Development and application of methodology for assessing the role of lysosomes in experimental ulcerogenesis in the guinea pig

In order to determine if lysosomes are causally involved in gastric ulcerogenesis, we (a) systematically characterized homogenization techniques and assay conditions for measurement of lysosomal enzymes in guinea pig gastric mucosa, and (b) assessed the relationship among histamine-induced gastric erosions, lysosomal enzyme activities, and the integrity of lysosomal membranes. We developed procedures that yielded tissue homogenates of gastric mucosa in which a majority of cells had been disrupted, but at least two-thirds of the lysosomes were preserved. We also demonstrated that two lysosomal enzymes from gastric mucosa, N-acetyl-β-glucosaminidase and β-glucuronidase, had acid pH optima and activities that were linear with time, mucosal protein, and substrate concentration, and exhibited Michaelis-Menten kinetics. Moreover, using isopycnic centrifugation of light mitochondrial fractions on continuous and discontinuous sucrose gradients, we showed that Triton WR-1339, a nonionic detergent known to accumulate in hepatic cells, also accumulates in gastric mucosal cell lysosomes, causing a decrease in their density and an increase in their fragility. Finally, we found no correlation between histamine-induced gastric erosions and the integrity of gastric mucosal cell lysosomes; pretreatment of guinea pigs with Triton WR-1339 increased the fragility of gastric cell lysosomes, but did not enhance the ulcerogenic effect of histamine. Our findings do not support a role for gastric cell lysosomes in histamine-induced gastric mucosal injury.