| 1. |
- Friberg, Andrew S, 1979-
(författare)
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Standardization of Islet Isolation and Transplantation Variables
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Currently, the transplantation of islets of Langerhans is a viable means to maintain control of blood sugar levels and reduce the risk of hypoglycemia in defined populations with brittle type I diabetes mellitus or those requiring pancreatectomy. However, the process of islet isolation is highly variable and not all isolations result in islet numbers or quality suitable for transplantation. This thesis aimed to improve transplantation success through optimization and standardization of the isolation process and to identify pretransplant variables associated with early islet engraftment. A previously disregarded enzyme activity, tryptic-like activity (TLA), has been identified to influence pancreas digestion efficiency and islet isolation success in both the preclinical and clinical situations. For human pancreases, islet isolation success rates improved from 0% in the lowest TLA group to over 50% in the highest TLA groups without affecting islet quality. These findings should help standardize evaluation of enzymes for clinical islet isolation. A closed, automated, pump-made gradient system was compared to the open, manual method for islet separation. No differences were observed in expected gradient volumes, islet yields or total purities between the two methods. The pump-made gradient system successfully removed manual influences on density gradient production while fulfilling regulatory requirements for closed system processing. Islet quantification was evaluated with computer-assisted digital imaging analysis (DIA) and a semi-closed assessment system. By using the DIA system method, which measures islet purity and pellet volume instead of manual counting methods, variation in islet counts and purity reduced by almost half. By using a transplant outcome measurement of C-peptide adjusted by blood glucose and creatinine, we identified four pretransplant factors that affect early transplant outcome. Of the four factors, one was related to the organ transport time, one to function of the islets, and two to the transplanted tissue volume. When these four factors were put into a predictive model, it accounted for about 40% of the transplant outcome. The work contained in this thesis identifies and optimizes a number of critical elements related to islet isolation and transplantation protocols.
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| 2. |
- Johnson, Magnus S.C. 1969
(författare)
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Structure and function of the HDL receptor SR-BI : scavenger receptor class B type I
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low plasma levels of high-density lipoprotein (HDL) and high levels of low-density lipoprotein (LDL) are well-recognized risk factors for cardiovascular disease. The uptake and degradation of LDL cholesterol have been characterized in detail at the molecular level. Less is known about the metabolism and cellular uptake of HDL cholesterol. In 1996 a novel receptor, scavenger receptor class B type I (SR-BI), was proposed to be an authentic HDL receptor. The aim of this thesis was to study the relevance of SR-BI as an HDL and scavenger receptor.The rat SR-BI cDNA was cloned and characterized. It encodes a protein containing 509 amino acids with two putative transmembrane domains and several motifs, including a peroxisomal targeting sequence, a leucine zipper domain and potential intracellular phosphorylation sites. The predicted double-transmembrane hairpin topology of SR-BI was verified experimentally and the SR-BI gene was localized on rat and human chromosomes.Expression of SR-BI was high in rat ovary, adrenal cortex and liver. In the rat ovary, expression of SR-BI was found in corpus luteum, known to use exogenous cholesterol as substrate for steroid synthesis, and in theca cells of follicles at all stages of development, including atretic follicles. Theca cells and cells overexpressing SR-BI bound apoptotic granulosa cells in vitro, suggesting a scavenger receptor function of SR-BI in the removal of apoptotic cells as part of the remodeling of atretic follicles to secondary interstitial cells. In the gallbladder, SR-BI was present at the apical portion of columnar epithelial cells, suggesting that this receptor may also influence the composition of the bile.The role of the carboxy(C-)terminal intracellular domain of SR-BI was studied with respect to protein interaction, targeting and function of the receptor. At the C-terminus of SR-BI a peroxisomal targeting motif was identified, indicating possible interaction with peroxisomes. SR-BI was shown by coimmunoprecipitation to interact with the peroxisomal targeting import receptor, Pex5p, and overexpression of the C-terminal intracellular domain of SR-BI resulted in translocation to peroxisomes, in vitro. The C-terminal intracellular domain of SR-BI was not required for HDL lipid uptake, but was found important for cellular sorting/targeting of the receptor. The leucine zipper domain was shown to be of potential importance for dimerization of SR-BI and for receptor-mediated HDL binding and lipid transfer.Structural and functional analyses of SR-BI in vitro and in vivo support its proposed role as a physiologically relevant HDL receptor. Further studies of structure and function of SR-BI may increase the understanding of the physiology and pathophysiology relating to HDL cholesterol metabolism and possibly contribute to novel therapeutic strategies.
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| 3. |
- Liljeblad, Jonathan F. D., 1978-
(författare)
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A Spectroscopic Study of Interfacial Films: Internal Structuring, Stability, and Hydration
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Monolayers of molecules are capable of completely changing the nature of surfaces and their interactions with the surroundings despite their almost negligible thickness. In the research presented in this doctoral thesis the surface specific technique Vibrational Sum Frequency Spectroscopy (VSFS) was combined with the Langmuir trough to investigate various manifestations of monolayers, such as biomimetic membranes, mono methyl branched long chain fatty acids in contact with air, and hydrophobic silane monolayers in contact with water.VSFS was applied to in situ studies of the oxidative degradation of Langmuir monolayers of 1,2-diacylphosphocholines with identical C-18 chains featuring various degrees of unsaturation. The monolayer area and vinyl CH signal intensity were probed at constant surface pressure to monitor the degradation. The rapid degradation of the unsaturated lipids in contact with the ambient air is attributed to oxidation of the C=C bonds mediated by reactive species in the air and can be inhibited by purging the compartment surrounding the monolayer with nitrogen.The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The monolayers are conformationally well ordered at all surface pressures and the signal intensity increases due to larger molecular number density at increasing surface pressures. Also, water signals with different vibrational frequencies are observed in different polarization combinations.Additionally, a selection of common phospholipids (18:0 PC, 18:0 PC-D83 and 18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and the CH- and OH-stretching regions as well as lower wavenumber regions were probed using VSFS. The orientation of the conformationally well ordered aliphatic chains was determined to be approximately perpendicular to the sample surface.Monolayers of eicosanoic acid, its iso (19-MEA), and anteiso (18-MEA) analogues were investigated with VSFS, AFM imaging, and the Langmuir trough. The EA forms smooth, featureless monolayers when deposited on silica, while 19-MEA and 18-MEA form 10 -50 nm large domains with homogeneous size distribution. It was not possible to discriminate between the monolayers of racemic and chiral 18-MEA using any of the techniques employedThe influence of the experimental geometry on the SF spectral shape and en-hancement at and near total internal reflection conditions (TIR) were systematically investigated by comparing simulations with recorded data from a hydrophobized silica / water interface. The data agree qualitatively, but not quantitatively, with the simulations, and the reasons were critically discussed.The water structure next to ordered and disordered hydrophobic silane monolayers on silica was investigated using VSFS. The results indicate that the structure of water next to a well ordered hydrophobic monolayer, with the exception of the first layer of water molecules, is not much different from that in the isotropic bulk. This is in contrast to the previous notion where such monolayers were assumed to induce a more ordered interfacial water structure.
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| 4. |
- Zhao, Weijie
(författare)
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Nanoscale studies of the atmospheric corrosion of copper protected by ultrathin organic films
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Copper (Cu) has been utilised by humans for millenniums and has become an indispensable metal in modern industry and in our infrastructure. However, corrosion, as a natural process for metallic materials, takes place on copper surfaces in most environments. Thus, understanding corrosion and corrosion protection of copper is of utmost importance to maintain its performance and prolong the lifetime of the applications. Corrosion has been revealed to start from local weak areas of the copper surface. However, the corrosion initiation and propagation mechanism on copper on a molecular level are far from clear.In this thesis, the corrosion initiation of copper under a simulated indoor atmosphere where formic acid and humidity are present was studied. The corrosion process was monitored in-situ, and the formed corrosion products were characterised on the macro-, micro-, and nanoscale by various analytical techniques from both horizontal and vertical directions of the corroded surfaces. The localised dissolution and formation of the Cu2O layer on narrowly separated areas on the nanoscale were observed both microscopically and spectroscopically. A novel technique, nano infrared spectroscopy (nano-FTIR), was used to probe the formed corrosion products on the nanoscale. Due to the novelty of nano-FTIR, only a few studies in corrosion science using this technique were reported. Thus, this thesis also shows the capability of employing nano-FTIR in corrosion studies.The ability of ultrathin organic films to protect copper under indoor atmospheres was also studied in this thesis. The main focus was on octadecylphosphonic acid (ODPA), for which the self-assembly process was examined in detail. A multilayer formation of ODPA on copper was observed under the self-assembly deposition, and the thickness of ODPA films increased with the deposition time. The reason for forming multilayers was attributed to the Cu+ ion release during the deposition, resulting in the formation of a Cu+-ODPA complex. The protective ability of these self-assembled ODPA films as well as Langmuir-Blodgett (LB)-deposited films on non-oxidised and pre-oxidised copper was examined under the same exposure conditions as for the unprotected copper. A remarkable ability to protect the surface was observed for the self-assembled and LB-deposited ODPA films on pre-oxidised copper.
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