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Voltammetric detection of 27-hydroxycholesterol on boron-doped diamond electrode
Michnová, Kristýna ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this bachelor thesis was to study the voltammetric behavior of 27-hydroxycholesterol using boron-doped diamond electrode. The influence of several factors on the current response of 27-hydroxycholesterol was investigated: the effect of the supporting electrolyte, concentration of perchloric acid, polarization rate, water content, and pH effect. The study was conducted using cyclic voltammetry in a perchloric acid or sodium perchlorate in acetonitrile. 27-hydroxycholesterol provided a current response in the anodic region with a potential around +1450 mV vs. Ag/0.01 mol l-1 AgNO3 in 1 mol l-1 NaClO4 in acetonitrile in the presence of 0.1 mol l−1 perchloric acid in acetonitrile (water content 0.43 %) and 0.1 mol l−1 sodium perchlorate in acetonitrile. Furthermore, concentration dependence was measured using differential pulse voltammetry resulting in a limit of detection (LOD) of 2.71 μmol l−1 and a limit of quantitation (LOQ) of 9.04 μmol l−1 . It was demonstrated that the direct current voltammetry method does not achieve comparable limit values. Key words 27-hydroxycholesterol, boron-doped diamond electrode, oxidation, oxysterols, voltammetry
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Voltammetry and liquid chromatography of cholesterol, its precursors, and oxidation products
Kubešová, Jana ; Schwarzová, Karolina (advisor) ; Baluchová, Simona (referee)
Electrochemical detection of sterols is difficult. This thesis aims to study the voltammetric behaviour of selected oxysterols, i.e. 25-hydroxycholesterol and 7-ketocholesterol on the boron-doped diamond electrode. Further, an HPLC method with spectrophotometric and electrochemical detection was developed for separation of selected sterols. The study was performed using cyclic and differential pulse voltammetry. 0.1 mol l−1 perchloric acid in acetonitrile (water content 0.55 %) was chosen as the most suitable electrolyte. 25- hydroxycholesterol provides anodic signal at the potential of +1500 mV and 7-ketocholesterol at +1900 mV in that media. Electrochemical reduction of 7-ketocholesterol was also studied. However, the observed cathodic signal isn't reproducible. The stability of oxysterols in the presence of perchloric acid was confirmed by UV-VIS spectroscopy. Calibration dependence of oxysterols was measured using differential pulse voltammetry and resulted in the limit of detection of 0.82 µmol l−1 for 25-hydroxycholesterol and 0.66 µmol l−1 for 7-ketocholesterol. In the second part of the thesis, an HPLC method was developed for the separation of a sterol mixture on a reversed-phase C18 column using a mobile phase containing 50 mmol l−1 sodium perchlorate in acetonitrile with 0% or 6% water...
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Voltammetric detection of 7α-hydroxycholesterol on boron doped diamond electrode
Serbanová, Lucie ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
This bachelor's thesis is dedicated to the electrochemical determination of 7α-hydroxycholesterol (7α-OHC) using boron-doped diamond electrode (BDDE). The work includes the optimization of experimental conditions and the measurement of the concentration dependence of 7α-OHC. The influence of various factors, such as water content in the solution and scan rate, on the electrochemical response of 7α-OHC was investigated. Various electrochemical methods, including cyclic voltammetry and differential pulse voltammetry, were used in the experiments. The electrochemical behavior of 7α-OHC in a solution of chloric acid and acetonitrile were analyzed. Important factors such as electrode passivation and response stability were carefully evaluated. The measurement of concentration dependence of 7α-OHC exhibited a linear response within the concentration range from 2∙10−5 mol l−1 to 1∙10−4 mol l−1 . Limits of detection (LOD) and quantification (LOQ) of 1,33 µmol l−1 and 4,43 µmol l−1 were determined. Comparison with other methods revealed that the electrochemical determination of 7α-OHC on BDDE achieves comparable sensitivity. The results of this work provide crucial insights into the electrochemical behavior of 7α-OHC, highlighting the advantages of BDDE for sensitive and reliable determination of...
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Gene expression study of oxysterol signal pathway in breast cancer patients
Kloudová, Alžběta ; Souček, Pavel (advisor) ; Vopálenský, Václav (referee)
Hormonal therapy is a common part of breast carcinoma treatment in patients whose tumors express estrogen and progesterone receptors. The aim of hormonal therapy is to prevent proliferative effect of hormones througt their receptor proteins in order to inhibit tumor growth. However, certain number of tumors is resistant to hormonal therapy despite expression of hormonal receptors. Presently, the reasons of this resistance are not fully understood. Oxysterols are hydroxylated cholesterol derivates, which may play some role in development of the resistance. They may interfere with hormonal therapy effect and influence some signal pathways leading to cancer progression. This study comes with results of gene expression of proteins influenced by oxysterol action, metabolic and transport proteins, transcription factors and members of signaling pathways that may be related to oxysterol effect. This thesis identifies some candidate genes for future analysis on the basis of comparison of gene expression between estrogen receptor positive and negative tumors and correlation with clinopathological data. The final goal should lead to discovery of new diagnostic markers for breast cancer therapy. Powered by TCPDF (www.tcpdf.org)
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Gene expression study of oxysterol signal pathway in breast cancer patients
Kloudová, Alžběta ; Souček, Pavel (advisor) ; Vopálenský, Václav (referee)
Hormonal therapy is a common part of breast carcinoma treatment in patients whose tumors express estrogen and progesterone receptors. The aim of hormonal therapy is to prevent proliferative effect of hormones througt their receptor proteins in order to inhibit tumor growth. However, certain number of tumors is resistant to hormonal therapy despite expression of hormonal receptors. Presently, the reasons of this resistance are not fully understood. Oxysterols are hydroxylated cholesterol derivates, which may play some role in development of the resistance. They may interfere with hormonal therapy effect and influence some signal pathways leading to cancer progression. This study comes with results of gene expression of proteins influenced by oxysterol action, metabolic and transport proteins, transcription factors and members of signaling pathways that may be related to oxysterol effect. This thesis identifies some candidate genes for future analysis on the basis of comparison of gene expression between estrogen receptor positive and negative tumors and correlation with clinopathological data. The final goal should lead to discovery of new diagnostic markers for breast cancer therapy. Powered by TCPDF (www.tcpdf.org)
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