Endocrine Abstracts

Recent years have demonstrated increasing focus on augmenting secretion of glucagon-like peptide (GLP)-1 from intestinal L cells, to improve the treatment and/or prevention of obesity and type 2 diabetes. However, finding strong stimuli and identifying novel compounds has proven difficult. To discover new GLP-1 secretagogues, we gave 49 individuals (76% female, BMI 28.3±4.8 kg/m²) a high-fat liquid mixed meal (250 mL Nutridrink, Nutricia®). Plasma samples, taken before and repeatedly after the meal, were analysed for total GLP-1 (using radioimmunoassay) and subjected to untargeted metabolomics (LC-MS/MS, Metabolon). Using machine learning statistical techniques, we identified that among over 900 metabolites, the meal-induced increase in sphinganine was the strongest predictor of a strong GLP-1 response. In those subjects with high GLP-1 secretion, the increase in sphinganine was significantly higher (P=0.027). When murine GLUTag cells were exposed to sphinganine for 2 h, a dose-dependent increase in GLP-1 was seen (10 µM=28% [95%-CI 8–48]; 100 µM=[55% [37–73]). Moreover, sphinganine increased intracellular calcium mobilization (10 µM=3.9% [1.1–6.7]), as assessed using Fluo-4. This effect was reduced by concomitant exposure to 2-APB (IP-3 blocker, reduction 46%) and nifedipine (calcium-channel blocker, reduction 59%), suggesting a Gq-mediated pathway. Antagonists of GPR40, GPR55, GPR119 and S1PR1 reduced the effects of sphinganine by 30-59%. Next, we studied isolated intestinal and, separately, colon perfusion models in Wistar rats. In male rats, luminal perfusion with 100 µM sphinganine increased intestinal GLP-1 secretion (26% [1–52]) and tended to increase colonic GLP-1 secretion (18% [0-37]). Vascular administration did not affect GLP-1 secretion. In female rats, there were no significant effects. Single-dose sphinganine (20 mg/kg) given via oral gavage to male and female C57Bl6/JRj mice did not increase GLP-1 levels (measured with ELISA) compared to saline. Finally, male C57Bl6/JRj were fed a high-fat diet with or without sphinganine (dose of 0.05% w/w). After 21 days, sphinganine-fed mice had gained less weight compared to control diet (7% vs 13%, P=0.045). Sphinganine had no effect on food intake. No significant differences were seen during an insulin tolerance test and oral glucose tolerance test (OGTT), and sphinganine did not increase GLP-1 levels during the OGTT. In conclusion, sphinganine increases GLP-1 secretion in vitro and in perfusion studies in male rats. In mice, the effect of sphinganine on GLP-1 secretion is not evident, yet it reduces weight gain during high-fat feeding. As such, further studies for metabolic benefits of sphingolipids are warranted.