Degradation of N-nitrosamines by intestinal bacteria

Overview of the Mechanistic Potential of Probiotics and Prebiotics in Cancer Chemoprevention

Despite of strides in modern cancer therapeutic strategies, there has not been a successful cure for it until now and prognostic side effects and substantial toxicity to chemotherapy and subsequent homeostatic imbalance remains a major concern for professionals in this field. The significance of the human microbiome in the pathogenesis of cancer is being recognized, documented, and established worldwide. Probiotics and prebiotics are some of the most extensively researched approaches to modulate the microbiota for therapeutic purposes, and research on their potential to prevent and treat cancer has sparked an immense amount of interest. The characteristics of probiotics and prebiotics allow for an array of efficient applications in cancer preventive measures. Probiotics can also be administered coupled with chemotherapy and surgery to alleviate their side effects and help promote the effectiveness of chemotherapeutic drugs. Besides showing promising results they are accompanied by potential risks and controversies that may eventually result in clinical repercussions. This review emphasizes the mechanistic potential and oncosuppressive effects of probiotic and prebiotics through maintenance of intestinal barrier function, modifying innate immune system, immunomodulation, intestinal microbiota metabolism, inhibition of host cell proliferation, preventing pathogen colonization, and exerting selective cytotoxicity against tumor cells.

Anticancer activity of lactic acid bacteria

Lactic acid bacteria (LAB), a group of Gram-positive microorganisms naturally occurring in fermented food products and used as probiotics, have been gaining the interest of researchers for years. LAB are potent, albeit still not wholly understood, source of bioactive compounds with various functions and activity. Metabolites of LAB, among others, short-chain fatty acids, exopolysaccharides and bacteriocins have promising anticancer potential. Research on the interactions between the bioactive metabolites of LAB and immune mechanisms demonstrated that these substances could exert a strong immunomodulatory effect, which would explain their vast therapeutic potential. The anticancer activity of LAB was confirmed both in vitro and in animal models against cancer cells from various malignancies. LAB inhibit tumor growth through various mechanisms, including antiproliferative activity, induction of apoptosis, cell cycle arrest, as well as through antimutagenic, antiangiogenic and anti-inflammatory effects. The aim of this review was to summarize the most recent data about the anticancer activity of LAB, with particular emphasis on the most promising bioactive compounds with potential clinical application.

The Role of Probiotics in Cancer Prevention

Simple Summary

Cancer is considered one of the leading causes of human mortality in the world and is the subject of much research. The risk of developing cancer depends on genetic factors, as well as the body’s immune status. The intestinal microbiome plays very important role in maintaining homeostasis in the human body. Probiotics have gained increasing medical significance due to the beneficial effect on the human body associated with the prevention and support of the treatment of many chronic diseases, including cancer in the absence of side effects. The aim of this review was to summarize the knowledge about the effect of probiotic microorganisms in the prevention of cancer. There is a lot of evidence that the use of probiotics can play an important role in cancer prevention and support anti-cancer therapies.

Abstract

The gut microbiome can play important role in maintaining homeostasis in the human body. An imbalance in the gut microbiome can lead to pro-inflammatory immune responses and the initiation of disease processes, including cancer. The research results prove some strains of probiotics by modulating intestinal microbiota and immune response can be used for cancer prevention or/and as adjuvant treatment during anticancer chemotherapy. This review presents the latest advances in research into the effectiveness of probiotics in the prevention and treatment support of cancer. The described issues concern to the anticancer activity of probiotic microorganisms and their metabolites. In addition, we described the potential mechanisms of probiotic chemoprevention and the advisability of using probiotics.

Shaping functional gut microbiota using dietary bioactives to reduce colon cancer risk

Colon cancer is a multifactorial disease associated with a variety of lifestyle factors. Alterations in the gut microbiota and the intestinal metabolome are noted during colon carcinogenesis, implicating them as critical contributors or results of the disease process. Diet is a known determinant of health, and as a modifier of the gut microbiota and its metabolism, a critical element in maintenance of intestinal health. This review summarizes recent evidence demonstrating the role and responses of the intestinal microbiota during colon tumorigenesis and the ability of dietary bioactive compounds and probiotics to impact colon health from the intestinal lumen to the epithelium and systemically. We first describe changes to the intestinal microbiome, metabolome, and epithelium associated with colon carcinogenesis. This is followed by a discussion of recent evidence indicating how specific classes of dietary bioactives, prebiotics, or probiotics affect colon carcinogenesis. Lastly, we briefly address the prospects of using multiple 'omics' techniques to integrate the effects of diet, host, and microbiota on colon tumorigenesis with the goal of more fully appreciating the interconnectedness of these systems and thus, how these approaches can be used to advance personalized nutrition strategies and nutrition research.

Evaluating the efficacy of probiotic on treatment in patients with small intestinal bacterial overgrowth (SIBO)--a pilot study

BACKGROUND & OBJECTIVES

Small intestinal bacterial overgrowth (SIBO) leads to several gastrointestinal (GI) problems and complications leading to malabsorption. The effectiveness of probiotics in the treatment of SIBO syndrome has not been well studied. This pilot study was aimed to assess the efficacy of a probiotic consisting of lactobacilli in the treatment of SIBO.

METHODS

In this study, 30 cases suffering from chronic abdominal pain or diarrhoea and with a positive hydrogen breath test were randomized in a double-blind manner into two groups: probiotic drug user and control group. After an initial 3-week aggressive therapy with broad-spectrum antibiotics, a 15-day maintenance antibiotic therapy with lactol was administered for the study group and the same regimen without lactol for the control group. After six months the HBT result and the GI symptoms were analyzed and compared between the two groups.

RESULTS

The result of hydrogen breath test and the clinical symptoms in patients receiving the maintenance regimen with lactol probiotic showed a better response. The hydrogen breath test turned negative in 93.3 per cent of those receiving lactol compared to 66.7 per cent of the controls. In all the cases receiving lactol, the abdominal pain disappeared completely ( p =0.002). In addition, other GI problems including flatulence, belching and diarrhoea significantly improved in the study group ( p < 0.05).

INTERPRETATION & CONCLUSIONS

Based on the preliminary data it seems that adding lactol probiotic to the maintenance therapy of small intestinal bacterial overgrowth patients on routine antibiotic therapy will be beneficial in preventing the complications of this syndrome.

Detection and occurrence of N-nitrosamines in archived biosolids from the targeted national sewage sludge survey of the U.S. Environmental Protection Agency

The occurrence of eight carcinogenic N-nitrosamines in biosolids from 74 wastewater treatment plants (WWTPs) in the contiguous United States was investigated. Using liquid chromatography-tandem mass spectrometry, seven nitrosamines [(N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine, N-nitrosodi-n-propylamine (NDPA), N-nitrosodibutylamine, N-nitrosopyrrolidine, N-nitrosopiperidine (NPIP), and N-nitrosodiphenylamine (NDPhA)] were detected with varying detection frequency (DF) in 88% of the biosolids samples (n = 80), with five of the seven being reported here for the first time in biosolids. While rarely detected (DF 3%), NDMA was the most abundant compound at an average concentration of 504 ± 417 ng/g dry weight of biosolids. The most frequently detected nitrosamine was NDPhA (0.7-147 ng/g) with a DF of 79%, followed by NDPA (7-505 ng/g) and NPIP (51-1185 ng/g) at 21% and 11%, respectively. The DF of nitrosamines in biosolids was positively correlated with their respective n-octanol-water partition coefficients (R(2) = 0.65). The DF and sum of mean concentrations of nitrosamines in biosolids increased with the treatment capacity of WWTPs. Given their frequent occurrence in nationally representative samples and the amount of U.S. biosolids being applied on land as soil amendment, this study warrants more research into the occurrence and fate of nitrosamines in biosolids-amended soils in the context of crop and drinking water safety.

Intestinal formation of N-nitroso compounds in the pig cecum model

N-Nitroso compounds (NOC) are a group of compounds including N-nitrosamines and N-nitrosamides, which are well-known for their carcinogenic, mutagenic, and teratogenic properties. Humans can be exposed to NOC through the diet and environmentally, or NOC can be formed endogenously in the stomach and intestine. In the intestine, the formation of NOC is supposed to be afforded by the gut microbiota. In this study, the formation of the N-nitrosamines, N-nitrosomorpholine (NMOR) and N-nitrosopyrrolidine (NPYR), and the N-nitrosamides, N-nitrosomethylurea (NMU) and N-nitrosoethylurea (NEU), was investigated in the pig cecum model after the incubation of the corresponding precursor amine or amide with nitrite or nitrate. Following the incubation with nitrate, the formation of NMOR, NPYR, NMU, and NEU was detectable with the microbiota being responsible for the reduction of nitrate to nitrite. After the incubation of nitrite a chemical formation of NOC was shown.

Fate of N-nitrosomorpholine in an anaerobic aquifer used for managed aquifer recharge: a column study

The fate of N-nitrosomorpholine (NMOR) was evaluated at microgram and nanogram per litre concentrations. Experiments were undertaken to simulate the passage of groundwater contaminants through a deep anaerobic pyritic aquifer system, as part of a managed aquifer recharge (MAR) strategy. Sorption studies demonstrated the high mobility of NMOR in the Leederville aquifer system, with retardation coefficients between 1.2 and 1.6. Degradation studies from a 351 day column experiment and a 506 day stop-flow column experiment showed an anaerobic biologically induced reductive degradation process which followed first order kinetics. A biological lag-time of less than 3 months and a transient accumulation of morpholine (MOR) were also noted during the degradation. Comparable half-life degradation rates of 40-45 days were observed over three orders of magnitude in concentration (200 ng L(-1) to 650 μg L(-1)). An inhibitory effect on microorganism responsible to the biodegradation of NMOR at 650 μg L(-1) or a threshold effect at 200 ng L(-1) was not observed during these experiments.

Aerobic biodegradation of N-nitrosodimethylamine by the propanotroph Rhodococcus ruber ENV425

The propanotroph Rhodococcus ruber ENV425 was observed to rapidly biodegrade N-nitrosodimethylamine (NDMA) after growth on propane, tryptic soy broth, or glucose. The key degradation intermediates were methylamine, nitric oxide, nitrite, nitrate, and formate. Small quantities of formaldehyde and dimethylamine were also detected. A denitrosation reaction, initiated by hydrogen atom abstraction from one of the two methyl groups, is hypothesized to result in the formation of n-methylformaldimine and nitric oxide, the former of which decomposes in water to methylamine and formaldehyde and the latter of which is then oxidized further to nitrite and then nitrate. Although the strain mineralized more than 60% of the carbon in [(14)C]NDMA to (14)CO(2), growth of strain ENV425 on NDMA as a sole carbon and energy source could not be confirmed. The bacterium was capable of utilizing NDMA, as well as the degradation intermediates methylamine and nitrate, as sources of nitrogen during growth on propane. In addition, ENV425 reduced environmentally relevant microgram/liter concentrations of NDMA to <2 ng/liter in batch cultures, suggesting that the bacterium may have applications for groundwater remediation.

Role of probiotics, prebiotics and synbiotics in chemoprevention for colorectal cancer

Colorectal cancer is the third most common form of cancer. Current treatments are all associated with a high risk of complications and a low success rate. Recently, synbiotics have been proposed as a new preventive and therapeutic option. There is no direct experimental evidence for cancer suppression in humans as a result of the consumption of pro-, pre- or synbiotics. However, there is a wealth of evidence emerging from laboratory studies. The mechanisms by which pro-, pre- and synbiotics may inhibit colon cancer are now beginning to be understood and will be addressed in the present review.

Biotransformation of N-nitrosodimethylamine by Pseudomonas mendocina KR1

N-Nitrosodimethylamine (NDMA) is a potent carcinogen and an emerging contaminant in groundwater and drinking water. The metabolism of NDMA in mammalian cells has been widely studied, but little information is available concerning the microbial transformation of this compound. The objective of this study was to elucidate the pathway(s) of NDMA biotransformation by Pseudomonas mendocina KR1, a strain that possesses toluene-4-monooxygenase (T4MO). P. mendocina KR1 was observed to initially oxidize NDMA to N-nitrodimethylamine (NTDMA), a novel metabolite. The use of 18O2 and H(2)18O revealed that the oxygen added to NDMA to produce NTDMA was derived from atmospheric O2. Experiments performed with a pseudomonad expressing cloned T4MO confirmed that T4MO catalyzes this initial reaction. The NTDMA produced by P. mendocina KR1 did not accumulate, but rather it was metabolized further to produce N-nitromethylamine (88 to 94% recovery) and a trace amount of formaldehyde (HCHO). Small quantities of methanol (CH3OH) were also detected when the strain was incubated with NDMA but not during incubation with either NTDMA or HCHO. The formation of methanol is hypothesized to occur via a second, minor pathway mediated by an initial alpha-hydroxylation of the nitrosamine. Strain KR1 did not grow on NDMA or mineralize significant quantities of the compound to carbon dioxide, suggesting that the degradation process is cometabolic.

Metabolism of the food-associated carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by human intestinal microbiota

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine is a putative human carcinogenic heterocyclic aromatic amine formed from meat and fish during cooking. Although the formation of hazardous PhIP metabolites by mammalian enzymes is well-documented, nothing is known about the PhIP transformation potency of human intestinal bacteria. In this study, the in vitro metabolism of PhIP by human fecal samples was investigated. Following anaerobic incubation of PhIP with stools freshly collected from six healthy volunteers, we found that PhIP was extensively transformed by the human intestinal bacteria. HPLC analysis showed that the six human fecal microbiota transformed PhIP with efficiencies from 47 to 95% after 72 h incubation, resulting in one major derivative. ESI-MS/MS, HRMS, 1D (1H, 13C, DEPT) and 2D (gCOSY, gTOCSY, gHMBC, gHSQC) NMR, and IC analysis elucidated the complete chemical identity of the microbial PhIP metabolite as 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3',2':4,5]imidazo[1,2-a]pyrimidin-5-ium chloride. At present, no information is available about the biological activity of this newly discovered bacterial PhIP metabolite. Our findings however suggest that bacteria derived from the human intestine play a key role in the activation or detoxification of PhIP, a digestive fate ignored so far in risk assessments. Moreover, the variation in transformation efficiency between the human microbiota indicates interindividual differences in the ability to convert PhIP. This may predict individual susceptibility to carcinogenic risk from this suspected dietary carcinogen.

Probiotics and prebiotics: can regulating the activities of intestinal bacteria benefit health?

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N-Nitroso compounds, bacteria, and carcinoembryonic antigen in the gastric stump

Analyses of biochemical and microbiological parameters such as pH, N-nitroso compound (NOC) concentration, carcinoembryonic antigen (CEA) level, and total viable counts (TVCs), and identification of microorganisms were carried out on 65 fasting gastric juice samples obtained at endoscopy from 45 patients previously submitted to partial gastrectomy for benign peptic ulcer disease (23 Billroth I, 22 Billroth II/Reichel-Polya) and 20 normal controls. Biopsy specimens were taken to determine histology, the Helicobacter pylori status, and both tissue CEA immunoreactivity and level. Significantly higher mean pH values, NOC and CEA concentrations, and TVCs were found in partial gastrectomies compared with normal controls. In relation to surgical methods, higher mean pH values, NOC concentrations, TVCs, and anaerobic bacterial counts were observed in the juice of patients with Billroth II compared with Billroth I gastrectomies. Mild CEA immunoreactivity and apical CEA localization were found significantly more often in Billroth II than in Billroth I stumps. Intensive CEA immunoreactivity and cytoplasmatic localization were found significantly more often in Billroth I than in Billroth II stumps. Independent of the type of surgical reconstruction, higher mean NOC levels were recorded in patients with more severe histological changes and H. pylori infection. Higher mean CEA levels in gastric juice and tissue were detected in the gastric stumps with more severe histological changes. All these data suggest that high levels of NOCs in the gastric juice could be a cofactor in gastric stump carcinogenesis and determination of CEA level in gastric juice and tissue could be included as a very useful marker in quantifying this process.

Transport and metabolism of glucose and arabinose in Bifidobacterium breve

Glucose was required for the transport of arabinose into Bifidobacterium breve. The non-metabolisable glucose analogue 2-deoxy-D-glucose (2-DG) did not facilitate assimilation of arabinose. Studies using D-[U-14C]-labelled arabinose showed that it was fermented to pyruvate, formate, lactate and acetate, whereas the principal metabolic products of D-[U-14C]-labelled glucose were acetate and formate. In contrast to glucose, arabinose was not incorporated into cellular macromolecules. A variety of metabolic inhibitors and inhibitors of sugar transport (proton ionophores, metal ionophores, compounds associated with electron transport) were used to investigate the mechanisms of sugar uptake. Only NaF, an inhibitor of substrate level phosphorylation, and 2-DG inhibited glucose assimilation. 2-DC had no effect on arabinose uptake, but NaF was stimulatory. High levels of phosphorylation of glucose and 2-DC by PEP and to a lesser degree, ATP were seen in phosphoenolpyruvate: phosphotransferase (PEP:PTS) assays. These data together with strong inhibition of glucose uptake by NaF suggest a role for phosphorylation in the transport process. Arabinose uptake in B. breve was not directly dependent on phosphorylation or any other energy-linked form of transport but may be assimilated by glucose-dependent facilitated diffusion.

Inhibitory effect of some intestinal bacteria on liver tumorigenesis in gnotobiotic C3H/He male mice

Liver tumorigenesis in gnotobiotic C3H/He male mice was markedly promoted by association with a bacterial combination of Escherichia coli, Streptococcus faecalis, and Clostridium paraputrificum. This study demonstrated that this promoting effect was suppressed by addition of certain intestinal bacteria, such as Bifidobacterium longum, Lactobacillus acidophilus, and Eubacterium rectale.

Metabolism and activation of chemical carcinogens

A great deal of effort has gone into research on the mechanisms of action of chemical carcinogens. The action of the host on the carcinogen represents one approach--to determine what metabolic products may be involved. Study of the action of the carcinogen on the host requires a thorough comparison of changes wrought in cellular constituents by the carcinogen. Meshing of these two approaches increases the potential to discover the detailed mechanisms involved. Despite the increase in knowledge, many crucial molecular events and their consequences in the process of carcinogenesis still remain a mystery.

Microbial metabolism of N-nitrosodiethanolamine in lake water and sewage

The carcinogenic nitrosamine, N-nitrosodiethanolamine (NDElA), was degraded in samples of sewage and two lake waters, and microorganisms were responsible for the transformation. However, the rate of NDElA disappearance was slow. In the samples of lake water, the rate and extent of NDElA metabolism varied with the time of year, and no disappearance occurred in samples taken in winter. The products formed from NDEIA were persistent in lake water. In sewage, no seasonal effect on the microbial conversion was evident, and the products of metabolism were slowly mineralized. NDElA is apparently converted to the same organic products in samples of all three environments. Although the products were not identified, the data suggest that they were modified dimers of NDElA.

The absorption and metabolism in rats of small oral doses of dimethylnitrosamine. Implication for the possible hazard of dimethylnitrosamine in human food

1. Groups of rats were given one dose of the carcinogen dimethylnitrosamine by gastric intubation. The dose was varied between 10mg/kg body wt. and 1 microgram/kg body wt. 2. The dose was rapidly absorbed. 3. The methylation of liver DNA resulting from the administration of this carcinogen was proportional to dose. This suggests that small doses are absorbed from the gut with no more loss than large doses. 4. As the dose was decreased there was a disproportionately greater decrease in the alkylation of kidney DNA, and when the dose was less than 40 microgram/kg body wt. the methylation of kidney DNA was no longer detectable. This possibly explains why small amounts of dimethylnitrosamine in the diet do not induce kidney tumours. 5. Comparison of the relative alkylation of liver DNA and kidney DNA resulting from an oral and from an intravenous dose of dimethylnitrosamine suggest that small amounts of dimethylnitrosamine absorbed into the portal blood from the gut are completely metabolized by the liver and do not enter the general circulation. 6. The implications of these results for the possible hazard of dimethylnitrosamine in human food is discussed.