PHOSPHOLIPASE-ACTIVITY OF HELICOBACTER-PYLORI AND ITS INHIBITION BY BISMUTH SALTS - BIOCHEMICAL AND BIOPHYSICAL STUDIES

In this study we measured phospholipase A (PLA) and C (PLC) activity o f media filtrates and French Press lysates of the gastritis-inducing b acteria Helicobacter pylori. We report here that both H. pylori lysate s and filtrates contain PLA1, PLA2, and C enzymes, which readily hydro lyze a radiolabeled dipalmitoylphosphatidylcholine (DPPC) and phosphor ylcholine substrates, respectively. The specific activity of both PL4 and C enzymes were greatest in the 6.5-7.0 and 8.4-8.8 pH ranges, resp ectively. Colloidal bismuth subcitrate (CBS) induced a dose-dependent inhibition of PLA2 and C activity of both H. pylori lysates and filtra tes. This inhibitory effect of CBS on PLA2 was antagonized in a dose-d ependent fashion by the addition of CaCl2 to the incubation mixture, s uggesting that calcium and bismuth may be competing for the same site on the enzyme. In contrast, the ability of bismuth salts to inhibit PL C activity of H. pylori lysates was not antagonized by CaCl2. Employin g a biophysical assay system for surface wettability, it was determine d that H. pylori lysates had the capacity to remove a synthetic phosph olipid monolayer off a glass in a dose-dependent fashion. This ability of the bacterial lysates to catalyze the transformation of a hydropho bic surface to a wettable state was significantly attenuated in the pr esence of bismuth salts. Our experimental results are, therefore, cons istent with the possibility that H. pylori colonization compromises th e stomach's barrier to acid by eroding a phospholipid lining, possibly a monolayer, on the surface of the gastric mucus gel and that this pr ocess is blocked in response to bismuth therapy.