Impact of stable ghrelin receptor agonists and antagonists on food intake regulation

The thesis is focused on the effect of ghrelin receptor (GHS-R1a) agonists and antagonist on food intake regulation. Ghrelin is the only known periferally produced orexigenic hormone and the only known acylated hormone. GHS-R1a agonists and antagonists could be useful in the treatment of cachexia and obesity, respectively. In the first part of the thesis, newly designed peptidic GHS-R1a agonists were characterized. The agonists were stabilized by replacing octanoylated Ser3 with a fatty acid coupled to diaminopropionic acid by a stable amide bond. Other noncoded amino acids were also incorporated. Ghrelin analogs were modified by replacing the octanoyl group with another fatty acid, incorporation of the second fatty acid or shortening the peptide chain. Most of the tested GHS-R1a agonists were found to possess high affinities for GHS-R1a (Ki = 10-9 - 10-10 nM) and to activate signaling pathways of ghrelin. After subcutaneous (SC) administration to mice, agonists showed significant and prolonged orexigenic effect. In the second part of the thesis, acute and long-term effects of pseudopeptide GHS- R1a agonist JMV1843 were tested in lean C57BL/6 mice. Acute SC administration of JMV1843 to fed mice increased food intake in a dose-dependent manner (ED50 = 1.94 mg/kg). JMV1843 was stable in blood serum..