Glucose and weight control in mice with a designed ghrelin O-acyltransferase inhibitor.

Ghrelin is a gastric peptide hormone that stimulates weight gain in vertebrates. The biological activities of ghrelin require octanoylation of the peptide on Ser(3), an unusual posttranslational modification that is catalyzed by the enzyme ghrelin O-acyltransferase (GOAT). Here, we describe the design, synthesis, and characterization of GO-CoA-Tat, a peptide-based bisubstrate analog that antagonizes GOAT. GO-CoA-Tat potently inhibits GOAT in vitro, in cultured cells, and in mice. Intraperitoneal administration of GO-CoA-Tat improves glucose tolerance and reduces weight gain in wild-type mice but not in ghrelin-deficient mice, supporting the concept that its beneficial metabolic effects are due specifically to GOAT inhibition. In addition to serving as a research tool for mapping ghrelin actions, GO-CoA-Tat may help pave the way for clinical targeting of GOAT in metabolic diseases.

Barnett BP, et al. Science. 2010 Dec 17;330(6011):1689-92.

Ghrelin but not obestatin regulates insulin secretion from INS1 beta cell line via UCP2-dependent mechanism.

The mitochondrial UCP2 mediates glucose-stimulated insulin secretion by decreasing intracellular ATP/ADP ratio. Insulin secretion is a tightly regulated process. Ghrelin, as well as obestatin, were intensively studied to determine their ability to modify insulin secretion. Ghrelin is considered to be an inhibitor of insulin release from pancreatic islets, however little is known about the effects of obestatin. In our study we demonstrate the stimulating effects of both peptides on insulin secretion in INS1 cells. Furthermore, we investigate the potential role of UCP2 in mediating the effects of both peptides on insulin secretion. UCP2 mRNA expression was down-regulated by ghrelin in the presence of 26.4 mM glucose, however it was unchanged after obestatin treatment. Our results confirm that UCP2 could be involved in the stimulating effect of ghrelin on insulin release from INS1 cells.

Chmielewska J, et al. J Biol Regul Homeost Agents. 2010 Oct-Dec;24(4):397-402.

Endocrine Society Meeting (2010) Poster

GOAT links dietary lipids with the endocrine control of energy balance

Central nervous system nutrient sensing and afferent endocrine signaling have been established as parallel systems communicating metabolic status and energy availability in vertebrates. The only afferent endocrine signal known to require modification with a fatty acid side chain is the orexigenic hormone ghrelin. We find that the ghrelin O-acyl transferase (GOAT), which is essential for ghrelin acylation, is regulated by nutrient availability, depends on specific dietary lipids as acylation substrates and links ingested lipids to energy expenditure and body fat mass. These data implicate the ghrelin-GOAT system as a signaling pathway that alerts the central nervous system to the presence of dietary calories, rather than to their absence as is commonly accepted.

Kirchner et al. Nat Med. 2009 Jul;15(7):741-5.

 

Inhibition of ghrelin O-acyltransferase (GOAT) by octanoylated pentapeptides

The discovery of ghrelin O-acyltransferase (GOAT) opens the way to the design of drugs that block the attachment of an octanoyl group to the appetite-stimulating peptide hormone ghrelin, potentially preventing obesity. Here, we develop a biochemical assay that uses membranes from insect cells infected with baculovirus encoding mouse GOAT. The GOAT-containing membranes transferred the [3H]octanoyl group from [3H]octanoyl CoA to recombinant proghrelin in vitro. Transfer depended on the serine at residue 3 of proghrelin, which is the known site of acylation. GOAT also transferred [3H]octanoyl to a pentapeptide containing only the N-terminal five amino acids of proghrelin. GOAT activity could be inhibited by an octanoylated ghrelin pentapeptide, and its potency was enhanced 45-fold when the octanoylated serine-3 was replaced by octanoylated diaminopropionic acid. The data suggest that GOAT is subjected to end-product inhibition and this inhibition is better achieved with substrates having the octanoyl group attached through an amide linkage rather than the corresponding ester. These insights may facilitate the future design of useful inhibitors of GOAT.

Yang J., et al. PNAS. 2008, July 31

 

A few octanoylated N-terminal Ghrelin peptides had been synthesized at Phoenix Pharmaceuticals a few years ago by Dr. Jawkang Chang for new drug screening:

• Octanoylated Ghrelin Pentapeptide/Ghrelin (1-5)-Amide (Human, Rat, Mouse), Catalog No.031-41
• Ghrelin (1-5)-Amide [Ser3(Des-Octanoyl)] (Human, Rat, Mouse), Catalog No. 031-42
• Ghrelin [Dap-Octanyol3] (Human, Rat, Mouse), Catalog No. 031-58
• Ghrelin (1-4)-Amide (Human, Rat, Mouse), Catalog No. 031-67
• [Dap3] Octanoyl-Ghrelin (1-5) Amide (Human, Rat, Mouse), Catalog No.: 032-14

Mapping in Human Stomach Tissues stained by Human GOAT (181-199) Antibody (H-032-11)

Mapping in Human Pancreas Tissues stained by Human GOAT (356-375) Antibody (H-032-12)