Medicine (St Vincent's) - Theses
Now showing items 1-12 of 158
The contribution of the pulmonary circulation and cardiac function to exercise intolerance in people with diabetes
Diabetes mellitus (DM), and in particular type 2 DM (T2DM), is approaching epidemic proportions globally. Relative to people without diabetes, exercise performance is reduced by approximately 20% in T2DM subjects universally, whereas impairment in type 1 DM (T1DM) is less consistently reported. Risk of cardiovascular disease (CVD) is significantly elevated in both T1DM and T2DM, and thus emphasis is placed on cardiovascular constraints to exercise capacity, including subclinical cardiac dysfunction and the entity of diabetic cardiomyopathy (DMC). A clear bidirectional association between heart failure and T2DM exists, with numerous pathophysiological mechanisms identified in animal models. Longitudinal data suggests a low prevalence of heart failure in T1DM, on the other hand, which insinuates the pathological mechanisms thought to underpin DMC may be exclusive of chronic hyperglycemia which unifies the diagnosis of T1DM and T2DM. The pulmonary microvasculature is targeted in diabetes, meanwhile, and may be an under-appreciated contributor to exercise limitation. It is thought that the lungs are protected from deleterious effects of subclinical microvascular disease by virtue of their substantial size, although the ability to assess pulmonary microvascular function during exercise has been limited. This thesis assesses exercise performance (VO2peak) in people with T1DM and T2DM, evaluates the contribution of cardiac function and the pulmonary circulation using comprehensive traditional and novel echocardiographic analyses, and investigates the effect of phosphodiesterase type 5 (PDE5) inhibitor Sildenafil on exercise capacity. VO2peak is demonstrated to be impaired in only the T2DM cohort of the study group, and independently associated with sedentary lifestyle and reduced left ventricular end diastolic volume. Comprehensive resting and exercise echocardiographic measurements of biventricular systolic function and LV diastolic function, in addition to speckle-tracking global longitudinal strain and LV twist mechanics, are normal. The novel echocardiographic assessment of pulmonary microvascular function by measuring the pulmonary transit of agitated contrast (PTAC) identifies less PTAC (low-PTAC) in DM subjects, and associations with reduced RV function, higher pulmonary artery pressures, and lower exercise capacity. Finally, Sildenafil improves a number of central hemodynamic parameters but does not improve VO2peak. Results of this thesis support the argument that in the presence of impaired exercise performance and longstanding DM, subclinical cardiac dysfunction and DMC should not be universally anticipated. Diagnosis of pulmonary microvascular dysfunction using PTAC is feasible and readily accessible, and pulmonary microvascular disease is associated with reduced exercise capacity. Nonetheless, quantification of pulmonary microvascular disease remains imperfect, and the pulmonary vasodilator Sildenafil is ineffective in improving exercise performance presumably due to the mismatch between the pathophysiology thought to underpin diabetic lung disease and the more proximal smooth muscle vascular target of Sildenafil.
Molecular Investigation of the Fanconi Anemia DNA repair pathway
Chemotherapeutic drugs often kill cancer cells by inducing toxic DNA interstrand crosslinks (ICLs) that inhibit DNA replication or transcription. Cells from patients with the genetic disorder Fanconi Anaemia (FA) are extremely sensitive to such DNA crosslinking agents. A critical step in the repair of ICLs is the biochemical modification of FANCI:FANCD2 protein by monoubiquitination. This monoubiquitination reaction is defective in 95% of FA patients, however the exact function of this process remains unclear. This thesis aims to better investigate how FANCI:FANCD2 monoubiquitination is regulated. To determine how monoubiquitinated proteins regulate the FA DNA repair pathway, several targets of monoubiquitination including FANCI:FANCD2, PCNA trimer and nucleosomes ubiquitinated by BRCA1:BARD1 were purified using Avi-ubiquitin. This thesis presents a minimal approach to purify challenging DNA repair proteins, which could potentially be applied to elucidate signalling mechanisms of other ubiquitination-mediated DNA repair pathways. Biochemical reconstitution of the FA pathway using recombinant human proteins revealed that FANCI:FANCD2 monoubiquitination is dependent on DNA and low ionic strength buffers. In addition, electrophoretic mobility shift assays revealed that monoubiquitination locks FANCI:FANCD2 on double-stranded DNA (dsDNA). Affinity pulldown of monoubiquitinated FANCI:FANCD2 confirmed that the complex remained bound to dsDNA, reflecting the monoubiquitination’s role in stabilising the FANCI:FANCD2 complex. The increased affinity of monoubiquitinated proteins on dsDNA suggests a conformational change on FANCI:FANCD2 after monoubiquitination. Using a newly developed Avi-tag-ubiquitin construct, the first successful purification of dually-monoubiquitinated FANCI:FANCD2 complex bound to DNA was reported. Strikingly, single-particle electron microscopy analysis revealed that monoubiquitinated FANCI:FANCD2 forms oligomers on dsDNA. This unexpected discovery hints that the function of monoubiquitination is to lock FANCI:FANCD2 oligomers on chromatin to initiate DNA repair. FANCI phosphorylation was previously reported to play a key role in stimulating FANCI:FANCD2 monoubiquitination. Mass spectrometry and western blot using phospho-specific antibodies revealed that ATR-mediated FANCI phosphorylation at specific serine-glutamate (SQ) clusters regulate both ubiquitination and deubiquitination of FANCI:FANCD2 complex. These results indicate a mechanistic view where FANCI phosphorylation is required for ubiquitination-mediated DNA repair which gives insights into the biology of FA pathway and potential chemosensitiser development. Collectively, the results presented in this thesis elucidate the role of monoubiquitination in locking FANCI:FANCD2 on DNA to form oligomers to initiate DNA repair. This work uncovers a new role of monoubiquitinated FANCI:FANCD2 during interstrand crosslink repair and provides new potential chemotherapeutic targets.
Novel aspects of commonly encountered pituitary adenomas in clinical practice
Clinically relevant pituitary adenomas are common in the general population occurring in 1 per 865-1470 people. Prolactinomas and non-functioning pituitary adenomas account for more than 80% of pituitary adenoma types. My thesis is composed of several studies, undertaken at a single centre specialising in the multidisciplinary care of pituitary diseases, investigating clinical issues pertinent to the management of patients with the above adenomas. The findings of these studies contribute to the understanding of outcomes in the local practice, as well as being an Australian contribution to the international experience of managing these adenomas. Firstly, I examine the issue of valvular heart disease in prolactinoma patients treated with cabergoline therapy. By studying a local cohort and by a systematic review I found that the prevalence of cabergoline-associated valvular heart disease (CAV) in prolactinoma patients to be extremely low, with just three confirmed cases amongst 1800 patients described in the literature. I have shown evidence that a simple annual cardiovascular examination is a suitable screening tool for this rare condition and made recommendations on when to consider a diagnostic echocardiogram. Secondly, I examine two clinical issues affecting patients with surgically treated non-functioning pituitary macroadenomas (NFPMAs): the issues of regrowth and recurrence, and of hormonal outcomes. In the largest Australian cohort of cases with NFPMAs to be described, it was found that residual disease is a common finding post-surgery. In cases with residual disease, regrowth occurred in 40% of these cases compared to only 12.5% in cases without residual disease, at a median of 3.6 years of follow-up. Not surprisingly, larger baseline adenoma size was a predictor of regrowth and recurrence. In multivariate analysis, the presence of residual disease and younger age (under 41 years) at presentation were independent risk factors for regrowth and recurrences. Based on this risk factor of younger age, I have recommended that these cases have lifelong radiological follow-up. Results of hormonal outcomes in cases with NFPMAs treated with surgery showed the novel finding of gender differences in hormonal outcomes, with males having a higher prevalence of multiple (more than two) hormone deficiencies (MHD) at presentation than females, and after surgery. In particular, pre-menopausal females had very few hormone deficiencies post-operatively and demonstrated a propensity to recover function. These gender subgroup differences are the first to be noted in the literature and have important clinical implications particularly for pre-menopausal females where fertility preservation is an issue. I also found that pre-menopausal females had smaller adenomas than males suggesting that they may present earlier in the natural history of the disease. In multivariate analysis, larger adenoma size remained a significant factor associated with post-operative MHD. The final part of this thesis is an exploratory study of intrasellar pressure (ISP) and how it relates to adenoma size and hormonal outcomes in cases with NFPMAs undergoing surgery. I did not find that ISP was correlated to adenoma size, but results did suggest that raised ISP may play a role in more frequent hormone deficiencies at presentation. In this study adenoma size was again noted to be showing a trend towards influencing hormonal outcomes. The findings from this study will require a larger cohort in order to better quantify how ISP and adenoma size interact to contribute to the pathophysiology of hormone deficiencies. In these three studies of NFPMAs adenoma size has emerged as an important factor influencing surgical and hormonal outcomes; smaller adenomas are more likely to be fully resected and less likely to result in hormone deficiencies. This thesis lays the foundations for advocating for the consideration of early surgical intervention of NFPMAs (when adenomas are smaller and earlier in the natural history of the disease), in order to optimise surgical and hormone outcomes. The above should now be an important clinical consideration in the multidisciplinary care of these patients.
Echocardiographic evaluation of the evolution of cardiac dysfunction in the community and risk of heart failure, using the SCReening Evaluation of the Evolution of New Heart Failure (SCREEN-HF) cohort
Heart failure (HF) is a major cause of morbidity and mortality in the community. Outcomes for HF with reduced ejection fraction (HFrEF) remain poor despite available treatments, and no medical therapy has been shown to improve survival in HF with preserved ejection fraction (HFpEF). Consequently, HF prevention is urgently required to curb the growth of HF in our communities. HF prevention requires that we improve our ability to identify individuals at high-risk of HF who may benefit from preventative measures. Although cardiovascular disease prevention has traditionally focused on risk assessment using cardiovascular risk factors, HF risk is further increased by the additional presence of cardiac structural and functional abnormalities. Cardiac dysfunction detected by echocardiography may therefore aid in improving risk stratification in HF. The SCReening Evaluation of the Evolution of New Heart Failure (SCREEN-HF) study is a community-based evaluation of individuals aged 60 years or over with cardiovascular risk factors followed longitudinally for the development of HF. Baseline transthoracic echocardiographic examinations were performed to document the asymptomatic cardiac dysfunction which preceded the development of incident HFpEF and HFrEF, and follow-up echocardiography was performed approximately four years later to document age-related cardiac changes. Using data from the SCREEN-HF cohort, this thesis investigated the clinical and echocardiographic predictors of incident HFpEF and HFrEF, in order to gain insights into HF development, and the role of echocardiography in the risk assessment of HFpEF and HFrEF. Contrasting clinical predictors of HFpEF and HFrEF provided insight into their underlying mechanisms. Risk factors associated with atherosclerosis, including smoking and abdominal adiposity, predicted only HFrEF, while pro-inflammatory conditions such as diabetes, obesity and renal dysfunction, and additionally high white cell count predicted only HFpEF. These pro-inflammatory risk factors were present approximately four years prior to clinical HFpEF, suggesting that focused risk factor management is an important strategy in HFpEF prevention. Baseline echocardiographic data from over 3000 subjects was used to investigate the role of echocardiography in HFpEF and HFrEF risk assessment. Diastolic dysfunction is an integral feature of HFpEF and diastolic dysfunction determined using current guideline algorithms was shown to predict incident HFpEF. In addition, individual echocardiographic parameters reflecting diastolic dysfunction, long axis systolic dysfunction and increased left ventricular mass predicted both HFpEF and HFrEF, while left ventricular enlargement and low left ventricular ejection fraction predicted only HFrEF. Using combined echocardiographic abnormalities, a low- and high-risk subgroup for HFpEF and HFrEF were identified, and echocardiography also assisted in differentiating between HFpEF and HFrEF risk. Older individuals are more likely affected by HFpEF than HFrEF. Using serial echocardiographic examinations from over 2300 subjects, age-related changes in cardiac structure and function were evaluated to provide insight into the tendency for older individuals to develop HFpEF. The pattern of age-related cardiac remodeling, particularly in women, was found to parallel the cardiac changes seen in HFpEF, providing one explanation for the propensity of older women to develop HFpEF. This thesis provides insights into HF development and provides evidence for the utility of echocardiography in HF risk stratification. These results serve as a platform on which echocardiography-guided management of HF risk can be further evaluated.
Predicting response to anti-TNF therapy in Crohn's disease: clinical and metabolic studies
Crohn’s disease is a chronic, disabling inflammatory condition that affects the gastrointestinal tract that is associated with significant morbidity. Up to 80 percent of patients require surgery at some point in their lives. A third of patients require surgery within five year of diagnosis even in the era of biologic therapy. Ant- Tumour Necrosis Factor alpha (Anti-TNF) therapies form the backbone of drug therapy in patients with moderate to severe Crohn’s disease and remain the most effective biologic drugs available. There are currently three classes of biological drugs available on the Pharmaceutical Benefits Scheme (PBS) for Australians with many more under development. Up to thirty percent of patients fail to have an adequate response to anti-TNF therapy and loss of response occurs at a rate of ten percent per year. There are at present no highly sensitive biomarkers of response to anti-TNF therapies. Without biomarkers to assist with selecting the most effective biologic for a particular patient, there is a risk of exposing patients to ineffective drug therapies with unnecessary side-effects and costs. This thesis comprises a range of clinical and scientific studies that seek to identify predictors of loss of response to anti-TNF therapies in Crohn’s disease. Two types of loss of response have been identified: Primary nonresponse (PNR), is defined as a lack of response to the initial drug therapy as determined at 12 weeks post induction, and Secondary Loss of Response (SLOR) is defined as the loss of response after the patient has had an initial response to the drug. Based on the clinical observation that patients with altered body composition and those with strictures have a variable to response to anti-TNF therapy, we sought to identify whether there were specific clinical, endoscopic, histologic and biochemical parameters that correlated with response to anti-TNF therapy amongst patients from whom longitudinal body composition and endoscopic data had been collected. A prospective cohort study of patients who had been newly started on anti-TNF therapies was also undertaken. In this cohort samples of urine, blood and faeces were taken prior to anti-TNF therapy delivery (baseline) and then at 3 monthly intervals thereafter. A combination of bioinformatic analyses and novel techniques evaluating the metabolome were applied to the cohort, in order to find clinical factors and biomarkers that might correlate with therapeutic response to anti-TNF therapy. This series of studies presented in this thesis on clinical and metabolic predictors of outcomes in patients receiving anti-TNF therapy for Crohn’s disease reveals new insights into the pathophysiology of Crohn’s disease and has identified biomarkers for the prediction of therapeutic response – thereby helping to come a step closer towards the ultimate goal of precision medicine.
Topographic rod function in intermediate age-related macular degeneration
Background Age-related macular degeneration (AMD) is a complex multifactorial disease that affects the elderly. In the early stages of disease, dark adaptation problems are more significant for patients than visual acuity impairment. For decades, studies of rod function related to dark adaptation issues suggested that rod function could be useful as a functional marker for differentiating AMD severity and monitoring disease progression. However, there remains many unanswered questions about how best to investigate rod function in the early stages of AMD. Earlier studies were not able to phenotype AMD cases to the extent we can today as they relied only on colour fundus photographs to determine AMD subgroups. We now have the opportunity to look at different AMD phenotypes using multimodal imaging techniques. These advances have added clarity to the phenotyping of AMD, as high-risk features such as reticular pseudodrusen (RPD), hyperreflective foci (HRF), and nascent geographic atrophy (nGA) can now be identified. At the same time as the advances in detecting anatomical changes were made, instruments that could measure rod function in a more thorough way were improving. Previously, instruments measured rod function at only a single retinal location, or could only detect large losses in sensitivity due to a lack of dynamic range. Recent advances have seen perimeters that are able to measure rod function at multiple locations in the one setting and also have a larger dynamic range to detect subtle rod dysfunction. I have used one of these new tools in my studies. Aims Two-color dark-adapted chromatic perimeter (DACP) is a novel device, designed and manufactured in Melbourne, Australia. It was first used in 2015 when I commenced my PhD. This perimeter measures rod function at multiple locations with sufficiently large range of stimulus intensities to detect subtle changes seen in early AMD. My thesis aimed to investigate the ability of the DACP to reliably detect and record rod sensitivities. I then utilized this new perimeter to investigate the ability of rod function to act as a robust functional biomarker that could be used to determine AMD disease severity and to monitor disease progression, and to compare rod function in AMD cases to normal control participants. I was also able to separate my AMD cohort into those with or without RPD, a high-risk AMD phenotype, to investigate the impact of this phenotype on rod function. Both static and dynamic rod functional changes were recorded at baseline visits and then again at 6- and 12-months. The results of this study will contribute to our understanding of functional loss in AMD and help clinicians and researchers when designing research protocols aiming to evaluate rod functional impairment before vision loss. Methods This study was conducted between 2015 and 2018 at the Macular Research Unit, Centre for Eye Research Australia. During that time, three main studies were completed. An initial assessment of test-retest reliability of the DACP was followed by a cross-sectional study comparing the severity of rod dysfunction based on point wise sensitivity (PWS) and point wise sensitivity difference (PWSD) of two color sensitivities. AMD cases were divided into an AMD group with traditional drusen only and an RPD group, and rod function was evaluated at multiple ring eccentricities within 24º of the central macula. A further 12-months evaluation of static (PWSD) and dynamic rod functional changes (rod intercept time (RIT) and rod recovery rate (RRR)) within the central 12º was conducted in participants with intermediate AMD with and without RPD as well as normal control eyes. Results The DACP did not have ceiling or floor issues during the intrasession and intersession testing, with a coefficient of repeatability of ± 5 dB. Intermediate AMD (iAMD) with the presence of RPD was found to be associated with poorer rod function compared with iAMD without RPD and normal control eyes, but only within the central macular 8º. Rod dysfunction was more significant if the eyes were prebleached before undertaking the sensitivity measurements. In a longitudinal study, dynamic rod functional changes, ie. RRR, was the only parameter that changed over 12 months, and only in the iAMD without RPD group. Change was found only at the peripheral 12º ring eccentricities. Conclusion The DACP offers a great opportunity to evaluate topographic rod function when eyesight is still normal. The findings from this study support that concept of rod function being impaired in the early stages of AMD. The presence of RPD in cases of iAMD were associated with further reductions in rod function. Measuring dynamic rod function offers a more sensitive functional marker in determining severity of AMD within the central 8 degrees of the macula, but changes over time were only detected at more peripheral locations. Longer follow-up will be beneficial to determine how rod function deteriorates over time and correlates with progression to vision loss.
An Australian population-based study of the incidence and outcomes of hepatocellular carcinoma: the Hepatomas of Melbourne Epidemiological Research (HoMER) study
Liver cancer, the world’s second highest cause of cancer death, is reportedly increasing in incidence in developed countries including Australia. Hepatocellular carcinoma (HCC), the predominant type of liver cancer, has a complex epidemiology involving the interplay of many dynamic risk factors including chronic viral hepatitis B and C, alcohol-related liver disease and non-alcoholic fatty liver disease. Recent trends in these risk factors, changes in Melbourne’s population demographics, together with advances in HCC diagnostics are thought to be increasing HCC incidence, although this may be currently underreported by the cancer registry. Accurate local epidemiology is required to inform healthcare policy for the appropriate allocation of resources for treatment, prevention and research that will improve clinical and economic outcomes. The major study of this thesis, to my knowledge, is the first in the world to determine the population incidence of HCC using clinical case capture independent of the cancer registry. In doing so, it is also the first study to validate the completeness and accuracy of a cancer registry in reporting HCC, which is critical given that the HCC epidemiology literature has been mostly dependent on local registry data. Over 12 months (July 2012 to June 2013), there were 272 new cases of HCC identified from multiple primary sources including multidisciplinary meeting reviews, hospital inpatient, outpatient and emergency attendance at any of Melbourne’s seven tertiary hospital networks, pathology, radiology and pharmacy databases. After cross- referencing with the Victorian Cancer Registry cases for the same period, the HCC incidence determined by this study was found to be twice as high as that reported by the registry. The recruited population-based prospective cohort of HCC patients then provided the opportunity to examine clinical outcomes across the breadth of presentation, demographics and institutional expertise. This allowed for the determination of factors associated with improved survival, in particular, the influence of HCC surveillance participation. The commonest risk factors for HCC were chronic hepatitis C (41%) and alcohol-related liver disease (39%) followed by chronic hepatitis B (22%). While participation rates were low (40%), surveillance was associated with earlier tumour stage at diagnosis, being offered curative therapies, and improved survival probability. In the era of advanced diagnostic imaging and therapeutics for HCC, only some of which is publicly funded, the economic cost of the HCC disease burden is an important consideration in cost-effectiveness analyses. This HCC incidence cohort provides the basis for the first direct costings study of HCC management in Australia, with associated clinical factors that determine high cost. The highest costs occurred at both of ends of the disease spectrum, with early stage disease curable by liver transplantation or surgical resection, as well as in the sickest patients with advanced disease and only palliative options available. Thus, investment of healthcare expenditure towards disease prevention and early detection would likely be most cost-effective with improved survival and reduced morbidity achieved. This world-first research, using a novel methodology for clinical case capture, determined the population-based incidence of HCC in Melbourne, confirmed the underreporting of incidence by the cancer registry and contributed to the correction of registry classification practices. For cancers with rapidly changing epidemiology such as HCC, accurate and contemporary local data is important in disease prevention and management and in guiding healthcare policy and research.
Quality of life outcomes following surgery for extremity sarcoma in Victoria, Australia: an observational prospective cohort study
This study was part of the Victorian Sarcoma Service (VSS) – a statewide Australian service comprising multidisciplinary teams dedicated to managing sarcoma. We followed a cohort of 76 people from the time of diagnosis of a new, surgically resectable extremity sarcoma (ES) to one year after surgery. Baseline characteristics that were collected included medical, sociodemographic and employment-related information, as well as information about received and perceived adequacy of social support. Physical function limitations, quality of life (QoL) as well as levels of depression, anxiety and stress were assessed at baseline, six months after surgery and one year after surgery. About a third of our cohort reported symptoms suggestive of psychological distress at each of the time points assessed. A history of previous psychiatric morbidity was associated with symptoms of depression, anxiety and stress throughout the cancer journey, perhaps suggesting increased vulnerability to distress. Other associations with distress included poor self-reported QoL, financial stress, increased levels of pain and higher levels of physical function limitations. A quarter of our participants reported poor QoL. Factors associated with poor QoL included psychological distress and physical function impairment. We found that majority of our cohort was engaged in paid employment prior to the diagnosis of ES. After a year from surgery, less than a third had returned to their usual work whilst almost a quarter did not return to work at all. Those that had difficulty returning to work reported difficulty keeping up with work early on, even before surgery. The most common reason for not returning to one’s usual level of work was due to the complications or side effects of ES and / or treatment – including pain, stiffness, weakness and fatigue. We identified that a significant proportion of people did not return to work due to mental health related reasons. Furthermore, there was a strong association between difficulty with performing work-related tasks and psychological distress, financial stress, physical function and poor QoL. Overall, we have identified that employment related difficulties are common and become apparent early on. We propose that early screening for employment-related difficulties and appropriate counselling with or without job re-training may have some benefit in improving outcomes for people with ES.
Investigating the natural history, serologic and genetic associations with disease outcomes, disability and cost of care in inflammatory bowel disease
Inflammatory bowel disease (IBD) is an emerging global health condition. In the second half of the 20th century, the incidence of Crohn’s disease (CD) and ulcerative colitis (UC) increased dramatically in the Western world. In the last two decades a corresponding rise has been observed in South East Asia(1) and Australia has one of the highest incidences of IBD in the world.(2) At this point in time there is no cure for IBD, and individuals with the condition usually receive lifelong treatment and a significant proportion will need intestinal surgery.(3) Early aggressive treatment with immunomodulator (IM) and biologic therapy can improve steroid free remission rates, reduce the need for surgery and hospitalisation, and reduce the rate of progression to a complex disease phenotype. (4-9) Medicare-subsidised biologic therapy for CD was first made available in Australia in late 2007, while infliximab was not available for use in UC in Australia until 2014. Although the rate of biologic prescription is steadily rising, the impact of increasing biologic use on the natural history and cost of care in the real-world is not clear. Furthermore, it is difficult to identify patients who would benefit from early biologic therapy, and it is uncertain if advancements in treatment are translating into improved patient function and reduced disability. Previous Australian researchers established a prospective community-based IBD inception registry in Barwon, Victoria in 2007 and collected cases to June 2013.(2, 10, 11) The initial aim of the registry was to establish the incidence and prevalence of IBD in Australia, to identify environmental exposures associated with disease aetiology, and to assess the course of disease and healthcare costs in the first 12 months from diagnosis. The aims of the work presented in this thesis were to use the community-based cohort from Barwon, in addition to a newly constructed tertiary IBD center hospital-cohort to determine the natural history of IBD in the first five years of disease, to identify clinical, serologic and genetic associations with disease course and outcomes in IBD, to determine the health care cost of IBD within the first four years of diagnosis from a health care system perspective and identify early clinical predictors of high cost of care, and to describe the burden of disability and identify determinants of disability in IBD. Incident cases diagnosed from July 2013 to April 2016 were identified through a multifaceted approach from Barwon and St Vincent’s Hospital Melbourne to ensure complete capture. Cases were enrolled into the IBD registry that was used as a basis to collect outcome data on disease course, healthcare costs, and disability. Serological analysis was performed for anti-Saccharomyces cerevisiae (ASCA) IgG and IgA antibodies in CD patients, as well as perinuclear anti-Neutrophil Cytoplasmic antibodies (p-ANCA) in CD and UC patients. DNA analysis was performed using 26 single nucleotide polymorphisms (SNPs) that were identified from the literature as potentially having a prognostic role. A total of 408 patients [243(59.6%) CD and 165(40.4%) UC] were included in the analysis of natural history, as well as the cost analysis. 56% of CD and 62% of UC patients were from the Community cohort. 20.8% of CD patients needed intestinal surgery at 5 years which is lower than older population-based studies from the pre-biologic era. 28.1% of CD patients progressed to complex disease phenotype and 8.9% of UC patients underwent colectomy by 5 years which is similar to population-based studies from the pre-biologic era. There was no significant difference in disease outcomes in CD or UC between the hospital and community cohorts. 38% of CD patients and 15% of UC patients were exposed to biologic therapy. Anti-Saccharomyces cerevisiae positivity was associated with progression to complex disease and surgery in CD. Anti-Neutrophil Cytoplasmic Antibody positivity was associated with the need for biologic therapy in UC. There were no significant genetic associations with disease outcomes in CD or UC. In both CD and UC, medication costs accounted for over 50% of total cost, of which biologics accounted for the majority of medication cost. In CD, the mean medication cost per patient per year increased by $3,144 between years 1 to 4 (<0.01), which was offset by a fall in medical and surgical hospitalisation costs of $1,547 (p <0.01) and $3,321 (p <0.01) respectively leading to a reduction in total cost of care over 4 years. There were no significant changes in cost over time in UC. In both CD and UC, surgery, biologic use, and hospitalisation use were associated with higher cost of care. Disability was measured using the newly developed and validated IBD Disability Index (IBD-DI). 334 patients completed the IBD-DI. 56% of all patients had no or only mild disability while 32% of patients in remission had moderate to severe disability. Patients who had previous surgery or current biologic therapy but were currently in remission were more likely to be disabled. Factors associated with greater disability on multivariate regression analysis were active disease, female gender, socioeconomic disadvantage, and biologic use. In summary, this thesis has shown a numerically lower rate of intestinal surgery in CD compared with studies from the true pre-biologic era. Colectomy rates in UC were stable compared with historical controls however biologic exposure rates in UC were modest. We have demonstrated for the first time the nature of changes in IBD-associated healthcare costs over 4 years. After the first year of diagnosis, the use of IM and biologics rose significantly in CD, while surgery and hospitalisation rates declined. Over this time, healthcare cost profiles shifted in a similar fashion, in that as biologic usage rates increased, so did the cost of medications. As hospitalisation and surgical rates fell, so too did their corresponding costs. Disability in IBD is prevalent, and although active disease is an important contributor to disability, a significant proportion of patients were disabled despite being in remission. This novel finding indicates that other factors such as mental health issues may be contributing to disability in IBD.
Integration of advanced echocardiographic metrics and biomarkers to the fields of heart failure and exercise physiology in the era of precision medicine
Exercise testing is widely used for risk stratification of ischaemic heart disease, however, its application in other cardiovascular conditions, specifically heart failure and other disease states is less defined. Heart failure is a leading cause of mortality and morbidity. Despite advances in medical therapy, its prevalence is expected to increase. Recent developments in cardiac echocardiography, exercise testing and reducing costs of biomarker assays provides the opportunity to improve identification and prognostication of the heart failure syndrome. These principles may also prove useful in the discrimination of other disease states, in which a diagnostic biomarker is lacking. The principle aim of this thesis was to identify novel echocardiographic and non-invasive cardiopulmonary parameters during exercise that provide incremental prognostic value to established risk markers in heart failure. An exploratory sub aim was to investigate the ability of a personalised exercise test to discriminated disease states outside the cardiovascular system. Cohorts of heart failure patients undergoing assessment with echocardiography and cardiopulmonary exercise testing were selected to assess the incremental value of novel parameters. Recently, deformation imaging, also known as strain and quantitative measures of the right heart have shown prognostic value in patients with heart failure. These measures have rarely been analysed with cardiopulmonary exercise testing, therefore, their prognostic value in outcome models and contemporary risk scores were assessed. Dynamic changes in selected parameters were evaluated with regard to risk stratification potential. Finally, as biomarker assays are becoming increasingly used to identify the heart failure syndrome, their contribution to discrimination of disease and risk modeling when performed in conjunction with an exercise test was evaluated. In summary the main findings of this thesis were: 1. Echocardiographic contractile reserve and cardiopulmonary exercise testing parameters provide complementary information, therefore, in combination provide an opportunity to improve prognostication in heart failure. 2. Right heart metrics specifically, right atrial volume and exercise performance add value to previously validated heart failure risk scores in dilated cardiomyopathy. 3. The combination of exercise performance, left ventricular strain and left atrial volume presents a simple model for predicting heart failure outcomes in hypertrophic cardiomyopathy. 4. Percent predicted values of maximal oxygen consumption derived from the Fitness Registry and the Importance of Exercise National Database (FRIEND) registry equation appear to accurately predict heart failure outcomes. 5. Cytokine profiling post exercise appears to have greater discriminatory power than at rest when used to identify patients with myalgic encephalomyelitis / chronic fatigue syndrome; Echocardiographic parameters, have limited value. 6. The integration of cardiac biomarkers, cytokine profiling, exercise performance and cardiac imaging in a personalised exercise test is achievable and has the potential to improve risk profiling. In conclusion, this thesis demonstrated the opportunity to further refine risk stratification in heart failure using novel images techniques, specifically deformation imaging, right heart metrics and exercise performance. The use of serum samples post a bout of exercise may provide an opportunity to further refine diagnostics in the field. Future studies should address biological variability of serum biomarkers and investigate their value when integrated with established markers of risk.
Inflammation in atherosclerosis: exploring novel risk factors, prognostic markers and role of colchicine as an anti-inflammatory therapy in acute coronary syndromes
Inflammation plays a crucial role in the pathophysiology of atherosclerosis and clinical manifestation of acute coronary syndromes (ACS). Despite optimal medical therapy and contemporary percutaneous coronary intervention (PCI) technology, ACS patients remain at heightened risk for recurrent events and adverse clinical outcomes. It is known that inflammation is a global phenomenon and inflammatory milieu is intensified during ACS. In addition, inflammation, microvascular dysfunction (MVD) and myocardial injury/oedema are independently associated with adverse cardiovascular outcomes in patients with ischaemic heart disease despite there been scarce evidence to suggest the potential links between them. Diagnosis of MVD and myocardial oedema involves cumbersome invasive catheterisation procedures and radiology scans, which may not be necessarily accessible to all patients. Therefore, there is a need to explore potential surrogate markers that are simple, readily available, reproducible and inexpensive. Furthermore, colchicine has recently gained attention as a potential anti-inflammatory therapy in cardiovascular disease. However, the safety and feasibility of long-term colchicine administration in ACS population has not been examined. The principle aims of this thesis were to delineate the associations between inflammation, microvascular injury and myocardial injury, to explore the utility and prognostic values of various biomarkers, and to examine the potential of colchicine as a novel anti-inflammatory therapy in ACS management. A number of study protocols were conducted to achieve the aims. These include assessing coronary microvascular function using pressure/temperature sensor guidewire in catheterisation laboratory, evaluating for presence of myocardial oedema on cardiac magnetic resonance (CMR) imaging, capturing long-term cardiovascular events in a cohort of ACS patients via telephone follow-up, and lastly conducting a double-blind, placebo-controlled randomised trial involving colchicine in ACS population. In summary, the main findings of this thesis are: (a) Inflammation is associated with MVD, and C-reactive protein (CRP) is a significant predictor of MVD. (b) Resting coronary microcirculatory status is related to degree of myocardial injury in patients with ischaemic heart disease. (c) An ischaemic ECG, peak serum troponin and CRP levels are significant predictors of myocardial oedema (d) Leukocyte parameters such as platelet-to-lymphocyte ratio (PLR) and neutrophil-to-lymphocyte ratio (NLR) are associated with long-term all-cause mortality in ACS patients. (e) Colchicine in addition to standard secondary prevention therapy can be safely administered in ACS population. (f) Long-term adherence to ACS guideline-recommenced medical therapy remains unsatisfactory. The findings of this PhD are novel and have potential implications for future risk-stratification and management strategies in patients presenting with ACS. Larger studies are warranted to validate the prognostic value and clinical utility of these biomarkers before they could be incorporated into current risk prediction models or utilised in routine clinical practice. Lastly, the colchicine feasibility study has paved the way for a large randomised controlled trial which is currently underway to assess the efficacy of colchicine in improving long-term cardiovascular outcomes in ACS patients.
New approaches to induce tolerance in autoantigen-specific memory T cells in type 1 diabetes
Autoimmune disorders like type 1 diabetes (T1D) result from the failure of immune tolerance mechanisms. Antigen-specific therapy constitutes an attractive approach to re-establish a tolerant state but has so far not been successful in clinical settings. Importantly, treatment after the onset of autoimmunity is likely to be less effective due to established autoimmune responses and active inflammation in the islets. Moreover, a major hurdle might be the persistence of antigen-experienced islet-reactive T cells and the induction of tolerance in these memory cells is challenging. Hence, therapies intended to induce antigen-specific tolerance may need additional immunomodulatory treatments to be effective in individuals with established autoimmunity. Here, we aimed to identify a combination of interventions that induces tolerance in antigen-specific memory T cells. For this study, we generated non-obese diabetic (NOD) mice with tetracycline-regulated expression of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) in antigen presenting cells (TII mice) and tracked IGRP-specific CD8+ T cells using tetramer enrichment. Notably, while naïve IGRP-specific T cells are eliminated upon antigen expression, memory T cells are refractory to cell depletion. Interestingly, these memory T cells up-regulated several exhaustion markers in response to antigen exposure but showed no functional impairment. We hypothesized that combining short-term treatment with non-Fc-binding anti-CD3 F(ab’)2 and the co-stimulation blocker abatacept together with antigen expression might induce effective tolerance in TII mice. However, after initial depletion of antigen-experienced IGRP-specific cells by anti-CD3 F(ab’)2, these cells re-expanded and were still functional. Thus, our combination approach has only limited efficacy in established autoimmunity. Combination therapies of antigen-specific therapies with agents that support the induction of complete T cell exhaustion might be more successful and should be tested in future studies.