title: Thiopurine methyltransferase activity in the erythrocytes of adults and children: and HPLC-linked assay.
abstract: A non-radioactive method that uses reverse-phase high performance liquid chromatography is described for the determination of thiopurine methyltransferase (E.C. 2.1.1.67) activity in human erythrocytes. The method is based on the direct quantitation of 6-methyl-mercaptopurine produced from 6-mercaptopurine by crude erythrocyte lysates. The method is accurate and reliable and suitable for diagnostic use. Activity values in control adults ranged from 5 to 32 pmol/h/mg haemoglobin. The activity in the erythrocytes of adult males was significantly higher compared to females (21 +/- 5 and 15 +/- 8 pmol/h/mg haemoglobin, respectively). The activity measured in the erythrocytes of children (22 +/- 5 pmol/h/mg haemoglobin) did not show any significant difference compared to adults. Thiopurine methyltransferase activity was measured in a female patient with systemic sclerosis who developed severe bone marrow depression after treatment with azathioprine and allopurinol. Activity (6.3 +/- 0.5 pmol/h/mg haemoglobin) was found in the lowest range of controls thus supporting the hypothesis that it could be responsible for increased azathioprine cytotoxicity.
authors.affiliation: Dipartimento di Biologia Molecolare, Università di Siena, Policlinico Le Scotte, Siena, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Micheli
authors.forename: G
authors.initials: G
authors.lastname: Jacomelli
authors.forename: A
authors.initials: A
authors.lastname: Fioravanti
authors.forename: G
authors.initials: G
authors.lastname: Morozzi
authors.forename: R
authors.initials: R
authors.lastname: Marcolongo
authors.forename: G
authors.initials: G
authors.lastname: Pompucci
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004912:Erythrocytes / Q000201:enzymology*; D005260:Female; D006801:Humans; D008297:Male; D015122:Mercaptopurine / Q000031:analogs & derivatives / Q000378:metabolism; D008780:Methyltransferases / Q000097:blood*
chemical_list: C010240:6-methylthiopurine; D015122:Mercaptopurine; D008780:Methyltransferases; C022745:thiopurine methyltransferase