Acute Toxicity of Perfluorodecanoic Acid in C57BL/6 Mice Differs from 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Perfluorodecanoic acid (PFDA) is a 10-carbon straight-chainfatty acid. Its toxicity in rats has been reported to resemblethat produced by exposure to 2,3,7,8-tetrachlorodibenzo-P-dioxin(TCDD). Mice which are "responsive" to TCDD toxicity carry theAh^b allele, while mice homozygous for the Ah^d gene are lesssensitive to TCDD toxicity. To characterize the toxicity ofPFDA and determine if it is under the control of the Ah locus,female responsive C57BL/6N (Ah^b/d) mice and congenic C57BL/6Jmice, differing only at the Ah locus (responsive, Ah^b/b; heterozygousresponsive, Ah^b/d and "nonresponsive," Ah^d/d), were administereda single oral dose of PFDA, at levels from 0 to 320 mg/kg bodyweight, observed daily for overt signs of toxicity, and weighedthree times weekly. In the wild-type congenic C57BL/6J (Ah^b/b)subline, mice were killed at 2, 7, 14, and 30 days followingexposure. All other mice were killed on Day 30. Serum was takenfrom the C57BL/6N mice for analysis of thyroid hormone levels.Selected organs from all mice were weighed and fixed for histopathologicalexamination. Dose-related mortality was observed as early as5 days postexposure and time-to-death was inversely relatedto dose. Dramatic decreases in body weight occurred shortlyfollowing treatment in all strains. Serum triiodothyronine (T₃)and thyroxine (T₄) levels increased with increasing dose. Therewas a marked increase (p < 0.05) in absolute and relativeliver weights and a significant decrease in thymus weights.Hepatocellular hypertrophy was observed in all treated miceother than controls. A marked increase in hepatocyte peroxisomeswas observed in all treatment groups. Thus, in contrast to TCDD,the acute toxicity of PFDA in the female C57BL/6 mouse doesnot vary with the Ah allele and is distinct from that reportedfor TCDD.     

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) 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.     

Induction of Oxidative Stress in Brain Tissues of Mice after Subchronic Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

The ability of single doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) to induce oxidative stress in hepatic and some extrahepatictissues of animals is well documented. However, no previousstudy has examined the ability of TCDD to induce oxidative stressand tissue damage in brain in vivo. In this study the abilityof TCDD to induce oxidative stress in brain tissues of micewas studied after subchronic exposures. Groups of female B6C3F1mice were treated orally with TCDD (0, 0.45, 1.5, 15, and 150ng/kg/day) for 13 weeks, 5 days/week. The animals were euthanized3 days after the last treatment and brain tissues were collected.Biomarkers of oxidative stress including production of superoxideanion, lipid peroxidation, and DNA-single-strand breaks (SSB)were determined. TCDD treatment resulted in significant anddose-dependent increases in the production of superoxide anionas assessed by reduction of cytochrome c. Significant increaseswere also observed in lipid peroxidation and DNA-SSB in thosetissues, as assessed by the presence of thiobarbituric acid-reactivesubstances and the alkaline elution technique, respectively.These results clearly indicate that subchronic exposure to lowdoses of TCDD can induce oxidative tissue damage in brain tissueswhich may at least in part play a role in the effects of TCDDon the central nervous system.     

Developmental Toxicity of Perfluorodecanoic Acid in C57BL/6N Mice

Developmental Toxicity of Perfluorodecanoic Acid in C57BL/6NMice. HARRIS, M. W., AND BIRNBAUM, L. S. (1989). Fundam Appl.Toxicol. 12, 442–448. Perfluorodecanoic acid (PFDA) isa representative of the perfluorinated carboxylic acids usedas commercial wetting agents and flame retardants. Signs ofPFDA toxicity have been reported to resemble those seen afterexposure to TCDD. To determine if PFDA exhibits teratogeniceffects similar to those of TCDD or is a developmental toxin,time-mated C57BL/6N mice were administered PFDA by gavage incorn oil (10 ml/kg) on gestation days (gd) 10–13 or gd6–15 at levels of 0, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0,or 32.0 mg/kg/day or 0, 0.03, 0.3, 1.0, 3.0, 6.4, or 12.8 mg/kg/day,respectively. Dams were killed on gd 18 and maternal and fetaltoxicity was assessed. Fetuses were examined for external, visceral,or skeletal malformations. Maternal body weight gain (correctedfor the weight of the gravid uterus) was significantly reducedas a result of PFDA treatment at 6.4 and 12.8 mg/kg/day (gd6–15) and 16.0 and 32.0 mg/kg/day (gd 10–13). Fetalviability was decreased only in those groups showing extensivematernal body weight loss. Fetal body weights were significantlyreduced at levels as low as 0.1 mg/kg/day (gd 6–15) and0.5 mg/kg/day (gd 10–13). No hydronephrosis, cleft palate,or edema was observed nor were any other soft tissue or skeletalmalformations detected. Thus, PFDA does not produce malformationsin C57BL/6N mice, and the developmental toxicity observed (increasedfetal mortality and decreased live fetal body weight) was seenonly at doses that were maternally toxic.     

Teratologic Evaluation of Hexabrominated Naphthalenes in C57BL/6N Mice

Teratologic Evaluation of Hexabrominated Naphthalenes in C57BL/6NMice. MILLER, C. P., AND BIRNBAUM, L. S. (1986). Fundam. Appl.Toxicol. 7, 398-405. Hexabrominated naphthalenes (HBNs) havebeen identified as contaminants in the commercial PBB mixture,Fire-master. Similarities between polyhalogenated naphthalenesand polyhalogenated biphenyls, di-benzofurans, and dibenzo-p-dioxinswith regards to structure and capacity to elicit certain toxi-cologicalresponses in laboratory animals have previously been evaluated.In this study, teratogenicity and embryo/fetal toxicity, whichhave been associated with maternal exposure to other toxic polyhalogenatedaromatics, was characterized for a synthetic mixture of HBNsin C57BL/6N mice. Pregnant adult mice were treated on gestationDays 6 through 15 with 0.5, 1.0,2.5,5.0,7.5, and 10.0 mg HBN/kgbody wt/day and sacrificed on gestation Day 18. Maternal toxicityas evidenced by decreased body weight gain or actual weightloss was observed at 7.5 and 10.0 mg/kg/day. Maternal liver-to-bodyweight ratios were increased relative to controls at all exposurelevels. Dose-related increases were recorded in fetal mortalityat 5.0, 7.5, and 10.0 mg/kg/day, and in the incidence of variousteratogenic effects at all dose levels. Kidney lesions, bestdescribed as apparent hydronephrosis, were the most sensitivefetal abnormality observed, followed by a reduction in the sizeof lymphatic organs (thymus and spleen), cleft palate, subcutaneousedema, sternebral anomalies, and delayed cranial ossification.HBNs are concluded to be potent fetotoxic and teratogenic agentsproducing similar effects to TCDD and other toxic polyhalogenatedaromatic hydrocarbons.     

Retinoic acid and 2,3,7,8-tetrachlorodibenzo-p-dioxin selectively enhance teratogenesis in C57BL/6N mice

TCDD is one of the most toxic man-made compounds and an extremely potent teratogen in mice. Many of its toxic symptoms resemble those seen during vitamin A deficiency. Vitamin A and its derivatives, such as alltrans-retinoic acid (RA), are also teratogenic in mice, as well as many other species. Both TCDD and RA produce cleft palate in susceptible strains of mice. However, while TCDD produces hydronephrosis, RA does not, and TCDD does not produce limb bud defects while RA does. To determine whether TCDD and RA would enhance or antagonize the teratogenic effects of the other compound, C57BL/6N dams were treated po on Gestation Day (gd) 10 or 12 with 10 ml corn oil/kg containing TCDD (0-18 micrograms/kg), RA (0-200 mg/kg), or combinations of the two chemicals. Dams were killed on gd 18 and toxicity and teratogenicity assessed. Coadministration of TCDD and RA had no effect on maternal or fetal toxicity beyond what would be expected by either compound alone. Cleft palate was induced by RA at lower doses on gd 10 than on gd 12, but by TCDD at lower doses on gd 12 than on gd 10. Sensitivity to TCDD-induced hydronephrosis was similar on both gd 10 and 12. The limb bud defects were only observed when RA was administered on gd 10, not when given on gd 12. No other soft tissue or skeletal malformations were related to administration of TCDD or RA. No effect of TCDD was observed on the incidence or severity of limb bud defects induced by RA, nor did RA influence the incidence or severity of hydronephrosis induced by TCDD. However, the incidence of cleft palate was dramatically enhanced by coadministration of the xenobiotic and vitamin. On both gd 10 and 12, the dose-response curves for cleft palate induction were parallel, suggesting some similarities in mechanism between the two compounds. However, combination treatment resulted in a synergistic response that varied with the stage of development and was tissue specific.     

Teratogenic effects of 2,3,7,8-tetrabromodibenzo-p-dioxin and three polybrominated dibenzofurans in C57BL/6N mice

Brominated flame retardants involved in many industrial uses contain polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs) as contaminants. The levels of these contaminants can be dramatically increased by combustion. These chemicals are closely related in structure to the polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), of which 2,3,7,8-tetrachloridibenzo-p-dioxin (TCDD) is the most toxic isomer. TCDD and related PCDFs are potent mouse teratogens inducing cleft palate and hydronephrosis at doses below those at which overt maternal and embryo/fetal toxicity occurs. This study examines the teratogenic effects of 2,3,7,8-tetrabromodibenzo-p-dioxin (TBDD), 2,3,7,8-tetrabromodibenzofuran (TBDF), 1,2,3,7,8-pentabromodibenzofuran (1PeBDF), and 2,3,4,7,8-pentabromodibenzofuran (4PeBDF) in C57BL/6N mice treated on gestation day (gd) 10 and examined on gd 18. Pregnant dams were treated with 0-4000 micrograms of each congener per kilogram body weight in 10 ml corn oil/kg. Dose selection was based on the relative toxicity of the chlorinated isomers. Maternal toxicity and developmental toxicity were assessed, and the hard palate and kidney, the target organs for the teratogenic effects of TCDD and related compounds, were examined for structural abnormalities. While the maternal liver weight increased at all dose levels examined for all four compounds, there was no evidence of any maternal toxicity. Embryo/fetal mortality was increased only at greater than or equal to 500 microgram TBDF/kg, while fetal weight increased in a dose-related manner following exposure to TBDD and TBDF. All compounds produced hydronephrosis (HN) at doses below that at which cleft palate (CP) occurred. The incidence of HN was significantly increased above background levels at the following doses (micrograms/kg): TBDD, 3; TBDF, 25; 1PeBDF, 500; 4PeBDF, 400. The LOELs (micrograms/kg) for CP were: TBDD, 48; TBDF, 200; 1PeBDF, 4000; 4PeBDF, 2400. The cleft palate incidence for all four brominated compounds and TCDD could be fit to a common slope, compatible with the concept that these chemicals all exert their teratogenic effects through a common mechanism. The potency of these chemicals, relative to TCDD as 1 for the induction of cleft palate, is TBDD, 0.24; TBDF, 0.10; 1PeBDF, 0.004; and 4PeBDF, 0.005. Previous studies from our laboratory had determined that the chlorinated dibenzofuran isomers had relative potencies of 0.05 (TCDF), 0.03 (1PeCDF), and 0.09 (4PeCDF). Thus, bromination decreases the teratogenic activity of TBDD relative to TCDD and of both 1- and 4PeBDF relative to the chlorinated isomers. However, substitution of bromines for chlorines increases the potency of TBDF relative to TCDF.(ABSTRACT TRUNCATED AT 400 WORDS)     

C57BL/6J糖尿病小鼠模型的优化研究

目的 优化链脲佐菌素（streptozotocin,STZ）诱导的C57BL/6J糖尿病小鼠模型。方法 采用单用不同剂量STZ（180 mg·kg^-1单次给药和275 mg·kg^-1均分5次,每次55 mg·kg^-1,连续5 d）或4周高脂饮食联合不同剂量STZ（50 mg·kg^-1单次给药;100 mg·kg^-1单次给药;150 mg·kg^-1单次给药;200 mg·kg^-1均分2次给药,间隔72 h）,建立糖尿病小鼠模型,检测各组小鼠空腹血糖、体质量、日饮水量及日进食量,比较各组造模成功率及稳定性。结果 STZ 180 mg·kg^-1单次给药、高脂饮食4周+STZ 150 mg·kg^-1单次给药、高脂饮食4周+STZ 200 mg·kg^-1均分2次给药得到的糖尿病小鼠模型,其高血糖的持续时间较长且稳定。结论 STZ 180 mg·kg^-1单次给药是较为理想的1型糖尿病模型;4周高脂饮食联合STZ 150 mg·kg^-1单次给药或200 mg·kg^-1均分2次给药均是较为理想的2型糖尿病模型。     

Teratogenicity of three polychlorinated dibenzofurans in C57BL/6N mice

Polychlorinated dibenzofurans (PCDFs) are widespread environmental contaminants which have been detected in human tissues and implicated in several poisoning incidents. Their toxic effects are similar to those observed with other related halogenated aromatic hydrocarbons such as TCDD. The teratogenic effects of three PCDFs, 1,2,3,7,8-pentachlorodibenzofuran (1-PeCDF), 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF), and 1,2,3,4,7,8-hexachlorodibenzofuran (HCDF), were assessed in C57BL/6N mice. Pregnant mice were exposed on Gestation Days 10-13 to 10 ml corn oil/kg containing PCDFs. The dams were killed on Gestation Day 18 and maternal and fetal toxicity were assessed. All three compounds were highly teratogenic, with very steep and parallel dose-response curves for the two diagnostic indicators of dioxin-like teratogenicity, hydronephrosis, and cleft palate. 4-PeCDF was the most teratogenic with an ED50 of 36 micrograms/kg for cleft palate and 7 micrograms/kg for hydronephrosis. 4-PeCDF was approximately 4 times as potent as 1-PeCDF and 10 times as potent as HCDF. The teratogenic responses occurred at a dose below that where any obvious maternal or fetal toxicity was detected. Thus, these three compounds cause teratogenic responses similar to those seen with TCDD but are only 1/10 to 1/100 as potent.     

Comparison of 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated hepatotoxicity in C57BL/6J and DBA/2J mice

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examined by clinical chemistry and liver histopathology in Ah-responsive C57BL/6J (C57) and Ah-nonresponsive DBA/2J (DBA) mice. Hepatotoxicity was assessed at 1, 3, and 7 d following a single ip injection of TCDD at doses that maximally induce hepatic aryl hydrocarbon hydroxylase (AHH) activity (3 micrograms/kg for C57 and 30 micrograms/kg for DBA mice) and at doses approaching the LD50 (150 micrograms/kg for C57 and 600 micrograms/kg for DBA mice). Histological examination of liver sections was found to be a more sensitive detection method for TCDD-induced hepatic changes than clinical chemistry analyses. Dramatic differences in the development and type of liver injury were observed between TCDD-treated C57 and DBA mice. C57 mice given 3 micrograms TCDD/kg developed mild to moderate hepatic lipid accumulation in the absence of both inflammation and necrosis. Severe fatty change and mild inflammation and necrosis occurred in C57 mice that received 150 micrograms TCDD/kg. In contrast, DBA mice exposed to 30 micrograms TCDD/kg developed hepatocellular necrosis and inflammation without any fatty change. Only slight hepatic lipid accumulation occurred with some necrosis and inflammation in DBA mice given 600 micrograms TCDD/kg. The Ah locus may play a role in determining the sensitivity of C57 mice to the steatotic effects of TCDD.     

The Structure-Dependent Effects of Heptachlorodibenzofuran Isomers in Male C57BL/6 Mice: Immunotoxicity and onooxygenase Enzyme Induction

The Structure-Dependent Effects of Heptachlorodibenzofuran Isomersin Male C57BL/6 Mice: Immunotoxicity and Monooxygenase EnzymeInduction. DICKERSON, R., HOWIE, L., DAVIS, D., AND SAFE, S.(1990). Fundam. Appl. Toxicol. 15,298/307. The dose-responseeffects of the 1,2,3,4,6,7,8-, 1,2,3,4,7,8,9-, 1,2,3,4,6,8,9-,and 1,2,3,4,6,7,9-heptachlorodibenzofurans (HpCDFs) on the splenicplaque-forming cell (PFC) response to sheep erythrocytes andon the induction of hepatic microsomal aryl hydrocarbon hydroxylase(AHH) and ethoxyresorufin-O-deethylase (EROD) activities weredetermined in male C57BL/6 mice. The ED50 values for the decreasein the PFCs/spleen, the number of PFCs/10 viable cells, andthe induction of AHH and EROD activities were 1,2,3,4,6,7,8-HpCDF,0.011,0.018,0.11, and 0.315 /imol/kg, respectively; 1,2,3,4,7,8,9-HpCDF,0.012, 0.054, 0.70, and 0.20 Mmol/kg, respectively; 1,2,3,4,6,7,9-HpCDF,1.2, 1.3, >43, and >43 Mmol/kg, respectively, 1,2,3,4,6,8,9-HpCDF,1.5, 3.4, 22, and 22 Mmol/kg, respectively. It was apparentfrom these studies that the 2,3,7,8-substituted HpCDF isomers(1,2,3,4,6,7,8- and 1,2,3,4,7,8,9-) were significantly morepotent than the compounds which contained only three lateralCl groups. These results were obtained using a multiple dosingregimen in which 10 separate doses of the HpCDF isomers wereadministered to the mice by intraperitoneal injection over aperiod of 12 days. However, when the mice were treated witha single dose of an HpCDF congener, which was equivalent tothe total dose used in the multiple dose study, the responseswere comparable. A comparison of the relative immunotoxic potenciesof the 2,3,7,8-substituted HpCDFs and 2,3,7,8-tetrachlorodibenzo-/>-dioxinshowed that the latter compound was approximately 10 times moreactive than the HpCDFs     

6-Methyl-1,3,8-trichlorodibenzofuran (MCDF) as a 2,3,7,8-tetrachlorodibenzo-p-dioxin antagonist in C57BL/6 mice

6-Methyl-1,3,8-trichlorodibenzofuran (MCDF), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and TCDD plus MCDF were administered to C57BL/6 mice and their effects on several aryl hydrocarbon (Ah) receptor-mediated responses including hepatic microsomal aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) induction, immunotoxicity and teratogenicity were determined. MCDF did not induce hepatic microsomal AHH and EROD at doses up to 500 mumol/kg, however, co-administration of MCDF (50 mumol/kg) with a dose of TCDD which elicited a submaximal induction response (i.e. ED80-100, 15 nmol/kg) resulted in some small but significant inhibition of the induction of hepatic microsomal AHH and EROD (14 and 17%, respectively) compared to that observed with TCDD alone. Co-administration of TCDD and other doses of MCDF (10, 100, 200 or 500 mumol/kg) did not effect the induction response. These results were in contrast to the effectiveness of MCDF as an antagonist of the induction of AHH and EROD by TCDD in the rat (up to 50% inhibition of monooxygenase induction). Administration of MCDF (4, 20 and 40 mumol/kg) to C57BL/6 mice caused some inhibition of the splenic plaque-forming cell response to sheep erythrocytes only at the highest dose (26% decrease); the interaction of MCDF (4, 20 and 40 mumol/kg) and an immunotoxic dose of TCDD (3.7 nmol/kg) resulted in significant protection from the immunotoxic effects of TCDD at the 2 higher dose levels of MCDF. Similarly, MCDF (400 mumol/kg) did not cause cleft palate in mice but at this dose level MCDF afforded some protection from TCDD (20 micrograms/kg)-mediated cleft palate in mice. However, studies utilizing [3H]TCDD suggested that the protective effects may be due to modulation of TCDD reaching the palate in the co-treated animals (MCDF plus TCDD). Although both MCDF and Aroclor 1254 were both weak Ah receptor agonists in C57BL/6 mice, the former compound was much less effective as a TCDD antagonist. The observed species-specific effects for these 2 TCDD antagonists may be related species-dependent differences in receptor structure and receptor-ligand (i.e. agonist or antagonist) interactions.     

Immunosuppressive and Monooxygenase Induction Activities of Highly Chlorinated Diphenyl Ether Congeners in C57BL/6 and DBA/2 Mice

The dose-response effects of 2,2',3,3',4,5,5',6,6'–,2,2',3,3',4,4',5,6,6'-and2,2',3,3',4,4',5,5',6-nonachlorodiphenyl ether (non-aCDE) anddecachlorodiphenyl ether (decaCDE) on the splenic plaque-formingcell (PFC) response to sheep red blood cells (SRBCs) and theinduction of hepatic microsomal ethoxyresorufin O-deethylase(EROD) activity was determined in aryl hydrocarbon (Ah)-responsiveC57BL/6 and less Ah-responsive DBA/2 mice. All the congenersexhibited immunotoxicity at doses between 2.5 and 10 µmol/kgin C57BL/6 mice whereas in DBA/2 mice doses25 µmol/kgwere required to cause inhibition of the PFC response to SRBCs.The results also showed that the nonaCDE isomers and decaCDEwere more active as inducers of hepatic EROD activity in C57BL/6than DBA/2 mice; however, there was not a correlation betweenthe induced EROD activity and the CYP1A1 and CYP1A2 mRNA levelsin the C57BL/6 mice. These data suggested that the immunotoxicityof these compounds was mediated through the Ah receptor. However,the results showed that the immunotoxicity of the nonaCDE isomersand decaCDE was unexpectedly high compared to that of lowerchlorinated diphenyl ethers and there were no apparent structure-activityrelationships among the higher chlorinated congeners. This suggeststhat some of the immunosuppressive effects observed for thenonaCDE isomers and decaCDE may be Ah receptor-independent.     

Effects of thyroid hormones on the induction of cleft palate by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in C57BL/6N mice

The induction of cleft palate by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administered with thyroid hormones triiodothyronine (T3) or thyroxine (T4) was investigated in C57BL/6N mice. Timed-pregnant mice were treated with vehicle, TCDD, T3, T4, TCDD plus T3, or TCDD plus T4 on Days 10 to 13 of gestation. No cleft palates were observed in any control fetuses in this study, nor have there been any cleft palates in 1193 fetuses or 154 control litters in the past 24 months. TCDD (3 micrograms/kg/day) caused about 8% cleft palates per litter, while T3 (120, 240, 480 micrograms/kg/day) and T4 (625, 1250, 2500 micrograms/kg/day) resulted in no more than 1.2% cleft palates per litter in any of the treatment groups and the incidence was not dose related. The combination of TCDD (3 micrograms/kg/day) plus T3 at 120, 240, and 480 micrograms/kg/day resulted in 15.9, 20.6, and 31.4% cleft palates per litter, respectively. TCDD plus T4 at 625, 1250 and 2500 micrograms/kg/day caused 15.1, 22.9, and 27.2% cleft palates per litter. No cleft palates were observed when large doses of T3 were given in combination with T4. These data demonstrated that coadministration of T3 or T4 with TCDD increased the incidence of cleft palate to incidences greater than expected from the separate administration of the hormones plus TCDD.     

Phenotypic Analysis of Spleen, Thymus, and Peripheral Blood Cells in Aged C57BI/6 Mice Following Long-Term Exposure to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

A mouse model was used to identify potential biomarkers of exposureto the environmental contaminant 2,3,7,8-tetrachiorodibenzo-p-dioxin(TCDD). Female C57B1/6 mice were treated weekly with 0.2 µgTCDD/kg body weight or vehicle for 14–15 months. Phenotypicanalysis by flow cytometry identified the major cell subpopulationsin the spleen, thymus, and peripheral blood as defined by theexpression of CD4, CD8, B220, and Mac-1 molecules. These subpopulationswere further characterized for the expression of I-A, Pgp-1,CD45RB, and/or T cell receptor antigens (CD3, ß ).A group of young (4 months old) mice was evaluated concurrentlyto document immunophenotype alterations associated with aging.Results showed several age-related changes in phenotype distributionin the spleen and blood, but not in the thymus, despite significantage-dependent thymic involution. The age-dependent changes insplenic phenotypes included a decreased frequency of CD4⁺ cellsand a major shift in the frequency distribution from naive Tcells to effector and memory T cells as defined by Pgp-1 andCD45RB expression. These phenotypic changes in the spleen dueto aging correlated with similar changes in the blood, providingpreliminary support for the use of spleen cells as surrogatesfor blood in the development of biomarkers of immunotoxicity.Long-term exposure to a total cumulative dose 12–13 µgTCDD/kg body weight resulted in no overt toxicity, a 16-foldelevation of hepatic ethoxyresorufin-O-deethylase activity,and residue levels of 1.27 ± 0.16 ng TCDD/g abdominalfat. In comparison to the effects of aging, TCDD treatment producedrelatively subtle changes in immunophenotypes. In the TCDD-treatedthymus, the proportion of CD4^–CD8^– cells was increasedas was the proportion of ⁺ thymocytes. These effects were verysmall but of interest in that similar thymic effects have beenpreviously reported following prenatal exposure to TCDD. Inthe spleen, TCDD exposure did not alter the frequency of CD4⁺or CD8⁺ T cells, B cells, or macrophages but significantly alteredfunctionally discrete subpopulations within the T cell compartment.The most definitive change in TCDD-treated mice was a decreasein the frequency of memory T helper cells, defined as CD4⁺ Pgp-1^hiCD45RB^lo, with a concomitant increase in the proportion ofnaive T helper cells identified as CD4⁺Pgp-1^loCD45RB^hi. Thesechanges are consistent with the known immunosuppressive activityof TCDD. Thus, these results identify Pgp-1 and CD45RB as potentialbiomarkers of TCDD immunotoxicity.     

Distribution and excretion of 2,3,7,8-tetrachlorodibenzofuran in C57BL/6J and DBA/2J mice

The distribution and excretion of the toxic pollutant, 2,3,7,8-tetrachlorodibenzofuran (TCDF), was studied in male C57BL/6J and DBA/2J mice (22–29 g). [¹⁴C]TCDF was administered iv at a dose of 0.1 μmmol/kg. The liver was the major site of TCDF accumulation, with more TCDF in the livers of C57BL/6J mice compared to DBA/2J mice. TCDF had a half-life of approximately 1.8 days in the livers of both strains. At 7 hr and 1 day, respectively, radioactivity was redistributed to adipose tissue of C57BL/6J mice and DBA/2J mice. The terminal $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of TCDF in adipose tissue of C57BL/6J mice was 1.1 days, whereas it was 6.8 days in DBA/2J mice; the sixfold longer half-life in DBA/2J mice may be related to the approximately 36% greater adipose tissue content of this strain which may sequester more TCDF. More than 80 and 55% of the dose was excreted in the feces of C57BL/6J and DBA/2J mice, respectively, within 10 days as polar metabolites. The whole body half-life of TCDF was 2 days in C57BL/6J and 4 days in DBA/2J mice. Thus, DBA/2J mice sequester more of the TCDF dose in adipose tissue, accounting for a relatively slower rate of clearance and lower concentrations of TCDF at the putative target site(s) for toxic action.     

Hemopoietic progenitor cells are sensitive targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin in C57BL/6J mice.

Treatment of adult C57BL6J mice with tetrachlorodibenzo-p-dioxin (TCDD) elicits altered bone marrow hemopoietic cellular potentials and markedly reduced T-lymphoid-reconstituting activity. The latter has been hypothesized to play a role in TCDD-induced thymic atrophy. To investigate cellular targets responsible for reduced prothymocyte capacity, bone marrow cells from TCDD-treated C57BL/6J mice were assessed for hemopoietic alterations within the lineage-negative (lin-) compartment by the examination of Sca-1 and c-Kit levels. Lin- hemopoietic cells from C57BL/6J mice, treated with 30 microg/kg of TCDD, were assessed for phenotypic alterations following 24 h through 31 days. The responses of lin- cells to TCDD doses ranging from 0.3 to 30 microg/kg were also assessed at 2 days following TCDD treatment. The data reveal increases in the number of bone marrow lin- Sca-1+ c-Kit+ cells, relative to control, over 24 h through 31 days following treatment, as well as dose-dependent increases in this population when examined at 2 days. Increases in lin- Sca-1+ c-Kit- cells occurred on a more transient basis and were also dependent upon TCDD dose. These data suggest that proliferation and/or differentiation processes of hemopoietic stem cells are affected by TCDD and that these effects contribute to a reduced capacity of bone marrow to generate pro-T lymphocytes.     

A physiologically based pharmacokinetic model for 2,3,7,8-tetrachlorodibenzo-p-dioxin in C57BL/6J and DBA/2J mice

A five-compartment physiologically based pharmacokinetic (PB-PK) model was developed to describe the time course of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the tissues of both C57BL/6J and DBA/2J mice. The PB-PK model included binding in blood and two hepatic binding sites, one in the cytosol and the other in the microsomes. First-order metabolism occurred in the liver. Model simulations were compared to literature results for the disposition of a single intraperitoneal dose of 10 micrograms/kg of [3H]TCDD, reported by Gasiewicz et al. [Drug Metab. Dispos. 11 (1983) 397-403]. In contrast to previous speculation, the greater accumulation of TCDD in the liver of the C57BL/6J mouse, as compared to the DBA/2J mouse, was not attributable to the higher fat content in the DBA/2J mouse. Instead, the disposition of TCDD in these mice was more dependent on the affinity of the microsomal binding proteins than on fat content. The microsomal dissociation constant in the C57BL/6J mouse estimated by the PB-PK model was about one-third its value in the DBA/2J mouse (20 versus 75 nM), i.e. there is more avid microsomal binding in the liver of the C57BL/6J mouse. In the concentration range covered in these time-course studies, the cytosolic receptor, with its low capacity and very high affinity binding characteristics, does not play a major role in determining the overall tissue distribution pattern. The concentration and affinity of the microsomal binding protein in the liver appear to be primarily responsible for explaining the differences in the liver/fat concentration ratios between various strains and species of laboratory animals.