Combination of low dose of the anti-adipogenic agents resveratrol and phenelzine in drinking water is not sufficient to prevent obesity in very-high-fat diet-fed mice.

PURPOSE: Resveratrol inhibits lipid accumulation but suffers from limited bioavailability. The anti-depressive agent phenelzine limits adipogenesis in various models of cultured preadipocytes, and this hydrazine derivative also inhibits de novo lipogenesis in mature adipocytes. It was therefore tested whether resveratrol effects on adiposity reduction and glucose tolerance improvement could be reinforced by co-administration with phenelzine. METHODS: Mice fed a very-high-fat diet (VHFD, 60% calories as fat) were subjected to drinking solution containing low dose of resveratrol (0.003%) and/or 0.02% phenelzine for 12 weeks. Body fat content, glucose tolerance, food and water consumption were checked during treatment while fat depot mass was determined at the end of supplementation. Direct influence of the agents on lipogenesis and glucose uptake was tested in adipocytes. RESULTS: Epididymal fat depots were reduced in mice drinking phenelzine alone or with resveratrol. No limitation of body weight gain or body fat content was observed in the groups drinking resveratrol or phenelzine, separately or in combination. The altered glucose tolerance and the increased fat body composition of VHFD-fed mice were not reversed by resveratrol and/or phenelzine. Such lack of potentiation between resveratrol and phenelzine prompted us to verify in vitro their direct effects on mouse adipocytes. Both molecules inhibited de novo lipogenesis, but did not potentiate each other at 10 or 100 µM. Only resveratrol inhibited hexose uptake in a manner that was not improved by phenelzine. CONCLUSIONS: Phenelzine has no interest to be combined with low doses of resveratrol for treating/preventing obesity, when considering the VHFD mouse model.

Long-term activation of semicarbazide-sensitive amine oxidase lowers circulating levels of uric acid in diabetic conditions.

Uric acid is involved in nitrogenous waste in animals, together with ammonia and urea. Uric acid has also antioxidant properties and is a surrogate marker of metabolic syndrome. We observed that the elevated plasma uric acid of high-fat fed mice was normalized by benzylamine treatment. Indeed, benzylamine is the reference substrate of semicarbazide-sensitive amine oxidase (SSAO), an enzyme highly expressed in fat depots and vessels, which generates ammonia when catalysing oxidative deamination. Ammonia interferes with uric acid metabolism/solubility. Our aim was therefore to investigate whether the lowering action of benzylamine on uric acid was related to an improvement of diabetic complications, or was connected with SSAO-dependent ammonia production. First, we observed that benzylamine administration lowered plasma uric acid in diabetic db/db mice while it did not modify uric acid levels in normoglycemic and lean mice. In parallel, benzylamine improved the glycemic control in diabetic but not in normoglycemic mice, while plasma urea remained unaltered. Then, uric acid plasma levels were measured in mice invalidated for AOC3 gene, encoding for SSAO. These mice were unable to oxidize benzylamine but were not diabetic and exhibited unaltered plasma uric levels. Therefore, activated or abolished ammonia production by SSAO was without influence on uric acid in the context of normoglycemia. Our observations confirm that plasma uric acid increases with diabetes and can be normalized when glucose tolerance is improved. They also show that uric acid, a multifunctional metabolite at the crossroads of nitrogen waste and of antioxidant defences, can be influenced by SSAO, in a manner apparently related to changes in glucose homeostasis.

Histamine oxidation in mouse adipose tissue is controlled by the AOC3 gene-encoded amine oxidase.

INTRODUCTION: Histaminergic status can modify adipose tissue (AT) development: histamine-free mice exhibit visceral obesity, and treatments with H3-antagonists reduce body weight gain. However, direct histamine effects on AT remain poorly documented: it has been observed that histamine stimulates lipolysis in rodent adipocytes when its oxidation by amine oxidases (AOs) is blocked by inhibitors such as semicarbazide. OBJECTIVE: The aim of this work was to study the influence of AOC3 gene invalidation, encoding for semicarbazide-sensitive AO (SSAO), on histamine oxidation and on histamine lipolytic activity in AT. MATERIALS AND METHODS: Expression of AOC- and MAO-encoding genes was determined by real-type PCR in wild-type (WT) and SSAO-deficient (AOC3-KO) mice. Lipolysis was assessed by glycerol release in isolated adipocytes and AO activity by substrate-induced hydrogen peroxide formation in kidney, ileum and AT. RESULTS: The expression levels of the genes encoding AOC1, AOC2 or MAOA and MAOB were not modified in the AT of AOC3-KO mice. In WT mice, histamine oxidation was lower than that of the reference SSAO-substrate benzylamine in AT, but not in ileum. The order of magnitude regarding benzylamine oxidation was AT > ileum >> kidney. In AOC3-KO mice, benzylamine oxidation was abolished in all tissues, while histamine oxidation was abolished in AT but not in ileum. Histamine was inactive on lipolysis in WT but stimulated lipolysis in fat cells from AOC3-KO mice, without reaching the maximal intensity of beta-adrenergic stimulation. CONCLUSION: Histamine was mainly oxidized by diamine oxidase (AOC1 product) in intestine, but by SSAO (AOC3 product) in AT. When protected from its oxidation by SSAO in AT, histamine moderately activated lipolysis in adipocytes in AOC3-KO mice.

Influence of prolonged fasting on monoamine oxidase and semicarbazide-sensitive amine oxidase activities in rat white adipose tissue.

Monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) activities are very high in white adipose tissue (WAT). SSAO, also known as Vascular Adhesion Protein-1 in vessels, is present at the surface of fat cells and independent approaches have evidenced its impressive increase during adipogenesis. However, the factors that might regulate the expression SSAO and MAO in adipose tissue are still poorly defined. Here, we report the influence of fasting on MAO and SSAO activities in adipose depots. A decrease of MAO activity occurred after three days of starvation in the intra-abdominal adipose tissue (INWAT) of male Wistar rats, regardless of their initial adiposity or fat loss. The reduced fat stores of seven-week old rats, loosing 59 % of INWAT mass during fasting, contained only one half of the MAO activity found in fed control. The same reduction of MAO was observed after prolonged fasting in older rats which lose only 26% of their INWAT during the same starvation duration, leading to a fat mass comparable to that of younger fed control rats. It was therefore the endocrine and metabolic changes occurring during fasting that were responsible for the reduced MAO activity and not the amount of INWAT. Surprisingly, SSAO activity remained unchanged during starvation. In subcutaneous WAT, the changes in MAO and SSAO activities exhibited the same tendencies than those found in INWAT. Taken together, these data show that both MAO and SSAO activities increase in INWAT with age-dependent fattening, and indicate that only MAO diminishes during fasting.

Influencia del ayuno prolongado sobre la actividad monoamino oxidasa y amino oxidasa sensible al semicarbazide en el tejido adiposo blanco de rata / Influence of prolonged fasting on monoamine oxidase and semicarbazide-sensitive amine oxidase activities in rat white adipose tissue

Monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO)activities are very high in white adipose tissue (WAT). SSAO, also known as VascularAdhesion Protein-1 in vessels, is present at the surface of fat cells and independentapproaches have evidenced its impressive increase during adipogenesis. However, thefactors that might regulate the expression SSAO and MAO in adipose tissue are stillpoorly defined. Here, we report the influence of fasting on MAO and SSAO activitiesin adipose depots. A decrease of MAO activity occurred after three days of starvationin the intra-abdominal adipose tissue (INWAT) of male Wistar rats, regardlessof their initial adiposity or fat loss. The reduced fat stores of seven-week old rats,loosing 59 % of INWAT mass during fasting, contained only one half of the MAOactivity found in fed control. The same reduction of MAO was observed after prolongedfasting in older rats which lose only 26 % of their INWAT during the samestarvation duration, leading to a fat mass comparable to that of younger fed controlrats. It was therefore the endocrine and metabolic changes occurring during fastingthat were responsible for the reduced MAO activity and not the amount of INWAT.Surprisingly, SSAO activity remained unchanged during starvation. In subcutaneousWAT, the changes in MAO and SSAO activities exhibited the same tendencies thanthose found in INWAT. Taken together, these data show that both MAO and SSAOactivities increase in INWAT with age-dependent fattening, and indicate that onlyMAO diminishes during fasting(AU)

La actividad monoamino oxidasa (MAO) yaminooxidasa sensible al semicarbazide(SSAO) están muy elevadas en el tejido adiposoblanco (TAB). SSAO, también conocidacomo proteína de adhesión vascular-1, estápresente en la superficie de los adipocitosmaduros. Diferentes investigaciones muestranincremento de su expresión durante la adipogénesis,aunque los factores que regulan laexpresión en el TAB no son bien conocidos.Este trabajo describe la influencia del ayunosobre la actividad MAO y SSAO en TAB. Seha observado que tras tres días de ayuno disminuyela actividad MAO en el tejido adiposointra-abdominal (INWAT) de ratas machoWistar, independientemente de la grasa inicialo de la pérdida de peso inducida por el ayuno.El ayuno redujo un 59 % el peso del INWATy un 50% la actividad MAO en ratas de 7semanas de edad comparadas con su control(ratas sin ayuno). La misma disminución de laactividad MAO se encontró en ratas de mayoredad (10 semanas) aunque solo perdieron el 26% de su INWAT durante el mismo ayuno,igualando dicha reserva grasa a la de las ratasmás jóvenes sin ayunar. Los resultados indicanque serían los cambios endocrinos y metabólicosque ocurren durante el ayuno los responsablesde la disminución de la actividad MAO yno la perdida de tejido adiposo en sí. Sorprendentemente,no se observó ningún cambio significativoen la actividad SSAO durante elayuno. En el tejido adiposo subcutáneo, loscambios de actividad MAO y SSAO mostraronlas mismas tendencias que en el INWAT.Los resultados muestran que la edad conllevaun aumento de la actividad de la MAO y de laSSAO en tejido adiposo blanco de rata y que elayuno reduce la actividad de la MAO, no la dela SSAO(AU)

Limitation of adipose tissue enlargement in rats chronically treated with semicarbazide-sensitive amine oxidase and monoamine oxidase inhibitors.

Inhibition of semicarbazide-sensitive amine oxidases (SSAO) and monoamine oxidases (MAO) reduces fat deposition in obese rodents: chronic administration of the SSAO-inhibitor semicarbazide (S) in combination with pargyline (MAO-inhibitor) has been shown to reduce body weight gain in obese Zucker rats, while (E)-2-(4-fluorophenethyl)-3-fluoroallylamine, an SSAO- and MAO-B inhibitor, has been reported to limit weight gain in obese and diabetic mice. Our aim was to state whether such weight gain limitation could occur in non-obese, non-diabetic rats and to extend these observations to other amine oxidase inhibitors. Prolonged treatment of non-obese rats with a high dose of S (900 micromol kg(-1) day(-1)) reduced body weight gain and limited white adipose tissue enlargement. When chronically administered at a threefold lower dose, S also inhibited SSAO activity but not fat depot enlargement, suggesting that effects other than SSAO inhibition were involved in adipose tissue growth retardation. However, combined treatment of this lower dose of S with pargyline inhibited SSAO, MAO, energy intake, weight gain and fat deposition. Adipocytes from treated rats exhibited unchanged insulin responsiveness but impaired antilipolytic responses to amine oxidase substrates. Phenelzine clearly inhibited both MAO and SSAO when tested on adipocytes. Obese rats receiving phenelzine i.p. at 17 micromol kg(-1) day(-1) for 3 weeks, exhibited blunted MAO and SSAO activities in any tested tissue, diminished body weight gain and reduced intra-abdominal adipose tissue. Their adipocytes were less responsive to lipogenesis activation by tyramine or benzylamine. These observations suggest that SSAO inhibition is not sufficient to impair fat deposition. However, combined MAO and SSAO inhibition limits adiposity in non-obese as well as in obese rats.

Influence of acute and chronic administration of benzylamine on glucose tolerance in diabetic and obese mice fed on very high-fat diet

The combination of vanadate plus benzylamine has been reported to stimulateglucose transport in rodent adipocytes and to mimic other insulin actions in diversestudies. However, benzylamine alone activates glucose uptake in human fat cells andincreases glucose tolerance in rabbits. The aim of this work was to unravel the benzylamineantihyperglycemic action and to test whether its chronic oral administrationcould restore the defective glucose handling of mice rendered slightly obese anddiabetic by very high-fat diet (VHFD). When VHFD mice were i.p. injected withbenzylamine at 0.7 to 700 ìmol/kg before glucose tolerance test, they exhibitedreduced hyperglycemic response without alteration of insulin secretion. Whole bodyglucose turnover, as assessed by the glucose isotopic dilution technique, wasunchanged in mice perfused with benzylamine (total dose of 75 ìmol/kg). However,their in vivo glycogen synthesis rate was increased. Benzylamine appeared thereforeto directly facilitate glucose utilisation in peripheral tissues. When given chronicallyat 2000 or 4000 ìmol/kg/d in drinking water, benzylamine elicited a slightreduction of water consumption but did not change body weight or adiposity anddid not modify oxidative stress markers. Benzylamine treatment improved glucosa tolerance but failed to normalize the elevated glucose fasting plasma levels of VHFDmice. There was no influence of benzylamine ingestion on lipolytic activity, basal andinsulin-stimulated glucose uptake, and on inflammatory adipokine expression inadipocytes. The improvement of glucose tolerance and the lack of adverse effects onadipocyte metabolism, reported here in VHFD mice allow to consider orally givenbenzylamine as a potential antidiabetic strategy which deserves to be further studied in other diabetic models (AU)

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Influence of acute and chronic administration ofbenzylamine on glucose tolerance in diabetic andobese mice fed on very high-fat diet

The combination of vanadate plus benzylamine has been reported to stimulateglucose transport in rodent adipocytes and to mimic other insulin actions in diversestudies. However, benzylamine alone activates glucose uptake in human fat cells andincreases glucose tolerance in rabbits. The aim of this work was to unravel the benzylamineantihyperglycemic action and to test whether its chronic oral administrationcould restore the defective glucose handling of mice rendered slightly obese anddiabetic by very high-fat diet (VHFD). When VHFD mice were i.p. injected withbenzylamine at 0.7 to 700 ìmol/kg before glucose tolerance test, they exhibitedreduced hyperglycemic response without alteration of insulin secretion. Whole bodyglucose turnover, as assessed by the glucose isotopic dilution technique, wasunchanged in mice perfused with benzylamine (total dose of 75 ìmol/kg). However,their in vivo glycogen synthesis rate was increased. Benzylamine appeared thereforeto directly facilitate glucose utilisation in peripheral tissues. When given chronicallyat 2000 or 4000 ìmol/kg/d in drinking water, benzylamine elicited a slightreduction of water consumption but did not change body weight or adiposity anddid not modify oxidative stress markers. Benzylamine treatment improved glucose tolerance but failed to normalize the elevated glucose fasting plasma levels of VHFDmice. There was no influence of benzylamine ingestion on lipolytic activity, basal andinsulin-stimulated glucose uptake, and on inflammatory adipokine expression inadipocytes. The improvement of glucose tolerance and the lack of adverse effects onadipocyte metabolism, reported here in VHFD mice allow to consider orally givenbenzylamine as a potential antidiabetic strategy which deserves to be further studiedin other diabetic models (AU)

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Reduction of fat deposition by combined inhibition of monoamine oxidases and semicarbazide-sensitive amine oxidases in obese Zucker rats.

Semicarbazide-sensitive amine oxidase (SSAO) and monoamine oxidases (MAO) are highly expressed in adipocytes and generate hydrogen peroxide when activated. Consequently, high concentrations of MAO- or SSAO-substrates acutely stimulate glucose transport and inhibit lipolysis in isolated adipocytes in a hydrogen peroxide-dependent manner. Chronic treatments with MAO and SSAO substrates also increase in vitro adipogenesis and in vivo glucose utilization and fat deposition in diabetic rodents. To further investigate the interplay between amine oxidases, energy balance and fat deposition, prolonged MAO and/or SSAO blockade was performed in obese rats. Pargyline (P, MAO inhibitor), semicarbazide (S, SSAO inhibitor), alone or in combination (P+S), were daily i.p. administered for 3-5 weeks to obese Zucker rats at doses ranging from 20 to 300 micromol/kg. P+S treatments abolished MAO and SSAO activities in any tested tissue. P and S led to a 12-17% reduction of food intake when given in combination but were inactive when given separately. Despite a similar body weight gain reduction in P+S-treated and pair-fed rats, the mitigation of fat deposition was greater in rats receiving both inhibitors. Adipocytes from P+S-treated rats responded as control to insulin but exhibited impaired responses to tyramine, benzylamine or methylamine plus vanadate when considering glucose transport activation or lipolysis inhibition. Although our results did not directly demonstrate that amines are able to spontaneously produce in vivo the insulin-like effects described in vitro, we propose that P+S-induced reduction of fat deposition results from decreased food intake and from impaired MAO- and SSAO-dependent lipogenic and antilipolytic actions of endogenous or alimentary amines.

Influence of acute and chronic administration of benzylamine on glucose tolerance in diabetic and obese mice fed on very high-fat diet.

The combination of vanadate plus benzylamine has been reported to stimulate glucose transport in rodent adipocytes and to mimic other insulin actions in diverse studies. However, benzylamine alone activates glucose uptake in human fat cells and increases glucose tolerance in rabbits. The aim of this work was to unravel the benzylamine antihyperglycemic action and to test whether its chronic oral administration could restore the defective glucose handling of mice rendered slightly obese and diabetic by very high-fat diet (VHFD). When VHFD mice were i.p. injected with benzylamine at 0.7 to 700 micromol/kg before glucose tolerance test, they exhibited reduced hyperglycemic response without alteration of insulin secretion. Whole body glucose turnover, as assessed by the glucose isotopic dilution technique, was unchanged in mice perfused with benzylamine (total dose of 75 micromol/kg). However, their in vivo glycogen synthesis rate was increased. Benzylamine appeared therefore to directly facilitate glucose utilisation in peripheral tissues. When given chronically at 2000 or 4000 micromol/kg/d in drinking water, benzylamine elicited a slight reduction of water consumption but did not change body weight or adiposity and did not modify oxidative stress markers. Benzylamine treatment improved glucose tolerance but failed to normalize the elevated glucose fasting plasma levels of VHFD mice. There was no influence of benzylamine ingestion on lipolytic activity, basal and insulin-stimulated glucose uptake, and on inflammatory adipokine expression in adipocytes. The improvement of glucose tolerance and the lack of adverse effects on adipocyte metabolism, reported here in VHFD mice allow to consider orally given benzylamine as a potential antidiabetic strategy which deserves to be further studied in other diabetic models.