Vanadium-dependent activation of glucose transport in adipocytes by catecholamines is not mediated via adrenoceptor stimulation or monoamine oxidase activity

BACKGROUND Benzylamine and methylamine activate glucose uptake in adipocytes.For tyramine,this effect has even been extended to cardiomyocytes.AIM To investigate the effects of catecholamines and other amines on glucose uptake.METHODS A screening compared 25 biogenic amines on 2-deoxyglucose(2-DG)uptake activation in rat adipocytes.Pharmacological approaches and transgenic mouse models were then used to decipher the mode of action of several hits.RESULTS In rat adipocytes,insulin stimulation of 2-DG uptake was reproduced with catecholamines.100μmol/L or 1 mmol/L adrenaline,noradrenaline,dopamine and deoxyepinephrine,maximally activated hexose transport only when sodium orthovanadate was added at 100μmol/L.Such activation was similar to that already reported for benzylamine,methylamine and tyramine,well-recognized substrates of semicarbazide-sensitive amine oxidase(SSAO)and monoamine oxidase(MAO).Several,but not all,tested agonists ofβ-adrenoreceptors(β-ARs)also activated glucose transport whileα-AR agonists were inactive.Lack of blockade byα-andβ-AR antagonists indicated that catecholamine-induced 2-DG uptake was not mediated by AR stimulation.Adipocytes from mice lackingβ1-,β2-andβ3-ARs(triple KO)also responded to millimolar doses of adrenaline or noradrenaline by activating hexose transport in the presence of 100μmol/L vanadate.The MAO blocker pargyline,and SSAO inhibitors did not block the effects of adrenaline or noradrenaline plus vanadate,which were blunted by antioxidants.CONCLUSION Catecholamines exert unexpected insulin-like actions in adipocytes when combined with vanadium.For limiting insulin resistance by activating glucose consumption at least in fat stores,we propose that catecholamine derivatives combined with vanadium can generate novel complexes that may have low toxicity and promising anti-diabetic properties.

Novel assay for identification of semicarbazide-sensitive amine oxidase by a priority-based strategy in mass spectrometry

A novel assay for the identification of semicarbazide sensitive amine oxidase in human umbilical artery tissue by a priority based strategy in the mass spectrometry was developed. The pro tein extract was separated by SDS PAGE, and then an entire band at 96 KDa was excised and digested by trypsin. The digested peptides were separated by capillary ClS analytical column and detected by ESI MS MS. In the direct data dependent method （also called traditional method）, the semicarbaz ide sensitive amine oxidase （SSAO） cannot be identified by LC-ESI-MS-MS. Compared with the tra ditional method, our assay by a priority based strategy in the mass spectrometry can successfully identify the target protein SSAO in the complex biological sample. As 60 μg, 120μg, 240 μg of total protein extract were loaded on the SDS PAGE, the Mascot result showed that SSAO score was 46, 86 and 137, the sequence coverage was 2 % , 5 % and 10 % , and the peptide count was 2, 6 and 10, re spectively. The MS/MS spectra of two unique peptides of SSAO were confirmed by manual identifica tion. The band at 96 KDa included SSAO was validated by the Western blot. The assay significantly improved the score and coverage of target protein and enhanced the identification of reliability and the confidence.

Increased monoamine oxidase activity and imidazoline binding sites in insulin-resistant adipocytes from obese Zucker rats

BACKGROUND Despite overt insulin resistance,adipocytes of genetically obese Zucker rats accumulate the excess of calorie intake in the form of lipids.AIM To investigate whether factors can replace or reinforce insulin lipogenic action by exploring glucose uptake activation by hydrogen peroxide,since it is produced by monoamine oxidase(MAO)and semicarbazide-sensitive amine oxidase(SSAO)in adipocytes.METHODS 3H-2-deoxyglucose uptake(2-DG)was determined in adipocytes from obese and lean rats in response to insulin or MAO and SSAO substrates such as tyramine and benzylamine.14C-tyramine oxidation and binding of imidazolinic radioligands[3H-Idazoxan,3H-(2-benzofuranyl)-2-imidazoline]were studied in adipocytes,the liver,and muscle.The influence of in vivo administration of tyramine+vanadium on glucose handling was assessed in lean and obese rats.RESULTS 2-DG uptake and lipogenesis stimulation by insulin were dampened in adipocytes from obese rats,when compared to their lean littermates.Tyramine and benzylamine activation of hexose uptake was vanadate-dependent and was also limited,while MAO was increased and SSAO decreased.These changes were adipocyte-specific and accompanied by a greater number of imidazoline I2 binding sites in the obese rat,when compared to the lean.In vitro,tyramine precluded the binding to I2 sites,while in vivo,its administration together with vanadium lowered fasting plasma levels of glucose and triacylglycerols in obese CONCLUSION The adipocytes from obese Zucker rats exhibit increased MAO activity and imidazoline binding site number.However,probably as a consequence of SSAO down-regulation,the glucose transport stimulation by tyramine is decreased as much as that of insulin in these insulin-resistant adipocytes.The adipocyte amine oxidases deserve more studies with respect to their putative contribution to the management of glucose and lipid handling.

COPPER AMINE OXIDASE1 （CuAO1） of Arabidopsis thaliana Contributes to Abscisic Acid- and Polyamine-lnduced Nitric Oxide Biosynthesis and Abscisic Acid Signal Transduction

Polyamines （PA）, polyamine oxidases, copper amine oxidases, and nitric oxide （NO） play important roles in physiology and stress responses in plants. NO biosynthesis as a result of catabolism of PA by polyamine oxidases and copper amine oxidases may explain in part PA-mediated responses. Involvement of a copper amine oxidase gene, COPPER AMINE OXIDASEI （CuAO1）, of Arabidopsis was tested for its role in stress responses using the knockouts cuao1-1 and cuaol-2. PA-induced and ABA-induced NO production investigated bY fluorometry and fluorescence microscopy showed that the cuaol-1 and cuaol-2 are impaired in NO production, suggesting a function of CuAO1 in PA and ABA-mediated NO production. Furthermore, we found a PA-dependent increase in protein S-nitrosylation. The addition of PA and ABA also resulted in H2O2 increases, cuao1-1 and cuao1-2 showed less sensitivity to exogenous ABA supplementation during germination, seedling establishment, and root growth inhibition as compared to wild-type. In response to ABA treatment, expression levels of the stress-responsive genes RD29A and ADH1 were significantly lower in the knockouts. These observations characterize cuao1-1 and cuao1-2 as ABA-insensitive mutants. Taken together, our findings extend the ABA signal transduction network to include CuAO1 as one potential contributor to enhanced NO production by ABA.

High doses of catecholamines activate glucose transport in human adipocytes independently from adrenoceptor stimulation or vanadium addition

BACKGROUND When combined with vanadium salts,catecholamines strongly activate glucose uptake in rat and mouse adipocytes.AIM To test whether catecholamines activate glucose transport in human adipocytes.METHODS The uptake of 2-deoxyglucose(2-DG)was measured in adipocytes isolated from pieces of abdominal subcutaneous tissue removed from women undergoing reconstructive surgery.Pharmacological approaches with amine oxidase inhibitors,adrenoreceptor agonists and antioxidants were performed to unravel the mechanisms of action of noradrenaline or adrenaline(also named epinephrine).RESULTS In human adipocytes,45-min incubation with 100μmol/L adrenaline or noradrenaline activated 2-DG uptake up to more than one-third of the maximal response to insulin.This stimulation was not reproduced with millimolar doses of dopamine or serotonin and was not enhanced by addition of vanadate to the incubation medium.Among various natural amines and adrenergic agonists tested,no other molecule was more efficient than adrenaline and noradrenaline in stimulating 2-DG uptake.The effect of the catecholamines was not impaired by pargyline and semicarbazide,contrarily to that of benzylamine or methylamine,which are recognized substrates of semicarbazide-sensitive amine oxidase.Hydrogen peroxide at 1 mmol/L activated hexose uptake but not pyrocatechol or benzoquinone,and only the former was potentiated by vanadate.Catalase and the phosphoinositide 3-kinase inhibitor wortmannin inhibited adrenaline-induced activation of 2-DG uptake.CONCLUSION High doses of catecholamines exert insulin-like actions on glucose transport in human adipocytes.At submillimolar doses,vanadium did not enhance this catecholamine activation of glucose transport.Consequently,this dismantles our previous suggestion to combine the metal ion with catecholamines to improve the benefit/risk ratio of vanadium-based antidiabetic approaches.

Hyperglycemia and reduced adiposity of streptozotocin-induced diabetic mice are not alleviated by oral benzylamine supplementation

BACKGROUND Benzylamine(Bza)oral administration delays the onset of hyperglycemia in insulin-resistant db-/-mice;a genetic model of obesity and type 2 diabetes.AIM To extend the antihyperglycemic properties of oral benzylamine to a model of insulin-deficient type 1 diabetes.METHODS Male Swiss mice were rendered diabetic by streptozotocin treatment(STZ)and divided in two groups:one received 0.5%Bza as drinking solution for 24 d(STZ Bza-drinking)while the other was drinking water ad libitum.Similar groups were constituted in age-matched,nondiabetic mice.Food intake,liquid intake,body weight gain and nonfasting blood glucose levels were followed during treatment.At the end of treatment,fasted glycemia,liver and white adipose tissue(WAT)mass were measured,while glucose uptake assays were performed in adipocytes.RESULTS STZ diabetic mice presented typical features of insulin-deficient diabetes:reduced body mass and increased blood glucose levels.These altered parameters were not normalized in the Bza-drinking group in spite of restored food and water intake.Bza consumption could not reverse the severe fat depot atrophy of STZ diabetic mice.In the nondiabetic mice,no difference was found between control and Bza-drinking mice for any parameter.In isolated adipocytes,hexose uptake was partially activated by 0.1 mmol/L Bza in a manner that was obliterated in vitro by the amine oxidase inhibitor phenelzine and that remained unchanged after Bza supplementation.Oxidation of 0.1 mmol/L Bza in WAT was lower in STZ diabetic than in normoglycemic mice.CONCLUSION Bza supplementation could not normalize the altered glucose handling of STZ diabetic mice with severe WAT atrophy.Consequently,its antidiabetic potential in obese and diabetic rodents does not apply to lipoatrophic type 1 diabetic mice.