Optimierter Radioextraktionsassay zur quantitativen Bestimmung der Aktivität von Diaminooxidase (DAO) in humanem Serum und Plasma

Patients intolerant to histamine-containing foods (histamine intolerance) frequently suffer from diminished histamine degradation based on deficiency or reduced activity of the enzyme diamine oxidase (DAO). Here, we present an easy-to-use, commercially available test kit for the quantification of DAO activity in blood. Radiolabeled putrescine is added as a substrate to 100 μl of plasma or serum. DAO converts one amino group to an aldehyde. The resulting molecule spontaneously reacts to cyclic Δ 1 -pyrroline which can be extracted selectively by ethylacetate. With an optimized buffer system, we could improve the yield of extractable reactants four-fold compared to previous systems. A calibration curve with DAO from porcine kidney is used for quantification. Intraassay variation is < 10% (3.5 - 14%,n = 20), interassay variation is < 15% (4 - 21%, n = 10). Mean recovery of DAO added to samples was 104% (86 - 123%, n = 20). Results are available within three hours. DAO activity in samples was stable at 4 °C for one week, storage at -20 °C with repeated freeze cycles did not affect activity. This assay is a reliable tool for the determination of blood DAO activity and is a helpful tool in the diagnosis of non-allergic food hypersensitivities. Due to the good stability of DAO, blood samples may be drawn in the doctors office and shipped to the diagnostic lab.