Received on October 25, 2006
Accepted on March 15, 2007

Molecular Diagnostics and Genetics

Real-Time PCR Determination of IMPDH1 and IMPDH2 Expression in Blood Cells

¹ Department of Medical Biochemistry, Rikshospitalet-Radiumhospitalet Medical Centre, Oslo, Norway, and Institute of Clinical Biochemistry, Faculty Division Rikshospitalet, University of Oslo, Norway

^* To whom correspondence should be addressed. E-mail: stein.bergan{at}rikshospitalet.no.

Background: Inosine monophosphate dehydrogenase (IMPDH) catalyzes the rate-limiting step in de novo guanine nucleotide synthesis and is implicated in cell cycle control. Inhibition of this enzyme is associated with immunosuppressive, antiviral, and antitumor activity. IMPDH basal activity increases after initiation of immunosuppressive therapy.

Methods: A real-time reverse-transcription PCR assay was developed and validated for mRNA quantification of the 2 human IMPDH isoforms. Target gene expressions were normalized to the geometric mean of 3 housekeeping genes. Assay utility was tested by analyzing patient samples and cultured cells exposed to immunosuppressive drugs such as the IMPDH inhibitor mycophenolic acid.

Results: The assay was linear over 6 logs of cDNA input and demonstrated specific quantification of IMPDH1 and IMPDH2 expression in cultured cells and patient samples. Limits of detection and quantification were 10 and 10³ copies of cDNA per reaction, respectively. Within-run and total between-day CVs were <15% for normalized expression. Changes in IMPDH1 and 2 expression were observed in patient samples after initiation of an immunosuppressive regimen that included calcineurin inhibitors, mycophenolate mofetil, and steroids.

Conclusions: This assay can be used to study the regulation of IMPDH expression and the involvement of the enzymes in immunological and malignant proliferative conditions. This may contribute to the processes of drug development and to the establishment of monitoring strategies for treatment effect and disease activity.