SFEBES2013 Poster Presentations Steroids (37 abstracts)
19F-magnetic resonance spectroscopy as a tool to quantify 11β-hydroxysteroid dehydrogenase activity in vivo
Gregorio Naredo-Gonzalez 1, , Maurits Jansen 2 , Rita Upreti 1 , Scott Semple 3 , Gavin Merrifield 2 , Oliver Sutcliffe 4 , Michael Hansen 5 , Ian Marshall 6 , Ruth Andrew 1, & Brian Walker 1,
1Endocrinology, University/BHF Centre for Cardiovascular Sciences, University of Edinburgh, Edinburgh, UK; 2Edinburgh Preclinical Imaging, University/BHF Centre for Cardiovascular Sciences, University of Edinburgh, Edinburgh, UK; 3Clinical Research Imaging Centre, University of Edinburgh, Edinburgh, UK; 4Division of Chemistry and Environmental Science, School of Science and the Environment, Manchester Metropolitan University, Manchester, UK; 5Johnson & Johnson Pharmaceutical Research and Development, New Jersey, USA; 6Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK; 7Mass Spectrometry Core, Wellcome Trust Clinical Research Facility, University of Edinburgh, Edinburgh, UK.
Non-invasive methods to measure enzyme activity in vivo can provide a useful tool for the development of selective inhibitors. Tissue-specific dysregulation of 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), a reductase enzyme that amplifies active intracellular glucocorticoid levels, has been shown in obese patients using invasive tools (biopsy, microdialysis and arteriovenous sampling with stable isotope tracers). 11β-HSD1 inhibitors are efficacious in pre-clinical models of obesity, diabetes, atherogenesis and cognitive dysfunction, but unpredictable pharmacodynamics may explain disappointing results in phase 2 trials. We have explored the use of 19F-magnetic resonance spectroscopy (MRS) and identified suitable fluorinated keto tracer substrates for the in vivo monitoring of hepatic 11β-HSD1 both in rat and human. The effect of tracer structure (equivalent fluorine atoms per molecule and distance to the keto/hydroxy group), tracer abundance, scanning time and biological matrix was studied using seven Tesla (small animal) and three Tesla (human) MRI scanners. 19F-MRS responses were linearly related to the total amount of equivalent fluorine atoms. Signals from keto and hydroxy forms differing as little as 0.6 ppm could be resolved and measured simultaneously. We have determined in vitro LODF (limit of detection as absolute fluorine content) of 0.250 μmol in chloroform and 0.625 μmol in blood, using 400 s/spectrum. In vivo detection of tracer 2-(phenylsulfonyl)-1-(4-(trifluoromethyl)phenyl)ethanone and its hydroxy metabolite was achieved in rat liver (7T scanner) after very low oral doses of tracer (5-8 mg). However, this tri-fluorinated tracer is not a licensed pharmaceutical, so studies in humans were progressed with monofluorinated dexamethasone. Oral doses of 10–14 mg were used and under these conditions neither substrate nor product could be detected in human liver. We conclude that MRS monitoring of 11β-HSD1 is feasible, but requires novel multi-fluorinated tracers.
Declaration of funding: This work was supported by an award from the Translational Medicine Research Collaboration (a consortium of the Universities of Aberdeen, Dundee, Edinburgh and Glasgow, the associated NHS Health Boards), Scottish Enterprise and Wyeth (now Pfizer) Pharmaceuticals, grant reference CVMD/EU/016 and British Heart Foundation (BHF) Programme Grant RG/200016.
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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