Inhibition of the intestinal sodium-coupled glucose transporter 1 (SGLT1) by extracts and polyphenols from apple reduces postprandial blood glucose levels in mice and humans

Scope: There is a growing interest in food constituents that could reduce intestinal glucose absorption to prevent overshooting plasma glucose and insulin levels in patients with prediabetes and diabetes mellitus type 2. Methods and results: We here demonstrate that an extract and individual polyphenols from apple diminish sodium-coupled glucose transporter 1 (SGLT1) mediated glucose uptake in vitro and in vivo. Inhibition of transport of sugars by SGLT1 was shown in Xenopus oocytes and in mice jejunal segments. Strongest inhibition was observed for phlorizin with IC₅₀ values for transport inhibition of 0.46 ± 0.19 and 4.1 ± 0.6 μM in oocytes and intestinal segments, respectively. An oral glucose tolerance test performed in volunteers with prior administration of the apple extract reduced venous blood glucose and plasma insulin levels, similar to findings obtained in C57BL/6N mice. Analysis of human urine samples revealed that the extract increased modestly renal glucose loss that is most likely a result of inhibition of renal glucose reabsorption by phloretin derivatives found in plasma of the volunteers. Conclusion: Although the apple extract substantially decreased intestinal glucose absorption in all test systems, the finding that there are systemic effects that relate to inhibition of glucose transport processes beyond the intestine addresses safety issues that need further exploitation.