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

1. A genetic polymorphism in human erythrocyte thiopurine methyltransferase activity (RBC TPMT) resulting in a trimodal phenotypic distribution has been demonstrated both in a North American population and in British children. 2. We studied whether such a polymorphism may be also present in a white French population by testing RBC TPMT activity in 303 randomly selected blood donors. 3. We found a large inter-individual variation in RBC TPMT activity which ranged from 2 to 40 nmol ml-1 packed RBC h-1, with a mean value of 15.4 +/- 7.0 nmol ml-1 packed RBC h-1. The enzyme activity was not significantly influenced by the sex and age of the subjects. 4. In our population sample, we found no subject with undetectable enzyme activity. However, the probit plot of the log RBC TPMT activity showed a highly significant change in slope at a TPMT activity of 7.5 nmol ml-1 packed RBC h-1. Thirty four subjects (11% of our population) had TPMT activities below 7.5 nmol ml-1 packed RBC h-1. 5. These data are consistent with the view that the genetic polymorphism of TPMT activity described in populations from North America and the United Kingdom is also present in a French population, with about 89% of subjects exhibiting a high activity and 11% an intermediate activity.
Br J Clin Pharmacol 1991 Dec
PMID:Pharmacogenetics of human erythrocyte thiopurine methyltransferase activity in a French population. 176 66

Thiopurine methyltransferase deficiency, inherited as an autosomal codominant trait, is associated with aberrant mercaptopurine metabolism leading to excessive cellular accumulation of 6-thioguanine nucleotides, the active metabolites of mercaptopurine. We describe a case of severe thiopurine methyltransferase deficiency (activity less than 1 U/8 x 10(8) erythrocytes) in a young girl with acute lymphocytic leukemia. The level of 6-thioguanine nucleotide in the patient's erythrocytes was seven times the population median value, and she had intolerable hematologic toxic effects during postremission therapy with a standard dosage of mercaptopurine (75 mg/m2 per day). Subsequent therapy with 6% of this dosage (10 mg/m2 three times weekly) yielded erythrocytic 6-thioguanine nucleotide concentrations consistently above the population median but not associated with prohibitively toxic effects. This case demonstrates that thiopurine methyltransferase deficiency does not absolutely contraindicate mercaptopurine therapy, and it also provides insight into the mechanism of excessive toxic effects of mercaptopurine sometimes observed in children with acute lymphocytic leukemia.
J Pediatr 1991 Dec
PMID:Altered mercaptopurine metabolism, toxic effects, and dosage requirement in a thiopurine methyltransferase-deficient child with acute lymphocytic leukemia. 196 Jun 24

We have examined red blood cell (RBC) thiopurine methyltransferase (TPMT) activity in a healthy population sample of Norwegian children, age 1-10 years. Boys had mean RBC TPMT activity of 11.1 +/- 2.0 U (n = 87) vs. 10.6 +/- 2.2 U (n = 71) in girls, the difference was not significant (P = 0.3). Age was negatively correlated to RBC TPMT activity (rs = -0.2, P = 0.01). As boys with acute lymphoblastic leukemia (ALL) tolerate more 6-mercaptopurine (6-MP) than girls and have a higher risk of relapse, we have searched for pharmacokinetic causes of these gender differences. The gender difference in 6-MP tolerance and clinical outcome in children with ALL cannot be explained by the minor and nonsignificant higher RBC TPMT activity in boys compared to girls.
Med Pediatr Oncol 1995 Dec
PMID:Is there a gender difference in red blood cell thiopurine methyltransferase activity in healthy children? 756 6

Pharmacogenetics has emerged as a novel and challenging area of interest in oncology. Cancer chemotherapy is characterized by major intersubject variability in tumor responses and host toxicity. This variation may be caused by genetic differences in the enzymes involved in the metabolism of anticancer agents. Anticancer agents, such as 6-mercaptopurine, 5-fluorouracil, and irinotecan, have a narrow therapeutic index that can sometimes result in severe life-threatening toxicities. The impact of polymorphisms in metabolizing enzymes (thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase, and uridine diphosphate glucuronosyltransferase) that participate significantly in the disposition of these anticancer agents is discussed.
Mol Diagn 1999 Dec
PMID:Inherited variations in drug-metabolizing enzymes: significance in clinical oncology. 1067 43

Knowledge about the clinical pharmacology of medical therapy of inflammatory bowel disease has incrementally advanced. Small studies with mesalamine have suggested that intestinal mucosal concentrations of mesalamine may predict clinical response to mesalamine therapy. Increased expression of glucocorticoid receptor beta and increased expression of the multidrug resistance drug pump P-glycoprotein 170 have been proposed as markers of drug resistance to glucocorticoids. A baseline determination of thiopurine methyltransferase phenotype or genotype may predict early leukopenia in patients treated with azathioprine or 6- mercaptopurine. Serial measurement of erythrocyte 6-thioguanine nucleotides may be useful in tailoring the dose of these medications. A loading dose of intravenous azathioprine does not accelerate the time to response in patients with steroid-treated Crohn's disease; however, standard azathioprine may work more quickly than previously reported. Methotrexate, 15 to 25 mg/wk, is effective for the treatment of Crohn's disease (active or in remission), and there is no significant difference in the erythrocyte concentrations of methotrexate polyglutamate in patients with inflammatory bowel disease receiving 15 mg, compared with 25 mg, subcutaneously on a weekly basis.
Curr Gastroenterol Rep 2000 Dec
PMID:Clinical pharmacology of inflammatory bowel disease therapies. 1107 44

Management of Crohn's disease has changed considerably in recent years. The discovery of tumor necrosis factor (TNF) as a pivotal cytokine in the inflammatory cascade has led to the development of several neutralizing antibodies, soluble receptors, and small molecules, interfering with TNF gene transcription and expression. Infliximab is the only monoclonal antibody that is commercially available. This potent molecule is effective for both active and fistulizing disease in the acute and maintenance phases of treatment. In addition to anti-TNF agents, weekly methotrexate injection and the classic "antimetabolites" azathioprine and 6-mercaptopurine remain highly valuable as maintenance drugs. "Tailored" antimetabolite therapy has now become possible with metabolite measurements and determination of the TPMT gene. The active metabolite thioguanine itself could be a promising alternative in patients who are intolerant of 6-mercaptopurine. In fistulizing disease, infliximab is becoming the treatment of choice, although fistula tracks do not disappear permanently and many patients still need surgical intervention.
Curr Gastroenterol Rep 2002 Dec
PMID:Advances in medical therapy for Crohn's disease. 1244 Oct 41

6-Mercaptopurine (6-MP) and its prodrug azathioprine (AZA) remain the mainstay of immunomodulator therapy for the maintenance of steroid-free remission in patients with inflammatory bowel disease (IBD). Traditional dosing strategies for initiation of thiopurines are often based on weight or empirically chosen. Dosing based on an understanding of an inherited difference in drug disposition and metabolism may provide a safer alternative. The thiopurine methyltransferase (TPMT) enzyme plays a pivotal role in the metabolism of 6-MP and AZA and is critical to the determination of thiopurine toxicity. The therapeutic benefits of thiopurines correlate best with concentration of the active 6-thioguanine (6-TGN) metabolites. Reports suggest that therapeutic response can be maximized when patients achieve therapeutic 6-TGN levels. Pharmacogenetic dosing based on TPMT and pharmacokinetic dosing based on 6-TGN levels may offer a safety and efficacy advantage over traditional dosing strategies and provide a novel mechanism for optimizing immunomodulator therapy in IBD.
Curr Gastroenterol Rep 2003 Dec
PMID:Optimizing immunomodulator therapy for inflammatory bowel disease. 1460 61

A non-extraction high-performance liquid chromatographic (HPLC) method has been developed for the determination of 6-methylthioguanine (6-MTG), as part of the determination of thiopurine S-methyltransferase activity (TPMT) in erythrocytes. Erythrocyte lysate is added to a glass vial containing substrates and incubation buffer, which is then sealed for the rest of the analysis. Enzyme incubation, sample preparation, and analysis are then undertaken without further sample-handling steps. The need for a solvent extraction step has been overcome by heating the incubate to 85 degrees C to stop the enzyme reaction. The heat inactivation step precipitates protein which upon centrifugation forms a thin film in the bottom of the glass vial enabling the supernatant to be injected directly onto the HPLC system. The assay shows excellent precision and recovery with a within-batch imprecision giving a co-efficient of variation of 2.9% (mean=41.5 nmol 6-MTG/gHb/h, n=10) and 5.1% (mean=12.6 nmol 6-MTG/g Hb/h, n=10). The between-batch imprecision gives a co-efficient of variation of 8.2% (mean=11.1 nmol 6-MTG/gHb/h, n=11) and 7.3% (mean=41.0 nmol 6-MTG/gHb/h, n=16). Determination of the TPMT activity in 120 people shows a range of enzyme activity of 11.3-63.8 nmol 6-MTG/gHb/h with a mean and median activity of 34.8 and 34.2 nmol 6-MTG/gHb/h, respectively. TPMT is increasingly used in clinical practice to ensure optimisation of treatment with thioguanine drugs. This direct HPLC method minimises sample-handling, reduces inherent imprecision, the possibility of laboratory error and with the potential for further automation, makes it ideal for use in a regional referral laboratory.
J Chromatogr B Analyt Technol Biomed Life Sci 2003 Dec 05
PMID:Determination of thiopurine S-methyltransferase activity in erythrocytes using 6-thioguanine as substrate and a non-extraction liquid chromatographic technique. 1463 Mar 65

This study examined thiopurine methyltransferase (TPMT) and the relationship to thioguanine nucleotides (TGN) and methylthioinosine monophosphate (meTIMP) in a large Swedish patient population. The current hypothesis is that the cytotoxic effects of thiopurine drugs are mediated by the incorporation of TGN into DNA. The authors assayed the TPMT activity in red blood cells from 1151 subjects and the concentrations of TGN (n = 602) and meTIMP (n = 593) from patients treated with thiopurine drugs. The TPMT frequency distribution in both adults and children showed some differences from what had been found in unselected general populations. Children had lower median TPMT activity than adults (12.0 versus 12.9 U/mL RBC; P < 0.001). Relative differences in both TGN formation [medians: normal TPMT, 1.3; intermediate TPMT, 3.3; low TPMT, 47.9 pmol/8 x 10(8) RBC per mg azathioprine (AZA); P < 0.001] and meTIMP formation (medians: normal TPMT, 13; intermediate TPMT, 7.3; low TPMT, 0 pmol/8 x 10(8) RBC per mg AZA; P = 0.001) per 1 mg administered drug were noted among the 3 TPMT activity groups. Women formed higher concentrations of both TGN (1.5 versus 1.3 pmol/8 x 10(8) RBC per mg AZA; P = 0.01) and meTIMP (14.4 versus 10.7 pmol/8 x 10(8) RBC per mg AZA; P = 0.01) than men did. There was a significant correlation between the AZA dose and the meTIMP concentrations (r = 0.45; P < 0.001). Furthermore, dose alterations made in subjects with normal TPMT (n = 84) and intermediate TPMT (n = 22) activity resulted in more pronounced increases in TGN concentrations (170 versus 30 pmol/8 x 10(8) RBC; P < 0.001) in intermediate TPMT activity, whereas in normal TPMT activity changes in meTIMP concentrations were more pronounced (1.3 versus 0 nmol/8 x 10(8) RBC; P < 0.001). In normal TPMT activity both metabolites increased in a dose-dependent fashion, whereas in intermediate TPMT activity only TGN concentrations increased. The results of this study demonstrate the dynamic nature of thiopurine metabolism and its importance for thiopurine dosing.
Ther Drug Monit 2004 Dec
PMID:Assessment of thiopurine methyltransferase and metabolite formation during thiopurine therapy: results from a large Swedish patient population. 1557 Jan 93

Azathioprine has been available as an immunosuppressive agent for over 40 years, and current routine usage in dermatology is not restricted to licensed indications. Advances in understanding the metabolic fate of azathioprine have led to significant changes in prescribing practice and toxicity monitoring by U.K. dermatologists. The current state of knowledge concerning the use of azathioprine in dermatology is summarized, with identification of strength of evidence. Clinical indications and contraindications for azathioprine usage in dermatology are identified. Evidence-based recommendations are made for routine safety monitoring of patients treated with azathioprine, including pretreatment assessment of red blood cell thiopurine methyltransferase activity.
Br J Dermatol 2004 Dec
PMID:Guidelines for prescribing azathioprine in dermatology. 1560 6


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