THE EFFECT OF ITPA POLYMORPHISMS ON THE ENZYME KINETIC PROPERTIES OF HUMAN ERYTHROCYTE INOSINE TRIPHOSPHATASE TOWARD ITS SUBSTRATES ITP AND 6-THIO-ITP
THE EFFECT OF ITPA POLYMORPHISMS ON THE ENZYME KINETIC PROPERTIES OF HUMAN ERYTHROCYTE INOSINE TRIPHOSPHATASE TOWARD ITS SUBSTRATES ITP AND 6-THIO-ITP
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DOI：
10.1080/15257770.2011.606789
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发表时间：
2011-01-01
影响因子：
1.3
通讯作者：
Bierau, Jorgen
中科院分区：
文献类型：
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作者：
Bakker, Jaap A.;Lindhout, Martijn;Bierau, Jorgen
肌苷三磷酸酶（ITPase）在硫嘌呤治疗相关药物不良反应中的作用仍存在激烈争论。令人惊讶的是，人们对 ITPase 处理硫嘌呤的方式知之甚少。我们研究了 ITPA 多态性对三磷酸肌苷 (ITP) 和三磷酸硫代肌苷 (TITP) 处理的影响，以更深入地了解这一现象。使用既定方案通过与 ITP 一起孵育来测量人红细胞 ITP 酶活性，并使用离子对 RP-HPLC 测量生成的肌苷单磷酸 (IMP)。对 ITPA 基因进行分子分析以确定基因型。使用上述方案为 ITP 和 TITP 作为底物的两种常见多态性建立了动力学参数。 ITP 和 TITP 都是 ITPase 的底物，它们的酶活性相当。不同 ITPA 多态性中的底物结合没有改变。结果表明，当 c.94C > A 多态性存在时，无论是杂合状态还是纯合状态，焦磷酸水解的速度都会受到影响。 TITP 由 ITPase 处理，其处理方式与 ITP 类似，这意味着 TITP 会在 ITPase 缺乏的患者的红细胞中积聚，导致硫嘌呤治疗出现药物不良反应 (ADR)。在ITPA多态性携带者中，情况更加复杂，ADR的发展可能取决于额外的表观遗传因素，而不是硫代嘌呤核苷酸的积累。
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.