Preliminary Studies On Antibacterial And Antitumor Activity Of The Cecropin-like Antibacterial Peptide From Helicobacter Pylori

Backgroud/ObjectiveHelicobacter pylori, which is responsible for the most common infection worldwide, has been implicated in several gastrointestinal diseases, such as peptic ulcer disease, gastric adenocarcinoma, and mucosa-associated lymphoid tissue (MALT) lymphoma. H. pylori-induced inflammation is a risk factor for the development of gastric adenocarcinoma, but the mechanisms involved in H.pylori-associated carcinogenesis are poorly understood. A cecropin-like H. pylori peptide, Hp(2-20), was found to be a monocyte chemoattractant and activated the monocyte NADPH-oxidase to produce oxygen radicals. Hp(2-20)-activated monocytes inhibited lymphocytes with antitumor properties. H. pylori expression of this monocyte activating peptide contributes to its ability to attract and activate monocytes and reduces the function and viability of antineoplastic lymphocytes. H pylori apparently undergoes 'altruistic lysis' in vivo and that this bacterial lysis in the gastric lumen may release cecropin-like peptides that are active against faster growing microorganisms. This may conceivably lead to inhibition of colonization and growth of other organisms in the gastrointestinal tract that may prove deleterious to the host. The aims of this paper is to study the in vitro effects of cecropin-like antibacterial peptide from Helicobacter pylori Hp (2-20) on the gastric epithelial cells, gastric cancer cells and the in vitro killing effects of the Hp (2-20) on the gastrointestinal bacterial pathogens.MethodsThe inhibition zone assay was used to determine anti-bacterial activity and lethal concentrations of Helicobacter peptide Hp (2-20) and Cecropin B on E.coli K12D31 (standard strain). The cytotoxicity and IC50 of the Hp (2-20)peptides and Cecropin B on human gastric epithelial cell and gastric cancer cell lines was measured by MTT (microculture tetrazolium) colorimatric methods. The inhibition zone assay was used to determine anti-bacterial activity and lethal concentrations of Helicobacter peptide Hp (2-20) on the gastrointestinal bacterial pathogens. The killing rate of E. coli K12D31 by Hp (2-20) was estimated by counting viable bacteria based on counting of clone forming units grown in Luria-Bertani plate. The proliferating effects of the Hp (2-20) peptides on human gastric epithelial cell line was measured.ResultsIn vitro studies, The lethal concentrations (LC) of Hp (2-20) and Cecropin B on E. coli K12D31 are 65μmol/L and 0.44μmol/L. The killing effects of Cecropin B were more pronounced than Helicobacter peptide Hp (2-20). The synthetic peptide Hp(2-20) and Cecropin B showed lytic or toxic activity against the human gastric cancer cell line SGC-7901 on concentration dependent relationship. The Hp(2-20) proliferates the gastric epithelial cell GES-1 on the concentration lower than 200μmol/L. The Cecropin B has no lytic or toxic activity against gastric epithelial cell GES-1 on the concentration from 5μmol/L to 20μmol/L. The IC50 of Hp (2-20) are 531μ mol/L for GES-1 cells and 500.8μmol/L for SGC-7901 cells. The IC50 of Cecropin B are 102μ mol/L for GES-1 cells and 25μmol/L for SGC-7901 cells. In vitro studies, the Hp (2-20) destroyed the gastrointestinal bacterial pathogens such as Shigella flexneri, Salmonella typhi, Salmonella paratyphi and enteropathogenic E. coli. The lethal concentrations (LC) are 65-197μ mol/L. The viable bacterial count dropped to zero after 12 min incubation with Hp (2-20) concentration closed to the LC value. The Hp(2-20) was inactive against the strains of Yersinia enterocolitica and Staphylococcus aureus and have much higher LC (over 1014μmol/L). The killing effects of Cecropin B were more pronounced than Helicobacter peptide Hp (2-20). The syntheticpeptide Hp(2-20) showed no lytic or toxic activity against the human gastric epithelial cell line GES-1.ConclusionsThe Hp (2-20) has lower anti-bacterial activity than Cecropin B and there is concentration dependent relationship cytotoxicity effect on the gastric cancer cells. The cecropin-like antib...