Protective mechanism of epigallocatechin-3-gallate against Helicobacter pylori-induced gastric epithelial cytotoxicity via the blockage of TLR-4 signaling.
BACKGROUND
Helicobacter pylori infection leads to gastric mucosal damage by several mechanisms including the direct effect of virulence factors produced by H. pylori, propagation of inflammation, oxidative stress, DNA damage, and induction of apoptosis. (-)-Epigallocatechin-3-gallate (EGCG), one of the green tea catechins, is known to suppress H. pylori-induced gastritis through its antioxidative and antibacterial actions. In this study, we evaluated the protective mechanism of EGCG against H. pylori-induced cytotoxicity in gastric epithelial cells.


METHODS
MTT assays and dye exclusion assays were performed to analyze the effect of EGCG on the viability of gastric epithelial cells. The degree of DNA damage was evaluated by Comet assay and apoptotic DNA fragmentation assay. To investigate the effect of EGCG on H. pylori-induced toll-like receptor 4 (TLR-4) signaling, reverse transcription-polymerase chain reaction and Western blot analysis corresponding to glycosylated TLR-4 were carried out. Lipoxygenase metabolites were measured with reverse-phase, high-performance liquid chromatography.


RESULTS
EGCG pretreatment effectively rescued gastric mucosal cells from the H. pylori-induced apoptotic cell death and DNA damage, and administration of this catechin enhanced gastric epithelial cell proliferation. Helicobacter pylori infection stimulated the glycosylation of TLR-4, which initiates intracellular signaling in the infected host cell, but the pretreatment with EGCG completely blocked the TLR-4 glycosylation. The blockage of TLR-4 activation by EGCG resulted in inactivation of extracellular signal response kinase 1/2 and of nuclear factor-kappaB, the downstream molecules of TLR-4 signaling induced by H. pylori. This disturbance of H. pylori-induced host cell signaling by EGCG attenuated the synthesis of the proinflammatory mediator, hydroxyeicosatetraenoic acid.


CONCLUSIONS
EGCG pretreatment showed significant cytoprotective effects against H. pylori-induced gastric cytotoxicity via interference of the TLR-4 signaling induced by H. pylori. Thus, our result implies that continuous intakes of green tea could prevent the deleterious consequences of H. pylori infection.
Lee
Kee-Myung
KM
Genomic Research Center for Gastroenterology, Department of Gastroenterology, Ajou University School of Medicine, Suwon, Korea.
Yeo
Marie
M
Choue
Jung-Sun
JS
Jin
Joo-Hyun
JH
Park
Soo Jin
SJ
Cheong
Jae-Youn
JY
Lee
Kwang Jae
KJ
Kim
Jin-Hong
JH
Hahm
Ki-Baik
KB
D017209:Apoptosis / Q000187:drug effects; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005753:Gastric Mucosa / Q000187:drug effects / Q000382:microbiology; D006031:Glycosylation / Q000187:drug effects; D016480:Helicobacter pylori / Q000187:drug effects*; D006801:Humans; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects*; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D011956:Receptors, Cell Surface; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D002392:Catechin; C045651:epigallocatechin gallate; D048052:Mitogen-Activated Protein Kinase 3; D048370:MAP Kinase Kinase 2