The role of small molecular weight compounds to increase vacuolation induced by VacA toxin in vitro

VacA is a vacuolation protein toxin secreted by Helicobacter pylori. Many compounds have been implicated in the regulation of VacA toxin activity. In this study, regulation of cell vacuolation induced by VacA was observed with the addition of glycine, glycine hydrochloride, xylitol, and taurine by neutral red dye uptake assay using gastric human epithelial cell cultures. Glycine, xylitol, and taurine increased cell vacuolation significantly after 48h (p<0.05), with their effect apparent in a wide concentration range (0.2mM to about 100mM). Changes were sharp in respect of concentration and showed little dose-response characteristics. In contrast, upregulation of glycine hydrochloride on cell vacuolation in weak acidic extracellular pH was much retarded with VacA activity not initiated until 72h. In addition, our results showed that cell vacuolation was highest when the pH was 6.8. The increase in vacuolation was gentle in weak acidic extracellular pH and the increase dose-dependent with a Pearson correlation coefficient (r) of 0.986 from 0.2 to 6.25mM. In this concentration range and at the same time point, the pH decrease was negatively correlated with vacuolating activity (r=0.922, p<0.01). In conclusion, our study showed that three small molecular compounds can increase vacuolation induced by VacA toxin in vitro.