Cytotoxicity and modulation of gene expression in adult rat hepatocytes by benzo(a)pyrene and related aromatic hydrocarbons /
The goal of the present study was to define the cellular and
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739668201&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The goal of the present study was to define the cellular and molecular targets of BaP and related AHs in liver parenchymal cells, and to define the relative contribution of AhR-dependent events and/or free radical mechanisms in the responses elicited by these chemicals. The cytotoxic responses of rat hepatocytes to selected AHs were assessed to determine if class-specific differences in toxicity potential exist among these chemicals. Hepatocytes were exposed to various concentrations of BaP, TCDD, TCDF, NAPH, 2-MNAPH, or PCP for designated times. 3H-Thymidine incorporation into DNA, cellular levels of GSH, mitochondrial membrane fragility, and LDH leakage were monitored as indices of cytotoxicity. The data indicated that BaP, TCDD and TCDF induced a concentration-dependent inhibition of DNA synthesis, while NAPH, 2-MNAPH, and PCP were without effect. Significant increases in GSH levels were induced by BaP at all concentrations, while only modest increases occurred in cultures treated with TCDD or TCDF. Upregulation of cellular GSH levels in treated cultures was preceded by depletion at 6 to 18 hr. All other hydrocarbons failed to modulate cellular GSH levels significantly, Only BaP and PCP induced significant increases of mitochondrial membrane fragility after exposure for 4 hr, while LDH leakage was only observed in hepatocytes treated with PCP at 1000 []m. To study molecular targets of AHs in hepatocytes, we investigated the modulation of protooncogene expression induced by BaP or TCDD. Hepatocytes were exposed to 3 []M BaP or 1 nM TCDD for 4 hr and patterns of c-fos, c-jun, c-myc, and c-Ha-ras expression monitored by Northern analysis. BaP and TCDD increased c-ras and c-myc gene expression, but decreased c- fos and c-jun mRNA levels. Inhibition of AP1-TRE binding was observed using a gel shift assay when hepatocytes were exposed to 3 []M BaP, but not 1 nM TCDD for 2 hr. To investigate the contribution of AhR-dependent events to the responses elicited by BaP and related AHs, the effects of AhR antagonists ([]-naphthoflavone) or of inhibitors of CYPlAl- catalyzed metabolism of AHs (ellipticine), as well as AH analogs of low affinity for the Ah receptor (e.g. BeP and perylene) on selected endpoints were examined. The results of these studies implicated the AhR in the inhibition of DNA synthesis and cellular GSH levels, as well as in the modulation of protooncogene expression. In studies to assess the role of free radical mechanisms in the hepatotoxic effects of BaP and related AHs, we found that treatment of cells with diamide to induce oxidative stress and downregulate antioxidant capacity increased mitochondrial membrane fragility and protooncogene expression in a manner consistent with the pattern induced by BaP. Collectively, these data suggest that the hepatotoxic effects of BaP and related AHs involve AhR-, as well as oxidative stress- mediated effects. |
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| Item Description: | Vita. "Major Subject: Toxicology". |
| Physical Description: | xi, 130 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 95-128. |