Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.1.1.67 (thiopurine methyltransferase)
 551 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Azathioprine-induced myelosuppression is the most important side effect observed in kidney transplantation. We report a case of severe neutropenia after kidney transplantation due to a thiopurine methyltransferase deficiency. This cause of azathioprine-induced myelotoxicity is rare, but its infectious consequences may be severe. Thiopurine methyltransferase deficiency must therefore be suspected when early and severe leukopenia occurs during azathioprine therapy. Erythrocyte thiopurine methyltransferase activity measurement confirms the diagnosis. Azathioprine and 6-mercaptopurine must afterwards be definitively avoided.
Presse Med 1995 Sep 23
PMID:[Homozygote deficiency of thiopurine methyltransferase. A contraindication to the use of azathioprine in kidney transplantation]. 750 7

Azathioprine can cause severe myelosuppression. The inherited activity of the enzyme thiopurine methyltransferase has been recently recognised as a major factor in the susceptibility to myelosuppression. Thiopurine methyltransferase deficiency occurs at a frequency of one in 300 and is associated with profound myelosuppression after a short course of azathioprine. Very low thiopurine methyltransferase activity represents the TPMTL/TPMTL genotype, and can be detected before therapy with azathioprine is started. We describe the first documented case of azathioprine-induced severe myelosuppression due to thiopurine methyltransferase deficiency in autoimmune liver disease. The azathioprine dose was low (1 mg/kg) and pancytopenia occurred after 56 days therapy. It would be advisable to measure thiopurine methyltransferase activity before patients with autoimmune hepatitis are exposed to azathioprine.
J Hepatol 1995 Sep
PMID:Azathioprine-induced myelosuppression due to thiopurine methyltransferase deficiency in a patient with autoimmune hepatitis. 855 Oct 1

1. 2-(Allylthio)pyrazine (2-AP) has been demonstrated to protect the liver against toxicants by inhibiting CYP2E1 activity. Since 2-mercaptopyrazine (2-MP) is presumed to be a metabolite of 2-AP, the experiments were performed to determine whether rat liver microsomal and/or cytosolic preparations could catalyse the S-methylation of 2-MP. 2. It was found that both rat liver microsomes and cytosol could catalyse the S-methylation of 2-MP. The microsomal activity displayed biphasic substrate kinetics, with apparent Km = 8.44+/-2.68 and 417+/-74 microM for the high- and low-affinity activities respectively. The high-affinity activity had an apparent Km for S-adenosyl-L-methionine (Ado-Met) of 3.52 microM. The cytosolic activity also displayed biphasic substrate kinetics, with apparent Km of 3.26+/-0.62 and 91.6+/-23.1 microM for the high- and low-affinity activities respectively. 3. The microsomal S-methylation of 2-MP was inhibited by 2,3-dichloro-alpha-methylbenzylamine (DCMB), SKF-525A and benzylamine, known microsomal thiol methyltransferase (TMT) inhibitors, whereas cytosolic activity was inhibited by anisic acid and 3-chlorobenzoate, which also inhibit cytosolic thiopurine methyltransferase (TPMT). Both activities were inhibited by S-adenosyl-L-homocysteine (Met-Hcy). 4. These results suggest that both TMT and TPMT may be involved in the in vivo methylation of 2-MP.
Xenobiotica 1999 Sep
PMID:S-methylation of 2-mercaptopyrazine in rat liver microsomes and cytosol. 1054 51

The activity of thiopurine S-methyltransferase (TPMT) is inherited as an autosomal co-dominant trait. In most large world populations studied to date, approximately 10% of the population have intermediate activity due to heterozygosity at the TPMT locus, and about 0.33% is TPMT deficient. TPMT is now one of the most well characterized genetic polymorphisms of drug metabolism, with the genetic basis having been well defined in most populations, providing molecular strategies for studying this genetic polymorphism in human and experimental models. Three mutant alleles, TPMT(*)2, TPMT(*)3A and TPMT(*)3C, account for the great majority of mutant alleles in all human populations studied to date. Significant ethnic differences occur in the frequencies of these mutant alleles. Progress in DNA analysis has made it practical to use genotyping techniques for the molecular diagnosis of TPMT deficiency and heterozygosity, thereby avoiding adverse effects that are more prevalent in TPMT-deficient and heterozygous patients prescribed thiopurine medications.
Pharmacology 2000 Sep
PMID:Genetic polymorphism of thiopurine S-methyltransferase: molecular mechanisms and clinical importance. 1097 Nov 99

S-Methylation by thiopurine methyltransferase (TPMT) is an important route of metabolism for the thiopurine drugs. About one in 300 individuals are homozygous for a TPMT mutation associated with very low enzyme activity and severe myelosuppression if treated with standard doses of drug. To validate the use of molecular genetic techniques for the detection of TPMT deficiency, we have determined red blood cell TPMT activity in 240 adult blood donors and 55 normal children. Genotype was determined by restriction fragment length analysis of polymerase chain reaction products in a cohort of 79 of the blood donors and five cases of azathioprine-induced myelosupression, and this confirmed a close relationship between genotype and phenotype. In 17 of the 24 cases in which mutations were found, DNA was also available from remission bone marrow. In one of these cases, DNA from the remission marrow sample indicated the presence of a non-mutated allele that had not been seen in the blast DNA sample obtained at presentation. These results indicate that polymerase chain reaction-based assays give reliable and robust results for the detection of TPMT deficiency, but that caution should be exercised in relying exclusively on DNA obtained from lymphoblasts in childhood leukaemia.
Br J Haematol 2000 Sep
PMID:A comparison of molecular and enzyme-based assays for the detection of thiopurine methyltransferase mutations. 1099 70

Significant fractions of health budgets must be spent for treatment of drug side effects and for inefficient drug therapy. Hereditary variants in drug metabolizing enzymes, drug transporters, and drug targets are important determinants of drug response and toxicity and may therefore aid in selection and dosage of drugs. Today there is extensive knowledge of genetic polymorphisms of cytochrome P450 (CYP) enzymes 2A6, 2C9, 2C19, and 2D6; of phase-2 enzymes such as thiopurine S-methyltransferase; and more recently of drug transporters such as the MDR-1 gene-product P-glycoprotein, affecting a significant share of currently used drugs. However, application of pharmacogenetic knowledge to clinical routine is limited in current practice. To promote the application of pharmacogenetic knowledge in clinical routine, research on genotype-based dose adjustments is still necessary - as is the promotion of faster and cheaper genotype analyses. Furthermore, the benefits of CYP genotype-directed drug therapy should be evaluated in properly designed prospective studies. Once such steps have been successfully taken, drug therapy could well become more prevention-directed and patient-tailored than it is possible today, replacing the current "one drug in one dose for one disease" strategy by a more individualized approach.
Clin Chem Lab Med 2000 Sep
PMID:How to manage individualized drug therapy: application of pharmacogenetic knowledge of drug metabolism and transport. 1109 42

There are pharmacological differences between women and men that have important clinical consequences. For several drugs, there is a higher incidence in women of drug-induced QT prolongation and a potentially fatal arrhythmia, torsades de pointes. This may be a reflection of the longer baseline QT interval in women. A difference in cardiovascular disease between women and men is that women have a higher mortality rate after myocardial infarction (MI). Women also have a higher rate of hemorrhagic stroke after receiving thrombolytic therapy for an MI. Differences in effectiveness of analgesics have been demonstrated, with kappa opioids providing pain relief for women but not men. Drugs may have different pharmacokinetics in women and men because of differences in phase I and phase II enzymes that metabolize drugs. Conflicting results about biological sex differences have been reported for the major drug metabolizing enzyme, cytochrome P450 3A4 (3A4) and may be related to a role for P-glycoprotein, a cell membrane transporter, reported as two times higher in male livers than those of females. It has been reported that boys need a higher dose of 6-mercaptopurine, which is metabolized by thiopurine methyltransferase (TPMT). TPMT is reported to be 14% higher in male human liver biopsies than those from females. Verapamil, a drug for angina and hypertension, has different clearance and side effects in men and women. Ethnic/racial variations have also been demonstrated with the drug metabolizing enzymes, CYP2C9, 2C19, and 2D6.
J Womens Health Gend Based Med 2002 Sep
PMID:Biologic and molecular mechanisms for sex differences in pharmacokinetics, pharmacodynamics, and pharmacogenetics: Part I. 1239 93

S-Adenosyl-L-methionine (AdoMet) which is biologically synthesized by AdoMet synthetase bears an S configuration at the sulfur atom. The chiral sulfonium spontaneously racemizes to form a mixture of S and R isomers of AdoMet under physiological conditions or normal storage conditions. The chirality of AdoMet greatly affects its activity; the R isomer is not accepted as a substrate for AdoMet-dependent methyltransferases. We report a stereospecific colorimetric assay for (S,S)-adenosylmethionine quantification based on an enzyme-coupled reaction in which (S,S)-AdoMet reacts with 2-nitro-5-thiobenzoic acid to form AdoHcy and 2-nitro-5-methylthiobenzoic acid. The transformation is catalyzed by recombinant human thiopurine S-methyltransferase (TPMT, EC 2.1.1.67) and is associated with a large spectral change at 410 nm. Accumulation of the S-adenosylhomocysteine (AdoHcy) product, a feedback inhibitor of TPMT, slows the assay. AdoHcy nucleosidase (EC 3.2.2.9) irreversibly cleaves AdoHcy to adenine and S-ribosylhomocysteine, significantly shortening the assay time to less than 10 min. The assay is linear from 5 to at least 60 microM (S,S)-AdoMet.
Anal Biochem 2002 Sep 15
PMID:A stereospecific colorimetric assay for (S,S)-adenosylmethionine quantification based on thiopurine methyltransferase-catalyzed thiol methylation. 1241 50

The metabolism of MK-0767, (+/-)-5-[(2,4-dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl) phenyl]methyl]benzamide, a thiazolidinedione (TZD)-containing peroxisome proliferator-activated receptor alpha/gamma agonist, was studied in liver microsomes and hepatocytes from humans and rat, dog, and rhesus monkey, to characterize the enzyme(s) involved in its metabolism. The major site of metabolism is the TZD ring, which underwent opening catalyzed by CYP3A4 to give the mercapto derivative, M22. Other metabolites formed in NADPH-fortified liver microsomes included the TZD-5-OH derivative (M24), also catalyzed by CYP3A4, and the O-desmethyl derivative (M28), whose formation was catalyzed by CYP2C9 and CYP2C19. Metabolite profiles from hepatocyte incubations were different from those generated with NADPH-fortified microsomal incubations. In addition to M22, M24, and M28, hepatocytes generated several S-methylated metabolites, including the methyl mercapto (M25), the methyl sulfoxide amide (M16), and the methyl sulfone amide (M20) metabolites. Addition of the methyl donor, S-adenosyl methionine, in addition to NADPH, to microsomal incubations enhanced the turnover and resulted in metabolite profiles similar to those in hepatocyte incubations. Collectively, these results indicated that methyltransferases played a major role in the metabolism of MK-0767. Using enzyme-specific inhibitors, it was concluded that microsomal thiol methyltransferases play a more important role than the cytosolic thiopurine methyltransferase. Baculovirus-expressed human flavin-containing monooxygenase 3, as well as CYP3A4, oxidized M25 to M16, whereas further oxidation of M16 to M20 was catalyzed mainly by CYP3A4. Esterases were involved in the formation of the methyl sulfone carboxylic acids, minor metabolites detected in hepatocytes.
Drug Metab Dispos 2004 Sep
PMID:In vitro metabolism of MK-0767 [(+/-)-5-[(2,4-dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl) phenyl]methyl]benzamide], a peroxisome proliferator-activated receptor alpha/gamma agonist. I. Role of cytochrome P450, methyltransferases, flavin monooxygenases, and esterases. 1531 44

6-Mercaptopurine and its prodrug azathioprine remain the mainstay of immunomodulator therapy for the maintenance of a steroid-free remission in patients with IBD. Recent evidence suggests that the cytotoxic and immunosuppressive effects of azathioprine might be mediated via the induction of lymphocyte apoptosis by its active metabolites, 6-thioguanine nucleotides. The therapeutic benefits of thiopurines have been shown to correlate with the concentration of 6-thioguanine nucleotides. Inherited differences in drug metabolism and disposition can significantly impact the safety and efficacy of these drugs. The thiopurine methyltransferase enzyme plays an important role in the metabolism of 6-mercaptopurine and azathioprine and in the determination of thiopurine cytotoxicity. By gaining an understanding of the pharmacology and metabolism of thiopurine therapy and putting it into the clinical context, clinicians will be able to optimize thiopurine therapy in IBD.
Clin Gastroenterol Hepatol 2004 Sep
PMID:Azathioprine, 6-mercaptopurine in inflammatory bowel disease: pharmacology, efficacy, and safety. 1535 73


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