Browsing by Subject "Biomarkers"
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Item A 1,500-year record of late Holocene temperature variability and recent warming from Laguna Chingaza, Colombia(2012-08) Bixler, Curtis William; Shanahan, Timothy M.Rapid tropical glacier retreat over the last 50 years has been well documented, and has received significant media attention. Many studies suggest these changes are due to rising global surface air temperatures, however disentangling the effects of temperature and precipitation has hampered scientific consensus. Furthermore, because of the shortness of the instrumental record, it is difficult to assess the larger significance of the climate changes associated with the decline of tropical glaciers. Here, we present a locally calibrated, independent temperature reconstruction for the past 1,500 years from Laguna Chingaza, Colombia based on distributions of branched Glycerol Dialkyl Glycerol Tetraethers (brGDGTs) in order to assess the controls on long term temperature variability in the tropical Andes, and their relationship with growth and demise of Andean glaciers. Comparison of reconstructed temperatures with the instrumental record suggests that our proxy record faithfully records decadal to century scale trends in temperature. The largest temperature decline over the last 1,500 years was a decrease of 2.5 ± 0.3 °C during the Little Ice Age (LIA), reaching lowest temperatures during the mid-17th century, and is broadly consistent with terrestrial temperature reconstructions throughout the tropics and the higher latitudes. The structure and timing of temperature changes at Laguna Chingaza are remarkably similar to recent terrestrial temperature reconstructions from elsewhere in the tropics, including sites in the tropical Pacific and equatorial Africa, suggesting that these changes are widespread in the tropics. Together, these records suggest that warming over the last few decades is unprecedented over the last 1,500 years, including the Medieval Climate Anomaly (800-1150 AD). Comparison of these temperature changes with records of Andean glacier limits suggests that temperature is the dominant driver of glacial retreat, particularly over the past few decades. Additionally, paleotemperatures inferred from LIA and recent glacial equilibrium line altitudes (ELAs) underestimate past changes in temperature when compared with brGDGTs reconstructions, suggesting that changes in precipitation complicate the use of glacier ELAs to reconstruct past temperatures. The coupling of temperature and ice extent in South America suggests that with projected future warming, the health of tropical glaciers could be in jeopardy, significantly impacting the communities and ecosystems that depend on them.Item Biomarkers of exposure to complex environmental mixtures(2009-05-15) Naufal, Ziad SamiMaternal exposure to genotoxic chemicals may produce a variety of adverse birth outcomes. Depending on the dose and duration of exposure, adverse birth outcomes can range from premature or low-birth weight, to congenital abnormalities including neural tube defects (NTDs). The research described in this dissertation focused on several rural counties in Shanxi province, China. Shanxi has one of the highest rates of NTDs in the world. In 2005, the incidence of NTDs in the study counties ranged from 8 to 24 cases per 1,000 births. While some of these birth defects are likely to be related to nutrition, it is also suggested that environmental factors play a significant role. One such factor includes polycyclic aromatic hydrocarbon (PAH) exposure as a result of combustion of coal for indoor heating and cooking. Human populations in Shanxi depend heavily on coal as their main source of energy. This study determined the concentrations of PAHs in house dust, venous blood and placenta of study participants. Dust was collected from homes in the study site. Carcinogenic PAH levels in dust collected from kitchen floors ranged from 12 to 2,000 ?g/m2. The genotoxic potential of dust was confirmed by shortterm bioassays. Median concentrations of total PAHs in placenta from children born with NTDs were elevated compared to matched controls and appeared to be associated with the risk of having a child with a NTD. Tobacco smoking was not associated with elevated levels of PAH biomarkers in this study population. Levels of bulky DNA adducts in placenta have also been quantified using 32P-postlabeling. Adduct levels do not appear to be significantly different between cases and controls and were not associated with deletions in enzymes GSTM1 or GSTT1. These data suggest that children born with NTDs may be at increased risk due to exposure to genotoxic PAHs. Studies with a larger number of subjects are needed to further elucidate the relationship between PAH exposure and adverse birth outcomes.Item Development and validation of microcystin biomarkers for exposure studies(2006-05) Billam, Madhavi; Wang, Jia-Sheng; Anderson, Todd; Pence, Barbara; Shen, Leslie; Smith, ErnestMicrocystins (MCs) are hepatotoxic cyanotoxins produced mainly by the cyanobacteria Microcystis spp. They are distributed in waterbodies worldwide, and the toxicity on exposure to MCs was reported worldwide in fish, animals and in humans for over a century. There are about 70 known variants of MCs to date and of them the most toxic and widely distributed MC is Microcystin-LR (MCLR). MCLR is hepatotoxic and a potent tumor promoter. Epidemiological studies in China have linked exposure to MCs with high incidence of liver cancer. Although analytical tools have been reported to detect MCs in water and in food samples, and biomarkers for biochemical alterations like inhibition of protein phosphatases (PP) have been proposed, to date, validation of these analytical methods for simultaneous measurement of MCs in environmental samples and in body fluids of exposed individuals has not yet been done. In this study, we have developed new methods and validated existing methods to detect MCLR and its biomarkers in body fluids of animals and human hepatic cells treated with different concentrations of MCLR. The methods thus validated were used to monitor the seasonal fluctuations in MCLR concentrations in two lakes of western Texas. Studies were also conducted to explore molecular level targets of MCLR in normal (THLE-2) and cancerous (HepG2) human hepatic cell lines. Effect of MCLR on cell proliferation was explored, and validated methods were used to detect alteration in PP activity in these cell lines on exposure to MCLR. Alteration in expression of apoptosis regulatory proteins like Bax, Bcl2, Bad and PP2A on exposure to MCLR was also studied by immunoblotting in these cell lines. Studies were also conducted to explore molecular level targets of MCLR on acute exposure to a single dose, and on subacute exposure to repeated doses of MCLR in F-344 rats. We observed a dose dependent alteration in expression of PP2A, Bax, Bcl2 and Bad in both acute and subchronic exposures, as quantified by western blotting and immunohistochemistry. The study also focused on alteration in levels of sphingolipids in serum on exposure to MCLR. In another experiment, the combinative toxic effect of MCLR along with the tumor initiator aflatoxin-B1 was studied in normal and hepatocarcinoma cell lines, and the mechanism involved was explored.Item Development and validation of microcystin biomarkers for exposure studies(Texas Tech University, 2006-05) Billam, Madhavi; Wang, Jia-Sheng; Pence, Barbara; Smith, Ernest; Shen, Leslie; Anderson, ToddMicrocystins (MCs) are hepatotoxic cyanotoxins produced mainly by the cyanobacteria Microcystis spp. They are distributed in waterbodies worldwide, and the toxicity on exposure to MCs was reported worldwide in fish, animals and in humans for over a century. There are about 70 known variants of MCs to date and of them the most toxic and widely distributed MC is Microcystin-LR (MCLR). MCLR is hepatotoxic and a potent tumor promoter. Epidemiological studies in China have linked exposure to MCs with high incidence of liver cancer. Although analytical tools have been reported to detect MCs in water and in food samples, and biomarkers for biochemical alterations like inhibition of protein phosphatases (PP) have been proposed, to date, validation of these analytical methods for simultaneous measurement of MCs in environmental samples and in body fluids of exposed individuals has not yet been done. In this study, we have developed new methods and validated existing methods to detect MCLR and its biomarkers in body fluids of animals and human hepatic cells treated with different concentrations of MCLR. The methods thus validated were used to monitor the seasonal fluctuations in MCLR concentrations in two lakes of western Texas. Studies were also conducted to explore molecular level targets of MCLR in normal (THLE-2) and cancerous (HepG2) human hepatic cell lines. Effect of MCLR on cell proliferation was explored, and validated methods were used to detect alteration in PP activity in these cell lines on exposure to MCLR. Alteration in expression of apoptosis regulatory proteins like Bax, Bcl2, Bad and PP2A on exposure to MCLR was also studied by immunoblotting in these cell lines. Studies were also conducted to explore molecular level targets of MCLR on acute exposure to a single dose, and on subacute exposure to repeated doses of MCLR in F-344 rats. We observed a dose dependent alteration in expression of PP2A, Bax, Bcl2 and Bad in both acute and subchronic exposures, as quantified by western blotting and immunohistochemistry. The study also focused on alteration in levels of sphingolipids in serum on exposure to MCLR. In another experiment, the combinative toxic effect of MCLR along with the tumor initiator aflatoxin-B1 was studied in normal and hepatocarcinoma cell lines, and the mechanism involved was explored.Item Understanding complex Earth systems: volatile metabolites as microbial ecosystem proxies and student conceptual model development of coastal eutrophication(2009-05-15) McNeal, Karen SueUnderstanding complex Earth systems is challenging for scientists and students alike, because of the characteristics (e.g. bifurcations, self-organization, chaotic response) that are associated with these systems. This research integrates two research strands which contribute to the scientific and pedagogical understanding of complex Earth systems. In the first strand, a method that characterizes volatile organic compounds (VOCs) as ecological proxies of soil microbial ecosystems was validated. Unlike other measures of microbial community structure (e.g. Biolog and FAME), VOCs are advantageous because they are non-destructive and can provide temporal and spatial data. Additionally they are rich sources of information that describe the microbial metabolism, community structure, and organic carbon substrates utilized by soil microorganisms. Statistical results indicate that the detected and identified VOCs were significant (p < 0.05) indicators of microbial community composition shift in soil microcosm studies. Geographical information systems (GIS) illustrates that VOCs varied with space and time in south Texas soils. The second strand focuses on a geoscience education study exploring student conceptual model development of complex Earth systems. The efficacy of multiple representations and inquiry was tested as the pedagogical strategy in upper and lower level undergraduate courses to support students? conceptual model development of complex Earth systems. Comparisons in student performance were based on prior knowledge (low and high) and on exposure to the implemented pedagogy (control and experimental groups). Results indicate that an inquiry-based learning model coupled with the use of multiple representations had significant positive performance impacts on students? conceptual model development and content knowledge. This dissertation model integrates science and education research and is particularly useful for graduate students who intend to pursue a career in academia and envision teaching as part of their professional duties. It allows for synergy between teaching and research to be achieved where the classroom becomes a laboratory for research. Ultimately, the research conducted in the classroom informs pedagogy and enhances scholarship. Graduates learn to bridge the gap between education and science departments where they become leaders in science who conduct cutting-edge scientific research and also value making a broader impact on society through enhancing public education.