Virtual screening as a strategy for the identification of xenobiotics disrupting corticosteroid action

Impaired corticosteroid action caused by genetic and environmental influence, including exposure to hazardous xenobiotics, contributes to the development and progression of metabolic diseases, cardiovascular complications and immune disorders. Novel strategies are thus needed for identifying xenobiotics that interfere with corticosteroid homeostasis. 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) and mineralocorticoid receptors (MR) are major regulators of corticosteroid action. 11β-HSD2 converts the active glucocorticoid cortisol to the inactive cortisone and protects MR from activation by glucocorticoids. 11β-HSD2 has also an essential role in the placenta to protect the fetus from high maternal cortisol concentrations.; We employed a previously constructed 3D-structural library of chemicals with proven and suspected endocrine disrupting effects for virtual screening using a chemical feature-based 11β-HSD pharmacophore. We tested several in silico predicted chemicals in a 11β-HSD2 bioassay. The identified antibiotic lasalocid and the silane-coupling agent AB110873 were found to concentration-dependently inhibit 11β-HSD2. Moreover, the silane AB110873 was shown to activate MR and stimulate mitochondrial ROS generation and the production of the proinflammatory cytokine interleukin-6 (IL-6). Finally, we constructed a MR pharmacophore, which successfully identified the silane AB110873.; Screening of virtual chemical structure libraries can facilitate the identification of xenobiotics inhibiting 11β-HSD2 and/or activating MR. Lasalocid and AB110873 belong to new classes of 11β-HSD2 inhibitors. The silane AB110873 represents to the best of our knowledge the first industrial chemical shown to activate MR. Furthermore, the MR pharmacophore can now be used for future screening purposes

Schematic overview of corticosteroid receptor regulation by 11β-HSD enzymes.

<p>Schematic overview of corticosteroid receptor regulation by 11β-HSD enzymes.</p

Increased mitochondrial superoxide generation and induction of IL-6 production upon MR activation in BV2 cells.

<p>BV2 microglial cells were incubated for 24 h with increasing concentrations of aldosterone (<i>A</i>) or silane AB110873 (<i>B</i>) in the presence or absence of 1 µM spironolactone, followed by determination of mitochondrial superoxide using MitoSox staining as described in the Methods section. Fluorescence was analyzed using a Cellomics ArrayScan high-content screening system. <i>C</i>, BV2 cells were incubated for 24 h with aldosterone (5 nM) or various concentrations of silane AB110873 in the presence or absence of spironolactone, followed by quantification of IL-6 protein levels in the medium of the cultured cells by ELISA. Data (mean ± SD) were obtained from three independent experiments each performed in six replicates.</p

11β-HSD inhibitors pharmacophore model.

<p>The hydrogen bond acceptor features are represented in green, and the hydrophobic features in blue. The shape of carbenoxolone, as a steric constraint to prevent too large molecules from fitting, is shown as a grey volume.</p

Binding of aldosterone and the silane AB110873 to the MR.

<p><i>A</i>, MR pharmacophore model with the cocrystallized ligand aldosterone. <i>B,</i> the silane AB110873 fitted to the MR ligand binding site with the pharmacophore model. Hydrogen bond acceptors are shown as red arrows, hydrophobic areas as yellow spheres. Exclusion volumes are not shown for clarity. Receptor binding pocket is colored by aggregated lipophilicity (grey)/hydrophilicity (blue).</p

AB110873 binds to both 11β-HSD2 and MR.

<p>Proposed binding modes of AB110873 in 11β-HSD2 (<i>A,B</i>) and in the MR (<i>C,D</i>). In the 3D-figures, selected amino acid residues are highlighted with ball and stick, and the receptor binding pockets are colored by aggregated lipophilicity (grey)/hydrophilicity (blue). The 2D figures represent the binding interactions, color-coded as following: red arrow – hydrogen bond acceptor, yellow – hydrophobic interaction.</p

MR with silane AB110873.

<p>The amino acids that form the hydrogen bond network with steroidal agonists are highlighted in ball and stick style. AF-2 (helix 12) is colored in dark blue, helix 5 in green, helix 3 in light blue, and the β-sheet in lilac. The buried hydrophobic pocket additionally occupied by AB110873 is formed by amino acids from helices 3 (Val780) and 5 (Leu809, Ala813), and from the β-sheet (Val750).</p

Inhibition of human 11β-HSD2 by AB110873 and lasalocid.

<p>Concentration-dependent inhibition of 11β-HSD2 by the silane-coupling agent AB110873 (<i>A</i>) and the anti-biotic lasalocid (<i>B</i>) measured in cell lysates of stably transfected HEK-293 cells. Data represent mean ± SD from three independent experiments.</p

Effect of the silane AB110873 on the activation of mineralocorticoid (MR) and glucocorticoid receptors (GR).

<p>The impact of silane AB110873 on MR and GR transactivation was measured in HEK-293 cells transfected with MMTV-LacZ reporter, MR (<i>A,B</i>) or GR (<i>C</i>) and luciferase transfection control. Cells were incubated with the receptor ligands for 24 h, followed by analysis of reporter activity as given in the Methods section. <i>A</i>, Concentration-dependent activation of the human MR by the silane AB110873. Maximal activation at 30 µM was set as 100%. <i>B</i>, effect of the antagonist spironolactone (1 µM) on MR activation by aldosterone (5 nM) or by the silane AB110873 (20 µM); <i>C</i>, activation of human GR by cortisol (100 nM) and effect of AB110873 (20 µM) and antagonist RU-486 (1 µM) (MR and GR activity of the vehicle control was set as 1, data represent fold activation). Data were obtained from four independent experiments, each performed in triplicates (mean ± SD).</p