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This dissertation, Analysis of Free Radical Characteristics in Biological Systems Based on EPR Spectroscopy, Employing Blind Source Separation Techniques by Jiyun, Ren, 任紀韞, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Analysis of Free Radical Characteristics in Biological Systems Based on EPR Spectroscopy, Employing Blind Source Separation Techniques Submitted by Ren Jiyun for the degree of Doctor of Philosophy at The University of Hong Kong in June 2006 Free radicals, such as nitric oxide (NO), are highly reactive molecules that have been implicated critical in many physiological and pathophysiological pathways. Electron paramagnetic resonance (EPR) is recognized as a direct and reliable technique to measure a free radical, but the precise measurement of a free radial is still difficult to achieve. This thesis is therefore focused on the following two subjects. The first objective of the study is to find a proper method that can accurately separate the 'pure' components from mixed EPR spectra, as EPR spectrum of a free radical is often superimposed by overlapping spectra of other species. Two blind source separation (BSS) techniques, one based on independent component analysis (ICA), and the other based on sparse component analysis (SCA), were for the first time applied to EPR spectroscopy analysis. The studies, on both computer simulated free radical spectra and biologically obtained signals, show that both BSS techniques could give good separation provided that the source component spectra lines are not very broad and there are prominent non-overlapping peaks. The implementation of this method is simple, automatic, efficient, and does not require the component spectra to be known in advance. The novel method demonstrated a big improvement to the traditional means of manual work or with more sophisticated biomedical experiments. Moreover, compared to the automatic PCA and self-modeling techniques which have previously been used to separate complex EPR spectra, this study confirms that the two BSS techniques are more accurate, robust to noise, and simpler to implement in the cases of three and even more components. Within the two BSS approaches, the SCA approach, which is novelly developed exploiting the sparse property of signals, achieves even more accurate results. With the help of BSS techniques to extract the pure NO signal from the measured mixture signal, the second objective in the present study is to investigate experimentally the NO radical level which helps interpret the possible actions and mechanisms of NO during renal ischemia-reperfusion (I/R) of rats. When EPR is used to detect NO production, the two NO spin-trapping methods, internal hemoglobin trapping and external DETC-Fe trapping, result in two NO spin adducts, namely 2+ DETC -Fe -NO and HbNO. This thesis presents a novel comparison study on the properties of the two spin-trapping methods. Renal I/R model on rats were established through occluding the left renal artery for 30 min or 60 min. Animal experiments show that the external DETC-Fe trapping method is more sensitive, but 2+ DETC -Fe -NO in kidney would quickly decompose, thus can only be used for short-term I/R injury study; whereas the internal hemoglobin trapping is not so sensitive to small amount of NO, but more stable and tend to accumulate in blood, hence suitable for long-term in vivo I/R injury study. This property allows a novel dynamic monitoring of NO level (indicated by internal spin trap adduct HbNO) during renal I/R with X-band E

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