Aims/hypothesis Orexin A (OXA) modulates body weight, food intake and energy expenditure. In vitro, OXA increases PPARγ (also known as PPARG) expression and inhibits lipolysis, suggesting direct regulation of lipid metabolism. Here, we characterise the metabolic effects and mechanisms of OXA action in adipocytes. Methods Isolated rat adipocytes and differentiated murine 3T3-L1 adipocytes were exposed to OXA in the presence or absence of phosphoinositide 3-kinase (PI3K) inhibitors. Pparγ expression was silenced using small interfering RNA. Glucose uptake, GLUT4 translocation, phosphatidylinositol (3,4,5)-trisphosphate production, lipogenesis, lipolysis, and adiponectin secretion were measured. Adiponectin plasma levels were determined in rats treated with OXA for 4 weeks.Results OXA PI3K-dependently stimulated active glucose uptake by translocating the glucose transporter GLUT4 from cytoplasm into the plasma membrane. OXA increased cellular triacylglycerol content via PI3K. Cellular triacylglycerol accumulation resulted from increased lipogenesis as well as from a decrease of lipolysis. Adiponectin levels in chow-and high-fat diet-fed rats treated chronically with OXA were increased. OXA stimulated adiponectin expression and secretion in adipocytes. Both pharmacological blockade of peroxisome proliferator-activated receptor γ (PPARγ) activity or silencing Pparγ expression prevented OXA from stimulating triacylglycerol accumulation and adiponectin production. Conclusions/interpretation Our study demonstrates that OXA stimulates glucose uptake in adipocytes and that the evolved energy is stored as lipids. OXA increases lipogenesis, inhibits lipolysis and stimulates the secretion of adiponectin. These effects are conferred via PI3K and PPARγ2. Overall, OXA's effects on lipids and adiponectin secretion resemble that of insulin sensitisers, suggesting a potential relevance of this peptide in metabolic disorders.Electronic supplementary material The online version of this article

Spexin (SPX) and kisspeptin (KISS) are novel peptides relevant in the context of regulation of metabolism, food intake, puberty and reproduction. Here, we studied changes of serum SPX and KISS levels in female non-obese volunteers (BMI<25 kg/m2) and obese patients (BMI>35 kg/m2). Correlations between SPX or KISS with BMI, McAuley index, QUICKI, HOMA IR, serum levels of insulin, glucagon, leptin, adiponectin, orexin-A, obestatin, ghrelin and GLP-1 were assessed. Obese patients had lower SPX and KISS levels as compared to non-obese volunteers (SPX: 4.48±0.19 ng/ml vs. 6.63±0.29 ng/ml; p<0.001, KISS: 1.357±0.15 nmol/l vs. 2.165±0.174 nmol/l; p<0.01). SPX negatively correlated with BMI, HOMA-IR, insulin, glucagon, active ghrelin and leptin. Positive correlations were found between SPX and QUICKI index, McAuley index, serum levels of obestatin, GLP-1 and adiponectin and orexin-A Serum KISS negatively correlated with BMI, HOMA-IR, serum levels of insulin, glucagon, active ghrelin and leptin. KISS positively correlated with QUICKI index, McAuley index and adiponectin. In summary, SPX and KISS show negative correlations with obesity, insulin resistance indices, and hormones known to affect insulin sensitivity in females. Both, SPX and KISS could be therefore relevant in the pathophysiology of obesity and insulin resistance.

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Aims/hypothesis Glucagon reduces body weight by modifying food intake, glucose/lipid metabolism and energy expenditure. All these physiological processes are also controlled by fibroblast growth factor 21 (FGF-21), a circulating hepatokine that improves the metabolic profile in obesity and type 2 diabetes. Animal experiments have suggested a possible interaction between glucagon and FGF-21 however, the metabolic consequences of this crosstalk are not understood. Methods The effects of exogenous glucagon on plasma FGF-21 levels and lipolysis were evaluated in healthy volunteers and humans with type 1 diabetes, as well as in rodents with streptozotocin (STZ)-induced insulinopenic diabetes. In vitro, the role of glucagon on FGF-21 secretion and lipolysis was studied using isolated primary rat hepatocytes and adipocytes. Fgf-21 expression in differentiated rat pre-adipocytes was suppressed by small interfering RNA and released FGF-21 was immunoneutralised by polyclonal antibodies. Results Glucagon induced lipolysis in healthy human volunteers, patients with type 1 diabetes, mice and rats with STZ-induced insulinopenic diabetes, and in adipocytes isolated from diabetic and non-diabetic animals. In addition, glucagon increased circulating FGF-21 in healthy humans and rodents, as well as in patients with type 1 diabetes, and insulinopenic rodents. Glucagon stimulated FGF-21 secretion from isolated primary hepatocytes and adipocytes derived from animals with insulinopenic diabetes. Furthermore, FGF-21 stimulated lipolysis in primary adipocytes isolated from non-diabetic and diabetic rats. Reduction of Fgf-21 expression (by approximately 66%) or immunoneutralisation of released FGF-21 markedly attenuated glucagon-stimulated lipolysis in adipocytes. Conclusions/interpretation These results indicate that glucagon increases circulating FGF-21 independently of endogenous insulin levels. FGF-21 participates in glucagon-induced stimulation of lipolysis.

The effect of the isoflavone, genistein, on the lipid metabolism of ovariectomized rats was studied. Three types of experiments were performed. In the first one, the rats were fed diets supplemented with 0.01 or 0.1% of genistein for 14 days. In the second and third experiments, the direct effect of genistein on the liver and fat tissue were measured respectively by means of liver perfusion or incubation of isolated adipocytes with the isoflavone. Genistein in food significantly decreased blood serum and muscle triglyceride concentrations and increased the level of free fatty acids in serum. Serum free cholesterol was diminished and liver cholesterol was enhanced after genistein ingestion. When genistein acted directly on the liver during perfusion, a smaller incorporation of ¹⁴C-glucose into lipids was observed, and in parallel a greater output of free fatty acids into the medium was noticed. These changes were accompanied by diminution of the liver triglyceride contents. Genistein, acting on the adipocytes strongly depressed both basal and insulin-induced lipid synthesis, when glucose was used as a substrate. The effect of the isoflavone alone on the lipolysis in the adipocytes was negligible. However, it intensified lipolysis induced by epinephrine. The results obtained let us conclude that genistein in food can reduce the fattening processes in ovariectomized rats. This effect of genistein may be attributed, at least in part, to its direct influence on lipid metabolism in the liver and adipose tissue.

Aims/hypothesis While the mechanisms of specification and the reciprocal relationships of the four types of endocrine cell (alpha, beta, delta and pancreatic polypeptide cells) within the human endocrine pancreas are well described in adults and during fetal development, ghrelin-immunoreactive cells (epsilon cells) remain poorly understood. Methods We studied epsilon cells in 24 human fetal pancreases between 11 and 39 weeks of development and in 32 pancreases from adult organ donors. Results We observed single epsilon cells scattered in primitive exocrine tissue from gestational week 13 in developing pancreas. Later in the developmental process, epsilon cells started to aggregate into clusters. From gestational week 21, epsilon cells were observed located around developing islets, forming an almost continuous layer at the peripheral rim of the islets. They remain localised on the mantle of the islets, although at different amounts, in the adult pancreas. Coproduction of ghrelin with insulin, glucagon or somatostatin was not detected during fetal development. Co-production with pancreatic polypeptide was evident sporadically. Epsilon cells co-produced NK2 homeobox 2 and ISL LIM homeobox 1, but not NK6 homeobox 1 and paired box 6. A quantitative analysis was performed in the adult pancreas: there was an average of 1.17+1.17 epsilon cells per islet, the relative epsilon cell volume was 0.14+0.16% and the epsilon cell mass was 0.13+0.15 g. Neither sex nor age affected the epsilon cell mass, although there was a significant inverse correlation with BMI. Conclusions/interpretation During fetal development epsilon cells show an ontogenetic and morphogenetic pattern that is distinct from that of alpha and beta cells.

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