Intestinal Microbiota and Bacterial Translocation: Impact of Diet, Obesity and Insulin Resistance

• Author / Creator

  Singh, Vijay

• Introduction: The metabolic syndrome (MetS) is associated with factors that increase the risk of Type 2 Diabetes and cardiovascular disease. Recently, intestinal microbiota has attracted attention as an important environmental factor that plays a role in regulating weight gain and development of type 2 diabetes (T2D). Type 2 diabetes is characterized by insulin resistance, impaired glucose metabolism, low-grade inflammation and has also been linked to the quality of microbiota. However, studies in humans are yet to report a consistent relationship between intestinal bacterial composition and diabetes. We do know that altered gut microbial composition can result in the leakage of bacterial products [such as lipopolysaccharide (LPS)] and viable bacteria (known as the bacterial translocation). Additionally, studies have shown that low birth weight (LBW) and postnatal nutrition are risk factors for adult metabolic diseases. However, the interaction between LBW, diet and intestinal lipid absorption/secretion leading to adult metabolic disease remains unclear. Hypothesis and objectives: We hypothesized that over-nutrition would alter gut microbiota composition in a spontaneous animal model of insulin resistance (the JCR:LA-cp rat). Similarly, addition of an energy rich diet (high fat-HFD) would further exacerbate microbial dysbiosis and subsequently, facilitate increased bacterial translocation. Using a complementary approach in swine, we hypothesized that LBW pigs fed a western diet (high-fat, high-carbohydrate [HFHC] diet ) would develop metabolic complications and induce dysbiosis in gut microbiota. We further proposed that a diet rich in a novel bioactive monounsaturated fatty acid [(vaccenic acid or VA) 1.7 % w/w of diet or 10% of the fat] would result in an improved gut dysbiosis and lipid metabolism profile. Material methods: For our rodent studies, 6-week-old obese homozygous and lean heterozygous JCR:LA-cp rats were randomly assigned to control or HFD diet for 6 weeks. Samples of lymph and portal vein blood were cultured and processed for sanger sequencing. For gut microbiota analysis from cecal samples, total DNA was extracted and further processed by next generation sequencing. For the first of two swine studies, pigs were fed a control or HFHC diet for 6 weeks, (post-weaning) until 13 weeks of age. In the second swine study pigs were fed either control, HFHC or HFHC enriched in VA for 6 weeks. For both swine studies, we combined a 2-step modified oral glucose tolerance and fat challenge test. Lymph was collected followed by exsanguination under anesthesia and tissue collection. Results: Experiments in rodents showed an effect of HFD on gut microbiota however, our results did not find any impact of insulin resistance per se. We found evidence of bacterial translocation but neither obesity nor HFD was found to exacerbate the condition. Studies in swine found that LBW pigs fed on HFHC diets displayed fasting and postprandial hypertriglyceridemia as well as a higher insulin excursion. In the second swine experiment, addition of VA showed mild insulin sensitizing effects. In terms of gut microbiota, HFHC diet showed significant shift in gut microbiota in LBW pig with increase ratio of Firmicutes: Bacteroidetes. Interestingly, the addition of VA in HFHC diet normalized gut microbiota dysbiosis in LBW pigs. Conclusion: Findings from this thesis provide evidence that increased energy intake and the obese genotype per se does not necessarily affect the gut microbiota composition (at least in JCR:LA-cp rats). Whereas the addition of HFD showed substantial changes in intestinal microbiota. Experiments in pigs demonstrated that a HFHC diet also results in a dysbiotic gut microbiota, yet can be avoided with the addition of dietary VA. Our observations are consistent with both rodent and human studies and give reason for LBW swine to be utilized as a model for human translational research to better understand the relationship of microbiota and chronic disease.

• Subjects / Keywords

  • Intestinal Microbiota and Bacterial Translocation

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-gba2-gr59

• License

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