THE EFFECT OF ITPA POLYMORPHISMS ON THE ENZYME KINETIC PROPERTIES OF HUMAN ERYTHROCYTE INOSINE TRIPHOSPHATASE TOWARD ITS SUBSTRATES ITP AND 6-THIO-ITP

Jaap A. Bakker*, Martijn Lindhout, Daphna D. J. Habets, Arthur van den Wijngaard, Aimee D. C. Paulussen, Jorgen Bierau

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

11 Citations (Web of Science)

Abstract

The role of inosine triphosphatase (ITPase) in adverse drug reactions associated with thiopurine therapy is still under heavy debate. Surprisingly, little is known about the way thiopurines are handled by ITPase. We studied the effect of ITPA polymorphisms on the handling of inosine triphosphate (ITP) and thioinosine triphosphate (TITP) to gain more insight into this phenomenon. Human erythrocyte ITPase activity was measured by incubation with ITP using established protocols, and the generated inosine monophosphate (IMP) was measured using ion-pair RP-HPLC. Molecular analysis of the ITPA gene was performed to establish the genotype. Kinetic parameters were established for the two common polymorphisms for both ITP and TITP as substrates using the above mentioned protocol. Both ITP and TITP are substrates for ITPase and their enzyme activities are comparable. Substrate binding is not altered in the different ITPA polymorphisms. It is shown that the velocity of pyrophosphohydrolysis is compromised when the c.94C > A polymorphism is present, both in the heterozygous and in the homozygous state. TITP is handled by ITPase in a similar way as for ITP, which implies that TITP will accumulate in the erythrocytes of patients with an ITPase deficiency, resulting in adverse drug reactions (ADRs) on thiopurine therapy. In carriers of ITPA polymorphisms, the matter is more complex and the development of ADR may depend on additional epigenetic factors rather than on the accumulation of thiopurinenucleotides.
Original languageEnglish
Pages (from-to)839-849
JournalNucleosides Nucleotides & Nucleic Acids
Volume30
Issue number11
DOIs
Publication statusPublished - 2011

Keywords

  • ITPase
  • thiopurines
  • adverse drug reactions
  • substrate specificity
  • pharmacogenetics

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