A novel assay to diagnose hereditary angioedema utilizing inhibition of bradykinin-forming enzymes.

Abstract

BACKGROUND:

Hereditary angioedema types I and II are caused by a functional deficiency of C1 inhibitor (C1-INH), leading to overproduction of bradykinin. The current functional diagnostic assays employ inhibition of activated C1s; however, an alternative, more physiologic method is desirable.

METHODS:

ELISAs were developed using biotinylated activated factor XII (factor XIIa) or biotinylated kallikrein bound to avidin-coated plates. Incubation with plasma was followed by detection of bound C1-INH.

RESULTS:

After standard curves were developed for quantification of C1-INH, serial dilutions of normal plasma were employed to validate the ability to detect known concentration of C1-INH in the plasma as a percent of normal. Hereditary angioedema (HAE) types I and II were then tested. The level of functional C1-INH in all HAE types I and II plasma tested was less than 40% of our normal control. This was evident regardless of whether we measured factor XIIa-C1-INH or kallikrein-C1-INH complexes, and the two assays were in close agreement. By contrast, testing the same samples utilizing the commercial method (complex ELISA, Quidel Corp.) revealed the levels of C1-INH between 0 and 57% of normal (mean, 38%), and 42 samples were considered equivocal (four controls and 38 patients).

CONCLUSIONS:

Diagnosis of HAE types I and II can be ascertained by inhibition of enzymes of the bradykinin-forming cascade, namely factor XIIa and kallikrein. Either method yields functional C1-INH levels in patients with HAE (types I and II) that are clearly abnormal with less variance or uncertainty than the commercial method.

• Authors: K Joseph, S Bains, B G Tholanikunnel, A Bygum, A Aabom, C Koch, H Farkas, L Varga, B Ghebrehiwet, A P Kaplan
• Journal: Allergy (Allergy) Vol. 70 Issue 1 Pg. 115-9 (Jan 2015) ISSN: 1398-9995 [Electronic] Denmark
• PMID: 25186184 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Chemical References

• Complement C1 Inhibitor Protein
• Plasma Kallikrein
• Factor XIIa
• Bradykinin

Topics

• Angioedemas, Hereditary (diagnosis, enzymology)
• Bradykinin (biosynthesis)
• Case-Control Studies
• Complement C1 Inhibitor Protein (metabolism)
• Enzyme-Linked Immunosorbent Assay
• Factor XIIa
• Humans
• Plasma Kallikrein
• Reproducibility of Results
• Sensitivity and Specificity