title: Analysis of methylated 6-mercaptopurine metabolites in human red blood cells: comparison of two methods.
abstract: Blood samples from 34 recipients of kidney transplants who were on multidrug therapy including azathioprine were analyzed using two methods in parallel for red blood cell (RBC) concentrations of methylated 6-mercaptopurine (6-MP) metabolites. Chemical hydrolysis with high-performance liquid chromatography (HPLC) showed values ranging from 0 to 20,259 pmol/8 x 10(8) RBCs, compared with enzymatic hydrolysis with HPLC that resulted in values ranging from 16 to 22,252 pmol/100 microl packed RBC. Results of the two methods were highly correlated; the coefficient of correlation (r) was equal to 0.93 (95% confidence interval [CI] = 0.87-0.97 [y = 1.12x + 187]). Within series imprecision was 3.1% compared with 6.3%, and between-run imprecision was 10.3% compared with 20.7%, for the enzymatic and chemical methods, respectively. The enzymatic method was found to be more specific and to save time and labor, but with the chemical method methylated metabolites and 6-thioguanine nucleotides (6-TGN), the main active metabolites of azathioprine and 6-MP, can be measured in the same run. The results indicate that methylated 6-MP metabolites mainly exist as ribonucleotides in RBCs.
authors.affiliation: Department of Pharmacology, Institute of Medical Biology, University of Tromsø, Norway.
authors.forename: T
authors.initials: T
authors.lastname: Giverhaug
authors.forename: S
authors.initials: S
authors.lastname: Bergan
authors.forename: T
authors.initials: T
authors.lastname: Loennechen
authors.forename: H E
authors.initials: HE
authors.lastname: Rugstad
authors.forename: J
authors.initials: J
authors.lastname: Aarbakke
mesh_terms: D001379:Azathioprine / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D016030:Kidney Transplantation; D015122:Mercaptopurine / Q000097:blood*; D008745:Methylation; D008778:Methylthioinosine / Q000097:blood*
chemical_list: D008778:Methylthioinosine; D015122:Mercaptopurine; D001379:Azathioprine