Novel Mechanism of Fatty Acid Sensing in Enteroendocrine Cells: Specific Structures in Oxo-Fatty Acids Produced by Gut Bacteria Are Responsible for CCK Secretion in STC-1 Cells via GPR40.

Abstract

The secretion of gut hormones, such as cholecystokinin (CCK) is stimulated by fatty acids. Although a chain length-dependent mechanism has been proposed, other structural relationships to releasing activity remain unclear. We aimed to elucidate specific structures in fatty acids that are responsible for their CCK-releasing activity, and related sensing mechanisms in enteroendocrine cells. CCK secretory activities were examined in a murine CCK-producing cell line STC-1 by exposing the cells to various modified fatty acids produced by gut lactic acid bacteria. The effects of fatty acids on gastric emptying rate as a CCK-mediated function were examined using acetaminophen and phenol red methods in rats. Out of more than 30 octadecanoic-derived fatty acids tested, 5 oxo-fatty acids potently stimulated CCK secretion without cytotoxic effects in STC-1 cells. Three fatty acids had a distinct specific structure containing one double bond, whereas the other two had two double bonds, nearby an oxo residue. CCK secretion induced by representative fatty acids (10-oxo-trans-11-18:1 and 13-oxo-cis-9,cis-15-18:2) was attenuated by a fatty acid receptor G-protein coupled receptor 40 antagonist. Oral administration of 13-oxo-cis-9,cis-15-18:2 lowered the gastric emptying rate in rats in a dose- and structure-dependent manner. These results reveal a novel fatty acid-sensing mechanism in enteroendocrine cells.