title: Thiopurine metabolites variations during co-treatment with aminosalicylates for inflammatory bowel disease: effect of N-acetyl transferase polymorphisms.
abstract: OBJECTIVE
  To evaluate variation of the concentration of thiopurine metabolites after 5-aminosalicylate (5-ASA) interruption and the role of genetic polymorphisms of N-acetyl transferase (NAT) 1 and 2.
  
  
  METHODS
  Concentrations of thioguanine nucleotides (TGN) and methymercaptopurine nucleotides (MMPN), metabolites of thiopurines, were measured by high performance liquid chromatography in 12 young patients (3 females and 9 males, median age 16 years) with inflammatory bowel disease (6 Crohn's disease and 6 ulcerative colitis) treated with thiopurines (7 mercaptopurine and 5 azathioprine) and 5-ASA. Blood samples were collected one month before and one month after the interruption of 5-ASA. DNA was extracted and genotyping of NAT1, NAT2, inosine triphosphate pyrophosphatase (ITPA) and thiopurine methyl transferase (TPMT) genes was performed using PCR assays.
  
  
  RESULTS
  Median TGN concentration before 5-ASA interruption was 270 pmol/8 x 10(8) erythrocytes (range: 145-750); after the interruption of the aminosalicylate, a 35% reduction in TGN mean concentrations (absolute mean reduction 109 pmol/8 × 10(8) erythrocytes) was observed (median 221 pmol/8 × 10(8) erythrocytes, range: 96-427, P value linear mixed effects model 0.0011). Demographic and clinical covariates were not related to thiopurine metabolites concentrations. All patients were wild-type for the most relevant ITPA and TPMT variants. For NAT1 genotyping, 7 subjects presented an allele combination corresponding to fast enzymatic activity and 5 to slow activity. NAT1 genotypes corresponding to fast enzymatic activity were associated with reduced TGN concentration (P value linear mixed effects model 0.033), putatively because of increased 5-ASA inactivation and consequent reduced inhibition of thiopurine metabolism. The effect of NAT1 status on TGN seems to be persistent even after one month since the interruption of the aminosalicylate. No effect of NAT1 genotypes was shown on MMPN concentrations. NAT2 genotyping revealed that 6 patients presented a genotype corresponding to fast enzymatic activity and 6 to slow activity; NAT2 genotypes were not related to thiopurine metabolites concentration in this study.
  
  
  CONCLUSIONS
  NAT1 genotype affects TGN levels in patients treated with thiopurines and aminosalicylates and could therefore influence the toxicity and efficacy of these drugs; however the number of patients evaluated is limited and this has to be considered a pilot study.
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Stocco
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Eva
authors.initials: E
authors.lastname: Cuzzoni
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: De Iudicibus
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Favretto
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Noelia
authors.initials: N
authors.lastname: Malusà
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Martelossi
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Pozzi
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Lionetti
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Ventura
authors.affiliation: Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Decorti
mesh_terms: D000293:Adolescent; D000893:Anti-Inflammatory Agents / Q000097:blood / Q000627:therapeutic use*; D001191:Arylamine N-Acetyltransferase / Q000235:genetics* / Q000378:metabolism; D001379:Azathioprine / Q000097:blood / Q000627:therapeutic use*; D001711:Biotransformation; D002648:Child; D002851:Chromatography, High Pressure Liquid; D003093:Colitis, Ulcerative / Q000175:diagnosis / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D003424:Crohn Disease / Q000175:diagnosis / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D004359:Drug Therapy, Combination; D005260:Female; D005838:Genotype; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D008297:Male; D015122:Mercaptopurine / Q000097:blood / Q000627:therapeutic use*; D019804:Mesalamine / Q000627:therapeutic use*; D010597:Pharmacogenetics; D010641:Phenotype; D010865:Pilot Projects; D011110:Polymorphism, Genetic; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D000893:Anti-Inflammatory Agents; D007527:Isoenzymes; D019804:Mesalamine; D015122:Mercaptopurine; D001191:Arylamine N-Acetyltransferase; C089384:N-acetyltransferase 1; C478900:NAT2 protein, human; D001379:Azathioprine
keywords: Aminosalicylates; Inflammatory bowel diseases; N-acetyl transferase; Pharmacogenomics; Thiopurines
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