Influence of Helicobacter pylori infection on the expression of MLH1 and MGMT in patients with chronic gastritis and gastric cancer

Decoding the Key Functional Combined Components Group and Uncovering the Molecular Mechanism of Longdan Xiegan Decoction in Treating Uveitis

Objective

Longdan Xiegan Decoction (LXD) is a famous herbal formula in China. It has been proved that LXD has been shown to have a significant inhibitory effect on suppresses the inflammatory cells associated with uveitis. However, the key functional combination of component groups and their possible mechanisms remain unclear.

Methods

The community detecting model of the network, the functional response space, and reverse prediction model were utilized to decode the key components group (KCG) and possible mechanism of LXD in treating uveitis. Finally, MTT assay, NO assay and ELISA assay were applied to verify the effectiveness of KCG and the accuracy of our strategy.

Results

In the components-targets-pathogenic genes-disease (CTP) network, a combination of Huffman coding and random walk algorithm was used and eight foundational acting communities (FACs) were discovered with important functional significance. Verification has shown that FACs can represent the corresponding C-T network for treating uveitis. A novel node importance calculation method was designed to construct the functional response space and pick out 349 effective proteins. A total of 54 components were screened and defined as KCG. The pathway enrichment results showed that KCG and their targets enriched signal pathways of IL-17, Toll-like receptor, and T cell receptor played an important role in the pathogenesis of uveitis. Furthermore, experimental verification results showed that important KCG quercetin and sitosterol markedly inhibited the production of nitric oxide and significantly regulated the level of TNF-α and IFN-γ in Lipopolysaccharide-induced RAW264.7 cells.

Discussion

In this research, we decoded the potential mechanism of the multi-components-genes-pathways of LXD’s pharmacological action mode against uveitis based on an integrated pharmacology approach. The results provided a new perspective for the future studies of the anti-uveitis mechanism of traditional Chinese medicine.

Helicobacter pylori Eradication Modulates Aberrant CpG Island Hypermethylation in Gastric Carcinogenesis

Background/Aims

Helicobacter pylori infection induces aberrant DNA methylation in gastric mucosa. We evaluated the long-term effect of H. pylori eradication on promotor CpG island hypermethylation in gastric carcinogenesis.

Methods

H. pylori-positive patients with gastric adenoma or early gastric cancer who underwent endoscopic resection were enrolled. According to H. pylori eradication after endoscopic resection, the participants were randomly assigned to H. pylori eradication or non-eradication group. H. pylori-negative gastric mucosa from normal participants provided the normal control. CpG island hypermethylation of tumor-related genes (p16, CDH1, and RUNX-3) was evaluated by quantitative MethyLight assay in non-tumorous gastric mucosa. The gene methylation rate and median values of hypermethylation were compared after one year by H. pylori status.

Results

In H. pylori-positive patients, hypermethylation of p16 was found in 80.6%, of CDH1 in 80.6%, and of RUNX-3 in 48.4%. This is significantly higher than normal control (p16, 10%; CDH1, 44%; RUNX-3, 16%) (p<0.05). In the H. pylori eradication group, methylation rates of p16 and CDH1 decreased in 58.1% and 61.3% of the patients, and the median values of hypermethylation were significantly lower at one year compared with the non-eradication group. However, RUNX-3 hypermethylation did not differ significantly at one year after H. pylori eradication. The non-eradication group hypermethylation did not change after one year.

Conclusions

H. pylori infection was associated with promotor hypermethylation of genes in gastric carcinogenesis, and H. pylori eradication might reverse p16 and CDH1 hypermethylation.

Epigenetic regulation of DNA repair machinery in Helicobacter pylori-induced gastric carcinogenesis

Although thousands of DNA damaging events occur in each cell every day, efficient DNA repair pathways have evolved to counteract them. The DNA repair machinery plays a key role in maintaining genomic stability by avoiding the maintenance of mutations. The DNA repair enzymes continuously monitor the chromosomes to correct any damage that is caused by exogenous and endogenous mutagens. If DNA damage in proliferating cells is not repaired because of an inadequate expression of DNA repair genes, it might increase the risk of cancer. In addition to mutations, which can be either inherited or somatically acquired, epigenetic silencing of DNA repair genes has been associated with carcinogenesis. Gastric cancer represents the second highest cause of cancer mortality worldwide. The disease develops from the accumulation of several genetic and epigenetic changes during the lifetime. Among the risk factors, Helicobacter pylori (H. pylori) infection is considered the main driving factor to gastric cancer development. Thus, in this review, we summarize the current knowledge of the role of H. pylori infection on the epigenetic regulation of DNA repair machinery in gastric carcinogenesis.

MGMT and MLH1 methylation in Helicobacter pylori-infected children and adults

AIM

To evaluate the association between Helicobacter pylori (H. pylori) infection and MLH1 and MGMT methylation and its relationship with microsatellite instability (MSI).

METHODS

The methylation status of the MLH1 and MGMT promoter region was analysed by methylation specific methylation-polymerase chain reaction (MSP-PCR) in gastric biopsy samples from uninfected or H. pylori-infected children (n = 50), from adults with chronic gastritis (n = 97) and from adults with gastric cancer (n = 92). MLH1 and MGMT mRNA expression were measured by real-time PCR and normalised to a constitutive gene (β actin). MSI analysis was performed by screening MSI markers at 4 loci (Bat-25, Bat-26, D17S250 and D2S123) with PCR; PCR products were analysed by single strand conformation polymorphism followed by silver staining. Statistical analyses were performed with either the χ(2) test with Yates continuity correction or Fisher's exact test, and statistical significance for expression analysis was assessed using an unpaired Student's t-test.

RESULTS

Methylation was not detected in the promoter regions of MLH1 and MGMT in gastric biopsy samples from children, regardless of H. pylori infection status. The MGMT promoter was methylated in 51% of chronic gastritis adult patients and was associated with H. pylori infection (P < 0.05); this region was methylated in 66% of gastric cancer patients, and the difference in the percentage of methylated samples between these patients and those from H. pylori-infected chronic gastritis patients was statistically significant (P < 0.05). MLH1 methylation frequencies among H. pylori-infected and non-infected chronic gastritis adult patients were 13% and 7%, respectively. We observed methylation of the MLH1 promoter (39%) and increased MSI levels (68%) in samples from gastric cancer patients in comparison to samples from H. pylori-infected adult chronic gastritis patients (P < 0.001 and P < 0.01, respectively). The frequency of promoter methylation for both genes was higher in gastric cancer samples than in H. pylori-positive chronic gastritis samples (P < 0.05). The levels of MLH1 and MGMT mRNA were significantly reduced in chronic gastritis samples that were also hypermethylated (P < 0.01).

CONCLUSION

In summary, MGMT and MLH1 methylation did not occur in earlier-stage H. pylori infections and thus might depend on the duration of infection.

Emerging avenues linking inflammation and cancer

The role of inflammation in carcinogenesis has been extensively investigated and well documented. Many biochemical processes that are altered during chronic inflammation have been implicated in tumorigenesis. These include shifting cellular redox balance toward oxidative stress; induction of genomic instability; increased DNA damage; stimulation of cell proliferation, metastasis, and angiogenesis; deregulation of cellular epigenetic control of gene expression; and inappropriate epithelial-to-mesenchymal transition. A wide array of proinflammatory cytokines, prostaglandins, nitric oxide, and matricellular proteins are closely involved in premalignant and malignant conversion of cells in a background of chronic inflammation. Inappropriate transcription of genes encoding inflammatory mediators, survival factors, and angiogenic and metastatic proteins is the key molecular event in linking inflammation and cancer. Aberrant cell signaling pathways comprising various kinases and their downstream transcription factors have been identified as the major contributors in abnormal gene expression associated with inflammation-driven carcinogenesis. The posttranscriptional regulation of gene expression by microRNAs also provides the molecular basis for linking inflammation to cancer. This review highlights the multifaceted role of inflammation in carcinogenesis in the context of altered cellular redox signaling.

When bacteria become mutagenic and carcinogenic: lessons from H. pylori

More and more convincing data link bacteria to the development of cancers. How bacteria act as mutagens by altering host genomes, what are the different strategies they develop and what consequences do they have on infection-associated pathogenesis are the main questions addressed in this review, which focuses in particular on Helicobacter pylori infection. H. pylori is a major risk factor for gastric cancer development. Its oncogenic role is mediated by the chronic active inflammation it elicits in the gastric mucosa, associated with its capacity to persistently colonize the human stomach. However, direct genotoxicity of H. pylori through the action of bacterial cytotoxin or resulting from a DNA damaging effect of its metabolic derivatives as nitroso compounds cannot be excluded. Numerous studies have investigated inflammation-associated DNA damaging activity and mutagenic response due to H. pylori infection in both human and animal models. Recent findings on its mutagenic effects at the nuclear and mitochondrial genome and related DNA damage are reviewed. This genotoxic activity associated with oxidative species produced during inflammation is linked to the decreased efficiency of DNA repair systems. DNA methylation, which plays an important role in the regulation of the host response to H. pylori infection, is also documented. Furthermore, H. pylori affects genome integrity by increasing activation-induced cytidine deaminase (AID), a DNA/RNA editing cytidine deaminase linking mutagenesis and tumorigenesis. These different strategies occurring during bacteria-host cell interaction, lead to nucleotide modifications and genome instabilities recognized as early events in the carcinogenesis process and contribute to the oncogenic properties of H. pylori infection.

CpG methylation and reduced expression of O6-methylguanine DNA methyltransferase is associated with Helicobacter pylori infection

BACKGROUND & AIMS

The gastric epithelium genome undergoes extensive epigenetic alterations during Helicobacter pylori-induced gastritis. Expression of the gene encoding the DNA repair protein O6-methylguanine DNA methyltransferase (MGMT) might be reduced via hypermethylation of its promoter in patients with H pylori gastritis. We characterized expression of MGMT and its epigenetic regulation via CpG methylation in gastric tissue from patients with H pylori gastritis and investigated the effects of H pylori infection eradication on MGMT expression.

METHODS

Gastric biopsy samples were collected from patients with H pylori gastritis before and after eradication and from H pylori-negative control subjects. AGS cells were cocultured with H pylori to study the effects of H pylori infection on MGMT RNA, protein expression, and CpG methylation.

RESULTS

CpG methylation of MGMT was more frequent in the gastric mucosa of patients with H pylori gastritis (69.7%) than in those without (28.6%, P = .022). MGMT methylation was significantly reduced after H pylori eradication (from 70% to 48% of cases, P = .039), and mean levels of CpG methylation decreased from 12.6% to 5.7% (P = .025), increasing MGMT expression. MGMT methylation was significantly associated with CagA-positive H pylori (P = .035). H pylori reduced MGMT protein and RNA levels and induced MGMT CpG methylation in gastric AGS cells.

CONCLUSIONS

H pylori gastritis, particularly in patients infected with H pylori CagA-positive strains, is associated with hypermethylation of MGMT and reduced levels of MGMT in the gastric epithelium. MGMT promoter methylation is partially reversible after eradication of H pylori infection. These data indicate that DNA repair is disrupted during H pylori gastritis, increasing mutagenesis in H pylori-infected gastric mucosa.