Effects of Chemical Structures Interacting with Amine Oxidases on Glucose, Lipid and Hydrogen Peroxide Handling by Human Adipocytes.

Benzylamine is a natural molecule present in food and edible plants, capable of activating hexose uptake and inhibiting lipolysis in human fat cells. These effects are dependent on its oxidation by amine oxidases present in adipocytes, and on the subsequent hydrogen peroxide production, known to exhibit insulin-like actions. Virtually, other substrates interacting with such hydrogen peroxide-releasing enzymes potentially can modulate lipid accumulation in adipose tissue. Inhibition of such enzymes has also been reported to influence lipid deposition. We have therefore studied in human adipocytes the lipolytic and lipogenic activities of pharmacological entities designed to interact with amine oxidases highly expressed in this cell type: the semicarbazide-sensitive amine oxidase (SSAO also known as PrAO or VAP-1) and the monoamine oxidases (MAO). The results showed that SZV-2016 and SZV-2017 behaved as better substrates than benzylamine, releasing hydrogen peroxide once oxidized, and reproduced or even exceeded its insulin-like metabolic effects in fat cells. Additionally, several novel SSAO inhibitors, such as SZV-2007 and SZV-1398, have been evidenced and shown to inhibit benzylamine metabolic actions. Taken as a whole, our findings reinforce the list of molecules that influence the regulation of triacylglycerol assembly/breakdown, at least in vitro in human adipocytes. The novel compounds deserve deeper investigation of their mechanisms of interaction with SSAO or MAO, and constitute potential candidates for therapeutic use in obesity and diabetes.

Novel Facet of an Old Dietary Molecule? Direct Influence of Caffeine on Glucose and Biogenic Amine Handling by Human Adipocytes.

Caffeine is a plant alkaloid present in food and beverages consumed worldwide. It has high lipid solubility with recognized actions in the central nervous system and in peripheral tissues, notably the adipose depots. However, the literature is scant regarding caffeine's influence on adipocyte functions other than lipolysis, such as glucose incorporation into lipids (lipogenesis) and amine oxidation. The objective of this study was to explore the direct effects of caffeine and of isobutylmethylxanthine (IBMX) on these adipocyte functions. Glucose transport into fat cells freshly isolated from mice, rats, or humans was monitored by determining [3H]-2-deoxyglucose (2-DG) uptake, while the incorporation of radiolabeled glucose into cell lipids was used as an index of lipogenic activity. Oxidation of benzylamine by primary amine oxidase (PrAO) was inhibited by increasing doses of caffeine in human adipose tissue preparations with an inhibition constant (Ki) in the millimolar range. Caffeine inhibited basal and insulin-stimulated glucose transport as well as lipogenesis in rodent adipose cells. The antilipogenic action of caffeine was also observed in adipocytes from mice genetically invalidated for PrAO activity, indicating that PrAO activity was not required for lipogenesis inhibition. These caffeine inhibitory properties were extended to human adipocytes: relative to basal 2-DG uptake, set at 1.0 ± 0.2 for 6 individuals, 0.1 mM caffeine tended to reduce uptake to 0.83 ± 0.08. Insulin increased uptake by 3.86 ± 1.11 fold when tested alone at 100 nM, and by 3.21 ± 0.80 when combined with caffeine. Our results reinforce the recommendation of caffeine's potential in the treatment or prevention of obesity complications.

Oral Phenelzine Treatment Mitigates Metabolic Disturbances in Mice Fed a High-Fat Diet.

Novel mechanisms and health benefits have been recently suggested for the antidepressant drug phenelzine (PHE), known as a nonselective monoamine oxidase inhibitor. They include an antilipogenic action that could have an impact on excessive fat accumulation and obesity-related metabolic alterations. We evaluated the metabolic effects of an oral PHE treatment on mice fed a high-fat diet (HFD). Eleven-week-old male C57BL/6 mice were fed a HFD and either a 0.028% PHE solution (HFD + PHE) or water to drink for 11 weeks. PHE attenuated the increase in body weight and adiposity without affecting food consumption. Energy efficiency was lower in HFD + PHE mice. Lipid content was reduced in subcutaneous fat pads, liver, and skeletal muscle. In white adipose tissue (WAT), PHE reduced sterol regulatory element-binding protein-1c and phosphoenolpyruvate carboxykinase mRNA levels, inhibited amine-induced lipogenesis, and did not increase lipolysis. Moreover, HFD + PHE mice presented diminished levels of hydrogen peroxide release in subcutaneous WAT and reduced expression of leukocyte transmigration markers and proinflammatory cytokines in visceral WAT and liver. PHE reduced the circulating levels of glycerol, triacylglycerols, high-density lipoprotein cholesterol, and insulin. Insulin resistance was reduced, without affecting glucose levels and glucose tolerance. In contrast, PHE increased rectal temperature and slightly increased energy expenditure. The mitigation of HFD-induced metabolic disturbances points toward a promising role for PHE in obesity treatment and encourages further research on its mechanisms of action. SIGNIFICANCE STATEMENT: Phenelzine reduces body fat, markers of oxidative stress, inflammation, and insulin resistance in high-fat diet mice. Semicarbazide-sensitive amine oxidase, monoamine oxidase, phosphoenolpyruvate carboxykinase, and sterol regulatory element-binding protein-1c are involved in the metabolic effects of phenelzine. Phenelzine could be potentially used for the treatment of obesity-related complications.

Regulation of glucose metabolism by bioactive phytochemicals for the management of type 2 diabetes mellitus.

Type 2 diabetes mellitus (T2DM) is the most prevalent disease and becoming a serious public health threat worldwide. It is a severe endocrine metabolic disorder that has the ability to induce serious complications in all kinds of organs. Although mechanisms of anti-diabetics have been described before, we focus here on the cellular and physiological mechanisms involved in the modulation of insulin and glucose blood levels. As obesity and inflammation are intimately associated with the development of T2DM, their possible relationships are also described. The effects of gut microbiota on insulin resistance have been recently investigated in clinical trials, and we discuss the potential mechanisms by which gut microbiota may improve glucose handling, especially via the metabolism of ingested phytochemicals. Among the historically supported effects of phytochemicals, their therapeutic potential for T2DM leads to consider these natural products as an important pool for the identification of novel anti-diabetic drug leads. This current research extends the descriptions of anti-diabetic effects of plants that are used in traditional medicines or as nutraceuticals. The objective of the present review is to make a systematic report on glucose metabolism in T2DM as well as to explore the relationships between natural phytochemicals and glucose handling.

Metabolic Effects of Oral Phenelzine Treatment on High-Sucrose-Drinking Mice.

Phenelzine has been suggested to have an antiobesity effect by inhibiting de novo lipogenesis, which led us to investigate the metabolic effects of oral chronic phenelzine treatment in high-sucrose-drinking mice. Sucrose-drinking mice presented higher body weight gain and adiposity versus controls. Phenelzine addition did not decrease such parameters, even though fat pad lipid content and weights were not different from controls. In visceral adipocytes, phenelzine did not impair insulin-stimulated de novo lipogenesis and had no effect on lipolysis. However, phenelzine reduced the mRNA levels of glucose transporters 1 and 4 and phosphoenolpyruvate carboxykinase in inguinal white adipose tissue (iWAT), and altered circulating levels of free fatty acids (FFA) and glycerol. Interestingly, glycemia was restored in phenelzine-treated mice, which also had higher insulinaemia. Phenelzine-treated mice presented higher rectal temperature, which was associated to reduced mRNA levels of uncoupling protein 1 in brown adipose tissue. Furthermore, unlike sucrose-drinking mice, hepatic malondialdehyde levels were not altered. In conclusion, although de novo lipogenesis was not inhibited by phenelzine, the data suggest that the ability to re-esterify FFA is impaired in iWAT. Moreover, the effects on glucose homeostasis and oxidative stress suggest that phenelzine could alleviate obesity-related alterations and deserves further investigation in obesity models.

The Dietary Antioxidant Piceatannol Inhibits Adipogenesis of Human Adipose Mesenchymal Stem Cells and Limits Glucose Transport and Lipogenic Activities in Adipocytes.

Phenolic compounds are among the most investigated herbal remedies, as is especially the case for resveratrol. Many reports have shown its anti-aging properties and the ability to reduce obesity and diabetes induced by high-fat diet in mice. However, such beneficial effects hardly translate from animal models to humans. The scientific community has therefore tested whether other plant phenolic compounds may surpass the effects of resveratrol. In this regard, it has been reported that piceatannol reproduces in rodents the anti-obesity actions of its parent polyphenol. However, the capacity of piceatannol to inhibit adipocyte differentiation in humans has not been characterized so far. Here, we investigated whether piceatannol was antiadipogenic and antilipogenic in human preadipocytes. Human mesenchymal stem cells (hMSC), isolated from adipose tissues of lean and obese individuals, were differentiated into mature adipocytes with or without piceatannol, and their functions were explored. Fifty µM of piceatannol deeply limited synthesis/accumulation of lipids in both murine and hMSC-derived adipocytes. Interestingly, this phenomenon occurred irrespective of being added at the earlier or later stages of adipocyte differentiation. Moreover, piceatannol lowered glucose transport into adipocytes and decreased the expression of key elements of the lipogenic pathway (PPARγ, FAS, and GLUT4). Thus, the confirmation of the antiadipogenic properties of piceatanol in vitro warrants the realization of clinical studies for the application of this compound in the treatment of the metabolic complications associated with obesity.

Pterostilbene Inhibits Lipogenic Activity similar to Resveratrol or Caffeine but Differently Modulates Lipolysis in Adipocytes.

The anti-obesity effects of resveratrol shown in rodents are not transposed into an efficient therapy of human obesity. Consequently, the search for molecules mimicking or surpassing resveratrol actions is ongoing. The natural phenolic compound pterostilbene exhibits beneficial health effects and has the capacity to limit fat mass in animal models. In this study, we tested whether pterostilbene modulates triacylglycerol accumulation/breakdown. Prolonged exposure to pterostilbene or resveratrol inhibited adipocyte differentiation in 3T3-F442A preadipocytes. Acute effects on lipolysis, antilipolysis and lipogenesis were determined for pterostilbene in mouse adipocytes, and compared with resveratrol. Pterostilbene was also tested on glycerol release and glucose uptake in subcutaneous human adipocytes. Dose-response analyses did not reveal a clear lipolytic effect in both species. The antilipolytic effect of insulin was improved by pterostilbene at 1-10 µM in mouse fat cells only, while at 1 mM, the phenolic compound was antilipolytic in human fat cells in a manner not additive to insulin. Pterostilbene dose-dependently inhibited glucose incorporation into lipids similarly to resveratrol and caffeine. However, only the former did not inhibit insulin-stimulated glucose uptake. Indeed, pterostilbene abolished the insulin lipogenic effect without inhibiting its antilipolytic action and rapid activation of glucose uptake. Pterostilbene therefore exhibits a unique panel of direct interactions with adipocytes that relies on its reported anti-obesity and antidiabetic properties. Copyright © 2017 John Wiley & Sons, Ltd.

Advances in Integrating Traditional and Omic Biomarkers When Analyzing the Effects of the Mediterranean Diet Intervention in Cardiovascular Prevention.

Intervention with Mediterranean diet (MedDiet) has provided a high level of evidence in primary prevention of cardiovascular events. Besides enhancing protection from classical risk factors, an improvement has also been described in a number of non-classical ones. Benefits have been reported on biomarkers of oxidation, inflammation, cellular adhesion, adipokine production, and pro-thrombotic state. Although the benefits of the MedDiet have been attributed to its richness in antioxidants, the mechanisms by which it exercises its beneficial effects are not well known. It is thought that the integration of omics including genomics, transcriptomics, epigenomics, and metabolomics, into studies analyzing nutrition and cardiovascular diseases will provide new clues regarding these mechanisms. However, omics integration is still in its infancy. Currently, some single-omics analyses have provided valuable data, mostly in the field of genomics. Thus, several gene-diet interactions in determining both intermediate (plasma lipids, etc.) and final cardiovascular phenotypes (stroke, myocardial infarction, etc.) have been reported. However, few studies have analyzed changes in gene expression and, moreover very few have focused on epigenomic or metabolomic biomarkers related to the MedDiet. Nevertheless, these preliminary results can help to better understand the inter-individual differences in cardiovascular risk and dietary response for further applications in personalized nutrition.

The amine oxidase inhibitor phenelzine limits lipogenesis in adipocytes without inhibiting insulin action on glucose uptake.

The antidepressant phenelzine is a monoamine oxidase inhibitor known to inhibit various other enzymes, among them semicarbazide-sensitive amine oxidase (currently named primary amine oxidase: SSAO/PrAO), absent from neurones but abundant in adipocytes. It has been reported that phenelzine inhibits adipocyte differentiation of cultured preadipocytes. To further explore the involved mechanisms, our aim was to study in vitro the acute effects of phenelzine on de novo lipogenesis in mature fat cells. Therefore, glucose uptake and incorporation into lipid were measured in mouse adipocytes in response to phenelzine, other hydrazine-based SSAO/PrAO-inhibitors, and reference agents. None of the inhibitors was able to impair the sevenfold activation of 2-deoxyglucose uptake induced by insulin. Phenelzine did not hamper the effect of lower doses of insulin. However, insulin-stimulated glucose incorporation into lipids was dose-dependently inhibited by phenelzine and pentamidine, but not by semicarbazide or BTT2052. In contrast, all these SSAO/PrAO inhibitors abolished the transport and lipogenesis stimulation induced by benzylamine. These data indicate that phenelzine does not inhibit glucose transport, the first step of lipogenesis, but inhibits at 100 µM the intracellular triacylglycerol assembly, consistently with its long-term anti-adipogenic effect and such rapid action was not found with all the hydrazine derivatives tested. Therefore, the alterations of body weight control consecutive to the use of this antidepressant drug might be not only related to central effects on food intake/energy expenditure, but could also depend on its direct action in adipocytes. Nonetheless, phenelzine antilipogenic action is not merely dependent on SSAO/PrAO inhibition.

5-hydroxytryptamine actions in adipocytes: involvement of monoamine oxidase-dependent oxidation and subsequent PPARγ activation.

Serotonin (5-HT) is a brain neurotransmitter instrumental for the antidepressant action of selective inhibitors of serotonin reuptake (SSRIs) while it also plays important roles in peripheral organs. Recently, the 5-HT oxidation products, 5-hydroxyindoleacetate and 5-methoxy-indoleacetate, have been shown to bind to peroxisome proliferator-activated receptor γ (PPARγ) and to enhance lipid accumulation in preadipocytes. Since we already reported that adipocytes exhibit elevated monoamine oxidase (MAO) and primary amine oxidase activities, we verified how adipocytes readily oxidize 5-HT, with the objective to determine whether such oxidation promotes PPARγ activation and lipid storage. To this aim, serotonin was tested on cultured 3T3 F442A preadipocytes and on human adipocytes. Results showed that 5-HT was oxidized by MAO in both models. Daily treatment of 3T3 F442A preadipocytes for 8 days with 100-500 µM 5-HT promoted triglyceride accumulation and emergence of adipogenesis markers. At 250 µM, 5-HT alone reproduced half of 50 nM insulin-induced adipogenesis, and exhibited an additive differentiating effect when combined with insulin. Moreover, the 5-HT-induced expression of PPARγ-responsive genes (PEPCK, aP2/FABP4) was blocked by GW 9662, a PPARγ-inhibitor, or by pargyline, a MAO-inhibitor. In human fat cells, 6-h exposure to 100 µM 5-HT increased PEPCK expression as did the PPARγ-agonist rosiglitazone. Since hydrogen peroxide, another amine oxidation product, did not reproduce such enhancement, we propose that serotonin can promote PPARγ activation in fat cells, via the indoleacetate produced during MAO-dependent oxidation. Such pathway could be involved in the adverse effects of several antidepressant SSRIs on body weight gain.

The anxiolytic drug opipramol inhibits insulin-induced lipogenesis in fat cells and insulin secretion in pancreatic islets.

The antidepressant drug opipramol has been reported to exert antilipolytic effect in human adipocytes, suggesting that alongside its neuropharmacological properties, this agent might modulate lipid utilization by peripheral tissues. However, patients treated for depression or anxiety disorders by this tricyclic compound do not exhibit the body weight gain or the glucose tolerance alterations observed with various other antidepressant or antipsychotic agents such as amitriptyline and olanzapine, respectively. To examine whether opipramol reproduces or impairs other actions of insulin, its direct effects on glucose transport, lipogenesis and lipolysis were investigated in adipocytes while its influence on insulin secretion was studied in pancreatic islets. In mouse and rat adipocytes, opipramol did not activate triglyceride breakdown, but partially inhibited the lipolytic action of isoprenaline or forskolin, especially in the 10-100 µM range. At 100 µM, opipramol also inhibited the glucose incorporation into lipids without limiting the glucose transport in mouse adipocytes. In pancreatic islets, opipramol acutely impaired the stimulation of insulin secretion by various activators (high glucose, high potassium, forskolin...). Similar inhibitory effects were observed in mouse and rat pancreatic islets and were reproduced with 100 µM haloperidol, in a manner that was independent from alpha2-adrenoceptor activation but sensitive to Ca2+ release. All these results indicated that the anxiolytic drug opipramol is not only active in central nervous system but also in multiple peripheral tissues and endocrine organs. Due to its capacity to modulate the lipid and carbohydrate metabolisms, opipramol deserves further studies in order to explore its therapeutic potential for the treatment of obese and diabetic states.

Notch activation shifts the fate decision of senescent progenitors toward myofibrogenesis in human adipose tissue.

Senescence is a key event in the impairment of adipose tissue (AT) function with obesity and aging but the underlying molecular and cellular players remain to be fully defined, particularly with respect to the human AT progenitors. We have found distinct profiles of senescent progenitors based on AT location between stroma from visceral versus subcutaneous AT. In addition to flow cytometry, we characterized the location differences with transcriptomic and proteomic approaches, uncovering the genes and developmental pathways that are underlying replicative senescence. We identified key components to include INBHA as well as SFRP4 and GREM1, antagonists for the WNT and BMP pathways, in the senescence-associated secretory phenotype and NOTCH3 in the senescence-associated intrinsic phenotype. Notch activation in AT progenitors inhibits adipogenesis and promotes myofibrogenesis independently of TGFß. In addition, we demonstrate that NOTCH3 is enriched in the premyofibroblast progenitor subset, which preferentially accumulates in the visceral AT of patients with an early obesity trajectory. Herein, we reveal that NOTCH3 plays a role in the balance of progenitor fate determination preferring myofibrogenesis at the expense of adipogenesis. Progenitor NOTCH3 may constitute a tool to monitor replicative senescence and to limit AT dysfunction in obesity and aging.

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 rats. 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.

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 100 µmol/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.

Multiple Direct Effects of the Dietary Protoalkaloid N-Methyltyramine in Human Adipocytes.

Dietary amines have been the subject of a novel interest in nutrition since the discovery of trace amine-associated receptors (TAARs), especially TAAR-1, which recognizes tyramine, phenethylamine, tryptamine, octopamine, N-methyltyramine (NMT), synephrine, amphetamine and related derivatives. Alongside the psychostimulant properties of TAAR-1 ligands, it is their ephedrine-like action on weight loss that drives their current consumption via dietary supplements advertised for 'fat-burning' properties. Among these trace amines, tyramine has recently been described, at high doses, to exhibit an antilipolytic action and activation of glucose transport in human adipocytes, i.e., effects that are facilitating lipid storage rather than mobilization. Because of its close structural similarity to tyramine, NMT actions on human adipocytes therefore must to be reevaluated. To this aim, we studied the lipolytic and antilipolytic properties of NMT together with its interplay with insulin stimulation of glucose transport along with amine oxidase activities in adipose cells obtained from women undergoing abdominal surgery. NMT activated 2-deoxyglucose uptake when incubated with freshly isolated adipocytes at 0.01-1 mM, reaching one-third of the maximal stimulation by insulin. However, when combined with insulin, NMT limited by half the action of the lipogenic hormone on glucose transport. The NMT-induced stimulation of hexose uptake was sensitive to inhibitors of monoamine oxidases (MAO) and of semicarbazide-sensitive amine oxidase (SSAO), as was the case for tyramine and benzylamine. All three amines inhibited isoprenaline-induced lipolysis to a greater extent than insulin, while they were poorly lipolytic on their own. All three amines-but not isoprenaline-interacted with MAO or SSAO. Due to these multiple effects on human adipocytes, NMT cannot be considered as a direct lipolytic agent, potentially able to improve lipid mobilization and fat oxidation in consumers of NMT-containing dietary supplements.

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.

High doses of tyramine stimulate glucose transport in human fat cells.

Among the dietary amines present in foods and beverages, tyramine has been widely studied since its excessive ingestion can cause catecholamine release and hypertensive crisis. However, tyramine exerts other actions than depleting nerve endings: it activates subtypes of trace amine associated receptors (TAARs) and is oxidized by monoamine oxidases (MAO). Although we have recently described that tyramine is antilipolytic in human adipocytes, no clear evidence has been reported about its effects on glucose transport in the same cell model, while tyramine mimics various insulin-like effects in rodent fat cells, such as activation of glucose transport, lipogenesis, and adipogenesis. Our aim was therefore to characterize the effects of tyramine on glucose transport in human adipocytes. The uptake of the non-metabolizable analogue 2-deoxyglucose (2-DG) was explored in adipocytes from human subcutaneous abdominal adipose tissue obtained from women undergoing reconstructive surgery. Human insulin used as reference agent multiplied by three times the basal 2-DG uptake. Tyramine was ineffective from 0.01 to 10 µM and stimulatory at 100 µM-1 mM, without reaching the maximal effect of insulin. This partial insulin-like effect was not improved by vanadium and was impaired by MAO-A and MAO-B inhibitors. Contrarily to benzylamine, mainly oxidized by semicarbazide-sensitive amine oxidase (SSAO), tyramine activation of glucose transport was not inhibited by semicarbazide. Tyramine effect was not dependent on the Gi-coupled receptor activation but was impaired by antioxidants and reproduced by hydrogen peroxide. In all, the oxidation of high doses of tyramine, already reported to inhibit lipolysis in human fat cells, also partially mimic another effect of insulin in these cells, the glucose uptake activation. Thus, other MAO substrates are potentially able to modulate carbohydrate metabolism.

Randomized Clinical Trial: Effects of ß-Hydroxy-ß-Methylbutyrate (HMB)-Enriched vs. HMB-Free Oral Nutritional Supplementation in Malnourished Cirrhotic Patients.

ß-Hydroxy-ß-methylbutyrate (HMB) supplementation increases muscle and strength mass in some muscle-wasting disorders. Malnutrition and sarcopenia are often present in liver cirrhosis. We aimed to investigate the effects of oral HMB supplementation on changes in body composition and liver status in patients with cirrhosis and malnutrition. In a randomized, controlled, double-blind trial, 43 individuals were randomized to receive twice a day and for 12 weeks an oral nutritional supplement (ONS) enriched with 1.5 g of calcium HMB per bottle or another supplement with similar composition devoid of HMB. Inclusion criteria were liver cirrhosis with at least one previous decompensation and clinical malnutrition. Liver function, plasma biochemistry analyses, and physical condition assessment were carried out at baseline, then after six and 12 weeks of supplementation. A total of 34 patients completed the clinical trial. An improvement in liver function and an increase in fat mass index were observed in both groups. None of the two ONS changed the fat-free mass. However, we observed an upward trend in handgrip strength and a downward trend in minimal hepatic encephalopathy in the HMB group. At the end of the trial and regardless of the supplement administered, fat mass content increased with no change in fat-free mass, while liver function scores and nutritional analytic markers also improved.

Increased primary amine oxidase expression and activity in white adipose tissue of obese and diabetic db-/- mice.

The major form of primary amine oxidase expressed in adipose tissue (AT) is encoded by AOC3 gene and is known as semicarbazide-sensitive amine oxidase, identical to vascular adhesion protein-1 (SSAO/VAP-1). Exogenous substrates of SSAO/VAP-1 (e.g. benzylamine) stimulate glucose transport in adipocytes and improve glucose tolerance when injected in diabetic rodents. Numerous reports on the circulating, soluble SSAO/VAP-1 have univocally evidenced an increase in diabetic conditions. However, only scarce studies have investigated whether obesity and/or diabetes is accompanied with variations of AOC3 expression in AT. Therefore, we compared the SSAO/VAP-1 content in different fat depots of db-/- mice (lacking leptin receptor and being hyperphagic, diabetic and obese) and db+/- littermates (normoglycemic and lean). AOC3 expression was increased in perigonadal and subcutaneous AT of db-/- mice, while the maximal velocity of benzylamine oxidation (V (max), expressed as pmoles of hydrogen peroxide produced/min/mg protein) increased only in the latter. Indeed, the relative abundance of primary amine oxidase was increased in subcutaneous AT of db-/- mice at all the levels: mRNA, protein and activity. While considering the overall capacity to oxidise amines contained in each depot, there was an increase in the hypertrophic fat pads of the obese db-/- mice, irrespective of their anatomical location, as a result of their dramatically larger mass than in lean db+/- control. Such higher amount of AT-bound primary amine oxidase warrants further studies to determine whether SSAO/VAP-1 inhibition or activation may be useful in treating metabolic diseases.

Special Issue: 2019 Consortium for Trans-Pyrenean Investigations on Obesity and Diabetes.

This Special Issue of the Journal of Physiology and Biochemistry contains 6 contributions that exemplify the advances obtained by the mini-network entitled "Consortium of Trans-Pyrenean Investigations on Obesity and Diabetes" (CTPIOD), which is on its 16th year of existence. This scientific community, essentially based in France and Spain, but also open to participants coming from all over the world, is focusing its attention on the prevention and the novel treatments of obesity, diabetes, and other non-communicable diseases. Accordingly, this special issue will cover some nutritional, pharmacologic, and genetic aspects of the current knowledge of metabolic diseases. Some of these papers emerge from the lectures of the 16th Conference on Trans-Pyrenean Investigations in Obesity and Diabetes, held in Soria (Spain) in June 2019.