Researchers from the Queen Mary Hospital, Hong Kong, developed an enzyme-linked immunosorbent assay (ELISA) for the bradykinin pathway, a novel approach with potential application in hereditary angioedema (HAE) diagnosis and treatment response monitoring.
“The current functional diagnostic assays employ complement inhibition, but there was no commercial physiological assay for [the] bradykinin pathway,” the researchers explained in an abstract published in Pathology.
Using the assay, the researchers found that C1 function via kallikrein inhibition was lower in patients with HAE or acquired angioedema (AAE), compared with both healthy individuals and disease controls (14.9 vs 75.3 vs 87.6, respectively).
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In terms of diagnostic performance, the assay showed 99.88% area under the curve, 100% sensitivity, and 100% specificity when related to clinical diagnosis. The optimal diagnostic cut-off was set to at least 37.8%. The assay reached 96.1% agreement with the traditional chromogenic assay.
To develop the assay, the researchers bound biotinylated kallikrein, the enzyme involved in bradykinin production, to avidin-coated plates. Then, they used plasma samples from 12 patients with HAE/AAE, 31 patients with bradykinin-unrelated disease, and 120 healthy controls to detect C1 inhibitor (C1-INH). The researchers evaluated the diagnostic performance of the assay based on accuracy, precision, linearity, limit of blank, limit of detection, and receiver operating curve (ROC).
Bradykinin Production Bypasses the Kallikrein-Kinin System in HAE-PLG
C1-INH is a key mediator of 3 signaling cascades: the kallikrein-kinin pathway, the complement cascade, and the fibrinolytic system. It regulates both factor XIIa, which cleaves the plasma pre-kallikrein/high-molecular-weight kininogen complex, and pre-kallikrein. C1-INH deficiency or dysfunction, as occurs in type 1 and type 2 HAE, leads to excessive formation of the vasoactive peptide bradykinin causing a local increase in vascular permeability.
Lam K, Ip WK, Leung JCW, Yeung HHF, Tung EKK, Au E. An in-house ELISA assay for C1 inhibitor function via inhibition of kallikrein. Pathology. 2023;55:S37. doi:10.1016/j.pathol.2022.12.123