Association between Helicobacter pylori and gastric cancer: current knowledge and future research

Treatment of Helicobacter pylori and prevention of gastric cancer

Gastric cancer is the second commonest fatal malignancy in the world with a high incidence in China. Helicobacter pylori infection is an important factor in the pathogenesis of gastric cancer. Epidemiological studies have shown a strong causal relationship between H. pylori infection and gastric cancer. Animal studies also show that eradication of H. pylori infection, especially at the early stage, is effective in preventing H. pylori-related gastric carcinogenesis. H. pylori eradication leads to regression and prevents the progression of gastric precancerous lesions, but only in a minority of cases. H. pylori eradication appears to be the most promising approach in gastric cancer prevention. The current available data in human studies showed that H. pylori eradication can reduce the risk of developing gastric cancer and this strategy is more useful in patients without atrophic gastritis or intestinal metaplasia. A longer follow-up and additional studies are needed for better understanding this issue.

Helicobacter pylori eradication for gastric cancer prevention

Gastric cancer is the second most common fatal malignancy in the world. Its incidence is high in East Asia. Helicobacter pylori infection is an important factor in the pathogenesis of gastric cancer. Epidemiological studies have established a strong causal relationship between H. pylori infection and gastric cancer. H. pylori eradication is therefore likely to be one of the most promising approaches to gastric cancer prevention. Animal studies have shown that eradication of H. pylori infection, especially at the early stage, is effective in preventing H. pylori-related gastric carcinogenesis. However, the available data from human studies show that H. pylori eradication does not completely prevent gastric cancer and that it might be useful only in patients without atrophic gastritis or intestinal metaplasia at baseline. Longer follow-up and additional studies are needed to clarify this issue.

The best method of detecting prior Helicobacter pylori infection

AIM

Prior Helicobacter pylori (H pylori) infection has often been underestimated. These underestimations have misled physicians attempting to determine the significance between H pylori and certain gastrointestinal lesions such as intestinal metaplasia, atrophic gastritis, and gastric cancer. Our study endeavored to detect past H pylori infections accurately, easily, and rapidly with the newly developed immunoblot kit, Helico Blot 2.1.

METHODS

Thirty-three patients, including 25 H pylori infected and 8 uninfected cases, were enrolled in our study. All patients received consecutive gastroendoscopic examinations and (13)C-urea breath test (UBT) tests at 6- or 12-mo intervals for up to 4 years. Serum samples were obtained from each patient at the same time. Intragastric H pylori infection was confirmed in accordance with the gold standard. Twenty-five H pylori-infected patients received triple therapies after initial bacterial confirmation, and were successful in eradicating their infections. Serially obtained sera were tested by means of Helico Blot 2.1.

RESULTS

Current infection marker detected by Helico Blot 2.1 was unreliable for representing ongoing H pylori infection. Only 35 and 37 ku antibodies of H pylori had significant seroconversion rates 1 year after having been cured. The seropositive rates of 116 ku (cytotoxin-associated antigen (CagA)) and Helico Blot 2.1 were nearly 100% during 4-year follow-up period. Both CagA antigen and Helico blot 2.1 could serve as indicators of long-term H pylori infection.

CONCLUSION

Helico Blot 2.1 can detect past H pylori infections for up to 4 years, and is the best method to date for detecting previous long-term H pylori infection.

Expression of Helicobacter pylori Hsp60 protein and its immunogenicity

AIM: To express Hsp60 protein of H pylori by a constructed vector and to evaluate its immunogenicity.

METHODS: Hsp60 DNA was amplified by PCR and inserted into the prokaryotie expression vector pET-22b (+), which was transformed into BL21 (DE3) E.coli strain to express recombinant protein. Immunogenicity of expressed Hsp60 protein was evaluated with animal experiments.

RESULTS: DNA sequence analysis showed Hsp60 DNA was the same as GenBank’s research. Hsp60 recombinant protein accounted for 27.2% of the total bacterial protein, and could be recognized by the serum from H pylori infected patients and Balb/c mice immunized with Hsp60 itself.

CONCLUSION: Hsp60 recombinant protein might become a potential vaccine for controlling and treating H pylori infection.

Construction of expression systems for flaA and flaB genes of Helicobacter pylori and determination of immunoreactivity and antigenicity of recombinant proteins

AIM: To clone flagellin genes A (flaA) and B (flaB) from a clinical strain of Helicobacter pylori (H pylori) and to construct prokaryotic expression systems of the genes and identify immunity of the fusion proteins.

METHODS: The flaA and flaB genes from a clinical H pylori isolate Y06 were amplified by high fidelity PCR. The nucleotide sequences of target DNA amplification fragments from the two genes were sequenced after T-A cloning. The recombinant expression vector pET32a inserted with flaA and flaB genes was constructed, respectively. The expressions of FlaA and FlaB fusion proteins in E. coli BL21DE3 induced by isopropylthio-β-D-galactoside (IPTG) at different concentrations were examined by SDS-PAGE. Western blot using commercial antibodies against whole cell of H pylori and immunodiffusion assay using self-prepared rabbit antiserum against FlaA (rFlaA) or FlaB (rFlaB) recombinant proteins were applied to the determination of the fusion proteins immunity. ELISA was used to detect the antibodies against rFlaA and rFlaB in sera of 125 H pylori infected patients and to examine rFlaA and rFlaB expression in 98 clinical isolates of H pylori, respectively.

RESULTS: In comparison with the reported corresponding sequences, the nucleotide sequence homologies of the cloned flaA and flaB genes were from 96.28%-97.13% and 96.31%-97.73%, and their putative amino acid sequence homologies were 99.61%-99.80% and 99.41%-100% for the two genes, respectively. The output of rFlaA and rFlaB expressed by pET32a-flaA-BL21DE3 and pET32a-flaB-BL21DE3 systems was as high as 40%-50% of the total bacterial proteins. Both rFlaA and rFlaB were able to combine with the commercial antibodies against whole cell of H pylori and to induce rabbits to produce specific antibodies with the same 1:2 immunodiffusion titers after the animals were immunized with the two recombinant proteins. Ninety-eight and zero point 4 and 92.80% of the serum samples from 125 patients infected with H pylori were positive for rFlaA and rFlaB antibodies, respectively. One hundred percent and 98.98% of the 98 tested isolates of H pylori were detectable for rFlaA and rFlaB epitopes, respectively.

CONCLUSION: Two prokaryotic expression systems with high efficiency of H pylori flaA and flaB genes were successfully established. The expressed rFlaA and rFlaB showed satisfactory immunoreactivity and antigenicity. High frequencies of FlaA and FlaB expression in different H pylori clinical strains and the general existence of specific antibodies against FlaA and FlaB in H pylori infected patients strongly indicate that FlaA and FlaB are excellent antigen candidates for developing H pylori vaccine.

Construction of hpaA gene from a clinical isolate of Helicobacter pylori and identification of fusion protein

AIM: To clone hpaA gene from a clinical strain of Helicobacter pylori and to construct the expression vector of the gene and to identify immunity of the fusion protein.

METHODS: The hpaA gene from a clinical isolate Y06 of H. pylori was amplified by high fidelity PCR. The nucleotide sequence of the target DNA amplification fragment was sequenced after T-A cloning. The recombinant expression vector inserted with hpaA gene was constructed. The expression of HpaA fusion protein in E.coli BL21(DE3) induced by IPTG at different dosages was examined by SDS-PAGE. Western blot with commercial antibody against whole cell of H. pylori as well as immunodiffusion assay with self-prepared rabbit antiserum against HpaA fusion protein were applied to determine immunity of the fusion protein. ELISA was used to detect the antibody against HpaA in sera of 125 patients infected with H. pylori and to examine HpaA expression of 109 clinical isolates of H. pylori.

RESULTS: In comparison with the reported corresponding sequences, the homologies of nucleotide and putative amino acid sequences of the cloned hpaA gene were from 94.25%-97.32% and 95.38%-98.46%, respectively. The output of HpaA fusion protein in its expression system of pET32a-hpaA-BL21(DE3) was approximately 40% of the total bacterial proteins. HpaA fusion protein was able to combine with the commercial antibody against whole cell of H. pylori and to induce rabbit producing specific antiserum with 1:4 immunodiffusion titer after the animal was immunized with the fusion protein. 81.6% of the serum samples from 125 patients infected with H. pylori (102/125) were positive for HpaA antibody and all of the tested isolates of H. pylori (109/109) were detectable for HpaA.

CONCLUSION: A prokaryotic expression system with high efficiency of H. pylorihpaA gene was successfully established. The HpaA expressing fusion protein showed satisfactory immunoreactivity and antigenicity. High frequencies of HpaA expression in different H. pylori clinical strains and specific antibody production in H. pylori infected patients indicate that HpaA is an excellent and ideal antigen for developing H. pylori vaccine.

Overexpression of c-fos in Helicobacter pylori-induced gastric precancerosis of Mongolian gerbil

AIM: To explore dysregulation of c-fos in several human malignancies, and to further investigate the role of c-fos in Helicobacter pylori (H. pylori)-induced gastric precancerosis.

METHODS: Four-week-old male Mongolian gerbils were employed in the study. 0.5 mL 1 × 10⁸ cfu·L^-1 suspension of H. pylori NCTC 11637 in Brucella broth were inoculated orally into 20 Mongolian gerbils. Another 20 gerbils were inoculated with Brucella broth as controls. 10 of the infected gerbils and 10 of the non-infected control gerbils were sacrificed at 25 and 45 weeks after infection. The stomach of each gerbil was removed and opened for macroscopic observation. The expression of c-fos was analyzed by RT-PCR and immunohistochemical studies in H. pylori-induced gastric precancerosis of Mongolian gerbil. Half of each gastric antrum mucosa was dissected for RNA isolation and RT-PCR. β-actin was used as the housekeeping gene and amplified with c-fos as contrast. PCR products of c-fos were analyzed by gel image system and the level of c-fos was reflected with the ratio of c-fos/β-actin. The immunostaining for c-fos was conducted using monoclonal antibody of c-fos and the StreptAvidin-Biotin-enzyme Complex kit.

RESULTS: H. pylori was constantly found in all infected animals in this study. After infection of H. Pylori for 25 weeks, ulcers were observed in the antral and the body of stomach of 60% infected animals (6/10). Histological examination showed that all animals developed severe inflammation, especially in the area close to ulcers, and multifocal lymphoid follicles appeared in the lamina propria and submucosa. After infection of H. Pylori for 45 weeks, severe atrophic gastritis in all infected animals, intestinal metaplasia in 80% infected animals (8/10) and dysplasia in 60% infected animals (6/10) could be observed. C-fos mRNA levels were significantly higher after infection of H. pylori for 25 weeks (1.84 ± 0.79), and for 45 weeks (1.59 ± 0.37) than those in control-animals (0.74 ± 0.22, P < 0.01). C-fos mRNA levels were increased 2.5-fold by 25th week (P < 0.01) and 2.1-fold by 45th week (P < 0.01) in precancerosis induced by H. pylori, when compared with normal gastric epithelium of Mongolian gerbil. Immunohistochemical staining revealed exclusive nuclear staining of c-fos. Furthermore, there was a sequential increase in c-fos positive cells from normal epithelium to precancerosis.

CONCLUSION: The study suggested that overexpression of c-fos occurs relatively early in gastric tumorigenesis in this precancerosis model induced by H. pylori.

Expression of vascular endothelial growth factor and its receptors KDR and Flt-1 in gastric cancer cells

AIM: The expression of vascular endothelial growth factor (VEGF) and its receptors KDR and Flt-1 by gastric carcinoma tissues and different gastric carcinoma cell lines was detected to elucidate the molecular mechanism of this growth factor in promoting tumor growth.

METHODS: The expression of VEGF, Flt-1 and KDR was determined by reverse transcription-polymerase chain reaction (RT-PCR) in gastric cancer cell lines RF-1, RF-48, AGS-1, NCI-N87, NCI-SNU-1, NCI-SNU-5, NCI-SNU-16 and KATO-III. The expression of Flt-1 and KDR in paraffin-embedded specimens of gastric cancer was determined by immunohistochemistry. The 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was used to assess the role of VEGF in tumor cell proliferation.

RESULTS: All 8 gastric cancer cell lines analyzed expressed VEGF₁₂₁ and VEGF₁₆₅ and six of them expressed both Flt-1 and KDR, while cell line NCI-SNU-5 expressed Flt-1 only and cell line KATOIII expressed neither Flt-1 nor KDR. The gastric carcinoma tissues expressed Flt-1 and KDR widely, with the positive rate of expression of Flt-1 and KDR being 84.6% and 70% respectively. The exogenous VEGF stimulated the growth of KDR-positive cell lines NCI-N87 and AGS-1 in a dose-dependent manner but exhibited no effect on the growth of KDR-negative cell line NCI-N87.

CONCLUSION: VEGF and its receptors KDR and Flt-1 were expressed widely in gastric carcinoma cells and the VEGF stimulated KDR-positive tumor cell growth directly. These results suggest that VEGF may play a role in promoting tumor growth and metastasis by participating in both paracrine and autocrine pathways.

Field population-based blocking treatment of esophageal epithelia dysplasia

AIM

To confirm the value of blocking treatment by zenshengping (ZSP), a Chinese herb composite, and Riboflavin for esophageal epithelia dysplasia cases screened out in high risk area in northern china by exfoliative balloon cytology (EBC), so to reduce the incidence rate of esophageal cancer(EC).

METHODS

Esophageal epithelium dysplasia cases including mind esophageal epithelium dysplasia (MEED), stage one severe esophageal epithelium dysplasia (SEED I), and stage two severe esophageal epithelium dysplasia (SEED II) were screened out from people aged 40 years and older in the high risk area of Chixian. These cases were randomly divided into a treatment and control group. Subjects in the treatment and control groups took ZSP, riboflavin, and placebo daily for three years. EC cases registered by cancer registry and identified by EBC re-screening in the treatment and control groups were used to calculate incidence and blocking rates to demonstrate the effects of blocking medication.

RESULTS

It was found that 31.92% and 24.15% of people aged 40 years and older in Cixian could been diagnosed as MEED and SEED cases. The severity of dysplasia increased with age. ZSP had blocked EC occurrence by 47.79% after 3 year medication among the SEED cases.

CONCLUSION

ZSP can block the development from SEED I and SEED II to EC by 47.79%. Efforts should be made to screen and treat dysplasia cases in people aged 40 years and older in high risk areas to reduce the mortality figures.

Methionine-dependence and combination chemotherapy on human gastric cancer cells in vitro

AIM: To elucidate whether human primary gastric cancer and gastric mucosa epithelial cells in vitro can grow normally in a methionine (Met) depleted environment, i.e. Met-dependence, and whether Met-depleting status can enhance the killing effect of chemotherapy on gastric cancer cells.

METHODS: Fresh human gastric cancer and mucosal tissues were managed to form monocellular suspensions, which were then cultured in the Met-free but homocysteine-containing (Met^-Hcy⁺) medium, with different chemotherapeutic drugs. The proliferation of the cells was examined by cell counter, flow cytometry (FCM) and microcytotoxicity assay (MTT).

RESULTS: The growth of human primary gastric cancer cells in Met^-Hcy⁺ was suppressed, manifested by the decrease of total cell counts [1.46 ± 0.42 (× 10⁹•L⁻¹) in Met^-Hcy⁺vs 1.64 ± 0.44 (× 10⁹•L⁻¹) in Met⁺Hcy^-, P < 0.01], the decline in the percentage of G₀G₁ phase cells (0.69 ± 0.24 in Met^-Hcy⁺vs 0.80 ± 0.18 in Met⁺Hcy^-, P < 0.01) and the increase of S cells (0.24 ± 0.20 in Met^-Hcy⁺vs 0.17 ± 0.16 in Met⁺Hcy^-, P < 0.01); however, gastric mucosal cells grew normally. If Met^-Hcy⁺medium was used in combination with chemotherapeutic drugs, the number of surviving gastric cancer cells dropped significantly.

CONCLUSION: Human primary gastric cancer cells in vitro are Met-dependent; however, gastric mucosal cells have not shown the same characteristics. Met^-Hcy⁺ environment may strengthen the killing effect of chemotherapy on human primary gastric cancer cells.

Construction of cDNA representational difference analysis based on two cDNA libraries and identification of garlic inducible expression genes in human gastric cancer cells

AIM: To elucidate molecular mechanism of chemopreventive efficacies of garlic against human gastric cancer (HGC).

METHODS: HGC cell line BGC823 was treated with Allitridi (a kind of garlic extract) and Allitridi-treated and parental BGC823 cDNA libraries were constructed respectively by using λZAP II vector. cDNA Representational Difference Analysis (cDNA RDA) was performed using BamH I cutting-site and abundant cDNA messages provided by the libraries. Northern blot analysis was applied to identify the obtained difference products.

RESULTS: Two specific cDNA fragments were obtained and characterized to be derived from homo sapiens folate receptorα (FRα) gene and calcyclin gene respectively. Northern blot results showed a 4-fold increase in FRα gene expression level and 9-fold increase in calcyclin mRNA level in BGC823 cells after Allitridi treatment for 72 h.

CONCLUSION: The method of cDNA RDA based on cDNA libraries combines the high specificity of cDNA RDA with abundant cDNA messages in cDNA library; this expands the application of cDNA library and increases the specificity of cDNA RDA. Up-regulation of FRα gene and calcyclin gene expressions induced by Allitridi provide valuable molecular evidence for the efficacy garlic in treating HGC as well as other diseases.

Detection of H.pylori DNA in gastric epithelial cells by in situ hybridization

AIM

To investigate the presence of H.pylori DNA within gastric epithelial cells in patients with H.pylori infection and its possible carcinogenic mechanism.

METHODS

Total 112 patients, with pathologically confirmed chronic superficial gastritis, chronic atrophic gastritis, intestinal metaplasia, atypical hyperplasia or gastric cancer were studied. Among them, 28 were H.pylori negative and 84 H.pylori positive. H.pylori DNA in gastric epithelial cells was detected by GenPoint catalyzed signal amplification system for in situ hybridization.

RESULTS

In the H.pylori positive group, zero out of 24 chronic superficial gastritis (0.0%), four out of 25 precancerous changes (16.0%) and thirteen out of 35 gastric cancers (37.1%) showed H.pylori DNA in the nucleus of gastric epithelial cells, the positive rates of H.pylori DNA in the nucleus of gastric epithelial cells were progressively increased in chronic superficial gastritis, precancerous changes and gastric cancer groups (chi(2)=12.56, P=0.002); One out of 24 chronic superficial gastritis (4.2%), eleven out of 25 precancerous changes (44.0%) and thirteen out of 35 gastric cancers (37.1%) showed H.pylori DNA in the cytoplasm of gastric epithelial cells (chi(2)=10.86, P=0.004). In the H.pylori negative group, only one patient with gastric cancer was found H.pylori DNA in the nucleus of gastric epithelial cells; Only two patients, one patient with precancerous changes and another with gastric cancer, showed H.pylori DNA in the cytoplasm of gastric epithelial cells. Furthermore, H.pylori DNA must have been in the cytoplasm as long as it existed in the nucleus of gastric epithelial cells.

CONCLUSION

H.pylori DNA exists both in the nucleus and the cytoplasm of gastric epithelial cells in patients with H.pylori infections. The pathological progression from chronic superficial gastritis, precancerous changes to gastric cancer is associated with higher positive rates of H.pylori DNA presence in the nucleus of gastric epithelial cells.

Overexpression of cyclin E in Mongolian gerbil with Helicobacter pylori- induced gastric precancerosis

AIM: To explore dysregulation of cyclin E in malignancies, and to further investigate the role of cyclin E in Helicobacter pylori (H. pylori)-induced gastric precancerosis.

METHODS: Four-week-old specific pathogen-free male Mongolian gerbils were employed in the study. 0.5 mL 1 × 10⁸ cfu·L^-1 suspension of H. pylori NTCC11637 in Brucella broth was inoculated orally into each of 20 Mongolian gerbils, and a further 20 gerbils were inoculated with Brucella broth as controls. 10 of the infected gerbils and 10 of the non-infected control gerbils were sacrificed at 25, 45 wk after infection. The expression of cyclin E was analyzed by RT-PCR and immunohistochemical studies with monoclonal antibody to cyclin E in Mongolian gerbil of H. pylori-induced gastric precancerosis.

RESULTS: H. pylori was constantly detected in all infected animals throughout the study. At 25 wk after infection of H. pylori. ulcers were observed in the antral and body of stomach (n = 6). Histological examination showed that all animals developed severe inflammation and multifocal lymphoid follicles appeared in the lamina propria and submucosa of gastric antrum. At 45 wk after infection of H. pylori, severe atrophic gastritis (n = 10). intestinal metaplasia (n = 8) and dysplasia (n = 6) could be observed. Cyclin E mRNA levels were significantly more at 25 wk after infection of H. pylori (1.27 ± 0.26), and at 45 wk after infection of H. pylori ( 1.82 ± 0.39) than control-animals (0.59 ± 0.20,P < 0.01); cyclin E mRNA levels were evaluated by 2.2-fold at 25 wk (P < 0.01) and 3.1-fold at 45 wk (P < 0.01) precancerosis induced by H. pylori, when compared with control gastric epithelium of Mongolian gerbil. Immunohistochemical staining revealed exclusive nuclear staining of cyclin E. Furthermore, there was a sequential increase in cyclin E positive cells from normal epithelium to precancerosis.

CONCLUSION: Overexpression of cyclin E occurs relatively early in gastric tumorigenesis in this model.

Glutathione S-transferases M1, T1 genotypes and the risk of gastric cancer: A case-control study

AIM: Glutathione S-transferases (GSTs) are involved in the detoxification of many potential carcinogens and appear to play a critical role in the protection from the effects of carcinogens. The contribution of glutathione S-transferases M1 and T1 genotypes to susceptibility to the risk of gastric cancer and their interaction with cigarette smoking are still unclear. The aim of this study was to determine whether there was any relationship between genetic polymorphisms of GSTM1 and GSTT1 and gastric cancer.

METHODS: A population based case-control study was carried out in a high-risk area, Changle County, Fujian Province, China. The epidemiological data were collected by a standard questionnaire and blood samples were obtained from 95 incidence gastric cancer cases and 94 healthy controls. A polymerase chain reaction method was used to detect the presence or absence of the GSTM1 and GSTT1 genes in genomic DNA. Logistic regression model was employed in the data analysis.

RESULTS: An increase in risk for gastric cancer was found among carriers of GSTM1 null genotype. The adjusted odds ratio (OR) was 2.63 [95% Confidence Interval (95%CI) 1.17-5.88], after controlling for age, gender, cigarette smoking, alcohol drinking, and fish sauce intake. The frequency of GSTT1 null genotype in cancer cases (43.16%) was not significantly different from that in controls (50.00%). However, the risk for gastric cancer in those with GSTM1 null and GSTT1 non-null genotype was significantly higher than in those with both GSTM1 and GSTT1 non-null genotype (OR = 2.77, 95%CI 1.15-6.77). Compared with those subjects who never smoked and had normal GSTM1 genotype, ORs were 1.60 (95%CI: 0.62-4.19) for never smokers with GSTM1 null type, 2.33 (95%CI 0.88-6.28) for smokers with normal GSTM1, and 8.06 (95%CI 2.83-23.67) for smokers with GSTM1 null type.

CONCLUSIONS: GSTM1 gene polymorphisms may be associated with genetic susceptibility of stomach cancer and may modulate tobacco-related carcinogenesis of gastric cancer.