An in vivo microdialysis coupled with liquid chromatography/tandem mass spectrometry study of cortisol metabolism in monkey adipose tissue

It is postulated that elevated tissue concentrations of cortisol may be associated with the development of metabolic syndrome, obesity, and type 2 diabetes. The 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme regenerates cortisol from inactive cortisone in tissues such as liver and adipose. To better understand the pivotal role of 11β-HSD1 in disease development, an in vivo microdialysis assay coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis using stable isotope-labeled (SIL) cortisone as a substrate was developed. This assay overcomes the limitations of existing methodologies that suffer from radioactivity exposure and analytical assay sensitivity and specificity concerns. Analyte extraction efficiencies (E_d) were evaluated by retrodialysis. The conversion of SIL-cortisone to SIL-cortisol in rhesus monkey adipose tissue was studied. Solutions containing 100, 500, and 1000 ng/mL SIL-cortisone were locally delivered through an implanted 30-mm microdialysis probe in adipose tissue. At the delivery rate of 1.0 and 0.5 μL/min, E_d values for SIL-cortisone were between 58.7 ± 5.6% (n = 4) and 72.7 ± 1.3% (n = 4), whereas at 0.3 μL/min E_d reached nearly 100%. The presence of 11β-HSD1 activities in adipose tissue was demonstrated by production of SIL-cortisol during SIL-cortisone infusion. This methodology could be applied to cortisol metabolism studies in tissues of other mammalian species.