NUDT15 variance increases DNA-incorporated thiopurine metabolites and lymphocyte apoptosis in patients with inflammatory bowel disease

Abstract Background A novel thiopurine metabolizing enzyme, nucleotide diphosphate-linked moiety X-type motif 15 (NUDT15) was associated with drug-induced leukopenia in patients with non-synonymous genetic polymorphisms. Thiopurine-induced leukopenia in Japanese patients with genetic variance in NUDT15 (c.415C>T) appears to be independent of the 6-thioguanine nucleotide concentration in red blood cells. However, detailed molecular mechanism how NUDT15 variance causes thiopurine-induced leukopenia remains unclear and NUDT15-associated subcellular thiopurine metabolism has not been investigated in patients with inflammatory bowel diseases (IBD). Methods DNA-incorporated deoxythioguanosine (dTG) was measured in the peripheral blood mononuclear cells (PBMCs) of Japanese patients with IBD under thiopurine treatment. Association of a single-nucleotide polymorphism for NUDT15 (c.415C>T) with dTG in PBMCs (dTGPBMC) was examined. Peripheral blood T lymphocytes were cultured in vitro with 6-thioguanine (6-TG) to examine the Impact of NUDT15 genotypes on incorporation into DNA, cell proliferation and apoptosis. Results NUDT15 variants had significantly higher dTGPBMC per thiopurine dosage than non-variants (homozygous variants (TT) vs. heterozygous variants (CT) vs. non-variants (CC), 4418.0 vs. 663.0 vs. 295.3 dTG mol/106 moles dA per mg/kg/day of 6-MP (Figure A)). dTGPBMC and peripheral lymphocyte counts showed a negative correlation (r = −0.30, p = 0.015) (Figure B). Peripheral blood lymphocytes from patients with NUDT15 variance showed a higher DNA-incorporated dTG associated with increased apoptosis (increase of Annexin V+ PI+ CD4+ lymphocytes; TT vs. CT vs. CC, 158.5 % vs. 80.1 % vs. 57.9 % (p = 0.0427)) (Figure C) and decreased proliferation (decrease of proliferative CD4+ lymphocytes, TT vs. CT vs. CC, 49.0 % vs. 25.0 % vs. 19.1 % (p = 0.0098)) (Figure D) when cultured with 6-thioguanine in vitro. Conclusion DNA-incorporated dTG affected by NUDT15 genotypes induces T lymphocyte apoptosis in patients with IBD.