D1.499 - A clinically validated kinin biomarker assay to differentiate bradykinin-mediated from mast cell-mediated angioedema

Angioedema (AE) is a predominant manifestation in multiple medical conditions and is generally mediated by histamine or bradykinin (BK). Differentiating bradykinin (BK)-mediated angioedema (AE-BK) from other types of AE remains a challenge in clinical practice leading to misdiagnoses, unnecessary treatments and medical procedures, hospitalizations, and increased disease burden. Development of a biomarker assay to accurately measure plasma levels of BK and related peptides and assess sensitivity of BK-forming pathways may aid in identifying and managing AE-BK.

An ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to measure kinin peptides in human plasma. Kinin levels were analyzed before and after exposure to 4°C for 24 hours, in plasma samples from 30 people with hereditary AE (HAE) due to C1 inhibitor deficiency (HAE-C1INH), four with AE due to acquired C1INH deficiency (AAE-C1INH), four having HAE with normal C1INH levels and function (HAE-nC1INH, with genetic variants in F12 or PLG genes), three with HAE of unknown etiology (HAE-UNK), three with AE of unknown etiology AE-UNK, 28 with mast cell-mediated AE (AE-MC), and 30 healthy volunteers (HVs). All participants provided informed consent.

Cold exposure resulted in a significant (p<0.001) increase in kinin levels in plasma samples from people with HAE-C1INH, AAE-C1INH, and HAE-nC1INH compared to people with AE-MC and HVs: mean BK levels following cold activation were 309 ng/mL, 775 ng/mL, 483 ng/mL, 4 ng/mL and 4 ng/mL, respectively. Cold exposure also resulted in a significant increase of BK levels in plasma samples from some people in the combined group with HAE-UNK and AE-UNK (mean BK level 135 ng/mL), suggesting a possible role of BK in mediating AE attacks in these individuals.

These results suggest that the qualified and clinically validated kinin biomarker assay using cold activation can be applied to reliably assess the sensitivity and hyper-activatable state of the BK-forming cascades and to differentiate people with different types of AE-BK from people with AE-MC. The clinically validated kinin biomarker assay may become a key tool for identifying, studying, and managing BK-mediated conditions, including AE-BK