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1 Division of Endocrinology, Metabolism and Molecular Medicine, UCLA School of Medicine, The Charles Drew University of Medicine and Science, 1731 East 120th Street, Los Angeles, California 90059, USA2 Department of Pediatrics, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan3 Department of Endocrinology and Metabolism, Shanghai Diabetes Institute, Shanghai Jiaotong University Affiliated Sixth People's Hospital, Shanghai 200233, China4 Department of Pediatrics, First Hospital, JiLin University, ChangChun 130021, China5 Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, 309 East 2nd Street, Pomona, California 91766, USA
(Correspondence should be addressed to Y Liu; Email: dryanjunliu{at}hotmail.com)
Intracellular glucocorticoid (GC) receptor (GR) function determines tissue sensitivity to GCs and strongly affects the development of type 2 diabetes and obesity. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) mediates intracellular steroid exposure to mouse liver GR by prereceptor reactivation of GCs and is crucially dependent on hexose-6-phosphate dehydrogenase (H6PDH)-generating NADPH system. Pharmacological inhibition of 11β-HSD1 improves insulin intolerance and obesity. Here, we evaluated the potential beneficial effects of 11β-HSD1 inhibitor carbenoxolone (CBX) in diet-induced obese (DIO) and insulin-resistant mice by examining the possible influence of CBX on the expression of GR, 11β-HSD1, and H6PDH in vivo and in vitro in hepatocytes. Treatment of DIO mice with CBX markedly reduced hepatic GR mRNA levels and reduced weight gain, hyperglycemia, and insulin resistance. The reduction of hepatic GR gene expression was accompanied by CBX-induced inhibition of both 11β-HSD1 and H6PDH activity and mRNA in the liver. Moreover, CBX treatment also suppressed the expression of both phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase enzyme (G6Pase) mRNA and improved hepatic [1, 2-3H] deoxy-D-glucose uptake in DIO mice. In addition, the treatment of primary cultures of hepatocytes with increasing concentrations of CBX led to a dose-dependent downregulation of GR mRNA levels, which correlated with the suppression of both 11β-HSD1 and H6PDH activity and their gene expression. Addition of CBX to primary hepatocytes also resulted in suppression of both PEPCK and G6Pase mRNA levels. These findings suggest that CBX exerts some of its beneficial effects, at least in part, by inhibiting hepatic GR and H6PDH expression.
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