The potential role of bacterial metabolic toxins in the development of diabetes

Irritable bowel syndrome is one of the most common problems reported to general practitioners and gastroenterologists. It has been shown that many of the gut and systemic symptoms are due to lactose sensitivity, the sugar found mainly in milk. Undigested carbohydrates and other foods absorbed by the small intestine reach the bacteria in the large intestine. There is little oxygen here, the bacteria metabolise these to produce gases such as hydrogen and methane, and a variety of small organic metabolites such as methylglyoxal. These metabolites are absorbed into the bloodstream and can affect tissues around the body. The overall aim of this thesis was to investigate the potential role of the bacterial metabolic toxin hypothesis in the development of diabetes. To specifically investigate the ability of these toxins to covalently modify proteins and to investigate the biological activity of these modified proteins on glucose uptake and cell differentiation. Albumin and insulin have been shown to exhibit mono-oxygenase activity demonstrated by coelenterazine chemiluminescence. It was heat denaturable, demonstrated saturable substrate characteristics, was inhibited or activated by cations (Fe2+, Fe3+, Zn2+ and Ca2+) known to bind to these proteins and was inhibited by drugs that are known to bind to Sudlow’s site I on albumin. The inhibition of albumin catalysed coelenterazine chemiluminescence observed in the presence of drugs that are known to bind to Sudlow’s site I on albumin proposes that this is also the coelenterazine binding site. Molecular 3D modelling confirmed that coelenterazine binds to this site. Methylglyoxal covalently modified these proteins resulting in reduced biological activity. Tetraethylammonium significantly inhibited 3T3-L1 cell differentiation in the presence of insulin. However, methylglyoxal and tetrandrine did not significantly inhibit 3T3-L1 cell differentiation. The results in this thesis support the hypothesis that bacterial metabolic toxins can covalently modify proteins and alter their biological activity