Feed has a predominant weight in determining the production costs and the sustainability of aquaculture. In vivo feeding trials are fundamental for developing new feeds, but also have some limitations, due to their length, costs, and the need to sacrifice many animals. Therefore, an in vitro platform could provide an effective screening tool to test feed nutritional and health values. Here we tested bicameral platforms recently developed1 in our laboratory, based on cell lines derived respectively from the proximal (RTpiMI) and distal (RTdiMI) intestine. We evaluated the effects of a prolonged exposure (21 days) to: a reference diet (RD), rich in fish meal and fish oil; a diet in which animal proteins were replaced with soy-derived proteins (SD); an experimental diet in which fish components were partially substituted by feather meal obtained from by-products of the poultry industries (FD); L-15 medium with no feed (Control). Barrier integrity was evaluated measuring transepithelial electrical resistance (TEER), cell morphology and alanine aminopeptidase enzyme activity. Results showed that SD disrupted epithelial barrier integrity of the proximal but not the distal intestine platform after 3 days of exposure (fig. 1). However, the effect was reversible since, barrier integrity was fully restored after SD was removed. On the other hand, RD and FD stimulated a progressive cell proliferation response along the 21 days of exposure in both platforms.
We conclude that proximal intestine cells are more sensitive than those of distal intestine, particularly to SD. The other diets had a milder effect and caused cell proliferation, rather than epithelial barrier disruption. We interpret this reaction as a sign of inflammation, probably due to the lack of mucus protection, similar to the one observed in vivo when challenging diets induce an intestinal folds branching2 increase. In addition, RTpiMI cells ability to fully recover from the initial damage caused by SD is of great interest, since it suggests the possibility to use this platform to identify target molecules that can mitigate the effects of anti-nutritional factors. We are currently studying cell ability to absorb single amino acids as a possible way to discriminate the effects of different diets more subtly. Overall, our data indicate that the use of feed pellets digested in vitro with fish enzymes, combined with their exposure to intestinal cell platforms, provides useful indication on the nutritional and health value of different diets.
Acknowledgements: This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 828835.
References
Verdile, N. et al., Aquaculture, 2023. https://doi.org/10.1016/j.aquaculture.2022.739031