Ghrelin Derivatives Reveal Smallest Potent Growth Hormone Secretagogue Core
Background
Ghrelin is a naturally occurring 28-amino acid hormone renowned for its role as an endogenous growth hormone (GH) secretagogue, meaning it stimulates the release of growth hormone. Previous intensive investigations had already pinpointed the N-terminus tetrapeptide, specifically with an octanoyl group at Ser(3), as the minimum active core responsible for ghrelin's effects. This study aimed to further dissect the intricate structure-function relationships within this crucial N-terminal portion of ghrelin to identify even smaller and more potent derivatives.
Results
Through these systematic modifications, the team successfully identified 5-aminopentanoyl-Ser(Octyl)-Phe-Leu-aminoethylamide as the smallest and most potent ghrelin derivative discovered in this study. This novel compound demonstrated activity comparable to the natural ghrelin molecule in stimulating GHSR activation, indicating its high efficacy. The most significant finding was that this 5-aminopentanoyl-Ser(Octyl)-Phe-Leu-aminoethylamide derivative achieved activity comparable to natural ghrelin, making it the smallest known potent analogue identified in this study. Further structural analysis indicated that the Gly(1)-Ser(2) unit functions as a spacer, maintaining an optimal distance between the N(alpha)-amino group and the n-octanoyl group for maximal activity. Replacing the 3rd and 4th amino acid residues with D-isomers suggested their crucial role in shaping the biologically active geometry, influencing the conformation of subsequent residues and demonstrating their importance for receptor binding and activation.
Why It Matters
This research significantly deepens our understanding of ghrelin's structure-activity relationship, particularly concerning its minimal active core and the critical role of specific amino acid positions. The identification of a smaller, yet highly potent, ghrelin derivative provides a valuable template for designing novel, highly effective growth hormone secretagogues with potentially improved pharmacological properties. These findings could accelerate the development of new therapeutic agents for conditions such as growth hormone deficiency, sarcopenia (age-related muscle wasting), or cachexia, potentially paving the way for future human clinical trials.