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- Andersson, E. Axel
(författare)
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Blood Vessels, Biomarkers, and Broken Barriers: lnvestigations of the Brain Vasculature in Models of Neonatal Brain lnjuries
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Brain injury during the perinatal period can lead to lifelong impairment in cognitive and motor function, or an early death. Term neonatal encephalopathy and preterm germinal matrix haemorrhage are two conditions that can irreversibly injure the brain, but clinical tools for diagnosing and treating these pathologies are lacking. It is known that the cerebrovasculature, i.e. the blood vessels of the brain and blood/brain barrier (BBB) plays a role during the course and recovery of injury. This thesis investigated the cerebrovascular involvement in two animal models of neonatal brain injury in an attempt to elucidate injury mechanisms, find potential new treatments, and identify biomarkers for brain vascular dysfunction. Using rodent models for hypoxic/ischemic encephalopathy (HIE) and germinal matrix‐intraventricular haemorrhage (GM‐IVH) we found raised levels of tight‐junction proteins claudin‐5 and occludin, two integral components of the BBB, in blood plasma and cerebrospinal fluid at different time points. In the HIE model, levels of tight‐junction proteins in the circulation were sex‐dependent and the amount of claudin‐5 in CSF correlated with the severity of brain injury. These proteins thus have potential as biomarkers for early detection of cerebrovascular insults. In addition, we did in‐depth assessments of the BBB function in both models and detailed the temporal and regional increases of barrier permeability after injury by measuring the extravasation of radiolabelled sucrose, visible dyes, and molecular tracers. Studies of the cerebral vasculature and angiogenesis after HI showed that the density of proliferating endothelial cells were largely unaffected after injury, but the number of growing endothelial tip cells were strongly reduced in the entire brain, accompanied by changes in the expression of angiogenesis genes. The thesis also includes the first trial of endogenous RNAse A as a neuroprotective treatment for neonatal brain injury, a treatment that has shown promise in adult models of other pathologies with cardiovascular aspects. We found significant reductions of grey and white matter tissue loss after RNAse A administration in HI animals, but no protection of BBB function or evidence for a reduced neuroinflammatory response. Taken together, this thesis contains new insights into several aspects of the vascular mechanisms involved in the pathogenesis of two major forms of injury that can occur in the neonatal brain.
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| 2. |
- Andersson, Sara B. E., 1987-
(författare)
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Novel and refined small-scale approaches to determine the intrinsic dissolution rate of drugs
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many drugs are administered as crystalline particles compressed into tablets and taken orally. When the tablet reaches the gastrointestinal tract, it disintegrates and the drug particles dissolve in the gastrointestinal fluid. The dissolved molecules are absorbed across the intestinal membranes into the bloodstream to reach their target sites. Only dissolved molecules can be absorbed, and if a drug has low solubility and/or dissolution rate in gastrointestinal fluid, the drug absorption might be insufficient. Hence, knowing the solubility and dissolution behaviour of a potential drug candidate is necessary early in the drug development process. The aim of this thesis was to evaluate and refine different approaches for measuring and determining dissolution rate, as well as to develop novel in vitro small-scale dissolution methods. First, interlaboratory variability in determination of intrinsic dissolution rate (IDR) and apparent solubility (Sapp) was investigated using a miniaturized dissolution instrument. To minimize the interlaboratory variability, standardized protocols for both the experimental design and the data analyses were required, and a flow chart for performing standardized powder and disc IDR measurements was established. Next, as an alternative to the powder and disc methods, carefully dispersed suspensions were used to determine the IDR, and rapid and more controlled IDR measurements were obtained using suspensions with dispersed primary particles. From the suspension measurements, an IDR/Sapp ratio of the compounds were determined. This ratio can potentially be used to identify whether a compound is likely to show dissolution rate-limited absorption and hence is sensitive to particle size reduction. The final experiments used a single particle dissolution approach to determine the IDR at four different fluid velocities. Computational fluid dynamics (CFD) simulations were used to theoretically investigate the flow conditions and dissolution rates. Single particle dissolution measurements under well-defined conditions gave high-quality dissolution data. An IDR was determined within 5-60 minutes using particles with initial diameters of 37.5-104.6 μm. The single particle dissolution experiments were used to determine the thickness of the effective hydrodynamic boundary layer (heff). The heff values were also assessed by CFD simulations, and a good concordance between experimental and simulated heff values was obtained. The approaches presented in this thesis can be used to derive qualified knowledge about the dissolution properties of drugs with several potential applications in drug development, such as profiling of solid drugs, informed formulation decisions, assisting the modelling of drug dissolution and providing improved understanding of the in vivo-dissolution behaviour
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