Effect of prolonged treatment with tyramine on glucose tolerance in streptozotocin-induced diabetic rats

The biogenic amine tyramine has been reported to stimulatein vitro glucose transport in adipocytes, cardiomyocytes and skeletal muscle, and to improvein vivo glucose utilization in rats. These effects were dependent on amine oxidation, since they were blocked by inhibitors of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO). We thus tested in this work whether a prolonged treatment with tyramine could improve glucose tolerance in streptozotocin-induced diabetic rats. First, tyramine content of standard rodent chow was determined by HPLC and daily tyramine intake of control rats was estimated to be around 26 μmol/kg body weight. Then, tyramine was administred during 3 weeks in streptozotocin-induced diabetic rats at 29 μmol/kg by daily i.p. injection alone or together with vanadate 0.02 μmol/kg. In another group of diabetic rats, tyramine was subcutaneously delivered at 116 μmol/kg/day by osmotic minipumps. All tyramine treatments resulted in a decrease of the hyperglycemic responses to an i.p. glucose load. Adipocytes isolated from either untreated or treated diabetic rats were sensitive to the stimulation of glucose uptake by tyramine. However, diabetic animals receiving tyramine for three weeks did not recover from their hyperglycemia, hypoinsulinemia and glucosuria. These results show that the improvement of glucose tolerance induced by prolonged tyramine administration occurs in an insulin-depleted model and probably results from peripheral insulin-like actions of the oxidation of MAO/SSAO substrates, such as the stimulation of glucose uptake into adipocytes

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

International audienceINTRODUCTION: 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

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

International audienceSemicarbazide-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

Prolonged treatment with aminoguanidine strongly inhibits adipocyte semicarbazide-sensitive amine oxidase and slightly reduces fat deposition in obese Zucker rats.

International audienceBeneficial effects of aminoguanidine (AG) on diabetic vascular complications result from prevention of protein glycation, inhibition of inductible NO synthase, and inhibition of vascular semicarbazide-sensitive amine oxidase (SSAO). However, influence of AG on adipose tissue deposition has been poorly investigated in obesity. Considering that SSAO is highly expressed in fat cells, and that a SSAO blocker has been recently reported to reduce body weight gain in obese mice, this work aimed to investigate the influence of AG on adipose tissue functions. First, AG was shown to directly inhibit SSAO activity in cultured adipocytes. Although AG did not directly alter lipolytic activity in human adipocytes, it inhibited benzylamine-induced antilipolysis via SSAO (but not NO synthase) inhibition. When AG was i.p. administered to obese Zucker rats (270 micromol kg(-1)day(-1) for 3 weeks), treated rats lost their capacity to oxidize benzylamine in a SSAO-dependent manner in adipose tissues and in cerebral vessels. Monoamine oxidase activity was unmodified in liver, skeletal muscles or adipose tissues and tended to increase in brain vessels. AG-treatment did not change body weight gain or hyperinsulinemic state of obese rats but slightly reduced subcutaneous fat deposition. AG did not modify insulin responsiveness in adipocytes but impaired the effects of SSAO substrates, such as glucose transport activation and lipolysis inhibition by methylamine or benzylamine plus vanadate. These results show that complete impairment of SSAO activity produced by AG-treatment in obese rats was likely responsible for a weak limitation of fat deposition. Previously proposed for prophylaxis in diabetes, AG may be useful for treating obesity via its SSAO blocking properties

Apelin stimulates glucose uptake but not lipolysis in human adipose tissue ex vivo.

International audienceApelin is a peptide present in different cell types and secreted by adipocytes in humans and rodents. Apelin exerts its effects through a G-protein coupled receptor called APJ. During the last years, a role of apelin/APJ in energy metabolism has emerged. Apelin was shown to stimulate glucose uptake in skeletal muscle through an AMP-activated protein kinase (AMPK)-dependent pathway in mice. So far, no metabolic effects of apelin have been reported on human adipose tissue (AT). Thus, the effect of apelin on AMPK in AT was measured as well as AMPK-mediated effects such as inhibition of lipolysis and stimulation of glucose uptake. AMPK and Acetyl-CoA Carboxylase phosphorylation were measured by western blot to reflect AMPK activity. Lipolysis and glucose uptake were measured, ex vivo, in response to apelin on isolated adipocytes and explants from AT of the subcutaneous region of healthy subjects (BMI: 25.6 ± 0.8 kg/m2, n = 30 in total). APJ mRNA and protein were present in human AT and isolated adipocytes. Apelin stimulated AMPK phosphorylation at Thr-172 in a dose-dependent manner in human AT which was associated to increased glucose uptake since, C Compound (20 μM), an AMPK inhibitor, completely prevented apelin-induced glucose uptake. However, in isolated adipocytes or AT explants, apelin had no significant effect on basal and isoprenaline-stimulated lipolysis. Thus, these results reveal, for the first time, that apelin is able to act on human AT in order to stimulate AMPK and glucose uptake

Effect of prolonged treatmen with tyramine on glucose tolerance in streptozotocin-induced diabetic rats

The biogenic amine tyramine has been reported to stimulate in vitro glucose transport in adipocytes, cardiomyocytes and skeletal muscle, and to improve in vivo glucose utilization in rats. These effects were dependent on amine oxidation, since they were blocked by inhibitors of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO). We thus tested in this work whether a prolonged treatment with tyramine could improve glucose tolerance in streptozotocin-induced diabetic rats. First, tyramine content of standard rodent chow was determined by HPLC and daily tyramine intake of control rats was estimated to be around 26 µmol/kg body weight. Then, tyramine was administred during 3 weeks in streptozotocin-induced diabetic rats at 29 µmol/kg by daily i.p. injection alone or together with vanadate 0.02 µmol/kg. In another group of diabetic rats, tyramine was subcutaneously delivered at 116 µmol/kg/day by osmotic minipumps. All tyramine treatments resulted in a decrease of the hyperglycemic responses to an i.p. glucose load. Adipocytes isolated from either untreated or treated diabetic rats were sensitive to the stimulation of glucose uptake by tyramine. However, diabetic animals receiving tyramine for three weeks did not recover from their hyperglycemia, hypoinsulinemia and glucosuria. These results show that the improvement of glucose tolerance induced by prolonged tyramine administration occurs in an insulin-depleted model and probably results from peripheral insulin-like actions of the oxidation of MAO/SSAO substrates, such as the stimulation of glucose uptake into adipocytesSe ha descrito que la amina biogénica tiramina estimula in vitro el transporte de glucosa en adipocitos, cardiomiocitos y músculo esquelético y mejora la utilización de glucosa en la rata. Estos efectos eran dependientes de la oxidación de la tiramina por la monoamina oxidasa (MAO) y la amina oxidasa sensible a semicarbazida (SSAO). En este trabajo, se estudia si un tratamiento crónico con tiramina aumenta la tolerancia a la glucosa en ratas diabéticas por estroptozotocina. El contenido en tiramina del alimento estándar para roedores se determinó por HPLC y se estimo que el consumo diario de tiramina en ratas control era de unos 26 µmol/kg de peso corporal. Por tanto, se administró diariamente durante 3 semanas tiramina por vía i.p. a la dosis de 29 µmol/kg, sola o con vanadato 0.02 µmol/kg a ratas diabéticas por estroptozotocina. Otro grupo recibió tiramina por vía subcutánea mediante minibombas osmóticas que liberaban 116 µmol/kg/día. Los tratamientos con tiramina han inducido disminución de las respuestas hiperglucemiantes a la sobrecarga de glucosa. En adipocitos aislados de ratas diabéticas, tratadas o no, la tiramina estimula el transporte de glucosa. Sin embargo, los animales diabéticos tratados con tiramina no se recuperaron de su hiperglucemia, hipoinsulinemia y glucosuria. Nuestros datos sugieren que la mejora de la tolerancia a la glucosa inducida por el tratamiento crónico con tiramina se observa en un modelo deficiente en insulina y probablemente se debe a acciones insulinomiméticas. Esto tambien indica que la administración de sustratos de MAO/SSAO podría constituir la base de nuevos tratamientos para mejorar la utilización de la glucos

Adipogenesis-related increase of semicarbazide-sensitive amine oxidase and monoamine oxidase in human adipocytes.

International audienceA strong induction of semicarbazide-sensitive amine oxidase (SSAO) has previously been reported during murine preadipocyte lineage differentiation but it remains unknown whether this emergence also occurs during adipogenesis in man. Our aim was to compare SSAO and monoamine oxidase (MAO) expression during in vitro differentiation of human preadipocytes and in adipose and stroma-vascular fractions of human fat depots. A human preadipocyte cell strain from a patient with Simpson-Golabi-Behmel syndrome was first used to follow amine oxidase expression during in vitro differentiation. Then, human preadipocytes isolated from subcutaneous adipose tissues were cultured under conditions promoting ex vivo adipose differentiation and tested for MAO and SSAO expression. Lastly, human adipose tissue was separated into mature adipocyte and stroma-vascular fractions for analyses of MAO and SSAO at mRNA, protein and activity levels. Both SSAO and MAO were increased from undifferentiated preadipocytes to lipid-laden cells in all the models: 3T3-F442A and 3T3-L1 murine lineages, human SGBS cell strain or human preadipocytes in primary culture. In human subcutaneous adipose tissue, the adipocyte-enriched fraction exhibited seven-fold higher amine oxidase activity and contained three- to seven-fold higher levels of mRNAs encoded by MAO-A, MAO-B, AOC3 and AOC2 genes than the stroma-vascular fraction. MAO-A and AOC3 genes accounted for the majority of their respective MAO and SSAO activities in human adipose tissue. Most of the SSAO and MAO found in adipose tissue originated from mature adipocytes. Although the mechanism and role of adipogenesis-related increase in amine oxidase expression remain to be established, the resulting elevated levels of amine oxidase activities found in human adipocytes may be of potential interest for therapeutic intervention in obesity

Potential involvement of adipocyte insulin resistance in obesity-associated up-regulation of adipocyte lysophospholipase D/autotaxin expression.

AIMS/HYPOTHESIS: Autotaxin is a lysophospholipase D that is secreted by adipocytes and whose expression is substantially up-regulated in obese, diabetic db/db mice. The aim of the present study was to depict the physiopathological and cellular mechanisms involved in regulation of adipocyte autotaxin expression. METHODS: Autotaxin mRNAs were quantified in adipose tissue from db/db mice (obese and highly diabetic type 2), gold-thioglucose-treated (GTG) mice (highly obese and moderately diabetic type 2), high-fat diet-fed (HFD) mice (obese and moderately diabetic type 2), streptozotocin-treated mice (thin and diabetic type 1), and massively obese humans with glucose intolerance. RESULTS: When compared to non-obese controls, autotaxin expression in db/db mice was significantly increased, but not in GTG, HFD, or streptozotocin-treated mice. During db/db mice development, up-regulation of autotaxin occurred only 3 weeks after the emergence of hyperinsulinaemia, and simultaneously with the emergence of hyperglycaaemia. Adipocytes from db/db mice exhibited a stronger impairment of insulin-stimulated glucose uptake than non-obese and HFD-induced obese mice. Autotaxin expression was up-regulated by treatment with TNFalpha (insulin resistance-promoting cytokine), and down-regulated by rosiglitazone treatment (insulin-sensitising compound) in 3T3F442A adipocytes. Finally, adipose tissue autotaxin expression was significantly up-regulated in patients exhibiting both insulin resistance and impaired glucose tolerance. CONCLUSIONS/INTERPRETATION: The present work demonstrates the existence of a db/db-specific up-regulation of adipocyte autotaxin expression, which could be related to the severe type 2 diabetes phenotype and adipocyte insulin resistance, rather than excess adiposity in itself. It also showed that type 2 diabetes in humans is also associated with up-regulation of adipocyte autotaxin expression