Evaluation of a spectrophotometric method for measurement of activity of diamine oxidase in newborn infants

Diamine oxidase (DAO) is an enzyme synthesized primarily in the gastrointestinal mucosal cells. Serum levels of DAO have been used as an indicator of the integrity and/or functional mass of the intestinal mucosa. The enzyme is also produced by the placenta and is elevated in newborn serum. Previous radiometric methods for DAO used tritiated putrescine or cadaverine as substrate. A simple and rapid spectrophotometric procedure for DAO with use of histamine as substrate was developed, and this assay was utilized to evaluate the developmental pattern of activity of DAO in umbilical cord blood of newborn full-term and premature infants, in sequential samples from premature infants, and in samples from infants with necrotizing enterocolitis. The spectrophotometric assay was linear to 200 U per L and was also precise with total imprecision (CV) of 11.9 percent and 3.7 percent at DAO activities of 25.6 U per l and 126.1 U per L, respectively. Triglycerides above 275 mg per dL caused a significant reduction in measured activity of DAO; however, this effect could be eliminated by use of ultracentrifugation to remove lipemia. Plasma samples with heparin or ethylenediamine tetraacetic acid (EDTA) as anticoagulant were unsuitable for analysis since DAO activity showed a 24 percent and 32 percent decrease in activity at concentrations of 20 U per mL (heparin) and two mg per mL (EDTA), respectively. Serum samples are the specimen of choice. In infants it was found that the serum activity declined to adult levels by day 12 of life and that this decline is not affected by necrotizing arterocolitis.