Background and aims: The small intestinal free fatty acid (FFA) sensors, FFA receptor 1 (FFAR1), FFAR4, G-protein receptor 119 (GPR119) and cluster of differentiation-36 (CD36), mediate the fat-induced release of gastrointestinal (GI) hormones. We investigated whether expression of duodenal FFA sensors in humans was (i) altered by intraduodenal (ID) lipid infusion, (ii) disordered in overweight or obese individuals, (iii) related to lipid-induced GI hormone secretion or (iv) affected by habitual dietary patterns.
Methods: Endoscopic duodenal biopsies were collected from 20 lean (body mass index (BMI): 22±1 kg m-2), 18 overweight (BMI: 27±1 kg m-2) and 19 obese (BMI: 35±1 kg m-2) participants at baseline, and following a 30 min ID Intralipid infusion (2 kcal min-1); FFA sensor expression was quantified by reverse transcription-PCR. On a separate day, participants underwent ID Intralipid infusion (2 kcal min-1) for 120 min, to assess GI hormone responses. Habitual diet was evaluated using food frequency questionnaires.
Results: Baseline FFAR1 and FFAR4 expression were lower, and CD36 was higher, in obese participants compared with lean participants. ID lipid increased GPR119 and FFAR1 expression equally across study groups, but did not alter FFAR4 or CD36 expression. Increased FFAR1 expression correlated positively with glucose-dependent insulinotropic polypeptide (GIP) secretion (r=0.3, P<0.05), whereas there was no relationship between habitual diet with the expression of FFA sensors.
Conclusions: Obesity is associated with altered duodenal expression of FFAR1, FFAR4 and CD36, suggesting altered capacity for the sensing, absorption and metabolism, of dietary lipids. GPR119 and FFAR1 are early transcriptional responders to the presence of ID lipid, whereas FFAR1 may be an important trigger for lipid-induced GIP release in humans.