Oea Signaling Pathways and the Metabolic Benefits of Vertical Sleeve Gastrectomy

Abstract

Objective: The aim of this study was to determine whether downstream [peroxisome proliferator-activated-receptor alpha (PPARα) and the G-protein coupled receptor, GPR119] and upstream (a fatty acid translocase, CD36) signaling targets of N-oleoylethanolamide (OEA) were necessary for weight loss, metabolic improvements, and diet preference following vertical sleeve gastrectomy (VSG).

Summary background data: OEA is an anorectic N-acylethanolamine produced from dietary fats within the intestinal lumen that can modulate lipid metabolism, insulin secretion, and energy expenditure by activating targets such as PPARα and GPR119.

Methods: Diet-induced obese mice, including wild-type or whole body knockout (KO) of PPARα, GPR119, and CD36, were stratified to either VSG or sham surgery before body weight, body composition, diet preference, and glucose and lipid metabolic endpoints were assessed.

Results: We found increased duodenal production of OEA and expression of both GPR119 and CD36 were upregulated in wild-type mice after VSG. However, weight loss and glucose tolerance were improved in response to VSG in PPARαKO, GPR119KO, and CD36KO mice. In fact, VSG corrected hepatic triglyceride dysregulation in CD36KO mice, and circulating triglyceride and cholesterol levels in PPARαKO mice. Lastly, we found PPARα-mediated signaling contributes to macronutrient preference independent of VSG, while removal of CD36 signaling blunts the VSG-induced shift toward carbohydrate preference.

Conclusions: In the search for more effective and less invasive therapies to help reverse the global acceleration of obesity and obesity-related disease OEA is a promising candidate; however, our data indicate that it is not an underlying mechanism of the effectiveness of VSG.

FIGURE 1.

OEA levels and receptor expression in rodent intestine after VSG. Duodenal OEA was increased in WT high-fat diet fed A, rats and B, mice after VSG compared with sham-surgery control mice after ad lib feeding. No such increase was seen within the jejunum of mice and rats or the ileum of rats. C, WT mouse duodenal mRNA expression of OEA receptor targets showed an upregulation of GPR119 and CD36 after VSG compared with sham surgery counterparts. No change in WT PPARα mRNA expression was seen after VSG. (Student t test; *P < 0.05; **P < 0.01; ***P < 0.001).

FIGURE 2.

Ablation of PPARα and GPR119 receptors did not impact body weight loss after VSG. A, Body mass, expressed as percent of baseline, after VSG decreased throughout the 11 postoperative weeks in WT and to a greater extent in PPARαKO mice compared with respective sham controls (^aP < 0.05, main effect of surgery; ^bP < 0.05, main effect of genotype). B, The change in fat mass from presurgical to 11 weeks after surgery was reduced in VSG groups of both WT and PPARαKO mice compared with respective sham controls (^aP < 0.001, main effect of surgery). C, VSG led to decreased body mass, expressed as percent of baseline, in GPR119KO and WT mice compared with respective sham controls throughout 10 weeks postoperatively (^aP < 0.0001, time × surgery interaction). D, A similar decrease in fat mass after VSG was seen in GPR119KO and WT mice compared with respective sham controls from presurgical to 9 weeks after surgery (^aP < 0.001, main effect of surgery).

FIGURE 3.

Glucose regulation through PPARα and GPR119 signaling after VSG. A, Ad lib fed glucose levels were decreased after VSG in the WT group but no change was seen after VSG in PPARαKO mice. PPARαKO mice had overall lowered ad lib fed glucose levels compared with WT sham mice (*P < 0.05 compared with all other groups). B, Regardless of surgical intervention, PPARαKO mice had lower fasted glucose levels at baseline, 60-, and 120-min time points compared with WT mice after an oral glucose (2 g/kg) challenge (+P < 0.05, time × genotype interaction). VSG improved glucose tolerance in both genotypes at the 30- and 45-minutes time points (*P < 0.05, time × surgery interaction). C, Both WT and GPR119KO mice decreased ad lib fed glucose levels after VSG compared with sham-operated controls (^aP < 0.05, main effect of surgery). D, After an oral glucose load, VSG improved glucose tolerance at the 15- and 30-minute time points in both WT and GPR119KO mice (*P < 0.05, time × surgery interaction). E, After a mixed meal gavage (EnsurePlus with 25% glucose; 200 µL), total plasma GLP-1 increased in both WT and GPR119KO groups after VSG compared with respective sham controls (^aP < 0.001, main effect of surgery).

FIGURE 4.

Lipid responses in PPARαKO and GPR119KO mice after VSG. A, Plasma triglyceride levels in sham-operated PPARαKO mice were significantly higher than all other groups in the fed state (fed: *P < 0.05), while under fasting conditions PPARαKO mice showed increased triglyceride levels compared with WT mice regardless of surgery (fasted: ^bP < 0.01, main effect of genotype). B, Postprandial plasma cholesterol levels were elevated in PPARαKO mice compared to WT mice but decreased after VSG in both genotypes (fed: ^bP < 0.01, main effect of genotype; ^aP < 0.0001, main effect of surgery). VSG decreased fasted plasma cholesterol levels in both genotypes (fasted: ^aP < 0.05, main effect of surgery). C, Hepatic triglyceride (^aP < 0.001, main effect of surgery) and D, hepatic cholesterol (^aP < 0.0001, main effect of surgery) levels were significantly decreased in both WT and PPARαKO mice after VSG compared with respective sham controls. E, No statistical change in plasma triglyceride levels was identified between genotypes or surgical groups in either dietary condition within the GPR119KO cohort. F, Neither genotype nor surgery impacted plasma cholesterol levels after fasting, however, VSG decreased fed levels of plasma cholesterol in WT and GPR119KO mice (fed: ^aP < 0.05, main effect of surgery). G, Hepatic triglyceride levels in GPR119KO and WT mice decreased after VSG compared with respective sham controls (^aP < 0.001, main effect of surgery). H, Hepatic cholesterol levels were statistically unchanged after VSG and between genotypes within the GPR119KO cohort.

FIGURE 5.

Macronutrient preference test in PPARaKO and GPR119KO mice after VSG. A, Although macronutrient preference for fat was unchanged after VSG in WT and PPARαKO mice, an overall decrease in fat preference was observed in PPARαKO mice (^bP < 0.01, main effect of genotype). B, Similarly, carbohydrate preference was unchanged after VSG in WT and PPARαKO mice, but an overall increase in carbohydrate preference was observed in PPARαKO mice (^bP < 0.001, main effect of genotype). C, Average daily kilocalorie (kcal) intake was increased in sham-operated WT mice compared with sham-operated PPARαKO mice (*P < 0.05). D, Fat intake was decreased (^aP < 0.05, main effect of surgery) and E, carbohydrate intake was increased (^aP < 0.05, main effect of surgery) in both WT and GPR119KO mice after VSG compared with respective sham surgery counterparts. F, No differences in overall daily kilocalorie intake was detected between surgery or genotype in the GPR119KO mouse cohort. Data are expressed as % macronutrient of total kcal intake (mean ± SEM) over a 5-day period of testing.

FIGURE 6.

Body mass and glucose regulation after VSG in CD36KO mice. A, VSG decreased body mass (% baseline) in both WT and CD36KO up to 12 weeks postoperatively (^aP < 0.01, time × surgery interaction), and CD36KO mice had overall lower body mass compared with WT mice (^bP < 0.0001, time × genotype interaction). B, The change in fat mass between preoperative levels and 8 weeks after surgery revealed both WT and CD36KO lost fat-specific mass compared with respective sham controls (^aP < 0.01, main effect of surgery) and that CD36KO mice had lower fat mass compared with WT mice (^bP < 0.01, main effect of genotype). C, CD36KO mice had decreased ad lib fed glucose levels 2 weeks after surgery compared with WT mice (^bP < 0.05, main effect of genotype). D, VSG increased the glucose response 15 minutes after an oral glucose load (2 g/kg) compared with sham-operated mice (*P < 0.001, time×surgery interaction), and improved glucose tolerance at the 30-minute time point (*P < 0.01, time×surgery interaction).

FIGURE 7.

Lipid responses and macronutrient preference after VSG in CD36KO mice. A, Circulating plasma triglyceride levels were unchanged between genotype or surgery in both the fed and fasted state. B, Plasma cholesterol levels in both WTand CD36KO were improved with VSG after feeding (fed: ^aP < 0.001, main effect of surgery), and fasting (fasted: ^aP < 0.0001, main effect of surgery), without differences between genotypes. C, Hepatic triglycerides were elevated in CD36KO mice compared with WT mice but were reduced after VSG in both genotypes (^aP < 0.01, main effect of surgery; ^bP < 0.01, main effect of genotype). D, Hepatic cholesterol levels were unchanged between genotype or surgical groups. E, During a macronutrient preference test, WT mice increased carbohydrate intake after VSG, while CD36KO mice show no effect of surgery on carbohydrate intake (*P < 0.05). F, Both WT and CD36KO mice decrease preference for fat intake after VSG (^aP < 0.05, main effect of surgery). G, No change in average daily caloric intake was noted between either genotype or surgical intervention.