Individual variability of cortisone/cortisol ratio correlated to the cortisol concentration in human urine as a new index for phenotyping in vivo 11β-hydroxysteroid dehydrogenase 2 activity

Akitomo Yokokawa, Hiromi Shibasaki, Takashi Furuta. School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, Department of Medicinal Chemistry and Clinical Pharmacy, Japan

11β-Hydroxysteroid dehydrogenase 2 (11β-HSD2) is expressed in aldosterone target tissues, especially in human kidney. The enzyme converts physiologically active cortisol into inactive cortisone. Of the 2 hormones, only cortisol has an affinity for mineralocorticoid receptors (MRs) and thus induces mineralocorticoid effects. Normal activity of 11β-HSD2 is crucial for the prevention of mineralocorticoid activity of cortisol. The absence of or decrease in 11β-HSD2 activity results in apparent mineralocorticoid excess (AME) and cortisol-mediated hypermineralocorticoid hypertension. Urinary ratio of free cortisol and cortisone (UFE/UFF ratio) has been used as an index of 11β-HSD2 activity in vivo. The problem of estimating the in vivo enzyme activity is that there are large variations in the UFE/UFF ratio influenced by some factors. Recently, we found that the urinary concentration of cortisol was highly correlated with the UFE/UFF ratio in urine (r = 0.858), indicating that the in vivo activity of 11β-HSD2 (UFE/UFF ratio) should fluctuate with the changes of the urinary concentration of cortisol. We then proposed a new estimation method of in vivo activity of 11β-HSD2 in humans using the UFE/UFF ratio correlated with the urinary concentration of cortisol (UFE/UFF–cortisol concentration). The usefulness of this estimation method was confirmed by an inhibitory effect of glycyrrhetinic acid on the activity of 11β-HSD2 in healthy volunteers. In the present study, the inter- and intra-individual variabilities of in vivo 11β-HSD2 activity were evaluated by the UFE/UFF–cortisol concentration. Urinary excreted amounts of cortisol and cortisone were analyzed by stable isotope dilution mass spectrometric analysis using GC/MS. The mean in vivo 11β-HSD2 activity in 15 healthy subjects showed that there were no significant within-day (10:00 to 22:00) variations in 11β-HSD2 activity, indicating that 11β-HSD2 activity can be accurately evaluated by only measuring cortisol and cortisone concentrations in spot urine samples. However, it was found that the 11β-HSD2 activity in the nighttime (22:00 to 10:00) (0.76±0.16) was lower than that in the daytime (10:00 to 22:00) (0.96±0.14). 11β-HSD2 activities in a healthy subject were also followed for 40 days by evaluating the UFE/UFF–cortisol concentration index in urine (10:00 to 12:00). The mean in vivo 11β-HSD2 activity was 1.01±0.11. The intra-individual variation of 11β-HSD2 activity (1.39 fold) was within the range of the daytime activity evaluated in 15 subjects (2.09 fold) and there was no characteristic rhythm in the activity for 40 days.