TCDD and chemically related PCBs are of continuing public concern because of their high toxicity for some species. Mechanisms for their toxicity and the role of the large increases in specific cytochrome P450 isozymes are not understood. This proposal is based on the premise that elucidating mechanisms for TCDD toxicity and protective responses in a sensitive model species will strengthen the scientific basis for evaluating human risks. This laboratory is investigating the novel hypothesis that TCDD-induced P450 participates in TCDD toxicity by metabolizing endogenous compounds, such as the membrane fatty acid, arachidonic acid (AA) to biologically active metabolites that can affect cell signals and thereby modulate toxicity. We will continue to use principally a well established chick embryo model. TCDD treatment was found to increase metabolism of AA by P450 to specific AA epoxides and monohydroxylated products with biologic activities resembling changes in TCDD toxicity. TCDD increases AA epoxides by a specific TCDD-induced P450, TCDD/AA, distinct from the TCDD induced P-450 catalyzing AHH and 7- EROD, TCDD/AHH. TCDD treatment also increases AA release from liver cells, making AA available to TCDD/AA and depresses formation of constitutive omega-OH AA. In the next period we will investigate the mechanisms behind these changes and the increase by TCDD treatment in [Ca2+]/i and their consequences for cell function. SA1 will establish whether AA release is increased by TCDD in cells where P450 is not increased, whether it is preferentially increased by TCDD in response to hormonal stimuli and whether it occurs after TCDD exposure in cells in situ as well as in ovo. The role in AA release of phospholipases, protein kinase C, P450 and transcriptional events will be determined using freshly prepared hepatocyte and cardiac myocyte cell suspensions or cell cultures. SA2 will examine cellular consequences in liver and heart cells of changes by TCDD in AA release and P450 AA metabolites on AA metabolism, [Ca2+]/i, lipid composition, and protein kinase C, all major determinants of cell function. The mechanism for the inhibition of omega-OH AA by TCDD will also be examined. SA3 will investigate involvement of the Ah receptor in the increase by TCDD in AA metabolism, AA release and [Ca2+]/i by examining if known Ah receptor ligands and non ligands including PCB congeners elicit these effects and whether the increase by TCDD in P450 AA metabolism occurs in congenic mice differing in Ah receptor sensitivity. In SA4, it is proposed to clone and sequence TCDD/AA and TCDD/AHH cDNAs. The probes obtained will be used to examine effects of TCDD on mRNA expression and transcription for these P450s and to use SA5 to examine the cellular distribution of the genes for these P450s by in situ hybridization and of the P450 proteins by immunohistochemistry using monospecific antibodies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Research Project (R01)
Project #
5R01ES003606-13
Application #
2770712
Study Section
Toxicology Subcommittee 2 (TOX)
Project Start
1984-12-01
Project End
2001-08-31
Budget Start
1998-09-01
Budget End
2001-08-31
Support Year
13
Fiscal Year
1998
Total Cost
Indirect Cost
Name
Weill Medical College of Cornell University
Department
Pharmacology
Type
Schools of Medicine
DUNS #
201373169
City
New York
State
NY
Country
United States
Zip Code
10065
Diani-Moore, Silvia; Ma, Yuliang; Gross, Steven S et al. (2014) Increases in levels of epoxyeicosatrienoic and dihydroxyeicosatrienoic acids (EETs and DHETs) in liver and heart in vivo by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in hepatic EET:DHET ratios by cotreatment with TCDD and the soluble epoxide hydrolas Drug Metab Dispos 42:294-300
Diani-Moore, Silvia; Zhang, Sheng; Ram, Payal et al. (2013) Aryl hydrocarbon receptor activation by dioxin targets phosphoenolpyruvate carboxykinase (PEPCK) for ADP-ribosylation via 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly(ADP-ribose) polymerase (TiPARP). J Biol Chem 288:21514-25
Diani-Moore, Silvia; Ma, Yuliang; Labitzke, Erin et al. (2011) Discovery and biological characterization of 1-(1H-indol-3-yl)-9H-pyrido[3,4-b]indole as an aryl hydrocarbon receptor activator generated by photoactivation of tryptophan by sunlight. Chem Biol Interact 193:119-28
Diani-Moore, Silvia; Ram, Payal; Li, Xintian et al. (2010) Identification of the aryl hydrocarbon receptor target gene TiPARP as a mediator of suppression of hepatic gluconeogenesis by 2,3,7,8-tetrachlorodibenzo-p-dioxin and of nicotinamide as a corrective agent for this effect. J Biol Chem 285:38801-10
Nair, Sudhir; Kekatpure, Vikram D; Judson, Benjamin L et al. (2009) UVR exposure sensitizes keratinocytes to DNA adduct formation. Cancer Prev Res (Phila) 2:895-902
Labitzke, Erin M; Diani-Moore, Silvia; Rifkind, Arleen B (2007) Mitochondrial P450-dependent arachidonic acid metabolism by TCDD-induced hepatic CYP1A5;conversion of EETs to DHETs by mitochondrial soluble epoxide hydrolase. Arch Biochem Biophys 468:70-81
Diani-Moore, Silvia; Labitzke, Erin; Brown, Richard et al. (2006) Sunlight generates multiple tryptophan photoproducts eliciting high efficacy CYP1A induction in chick hepatocytes and in vivo. Toxicol Sci 90:96-110
Rifkind, Arleen B (2006) CYP1A in TCDD toxicity and in physiology-with particular reference to CYP dependent arachidonic acid metabolism and other endogenous substrates. Drug Metab Rev 38:291-335
Diani-Moore, Silvia; Papachristou, Fotini; Labitzke, Erin et al. (2006) Induction of CYP1A and cyp2-mediated arachidonic acid epoxygenation and suppression of 20-hydroxyeicosatetraenoic acid by imidazole derivatives including the aromatase inhibitor vorozole. Drug Metab Dispos 34:1376-85
Wood, Emily; Broekman, M Johan; Kirley, Terence L et al. (2002) Cell-type specificity of ectonucleotidase expression and upregulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Arch Biochem Biophys 407:49-62

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