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S Safe

Publications and source records attributed to S Safe.

At least 127 records · Page 7Linked to original sources
PubMed1993

Immunosuppressive effects of highly chlorinated biphenyls and diphenyl ethers on T-cell dependent and independent antigens in mice.

The dose-dependent effects of 2,2',3,3',4,4',5,5',6-nonachlorobiphenyl (nonaCB), 2,2',3,3',4,4',5,6,6'-nonaCB, 2,2',3,3',4,5,5',6,6'-nonaCB and decaCB on the suppression of the splenic plaque-forming cell (PFC) response to the T-cell-dependent antigen, sheep red blood cells (SRBCs) and the T-cell-independent antigen, trinitrophenyl-lipopolysaccharide (TNP-LPS), were determined in genetically inbred mice. In addition, the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was also measured. The highly chlorinated biphenyls suppressed the splenic PFC response to SRBCs in C57BL/6 and DBA/2 mice and were relatively more active in the former strain. The C57BL/6 mice are more responsive to aryl hydrocarbon (Ah) receptor agonists than DBA/2 mice and these data support a possible role for the Ah receptor in mediating this response. However, previous studies with polychlorinated biphenyls (PCBs) indicate that congeners with 3 or 4 ortho-chloro substituents are inactive as Ah receptor agonists and this was consistent with the minimal induction of hepatic microsomal EROD activity by the highly chlorinated biphenyls in both strains of mice. Thus, the results suggest that the inhibition of the splenic PFC response to SRBCs observed in this study was primarily an Ah receptor-independent response. Some of the highly chlorinated diphyenyl ethers namely decachlorodiphenyl ether and 2,2',3,3',4,4',5,6,6'-nonachlorodiphenyl ether, inhibited the antigenic response to TNP-LPS in C57 BL/6 mice. The results indicate that the suppression of the TNP-LPS-mediated immune response may be a more reliable indicator of the Ah receptor-dependent immunotoxicity of halogenated hydrocarbons.

Animals↗
PubMed1993

Immunotoxic potencies of polychlorinated biphenyl (PCB), dibenzofuran (PCDF) and dibenzo-p-dioxin (PCDD) congeners in C57BL/6 and DBA/2 mice.

The dose-dependent effects of a single acute exposure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 1,2,3,7,9-PeCDF, 1,3,6,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4',5-pentachlorobiphenyl (pentaCB), and 3,3,',4,4',5,5'-hexaCB on the suppression of the splenic plaque-forming cell (PFC) response to the T-cell-independent antigen trinitrophenyl-lipopolysaccharide were determined in C57BL/6 and DBA/2 mice. In addition, the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was also measured in these animals. 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF were the most immunotoxic congeners in both strains of mice and with the exception of the latter congener, the ED50 values for each compound were lower in the C57BL/6 than the DBA/2 mice. 2,3,7,8-TCDD induced hepatic microsomal EROD activity in both strains of mice whereas the other congeners were considerably less active or inactive as inducers. The results of this study demonstrated that for the halogenated aromatic hydrocarbons the immunotoxic response was a more sensitive indicator of exposure than the induction of CYP1A1 activity. The rank order for the immunotoxic potencies of the chlorinated aromatic compounds used in this study was 2,3,7,8-TCDD approximately 2,3,4,7,8-PeCDF > 3,3',4,4',5-pentaCB approximately 3,3',4,4',5,5'-hexaCB > 1,2,3,7,9-PeCDF > 1,3,6,8-TCDF. The order of activity for these congeners was similar for other Ah receptor-mediated responses and these results coupled with the differential responsiveness of the C57BL/6 and DBA/2 mice confirms the role of aryl hydrocarbon (Ah) receptor in mediating the suppression of this T-cell-independent response.

Animals↗
PubMed1993

Characterization of the aryl hydrocarbon receptor and aryl hydrocarbon responsiveness in human ovarian carcinoma cell lines.

The human ovarian carcinoma cell lines PE01, PE04, and PE06 express the estrogen receptor and studies with the PE04 cells have shown that tamoxifen inhibits 17 beta-estradiol-induced proliferation. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a broad spectrum antiestrogen which works through the aryl hydrocarbon receptor. Incubation of the three cell lines with [3H]TCDD followed by isolation of nuclear extracts showed that the PE01, PE04, and PE06 cells express the aryl hydrocarbon receptor (23 to 87 fmol/mg protein) which exhibits sedimentation properties (7.5 to 7.9 S) on sucrose gradients similar to that observed in other mammalian species. Aryl hydrocarbon responsiveness was determined by the induction of P4501A1 mRNA levels and ethoxyresorufin O-deethylase activity by TCDD. Induction of both parameters was observed only in the PE04 cells. Gel mobility shift assays with a consensus dioxin-responsive element (DRE, 26-mer) showed that after incubation of the nuclear extracts from the 3 cell lines with 32P-DRE a retarded band formed only with nuclear receptor complex from PE04 cells. 17 beta-Estradiol stimulated proliferation of the PE04 and PE06 but not the PE01 cells; 1 nM TCDD alone either did not affect or inhibited the growth of these cells and 1 nM TCDD significantly inhibited the 17 beta-estradiol-induced proliferation of the PE04 and PE06 cells. Treatment of the PE04 cells with 1 nM 17 beta-estradiol resulted in a time-dependent enhanced secretion of the M(r) 52,000 protein (procathepsin D) and, after 48 h, a 51% increase in the secretion of this protein was observed. Cotreatment of the PE04 cells with 0.1 or 1.0 nM TCDD completely inhibited the 17 beta-estradiol-induced secretion of the M(r) 52,000 protein. These data show that TCDD exhibits antiestrogenic activity in estrogen receptor-positive ovarian carcinoma cell lines; however, in the PE06 cells, there was no correlation between the effects of TCDD on the induction of CYP1A1 gene expression and the results of the gel shift assay (i.e., nonresponsiveness) versus the observed antiestrogenic activity.

Adenocarcinoma↗
PubMed1993

Teratogenicity and immunotoxicity of 3,3',4,4',5-pentachlorobiphenyl in C57BL/6 mice.

Administration of 3,3',4,4',5-pentachlorobiphenyl (pentaCB) to female C57BL/6 mice at doses from 130.5 to 522 micrograms/kg body weight resulted in the dose-dependent formation of fetal cleft palate and hydronephrosis. The estimated relative potency of 3,3',4,4',5-pentaCB compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was in the range of < 0.07-0.04. The immunotoxicity of 3,3',4,4',5-pentaCB and two structurally-related congeners, 3,3',4,4'-tetraCB and 3,3',4,4',5,5'-hexaCB, was investigated in male C57BL/6 mice by determining their suppression of the splenic plaque-forming cell response to sheep red blood cells. The potencies of these compounds relative to TCDD were determined from the ratios of their corresponding ED50 values and were 0.77-0.55 (3,3',4,4',5-pentaCB), 1.1-0.29 (3,3',4,4',5,5'-hexaCB) and 0.14-0.03 (3,3',4,4'-tetraCB). These results demonstrate that the immunosuppressive activities of the PCB congeners relative to TCDD were much higher than observed for many other TCDD-like responses in mice and other laboratory animals.

Abnormalities, Drug-Induced↗
PubMed1993

Potentiation of CYP1A1 gene expression in MCF-7 human breast cancer cells cotreated with 2,3,7,8-tetrachlorodibenzo-p-dioxin and 12-O-tetradecanoylphorbol-13-acetate.

In MCF-7 cells treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 12-O-tetradecanoylphorbol-13-acetate (TPA) causes a time- and concentration-dependent modulation of TCDD-induced CYP1A1 gene expression. Treatment of MCF-7 cells with 1 nM TCDD for 24 h resulted in the induction of ethoxyresorufin O-deethylase (EROD) activity and CYP1A1 mRNA levels. In cells treated with TCDD for 24 h and 100 ng/ml TPA for 26 and 30 h, the TCDD-induced CYP1A1 gene expression was detected. For example, TCDD-induced EROD activity decreased from 122 pmol/min/mg to 25.5 pmol/min/mg after treatment of MCF-7 cells with TPA for 26 h and this was also paralleled by a 44% decrease in CYP1A1 mRNA levels. There was also a decrease in nuclear Ah receptor levels and the binding of nuclear extracts to a 32P-labeled dioxin responsive element (DRE) in a gel mobility shift assay. In parallel studies which measured EROD activities, similar TCDD/TPA interactions were observed in wild-type Hepa 1c1c7 cells, whereas no interactive effects were observed in T47-D human breast cancer cells. In MCF-7 cells treated with TPA for 36 or 48 h, the TCDD-induced EROD activity and CYP1A1 mRNA levels were restored and in cells exposed to TPA for 72 or 96 h superinducibility of CYP1A1 gene expression was observed; there was a 2.8- and 2.2-fold increase in EROD activity and CYP1A1 mRNA levels, respectively, compared to MCF-7 cells treated with TCDD alone. The biphasic temporal effects of TPA on TCDD-induced CYP1A1 gene expression in MCF-7 cells were paralleled by comparable changes in nuclear Ah receptor levels and binding to a synthetic DRE. In contrast, prolonged exposure of the wild-type Hepa 1c1c7 or T47-D cells to both TCDD plus TPA gave results similar to those observed after 24 h. These data show that the effects of TPA on TCDD-induced expression of CYP1A1 are cell-specific and suggest that the proposed protein kinase C (PKC)-dependent activation of the nuclear Ah receptor complex may not be required in MCF-7 cells since TPA downregulates PKC activity within 11 h and this inactivation persists for at least 96 h.

Base Sequence↗
PubMed1993

6-substituted 3,4-benzocoumarins: a new structural class of inducers and inhibitors of CYP1A1-dependent activity.

A new synthetic route was utilized to prepare 6-substituted 3,4-benzocoumarins where the substituents were iodo, fluoro, trifluoromethyl, bromo, chloro, isopropyl, ethyl, t-butyl, methyl, hydrogen, amino, phenyl, or nitro; 3,4-naphthocoumarin was also synthesized. The relative affinities of these congeners for the aryl hydrocarbon (Ah) receptor were determined using rat hepatic cytosol and 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin ([3H]TCDD) as the radioligand. In addition, the Ah receptor agonist activity of the 6-substituted 3,4-benzocoumarins was determined from their concentration-dependent induction of ethoxyresorufin O-deethylase (EROD) activity. In contrast with many other structural classes of halogenated aromatics, there was not a correlation between the structure-binding versus structure induction relationships for the 6-substituted 3,4-benzocoumarins. These results suggested that some of these congeners may exhibit partial Ah receptor antagonist activities and this was investigated by determining the inhibitory effects of 6-substituted 3,4-benzocoumarins on TCDD-induced EROD activity in rat hepatoma H4II E cells in culture. Only four compounds (6-isopropyl, 6-phenyl, 6-fluoro, and 6-t-butyl) inhibited the TCDD-induced response (21.7 to 64.4% inhibition) and the mechanism of action of the most active inhibitor, 6-t-butyl-3,4-benzocoumarin, was further investigated. In contrast, with other partial Ah receptor antagonists such as alpha-naphthoflavone, cotreatment of rat hepatoma H4II E cells with 1 nM TCDD plus 1 and 10 microM 6-t-butyl-3,4-benzocoumarin did not result in decreased levels of the Ah receptor complex (liganded with TCDD). In addition, there was not significant inhibition of TCDD-induced CYP1A1 mRNA levels or protein as determined by Northern and Western blot analyses. The results suggest that 6-t-butyl-3,4-benzocoumarin or one of its metabolites is a post-translational inhibitor of CYP1A1-dependent enzyme (EROD) activity in this cell line and thus represents a novel Ah receptor-independent inhibition of CYP1A1.

Animals↗
PubMed1993

Comparative potencies of Aroclors 1232, 1242, 1248, 1254, and 1260 in male Wistar rats--assessment of the toxic equivalency factor (TEF) approach for polychlorinated biphenyls (PCBs).

Immature male Wistar rats were treated with several different doses of the commercial polychlorinated biphenyls (PCBs) Aroclors 1232, 1242, 1248, 1254, and 1260 (10, 40, 160, 480, and 2000 mg/kg) and the effects on body weight gain, thymic atrophy, and the induction of hepatic microsomal aryl hydrocarbon hydroxylase (AHH), ethoxyresorufin O-deethylase (EROD), and pentoxyresorufin O-deethylase (PROD) activities were measured 14 days after treatment. A significant inhibition in body weight gain was observed only in rats treated with high doses of Aroclors 1232 and 1248 and thymic atrophy was not observed for any of the Aroclors. All the Aroclors caused a dose-dependent increase in hepatic microsomal AHH, EROD, and PROD activities. The corresponding ED50 values for the induction of AHH-EROD activities varied from 51 to 678 mg/kg. Aroclor 1260 was the least active inducer of the P4501A1-mediated enzyme activities. In contrast, Aroclor 1260 was a potent inducer of PROD activity (ED50 = 37 mg/kg), but Aroclors 1232, 1242, 1248, and 1254 did not induce 50% of the maximal response at the highest dose used in this experiment (2000/kg). Previous studies have quantitated the levels of those PCB congeners which induce AHH or EROD activities in Aroclors 1232, 1242, 1254, and 1260 and their potencies or toxic equivalency factors (TEFs) relative to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have also been estimated or experimentally determined. Using highly conservative TEF values it was demonstrated that the calculated ED50s for the Aroclors as inducers of AHH and EROD activity were significantly lower than the observed ED50 values.2

Animals↗
PubMed1993

Immunosuppressive and monooxygenase induction activities of highly chlorinated diphenyl ether congeners in C57BL/6 and DBA/2 mice.

The dose-response effects of 2,2',3,3',4,5,5',6,6'-2,2',3,3',4,4',5,6,6'- and 2,2',3,3',4,4',5,5',6- nonachlorodiphenyl ether (non-aCDE) and decachlorodiphenyl ether (decaCDE) on the splenic plaque-forming cell (PFC) response to sheep red blood cells (SRBCs) and the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was determined in aryl hydrocarbon (Ah)-responsive C57BL/6 and less Ah-responsive DBA/2 mice. All the congeners exhibited immunotoxicity at doses between 2.5 and 10 mumol/kg in C57BL/6 mice whereas in DBA/2 mice doses > or = 25 mumol/kg were required to cause inhibition of the PFC response to SRBCs. The results also showed that the nonaCDE isomers and decaCDE were more active as inducers of hepatic EROD activity in C57BL/6 than DBA/2 mice; however, there was not a correlation between the induced EROD activity and the CYP1A1 and CYP1A2 mRNA levels in the C57BL/6 mice. These data suggested that the immunotoxicity of these compounds was mediated through the Ah receptor. However, the results showed that the immunotoxicity of the nonaCDE isomers and decaCDE was unexpectedly high compared to that of lower chlorinated diphenyl ethers and there were no apparent structure-activity relationships among the higher chlorinated congeners. This suggests that some of the immunosuppressive effects observed for the nonaCDE isomers and decaCDE may be Ah receptor-independent.

Animals↗
PubMed1993

Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) as antiestrogens in MCF-7 human breast cancer cells: quantitative structure-activity relationships.

The concentration-dependent effects of several PCB, PCDD, and PCDF congeners and several commercial PCB preparations as antiestrogens were determined in the aryl hydrocarbon (Ah)-responsive MCF-7 human breast cancer cell lines. The inhibition of the 17 beta-estradiol-induced secretion of the 52-kDa protein (procathepsin D) was measured using a combination of polyacrylamide gel electrophoresis, double-staining of the protein bands with ISS ProBlue and silver stain, and quantitation by densitometric analysis. For the PCBs, the order of antiestrogenic potency was 3,3',4,4',5-pentachlorobiphenyl > 3,3',4,4',5,5'-hexachlorobiphenyl approximately 3,3',4,4'-tetrachlorobiphenyl > 2,3,3',4,4',5'-hexa, 2,3,3',4,4'- and 2,3,4,4',5-pentachlorobiphenyl > Aroclors 1221, 1232, 1248, 1254, and 1260 were inactive as antiestrogens at the highest concentrations used in this study (10(-6) M). For the PCDDs and PCDFs, the order of antiestrogenic potency was 2,3,7,8-tetrachlorodibenzo-p-dioxin > 2,3,7,8-tetrachlorodibenzofuran > 2,3,4,7,8-pentachlorodibenzofuran > 1,2,3,7,9-pentachlorodibenzofuran > 1,3,6,8-tetrachlorodibenzofuran. With few exceptions, the order of potency for all these congeners and mixtures paralleled their relative activities as agonists for other Ah receptor-mediated responses and their competitive binding affinities for the Ah receptor. The results of this study support the role for the Ah receptor in mediating the inhibition of the 17 beta-estradiol-induced secretion of the 52-kDa protein in MCF-7 cells and also points out the utility of this technique as a bioassay for this class of compounds.

Aroclors↗
PubMed1993

Mechanism of action of alpha-naphthoflavone as an Ah receptor antagonist in MCF-7 human breast cancer cells.

alpha-Naphthoflavone (alpha NF) and 6-methyl-1,3,8-trichlorodibenzofuran (MCDF) inhibited 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced CYP1A1 gene expression in MCF-7 human breast cancer cells and also decreased the accumulation of the nuclear [3H]TCDD-aryl hydrocarbon (Ah) receptor complex. Nuclear extracts from cells treated with 10(-6) M alpha NF and incubated with a dioxin responsive element (DRE, 26-mer) did not form a retarded band in a gel mobility shift assay. In contrast, incubation of nuclear extracts from cells treated with 10(-6) M MCDF and DRE gave a retarded band and this is consistent with the antiestrogenic and Ah receptor agonist activity of MCDF in human breast cancer cells. alpha NF was further investigated as an Ah receptor antagonist by determining the inhibition by alpha NF of TCDD-induced antiestrogenicity in MCF-7 cells. TCDD (10(-9) M) inhibited the 17 beta-estradiol-induced proliferation of MCF-7 cells and the secretion of the 52-kDa protein. In cotreatment studies, alpha NF (10(-8) to 10(-6) M) caused a concentration-dependent decrease in the antiestrogenic responses elicited by TCDD. In addition, alpha NF inhibited the TCDD-induced down-regulation of nuclear estrogen receptor levels in MCF-7 cells. alpha NF (10(-6) M) alone was inactive as an estrogen or antiestrogen and in cotreatment studies did not affect 17 beta-estradiol-induced responses in MCF-7 cells. Tamoxifen (10(-7) M), an antiestrogen which acts through the estrogen receptor, also inhibited 17 beta-estradiol-induced cell proliferation and alpha NF did not affect the tamoxifen-mediated antiproliferative response. Thus, alpha NF antagonized TCDD-induced CYP1A1 gene expression in MCF-7 cells and also acted as an anti-antiestrogen for TCDD-mediated antiestrogenicity in these cells. These results were consistent with the low levels of DRE binding observed with nuclear extracts from cells treated with 10(-9) M TCDD plus alpha NF (10(-8) to 10(-6) M) or 10(-6) M alpha NF alone. Thus, alpha NF appears to act as an Ah receptor antagonist in MCF-7 cells by decreasing the levels of transcriptionally active nuclear Ah receptor complexes.

Benzoflavones↗
PubMed1993

Synergistic activity of polynuclear aromatic hydrocarbon mixtures as aryl hydrocarbon (Ah) receptor agonists.

The relative potencies of benzo[a]pyrene and a complex mixture of polynuclear aromatic hydrocarbons (PAHs) produced as by-products of manufactured gas plant (MGP) residues as inducers of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity were determined in the B6C3F1 mouse. The ED50 values for the induction response were 78 and 65 mg/kg for benzo[a]pyrene and the MGP-PAH mixture, respectively. Analysis of the MGP-PAH mixture indicated that benzo[a]pyrene and other compounds containing four or more rings and which are known to induce EROD activity were only present as trace components of this mixture. A comparison of the EROD induction potencies of benzo[a]pyrene and the MGP-PAH mixture showed that the mixture was approximately 706 times more potent than expected based on its benzo[a]pyrene content (0.17%). This induced P-450 activity could significantly increase the metabolism of the carcinogenic PAHs and thereby modulate the overall carcinogenicity of the mixture. The apparent synergistic activity of the MGP-PAH mixture was further investigated by comparing the activities of this mixture and benzo[a]pyrene for several other aryl hydrocarbon (Ah) receptor-mediated responses including (i) induction of hepatic CYP1A1 mRNA levels, (ii) transformation of the rat cytosolic Ah receptor to a complex which binds to a dioxin responsive element, (iii) induction of EROD activity and (iv) antiestrogenicity in MCF-7 human breast cancer cells, and (v) inhibition of the splenic plaque-forming cell (PFC) response to both T cell-dependent and independent antigens in B6C3F1 mice. For the EROD and CYP1A1 mRNA induction and cytosolic transformation activities and immunosuppressive effects, the MGP-PAH mixture was approximately 100-900 times more potent as an Ah receptor agonist than expected based on its benzo[a]pyrene content. The synergistic activity was lower (19-fold) for the antiestrogenic response in MCF-7 cells. The reason for the synergistic effects of the MGP-PAH mixture were not due to contamination of the mixture by 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds and the results suggest that the enhanced potency of the mixture is due to unknown interactions between the individual PAHs present in the mixture.

Animals↗
PubMed1993

Structure-dependent, competitive interaction of hydroxy-polychlorobiphenyls, -dibenzo-p-dioxins and -dibenzofurans with human transthyretin.

Previous results from our laboratory indicated specific and competitive interactions of hydroxylated metabolites of 3,3', 4,4'-tetrachlorobiphenyl with the plasma thyroid hormone transport protein, transthyretin (TTR), in rats in vivo and with human TTR in vitro. In the present study the structural requirements for competition with thyroxine (T4) for TTR-binding were investigated in more detail. Several hydroxylated polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were tested in an in vitro competitive binding assay, using purified human TTR and [125I]T4 as a displaceable radioligand. All hydroxylated PCBs, but not the single PCB tested, competitively displaced [125I]T4 from TTR with differential potency. The highest competitive binding potency was observed for hydroxylated PCB congeners with the hydroxygroup substituted on meta or para positions and one or more chlorine atoms substituted adjacent to the hydroxy group on either or both aromatic rings (IC50 range 6.5-25 nM; Ka range: 0.78-3.95 x 10(8) M-1). The relative potency of all meta or para hydroxylated PCBs was higher than that of the physiological ligand, T4 (relative potency range: 3.5-13.6 compared to T4). There were no marked distinctions in TTR-T4 competitive binding potencies between the ortho- and non-ortho-chlorine substituted hydroxy-PCB congeners tested. Marked differences in TTR-T4 binding competition potency were observed between the limited number of hydroxylated PCDDs and PCDFs tested. The hydroxy-PCDD/Fs, with chlorine substitution adjacent to the hydroxy-group, i.e. 7-OH-2,3,8-trichlorodibenzo-p-dioxin, 2-OH-1,3,7,8-tetrachlorodibenzo-p-dioxin and 3-OH-2,6,7,8-tetrachlorodibenzofuran, all showed a similar or higher relative binding potency, i.e. 1, 4.4 and 4.5 times higher, respectively, than T4. No detectable [125I]T4 displacement was observed with 2-OH-7,8-dichlorodibenzofuran, 8-OH-2,3,4-trichlorodibenzofuran and 8-OH-2,3-dichlorodibenzo-p-dioxin, which did not contain chlorine substitution adjacent to the OH-group. These results indicate a profound similarity in structural requirements for TTR binding between hydroxy-PCB, -PCDD and -PCDF metabolites and the physiological ligand, T4, e.g. halogen substitution adjacent to the para hydroxy group, while planarity does not seem to influence the ligand-binding potency.

Benzofurans↗
PubMed1993

Effects of polychlorinated dibenzofurans on compounds in hepatic DNA of female Sprague-Dawley rats: structure dependence and mechanistic considerations.

Previous work indicated that covalent age-dependent DNA modifications of endogenous origin termed I-compounds may represent useful biomarkers for tumor promotion/carcinogenesis, as various tumor promoters/carcinogens, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and phenobarbital, reduce rat I-compound levels in liver, the target organ. The present study addressed the question as to whether polychlorinated dibenzofurans (PCDFs), which are related to TCDD and its congeners with regard to their toxic and biochemical properties, would also affect hepatic I-compound patterns and levels, and whether such effects would be chemical structure-dependent. Female Sprague-Dawley rats were treated once a week with a single dose (100 micrograms/kg) of 1,2,3,7,8-pentachlorodibenzofuran (1,2,3,7,8-PeCDF), 1,2,4,7,8-PeCDF, 2,3,4,7,8-PeCDF, or 2,3,4,6,7,8-hexachlorodibenzofuran (2,3,4,6,7,8-HeCDF) for 4 weeks and liver DNA was analyzed at the end of the last week by 32P-postlabeling assay. No carcinogen-DNA adducts were detected; however, levels of both non-polar and polar I-compounds were reduced in a structure-dependent manner. Potencies increased in the order, control (100%, 122 modifications in 10(9) DNA nucleotides = 1,2,4,7,8-PeCDF (104%) < 1,2,3,7,8-PeCDF (80%) < 2,3,4,7,8-PeCDF (61%) and 2,3,4,6,7,8-HeCDF (61%). Structure-activity relationships for total I-compounds, therefore, paralleled those reported for Ah receptor agonist activity, i.e., compounds that exhibit high cytosolic Ah receptor binding affinities and are also potent inducers of aryl hydrocarbon hydroxylase activity (1,2,3,7,8-PeCDF, 2,3,4,7,8-PeCDF, and 2,3,4,6,7,8-HeCDF) were active, while 1,2,4,7,8-PeCDF, which is a less potent Ah receptor agonist, was inactive. Polar I-compounds responded to a greater extent than did non-polar ones and, in general, individual I-compounds were affected differentially, thus decreased formation or increased removal of I-compounds played a role in the observed effects of the toxins on DNA. It is proposed that Ah receptor-mediated enzyme induction, particularly of cytochrome P450, is involved in reduced hepatic I-compound formation and that subnormal I-compound levels may contribute to tumor promotion.

Animals↗
PubMed1993

Mechanism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated decrease of the nuclear estrogen receptor in MCF-7 human breast cancer cells.

Treatment of MCF-7 cells with 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 1 nM [3H]17 beta-estradiol resulted in decreased radiolabeled nuclear estrogen receptor (ER) levels as determined by velocity sedimentation analysis. In parallel studies, nuclear extracts from TCDD-treated cells also exhibited decreased binding to a consensus 32P-genomic estrogen responsive element (ERE) as determined in a gel mobility shift assay. Time-course studies showed that the decreases in nuclear ER and ER-ERE binding in TCDD-treated cells were observed within 1 to 3 h after treatment, respectively, and persisted for up to 24 h. Cycloheximide (10 microM) did not affect the TCDD-mediated response, whereas 1 microM alpha-naphthoflavone, an aryl hydrocarbon (Ah) receptor antagonist, partially blocked downregulation of nuclear ER binding by TCDD. TCDD did not significantly affect steady state ER mRNA levels as determined by Northern analysis or the rate of ER gene transcription in a nuclear run-on assay. These results suggest that the TCDD-mediated decrease in nuclear ER levels is an Ah receptor-mediated response which occurs at the translational or post-translational level.

Analysis of Variance↗
PubMed1993

Interaction of 2,3,7,8-tetrachlorodibenzo-p-dioxin, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 17 beta-estradiol in MCF-7 human breast cancer cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and 12-O-tetradecanoylphorbol-13-acetate (TPA) are both tumor promoters which act through different mechanisms. In MCF-7 human breast cancer cells, both TCDD and TPA inhibited constitutive and 17 beta-estradiol-induced cell proliferation but showed no apparent interactive effects. TCDD also inhibited the 17 beta-estradiol-induced secretion of the 52-kDa protein (procathepsin D) and induced CYP1A1 gene expression whereas TPA alone was inactive for these responses. Moreover, TPA did not modulate the TCDD-mediated antiestrogenic or induction responses and did not decrease levels of the nuclear Ah receptor complex as determined in a gel mobility shift assay using a 32P-dioxin responsive element (DRE). The interactions of TPA and TCDD on the metabolism of [13C]glucose to [13C]lactate was also investigated using 13C-nuclear magnetic resonance spectroscopy. The rate of formation of [13C]lactate from [13C]glucose in MCF-7 cells treated with DMSO (control), 1 nM 17 beta-estradiol, 1 nM TCDD, 1 nM TCDD plus 1 nM 17 beta-estradiol, and 0.1 ng/ml TPA plus 1 nM 17 beta-estradiol was 28, 48, 20, 22 and 50 fmol lactate formed/cell/h, respectively. Thus, TCDD, but not TPA, inhibited this estrogen-induced response. However, a comparison of the rate of lactate formation in cells treated with TCDD plus 17 beta-estradiol (22 fmol/cell/h) or TCDD plus 17 beta-estradiol plus TPA (61 fmol/cell/h) showed that TPA significantly inhibited the TCDD-mediated antiestrogenic response. The results of these studies in MCF-7 cells demonstrate that the interactions of TCDD and TPA are highly response-specific and do not involve TPA-mediated downregulation of the nuclear Ah receptor complex.

Base Sequence↗
PubMed1993

Effects of cycloheximide on the induction of CYP1A1 gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in three human breast cancer cell lines.

Treatment of MCF-7, MDA-MB-231 and Hs578-T human breast cancer cell lines with 10(-9) M 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces CYP1A1 gene expression in the MCF-7 but not in the MDA-MB-231 or Hs578-T cells. Pretreatment of the cells with 10(-5) M cycloheximide results in significantly increased P4501A1 mRNA levels in all three cells lines. However, in cells co-treated with 10(-5) M cycloheximide plus 10(-9) M TCDD, an induced response by TCDD was observed in the MCF-7 and MDA-MB-231 but not in Hs578-T cells. Gel-retardation assays of nuclear extracts from the three cell lines complexed with a 32P-labeled dioxin-responsive element (DRE) gave a TCDD-inducible retarded band only in the MCF-7 and MDA-MB-231 cells. A retarded band with a similar mobility was observed in nuclear extracts from Hs578-T cells treated with either 10(-9) M TCDD or DMSO (solvent control). These results suggest that aryl hydrocarbon non-responsive MDA-MB-231 and Hs578-T human breast cancer cell lines contain the CYP1A1 gene and treatment with cycloheximide increases both constitutive and TCDD-induced CYP1A1 gene expression.

Base Sequence↗
PubMed1993

Toxicology, structure-function relationship, and human and environmental health impacts of polychlorinated biphenyls: progress and problems.

Polychlorinated biphenyls (PCBs) are industrial compounds that have been detected as contaminants in almost every component of the global ecosystem including the air, water, sediments, fish, and wildlife and human adipose tissue, milk, and serum. PCBs in commercial products and environmental extracts are complex mixtures of isomers and congeners that can now be analyzed on a congener-specific basis using high-resolution gas chromatographic analysis. PCBs are metabolized primarily via mixed-function oxidases into a broad spectrum of metabolites. The results indicate that metabolic activation is not required for PCB toxicity, and the parent hydrocarbons are responsible for most of the biochemical and toxic responses elicited by these compounds. Some of these responses include developmental and reproductive toxicity, dermal toxicity, endocrine effects, hepatotoxicity, carcinogenesis, and the induction of diverse phase I and phase II drug-metabolizing enzymes. Many of the effects observed for the commercial PCBs are similar to those reported for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. Structure-function relationships for PCB congeners have identified two major structural classes of PCBs that elicit "TCDD-like" responses, namely, the coplanar PCBs (e.g., 3,3',4,4'-tetraCB, 3,3'4,4',5-pentaCB and 3,3',4,4',5,5'-hexaCB) and their mono-ortho coplanar derivatives. These compounds competitively bind to the TCDD or aryl hydrocarbon (Ah) receptor and exhibit Ah receptor agonist activity. In addition, other structural classes of PCBs elicit biochemical and toxic responses that are not mediated through the Ah receptor. The shor-term effects of PCBs on occupationally exposed humans appear to be reversible, and no consistent changes in overall mortality and cancer mortality have been reported. Recent studies have demonstrated that some developmental deficits in infants and children correlated with in utero exposure to PCBs; however, the etiologic agent(s) or structural class of PCBs responsible for these effects have not been delineated. In contrast, based on a toxic equivalency factor approach, the reproductive and developmental problems in certain wildlife populations appear to be related to the TCDD-like PCB congeners.

Air Pollutants, Occupational↗