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- Title
- THE EFFECTS OF ARSENITE ON SELENOPROTEINS BIOSYTHESIS.
- Creator
-
Konate, Fanta, Self, William, University of Central Florida
- Abstract / Description
-
Arsenic contamination of drinking water is a real public health problem in certain areas of South-East Asia where chronic exposure has been correlated to higher rates of lung, skin, bladder, kidney, and liver cancer. Although arsenic carcinogenicity is well established, the mechanism by which it induces cancer is poorly understood. Recent evidence suggests that oxidative stress could be a possible mechanism for the carcinogenic effects of arsenic. Selenium, in the form of selenocysteine, is...
Show moreArsenic contamination of drinking water is a real public health problem in certain areas of South-East Asia where chronic exposure has been correlated to higher rates of lung, skin, bladder, kidney, and liver cancer. Although arsenic carcinogenicity is well established, the mechanism by which it induces cancer is poorly understood. Recent evidence suggests that oxidative stress could be a possible mechanism for the carcinogenic effects of arsenic. Selenium, in the form of selenocysteine, is necessary for the activity of several enzymes with a role in the defense against reactive oxygen species (ROS), primarily thioredoxin reductases (TrxR) and glutathione peroxidases (Gpx). One of the key enzymes in the incorporation of Se into selenoproteins is selenophosphate synthetase (SPS). SPS catalyzes the activation of Se to selenophosphate, and is the first step in the pathway of selenoprotein biosynthesis. SPS contains a conserved vicinal dithiol motif (CXC) within a region of amino acids that have been predicted to be a selenium binding site. Our hypothesis is that arsenite inhibits new selenoprotein synthesis, thus indirectly increasing the level of ROS. In this study we have developed a spectrophotometric assay for SPS. Using this assay, we have determined that arsenite inhibits SPS activity. Kinetic analysis of this inhibition showed that arsenite, a trivalent form of arsenic, acts as a competitive inhibitor with the substrate, sodium selenide. This inhibition of SPS could represent a potential molecular mechanism for oxidative stress induced upon arsenite treatment of human cell lines in culture. To further study the effects of trivalent arsenicals at a cellular level we decided to use a human keratinocyte cell line, HaCaT as a cell culture model. Our study showed that although arsenite does not alter cell proliferation or protein synthesis, it specifically inhibits new selenoprotein synthesis. However, short term or long term exposure of HaCaT cells to arsenite failed to result in changes to Gpx and TrxR levels. Since the radioisotope selenium used in labeling studies is selenite, these results indicate that an alternate source of selenium may bypass the inhibitory effects of arsenite. Future studies will focus on studying the effects of arsenicals on keratinocytes cultured in a defined medium allowing a better control of the selenium source.
Show less - Date Issued
- 2005
- Identifier
- CFE0000453, ucf:46406
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000453
- Title
- THE EFFECTS OF TRIVALENT ARSENICALS AND THIOREDOXIN REDUCTASE INHIBITORS ON SELENIUM METABOLISM IN LUNG CELL CULTURE MODELS.
- Creator
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Talbot, Sarah, Self, William, University of Central Florida
- Abstract / Description
-
Arsenic exposure, through various routes, is associated with the development of cancer of the skin, lung, liver, kidney, and bladder. Treatment of cells in culture with trivalent arsenicals has been shown to increase reactive oxygen species (ROS). In particular, monomethylarsonous acid (MMAIII), a trivalent metabolite of arsenite, is highly cytotoxic and possibly carcinogenic. Three trivalent arsenicals; arsenite, arsenic trioxide (ATO), and MMAIII, are also known inhibitors of the...
Show moreArsenic exposure, through various routes, is associated with the development of cancer of the skin, lung, liver, kidney, and bladder. Treatment of cells in culture with trivalent arsenicals has been shown to increase reactive oxygen species (ROS). In particular, monomethylarsonous acid (MMAIII), a trivalent metabolite of arsenite, is highly cytotoxic and possibly carcinogenic. Three trivalent arsenicals; arsenite, arsenic trioxide (ATO), and MMAIII, are also known inhibitors of the selenoprotein thioredoxin reductase (TrxR). Selenium, an essential micronutrient in mammals, is needed in the form of selenocysteine for activity of this enzyme and other selenoproteins. TrxR is part of a key component of the cell's ability to defend against ROS. It has been speculated that TrxR is also involved directly in selenium metabolism, but this has yet to be demonstrated in vivo. The promoter region of the gene encoding the cytosolic TrxR (TrxR1) also contains an antioxidant responsive element (ARE). The ARE is activated by the transcription factor, Nrf2, which is governed by the Nrf2/Keap1 response, and can be triggered by certain oxidants. ATO and arsenite both inhibited incorporation of selenium into selenoproteins. Auranofin, a gold chemotherapeutic inhibitor of TrxR1, also inhibited selenoprotein synthesis. These results seem to support the hypothesis that TrxR1 is needed for selenoprotein synthesis. However, siRNA mediated reduction of TrxR1 did not block incorporation of selenium into selenoproteins. It is likely that ATO and auranofin are forming As-Se and Au-Se complexes, respectively. We also found that exposure of primary lung fibroblasts (WI-38) to MMAIII led to increased synthesis of TrxR1. This increase was dependent on the activation of transcription of the TrxR1 gene, specifically mediated through the ARE element. These results indicate exposure to MMAIII induces the Nrf2 response. The results obtained in these studies aid in both our understanding of the carcinogenic potential of arsenic as well as give new insight into the mechanism of action of emerging cancer drugs.
Show less - Date Issued
- 2007
- Identifier
- CFE0001943, ucf:47467
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001943
- Title
- TOWARDS DIRECT WRITING OF 3-D PHOTONIC CIRCUITS USING ULTRAFAST LASERS.
- Creator
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Zoubir, Arnaud, Richardson, Martin, University of Central Florida
- Abstract / Description
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The advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are...
Show moreThe advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are fabricated in oxide glass, chalcogenide glass, and polymers, these being the three major classes of materials for the telecommunication industry. Standard waveguide metrology is performed on the fabricated waveguides, including refractive index profiling and mode analysis. Furthermore, a finite-difference beam propagation method for wave propagation in 3D-waveguides is proposed. The photo-structural modifications underlying the changes in the material optical properties after exposure are investigated. The highly nonlinear processes of the light/matter interaction during the writing process are described using a free electron model. UV/visible absorption spectroscopy, photoluminescence spectroscopy and Raman spectroscopy are used to assess the changes occurring at the atomic level. Finally, the impact of laser direct writing on nonlinear waveguide applications is discussed.
Show less - Date Issued
- 2004
- Identifier
- CFE0000236, ucf:46252
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000236
