Enhancement of dietary protein digestion by conjugated bile acids.
OBJECTIVE
Conjugated bile acids promote absorption of dietary lipids by solubilizing them in mixed micelles. Bile acids are not considered to facilitate the digestion of other nutrients.


METHODS
The effect of conjugated bile acids on the rate of protein hydrolysis by trypsin and chymotrypsin was examined in vitro. Common dietary proteins and 2 bacterial glutenases (proposed oral therapies for celiac sprue) were proteolyzed in the absence or presence of a 10 mmol/L conjugated bile acid mixture, simulating human bile composition. Lipolysis products (monoolein) and fatty acid were also evaluated to simulate postprandial intestinal contents.


RESULTS
Conjugated bile acids dramatically enhanced the proteolysis of several dietary proteins, including beta-lactoglobulin, bovine serum albumin, myoglobin, and a commercially available dietary protein supplement. For beta-lactoglobulin, a cow's milk allergen that is resistant to pepsin cleavage, bile acids enhanced its proteolysis by pancreatic proteases even after incubation under gastric conditions. Exposure of prolyl endopeptidases to bile acids made them more susceptible to pancreatic proteases under simulated intestinal conditions. The conjugated bile acid effect was most pronounced in the presence of dihydroxy bile acids and was observable at bile concentrations below the critical micellar concentration but to a much greater extent at concentrations above the critical micellar concentration.


CONCLUSIONS
We propose that, in addition to promoting lipid absorption, conjugated bile acids affect the digestion and assimilation of dietary proteins by accelerating hydrolysis by pancreatic proteases. These findings have implications for intraluminal protein breakdown and assimilation in the upper small intestine.
Gass
Jonathan
J
Department of Chemical Engineering, Stanford University, Stanford, California, USA.
Vora
Harmit
H
Hofmann
Alan F
AF
Gray
Gary M
GM
Khosla
Chaitan
C
D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism* / Q000494:pharmacology*; D002792:Cholestyramine Resin / Q000378:metabolism / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin / Q000378:metabolism / Q000494:pharmacology; D004044:Dietary Proteins / Q000378:metabolism*; D004063:Digestion; D004789:Enzyme Activation / Q000187:drug effects; D005983:Glutens / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008066:Lipolysis; D012995:Solubility; D014357:Trypsin / Q000378:metabolism / Q000494:pharmacology
D001647:Bile Acids and Salts; D004044:Dietary Proteins; D002792:Cholestyramine Resin; D005983:Glutens; D002918:Chymotrypsin; D014357:Trypsin