Azathioprine Biotransformation in Young Patients with Inflammatory Bowel Disease: Contribution of Glutathione-S Transferase M1 and A1 Variants.

Marianna Lucafò,Diego Favretto,Samuele Naviglio,Giuseppe Toffoli,Noelia Malusà,Erika Cecchin,Matteo Bramuzzo,Gabriele Stocco,Angela Lora,Stefano Martelossi,Giuliana Decorti,Alessandro Ventura,Raffaella Franca

doi:10.3390/genes10040277

Abstract

The contribution of candidate genetic variants involved in azathioprine biotransformation on azathioprine efficacy and pharmacokinetics in 111 young patients with inflammatory bowel disease was evaluated. Azathioprine doses, metabolites thioguanine-nucleotides (TGN) and methylmercaptopurine-nucleotides (MMPN) and clinical effects were assessed after at least 3 months of therapy. Clinical efficacy was defined as disease activity score below 10. Candidate genetic variants (TPMT rs1142345, rs1800460, rs1800462, GSTA1 rs3957357, GSTM1, and GSTT1 deletion) were determined by polymerase chain reaction (PCR) assays and pyrosequencing. Statistical analysis was performed using linear mixed effects models for the association between the candidate variants and the pharmacological variables (azathioprine doses and metabolites). Azathioprine metabolites were measured in 257 samples (median 2 per patient, inter-quartile range IQR 1-3). Clinical efficacy at the first evaluation available resulted better in ulcerative colitis than in Crohn’s disease patients (88.0% versus 52.5% responders, p = 0.0003, linear mixed effect model, LME). TGN concentration and the ratio TGN/dose at the first evaluation were significantly higher in responder. TPMT rs1142345 variant (4.8% of patients) was associated with increased TGN (LME p = 0.0042), TGN/dose ratio (LME p < 0.0001), decreased azathioprine dose (LME p = 0.0087), and MMPN (LME p = 0.0011). GSTM1 deletion (58.1% of patients) was associated with a 18.5% decrease in TGN/dose ratio (LME p = 0.041) and 30% decrease in clinical efficacy (LME p = 0.0031). GSTA1 variant (12.8% of patients) showed a trend (p = 0.046, LME) for an association with decreased clinical efficacy; however, no significant effect on azathioprine pharmacokinetics could be detected. In conclusion, GSTs variants are associated with azathioprine efficacy and pharmacokinetics.

Highlights

Inflammatory bowel disease (IBD) is a chronic, relapsing and remitting disease of the gastrointestinal tract that comprises two main entities, Crohn’s disease (CD) and ulcerative colitis (UC)
Mercaptopurine is metabolized by the enzyme xanthine oxidase in the liver, and by thiopurine methyltransferase (TPMT) and inosine triphosphatase (ITPA), mainly in extra hepatic tissues [10]
For the association between patients with variant TPMT were in remission at the first evaluation of thiopurine metabolites, in genetic variants and azathioprine pharmacokinetics, TPMT rs1142345 variant (4.8% of patients) was comparison to 65% of patients with wild-type TPMT (LME p = 0.041, Figure 2)

Summary

Introduction

Inflammatory bowel disease (IBD) is a chronic, relapsing and remitting disease of the gastrointestinal tract that comprises two main entities, Crohn’s disease (CD) and ulcerative colitis (UC). Azathioprine is mainly used as an immunosuppressant in IBD, and, it has a well described risk benefit profile, adverse drug reactions are relatively common, occurring in 15–18% of patients, and can be severe enough to require the withdrawal of therapy [3,4] In addition, a significant proportion of patients does not respond to therapy with this agent [5,6,7] The reasons of this high heterogeneity in clinical response is not clear yet [8]; variability in azathioprine metabolism can be important; azathioprine is a prodrug that requires metabolic conversion to its active form. Polymorphisms in genes involved in azathioprine metabolism can influence the efficacy and toxicity of this drug [6]

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