Identificazione di nuove strategie terapeutiche per il controllo dell'obesità e della cachessia mediante utilizzo di nuovi composti peptidomimetici dotati di attività antagonista o agonista dell'ormone peptidico endogeno ghrelin

It is known that food intake is regulated by interactions between neuronal and hormonal signals arising throughout the body and specific areas of the brain, mainly in the hypothalamus. Among the peripheral mediators, ghrelin could have a primary role in the regulation of feeding. Ghrelin is an endogenous 28 amino acid peptide produced and secreted mainly by the stomach, and it is characterized by endocrine and extra-endocrine effects including the ability to stimulate GH secretion and feeding behaviour. In the last several years new synthetic peptidic and non peptidic compounds, named growth hormone secretagogues, have been shown to share with ghrelin many activities. The purpose of this study was the characterization of new peptide-mimetic analogues of ghrelin, synthesized at the Institut des Biomolecules Max Mousseron, University of Montpellier, that might be considered for developing novel therapeutic agents useful in the treatment of cachexia or, at the opposite, of diet-induced obesity. Cachexia is a condition characterized by loss of lean and fat body mass, anorexia, asthenia and increased energy expenditure. On the other hand obesity results in a chronic imbalance between energy intake and energy expenditure. We set up a chinese hamster ovary (CHO) cell line stably expressing the human GHS-R1a. The activity of the novel compounds was studied using an intracellular mobilization calcium assay. Cells stimulated with ghrelin or hexarelin showed a significant and specific increase in intracellular free calcium. Hexarelin, a synthetic hexapeptide, known to be a full agonist of the GHS-R1a, was used as positive control in all the following experiment. This in vitro model allowed to characterize four agonists and four antagonists of the GHS-R1a. Next, the agonists have been tested in vivo in a rat model of cachexia. Rats were treated daily with 1 mg/kg cisplatin from day 1 through day 3, whereas the test compounds were administered twice a day from day 1 through day 11. In all experimental groups cisplatin induced a significant weight loss that reached the maximum at day four, then the weight started to increase again. Rats treated with JMV2894 had a faster body weight gain compared to the other experimental groups. Interestingly, despite the different rate of body weight gain, the total amount of food eaten over the treatment period was not significantly different among the different groups. These data suggest that the recovery of body weight was not correlated to the orexigenic effect of the agonists used. In the obesity model, mice were fed for 9 weeks with a hypercaloric high-fat diet (HFD) or a standard diet until the body weight of HFD group was doubled compared to controls. Thereafter groups of mice were treated with antagonists of the GHS-R1a, namely JMV 2959 and EP 80317. Interestingly, the treatment with EP80317 inhibited body weight gain in HFD mice. In conclusion, the data of this research show that JMV 2894 is capable to counteract the weight loss induced by cisplatin cachexia, whereas EP 80317 is effective in inhibiting body weight gain in a model of diet-induced obesity.