Retrospective Study
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Mar 28, 2015; 21(12): 3571-3578
Published online Mar 28, 2015. doi: 10.3748/wjg.v21.i12.3571
Thiopurine metabolites variations during co-treatment with aminosalicylates for inflammatory bowel disease: Effect of N-acetyl transferase polymorphisms
Gabriele Stocco, Eva Cuzzoni, Sara De Iudicibus, Diego Favretto, Noelia Malusà, Stefano Martelossi, Elena Pozzi, Paolo Lionetti, Alessandro Ventura, Giuliana Decorti
Gabriele Stocco, Giuliana Decorti, Department of Life Sciences, University of Trieste, I-34127 Trieste, Italy
Eva Cuzzoni, PhD School in Sciences of Reproduction and Development, University of Trieste, I-34127 Trieste, Italy
Alessandro Ventura, Department of Medical, Surgical and Health Sciences, University of Trieste, I-34127 Trieste, Italy
Sara De Iudicibus, Diego Favretto, Stefano Martelossi, Alessandro Ventura, Institute for Maternal and Child Health IRCCS Burlo Garofolo, I-34127 Trieste, Italy
Noelia Malusà, Department of Prevention, Sanitary Services Agency Number 1, I-34127 Trieste, Italy
Elena Pozzi, Paolo Lionetti, Research Children’s Hospital “Meyer”, I-50139 Florence, Italy
Author contributions: Stocco G, Martelossi M, Ventura A and Decorti G designed the study; Martelossi S, Lionetti P, Pozzi E and Ventura A enrolled the patients; Cuzzoni E, De Iudicibus S, Favretto D and Malusà N genotyped samples and performed the high performance liquid chromatography analyses; Stocco G, Cuzzoni E, De Iudicibus S and Decorti G wrote the paper; all authors critically discussed the results.
Supported by Italian Ministry of Health, and Fondazione Benefica Alberto e Kathleen Casali.
Ethics approval: The study was reviewed and approved by the Institute for Maternal and Child Health I.R.C.C.S. Burlo Garofolo Medical Etics Review Board, approval Trieste (n. 58/05, 12/12/2005) and by the Institutional Research Board (#23/05).
Informed consent: All study participants, or their legal guardian, provided informed written consent prior to study enrollment.
Conflict-of-interest: All authors declare they have no conflict of interest.
Data sharing: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Giuliana Decorti, MD, Professor, Department of Life Sciences, University of Trieste, via Fleming 22, I-34127 Trieste, Italy. decorti@units.it
Telephone: +39-40-5588777 Fax: +39-40-5582134
Received: October 1, 2014
Peer-review started: October 3, 2014
First decision: October 29, 2014
Revised: November 23, 2014
Accepted: January 16, 2015
Article in press: January 16, 2015
Published online: March 28, 2015
Processing time: 179 Days and 20.8 Hours
Abstract

AIM: 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 108 erythrocytes (range: 145-750); after the interruption of the aminosalicylate, a 35% reduction in TGN mean concentrations (absolute mean reduction 109 pmol/8 × 108 erythrocytes) was observed (median 221 pmol/8 × 108 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.

CONCLUSION: 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.

Keywords: Thiopurines; Aminosalicylates; Inflammatory bowel diseases; N-acetyl transferase; Pharmacogenomics

Core tip: During treatment of inflammatory bowel disease with thiopurines and aminosalicylates, interruption of the aminosalicylate results in a significant decrease in thiopurines’ thioguanine nucleotides (TGN) active metabolites. Genetic polymorphisms in genes involved in aminosalicylates biotransformation (NAT1 genotype) affects TGN levels in patients treated with thiopurines and aminosalicylates and could therefore influence the toxicity and efficacy of these drugs.