2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced decrease in the fluidity of rat liver membranes

1. 2,3,7,8-Tetrachlorodibenzo-ρ-dioxin (TCCD)-induced lipid peroxidation has previously been demonstrated by assessing the hepatic content of thiobarbituric acid reactive substances (TBARS) as well as the NADPH-dependent microsomal formation of TBARS as well as the NADPH-dependent microsomal formation of TBARS using malondialde-hyde as the standard.

2. Changes in membrane fluidity as a result of lipid peroxidation may occur. Therefore the dose- and time-dependent effects of TCDD on lipid peroxidation in mitochondrial, microsomal, and plasma membranes, and changes in membrane fluidity in these subcellular fractions, were examined. Animals were treated with either 50 or 100 μg TCDD/kg orally, and killed 3, 6, or 9 days post-treatment.

3. Time-dependent increases occurred in TBARS content and formation following TCDD administration for all three membranes. Similar results were observed after 50 and 100 μg TCDD/kg.

4. Following TCDD administration, fluorescence polarization measurements as determined by the fluorescence polarization (r) and anisotropy parameter (a.p.) values demonstrated significant decreases in membrane fluidity in all membrane fractions, indicative of membrane structural alterations.

5. Excellent inverse correlations between lipid peroxidation and membrane fluidity were observed. Thus, decreased membrane fluidity and increased membrane damage may contribute to the toxic manifestations of TCDD as a consequence of an oxidative stress.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced decrease in the fluidity of rat liver membranes

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCCD)-induced lipid peroxidation has previously been demonstrated by assessing the hepatic content of thiobarbituric acid reactive substances (TBARS) as well as the NADPH-dependent microsomal formation of TBARS as well as the NADPH-dependent microsomal formation of TBARS using malondialdehyde as the standard. 2. Changes in membrane fluidity as a result of lipid peroxidation may occur. Therefore the dose- and time-dependent effects of TCDD on lipid peroxidation in mitochondrial, microsomal, and plasma membranes, and changes in membrane fluidity in these subcellular fractions, were examined. Animals were treated with either 50 or 100 micrograms TCDD/kg orally, and killed 3, 6, or 9 days post-treatment. 3. Time-dependent increases occurred in TBARS content and formation following TCDD administration for all three membranes. Similar results were observed after 50 and 100 micrograms TCDD/kg. 4. Following TCDD administration, fluorescence polarization measurements as determined by the fluorescence polarization (r) and anisotropy parameter (a.p.) values demonstrated significant decreases in membrane fluidity in all membrane fractions, indicative of membrane structural alterations. 5. Excellent inverse correlations between lipid peroxidation and membrane fluidity were observed. Thus, decreased membrane fluidity and increased membrane damage may contribute to the toxic manifestations of TCDD as a consequence of an oxidative stress.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and long term immunologic memory.

The highlighted article by B. Paige Lawrence and Beth Vorderstrasse addresses an oft forgotten aspect of immunotoxicity, the effects of environmental toxins on immunologic memory. Here, the authors take a step towards filling that information gap by evaluating the effects of a prototypic environmental toxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on memory responses to a real-world pathogen, influenza A virus, presented to an animal model in a physiologically relevant manner. Multiple outcomes are evaluated, the vast majority of which suggest important and long-term TCDD-induced changes in the immune system after both primary and secondary exposure to this pathogen. The implications of these studies with regard to the immuno-competence of TCDD-exposed individuals are far reaching.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced activation of mitogen-activated protein kinase signaling pathway in Jurkat T cells

The present study was performed to examine mitogen-activated protein kinase associated pathways in mediation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced cell apoptosis in cultured Jurkat T cells. TCDD significantly decreased cell viability in a concentration-dependent manner (P<0.05 at 10-300 nM). TCDD (10 nM) also time-dependently decreased cell viability (P<0.05 at 12-48 hr). c-Jun NH2-terminal kinase was significantly phosphorylated with TCDD treatment in a time dependent manner. p38 Mitogen-activated protein kinase was not significantly changed with TCDD treatment. Extracellular signal-regulated protein kinase was significantly phosphorylated with TCDD treatment for 8 hr and gradually returned to baseline. TCDD induced up-regulation of ASK1 and C-Jun, which are up- and down-stream of JNK, respectively, and up-regulation of cytosolic cytochrome c and caspase-3. These results demonstrate that MAPK signaling pathways including JNK and ERK 1/2, are activated with the treatment of TCDD in Jurkat T cells, which suggest that MAPK pathways may be involved in TCDD-induced cell death.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced appetite suppression in the Sprague-Dawley rat is not a direct effect on feed intake regulation in the brain

The most striking sign of acute toxicity of TCDD in animals is a progressive reduction of feed intake, accompanied by loss of body weight eventually resulting in death. The mechanism(s) of this voluntary feed refusal is (are) not known but it is generally accepted that both centrally and peripherally (via feedback) acting anorectic agents exert their effect(s) in the hypothalamus. In this study direct administration into the lateral cerebral ventricle of rats resulted in much higher concentrations of TCDD in the hypothalamus and also in other regions of the brain than after a lethal intravenous (iv) injection. While rats injected iv displayed the expected cachectic syndrome, intracerebroventricularly (icv)-dosed animals ate and gained weight normally. These findings preclude the possibility of a direct effect of TCDD on appetite-regulating areas of the brain. Moreover, these results require the assumption that the appetite suppressive effect of TCDD is due to a (feedback) mechanism originating in the periphery.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) enhances terminal differentiation of cultured human epidermal cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and isosteric halogenated analogs produce a spectrum of pathologic changes in the epidermis of humans. In this study, the actions of TCDD on cultured human epidermal cells were characterized to determine whether these cells are an appropriate in vitro model to examine the mechanisms of TCDD toxicity to human skin. The differential staining properties of TCDD-treated cultures indicated that TCDD decreased basal cell numbers and increased the degree of keratinization. Histologic examination of cross-sections of the cultures confirmed a loss of small nucleated cells and increased cell layering in response to TCDD. TCDD produced no change in total cell number or cell protein, but decreased the number of small (basal) cells and DNA synthesis. TCDD increased the number of cells containing spontaneous envelopes, as well as the number of envelope-competent cells. The quantitative changes observed in these parameters were consistent with a TCDD-induced commitment of proliferating cells to terminal differentiation. TCDD also decreased epidermal growth factor (EGF) specific binding. Maximal changes in EGF binding occurred after 4 days, and in small cell number after 5 days. The decreases in EGF binding and small cell number were stereospecific and concentration dependent (EC50, 1 to 2 nM), implicating the human Ah receptor in mediating these responses to TCDD. These data indicate that TCDD treatment produces hyperkeratinization in cultured human epidermal cells. It is proposed that TCDD acts on epidermal basal cells to enhance terminal differentiation through mechanisms regulated at least in part by the Ah receptor.     

Acute Neurobehavioural Effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in Han/Wistar Rats

Abstract: The neurobehavioural effects of a single non-lethal dose (1000 μg/kg intraperitonelly) of 2,3,7,8-tetrachlorodi-benzo-p-dioxin (TCDD) were assessed in young male Han/Wistar rats, highly resistant to acute lethality of TCDD. TCDD decreased body weight significantly compared with ad libitum fed controls. TCDD did not change the behaviour or the motility of rats in the open field test 8 days after the treatment nor did it affect the spontaneous motor activity up to 27 days after the exposure. In the elevated plus-maze test for anxiety, TCDD-treated rats did not differ from either ad libitum fed controls or pair-fed controls. In the 24-hr passive avoidance test, the learning of TCDD-treated rats did not differ significantly from that of ad libitum fed controls or pair-fed controls from 8 hr to 16 days after the treatment. TCDD did not affect the motor coordination or the maintenance of balance on the rotating rod but it impaired them slightly in the elevated horizontal bridge test 16 hr after exposure. It did not affect nociception in the hot plate test 16 hr or 8 days after the injection. The results suggest that a single sublethal dose of TCDD does not alter markedly the general behaviour of Han/Wistar rats, in contrast to its striking effect on feeding behaviour which results in a marked decrease in body weight gain.     

Effect of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on Influenza Virus Host Resistance in Mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes numerous immunotoxiceffects including thymic involution and an immunosuppressionof nonspecific as well as specific cell- and humoralmediatedimmunity. TCDD administration to laboratory animals also resultsin a decreased resistance to numerous bacteria, viruses, andparasites. Effects on virus host resistance appear to be amongthe most sensitive effects of TCDD immunotoxicity. However,previous studies have not achieved a no effect level. The presentstudies utilized an influenza virus host resistance model inmice to quantify the sensitivity of this model to TCDD and todetermine the NOAEL (no observed adverse effect level) of TCDDfor influenza virus. Results indicated that a single dose ofTCDD at 0.10, 0.05, or 0.01 µg/kg resulted in an increasedmortality to Hong Kong influenza virus when mice were challenged7 days after TCDD administration. Increased mortality was notcorrelated with increased virus titers in the lungs. TCDD at0.005 or 0.001 µg/kg had no effect on influenza-inducedmortality. TCDD alone did not affect thymus weight at any doseadministered in this study. TCDD also did not alter the virus-enhancedincrease in lung weight:body weight ratio nor the virus-induceddecrease in thymus weight. Thus, low levels of TCDD exposurelead to enhanced mortality to influenza virus; however, themechanism of this effect remains to be elucidated. Nonetheless,enhanced mortality to influenza virus in mice following a singledose of 10 ng TCDD/kg represents the most sensitive adverseeffect yet reported for TCDD.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Related Compounds as Antioestrogens: Characterization and Mechanism of Action

Abstract: In the female Sprague-Dawley rat uterus 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds exhibited a broad spectrum of antioestrogenic responses. For example 2,3,7,8-TCDD inhibited the 17β-oestradiol-induced uterine wet weight increase, peroxidase activity, oestrogen and progesterone receptor levels, epidermal growth factor (EGF) receptor binding, and EGF receptor and c-fos protooncogene mRNA levels. The aryl hydrocarbon (Ah) receptor was identified in the rat uterus and the antioestrogenic activities of TCDD and related compounds were structure-dependent. In parallel studies, the effects of TCDD as an antioestrogen in MCF-7 human breast cancer cells was also investigated. TCDD inhibited the 17β-oestradiol-induced proliferation of these cells and the secretion of the 34-, 52- and 160-kDa proteins. Treatment of MCF-7 cells with 1 nM [³H]-β-oestradiol resulted in a rapid accumulation of nuclear oestrogen receptor (ER) complexes. Pretreatment of the cells with TCDD caused a rapid decrease in nuclear ER binding activity and immunoreactive protein; moreover, the structure-dependent potencies of TCDD and related compounds as antioestrogens were similar to their Ah receptor binding affinities. TCDD also caused a decrease in nuclear ER levels in wild-type Ah-responsive Hepa lclc7 cells but was inactive in Ah non-responsive mutant Hepa lclc7 cells. Moreover, in the wild-type cells, both antinomycin D and cycloheximide blocked the effects of TCDD. 6-Methyl-1,3,8-trichlorodibenzofuran (MCDF) has previously been characterized as a TCDD antagonist in rodents and in transformed rodent cell lines. However, like TCDD, MCDF also exhibited a broad spectrum of antioestrogenic activities in both the female Sprague-Dawley rat uterus and MCF-7 cells. MCDF is relatively non-toxic compared to TCDD and is being investigated as a compound which may be clinically useful for the treatment of mammary cancer.     

Host Resistance to Trichinella spiralis Infection in Rats Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)

We have previously shown decreased resistance to Trichinellaspiralis (Ts) infection and reduced parasite antigen-specificresponses in B6C3F1 mice exposed to TCDD before infection. Thecurrent study was done to characterize the effects of preinfectionadministration of 1, 10, or 30 µg TCDD/kg on host resistanceof female F344 rats to Ts infection and to examine parasiteantigen-specific responses in the spleen and mesenteric lymphnodes of infected animals. TCDD exposure did not affect adultparasite elimination from the small intestine or the numbersof encysted larvae in the muscle, although host control of newbornlarvae production in female parasites isolated from the highestdose group was compromised. Proliferative responses of lymphocytescultured with parasite antigen were enhanced in groups of ratsexposed to 30 µg TCDD/kg. These results, which are inmarked contrast to the effects obtained in B6C3FI mice, demonstratea clear species difference in the effects of TCDD on immunefunction in rodents and underscore the need to determine whichspecies more closely reflects the potential outcome of humanexposure to TCDD.     

Ingestion of Soil Contaminated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Alters Hepatic Enzyme Activities in Rats

Ingestion of Soil Contaminated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) Alters Hepatic Enzyme Activities in Rats. LUCIER, G.W., RUMBAUGH, R. C., MCCOY, Z., HASS, R., HARVAN, D., AND ALBRO,P. (1986). Fundam. Appl. Toxicol. 6, 36.4–371. Femalerats were treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)in either corn oil or contaminated soil from the Minker sitein Missouri. Eight doses ranging from 0.015 to 5 µg TCDD/kgwere used in the corn oil group; the range was 0.015 to 5.5TCDD/kg in the TCDD-contaminated soil group. Rats in a thirdgroup were given equal amounts of soil uncontaminated with TCDD.No acute toxicity or effects on body weight gain were observedat these doses. In general, equivalent doses of TCDD in cornoil or TCDD in soil produced similar increases in hepatic arylhydrocarbon hydroxylase activity (AHH) and UDP glucuronyltransferaseactivity although effects were slightly greater in the TCDD–cornoil groups. In the corn oil groups, the induction of AHH rangedfrom about 30-fold at the highest dose to twofold at the lowestdose studied. TCDD also caused an increase in cytochrome P-450concentration and a shift in spectral peak from 450 to 448 nm.There was no effect of TCDD on ethylmorphine N-demethylase,consistent with previous reports. Liver concentrations of TCDD(mean ± SD) in the 5-µg/kg groups were 40.8 ±6.3 ppb in the TCDD- corn oil group and 20.3 ± 12.9 ppbin the TCDD-contaminated soil group. Our results suggest thatthe bioavailability of TCDD in soil in rats is approximately50%. Therefore, ingestional exposure to TCDD-contaminated soilmay constitute a significant health hazard in view of its extremelyhigh toxicity and relatively high bioavailability.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters the regulation of Pax5 in lipopolysaccharide-activated B cells.

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces a profound suppression of the primary immunoglobulin-M (IgM) antibody response. The suppression of IgM production by TCDD can occur through direct interactions with the B cell, is aryl hydrocarbon receptor-dependent, and is mediated through alterations in the differentiation of B cells into plasma cells. The objective of the present investigation was to characterize the effects of TCDD on the regulation of Pax5, a crucial repressor of B-cell differentiation, and four downstream targets that are directly regulated by Pax5 and involved in immunoglobulin regulation, immunoglobulin heavy chain (IgH), kappa light chain (Igkappa), J chain, and X box protein-1 (XBP-1). Lipopolysaccharide (LPS) activation of aryl hydrocarbon receptor-expressing CH12.LX cells induced B cell differentiation and robust immunoglobulin secretion that was markedly (~50%) suppressed in the presence of 10 nM TCDD. Kinetic studies show that LPS-activation induced a time-dependent decrease in Pax5 mRNA levels, protein, and DNA binding activity during a 72-h culture period that was almost completely blocked in the presence of TCDD. Concomitant with the time-dependent down-regulation of Pax5 in LPS-activated control CH12.LX cells, a reciprocal induction of IgH, Igkappa, J chain mRNA levels, and cellular XBP-1 was observed. Conversely, and consistent with the absence of Pax5 down-regulation associated with TCDD treatment, IgH, Igkappa, J chain mRNA, and XBP-1 protein were persistently repressed in LPS-activated CH12.LX cells. Collectively, these studies demonstrate the involvement of altered Pax5 regulation in the suppression of the primary IgM antibody response by TCDD.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) effects on hepatic microsomal cytochrome P-448-mediated enzyme activities.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on hepatic microsomal mixed function oxidase (MFO) enzyme systems were examined in female rats. Although TCDD had little effect on NADPH-cytochrome c reductase activity and cytochrome P-450 content, the activities of the cytochrome P-448-mediated enzymes benzo[α]pyrene hydroxylase, ethoxyresorufin O-deethylase, and biphenyl 2-hydroxylase were greatly increased. Three months after a single oral dose of 2 μg/kg TCDD, the cytochrome P-450 content and benzo[α]pyrene hydroxylase and ethoxyresorufin O-deethylase activities were still significantly increased. In addition, the microsomal metabolism of the novel substrate 4,4′-dimethylbiphenyl was greatly increased by TCDD pretreatment. Low dose studies revealed that the ED50 of TCDD induction of benzo[α]pyrene hydroxylase was 0.63 μg/kg and the lowest dose of TCDD which caused a significant increase in enzyme activity was 0.002 μg/kg. Studies in which [1,6-³H]TCDD was used to determine the extent of hepatic uptake of orally administered TCDD at the lowest effective dose of 0.002 μg/kg lead to the estimate that only 65 molecules of TCDD per hepatocyte were required to produce a measurable increase in benzo[α]pyrene hydroxylation. These results attest to the specificity and persistence of TCDD in the induction of cytochrome P-448-mediated enzyme activities in rat liver. The small number of molecules required to induce benzo[α]pyrene hydroxylase suggests that TCDD is among the most potent MFO-inducing agents yet demonstrated in mammalian liver.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-mediated membrane translocation of c-Src protein kinase in liver WB-F344 cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a widespread environmental contaminant and the most potent agonist of the aryl hydrocarbon receptor (AhR). Persistent activation of the AhR has been shown to be responsible for most TCDD-mediated toxic responses, including liver tumour promotion. However, the mechanisms responsible for these complex toxic reactions are still unknown. TCDD (1 nM) has previously been shown to reduce DNA synthesis of primary hepatocyte cultures and cell contact inhibition of confluent WB-F344 cells. The latter model was used to study early effects of TCDD on protein tyrosine kinase c-Src in confluent WB-F344 cells. It was found that TCDD decreased cytosolic c-Src (protein and tyrosine kinase activity) after 20–60 min, and increased c-Src in the membrane fraction. Membrane translocation of c-Src occurred in the presence of 100 μM cycloheximide and was observed after treatment with 1 nM TCDD or 50 nM 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin. Under these conditions epidermal growth factor (EGF) receptor tyrosine phosphorylation was also studied. As expected, its phosphorylation was low in confluent cells but was significantly enhanced by TCDD treatment. Pretreatment of WB-F344 cells for 1 h with 1 μM geldanamycin, which disrupts cytosolic heat shock protein Hsp90 complexes with AhR and Src, abolished TCDD-mediated Src translocation and TCDD-mediated reduction of cell contact inhibition. The WB-F344 cell model appears to be very useful to study TCDD effects on protein tyrosine kinases and of signaling pathways responsible for modulation of the cell cycle by TCDD. Received: 21 December 1998 / Accepted: 15 February 1999     

Toxicokinetics of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in Two Substrains of Male Long-Evans Rats after Intravenous Injection

Toxicokinetics of a nontoxic intravenous dose of ¹⁴C-labeledTCDD were studied in two substrains of Long-Evans (L-E) ratswith a fivefold difference in sensitivity in terms of TCDD-inducedmortality. The Turku/AB Long-Evans rat (T L-E) is the most sensitiverat strain with an oral LD50 of 17.7 µg/kg, whereas theCharles River Long-Evans rat (CR L-E) is a more resistant strain(oral LD50 95.2 µg/kg). Samples of 18 tissues were collected1, 2, 4, 8, 16, and 32 days after dosing and analyzed for radioactivity.Body weight and fecal and urinary excretion of radioactivitywere monitored daily during the 32-day study period. CR L-Erats grew significantly faster than T L-E rats, increasing theirbody weight by 60% in 32 days compared with only 16% in T L-Erats. This difference was not caused by toxicity, because theweight gain was identical in control and TCDD-treated rats ofboth substrains. Tissue concentrations of [¹⁴C]TCDD-associatedradioactivity and area under the curve (AUC) values were lowerin CR L-E than in T L-E rats. The most pronounced differenceswere found in thymus, white adipose tissue, brown adipose tissue,and adrenals. The decrease of TCDD concentration in tissueswas faster in CR L-E than in T L-E rats, whereas fecal and urinaryexcretion was faster in T L-E than in C L-E rats. Eliminationhalf-life was 20.0 days in T L-E rats and 28.9 days in CR L-Erats. Differential toxicokinetics of TCDD in the two L-E substrainsprovide a likely explanation for the greater sensitivity ofthe T L-E strain, since observed differences in tissue concentrationsand AUC values are in good agreement with the difference insusceptibility. In addition to the more efficient tissue uptakeof TCDD in T L-E rats than in CR L-E rats, the major contributingfactor to differences in toxicokinetics seems to be a differentialgrowth rate (dilution by growth), which in turn appears to providean explanation for the difference in susceptibility. More rapidexcretion of TCDD in T L-E rats than in CR L-E rats is clearlya result of higher tissue concentrations in T L-E rats. However,this faster excretion rate is not sufficient to counterbalancethe much slower dilution by growth in T L-E rats than in CRL-E rats. Thus, dilution by growth can be a more important factorin determining the toxicokinetics and toxicity of TCDD in rodentsthan is excretion.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related compounds as antioestrogens: characterization and mechanism of action.

In the female Sprague-Dawley rat uterus 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds exhibited a broad spectrum of antioestrogenic responses. For example 2,3,7,8-TCDD inhibited the 17 beta-oestradiol-induced uterine wet weight increase, peroxidase activity, oestrogen and progesterone receptor levels, epidermal growth factor (EGF) receptor binding, and EGF receptor and c-fos protooncogene mRNA levels. The aryl hydrocarbon (Ah) receptor was identified in the rat uterus and the antioestrogenic activities of TCDD and related compounds were structure-dependent. In parallel studies, the effects of TCDD as an antioestrogen in MCF-7 human breast cancer cells was also investigated. TCDD inhibited the 17 beta-oestradiol-induced proliferation of these cells and the secretion of the 34-, 52- and 160-kDa proteins. Treatment of MCF-7 cells with 1 nM [3H]-17 beta-oestradiol resulted in a rapid accumulation of nuclear oestrogen receptor (ER) complexes. Pretreatment of the cells with TCDD caused a rapid decrease in nuclear ER binding activity and immunoreactive protein; moreover, the structure-dependent potencies of TCDD and related compounds as antioestrogens were similar to their Ah receptor binding affinities. TCDD also caused a decrease in nuclear ER levels in wild-type Ah-responsive Hepa 1c1c7 cells but was inactive in Ah non-responsive mutant Hepa 1c1c7 cells. Moreover, in the wild-type cells, both actinomycin D and cycloheximide blocked the effects of TCDD. 6-Methyl-1,3,8-trichlorodibenzofuran (MCDF) has previously been characterized as a TCDD antagonist in rodents and in transformed rodent cell lines. However, like TCDD, MCDF also exhibited a broad spectrum of antioestrogenic activities in both the female Sprague-Dawley rat uterus and MCF-7 cells. MCDF is relatively non-toxic compared to TCDD and is being investigated as a compound which may be clinically useful for the treatment of mammary cancer.     

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced accumulation of biliverdin and hepatic peliosis in rats.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a widespread, persistent, and highly toxic environmental pollutant. The most TCDD-sensitive and the most TCDD-resistant rat strains (Long-Evans [Turku/AB] and Han/Wistar [Kuopio], respectively) were crossbred to separate the alleles of two genes (Ahrand an unidentified gene "B") mediating resistance against TCDD toxicity. During crossbreeding, a new type of toxicity in livers of both sexes was detected, characterized macroscopically by intense dark green to black color and swelling that appeared most frequently after a large dose (300 micro g/kg or more as a single intragastric dose) and a follow-up period of more than three weeks. Therefore, studies were undertaken to identify the causative pigment chemically and to examine the hepatotoxicity histologically. The pigment fractions were separated by thin layer chromatography and then analyzed by HPLC and electrospray mass spectrometry. The pigment was found to consist of biliverdin and several biliverdin-related compounds. In liver histopathology carried out on male rats, progressive sinusoidal distension and hepatic peliosis with membrane-bound cysts were seen. The clinical manifestations of pigment accumulation were recorded most often in intermediately resistant rat lines such as line B (homozygous for the gene B), but never occurred in rats expressing only the Han/Wistar (Kuopio)-type Ah receptor with an altered transactivation domain structure.     

Nrf2 protects against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced oxidative injury and steatohepatitis

Previous studies demonstrate that Nrf2, a master regulator of antioxidative responses, is essential in mediating induction of many antioxidative enzymes by acute activation of the AhR. However, the role of Nrf2 in protecting against oxidative stress and DNA damage induced by sustained activation of the AhR remains unknown and was investigated herein. Tissue and blood samples were collected from wild-type (WT) and Nrf2-null mice 21 days after administration of a low-toxic dose (10 μg/kg ip) of TCDD. Only Nrf2-null mice lost body weight after TCDD treatment; however, blood levels of ALT were not markedly changed in either genotype, indicating a lack of extensive necrosis. Compared to livers of TCDD-treated WT mice, livers of TCDD-treated Nrf2-null mice had: 1) degenerated hepatocytes, lobular inflammation, marked fat accumulation, and higher mRNA expression of inflammatory and fibrotic genes; 2) depletion of glutathione, elevation in lipid peroxidation and marker of DNA damage; 3) attenuated induction of phase-II enzymes Nqo1, Gsta1/2, and Ugt2b35 mRNAs, but higher induction of cytoprotective Ho-1, Prdx1, Trxr1, Gclc, and Epxh1 mRNAs; 4) higher mRNA expression of Fgf21 and triglyceride-synthesis genes, but down-regulation of bile-acid-synthesis genes and cholesterol-efflux transporters; and 5) trend of induction/activation of c-jun and NF-kB. Additionally, TCDD-treated Nrf2-null mice had impaired adipogenesis in white adipose tissue. In conclusion, Nrf2 protects livers of mice against oxidative stress, DNA damage, and steatohepatitis induced by TCDD-mediated sustained activation of the AhR. The aggravated hepatosteatosis in TCDD-treated Nrf2-null mice is due to increased lipogenesis in liver and impaired lipogenesis in white adipose tissue.     

Effect of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on Pulmonary Influenza Virus Titer and Natural Killer (NK) Activity in Rats

Suppression of immune function and enhanced susceptibility toinfection in mice is one of the more sensitive indicators ofTCDD toxicity. Recent efforts to demonstrate similar effectsin the rat have shown that there are considerable differencesbetween the two species. The purpose of this study was to determinethe effect of TCDD exposure on (a) an influenza virus host resistancemodel in rats and (b) natural killer cell activity in the lungand spleen. Fischer 344 rats were treated with 10 µg TCDD/kgbody weight via gavage and infected intranasally with rat-adaptedinfluenza virus (RAIV) 7 days later. Virus-augmented NK activityassessed at 48 hr postinfection in the lung was significantlysuppressed in rats treated with 3, 10, or 30 µg TCDD/kgbody weight. Spontaneous NK activity in either lung or spleenwas not affected by TCDD exposure. Significantly higher virustiters were observed on Days 2, 3, and 4 postinfection in thelungs of rats treated with TCDD (10 µg/kg) TCDD had noeffect on the amount of virus recovered from nasal lavage. Acuteexposure to TCDD did not significantly affect lung and bodyweights in rats infected with RAIV except in the highest dose(30 µg/kg) treated rats. Rats exposed to repeated dosesof TCDD showed a significant increase of lung weights and L/Bratios when rats were infected with RAIV after TCDD exposure.Virus-augmented pulmonary NK activity in these rats was significantlysuppressed; however, the suppression was not more profound thanthat in rats exposed to a single dose of TCDD. However, an increaseof lung weights and lung/body weight ratios was observed inRAIV infected rats which were exposed to repeated doses of TCDD(cumulative dose of 10 µg/kg). Virus-augmented NK activitywas significantly sup pressed in rats exposed to repeated dosesof TCDD. Our results showed that TCDD suppressed virus-augmentedpulmonary NK activity and this effect may at least in part berelated to enhanced susceptibility of rats to influenza virus.