Chronic spontaneous urticaria: Focus on pathophysiology to unlock treatment advances.

Chronic spontaneous urticaria (CSU) is a debilitating skin disease characterized by intensely itchy wheals, angioedema, or both. Symptoms recur spontaneously, on a near-daily basis, over >6 weeks; many patients experience flare-ups over several years and, consequently, reduced quality of life. Differences between the inflammatory profiles of the skin of CSU patients (wheals and nonlesional sites) and healthy controls indicate that key drivers such as mast cells, eosinophils, and basophils interact, release vasoactive mediators, and prime the skin, leaving patients predisposed to symptoms. Many cytokines and chemokines involved in these inflammatory networks and their corresponding intracellular signaling cascades have been identified. These insights informed the development of therapies such as omalizumab, dupilumab, and Bruton's tyrosine kinase (BTK) inhibitors, marking a renewed focus on pathogenesis in CSU clinical research. Despite progress, current therapies provide symptomatic control but do not appear to redress the inflammatory balance in the skin permanently. A deeper understanding of CSU pathogenesis will permit a more targeted approach to developing novel treatments with curative intent. Here, we review what is known about the pathogenesis of CSU and consider how this can be used to identify rational targets to improve patient care further.

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.

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? and (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.

The international EAACI/GA²LEN/EuroGuiDerm/APAAACI guideline for the definition, classification, diagnosis, and management of urticaria.

This update and revision of the international guideline for urticaria was developed following the methods recommended by Cochrane and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) working group. It is a joint initiative of the Dermatology Section of the European Academy of Allergology and Clinical Immunology (EAACI), the Global Allergy and Asthma European Network (GA²LEN) and its Urticaria and Angioedema Centers of Reference and Excellence (UCAREs and ACAREs), the European Dermatology Forum (EDF; EuroGuiDerm), and the Asia Pacific Association of Allergy, Asthma and Clinical Immunology with the participation of 64 delegates of 50 national and international societies and from 31 countries. The consensus conference was held on 3 December 2020. This guideline was acknowledged and accepted by the European Union of Medical Specialists (UEMS). Urticaria is a frequent, mast cell-driven disease that presents with wheals, angioedema, or both. The lifetime prevalence for acute urticaria is approximately 20%. Chronic spontaneous or inducible urticaria is disabling, impairs quality of life, and affects performance at work and school. This updated version of the international guideline for urticaria covers the definition and classification of urticaria and outlines expert-guided and evidence-based diagnostic and therapeutic approaches for the different subtypes of urticaria.

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 ß2 receptor with sustained action properties, testing of products to determine whether the ß1 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%.

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 (KD  ≤ 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.

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.

Cytokine and estrogen stimulation of endothelial cells augments activation of the prekallikrein-high molecular weight kininogen complex: Implications for hereditary angioedema.

BACKGROUND: When the prekallikrein-high molecular weight kininogen complex is bound to endothelial cells, prekallikrein is stoichiometrically converted to kallikrein because of release of heat shock protein-90 (Hsp90). Although bradykinin formation is typically initiated by factor XII autoactivation, it is also possible to activate factor XII either by kallikrein, thus formed, or by plasmin. OBJECTIVE: Because attacks of hereditary angioedema can be related to infection and/or exposure to estrogen, we questioned whether estrogen or cytokine stimulation of endothelial cells could augment release of Hsp90 and prekallikrein activation. We also tested release of profibrinolytic enzymes, urokinase, and tissue plasminogen activator (TPA) as a source for plasmin formation. METHODS: Cells were stimulated with agonists, and secretion of Hsp90, urokinase, and TPA was measured in the culture supernatants by ELISA. Activation of the prekallikrein-HK complex was measured by using pro-phe-arg-p-nitroanilide reflecting kallikrein formation. RESULTS: Hsp90 release was stimulated with optimal doses of estradiol, IL-1, and TNF-α (10 ng/mL) from 15 minutes to 120 minutes. TPA release was not augmented by any of the agonists tested but urokinase was released by IL-1, TNF-α, and thrombin (positive control), but not estrogen. Augmented activation of the prekallikrein-HK complex to generate kallikrein was seen with each agonist that releases Hsp90. Addition of 0.1% factor XII relative to prekallikrein-HK leads to rapid formation of kallikrein; factor XII alone does not autoactivate. CONCLUSIONS: IL-1, TNF-α, and estrogen stimulate release of Hsp90 and augment activation of the prekallikrein-HK complex to generate kallikrein and bradykinin. IL-1 and TNF-α stimulate release of urokinase, which can convert plasminogen to plasmin and represents a possible source for plasmin generation in all types of hereditary angioedema, but particularly hereditary angioedema with normal C1 inhibitor with a factor XII mutation. Both kallikrein and plasmin activate factor XII; kallikrein is 20 times more potent on a molar basis.

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.

Timing and duration of omalizumab response in patients with chronic idiopathic/spontaneous urticaria.

BACKGROUND: Few data are available that describe response patterns in patients with chronic idiopathic urticaria (CIU)/chronic spontaneous urticaria (CSU) treated with omalizumab. OBJECTIVE: We sought to describe response patterns by using data from the 3 pivotal omalizumab CIU/CSU trials. METHODS: Every 4 weeks, randomized patients received dosing with placebo or 75, 150, or 300 mg of omalizumab (ASTERIA I: n = 318, 24 weeks; ASTERIA II: n = 322, 12 weeks) or placebo or 300 mg of omalizumab (GLACIAL: n = 335, 24 weeks). Response was defined as well-controlled urticaria (weekly Urticaria Activity Score [UAS7] ≤ 6) or complete response (UAS7 = 0). RESULTS: Response rates were dose dependent and highest with 300 mg of omalizumab. Some patients responded early (before week 4). At week 12, a higher proportion of patients treated with 300 mg of omalizumab reported a UAS7 ≤ 6 (26.0% [75 mg of omalizumab], 40.0% [150 mg of omalizumab], 51.9% [300 mg of omalizumab], and 11.3% [placebo] for ASTERIA I; 26.8% [75 mg of omalizumab], 42.7% [150 mg of omalizumab], 65.8% [300 mg of omalizumab], and 19.0% [placebo] for ASTERIA II; and 52.4% [300 mg of omalizumab] and 12.0% [placebo] for GLACIAL) or a UAS7 = 0 (11.7% [75 mg of omalizumab], 15.0% [150 mg of omalizumab], 35.8% [300 mg of omalizumab], and 8.8% [placebo] for ASTERIA I; 15.9% [75 mg of omalizumab], 22.0% [150 mg of omalizumab], 44.3% [300 mg of omalizumab], and 5.1% [placebo] for ASTERIA II; and 33.7% [300 mg of omalizumab] and 4.8% [placebo] for GLACIAL). In patients receiving 300 mg of omalizumab with 24 weeks of treatment, median time to achieve a UAS7 ≤ 6 was 6 weeks (ASTERIA I and GLACIAL) and median time to achieve a UAS7 = 0 was 12 or 13 weeks (ASTERIA I and GLACIAL, respectively). Some patients who achieved well-controlled urticaria or complete response sustained response throughout the treatment period. CONCLUSION: Benefits of omalizumab treatment were evident early (before week 4) in some patients and persisted to week 24. Use of 300 mg of omalizumab demonstrated best results in controlling CIU/CSU symptoms.

Omalizumab for the treatment of chronic idiopathic or spontaneous urticaria.

BACKGROUND: Many patients with chronic idiopathic urticaria (also called chronic spontaneous urticaria) do not have a response to therapy with H-antihistamines, even at high doses. In phase 2 trials, omalizumab, an anti-IgE monoclonal antibody [corrected] that targets IgE and affects mast-cell and basophil function, has shown efficacy in such patients. METHODS: In this phase 3, multicenter, randomized, double-blind study, we evaluated the efficacy and safety of omalizumab in patients with moderate-to-severe chronic idiopathic urticaria who remained symptomatic despite H-antihistamine therapy (licensed doses). We randomly assigned 323 patients to receive three subcutaneous injections, spaced 4 weeks apart, of omalizumab at doses of 75 mg, 150 mg, or 300 mg or placebo, followed by a 16-week observation period. The primary efficacy outcome was the change from baseline in a weekly itch-severity score (ranging from 0 to 21, with higher scores indicating more severe itching). RESULTS: The baseline weekly itch-severity score was approximately 14 in all four study groups. At week 12, the mean (±SD) change from baseline in the weekly itch-severity score was -5.1±5.6 in the placebo group, -5.9±6.5 in the 75-mg group (P=0.46), -8.1±6.4 in the 150-mg group (P=0.001), and -9.8±6.0 in the 300-mg group (P<0.001). Most prespecified secondary outcomes at week 12 showed similar dose-dependent effects. The frequency of adverse events was similar across groups. The frequency of serious adverse events was low, although the rate was higher in the 300-mg group (6%) than in the placebo group (3%) or in either the 75-mg or 150-mg group (1% for each). CONCLUSIONS: Omalizumab diminished clinical symptoms and signs of chronic idiopathic urticaria in patients who had remained symptomatic despite the use of approved doses of H-antihistamines. (Funded by Genentech and Novartis Pharma; ClinicalTrials.gov number, NCT01292473.).

Angioedema in the omalizumab chronic idiopathic/spontaneous urticaria pivotal studies.

BACKGROUND: Angioedema, present in some patients with chronic idiopathic/spontaneous urticaria (CIU/CSU), may have a negative effect on patient quality of life. OBJECTIVE: To describe patient-reported angioedema and its management in the pivotal omalizumab studies (ASTERIA I, ASTERIA II, GLACIAL). METHODS: Enrolled patients with CIU/CSU remained symptomatic despite treatment with histamine1 (H1)-antihistamines at licensed doses (ASTERIA I, ASTERIA II) or H1-antihistamines at up to 4 times the approved dose plus H2-antihistamines and/or a leukotriene receptor antagonist (GLACIAL). All studies administered omalizumab (75, 150, or 300 mg in ASTERIA I and ASTERIA II; 300 mg in GLACIAL) or placebo subcutaneously every 4 weeks for at least 12 weeks. Urticaria Patient Daily Diary entries were completed by patients and summarized. RESULTS: At baseline, angioedema prevalence was higher in GLACIAL (53.1%) than in ASTERIA I (47.5%) or ASTERIA II (40.7%). The mean proportion of angioedema-free days during weeks 4 to 12 was greater for patients treated with 300 mg of omalizumab than placebo in ASTERIA I (96.1% vs 88.2%, P < .001), ASTERIA II (95.5% vs 89.2%, P < .001), and GLACIAL (91.0% vs 88.7%, P = .006). Most patient-reported angioedema was managed by low-intensity interventions (doing nothing or taking medication). CONCLUSION: Treatment with 300 mg of omalizumab was efficacious in reducing patient-reported angioedema. Low-intensity interventions were generally used to manage angioedema episodes. TRIAL REGISTRATION: clinicaltrials.gov Identifiers: NCT01287117 (ASTERIA I), NCT01292473 (ASTERIA II), and NCT01264939 (GLACIAL).

A Case Series Characterizing Pilomyxoid Astrocytomas in Childhood.

BACKGROUND: The term pilomyxoid astrocytoma (PMA) was added to the World Health Organization Classification of Tumours of the central nervous system in 2007. Pilomyxoid tumors are grade II tumors, considered to be variants of pilocytic astrocytomas. We attempted to determine if positron emission tomography (PET), proliferative index (PI), and BRAF V600E mutation help better define PMAs. OBSERVATIONS: We report 5 patients' clinical and neuroimaging findings, pathology (PI), and outcome. Four of the 5 patients had PET scans. Three patients showed [18F]fluoro-deoxyglucose hypermetabolism. The PI was elevated in all 5 cases and the BRAF V600E mutation was found in 3 of the 3 patients tested. CONCLUSION: Our data suggest that PMAs are hypermetabolic on PET, have elevated PIs and BRAF V600E mutations, and behave aggressively.