Abstract
BACKGROUND: Helicobacter pylori infection is a major global health issue associated with chronic gastritis, peptic ulcers, and gastric cancer. Due to the increasing resistance of H. pylori to conventional antibiotics, there is growing interest in researching alternative therapeutic agents, particularly those from medicinal plants. METHODS: Preparation and purification of extracts from two plant species, Plectranthus asirensis and Premna resinosa, were performed by cold maceration. The anti-microbial activity of two extracts was then evaluated against H. pylori to determine the minimum inhibitory concentration (MIC). The activity of the extracts was further analyzed by electron microscopy, bacterial cell lysis and Western blotting. The effects on AGS gastric epithelial cells upon infection were monitored by cell scattering, cell vacuolization, DNA damage analysis, NF-κB reporter assay and chemokine ELISA. RESULTS: We determined the MIC of P. asirensis and P. resinosa extracts on treated H. pylori as 200 µg/mL and 35 µg/mL, respectively. Electron microscopy showed severe deformation of the bacterial cells. We obtained no bacterial cell lysis and only minimal changes in protein expression levels of the virulence factors CagA, CagY, HopQ, urease, and flagellin. However, we found that cleavage of the vacuolating cytotoxin VacA p98 pro-form to the p88 active form was significantly downregulated. The enzymatic urease activity was also impaired by the addition of both extracts, while the proteolytic activity of serine protease HtrA was not affected. Infection of AGS cells in the presence of both extracts revealed that type IV secretion system (T4SS)-dependent CagA injection, cell scattering and motility, as well as VacA-dependent cellular vacuolation were completely inhibited. Furthermore, H. pylori-induced pro-inflammatory transcription factor NF-κB and interleukin-8 release were also significantly downregulated. Finally, both extracts prevented T4SS-induced DNA double-strand breaks (DSBs) and chromosomal fragmentation in the nuclei of host cells. CONCLUSIONS: Taken together, we have discovered natural compounds of P. asirensis and P. resinosa that exhibit potent anti-H. pylori activities, not only inhibiting bacterial growth, but also suppressing key virulence mechanisms involved in epithelial cell damage, inflammation and genomic instability. These extracts are promising candidates for future therapeutic applications in patients, which could help minimizing H. pylori infections and gastric cancer development.