Intestinal Sucrase as a Novel Target Contributing to the Regulation of Glycemia by Prebiotics

Abstract

Inulin-type fructans (ITF) are known for their capacity to modulate gut microbiota, energy metabolism and to improve glycemia in several animal models of obesity, and in humans. The potential contribution of ITF as modulators of sugar digestion by host enzymes has not been evaluated yet. A sucrose challenge has been performed on naive mice fed a standard diet supplemented with or without native chicory inulin (Fibruline 5%) for 3 weeks. The area under the curve of glycemia as well as sucrase activity in the small intestine were lowered after inulin treatment. Pyrosequencing of the 16S rRNA gene confirmed important changes in gut microbiota (mostly in favor of Blautia genus) due to inulin extract supplementation. Interestingly, the suppressive effect of inulin extract on postprandial glycemia also occurred when inulin was directly added to the sucrose solution, suggesting that the effect on sucrose digestion did not require chronic inulin administration. In vitro tests confirmed a direct inhibition of sucrase enzyme by the inulin extract, thereby suggesting that native chicory inulin, in addition to its well-known prebiotic effect, is also able to decrease the digestibility of carbohydrates, a phenomenon that can contribute in the control of post prandial glycemia. We may not exclude that the sucrose escaping the digestion could also contribute to the changes in the gut microbiota after a chronic treatment with inulin.

Fig 1. Sucrase activity in the small intestine.

Mice fed a control diet (CT) or a diet supplemented with 5% inulin (INU) for 27 days. *p<0.05 (Student t test).

Fig 2. Spatial ordination, bacterial diversity and taxonomical distribution deduced by 16S profiling.

Non metric dimensional scaling (three axis) with ellipse showing standard deviation (95% confidence) (A). Bacterial diversity (Inverse Simpson Biodiversity Index), bacterial richness (Chao1 Richness Index) and bacterial evenness (deduced from Simpson Index) (B). Mean Phylotype distribution (Phylum, family and genus levels) expressed as mean cumulated relative abundance (C). Mice were fed fed a control diet (CT, green) or a diet supplemented with 5% inulin (INU, blue) for 27 days.

Fig 3. qPCR analysis of the caecal luminal microbiota.

Levels of Blautia (A), Bifidobacterium spp. (B) and total bacteria (C) in the caecal content of mice fed a control diet (CT) or a diet supplemented with 5% inulin (INU) for 27 days. *p<0.05 (Student t test).

Fig 4. Effect of long term administration of inulin extract on postprandial blood glucose and serum insulin levels in sucrose-loaded mice.

Mice were fed a control diet (CT) or a diet supplemented with 5% inulin (INU) for 3 weeks. Plasma glucose excursion after the oral sucrose load (A), area under the curve (AUC) of the glucose excursion (B), fasting insulinemia (C) and insulin response (Δ insulin concentrations 30 min before and 15 min after the sucrose load) (D). *p<0.05 (Student t test).

Fig 5. Effect of inulin extract addition (5%) in the sucrose solution on the postprandial blood glucose and serum insulin levels in sucrose-loaded mice fed a control diet.

Plasma glucose excursion after the oral sucrose load (A), area under the curve (AUC) of the glucose excursion (B), fasting insulinemia (C) and insulin response (Δ insulin concentration 30 min before and 15 min after the oral sucrose load) (D). *p<0.05 (Student t test).

Fig 6. Sucrase activity in vitro.

Inhibitory effect of inulin extract (INU) and acarbose on sucrase activity of small intestinal mucosa obtained from naïve mice (A). Michaelis-Menten (B) and Lineweaver-Burk (C) plots of the sucrase hydrolysis reaction with variable sucrose concentrations ([S] from 0 to104 mM) and at fixed concentration of inulin extract (0mM (▲), 3mM(□), 6mM(■), 11mM(○), 23mM(●), acarbose 5 mM(△)).