Role of Helicobacter pylori infection in gastric cancer pathogenesis: a chance for prevention

New advances in targeted gastric cancer treatment

Despite a decrease in incidence over past decades, gastric cancer remains a major global health problem. In the more recent period, survival has shown only minor improvement, despite significant advances in diagnostic techniques, surgical and chemotherapeutic approaches, the development of novel therapeutic agents and treatment by multidisciplinary teams. Because multiple genetic mutations, epigenetic alterations, and aberrant molecular signalling pathways are involved in the development of gastric cancers, recent research has attempted to determine the molecular heterogeneity responsible for the processes of carcinogenesis, spread and metastasis. Currently, some novel agents targeting a part of these dysfunctional molecular signalling pathways have already been integrated into the standard treatment of gastric cancer, whereas others remain in phases of investigation within clinical trials. It is essential to identify the unique molecular patterns of tumours and specific biomarkers to develop treatments targeted to the individual tumour behaviour. This review analyses the global impact of gastric cancer, as well as the role of Helicobacter pylori infection and the efficacy of bacterial eradication in preventing gastric cancer development. Furthermore, the paper discusses the currently available targeted treatments and future directions of research using promising novel classes of molecular agents for advanced tumours.

Pepsinogens to Distinguish Patients With Gastric Intestinal Metaplasia and Helicobacter pylori Infection Among Populations at Risk for Gastric Cancer

OBJECTIVES

The objectives of this study were to investigate the serum pepsinogen test for the prediction of OLGIM (Operative Link on Gastric Intestinal Metaplasia Assessment) stages in first-degree relatives (FDR-GC) of patients with gastric cancer (GC) and autoimmune chronic atrophic gastritis (ACAG).

METHODS

In 67 consecutive patients with ACAG, 82 FDR-GC, and 53 controls (CTRL) without gastric disease (confirmed by biopsy), serum levels of pepsinogen 1 (PG1), pepsinogen 2 (PG2), G17, and the PG1/2 ratio were assessed by enzyme-linked immunosorbent assay kit. All ACAG patients had positive antiparietal cell antibody levels, estimated by indirect immunofluorescence. Biopsies taken in duplicate from the antrum, corpus, and fundus were stained with Giemsa for Helicobacter pylori detection. Endoscopic detection of metaplasia was confirmed by histological diagnosis. Histological classification of OLGIM stages was applied by using the criteria of severity and topography of intestinal metaplasia (IM).

RESULTS

The highest discrimination capacity for distinguishing ACAG from other groups of patients was the gastrin G17 test. The lowest mean for PG1 and PG2 serum levels was found in ACAG. In multivariate analysis by age, PG1 and PG1/PG2 were independent prognostic factors for metaplasia, and PG2 also for the presence of a histological H. pylori infection. The serum PG1 level was significantly lower in individuals with IM at OLGIM stage >2 than in those with IM at OLGIM stage <2, resulting in a useful method for the prediction of OLGIM stage. With the inclusion of patient age at diagnosis in the prediction of ≥2 vs. 0-1 OLGIM stages, the receiver operating characteristic (ROC) curve at 47.9 ng/ml PG1 level reached a significant area under the curve (AUC) value (0.978, P<0.001). We also observed a slight difference in PG2 serum levels between histological H. pylori-positive and H. pylori-negative subjects (ROC AUC: 0.599).

CONCLUSIONS

This study demonstrated an important increase in gastrin G17 serum level in autoimmune gastritis. PG1 serum level corrected by patient age can be used in the management of patients at risk for GC with a high predicted probability of having an OLGIM stage ≥2. Using a cutoff of 47.9 ng/ml, PG1 testing in FDR-GC and ACAG patients had a sensitivity of 95.83% and a specificity of 93.37. Although these results could be validated in a prospective study, the known importance of higher OLGIM stages in increasing the risk of GC development supports the rationale of proposing PG1 algorithm as a diagnostic tool for the selection of high-risk FDR-GC and ACAG patients at high-risk stages for subsequent detailed endoscopic examination to detect dysplasia and asymptomatic GC. In addition, serum PG1 and PG2 levels could stratify patients based on both H. pylori infection and OLGIM risk in consideration of the increased acknowledge regarding the role of H. pylori in the progression of gastritis to GC.

Association of THBS1 rs1478605 T>C in 5'-untranslated regions with the development and progression of gastric cancer

Thrombospondin 1 (THBS1) plays an important role in angiogenesis and tumor progression. The aim of the present study was to investigate the effects of single-nucleotide polymorphisms (rs1478605 and rs3743125) in the untranslated regions of the THBS1 gene on the development and progression of gastric cancer. In the case-control study, 275 gastric cancer patients and 275 cancer-free controls were successfully genotyped using polymerase chain reaction-restriction fragment length polymorphism. The data demonstrated that THBS1 rs1478605 genotypic distributions significantly differed between the patient and control groups (P=0.005). Carriers of the CC genotype exhibited a decreased risk of developing gastric cancer compared to the carriers of the CT and TT genotypes [adjusted odd ratio (OR), 0.56; 95% confidence interval (CI), 0.39-0.79; P=0.001]. The CC genotype of rs1478605 was negatively associated with gastric cancer lymph node metastasis (OR, 0.41; 95% CI, 0.23-0.71; P=0.001) and was associated with a reduced risk of lymph node metastasis in male patients (OR, 0.27; 95% CI, 0.14-0.52; P<0.001). The THBS1 CT haplotype was associated with a reduced risk of developing gastric cancer (OR, 0.56; 95% CI, 0.33-0.93; P=0.02). By contrast, no association was observed between THBS1 rs3743125 and the development and progression of gastric cancer. These results suggest that THBS1 rs1478605 represents a potential molecular marker for gastric cancer.

Virulence Factors of Helicobacter pylori: A Review

Helicobacter pylori is a spiral-shaped Gram-negative bacterium that colonizes the human stomach and can establish a long-term infection of the gastric mucosa, a condition that affects the relative risk of developing various clinical disorders of the upper gastrointestinal tract, such as chronic gastritis, peptic ulcer disease, mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric adenocarcinoma. H. pylori presents a high-level of genetic diversity, which can be an important factor in its adaptation to the host stomach and also for the clinical outcome of infection. There are important H. pylori virulence factors that, along with host characteristics and the external environment, have been associated with the different occurrences of diseases. This review is aimed to analyzing and summarizing the main of them and possible associations with the clinical outcome.

Helicobacter pylori in humans: Where are we now?

Helicobacter pylori has been associated with colonization of gastro duodenal mucosa of humans from millions of years. The main burden of the disese is in the developing countries, due to overcrowding and poor hygiene. If left untreated it leads to lot of sequlae from minor to sinister diseases over a period of time. The main challenges that remain are prevention of H. pylori-related diseases by effective treatment and screening procedures and development of a vaccine, which can address all these issues including beneficial aspects of H. pylori. The literature pertaining to different aspects of H. pylori were scrutinized from Pubmed. Material on clinical behavior, complications of chronic gastric involvement, and prevention besides role of H. pylori in nongastric diseases and the latest trends of management was collected for research and review. We continue to face many challenges. The prevention of cancer of the stomach, a worst sequlae of H. pylori continues to be a big challenge despite population screening and prevention surveys being underway in many countries. On the other hand continued scientific work has now unfolded involvement of H. pylori in extragastric diseases like cerebrovascular, cardiovascular, idiopathic thrombocytopenia, sideroblastic anemia, mental diseases, and collagen vascular diseases. In contrast, the beneficial effects of H. pylori with respect to allergic diseases and obesity are now clear. Moreover, problem of drug resistance for eradication of H. pylori has arisen for which novel treatments are being tried. Lactobacillus reuteri having anti H. pylori action is emerging as one of the promising treatment.

Lack of an association between the XRCC1 Arg399Gln polymorphism and gastric cancer based on a meta-analysis

Association between the XRCC1 Arg399Gln polymorphism and susceptibility to gastric cancer has been investigated; overall, the results have been inconclusive. We made a meta-analysis of 13 case-control studies, including 3278 cases and 6243 controls. Crude odds ratios (OR) with 95% confidence intervals (95%CI) were used to assess this possible association. We found no evidence of a significant association between the XRCC1 Arg399Gln polymorphism and gastric cancer risk (in the additive inheritance model, OR = 0.986, 95%CI = 0.831-1.156, in the dominant inheritance model, OR = 1.044, 95%CI = 0.890-1.224 and in the recessive inheritance model, OR = 0.975, 95%CI = 0.894-1.063). We conclude that the XRCC1 Arg399Gln polymorphism is not a risk factor for developing gastric cancer.

Eradication Treatment of Helicobacter pylori Infection: Its Importance and Possible Relationship in Preventing the Development of Gastric Cancer

Helicobacter pylori is the most important carcinogen for gastric adenocarcinoma. Bacterial virulence factors are essential players in modulating the immune response involved in the initiation of carcinogenesis in the stomach; host genetic factors contribute to the regulation of the inflammatory response and to the aggravation of mucosal damage. In terms of environmental factors, salt intake and smoking contribute to the development of lesions. Various therapeutic schemes are proposed to eradicate H. pylori infection, which could potentially prevent gastric cancer, offering the greatest benefit if performed before premalignant changes of the gastric mucosa have occurred.

Structural and biochemical characterization of HP0315 from Helicobacter pylori as a VapD protein with an endoribonuclease activity

VapD-like virulence-associated proteins have been found in many organisms, but little is known about this protein family including the 3D structure of these proteins. Recently, a relationship between the Cas2 family of ribonucleases associated with the CRISPR system of microbial immunity and VapD was suggested. Here, we show for the first time the structure of a member of the VapD family and present a relationship of VapD with Cas2 family and toxin-antitoxin (TA) systems. The crystal structure of HP0315 from Helicobacter pylori was solved at a resolution of 2.8 Å. The structure of HP0315, which has a modified ferredoxin-like fold, is very similar to that of the Cas2 family. Like Cas2 proteins, HP0315 shows endoribonuclease activity. HP0315-cleaved mRNA, mainly before A and G nucleotides preferentially, which means that HP0315 has purine-specific endoribonuclease activity. Mutagenesis studies of HP0315 revealed that D7, L13, S43 and D76 residues are important for RNase activity, in contrast, to the Cas2 family. HP0315 is arranged as an operon with HP0316, which was found to be an antitoxin-related protein. However, HP0315 is not a component of the TA system. Thus, HP0315 may be an evolutionary intermediate which does not belong to either the Cas2 family or TA system.

Animal models of gastric cancer

Gastric cancer is the second most common cause of cancer-related mortality (9.7% of the total) worldwide. Gastric carcinogenesis is a multiple-step process that involves multiple factors, such as bacteria, immune response and host factors. Animal models play a crucial role in the research of the biological behavior, diagnosis and treatment of gastric cancer. In this article we will review current advances in the development of animal models of gastric cancer in terms of microorganism-induced models, chemical carcinogen-induced models, tumor cell implantation, genetically modified models and in silico models.

Antigenic diversity among Portuguese clinical isolates of Helicobacter pylori

BACKGROUND

 The human gastroduodenal pathogen, Helicobacter pylori, is characterized by an unusual extent of genetic heterogeneity. This dictates differences in the antigenic pattern of strains resulting in heterogeneous human humoral immune responses. Here, we examined the antigenic variability among a group of 10 strains isolated from Portuguese patients differing in age, gender, and H. pylori-associated gastric diseases.

MATERIAL AND METHODS

 Immunoassays were performed on two-dimensional electrophoresis gels obtained for the proteome of each strain, using a commercial pool of antibodies produced in rabbit, against the whole cell lysate of an Australian H. pylori strain. Relevant proteins were identified by mass spectrometry.

RESULTS

Immunoproteomes of the Portuguese strains showed no correlation between the number of antigenic proteins or the antigenic profile, and the disease to which each strain was associated. The Heat shock protein B was the unique immunoreactive protein common to all of them. Additionally, seven proteins were found to be antigenic in at least 80% of strains: enoyl-(acyl-carrier-protein) reductase (NADH); Catalase; Flagellin A; 2 isoforms of alkyl hydroperoxide reductase; succinyl-CoA transferase subunit B; and an unidentified protein. These proteins were present in the proteome of all tested strains, suggesting that differences in their antigenicity are related to antigenic variance.

CONCLUSIONS

 This study showed evidence of the variability of antigenic pattern among H. pylori strains. We believe that this fact contributes to the failure of anti-H. pylori vaccines and the low accuracy of serological tests based on a low number of proteins or antigens of only one strain.

Could Malassezia yeasts be implicated in skin carcinogenesis through the production of aryl-hydrocarbon receptor ligands?

Malassezia yeasts are found on the skin of all humans and many warm-blooded animals. In vitro they have the ability to synthesize potent ligands (indolo[3,2-b]carbazole, malassezin and indirubin) of the aryl-hydrocarbon receptor (AhR; synonym: dioxin receptor) when the sweat contained L-tryptophan is used as the single nitrogen source. The production of these AhR-ligands has been associated with pathogenic strains of a certain Malassezia species (Malassezia furfur) but recent evidence shows that this property is widely distributed in almost all currently known Malassezia species. AhR is associated with carcinogenesis and the potential connection of these ubiquitous skin symbionts, and putative pathogens, with skin neoplasia should be evaluated mainly focusing on mechanisms related to the distinctive ability of the yeast to produce potent AhR ligands.

HYPOTHESIS

Synthesis of available pertinent data show a possible link between Malassezia produced AhR ligands and skin carcinogenesis, particularly of basal cell carcinoma (BCC). BCCs are almost exclusively observed in animal species colonized by Malassezia. In humans and animals there is overlapping in the skin regions colonized by this yeast and affected by BCC. The potent AhR ligands synthesized by pathogenic Malassezia strains could contribute to tumor promotion by: modification of the UV radiation carcinogenesis, alterations in the salvage/survival of initiated tumor cells, inhibition of cell senescence, interaction with vitamin D metabolism, promotion of immune tolerance and finally pro-carcinogenic modulation of cell cycle progression and apoptosis.

Helicobacter pylori infection and current clinical areas of contention

PURPOSE OF REVIEW

The indication for Helicobacter pylori (H. pylori) eradication has been extended to few extragastroduodenal diseases. Scientific rigor needs to be applied as the list of clinical manifestations potentially related to H. pylori has disproportionally grown to its scientific evidence. Some potential beneficial aspects of H. pylori in allergic diseases and in the context of obesity are critically addressed in this review. The main challenge, however, continues to be the prevention of gastric cancer by H. pylori eradication. Strategies for identification of individuals and populations at risk are reported as well. A final aspect is dedicated to novel treatment regimens for overcoming the increasing treatment failures with proton pump inhibitor-based triple standards.

RECENT FINDINGS

H. pylori infection is associated with some extragastric diseases such as idiopathic thrombocytic purpura and iron deficiency anemia that benefit from eradication therapy. The inverse relation of H. pylori prevalence and the increase in allergies and obesity, as reported from epidemiological studies, has prompted research for elucidating potential underlying pathophysiological mechanisms. Strategies for gastric cancer prevention include serological screening, which allow adopting eradication therapy in individuals at high risk. New treatments for H. pylori include sequential, bismuth-based quadruple and nonbismuth-based quadruple therapies.

SUMMARY

The main clinical challenge remains prevention of H. pylori-related diseases by effective treatment and screening procedures.

Clinical aspects of gastric cancer and Helicobacter pylori--screening, prevention, and treatment

Gastric cancer still represents a global health care burden, and in the absence of strategies implemented for early detection, the disease continues to have a dismal prognosis. Patients presenting with clinical manifestations of gastric cancer have limited options for cure. Thus, early detection and prevention play a key role in the fight against gastric cancer. Serologic-based test methods have the potential to detect a subset of patients at high risk of gastric cancer that require a close clinical and endoscopic follow-up. More data have been produced to support Helicobacter pylori eradication as an efficient strategy to prevent gastric cancer. Treatment options for patients with an advanced disease are still limited, but the introduction of new agents opens a more optimistic perspective for the future.