Angiotensin-Converting Enzyme and Blood Basic Carboxypeptidases CPB2 and CPN Activity is an Indicator for Serum Quality: A Quick Lab Test

Abstract

The vasoactive neuropeptide bradykinin (BK) is involved in major pathophysiological pathways such as the kinin-kallikrein system (KKS) and the renin-angiotensin system (RAS). It is a substrate of important enzymes, namely angiotensin-converting enzyme (ACE) and basic carboxypeptidases N (CPN) and B2 (CPB2). We use its dabsylated form (DBK) as a reporter substance to monitor the serum activity of these proteases. The activity of the enzymes is responsible for the formation of two DBK fragments, which can be detected with this neuropeptide reporter assay (NRA) to elucidate disease-related changes in RAS and KKS. The assay is also sensitive to serum quality. Hemolytic serum shows significantly reduced serum protease activity in the NRA, but it can already be visually identified by its colour. With the NRA, we detected samples from healthy controls, which were not visibly hemolytic and still exhibited the same poor results. This observation was traced back to lax use of the sampling protocol in the clinic. The incorporation of such samples of poor serum quality in biochemical studies would impact on their outcome and reproducibility. Thus, we have simplified the NRA workflow in order to generate a quick test, which can help to weed out samples of poor quality.