11Beta-hydroxysteroid dehydrogenase 1 expression in squamous cell carcinomas of the head and neck

Loss of 11βHSD1 enhances glycolysis, facilitates intrahepatic metastasis, and indicates poor prognosis in hepatocellular carcinoma

11Beta-hydroxysteroid dehydrogenase type 1 (11βHSD1), converting glucocorticoids from hormonally inactive cortisone to active cortisol, plays an essential role in glucose homeostasis. Accumulating evidence suggests that enhanced glycolytic activity is closely associated with postoperative recurrence and prognosis of hepatocellular carcinoma (HCC). Whether 11βHSD1 contributes to HCC metastasis and recurrence remains unclear. Here we found that expression of 11βHSD1 in human HCC (310 pairs) was frequently decreased compared to the adjacent non-neoplastic liver tissues (ANT), which correlated well with the intrahepatic-metastatic index, serum glycemia, and other malignant clinicopathological characteristics of HCC and predicted poor prognosis. Knockdown of 11βHSD1 in BEL-7402 cells drastically reduced the pH of culture medium and induced cell death. Meanwhile, overexpression of 11βHSD1 in SMMC-7721 HCC cells resulted in repression of cell migration, invasion, angiogenesis, and proliferation in vitro. When transferred into BALB/c nude mice, 11βHSD1 overexpression resulted in decreased intrahepatic metastasis, angiogenesis, and tumor size. F-18-2-fluoro-2-deoxyglucose accumulation assay measured by positron emission tomography elucidated that 11βHSD1 reduced glucose uptake and glycolysis in SMMC-7721 cells in vitro, and intrahepatic metastasis foci and subcutaneous tumor growth in vivo. We showed that 11βHSD1 repressed cell metastasis, angiogenesis and proliferation of HCC by causing disruption of glycolysis via the HIF-1α and c-MYC pathways. In conclusion, 11βHSD1 inhibits the intrahepatic metastasis of HCC via restriction of tumor glycolysis activity and may serve as a prognostic biomarker for patients.

Carbonyl reduction of bupropion in human liver

Bupropion is metabolized extensively in humans by oxidative and reductive processes. CYP2B6 mediates oxidation of bupropion to hydroxybupropion, but the enzyme(s) catalyzing carbonyl reduction of bupropion to erythro- and threohydrobupropion in human liver is unknown. The objective of this study was to examine the enzyme kinetics of bupropion reduction in human liver. In human liver cytosol, the reduction of bupropion to erythro-and threohydrobupropion was NADPH dependent with Cl(int) values of 0.08 and 0.60 µL·min(-1)mg(-1) protein, respectively. Bupropion reduction in liver microsomes was also NADPH dependent with Cl(int) values of 10.4 and 280 µL·min(-1)mg(-1) protein, respectively. Formation of erythro-and threohydrobupropion in microsomes exceeded that in cytosol by 70 and 170 fold, respectively. Menadione, an inhibitor of cytosolic carbonyl reducing enzymes (e.g. CBRs), inhibited erythro-and threohydrobupropion formation in cytosol with IC(50) of 30 and 54 µM, respectively. In microsomes 18β-glycyrrhetinic acid, an inhibitor of microsomal carbonyl reductases (e.g. 11β-HSDs), inhibited their formation with IC(50) of 25 and 26 nM, respectively. Our findings, in agreement with recent human placental studies, show that carbonyl reducing enzymes in hepatic microsomes are significant players in bupropion reduction. Contrary to past studies, we found that threohydrobupropion (not hydroxybupropion) is the major microsomal generated hepatic metabolite of bupropion.

Keratinocytes synthesize and activate cortisol

The bioavailability of circulating and/or endogenous hydrocortisone (cortisol) in epidermal cells is a key determinant in inflammatory disease and chronic wounds. It is not known, however, whether epidermal cells can regulate tissue cortisol and whether they are capable of producing endogenous glucocorticoids. In the present study, we show by microarray analysis that epidermal cells express mRNAs to all the major enzymes involved in the metabolic chain from cholesterol to cortisol, including cytocrome P450 chain, 11β-hydroxysteroid dehydrogenases (HSD11Bs), adrenocorticotropic hormone (ACTH) receptor (MC2R), and glucocorticoid receptor. The two enzymes mediating activation/deactivation of cortisone to cortisol, namely HSD11B1 and HSD11B2, were expressed at the protein level in cultured keratinocytes as well as human skin samples, as shown by Western blotting and immunohistochemistry, respectively. In functional assays, we show that keratinocytes are not only able to activate cortisone to cortisol in a HSD11B-dependent manner but also silencing of either HSD11B1 or HSD11B2 specifically modulates the bioavailability of the inactive glucocorticoid and the active steroid, respectively. A further key observation was that keratinocytes responded to stimulation with ACTH by a significant increase in the de novo synthesis of cortisol. Taken together, we provide evidence for a novel non-adrenal steroideal system in human keratinocytes.

Characterization of activity and binding mode of glycyrrhetinic acid derivatives inhibiting 11β-hydroxysteroid dehydrogenase type 2

Modulation of intracellular glucocorticoid availability is considered as a promising strategy to treat glucocorticoid-dependent diseases. 18β-Glycyrrhetinic acid (GA), the biologically active triterpenoid metabolite of glycyrrhizin, which is contained in the roots and rhizomes of licorice (Glycyrrhiza spp.), represents a well-known but non-selective inhibitor of 11β-hydroxysteroid dehydrogenases (11β-HSDs). However, to assess the physiological functions of the respective enzymes and for potential therapeutic applications selective inhibitors are needed. In the present study, we applied bioassays and 3D-structure modeling to characterize nine 11β-HSD1 and fifteen 11β-HSD2 inhibiting GA derivatives. Comparison of the GA derivatives in assays using cell lysates revealed that modifications at the 3-hydroxyl and/or the carboxyl led to highly selective and potent 11β-HSD2 inhibitors. The data generated significantly extends our knowledge on structure-activity relationship of GA derivatives as 11β-HSD inhibitors. Using recombinant enzymes we found also potent inhibition of mouse 11β-HSD2, despite significant species-specific differences. The selected GA derivatives potently inhibited 11β-HSD2 in intact SW-620 colon cancer cells, although the rank order of inhibitory potential differed from that obtained in cell lysates. The biological activity of compounds was further demonstrated in glucocorticoid receptor (GR) transactivation assays in cells coexpressing GR and 11β-HSD1 or 11β-HSD2. 3D-structure modeling provides an explanation for the differences in the selectivity and activity of the GA derivatives investigated. The most potent and selective 11β-HSD2 inhibitors should prove useful as mechanistic tools for further anti-inflammatory and anti-cancer in vitro and in vivo studies. Article from the Special issue on Targeted Inhibitors.

11beta-hydroxysteroid dehydrogenase type 1: a tissue-specific regulator of glucocorticoid response

11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) interconverts inactive cortisone and active cortisol. Although bidirectional, in vivo it is believed to function as a reductase generating active glucocorticoid at a prereceptor level, enhancing glucocorticoid receptor activation. In this review, we discuss both the genetic and enzymatic characterization of 11beta-HSD1, as well as describing its role in physiology and pathology in a tissue-specific manner. The molecular basis of cortisone reductase deficiency, the putative "11beta-HSD1 knockout state" in humans, has been defined and is caused by intronic mutations in HSD11B1 that decrease gene transcription together with mutations in hexose-6-phosphate dehydrogenase, an endoluminal enzyme that provides reduced nicotinamide-adenine dinucleotide phosphate as cofactor to 11beta-HSD1 to permit reductase activity. We speculate that hexose-6-phosphate dehydrogenase activity and therefore reduced nicotinamide-adenine dinucleotide phosphate supply may be crucial in determining the directionality of 11beta-HSD1 activity. Therapeutic inhibition of 11beta-HSD1 reductase activity in patients with obesity and the metabolic syndrome, as well as in glaucoma and osteoporosis, remains an exciting prospect.

11beta-hydroxysteroid dehydrogenases, cell proliferation and malignancy

The enzymes 11beta-hydroxysteroid dehydrogenase type 1 and 2 (11beta-HSD1 and 2) have well-defined roles in the tissue-specific metabolism of glucocorticoids which underpin key endocrine mechanisms such as adipocyte differentiation (11beta-HSD1) and mineralocorticoid action (11beta-HSD2). However, in recent studies we have shown that the effects of 11beta-HSD1 and 2 are not restricted to distinct tissue-specific hormonal functions. Studies of normal fetal and adult tissues, as well as their tumor equivalents, have shown a further dichotomy in 11beta-HSD expression and activity. Specifically, most normal glucocorticoid receptor (GR)-rich tissues such as adipose tissue, bone, and pituitary cells express 11beta-HSD1, whereas their fetal equivalents and tumors express 11beta-HSD2. We have therefore postulated that the ability of 11beta-HSD1 to generate cortisol acts as an autocrine anti-proliferative, pro-differentiation stimulus in normal adult tissues. In contrast, the cortisol-inactivating properties of 11beta-HSD2 lead to pro-proliferative effects, particularly in tumors. This proposal is supported by experiments in vitro which have demonstrated divergent effects of 11beta-HSD1 and 2 on cell proliferation. Current studies are aimed at (1) characterizing the underlying mechanisms for a "switch" in 11beta-HSD isozyme expression in tumors; (2) defining the molecular targets for glucocorticoids as regulators of cell proliferation; (3) evaluating the potential for targeting glucocorticoid metabolism as therapy for some cancers. These and other issues are discussed in the present review.