Gut microbiota in human type 2 diabetes : in-vivo and in-vitro studies.

The gut microbiota plays an important role in the development of type 2 diabetes (T2D), which is an alteration in the diversity and abundance of the gut microbiota, favouring the growth of Gram-negative bacteria. Although a lot of studies have shown this to be the case, most of this work has been done in animal models with few studies in humans. In animal models of T2D, it is known that a high-fat diet alters the gut microbiota in favour of the growth of Gram–negative bacteria. The outer membrane of Gram-negative bacteria contains lipopolysaccharide (LPS) which is an endotoxin that can trigger inflammation leading to metabolic disorders such insulin resistance and T2D, hence T2D is considered a low grade inflammatory disorder. In this thesis, the effect of Galactooligosaccharide (GOS), a prebiotic, on the composition of the gut microbiota was investigated. Next generation sequencing (NGS) of the gut microbiota of T2D and healthy control subjects showed no significant difference at the phylum level between the two groups. Furthermore, T2D patients in the prebiotic group had a significant increase in the level of Firmicutes compared to the placebo group. Also, although not significant, T2D patients on metformin had increased level of Bacteroidetes, Proteobacteria and Actinobacteria compared to those not on metformin. The ability of human faecal water (FW) to distinguish between healthy and T2D patients using an in vitro model of the intestinal mucosa was studied. FW from T2D patients decreased Caco-2 cell monolayer integrity when compared to the healthy controls and in the T2D patients, FW activity in vitro correlated with biological markers of T2D severity measured in vivo. Additionally, cytokines were measured in T2D faecal samples using a human cytokine array. Finally, GOS anti-cytotoxic activity was also assessed in vitro using cell viability assays and the anti-cytotoxic effect of GOS was time and concentration dependent. Together, the thesis explored potential new ways of using faecal samples as biomarker for T2D in vitro and relating it to in vivo parameters of the patients. Also future work in this area may reveal mechanistic insight to the use of FW as a non-invasive biomarker for T2D