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Organotins disrupt the 11beta-hydroxysteroid dehydrogenase type 2-dependent local inactivation of glucocorticoids.

ABSTRACT: Organotins, important environmental pollutants widely used in agricultural and industrial applications, accumulate in the food chain and induce imposex in several marine species as well as neurotoxic and immunotoxic effects in higher animals. Reduced birth weight and thymus involution, observed upon exposure to organotins, can also be caused by excessive glucocorticoid levels. We now demonstrate that organotins efficiently inhibit 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), converting active 11beta-hydroxyglucocorticoids into inactive 11-ketoglucocorticoids, but not 11beta-HSD1, which catalyzes the reverse reaction. Di- and tributyltin as well as di- and triphenyltin inhibited recombinant and endogenous 11beta-HSD2 in lysates and intact cells with IC50 values between 500 nM and 3 microM. Dithiothreitol protected 11beta-HSD2 from organotin-dependent inhibition, indicating that organotins act by binding to one or more cysteines. Mutational analysis and 3-D structural modeling revealed several important interactions of cysteines in 11beta-HSD2. Cys90, Cys228, and Cys264 were essential for enzymatic stability and catalytic activity, suggesting that disruption of such interactions by organotins leads to inhibition of 11beta-HSD2. Enhanced glucocorticoid concentrations due to disruption of 11beta-HSD2 function may contribute to the observed organotin-dependent toxicity in some glucocorticoid-sensitive tissues such as thymus and placenta.

SUBMITTER: Atanasov AG

PROVIDER: S-EPMC1310925 | biostudies-literature | 2005 Nov

REPOSITORIES: biostudies-literature

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Organotins disrupt the 11beta-hydroxysteroid dehydrogenase type 2-dependent local inactivation of glucocorticoids.

Atanasov Atanas G AG Nashev Lyubomir G LG Tam Steven S Baker Michael E ME Odermatt Alex A

Environmental health perspectives 20051101 11

Organotins, important environmental pollutants widely used in agricultural and industrial applications, accumulate in the food chain and induce imposex in several marine species as well as neurotoxic and immunotoxic effects in higher animals. Reduced birth weight and thymus involution, observed upon exposure to organotins, can also be caused by excessive glucocorticoid levels. We now demonstrate that organotins efficiently inhibit 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), convert ...[more]

PMID: 16263518

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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.

Project description:BACKGROUND: Leydig cells are the primary source of testosterone in male vertebrates. The biosynthesis of testosterone in Leydig cells is strictly dependent on luteinizing hormone (LH). On the other hand, it can be directly inhibited by excessive glucocorticoid (Corticosterone, CORT, in rats) which is beyond the protective capability of 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) and type 2 (11beta-HSD2; encoded by gene Hsd11b2 in rats) in Leydig cells. Our previous study found that LH increases 11beta-HSD1 expression in rat Leydig cells, but the effect of LH on the expression and activity of 11beta-HSD2 is not investigated yet. METHODS: The Leydig cells were isolated from male Sprague-Dawley rats (90 days of age). After Leydig cells were incubated either for 24 h with various concentrations of LH (2.5, 5, 10 and 20 ng/mL) or for different time periods (2, 8, 12 and 24 h) with 20 ng/mL LH, the mRNA expression of 11beta-HSD2 was measured by real-time PCR. 11beta-HSD2 protein levels in Leydig cells were assayed by Western Blot and 11beta-HSD2 enzyme activity was determined by calculating the ratio of conversion of [3H]CORT to [3H]11-dehydrocorticosterone by 24 h after stimulation with 20 ng/ml LH. Four reporter gene plasmids containing various lengths of Hsd11b2 promoter region were constructed and transfected into mouse Leydig tumor cells to investigate the effect of LH on Hsd11b2 transcription. A glucocorticoid-responsive reporter gene plasmid, GRE-Luc, was constructed. To evaluate influence of LH on intracellular glucocorticoid level, rat Leydig cells were transfected with GRE-Luc, and luciferase activities were measured after incubation with CORT alone or CORT plus LH. RESULTS: We observed dose- and temporal-dependent induction of rat 11beta-HSD2 mRNA expression in Leydig cells subject to LH stimulation. The protein and enzyme activity of 11beta-HSD2 and the luciferase activity of reporter gene driven by promoter regions of Hsd11b2 were increased by LH treatment. LH decreased the glucocorticoid-induced luciferase activity of GRE-Luc reporter gene. CONCLUSION: The results of the present study suggest that LH increases the expression and enzyme activity of 11beta-HSD2, and therefore enhances capacity for oxidative inactivation of glucocorticoid in rat Leydig cells in vitro.

Project description:INTRODUCTION: The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyzes the conversion of the hormonally inactive cortisone to active cortisol, thus facilitating glucocorticoid receptor activation in target tissues. Increased expression of 11beta-HSD1 in adipose tissue has been associated with obesity and insulin resistance. In this study, we investigated the association of two 11beta-HSD1 gene (HSD11B1) polymorphisms with the metabolic syndrome (MetS) and its characteristics in the Bosnian population. MATERIALS AND METHODS: The study included 86 participants: 43 patients diagnosed with MetS and 43 healthy controls. Subjects were genotyped for two HSD11B1 gene polymorphisms: rs846910: G > A and rs45487298: insA, by the high resolution melting curve analysis. Genotype distribution and an influence of genotypes on clinical and biochemical parameters were assessed. RESULTS: There was no significant difference in the mutated allele frequencies for the two HSD11B1 gene polymorphisms between MetS patients and controls. In MetS patients, no significant associations between disease-associated traits and rs45487298: insA were found. Regarding rs846910: G > Avariant, heterozygous patients (G/A) had significantly lower systolic (P = 0.017) and diastolic blood pressure (P = 0.015), lower HOMA-IR index (P = 0.011) and higher LDL-cholesterol levels (P = 0.049), compared to the wild-type homozygotes. In the control group, rs45487298: insA polymorphism was associated with lower fasting plasma insulin levels (P = 0.041), lower homeostasis model assessment insulin resistance (HOMA-IR) index (P = 0.041) and lower diastolic blood pressure (P = 0.048). Significant differences between rs846910: G > A genotypes in controls were not detected. Haplotype analysis confirmed the association of rs45487298: insA with markers of insulin resistance in the control subjects. CONCLUSIONS: Our results indicate that a common rs45487298: insA polymorphism in HSD1181 gene may have a protective effect against insulin resistance.

Project description:11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) acts as a reductase in vivo, regenerating active glucocorticoids within cells from circulating inert 11-keto forms, thus amplifying local glucocorticoid action. 11beta-HSD1 is predominantly expressed in liver and also adipose tissue and brain. Mice deficient in 11beta-HSD1 (11beta-HSD1(-/-)) exhibit adrenal hyperplasia, raised basal corticosterone levels, and increased hypothalamic-pituitary-adrenal (HPA) axis responses to stress. Whereas reduced peripheral glucocorticoid regeneration may explain adrenal hypertrophy and exaggerated stress responses, elevated basal glucocorticoid levels support a role for 11beta-HSD1 within the brain in amplifying glucocorticoid feedback. To test this hypothesis, apolipoprotein E-HSD1 mice overexpressing 11beta-HSD1 in liver were intercrossed with 11beta-HSD1(-/-) mice to determine whether complementation of hepatic 11beta-HSD1 can restore adrenal and HPA defects. Transgene-mediated delivery of 11beta-HSD1 activity to the liver rescued adrenal hyperplasia and reversed exaggerated HPA stress responses in 11beta-HSD1(-/-) mice. Unexpectedly, elevated nadir plasma corticosterone levels were also restored to control levels. Consistent with this, CYP11B1 mRNA expression in the adrenal cortex of 11beta-HSD1(-/-) mice was increased by 50% but returned to control levels in 11beta-HSD1(-/-) mice bearing the apolipoprotein E-HSD1 transgene. 11beta-HSD1(-/-) mice have lower plasma glucose levels, but the fall in plasma corticosterone with sucrose supplementation was similar in 11beta-HSD1(-/-) and control mice, suggesting glucose deficiency is not the main mechanism whereby basal corticosterone levels are elevated in the null mice. Thus, regeneration of glucocorticoids by 11beta-HSD1 in the liver normalizes all aspects of HPA axis dysregulation in 11beta-HSD1(-/-) mice, without restoration of enzyme activity in key feedback areas of the forebrain. Therefore, hepatic glucocorticoid metabolism influences basal as well as stress-associated functions of the HPA axis.

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Organotins disrupt the 11beta-hydroxysteroid dehydrogenase type 2-dependent local inactivation of glucocorticoids.

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Organotins disrupt the 11beta-hydroxysteroid dehydrogenase type 2-dependent local inactivation of glucocorticoids.

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