Zhang Li-Rong, Song Dong-Kui, Zhang Wei, Zhao Jun, Jia Lin-Jing, Xing Dong-Liang
Department of Clinical Pharmacology, School of Medicine, Zhengzhou University, 40 Daxue Road, Zhengzhou 450052, China.
Clin Chim Acta. 2007 Feb;376(1-2):45-51. doi: 10.1016/j.cca.2006.07.010. Epub 2006 Jul 14.
Thiopurine S-methyltransferase (TPMT) is an enzyme that catalyzed the S-methylation of thiopurine drugs. TPMT activity exhibits an interindividual variability, mainly as a result of genetic polymorphism. Patients with intermediate or deficient TPMT activity are at risk for toxicity after receiving standard doses of thiopurine drugs. We determined a cut-off concentration of the TPMT activity assay less than which genotyping of the TPMT gene should be performed. In addition, the influence of hemodialysis on TPMT activity in uremic patients was examined.
In 248 healthy subjects and 30 uremic patients, PCR-based methods were used to analyze the most common functional mutations TPMT2, 3A, 3B and 3C. A HPLC assay was used to measure erythrocyte TPMT activity in the whole population.
Seven TPMT3C heterozygotes were identified, while TPMT2, 3A and 3B alleles were not detected in 248 healthy subjects. The frequency of TPMT3C allele was 1.4% (7/496). The TPMT activity in healthy subjects was normally distributed, ranged from 6.09 to 28.65 nmol/h/ml pRBC with a mean of 16.03 +/- 4.16 nmol/h/ml pRBC. The cut-off for high TPMT activity and intermediate TPMT activity was 10.07 nmol/h/ml pRBC. There were 19 intermediate activity healthy subjects (7.7%) and 229 high activity healthy subjects (92.3%), and no TPMT deficiency subject was found. All of the 229 healthy subjects with high activity had no mutant alleles, while 7 of the 19 subjects with intermediate activity had a mutant allele. Phenotypes were in good agreement with genotypes for 95% of subjects. The uremic patients were all homozygous for the wild-type allele whose TPMT activity was activated significantly before hemodialysis compared with TPMT activity after hemodialysis.
We defined the cut-off values for the TPMT phenotyping assay at 10.07 nmol/h/ml pRBC, less than which additional genotyping elucidates the individual risk for drug therapy. In uremic patients, TPMT activity is increased by some uremic factors, and dialysis shifted their TPMT activity close to that of a healthy control group.
硫嘌呤甲基转移酶（TPMT）是一种催化硫嘌呤类药物S-甲基化的酶。TPMT活性存在个体差异，主要是由于基因多态性所致。TPMT活性中等或缺乏的患者在接受标准剂量硫嘌呤类药物后有发生毒性反应的风险。我们确定了TPMT活性测定的一个临界浓度，低于该浓度时应进行TPMT基因分型。此外，还研究了血液透析对尿毒症患者TPMT活性的影响。
在248名健康受试者和30名尿毒症患者中，采用基于聚合酶链反应（PCR）的方法分析最常见的功能性突变TPMT2、3A、3B和3C。采用高效液相色谱（HPLC）法测定所有研究对象的红细胞TPMT活性。
在248名健康受试者中鉴定出7名TPMT3C杂合子，未检测到TPMT2、3A和3B等位基因。TPMT3C等位基因频率为1.4%（7/496）。健康受试者的TPMT活性呈正态分布，范围为6.09至28.65 nmol/h/ml 每百万红细胞（pRBC），平均为16.03±4.16 nmol/h/ml pRBC。TPMT高活性和中等活性的临界值为10.07 nmol/h/ml pRBC。有19名健康受试者TPMT活性中等（7.7%），229名健康受试者TPMT活性高（92.3%），未发现TPMT缺乏的受试者。229名TPMT活性高的健康受试者均无突变等位基因，而19名TPMT活性中等的受试者中有7名有突变等位基因。95%的受试者表型与基因型相符。尿毒症患者均为野生型等位基因纯合子，与血液透析后相比，其TPMT活性在血液透析前显著升高。
我们将TPMT表型分析测定的临界值定义为10.07 nmol/h/ml pRBC，低于该值时进一步的基因分型可阐明个体药物治疗风险。在尿毒症患者中，某些尿毒症因素可使TPMT活性升高，透析使他们的TPMT活性接近健康对照组。
