Is the intestinal mucous layer a natural deep eutectic solvent-based digestion matrix?

Abstract

In plants, a third solubilization matrix (besides water and lipids) has been proposed, composed of natural deep eutectic solvents (NADESs). Such matrices allow for the solubilization of many biologically important molecules, such as starch, which are insoluble in water or lipids. NADES matrices also support enzyme activity, such as amylase, at higher rates than water or lipid-based matrices. We contemplated if a NADES environment could play a role in small intestinal starch digestion. The intestinal mucous layer (encompassing both the glycocalyx and the secreted mucous layer) has a chemical composition that fits well with NADES (e.g., glycoproteins with exposed sugars, amino sugars, and amino acids like proline and threonine, as well as quaternary amines like choline and ethanolamine and organic acids like citric and malic acid). Various studies have indeed shown that amylase binds to glycoproteins within the mucous layer of the small intestine where it performs its digestive action. Dislodging amylase from these binding sites impedes starch digestion and it may well cause digestive health problems as a result. Hence, we propose that the mucous layer in the small intestines harbors digestive enzymes like amylase, while starch, due to solubility, redistributes from the lumen into the mucous layer where it is subsequently digested by amylase. The mucous layer would thus constitute a NADES-based digestion matrix in the intestinal tract.