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11?-Hydroxysteroid dehydrogenase type 1 contributes to the balance between 7-keto- and 7-hydroxy-oxysterols in vivo.

ABSTRACT: 11?-Hydroxysteroid dehydrogenase 1 (11?HSD1; EC 1.1.1.146) generates active glucocorticoids from inert 11-keto metabolites. However, it can also metabolize alternative substrates, including 7?-hydroxy- and 7-keto-cholesterol (7?OHC, 7KC). This has been demonstrated in vitro but its consequences in vivo are uncertain. We used genetically modified mice to investigate the contribution of 11?HSD1 to the balance of circulating levels of 7KC and 7?OHC in vivo, and dissected in vitro the kinetics of the interactions between oxysterols and glucocorticoids for metabolism by the mouse enzyme. Circulating levels of 7KC and 7?OHC in mice were 91.3±22.3 and 22.6±5.7 nM respectively, increasing to 1240±220 and 406±39 nM in ApoE(-/-) mice receiving atherogenic western diet. Disruption of 11?HSD1 in mice increased (p<0.05) the 7KC/7?OHC ratio in plasma (by 20%) and also in isolated microsomes (2 fold). The 7KC/7?OHC ratio was similarly increased when NADPH generation was restricted by disruption of hexose-6-phosphate dehydrogenase. Reduction and oxidation of 7-oxysterols by murine 11?HSD1 proceeded more slowly and substrate affinity was lower than for glucocorticoids. in vitro 7?OHC was a competitive inhibitor of oxidation of corticosterone (Ki=0.9 ?M), whereas 7KC only weakly inhibited reduction of 11-dehydrocorticosterone. However, supplementation of 7-oxysterols in cultured cells, secondary to cholesterol loading, preferentially slowed reduction of glucocorticoids, rather than oxidation. Thus, in mouse, 11?HSD1 influenced the abundance and balance of circulating and tissue levels of 7?OHC and 7KC, promoting reduction of 7KC. In health, 7-oxysterols are unlikely to regulate glucocorticoid metabolism. However, in hyperlipidaemia, 7-oxysterols may inhibit glucocorticoid metabolism and modulate signaling through corticosteroid receptors.

SUBMITTER: Mitic T

PROVIDER: S-EPMC3694296 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature

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11β-Hydroxysteroid dehydrogenase type 1 contributes to the balance between 7-keto- and 7-hydroxy-oxysterols in vivo.

Mitić Tijana T Shave Steven S Semjonous Nina N McNae Iain I Cobice Diego F DF Lavery Gareth G GG Webster Scott P SP Hadoke Patrick W F PW Walker Brian R BR Andrew Ruth R

Biochemical pharmacology 20130213 1

11β-Hydroxysteroid dehydrogenase 1 (11βHSD1; EC 1.1.1.146) generates active glucocorticoids from inert 11-keto metabolites. However, it can also metabolize alternative substrates, including 7β-hydroxy- and 7-keto-cholesterol (7βOHC, 7KC). This has been demonstrated in vitro but its consequences in vivo are uncertain. We used genetically modified mice to investigate the contribution of 11βHSD1 to the balance of circulating levels of 7KC and 7βOHC in vivo, and dissected in vitro the kinetics of th ...[more]

PMID: 23415904

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Project description:BACKGROUND: The role of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in the regulation of energy metabolism and immune system by locally reactivating glucocorticoids has been extensively studied. Experiments determining initial rates of enzyme activity revealed that 11beta-HSD1 can catalyze both the reductase and the dehydrogenase reaction in cell lysates, whereas it predominantly catalyzes the reduction of cortisone to cortisol in intact cells that also express hexose-6-phosphate dehydrogenase (H6PDH), which provides cofactor NADPH. Besides its role in glucocorticoid metabolism, there is evidence that 11beta-HSD1 is involved in the metabolism of 7-keto- and 7-hydroxy-steroids; however the impact of H6PDH on this alternative function of 11beta-HSD1 has not been assessed. METHODOLOGY: We investigated the 11beta-HSD1-dependent metabolism of the neurosteroids 7-keto-, 7alpha-hydroxy- and 7beta-hydroxy-dehydroepiandrosterone (DHEA) and 7-keto- and 7beta-hydroxy-pregnenolone, respectively, in the absence or presence of H6PDH in intact cells. 3D-structural modeling was applied to study the binding of ligands in 11beta-HSD1. PRINCIPAL FINDINGS: We demonstrated that 11beta-HSD1 functions in a reversible way and efficiently catalyzed the interconversion of these 7-keto- and 7-hydroxy-neurosteroids in intact cells. In the presence of H6PDH, 11beta-HSD1 predominantly converted 7-keto-DHEA and 7-ketopregnenolone into their corresponding 7beta-hydroxy metabolites, indicating a role for H6PDH and 11beta-HSD1 in the local generation of 7beta-hydroxy-neurosteroids. 3D-structural modeling offered an explanation for the preferred formation of 7beta-hydroxy-neurosteroids. CONCLUSIONS: Our results from experiments determining the steady state concentrations of glucocorticoids or 7-oxygenated neurosteroids suggested that the equilibrium between cortisone and cortisol and between 7-keto- and 7-hydroxy-neurosteroids is regulated by 11beta-HSD1 and greatly depends on the coexpression with H6PDH. Thus, the impact of H6PDH on 11beta-HSD1 activity has to be considered for understanding both glucocorticoid and neurosteroid action in different tissues.

Dataset Information

11?-Hydroxysteroid dehydrogenase type 1 contributes to the balance between 7-keto- and 7-hydroxy-oxysterols in vivo.

Publications

11β-Hydroxysteroid dehydrogenase type 1 contributes to the balance between 7-keto- and 7-hydroxy-oxysterols in vivo.

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