Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Made available in DSpace on 2015-07-22T20:49:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-12-31 / O rim é responsável pela maior parte da excreção de substâncias, tornando-se alvo de componentes tóxicos, tais como os meios de contrastes (MCTR). Os MCTR a base de iodo são substâncias utilizadas na angiografia, urologia ou tomografia computadorizada. Essas substâncias não deveriam interagir com o organismo, porém, na prática clínica, demonstram certo grau de interação orgânica onde são filtradas e metabolizadas livremente pelos rins, podendo ocasionar insuficiência renal aguda (IRA) devido a vasoconstrição e a isquemia medular O objetivo do presente estudo foi identificar, por meio de análise bidimensional, proteínas da célula mesangial imortalizada (CMI), que poderiam eStar sub ou supra expressas quando em contato com o MCTRH e, por conseqOência desta alteração, estejam envolvidas no processo de nefrotoxicidade Essas células foram divididas em 3 grupos" controle (Ct), manitol (Man) e tratado com HexabrixR (Hx), as quais foram tratadas e em seguida, aplicou-se a análise por gel de eletroforese bidimensional (2-DE). O método inicia-se pela focalização isoelétrica (1. dimensão), onde as proteínas são separadas de acordo com seu pl. Em seguida, essas proteínas são submetidas a uma separação de acordo com sua massa molecular (2. dimensão). Como os parâmetros usados anteriormente são independentes, uma grande resolução de spots (marcações protéicas) foi atingida. Os géis bidimensionais foram corados com Coomassie. Após a identificação dos spots nos géis 2-DE, extração das proteínas e análise por espectrometria de massa, constatamos o aparecimento de algumas proteínas com expressões variadas entre os géis Ct, Man e Hx. Dentre as proteínas identifica das localizamos algumas apenas nos géis submetidos à Hx, como. Canal de tropomiosina-1alfa (TPMA), e antígeno de proliferação de núcleo celular (PCNA). Outras localizadas nos géis Man e H x estavam supra expressas em relação ao gel Ct, como a proteína de controle da translação tumoral. Em contrapartida, houve proteínas que foram apenas expressas nos géis Ct e Man, evidenciando que provavelmente o iodo contido no HexabrixR tenha ocasionado uma sub expressão dessas proteínas, tais como anexina3 e Dna ligase. Finalmente houve a identificação de proteínas que estavam expressas nos três géis (Ct, Man e Hx) embora em concentrações variáveis, como Hsp27, Erp57 e Beta actina-1. De maneira geral, fatos relevantes foram analisados, um deles é de que todas as proteínas que foram expressas nos géis Ct e Hx, também foram detectadas nos géis Man, permitindo- nos enfatizar a possibilidade de descartar o papel da osmolaridade no aumento da expressão das proteínas que foram identificadas somente no gel Hx, sugerindo, portanto, ser o iodo e não a osmolaridade o fator desencadeador das alterações da expressão protéica. Em contrapartida supõe- se ainda que a osmolaridade tenha sido a causadora do aumento da expressão de algumas proteínas apenas nos géis Man e Hx, e não no CT. Sendo assim sugerimos que o MCTR, tanto pela sua osmolaridade como por outros fatores entre eles a influência da molécula do iodo, pode regular a síntese e/ou expressão das proteínas nas células mesangiais. / The kidney is a common target organ for toxic agents, like contrast media (CM). The CM with iodine is normally used in angiography, urography and tomography. CM is filtrated and metabolized in the kidney, being the major cause of acute renal failure (ARF). Nowadays, proteome is actually a powerful tool in the Nephrology Research, mainly in the identification of protein modifications when in contact with toxic agents. This technique also gives the possibility of biomarkers identification to help the physicians in the patient treatments. The aim of this study was to separate by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and to identify by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry the proteins that were up- or down-regulated in immortalized mesangial cell in culture (IMC) in the presence of CM. We evaluated three groups of IMC: control (CT), manitol (Man) and HexabrixTM (Hx). The samples were treated and submitted to the 2D-PAGE analysis, where the proteins were separated according to their isoelectric points and molecular weights. We identified by MALDI-TOF around 11 proteins. Some proteins were expressed only in the Hx group (Proliferating Cell Nuclear Antigen and Masp 1); others were more expressed in the Man group when compared with Hx and Ct groups (Translationally Controlled Tumor Protein). On the other hand, some proteins were expressed only in the Ct and Man groups (Annexin A3 and DNA ligase), suggesting that probably the Hx caused injury in these cells and it was responsible for the down-regulation of these proteins. Finally, we identified proteins that were expressed in the three cell groups (Heat Shock Protein 27, Heat Shock Protein 84), but with different levels. We concluded that the osmolarity of manitol and Hx could influenciate the alterations in the concentration of a specific protein. We believe that osmolarity and other factors of the CM could be responsible for the nephrotoxicity observed in this model. Proteomic analysis is a promising tool to study the renal pathophysiology making possible in the future the identification of biomarkers of renal diseases that can constitute therapeutically targets, minimizing the actual damages for the ARF. / TEDE / BV UNIFESP: Teses e dissertações

Yes / Although the risks associated with iodinated contrast administration are acknowledged to be very low, screening of kidney function prior to administration is still standard practice in many hospitals. This study has evaluated the feasibility of implementing a screening form in conjunction with point of care (PoC) creatinine testing as a method to manage the risks of post contrast acute kidney injury (PC-AKI) within the CT imaging pathway. Method: Over an eight-week period 300 adult outpatients attending a UK CT department for contrast-enhanced scans were approached. Participants completed a screening questionnaire for co-morbidities linked to kidney dysfunction and consented to have a PoC and laboratory creatinine tests. Comparison was made against with previous baseline blood tests obtained within the preceding 3 months, as required by the study site. Participants were also invited to attend for follow up PoC and laboratory bloods tests at 48–72 h. Results: 14 patients (4.7%) had a scan-day eGFR below 45mL/min/1.73m2, all identified through screening. The majority of patients (n=281/300; 93.7%) fell in the same risk category based on previous and scan-day blood results. Six PoC test failures were recorded on the scan day. The constant error between the Abbott i-STAT PoC scan-day measurements and the laboratory scan-day measurements was -3.71 (95% CI: -6.41 to -0.50). Five patients had an elevated creatinine (≥25% from baseline) post contrast administration, but no instances of PC-AKI (≥50% from baseline) were identified. Conclusion: PoC creatinine testing is a practical method of ensuring renal function and is feasible in the radiology environment. / National Cancer Diagnostics Capacity Fund, NHS England. Andrew Lewington, Bethany Shinkins and Michael Messenger are currently supported by the NIHR MIC- Leeds In Vitro Diagnostics Co-operative (was previously NIHR Leeds Diagnostic Evidence Co-operative)

Iron oxide nanoparticles are of great interest as contrast agents for research and potentially clinical molecular magnetic resonance imaging (MRI). Biochemically modifying the surface coatings of the particles with proteins and polysaccharides enhances their utility by improving cell receptor specificity, increasing uptake for cell labeling and adding therapeutic molecules. Together with the high contrast they produce in MR images, these characteristics promise an expanding role for iron oxide nanoparticles and molecular MR imaging for studying, diagnosing and treating diseases at the molecular level. However, these contrast agents produce areas of signal loss with traditional MRI sequences that are not specific to the nanoparticles and cannot easily quantify the contrast agent concentration. With the expanding role of iron oxide nanoparticles in molecular imaging, new methods are needed to produce a quantitative contrast that is specific to the iron oxide nanoparticle. This dissertation presents a new method for detecting and quantifying iron oxide nanoparticles using an adiabatic preparation pulse and the failure of the adiabatic condition for spins diffusing near the particles. In the first aim, the theoretical foundation of the work is presented, and a Monte Carlo simulation supporting the proposed mechanism of the contrast is described. Adiabatic pulse prepared imaging sequences are also developed for imaging at 3 Tesla and 9.4 Tesla to highlight the translational potential of the approach for clinical examinations and scientific research, and the linear correlation of the contrast with iron concentration ideal for quantification is presented. Further, the physical characteristics of the nanoparticles and the parameters of the MRI sequence are modified to characterize the approach. In the second aim, the contrast is characterized in more realistic phantoms and in vitro, and a method to more accurately quantify nanoparticle concentration in the presence of magnetization transfer is presented. Finally, accelerated imaging methods are implemented to acquire the adiabatic contrast in a time compatible with in vivo imaging, and the technique is evaluated in an in vivo model of quantitative iron oxide nanoparticle imaging. Together, these aims present a method using an adiabatic preparation pulse to generate an MR contrast based on the microscopic magnetic field gradients surrounding the iron oxide nanoparticles that is suitable for in vivo quantitative, molecular imaging.

Ioversol and Iomeprol are radiological contrast media commonly used interchangeably in many South African imaging facilities for coronary angiography. Despite differences in chemical composition, they are presumed to have similar renal safety profiles. However, no studies directly compare the renal safety of these two contrast media for coronary angiography in a predominantly healthy population. A systematic review was performed to establish which contrast medium is safer. Articles were sourced from Medline, CINAHL, Scopus, Science Direct, and PubMed Clinical Queries databases. Eligible studies were peer-reviewed articles of coronary angiography examinations carried out on a healthy adult population, where Ioversol or Iomeprol or both were administered, with contrast-induced nephropathy as an end-point. Six articles with a total population of 2431 patients were selected. The Cochrane Risk of Bias Tool was used in evaluating included articles. Pooling studies using the random effects model did not show a statistically significant reduction in contrast-induced nephropathy when Iomeprol was administered (Risk ratio 1.14, 95% confidence interval 0.797-1.643, p = 0.466). Moderate heterogeneity (I2=54.21%) across the studies was observed. Study limitations included potential bias during data extraction because this was performed by a single reviewer, and language restrictions to include only English titles. Iomeprol may be better for use in the clinical setting because of more a predictable renal safety profile. / Health Studies / M. P. H. (Health Studies)

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The current trend in magnetic resonance imaging (MRI) is towards higher external magnetic field strengths (B0) to take advantage of increased sensitivity and signal to noise ratio (SNR). Unfortunately, as (B0) increases the effectiveness (relaxivity) of clinical gadolinium (Gd3+)-based contrast agents (CAs) administered to enhance image contrast is significantly reduced. Excellent soft tissue contrast can be generated with current agents despite their non-optimum relaxivities but necessitates large doses. The limits of detection of a CA at high B0 fields can be lowered by recovering the lost relaxivity and is a pre-requisite to the goal of molecular imaging in which CAs are bound to biomarkers of pathology that exist at very low concentrations. Traditional methods for increasing the detectability of CAs have focused on optimizing critical parameters identified from the Solomon-Bloembergen-Morgan (SBM) theory that affect relaxivity. Gains in relaxivity with these methods to date have been modest and are far from the theoretical maximum possible. Although researchers continue to investigate novel complexes that provide improved relaxivities, any such complex would require a lengthy and costly approval process with the U.S. Food and Drug Administration (FDA). Therefore, a method that affords improved relaxivities of current clinically approved CAs, particularly at high B0 fields, that could be adopted into clinical practice rapidly, is of great interest. Spin locking is a nuclear magnetic resonance (NMR) technique that was introduced for imaging in 1985, but has received very little attention in combination with Gd3+-based CAs. The technique employs a low power long duration radiofrequency (RF) pulse (B1) parallel to the net magnetization in the x,y-plane. This locks the magnetization into lower precessional frequencies around an "effective" field (Beff) that is reduced with respect to B0 but maintains the high field advantages required for imaging. When considered in the rotating frame, longitudinal relaxation of the magnetization against Beff exhibits shorter time constants (T1p) expected at these lower precessional frequencies. This leads to higher relaxivities, which has implications for increasing CA detectability. The experiments described herein show that rotating frame longitudinal relaxivities (r1p) for current clinical Gd3+-based CAs are essentially independent of the strength of the spin lock pulse (yB1) as predicted by theory. This result is important because it allows the value of yB1 to be neglected when comparing r1p of Gd3+-based CAs across several B0 fields. The magnetic field dependence of r1p for all clinical agents showed that relaxivity, lost by moving to higher fields, could be "recovered" and that r1p was sensitive to the rotational correlation time constant (TR) of the agent. Using high molecular weight Nanoassembled capsules (NACs) containing a Gd3+-based CA to probe this finding further, we were able to generate relaxivities at high field up to an order of magnitude greater than clinical agents at current imaging fields. These are beyond anything previously reported, or likely to be, with current techniques. Finally, we demonstrated that by spin locking Mn2+ agents, relaxivities at high field increased by a factor of ~ 30 than without spin locking, due to their larger dependence on scalar coupling. These findings show the potential of spin locking to increase detection limits dramatically at high field and are an exciting development towards the goal of molecular imaging.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016 / The theoretical and experimental investigation of electron spin-resonance relaxation to deposit thermal energy into liquid gadolinium-based contrast agents for cancer hyperthermia treatment is presented. Previous works suggest that using protons in water are inadequate, with a thermal deposition rate of approximately 1 ◦C per two years. A novel component of this research relies on the use of gadolinium-chelated molecules, which are currently used as contrast agents in clinical MRI scans. The chelating agents, or ligands, investigated are Gadobenate (MultiHance R ), Gadopentetate (Magnevist R ), Gadoterate (DotaremR ) and Gadoteridol (ProHance R ). The gadolinium atom has seven unpaired electrons in its inner f shell orbital and as a result has a 660 times stronger paramagnetic response when placed in an external magnetic field. The research tests the hypothesis that by using an appropriate external homogeneous DC magnetic field, together with a radiofrequency excited resonator, that a measurable amount of thermal energy is deposited into a liquid gadolinium-based contrast agent. The aim of this research is to ultimately discover a new cancer hyperthermia treatment. The research theory suggests that a temperature rate of 13.4 ◦C · s−1 can be achieved using the gadolinium-based contrast agents under certain experimental conditions, and a maximum of 29.4 ◦C · s−1 under more optimal conditions. The temperature rates are calculated using parameter values commonly found in literature and practice. The simulation and design of the DC magnetic field coil system is discussed, together with the simulation results and design parameters of the radiofrequency loop-gap resonator. The experimental results and analysis indicate that the selected contrast agents have varied responses based on their chemical nature and that only two out of the four contrast agents, Dotarem and ProHance, show a measurable effect albeit sufficiently small that statistical techniques were necessary to distinguish the effect from background. A model fit to the data is performed in order to determine the spin-lattice relaxation time of the contrast agents under the specified experimental conditions. The model estimate is significantly smaller than the values found in literature under similar conditions, with a spin-lattice relaxation time τ1e of approximately 0.2 ps compared to the literature value of 0.1 ns. Although the observed electron spin resonance heating rate is in the milli-Watt range it is still notably larger (167 000 times) compared to the heating rate obtained using protons. The low temperature rates suggest that a more suitable agent or molecule with a larger spin-relaxation time be used, in order to achieve clinical useful temperature rates in the range of 14 ◦C · s−1. / MT2017

Generating MR image contrast from exogenous contrast media through chemical exchange saturation transfer (CEST) offers several exciting new possibilities, such as multicolored imaging, the interleaving of pre- and post-contrast images, and the potential to perform ratiometric metabolic imaging. The major limitation of the deployment of CEST imaging is the comparatively high detection limits of exogenous agents and particularly at the low B1 power levels required to meet SAR requirements. The large chemical shifts afforded by paramagnetic (paraCEST) agents permit more rapid exchange kinetics and therefore potentially more effective contrast agents. Despite comparatively large chemical shifts, many Ln3+ DOTA-tetraamide (DOTAM) chelates traditionally investigated as CEST agents are predicted to have exchange kinetics that are considerably faster than optimal at very low B1 powers. This work explores two methodologies for slowing water exchange kinetics in Ln3+ DOTAM chelates and improving CEST imaging: structural manipulation and encapsulation. In the first method, rigid Ln3+ NB-DOTAM chelates with hydrophobic amide substituents was thoroughly studied using NMR spectroscopy techniques in order to assess their ability to produce CEST contrast at low B1 power levels. NMR techniques utilized included 1H NMR, variable temperature, COSY, and CEST experiments. The phenyl amide substituent in the pseudo-axial position afforded chelates with considerably slow water proton exchange rates and appreciably more CEST contrast than isomeric chelates with the amide substituent in the pseudo-equatorial position. The second method involved characterizing a vesicle system to be used for encapsulating a Ln3+ DOTAM chelate. The vesicles prepared were analyzed using the following NMR techniques: 1H NMR, T1, shift reagent, and CEST experiments. The vesicle system chosen for study did not afford slow water exchange kinetics to enhance CEST contrast. A second vesicle system was attempted but the vesicle synthesis was difficult, parameters studied were not optimized, and the second system did not exhibit slow water exchange with the limited amount of experiments run and data collected.