Transport across Caco-2 monolayers of peptides arising from in vitro digestion of bovine milk proteins

Transport across monolayers of human colon adenocarcinoma (Caco-2) cells represents one of the
most widely accepted in vitro models of the intestinal uptake of nutrients and drugs. Herein, the
entire panel of peptides produced from caseins (CN) and whey proteins (WP) that survive in vitro
sequential gastro-pancreatic digestion and translocate across the Caco-2 monolayers have been
characterized by high-performance liquid chromatography (HPLC) and mass spectrometry (MS).
Except for traces of casein phosphopeptides, we did not detect any milk-derived peptides with
proposed bioactivity. The absorption behavior of two resistant ?-Lactoglobulin (?-Lg) domains, ?-
Lg 125-135 and ?-Lg 40-60, was studied in detail using synthetic peptides. The IgE-binding
properties of the peptide digests and synthetic peptides recovered from both the apical and
basolateral compartments of the monolayers were evaluated by a dot-immunobinding assay using
the sera of children (N=5) diagnosed with cow's milk allergy. Outcomes indicated that ?-Lg 127-
135, which is a Caco-2 processed form of ?-Lg 125-135, is a possible "immune sensitizing factors"
in vivo. The almost complete loss of the IgE-binding affinity of both CN and WP after enzymatic
digestion and transepithelial transport also points out the need of designing in vivo experiments to
track the metabolic fate of dietary proteins.