Human Gastrointestinal Juices Intended for Use in In Vitro Digestion Models

Abstract

The aim of this study was to characterise the individual human gastric and duodenal juices to be used in in vitro model digestion and to examine the storage stability of the enzymes. Gastroduodenal juices were aspirated, and individual variations in enzymatic activities as well as total volumes, pH, bile acids, protein and bilirubin concentrations were recorded. Individual pepsin activity in the gastric juice varied by a factor of 10, while individual total proteolytic activity in the duodenal juice varied by a factor of 5. The duodenal amylase activity varied from 0 to 52.6 U/ml, and the bile acid concentration varied from 0.9 to 4.5 mM. Pooled gastric and duodenal juices from 18 volunteers were characterised according to pepsin activity (26.7 U/ml), total proteolytic activity (14.8 U/ml), lipase activity (951.0 U/ml), amylase activity (26.8 U/ml) and bile acids (4.5 mM). Stability of the main enzymes in two frozen batches of either gastric or duodenal juice was studied for 6 months. Pepsin activity decreased rapidly and adjusting the pH of gastric juice to 4 did not protect the pepsin from degradation. Lipase activity remained stable for 4 months, however decreased rapidly thereafter even after the addition of protease inhibitors. Glycerol only marginally stabilised the survival of the enzymatic activities. These results of compositional variations in the individual gastrointestinal juices and the effect of storage conditions on enzyme activities are useful for the design of in vitro models enabling human digestive juices to simulate physiological digestion.

Fig. 1

a Detailed description of the three-lumen tube used for the aspiration of gastric and duodenal juices. HGJ gastric juice, HDJ duodenal juice (photo: Ellen K. Ulleberg). b Correct placement of the three-lumen aspiration tube in the stomach and duodenum of a volunteer as monitored by radiology (photo: Espen B. Herud)

Fig. 2

Percentage remaining pepsin activity in a pooled sample of human gastric juice and remaining amylase, lipase and total proteolytic activities in a pooled sample of human duodenal juice stored at −80 °C for 6 months

Fig. 3

Long-term storage stability of pepsin in a frozen sample of pooled human gastric juice and stability of total proteolytic, amylase and lipase activities in a frozen sample of pooled human duodenal juices stored at −20 °C or −80 °C. The individual juices had been collected and stored at −80 °C from 7 to 15 months prior to pooling them and were then observed for 12 months