Search

I have investigated the potential role of Toll-Like Receptors (TLRs) in mediating adipose inflammation in obesity. TLRs are a family of pattern recognition receptors that play a key role in host defence and are also implicated in chronic inflammatory disorders. The finding that TLR4-deficient mice are protected against obesity-induced diabetes led me to hypothesise that TLR expression on adipocytes could play a role in obesity-induced adipose inflammation and metabolic dysfunction. The first chapter investigates the expression and function of TLRs in in vitro differentiated human subcutaneous adipocytes. I found that stimulation with ligands for TLR2, TLR3 and TLR4 but not the other TLRs, induces the expression of pro-inflammatory cytokines. I also explored the use of the TLR adapter molecules MyD88, Mal and TRIF by different TLRs. The second chapter examines whether TLR activation in adipocytes has an effect on glucose uptake. I established a 3H-2-deoxy-D-glucose (2DOG) uptake assay which led to an interesting yet unexpected observation: Stimulation with TLR3 and TLR4 ligands led to a decrease in insulin-stimulated glucose uptake but at the same time, insulin-independent glucose uptake was increased. I showed that these observations are at least partly due to altered expression of different glucose transporter (GLUT) isoforms. As the effects were seen only after prolonged TLR stimulation, I speculated that this was mediated via a secondary secreted factor. The third chapter is based on a cytokine and adipokine array, which I performed to identify cytokines that may be responsible for the effects described in Chapter 2. The secretion of several cytokines/chemokines with diverse pro-inflammatory functions was observed following stimulation with TLR3 and TLR4 ligands. The contribution of some of these factors to altered glucose handling was investigated. Whilst a contribution for ENA-78 was ruled out, I present evidence that IL-1 can contribute to this.

Patients with chronic kidney disease (CKD) are at increased risk of mortality and cardiovascular (CV) disease and those on maintenance haemodialysis (MHD) are at particularly high risk. Insulin resistance (IR) is known as a contributing factor to many of the conditions classified as "classic CV risk factors" and understanding changes in IR is thought to be of key importance in targeting potential medication. A prospective observational study of individuals with CKD was designed to better establish the relationship between CV risk factors and events, before and after the onset of MHD. In addition, a subgroup study was set up to examine if changes in IR affect CV outcome and mortality. 519 patients were recruited for this study, 210 were on MHD at entry and 309 had CKD stages 3, 4 and 5. Subjects were followed prospectively for 24 months and the relationship between body mass index (BMI), blood pressure (BP), total cholesterol (TC), triglycerides (TG), diabetes status and glycosylated haemoglobin (HbA1c) and CV events analysed in both MHD and non-MHD groups using logistic regression. A small study was also carried out to determine the reliability of HbA1c in MHD subjects. 106 of these subjects were recruited into the subgroup study, where baseline assessment of their IR (using the HOMA-IR model) was carried out as well as other relevant tests. 103 subjects reached an endpoint, and analysis of the whole cohort identified high SBP and diabetes as significant CV risk factors. TC was recognized as a protective factor as lower TC was associated with higher CV risk. The mean HOMA-IR increased through the CKD stages 3-5 before significantly falling in the MHD group. HbA1c showed poor association with glycaemia as measured by use of 48-hour continuous glucose monitors (CGM). These results suggest that CV risk factors may vary at different stages of CKD. The “reverse” TC result only in the non-dialysis group differs from current theories, where low cholesterol is considered a CV risk factor putatively as a surrogate marker of malnutrition. This study shows that IR increases as renal function deteriorates but is significantly decreased with MHD. In this cohort changes in IR were not predictive of CVE or mortality.