Antigenotoxic properties of lactic acid bacteria in the S. typhimurium mutagenicity assay

Microbial Metabolites as Molecular Mediators of Host-Microbe Symbiosis in Colorectal Cancer

The symbiosis between the gut microbiota and the host has been identified as an integral part of normal human physiology and physiological development. Research in germ-free or gnotobiotic animals has demonstrated the importance of this symbiosis in immune, vascular, hepatic, respiratory and metabolic systems. Disruption of the microbiota can also contribute to disease, and the microbiota has been implicated in numerous intestinal and extra-intestinal pathologies including colorectal cancer. Interactions between host and microbiota can occur either directly or indirectly, via microbial-derived metabolites. In this chapter, we focus on two major products of microbial metabolism, short-chain fatty acids and bile acids, and their role in colorectal cancer. Short-chain fatty acids are the products of microbial fermentation of complex carbohydrates and confer protection against cancer risk, while bile acids are compounds which are endogenous to the host, but undergo microbial modification in the large intestine leading to alterations in their bioactivity. Lastly, we discuss the ability of microbial modulation to mediate cancer risk and the potential to harness this ability as a prophylactic or therapeutic treatment in colorectal cancer.

Antimutagenic action of the live yeast can be transmitted to the offspring of Drosophila melanogaster. A genetic study using the wing spot assay

The present study evaluates whether the protective effect of live yeast (LY) against direct and indirect mutagenic agents, persists in the offspring from individuals fed with LY. The wing-spot test in Drosophila was used; four different mates were performed: a) neither females nor males were fed with LY-enriched food (NLYxNLY); b) only females were fed (LYxNLY); c) males were fed (NLYxLY) or d) both progenitors were fed (LYxLY). Results confirm that LY strongly stimulates fecundity in females but not in males and provides strength to the egg for survive. A greater reduction in mutation rate was observed when females were feed, in the following relationship: LYxNLY>LYxLY>NLYxLY. No protection was found against action in any of the promutagens tested. Results suggest that LY has a very powerful antimutagenic action, predominantly against the action of ionizing radiation and Chromium trioxide that can be transmitted mainly through the female.

Role of the Microbiota in Colorectal Cancer: Updates on Microbial Associations and Therapeutic Implications

Genetic, environmental, and dietary factors have been found to influence the development and progression of colorectal cancer (CRC). More recently, accumulating evidence associates the intestinal microbiota with the initiation and progression of this disease. While studies have shown that individuals with CRC display alterations in gut bacterial composition, it remains somewhat unclear whether such differences drive cancer development or whether they are a response to tumorigenesis. In this review, the authors assess new evidence linking the community structure or specific bacterial factors of the intestinal microbiota to CRC development and progression, with insights into therapeutic implications.

A potential role of probiotics in colorectal cancer prevention: review of possible mechanisms of action

A number of investigations, mainly using in vitro and animal models, have demonstrated a wide range of possible mechanisms, by which probiotics may play a role in colorectal cancer (CRC) prevention. In this context, the most well studied probiotics are certain strains from the genera of lactobacilli and bifidobacteria. The reported anti-CRC mechanisms of probiotics encompass intraluminal, systemic, and direct effects on intestinal mucosa. Intraluminal effects detailed in this review include competitive exclusion of pathogenic intestinal flora, alteration of intestinal microflora enzyme activity, reduction of carcinogenic secondary bile acids, binding of carcinogens and mutagens, and increasing short chain fatty acids production. Reduction of DNA damage and suppression of aberrant crypt foci formation have been well demonstrated as direct anti-CRC effects of probiotics on intestinal mucosa. Existing evidence clearly support a multifaceted immunomodulatory role of probiotics in CRC, particularly its ability to modulate intestinal inflammation, a well known risk factor for CRC. The effectiveness of probiotics in CRC prevention is dependent on the strain of the microorganism, while viability may not be a prerequisite for certain probiotic anticancer mechanisms, as indicated by several studies. Emerging data suggest synbiotic as a more effective approach than either prebiotics or probiotics alone. More in vivo especially human studies are warranted to further elucidate and confirm the potential role of probiotics (viable and non-viable), prebiotics and synbiotics in CRC chemoprevention.

Suppression of UVC-induced cell damage and enhancement of DNA repair by the fermented milk, Kefir

An aqueous extract of Kefir, fermented milk originally produced in the Caucasus mountains, suppressed morphological changes of human melanoma HMV-1 and SK-MEL cells and human normal fibroblastTIG-1 cells caused by UVC-irradiation, suggesting that UV damage can be suppressed by the Kefir extract. The addition of the Kefir extract after UVC-irradiation of HVM-1 cells resulted in a remarkable decrease in intracellular reactive oxygen species (ROS) which had been increased by UVC irradiation. The Kefir extract also stimulated unscheduled DNA synthesis and suppressed UVC-induced apoptosis of HMV-1 cells. A colony formation assay revealed that the Kefir extract rescued HMV-1 cells from cell death caused by UVC irradiation. The Kefir extract, as well as methyl methanethiosulfonate which is known to enhance the nucleotide excision repair (NER) activity, exhibited strong thymine dimer repair-enhancing activity. Epigalocatechin exhibited a weak NER activity but vitamins A, C, and E and catechin showed no NER activity. The thymine dimer repair-enhancing factors in the Kefir extract were heat-stable and assumed to be molecules with a molecular weight of less than 5000. The treatment of HMV-1 cells with the Kefir extract during or before UVC- irradiation also prevented the generation of ROS and thymine dimmer, and suppressed the apoptosis of HMV-1 cells, suggesting that application of Kefir can prevent UV damage.

Review: functional properties of kefir

Kefir is a unique cultured dairy product due to combined lactic acid and alcoholic fermentation of lactose in milk. Kefir is produced by microbial activity of "kefir grains" which have a relatively stable and specific balance of lactic acid bacteria and yeast. Due to the claimed health benefits of kefir which include reduction of lactose intolerance symptoms, stimulation of the immune system, lowering cholesterol, and antimutagenic and anticarcinogenic properties, kefir has become an important functional dairy food and consequently, research on kefir has increased in the past decade. In the following review, recent studies on the functional properties of kefir are reviewed.

Cancer-preventing attributes of probiotics: an update

Cancer is a serious global public health problem. Cancer incidence and mortality have been steadily rising throughout the past century in most places of the world. There are several epidemiological evidences that support a protective role of probiotics against cancer. Lactic acid bacteria and their probioactive cellular substances exert many beneficial effects in the gastrointestinal tract, and also release various enzymes into the intestinal lumen and exert potential synergistic (LAB) effects on digestion and alleviate symptoms of intestinal malabsorption. Consumption of fermented dairy products with LAB may elicit anti-tumor effects. These effects are attributed to the inhibition of mutagenic activity, the decrease in several enzymes implicated in the generation of carcinogens, mutagens, or tumor-promoting agents, suppression of tumors, and epidemiology correlating dietary regimes and cancer. Specific cellular components in lactic acid bacteria seem to induce strong adjuvant effects including modulation of cell-mediated immune responses, activation of the reticulo-endothelial system, augmentation of cytokine pathways, and regulation of interleukins and tumor necrosis factors. Studies on the effect of probiotic consumption on cancer appear promising, since recent in vitro and in vivo studies have indicated that probiotic bacteria might reduce the risk, incidence and number of tumors of the colon, liver and bladder. The protective effect against cancer development may be ascribed to binding of mutagens by intestinal bacteria, may suppress the growth of bacteria that convert procarcinogens into carcinogens, thereby reducing the amount of carcinogens in the intestine, reduction of the enzymes beta-glucuronidase and beta-glucosidase and deconjugation of bile acids, or merely by enhancing the immune system of the host. There are isolated reports citing that administration of LAB results in increased activity of anti-oxidative enzymes or by modulating circulatory oxidative stress that protects cells against carcinogen-induced damage. These include glutathione-S-transferase, glutathione, glutathione reductase, glutathione peroxidase, superoxide dismutase and catalase. However, there is no direct experimental evidence for cancer suppression in human subjects as a result of the consumption of probiotic cultures in fermented or unfermented dairy products, but there is a wealth of indirect evidence based largely on laboratory studies.

Improving the stability of probiotic bacteria in model fruit juices using vitamins and antioxidants

This study examined the survival of probiotic bacteria in a model fruit juice system. Three different strains of probiotic bacteria were used in this study: HOWARU Lactobacillus rhamnosus HN001, HOWARU Bifidobacterium lactis HN001, and Lactobacillus paracasei LPC 37. The probiotic bacteria were inoculated into model juice with various vitamins and antioxidants, namely white grape seed extract, green tea extract, vitamin B2, vitamin B3, vitamin B6, vitamin C, and vitamin E. The model juice without any additives was used as a control. Their viability was assessed on a weekly basis using plate count method. The model juice was made with sucrose, sodium citrate, citric acid powder, and distilled water and was pasteurized before use. Our findings showed that probiotic bacteria did not survive well in the harsh environment of the model fruit juice. However, the model juice containing vitamin C, grape extract, and green tea extract showed better survival of probiotic bacteria. The model juice containing grape seed extract, green tea extract, and vitamin C had the same initial population of 8.32 log CFU/mL, and at the end of the 6-wk storage period it had an average viability of 4.29 log CFU/mL, 7.41 log CFU/mL, and 6.44 log CFU/mL, respectively. Juices containing all other ingredients tested had viable counts of <10 CFU/mL at the end of the 6-wk storage period.

Modulatory activity of a Lactobacillus casei strain on 1,2-dimethylhydrazine-induced genotoxicity in rats

The present study was designed to investigate the putative antigenotoxic effects of supplementing the diet of rats treated with the colon carcinogen 1,2-dimethylhydrazine hydrochloride (DMH) with a Lactobacillus casei strain using an in vivo approach. The antigenotoxic response was evaluated in colon and liver cells using the alkaline comet assay. Since the balance between the bioactivation and detoxification metabolic pathways is crucial for the formation of toxic and genotoxic metabolites, alterations in the level of some xenobiotic metabolizing enzymes (XME) were studied in liver preparations. In the challenge group (L. casei + DMH), lactobacilli-supplemented diet, there was a decrease in the extent of DMH-induced DNA damage, especially in colon cells. Compared with control rats, there was less basal DNA damage in colon cells of rats fed on a lactobacilli-supplemented diet. These findings are the first to give clear evidence of DNA-protective effects of lactobacilli against basal DNA damage. Moreover, the chemopreventive effects were accompanied by changes in the activities of several XME. The observed decrease in the concentration of nonenzymatic antioxidants (i.e. GSH) and the reduced activity of enzymatic antioxidants (i.e., GST, GPx, and SOD) in liver could reflect an overall reduction in the level of oxidative stress in rats on a diet supplemented with the L. casei suspension compared with control rats (basal state). Thus, the concentrations of GSH and the activities of GST, GPx, and SOD could be downregulated by supplementing the diet with L. casei as a response to an improved antioxidant status.

Kefir Extracts SuppressIn VitroProliferation of Estrogen-Dependent Human Breast Cancer Cells but Not Normal Mammary Epithelial Cells

Anti-tumorigenic effects have been demonstrated in animal studies from the intake of kefir, a traditional fermented milk product believed to originate from the Caucasian mountains of Russia. In the present study, the antiproliferative effects of extracts of kefir, yogurt, and pasteurized cow's milk on human mammary cancer cells (MCF-7) and normal human mammary epithelial cells (HMECs) was investigated at doses of 0.31%, 0.63%, 1.25%, 2.5%, 5%, and 10% (vol/vol). After 6 days of culture, extracts of kefir-fermented milk depressed MCF-7 cell growth in a dose-dependent manner, showing 29% inhibition of proliferation at a concentration as low as 0.63%, whereas yogurt extracts began to show dose-dependent antiproliferative effects only at the 2.5% dose. Moreover, at the 2.5% dose, kefir extracts decreased the MCF-7 cell numbers by 56%, while yogurt extracts decreased MCF-7 cell proliferation by only 14%. No antiproliferative effects of kefir extracts were observed in the HMECs, while the yogurt extracts exerted antiproliferative effects on HMECs at the 5% and 10% doses. Unfermented milk extracts stimulated proliferation of MCF-7 cells and HMECs at concentrations above 0.31%. Peptide content and capillary electrophoresis analyses showed that kefir-mediated milk fermentation led to an increase in peptide concentrations and a change in peptide profiles relative to milk or yogurt. The present findings suggest that kefir extracts contain constituents that specifically inhibit the growth of human breast cancer cells, which might eventually be useful in the prevention or treatment of breast cancer.

Antigenotoxic effect of Saccharomyces cerevisiae on the damage produced in mice fed with aflatoxin B(1) contaminated corn

The potential of Saccharomyces cerevisiae (Sc) was evaluated for reducing the micronucleated normochromatic erythrocytes (MNNE) rate in mice fed AFB(1) contaminated corn. The study included two groups fed AFB(1) contaminated corn (0.4 and 0.8 mg/kg), a control fed uncontaminated corn, another group fed uncontaminated corn and 0.3% of Sc (1 x 10(8) live cells/g), and two groups fed AFB(1) contaminated corn (0.4 and 0.8 mg/kg) plus 0.3% Sc. Weight and MNNE were determined weekly for six weeks. Subsequently, the same determinations were made for another three-week period, but in mice receiving only a normal diet, without AFB(1) and Sc. Results in the first period revealed the following: control and Sc fed mice had similar constant weight increase, and low MNNE rate; mice fed only AFB(1) showed weight decrease and significant MNNE increase; finally, Sc improved weight gain and reduced MNNE produced by AFB(1). In the second period, results exhibited a tendency similar to that of the previous phase in the control and Sc fed mice; the weight and MNNE values improved in the other groups. We also determined the capacity of Sc for adsorbing and modifying the mycotoxin structure. The mixture was filtered to obtain two phases, and AFB(1) content was measured. Sc revealed a potent adsorbent capacity; however, chromatographic determination suggested no structural modification.

The potential mechanisms involved in the anti-carcinogenic action of probiotics

Probiotic bacteria are live microbial food ingredients that provide a health benefit to the consumer. In the past it was suggested that they served to benefit the host primarily through the prevention of intestinal infections. More recent studies have implicated probiotic bacteria in a number of other beneficial effects within the host including: *The suppression of allergies. *Control of blood cholesterol levels. *Modulation of immune function. *And the prevention of cancers of the colon. The reputed anti-carcinogenic effect of probiotics arises from in vivo studies in both animals and to a limited extent in man; this evidence is supported by in vitro studies with carcinoma cell lines and anti-mutagenicity assays. However, the mechanisms involved in any effect have thus far been difficult to elucidate; studies offer evidence for a variety of mechanisms; we have reviewed these and come to the opinion that, the anti-carcinogenic effect may not be attributable to a single mechanism but rather to a combination of events not yet fully elucidated or understood.

Fecal Water Genotoxicity Is Predictive of Tumor-Preventive Activities by Inulin-Like Oligofructoses, Probiotics (Lactobacillus rhamnosus and Bifidobacterium lactis), and Their Synbiotic Combination

The measurement of fecal water genotoxicity in human colon cells could be a useful biomarker to study effects of diet in the colon. Here we assessed aqueous fecal extracts of samples from a chronic study with rats fed prebiotics, probiotics, and their combination. Treatments were maltodextrins (controls), inulin/oligofructoses (prebiotic), Lactobacillus rhamnosus, and Bifidobacterium lactis (probiotics) or both (synbiotic). Azoxymethane (AOM) was administered to initiate tumors. Rat feces were collected at 0 and 10 days and 2, 4, and 8 mo, and cecal contents were collected at 8 mo. Aqueous phases were prepared and tested for genotoxicity in HT29 colon cells using the comet assay. The studied types of intervention reduced fecal and cecal genotoxicity. DNA damage by samples from AOM-treated, tumor-free rats was significantly lower than from tumor-bearing animals, especially after 4 mo of synbiotic and prebiotic interventions. Inulin-based diets reduced exposure to genotoxins in the feces, directly reflecting the reported reduction of tumor incidence in these animals. Evidence is provided for the validity of this measurement as a biomarker of chemoprevention because 1) fecal water genotoxicity reflected genotoxic exposure in the cecum, 2) tumor incidence and fecal genotoxicity were directly related, and 3) these interventions reduced tumor risks by reducing exposure to genotoxins in the gut.

Advances in the modulation of the microbial ecology of the gut in early infancy

It is now generally accepted that the microbiota of the human gut may influence health and well-being. Lactic acid bacteria are the most important microorganisms associated with these beneficial effects and the elevated bifidobacterial count may be one of the greatest advantages that breastfed infants have over infants fed with milk formulas. Several studies relative to the selective growth stimulation of bifidobacteria, both in vitro and in vivo, are reported in this review. Over the years, diverse human milk components have been identified as the specific factors able to modulate the growth of bifidobacteria. Even if there is a certain agreement that the bifidogenic activity of human milk may be based not on single growth substances, but on a complex set of interacting factors, the present state of knowledge indicates that the use of non-digestible but fermentable carbohydrates may be an easy and reliable method to influence the growth of lactic acid bacteria. In this context, some of the characteristics of the major physiological effects of inulin-type fructans, of galacto-oligosaccharides, but also of lactoferrin, a milk whey protein fraction with purported bifidogenic activity, are briefly examined.

Prospective study on milk products, calcium and cancers of the colon and rectum

OBJECTIVE

To study the relationship between consumption of milk and milk products, calcium, lactose and vitamin D and occurrence of colorectal cancers.

DESIGN

Prospective cohort study.

SUBJECTS

A total of 9959 men and women aged 15 y or older without history of cancer at baseline. During a 24 y follow-up, 72 new cancers of the large bowel (38 in the colon and 34 in the rectum) were detected.

RESULTS

Consumption of milk and total milk products was suggested to be inversely related to colon cancer incidence, whereas no similar association was seen for rectal cancer. The relative risk between the highest and lowest quartiles of intake adjusted for potential confounding factors was 0.46 (95% confidence interval 0.14-1.46, P for trend 0.09) for milk and 0.37 (95% CI=0.12-1.39, P for trend 0.06) for total milk products. Lactose intake showed a similar inverse relationship with colon cancer: the relative risk was 0.31 (95% CI=0.08-1.15, P for trend 0.03). Intake of vitamin D or total dietary calcium was not significantly related to colorectal cancer risk, whereas calcium provided by fermented milk products was associated with increased colorectal cancer incidence; in the highest quartile the multivariate adjusted relative risk for colorectal cancer was 2.07 (95% CI=1.00-4.28).

CONCLUSIONS

Our results indicate that individuals showing high consumption of milk have a potentially reduced risk of colon cancer; however, the association does not appear to be due to intake of calcium, vitamin D, or to specific effects of fermented milk.

SPONSORSHIP

This study was supported by a grant from the Swedish Cancer Foundation.

Binding activity of natto (a fermented food) and Bacillus natto isolates to mutagenic-carcinogenic heterocyclic amines

The fermented food, whole meal Natto, viscous polymeric material from Natto, Natto bean, cooked soya bean, and 28 bacterial isolates from Natto were studied for their binding capacity to foodborne mutagenic-carcinogenic heterocyclic amines. The mutagenic heterocyclic amines used were Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole); Trp-P-2 (3-amino-1-methyl-5H-pyrido(4,3-b)indole); Glu-P-1 (2-amino-6-methyldipyrido(1,2-a:3'2'-d)imidazole); PhIP (2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine); IQ (2-amino-3-methylimidazo(4,5-f)quinoline); MeIQ (2-amino-3,4-dimethylimidazo(4,5-f)quinoxaline); MeIQx (2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline); and MeAalphaC (2-amino-3-methyl-9H-pyrido(2,3)indole). The lyophilized Natto and other fractions of Natto exhibited high binding activity towards Trp-P-1, Trp-P-2, PhIP, and MeAalphaC, while Glu-P-1, IQ, and MeIQ were not effectively bound. The binding capacity of bacterial isolates (Bacillus natto) were isolate-mutagen dependent. Heat treated lyophilized cells, cell wall, and cytoplasmic contents of the bacterial isolate with the highest binding capacity were analyzed for their ability to bind different heterocyclic amines. The results indicate the importance of the cell wall in binding to heterocyclic amines, whereas the cytoplasmic contents were less effective. Heat-treated cells were not much different from that of viable cells in their binding. The impact of different factors, such as pH, incubation time, metal ions, different concentrations of sodium chloride and alcohol, various enzymes, and acetylation of mutagens on binding of Trp-P-1 and IQ, were discussed. The significance of the present results is also discussed from the viewpoint that Natto, a fermented food, is able to scavenge dietary mutagenic heterocyclic amines through binding.

Taxonomy and important features of probiotic microorganisms in food and nutrition

Lactic acid bacteria are among the most important probiotic microorganisms typically associated with the human gastrointestinal tract. Traditionally, lactic acid bacteria have been classified on the basis of phenotypic properties, eg, morphology, mode of glucose fermentation, growth at different temperatures, lactic acid configuration, and fermentation of various carbohydrates. Studies based on comparative 16S ribosomal RNA sequencing analysis, however, showed that some taxa generated on the basis of phenotypic features do not correspond with the suggested phylogenetic relations. Thus, some species are not readily distinguishable by phenotypic characteristics. This is especially true for the so-called Lactobacillus acidophilus group, the Lactobacillus casei and Lactobacillus paracasei group, and some bifidobacteria, strains of which have been introduced in many probiotic foods, eg, the novel yogurt-like commodities. Consequently, modern molecular techniques, including polymerase chain reaction-based and other genotyping methods, have become increasingly important for species identification or for the differentiation of probiotic strains. Probiotic strains are selected for potential application on the basis of particular physiologic and functional properties, some of which may be determined in vitro. The classification and identification of a probiotic strain may give a strong indication of its typical habitat and origin. The species, or even genus name, may also indicate the strain's safety and technical applicability for use in probiotic products. Molecular typing methods such as pulsed-field gel electrophoresis, repetitive polymerase chain reaction, and restriction fragment length polymorphism are extremely valuable for specific characterization and detection of such strains selected for application as probiotics.

Protective role of probiotics and prebiotics in colon cancer

Ingestion of viable probiotics or prebiotics is associated with anticarcinogenic effects, one mechanism of which is the detoxification of genotoxins in the gut. This mechanism was shown experimentally in animals with use of the rat colon carcinogen 1,2-dimethylhydrazine and by determining endpoints that range from tumorigenesis to induction of DNA damage. Because of the complexity of cancer initiation, cancer progression, and the exposure of cancer in the gut, many types of interactions may be envisaged. Notably, some of our newer studies showed that short-lived metabolite mixtures isolated from milk that was fermented with strains of Lactobacillus bulgaricus and Streptococcus thermophilus are more effective in deactivating etiologic risk factors of colon carcinogenesis than are cellular components of microorganisms. Ingestion of prebiotics results in a different spectrum of fermentation products, including the production of high concentrations of short-chain fatty acids. Gut flora, especially after the ingestion of resistant starch, induces the chemopreventive enzyme glutathione transferase pi in the colon of the rat. Together, these factors lead to a reduced load of genotoxic agents in the gut and to an increased production of agents that deactivate toxic components. Butyrate is one such protective agent and is associated with lowering cancer risk. It was recently shown that buytrate may inhibit the genotoxic activity of nitrosamides and hydrogen peroxide in human colon cells. In humans, the ingestion of probiotics leads to the excretion of urine with low concentrations of components that are genotoxic in human colon cells and high concentrations of components that induce oxidized DNA bases.

Inter- and intra-individual variation of faecal water - genotoxicity in human colon cells

Exogenous nutritional factors modulate the faecal contents leading to an enhanced or reduced burden with toxic and cancerogenic factors. These factors are thought to contribute to colon cancer by inducing mutations or enhancing proliferation in colon cells. Faecal water more or less causes these effects in model systems and thus could be the basis for valuable biomarker approaches. Our investigations are aimed at determining geno- and cytotoxicity of faecal water in human colon cell lines in vitro. We are developing techniques for their applicability as biomarker tests during dietary intervention studies. Faecal water is isolated by centrifugation of the faeces at 25000xg and added to cultured human colon cells (HT29). Membrane damage as assessed by trypan blue exclusion is determined as a measure for cytotoxicity. Semiquantitative analysis of inducible DNA damage (breaks and alkali labile sites) are analysed with the single cell microgelelectrophoresis assay (comet-assay) and oxidised DNA bases by the additional use of repair specific enzymes. We have now determined baseline toxic activities and calculated inter- and intra-individual and -experimental coefficients of variation for faecal water from different subjects consuming similar or different diets. Most faecal water induced DNA damage and oxidised DNA bases in HT29 clone 19a cells (0.9-9.14 fold and 1.7-4.9 fold, respectively in comparison to the NaCl controls). Intra- and inter-experimental coefficients (CV) of variation, were in a similar order of magnitude and ranged from 6.9 to 31.4. In contrast both intra- and inter-individual variability were considerably higher (CV-ranges of 29.7-76.6 and 21.3-64.0, respectively). Interestingly, these inter-individual values were not lowered when subjects consumed identical diets (CV-ranges of 28.4-126.0). However, following intervention with certain protective dietary regimens (e.g. lignan containing bread) significant reductions of faecal water-induced genotoxicity can be observed. Therefore, in spite of the expected and observed degrees of variation in this methodology, effective experimental protocols may still lead to detectable modulations of the level of toxic and genotoxic effects.

The role of probiotic bacteria in cancer prevention

Colorectal cancer is one of the most important causes of cancer morbidity and mortality in western countries [1]. A myriad of healthful effects have been attributed to the probiotic lactic acid bacteria; perhaps the most controversial remains that of anticancer activity. There is no direct experimental evidence for cancer suppression in humans as a result of consumption of lactic cultures in fermented or unfermented dairy products. However, there is a wealth of indirect evidence, based largely on laboratory studies, in the literature and this will be summarised in the present paper.

Inhibitory effects of freeze-dried milk fermented by selected Lactobacillus bulgaricus strains on carcinogenesis induced by 1,2-dimethylhydrazine in rats and by diethylnitrosamine in hamsters

Fermented milk products might be used for cancer chemoprevention due to their putative anticarcinogenic and antitumor activities. The diet was supplemented with freeze-dried milk fermented by Lactobacillus bulgaricus strain LBB.B 144 (product FFM.B 144) added throughout the experiment at doses of 1.3 g and 2.5 g per rat, 5 times a week starting 3 weeks before the first carcinogen injection. This treatment significantly inhibited, by 26.2-28.6% and by 34.2%, the total intestinal carcinogenesis induced by 1,2-dimethylhydrazine (DMH, 21 mg/kg, s.c., once per week for 20 weeks) in male and female BD6 rats, respectively. FFM.B144 decreased the tumor incidence and multiplicity in large bowel, caecum, and duodenum. Protective effects were better expressed in female animals, with exception of that observed in duodenum. Supplementation of diet with freeze-dried milk fermented by Lactobacillus bulgaricus strain LBB.B5 (product FFM.B5) inhibited DMH-induced carcinogenesis only in the large bowel, but had no significant protective effect when all intestinal tumors were taken into account. However, both freeze-dried products favorably shifted the differentiation of large bowel tumors by increasing the proportion of benign and highly differentiated malignant tumors and decreasing in parallel the number of poorly differentiated carcinomas without influencing the tumor size. A lower number of cases with visible mesenterial metastasis was also observed in FFM-treated rats. In addition, both FFM.B 144 and FFM.B5 significantly inhibited, by 26-33%, the induction in the same rats of ear-duct tumors. FFM.B144 but not FFM.B5 was also effective in inhibiting the tracheal carcinogenesis induced in Syrian golden hamsters by diethylnitrosamine (DEN, 100 mg/kg, two s.c. injections), the protective effect being better expressed in female animals. The anticarcinogenic potential of some fermented milk products might be exploited in chemoprevention of cancer in humans.

Antimutagenicity of milk fermented by Enterococcus faecium

The diethyl ether extracts isolated from unfermented milk and milk fermented by Enterococcus faecium exhibited dose-dependent inhibition of mutagenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), nitrovin (NIT), 5-nitro-2-furylacrylic acid (NFA) and UV-irradiation on the Ames bacterial test (Salmonella typhimurium strains TA97 and TA100) and the unicellular flagellate Euglena gracilis. Overall, the fermented milk extract was the most active against UV-irradiation, less active against NIT and MNNG, and the least active against NFA on bacteria. The highest antibleaching effects were observed against MNNG. The differences between antimutagenic effects from fermented and unfermented milk extracts were determined to be statistically significant at the 0.95 CI level.

Bacteria used for the production of yogurt inactivate carcinogens and prevent DNA damage in the colon of rats

Lactic acid-producing bacteria prevent carcinogen-induced preneoplastic lesions and tumors in rat colon. Because the mechanisms responsible for these protective effects are unknown, two strains of lactic acid bacteria, Lactobacillus delbrueckii ssp. bulgaricus 191R and Streptococcus salivarius ssp. thermophilus CH3, that are used to produce yogurt, were investigated in vitro and in vivo to elucidate their potential to deactivate carcinogens. Using the "Comet assay" to detect genetic damage, we found that L. bulgaricus 191R applied orally to rats could prevent 1, 2-dimethylhydrazine-induced DNA breaks in the colon in vivo, whereas St. thermophilus CH3 were not effective. However, in vitro, both strains prevented DNA damage induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in isolated primary rat colon cells. Extracts prepared from milk fermented with St. thermophilus CH3 were as efficient in deactivating MNNG as was L-cysteine. Isolated metabolites arising from bacteria during fermentation in the colon or in milk [L(+) lactate, D(-) lactate, palmitic acid and isopalmitic acid] were not effective. We postulate that thiol-containing breakdown products of proteins, via catalysis by bacterial proteases, could be one mechanism by which MNNG or other carcinogens are deactivated in the gut lumen resulting in reduced damage to colonic mucosal cells.

Overview of gut flora and probiotics

Scientific developments in recent years have opened new frontiers and enable a better understanding of the gastrointestinal tract (GIT) as a complex and delicately balanced ecosystem. This paper focuses on more recent information related to the microbial population of the GIT and its functional role in human physiology and health. Special attention is also given to modern approaches for improving or stabilising the intestinal system and its functioning by the deliberate application of viable microbial cultures, so-called 'probiotics', selected for special functional properties.

Calcium, phosphorus, vitamin D, dairy products and colorectal carcinogenesis: a French case--control study

A protective effect of calcium against colorectal cancer has been described in Anglo-Saxon but not in Latin communities, and no such effect has been observed regarding adenomas. We investigated the relationship between calcium, dairy products and the adenoma-carcinoma sequence in a French region by comparing small adenoma ( < 10 mm, n = 154), large adenoma (n = 208) and polyp-free (n = 426) subjects, and cancer cases (n = 171) with population controls (n = 309). There was no protective effect of calcium against colorectal tumours except for low fat calcium and large adenomas in men (OR for highest quintile = 0.3, P for trend = 0.06). There was even a trend towards an increased risk of cancer with dairy calcium in men and non-dairy calcium in women. Vitamin D was inversely related to the risk of small adenomas in women (OR for highest quintile = 0.4, P for trend = 0.04). Regarding dairy products, only consumption of yoghurt displayed an inverse relationship with risk of large adenomas, in both men and women. These data failed to demonstrate a protective effect of calcium against colorectal carcinogenesis. They suggest that the type of dairy product might be the important factor with regard to prevention of colorectal tumours.

The effect of Lactobacillus GG on the initiation and promotion of DMH-induced intestinal tumors in the rat

Male Fischer 344 rats were fed a 20% or a 5% corn oil diet and were injected subcutaneously with dimethylhydrazine (DMH) weekly for 16 weeks. In addition, an approximately equal number of animals challenged with DMH were fed daily, until the end of the study, 2 x 10(10) Lactobacillus casei subsp. rhamnosus strain GG starting three weeks before DMH administration or after the ninth weekly injection. The feeding of the Lactobacillus GG before and during carcinogen treatment resulted in a significant decrease in the incidence of colon tumors and the number of small intestinal and colon tumors per tumor-bearing animal for rats fed a 20% corn oil diet. This decrease in tumor incidence or number of tumors was not seen when animals were fed the Lactobacillus after the ninth week of carcinogen treatment. Animals fed a 5% corn oil diet had a lower tumor incidence and number of tumors resulting from the decrease in dietary fat; in addition the feeding of Lactobacillus GG before the carcinogen challenge resulted in a lower incidence of colon tumors. These studies show that a specific strain of L. casei subsp. rhamnosus designated GG can interfere with the initiation or early promotional stages of DMH-induced intestinal tumorigenesis, and this effect is most pronounced for animals fed a high-fat diet.

Antimutagenicity of components of dairy products

This paper reports the potential antimutagenicity of some components of dairy products. For both milk and fermented milk, Bifidobacterium sp. Bio (strain Danone 173010), casein and calcium showed a dose-dependent antimutagenic activity against benzo[a]pyrene mutagenicity in the Ames test using Salmonella typhimurium TA98. Fatty compounds present in milk had no antimutagenic effect. At the level occurring in cultured or uninoculated milks, and even more, the bifidobacteria, casein and calcium showed less antimutagenic activity than fermented and uninoculated milks. So, the mix of all these components must contribute to the total protective effect of dairy products against induced mutagenicity, and this does not rule out the possibility of contribution of other unknown substances. The total antimutagenicity of uninoculated skim milk corresponds to the additional activity of casein and calcium. The observed antimutagenic activity of fermented skim milk remains lower than expected.

Colonic microflora: nutrition and health. Summary and conclusions of an International Life Sciences Institute (ILSI) [Europe] workshop held in Barcelona, Spain

The colonic microflora is an organism that performs a variety of unique activities. It is more important to evaluate these activities than to analyze bacterial composition in terms of genera, species, or strains. Unless the bacteria translocate, it is the activities of the colonic microflora that affect colonic and systemic physiology and not the bacteria themselves.

Antimutagenicity of an acetone extract of yogurt

Reconstituted non-fat dry milk powder, fermented by a mixture of Streptococcus thermophilus CH3 and Lactobacillus bulgaricus 191R to produce yogurt, was freeze-dried and extracted in acetone. After evaporation of the acetone, the extract was dissolved in dimethyl sulfoxide (DMSO) and tested for antimutagenicity. In the Ames test, significant dose-dependent activity was observed against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitro-quinoline-N-oxide (4NQO), 3,2'-dimethyl-4-aminobiphenyl (DMAB), 9,10-dimethyl-1,2-benz[a]anthracene (DMBA), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-P-2). Weak activity was observed against 1,2,7,8-diepoxyoctane (DEO), and no activity was observed against methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), or aflatoxin B1 (AFB1). In a related assay (Saccharomyces cerevisiae D7), significant antimutagenic activity was detected against MNNG and 4NQO. Activity against the experimental colon carcinogens MNNG and DMAB was examined further, as assayed in the Ames test (Salmonella typhimurium TA100). Compounds responsible for both activities were less soluble in aqueous solutions than in DMSO. Adjustment of yogurt pH to 3, 7.6, or 13 prior to freeze-drying and acetone extraction did not significantly alter the amount of anti-MNNG activity recovered. In contrast, extractability of anti-DMAB activity was significantly greater at acidic pH. Conjugated linoleic acid, a known dairy anticarcinogen, failed to inhibit mutagenesis caused by either mutagen, suggesting that other yogurt-derived compound(s) are responsible. Unfermented milk was treated with lactic acid, yogurt bacteria without subsequent growth, or both, to determine if formation of antimutagenic activity required bacterial growth. Extracts of the milk treatments exhibited the same weak antimutagenicity observed in unfermented milk, approximately 2.5-fold less than in the yogurt extracts, suggesting that antimutagenic activity is associated with bacterial growth.

Antigenotoxic properties of lactic acid bacteria in vivo in the gastrointestinal tract of rats

In view of the high incidence of dietary-related tumors, one important research goal is to identify the participating genotoxic carcinogens and the nutritional factors that may counteract their activities. We therefore have further developed a method to assess DNA damage in tumor target tissues of the gastrointestinal tract. Subsequently the prevention of this inducible DNA damage by lactic acid bacteria and by milk products fermented with probiotics was studied as well. The microgel electrophoresis technique was applied to cells of the esophageal, gastric, duodenal, and colonic mucosa. Cells were grouped according to their degree of DNA damage, the simplest measure of which is to discriminate between those with damage (comets) and those without damage. When these cells were isolated from animals treated with a genotoxic carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and exposed to MNNG for 1-24 hours, it was possible to follow the course of genotoxicity throughout the gastrointestinal tract. After the animals were treated with the lactic acid bacteria under study, it was possible to detect antigenotoxic properties as well. The gavage of 10(10) viable Lactobacillus casei cells in 10 ml of 0.9% NaCl per kilogram body weight immediately before the oral administration of MNNG (5 mg/kg body wt) resulted in a reduction of induced DNA damage in gastric and colonic mucosa cells. A sequential treatment schedule was even more effective: when the animals were treated orally with lactic acid bacteria or yogurt (10 ml/kg body wt) in the morning followed by MNNG (7.5 mg/kg body wt) eight hours later and the colon cells were isolated 16 hours later, the percentages of cells remaining intact were distinctly higher in the combination groups (68 +/- 10 and 68 +/- 19 for L. casei and a "Bio" yogurt, respectively) than in the group receiving only MNNG (45 +/- 17). The effect of heating L. casei was studied and was found to yield less clear-cut effects in preventing genotoxicity. The method is an efficient tool to elucidate antigenotoxic properties of food components in vivo in those target tissues actually afflicted by dietary-related tumors.