Helicobacter pylori infection and colorectal carcinoma: is there a causal association?

Gut microbiota-derived metabolites in CRC progression and causation

BACKGROUND

Based on recent research reports, dysbiosis and improper concentrations of microbial metabolites in the gut may result into the carcinogenesis of colorectal cancer. Recent advancement also highlights the involvement of bacteria and their secreted metabolites in the cancer causation. Gut microbial metabolites are functional output of the host-microbiota interactions and produced by anaerobic fermentation of food components in the diet. They contribute to influence variety of biological mechanisms including inflammation, cell signaling, cell-cycle disruption which are majorly disrupted in carcinogenic activities.

PURPOSE

In this review, we intend to discuss recent updates and possible molecular mechanisms to provide the role of bacterial metabolites, gut bacteria and diet in the colorectal carcinogenesis. Recent evidences have proposed the role of bacteria, such as Fusobacterium nucleaturm, Streptococcus bovis, Helicobacter pylori, Bacteroides fragilis and Clostridium septicum, in the carcinogenesis of CRC. Metagenomic study confirmed that these bacteria are in increased abundance in CRC patient as compared to healthy individuals and can cause inflammation and DNA damage which can lead to development of cancer. These bacteria produce metabolites, such as secondary bile salts from primary bile salts, hydrogen sulfide, trimethylamine-N-oxide (TMAO), which are likely to promote inflammation and subsequently cancer development.

CONCLUSION

Recent studies suggest that gut microbiota-derived metabolites have a role in CRC progression and causation and hence, could be implicated in CRC diagnosis, prognosis and therapy.

The Bacterial Microbiota of Gastrointestinal Cancers: Role in Cancer Pathogenesis and Therapeutic Perspectives

The microbiota has an essential role in the pathogenesis of many gastrointestinal diseases including cancer. This effect is mediated through different mechanisms such as damaging DNA, activation of oncogenic pathways, production of carcinogenic metabolites, stimulation of chronic inflammation, and inhibition of antitumor immunity. Recently, the concept of "pharmacomicrobiomics" has emerged as a new field concerned with exploring the interplay between drugs and microbes. Mounting evidence indicates that the microbiota and their metabolites have a major impact on the pharmacodynamics and therapeutic responses toward anticancer drugs including conventional chemotherapy and molecular-targeted therapeutics. In addition, microbiota appears as an attractive target for cancer prevention and treatment. In this review, we discuss the role of bacterial microbiota in the pathogenesis of different cancer types affecting the gastrointestinal tract system. We also scrutinize the evidence regarding the role of microbiota in anticancer drug responses. Further, we discuss the use of probiotics, fecal microbiota transplantation, and antibiotics, either alone or in combination with anticancer drugs for prevention and treatment of gastrointestinal tract cancers.

Microbiota, Inflammation and Colorectal Cancer

Colorectal cancer, the fourth leading cause of cancer-related death worldwide, is a multifactorial disease involving genetic, environmental and lifestyle risk factors. In addition, increased evidence has established a role for the intestinal microbiota in the development of colorectal cancer. Indeed, changes in the intestinal microbiota composition in colorectal cancer patients compared to control subjects have been reported. Several bacterial species have been shown to exhibit the pro-inflammatory and pro-carcinogenic properties, which could consequently have an impact on colorectal carcinogenesis. This review will summarize the current knowledge about the potential links between the intestinal microbiota and colorectal cancer, with a focus on the pro-carcinogenic properties of bacterial microbiota such as induction of inflammation, the biosynthesis of genotoxins that interfere with cell cycle regulation and the production of toxic metabolites. Finally, we will describe the potential therapeutic strategies based on intestinal microbiota manipulation for colorectal cancer treatment.

Helicobacter pylori Antibody Reactivities and Colorectal Cancer Risk in a Case-control Study in Spain

Background: Several studies have suggested that Helicobacter pylori (H. pylori) infection is a risk factor for colorectal cancer (CRC), while others have not confirmed this hypothesis. This work aimed to assess the relation of CRC with H. pylori seropositivity and with seropositivity to 16 H. pylori proteins, in the MultiCase-Control study, MCC-Spain.

Methods: MCC-Spain is a multicase-control study carried out in Spain from 2008 to 2013. In total, 2,140 histologically-confirmed incident CRC cases and 4,098 population-based controls were recruited. Controls were frequency-matched by sex, age, and province. Epidemiological data were collected through a questionnaire fulfilled by face-to-face interviews and a self-administered food-frequency questionnaire. Seroreactivities against 16 H. pylori proteins were determined in 1,488 cases and 2,495 controls using H. pylori multiplex serology. H. pylori seropositivity was defined as positivity to ≥4 proteins. Multivariable logistic regression mixed models were used to estimate odds ratios (OR) and 95% confidence intervals (CI).

Results:H. pylori seropositivity was not associated with increased CRC risk (OR = 0.91; 95% CI: 0.71–1.16). Among H. pylori seropositive subjects, seropositivity to Cagδ showed a lower CRC risk, and risk decreased with increasing number of proteins seropositive. Seropositivity to the most recognized virulence factors, CagA and VacA, was not associated with a higher CRC risk. No statistically significant heterogeneity was identified among tumor sites, although inverse relations were stronger for left colon cancer. An interaction with age and sex was found: H. pylori seropositivity was associated with a lower CRC risk in men younger than 65 and with a higher risk in older women.

Conclusions: Our results suggest that neither H. pylori seropositivity, nor seropositivity to the virulence factor CagA are associated with a higher CRC risk. A possible effect modification by age and sex was identified.

Helicobacter Pylori Infection in Texas Hispanic and Non-Hispanic White Men: Implications for Gastric Cancer Risk Disparities

Chronic Helicobacter pylori ( H. pylori) infection is a major gastric adenocarcinoma (GA) risk factor. GA disproportionately affects U.S. Hispanics compared with non-Hispanic Whites (NHWs). Since H. pylori infection studies in Hispanics are few, infection rates in Hispanic and NHW men in Bexar County were compared, and relationships with ethnicity and obesity examined. Age- and zip code-matched participants from a community-dwelling cohort were randomly selected. Sera from 284 men were analyzed by enzyme immunoassay for H. pylori antibodies. Adjusted risk ratio estimation for matched data was conducted to identify differences. Hispanics had a markedly higher prevalence of infection (30.3%) than NHWs (9.2%). Matched risk ratio (mRR) analyses revealed a strong association between H. pylori seropositivity and Hispanic ethnicity (mRR = 3.31; 95% CI [1.91, 5.73], adjusted by BMI, smoking status, and family history of cancer (mRR range = 3.28-3.89). BMI mRRs (range = 1.19-1.22) were significant in all models. In this cohort, Hispanic men had higher H. pylori infection rates than NHWs, and parallel the disproportionately higher rates of GA; obesity contributes to this higher prevalence. Future studies should address country of origin, acculturation, and other factors influencing obesity to further elucidate risk of GA in Hispanic populations.

Tumor suppressor genes in familial adenomatous polyposis

Colorectal cancer (CRC) is mostly due to a series of genetic alterations that are being greatly under the influence of the environmental factors. These changes, mutational or epigenetic modifications at transcriptional forefront and/or post-transcriptional effects via miRNAs, include inactivation and the conversion of proto-oncogene to oncogenes, and/or inactivation of tumor suppressor genes (TSG). Here, a thorough review was carried out on the role of TSGs with the focus on the APC as the master regulator, mutated genes and mal-/dysfunctional pathways that lead to one type of hereditary form of the CRC; namely familial adenomatous polyposis (FAP). This review provides a venue towards defining candidate genes that can be used as new PCR-based markers for early diagnosis of FAP. In addition to diagnosis, defining the modes of genetic alterations will open door towards genome editing to either suppress the disease or reduce its progression during the course of action.

Long-term risk of gastrointestinal cancers in persons with gastric or duodenal ulcers

Peptic ulcer predicts gastric cancer. It is controversial if peptic ulcers predict other gastrointestinal cancers, potentially related to Helicobacter pylori or shared lifestyle factors. We hypothesized that gastric and duodenal ulcers may have different impact on the risk of gastrointestinal cancers. In a nationwide cohort study using Danish medical databases 1994-2013, we quantified the risk of gastric and other gastrointestinal cancers among patients with duodenal ulcers (dominantly H. pylori-related) and gastric ulcers (dominantly lifestyle-related) compared with the general population. We started follow-up 1-year after ulcer diagnosis to avoid detection bias and calculated absolute risks of cancer and standardized incidence ratios (SIRs). We identified 54,565 patients with gastric ulcers and 38,576 patients with duodenal ulcers. Patient characteristics were similar in the two cohorts. The 1-5-year risk of any gastrointestinal cancer was slightly higher for gastric ulcers patients (2.1%) than for duodenal ulcers patients (2.0%), and SIRs were 1.38 (95% CI: 1.31-1.44) and 1.30 (95% CI: 1.23-1.37), respectively. The SIR of gastric cancer was higher among patients with gastric ulcer than duodenal ulcer (1.92 vs. 1.38), while the SIRs for other gastrointestinal cancers were similar (1.33 vs. 1.29). Compared with gastric ulcer patients, duodenal ulcer patients were at lower risk of smoking- and alcohol-related gastrointestinal cancers. The risk of nongastric gastrointestinal cancers is increased both for patients with gastric ulcers and with duodenal ulcers, but absolute risks are low. H. pylori may be less important for the development of nongastric gastrointestinal cancer than hypothesized.