Use of Model-Based Compartmental Analysis to Study Effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Vitamin A Kinetics in Rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic,widespread environmental contaminant that has dramatic adverseeffects on the metabolism of vitamin A. We used model-basedcompartmental analysis to investigate sites and quantitativeimpacts of TCDD on vitamin A kinetics in rats given an oralloading dose of TCDD in oil (3.5 µg/kg) followed by weeklymaintenance doses (0.7 µg/kg) or oil only. [³H]retinylin its plasma transport complex (experiment 1) or lymph containingchylomicrons labeled mainly with [³H]retinyl esters (experiment2) were administered iv, and tracer kinetics in plasma, liver,carcass, urine, and feces were measured for up to 42 days. TCDDtreatment caused significant reductions in liver vitamin A levelsand significant changes in tracer kinetics and tracer excretion.A four-compartment model was used to fit tracer data for experiment1; for experiment 2, compartments were added to describe themetabolism of newly absorbed vitamin A. The compartmental modelspredict that TCDD caused a slight delay in plasma clearance(via an increased recycling to plasma), and in liver processing,of chylomicronderived vitamin A. Models for both experimentspredict that TCDD exposure did not affect the fractional uptakeof plasma retinol from the rapidly turning-over extravascularpool, but it doubled the fractional transfer of recycled retholfrom slowly turning-over pools of vitamin A to plasma The residencetime for vitamin A was reduced by 70% in TCDD-treated rats,transfer into urine and feces was tripled, and vitamin A utilizationrates were significantly increased. Since our results do notindicate that retino1 esterification is inhibited, we hypothesizethat some of the significant effects of TCDD on vitamin A metabolismresult from increased catabolism and mobilization of vitaminA from slowly turning-over pools (especially the liver).     

Tissue Distribution and Toxicokinetics of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Rats after Intravenous Injection

Tissue Distribution and Toxicokinetics of 2,3,7,8-Tetrachlorodibenzo-p-dioxinin Rats after Intravenous Injection. WEBER, L. W. D., ERNST,S. W., STAHL, B. U., AND ROZMAN, K. (1993). Fundam. Appl. Toxicol.21, 523–534. Male Sprague-Dawley rats (240–290 g) received intravenouslya nonlethal (9.25 µg/kg) or a lethal (72.7 µg/kg)dose of ¹⁴C-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)administered as an emulsion. Animals were euthanized between5 min and 16 days (lethal dose) or 32 days (nonlethal dose)after treatment. Tissue distribution was considered completeafter 24 hr, as by this time radioactivity levels in white adiposetissue had reached a maximum. The highest levels of radioactivitywere found in liver (5% of dose/g tissue), followed by whitefat (1% of dose/g tissue); serum was lowest at 0.01% of dose/mlserum. Relatively high levels of radioactivity were also detectedin most known target organs of TCDD toxicity, e.g., brown fat,adrenals, and thyroid. The pattern of organ distribution ofTCDD was essentially the same after the lethal and the nonlethaldose, but did not follow a simple lipophilicity relationship,as levels in liver were higher than those in white fat, andthose in brain were extremely low. A pool of TCDD in liposomesinitially trapped in lung and spleen was redistributed within24 hr mainly to liver and adipose tissue. Affinity of TCDD tostorage fat seemed to play a more important role as a drivingforce for redistribution than did induction of cytochrome P4501A2. The terminal slope of elimination of TCDD from tissuesindicated a half-life of 16 days after the nonlethal dose. Afterthe lethal dose radioactivity declined in all tissues for 2to 8 days and then increased again, reflecting shrinking tissuevolumes as well as remobilization of TCDD caused by the processof body mass wasting. Distribution data for 17 tissues and serumwere subjected to regression analysis and resulted in up totwo uptake phases and up to three elimination phases for a giventissue. After the nonlethal dose TCDD was mainly excreted viafeces; combined urinary and fecal excretions occurred with abiological half-life of 16.3 ± 3.0 days. Much longerhalf-lives were detected in white fat and skin. After the lethaldose, the fecal excretion of TCDD-derived radioactivity decreasedafter 8 days, and urinary excretion increased starting 12 daysafter dosing. Radioactivity in liver and white fat and the extractableportion in feces was mainly unchanged TCDD, as determined bythin-layer chromatography. Radioactivity in urine indicatedthe presence of a metabolite(s) of TCDD only.     

Drug Metabolism in Rats with Cancer Induced by N-Nitrosodiethylamine and Phenobarbital

Abstract: The metabolism of R- and S-warfarin in vivo and in vitro, bufuralol in vitro, and antipyrine and debrisoquine in vivo were studied in rats with cancer induced by N-nitrosodiethylamine and phenobarbital treatment. Microsomal cytochrome P-450 content was greatly reduced in both healthy and cancerous parts of the livers of tumour-bearing animals. The specific activities of R-warfarin and bufuralol 1′-hydroxylases were significantly elevated in rats with cancer. The activities of S-warfarin hydroxylases expressed per mg microsomal protein were reduced in animals with cancer, whereas those of R-warfarin and bufuralol 1′-hydroxylases were not. The urinary excretion of R-7-hydroxywarfarin was increased and those of S-6- and S-4′-hydroxywarfarin decreased in rats with cancer. The correlations between microsomal formation and urinary excretion of all warfarin metabolites were poor, except for R-7-hydroxywarfarin. Antipyrine oxidation was increased in the cancerous state but the urinary metabolic profiles were similar in rats with cancer and in controls. The metabolism of debrisoquine was decreased in tumour-bearing animals. Antipyrine metabolism did not show any correlation with either warfarin or debrisoquine metabolism, whereas several relationships were observed between warfarin and debrisoquine metabolism and between warfarin and bufuralol metabolism.     

Relationship of Alterations in Energy Metabolism to Hypophagia in Rats Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Relationship of Alterations in Energy Metabolism to Hypophagiain Rats Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin. POTTER,C. L., MENAHAN, L. A., AND PETERSON, R. E. (1986). Fundam. Appl.Toxicol. 6, 89–97. Efficiency of energy utilization wasevaluated temporally in 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD, 50 µg/kg)-treated male Sprague—Dawley rats(275–300 g), their pair-fed counterparts, and a groupwith ad libitum access to ground feed. TCDD treated rats exhibiteda progressive reduction in feed intake and body weight. Theweight loss of vehicle-treated rats, pair-fed to the TCDD-treatedgroup, was comparable to that found in rats receiving TCDD.Following treatment, rats administered TCDD were as efficientin absorbing feed energy from the gut as control rats. Thiswas evidenced by similar relative digestible energy values inTCDD-treated rats, their pair-fed partners, and a group withad libitum access to feed. Equivalent decreases in oxygen consumptionand carbon dioxide production in TCDD-treated rats and theirpair-fed counterparts, relative to rats with ad libitum accessto feed, suggested that the decrease in both of these parametersin TCDD-treated rats was secondary to hypophagia and/or weightloss. Decline of respiratory quotient (RQ) to almost 0.7 inboth TCDD-treated rats and their pair-fed counterparts is indicativeof fat combustion. By Day 17 post-treatment, RQ increased significantlyin the TCDD-treated and pair-fed groups possibly due to a limitationin the availability of lipid stores. Also, TCDD-treated ratsand their pair-fed partners diminished their water intake toa similar extent without reducing urine output. Likewise, urinaryexcretion of both energy and urea was decreased to the sameextent in rats treated with TCDD as it was in their pair-fedcounterparts. However, TCDD-treated rats tended to excrete moreurinary ammonia than their pair-fed partners on Days 10 and16 post-treatment. Thus, TCDD treatment does result in a reductionof caloric intake in the rat, yet efficiency of energy utilizationis preserved.     

Comparison of the T Cell-Independent Antibody Response of Mice and Rats Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmentalcontaminant that produces adverse effects on the immune systemof experimental animals. In this study, the effect that TCDDhas on the antibody plaque-forming cell (PFC) response to theT cell-independent (TI) antigen trinitrophenyl-lipopolysaccharide(TNP-LPS) was compared in adult female B6C3F1 mice and F344rats. Mice or rats were given a single intraperitoneal injectionof TCDD at doses ranging from 1 to 30 µg/kg, 7 days priorto immunization with TNP-LPS by intravenous injection. Threedays later body, spleen, thymus, and liver weights were measuredand the PFC response to TNP-LPS was determined. Thymus weightswere decreased at 10 and 30 µg TCDD/kg, whereas spleenweights were decreased and liver weights increased in mice dosedat 3,10, and 30 µg/kg. Mice dosed at 10 and 30 µgTCDD/kg had suppressed PFC responses and serum hemagglutinationliters. In rats, thymus weights were decreased and liver weightsincreased at 3, 10, and 30 µg TCDD/kg; however, the PFCresponse and serum hemagglutination titers to TNP-LPS were suppressedonly at 30 µg/kg TCDD. TCDD did not affect splenic lymphocytesubsets evaluated by flow cytometry. These results indicatethat TCDD suppresses the TI antibody response to TNP-LPS inboth B6C3F1 mice and F344 rats, with mice more sensitive tosuppression by TCDD than rats.     

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.     

Hypophagia-Induced Weight Loss in Mice, Rats, and Guinea Pigs Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Hypophagia-lnduced Weight Loss in Mice, Rats, and Guinea PigsTreated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin. KELLING, C.K, CHRISTIAN, B. J., INHORN, S. L., AND PETERSON, R. E. (1985).Fundam. Appl. Toxicol. 5, 700–712. C57BL/6 mice treatedwith 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 360 µ/kg)displayed a significant reduction in feed intake and body weightuntil just before death, when they developed ascites and subcutaneousedema. This caused body weight of the mice that died to suddenlyincrease during the terminal stage of toxicity. TCDD-treatedmice that survived did not develop ascites or edema, and maintaineda body weight that was slightly less than that of pair-fed mice.Cumulative lethality in TCDD-treated mice (69%) was greaterthan that of pair-fed controls (14%). In guinea pigs treatedwith TCDD (2 µ/kg) both the time course and magnitudeof hypophagja were closely associated with weight loss. Pair-fedguinea pigs did not lose quite as much weight as TCDD-treatedanimals because their total body water content was higher. Waterintake in pair-fed guinea pigs was greater than that of TCDD-treatedanimals. The time course and magnitude of lethality tended tobe similar in TCDD-treated guinea pigs (81%) and pair-fed controls(64%). In Fischer F-344 rats treated with TCDD (100 µg/kg)body weight loss was associated with a reduction in both feedand water intake. The time course and magnitude of weight lossin TCDD-treated and pair-fed rats was essentially identical.Lethality was higher in TCDD-treated rats (95%) than pair-fedcontrol animals (48%). Taken together, these findings suggestthat hypophagia is responsible for the loss of adipose and leantissue in mice, guinea pigs, and rats treated with a LD70–95dose of TCDD. Under these dosage conditions, weight loss contributesmore to the lethality of guinea pigs than to that of FischerF-344 rats or C57BL/6 mice     

The Importance of Pharmacokinetics in Determining the Relative Potency of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and 2,3,7,8-Tetrachlorodibenzofuran

The Importance of Pharmacokinetics in Determining the Relative Potency of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and 2,3,7,8-Tetrachlorodibenzofuran. Devito, M. J., and Birnbaum, L. S. (1995). Fundam. Appl. Toxicol.24, 145-148.Polychlorinated dibenzo-p-dioxins and dibenzofurans induce exthoxyresorufin-O-deethylase (EROD) activity, a marker for CYP1A1. Differences in potency of these compounds can be attributed to differences in their affinity for the Ah receptor as well as differences in pharmacokinetics. To test the role of pharmacokinetics in the in vivo potency of these chemicals, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzufuran (TCDF) were administered to female B6C3F1 mice for 4 or 13 weeks of treatment and EROD activity in liver and skin was determined. The doses were designed to be equally potent based on the published Toxic Equivalency Factor (TEF) values for these compounds. Mice received either 150 ng TCDD/kg/day or 1500 ng TCDF/kg/day, 5 days/week for either 4 or 13 weeks. At 4 weeks, hepatic EROD was induced 11- and 7-fold by TCDD and TCDF, respectively. These data indicate that the published TEFs accurately estimated the relative potency of TCDF after 4 weeks of treatment. After 13 weeks, hepatic EROD was induced 41- and 6-fold by TCDD and TCDF, respectively. The TEFs did not accurately estimate the relative inductive potency of these compounds when compared after 13 weeks of treatment. The inability of the TEFs to predict the relative potency of these compounds after 13 weeks of treatment may be due in part to the differences in the pharmacokinetic properties of each congener. The half-life of TCDF and TCDD is approximately 2 and 15 days, respectively. Steady-state levels of TCDD were not attained by 4 weeks, which is reflected in the increase in hepatic EROD between 4 and 13 weeks. In contrast, steady-state levels of TCDF were reached within 4 weeks. Thus, induction of hepatic EROD remained constant from 4 to 13 weeks. Similar results were observed for skin EROD activity. These data demonstrate that estimates of the relative potency of two chemicals is dependent upon the dosing regimen and the time of euthanization. Thus TEFs derived from short-term assays may not adequately predict the relative potencies of this class of compounds following chronic exposure.     

Toxicokinetics of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Female Sprague-Dawley Rats Including Placental and Lactational Transfer to Fetuses and Neonates

The toxicokinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)in virgin female Sprague-Dawley (S-D) rats, the effects of pregnancy,parturition, and lactation on the distribution and/or redistributionof TCDD, and placental and lactational transfer to fetuses andneonates were investigated. Doses of 5.6 µg/kg of ¹⁴C-labeledTCDD were given iv either to virgin rats or to pregnant ratson Day 18 of gestation and 1 day postparturition,, respectively.Virgin females were terminated on Day 1, 2, 4, 8, 16, or 32,pregnant rats on Day 1, 2, 4, or 8, after dosing to collecttissues. Two groups of neonates, which were born either to TCDD-treatedor nontreated dams were crossfostered beginning on the firstday after birth to simulate exposure to TCDD either by lactationaltransfer only or by both placental and lactatlonal transfer.Serum and 18 different tissues were collected from virgin ratsto evaluate the kinetic profile of TCDD. Serum and tissue samplesfrom liver, kidney, brown, and white adipose tissue were collectedfrom pregnant and postparturition rats. Liver samples from fetusesand neonates were obtained on Gestational Days 19 and 20, orpostnatally on Days 1 and 5. TCDD equivalents were caku latedfrom measurement of radioactivity. The results show that theprofile of TCDD distribution in virgin female rats similar tothat in male rats but that the concentration of TCDD in mosttissues was higher in females than in males. The ratios of tissueand serum areas under the curve and the ratio of half-livesbetween females and males were very similar to the ratio ofthe LD50s between male and female S-D rats, suggesting thatthe small gender difference in the acute toxicity of TCDD wasprobably due to the difference in toxicokinetics alone. Pregnancyand parturition as well as lactation significantly altered thetoxicokinetic profile of TCDD probably due to changing bodycomposition during pregnancy and nursing. The results also indicatedthat TCDD was predominantly transferred to the offspring bylactation rather than via the placenta. This highly efficientlactational transfer of TCDD in rats implied that breast feedingof children by mothers can result in effective transfer of TCDDvia mother's milk.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin in Pregnant Long Evans Rats: Disposition to Maternal and Embryo/Fetal Tissues

Prenatal exposue to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)interfereswith fetal development at doses lower than those causing overttoxicity in adult animals. In a multigeneration study (Murrayet al., 1979), female rats that were administered 0.01 µgTCDD/kg/day in their diet did not experience reduced fertility;however, reduced fertility was seen in the F₁ and F₂ generations.Exposure to TCDD during development produces alterations inthe reproductive system of the developing pups, such as delayedpuberty and reduced sperm counts in males (Mably et al., 1992a;Gray et al., 1995) and malformations in the external genitaliaof females (Gray and Ostby, 1995). Therefore, the objectivesof this study were to determine maternal and fetal tissue concentrationsof TCDD that are associated with the adverse reproductive effectsseen by Gray and co-workers. Pregnant Long Evans rats receiveda single oral dose of 1.15 µg [₃H]TCDD/kg on GestationDay (GD) 8 and maternal as well as fetal tissue concentrationsof TCDD were measured on GD9, GD16, and GD21. On GD9, the highestlevel of TCDD localized in the maternal liver (25.1% dose).In addition, the amount reaching all the embryos on GD9 was0.01% of the administered dose, which resulted in a concentrationof 0.02% dose/g . The amount of TCDD reaching the fetal compartment(fetuses + placentas) increased to 0.12% dose/tissue on GD16and 0.71% by GD21. The concentration of TCDD within the fetalcompartment (0.01% dose/g) on GD16 was comparable to that foundin the maternal blood and spleen. Concentrations of TCDD ina single embryo/fetus were 39.6, 18.1, and 22.1 pg/g on GD9,GD16, and GD21, respectively. Estimates of hepatic half-lifeof elimination in pregnant rats suggested that TCDD may be eliminatedfaster in pregnant LE rats. Therefore, measurements of biliaryelimination were made in pregnant and nonpregnant LE rats tocompare rates of metabolism; however, biliary elimination ofTCDD is not affected by pregnancy. In conclusion, this doseadministered during a critical period of organogenesis causesadverse effects on the developing reproductive system of rodents.This dose produced a body burden of 22.1 pg TCDD/g within asingle fetus on GD21. This indicates that low-level TCDD exposureduring the perinatal stage of life can produce adverse effectswithin the developing pups.     

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.     

Age-Related Changes in Dermal Absorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and 2,3,4,7,8-Pentachlorodibenzofuran

Age-Related Changes in Dermal Absorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxinand 2,3,4,7,8-Pentachlorodibenzofuran. BANKS, Y. B., BREWSTER,D. W., AND BIRNBAUM, L. S. (1990). Fundam. Appl. Toxicol. 15,163–173. Changes in the structure and function of agedskin may alter percutaneous absorption of environmental compoundssuch as the halogenated aromatic hydrocarbons. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)and 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) were previouslyfound to be poorly absorbed in 3 month male Fischer 344 ratswithin 3 days after dermal administration. In order to examineage-related changes in dermal absorption and changes in potentialfor systemic exposure, the absorption, distribution, and eliminationof TCDD and 4PeCDF were examined in male Fischer 344 rats ofvarious ages (TCDD: 10, 36, and 96 week; 4PeCDF: 10, 36, 64,96, and 120 week). Each compound was applied at a dose of 0.1µmol/kg and/or 0.04 µmol in 60 µ1 acetoneto a preclipped region of the back and covered with a stainless-steelperforated cap. Rats were housed in individual metabolism cagesfor 3 days. Dermal absorption of both compounds was decreasedin older age groups compared to 10 week rats. The major tissuedepots for both compounds were liver, adipose, skin, and muscleand in comparable age groups, the liver.fat ratio was greaterin 4PeCDF-treated animals. Age-related changes in the distributionof the administered dose and the absorbed dose varied with thecompound as well as the depot. Elimination of TCDD and 4PeCDFwas limited at all ages. Results indicate that percutaneousabsorption of these compounds is decreased in older animals,suggesting that systemic bioavailability may be decreased inolder organisms following dermal exposure to TCDD or 4PeCDF.     

雷公藤红素对蛋氨酸-胆碱缺乏饮食致小鼠NASH的干预作用及机制研究

目的:研究雷公藤红素对蛋氨酸-胆碱缺乏(MCD)饮食致小鼠非酒精性脂肪性肝炎(NASH)的干预作用及可能机制。方法:将雄性C57BL/6J小鼠随机分为正常对照组、模型组和雷公藤红素低、高剂量组[0.5、1 mg/(kg·d)],每组7只。正常对照组小鼠给予蛋氨酸-胆碱充足饮食,模型组和给药组小鼠给予MCD饮食以复制NASH模型;与此同时,正常对照组和模型组小鼠灌胃聚氧乙烯蓖麻油,各药物组小鼠灌胃相应药物,灌胃体积均为0.1 m L/g,每日1次,连续4周。观察各组小鼠肝脏形态,并采用苏木精-伊红染色和油红O染色法观察其肝组织的病理学变化;采用酶法检测血清肝酶[天冬氨酸转氨酶、丙氨酸转氨酶]、血清和肝组织中脂质指标[总胆固醇(TC)、三酰甘油(TG)]水平;采用Western blotting法检测小鼠肝组织中核因子κB p65(NF-κB p65)、肿瘤坏死因子α(TNF-α)、白细胞介素6(IL-6)的蛋白表达水平。结果:与正常对照组比较,模型组小鼠肝脏体积缩小且颜色泛黄,表面粗糙,肝组织中可见炎性细胞浸润以及脂肪空泡、脂滴聚集;其血清TC、TG水平均显著降低,血清肝酶水平以及肝组织中TG水平和NF-κB p65、TNF-α、IL-6蛋白表达水平均显著升高(P<0.01)。与模型组比较,各药物组小鼠肝脏表面红润光滑,无褐色斑点,肝组织中炎性细胞、脂肪空泡有所减少,脂滴覆盖面积有所缩小;其血清TC、TG水平均显著升高,血清肝酶水平以及肝组织中TG水平和NF-κB、TNF-α、IL-6(雷公藤红素低剂量组除外)的蛋白表达水平均显著降低(P<0.05或P<0.01)。结论:雷公藤红素能改善MCD饮食致NASH模型小鼠的肝损伤,其作用与减少肝组织中TG堆积、抑制炎症相关因子表达有关。     

Characterization of the Enhanced Responsiveness to Postingestive Satiety Signals in 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-Treated Han / Wistar Rats

Abstract: 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 g?/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.     

Teratology of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in a Complex Environmental Mixture from the Love Canal

The organic phase of a leachate (OPL) from the Love Canal chemicaldump site contains more than 100 organic compounds including2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD). The teratogenicpotential of OPL was determined in two inbred and one hybridmouse strain which differ in their sensitivity to aromatic hydrocarbon(Ah) receptor-mediated toxicity. OPL was orally administeredin corn oil on Days 6–15 of gestation to C57BL/6J mice(Ah^b/ Ah^b) at doses of 0, 0.1, 0.3, 0.5, and 0.7 g kg^–1day^–1 and to DBA/ZJ (Ah^d/Ah^d) females, which were matedwith either DBA/2J or C57BL/6J males, at 0, 0.5, 1, and 2.0g kg^–1 day^–1. In C57BL/6J mice, which express ahigh-affinity Ah receptor that avidly binds TCDD, the ED50'sof OPL for cleft palate and hydronephrosis were 0.44 and 0.11g OPL kg^–1 day^–1, respectively. Maternal mortalitywas 5% at the highest dose. In DBA/2J fetuses, which expressa low-affinity receptor, neither treatment-related cleft palatenor hydronephrosis was induced by dose levels that caused 36%maternal mortality. In hybrid D2B6F1 fetuses, the incidenceof cleft palate reached only 8% at 2 g OPL kg^–1 day^–1but the ED50 for hydronephrosis was 0.76 g OPL kg^–1 day^–1.TCDD was similarly administered to pregnant C57BL/6J mice at0, 0.5, 1, 2, and 4 µg kg^–1 day^–1 and to DBA/2Jmice at 0, 0.5, 2, 4, and 8 µg kg^–1 day^–1.In C57BL/6J fetuses, the ED50's for cleft palate and hydronephrosiswere 4.6 and 0.73 µg TCDD kg^–1 day^–1, respectively.In DBA/2J fetuses the ED50's for cleft palate and hydronephrosiswere 15.0 and 6.4 µg TCDD kg^–1 day^–1, respectively.Both the OPL and TCDD caused maternal hepatomegaly and thymicatrophy in all strains, but increased only C57BL/6J fetal weights.OPL decreased the number of fetuses per C57BL/6J dam at thetwo highest doses but there were no other reproductive effectsin any of the groups. It was concluded that the OPL is teratogenicand that hydronephrosis is a sensitive measure of TCDD toxicityin a complex organic mixture. Based on the ED50's of OPL- andTCDD-induced cleft palate and hydronephrosis in the C57BL/6Jstrain, the OPL had TCDD equivalence of 6.6 and 10.5 ppm, respectively.These values compare closely with the chemical analysis of 3ppm. The results suggest that the teratologic effects are dueprimarily to the TCDD in the OPL and that these effects aremediated through the Ah receptor, but that the maternal thymicatrophy and hepatomegaly were due primarily to the non-TCDDcomponents of the OPL.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin alters the differentiation pattern of human keratinocytes in organotypic culture.

Human exposure to the environmental toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces a severe skin pathology known as chloracne. In these studies we employed a three-dimensional, organotypic model system to study the effects of TCDD on human skin. This model uses the spontaneously immortalized human keratinocyte cell line NIKS and recapitulates both the three-dimensional microenvironment and epithelial-mesenchymal interactions found in intact human skin. Treatment of the organotypic cultures with TCDD causes alterations in the pattern of keratinocyte terminal differentiation. Analysis at both the light and electron microscope levels reveals a fully differentiated cornified layer in TCDD-treated organotypic cultures at earlier time points than observed in vehicle (dimethyl sulfoxide)-treated controls. Furthermore, TCDD-treated organotypic cultures exhibit aberrant distribution of several differentiation-specific protein markers. Basal cells in TCDD- and DMSO-treated organotypic cultures show no differences in proliferation as measured by quantification of 5-bromo-2'-deoxyuridine (BrdU)-positive nuclei. No aberrant BrdU uptake was detected outside of the basal layer. Neither TUNEL labeling nor immunohistochemical staining with an antibody to active caspase-3 revealed increased apoptosis in TCDD-treated organotypic cultures relative to controls. These data clearly indicate that TCDD modulates homeostasis in a model of human stratifying epithelium independent of changes in proliferation and apoptosis, exclusively by impacting keratinocyte terminal differentiation. This TCDD-induced effect on differentiation-specific proteins results in profound changes in the tissue architecture.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibits regression of the common cardinal vein in developing zebrafish.

A role for the aryl hydrocarbon receptor (AHR) pathway in vascular maturation has been implicated by studies in Ahr-null mice. In this study the hypothesis that activation of AHR signaling by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters common cardinal vein (CCV) development in the zebrafish embryo was investigated. The CCV is a paired vessel that grows across the yolk, connecting to the heart. It is extensively remodeled and regresses as the heart migrates dorsally within the pericardium. TCDD significantly reduced CCV growth as early as 44 h post fertilization (hpf), and CCV area was reduced to 63% of control at 62 hpf. This vascular response to TCDD was at least as sensitive as previously defined endpoints of TCDD developmental toxicity in zebrafish. TCDD also blocked regression of the CCV (by 80 hpf), possibly contributing to the "string-like" heart phenotype seen in TCDD-exposed zebrafish larvae. Dependence of the block in CCV regression on zebrafish (zf) AHR2 was investigated using a zfahr2 specific morpholino to knock down expression of AHR2. The zfahr2 morpholino had no effect on CCV regression in the absence of TCDD, but did protect against the TCDD-induced block of CCV regression. This demonstrates that the TCDD-induced block in CCV regression is AHR2 dependent. It is significant that decreased CCV growth occurs before and inhibition of CCV regression occurs concurrent with overt signs of TCDD developmental toxicity. This suggests that alterations of vascular growth and remodeling may play a role in TCDD developmental toxicity in zebrafish.     

Pulmonary Bioavailability and Fine Particle Enrichment of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Respirable Soil Particles

The pulmonary bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) and the enrichment of polychlorinated dioxins (PCDDs)and furans (PCDFs) in fine particles were evaluated to assessthe implications that these factors have on risk and exposureassessments. Respirable subfractions of PCDD-contaminated soilfrom a former 2,4,5-trichlorophenoxyacetic acid manufacturingsite were isolated by chemical dispersion and gravity sedimentation.Analysis of the subfractions revealed that there was a size-dependentenrichment of PCDDs and PCDFs, with smaller particles more highlycontaminated. TCDD was enriched up to 33-fold as compared tounfractionated soil. Soil and laboratory-recontaminated galliumoxide, which served as the positive control, were administeredby intratracheal instillation to female Sprague-Dawley rats.Animals were terminated up to 28 days following treatment andpulmonary bioavailability of TCDD was assessed by hepatic enzymeinduction and TCDD concentration. Enzyme induction was dependenton the duration of exposure with up to 56 and 918% increasesin cytochrome P450 and aryl hydrocarbon hydroxylase (AHH) activity,respectively, following exposure to PCDD-contaminated soil.There was no significant difference in AHH induction betweenanimals which received contaminated soil and those treated withthe positive control. Hepatic concentration of TCDD in soil-exposedrats was 115, 101, and 179% of positive controls at 1, 7, and28 days post-treatment, suggesting that the soil or co-contaminantsinfluenced retention of TCDD in the liver. These data indicatethat the relative pulmonary bioavailability of TCDD on respirablesoil particles is 100% as compared to laboratory-recontaminatedgallium oxide and that PCDDs and PCDFs are highly enriched onrespirable particles. Utilization of these results will reducethe uncertainty and improve the accuracy of envi ronmental riskassessments of PCDDs and PCDFs.     

Immunotoxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in a Complex Environmental Mixture from the Love Canal

Immunotoxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in a ComplexEnvironmental Mixture from the Love Canal. SILKWORTH, J. B.,CUTLER, D. S., AND SACK, G. (1989). Fundam. Appl Toxicol. 12,303-312.The organic phase ofthe leachate (OPL) from the Love Canal chemicaldump site contains more than 100 organic compounds including2,3,7.8-tetrachlorodibenzo-p-dioxin (TCDD). The immunotoxicpotential of OPL was determined in two mouse strains which differin their sensitivity to aromatic hydrocarbon (Ah) receptor-mediatedtoxicity. OPL was administered in corn oil in a single oralgavage to male BALB/cByJ (Ah^b/Ah_b) mice (0.5, 0.8, or 1.1 g/kg)and DBA/2J (Ah^b/Ah_b) mice (0.6, 0.9, or 1.3 g/kg). TCDD wassimilarly administered at 0.25, 1.0, 4.0, or 16.0 µg/kg.Two days later all mice were immunized with sheep erythrocytes(SRBC). The antibody response (PFC) and organ weights were evaluated4 days later. OPL produced thymic atrophy and hepatomegaly inboth strains at all dose levels. The PFC/spleen in BALB/cByJmice was significantly reduced at the three doses to 34, 13,and 15%, respectively, of the control response. Serum anti-SRBCantibody levels and relative spleen weights were also reduced.The only immune effect in the DBA/2J mice was a decrease ofthe PFC/spleen to 58% of the control at the highest dose. TCDDdecreased the relative thymus and spleen weights only in BALB/cByJmice. However, TCDD produced hepatomegaly, a decrease in serumantibody, and a decrease in PFC/spleen in both BALB/cByJ andDBA/B mice to 3 and 15%. rspectively, at 16 µg/kg. Thus,the TCDD dose required to cause a 50% suppression (ED50) ofPFC/spleen for the BALB/cByJ and DBA/2J strains was 1.84 and3.89 µg/kg, respectively. The ED50 for OPL was 0.24 g/kgin BALB/cByJ mice. The TCDD concentration in the OPL was estimatedto be 7.6 ppm, which agrees closely with the chemical analysis(3 ppm). The results suggest that the immunosuppression causedby OPL in BALB/cByJ mice was primarily due to TCDD. that thenon-TCDD components of OPL diminished the TCDD immunotoxicityin the DBA/2J strain, and that the thymic atrophy and hepatomegalywere caused primarily by the non-TCDD components of the OPL.