A study about the effect of fruit phytochemicals on the glucose and phenols intestinal absorption in a Caco-2TC7 monolayer model, by means of glucose and polyphenols amperometric biosensors.

Type 2 diabetes mellitus (T2DM) is currently affecting hundreds of million people worldwide. Fluctuations in blood glucose and hyperglycemia are one of the causes of reactive oxygen species production, thus determining several disfunctions to pancreatic β-cells and also insulin resistance and impaired glucose tolerance. So, it became extremely important to know how to manage post prandial hyperglycemia. (Ceriello and Motz, 2004, Wright Jr. et al., 2006). In light of this, nowadays diets based on bioactive molecules, such as polyphenols, are paying special attention in order to modulate glucose intestinal absorption. In this work, we present an original electrochemical device for real-time dynamic monitoring of the effects of natural compounds on the absorption of glucose and polyphenols through Caco-2TC7 monolayer cells. The device combines a glucose oxidase-based biosensor coupled with a laccase/tyrosinase-based biosensor, placed in the basal portion of a cell culture plate. Both types of biosensors are coupled with their respective sentinel sensors, in order to eliminate the impact of eventual interfering currents deriving from the matrix. The Caco-2TC7 monolayer, grown in a special insert, separates the apical compartment, simulating the intestinal lumen, from the basolateral portion, which virtually represents the bloodstream. In a first series of experiments, the cell culture was treated, in the apical compartment, with glucose 1 mM while the glucose biosensor recorded the currents derived from the glucose passed in the basolateral compartment, obtaining a bioavailability of about 5.1%. The further treatment with Phlorizin and Phloretin, inhibitors of SGLT1 and GLUT2 glucose transporters, produced a 10-fold reduction in glucose transport. By means of laccase/tyrosinase biosensor it was also possible to detect, in the basolateral compartment, low levels of absorbed Phlorizin and Phloretin, that showed bioavailability of 0.13% and 0.49% respectively. Then, in a successive series of experiments, blueberry and pomegranate juices, that contain relatively quite high amount of polyphenols (about 33% anthocyanins and about 53% anthocyanins), were also studied to evaluate their hypoglycemic potential. Actually, a treatment with those juices on Caco-2TC7 monolayer determined a sustained reduction in the glucose absorption: in particular, pomegranate juice determined a 0.8% of glucose bioavailability, while blueberry determined only the 0.17%, strongly demonstrating that blueberry and pomegranate juices exert a hypoglycemic effect on the monolayer. In this experiment, the polyphenols absorption was also evaluated, by means of laccase/tyrosinase biosensor, in the basolateral compartment. For both juices the same trend was highlighted. In fact, polyphenols’ concentrations showed an increase in the first 50 minutes of monitoring, then a slow decrease was monitored, demonstrating an active polyphenols’ transport through Caco-2-TC7 cell monolayer