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IMPDH activity in thiopurine-treated patients with inflammatory bowel disease - Relation to TPMT activity and metabolite concentrations
Linköping University, Department of Clinical and Experimental Medicine, Gastroenterology and Hepatology. Linköping University, Faculty of Health Sciences.
1Research and Development in Laboratory Medicine Laboratory Medicine, Ryhov Hospital, Jönköping.
Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Health Sciences, Clinical Pharmacology. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Oncology UHL.
Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Gastroenterology and Hepatology. Östergötlands Läns Landsting, Centre for Medicine, Department of Endocrinology and Gastroenterology UHL.
2008 (English)In: British Journal of Clinical Pharmacology, ISSN 0306-5251, E-ISSN 1365-2125, Vol. 65, no 1, 69-77 p.Article in journal (Refereed) Published
Abstract [en]

AIMS: Azathioprine and 6-mercaptopurine are steroid-sparing drugs used in inflammatory bowel disease (IBD). The polymorphic enzyme thiopurine S-methyltransferase (TPMT) is of importance for thiopurine metabolism and occurrence of adverse events. The role of other thiopurine-metabolizing enzymes is less well known. This study investigated the role of inosine-5′- monophosphate dehydrogenase (IMPDH), which is a key enzyme in the de novo synthesis of guanine nucleotides and also strategically positioned in the metabolic pathway of thiopurines. METHODS: IMPDH was measured in 100 healthy blood donors. IMPDH, TPMT and metabolite concentrations were studied in 50 patients with IBD on stable thiopurine therapy. IMPDH activity was measured in peripheral blood mononuclear cells. TPMT activity, 6-methylthioinosine 5′-monophosphate (meTIMP) and 6-thioguanine nucleotide (6-TGN) concentrations were measured in red blod cells, which is the current practice in clinical monitoring of thiopurines. Enzyme activities were related to metabolite concentrations and clinical characteristics. RESULTS: A wide range of IMPDH activity was observed both in healthy blood donors (median 13.1, range 4.7-24.2 nmol mg-1 protein h-1) and IBD patients (median 14.0, range 7.0-21.7). There was a negative correlation between IMPDH activity and dose-normalized meTIMP concentrations (rs = -0.31, P = 0.03), but no evident correlation to 6-TGN concentration or the meTIMP/6-TGN ratio. There were no significant correlations between TPMT activity and metabolite concentrations. CONCLUSION: Even though the meTIMP concentrations correlated inversely to the IMPDH activity, the role of IMPDH in balancing the formation of methylated and phosphorylated metabolites was not evident. Taken together, the results give cause to question established opinions about thiopurine metabolism. © 2007 The Authors.

Place, publisher, year, edition, pages
2008. Vol. 65, no 1, 69-77 p.
Keyword [en]
6-Mercaptopurine/*pharmacology Adult Aged Aged, 80 and over Azathioprine/*pharmacology Biological Markers Female Humans IMP Dehydrogenase/genetics/*metabolism Immunosuppressive Agents/*pharmacology Inflammatory Bowel Diseases/*drug therapy Male Methyltran
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-43268DOI: 10.1111/j.1365-2125.2007.02985.xLocal ID: 73262OAI: diva2:264127
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2011-03-15Bibliographically approved
In thesis
1. Interindividual differences in thiopurine metabolism: studies with focus on inflammatory bowel disease
Open this publication in new window or tab >>Interindividual differences in thiopurine metabolism: studies with focus on inflammatory bowel disease
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thiopurines, 6-mercaptopurine and its prodrug azathioprine, are used in the treatment of inflammatory bowel disease, ulcerative colitis and Crohn´s disease. The main active metabolites are the phosphorylated thioguanine nucleotides (6-TGNs) and methylated thioinosine monophosphate (meTIMP). Both groups contribute to the immunomodulatory effects. About 30-40% of patients fail to benefit from thiopurine treatment. A well-known cause of adverse reactions is decreased or absent thiopurine S-methyltransferase (TPMT) activity. Low TPMT activity is inherited as an autosomal codominant recessive trait and is present in approximately 10% of the population. Although several clinical issues can be solved from determination of TPMT activity, there are cases where it is not possible. In Sweden approximately 25% of IBD-patients display suboptimal 6-TGN concentrations and unexpectedly high concentrations of meTIMP despite a normal TPMT activity. A high meTIMP/6-TGN concentration ratio has been associated with both unresponsiveness to therapy and emergence of adverse reactions. Inosine 5’-monophosphate dehydrogenase (IMPDH) may constitute a candidate gene to explain this metabolite profile, as it is strategically positioned in the metabolic pathway of thiopurines where it competes with TPMT for their common substrate 6-TIMP.

In paper I a pyrosequencing method was developed for genotyping of at that time all known genetic variants of TPMT. The concordance between genotype and phenotype in 30 individuals was 93%. The allele frequencies of TPMT*3A, *3B, *3C and *2 in a Swedish background population (n=800) were in agreement with those in other Caucasian or European populations. In Paper II-IV we explored the molecular basis of different metabolite profiles, i.e. low, normal and high meTIMP/6-TGN concentration ratios. The activity of IMPDH was measured in mononuclear cells (MNC). Patients with high metabolite ratios had lower IMPDH activity than patients with normal or low ratios, explained by an inverse correlation to red blood cells concentration of meTIMP. No correlation to 6-TGN was observed. Downregulation of IMPDH activity in HEK293 cells with genetically engineered TPMT activity was associated with an increase in meTIMP, but unexpectedly also of 6-TGN, irrespective of the TPMT status. These results suggest effects of pharmacogenes other than TPMT and IMPDH. A whole genome expression analysis was performed, (1) to identify new candidate genes that could explain differences in metabolite profiles, and (2) to study genes with known associations to the metabolic pathway of (thio)purines. The whole genome expression analysis did not identify any significant group differences. In analysis of the thiopurine related genes, three clusters of co-regulated genes were defined. A co-operation between expression levels of SLC29A1 and NT5E in explaining the meTIMP/6-TGN concentration ratio was observed, and individually SLC29A1 and NT5E correlated to 6-TGN and meTIMP, respectively.

Pysosequencing is a convenient and flexible method which is now run in parallel to phenotyping in our laboratory. Our results also illustrate the complexity of the thiopurine metabolism and suggest that differences between metabolite profiles are explained either by interactions between several genes, each with a small contribution, or at the post-transcriptional level. Search for more precise tools to explain differences in metabolite profiles is needed. Furthermore, in order to investigate small effects it is necessary to analyse metabolite concentrations and gene expression levels, as well as enzyme activities in the target cells of therapy (MNC).

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 96 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1231
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-66434 (URN)978-91-7393-213-4 (ISBN)
Public defence
2011-04-15, Aulan, Länssjukhuset Ryhov, Jönköping, 13:00 (Swedish)
Available from: 2011-03-15 Created: 2011-03-15 Last updated: 2012-03-22Bibliographically approved

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Haglund, SofiePeterson, CurtAlmer, Sven
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Gastroenterology and HepatologyFaculty of Health SciencesClinical PharmacologyDepartment of Oncology UHLDepartment of Endocrinology and Gastroenterology UHL
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British Journal of Clinical Pharmacology
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