Bile enhances glucose uptake, reduces permeability, and modulates effects of lectins, trypsin inhibitors and saponins on intestinal tissue

Antinutritional factors (ANFs) can disrupt digestive and other intestinal functions. ANFs in soybean meal (SBM) are implicated in proliferative and inflammatory responses in the intestine of various (functionally) monogastric animals, including Atlantic salmon (Salmo salar L.). The goal of the current study was to investigate the effect of ex vivo exposure of mid and distal intestinal tissue of salmon to soybean saponins (SAP), lectin (LEC) and Kunitz' trypsin inhibitor (KTI), singly and in combination, on epithelial function, as assessed by measuring in vitro glucose uptake pathways along a glucose concentration gradient. As solubilization of SAP in the calcium-containing Ringer's solution was problematic but resolved with the addition of a physiological concentration of bile collected from the gall bladder of salmon, an evaluation of bile effects became an added element. Results indicated that bile increased baseline glucose absorption and possibly transport, and also had a protective effect on the epithelial barrier, at least partially due to taurocholate. Compared to controls, tissues exposed to LEC + bile, KTI + bile and LEC + KTI + bile exhibited increased glucose uptake at the higher glucose concentrations, apparently due to markedly increased tissue permeability. Addition of SAP, however, attenuated the response, possibly by binding bile components. SAP + bile, also in combination with LEC and/or KTI, as well as LEC, KTI and LEC + KTI without bile often reduced transcellular glucose uptake pathways, while maintaining low tissue permeability. SAP + LEC + KTI + bile, LEC and KTI caused the most marked reductions. The distal intestine was more affected, reflecting the restriction of in vivo SBM-induced inflammatory changes to this region.