The role of anaerobic bacteria in the development and prevention of colorectal cancer: A review study

Is the oral pathogen, Porphyromona gingivalis, associated to colorectal cancer?: a systematic review

BACKGROUND

The association between the oral pathogen Porphyromonas gingivalis (PG) and the gut microbiota in colorectal cancer (CRC) patients has been explored with inconsistent results. This study aims to systematically assess this potential association.

MATERIALS AND METHODS

A systematic review was conducted across three databases (Pubmed, Embase and Web of Science) from inception up to January 2023 and updated until November 2024. Inclusion criteria were observational studies examining PG in the microbiota of adults with CRC compared to healthy controls. Exclusion criteria were studies without control group of healthy individuals, other designs or without full-text access. Two reviewers independently selected and extracted data following a pre-registered protocol. Disagreements were resolved by consensus or with a third reviewer. Risk of bias (RoB) was assessed using the Newcastle-Ottawa Scale (NOS). Results were summarized with a flow diagram, tables, and narrative descriptions. Meta-analysis was not feasible, so Fisher's method for combining p-values and the sign test were used as alternative integration methods.

RESULTS

Finally, 18 studies, with 23 analysis units were included, providing a total sample of 4,373 participants (48.0% cases and 52.0%controls), 38.2% men and 61.8% women, with a similar distribution among cases and controls. The mean (SD) age of cases was 63.3 (4.382) years old and 57.0 (7.753) years for controls. Most of the studies analyzed the presence of PG in feces (70.0%) collected before colonoscopy (55.0%) and were classified with good quality (70.0%) in the RoB assessment. Results suggested an effect (Fisher's test, p = .000006) with some evidence towards a positive association of PG in CRC patients compared to healthy controls (Sign test, p = .039).

CONCLUSIONS

Results of the systematic review suggest that PG is associated with the microbiota of CRC patients. Lack of information to calculate the effect size prevented the performance of a meta-analysis. Future research should aim for standardized protocols and statistical approaches.

FUNDING

No funding was received for this work.

SYSTEMATIC REVIEW REGISTRATION

The research protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 2023 (registration number: CRD42023399382).

The intervention of B. longum metabolites in Fnevs' carcinogenic capacity: A potential double-edged sword

Colorectal cancer (CRC) ranks among the most prevalent malignant tumors globally. Fusobacterium nucleatum and its metabolites are effective biological targets for colon cancer promotion. Probiotics such as Bifidobacterium can block the occurrence and development of CRC by regulating the host intestinal mucosal immunity, eliminating carcinogens, and interfering with tumor cell proliferation and apoptosis. We selected six Bifidobacterium species to explore the inhibitory effect of their cell-free supernatant (CFS) on Fusobacterium nucleatum, and screened the best functional strain Bifidobacterium longum (B. longum) to explore its intervention effect on Fnevs infection of CRC cells. In the genus Bifidobacterium, B. longum-CFS can effectively inhibit the growth and membrane formation of Fusobacterium nucleatum. The metabolites of B. longum can inhibit the proliferation, migration and invasion of Fnevs-infected CRC cells. However, the transcriptomic analysis of Fnevs-infected CRC cells treated with Bl-CFS revealed that Bl-CFS exerted inhibitory effects on the expression of specific oncogenes (e.g., Myc, IL16, KCNN2, ACSBG1, Pum1, MET, NR5A2), while simultaneously promoting the expression of other oncogenes. This modulation potentially enhances the proliferation, epithelial-mesenchymal transition (EMT), stemness properties and other characteristics associated with CRC cells. Metabolomics also showed that Bl-CFS altered organic acid and lipid metabolism in Fnevs-infected CRC cells, and switched energy supply from aerobic glucose metabolism (TCA cycle) to anaerobic glycolysis, which increased the malignancy potential of CRC cells. The observed outcome may be attributed to the presence of both probiotics and toxic substances in the metabolites derived from Bifidobacterium longum. Therefore, this study concludes that the anti-colorectal cancer (CRC) effect of natural metabolites derived from Bifidobacterium longum is limited. Future investigations should focus on refining these natural substances and optimizing their composition ratios to extract their essence while eliminating impurities, thereby obtaining anticancer biologics with exceptional and consistent efficacy.

Bacterial small molecule metabolites implicated in gastrointestinal cancer development

Numerous associations have been identified between cancer and the composition and function of the human microbiome. As cancer remains the second leading global cause of mortality, investigating the carcinogenic contributions of microbiome members could advance our understanding of cancer risk and support potential therapeutic interventions. Although fluctuations in bacterial species have been associated with cancer progression, studying their small molecule metabolites offers one avenue to establish support for causal relationships and the molecular mechanisms governing host-microorganism interactions. In this Review, we explore the expanding repertoire of small molecule metabolites and their mechanisms implicated in the risk of developing gastrointestinal cancers.

Parvimonas micra-polarized M2-like tumor-associated macrophages accelerate colorectal cancer development via IL-8 secretion

Parvimonas micra (Pm), a periodontal pathogen, has been implicated in the impairment of anti-tumor responses in colorectal cancer (CRC). The tumor microenvironment in CRC involves tumor-associated macrophages (TAMs), which are pivotal in modulating tumor-associated immune responses. The polarization of TAMs towards an M2-like phenotype promotes CRC progression by suppressing the immune system. However, the mechanisms by which Pm affects the progression of CRC remain inadequately elucidated. In this study, we explored the impact of Pm infection on CRC cell characteristics, including proliferation, chemoresistance, migration, and macrophage polarization. We found that Pm-infected THP-1-derived macrophages exhibited elevated interleukin-10 levels, a well-established M2 marker. Conditioned media from Pm-treated THP-1 cells significantly enhanced CRC cell proliferation, cisplatin resistance, and migration, and interleukin-8 was identified as a key factor. Consistent with the in vitro results, an azoxymethane/dextran sodium sulfate mouse model treated with oral Pm showed accelerated CRC tumor growth. These results offer mechanistic insights into the influence of Pm infection on tumor microenvironment in CRC through M2-like macrophage polarization. The identified pathways may serve as potential targets for therapeutic interventions for CRC.

From pathogenesis to treatment: the impact of bacteria on cancer

The intricate relationship between cancer and bacteria has garnered increasing attention in recent years. While traditional cancer research has primarily focused on tumor cells and genetic mutations, emerging evidence highlights the significant role of microbial communities within the tumor microenvironment in cancer development and progression. This review aims to provide a comprehensive overview of the current understanding of the complex interplay between cancer and bacteria. We explore the diverse ways in which bacteria influence tumorigenesis and tumor behavior, discussing direct interactions between bacteria and tumor cells, their impact on tumor immunity, and the potential modulation of the tumor microenvironment. Additionally, we delve into the mechanisms through which bacterial metabolites and extracellular products May affect cancer pathways. By conducting a thorough analysis of the existing literature, we underscore the multifaceted and intricate relationship between bacteria and cancer. Understanding this complex interplay could pave the way for novel therapeutic approaches and preventive strategies in cancer treatment.

Parvimonas micra can translocate from the subgingival sulcus of the human oral cavity to colorectal adenocarcinoma

Oral and intestinal samples from a cohort of 93 colorectal cancer (CRC) patients and 30 healthy controls (non-CRC) were collected for microbiome analysis. Saliva (28 non-CRC and 94 CRC), feces (30 non-CRC and 97 CRC), subgingival fluid (20 CRC), and tumor tissue samples (20 CRC) were used for 16S metabarcoding and/or RNA sequencing (RNAseq) approaches. A differential analysis of the abundance, performed with the ANCOM-BC package, adjusting the P-values by the Holm-Bonferroni method, revealed that Parvimonas was significantly over-represented in feces from CRC patients (P-value < 0.001) compared to healthy controls. A total of 11 Parvimonas micra isolates were obtained from the oral cavity and adenocarcinoma of CRC patients. Genome analysis identified a pair of isolates from the same patient that shared 99.2% identity, demonstrating that P. micra can translocate from the subgingival cavity to the gut. The data suggest that P. micra could migrate in a synergistic consortium with other periodontal bacteria. Metatranscriptomics confirmed that oral bacteria were more active in tumor than in non-neoplastic tissues. We suggest that P. micra could be considered as a CRC biomarker detected in non-invasive samples such as feces.

The multispecies microbial cluster of Fusobacterium, Parvimonas, Bacteroides and Faecalibacterium as a precision biomarker for colorectal cancer diagnosis

The incidence of colorectal cancer (CRC) has increased worldwide, and early diagnosis is crucial to reduce mortality rates. Therefore, new noninvasive biomarkers for CRC are required. Recent studies have revealed an imbalance in the oral and gut microbiomes of patients with CRC, as well as impaired gut vascular barrier function. In the present study, the microbiomes of saliva, crevicular fluid, feces, and non-neoplastic and tumor intestinal tissue samples of 93 CRC patients and 30 healthy individuals without digestive disorders (non-CRC) were analyzed by 16S rRNA metabarcoding procedures. The data revealed that Parvimonas, Fusobacterium, and Bacteroides fragilis were significantly over-represented in stool samples of CRC patients, whereas Faecalibacterium and Blautia were significantly over-abundant in the non-CRC group. Moreover, the tumor samples were enriched in well-known periodontal anaerobes, including Fusobacterium, Parvimonas, Peptostreptococcus, Porphyromonas, and Prevotella. Co-occurrence patterns of these oral microorganisms were observed in the subgingival pocket and in the tumor tissues of CRC patients, where they also correlated with other gut microbes, such as Hungatella. This study provides new evidence that oral pathobionts, normally located in subgingival pockets, can migrate to the colon and probably aggregate with aerobic bacteria, forming synergistic consortia. Furthermore, we suggest that the group composed of Fusobacterium, Parvimonas, Bacteroides, and Faecalibacterium could be used to design an excellent noninvasive fecal test for the early diagnosis of CRC. The combination of these four genera would significantly improve the reliability of a discriminatory test with respect to others that use a single species as a unique CRC biomarker.

The emerging role of hypoxia and environmental factors in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic and debilitating disorder characterized by inflammation of the gastrointestinal tract. Despite extensive research, the exact cause of IBD remains unknown, hampering the development of effective therapies. However, emerging evidence suggests that hypoxia, a condition resulting from inadequate oxygen supply, plays a crucial role in intestinal inflammation and tissue damage in IBD. Hypoxia-inducible factors (HIFs), transcription factors that regulate the cellular response to low oxygen levels, have gained attention for their involvement in modulating inflammatory processes and maintaining tissue homeostasis. The two most studied HIFs, HIF-1α and HIF-2α, have been implicated in the development and progression of IBD. Toxicological factors encompass a wide range of environmental and endogenous agents, including dietary components, microbial metabolites, and pollutants. These factors can profoundly influence the hypoxic microenvironment within the gut, thereby exacerbating the course of IBD and fostering the progression of colitis-associated colorectal cancer. This review explores the regulation of hypoxia signaling at the molecular, microenvironmental, and environmental levels, investigating the intricate interplay between toxicological factors and hypoxic signaling in the context of IBD, focusing on its most concerning outcomes: intestinal fibrosis and colorectal cancer.

Promising dawn in tumor microenvironment therapy: engineering oral bacteria

Despite decades of research, cancer continues to be a major global health concern. The human mouth appears to be a multiplicity of local environments communicating with other organs and causing diseases via microbes. Nowadays, the role of oral microbes in the development and progression of cancer has received increasing scrutiny. At the same time, bioengineering technology and nanotechnology is growing rapidly, in which the physiological activities of natural bacteria are modified to improve the therapeutic efficiency of cancers. These engineered bacteria were transformed to achieve directed genetic reprogramming, selective functional reorganization and precise control. In contrast to endotoxins produced by typical genetically modified bacteria, oral flora exhibits favorable biosafety characteristics. To outline the current cognitions upon oral microbes, engineered microbes and human cancers, related literatures were searched and reviewed based on the PubMed database. We focused on a number of oral microbes and related mechanisms associated with the tumor microenvironment, which involve in cancer occurrence and development. Whether engineering oral bacteria can be a possible application of cancer therapy is worth consideration. A deeper understanding of the relationship between engineered oral bacteria and cancer therapy may enhance our knowledge of tumor pathogenesis thus providing new insights and strategies for cancer prevention and treatment.

Emerging strategies for combating Fusobacterium nucleatum in colorectal cancer treatment: Systematic review, improvements and future challenges

Colorectal cancer (CRC) is generally characterized by a high prevalence of Fusobacterium nucleatum (F. nucleatum), a spindle-shaped, Gram-negative anaerobe pathogen derived from the oral cavity. This tumor-resident microorganism has been closely correlated with the occurrence, progression, chemoresistance and immunosuppressive microenvironment of CRC. Furthermore, F. nucleatum can specifically colonize CRC tissues through adhesion on its surface, forming biofilms that are highly resistant to commonly used antibiotics. Accordingly, it is crucial to develop efficacious non-antibiotic approaches to eradicate F. nucleatum and its biofilms for CRC treatment. In recent years, various antimicrobial strategies, such as natural extracts, inorganic chemicals, organic chemicals, polymers, inorganic-organic hybrid materials, bacteriophages, probiotics, and vaccines, have been proposed to combat F. nucleatum and F. nucleatum biofilms. This review summarizes the latest advancements in anti-F. nucleatum research, elucidates the antimicrobial mechanisms employed by these systems, and discusses the benefits and drawbacks of each antimicrobial technology. Additionally, this review also provides an outlook on the antimicrobial specificity, potential clinical implications, challenges, and future improvements of these antimicrobial strategies in the treatment of CRC.

From the Colon to the Liver: How Gut Microbiota May Influence Colorectal Cancer Metastatic Potential

The gut microbiota's influence on human tumorigenesis is a burning topic in medical research. With the new ontological perspective, which considers the human body and its pathophysiological processes as the result of the interaction between its own eukaryotic cells and prokaryotic microorganisms living in different body niches, great interest has arisen in the role of the gut microbiota on carcinogenesis. Indeed, dysbiosis is currently recognized as a cancer-promoting condition, and multiple molecular mechanisms have been described by which the gut microbiota may drive tumor development, especially colorectal cancer (CRC). Metastatic power is undoubtedly one of the most fearsome features of neoplastic tissues. Therefore, understanding the underlying mechanisms is of utmost importance to improve patients' prognosis. The liver is the most frequent target of CRC metastasis, and new evidence reveals that the gut microbiota may yield an effect on CRC diffusion to the liver, thus defining an intriguing new facet of the so-called "gut-liver axis". In this review, we aim to summarize the most recent data about the microbiota's role in promoting or preventing hepatic metastasis from CRC, highlighting some potential future therapeutic targets.

Deciphering the mechanism of Peptostreptococcus anaerobius-induced chemoresistance in colorectal cancer: the important roles of MDSC recruitment and EMT activation

Peptostreptococcus anaerobius (P. anaerobius, PA) in intestinal flora of patients with colorectal cancer (CRC) are associated with poor prognosis. Studies have shown that P. anaerobius could promote colorectal carcinogenesis and progression, but whether P. anaerobius could induce chemoresistance of colorectal cancer has not been clarified. Here, both in vitro and in vivo experiments showed that P. anaerobius specifically colonized the CRC lesion and enhanced chemoresistance of colorectal cancer to oxaliplatin by recruiting myeloid-derived suppressor cells (MDSCs) into the tumor microenvironment. Furthermore, this study revealed that it was the increased secretion of IL-23 by MDSCs that subsequently facilitated the epithelial-mesenchymal transition (EMT) of tumor cells to induce chemoresistance of CRC by activating the Stat3-EMT pathway. Our results highlight that targeting P. anaerobius might be a novel therapeutic strategy to overcome chemoresistance in the treatment of CRC.

Integrating Transcriptomics and Metabolomics to Explore the Novel Pathway of Fusobacterium nucleatum Invading Colon Cancer Cells

Colorectal cancer (CRC) is a malignancy with a very high incidence and mortality rate worldwide. Fusobacterium nucleatum bacteria and their metabolites play a role in inducing and promoting CRC; however, no studies on the exchange of information between Fusobacterium nucleatum extracellular vesicles (Fnevs) and CRC cells have been reported. Our research shows that Fusobacterium nucleatum ATCC25586 secretes extracellular vesicles carrying active substances from parental bacteria which are endocytosed by colon cancer cells. Moreover, Fnevs promote the proliferation, migration, and invasion of CRC cells and inhibit apoptosis; they also improve the ability of CRC cells to resist oxidative stress and SOD enzyme activity. The genes differentially expressed after transcriptome sequencing are mostly involved in the positive regulation of tumor cell proliferation. After detecting differential metabolites using liquid chromatography-tandem mass spectrometry, Fnevs were found to promote cell proliferation by regulating amino acid biosynthesis in CRC cells and metabolic pathways such as central carbon metabolism, protein digestion, and uptake in cancer. In summary, this study not only found new evidence of the synergistic effect of pathogenic bacteria and colon cancer tumor cells, but also provides a new direction for the early diagnosis and targeted treatment of colon cancer.

Fecal microbiota transplantation inhibits colorectal cancer progression: Reversing intestinal microbial dysbiosis to enhance anti-cancer immune responses

Many lines of evidence demonstrate the associations of colorectal cancer (CRC) with intestinal microbial dysbiosis. Recent reports have suggested that maintaining the homeostasis of microbiota and host might be beneficial to CRC patients, but the underlying mechanisms remain unclear. In this study, we established a CRC mouse model of microbial dysbiosis and evaluated the effects of fecal microbiota transplantation (FMT) on CRC progression. Azomethane and dextran sodium sulfate were used to induce CRC and microbial dysbiosis in mice. Intestinal microbes from healthy mice were transferred to CRC mice by enema. The vastly disordered gut microbiota of CRC mice was largely reversed by FMT. Intestinal microbiota from normal mice effectively suppressed cancer progression as assessed by measuring the diameter and number of cancerous foci and significantly prolonged survival of the CRC mice. In the intestine of mice that had received FMT, there were massive infiltration of immune cells, including CD8⁺ T and CD49b⁺ NK, which is able to directly kill cancer cells. Moreover, the accumulation of immunosuppressive cells, Foxp3⁺ Treg cells, seen in the CRC mice was much reduced after FMT. Additionally, FMT regulated the expressions of inflammatory cytokines in CRC mice, including down-regulation of IL1a, IL6, IL12a, IL12b, IL17a, and elevation of IL10. These cytokines were positively correlated with Azospirillum_sp._47_25, Clostridium_sensu_stricto_1, the E. coli complex, Akkermansia, Turicibacter, and negatively correlated with Muribaculum, Anaeroplasma, Candidatus_Arthromitus, and Candidatus Saccharimonas. Furthermore, the repressed expressions of TGFb, STAT3 and elevated expressions of TNFa, IFNg, CXCR4 together promoted the anti-cancer efficacy. Their expressions were positively correlated with Odoribacter, Lachnospiraceae-UCG-006, Desulfovibrio, and negatively correlated with Alloprevotella, Ruminococcaceae UCG-014, Ruminiclostridium, Prevotellaceae UCG-001 and Oscillibacter. Our studies indicate that FMT inhibits the development of CRC by reversing gut microbial disorder, ameliorating excessive intestinal inflammation and cooperating with anti-cancer immune responses.

Therapeutic approaches to colorectal cancer via strategies based on modulation of gut microbiota

Colorectal cancer (CRC) ranks third in terms of global incidence and second in terms of death toll among malignant tumors. Gut microbiota are involved in the formation, development, and responses to different treatments of CRC. Under normal physiological conditions, intestinal microorganisms protect the intestinal mucosa, resist pathogen invasion, and regulate the proliferation of intestinal mucosal cells via a barrier effect and inhibition of DNA damage. The composition of gut microbiota and the influences of diet, drugs, and gender on the composition of the intestinal flora are important factors in the early detection of CRC and prediction of the results of CRC treatment. Regulation of gut microbiota is one of the most promising new strategies for CRC treatment, and it is essential to clarify the effect of gut microbiota on CRC and its possible mechanisms to facilitate the prevention and treatment of CRC. This review discusses the role of gut microbiota in the pathogenesis of CRC, the potential of gut microbiota as biomarkers for CRC, and therapeutic approaches to CRC based on the regulation of gut microbiota. It might provide new ideas for the use of gut microbiota in the prevention and treatment of CRC in the near future and thus reduce the incidence of CRC.