In vitrotransport and satiety of a beta-lactoglobulin dipeptide and beta-casomorphin-7 and its metabolites

Abstract

Understanding the digestive behaviour and biological activities of dairy proteins may help to develop model dairy products with targeted health outcomes including increased satiety and healthy weight maintenance. Caseins and whey proteins constitute over 95% of milk proteins with consumption of these proteins associated with increased satiety and a decreased prevalence of metabolic disorders. To investigate the in vitro digestive behaviour and satiety of dairy proteins at the intestinal epithelium, the in vitro transport and hydrolysis of 500-2000 μM β-casomorphin-7 (YPFPGPI or β-CM7) and a β-lactoglobulin (β-Lg) dipeptide (YL) was measured using Caco-2 cell monolayers grown on transwells as a model of the intestinal epithelium. Transport of YL was concentration dependent and ranged from 0.37-5.26 × 10(-6) cm s(-1), whereas transport of β-CM7 was only detected at 2000 μM and was significantly lower at 0.13 × 10(-6) cm s(-1). Rapid hydrolysis of β-CM7 in the apical chamber by the Caco-2 cells produced three peptide metabolites: YP, GPI and FPGPI. All of these metabolites were detected in the basolateral chamber after 30 min with both the YP and GPI peptides transporting at a higher rate than intact β-CM7. In vitro satiety was indicated by the secretion of cholecystokinin [26-33] (CCK-8) and glucagon-like peptide 1 (GLP-17-36NH2) in the STC-1 enteroendocrine cell model. CCK-8 secretion was highest in response to β-CM7 followed by the β-CM7 metabolite FPGPI. CCK-8 secretion however was not significantly stimulated by the tri- or dipeptides. Secretion of GLP-1 was not significantly stimulated by β-CM7 or YL. These in vitro results suggest that dairy peptide size enhances CCK-8 secretion, whilst limiting transport across Caco-2 monolayers.

Role of Bioactive Peptide Sequences in the Potential Impact of Dairy Protein Intake on Metabolic Health

“…These data are in agreement with the conclusions of two previous reports showing that intact or partially digested dietary proteins may exert stronger effects on satiety hormone release compared to protein hydrolysates and synthetic peptides [29], and that dipeptides and tripeptides may be ineffective in altering CCK release from STC-1 cells [107]. Furthermore, as to the possible synergistic effects of amino acids with different side chains, it has been previously observed that a mixture of l-tyrosine, l-threonine and l-methionine induced a significant change of CCK release whereas a single amino acid of the mixture had no significant effects [108].…”

“…In detail, somatostatin contributes to reduce the gastric acid secretion and gastric motility and inhibits the secretion of multiple gastroentericand pancreatic hormones [111]. Finally, β-CM7 and its fragment FPGPI stimulated the CCK secretion from STC-1 cells in vitro, whereas smaller fragments (YP and GPI) did not [8,107].…”

“…FPGPI and other derivatives were also found in yogurt as products of bacterial fermentation [112]. In vitro permeability assays across Caco-2 cell monolayer (an in vitro model of intestinal epithelial barrier) suggested the cleavage of β-CM7 by brush border membrane endopeptidases, and the release of FPGPI into both apical and basolateral medium [107]. Hence, we may conclude that there is evidence of an actual role of this peptide and its derivatives in mediating some effects associated with dairy product ingestion.…”

Whey proteins have beneficial effects on intestinal enteroendocrine cells stimulating cell growth and increasing the production and secretion of incretin hormones

“…Furthermore a recent study found that neither the BLG dipeptide YL nor beta-casomorphin-7 (YPFPGPI) could stimulate GLP-1 secretion (Osborne et al, 2014). Also, the highest induction of CCK-8 was in response to beta-casomorphin-7, followed by the metabolite (FPGPI) and trior dipeptides had no effect.…”

Food-Derived Hemorphins Cross Intestinal and Blood–Brain Barriers In Vitro

“…This study is a first report of the passage of food-derived hemorphins, i.e., exogenous hemorphins, through the intestinal as well as the BBB in vitro (Table 1 ). Information on the in vitro absorption of alimentary proteins or of well-defined peptide sequences derived thereof has been mainly garnered from tests with milk proteins ( 34 – 36 ), much less from tests with whey proteins ( 19 , 37 ), or lately from egg albumin ( 38 ) but this information was unknown for hemorphins. The tested peptide the closest in terms of structure to hemorphins, is endomorphine-1 for which a low permeability through a caco-2 cell monolayer was reported ( 39 ).…”