Food Intake Regulates Oleoylethanolamide Formation and Degradation in the Proximal Small Intestine

Abstract

Oleoylethanolamide (OEA) is a lipid mediator that inhibits food intake by activating the nuclear receptor peroxisome proliferator-activated receptor-␣. In the rodent small intestine OEA levels decrease during food deprivation and increase upon refeeding, suggesting that endogenous OEA may participate in the regulation of satiety. Here we show that feeding stimulates OEA mobilization in the mucosal layer of rat duodenum and jejunum but not in the serosal layer from the same intestinal segments in other sections of the gastrointestinal tract (stomach, ileum, colon) or in a broad series of internal organs and tissues (e.g. liver, brain, heart, plasma). Feeding also increases the levels of other unsaturated fatty acid ethanolamides (FAEs) (e.g. linoleoylethanolamide) without affecting those of saturated FAEs (e.g. palmitoylethanolamide). Feeding-induced OEA mobilization is accompanied by enhanced accumulation of OEA-generating N-acylphosphatidylethanolamines (NAPEs) increased activity and expression of the OEA-synthesizing enzyme NAPE-phospholipase D, and decreased activity and expression of the OEAdegrading enzyme fatty acid amide hydrolase. Immunostaining studies revealed that NAPE-phospholipase D and fatty acid amide hydrolase are expressed in intestinal enterocytes and lamina propria cells. Collectively, these results indicate that nutrient availability controls OEA mobilization in the mucosa of the proximal intestine through a concerted regulation of OEA biosynthesis and degradation.The gastrointestinal tract controls key aspects of feeding behavior through both neuronal and humoral mechanisms. Among the regulatory signals released by the gut, peptides such as cholecystokinin (CCK), 3 glucagon-like peptide-1, and ghrelin have attracted the most attention (1), but recent evidence indicates that lipid-derived messengers such as oleoylethanolamide (OEA) may also be involved (2). OEA is synthesized in the small intestine of various vertebrate species, where its levels decrease during food deprivation and increase upon refeeding (3-5). The possibility that these fluctuations represent a satiety signal is suggested by experiments in rodents which show that pharmacological administration of OEA delays meal initiation and prolongs the interval between successive meals, resulting in a persistent inhibition of food intake (3, 6 -8). These anorexiant effects are strikingly different from those elicited by traditional satiety factors such as CCK, which reduce meal size without affecting the interval between meals (9). Moreover, the hypophagic actions of OEA differ from those exerted by glucagon-like peptide-1 (10) and corticotropin-releasing factor (11) in that they are not accompanied by behavioral signs of malaise and anxiety or by changes in circulating corticosterone levels (3, 12). The molecular mechanism through which OEA inhibits feeding has been partially elucidated. In vitro studies have shown that OEA is a high affinity agonist of peroxisome proliferator-activated receptor-␣ (PPAR-␣) (13), a nuclear receptor pres...

Targeted enhancement of oleoylethanolamide production in proximal small intestine induces across-meal satiety in rats

“…1C). The characterization of the NAPE-PLD antibody used in these experiments is reported elsewhere (8). As shown in Fig.…”

“…Rats were killed with halothane, and tissues were rapidly collected and snap-frozen in liquid N 2. Frozen tissues were weighed and homogenized in methanol containing internal standards (8). Cells were harvested in 50% methanol in PBS containing internal standards.…”

“…Cells were harvested in 50% methanol in PBS containing internal standards. OEA and other fatty-acid ethanolamides (palmitoylethanolamide, anandamide), as well as their NAPE precursors, were quantified after lipid extraction by isotope-dilution liquid chromatography/ mass spectrometry, as described (8).…”

“…The fusion protein was expressed in Escherichia coli BL-21 cells (Novagen, Madison, WI) and purified using glutathione sepharose 4B (Amersham) following the manufacturer's instructions. The polyclonal NAPE-PLD antibody was raised in rabbits and characterized using standard procedures (8,22).…”

“…Among the signals released by the gut, peptides such as CCK or glucagonlike peptide-1 (GLP-1) have received the most attention (4,6), but evidence indicates that lipid-derived mediators may also be involved. For example, food ingestion stimulates cells in the mucosal layer of the duodenum and jejunum to produce the endogenous lipid amide oleoylethanolamide (OEA) (3,8,18), suggesting that this compound may participate in the induction of satiety. In support of this idea, pharmacological studies have shown that administration of exogenous OEA reduces feeding in rats and mice (2,9,13,15,18).…”