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.     

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.     

Characterization of the enhanced responsiveness to postingestive satiety signals in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-treated Han/Wistar rats.

Previous studies have shown that under free-feeding conditions, TCDD-treated Han/Wistar (H/W) rats consume less sucrose solution but ingest more saccharin solution than their controls thus implying hyperresponsiveness to postingestive satiety signals. In this study, nutrient preloads were employed to further elucidate this phenomenon. Male H/W rats were given a single high but usually non-lethal intraperitoneal dose (1000 micrograms/kg) of TCDD. Feed intake was stimulated by 24 hr feed deprivation at various time points after TCDD exposure. When TCDD-dosed rats were allowed to drink either a 20% sucrose or a 0.25% saccharin solution and then given access to feed, those that had had sucrose ate only about 50% of the amount consumed by the saccharin group. Although the preloads were similar in control rats, no such difference in subsequent feeding occurred. The sucrose solution also produced a longer-lasting suppression of feed intake in TCDD-treated compared with control rats when infused directly into the stomach. By contrast, TCDD-treated H/W rats failed to exhibit an augmented satiety response to parenterally applied glucose independent of testing time. Oral corn oil reduced feed intake in both control and TCDD-exposed rats, but the inhibition was slightly larger in TCDD-treated animals. TCDD did not markedly affect the responsiveness of H/W rats to the suppression of feeding by CCK-8 or bombesin. It is concluded that gastrointestinal factors appear critical to the exaggerated response of TCDD-treated H/W rats to nutrient energy.     

Acute neurobehavioural effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Han/Wistar rats.

The neurobehavioural effects of a single non-lethal dose (1000 micrograms/kg intraperitoneally) of 2,3,7,8-tetrachlorodibenzo-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.     

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.     

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

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.     

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) 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.     

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.     

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 2,3,7,8-tetrachlorodibenzofuran (TCDF) in pregnant C57BL/6N mice: distribution to the embryo and excretion

The distribution and excretion of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlordibenzofuran (TCDF) were studied in pregnant C57BL/6N mice following an oral dose of 30 g/kg ¹⁴C-TCDD and 800 g/kg ¹⁴C-TCDF on gestation day 11. The distribution in maternal blood and liver and excretion in urine and feces was similar to that previously reported in males of the same strain. However, the rates of elimination were more rapid in pregnant females for both chemicals. This was more pronounced for TCDD than for TCDF. At all time points examined, the levels of radioactivity in the individual embryos were below 0.5% of the total TCDD dose and below 0.05% of the total TCDF dose. Assuming that all radioactive material found in embryos was unmetabolized compound, no more than 2.6 ng (8 pmoles) TCDD and 6.4 ng (21 pmoles) TCDF per g tissue were detected. In light of recent findings which strongly suggest a direct effect of TCDD and related compounds on embryonic palatal tissue, our data clearly support the potent teratogenic effect of TCDD and TCDF on the development of the secondary palate.     

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.     

Remarkable residual alterations in responses to feeding regulatory challenges in Han/Wistar rats after recovery from the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Adult male Han/Wistar rats were treated with 1000 micrograms 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg body weight and allowed to restabilize their body weight at a lower level. Therefore, their feeding or drinking responses were determined to the following ip challenges: NaCl (1 M, 10 ml/kg body weight); 2-deoxy-D-glucose (2DG; 400 mg/kg); sodium mercaptoacetate (MA; 800 mumol/kg); 2DG + MA (200 mg/kg + 400 mumol/kg); insulin (10 U/kg). In addition, the suppressive effects of naloxone (10 mg/kg), glucose (1.36 mg/kg) and fructose (1.36 mg/kg) on feed intake stimulated by 24-hr food deprivation were examined. After the restabilization, the body weights of TCDD-treated rats followed the course of body changes in control rats. The responses to NaCl were also similar in TCDD-treated and control rats. However, marked differences were observed in all other responses studied. Pretreatment with TCDD abolished 2DG-induced feeding, attenuated the effects of insulin and naloxone, caused an aberrant decrease in feed intake following MA, and resulted in hypersensitivity to the satiating effects of glucose and fructose. These data show that exposure to a high dose of TCDD leads to notable distortions in responses to metabolic challenges in Han/Wistar rats, which are present even when they have seemingly recovered from the acute toxicity. The results also indicate that the central nervous system plays a crucial role in TCDD toxicity, and suggest hypersensitivity to peripheral satiety signals coupled with hyporesponsiveness to metabolic cues of energy deficit to be important mechanisms in the pathogenesis of the wasting syndrome.     

四氯二苯二氧芑对人舌鳞癌细胞增生机制的研究

应用人舌鳞癌细胞株SCC-15G和SCC-25,通过单层细胞生长的细胞数和~3H-TdR掺入DNA的观察,进一步阐明了2,3,7,8-四氯二苯二氧(艹己)(TCDD)诱导刺激上皮细胞增生是由于降低了高密度生长抑制的敏感性引起的。SCC-15G细胞可作为研究TCDD对上皮细胞作用机制的理想模型。SCC-25细胞对TCDD反应较弱且不稳定,不宜用于研究上皮细胞增生机制。     

Differential Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in C57BL/6J Mice Congenic at the Ah Locus

Differential Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) in C57BL/6J Mice Congenic at the Ah Locus. BIRNBAUM,L. S., MCDONALD, M. M., BLAIR, P.C., CLARK, A. M., AND HARRIS,M. W. (1990). Fundam. Appl. Toxicol 15, 186–200. The acutetoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examinedin male C57BL/6J mice differing only at the Ah locus. Wild typemice (Ah^b/b; "b/b") were treated once with 0, 50, 100, 200,300, and 400 eg TCDD/kg po while congenic mice (Ah^d/d; "d/d")received a single dose of 0, 400, 800, 1600,2400, and 3200µgTCDD/kg. Mice were checked daily, weighed twice a week, andthose that survived, killed 35 days post-treatment. The LD5Ovalues were 159 and 3351 µg/kg for b/b and d/d mice, respectively.Mean time to death was 22 days and was independent of dose andgenotype. Decrease in body weight gain was noted in both strains5 days after treatment and occurred at doses 100 µ/kgin b/b mice and 1600 µg/kg in d/d mice. Dose-related increasesin liver weight (both absolute and relative to body weight)and decreases in thymus, spleen, testes, and epididymal fatpad weights were observed at 8–24–fold higher dosesin d/d than in b/b mice. A dose-related increase in segmentedneutrophils was observed in both strains. Serum chemistry valuesindicated that 8–24x greater doses of TCDD were neededto elevate sorbitol dehydrogenase, alanine aminotransferase,and 5'-nucleotidase and to decrease total and esterifled cholesterolin d/d than in b/b mice. Few effects were seen on total bileacids, serum triglycerides, glucose, or nonesterifled cholesterol.In the liver, hepatocellular cytomegaly, fatty change, and bileduct hyperplasia occurred in both strains in a dose-relatedmanner, as did thymic and splenic atrophy. Necrosis of germinalepithelium in the testes and edema in the stomach submu cosaoccurred at acutely toxic doses. These lesions also occurredat doses 8–24x greater in did than in b/b mice. Thus,the spectrum of toxicity is independent of the allele at theAh locus, but the relative dose needed to bring about variousacute responses is approximately 8–24x greater in congenicmice homozygous for the "d" allele than for the wild type animalscarrying two copies of the "b" gene.     

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     

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.     

Relationships between tissue levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), mRNAs, and toxicity in the developing male Wistar(Han) rat.

We compared the effects of a single acute dose, or chronic fetal exposure, to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the male reproductive system of the Wistar(Han) rat. Tissue samples were taken from dams on gestation day (GD)16 and GD21, and from offspring on postnatal days (PND)70 and 120. Steady-state concentration of TCDD was demonstrated in the chronic study: body burdens were comparable in both studies. Fetal TCDD concentrations were comparable after acute and chronic exposure, and demonstrate more potent toxicity after chronic versus acute dosing. In maternal liver, cytochrome P450 (CYP)1A1 and CYP1A2 RNA were induced. In fetus, there was induction of both CYP1A1 and CYP1A2 RNA at medium and high doses, but inadequate evidence for induction at low dose in either study. The low level induction of CYP1A1 RNA at low dose in fetus argues against AhR activation in fetus as a mechanism of toxicity of TCDD in causing delay in balanopreputial separation (BPS), and the greater induction of CYP1A1 RNA in PND70 offspring liver from chronically-dosed dams suggests that lactational transfer of TCDD is crucial to this toxicity. These data characterize the maternal and fetal disposition of TCDD, induction of CYP1A1 RNA as a measure of AhR activation, and suggest that lactational transfer of TCDD determines the difference in delay in BPS between the two studies.