The lipid messenger OEA links dietary fat intake to satiety

Abstract

The association between fat consumption and obesity underscores the need to identify physiological signals that control fat intake. Previous studies have shown that feeding stimulates small-intestinal mucosal cells to produce the lipid messenger oleoylethanolamide (OEA) which, when administered as a drug, decreases meal frequency by engaging peroxisome proliferator-activated receptors-alpha (PPAR-alpha). Here, we report that duodenal infusion of fat stimulates OEA mobilization in the proximal small intestine, whereas infusion of protein or carbohydrate does not. OEA production utilizes dietary oleic acid as a substrate and is disrupted in mutant mice lacking the membrane fatty-acid transporter CD36. Targeted disruption of CD36 or PPAR-alpha abrogates the satiety response induced by fat. The results suggest that activation of small-intestinal OEA mobilization, enabled by CD36-mediated uptake of dietary oleic acid, serves as a molecular sensor linking fat ingestion to satiety.

Figure 1. Dietary fat stimulates OEA mobilization in proximal small intestine

(A) Effects of duodenal nutrient infusions on jejunal OEA mobilization. NI, No infusion; 1, Intralipid; 2, glucose; 3, peptone; 4, hypertonic saline; 5, isotonic saline. (B-E) Duodenal infusion of sodium oleate (OA), but not palmitate (PA), regulates jejunal levels of (B) OEA, (C) 1-stearoyl-2-arachidonoyl-sn-glycerol-3-phosphoethanolamine-N-oleyl (NOPE), (D) NAPE-PLD activity, and (E) FAAH activity. Infusions were conducted at 0.5 ml/min for 10 min with nutrients equicaloric at 2 kcal/ml. Jejunal tissue was harvested 30 min after starting the infusion; Values are expressed in pmol/g of wet tissue; one asterisk, p < 0.05; two asterisks, p < 0.01; three asterisks, p < 0.001; n = 5-6 per group.

Figure 2. The fatty-acid transporter CD36 is required for small-intestinal OEA production

Refeeding mice (RF) after a 6-h daytime fast (FD) increases levels of (A) OEA and (C) 1-stearoyl-2-arachidonoyl-sn-glycerol-3-phosphoethanolamine-N-oleyl (NOPE) in duodenum (Duod.) and jejunum (Jej.) of wild-type mice (+/+). No such effect is observed in CD36-null mice (-/-) (B,D). FD, food-deprived; RF, 30-min refed; one asterisk, p < 0.05; two asterisks, p < 0.01; n.s., not significantly different at p < 0.05; n = 3-4 per group.

Figure 3. Internalization of diet-derived oleic acid by CD36 enables OEA mobilization

Refeeding mice (RF) after a 6-h daytime fast (FD) increase oleic acid levels in duodenum (Duod.) and jejunum (Jej.) of wild-type (A), but not CD36-null mice (B). (C-E) duodenal infusion of the unnatural oleic acid analog 10Z-heptadecenoic acid (HAD) increases jejunal levels of (C) HDA, (D) heptadecenoylethanolamide (HDE), and (E) 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine-N-heptadecenoyl (NAPE), open bars, Vehicle (50 mM Tris buffer); closed bars, HAD infusion. Infusions were conducted at 0.5 ml/min for 10 min and jejunal tissue was harvested 30 min after starting the infusion. (F,G) Oral gavage of HDA (200 mg/kg in 1 ml of saline/polyethylene glycol/Tween 80, 90/5/5, vol/vol; closed bars) increases jejunal levels of HDA (F) and HDE (G) in wild-type (+/+), but not in CD36-null (-/-) mice, open bars, Vehicle (saline/polyethylene glycol/Tween 80, 90/5/5, vol/vol). One asterisk, p < 0.05; two asterisks, p < 0.01; three asterisks, p < 0.001; n = 5-6 per group.

Figure 4. Plasma-derived oleic acid is not utilized for OEA mobilization

Intraperitoneal administration of the oleic acid analog 10Z-heptadecenoic acid (HDA) (10 mg/kg) increases jejunal HDA levels (A) without affecting jejunal heptadecenoylethanolamide (HDE) levels (B) V, vehicle (saline/polyethylene glycol/Tween 80, 90/5/5, vol/vol, 2 ml/kg). Three asterisks, p < 0.001; n = 6 per group. Values are expressed as pmol/g of wet tissue.

Figure 5. CD36 and PPAR-α mediate fat-induced satiety

Duodenal infusion of the lipid emulsion Intralipid reduces intake of a liquid diet (Ensure^®) in wild-type mice (+/+), but not CD36-null mice (-/-) (A) or PPAR-α-null mice (-/-) (B). Closed bars, Intralipid; open bars, saline. Intake is expressed in ml/30min. Two asterisks, p < 0.01; n = 6-7.

Figure 6. OEA signaling at PPAR-α regulates normal feeding

(A) Meal patterns in free-feeding wild-type mice (open bars) and PPAR-α-null mice (closed bars) during the first 3 hours after dark onset (5:30 pm); bar lengths symbolize the duration (±s.e.m.) of each meal. No difference in meal pattern was observed between wild-type and PPAR-α-null mice after the fourth nocturnal meal (data not shown). (B) Latency for the first meal (min). (C) Satiety ratio values (min/g/kg) for the first 4 meals. (D) Meal frequency (meals/h) in the first 3 hours of nocturnal feeding. (E) Total food intake in 24 h (g/kg). (F) No difference in feeding-induced jejunal OEA mobilization in wild-type mice (+/+) and PPAR-α-null mice (-/-). FF, free-fed; FO, 24 hr food deprivation; RF, 30 min refed after 24 hr food deprivation. (G) Number of food-probing episodes (non-eating contacts with the food basket). (H) Average eating rate (g/min) for the 24-h observation period. One asterisk, p < 0.05; two asterisks, p < 0.01; three asterisks, p < 0.001; n = 8-12.

Figure 7. OEA mobilization links dietary fat intake to across-meal satiety

According to this hypothetical model, CD36 localized to the apical surface of small-intestinal enterocytes recognizes luminal oleic acid (OA) derived from the digestion of dietary fat and internalizes it. (Top) Most newly absorbed OA is channeled to the biosynthesis of triacylglycerol (TAG) and phosphatidylcholine (PC) en route to chylomicron formation. (Bottom) A small fraction of fatty acid is converted into OEA, which activates PPAR-α to prolong across-meal satiety and increase expression of lipid-metabolizing genes. Dashed arrows show that CD36 may further facilitate OEA mobilization (i) by stimulating NOPE production, presumably catalyzed by NAT activity; (ii) by enhancing NAPE-PLD activity, which converts NOPE to OEA; and (iii) by inhibiting FAAH activity, which hydrolyzes OEA and terminates its actions.