Bile acids inhibit pepsin activity against a refined substrate

Presence of small resistant peptides from new in vitro digestion assays detected by liquid chromatography tandem mass spectrometry: An implication of allergenicity prediction of novel proteins?

The susceptibility of newly expressed proteins to digestion by gastrointestinal proteases (e.g., pepsin) has long been regarded as one of the important endpoints in the weight-of-evidence (WOE) approach to assess the allergenic risk of genetically modified (GM) crops. The European Food Safety Authority (EFSA) has suggested that current digestion study protocols used for this assessment should be modified to more accurately reflect the diverse physiological conditions encountered in human populations and that the post-digestion analysis should include analytical methods to detect small peptide digestion products.The susceptibility of two allergens (beta-lactoglobin (β-Lg) and alpha-lactalbumin (α-La)) and two non-allergens (hemoglobin (Hb) and phosphofructokinase (PFK)) to proteolytic degradation was investigated under two pepsin digestion conditions (optimal pepsin digestion condition: pH 1.2, 10 U pepsin/μg test protein; sub-optimal pepsin digestion condition: pH 5.0, 1 U pepsin/10 mg test protein), followed by 34.5 U trypsin/mg test protein and 0.4 U chymotrypsin/mg test protein digestion in the absence or presence of bile salts. All samples were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in conjunction with Coomassie Blue staining and, in parallel, liquid chromatography tandem mass spectrometry (LC-MS) detection. The results provide following insights: 1) LC-MS methodology does provide the detection of small peptides; 2) Peptides are detected in both allergens and non-allergens from all digestion conditions; 3) No clear differences among the peptides detected from allergen and non-allergens; 4) The differences observed in SDS-PAGE between the optimal and sub-optimal pepsin digestion conditions are expected and align with kinetics and properties of the specific enzymes; 5) The new methodology with new digestion conditions and LC-MS detection does not provide any differentiating information for prediction whether a protein is an allergen. The classic pepsin resistance assay remains the most useful assessment of the potential exposure of an intact newly expressed protein as part of product safety assessment within a WOE approach.

Further studies on the inhibition of pepsin by bile salts

A higher incidence of peptic ulceration has been reported in patients recovering from operations that divert bile from the duodenum. Previous studies have shown that hydroxylated bile salts inhibit the proteolytic activity of pepsin, an integral agent in the production of peptic ulcer. In this study, the pepsin inhibitory activity of 16 bile salts (6 unconjugated, 5 glycoconjugated, and 5 tauroconjugated bile salts), including bile salts with no hydroxyl groups, was tested in vitro. All bile salts inhibited pepsin proteolytic activity and the degree of pepsin inhibition increased in proportion to their concentrations. The range of maximal inhibition was 90-73% for unconjugated bile salts; 74-35% for glycoconjugated bile salts; and 71-46% for tauroconjugated bile salts. These findings support the need for clinical studies to evaluate administration of bile acids to bile-diverted patients.

Inhibition of pepsin activity by ursodeoxycholic acids and chenodeoxycholic acids

The bile salts of ursodeoxycholic acid, glycoursodeoxycholic acid, tauroursodeoxycholic acid, chenodeoxycholic acid, glycochenodeoxycholic acid, and taurochenodeoxycholic acid were each found to inhibit pepsin proteolytic activity in vitro at various concentrations against the refined substrate n-APDT. The sodium salt of ursodeoxycholic acid was the most potent pepsin inhibitor among those tested.

Inhibition of pepsin activity by unconjugated bile acids. Inverse relation to number of hydroxyl groups

The unconjugated bile acids cholic, deoxycholic, chenodeoxycholic, and lithocholic acid were each found to inhibit pepsin activity in vitro against the refined substrate n-adenosyl-L-phenylalanyl-L-3,5-diiodotyrosine (n-APDT). The degree of inhibition was inversely proportional to the number of hydroxyl substituents on the bile acid molecule. The implications of these findings in relation to the occurrence of peptic ulceration in patients undergoing Roux-Y biliary diversion is discussed.