1
|
Antioxidant treatment prevents the development of fructose-induced abdominal adipose tissue dysfunction. Clin Sci (Lond) 2013; 125:87-97. [DOI: 10.1042/cs20120470] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In the present study, we tested the effect of OS (oxidative stress) inhibition in rats fed on an FRD [fructose-rich diet; 10% (w/v) in drinking water] for 3 weeks. Normal adult male rats received a standard CD (commercial diet) or an FRD without or with an inhibitor of NADPH oxidase, APO (apocynin; 5 mM in drinking water; CD-APO and FRD-APO). We thereafter measured plasma OS and metabolic-endocrine markers, AAT (abdominal adipose tissue) mass and cell size, FA (fatty acid) composition (content and release), OS status, LEP (leptin) and IRS (insulin receptor substrate)-1/IRS-2 mRNAs, ROS (reactive oxygen species) production, NADPH oxidase activity and LEP release by isolated AAT adipocytes. FRD-fed rats had larger AAT mass without changes in body weight, and higher plasma levels of TAG (triacylglycerol), FAs, TBARS (thiobarbituric acid-reactive substance) and LEP. Although no significant changes in glucose and insulin plasma levels were observed in these animals, their HOMA-IR (homoeostasis model assessment of insulin resistance) values were significantly higher than those of CD. The AAT from FRD-fed rats had larger adipocytes, higher saturated FA content, higher NADPH oxidase activity, greater ROS production, a distorted FA content/release pattern, lower insulin sensitivity together with higher and lower mRNA content of LEP and IRS-1-/2 respectively, and released a larger amount of LEP. The development of all the clinical, OS, metabolic, endocrine and molecular changes induced by the FRD were significantly prevented by APO co-administration. The fact that APO treatment prevented both changes in NADPH oxidase activity and the development of all the FRD-induced AAT dysfunctions in normal rats strongly suggests that OS plays an important role in the FRD-induced MS (metabolic syndrome) phenotype.
Collapse
|
2
|
Effect of pioglitazone on the fructose-induced abdominal adipose tissue dysfunction. PPAR Res 2012; 2012:259093. [PMID: 23091482 PMCID: PMC3469242 DOI: 10.1155/2012/259093] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Accepted: 08/23/2012] [Indexed: 12/31/2022] Open
Abstract
Aim. To test the potential role of PPARγ in the endocrine abdominal tissue dysfunction induced by feeding normal rats with a fructose rich diet (FRD) during three weeks. Methodology. Adult normal male rats received a standard commercial diet (CD) or FRD, (10% in drinking water) without or with pioglitazone (PIO) (i.p. 0.25 mg/Kg BW/day; CD-PIO and FRD-PIO). Thereafter, we measured circulating metabolic, endocrine, and oxidative stress (OS) markers, abdominal adipose tissue (AAT) mass, leptin (LEP) and plasminogen activator inhibitor-1 (PAI-1) tissue content/expression, and leptin release by isolated adipocytes incubated with different concentrations of insulin. Results. Plasma glucose, insulin, triglyceride, TBARS, LEP, and PAI-1 levels were higher in FRD rats; PIO coadministration fully prevented all these increments. AAT adipocytes from FRD rats were larger, secreted a higher amount of LEP, and displayed decreased sensitivity to insulin stimulation; these effects were significantly ameliorated by PIO. Whereas AAT LEP and PAI-1 (mRNA) concentrations increased significantly in FRD rats, those of insulin-receptor-substrate- (IRS-) 1 and IRS-2 were reduced. PIO coadministration prevented FRD effects on LEP, PAI-1, and IRS-2 (fully) and IRS-1 (partially) mRNAs in AAT. Conclusion. PPARγ would play a relevant role in the development of the FRD-induced metabolic-endocrine dysfunction.
Collapse
|
3
|
Sweet taste receptor signaling in beta cells mediates fructose-induced potentiation of glucose-stimulated insulin secretion. Proc Natl Acad Sci U S A 2012; 109:E524-32. [PMID: 22315413 DOI: 10.1073/pnas.1115183109] [Citation(s) in RCA: 164] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Postprandial insulin release is regulated by glucose, but other circulating nutrients may target beta cells and potentiate glucose-stimulated insulin secretion via distinct signaling pathways. We demonstrate that fructose activates sweet taste receptors (TRs) on beta cells and synergizes with glucose to amplify insulin release in human and mouse islets. Genetic ablation of the sweet TR protein T1R2 obliterates fructose-induced insulin release and its potentiating effects on glucose-stimulated insulin secretion in vitro and in vivo. TR signaling in beta cells is triggered, at least in part, in parallel with the glucose metabolic pathway and leads to increases in intracellular calcium that are dependent on the activation of phospholipase C (PLC) and transient receptor potential cation channel, subfamily M, member 5 (TRPM5). Our results unveil a pathway for the regulation of insulin release by postprandial nutrients that involves beta cell sweet TR signaling.
Collapse
|
4
|
Giroix MH, Agascioglu E, Oguzhan B, Louchami K, Zhang Y, Courtois P, Malaisse WJ, Sener A. Opposite effects of D-fructose on total versus cytosolic ATP/ADP ratio in pancreatic islet cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:773-80. [PMID: 16782044 DOI: 10.1016/j.bbabio.2006.05.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Revised: 04/12/2006] [Accepted: 05/03/2006] [Indexed: 12/01/2022]
Abstract
D-fructose (10 mM) augments, in rat pancreatic islets, insulin release evoked by 10 mM D-glucose. Even in the absence of D-glucose, D-fructose (100 mM) displays a positive insulinotropic action. It was now examined whether the insulinotropic action of D-fructose could be attributed to an increase in the ATP content of islet cells. After 30-60 min incubation in the presence of D-glucose and/or D-fructose, the ATP and ADP content was measured by bioluminescence in either rat isolated pancreatic islets (total ATP and ADP) or the supernatant of dispersed rat pancreatic islet cells exposed for 30 s to digitonine (cytosolic ATP and ADP). D-fructose (10 and 100 mM) was found to cause a concentration-related decrease in the total ATP and ADP content and ATP/ADP ratio below the basal values found in islets deprived of exogenous nutrient. Moreover, in the presence of 10 mM D-glucose, which augmented both the total ATP content and ATP/ADP ratio above basal value, D-fructose (10 mM) also lowered these two parameters. The cytosolic ATP/ADP ratio, however, was increased in the presence of D-glucose and/or D-fructose. Under the present experimental conditions, a sigmoidal relationship was found between such a cytosolic ATP/ADP ratio and either (86)Rb net uptake by dispersed islet cells or insulin release from isolated islets. These data provide, to our knowledge, the first example of a dramatic dissociation between changes in total ATP content or ATP/ADP ratio and insulin release in pancreatic islets exposed to a nutrient secretagogue. Nevertheless, the cationic and insulinotropic actions of d-glucose and/or d-fructose were tightly related to the cytosolic ATP/ADP ratio.
Collapse
Affiliation(s)
- Marie-Hélène Giroix
- Laboratory of Nutrition Physiopathology, CNRS UMR 7059, University of Paris 7, France
| | | | | | | | | | | | | | | |
Collapse
|
5
|
Sener A, Leclercq-Meyer V, Malaisse WJ. Immediate and delayed effects of D-fructose upon insulin, somatostatin, and glucagon release by the perfused rat pancreas. Endocrine 2004; 24:73-81. [PMID: 15249706 DOI: 10.1385/endo:24:1:073] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2004] [Revised: 05/07/2004] [Accepted: 05/10/2004] [Indexed: 11/11/2022]
Abstract
Novel information was recently provided concerning the reciprocal effects of D-glucose and D-fructose upon their respective metabolism in rat pancreatic islets. In the light of such findings, this study aims at comparing the effects of D-glucose and D-fructose on insulin, somatostatin, and glucagon release from the isolated perfused rat pancreas. A rise in D-glucose concentration from 3.3 to 5.0 or 7.3 mM or the administration of D-fructose (17 and 40 mM) in the presence of 3.3 mM D-glucose stimulated insulin release in a concentration-related manner, but failed to affect somatostatin output. The secretion of glucagon was decreased in all cases. The secretory response to L-arginine (5 mM), 25 min after restoring the basal concentration of D-glucose, was more markedly affected, in terms of potentiation of insulin and somatostatin release and reduction of glucagon output, after prior administration of D-fructose than after a prior increase in D-glucose concentration. These findings argue against any major role for a paracrine regulation of hormonal release and, instead, are consistent with a causal link between metabolic and secretory events in the islet cells. Nevertheless, the present results emphasize differences in the response of distinct pancreatic endocrine cell types to the same or distinct hexoses.
Collapse
Affiliation(s)
- Abdullah Sener
- Laboratory of Experimental Hormonology, Brussels Free University, Brussels, Belgium.
| | | | | |
Collapse
|
6
|
Scruel O, Sener A, Malaisse WJ. Hexose metabolism in pancreatic islets: effect of D-glucose upon D-fructose metabolism. Mol Cell Biochem 1999; 197:209-16. [PMID: 10485341 DOI: 10.1023/a:1006910201767] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the light of recent findings on the effect of D-glucose upon D-fructose phosphorylation by human B-cell glucokinase, the influence of the aldohexose upon the metabolism of the ketohexose was investigated in rat pancreatic islets. D-glucose, although slightly decreasing D-[5-(3)H]fructose utilization, augmented the oxidation of the ketohexose, indicating that the aldohexose stimulates preferentially the oxidative, as distinct from anaerobic, modality of glycolysis. Such was not the case in parotid cells, taken as representative of functionally nonglucose-responsive cells. In the islets exposed to D-fructose, D-glucose also decreased the fractional contribution of the pentose shunt to the generation of CO2 and D-glyceraldehyde 3-phosphate from the ketohexose, and increased the inflow into the Krebs cycle of dicarboxylic metabolites relative to that of fructose-derived acetyl-CoA. This glucose-induced remodeling of D-fructose metabolism may optimize the insulin secretory response of islet cells to these hexoses, e.g. after food intake.
Collapse
Affiliation(s)
- O Scruel
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | | | |
Collapse
|
7
|
Scruel O, Sener A, Malaisse WJ. Glucose-induced positive cooperativity of fructose phosphorylation by human B-cell glucokinase. Mol Cell Biochem 1997; 175:263-9. [PMID: 9350059 DOI: 10.1023/a:1006834010660] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Human B-cell glucokinase displays sigmoidal kinetics towards D-glucose or D-mannose, but fails to do so towards D-fructose. Yet, D-glucose, D-mannose and 2-deoxy-D-glucose confer to the enzyme positive cooperativity towards D-fructose. For instance, in the presence of 5 mM D-[U-14C]fructose, its rate of phosphorylation is increased to 214.3 +/- 11.0%, 134.0 +/- 4.3% and 116.5 +/- 3.0% of paired control value by D-glucose, D-mannose and 2-deoxy-D-glucose (each 6 mM), respectively. D-glucose and, to a lesser extent, D-mannose also display reciprocal kinetic cooperativity. D-fructose, however, fails to affect D-glucose or D-mannose phosphorylation under conditions in which positive cooperativity is otherwise observed. These findings are relevant to the reciprocal effects of distinct hexoses upon their phosphorylation by B-cell glucokinase and, as such, to the metabolic and functional response evoked in pancreatic islet B-cells by these sugars, when tested either separately or in combination.
Collapse
Affiliation(s)
- O Scruel
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | | | |
Collapse
|
8
|
Sener A, Malaisse WJ. Kinetics and specificity of human B-cell glucokinase: relevance to hexose-induced insulin release. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1312:73-8. [PMID: 8679719 DOI: 10.1016/0167-4889(96)00010-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The present study reevaluates the relevance of human B-cell glucokinase activity to the process of hexose-induced insulin release. Taking into account a phenomenon of positive cooperativity (Hill number: 1.34), the Km of the enzyme for glucose ( < or = 5.1 mM) was lower than the concentration of the hexose required to cause half-maximal stimulation of insulin release in intact islets. Likewise, there were obvious discrepancies between the kinetics of glucose, mannose and fructose phosphorylation by B-cell glucokinase, e.g. in terms of maximal velocity, and the secretory and metabolic responses to these hexoses in intact islets. Glucose 6-phosphate decreased, modestly but significantly, B-cell glucokinase activity, such an inhibitory action being of the non-competitive type. Mannoheptulose caused competitive inhibition of B-cell glucokinase. It is concluded that the intrinsic catalytic properties of B-cell glucokinase cannot fully account for the concentration dependency and sugar specificity of the secretory response to D-glucose or other hexoses in pancreatic islets.
Collapse
Affiliation(s)
- A Sener
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | |
Collapse
|
9
|
Malm D, Tollersrud OK, Vonen B, Florholmen J. The effect of fructose metabolism on the accumulation of inositol phosphates in rat pancreatic islets. Scand J Clin Lab Invest 1996; 56:129-34. [PMID: 8743105 DOI: 10.3109/00365519609088599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The mechanism by which glucose recognition of B cells results in the release of inositol 1,4,5-trisphosphate is not known at present. In pancreatic islets, fructose shares a common metabolic pathway with glucose from the second step of glycolysis and can augment insulin secretion at stimulatory glucose levels. To evaluate the impact of glycolysis on the release of inositol 1,4,5-trisphosphate, we studied the effect of glucose and fructose metabolism on insulin secretion and the activation of inositol-specific phospholipase C, using collagenase digested rat pancreatic islets incorporated with 3H-labelled myo-inositol. Inositol phosphates, generated by the cleavage of phosphatidyl inositol by inositol phospholipase C, were analyzed using fast protein liquid chromatography. The islets were exposed to 3.3, 5.5 and 12 mmol 1(-1) glucose for 45 min in the absence or presence of 10, 20 or 30 mmol 1(-1) fructose, and the amount of insulin released into the medium was measured. Intracellular inositol phosphate accumulation was measured under the same glucose concentrations with 0, 10 and 30 mmol 1(-1) fructose. As expected, fructose alone had no insulinotropic effect, but potentiated the glucose-induced (5.5 and 12 mmol 1(-1)) insulin secretion at concentrations of 10-30 mmol 1(-1). Glucose (12 vs. 3.3 mmol 1(-1)) significantly increased both intracellular content of inositol 1,4,5-trisphosphate, as well as its metabolite inositol 1,3,4-trisphosphate. Fructose, however, had no potentiating effects on the accumulation of inositol phosphates. It is therefore supposed that glucose does not activate inositol-specific phospholipase C via the glycolysis. Further, since fructose did not activate inositol-specific phospholipase C, this stimulation is likely to be induced by glucose as such.
Collapse
Affiliation(s)
- D Malm
- Department of Medicine, University Hospital of Tromsø, Norway
| | | | | | | |
Collapse
|
10
|
Kruszynska YT, Harry DS, Fryer LG, McIntyre N. Lipid metabolism and substrate oxidation during intravenous fructose administration in cirrhosis. Metabolism 1994; 43:1171-81. [PMID: 8084292 DOI: 10.1016/0026-0495(94)90062-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We used isotope dilution techniques (constant intravenous [IV] infusion of 2-3H-glycerol and 1-14C-palmitate) and indirect calorimetry to measure lipid kinetics and substrate oxidation rates during IV fructose administration at 200 and then 500 mg/kg/h in eight cirrhotic patients and seven normal control subjects. Fasting plasma glucose, glycerol, and glycerol appearance rate (Ra) were similar in both groups, but insulin levels were fourfold higher in cirrhotics (P < .01). Fasting serum nonesterified fatty acid (NEFA) levels (cirrhotics, 869 +/- 124, controls, 717 +/- 90 mumol/L) and NEFA Ra (7.1 +/- 0.8 v 5.5 +/- 0.9 mumol/min/kg) were higher in cirrhotics, but the differences were not significant. Plasma fructose was similar in both groups at both fructose infusion rates. Fructose appeared to stimulate insulin secretion. With i.v. fructose, serum NEFA levels decreased, reaching similar low levels when 500 mg/kg/h was infused, due to a reduction in NEFA Ra and an increase in the NEFA metabolic clearance rate (MCR). Glycerol levels showed little change. As glycerol Ra decreased by less than 20% in both groups, the decrease in serum NEFA was primarily due to enhanced reesterification of fatty acids both within adipose tissue (preventing their release) and in other tissues (enhancing their removal from plasma). Although total fructose utilization was normal in cirrhotics, they oxidized more of the infused fructose; nonoxidative disposal was reduced (first step, 242 +/- 12 v 318 +/- 16 mg/kg in 2 hours, P < .002; second step, 657 +/- 32 v 786 +/- 21 mg/kg in 2 hours, P < .005). Although tissue fructose uptake is insulin-independent, insulin resistance in cirrhosis may influence the intracellular metabolism of fructose.
Collapse
Affiliation(s)
- Y T Kruszynska
- University Department of Medicine, Royal Free Hospital School of Medicine, London, UK
| | | | | | | |
Collapse
|
11
|
Malaisse WJ, Sener A. Hexose metabolism in pancreatic islets. Activation of the Krebs cycle by nutrient secretagogues. Mol Cell Biochem 1991; 107:95-102. [PMID: 1791828 DOI: 10.1007/bf00225512] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In rat pancreatic islets, a rise in extracellular D-glucose concentration is known to cause a greater increase in the oxidation of D-[6-14C]glucose than utilization of D-[5-3H]glucose. In the present study, such a preferential stimulation of acetyl residue oxidation relative to glycolytic flux was mimicked by nutrient secretagogues such as 2-aminobicyclo[2,2,1]heptane-2-carboxylate, 3-phenylpyruvate, L-leucine, 2-ketoisocaproate, D-fructose and ketone bodies. The preferential stimulation of D-[6-14C]glucose oxidation by these nutrients was observed at all hexose concentrations (0.5, 6.0 and 16.7 mM), coincided with an unaltered rate of D-[3,4-14C]glucose oxidation, was impaired in the absence of extracellular Ca2+, and failed to be affected by NH4+. Although the ratio between D-[6-14C]glucose oxidation and D-[5-3H]glucose utilization in islets exposed to other nutrient secretagogues could be affected by factors such as isotopic dilution and mitochondrial redox state, the present data afford strong support to the view that the preferential stimulation of oxidative events in the Krebs cycle of nutrient-stimulated islets is linked to the activation of key mitochondrial dehydrogenases, e.g. 2-ketoglutarate dehydrogenase. The latter activation might result from the mitochondrial accumulation of Ca2+, as attributable not solely to stimulation of Ca2+ inflow into the islet cells but also to an increase in ATP availability.
Collapse
Affiliation(s)
- W J Malaisse
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | |
Collapse
|
12
|
Hayes DJ, Carter NS. An investigation of fructose utilization in Acanthocheilonema viteae. Parasitology 1990; 101 Pt 3:445-50. [PMID: 2092300 DOI: 10.1017/s0031182000060649] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The capacity of Acanthocheilonema viteae to metabolize fructose was investigated in vitro. In common with other filarial species A. viteae oxidized fructose to lactate but its rate of consumption was only 40% of the glucose-containing control value. Fructose was not incorporated into glycogen. Release of 14CO2 from [U-14C]fructose was not detected in the presence of glucose and was about 40% of the glucose-containing value under conditions where fructose was the sole hexose substrate. Fructose consumption and lactate excretion increased in proportion to the external concentration of fructose. However, worm viability was not maintained in fructose over a 120 h in vitro incubation. In the presence of fructose, protein synthesis (measured incorporation of [35S]methionine into acid-insoluble material) was reduced compared to the glucose-containing control group; but was significantly greater than the value obtained under glucose-free conditions.
Collapse
Affiliation(s)
- D J Hayes
- Biochemical Sciences, Wellcome Research Laboratories, Beckenham, Kent
| | | |
Collapse
|
13
|
Malaisse WJ, Lebrun P, Yaylali B, Camara J, Valverde I, Sener A. Ketone bodies and islet function: 45Ca handling, insulin synthesis, and release. THE AMERICAN JOURNAL OF PHYSIOLOGY 1990; 259:E117-22. [PMID: 2196820 DOI: 10.1152/ajpendo.1990.259.1.e117] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
D-(-)-beta-Hydroxybutyrate and acetoacetate cause a rapid, sustained, and rapidly reversible stimulation of insulin release from rat pancreatic islets incubated in the presence, but not absence, of D-glucose. This coincides with stimulation of both proinsulin biosynthesis and 45Ca net uptake. The ketone bodies also decrease 45Ca outflow from prelabeled islets perifused in the absence of Ca2+ and, in contrast, enhance effluent radioactivity in the presence of Ca2+. In the presence of D-glucose, the secretory response to D-(-)-beta-hydroxybutyrate is concentration related in the 2.5-20 mM range, abolished in the absence of Ca2+ or presence of KCN, and enhanced by theophylline and forskolin. It corresponds grossly to a shift to the left of the sigmoidal curve relating insulin output to the ambient concentration of D-glucose. The secretory, biosynthetic, and cationic response to acetoacetate is less marked than that evoked by an equimolar concentration of D-(-)-beta-hydroxybutyrate. These features are compatible with the view that the insulinotropic action of ketone bodies would be causally linked to their metabolism in islet cells.
Collapse
Affiliation(s)
- W J Malaisse
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | | | | | | | | | |
Collapse
|
14
|
Malaisse WJ, Malaisse-Lagae F, Davies DR, Van Schaftingen E. Presence of fructokinase in pancreatic islets. FEBS Lett 1989; 255:175-8. [PMID: 2551726 DOI: 10.1016/0014-5793(89)81085-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Homogenates of rat pancreatic islets that had been heated for 5 min at 70 degrees C to inactive hexokinases, catalyzed the ATP-dependent phosphorylation of D-fructose. This reaction was dependent on the presence of K+ and was inhibited by D-tagatose although not by D-glucose or D-glucose 6-phosphate. The phosphorylation product was identified as fructose 1-phosphate through its conversion to a bisphosphate ester by Clostridium difficile fructose 1-phosphate kinase. These findings allowed the conclusion that fructokinase (ketohexokinase) was responsible for this process. Similar results were observed with tumoral insulin-producing cells (RINm5F line). Fructokinase may account for a large share of fructose phosphorylation in intact islets, particularly in the presence of D-glucose.
Collapse
Affiliation(s)
- W J Malaisse
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | | | | | |
Collapse
|
15
|
Malaisse WJ, Sener A. Hexose metabolism in pancreatic islets. Feedback control of D-glucose oxidation by functional events. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 971:246-54. [PMID: 3139046 DOI: 10.1016/0167-4889(88)90139-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
A rise in extracellular D-glucose concentration in pancreatic islet cells causes a greater relative increase in the oxidation of pyruvate and acetyl residues than in glycolysis. A possible explanation for such an unusual situation was sought in the present study. The preferential stimulation of mitochondrial oxidative events was found to display a sigmoidal dependency on hexose concentration, and an exponential time course during prolonged exposure of the islets to a high concentration of D-glucose. The preferential stimulation of mitochondrial oxidative events was abolished in islets incubated in the presence of cycloheximide and absence of Ca2+, in which case the oxidation of D-[6-14C]glucose was more severely inhibited than that of D-[3,4-14C]glucose. Likewise, the inhibitor of protein biosynthesis and the absence of Ca2+ affected the oxidation of L-[U-14C]leucine preferentially, relative to that of L-[1-14C]leucine, in islets exposed to a high, but not a low, concentration of the amino acid. These results demonstrate that in pancreatic islets it is possible to dissociate both glycolysis from mitochondrial oxidative events and the oxidation of acetyl residues from their generation rate. Moreover, the experimental data suggest that nutrient-responsive and ATP-requiring functional processes exert a feedback control on mitochondrial respiration in this fuel-sensor organ.
Collapse
Affiliation(s)
- W J Malaisse
- Laboratory of Experimental Medicine, Brussels Free University, Belgium
| | | |
Collapse
|
16
|
Hexose metabolism in pancreatic islets. Feedback control of d-glucose oxidation by functional events. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1988. [DOI: 10.1016/s0005-2728(88)80038-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|