4,934 research outputs found
Lantana horrida sensu Moldenke, non Kunth
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The comparative cytotoxicity and genotoxicity of hexavalent chromium in humans and sea turtles.
Get PDFMonitoring the health effects of environmental contaminants can be achieved using sentinel species as models. Leatherback sea turtles (Dermochelys coriacea) are an endangered marine species that may experience prolonged exposures to environmental contaminants including hexavalent chromium [Cr(VI)]. While Cr(VI) has been identified as a known human carcinogen, the health effects in marine species are poorly understood. In this study the cytotoxic and genotoxic effects of particulate and soluble Cr(VI) were assessed in leatherback lung cells and compared to those in human lung cells. Cr(VI) induced a concentration-dependent increase in cytotoxicity and genotoxicity in leatherback lung cells indicating Cr(VI) may be a health concern for leatherbacks and other long-lived marine species. Additionally, these results were comparable to those in humans. Based on these results leatherbacks are an ideal model species for monitoring the health effects of Cr(VI) and therefore serve as an indicator species for environmental human exposures
Mechanisms of chromate-induced suppression of RAD51: a one environmental health approach.
Get PDFLung cancer is the leading cause of cancer death. Lung cancer is commonly associated with smoking, however, 1 in 5 women and 1 in 12 men who develop lung cancer are never-smokers. Environmental exposures, therefore, account for a significant portion of lung cancer cases. Hexavalent chromium [Cr(VI)] is a global environmental contaminant and known human lung carcinogen. Cr(VI) and other carcinogenic metals induce chromosome instability, an early event in lung cancer. Structural chromosome instability arises in part due to failed DNA repair. Particulate Cr(VI), the most potent form of Cr(VI), induces DNA double strand breaks and inhibits the high-fidelity DNA repair mechanism, homologous recombination. Specifically, the effector step of homologous recombination is affected shown by RAD51 failure. RAD51 failure is due to inhibited expression, inhibited localization to double strand breaks, or a combination of these two mechanisms. Little is known about the mechanisms of Cr(VI)-inhibited expression. However, Cr(VI) exposure results in downregulation of global expression, and it has been suggested epigenetic changes affect expression profiles after Cr(VI) exposure. Studies show changes in acetylation of the RAD51 promoter affect E2F1-mediated RAD51 transcription by altering the “histone code” as potential epigenetic mechanisms of inhibited expression. Studies also show changes in microRNAs are an additional epigenetic mechanism of Cr(VI)-altered expression, and this may provide an additional mechanism of inhibited RAD51 expression. The mechanisms of particulate Cr(VI)-induced RAD51 failure were investigated in a human lung cells, and key events were confirmed in a wildlife model, leatherback sea turtle (Dermochelys coriacea) cells. The leatherback model was included as a part of the One Environmental Health Approach to investigate particulate Cr(VI) carcinogenesis across species. This type of analysis is used to identify how two species with different environmental adaptations may have alternative responses to chemical exposures. Therefore, the hypothesis of this dissertation is: Prolonged exposure to particulate Cr(VI) inhibits RAD51 expression through E2F1-inhibited transcription and alteration of microRNA expression profiles, and these effects are paralleled in a leatherback sea turtle model. We found particulate Cr(VI) inhibits RAD51 and E2F1 nuclear and whole cell protein and mRNA levels in human lung cells. Therefore, we aimed to show E2F1 modulates the RAD51 response to particulate Cr(VI). We found E2F1 overexpression did not rescue particulate Cr(VI)-induced RAD51-failure after prolonged (120 h) exposure. However, when we knocked down E2F1 we found E2F1 knockdown does not inhibit RAD51 mRNA or protein expression but does reduce nuclear foci formation after acute (24 h) particulate Cr(VI) exposure when RAD51 is normally functional. These results suggest E2F1 may affect RAD51 localization to double strand breaks, but not expression after Cr(VI) exposure. As an alternative mechanism of inhibited RAD51 expression we next performed RNA sequencing (RNAseq) analysis to asses Cr(VI)-altered microRNA (miRNA) expression. This study showed Cr(VI) significantly affected global miRNA expression, a subset of which target homologous recombination genes and RAD51 expression directly. These data advance our understanding of how Cr interferes with a critical cellular pathway that contributes to carcinogenesis. We previously reported particulate Cr(VI) induces structural chromosome instability in leatherback lung cells similarly to data in human lung cells with some differences. In this dissertation we confirmed particulate Cr(VI) induces DNA double strand breaks in leatherback lung cells. In analysis of DNA repair we found lower levels RAD51 foci after prolonged particulate Cr(VI) exposure compared to acute exposure in leatherback lung cells. However, the sister chromatid exchange assay showed homologous recombination is functional after prolonged particulate Cr(VI) exposure. These results are dissimilar to results in human lung cells indicating there are significant differences in the mechanistic response to particulate Cr(VI) exposure between human and leatherback lung cells
Two-Loop Finiteness of Chern-Simons Field Theory in Background Field Method
Full text linkWe perform two-loop calculation of Chern-Simons in background field method
using the hybrid regularization of higher-covariant derivative and dimensional
regularization. It is explicitly shown that Chern-Simons field theory is finite
at the two-loop level. This finiteness plays an important role in the relation
of Chern-Simons theory with two-dimensional conformal field theory and the
description of link invariant.Comment: RevTex, 13 pages. The proof of the existence of the large topological
mass limit has been proved. Some typewritten mistakes have been correcte
Representativeness of meridional hydrographic sections in the western South Atlantic
Get PDFMany studies of the oceanic circulation are based on data collected during quasi-synoptic hydrographic surveys. After spatial averaging, to filter out the effects of mesoscale variability, it is often explicitly or implicitly assumed that the synoptic hydrographic gradients are representative of a quasi-steady mean state. Climatological tracer fields and float data at the depth of the North Atlantic Deep Water in the western South Atlantic (Brazil Basin) support the notion of a quasi-steady mean circulation characterized by alternating bands of primarily zonal flow with meridional scales of several hundreds of km. Visually, the mean circulation appears to dominate three samples of the large-scale meridional-density-gradient field taken between 1983 and 1994. A quantitative comparison reveals, however, that the baroclinic temporal variability of the zonal velocities is of the same magnitude as the mean and is associated with similar spatial scales. The synoptic geostrophic flow field is, therefore, only marginally representative of the mean state. Thus, the data do not support one of the central assumptions of reference-velocity methods, such as linear box-inverse models and the β-spiral, because baroclinic temporal variability renders the equation systems underlying these methods inconsistent. A modal decomposition of the temporally varying baroclinic zonal velocity field in the Brazil Basin indicates that the first two dynamical modes dominate, accounting for ≈90% of the rms velocities. The residual flow field that remains after removing the first two baroclinic modes from the three synoptic samples is dominated by the mean circulation. However, its magnitude is not sufficient to account for the float and tracer observations. Therefore, it is necessary to determine the projection of the mean zonal velocities onto the barotropic and the first two baroclinic modes in order to diagnose fully the mean zonal circulation in the western South Atlantic. There is evidence that the representativeness of synoptic hydrographic sections in other regions may be similarly marginal
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