Colloidal bismuth subcitrate inhibits peptic degradation of gastric mucus and epidermal growth factor in vitro

The effect of an antiulcer drug, colloidal bismuth subcitrate (De-Nol), on the proteolytic activity of pepsin toward gastric mucus and salivary epidermal growth factor was investigated. Samples of pig gastric mucus and mouse epidermal growth factor were incubated with pepsin in the absence and in the presence of De-Nol, and the released α-amino acid residues were quantified. Results of analysis revealed that, in the absence of De-Nol, the apparent K(m) value of pepsin toward gastric mucus was 1.4 g/L and that towards epidermal growth factor 120 μM. Introduction of De-Nol to the incubation mixtures led, in both cases, to reduction of the rates of proteolysis. With gastric mucus, the rate of proteolysis inhibition was proportional to the De-Nol concentration up to 1 x 10^-2 g/L, at which point a 54% reduction in mucus proteolysis occurred, whereas, with epidermal growth factor, this concentration of De-Nol caused nearly 52% inhibition in the rate of proteolysis. The apparent K(i) value for peptic degradation of gastric mucus in the presence of D-Nol was 2.1 x 10^-4 g/L and that for peptic degradation of epidermal growth factor 1.8 x 10^-2 g/L. The results suggest that among the beneficial effects of colloidal bismuth subcitrate on ulcer healing is its ability to interfere with peptic digestion of the protective gastric mucus coat and of such important bioactive protein as epidermal growth factor.