Abstract
11β-Hydroxysteroid dehydrogenase 1 (11β-HSD1; EC 1.1.1.146) generates active glucocorticoid hormones. Small molecule inhibitors have been developed to target 11β-HSD1 for the treatment of dementia; these must enter brain subregions, such as the hippocampus, to be effective. We previously reported mass spectrometry imaging measurement of murine tissue steroids, and deuterated steroid tracer infusion quantification of 11β-HSD1 turnover in humans. Here, these tools are combined to assess tissue pharmacokinetics and pharmacodynamics of an 11β-HSD1 inhibitor that accesses the brain.[9,11,12,12-2H]4-Cortisol was infused (1.75 mg/day) by minipump for 2 days into C57Bl6 mice (male, age 12 weeks, n = 3/group) after which an 11β-HSD1 inhibitor (UE2316) was administered (25 mg/kg oral gavage) and animals culled immediately or 1, 2 and 4 h post-dosing. Mice with global genetic disruption of Hsd11B1 were studied similarly. Turnover of d4-cortisol to d3-cortisone (by loss of the 11-deuterium) and regeneration of d3-cortisol (by 11β-HSD1-mediated reduction) were assessed in plasma, liver and brain using matrix assisted laser desorption ionization coupled to Fourier transform cyclotron resonance mass spectrometry.The tracer d4-cortisol was detected in liver and brain following a two day infusion. Turnover to d3-cortisone and on to d3-cortisol was slower in brain than liver. In contrast, d3-cortisol was not detected in mice lacking 11β-HSD1. UE2316 impaired d3-cortisol generation measured in whole body (assessed in plasma; 53.1% suppression in rate of appearance in d3-cortisol), liver and brain. Differential inhibition in brain regions was observed; active glucocorticoids were suppressed to a greater in extent hippocampus or cortex than in amygdala.These data confirm that the contribution of 11β-HSD1 to the tissue glucocorticoid pool, and the consequences of enzyme inhibition on active glucocorticoid concentrations, are substantial, including in the brain. They further demonstrate the value of mass spectrometry imaging in pharmacokinetic and pharmacodynamic studies.
Highlights
Glucocorticoids act in many tissues and when present in excess can induce obesity, hyperglycaemia, and cognitive dysfunction.⇑ Corresponding author.The reductase activity of 11b-hydroxysteroid dehydrogenase type 1 (11b-HSD1; EC 1.1.1.146) regenerates active glucocorticoid from inert keto-steroid substrates in glucocorticoid target tissues including liver, adipose tissue and brain
Tracer kinetics have been used in combination with arterio-venous sampling to quantify 11b-HSD1 turnover in humans, the data here provide the first information about tracer kinetics within tissues and, notably, within brain sub-regions
The data presented describe the tissue pharmacokinetics and pharmacodynamic responses of a brainpenetrant 11b-HSD1 inhibitor, confirming the potential for substantial effects on tissue glucocorticoid levels and illustrating the ratio increased again until 2 h reflected in a (E) reduced rate of appearance (Ra) of d3F, indicative of enzyme inhibition
Summary
Glucocorticoids act in many tissues and when present in excess can induce obesity, hyperglycaemia, and cognitive dysfunction. Mass spectrometry imaging (MSI) is increasingly being deployed as an alternative approach, albeit not for absolute quantitation [19] It offers the advantages of simultaneously identifying both drug and metabolites in tissues while providing a fingerprint of pharmacodynamic changes in the metabolome of responsive organs [19]. We report the combined application of stable-isotope tracer infusion with MSI to understand the pharmacodynamic responses to a pre-clinical tool molecule acting as a brain-penetrant 11b-HSD1 inhibitor, UE2316 [21,22,23,24,25], and demonstrate how these measurements can complement conventional measures of 11b-HSD1 activity ex vivo
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