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      Obesity-induced gut microbial metabolite promotes liver cancer through senescence secretome.

      Nature

      Risk Factors, Phenotype, metabolism, chemically induced, Obesity, Non-alcoholic Fatty Liver Disease, Mice, Inbred C57BL, Mice, Male, prevention & control, etiology, complications, Liver Neoplasms, deficiency, Interleukin-1beta, Humans, secretion, drug effects, cytology, Hepatic Stellate Cells, microbiology, Gastrointestinal Tract, pathology, Fatty Liver, Disease Models, Animal, pharmacology, adverse effects, Dietary Fats, blood, Deoxycholic Acid, DNA Damage, Cytokines, Cells, Cultured, Cell Aging, Carcinoma, Hepatocellular, Bile Acids and Salts, Bacteria, Anti-Bacterial Agents, Animals

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          Abstract

          Obesity has become more prevalent in most developed countries over the past few decades, and is increasingly recognized as a major risk factor for several common types of cancer. As the worldwide obesity epidemic has shown no signs of abating, better understanding of the mechanisms underlying obesity-associated cancer is urgently needed. Although several events were proposed to be involved in obesity-associated cancer, the exact molecular mechanisms that integrate these events have remained largely unclear. Here we show that senescence-associated secretory phenotype (SASP) has crucial roles in promoting obesity-associated hepatocellular carcinoma (HCC) development in mice. Dietary or genetic obesity induces alterations of gut microbiota, thereby increasing the levels of deoxycholic acid (DCA), a gut bacterial metabolite known to cause DNA damage. The enterohepatic circulation of DCA provokes SASP phenotype in hepatic stellate cells (HSCs), which in turn secretes various inflammatory and tumour-promoting factors in the liver, thus facilitating HCC development in mice after exposure to chemical carcinogen. Notably, blocking DCA production or reducing gut bacteria efficiently prevents HCC development in obese mice. Similar results were also observed in mice lacking an SASP inducer or depleted of senescent HSCs, indicating that the DCA-SASP axis in HSCs has key roles in obesity-associated HCC development. Moreover, signs of SASP were also observed in the HSCs in the area of HCC arising in patients with non-alcoholic steatohepatitis, indicating that a similar pathway may contribute to at least certain aspects of obesity-associated HCC development in humans as well. These findings provide valuable new insights into the development of obesity-associated cancer and open up new possibilities for its control.

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          Most cited references 37

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          Microbial ecology: human gut microbes associated with obesity.

          Two groups of beneficial bacteria are dominant in the human gut, the Bacteroidetes and the Firmicutes. Here we show that the relative proportion of Bacteroidetes is decreased in obese people by comparison with lean people, and that this proportion increases with weight loss on two types of low-calorie diet. Our findings indicate that obesity has a microbial component, which might have potential therapeutic implications.
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            Dose translation from animal to human studies revisited.

            As new drugs are developed, it is essential to appropriately translate the drug dosage from one animal species to another. A misunderstanding appears to exist regarding the appropriate method for allometric dose translations, especially when starting new animal or clinical studies. The need for education regarding appropriate translation is evident from the media response regarding some recent studies where authors have shown that resveratrol, a compound found in grapes and red wine, improves the health and life span of mice. Immediately after the online publication of these papers, the scientific community and popular press voiced concerns regarding the relevance of the dose of resveratrol used by the authors. The animal dose should not be extrapolated to a human equivalent dose (HED) by a simple conversion based on body weight, as was reported. For the more appropriate conversion of drug doses from animal studies to human studies, we suggest using the body surface area (BSA) normalization method. BSA correlates well across several mammalian species with several parameters of biology, including oxygen utilization, caloric expenditure, basal metabolism, blood volume, circulating plasma proteins, and renal function. We advocate the use of BSA as a factor when converting a dose for translation from animals to humans, especially for phase I and phase II clinical trials.
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              Induction of colonic regulatory T cells by indigenous Clostridium species.

              CD4(+) T regulatory cells (T(regs)), which express the Foxp3 transcription factor, play a critical role in the maintenance of immune homeostasis. Here, we show that in mice, T(regs) were most abundant in the colonic mucosa. The spore-forming component of indigenous intestinal microbiota, particularly clusters IV and XIVa of the genus Clostridium, promoted T(reg) cell accumulation. Colonization of mice by a defined mix of Clostridium strains provided an environment rich in transforming growth factor-β and affected Foxp3(+) T(reg) number and function in the colon. Oral inoculation of Clostridium during the early life of conventionally reared mice resulted in resistance to colitis and systemic immunoglobulin E responses in adult mice, suggesting a new therapeutic approach to autoimmunity and allergy.
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                Author and article information

                Journal
                23803760
                10.1038/nature12347

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