Medicine (Austin & Northern Health) - Theses
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ItemInvestigation of circulating RAGE in patients with cardiovascular disease( 2017)The receptor for advanced glycation end products (RAGE) is a widely expressed transmembrane receptor that binds multiple ligands including advanced glycation end products (AGEs), thereby perpetuating chronic inflammation and cellular dysfunction. There is compelling experimental data implicating RAGE activation in the pathogenesis of cardiovascular (CV) disease, including heart failure (HF), coronary artery disease (CAD) and atrial fibrillation (AF). There are also well-established links between glycation and myocardial stiffening in various experimental models of diabetes. Soluble RAGE (sRAGE) can be measured in serum using a commercially available assay that detects the total pool of circulating RAGE. Isoforms of RAGE present in human serum include cleaved RAGE, which is generated by membrane cleavage of the cell-surface receptor, and endogenous secretory RAGE (esRAGE), an alternatively-spliced variant with a unique C-terminus sequence that can be specifically measured. There is substantial controversy as to whether an elevation or reduction in one or both of these soluble biomarkers correlates with existing CV disease and/or predicts an adverse CV outcome. The primary aim of this thesis was to determine the cross-sectional association between isoforms of serum RAGE and CV disease. The secondary aims of this thesis were to determine the clinical utility of these markers to predict 12-month adverse CV outcomes and long-term mortality. Patients with diabetes attending for a routine surveillance echocardiogram and patients with and without diabetes undergoing coronary angiography or percutaneous coronary intervention (PCI) were prospectively recruited. Markers of glycation were measured in serum using an enzyme-linked immunosorbent assay (ELISA). Patients were followed for 12 months and adverse CV events were recorded. Long-term mortality was determined using data linkage. Serum AGEs and RAGE were elevated in patients with diabetes and diastolic dysfunction, but only serum AGEs were independently associated with non-invasively determined diastolic dysfunction. Isoforms of serum RAGE were independently associated with invasively determined diastolic dysfunction only in the presence of diabetes. Elevations in both isoforms of RAGE were cross-sectionally associated with HF and predicted future HF hospitalisation, regardless of diabetes status. Serum RAGE levels also predicted the presence of persistent AF compared with paroxysmal AF and sinus rhythm, independently of age, diabetes and prior HF. The relationship between serum RAGE and CAD proved to be complex. Although a reduction in esRAGE was present in patients presenting with unstable CAD, baseline elevations in both sRAGE and esRAGE were associated with a worse CV outcome at 12 months but did predict long-term mortality. A positive transcoronary gradient of esRAGE was identified in patients undergoing PCI suggesting there is cardiac production of this isoform, although the specific biological function of these soluble receptors remains unknown. Overall, this thesis found that elevated levels of serum RAGE correlated with the presence of non-coronary CV disease, including diastolic dysfunction, heart failure and AF and that elevated levels of both sRAGE and esRAGE independently predicted adverse CV events. Future studies are needed to determine the clinical utility of serum RAGE in guiding treatment decisions and whether targeting RAGE signalling improves CV outcomes.
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ItemThe utility of immune function monitoring in predicting clinical outcomes in cirrhosis and following liver transplantation( 2015)Background: Transplantation is a life-saving procedure offered to thousands of people around the world each year. In most cases, lifelong suppression of the recipient’s immune system is required to prevent allorecognition and organ rejection. However, immunosuppressive medications have significant side effects that are now responsible for much of the post-transplant morbidity and mortality. Balancing the risks of over and under immunosuppression is key to patient management, but without an objective marker of immune function, clinical events remain common. QuantiFERON-Monitor (QFM) is a net immune function biomarker that measures IFNγ after stimulation of whole blood with an innate and adaptive immune stimulant. It is potentially accessible as it is based on the same laboratory platform as the readily available QuantiFERON-gold assay. The studies within this thesis represent the first translational clinical studies evaluating this assay. Methods: A cross-sectional pilot study compared QFM in healthy controls with patients before and after liver transplantation. Subsequent studies focused on immune function biomarkers and correlation with clinical events both before and after transplantation. In a cirrhotic transplant-waitlisted population, the QFM assay was performed and patients prospectively monitored for infection prior to transplant. This was followed by a prospective observational post-transplant cohort study in which QFM was taken longitudinally to assess for clinical events including infection and rejection based on pre-defined criteria. The same cohort was monitored for cytomegalovirus (CMV) reactivation with a CMV-specific T-cell assay, to evaluate the potential for more specialised immune monitoring. A small subgroup of controls and rejectors were compared for pre-transplant cytokine production using an enhanced sensitivity bead array and flow cytometry. Results: The pilot study confirmed that QFM could discriminate between populations known to be immunosuppressed. Compared with healthy controls, lower QFM was seen in patients following transplantation when on immunosuppression. QFM did not vary by age, gender or disease aetiology. In the cohort of cirrhotic patients, low QFM was associated with the risk of infection prior to transplant. This risk was also demonstrated after transplantation, where a low QFM at one week was significantly associated with risk of infection, but not rejection. Conversely, a high week 1 QFM was significantly associated with rejection, but not infection. Based on the selected optimal cut-offs, approximately 70% of all transplant patients were identified as being over- or under-suppressed. The risk of post-transplant rejection was further heightened in patients who had lower pre-transplant baseline pro-inflammatory cytokine production. QFM was not associated with risk of CMV reactivation. However, a CMV-specific immune function assay was significantly associated with CMV in patients inappropriately classified as low-risk based on current standard of care. Conclusions: Without an objective marker of immune function, clinical events remain exceedingly common following liver transplantation. The studies within this thesis represent the first translational studies involving QFM - a net immune function biomarker which benefits from being accessible, rapid and comprising both innate and adaptive immune stimulants. Future individualisation and optimisation of immunosuppression based on immune monitoring could fundamentally alter the way patients are monitored and treated following transplantation.