Colorectal carcinoma belongs to non-communicable chronic diseases, causing one of the highest mortality and morbidity rates among neoplastic diseases. Colorectal cancer can be classified as a high-risk disease because of its high malignancy and frequent late diagnosis at an advanced stage. The development of the malignant process is more frequent in countries with more developed industry. In industrial countries, the incidence of colorectal cancer is four times higher (Haggar et al., 2009). In this publication, we present a current overview of knowledge from studies addressing probiotic culture intake in the diet and its impact on the risk of developing colorectal cancer.
The gastrointestinal tract consists of more than a thousand commensal species, defined as gut microbiota. Development of intestinal microbiota is most pronounced during the first three years of life (Gonzales et al., 2022). Gut microbiota is described as a complex ecosystem including bacteria, viruses, fungi and protozoa. Microbiota is considered one of the most important components for maintaining internal body homeostasis.
The term “probiotic” comes from Greek and means for life. FAO (Food and Agriculture Organization) and WHO (World Health Organization) define probiotic microorganisms as live microorganisms that have a beneficial effect on the human body. Among the probiotic microorganisms that most often appear in the diet are the strains Lactobacillus spp., Bifidobacterium spp., Lactococcus spp., Streptococcus spp. and Enterococcus spp. (Każmierczak-Siedlacka et al., 2020).
Materials and methods
By analysing published studies we provide a current overview of knowledge on the mechanisms of probiotic cultures consumed in the diet that inhibit the carcinogenicity of the colon. For this publication, we selected 5 main analyses:
- Production of anticarcinogenic and antimutagenic substances
- Quantitative changes in gut microbiota
- Qualitative changes in gut microbiota
- Binding and degradation of potential carcinogens
- Improvement of host immune response
Mechanisms of inhibiting carcinogenicity of probiotic microorganisms
Among the main mechanisms by which probiotic cultures inhibit the development of colorectal carcinoma are improvement of the host immune response, binding and degradation of potential carcinogens, quantitative and qualitative changes in intestinal microbiota, and production of antimutagenic substances that can alter the metabolic activity of gut microbiota. Clinical study results have shown the beneficial effect of probiotic microorganisms on the composition of intestinal microbiota. Probiotics help improve intestinal barrier integrity, inhibit the growth of pathogenic microorganisms and reduce carcinogenic substances (Ohara et al., 2010).
Production of anticarcinogenic and antimutagenic substances
Probiotic microorganisms compete with pathogenic microorganisms in adhesion and colonization of biological membranes during biofilm formation. A biofilm is characterised by structural heterogeneity, genetic diversity, a complex of extracellular substances, polysaccharides, proteins, nucleic acids and phospholipids (Ohland et al., 2010).
Bacteria such as Escherichia coli or Clostridium perfringens naturally present in the gut participate in the production of carcinogenic components. This property stems from the presence and activity of enzymes such as azoreductase, nitroreductase and beta-glucuronidase, which are capable of converting heterocyclic aromatic amines, polycyclic aromatic hydrocarbons and primary bile acids into carcinogenic and synthetic aglycones, ammonia, cresol and phenols. These metabolites have cytotoxic and genotoxic activity, leading to abnormal cellular growth (Dos Reis et al., 2017).
The Goldin and Gorbach study performed in 1980 was among the first to point to an association between a diet enriched with probiotic cultures and reduced incidence of colorectal cancer. This study used two strains of Lactobacillus acidophilus, N-2 and NCFM. The Lactobacillus acidophilus probiotic culture was able to reduce the activity of azoreductase and beta-glucuronidase in a group of healthy participants. These faecal enzymes were able to catalyse the conversion of procarcinogens. Lactobacillus strains caused a reduction in specific activity within 10 days of Lactobacillus culture intake (Goldin et al., 1980).
In vivo studies on laboratory animals showed that oral intake of probiotic microorganisms has a marked impact on reducing DNA damage induced by chemical carcinogens in the gastric and intestinal mucosa (PoolZobel et al., 1996). Tokano et al. (1985) studied the effect of fermented milk enriched with probiotic cultures on cancer development in laboratory animals. In their study, they reported that colorectal carcinogenesis induced by 1,2-dimethylhydrazine was reduced in a group of laboratory rats given fermented milk (Takano et al., 1985).
Quantitative changes in gut microbiota
Probiotic strains are responsible for maintaining balance between the quantity of natural gut microbiota and its metabolic activity. Healthy gut microbiota must be properly diversified to ensure bodily balance. Disturbance of this balance can lead to a deficiency of beneficial bacteria and initiation of a pathogenic process. Dysbiosis influences the development of chronic inflammation and promotes the production of carcinogenic substances, thereby increasing the risk of colorectal cancer (Dos Reis et al., 2017).
The ratio between proliferation and apoptosis of cancer cells determines the stage of cancer development. During carcinogenesis there is an increased rate of proliferation compared with the apoptosis process. Probiotic microorganisms can influence cell proliferation and apoptosis (Zhong et al., 2014).
Research by Sobhani et al. (2011) compared stool samples from healthy individuals with samples from patients diagnosed with colorectal carcinoma. The results confirmed that the quantity of bacteria from the genera Bacteroides and Prevotella was significantly higher in the diagnosed carcinoma group, while Lactobacillus bacteria were present in lower numbers. The results also confirmed that Salmonella and Clostridium bacteria were represented in larger amounts in this patient group. Some species of Bacteroides spp. and Clostridium spp. are characterized as species that initiate a pathogenic process leading to colorectal carcinoma. Bacteroides fragilis produces a toxin that influences inflammation induction, leading to progression of cancer growth (Sobhani et al., 2011).
Rafter et al. (2007) in their study assessed the effect of probiotic microorganisms on changes in gastrointestinal microbiota with a significant reduction in pathogenic bacteria and increase in probiotic microorganisms. After probiotic application, they observed a marked reduction of Clostridium perfringens in patients with polyps (Rafter et al., 2007).
Qualitative changes in gut microbiota
Probiotic cultures maintain the physico-chemical properties of the colon. Lowered pH leads to increased concentration of bile acids in stool. Bile acids act as cytotoxins targeting physiological epithelium, leading to changes in cells of the colonic mucosa (Jia et al., 2018).
Fermentation is one mechanism through which probiotic microorganisms can reduce the risk of colorectal cancer and influence the pH of the intestinal lumen. Bacterial fermentation of undigested carbohydrate residues produces short-chain fatty acids (acetate, propionate, butyrate) and gas. While gas is eliminated in faeces, short-chain fatty acids are nutrients and growth signals for the intestinal mucosa, thereby playing a significant role in cancer prevention. The aetiology of colorectal cancer has also been directly linked to a decrease in the amount of short-chain fatty acids (Dos Reis et al., 2017).
Published studies show that butyrate is one of the most significant representatives of short-chain fatty acids and can lower luminal pH, thereby contributing to reduced risk of colorectal cancer occurrence and progression. It is a preferred energy source for colonocytes and supports physiological growth of intestinal cells. The probiotic microorganism Propionibacterium spp. is capable of eliminating cancer cells through short-chain fatty acid metabolites. Bifidobacterium spp. and Lactobacillus spp. probiotic strains alter gut microbiome composition and then positively influence short-chain fatty acid production (Leblanc et al., 2017).
Probiotic microorganisms also participate in the production of another group of fatty acids, such as conjugated linoleic acid. This is a group of linoleic acid isomers that has been shown in published studies to have anti-inflammatory and anticarcinogenic effects. Scientific studies have shown that conjugated linoleic acid reduces colorectal tumour occurrence in laboratory animals (17). Ewaschuk et al. (2006) demonstrated the conversion of linoleic acid into conjugated linoleic acid form through probiotic strain intake. This ability of probiotic microorganisms reduces tumour-cell viability and induces apoptosis (Ewaschuk et al., 2006).
Binding and degradation of potential carcinogens
The gastrointestinal tract, especially the colon, contains a large population of bacteria. Most bacteria colonizing the colon are harmless, while some bacterial species are pathogenic (Manning et al., 2004). Studies indicate that the capacity to bind and degrade potential carcinogens is mainly expressed by probiotic strains of Lactobacillus spp. and Bifidobacterium spp.
Mutagenic compounds associated with increased risk of carcinogenesis in the colon are often found in unhealthy “fast food,” especially fried and grilled meat. Oral intake of Lactobacillus spp. probiotic cultures reduced the mutagenic effect in a group of volunteers, which was demonstrated by reduced excretion of heterocyclic aromatic amines. Heterocyclic aromatic amines are produced as a result of high-temperature thermal processing of meat. Gut microbiota can convert these amines into mutagenically active derivatives that alter intestinal mucosa and trigger carcinogenic mutations (Hayatsu et al., 1993).
Orrhage et al. (1994) focused on the in vitro capacity of Lactobacillus microorganisms to bind mutagenic heterocyclic aromatic amines formed during processing of a high-protein diet. The mutagen-binding capacity was analysed using high-performance liquid chromatography. The mutagen 3-amino-1-methyl-5H-pyrido-[4,3-b]indole was bound by Lactobacillus microorganisms in its full quantity, while the mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, belonging to the most widespread mutagen in the Western diet, reached 50% binding (Orrhage et al., 1994).
Improvement of host immune response
The immune system plays an important role in controlling progression of carcinogenic growth. Interaction of immune cells such as antigen-presenting cells, T and B lymphocytes and NK (natural killer) cells is decisive for forming an effective anticarcinogenic immune response (Gabrilovich et al., 2003). Probiotic microorganisms are capable of positively influencing host immune response.
Sekine et al. (1985) in their study published the stimulatory ability of the probiotic microorganism Bifidobacterium infantis on host immune response, which led to suppression and regression of carcinogenic growth (Sekine et al., 1985). Published studies show the effect of Lactobacillus spp. microorganisms in the formation of specific and non-specific mechanisms with an anticarcinogenic effect (Schiffrin et al., 1995). The probiotic microorganism Lactobacillus casei in published studies showed anticarcinogenic and antimutagenic effects in transplanted tumour cells and also demonstrated the ability to suppress chemically induced carcinogenesis in laboratory animals. Study results indicate that oral intake of Lactobacillus casei positively affects prevention of carcinoma, positively modulating the host immune system, especially cellular immune response (Matsuzaki, 1998).
Lee et al. (2004) reported in their study the effects of administering probiotic microorganisms Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium longum for four weeks. The study results showed increased survival in laboratory animals that were injected with tumour cells. The increased survival of animals correlates with increased cellular immunity, which was manifested by increased quantities of T lymphocytes, NK cells and MHC glycoproteins by flow cytometry analysis (Lee et al., 2004).
Discussion
An appropriate diet plays a key role in preventing colorectal cancer. Regular consumption of dairy products such as milk, yoghurt, cheese, milkshakes or other fermented dairy products containing probiotic cultures is associated with a lower incidence of colorectal cancer. Epidemiological studies have also confirmed the relationship between increased consumption of red meat and animal fat and increased risk of colorectal cancer development (Larsson et al., 2006).
The 2012 study by Aune et al. confirmed the link between dairy product consumption (except cheese) and reduced incidence of colorectal cancer. Research suggested the effectiveness of probiotic microorganisms in reducing human colorectal cancer cells Caco-2, HT-29, SW1116, HCT116, SW480, DLD-1 and LoVo in species such as Bacillus: polyfermentic, subtilis; Bifidobacterium: lactis, adeloscentis; Clostridium butyricum, Enterococcus faecium, Lactobacillus: acidophilus, casei, fermentum, delbrueckii, helveticus, paracasei, plantarum, pentosus, salivarius, Lactococcus lactis, Pediococcus pentosaceus, Propionibacterium acidopropionici, Streptococcus thermophilus (Aune et al., 2012).
Current focus is on reducing colorectal cancer risk by increased use of probiotic cultures as dietary supplements. Probiotic bacteria play an important role due to their properties and immunomodulation. Probiotics are capable of increasing and decreasing production of anti-inflammatory cytokines, which play a significant preventive role. Probiotic cultures also have the ability to activate phagocytosis in eliminating the early stages of tumour-cell growth (Górska et al., 2019).
Studies of the gut microbiome have confirmed that probiotic strains can influence the immune response of the organism, which can be used both for cancer prevention and as adjuvant therapy during chemotherapy. Research points to the possibility of using probiotic cultures in the preparation of therapeutics, cytokines and enzymes in colorectal cancer treatment. Probiotic cultures are indispensable as vectors, thanks to their high resistance to the gastrointestinal environment and their natural ability to colonize the intestinal mucosal surface. An innovative concept of probiotic medicine consists of oral administration of genetically modified probiotic cultures that allow direct transfer of therapeutic agents into the intestinal mucosa (Śliżewska et al., 2020).
Conclusion
The work points to the importance and impact of using probiotic cultures in the diet for preventing colorectal cancer. Probiotic cultures are considered very important in modern medicine because of their effect on the human body in cancer prevention and support of treatment without negative side effects. Use of probiotic microorganisms could bring breakthroughs in several areas of medicine in the future, not only in supporting immunotherapy in oncology and the treatment of oncological diseases, but also in other intestinal diseases and inflammations.
Authors: MVDr. Martina Tejová prof. MUDr. Kvetoslava Rimárová, CSc.
The work is supported by grant KEGA 010UPJŠ-4/2021 Implementácia multimediálnych technológii vo výučbe preventívnych intervencií v lekárskych a nelekárskych odboroch.
List of bibliographic references
AUNE, D, et al. 2012. Dairy products and colorectal cancer risk: a systematic review and meta-analysis of cohort studies. In Annals of oncology. 0923-7534, 2012, 23, 1, 37-45.
DOS REIS, Sandra, et al. 2017. Review of the mechanisms of probiotic actions in the prevention of colorectal cancer. In Nutrition Research, 0271-5317, 37, 1-19.
EVANS, Nicholas, et al. 2010. Conjugated linoleic acid ameliorates inflammation-induced colorectal cancer in mice through activation of PPARγ. In The Journal of nutrition, 0022-3166, 140, 3, 515-521.
EWASCHUK, Julia B, et al. 2006. Bioproduction of conjugated linoleic acid by probiotic bacteria occurs in vitro and in vivo in mice. In The Journal of nutrition, 0022-3166, 136, 6, 1483-1487.
GABRILOVICH, Dmitry. – PISAREV, Vladimir. 2003. Tumor escape from immune response: mechanisms and targets of activity. In Current drug targets, 1873-5592, 4, 7, 525-536.
GOLDIN, Barry R. – GORBACH, Sherwood L. 1980. Effect of Lactobacillus acidophilus dietary supplements on 1, 2-dimethylhydrazine dihydrochloride-induced intestinal cancer in rats. In Journal of the National Cancer Institute, 0027-8874, 64, 2, 263-265.7
GONZALES, Antonio, et al. 2022. The mind-body-microbial continuum. In Dialogues in clinical neuroscience, 1294-8322, 13, 1, 55-62.
GÓRSKA, Agata, et al. 2019. Probiotic bacteria: a promising tool in cancer prevention and therapy. In Current microbiology, 2319-7706, 76, 8, 939-949.
HAGGAR, Fatima. – BOUSHLEY, Robin P. 2009. Colorectal cancer epidemiology: incidence, mortality, survival, and risk factors. In Clinics in colon and rectal surgery, 1531-0043, 22, 04, 191-197.
HAYATSU, Hikoya. – HAYATSHU, Toshiko. 1993. Suppressing effect of Lactobacillus casei administration on the urinary mutagenicity arising from ingestion of fried ground beef in the human. In Cancer letters, 0304-3835, 73, 2-3, 173-179.
JIA, Wei. – XIE, G. – JIA, Weiping. 2018. Bile acid–microbiota crosstalk in gastrointestinal inflammation and carcinogenesis. In Nature reviews Gastroenterology & hepatology, 1759-5045, 15, 2, 111-128.
KAŻMIERCZAK-SIEDLACKA, Karolina, et al. 2020. Therapeutic methods of gut microbiota modification in colorectal cancer management–fecal microbiota transplantation, prebiotics, probiotics, and synbiotics. In Gut Microbes, 1949-0976, 11, 6, 1518-1530.
LARSSON, Susanna C. – WOLK, Alicja. 2006. Meat consumption and risk of colorectal cancer: a meta‐analysis of prospective studies. In International journal of cancer, 0020-7136, 119, 11, 2657-2664.
LEBLANC, Jean Guy, et al. 2017. Beneficial effects on host energy metabolism of short-chain fatty acids and vitamins produced by commensal and probiotic bacteria. In Microbial cell factories, 1475-2859, 16, 1, 1-10.
LEE, Jung Woo, et al. 2004. Immunomodulatory and antitumor effects in vivo by the cytoplasmic fraction of Lactobacillus casei and Bifidobacterium longum. In Journal of veterinary science, 1976-555X, 5, 1, 41-48.
MANNING, Thea Scantlebury. – GIBSON, GR. 2004. Microbial-gut interactions in health and disease. Prebiotics. In Best practice & research. Clinical gastroenterology, 1521-6918, 18, 2, 287-298.
MATSUZAKI, Takeshi. 1998. Immunomodulation by treatment with Lactobacillus casei strain Shirota. In International journal of food microbiology, 1879-3460, 41, 2, 133-140.
OHARA, Tadashi. – YOSHINO, Keiichi. – KITAJIMA, Masaki. 2010. Possibility of preventing colorectal carcinogenesis with probiotics. In Hepato-gastroenterology, 0172-6390, 57, 104, 1411-1415.
OHLAND, Christina L. – MACNAUGHTON, Wallace K. 2010. Probiotic bacteria and intestinal epithelial barrier function. In American journal of physiology-gastrointestinal and liver physiology, 0193-1857, 298, 6, G807-G819.
ORRHAGE, K, et al. 1994. Binding of mutagenic heterocyclic amines by intestinal and lactic acid bacteria. In Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, 0027-5107, 311, 2, 239-248.
POOL-ZOBEL, BL, et al. 1996. Lactobacillus- and Bifidobacterium-mediated antigenotoxicity in the colon of rats. In Nutrition Cancer, 1532-7914, 26, 3, 365-380.
RAFTER, Joseph, et al. 2007. Dietary synbiotics reduce cancer risk factors in polypectomized and colon cancer patients. In The American journal of clinical nutrition, 1938-3207, 85, 2, 488-496.
SCHIFFRIN, EJ, et al. 1995. Immunomodulation of human blood cells following the ingestion of lactic acid bacteria. In Journal of Dairy Science, 1525-3198, 78, 3, 491-497.
SEKINE, Kazunori, et al. 1985. A new morphologically characterized cell wall preparation (whole peptidoglycan) from Bifidobacterium infantis with a higher efficacy on the regression of an established tumor in mice. In Cancer Research, 0008-5472, 45, 3, 1300-1307.
ŚLIŻEWSKA, Katarzyna. - MARKOWIAK-KOPEĆ. - Paulina, ŚLIŻEVSKA, Weronika. 2020. The role of probiotics in cancer prevention. In Cancers, 2072-6694, 13, 1, 20.
SOBHANI, Iradj, et al. 2011. Microbial dysbiosis in colorectal cancer (CRC) patients. In PloS one, 1932-6203, 6, 1, e16393.
TAKANO, Toshiaki, et al. 1985. Effects of feeding sour milk on longevity and tumorigenesis in mice and rats. In Bifidobacteria and Microflora, 1884-5126, 4, 1, 31-37.
ZHONG, Li. – ZHANG, Xufei.- COVASA, Mihai. 2014. Emerging roles of lactic acid bacteria in protection against colorectal cancer. In World journal of gastroenterology: WJG, 2219-2840, 20, 24, 7878.