TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces depression-like phenotype

The etiology of major depressive disorder (MDD) remains poorly understood. Our previous studies suggest a role for the aryl hydrocarbon receptor (AhR) in depression. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental contaminant, with a high AhR binding affinity, and an established benchmark for assessing AhR activity. Therefore, this study examined the effect of TCDD on depression-like behaviors. Female mice were fed standard chow or a high-fat diet (HFD) for 11 weeks, and their weight was recorded. Subsequently, they were tested for baseline sucrose preference and splash test grooming. Then, TCDD (0.1 µg/kg/day) or vehicle was administered orally for 28 days, and mice were examined for their sucrose preference and performances in the splash test, forced swim test (FST), and Morris water maze (MWM) task. TCDD significantly decreased sucrose preference, increased FST immobility time, and decreased groom time in chow-fed mice. HFD itself significantly reduced sucrose preference. However, TCDD significantly increased FST immobility time and decreased groom time in HFD-fed mice. A small decrease in bodyweight was observed only at the fourth week of daily TCDD administration in chow-fed mice, and no significant effects of TCDD on bodyweights were observed in HFD-fed mice. TCDD did not have a significant effect on spatial learning in the MWM. Thus, this study demonstrated that TCDD induces a depression-like state, and the effects were not due to gross lethal toxicity. This study further suggests that more studies should examine a possible role for AhR and AhR-active environmental pollutants in precipitating or worsening MDD.

Co-induction of cytochrome P-450 isozymes in rat liver by 2,4,5,2',4',5'-hexachlorobiphenyl or 3-methoxy-4-aminoazobenzene

A multitude of xenobiotics have been demonstrated to co-induce either cytochromes P-450c and P-450d or cytochromes P-450b and P-450e in rat hepatic microsomes. Recently, the compounds 2,4,5,2',4',5'-hexachlorobiphenyl (HCB) and 3-methoxy-4-aminoazobenzene (3-MeO-AAB) have been suggested as selective inducers of cytochrome P-450b (Eur. J. Biochem. 151:67 (1985)) and P-450d (Biochem. Biophys. Res. Commun. 133:1072 (1985)), respectively. Since the identification of inducers with such unique characteristics would have implications with regard to the mechanism of induction of all four isozymes, we have examined the induction of cytochromes P-450b and P-450e by HCB and cytochromes P-450c and P-450d by 3-MeO-AAB in liver microsomes from adult male rats. Immunoblot analysis with monoclonal antibodies directed against cytochromes P-450b and P-450e indicate that HCB induces both isozymic species at the three dosage levels examined (10, 90, and 180 mg/kg). Similarly, 3-MeO-AAB does not appear to represent a unique inducer. Immunoblots of hepatic microsomes from animals treated with three different dosage regimens of 3-MeO-AAB demonstrate that, even at the lowest dosage level (50 mg/kg), both cytochromes P-450c and P-450d are induced. Moreover, immunoinhibition of 7-ethoxyresorufin O-deethylase (EROD) activity by monospecific antibody against either cytochrome P-450c or P-450d confirms this result. 3-MeO-AAB increases this enzyme activity 10-fold; approximately one-third of this induced activity is inhibited with monospecific anti-P-450c, while two-thirds is inhibited with monospecific anti-P-450d. This study also demonstrates that hepatic EROD activity is not an accurate estimate of cytochrome P-450c content since the majority of this enzyme activity in control and 3-MeO-AAB-treated rats is inhibited with monospecific anti-P-450d but not with monospecific anti-P-450c.

Flavone and Hydroxyflavones Are Ligands That Bind the Orphan Nuclear Receptor 4A1 (NR4A1)

It was recently reported that the hydroxyflavones quercetin and kaempferol bind the orphan nuclear receptor 4A1 (NR4A1, Nur77) and act as antagonists in cancer cells and tumors, and they inhibit pro-oncogenic NR4A1-regulated genes and pathways. In this study, we investigated the interactions of flavone, six hydroxyflavones, seven dihydroxyflavones, three trihydroxyflavones, two tetrahydroxyflavones, and one pentahydroxyflavone with the ligand-binding domain (LBD) of NR4A1 using direct-binding fluorescence and an isothermal titration calorimetry (ITC) assays. Flavone and the hydroxyflavones bound NR4A1, and their KD values ranged from 0.36 µM for 3,5,7-trihydroxyflavone (galangin) to 45.8 µM for 3'-hydroxyflavone. KD values determined using ITC and KD values for most (15/20) of the hydroxyflavones were decreased compared to those obtained using the fluorescence assay. The results of binding, transactivation and receptor-ligand modeling assays showed that KD values, transactivation data and docking scores for these compounds are highly variable with respect to the number and position of the hydroxyl groups on the flavone backbone structure, suggesting that hydroxyflavones are selective NR4A1 modulators. Nevertheless, the data show that hydroxyflavone-based neutraceuticals are NR4A1 ligands and that some of these compounds can now be repurposed and used to target sub-populations of patients that overexpress NR4A1.

alpha-Naphthoflavone-induced CYP1A1 gene expression and cytosolic aryl hydrocarbon receptor transformation

alpha-Naphthoflavone (alpha NF) is a weak aryl hydrocarbon (Ah) receptor agonist and inhibits the induction of CYP1A1 gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin. It has been suggested that the Ah receptor antagonist activity is due to the formation of alpha NF-cytosolic Ah receptor complexes that fail to undergo transformation. This hypothesis is consistent with data obtained in this and other studies using alpha NF concentrations from 10 to 1000 nM. However, 10 microM alpha NF exhibited Ah receptor agonist activity in several assays. Incubation of rat hepatic cytosol with 10 microM alpha NF caused transformation of the Ah receptor, as determined in a gel retardation assay using a 32P-labeled oligonucleotide containing a single dioxin-responsive element (DRE). Incubation of rat hepatoma (H-4-II E) cells with 10 microM alpha NF not only resulted in the induction of CYP1A1 mRNA levels but also increased chloramphenicol acetyltransferase activity from a DRE-containing chloramphenicol acetyltransferase reporter plasmid. Moreover, the DRE-transformed cytosolic Ah receptor complex liganded with either alpha NF or 2,3,7,8-tetrachlorodibenzo-p-dioxin did not undergo significant dissociation at 4 degrees. These data confirm that alpha NF is an Ah receptor agonist and, based on the results of previous studies, exhibits partial antagonist activity via competition for receptor binding sites.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on 17 beta-estradiol-induced glucose metabolism in MCF-7 human breast cancer cells: 13C nuclear magnetic resonance spectroscopy studies

The effects of 17 beta-estradiol, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and their combination on the metabolism of [1-13C] glucose were determined in cell suspensions of wild-type MCF-7 human breast cancer cells, by 13C NMR spectroscopy. Preliminary studies showed that, during the 7-hr duration of the NMR experiment, the cells maintained their viability and their aryl hydrocarbon responsiveness. Lactate was the major glucose metabolite detected in these studies, and the rate of lactate formation in the untreated (control) and 17 beta-estradiol (10(-9) M)-treated cells was 60 and 86 fmol/cell/hr, respectively; this represented a 40% increase in lactate formation in the cells treated with 17 beta-estradiol; comparable results were observed for the percentage of glucose converted into lactate. In contrast, TCDD (10(-9) M) did not significantly alter the rate of glucose metabolism or lactate formation. Co-treatment of the cells with 17 beta-estradiol (10(-9) M) plus TCDD (10(-8) to 10(-10) M) showed that TCDD completely inhibited the 17 beta-estradiol-induced metabolism of [13C] glucose to lactate in MCF-7 cells. In contrast, 2,8-dichlorodibenzo-p-dioxin (10(-8) M), a weak aryl hydrocarbon receptor agonist, did not inhibit estrogen-induced glucose-to-lactate metabolism in MCF-7 cells. In addition, it was shown that TCDD caused a significant decrease in 17 beta-estradiol-induced lactate formation within 1 hr after treatment, whereas the induction of monooxygenase activity was not observed until 3 hr after exposure of the cells to TCDD. These data indicate that TCDD-induced 17 beta-estradiol metabolism is not related to the decrease in the rate of conversion of glucose to lactate. These results further define the antiestrogenic responses elicited by TCDD and show that 13C NMR spectroscopy provides a unique method for measuring, in real time, the effects of TCDD on specific metabolic pathways.

Activation of Genes by Nuclear Receptor/Specificity Protein (Sp) Interactions in Cancer

The human nuclear receptor (NR) superfamily consists of 48 genes that are ligand-activated transcription factors that play a key role in maintaining cellular homeostasis and in pathophysiology. NRs are important drug targets for both cancer and non-cancer endpoints as ligands for these receptors can act as agonists, antagonists or inverse agonists to modulate gene expression. With two exceptions, the classical mechanism of action of NRs involves their interactions as monomers, dimers or heterodimers with their cognate response elements (cis-elements) in target gene promoters. Several studies showed that a number of NR-regulated genes did not directly bind their corresponding cis-elements and promoter analysis identified that NR-responsive gene promoters contained GC-rich sequences that bind specificity protein 1 (Sp1), Sp3 and Sp4 transcription factors (TFs). This review is focused on identifying an important sub-set of Sp-regulated genes that are indirectly coregulated through interactions with NRs. Subsequent studies showed that many NRs directly bind Sp1 (or Sp3 and Sp4), the NR/Sp complexes bind GC-rich sites to regulate gene expression and the NR acts as a ligand-modulated nuclear cofactor. In addition, several reports show that NR-responsive genes contain cis-elements that bind both Sp TFs and NRs, and mutation of either cis-element results in loss of NR-responsive (inducible and/or basal). Regulation of these genes involves interactions between DNA-bound Sp TFs with proximal or distal DNA-bound NRs, and, in some cases, other nuclear cofactors are required for gene expression. Thus, many NR-responsive genes are regulated by NR/Sp complexes, and these genes can be targeted by ligands that target NRs and also by drugs that induce degradation of Sp1, Sp3 and Sp4.

Exhaustive Chlorination as a Technique in the Analysis of Aromatic Hydrocarbons

Perchlorination reactions of aromatic compounds have been further investigated. The preparation and properties of decachlorodiphenyl ether and the isomeric o-, m-, and p-tetradecaehloroterphenyls are described. Anthracene, as an example of a polycyclic aromatic hydrocarbon, gave octachloroanthraquinone when treated with the antimony pentachloride iodine reagent, but quantitative conversion to decachloroanthracene could not be obtained with reagent BMC (sulfuryl chloride-aluminum chloride-sulfur monochloide). A new reagent, trichlorosulfur tetra-chloroaluminate (SCl3+ AlCl4–), was shown to convert Aroclor 1254 to decadilorobiphenyl. As an application of the perchlorination technique it was shown that polychlorodibenzofurans (dibenzofuran) are not present at 0.5 μg/g in samples of Halowax 1014 and technical naphthalene, respectively. Well defined derivatives could not be obtained when phthalate esters or “hexabromobiphenyl” (fireMaster BP-6) were treated with the BMC or SbCl5–I2 reagents.

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.

Peroxisome proliferator-activated receptor gamma agonists induce proteasome-dependent degradation of cyclin D1 and estrogen receptor alpha in MCF-7 breast cancer cells

Treatment of MCF-7 cells with the peroxisome proliferator-activated receptor (PPAR) gamma agonists ciglitazone or 15-deoxy-Delta 12,14-prostaglandin J2 resulted in a concentration- and time-dependent decrease of cyclin D1 and estrogen receptor (ER) alpha proteins, and this was accompanied by decreased cell proliferation and G(1)-G(0)-->S-phase progression. Down-regulation of cyclin D1 and ER alpha by PPARgamma agonists was inhibited in cells cotreated with the proteasome inhibitors MG132 and PSII, but not in cells cotreated with the protease inhibitors calpain II and calpeptin. Moreover, after treatment of MCF-7 cells with 15-deoxy-Delta 12,14-prostaglandin J2 and immunoprecipitation with cyclin D1 or ER alpha antibodies, there was enhanced formation of ubiquitinated cyclin D1 and ER alpha bands. Thus, PPARgamma-induced inhibition of breast cancer cell growth is due, in part, to proteasome-dependent degradation of cyclin D1 (and ER alpha), and this pathway may be important for other cancer cell lines.

Structure-dependent induction of aryl hydrocarbon hydroxylase in human breast cancer cell lines and characterization of the Ah receptor

The structure-dependent induction of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase by 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, and 1,2,4,7,8-pentachlorodibenzo-p-dioxin was determined in the MCF-7, T47-D, and MDA-MB-231 human breast cancer cell lines. Both the MCF-7 and T47-D cells were responsive to the induction effects of the halogenated aryl hydrocarbons and the structure-induction relationships were comparable to the reported structure-activity (induction, receptor binding, and toxicity) relationships observed in rodents and rodent cells in culture. The induction of ethoxyresorufin O-deethylase in the T47-D cells was the most sensitive aryl hydrocarbon (Ah) receptor-mediated response in both cell lines and this enzyme activity was more inducible than aryl hydrocarbon hydroxylase. In contrast, the three congeners were inactive as monooxygenase enzyme inducers in the MDA-MB-231 cells. Despite the differential Ah responsiveness of the cell lines, incubation of the cells with [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin followed by extraction of the nuclei with high salt and velocity sedimentation analysis of the extracts showed that specifically bound nuclear Ah receptor complexes were present in the three cell lines. The sedimentation coefficients (and levels) for the nuclear receptors were 6.6 S (32.1 fmol/mg protein/mg DNA), 6.9 S (61.6 fmol/mg protein/mg DNA), and 7.4 S (38.2 fmol/mg protein/mg DNA) in the T47-D, MCF-7, and MDA-MB-231 cell lines, respectively. Cytosolic receptor was also detected in the MCF-7 and MDA-MB-231 cells. Thus, despite the differences in Ah responsiveness of the T47-D and MDA-MB-231 cells, comparable levels of nuclear receptor were detected in both cell lines. Furthermore, the elution profiles of the nuclear receptors from DNA-Sepharose columns by using a salt gradient were similar and this suggested that defects in the DNA-binding activity of MDA-MB-231 nuclear receptor complexes were not major factors associated with their failure to respond to 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds.

Organochlorine exposure and risk for breast cancer

Organochlorine industrial compounds, combustion products and pesticides have been widely identified in the environment and residues have been detected in extracts prepared from fish, wildlife, human tissues as well as human milk and serum. Many of these compounds possess sex steroid activities and therefore have the potential to disrupt endocrine-regulated homeostasis. Organochlorines which exhibit hormonal activity include: (i) polychlorinated biphenyls (PCBs), hydroxylated PCBs, o,p'-DDT, and other organochlorine insecticides which exhibit estrogen receptor (ER) agonist activities; (ii) p,p'-DDE, a ligand for the androgen receptor which exhibits antiandrogen activity; (iii) PCBs, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and related aromatic hydrocarbons which bind the aryl hydrocarbon (Ah) receptor and exhibit tissue-specific antiestrogenic activity; and (iv) hydroxylated aromatics which bind transthyretin, a thyroid hormone binding protein. Although, it has been suggested that the estrogenic activity of PCBs and DDE may be a contributing factor for development of breast cancer in women, levels of these compounds are not consistently elevated in breast cancer patients and there is no evidence that women occupationally-exposed to relatively high levels of PCBs or DDE exhibit an increased incidence of breast cancer. In contrast, epidemiology studies suggest that women exposed to high levels of TCDD during an industrial accident in Seveso, Italy, have a decreased incidence of both breast and endometrial cancer. Based on the dietary intake of hormone or antihormone mimics derived from natural compounds in food, the estrogenic contribution of organochlorine compounds is small and their role in development of breast cancer is questionable.

Preparation, gas chromatographic behavior, and spectroscopic properties of hydroxylated chlorobiphenyls

Some useful methods for the preparation of chlorobiphenylols have been investigated. Twenty monohydroxy and dihydroxy derivatives of chlorobiphenyls are described; 10 are new compounds and several are known metabolic products from animals or microorganisms. The relationship between structure of the chlorobiphenylols and gas chromatographic retention time as well as electron capture detector response, including those of derivatives, has been examined. The ultraviolet, fluorescence, and mass spectra of these hydroxylated derivatives have also been examined with a view towards analysis and structure elucidation of metabolites.

The in vitro metabolism of 2,2',4,4',5,5'-hexabromobiphenyl

Radiolabelled 2,2',4,4',5,5'-hexabromobiphenyl was metabolized in vitro by rat liver microsomal enzymes to give more polar ether soluble lipophilic metabolites, trichloroacetic acid soluble conjugates and a macromolecular adduct fraction. The rates of formation of the three metabolic fractions were significantly enhanced using Firemaster BP-6 and 2,2',4,4',5,5'-hexabromobiphenyl induced microsomal enzymes. Comparative metabolic studies with the 4-brombiphenyl substrate showed that the lower brominated biphenyl substrate was more readily metabolized and the rate of metabolism was enhanced only with the Firemaster BP-6 induced microsomal enzymes and not the 2,2', 4,4',5,5'-hexabromobiphenyl induced enzyme system.