/or enzymes that are not yet possible (e.g., factor XIIa), new agents that target the β₂ receptor with sustained action properties, testing of products to determine whether the β₁ receptor contributes significantly to attacks of angioedema, disrupting protein synthesis by using RNA technology as an alternative to enzyme inhibition, and, finally, gene therapy to attempt to cure the disease. Complete inhibition of attacks may well require sustained blood levels of C1 inhibitor that exceed 85% of normal, and it may be possible to delete the prekallikrein gene (analogous to familial prekallikrein deficiency), which is the one factor that might alleviate bradykinin formation, even by factor XII-independent initiating mechanisms, with the possible exception of Mannose Associated Serine Protease 1 (MASP-1) cleavage of high molecular weight kininogen (HK). Deletion of the light chain of high-molecular-weight kininogen would eliminate all possibilities for bradykinin formation, except tissue kallikrein cleavage of low-molecular-weight kininogen to support normal physiologic function to at least 50%.

Protease activity in single-chain prekallikrein

Prekallikrein (PK) is the precursor of the trypsin-like plasma protease kallikrein (PKa), which cleaves kininogens to release bradykinin and converts the protease precursor factor XII (FXII) to the enzyme FXIIa. PK and FXII undergo reciprocal conversion to their active forms (PKa and FXIIa) by a process that is accelerated by a variety of biological and artificial surfaces. The surface-mediated process is referred to as contact activation. Previously, we showed that FXII expresses a low level of proteolytic activity (independently of FXIIa) that may initiate reciprocal activation with PK. The current study was undertaken to determine whether PK expresses similar activity. Recombinant PK that cannot be converted to PKa was prepared by replacing Arg371 with alanine at the activation cleavage site (PK-R371A, or single-chain PK). Despite being constrained to the single-chain precursor form, PK-R371A cleaves high-molecular-weight kininogen (HK) to release bradykinin with a catalytic efficiency ∼1500-fold lower than that of kallikrein cleavage of HK. In the presence of a surface, PK-R371A converts FXII to FXIIa with a specific activity ∼4 orders of magnitude lower than for PKa cleavage of FXII. These results support the notion that activity intrinsic to PK and FXII can initiate reciprocal activation of FXII and PK in solution or on a surface. The findings are consistent with the hypothesis that the putative zymogens of many trypsin-like proteases are actually active proteases, explaining their capacity to undergo processes such as autoactivation and to initiate enzyme cascades.

Chronic Spontaneous Urticaria: The Devil's Itch

Chronic urticaria is defined as the presence of urticaria for a period exceeding 6 weeks, assuming symptoms for most days of the week. It is divided into chronic inducible urticarias and chronic spontaneous urticaria, previously termed chronic idiopathic urticaria. The latter designation emphasizes that patients can experience urticaria independent of any exogenous stimulus even if one can define circumstances that may worsen symptoms. A search for such an external "cause" is fruitless because the underlying abnormality is "intrinsic," whether it is autoimmune, or some unknown process. Approximately 40% of patients with chronic spontaneous urticaria report accompanying episodes of angioedema, whereas 10% have angioedema as their primary manifestation. In most cases, it is a self-limiting disorder, persisting for 2 to 5 years in most cases, although 20% of patients suffer for more than 5 years. The treatment that has evolved is largely empiric, based on double-blind, placebo-controlled studies whenever possible, but is not yet targeted to any particular pathogenic mechanism. In this article, we review the current status regarding pathogenesis, discuss the diagnostic workup, and update the approach to treatment including consideration of published guidelines, our own experience, and guideline updates that are being prepared.

Diagnosis, pathogenesis, and treatment of chronic spontaneous urticaria

BACKGROUND

Chronic Spontaneous Urticaria (CSU) is an endogenous disorder that is strongly associated with autoimmunity, particularly with immunoglobulin G (IgG) antibody to the alpha subunit of the IgE receptor seen in 35-40% of patients. Basophils and cutaneous mast cells can be activated and lead to a late-phase-like perivascular infiltration about small venules and hive formation.

METHODS

Review of current literature.

RESULTS

Antibody to thyroid antigens are seen in 25% of patients; a small fraction of these may be clinically hypothyroid (Hashimoto's Thyroiditis). Forty percent of patients have angioedema, but not laryngeal edema. Therapy typically begins with second-generation antihistamines (H1 receptor blockers) up to four times a day. The failure rate is substantial, and estimates vary from 25% to 50%. The drug of choice for antihistamine resistant cases is omalizumab, at 300 mg/month, which is effective in 70% of patients. H-2-antagonists and leucotriene antagonists are no longer recommended because the literature does not support additional efficacy beyond blockage of H-1 receptors. For patients unresponsive to antihistamines and omalizumab, cyclosporine is recommended next. This is similarly effective in 65-70% of patients; however, assessment of blood pressure and renal function need to be followed every 4-6 weeks. Corticosteroid should not be employed chronically; however, a brief course of 3-10 days can be used acutely for severe exacerbations. Other agents, such as dapsone, sulfasalazine, or hydroxychloroquin, can be tried when the aforementioned medications fail, but the results are unpredictable because they have not been shown to have efficacy beyond the placebo effect (25-30%), and have not been studied in patients for whom the aforementioned approach i.e. antihistamines, omalizumab, and cyclosporine has failed.

CONCLUSION

High dose antihistamines, omalizumab and cyclosporine (in that order) are effective and recommended for therapy of CUS, an inflammatory skin disorder associated with autoimmunity in 45% of patients.

The Search for Biomarkers in Hereditary Angioedema

The unpredictable nature of attacks of tissue swelling in hereditary angioedema requires the identification of reliable biomarkers to monitor disease activity as well as response to therapy. At present, one can assess a C4 level (by ELISA) to assist in diagnosis but neither C4 nor C1 inhibitor levels reflect clinical course or prognosis. We will here review a collection of plasma proteins involved in blood coagulation, fibrinolysis, and innate immunity (Figure 1). A main focus is those proteins that are key to the formation of bradykinin (BK); namely, factor XII, plasma prekallikrein/kallikrein, high-molecular weight kininogen, and BK itself since overproduction of BK is key to the disease. Considerations include new approaches to measurement of active enzymes, ELISA methods that may supersede SDS gel analysis of bond cleavages, and examples of changes outside the BK cascade that may reflect when, where, and how an attack of swelling is initiated. We will discuss their usefulness as biomarker candidates, with pros and cons, and compare the analytical methods that are being developed to measure their levels or activity.

The complement and contact activation systems: partnership in pathogenesis beyond angioedema

The blood plasma contains four biologically important proteolytic cascades, which probably evolved from the same ancestral gene. This in part may explain why each cascade has very similar "initiating trigger" followed by sequential and cascade-like downstream enzymatic activation pattern. The four cascades are: the complement system, the blood clotting cascade, the fibrinolytic system, and the kallikrein-kinin system. Although much has been written about the interplay between all these enzymatic cascades, the cross-talk between the complement and the kinin generating systems has become particularly relevant as this interaction results in the generation of nascent molecules that have significant impact in various inflammatory diseases including angioedema and cancer. In this review, we will focus on the consequences of the interplay between the two systems by highlighting the role of a novel molecular link called gC1qR. Although this protein was first identified as a receptor for C1q, it is now recognized as a multiligand binding cellular protein, which serves not only as C1q receptor, but also as high affinity (K_D  ≤ 0.8 nM) binding site for both high molecular weight kininogen (HK) and factor XII (FXII). At inflammatory sites, where atherogenic factors such as immune complexes and/or pathogens can activate the endothelial cell into a procoagulant and proinflammatory surface, the two pathways are activated to generate vasoactive peptides that contribute in various ways to the inflammatory processes associated with numerous diseases. More importantly, since recent observations strongly suggest an important role for both pathways in cancer, we will focus on how a growing tumor cluster can employ the byproducts derived from the two activation systems to ensure not only its survival and growth, but also its escape into distal sites of colonization.

Omalizumab substantially improves dermatology-related quality of life in patients with chronic spontaneous urticaria

Background

Chronic spontaneous/idiopathic urticaria (CSU/CIU) has substantial detrimental effects on health‐related quality of life (HRQoL) with an effect comparable to or worse than many other skin diseases.

Objective

To assess the effect of omalizumab on CSU patients' HRQoL, measured by the Dermatology Life Quality Index (DLQI) in three phase III studies ASTERIA I, ASTERIA II and GLACIAL.

Methods

A post hoc analysis examined changes in DLQI scores, distribution of patients across DLQI bands and the proportion reaching minimal clinically important difference (MCID) following omalizumab vs. placebo.

Results

Omalizumab 300 mg significantly improved total DLQI scores vs. placebo, with a mean decrease from baseline to week 12 of −10.3 vs. −6.1 (P < 0.0001) in ASTERIA I, −10.2 vs. −6.1 (P = 0.0004) in ASTERIA II and −9.7 vs. −5.1 (P < 0.0001) in GLACIAL. A significant shift from high disease impact on life at baseline towards less impact at week 12 was seen with omalizumab 300 mg vs. placebo (P < 0.001; all studies). The proportion of patients where change in mean total DLQI score from baseline to week 12 reached an MCID of ≥4 was 74.1%, 76.0% and 77.2% in ASTERIA I, II and GLACIAL, respectively (P < 0.01; all studies).

Limitations

Maximum duration of omalizumab treatment was 24 weeks.

Conclusion

This additional analysis assessed the impact of CSU and benefit of treatment with omalizumab by exploring different facets of DLQI data by treatment arm at multiple assessment points. The original aspects of analysis included applying the concept of the recently validated score for the MCID of the DLQI, changes in DLQI domain scores and in the distribution of subjects based on validated total DLQI score bands. It showed consistently that omalizumab provides significant and clinically relevant improvements in many aspects of HRQoL that are important to patients with CSU. These results contribute to a better understanding of the impact of CSU and its treatment on patients and can support clinical decision‐making in routine medical practice.

Why a registry of Chronic Urticaria (CUR) is needed

Chronic urticaria (CU) has a major effect on patients’ quality of life. While there have been progressive advances regarding its pathogenesis and treatment, much remains to be done.

Registries of other chronic non-communicable diseases have shown many benefits, such as additional basic knowledge and management approaches to diabetes mellitus. Standards of care as well as diagnostic approaches can be elaborated and compared from different sites, using validated instruments. Registries in allergic diseases are also becoming well recognized, and the first registry on CU, accessible from SLaai’s webpage, includes parameters for identification, evaluation and management. In our vision, informatics strategies have the potential to improve care for chronic illnesses such as CU. The registry represents a valid instrument from which to obtain a sufficient sample size for epidemiological studies and/or clinical research planning, including feasibility and potential enrollment. It can also provide invaluable data for adapting guidelines to local populations, as well as diagnostic approaches and cost-effective interventions in the context of organizational efforts to improve patient care.

Chronic Spontaneous Urticaria: Pathogenesis and Treatment Considerations

The treatment of chronic spontaneous urticaria begins with antihistamines; however, the dose required typically exceeds that recommended for allergic rhinitis. Second-generation, relatively non-sedating H₁-receptor blockers are typically employed up to 4 times a day. First-generation antihistamines, such as hydroxyzine or diphenhydramine (Atarax or Benadryl), were employed similarly in the past. Should high-dose antihistamines fail to control symptoms (at least 50%), omalizumab at 300 mg/month is the next step. This is effective in 70% of antihistamine-refractory patients. H₂-receptor blockers and leukotriene antagonists are no longer recommended; they add little and the literature does not support significant efficacy. For those patients who are unresponsive to both antihistamines and omalizumab, cyclosporine is recommended next. This is similarly effective in 65%–70% of patients; however, care is needed regarding possible side-effects on blood pressure and renal function. Corticosteroids should not be employed chronically due to cumulative toxicity that is dose and time dependent. Brief courses of steroid e.g., 3–10 days can be employed for severe exacerbations, but should be an infrequent occurrence. Finally, other agents, such as dapsone or sulfasalazine, can be tried for those patients unresponsive to antihistamines, omalizumab, and cyclosporine.

Deficiency of plasminogen activator inhibitor 2 in plasma of patients with hereditary angioedema with normal C1 inhibitor levels

BACKGROUND

Hereditary angioedema with normal C1 inhibitor levels (HAE-N) is associated with a Factor XII mutation in 30% of subjects; however, the role of this mutation in the pathogenesis of angioedema is unclear.

OBJECTIVE

We sought evidence of abnormalities in the pathways of bradykinin formation and bradykinin degradation in the plasma of patients with HAE-N both with and without the mutation.

METHODS

Bradykinin was added to plasma, and its rate of degradation was measured by using ELISA. Plasma autoactivation was assessed by using a chromogenic assay of kallikrein formation. Plasminogen activator inhibitors (PAIs) 1 and 2 were also measured by means of ELISA.

RESULTS

PAI-1 levels varied from 0.1 to 4.5 ng/mL (mean, 2.4 ng/mL) in 23 control subjects, from 0.0 to 2 ng/mL (mean, 0.54 ng/mL) in patients with HAE-N with a Factor XII mutation (12 samples), and from 0.0 to 3.7 ng/mL (mean, 1.03 ng/mL) in patients with HAE-N without a Factor XII mutation (11 samples). PAI-2 levels varied from 25 to 87 ng/mL (mean, 53.8 ng/mL) in control subjects and were 0 to 25 ng/mL (mean, 4.3 ng/mL) in patients with HAE-N with or without the Factor XII mutation. Autoactivation at a 1:2 dilution was abnormally high in 8 of 17 patients with HAE-N (4 in each subcategory) and could be corrected by supplemental C1 inhibitor in 4 of them. Bradykinin degradation was markedly abnormal in 1 of 23 patients with HAE-N and normal in the remaining 22 patients.

CONCLUSIONS

Bradykinin degradation was normal in all but 1 of 23 patients with HAE-N studied. By contrast, there was a marked abnormality in PAI-2 levels in patients with HAE-N that is not seen in patients with C1 inhibitor deficiency. PAI-1 levels varied considerably, but a statistically significant difference was not seen. A link between excessive fibrinolysis and bradykinin generation that is estrogen dependent is suggested.

Similar Efficacy with Omalizumab in Chronic Idiopathic/Spontaneous Urticaria Despite Different Background Therapy

BACKGROUND

Data from the 3 omalizumab pivotal trials in patients with chronic idiopathic urticaria/chronic spontaneous urticaria (CIU/CSU) represent the largest database of patients reported to date with refractory disease (omalizumab, n = 733; placebo, n = 242).

OBJECTIVE

The objective of this study was to compare results from ASTERIA I and II, which included only approved doses of H1-antihistamine as background therapy based on regulatory authority requirements, to those from GLACIAL, which permitted higher doses of H1-antihistamines as well as other types of background therapy, in a post hoc analysis.

METHODS

Efficacy data from the placebo, omalizumab 150-mg, and omalizumab 300-mg treatment arms of ASTERIA I and II were pooled and analyzed (n = 162 and n = 160, respectively). The 300-mg treatment arm analyses were compared with the analysis of data from GLACIAL (n = 252) using analysis of covariance models. The key efficacy endpoint was change from baseline to week 12 in mean weekly itch severity score (ISS); other endpoints were also evaluated. Safety data were pooled from all 3 studies.

RESULTS

Mean ISS was significantly reduced from baseline at week 12 in the pooled ASTERIA I and II omalizumab 150- and 300-mg treatment arms and in the GLACIAL omalizumab 300-mg arm. The weekly ISS reduction magnitude at week 12 was similar between the omalizumab 300-mg groups in the ASTERIA I and II pooled and GLACIAL studies. Similar treatment effect sizes were observed across multiple endpoints. Omalizumab was well tolerated and the adverse-event profile was similar regardless of background therapy for CIU/CSU. The overall safety profile was generally consistent with omalizumab therapy in allergic asthma.

CONCLUSION

Omalizumab 300 mg was safe and effective in reducing CIU/CSU symptoms regardless of background therapy.

Neurotropin promotes NGF signaling through interaction of GM1 ganglioside with Trk neurotrophin receptor in PC12 cells

Activation of the high-affinity nerve growth factor (NGF) receptor Trk occurs through multiple processes consisted of translocation and clustering within the plasma membrane lipid rafts, dimerization and autophosphorylation. Here we found that a nonprotein extract of inflamed rabbit skin inoculated with vaccinia virus (Neurotropin(®)) enhanced efficiency of NGF signaling. In rat pheochromocytoma PC12 cells overexpressing Trk (PCtrk cells), Neurotropin augmented insufficient neurite outgrowth observed at suboptimal concentration of NGF (2ng/mL) in a manner depending on Trk kinase activity. Cellular exposure to Neurotropin resulted in an accumulation of Trk-GM1 complexes without affecting dimerization or phosphorylation states of Trk. Following NGF stimulation, Neurotropin significantly facilitated the time course of NGF-induced Trk autophosphorylation. These observations provide a unique mechanism controlling efficiency of NGF signaling, and raise the therapeutic potential of Neurotropin for various neurological conditions associated with neurotrophin dysfunction.

The thrombogenicity of C1 esterase inhibitor (human): review of the evidence

Thromboembolic events associated with human plasma-derived C1 esterase inhibitor (C1-INH) use in patients with hereditary angioedema (HAE) have been reported in the U.S. Food and Drug Administration (FDA) Adverse Event Reporting System database. The purpose of this article is to review and assess the strength of available evidence regarding the thrombogenicity of human plasma-derived C1-INH. A PubMed search was conducted of English language articles from January 1990 to December 2013 reporting the thrombogenicity of C1-INH. Original research articles were selected if the following criteria were met: (1) C1-INH was the focus of the study and (2) the authors addressed the pro- or antithrombotic potential of C1-INH. Additional articles on the clinical use of C1-INH in disease states other than HAE were obtained using reference lists of selected articles. Pivotal studies and prescribing information for C1-INH products were also reviewed. Limited animal and clinical data suggest that C1-INH, particularly at high doses of up to 500 U/kg (compared with the U.S. FDA-approved 20-U/kg dose), may be prothrombotic. In contrast, C1-INH has been used in some patients with myocardial infarction, ischemic stroke, sepsis, and capillary leak syndrome at off-label supratherapeutic doses (up to 100 U/kg) without evidence of a thrombogenic effect. Based on our review, thromboembolic events reported with C1-INH use are rare and patients with HAE who experienced such events often have underlying thromboembolic risk factors.

The bradykinin-forming cascade: a historical perspective

The formation of bradykinin in plasma requires interaction of three proteins, namely coagulation factor XII (Hageman factor), prekallikrein and high-molecular-weight kininogen (HK). Prekallikrein and HK circulate as a bimolecular complex. Initiation of the cascade upon binding to negatively charged surfaces (or macromolecules) is dependent on factor XII autoactivation, conversion of prekallikrein to kallikrein, and a feedback activation of factor XII by kallikrein. The latter reaction is extremely rapid relative to factor XII autoactivation. The kallikrein then digests HK to liberate bradykinin. The natural surface appears to be vascular endothelial cells which express binding proteins for factor XII and HK, and activation can proceed along the cell surface. Recent findings demonstrate that prekallikrein has enzymatic activity separate from that of kallikrein such that it can stoichiometrically bind and cleave HK to liberate bradykinin. It is normally prevented from doing so by the plasma C1 inhibitor. Release of heat shock protein 90 (HSP-90) from endothelial cells can convert prekallikrein to kallikrein (stoichiometrically) within the prekallikrein-HK complex, even in the absence of factor XII, and the prekallikrein-HK complex can autoactivate to generate kallikrein if phosphate is the buffering ion. The effects of phosphate ion and HSP-90 are additive. Thus, an active site appears to be induced in prekallikrein by binding to HK and any of the aforementioned reactions can generate kallikrein prior to factor XII activation by autoactivation of the HK-PK complex. This brief review highlights the major discoveries made over the past 50 years which have led to our current concepts regarding the constituents and mechanisms of activation of the plasma bradykinin-forming cascade.

The maddening itch: an approach to chronic urticaria

Chronic spontaneous urticaria (CSU) is defined as the presence of urticaria with daily or almost daily symptoms for 6 weeks or more. CSU affects 0.1%-0.8% of the population. Its pathogenesis involves autoimmunity, abnormalities in signal transduction, and the action of histamine on H1 receptors. Investigation of CSU should be guided by a thorough history and physical examination. A concise laboratory evaluation, including the CU index, is recommended. This index can provide useful data on severity and response to therapy. Initial treatment should involve increasing doses of nonsedating antihistamines until the intended effect is achieved. Only when a patient is unresponsive to high-dose nonsedating antihistamines (or sedating antihistamines) can we consider CSU refractory and consider immunomodulatory therapy. The most promising drugs are cyclosporine and, more recently, omalizumab.

In vitro comparison of bradykinin degradation by aliskiren, a renin inhibitor, and an inhibitor of angiotensin-converting enzyme

INTRODUCTION

Angiotensin-converting enzyme (ACE) inhibitors cause angioedema due to diminished degradation of bradykinin. Angiotensin receptor blockers may occasionally cause angioedema but the mechanism is unknown, and are generally considered safe, even in those who have reacted to ACE inhibitors. We determined whether aliskiren, a renin inhibitor, has an effect on the rate of bradykinin degradation.

METHODS

The ability of renin to metabolize bradykinin was studied and the rate of bradykinin degradation compared in the presence or absence of aliskiren. Enalapril, a known ACE inhibitor that causes angioedema served as positive control.

RESULTS

Renin was unable to digest bradykinin, indicating that a renin inhibitor is unlikely to affect the rate of bradykinin degradation. In a plasma system, aliskiren had no effect on the rate of bradykinin degradation while enalapril inhibited it appreciably. An inhibitory effect of aliskiren on the rate of bradykinin degradation by human pulmonary endothelial cells was observed, estimated to be about 5% of that of enalapril.

CONCLUSION

Aliskiren has no effect upon the rate of bradykinin degradation in plasma and a minimal effect employing vascular endothelial cells. The latter suggests inhibition of a non-renin enzyme that is a minor contributor to bradykinin degradation.