Inter-Alpha-Trypsin Inhibitor Heavy Chain 4 (ITIH4) as a Compensatory Protease Inhibitor in Hereditary Angioedema (HAE)

Anne Troldborg; Zsofia Godnic-Polai; László Cervenak; Annette G Hansen; Henriette Farkas; Steffen Thiel

doi:10.1016/j.jaci.2024.03.028

Inter-Alpha-Trypsin Inhibitor Heavy Chain 4 (ITIH4) as a Compensatory Protease Inhibitor in Hereditary Angioedema (HAE)

J Allergy Clin Immunol. 2024 Apr 22:S0091-6749(24)00405-6. doi: 10.1016/j.jaci.2024.03.028. Online ahead of print.

Authors

Anne Troldborg¹, Zsofia Godnic-Polai², László Cervenak³, Annette G Hansen⁴, Henriette Farkas², Steffen Thiel⁴

Affiliations

¹ Department of Biomedicine, Aarhus University, Denmark; Department of Clinical Medicine, Aarhus University, Denmark; Department of Rheumatology, Aarhus University, Denmark. Electronic address: amt@biomed.au.dk.
² Hungarian Angioedema Center of Reference and Excellence, Department of Internal Medicine and Haematology, Semmelweis University, Budapest, Hungary.
³ Department of Internal Medicine and Haematology, Semmelweis University, Budapest, Hungary.
⁴ Department of Biomedicine, Aarhus University, Denmark.

PMID: 38657796
DOI: 10.1016/j.jaci.2024.03.028

Abstract

Background: Hereditary angioedema (HAE) is a genetic disorder that manifests as recurrent angioedema attacks, most frequently due to absent or reduced C1 inhibitor (C1-INH) activity. C1-INH is a crucial regulator of enzymatic cascades in the complement, fibrinolytic, and contact systems. Inter-alpha-trypsin inhibitor heavy chain 4 (ITIH4) is an abundant plasma protease inhibitor that can inhibit enzymes in the proteolytic pathways associated with HAE. Nothing is known about its role in HAE.

Objective: Investigate ITIH4 activation in HAE, establish it as a potential biomarker, and explore its involvement in HAE-associated proteolytic pathways.

Methods: Specific immunoassays for non-cleaved ITIH4 (Intact ITIH4) and an assay detecting both intact and cleaved ITIH4 (Total ITIH4) were developed. We initially tested serum samples from HAE patients (n=20), ACEI-induced edema patients (ACEI) (n=20), and unknown HAE patients (U-HAE) (n=20). Validation involved an extended cohort of 80 HAE patients (60 type I, 20 type II), including samples taken at attack and quiescent disease periods, as well as 100 healthy controls.

Results: In 63% of HAE patients, the Intact ITIH4 assay showed lower signals than the Total ITIH4 assay. This difference was not observed in ACEI and U-HAE patients. Western blotting confirmed cleaved ITIH4 in low-Intact ITIH4 samples. In serum samples lacking intact endogenous ITIH4, we observed immediate cleavage of added recombinant ITIH4 suggesting continuous enzymatic activity in the serum. Confirmatory HAE cohort analysis revealed significantly lower intact ITIH4 levels in both HAE type 1 and type 2 patients compared to controls, with consistently low Intact/Total ITIH4 ratios during clinical HAE attacks.

Conclusion: The disease-specific low intact ITIH4 levels highlight its unique nature in HAE. The results suggest that ITIH4 may exhibit compensatory mechanisms in HAE, suggesting its utility as a diagnostic and prognostic biomarker. The variations during quiescent and active disease periods raise intriguing questions about the dynamics of proteolytic pathways in HAE.

Keywords: C1 inhibitor; Protease inhibitor activity; enzymatic cascades; hereditary angioedema; inter-alpha-trypsin inhibitor heavy chain 4; plasma kallikrein.