Molecular and Cellular Endocrinology 218 (2004) 49–55 An in vitro bioassay to determine individual sensitivity to glucocorticoids: induction of FKBP51 mRNA in peripheral blood mononuclear cells Harry Vermeer a , Brenda I. Hendriks-Stegeman a , Denise van Suylekom a , Ger T. Rijkers b , Sylvia C. van Buul-Offers a , Maarten Jansen a,∗ a Department of Pediatric Endocrinology, HP KC.03.063.0, Wilhelmina Children’s Hospital, University Medical Center Utrecht, P.O. Box 85090, 3508 AB, Utrecht, The Netherlands b Department of Pediatric Immunology, University Medical Center Utrecht, Utrecht, The Netherlands Received 4 June 2003; received in revised form 24 November 2003; accepted 22 December 2003 Abstract Individual variation in sensitivity to glucocorticoids (GCs) poses a dilemma to the clinician. Currently available assays to determine individual sensitivity to GCs either seem imprecise, or they are based on mitogen-activated lymphocytes, although mitogens themselves may affect cellular GC sensitivity. To avoid these disadvantages, we developed an assay based on the GC-induced accumulation of the 51kDa FK506 binding protein (FKBP51) mRNA in unstimulated peripheral blood mononuclear cells (PBMC), measured using real time PCR. Of several family members tested, only FKBP51 transcript levels showed to be GC-inducible. Furthermore, our bioassay was not affected by progesterone, estradiol, and testosterone. Immunological stimulation of PBMC using tetanus toxoid did not affect bioassay results, and isolated T- and B-lymphocytes showed a similar response to GC stimulation. The intra- and inter-assay variations were 10.6 and 15.9%, respectively. Our bioassay confirms previous reports that a wide variation in GC sensitivity exists in the normal population, yet is able to clearly discriminate a patient with familial GC hyposensitivity from controls. Our bioassay may be suitable to assess altered individual GC sensitivity, and the small amount of PBMC needed for a determination makes this assay easily applicable in a pediatric setting. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: FKBP51; Real time PCR; Bioassay; Glucocorticoid sensitivity 1. Introduction Glucocorticoids (GCs) are commonly prescribed as treat- ment for chronic inflammatory diseases. The development of serious side effects following systemic GC administra- tion, such as osteopenia, hypertension or suppression of the hypothalamic-pituitary-adrenal (HPA) axis has led to the development of topically administered GCs, with an al- leged minimal systemic availability (Crim et al., 2001; Kelly, 1999). However, some patients still develop GC-induced side effects, even on low doses of non-systemically applied GCs (Grebe et al., 1997; Saha et al., 1997; Zimmerman et al., 1998), while other patients, in contrast, do not show an ade- quate response to GC medication in the usual dosage (Kino ∗ Corresponding author. Tel.: +31-30-2504003; fax: +31-30-2505350. E-mail address: m.jansen@wkz.azu.nl (M. Jansen). and Chrousos, 2001; Lamberts et al., 1996). It is therefore important to identify GC hyper- or hyposensitive patients, in order to provide treatment tailored to the needs of the individual patient. Because of inter-individual variation in GC sensitivity, establishment of the optimal therapeutic dose requires in vivo dose finding. Apparent GC hyper- or hyposensitiv- ity can, among other things, be caused by differences in systemic absorption or pharmacokinetic handling (Johnson, 1996), or poor compliance with therapy (Delhaas et al., 1998). These factors can be assessed using a bioassay which measures GC bioavailability in serum (Raivio et al., 2002; Vermeer et al., 2003a). Alternatively, ‘true’ GC hyper- or hyposensitivity can be caused by inter-individual differences in cellular GC sensitivity (Bamberger et al., 1996; Lamberts et al., 1996; McKenna et al., 1999). The clinical symp- toms of systemic alterations in GC sensitivity are relatively mild, which may be one of the reasons that relatively few 0303-7207/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.mce.2003.12.011