Motoric cognitive risk: epidemiology of a walking speed-based syndrome to predict dementia

Dementia is a huge global health challenge without a cure. Identifying the early stages enables the implementation of risk-modifying interventions when they may be most effective. Slow gait speed and self-reported cognitive complaints are among the earliest findings reported in the preclinical stage of dementia. The Motoric Cognitive Risk (MCR) syndrome is a high-risk predementia state combining objective slow gait speed and subjective cognitive complaint in independent, dementia-free individuals. This thesis investigates the association between MCR and dementia using meta-analysis and several epidemiological approaches in a Scottish cohort of community-dwelling older adults. The first study presents a systematic review and meta-analysis of the prognostic ability of MCR. This review also outlined hypotheses regarding the underlying mechanisms of MCR, areas that are explored further in the final chapter of the thesis. It examined longitudinal cohort studies that compared an MCR group to a non-MCR group for any health outcome. A thorough search returned 705 records with 15 cohorts eligible for meta-analysis. The meta-analysis included only health outcomes reported from at least three cohorts and judged satisfactory by our clinical content experts. When a study reported an incompatible effect measure, I contacted authors to request data to allow for our own calculation, or I converted the effect measure where possible and appropriate. The meta-analysis found that participants with MCR were at an increased risk of cognitive impairment (adjusted Hazard Ratio [aHR] 1.76, 95% CI 1.49–2.08; I2 = 24.9%), dementia (aHR 2.12, 1.85–2.42; 33.1%), falls (adjusted relative risk 1.38, 1.15–1.66; 62.1%), and mortality (aHR 1.49, 1.16–1.91; 79.2%). There was considerable heterogeneity in how studies diagnosed MCR, cognitive impairment, and dementia. Our review of the underlying mechanisms of MCR suggested that interactions between MCR, poor brain health, falls, and increased mortality are likely due to a range of biological, psychological, and social mechanisms. A major strength of this systematic review and meta-analysis is the thoroughness of its methodology. The second study of the thesis described the prevalence of MCR and associated factors in the Lothian Birth Cohort 1936 (LBC1936). It was the first time MCR had been derived in a Scottish cohort, so it detailed how MCR was coded and implemented. This study also reported slow gait speed cut-offs for the first time in an older Scottish population. It also assessed the overlap of MCR with three other high-risk states of ageing - Mild Cognitive Impairment (MCI), Prefrailty, and Frailty, thus clarifying the degree of cross-over between these related states. MCR was derived in three waves of the cohort at mean ages of 76.3 years (n = 690), 79.3 years (n = 543) and 82 years (n = 425). MCR prevalence rate ranged from 5.3% to 5.7% across the three waves, a little lower than the global average. Factors associated with MCR in this cohort included age, socioeconomic status, and tests of executive function. There was partial overlap between individuals with MCR and MCI, indicating that these concepts, although derived using similar criteria, capture different cohorts of people. This supports the conceptualisation of MCR as complementary to MCI rather than an alternative. The study highlights the need to explore further the strong association between lower socioeconomic status in early and mid-life with MCR later in life. Building on a key finding from the second study of the thesis, the third study focused on socioeconomic status as a risk factor for MCR. This longitudinal observational study used logistic regression analysis adjusting for important demographic, lifestyle, and health covariates to explore the association between MCR at age 76 years, and years of education and occupational social class, categorised into manual versus non-manual occupations. The final model included 671 participants. Results show that lower socioeconomic status as defined by non-manual versus manual occupation (and not years of education) is associated with a greater than three-fold risk of having MCR later in life (adjusted odds ratio 3.55, 95% CI 1.46–8.74; p = 0.005). Putting this study in context with the literature is difficult as there is a paucity of work focussing on socioeconomic status as a risk factor for MCR. However, having a low socioeconomic status is a widely accepted predictor of ill health generally, and dementia more specifically. Therefore, it is no surprise that it was strongly associated with MCR, which is a high-risk state for dementia. This study highlights a novel risk factor for MCR and offers a hypothesis on underlying mechanisms but concludes by recommending further work to unravel the relationship between lower socioeconomic status and MCR. The fourth study shifted temporarily to focus on identifying dementia in LBC1936, an essential piece of work to allow for the later study of MCR as a predictor of dementia. Previously, the LBC1936 cohort lacked a clinically diagnosed dementia outcome. Our study introduced a novel approach to identifying dementia in cohort studies and reported for the first time the incidence and prevalence of all-cause dementia and its subtypes in the LBC1936. We comprehensively evaluated all participants' electronic health records to identify any indications of cognitive impairment. In addition, we performed in-person clinician assessments whenever a participant's cognition was in doubt. Clinical dementia specialists from Old Age Psychiatry, Neurology, and Geriatrics agreed on a diagnosis of probable dementia, possible dementia, or the absence of dementia, and determined the subtype whenever possible. Of the 865 LBC1936 participants included, 118 (13.6%) had dementia by an average age of approximately 86 years. Dementia was more common with increasing age and in women, and the most common type of dementia was due to Alzheimer disease (49.2%). Self-reported dementia diagnoses were positive in only 17.8% of clinically identified dementia diagnoses. This illustrates the importance of a robust clinical dementia diagnosis instead of relying on self-reported diagnoses. Our work will enable researchers to explore the extensive LBC936 data accumulated over a 16-year period for signals that differentiate participants currently living with dementia from those who are not. This includes my newly derived MCR measure, which brings us to the final study of the thesis. The fifth and final study provided a time-to-event analysis with MCR as the predictor variable and dementia as the outcome of interest. It also explored the various trajectories of participants diagnosed with MCR. It classified a total of 680 community-dwelling participants (mean [SD] age 76.3 [0.8] years) free from dementia into non-MCR or MCR groups. It used Cox proportional hazards methods and competing risk regression to evaluate the risk of developing all-cause dementia in the years following MCR diagnosis. The final model adjusted for potential confounders. Results show that, after 10 years of follow-up, 79 of 680 (11.6%) participants developed dementia. The presence of MCR increased the risk of dementia (aHR 2.34 [1.14 to 4.78, p=0.020]) in this Scottish cohort to a similar extent as in other populations. Individuals with MCR follow similar trajectories to the related predementia syndrome, MCI. This study reinforces that MCR could potentially identify a target group for early interventions of modifiable risk factors for dementia. However, it illustrates the heterogeneous nature of MCR progression and highlights that not all older adults with MCR will follow a similar path. This thesis explores the predementia syndrome MCR through meta-analysis and several epidemiological approaches in the Lothian Birth Cohort 1936. The findings represent a significant advancement in our understanding of MCR prevalence, risk factors, predictive ability, and trajectories. Since there are no effective treatments for dementia, prevention is paramount. By improving our understanding of this high-risk predementia state, this thesis brings us closer to the ultimate goal of intervening early in the lifecourse to reduce the number of people living with dementia

Proceedings Virtual Imaging Trials in Medicine 2024

This submission comprises the proceedings of the 1st Virtual Imaging Trials in Medicine conference, organized by Duke University on April 22-24, 2024. The listed authors serve as the program directors for this conference. The VITM conference is a pioneering summit uniting experts from academia, industry and government in the fields of medical imaging and therapy to explore the transformative potential of in silico virtual trials and digital twins in revolutionizing healthcare. The proceedings are categorized by the respective days of the conference: Monday presentations, Tuesday presentations, Wednesday presentations, followed by the abstracts for the posters presented on Monday and Tuesday

Mineralocorticoids and sodium in chronic kidney disease - regulation and cardiovascular implications

Chronic kidney disease is common and associated with an elevated cardiovascular risk, as well as the long-term risk of renal failure. At present, therapeutic approaches to managing chronic kidney disease (CKD) do not fully reverse these risks. This has led to study of the determinants of pathological outcomes in these patients, with the hope of further therapeutic interventions to reduce these risks. Mineralocorticoids, predominantly aldosterone, are produced by the adrenal cortex and have a vital role in maintaining sodium status and blood pressure. However, high levels of aldosterone in humans are known to produce an adverse phenotype of hypertension and a disproportionately elevated cardiovascular risk. Furthermore, in animal models of renal failure, elevated aldosterone levels stimulate renal damage, in the presence of a high sodium milieu. These laboratory findings have been translated to provide a basis for several short-term follow-up clinical trials looking at the impact of non-genomic non-natriuretic doses of mineralocorticoid receptor inhibition in patients with chronic kidney disease. These studies have shown a reduction in proteinuria, often independent of decline in blood pressure. However, there is a paucity of baseline physiological data relating to the normal regulation of mineralocorticoid synthesis and action in chronic kidney disease. The response of the adrenal cortex to renal failure is not understood. Is mineralocorticoid synthesis regulated in the usual way? Are the stimulators of mineralocorticoid production and release affected by uraemia? Is dietary sodium intake associated with steroid status and adverse outcomes in humans? The hypothesis of this thesis was that the renin-angiotensin-aldosterone system is inappropriately activated in patients with chronic kidney disease. Secondly, that high levels of mineralocorticoids are associated with adverse end-organ damage including proteinuria excretion, left ventricular hypertrophy, endothelial dysfunction, elevated pulse wave velocity and markers of renal fibrosis. Furthermore, that these deleterious effects are associated with sodium status and that an elevated dietary sodium intake is independently associated with increased renal and cardiovascular risk. In order to test these hypotheses, 70 patients with CKD and 30 patients with essential hypertension (EH) were recruited and underwent detailed clinical and biochemical phenotyping. This included 24 hour urinary steroid metabolite analysis, plasma renin and aldosterone measurement, cardiac magnetic resonance imaging, carotid-femoral pulse wave velocity and assessment of endothelial function. 20 It was shown that levels of the main mineralocorticoids (MC) (aldosterone and deoxycorticosterone) are not elevated in patients with CKD, as compared with patients with essential hypertension (EH). However, the determinants of levels of MC excretion differed between the two conditions. In CKD, excretion of MC metabolites was directly proportional to excretion of urinary sodium. A high urinary sodium (a marker of dietary sodium intake) was associated with a higher excretion of tetrahydroaldosterone (THALDO - the main aldosterone metabolite). In patients with EH, no relationship was seen between urinary steroid excretion and urinary sodium excretion. This is a novel relationship between the kidney and adrenal gland which questions the conventional wisdom that the adrenal cortex is unaffected by uraemia and prompts further study into the regulation of steroid synthesis in CKD. Furthermore, it was shown for the first time that 24h excretion of tetrahydrodeoxycorticosterone (THDOC) is an independent predictor of left ventricular mass index and that THALDO is an independent predictor of proteinuria excretion – demonstrating a relationship between mineralocorticoids and two of the main predictors of mortality in CKD. An interaction between sodium, MCs and these two features was also demonstrated. No association between levels of mineralocorticoids and vascular function was seen. Urinary 24 hour excretion of sodium was significantly associated with endothelial dysfunction in patients with CKD and pulse wave velocity in patients with essential hypertension. Retrospective data analysis further confirmed an association between a high dietary sodium intake and adverse outcomes. In a study of 498 patients with CKD and a median follow-up of 7 years, an elevated 24h urinary sodium to creatinine ratio was shown to be associated with an increased risk of death. There was however no independent association with renal progression or requirement for renal replacement therapy. This is the first time that sodium intake has been clearly linked to adverse outcomes in patients with CKD. Lastly, laboratory work demonstrated that steroid stimulation (aldosterone or cortisol) of human proximal tubular cells resulted in increased collagen 1 gene expression, but only in the context of a high sodium environment. Collagen 1 is deposited in renal interstitial fibrosis. This effect was inhibited by MR blockade, further expanding on the potential role 21 of steroids in the progression of CKD and again confirming the relationship between salt and steroids. In conclusion, in this thesis it has been demonstrated that production of MCs in patients with CKD is closely associated with urinary sodium excretion (a surrogate for dietary sodium intake). This relationship is novel and not seen in patients with essential hypertension. It suggests that the response of the adrenal cortex in the context of uraemia is altered. Moreover, levels of mineralocorticoids are independently associated with left ventricular mass index and proteinuria excretion, both significant predictors of mortality, in patients with CKD. Dietary sodium intake has been shown to be an independent predictor of mortality and laboratory studies have demonstrated that mineralocorticoid receptor binding in a high sodium environment is associated with collagen 1 gene upreguation. These findings have important implications for the role of adequate renin-angiotensin-aldosterone blockade in patients with CKD and suggest that the addition of a mineralocorticoid receptor blocker and dietary sodium restriction should be advocated

Investigating the contribution of synaptic and vascular pathology to neurodegeneration in mitochondrial disease

PhD ThesisMutations in mitochondrial DNA (mtDNA) lead to a genetically and phenotypically heterogeneous group of human diseases, mitochondrial disorders. Though patients with mtDNA disease present with multisystemic abnormalities, the central nervous system is usually severely affected. Of the neurological deficits, cerebellar ataxia is the most frequently presenting symptom of patients recruited to the UK MRC Mitochondrial Disease Patient cohort, with a prevalence of 70%. Furthermore, stroke-like episodes are prominent, but not restricted, to patients with the Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes (MELAS) syndrome, due to the m.3243A>G point mutation. Both neurological symptoms are associated with pronounced neurodegeneration. The aim of this thesis was to gain further insights into the mechanisms responsible for neuronal loss in patients who manifest with cerebellar ataxia and stroke-like episodes. A reliable, reproducible and quantitative quadruple immunofluorescent technique has been developed that allowed the quantification of respiratory chain protein expression in specific neuronal domains and cellular populations. Furthermore, three-dimensional reconstruction helped examine the structural characteristics of sub-cellular compartments. Close investigation of the intracerebellar microcircuitry provided evidence for respiratory chain protein expression defects in Purkinje cell bodies, dendrites and presynaptic terminals. Altered Purkinje cell innervation of respiratory chain deficient dentate nuclei neurons likely leads to neuronal disinhibition and is accompanied by partially disturbed glutamatergic connectivity to the region. Additionally, respiratory chain deficiencies were detected in the vasculature of vulnerable to stroke-like episodes brain regions (cerebellum, occipital and temporal lobe) in patients harbouring the m.3243A>G point mutation. Preliminary data suggest that stroke-like episode manifestation and cortical lesion development is due to an additive effect between neuronal/interneuronal and vascular pathology. These observations set the basis for studying the impact of mtDNA defects in synaptic, neuronal and vascular health in-vitro and have important implications for identifying good candidates for drug targeting in mitochondrial disease

Targeting farnesyl pyrophosphate synthase of Trypanosoma cruzi by fragment-based lead discovery

Trypanosoma cruzi (T. cruzi) is the causative agent of Chagas disease (CD), which mostly affects underprivileged populations in South and Central America. The current standard of care for this disease are the two empirically discovered drugs benznidazole and nifurtimox. They show low efficacy, difficulties in administration and severe side effects. Moreover, there are T. cruzi strains that have formed resistances. Thus, the development of a safe and efficient drug is urgently needed. T. cruzi is dependent on isoprenoid biosynthesis as ergosterol and other 24 alkylsterols are essential metabolites that cannot be acquired by other mechanisms. Therefore, it was hypothesised that enzymes along this pathway are promising drug targets. A number of compounds targeting these enzymes were tested and have been shown to inhibit parasite growth. Among those enzymes is farnesyl pyrophosphate synthase (FPPS), a key branch-point enzyme in the isoprenoid pathway, which is in the focus of this work. It catalyses the synthesis of farnesyl pyrophosphate (FPP), a C15 building block in sterol biosynthesis and in protein prenylation of signalling proteins. Bisphosphonates (BPs) are known active site directed FPPS inhibitors, which exhibit ideal pharmacokinetics to target bone mineral and are used to treat bone diseases. BPs can also combat T. cruzi flagellates but are not ideal to treat CD due to their pharmacokinetics. In the search for new chemotypes, several non-BP inhibitors that bind to another pocket were found for human FPPS (hFPPS) by fragment based screening (FBS). Recently, it was shown that the product of FPPS, farnesyl pyrophosphate (FPP), can bind to this pocket and locks the enzyme in an open and inactive state, thus showing the allosteric character of this pocket. The current work aims at the discovery of non-BP inhibitors of T. cruzi FPPS (TcFPPS), which could be starting points for the development of a treatment against CD. Towards this goal, recombinant expression in E. coli cells and purification by means of IMAC and SEC yielded pure und homogenous TcFPPS (chapter 5.1). This includes unlabelled, 13C15N labelled and in vivo biotinylated avi-tagged TcFPPS. Furthermore, a novel, reliable, highly reproducible, and well diffracting crystallization system was established. The system exhibits excellent properties for FBS as it was compatible with different types of 96-well plates. Apo crystals were stable for up to 24 h in 15% DMSO and allowed collection of data sets with a diffraction limit of around 1.6 Å. The best achieved diffraction limit was 1.28 Å for a soaked TcFPPS crystal (PDB ID 6R09). The allosteric region in TcFPPS was investigated by means of sequence analysis and structural superimposition of various orthologous FPPSs (chapter 5.2). This revealed that the allosteric region is less conserved than the active site. Differences among residues in equivalent positions that form the allosteric site were observed, which is surprising if it is assumed that all FPPSs can be product inhibited as hFPPS. A remarkable finding is that residue Phe50 in TcFPPS is an exception in an otherwise highly conserved position. It causes steric hindrance of the pocket in TcFPPS. An attempt to reposition established allosteric inhibitors of hFPPS showed binding affinity to TcFPPS but the two obtained crystal structures demonstrated their binding to sites on the protein surface (sites S1 and S2, PDB IDs 6R08 and 6R07, respectively). The Novartis core and fluorine library (1336 and 482 compounds) were screened on TcFPPS, which resulted in 63 and 45 validated fragment hits, respectively (chapter 5.3). Performing the same screen with T. brucei FPPS (TbFPPS), the causative agent of African sleeping sickness, and counter screening on hFPPS led to unique, pairwise and triple binders demonstrating selectivity at the early stage of FBS. Strikingly, TcFPPS has generally more binders than TbFPPS, and TcFPPS has many unique hits when compared to TbFPPS. Subsequent crystallization experiments with the core library hits resulted in 3D structures of two TcFPPS complexes. One ligand binds to the homodimer interface (site S12) and the other one in the active site. The latter was identified by using the statistical analysis tool Pan-Dataset Density Analysis (PanDDA). FBS by X-ray crystallography at the XChem facility in Harwell, UK, and the HTXlab in Grenoble, France, were conducted (chapter 5.4). The XChem screen identified 35 fragment binders (PDB IDs 5QPD – Z, 5QQ0 – 9, 5QQA – C) in binding sites that were distributed over the entire protein. This includes the active site, the allosteric site, the homodimer interface, sites on the surface and a new site in close proximity to the active site. Strikingly, the first two fragments binding to the allosteric site of TcFPPS in its open state were identified. Rotation of the phenyl side chain of Phe50 led to opening of the former closed pocket. The HTXlab screen identified additional binders for the active and allosteric site. In total 1244 data sets were collected and analysed. This process was accelerated using PanDDA. The first fragment-to-lead optimization by means of virtual screening using the web-based platform ANCHOR.QUERY was based on fragment hit LUY (chapter 5.5). Compounds were synthesised using one-pot one-step multi-component reactions. Synthesis of 11 compounds (MCR 1 – 11) was successful, but poor solubility was detrimental in subsequent testing on TcFPPS and crystallization experiments did not lead to a structural model of a complex. A second fragment to lead optimization using a fragment merging approach for chemical optimization was based on the active site directed binders AWM, LVV, LUY, LDV and AWV (chapter 5.6). A library of 12 compounds (MCN 1 – 12) was synthesised by reductive amination. X-ray structures revealed unexpected binding modes for compounds MCN-1, -4 and -8. Instead of retaining the binding site of the fragment, the merged compounds bind to the surface directed binding site S1 (PDB IDs 6R09, 6R0A, 6R0B). Nevertheless, the 50 new crystal structures of TcFPPS fragment complexes discussed in this work will pave the way for future drug discovery campaigns for CD. The large diversity of the fragments’ scaffolds and different binding sites are potential starting points for inhibitors with different physicochemical properties and a novel mode of action that might help to overcome the limitations related to the BP scaffold

PROGRAM and PROCEEDINGS THE NEBRASKA ACADEMY OF SCIENCES: 139th Anniversary Year, One Hundred-Twenty-Ninth Annual Meeting, April 12, 2019, NEBRASKA WESLEYAN UNIVERSITY, LINCOLN, NEBRASKA

PROGRAM AT-A-GLANCE FRIDAY, APRIL 12, 2019 7:30 a.m. REGISTRATION OPENS - Lobby of Lecture Wing, Olin Hall 8:00 Aeronautics and Space Science, Session A – Acklie 109 Aeronautics and Space Science, Session B – Acklie 111 Collegiate Academy; Biology, Session B - Olin B Biological and Medical Sciences, Session A - Olin 112 Biological and Medical Sciences, Session B - Smith Callen Conference Center Chemistry and Physics; Chemistry - Olin A 8:00 “Teaching and Learning the Dynamics of Cellular Respiration Using Interactive Computer Simulations” Workshop – Olin 110 9:30 “Life After College: Building Your Resume for the Future” Workshop – Acklie 218 8:25 Collegiate Academy; Chemistry and Physics, Session A – Acklie 007 8:36 Collegiate Academy; Biology, Session A - Olin 111 9:00 Chemistry and Physics; Physics – Acklie 320 9:10 Aeronautics and Space Science, Poster Session – Acklie 109 & 111 10:30 Aeronautics and Space Science, Poster Session – Acklie 109 & 111 11:00 MAIBEN MEMORIAL LECTURE: Dr David Swanson - OLIN B Scholarship and Friend of Science Award announcements 12:00 p.m. LUNCH – WESLEYAN CAFETERIA Round-Table Discussion – “Assessing the Academy: Current Issues and Avenues for Growth” led by Todd Young – Sunflower Room 12:50 Anthropology – Acklie 109 1:00 Applied Science and Technology - Olin 111 Biological and Medical Sciences, Session C - Olin 112 Biological and Medical Sciences, Session D - Smith Callen Conference Center Chemistry and Physics; Chemistry - Olin A Collegiate Academy; Biology, Session B - Olin B Earth Science – Acklie 007 Environmental Sciences – Acklie 111 Teaching of Science and Math – Acklie 218 1:20 Chemistry and Physics; Physics – Acklie 320 4:30 BUSINESS MEETING - OLIN B NEBRASKA ASSOCIATION OF TEACHERS OF SCIENCE (NATS) The 2019 Fall Conference of the Nebraska Association of Teachers of Science (NATS) will be held at the Younes Conference Center, Kearney, NE, September 19-21, 2019. President: Betsy Barent, Norris Public Schools, Firth, NE President-Elect: Anya Covarrubias, Grand Island Public Schools, Grand Island, NE AFFILIATED SOCIETIES OF THE NEBRASKA ACADEMY OF SCIENCES, INC. 1. American Association of Physics Teachers, Nebraska Section Web site: http://www.aapt.org/sections/officers.cfm?section=Nebraska 2. Friends of Loren Eiseley Web site: http://www.eiseley.org/ 3. Lincoln Gem & Mineral Club Web site: http://www.lincolngemmineralclub.org/ 4. Nebraska Chapter, National Council for Geographic Education 5. Nebraska Geological Society Web site: http://www.nebraskageologicalsociety.org Sponsors of a $50 award to the outstanding student paper presented at the Nebraska Academy of Sciences Annual Meeting, Earth Science /Nebraska Chapter, Nat\u27l Council Sections 6. Nebraska Graduate Women in Science 7. Nebraska Junior Academy of Sciences Web site: http://www.nebraskajunioracademyofsciences.org/ 8. Nebraska Ornithologists’ Union Web site: http://www.noubirds.org/ 9. Nebraska Psychological Association http://www.nebpsych.org/ 10. Nebraska-Southeast South Dakota Section Mathematical Association of America Web site: http://sections.maa.org/nesesd/ 11. Nebraska Space Grant Consortium Web site: http://www.ne.spacegrant.org

BIOMECHANICS AND BIOCHEMISTRY OF THE AORTA IN CHRONIC AORTIC DISSECTION

Chronic aortic dissection (AD) is defined as being one in which there is a tear which originates in aortic wall and has been present for more than 30 days. Chronic AD tends to be associated with a weakened aortic wall. Eventually the degenerated, weakened aortic wall may rupture. Although tensile or biaxial testing techniques have previously been used in vitro for biomechanical testing of AD tissues at the macro-scale, little is known about how localised changes in aortic structure and biomechanics contribute to progression of chronic AD. To find a way to address this challenge, the nanoindentation technique and ball indentation tests were used to investigate localised mechanical properties and time-dependent deformation behaviour respectively, of human aortic tissue samples from chronic AD patients. Using ovine aortic tissue as a model, the utility of the nanoindentation technique and ball indentation methods were validated and optimised. The data were correlated with conventional uniaxial indentation testing. Further, the mechanical properties and biochemical composition (collagen, elastin and GAG) were correlated across the entire aortic length. The human tissue work characterised the biomechanics, biochemistry, and histology of the dissection flap (FP), true lumen outer wall (TL) and false lumen outer wall (FL) in chronic dissection. These micromechanical properties and biochemical properties were compared with clinical data (interval of index event to operation (IIEO) and aortic growth rate). The main outcome of this thesis was the demonstration of how structural properties of dissection tissues within the aortic wall alter with time. FP and TL are stiffer with the arrangement of elastin fibres being highly compact, long, and aligned, whereas the FL was more compliant with localised loss of elastic fibres and increased elastin fragmentation that correlated with IIEO. Overall, the findings of this thesis suggest that indications for surgery in chronic AD, which are currently based on aortic size, may be independent of features such as aetiology, aortic dimensions, and anatomical segment