Reversible induction of mucous cell hyperplasia and parietal cell loss in rats dosed with DMP-777

Abstract

Parietal cell loss and mucous cell hyperplasia are important histological components of a spectrum of gastric mucosal diseases including Menetrier's disease and fundic H. pylori gastritis. Recent investigations using transgenic mouse strains have highlighted the importance of intrinsic mucosal growth factors such as TGFct in the differentiation of specific cell lineages in the gastric mucosa. Unfortunately, experiments in transgenic mice have been hampered by the irreversibility of atrophic-gastritis phenotypes. In three-month toxicity studies in rats, oral dosing with DMP-777 (50-200 mg/kg/day), a neutrophil elastase inhibitor, resulted in an unexpected phenotype of gastric mucous cell hyperplasia and parietal cell loss associated with hypergastrinemia. Routine histological staining (diastase-resistant PAS) and immunocytochemistry for BrdU, H/K-ATPase, spasmolytic peptide, gastrin, somatostatin and chromogranin A were utilized to determine alterations in mucosal lineages. Rats did not demonstrate any significant inflammatory infiltrate. Fundic mucosa demonstrated a prominent hyperplasia of surface mucous cells, 4 to 8-fold increases in isthmus zone BrdU-labeling index and a profound decrease in the numbers of parietal ceils, chief cells, somatostatin ceils and ECL ceils after 9 days of dosing with 200 mg/kg/day. The numbers of mucous neck cells were unaffected by drug treatment. Hyperplasia of gastrin cells was seen in the gastric antrum, but there was no hyperplasia of antral mucous cells. These changes were completely reversible after a threemonth drug-free recovery period. To examine the marked hypergastrinemia observed in DMP 777-treated rats, the effects of the drug on acid secretion were studied in the rat pylorus-ligation model, where DMP-777 was shown to be a potent inhibitor of gastric acid secretion when dosed orally. Additional in vitro tests showed that DMP-777 did not block histamine (H2), acetylcholine (M3) or gastrin receptors (novel and CCK-B receptors). In isolated rabbit parietal cells, 3 pM DMP-777 completely inhibited basal, histaminestimulated and forskolin-stimulated aminopyrine accumulation (ECso---0.6 pM). While the drug had no direct effect on the activity of the H/K-ATPase, 1-3 laM DMP-777 could dissipate completely an established stimulated proton gradient in isolated tubulovesicles loaded with acridine orange. These latter results suggest that DMP-777 is a protonophore. Since other regions of the gastrointestinal mucosa are not affected by the drug, unexpected effects of DMP-777 on the gastric mucosa may be due to a specific interaction with parietal cell, perhaps involving a specific partitioning of the drug into the parietal cell secretory canalicolus. Short term DMP-777 dosing of rats provides the first readily reversible model of parietal cell loss and mucous cell hyperplasia. This work was funded by DuPont-Merck Pharmaceuticals.