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REVIEW ARTICLE
Year : 2022 | Volume
: 18
| Issue : 7 | Page : 1855-1859
The relationship between Clostridium butyricum and colorectal cancer
Hairong Liu1, Xin Xu2, Jing Liang1, Jun Wang1, Yan Li1
1 Department of Oncology, The First Affiliated Hospital of Shandong First Medical University and Shandong Provincial Qianfoshan Hospital, Shandong Key Laboratory of Rheumatic Disease and Translational Medicine, Shandong Lung Cancer Institute, Jinan, Shandong, China
2 Shandong First Medical University, Shandong, China
Correspondence Address:
Yan Li
Department of Oncology, The Affiliated Hospital of Shandong First Medical University, and Shandong Provincial Qianfoshan Hospital, Shandong Key Laboratory of Rheumatic Disease and Translational Medicine, Shandong Lung Cancer Institute, Jinan, Shandong
China
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/jcrt.jcrt_1565_21
Gut microbiota dysbiosis is involved in intestinal diseases. The resident microorganisms in the digestive tract contribute to maintenance of gut homeostasis. Some bacterial species have been identified and are suspected to play a role in colorectal cancer (CRC). Many studies have found that Clostridium butyricum has a close relationship with CRC, and the mechanism is becoming increasingly clear. This review discusses the possible relationship between C. butyricum and CRC.
Keywords: Clostridium butyricum, colorectal cancer, gut microbiota
Hairong Liu and Xin Xu are Co First Authors
> Introduction
Colorectal cancer (CRC) is caused by both genetic and environmental factors. Environmental risk factors include a high-fat diet, large intake of red meat, aging, alcohol abuse, and chronic inflammation. Previous studies showed that patients with inflammatory bowel disease (IBD) are more susceptible to CRC.[1] Long-term chronic and recurrent bowel inflammation predisposes patients to develop colitis-associated CRC (CAC). Studies showed that the incidence of CAC increases in patients with IBD for 10 years, and the rate is 18% after 30 years.[2],[3]
Increasing evidence reported that gut microbiota influences the pathogenesis of IBD and CRC. Clostridium butyricum, Fusobacterium nucleatum, Bacteroides fragilis, Escherichia coli, and Enterococcus faecalis are most commonly related to the occurrence of CRC. Moreover, several bacterial metabolites have been implicated in either or both the initiation and progression of CRC.[4]
> Microbiota and CRCThe colon is usually colonized by ~103 different microbiota species, including bacteria, viruses, and fungi. However, the microbiota is primarily represented by a variety of bacteria. The colon contains ~1014 types of bacteria, and 70% of them make up the host microorganisms. The absolute number of microorganisms varies considerably between the mouth and the rectum, and the gut microbiota varies between individuals. The microorganisms in newborn are initially acquired from the mother's skin, vagina, and feces, then it matures during development. Microbiota formation is the result of interactions between physiological processes in the host and microorganisms from the environment.[5] After the initial stages, the microbiota are stabilized and maintain a consistent composition. Some fluctuations appear throughout adulthood due to environmental, physiological, and pathological events. In the elderly, although the microbiota composition alters slightly, the physiological functions of the microbiota remain the same.[1],[6],[7],[8]
Interestingly, animals raised in bacteria-free conditions have immune deficiencies; therefore, early acquisition of a diverse and balanced microbiota is important for the development and maturation of a healthy immune system. The microbiota is divided to two types according to their locations in the gut. Microbes in the lumen are called “luminal flora,” while microbes that penetrate the mucosal layer that overlays the intestinal epithelium are called “mucosa-associated flora.” As indicated, the mucus layers protect enterocytes from excessive exposure to microorganisms and dietary antigens in the intestine, particularly in the colon, thus preventing hypersensitivity responses. Moreover, the ratio of anaerobes to aerobes is lower at the mucosal surfaces than in the lumen, and the bacteria of the distal colon are also different from those of the proximal colon.[9]
In addition, the composition of murine gut microbiota is similar to that of humans, which allows for the use of mouse experimental models of gastrointestinal disease for research. The human gut microbiota is composed of three primary phyla: Firmicutes (30%–50%), Bacteroidetes (20%–40%), and Actinobacteria (1%–10%). The numbers and types of microorganisms are different among individuals, depending upon the different of lifestyle, diet, and the host genotype betwwen individuals. Strict anaerobes, including Bacteroides, Eubacterium, Bifidobacterium, Fusobacterium, Peptostreptococcus, and Atopobium, represent a major portion of the gut microbiota. Alternatively, facultative anaerobes, such as lactobacilli, enterococci, streptococci, and Enterobacteriaceae, constitute a minor proportion (~1000-fold lower levels) of the microorganisms.[10] In addition, increasing studies have suggested that probiotics regulate the gut flora, improve the intestinal microenvironment, prevent precancerous lesions, and inhibit the occurrence of CRC.[11],[12],[13]
Recently, research has focused on exploring the role of microbial infection in carcinogenesis and has found that microbes are suspected to be involved in ~20% of cancers, especially CRC. Helicobacter pylori has been verified to be related to gastric cancer, but the relationship to CRC is controversial. Interestingly, bacterial levels in the colon are 1 million-fold higher than in the small intestine, thus increasing the risk ~12-fold in colon-related cancer progression. Different hypotheses have emerged to explain the contribution of bacteria to CRC: (1) a disorganized microbial community with procarcinogenic features is capable of remodeling the microbiome to drive proinflammatory responses and epithelial cell transformation leading to cancer and (2) the “driver–passenger” theory states that the intestinal bacteria, termed “bacteria drivers,” initiate CRC by inducing epithelial DNA damage, in turn, promoting the proliferation of passenger bacteria in the tumoral microenvironment. Studies in mouse models of altered immune and inflammatory responses suggest that dysbiosis could be sufficient to promote tumorigenesis. However, the mechanisms that contribute to dysbiosis and alterations in bacteria are not understood, and it is unknown whether dysbiosis is a cause or a consequence of CRC.[12],[14]
The CRC microenvironment is characterized by host-derived immune and inflammatory responses that could impact microbial regulation, alter microbiota composition, and favor the by-product of specific bacteria that potentially have carcinogenic effects.[2],[9],[15] Dysbiosis in CRC could result in the selection of microbiota composition via a tumor-linked microenvironment, with the emergence of “keystone pathogens” that have strong effects on bacterial composition and subsequently amplify dysbiosis. Some bacterial species have been identified and are suspected to play a critical role in CRC. These species primarily include Streptococcus bovis, H. pylori, B. fragilis, E. faecalis, C. butyricum, Fusobacterium spp., and E. coli. More research is focused on the study of C. butyricum. Genomic analyses are increasingly identifying bacterial strains with health-promoting potential.[1],[11],[16],[17]
> C. butyricum: IntroductionC. butyricum is a Gram-positive, anaerobic, rod bacterium. It is found in humans, 26 animal species, and the environment. C. butyricum was first isolated from pig intestines by Prazmowski in 1880. It accounts for 10%–20% of all human stool samples by microbial culture, and it is one of the earliest colonizers in infants. C. butyricum ferments undigested dietary fibers and generates short-chain fatty acids (SCFAs), specifically butyrate and acetate, with butyrate being one of the dominant fermentation end-products. SCFAs produced by microbial organisms have many important effects on host health, including modulating intestinal immune homeostasis, improving gastrointestinal barrier function, and alleviating inflammation; however, the precise mechanisms have not been fully elucidated. C. butyricum may increase certain beneficial bacterial taxa such as Lactobacillus and Bifidobacterium[18] and can reduce insulin resistance through Glucagon-like peptide (GLP)- 1–induced activation of the insulin receptor substrate (IRS)-1/Akt pathway.[1],[19]
Clostridium perfringens produces heat-stable factors to suppress the growth of human colon cancer cells, suggesting that Clostridium spp. could be potential candidates for producing chemo-preventive substances. However, several strains of this species, such as Clostridium tetani, Clostridium botulinum, and C. perfringens, produce poisonous toxins, which are the cause of convulsive tension, musle necropathy, and food poisoning, indicating that they are not ideal for the production of chemo-preventive substances. C. butyricum is a species that encompasses various study strains. Strain MIYAIRI 588 was first isolated from the feces of a healthy humans by Dr. Chikaji Miyairi in 1933 and was later isolated from the soil in 1963. It is a commercially available probiotic widely used for the treatment of diarrhea caused by antimicrobial.[20],[21] Shinnoh found that C. butyricum MIYAIRI 588 showed antitumor effects by enhancing the release of TRAIL from neutrophils through matrix metalloproteinase 8 in vitro.[20] CBM588 is effective as a Bacillus Calmette-Guerin (BCG) against cancer cells by inducing apoptosis in vivo as well as in bladder cancer.
> Mechanism of C. butyricum Inhibition in CRCStudies have revealed that microorganisms have a close relationship with either or both the initiation and progression of CRC. Patients with CRC often showed a reduction in butyrate-producing bacteria in the gut microbiota, compared with healthy individuals.
The intestinal barrier consists of three layers: the mucus layer, the epithelium, and the lamina propria. The intestinal barrier prevents pathogen invasion, maintains the tolerance of gut microbiota, and promotes the absorption of nutrients.[22] This gel-like layer is primarily composed of glycoproteins secreted by goblet cells in the epithelium. Butyrate has been shown to increase mucin production by the goblet cells in vitro by increasing the expression of the MUC genes subjacent to the mucosal layer. Animal studies have shown that direct supplementation with sodium butyrate increases intestinal permeability.[19]C. butyricum promotes the production of anti-inflammatory lipid metabolites in mouse colonic tissues. The lipid metabolites contribute to the promotion of anti-inflammatory interleukin (IL)-10–secreting T cells in the colon, especially protectin D1.[18]
C. butyricum has a positive effect on the inhibition of intestinal inflammation and helps to maintain the intestinal function. C. butyricum secretes an abundance of SCFAs, including butyrate and acetate, which promote the proliferation of enterocytes. Thus, an increase in butyrate production in the colon could improve symptoms from IBD and promote the differentiation of regulatory T cells (Tregs).[19],[23],[24],[25]
C. butyricum plays an immunomodulatory role in the intestinal epithelium to promote the Treg response in the presence of pathogenic or proinflammatory signaling by mediating tolerogenic APC. The Treg response suppresses activation of inflammatory responses driven by effector T cells. T helper cell (Th) is directly suppressed by IL-10 production of intestinal epithelial cells or antigen presenting cell (APCs). Murine disease models have shown that C. butyricum promotes intestinal immune tolerance by increasing the abundance of Tregs. Several studies have found that C. butyricum increases the production of transforming growth factor-beta (TGF-β), a cytokine that induces Treg differentiation and targets colonic dendritic cells.[18],[26]
C. butyricum has shown antitumorigenic properties in several mouse models of CRC. Researchers have found that oral treatment with C. butyricum restored 1,2-dimethylhydrazine dihydrochloride (DMH)-induced weight decline, reduced tumor incidence, and decreased tumor size in mice. Two other studies of CAC showed that supplementation of C. butyricum decreases tumorigenesis and increases survival.[27]
Butyrate is one of the dominant fermentation end products of C. butyricum. Butyrate mainly provides energetic substrates for epithelial cells, anti-inflammatory responses, protects colonocytes from DNA damage induced by reactive oxygen species (ROS), and modulates oxidative stress as a histone deacetylase inhibitor. In addition, butyrate also induces the apoptosis of CRC cells by acting as a ligand for the G-protein–coupled receptor (GPR).[16],[17]
Arimochi et al.[21] found that the apoptosis-inducing substances produced from soybean proteins by C. butyricum had toxic effects on human colon carcinoma cells.[1] Meanwhile, Chen et al.[28] also demonstrated that C. butyricum and B. subtilis could inhibit the proliferation of CRC cells by cell cycle arrest and apoptosis. In vivo, supplementation with B. subtilis or C. butyricum showed decreased Th2 and Th17 expression in DMH-treated mice. The CD4/CD8 expression is decreased in the peripheral blood of DMH-treated mice; however, intervention with B. subtilis or C. butyricum rescued this downregulation. The expression of Toll-like receptor 4 (TLR4) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), as well as IL-22, the expression of which is harmful due to its cell proliferation effects, decreased both in vitro and in vivo. These two probiotics inhibited the progression of DMH-induced CRC. However, the molecular mechanism may be attributed to reduced inflammation and improved immune homeostasis.[29]
Enterotoxigenic B. fragilis (ETBF) is a primary pathogen in severe inflammatory diseases and CRC. Its biofilm plays a key role in the development of CRC. Da-Seul Shin found that C. butyricum cell-free supernatants (CFS) significantly suppressed the generation of proteins and extracellular nucleic acids involved in basic biofilm processing. Furthermore, C. butyricum CFS significantly downregulated the expression of virulence- and efflux pump-related genes. These findings suggest that C. butyricum can be used as a biotherapeutic agent by inhibiting the growth or biofilm assembly of ETBF.[27],[30]
Epithelial–mesenchymal transition (EMT) is a critical step for initiating tumor metastasis. The processes of EMT and metastasis are regulated by multiple mechanisms, including TGF-β1/zinc finger E-box binding homeobox 1 (ZEB) pathways and the miR-200 family. The miR-200 family includes five members (miR-200a, miR-200b, miR-200c, miR-429, and miR-141) and plays a critical role in regulating inflammation, metastasis,and prognosis of malignant tumors EMT and Mesenchymal-epithelial transition (MET). Particularly, miR-200c is the most representative miRNA in the miR-200 family and is crucial in the regulation of both EMT and MET processes and inflammation, which is downregulated in IBD and a variety of human cancers such as CRC. Xiao et al.[31] found that C. butyricum increased transepithelial barrier function and the transcripts of mir-200c in Caco2-BBE cells, and suggested that it partially regulates the development of colitis-associated cancer through miR-200c.
C. butyricum also suppresses the release of multiple cytokines, decreases the levels of cyclooxygenase-2 (COX-2) and phosphorylation of NF-κB, decreases the levels of B-cell lymphoma 2 (Bcl-2), and increases the expression of Bcl2-associated x protein (BAX). It attenuates the progression of colitis-associated colon cancer by inhibition of the NF-κB pathway and modulates gut microbiota in an azoxymethane and dextran sulfate sodium (AOM/DSS)-induced mouse model. Xin et al.[32] found that C. butyricum combined with apatinib inhibited CD31 expression in tumor-bearing mice, suggesting that it plays a synergistic antitumor role through inhibition of tumor angiogenesis. C. butyricum combined with apatinib inhibited the expressions of the cell proliferation marker, Proliferating cell nuclear antigen (PCNA), and the apoptosis-related marker, Bcl-2, in tumor-bearing mice. C. butyricum combined with apatinib promoted cleaved caspase-3 expression in tumor-bearing mice.
Two studies found that CRC cells treated with C. butyricum-conditioned media in vitro significantly inhibited cell proliferation and increased cell apoptosis. Chen et al.[26] found that C. butyricum significantly inhibited high-fat diet induced intestinal tumor development in ApcMin/+ mice. Moreover, intestinal tumor cells treated with C. butyricum exhibited decreased proliferation and increased apoptosis. It also suppressed the Wnt/β-catenin signaling pathway and modulated the gut microbiota composition, decreased some pathogenic bacteria, and increased some beneficial bacteria, including SCFA-producing bacteria.[26] Accordingly, C. butyricum increased the cecal SCFA quantities and activated GPRs. This effect was driven by an increased expression of p21, a cell cycle inhibitor, which is dependent on the activation of the SCFA receptor, GPR, in vivo. After silencing the GPR43 gene using small interfering RNA, the antiproliferative effect of C. butyricum decreased. They also found through analysis of clinical specimens, the expression of GPR43 and GPR109A in the human normal colonic tissue decreased from adenoma to carcinoma.[27],[31],[33]
In conclusion, the mechanism of C. butyricum in inhibiting CRC may have relationship with bacterial gene toxins, microbial metabolism, host defense, inflammatory pathway regulation, oxidative stress induction, and antioxidant defense regulation [Figure 1]. However, further studies are needed to elucidate the mechanisms of action of C. butyricum in CRC.[3],[4]
The mechanisms of inhibition of CRC by C. butyricum are as follows: 1) C. butyricum strengthens the intestinal barrier by promoting MUC gene expression and increasing mucin production. 2) C. butyricum promotes the Treg response by increasing the production of TGF-β to promote intestinal immune tolerance. 3) C. butyricum inhibits CRC progression by reducing the expression of Th2 and Th17 and promoting the expression of CD4/CD8. 4) C. butyricum inhibits NF-κB signaling (TLR4–MyD88–NF-κB) and decreases certain proinflammatory factors (IL-10 and IL-22), leading to a decrease in inflammation-associated carcinogenesis. Moreover, C. butyricum partially regulates the development of CAC through miR-200c. Finally, C. butyricum may also decrease CRC development by inhibiting the Wnt signaling pathway (β-catenin). There is likely crosstalk among these pathways, but it has not been elucidated. 5) C. butyricum increases the expression of SCFA receptors, GPR43 and GPR109A, in colonic and intestinal epithelial cells. Activation of GPR43 eventually leads to an increased expression of p21 and cell cycle arrest in cancer cells. This is likely via the activation of GPR43 and GPR109A. C. butyricum triggers a decrease in the antiapoptotic protein, Bcl-2, and an increase in the proapoptotic protein, BAX, resulting in the apoptosis of cancer cells. 6) C. butyricum reduces the incidence of CRC by inhibiting ETBF. 7) Butyric acid protects the colon cells from DNA damage induced by ROS.
Microbial-based therapy is an effective way for treating diseases such as colon cancer. Probiotics and prebiotics are extensively used as additives in food and pharmaceutical products. Among these bacteria, probiotic butyrate-producing organisms such as C. butyricum have become attractive candidates in the treatment of colon tumors.[30],[34],[35]
Abbreviations
Treg: regulatory T cell; TGF-β:transforming growth factor-beta; CRC: colorectal cancer; Th2/7: T helper 2/17; CD4/CD8: leukocyte differentiation antigen 4/8; NF-κB: nuclear factor kappa-light-chain-enhancer of activated B cells; IL-10/22: interleukin-10/22; SCFA: short-chain fatty acids; GPR43/109A: G-protein-coupled receptor 43/109A; Bcl2: B-cell lymphoma 2; BAX: Bcl2 associated x protein; ETBF: enterotoxigenic Bacteroides fragilis=ROS: reactive oxygen species; TLR4: Toll-like receptor 4
Acknowledgement
This work was supported by the Major Science and Technology Innovation Project of Shandong Province (2018CXGC1220).
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
> References
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