Translational models of coronary artery disease, myocardial infarction and heart failure. Development, validation and in vivo imaging studies using positron emission tomography

Coronary artery disease is an atherosclerotic disease, which leads to narrowing of coronary arteries, deteriorated myocardial blood flow and myocardial ischaemia. In acute myocardial infarction, a prolonged period of myocardial ischaemia leads to myocardial necrosis. Necrotic myocardium is replaced with scar tissue. Myocardial infarction results in various changes in cardiac structure and function over time that results in “adverse remodelling”. This remodelling may result in a progressive worsening of cardiac function and development of chronic heart failure. In this thesis, we developed and validated three different large animal models of coronary artery disease, myocardial ischaemia and infarction for translational studies. In the first study the coronary artery disease model had both induced diabetes and hypercholesterolemia. In the second study myocardial ischaemia and infarction were caused by a surgical method and in the third study by catheterisation. For model characterisation, we used non-invasive positron emission tomography (PET) methods for measurement of myocardial perfusion, oxidative metabolism and glucose utilisation. Additionally, cardiac function was measured by echocardiography and computed tomography. To study the metabolic changes that occur during atherosclerosis, a hypercholesterolemic and diabetic model was used with [18F] fluorodeoxyglucose ([18F]FDG) PET-imaging technology. Coronary occlusion models were used to evaluate metabolic and structural changes in the heart and the cardioprotective effects of levosimendan during post-infarction cardiac remodelling. Large animal models were used in testing of novel radiopharmaceuticals for myocardial perfusion imaging. In the coronary artery disease model, we observed atherosclerotic lesions that were associated with focally increased [18F]FDG uptake. In heart failure models, chronic myocardial infarction led to the worsening of systolic function, cardiac remodelling and decreased efficiency of cardiac pumping function. Levosimendan therapy reduced post-infarction myocardial infarct size and improved cardiac function. The novel 68Ga-labeled radiopharmaceuticals tested in this study were not successful for the determination of myocardial blood flow. In conclusion, diabetes and hypercholesterolemia lead to the development of early phase atherosclerotic lesions. Coronary artery occlusion produced considerable myocardial ischaemia and later infarction following myocardial remodelling. The experimental models evaluated in these studies will enable further studies concerning disease mechanisms, new radiopharmaceuticals and interventions in coronary artery disease and heart failure.

Lipotoxicity in Obesity and Coronary Artery Disease. Studies by PET, CT and MR

Lipotoxicity is a condition in which fatty acids (FAs) are not efficiently stored in adipose tissue and overflow to non-adipose tissue, causing organ damages. A defect of adipose tissue FA storage capability can be the primary culprit in the insulin resistance condition that characterizes many of the severe metabolic diseases that affect people nowadays. Obesity, in this regard, constitutes the gateway and risk factor of the major killers of modern society, such as cardiovascular disease and cancer. A deep understanding of the pathogenetic mechanisms that underlie obesity and the insulin resistance syndrome is a challenge for modern medicine. In the last twenty years of scientific research, FA metabolism and dysregulations have been the object of numerous studies. Development of more targeted and quantitative methodologies is required on one hand, to investigate and dissect organ metabolism, on the other hand to test the efficacy and mechanisms of action of novel drugs. The combination of functional and anatomical imaging is an answer to this need, since it provides more understanding and more information than we have ever had. The first purpose of this study was to investigate abnormalities of substrate organ metabolism, with special reference to the FA metabolism in obese drug-naïve subjects at an early stage of disease. Secondly, trimetazidine (TMZ), a metabolic drug supposed to inhibit FA oxidation (FAO), has been for the first time evaluated in obese subjects to test a whole body and organ metabolism improvement based on the hypothesis that FAO is increased at an early stage of the disease. A third objective was to investigate the relationship between ectopic fat accumulation surrounding heart and coronaries, and impaired myocardial perfusion in patients with risk of coronary artery disease (CAD). In the current study a new methodology has been developed with PET imaging with 11C-palmitate and compartmental modelling for the non-invasive in vivo study of liver FA metabolism, and a similar approach has been used to study FA metabolism in the skeletal muscle, the adipose tissue and the heart. The results of the different substudies point in the same direction. Obesity, at the an early stage, is associated with an impairment in the esterification of FAs in adipose tissue and skeletal muscle, which is accompanied by the upregulation in skeletal muscle, liver and heart FAO. The inability to store fat may initiate a cascade of events leading to FA oversupply to lean tissue, overload of the oxidative pathway, and accumulation of toxic lipid species and triglycerides, and it was paralleled by a proportional growth in insulin resistance. In subjects with CAD, the accumulation of ectopic fat inside the pericardium is associated with impaired myocardial perfusion, presumably via a paracrine/vasocrine effect. At the beginning of the disease, TMZ is not detrimental to health; on the contrary at the single organ level (heart, skeletal muscle and liver) it seems beneficial, while no relevant effects were found on adipose tissue function. Taken altogether these findings suggest that adipose tissue storage capability should be preserved, if it is not possible to prevent excessive fat intake in the first place.

Generation and Characterization of Knockout Mice and Analysis of Patient Material Demonstrates a Role for Tissue Inhibitor of Metalloproteinases 4 (Timp4) in the Cardiovascular System and Tumor Metastasis

This thesis focuses on tissue inhibitor of metalloproteinases 4 (TIMP4) which is the newest member of a small gene and protein family of four closely related endogenous inhibitors of extracellular matrix (ECM) degrading enzymes. Existing data on TIMP4 suggested that it exhibits a more restricted expression pattern than the other TIMPs with high expression levels in heart, brain, ovary and skeletal muscle. These observations and the fact that the ECM is of special importance to provide the cardiovascular system with structural strength combined with elasticity and distensibility, prompted the present molecular biologic investigation on TIMP4. In the first part of the study the murine Timp4 gene was cloned and characterized in detail. The structure of murine Timp4 genomic locus resembles that in other species and of the other Timps. The highest Timp4 expression was detected in heart, ovary and brain. As the expression pattern of Timp4 gives only limited information about its role in physiology and pathology, Timp4 knockout mice were generated next. The analysis of Timp4 knockout mice revealed that Timp4 deficiency has no obvious effect on the development, growth or fertility of mice. Therefore, Timp4 deficient mice were challenged using available cardiovascular models, i.e. experimental cardiac pressure overload and myocardial infarction. In the former model, Timp4 deficiency was found to be compensated by Timp2 overexpression, whereas in the myocardial infarct model, Timp4 deficiency resulted in increased mortality due to increased susceptibility for cardiac rupture. In the wound healing model, Timp4 deficiency was shown to result in transient retardation of re-epithelialization of cutaneous wounds. Melanoma tumor growth was similar in Timp4 deficient and control mice. Despite of this, lung metastasis of melanoma cells was significantly increased in Timp4 null mice. In an attempt to translate the current findings to patient material, TIMP4 expression was studied in human specimens representing different inflammatory cardiovascular pathologies, i.e. giant cell arteritis, atherosclerotic coronary arteries and heart allografts exhibiting signs of chronic rejection. The results showed that cardiovascular expression of TIMP4 is elevated particularly in areas exhibiting inflammation. The results of the present studies suggest that TIMP4 has a special role in the regulation of tissue repair processes in the heart, and also in healing wounds and metastases. Furthermore, evidence is provided suggesting the usefulness of TIMP4 as a novel systemic marker for vascular inflammation.

Spatial and temporal variation in fish populations and assemblages in coastal waters of the northern Baltic Proper

The distribution and traits of fish are of interest both ecologically and socio-economically. In this thesis, phenotypic and structural variation in fish populations and assemblages was studied on multiple spatial and temporal scales in shallow coastal areas in the archipelago of the northern Baltic Proper. In Lumparn basin in Åland Islands, the fish assemblage displayed significant seasonal variation in depth zone distribution. The results indicate that investigating both spatial and temporal variation in small scale is crucial for understanding patterns in fish distribution and community structure in large scale. The local population of Eurasian perch Perca fluviatilis L displayed habitat-specific morphological and dietary variation. Perch in the pelagic zone were on average deeper in their body shape than the littoral ones and fed on fish and benthic invertebrates. The results differ from previous studies conducted in freshwater habitats, where the pelagic perch typically are streamlined in body shape and zooplanktivorous. Stable isotopes of carbon and nitrogen differed between perch with different stomach contents, suggesting differentiation of individual diet preferences. In the study areas Lumparn and Ivarskärsfjärden in Åland Islands and Galtfjärden in Swedish east coast, the development in fish assemblages during the 2000’s indicated a general shift towards higher abundances of small-bodied lower-order consumers, especially cyprinids. For European pikeperch Sander lucioperca L., recent declines in adult fish abundances and high mortalities (Z = 1.06–1.16) were observed, which suggests unsustainably high fishing pressure on pikeperch. Based on the results it can be hypothesized that fishing has reduced the abundances of large predatory fish, which together with bottom-up forcing by eutrophication has allowed the lower-order consumer species to increase in abundances. This thesis contributes to the scientific understanding of aquatic ecosystems with new descriptions on morphological and dietary adaptations in perch in brackish water, and on the seasonal variation in small-scale spatial fish distribution. The results also demonstrate anthropogenic effects on coastal fish communities and underline the urgency of further reducing nutrient inputs and regulating fisheries in the Baltic Sea region.

Hälsans grund kan bara hjärtat förstå : ett sökande efter kunskap om hälsa i ljuset av Blaise Pascals tänkande

The aim of this thesis is to gain new understanding of health based on the work Penseés (Thoughts) by Blaise Pascal. The research interest originates from the motive of the heart for the greatness of man in conjunction with his baseness. The study is hermeneutic and the purpose is to describe health formulated as new abductive theses based on the assumption that caring science and caring theology can be conjoined in the same ontology. The work Penseés is, in Gadamer’s sense, alive since the text is constantly being made use of and is in this occurence interpreted through the requirements made by caring science. Pascal’s arguments continue through the historically effected consciousness while the interpretation is confronted with the ontological model of health. In the initial horizon we find the understanding of the motion of health and the extension towards text materials which is undertaken by Pascal’s Penseés. to open up the perspective and be able to project the horizon of the text. In the encounter with the text, the core content will first be discussed in an interpretative part after which the understanding gained will be summarized into new abductive assumptions. On the basis of Gadamer’s emphasis on the applications of the interpretations, the merging of the horizons will identify health as something desired by man, what he is and what he wants to accomplish. The creation of health is the reason of the heart, and on the basis of what man wants to confide in, the rise of health will be established. The totality of greatness and baseness of man is achieved by the accomplishment of health. That man owns spiritual devotedness means health whereas unhealthy means that he is insecure of his character and leads a life with ill-considered amusements. When according to Pascal, man’s desires and thoughts are joined in the heart, a connecting relation will arise. Hence the spiritual edification that man will fail to secure if he puts too much of his confidence in transient reason is included, something that is insufficient when it comes to understand the meaning of health.