Effects of curcumin on the bioavailability of dioxin-like pollutants in rats.

The effects of curcumin on the bioavailability of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) were investigated in Sprague-Dawley rats. Tetra- and penta-chlorinated PCDFs had the lowest bioavailability and hexa-chlorinated PCDD/Fs had the highest, while there was no obvious change in that of DL-PCBs. Curcumin markedly reduced the toxic equivalent (TEQ) of PCDD/Fs in rats, illustrating the potential to competitively inhibit absorption of PCDD/Fs by the epithelial cells of the small intestine due to the similar chemical structure (diphenyl) between curcumin and PCDD/Fs. Moreover, curcumin lowered the TEQ of DL-PCBs in the liver of male rats, but not female rats. The significant decrease in the bioavailability of PCDD/Fs and DL-PCBs demonstrates the potential detoxification mechanisms of curcumin.

Aryl Hydrocarbon Receptor Modulates the Expression of TNF-α and IL-8 in Human Sebocytes via the MyD88-p65NF-κB/p38MAPK Signaling Pathways.

Activation of Toll-like receptor (TLR)-2 and subsequent inflammatory response contribute to lesion development in acne vulgaris. A cross-talk between aryl hydrocarbon receptor (AhR), a cytosolic receptor protein that responds to environmental and physiological stress, and TLRs has recently been reported. In this study, we explored the possible role of AhR in the effects induced on cultured human SZ95 sebocytes by peptidoglycan (PGN), a classic TLR2 agonist. PGN-induced secretion of inflammatory factors TNF-α and IL-8 in human SZ95 sebocytes was suppressed after knockdown of AhR and pretreatment with the AhR antagonist CH223191. In addition, the AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) enhanced TNF-α and IL-8 secretion in PGN-pretreated sebocytes. Furthermore, PGN-induced expression of myeloid differentiation factor 88 (MyD88), phospho-p38MAPK (p-p38MAPK), and p-p65NF-κB was strengthened by TCDD and repressed by CH223191. AhR inhibition by transfecting shRNA blocked the ability of PGN to stimulate phosphorylation of p38MAPK and p65NF-κB in SZ95 sebocytes. Overall, these data demonstrate that AhR is able to modulate PGN-induced expression of TNF-α and IL-8 in human SZ95 sebocytes involving the MyD88-p65NF-κB/p38MAPK signaling pathway, which probably indicates a new mechanism in TLR2-mediated acne.

The citrus flavonone hesperetin attenuates the nuclear translocation of aryl hydrocarbon receptor.

The environmental polycyclic aromatic hydrocarbons (PAH) and dioxins are carcinogens and their adverse effects have been largely attributed to the activation of AhR. Hesperetin is a flavonone found abundantly in citrus fruits and has been shown to be a biologically active agent. In the present study, the effect of hesperetin on the nuclear translocation of AhR and the downstream gene expression was investigated in MCF-7 cells. Confocal microscopy indicated that 7, 12-dimethylbenz[α]anthracene (DMBA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) -induced nuclear translocation of AhR was deterred by hesperetin treatment. The reduced nuclear translocation could also be observed in Western analysis. Reporter-gene assay further illustrated that the induced XRE transactivation was weakened by the treatment of hesperetin. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay demonstrated that the gene expressions of CYP1A1, 1A2, and 1B1 followed the same pattern of AhR translocation. These results suggested that hesperetin counteracted AhR transactivation and suppressed the downstream gene expression.

Curcumin and its derivatives inhibit 2,3,7,8,-tetrachloro-dibenzo-p-dioxin-induced expression of drug metabolizing enzymes through aryl hydrocarbon receptor-mediated pathway.

Certain dioxins, including 2,3,7,8,-tetrachloro-dibenzo-p-dioxin (TCDD), are exogenous ligands for an aryl hydrocarbon receptor (AhR) and induces various drug-metabolizing enzymes. In this study, we examined the effect of curcumin on expression of drug-metabolizing enzymes through the AhR and NF-E2 related factor 2 (Nrf2) pathways. Curcumin dose-dependently inhibited TCDD-induced expression of phase I enzyme cytochrome P450 1A1 (CYP1A1) and phase II enzymes NAD(P)H:quinone oxidoreductase-1 (NQO1) and heme oxygenase 1 (HO-1) but not tert-butyl hydroquinone-induced NQO1 and HO-1, suggesting that curcumin inhibited only AhR pathway, but not Nrf2 one directly. Furthermore, we used 14 curcumin derivatives and obtained the correlation between hydrophobicity of the compounds and suppressive effect against AhR transformation. Results from the quantitative structure active correlative analysis indicated that methoxy groups and ß-diketone structure possessing keto-enol tautomerism in curcumin were necessary to inhibit AhR transformation, and the addition of methyl and methoxy group(s) to the curcumin increased the inhibition effect.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the development and function of the blood-brain barrier.

Prenatal exposure to environmental chemicals such as dioxins is known to have adverse effects on the developing central nervous system (CNS) in mammals. Because the fetal blood-brain barrier (BBB) is immature, dioxins are thought to exert their toxic effects on the CNS by crossing the BBB and acting on neural cells directly. However, little is known whether dioxins alter the BBB. In this study, to investigate the effects of dioxins on BBB function, we exposed an in vitro BBB system comprising rat endothelial cells, astrocytes, and pericytes to the toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) either before or after BBB formation. We assessed BBB permeability and the function of tight junctions by measuring transendothelial electric resistance (TEER) values following exposure. Subsequently, total RNA and proteins were obtained from the cells for analysis. TEER values following TCDD exposure before but not after BBB formation were lower than those of the control group. We also observed that the expression of the tight junction proteins ZO-1 and claudin-5 was suppressed following TCDD exposure. To examine the cause of this reduction in protein levels, we performed a real-time quantitative polymerase chain reaction assay and observed low expression of the glial cell line-derived neurotrophic factor (GDNF) mRNA in the exposed groups. Moreover, to rescue the effects of TCDD, we applied extrinsic GDNF with TCDD. The several disruptions caused by TCDD were rescued by the GDNF addition. Our findings suggest that exposure to TCDD during BBB formation disrupts and impairs BBB function in part by the suppression of GDNF action, which may contribute to the adverse effects of TCDD on the fetal CNS.

TCDD­induced chick cardiotoxicity is abolished by a selective cyclooxygenase­2 (COX­2) inhibitor NS398.

Halogenated aromatic hydrocarbons, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are known to cause severe heart defects in avian species. However, the mechanism of TCDD-induced chick cardiovascular toxicity is unclear. In this study, we investigated cyclooxygenase-2 (COX-2) as a possible mechanism of TCDD-induced cardiotoxicity. Fertile chicken eggs were injected with TCDD and a COX-2 selective inhibitor, NS398, and we investigated chick heart failure on day 10. We found that the chick heart to body weight ratio and atrial natriuretic factor mRNA expression were increased, but this increase was abolished with treatment of NS398. In addition, the morphological abnormality of an enlarged ventricle resulting from TCDD exposure was also abolished with co-treatment of TCDD and NS398. Our results suggested that TCDD-induced chick heart defects are mediated via the nongenomic pathway and that they do not require the genomic pathway.

[The antagonistic effect of folic acid and resveratrol on cleft palate in mice induced by TCDD].

OBJECTIVE: To evaluate whether or not administration of folic acid and resveratrol have preventive effects on cleft palate formation as well as the comparison of the two drugs' s effects. METHODS: Pregnant mice were randomly divided into 9 groups, with 8 mice in each group. The TCDD group mice were dosed with TCDD 28 microg/kg body weight on gestation day 10 (GD 10) animals in folic acid group were respectively dosed with folic acid 15, 10, 5 mg/kg and TCDD 28 microg/kg; resveratrol treated mice were divided into 3 groups: resveratrol 50 mg/kg were orally administered for 6 consecutive days, from gestational day GD 8 to GD13 in resveratrol (GD8-13 ) group; resveratrol 50 mg/kg were orally administered for 6 consecutive days, from gestational day GD 8 to GD13, followed hy an oral administered with TCDD on GD10 in resveratrol (GD8-13) + TCDD group; resveratrol 50mg/kg and TCDD 28 microg/kg were used by gavage administration at GD10 in resveratrol (GD10) + TCDD group. Control mice were treated with the same volume of water for 6 consecutive days from GD8 to GD13 and were given a single dose of corn oil on GD10. The pregnant mice weight and embryos, the number of live, cleft palate, dead and resorption fetal mice were recorded on GD 17.5. The coronal sections of the fetal mice heads were prepared at GD 17.5 and observed by microscopy. RESULTS: Total frequency of clefts was 92.86% in TCDD group, 84.00% (15 mg), 73.08% (10 mg), 84.00% (5 mg) in folic acid + TCDD groups, 0% in resveratrol (GD10) group, 74.51% (GD10), 57.78% (GD8-13) in resveratrol + TCDD groups. The frequency of cleft was 0% in the control group. Compared with the control and the TCDD groups, there were significant differences in the number of live, dead and resorption fetal mice in TCCD + resveratrol (GD8-13) group (P < 0.05). No significant differences in embryonic weight, live fetuses weight, the number of live, dead and resorption fetal mice were found in the other groups (P > 0.05). CONCLUSION: Test dose of folic acid and resveratrol both had certain antagonistic effect on cleft palate in mice induced by TCDD, with folic acid 10 mg/kg, resveratrol 50 mg/kg GD8-13 doses having stronger antagonistic action. Effects of both the two drugs have no significant difference, but resveratrol (50 mg/kg, GD8-13) significantly affects the fetal mice's growth and development under TCDD exposure in utero.

Antagonistic effect of the Ainu-selected traditional beneficial plants on the transformation of an aryl hydrocarbon receptor.

UNLABELLED: Transformation of an aryl hydrocarbon receptor (AhR) is the initial step to express the multiple toxicity of halogenated and polycyclic aromatic hydrocarbons (HAHs and PAHs) including dioxins. Therefore, it has been suggested that suppression of the transformation induced by HAHs and PAHs leads to reduce their toxicological effects. In this study, the antagonistic effect of 110 indigenous plants (192 plant parts) used as medicine and/or food by the Ainu on the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced AhR transformation was investigated. Of these, a stalk of Aralia elata (Miq.) Seemann and a bark of Fraxinus mandshurica Rupr. var. japonica Maxim. exhibited the strong antagonistic effect in a dose-dependent manner. An antioxidative activity and polyphenol content were also measured, and the strong correlation (r= 0.96) between these two parameters could be confirmed. However, correlation coefficients of the antagonistic effect of 192 extracts compared to their antioxidative activity and polyphenol content were 0.17 and 0.20, respectively. These results suggest that the Ainu-selected traditional beneficial plants are useful source for findings of novel AhR antagonists, and the antagonistic activity of these plants may be independent on their antioxidative activity and polyphenol content. PRACTICAL APPLICATION: Our findings lead to discovery of the valuable plants used by the Ainu and the novel active compounds useful for human's life, and furthermore, may contribute to the development of new medicines and functional foods.

Propolis protects against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced toxicity in rat hepatocytes.

The present experiment was undertaken to determine the effectiveness of propolis in alleviating the toxicity of TCDD on cultured primary rat hepatocytes. Propolis (25, 50 and 100 µM) was added to plain culture or simultaneously with TCDD (5 and 10 µM). The hepatocytes were treated with TCDD and propolis for 48 h. Then cell viability was detected by [3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide] (MTT) assay and lactate dehydrogenase (LDH) release, while total antioxidant capacity (TAC) and total oxidative stress (TOS) levels were determined to evaluate the oxidative injury. The DNA damage was also analyzed by liver micronucleus assay (LMN) and 8-oxo-2-deoxyguanosine (8-OH-dG). The results of MTT and LDH assays showed that TCDD decreased cell viability. TCDD also increased TOS level and decreased TAC level in rat hepatocytes. On the basis of increasing doses, the TCDD caused significant increases of micronucleated hepatocytes (MNHEPs) and 8-OH-dG levels as compared to control culture. In cultures treated with propolis alone, cell viability and TOS level were not affected, while the level of TAC was significantly increased in dose-dependent fashion. The presence of propolis with TCDD modulated its toxic effects on primary hepatocytes cultures. Noteworthy, propolis has a protective effect against TCDD-mediated DNA damages.

Quercetin prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced testicular damage in rats.

The protective effect of quercetin on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced testicular damage in rats was investigated. Twenty-two rats were equally divided into four groups; first group was kept as control and given corn oil as carrier. In second group, TCDD was orally administered at the dose of 2 µ (kg week)(-1) for 60 days. In third group, quercetin was orally administered at the dose of 20 mg (kg day)(-1) by gavages, and in fourth group TCDD and quercetin were given together at the same doses. Although TCDD increased the formation of thiobarbituric acid reactive substances (TBARS) significantly, it caused a significant decline in the levels of glutathione (GSH), catalase (CAT), GSH-Px and CuZn-Superoxide Dismutase (CuZn-SOD) in rats. In contrast, quercetin significantly increased the GSH, CAT, GSH-Px and CuZn-SOD levels but decreased the formation of TBARS. In addition, sperm motility, sperm concentration and serum testosterone levels were significantly decreased but abnormal sperm rate and testicular damage were increased with TCDD treatment. However, these effects of TCDD on sperm parameters, histological changes and hormone levels were eliminated by quercetin treatment. Our results show that administration of TCDD induces testicular damage (oxidative stress, testes tissue damage, serum hormone level and sperm parameters), and quercetin prevents TCDD-induced testicular damage in rats. Thus, quercetin may be useful for the prevention and treatment of TCDD-induced testicular damage.

Non-genomic action of TCDD to induce inflammatory responses in HepG2 human hepatoma cells and in liver of C57BL/6J mice.

To assess the significance of the non-genomic signaling of TCDD (=dioxin) on liver of C57BL/6 mice and HepG2 human hepatoma cells, we first determined the group of markers that are susceptible to inhibition by parthenolide, a compound known to specifically suppress NF-κB-mediated inflammation. Of those, the most consistent marker turned out to be SOCS3 (a suppressor of cytokine signaling) known to respond to inflammation. An early diagnostic test on the action of TCDD on HepG2 cells in vitro within 3-6 h indicated that Cox-2 and SOCS3 are mainly induced via a non-genomic route, whereas PAI-2 appears to be induced through the classical action route. More detailed diagnostic tests at later stages of action of TCDD in HepG2 cells revealed that induction of IL-1ß, BAFF, and iNOS are largely mediated by the protein kinase-dependent non-genomic route. An in vivo study on the 7 day action of TCDD on liver of AhR(NLS) mice showed that several early markers (e.g., Cox-2, MCP-1 and SOCS3) are induced, but not late markers such as IL-1ß. Together, these results show that the non-genomic pathway contributes significantly to the early stress response reactions to TCDD that includes inflammation in hepatoma cells as well as in the liver.

Is it possible to antagonize 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin- induced cleft palate by prenatal administration of folic acid? An experimental study.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can cause a high percentage of cleft palate in fetuses when administered during organogenesis in certain strains of mice including C57BL/6J. In this study, folic acid (FA) was tested for antiteratogenic effects on TCDD-induced cleft palate in fetal mice. The pregnant C57BL/6J mice were dosed with 24 microg TCDD/kg and/or 5 mg, 10 mg, 20 mg, 40 mg FA/kg body weight on gestation day (GD) 10. The control group mice received 50 mL sesame oil/kg body weight on GD10. The mice were sacrificed on GD12.5, GD13.5, GD14.5, GD15.5, and GD16.5. The harvested embryos were examined to detect the incidence of cleft palate and the developing palatal shelves on different phases were investigated morphologically and histologically among different groups. Total frequency of clefts was 55.56% in TCDD group and 17.50% (5 mg), 42.85% (10 mg), 42.10% (20 mg), 28.26% (40 mg) in TCDD + FA groups. FA (5 mg) reduced the incidence of the cleft palate from 55.56% to 17.50% (p = 0.005). There were no significant differences between the TCDD group and 10 mg, 20 mg, 40 mg TCDD + FA groups. Based on the these results, the present study suggests that FA can reduce the incidence of 2,3,7,8-TCDD-induced cleft palate in mice.

Peganum harmala L. is a candidate herbal plant for preventing dioxin mediated effects.

Dioxins are widespread environmental contaminants that have been linked with a variety of deleterious effects on human health including increased cancer rates. The detrimental effects of 2,3,7,8-tetrachlorodibenzo- P-dioxin (TCDD, one of the most common environmental dioxins) are mediated via the aryl hydrocarbon receptor (AhR). AhR is a transcription factor that regulates the expression of the carcinogen-activating enzyme, cytochrome P450 1a1 (Cyp1a1). In the present study, we examined the ability of the methanolic extract of Peganum harmala L. (Zygophyllaceae) fruiting tops to affect TCDD-activated AhR-mediated signal transduction in mouse hepatoma Hepa 1c1c7 cells. Our results showed that Peganum harmala extract significantly inhibited the TCDD-mediated induction of Cyp1a1 at mRNA, protein, and activity levels. A similar pattern of inhibition at the catalytic activity level was observed with the other AhR ligands tested. The ability of the extract to inhibit Cyp1a1 was strongly correlated with its ability to inhibit AhR-dependent luciferase activity and electrophoretic mobility shift assays. Harmine and harmaline were found to be the dominant components of the plant extract with a relative abundance of 7 and 4.85 % (w/w), respectively. In addition, both of the active alkaloids showed an inhibitory effect on TCDD-induced Cyp1a1 activity level. We concluded that Peganum harmala L. can interfere with AhR ligands-mediated effects.

Preferential blockade of dioxin-induced activation of the aryl hydrocarbon receptor by Antrodia camphorata.

Halogenated and polycyclic aromatic hydrocarbons are widely distributed pollutants in environments. These toxic substances activate the aryl hydrocarbon receptor (AhR) and thereby cause a broad spectrum of pathological changes. Development of AhR inhibitors will be useful for prevention of diseases caused by AhR activation. Using the dioxin responsive element (DRE)-based sensing via secreted alkaline phosphatase (DRESSA), we examined effects of Antrodia camphorata, a mycerial extract, on the activation of AhR by halogenated and polycyclic aromatic hydrocarbons. We found that Antrodia camphorata markedly suppressed activation of AhR triggered by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In contrast, activation of AhR by polycyclic aromatic hydrocarbons (benzo[a]pyrene and 3-methylcholanthrene) was inhibited only modestly by this mycelium. Similarly, Antrodia camphorata only mildly attenuated activation of AhR by cigarette smoke that contains polycyclic aromatic hydrocarbons. Consistent with these results, Northern blot analysis revealed that DRE-driven exogenous and endogenous gene expression triggered by TCDD was abolished by Antrodia camphorata, whereas it did not substantially affect DRE-induced transcription triggered by benzo[a]pyrene, 3-methylcholanthrene or cigarette smoke. We also found that the inhibitory effect of Antrodia camphorata on TCDD-induced AhR activation was ascribed to neither down-regulation of AhR, down-regulation of the AhR nuclear translocator, nor up-regulation of the AhR repressor. These results suggest that Antrodia camphorata preferentially inhibits AhR activation and DRE-dependent gene expression triggered by dioxin.

MG-132 inhibits the TCDD-mediated induction of Cyp1a1 at the catalytic activity but not the mRNA or protein levels in Hepa 1c1c7 cells.

Previous studies have shown that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced degradation of aryl hydrocarbon receptor (AhR) is inhibited by MG-132, a potent inhibitor of the 26S proteasome. Therefore, the current study aims to address the effect of MG-132 on the AhR-regulated gene, cytochrome P450 1a1 (Cyp1a1), using murine hepatoma Hepa 1c1c7 cells. Our results showed that MG-132 at the highest concentration tested, 10 microM significantly increased the Cyp1a1 at mRNA, protein and catalytic activity levels through a transcriptional mechanism. On the other hand, MG-132 further potentiated the TCDD-mediated induction of Cyp1a1 at mRNA but not at protein level. In contrast, MG-132 significantly inhibited the TCDD-mediated induction of Cyp1a1 catalytic activity. In addition, we showed that the decrease in Cyp1a1 catalytic activity is not Cyp specific, as MG-132 significantly inhibited Cyp2b1 and total cytochrome P450 catalytic activities. These results prompted us to examine the effect of MG-132 on total cellular heme content and heme oxygenase-1 (HO-1) mRNA, a rate limiting enzyme of heme degradation. Our results showed that MG-132 significantly induced HO-1 mRNA in a concentration-dependent manner. Furthermore, MG-132 potentiated the induction of HO-1 mRNA by TCDD in a concentration-dependent manner. The induction of HO-1 mRNA level coincided with a decrease in total cellular heme content. In conclusion, the present study demonstrates for the first time that MG-132, despite of increasing Cyp1a1 mRNA expression, it decreases its activity probably through decreasing its heme content.

Blockade of the dioxin pathway by herbal medicine Formula Bupleuri Minor: identification of active entities for suppression of AhR activation.

Environmental pollutants including dioxins activate the aryl hydrocarbon receptor (AhR) and cause a wide range of pathologies. Development of AhR antagonists will be useful for prevention and treatment of the diseases related to AhR activation. Towards this goal, we aimed at seeking for potential AhR antagonists in herbal medicines using the dioxin responsive element-based sensing via secreted alkaline phosphatase (DRESSA). Through initial rough screening, 4 formulae were selected from 20 herbal medicines and subjected to the second, detailed screening. We found that only Formula bupleuri minor (TJ-9) significantly inhibited activation of AhR by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Among 7 raw herb extracts in TJ-9, Glycyrrhizae Radix and Scutellariae Radix were responsible for the antagonistic effect of TJ-9 against dioxin. Some constituents including Bupleuri Radix and Zingiberis Rhizoma rather activated AhR. Among 12 major constituents of Glycyrrhizae Radix and Scutellariae Radix, we identified that licopyranocoumarin, glycyrrhizic acid and genistein in Glycyrrhizae Radix and baicalein, wogonin and daidzein in Scutellariae Radix had substantial antagonistic effects on AhR. Among these, baicalein most effectively blocked activation of AhR triggered by cigarette smoke, a strong activator of AhR. The antagonistic substances identified here may be useful for prevention from diseases associated with aberrant activation of AhR.

JNK inhibitor SP600125 is a partial agonist of human aryl hydrocarbon receptor and induces CYP1A1 and CYP1A2 genes in primary human hepatocytes.

SP600125, a specific inhibitor of c-Jun-N-Terminal kinase (JNK), was reported as a ligand and antagonist of aryl hydrocarbon receptor (AhR) [Joiakim A, Mathieu PA, Palermo C, Gasiewicz TA, Reiners Jr JJ. The Jun N terminal kinase inhibitor SP600125 is a ligand and antagonist of the aryl hydrocarbon receptor. Drug Metab Dispos 2003;31(11):1279-82]. Here we show that SP600125 is not an antagonist but a partial agonist of human AhR. SP600125 significantly induced CYP1A1 and CYP1A2 mRNAs in primary human hepatocytes and CYP1A1 mRNA in human hepatoma cells HepG2. This effect was abolished by resveratrol, an antagonist of AhR. Consistent with the recent report, SP600125 dose-dependently inhibited CYP1A1 and CYP1A2 genes induction by a prototype AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in human hepatocytes. Moreover, SP600125 displayed typical behavior of a partial agonist in HepG2 cells transiently transfected with a reporter plasmid containing two inverted repeats of the dioxin responsive element or with a plasmid containing 5'-flanking region of human CYP1A1 gene. SP600125 transactivated the reporter plasmids with EC(50) of 0.005 and 1.89 microM, respectively. On the other hand, TCDD-dependent transactivation of the reporter plasmids was inhibited by SP600125 with IC(50) values of 1.54 and 2.63 microM, respectively. We also tested, whether the effects of SP600125 are due to metabolism. Using liquid chromatography/mass spectrometry approach, we observed formation of two minor monohydroxylated metabolites of SP600125 in human hepatocytes, human liver microsomes but not in HepG2 cells. These data imply that biotransformation is not responsible for the effects of SP600125 on AhR signaling. In conclusion, we demonstrate that SP600125 is a partial agonist of human AhR, which induces CYP1A genes.

Inhibition of PCDD/F and PCB formation in co-combustion.

Co-combustion of coal-solid waste mixtures in pilot and laboratory-scale combustors with emphasis on monitoring of toxic chlorinated hydrocarbon emissions such as polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) and polychlorinated biphenyls (PCB) is elaborated. The objective of the work is to investigate the so-called primary measures technique. Twenty different thermally resistant inorganic compounds were added directly to the fuel as inhibitors of PCDD/F formation. The fuel-types used in this study included lignite coal, pre-treated municipal solid waste and polyvinyl chloride (PVC). Principle component analysis (PCA) provides the basis for a feasible discussion about the efficiency of 20 inhibitors on PCDD/F and PCB formation. The study showed that the metal oxides group investigated had no inhibitory effect. Although the single N- and S-containing compounds, used as additives for the type of lignite coal, solid waste and PVC fuel, are not very effective as inhibitors, all other N- and S-containing substances are capable to strongly reduce PCDD/F and PCB flue gas emission. The most effective inhibitors are (NH(4))(2)SO(4) and (NH(4))(2)S(2)O(3). (NH(4))(2)SO(4) present at 3% of the fuel can reduce the PCDD/F emissions to 90%. Its low cost and high efficiency favour them as useful for full-scale combustion units.

Autoradiographic localization of aromatic hydrocarbon receptor (AHR) in rhesus monkey ovary.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of a large class of manmade pollutants that persist in the environment. TCDD exerts its toxic effects, in part, by binding to its receptor known as the aromatic hydrocarbon receptor (AHR). TCDD is estrogen modulatory and in some systems its receptor associates directly with estrogen receptors via co-activator molecules. TCDD inhibits steroid synthesis in human ovarian granulosa cells and AHR is found in these cells. We have previously shown that AHR is found in whole rhesus monkey ovary, but have yet to establish its location. In the present study, we set out to show that radiolabeled TCDD binds to monkey ovarian follicles and that this binding is receptor mediated. Ovaries from Macaca mulatta were sectioned on a cryostat at 10 micro m; and sections were incubated with either control vehicle, (3)H-TCDD, or (3)H-TCDD plus alpha-naphthoflavone (ANF), a known receptor-blocking agent. Here, we show for the first time specific binding of TCDD to the granulosa cells of antral follicles and other regions of the rhesus monkey ovary. Our data indicate a 60-fold increase in binding with (3)H-TCDD over that of control, and that this binding is reduced to the levels seen in controls with the addition of the competitive antagonist ANF. These findings support the hypothesis that TCDD directly affects primate ovarian function via the AHR.

TCDD-induced CYP1A1 expression, an index of dioxin toxicity, is suppressed by flavonoids permeating the human intestinal Caco-2 cell monolayers.

Since the toxicological effects of dioxins are mainly mediated by the aryl hydrocarbon receptor (AhR), an in vitro assessment system for AhR activity was used in this study to search for flavonoids that attenuated dioxin toxicity through the intestinal epithelial monolayer. When AhR transformation in Hepa-1c1c7 cells was examined by southwestern ELISA, nine flavonoids among 34 kinds of flavonoids inhibited the transformation by more than one-half. When each flavonoid with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was added to dioxin-responsive HepG2 cells, seven flavonoids significantly restrained the TCDD-induced transcriptional activity of the CYP1A1 promoter. Furthermore, those seven flavonoids that had permeated the Caco-2 cell monolayers demonstrated an inhibitory effect on both the AhR transformation and on the transcriptional activity of the CYP1A1 promoter. The expression level of the CYP1A1 mRNA and protein induced by TCDD was suppressed by flavone, galangin, and tangeretin. It is proposed from these results that some flavonoids have the ability to suppress dioxin-induced AhR activity after permeating the human intestinal epithelial cell monolayer.