Evidence That the 11 β-Hydroxysteroid Dehydrogenase (11 β-HSD1) Is Regulated by Pentose Pathway Flux
2005; Elsevier BV; Volume: 281; Issue: 1 Linguagem: Inglês
10.1074/jbc.m506026200
ISSN1083-351X
AutoresKenneth McCormick, Xudong Wang, Gail J. Mick,
Tópico(s)Pharmacological Effects of Natural Compounds
Resumo11 β-hydroxysteroid dehydrogenase type 1 (11 β-HSD1) catalyzes the interconversion of biologically inactive 11 keto derivatives (cortisone, 11-dehydrocorticosterone) to active glucocorticoids (cortisol, corticosterone) in fat, liver, and other tissues. It is located in the intraluminal compartment of the endoplasmic reticulum. Inasmuch as an oxo-reductase requires NADPH, we reasoned that 11 β-HSD1 would be metabolically interconnected with the cytosolic pentose pathway because this pathway is the primary producer of reduced cellular pyridine nucleotides. To test this theory, 11 β-HSD1 activity and pentose pathway were simultaneously measured in isolated intact rodent adipocytes. Established inhibitors of NAPDH production via the pentose pathway (dehydroandrostenedione or norepinephrine) inhibited 11 β-HSD1 oxo-reductase while decreasing cellular NADPH content. Conversely these compounds slightly augmented the reverse, or dehydrogenase, reaction of 11 β-HSD1. Importantly, using isolated intact microsomes, the inhibitors did not directly alter the tandem microsomal 11 β-HSD1 and hexose-6-phosphate dehydrogenase enzyme unit. Metabolites of 11 β-HSD1 (corticosterone or 11-dehydrocorticosterone) inhibited or increased pentose flux, respectively, demonstrating metabolic interconnectivity. Using isolated intact liver or fat microsomes, glucose-6 phosphate stimulated 11 β-HSD1 oxo-reductase, and this effect was blocked by selective inhibitors of glucose-6-phosphate transport. In summary, we have demonstrated a metabolic interconnection between pentose pathway and 11 β-HSD1 oxo-reductase activities that is dependent on cytosolic NADPH production. These observations link cytosolic carbohydrate flux with paracrine glucocorticoid formation. The clinical relevance of these findings may be germane to the regulation of paracrine glucocorticoid formation in disturbed nutritional states such as obesity. 11 β-hydroxysteroid dehydrogenase type 1 (11 β-HSD1) catalyzes the interconversion of biologically inactive 11 keto derivatives (cortisone, 11-dehydrocorticosterone) to active glucocorticoids (cortisol, corticosterone) in fat, liver, and other tissues. It is located in the intraluminal compartment of the endoplasmic reticulum. Inasmuch as an oxo-reductase requires NADPH, we reasoned that 11 β-HSD1 would be metabolically interconnected with the cytosolic pentose pathway because this pathway is the primary producer of reduced cellular pyridine nucleotides. To test this theory, 11 β-HSD1 activity and pentose pathway were simultaneously measured in isolated intact rodent adipocytes. Established inhibitors of NAPDH production via the pentose pathway (dehydroandrostenedione or norepinephrine) inhibited 11 β-HSD1 oxo-reductase while decreasing cellular NADPH content. Conversely these compounds slightly augmented the reverse, or dehydrogenase, reaction of 11 β-HSD1. Importantly, using isolated intact microsomes, the inhibitors did not directly alter the tandem microsomal 11 β-HSD1 and hexose-6-phosphate dehydrogenase enzyme unit. Metabolites of 11 β-HSD1 (corticosterone or 11-dehydrocorticosterone) inhibited or increased pentose flux, respectively, demonstrating metabolic interconnectivity. Using isolated intact liver or fat microsomes, glucose-6 phosphate stimulated 11 β-HSD1 oxo-reductase, and this effect was blocked by selective inhibitors of glucose-6-phosphate transport. In summary, we have demonstrated a metabolic interconnection between pentose pathway and 11 β-HSD1 oxo-reductase activities that is dependent on cytosolic NADPH production. These observations link cytosolic carbohydrate flux with paracrine glucocorticoid formation. The clinical relevance of these findings may be germane to the regulation of paracrine glucocorticoid formation in disturbed nutritional states such as obesity. The intracellular peri-receptor availability of glucocorticoids is not determined simply by their circulating concentrations and protein binding interactive kinetics. Ostensibly, the intracellular concentration of the active glucocorticoids (cortisol, corticosterone) is governed more so by 11 β-hydroxysteroid dehydrogenase type 1 (11 β-HSD1), 2The abbreviations used are: 11 β-HSD111 β hydroxysteroid dehydrogenasePPpentose pathwayCcorticosterone11-DHC11 dehydrocorticosteroneDHEAdehydroandrostenedioneNEnorepinephrineG6Pglucose-6-phosphateH6PDhexose-6 phosphate dehydrogenaseCHAPSO3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonateERendoplasmic reticulum. a bidirectional enzyme that facilitates the equilibrium between the aforesaid active steroids and their biologically inactive 11-keto derivatives (cortisone, 11-dehydrocorticosterone) (1Seckl J.R. Walker B.R. Endocrinology. 2001; 142: 1371-1376Crossref PubMed Scopus (559) Google Scholar, 2Bujalska I.J. Kumar S. Stewart P.M. Lancet. 1997; 349: 1210-1213Abstract Full Text Full Text PDF PubMed Scopus (686) Google Scholar, 3Tomlinson J.W. Stewart P.M. Horm. Metab. 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Recently, 11 β-HSD1 has garnered attention as a potential participant in the pathoetiology of obesity, insulin resistance, and type II diabetes (2Bujalska I.J. Kumar S. Stewart P.M. Lancet. 1997; 349: 1210-1213Abstract Full Text Full Text PDF PubMed Scopus (686) Google Scholar, 3Tomlinson J.W. Stewart P.M. Horm. Metab. Res. 2002; 34: 746-751Crossref PubMed Scopus (40) Google Scholar, 8Lindsay R.S. Wake D.J. Nair S. Bunt J. Livingstone D.E. Permana P.A. Tataranni P.A. Walker B.R. J. Clin. Endocrinol. Metab. 2003; 88: 2738-2744Crossref PubMed Scopus (208) Google Scholar, 9Bujalska I.J. Walker E.A. Hewison M. Stewart P.M. J. Clin. Endocrinol. Metab. 2002; 87: 1205-1210PubMed Google Scholar). Specifically, the dysregulation of 11 β-HSD1 in particular tissues may augment intracellular active glucocorticoid concentrations. In addition, it is certainly plausible that in human obesity, although normal circulating blood cortisol levels are found, intracellular cortisol concentrations may be elevated, conceivably because an alteration in the NADPH/NADP ratio may foster 11 β-HSD1 reductase over dehydrogenase. Given the well recognized regulation by glucocorticoids of numerous homeostatic and metabolic processes of intermediary metabolism, the role of 11 β-HSD1 in obesity is under question (2Bujalska I.J. Kumar S. Stewart P.M. Lancet. 1997; 349: 1210-1213Abstract Full Text Full Text PDF PubMed Scopus (686) Google Scholar, 8Lindsay R.S. Wake D.J. Nair S. Bunt J. Livingstone D.E. Permana P.A. Tataranni P.A. Walker B.R. J. Clin. Endocrinol. Metab. 2003; 88: 2738-2744Crossref PubMed Scopus (208) Google Scholar, 10Ottosson M. Vikman-Adolfsson K. Enerback S. Olivecrona G. Bjorntorp P. J. Clin. Endocrinol. Metab. 1994; 79: 820-825Crossref PubMed Scopus (128) Google Scholar, 11Bujalska I.J. Kumar S. Hewison M. 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Antithetically, in disrupted cellular homogenates, the direction is reversed, where the enzyme functions preferentially as a dehydrogenase (6Agarwal A.K. Tusie-Luna M.T. Monder C. White P.C. Mol. Endocrinol. 1990; 4: 1827-1832Crossref PubMed Scopus (166) Google Scholar, 23Jamieson P.M. Chapman K.E. Edwards C.R. Seckl J.R. Endocrinology. 1995; 136: 4754-4761Crossref PubMed Google Scholar, 26Stulnig T.M. Waldhausl W. Diabetologia. 2004; 47: 1-11Crossref PubMed Scopus (117) Google Scholar). The grounds for this paradox are poorly understood, but obviously substrate concentrations, ionic milieu, pH, intracellular location, and membrane binding may explain the kinetic discordance between intact cells versus homogenates (where reactions are often measured under artificial Vmax conditions). All these factors notwithstanding, the most plausible determinate of the direction of 11 β-HSD1 is the mass action effect of pyridine nucleotide cofactors. To date, no studies using intact cells have attempted to correlate ongoing in situ pentose pathway flux, which is recognized as the major intracellular producer of NADPH, with the simultaneous measurement of 11 β-HSD1 activity. Furthermore, to what extent the hormonal and metabolic manipulation of adipocyte pentose pathway (PP) may impact in situ microsomal 11 β-HSD1 activity has yet to be explored. Materials—Tissue culture media and ingredients were from Invitrogen, general chemicals from Sigma, radioisotopes ([1-14C]glucose and [6-14C]glucose) from Amersham Biosciences, and 11-dehydrocorticosterone (11-DHC) from Steraloids, Inc., Newport, RI. Rat Adipocyte Preparation—Isolated adipocytes were prepared from gonadal depots by standard collagenase digestion methods (27Mick G. Wang X. McCormick K.L. Endocrinology. 2002; 143: 948-953Crossref PubMed Scopus (78) Google Scholar). Rodent Fat Cell Incubation Conditions—Isolated fat cells from 4–6 rats were pooled and distributed for metabolic studies into incubation tubes (three sets of duplicated tubes; set 1, measure PP flux with [1-14C] glucose, set 2, measure [6-14C] glucose oxidation (as below), and set 3, measure 11 β-HSD1 activity). All cell groups were distributed, handled, and analyzed in parallel under identical incubation conditions (37 °C). Isolated rat fat cells were incubated in 1–2-ml polypropylene tubes (set in 20-ml vials with Teflon/silicone membrane caps for CO2 collection, PP as below). Rat Microsome Preparation—Liver microsomes were prepared according to the methods of Raucy and Lasker (28Raucy J.L. Lasker J.M. Methods Enzymol. 1991; 206: 577-587Crossref PubMed Scopus (101) Google Scholar). Adipocyte microsomes were prepared from the pooled fat cells of three to four rats by similar methods (29Simpson I.A. Yver D.R. Hissin P.J. Wardzala L.J. Karnieli E. Salans L.B. Cushman S.W. Biochim. Biophys. Acta. 1983; 763: 393-407Crossref PubMed Scopus (347) Google Scholar). 11 β-HSD1 Activity—The oxo-reductase direction of 11 β-HSD1 in which dehydrocorticosterone (11-DHC) is converted to corticosterone (C) was measured in intact cells and microsomes. Isolated rodent fat cells (0.25 ml) were incubated in 0.1 mm glucose Krebs buffer at 37 °C (final assay volume 0.4 ml, final cell concentration 5–6 × 105 ml or with microsomes 50 μg of protein/ml). The reaction was initiated with 250–1000 nm 11-DHC (0.15 ml), incubated for 45–90 min, and terminated by freezing on dry ice. The appearance of C in the assay medium (conditioned medium) of isolated intact cells was determined by 3H radioimmune assay of corticosterone (MP Biomedicals, Irving, CA). Baseline studies examined the effect of substrate concentration (0–2 μm 11-DHC), cell number (0-5–6 × 106 fat cells/ml) and time (0–120 min) on corticosterone production to verify consistent linear rates of 11 β-HSD1 activity throughout the assay. The dehydrogenase reaction of 11 β-HSD1 (C → 11-DHC) was measured in intact cells under identical assay conditions by the disappearance of [3H] corticosterone (as above) at a final concentration of non-labeled substrate of 100 nm. Pentose Pathway Flux—The conversion of [1-14C]glucose to 14CO2 followed previously described methods for 14CO2 collection and quantification (30McCormick K.L. Hingre K. Brown J. Mick G.J. Biochim. Biophys. Acta. 1992; 1135: 1-7Crossref PubMed Scopus (3) Google Scholar, 31McCormick K.L. Mick G.J. Am. J. Physiol. 1991; 261: C476-C481Crossref PubMed Google Scholar, 32Mick G.J. Bonn T. Steinberg J. McCormick K. J. Biol. Chem. 1988; 263: 10667-10673Abstract Full Text PDF PubMed Google Scholar). To correct PP flux for minor 14CO2 release from [1-14C]glucose generated through the glycolytic/citric acid cycle (33Larrabee M.G. Biochem. J. 1990; 272: 127-132Crossref PubMed Scopus (27) Google Scholar, 34Katz J. Landau B.R. Bartsch G.E. J. Biol. Chem. 1966; 241: 727-740Abstract Full Text PDF PubMed Google Scholar, 35Larrabee M.G. J. Biol. Chem. 1989; 264: 15875-15879Abstract Full Text PDF PubMed Google Scholar), the release of 14CO2 from [6-14C] was also determined in parallel experiments. The incubation medium was a 0.1-mm glucose Krebs buffer, pH 7.4. Metabolic reactions were started by the addition of assay mixture containing substrate ([1-14C]glucose or [6-14C]glucose). Methods for this latter assay were identical to the PP assay with the exception that [6-14C]glucose replaces [1-14C]glucose. Glucose Dehydrogenase—Isolated microsomes were tested for glucose dehydrogenase activity in the presence and absence of CHAPSO (a zwitter ionic, non-denaturing detergent) as an index for microsomal membrane integrity. To mimic our experimental conditions, microsomes were first preincubated for 90 min at 37 °C in Krebs buffer. Next, they were washed once with 0.15 m Tris-HCL, pH 8.0 and incubated for 30 min at 4 °C with 0.8% CHAPSO. Glucose dehydrogenase activity was then monitored over 180 min at 25 °C in this same Tris buffer with 50 mm Na2SO4 (36Romanelli A. St-Denis J.F. Vidal H. Tchu S. van de Werve G. Biochem. Biophys. Res. Commun. 1994; 200: 1491-1497Crossref PubMed Scopus (25) Google Scholar, 37Bublitz C. Steavenson S. Biochim. Biophys. Acta. 1988; 965: 90-92Crossref PubMed Scopus (13) Google Scholar). NADPH Measurement—NADPH was measured by an ultrasensitive radioisotopic assay (38Sener A. Malaisse W.J. Anal. Biochem. 1990; 186: 236-242Crossref PubMed Scopus (50) Google Scholar). Statistical Analysis—Data are expressed as a % control (no modifier), mean ± S.D. (n = 3–4). In each case, "n" refers to an individual experiment performed on 1 day with a fresh batch of cells or microsomes. Statistical differences were determined by paired t-test. Baseline Characteristics of 11 β-HSD1 Oxo-reductase Assay—The 11 β-HSD1 oxo-reductase assay was measured in both isolated rat adipocytes and liver or fat microsomes. The reaction was linear over time (0–90 min), and its apparent Km was 0.25 μm 11-DHC. The baseline rate of corticosterone formation from 11-DHC was 32.9 ± 4.8 ng of corticosterone formed/h/105 in adipocytes and 213.5 ± 62.1 ng of corticosterone/mg protein/h liver microsomes (with 1 μm glucose-6-phosphate (G6P)). Dihydroepiandrostenedione (DHEA) and Norepinephrine (NE) Inhibit Both Pentose Pathway Flux and 11 β-HSD1 Oxo-reductase Activity—Pentose pathway and 11 β-HSD1 activities were simultaneously measured in isolated adipocytes without and with 100 μm DHEA (Fig. 1, A and B) or 1 μm NE (Fig. 1, C and D). DHEA inhibited both the PP and oxo-reductase activities by 56–60% (p 90% baseline) with or without either inhibitor. It is noteworthy that DHEA did not directly affect 11 β-HSD1 enzyme activities in ruptured or homogenized fat cells. To determine whether the inhibition of these agents directly affected hexose-6-phosphate dehydrogenase (H6PD), which is the microsomal counterpart of cytosolic G6PD, isolated liver microsomes were incubated with and without DHEA or NE and 11 β-HSD1 oxo-reductase measured. As shown in Fig. 2, neither agent altered microsomal 11 β-HSD1 oxo-reductase. To determine whether the inhibitory actions of DHEA and NE on 11 β-HSD1 (as shown in Fig. 1, B and D) were enzyme specific, the reverse reaction (11-dihydrocorticosterone formation) was measured with and without these compounds. If these agents inhibit 11 β-HSD1 oxo-reductase by curtailing the supply of NADPH, then, conversely, they should stimulate the dehydrogenase direction. Both agents stimulated the dehydrogenase reaction by 2.5–3-fold (Fig. 3), although the effect of NE was not statistically significant.FIGURE 2Effect of DHEA and NE on liver microsomal 11 β-HSD1 oxo-reductase activity. Intact liver microsomes (50 μg of protein/ml) were preincubated for 60 min with modifiers (1 or 10 μm NE and 10 or 100 μm DHEA), and then 11 β-HSD1 oxo-reductase activity was measured over 45 min in the incubation medium as shown under "Experimental Procedures." Results are given as a percent of control (no additions) and represent the mean ± S.D. for three separate experiments. There were no statistical differences for effect of modifier over control (no addition) by paired t-test. The control rate was 317 ± 52 ng corticosterone/h/mg protein.View Large Image Figure ViewerDownload Hi-res image Download (PPT)FIGURE 3Effect of DHEA and NE on the dehydrogenase reaction of 11 β-HSD1. Adipocytes were prepared fresh and preincubated for 45 min with 100 μm DHEA or 1 μm NE. 11 β-HSD1 dehydrogenase activity was measured as shown under "Experimental Procedures" as the disappearance of radiolabeled corticosterone over time. Results are expressed relative to control (no modifier). Statistical comparisons for the effect of either modifier on 11 β-HSD1 dehydrogenase activity are by paired t-test versus no additions (mean ± S.D., n = 3). The basal dehydrogenase rate was 0.9 ± 0.06 ng/h/105 cells.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Metabolites of the 11 β-HSD1 Enzyme Reaction Regulate Pentose Pathway Activity in Isolated Fat Cells—If PP and 11 β-HSD1 are metabolically linked, then the substrate/products of the 11 β-HSD1 reaction might in turn affect PP flux. To examine this possibility, fat cells were preincubated with either 10 μm corticosterone or 11-DHC and then pentose pathway flux measured over 45 min. As predicted from Fig. 10, corticosterone, which would promote dehydrogenase flux (stimulates 11-DHC formation and an increased NAPDH/NADP ratio), inhibited PP by 30% whereas 11-DHC (stimulates corticosterone formation and, hence, reduces the NAPDH/NADP ratio) stimulated PP by 23% (Fig. 4).FIGURE 4Regulation of pentose pathway by substrates of 11 β-HSD1 enzyme (11-DHC and corticosterone). Fat cells were preincubated with 10 μm 11-DHC or 10 μm corticosterone for 30 min, and then pentose pathway flux was measured over 90 min as shown under "Experimental Procedures". Results are given for three experiments and expressed as mean ± S.D. relative to control (no additions). Statistical differences by paired t-test are shown. The control (no additions) rate of pentose pathway activity was 7.14 ± 9.5 nmol/h/105 adipocytes.View Large Image Figure ViewerDownload Hi-res image Download (PPT) G6P Stimulates 11 β-HSD1 Oxo-reductase in Microsomes—If the microsomal membrane transports G6P, then generation of this metabolite by cytosolic PP would lead to enhanced 11 β-HSD1 activity. To test this relationship, isolated liver microsomes were incubated with increasing concentrations of G6P. G6P stimulated liver microsomal 11 β-HSD1 reductase activity (Fig. 5). However, this stimulating effect was less so in isolated adipocyte microsomal membranes with 1, 5, and 10 mm G6P inasmuch as this compound activated 11 β-HSD1 activity by 19 ± 3, 28 ± 3, and 60 ± 7% over basal (no G6P). These results were significant at p <0.025, p <0.01, and p <0.01, respectively. Microsomal Membrane Intactness Demonstrated by the Latency of Glucose Dehydrogenase Activity—The intactness of our experimental microsome preparation was tested by measuring glucose dehydrogenase activity following preincubation with and without the detergent membrane solubilizer (0.8% CHAPSO for 30 min at 4 °C). Glucose dehydrogenase is an NADP-requiring intraluminal microsomal enzyme whose activity is largely undetectable in intact microsomes (36Romanelli A. St-Denis J.F. Vidal H. Tchu S. van de Werve G. Biochem. Biophys. Res. Commun. 1994; 200: 1491-1497Crossref PubMed Scopus (25) Google Scholar). The results show that untreated microsomes were largely intact (no detectible glucose dehydrogenase activity over a 180-min incubation period) (Fig. 6). G6P Translocase Inhibitors Block Microsomal 11 β-HSD1 Activity— To determine whether microsomal 11 β-HSD1 activity was dependent on transport-dependent G6P uptake/metabolism we examined 11 β-HSD1 activity in whole microsomes with and without specific inhibitors of G6P uptake (chlorogenic acid or phlorizin). As an additional control for the specificity of G6P transport/metabolism, we tested the effect of an alternative sugar phosphate (galactose-1-phosphate). As shown using liver microsomes (Fig. 7), chlorogenic acid caused a 96% decrease in G6P-stimulated 11 β-HSD1 activity, whereas Gal-1-P was ineffective. Similarly, using isolated fat microsomes, 11 β-HSD1 activity in the presence of G6P was decreased to 52.6% ± 10.7 of basal (100%) with chlorogenic acid (p <0.05 versus basal) and to 41.0 ± 6.9% of basal with phlorizin (p <0.05 versus basal). DHEA and Norepinephrine Reduce Adipocyte NAPDH Content—If DHEA and norepinephrine regulate 11 β-HSD1 oxo-reductase indirectly by inhibiting PP, then these inhibitors should, consequently, diminish adipocyte NADPH content. Therefore, the cellular content of this pyridine nucleotide phosphate was measured after 45 min of preincubation with either 100 μm DHEA or 1 μm NE (Fig. 8). The respective results showed 28 ± 1.4 and 47 ± 15% reductions in total NADPH (p 7-fold) increase in the activity of this intraluminal enzyme, whereas NADH had a lesser activating effect (166 ± 15% of basal). On the other hand, NADP was inhibitory (74 ± 6% basal) (Fig. 9). These data, along with the evidence for membrane intactness (Fig. 6), support that the microsomal membrane is not completely impermeable to NADPH over a prolonged incubation. Numerous studies have commented on the enigmatic directionality of microsomal 11β-HSD1, seemingly dependent on the enzyme status: in intact cells oxo-reductase predominates, but when the enzyme is studied under cell-free conditions, the dehydrogenase direction prevails. Indirect evidence for the necessity of a renewable source of NADPH to sustain microsomal 11βHSD-1 reductase is manifest in patients with cortisol reductase deficiency (39Draper N. Walker E.A. Bujalska I.J. Tomlinson J.W. Chalder S.M. Arlt W. Lavery G.G. Bedendo O. Ray D.W. Laing I. Malunowicz E. White P.C. Hewison M. Mason P.J. Connell J.M. Shackleton C.H. Stewart P.M. Nat. Genet. 2003; 34: 434-439Crossref PubMed Scopus (260) Google Scholar). The latter results in inadequate regeneration of cortisol, subsequent overstimulation of adrenocorticotropin release, and a chronic mild androgen excess that promotes the polycystic ovarian phenotype. These patients have triallelic digenic mutations, ostensibly dosage dependent, involving not only 11β-HSD1 but also H6PD, the microsomal counterpart of cytosolic glucose-6-phosphate dehydrogenase. Notably, H6PD is a bifunctional enzyme that also has 6-phosphogluconolactonase catalytic activity; hence, it contains the oxidative portion of the pentose pathway (40Clarke J.L. Mason P.J. Arch. Biochem. Biophys. 2003; 415: 229-234Crossref PubMed Scopus (51) Google Scholar). Not only are these patients deficient in 11 β-HSD1 but they have a concomitant decrease in H6PD activity; therefore, impaired microsomal NADPH production nullifies any residual reductase activity. Another recent article buttresses the importance of luminal H6PD in the regulation of 11 β-HSD1. In human embryonic kidney 293 cells, in which endogenous expression of theses two enzymes is normally scant, co-expression studies revealed co-localization of these two enzymes in the ER. In addition, enhanced expression of H6PD stimulated 11 β-HSD1 reductase activity (41Atanasov A.G. Nashev L.G. Schweizer R.A. Frick C. Odermatt A. FEBS Lett. 2004; 571: 129-133Crossref PubMed Scopus (193) Google Scholar). In our fat cell experiments, after the targeted inhibition of G6P dehydrogenase with the non-competitive inhibitor DHEA, the resultant 56% reduction in adipocyte pentose flux (Fig. 1A) produced a significant attenuation of the oxo-reductase activity of 11 β-HSD1 (Fig. 1B). Cellular NADPH content likewise declined (Fig. 8). In addition, if there is a kinetic linkage between pentose pathway flux ↔ NADPH ↔ 11 β-HSD1, this reduction in NADPH by DHEA should promote the dehydrogenase direction for 11 β-HSD-1. Indeed, DHEA caused a significant 187% increase (Fig. 3). Further experimental corroboration for this linkage was borne out in the NE studies. Prior reports (34Katz J. Landau B.R. Bartsch G.E. J. Biol. Chem. 1966; 241: 727-740Abstract Full Text PDF PubMed Google Scholar) have confirmed that this hormone potently attenuates PP flux in adipocytes, most likely by stim
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