title: Automated dose-response analysis of the relative hepatic gene expression potency of TCDF in C57BL/6 mice.
abstract: Toxic equivalency factors (TEFs) are assigned to dioxin-like chemicals based on relative potency (REP) values of individual adaptive and toxic responses compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Agilent 4x44K oligonucleotide microarrays were used to examine the hepatic gene expression potency of 2,3,7,8-tetrachlorodibenzofuran (TCDF), relative to TCDD with complementary histopathology, TCDD and TCDF tissue level analysis, and ethoxyresorufin-O-deethylase (EROD) assay data. Immature ovariectomized C57BL/6 mice were gavaged with 0.03, 0.1, 0.3, 1, 3, 10, 30, or 100 microg/kg TCDD, the World Health Organization TEF-adjusted doses (10 x TCDD dose) of TCDF (0.3, 1, 3, 10, 30, 100, or 300 microg/kg), or sesame oil vehicle and killed at 72 h. Two thousand two hundred eighty-eight and 1347 genes were differentially expressed (P1(t) > 0.90) at one or more doses by TCDD and TCDF, respectively. Automated dose-response modeling (ToxResponse Modeler) identified a total of 1027 and 837 genes with either a sigmoidal, exponential, linear, Gaussian, or quadratic dose-response relationship 72 h after treatment in TCDD and TCDF, respectively. Two hundred seventy genes exhibited a sigmoidal TCDD-induced dose-response (ED(50s) from 0.08 to 42.2 microg/kg) compared to only 179 sigmoidal responsive genes (ED(50s) from 0.74 to 299.9 microg/kg) elicited by TCDF. Of the 1027 TCDD dose-responsive genes, 654 were not examined further due to the lack of a dose response elicited by TCDF. Of the 373 genes that exhibited a TCDD and TCDF dose response, REPs were calculated for the 83 genes that exhibited comparable sigmoidal curve shapes and slopes. The median REP for these 83 genes was 0.10, with a maximum REP of 0.56 and a minimum of 0.01. REPs of 0.04 were also calculated for EROD and increase in relative liver weight (RLW) at 72 h. Collectively, the lower number of TCDF-induced genes compared to TCDD and the 0.04 REPs for EROD activity and increased RLW are not consistent with the TEF of 0.10 for the hepatotoxicity of TCDF in C57BL/6 mice at 72 h.
authors.affiliation: Department of Biochemistry & Molecular Biology, Michigan State University, 501 Biochemistry Building, Wilson Road, East Lansing, MI 48824-1319, USA.
authors.forename: Lyle D
authors.initials: LD
authors.lastname: Burgoon
authors.forename: Qi
authors.initials: Q
authors.lastname: Ding
authors.forename: Alhaji
authors.initials: A
authors.lastname: N'jai
authors.forename: Ed
authors.initials: E
authors.lastname: Dere
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Burg
authors.forename: J Craig
authors.initials: JC
authors.lastname: Rowlands
authors.forename: Robert A
authors.initials: RA
authors.lastname: Budinsky
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Stebbins
authors.forename: Tim R
authors.initials: TR
authors.lastname: Zacharewski
mesh_terms: D000818:Animals; D001331:Automation; D001572:Benzofurans / Q000633:toxicity*; D001835:Body Weight / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D020869:Gene Expression Profiling; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D009929:Organ Size / Q000187:drug effects; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D016133:Polymerase Chain Reaction
chemical_list: D001572:Benzofurans; D000072317:Polychlorinated Dibenzodioxins; C014211:2,3,7,8-tetrachlorodibenzofuran