Long-term dietary intake influences the structure and activity of the trillions of microorganisms residing in the human gut, but it remains unclear how rapidly and reproducibly the human gut microbiome responds to short-term macronutrient change. Here we show that the short-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression. The animal-based diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale and Ruminococcus bromii). Microbial activity mirrored differences between herbivorous and carnivorous mammals, reflecting trade-offs between carbohydrate and protein fermentation. Foodborne microbes from both diets transiently colonized the gut, including bacteria, fungi and even viruses. Finally, increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat, bile acids and the outgrowth of microorganisms capable of triggering inflammatory bowel disease. In concert, these results demonstrate that the gut microbiome can rapidly respond to altered diet, potentially facilitating the diversity of human dietary lifestyles.

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Diet rapidly and reproducibly alters the human gut microbiome

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(00)04046-0.pdf

Inflammation and cancer: back to Virchow?

The importance of the ratio of omega-6/omega-3 essential fatty acids.

http://envismadrasuniv.org/Physiology/pdf/Gut%20flora%20in%20health%20and%20disease.pdf

Gut flora in health and disease

Organismal life encounters reactive oxidants from internal metabolism and environmental toxicant exposure. Reactive oxygen and nitrogen species cause oxidative stress and are traditionally viewed as being harmful. On the other hand, controlled production of oxidants in normal cells serves useful purposes to regulate signaling pathways. Reactive oxidants are counterbalanced by complex antioxidant defense systems regulated by a web of pathways to ensure that the response to oxidants is adequate for the body's needs. A recurrent theme in oxidant signaling and antioxidant defense is reactive cysteine thiol–based redox signaling. The nuclear factor erythroid 2–related factor 2 (Nrf2) is an emerging regulator of cellular resistance to oxidants. Nrf2 controls the basal and induced expression of an array of antioxidant response element–dependent genes to regulate the physiological and pathophysiological outcomes of oxidant exposure. This review discusses the impact of Nrf2 on oxidative stress and toxicity and how...

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Role of nrf2 in oxidative stress and toxicity.

In the NCI, Chemoprevention Branch drug development program, potential chemopreventive agents are evaluated for efficacy against chemical carcinogen-induced tumors in animal models This paper summarizes the results of 144 agents in 352 tests using various animal efficacy models Of these results, 146 were positive, representing 85 different agents The target organs selected for the animals model are representative of high-incidence human cancers The assays include inhibition of tumors induced by MNU in hamster trachea, DEN in hamster lung, AOM in rat colon (including inhibition of AOM-induced aberrant crypts), MAM in mouse colon, DMBA and MNU in rat mammary glands, DMBA promoted by TPA in mouse skin, and OH-BBN in mouse bladder The agents tested may be classified into various pharmacological and chemical structural categories that are relevant to their chemopreventive potential These categories include antiestrogens, antiinflammatories (eg, NSAIDs), antioxidants, arachidonic acid metabolism inhibitors, GST and GSH enhancers, ODC inhibitors, protein kinase C inhibitors, retinoids and carotenoids, organosulfur compounds, calcium compounds, vitamin D3 and analogs, and phenolic compounds (eg, flavonoids) The various categories of compounds have different spectra of efficacy in animal models In hamster lung, GSH-enhancing agents and antioxidants appear to have high potential for inhibiting carcinogenesis In the colon, NSAIDs and other antiinflammatory agents appear particularly promising Likewise, NSAIDs are very active in mouse bladder In rat mammary glands, retinoids and antiestrogens (as would be expected) are efficacious Several of the chemicals evaluated also appear to be promising chemopreventive agents based on their activity in several of the animal models Particularly, the ODC inhibitor DFMO was active in the colon, mammary glands, and bladder models, while the dithiolthione, oltipraz, was efficacious in all the models listed above (ie, lung, colon, mammary glands, skin, and bladder)

Preclinical efficacy evaluation of potential chemopreventive agents in animal carcinogenesis models: Methods and results from the NCI chemoprevention drug development program

Epidemiological studies suggest an inverse relationship between the intake of dietary fiber, particularly fiber from cereal grains, and colon cancer risk. Animal model assays have demonstrated that the protective effects of dietary fiber on colon cancer development depend on the nature and source of the fiber. Wheat bran (WB) appears to inhibit colon tumorigenesis more consistently than do oat bran or corn bran. This study was designed to determine whether specific WB fractions such as WB fiber, WB lipids, or phytic acid differentially affect colon carcinogenesis in a well-established colon cancer model. In addition, the modulating effect of specific fractions of WB on the activities of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-1 and COX-2 enzymes were assessed in colon tumors as those have been shown to play a role in tumor progression. At 5 weeks of age, groups of male F344 rats were assigned to one of six diets: a high-fat diet containing 10% WB (control diet) and experimental high-fat diets containing 10% dephytinized WB (WB-P), 10% defatted WB (WB-F), 10% dephytinized and defatted WB (WB-PF), 10% WB-PF fortified with 2% bran oil and/or with 0.4% phytate. At 7 weeks of age, all eats except those in the vehicle-treated groups were given two weekly s.c. injections of azoxymethane (AOM) at a dose rate of 15 mg/kg body weight/week. They continued to receive their respective diets until 50 weeks after carcinogen treatment and were then killed. Colon tumors were analyzed for iNOS, COX-1, and COX-2 expression and enzymatic activities. Colon tumors were evaluated histopathologically and classified as adenomas and adenocarcinomas. We found that removal of phytic acid (WB-P) or lipids (WB-F) from WB had no significant effect on colon tumor incidence (% animals with tumors) or multiplicity (tumors/ animal), whereas removal of both phytate and lipids from WB (WB-PF) significantly increased colon tumor multiplicity and volume. Interestingly, WB-PF fortified with excess bran oil or with bran oil plus phytate significantly inhibited colon tumor incidence, multiplicity, and volume; but supplementation of WB-PF with phytate alone had no significant effect on colon tumorigenesis in rats suggesting that lipid fraction of WB possesses tumor-inhibitory properties. Moreover, feeding WB-PF diet significantly increased iNOS, total COX and COX-2 enzyme activities, and iNOS protein expression in colon tumors as compared with wheat bran control diet. Feeding the WB-PF that was fortified with excess bran oil alone or with bran oil plus phytate significantly suppressed the activities of iNOS and COX-2 as well as the expression of iNOS and COX-2 in colon tumors compared with that in rats fed the WB diet or WB-PF diet. The study demonstrates for the first time that the lipid fraction of wheat bran has strong colon tumor inhibitor properties. The exact mechanism(s) by which the lipid fraction of WB inhibits colon carcinogenesis in addition to alteration of iNOS and COX activities remains to be elucidated. Additional studies are warranted to identify biologically active constituents of lipid fraction of WB and their relative role in colon tumor inhibition.

https://cancerres.aacrjournals.org/content/canres/60/17/4792.full.pdf

Preventive Potential of Wheat Bran Fractions against Experimental Colon Carcinogenesis: Implications for Human Colon Cancer Prevention

Since it was first suggested that high dietary fat is a risk factor in colon cancer, there have been several studies to test this hypothesis. Epidemiologic studies suggested a positive association between dietary fat and colon cancer. Laboratory animal model studies demonstrated that not only the amount of rat, but also types of fat differing in fatty acid composition are important determining factors in colon tumor development. Chemically-induced colon tumor incidence was increased in rats fed the semipurified diets containing 23% corn oil, safflower oil, lard or beef tallow (high-fat) as compared to those fed 5% corn oil, safflower oil, lard or beef tallow diets (low-fat). Diets containing 23% conconut oil, olive oil or fish oil, or high-fat diets containing varying levels oftrans fat, had no colon tumor-enhancing effect compared to their respective low fat diets. The stage at which the effect of dietary fat is exerted appears to be mostly during the post-initiation phase of colon carcinogenesis. Lack of a colon tumor enhancing effect of dietary fish oil is observed both during the initiation and postinitiation phases. The mechanisms by which various dietary fats increase colon carcinogenesis are not fully understood. In most instances, however, the high-fat diet appears to enhance tumorigenesis through elevation of agents, such as secondary bile acids, that act as promoters of tumor development. Lack of colon tumor promotion by dietary fish oil andtrans fat appears to be mediated through their effect on mucosal ornithine decarboxylase activity, colonic secondary bile acids and/or prostaglandin synthesis.

Dietary fat and colon cancer: Animal model studies

Sulforaphane (SFN) is an isothiocyanate that is present abundantly in widely consumed cruciferous vegetables and has a particularly high content in broccoli and cauliflower. It has been shown to be an effective inhibitor of some carcinogen-induced cancers in rodents. Here, we investigated the chemopreventive efficacy of SFN in the ApcMin/+ mouse model. ApcMin/+ mice were fed with diet supplemented with two different dose levels of SFN (300 and 600 p.p.m.) for 3 weeks. Our results clearly demonstrated that ApcMin/+ mice fed with SFN-supplemented diet developed significantly less and smaller polyps with higher apoptotic and lower proliferative indices in their small intestine, in a SFN dose-dependent manner. In addition, immunohistochemical (IHC) staining of the adenomas indicated that SFN significantly suppressed the expression of phosphorylated c-Jun N-terminal kinase (p-JNK), phosphorylated extracellular signal-regulated kinases (p-ERK) and phosphorylated-Akt (p-Akt), which were found to be highly expressed in the adenomas of ApcMin/+ mice. In contrast, expression of two important biomarkers of the Wnt signaling pathway, beta-catenin and cyclin-D1 was unaffected by SFN treatment. Measurement of SFN and its metabolite SFN-GSH in the small intestine using LC-MS indicates that the concentrations between 3 and 30 nmol/g are required to prevent, or retard adenoma formation in the gastrointestinal tract of ApcMin/+ mice.

/pdf/cancer-chemoprevention-of-intestinal-polyposis-in-apcmin-2ldknjoopy.pdf

Cancer chemoprevention of intestinal polyposis in ApcMin/+ mice by sulforaphane, a natural product derived from cruciferous vegetable

Oligofructose and inulin, selective fermentable chicory fructans, have been shown to stimulate the growth of bifidobacteria, which are regarded as beneficial strains in the colon. Studies were designed to evaluate inulin (Raftiline) and oligofructose (Raftilose) for their potential inhibitory properties against the development of colonic aberrant crypt foci (ACF) in rats. ACF are putative preneoplastic lesions from which adenomas and carcinomas may develop in the colon. The results of this study indicate that dietary administration of oligofructose and inulin inhibits the development of ACF in the colon, suggesting the potential colon tumor inhibitory properties of chicory fructans. The degree of ACF inhibition was more pronounced in animals given inulin than in those fed oligofructose. Because these prebiotics selectively stimulate the growth of bifidobacteria, ornithine decarboxylase (ODC) activities, ras-p21 ontoprotein expressions and tumor inhibitory activity of lyophilized cultures of Bifidobacterium longum against chemically induced colon and mammary carcinogenesis and against colonic tumor cell proliferation were examined. Dietary administration of lyophilized cultures of B. longum strongly suppressed colon and mammary tumor development and tumor burden. Inhibition of colon carcinogenesis was associated with a decrease in colonic mucosal cell proliferation and activities of colonic mucosal and tumor ornithine decarboxylase and ras-p21. Human clinical trials are likely to broaden our insight into the importance of the pre- and probiotics in health and disease.

Bandaru S. Reddy

Papers

Preclinical efficacy evaluation of potential chemopreventive agents in animal carcinogenesis models: Methods and results from the NCI chemoprevention drug development program

Preventive Potential of Wheat Bran Fractions against Experimental Colon Carcinogenesis: Implications for Human Colon Cancer Prevention

Dietary fat and colon cancer: Animal model studies

Cancer chemoprevention of intestinal polyposis in ApcMin/+ mice by sulforaphane, a natural product derived from cruciferous vegetable

Possible mechanisms by which pro- and prebiotics influence colon carcinogenesis and tumor growth.