Degradation of 100 ng/mL histamine (Sigma-Aldrich, St. Louis, MO, 53300) by 6 nM (1 µg/mL) rhDAO variants was measured in duplicate in phosphate buffered saline (PBS) with 1% human serum albumin (HSA; Albunorm; Octapharma, Vienna, Austria) or in EDTA plasma from a healthy volunteer, with or without 600 nM HMWH added (heparin, 1000 IU/mL equivalent to 2 mg/mL, Gilvasan, Vienna, Austria), using a Cisbio HTRF histamine 500 test kit (Biomedica, Vienna, Austria).
Plasma of seven mastocytosis patients and three healthy volunteers was spiked with 6 nM rhDAO-WT, 545 nM histamine, and 20 µM of the potent DAO-inhibitor diminazene aceturate (DIMAZ; Sigma-Aldrich, D7770) and histamine concentrations were determined in duplicate with a histamine ELISA (Immunotech IM2562, Beckman Coulter, Brea, CA) as described previously (Boehm et al., 2019 (link)).
Plasma of seven mastocytosis patients and three healthy volunteers was spiked with 6 nM rhDAO-WT, 545 nM histamine, and 20 µM of the potent DAO-inhibitor diminazene aceturate (DIMAZ; Sigma-Aldrich, D7770) and histamine concentrations were determined in duplicate with a histamine ELISA (Immunotech IM2562, Beckman Coulter, Brea, CA) as described previously (Boehm et al., 2019 (link)).