Variants of β-casofensin, a bioactive milk peptide, differently modulate the intestinal barrier: In vivo and ex vivo studies in rats

β-Casofensin is a bioactive milk peptide that modulates the intestinal barrier, particularly through itsaction on goblet cells. β-Casofensin corresponds to fragment (f) 94–123 of the bovine β-casein (β-CN) A2variant. Fifteen genetic variants of bovine β-CN (A1–3,B–G, H1–2, I–L) are known, of which the A2, A1, andB forms are the most common. These variants differfrom each other by the substitution of one or moreamino acids, some of which are localized in f94 to 123.The aim of our study was to compare the intestinaleffects of β-casofensin A2 and its 3 main variants: A1,A3, and B. For this purpose, a solution (0.1 µM; 10μL/g of body weight, postnatal d 10–20) containing β-casofensin A2, one of its variants (A1, A3, or B), ordrinking water (control; CT) was administered to rat pups orally. After euthanasia (postnatal d 20), intestinalsegments were collected for biochemical and histochemical analysis and also used to determine paracellularpermeability to fluorescein isothiocyanate-labeled 4-kDa dextran in an Ussing chamber. We also studiedthe direct effects of β-casofensin A2 and its A1 variant on the paracellular permeability of jejunum segmentsof adult rats. β-Casofensin A2 and its B variant significantly increased the population of goblet cells comparedwith the CT, A1, and A3 groups. The mucin 2 mRNA level was significantly higher in the β-casofensinA2 group than in the CT, A3, and B groups. Our results also revealed that the protein expression of zonulaoccludens-1 and occludin was reduced in the jejunum of rats in the A1, A3, and B groups compared with theCT group. However, the A1 variant was the only peptide to decrease jejunal permeability compared with theCT group. This variant, tested directly in the apical compartment of an Ussing chamber at a concentrationof 0.1 nM, also reduced jejunal permeability. In conclusion, the substitution of a single amino acid altersthe effect of β-CN sequence f94 to 123 on goblet cells and on intestinal permeability. A genetic polymorphismof β-CN can affect the biological activity of peptides derived from this protein. These data should be takeninto account in the production of bioactive foods. Key words: bioactive milk peptide, β-casein, β-CN(94-123), intestinal protectio