Comparative dermal absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin and three polychlorinated dibenzofurans

Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) are toxic environmental contaminants which have the potential to accumulate in human tissues. In order to examine the potential for systemic exposure following dermal exposure, the absorption, distribution, and elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-pentachlorodibenzofuran (1PeCDF), and 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) were evaluated in male F344 rats. TCDD (0.00015, 0.001, 0.01, 0.1, 0.5, and 1.0 mumol/kg) and the three PCDFs (0.1, 0.5, and 1.0 mumol/kg) were applied to a preclipped region on the back of the rat and covered with a perforated cap. The rats were held in individual metabolism cages for 3 days. In animals administered 0.1 mumol/kg, the absorption of TCDF was greater than that of 4PeCDF, 1PeCDF, and TCDD. Relative absorption (percentage of administered dose) declined with increasing dose while the absolute absorption (microgram/kg) increased nonlinearly with dose. Absorption of TCDF at 0.1 mumol/kg was 48% of the administered dose which was significantly greater than that of the other compounds. At this dose, absorption of 4PeCDF was greater than that of TCDD. Absorption at the higher doses was similar for all four compounds. Maximum relative absorption of TCDD (approximately 40% of the administered dose) was obtained at 0.001 and 0.00015 mumol/kg. Major tissue depots for these four chemicals included liver, adipose, skin, and muscle tissue; however, the liver:fat ratio for 4PeCDF was approximately fourfold higher than that for the other three compounds. When normalized to 100% of dose absorbed, the distribution of 4PeCDF-derived radioactivity in liver and adipose tissue was similar to that previously observed after oral and iv administration. In animals administered 0.1 mumol TCDF or 1PeCDF/kg, 56 and 32% of the respective absorbed dose was excreted as polar metabolites within 3 days. Very little of the absorbed dose of either TCDD (approximately 10%) or 4PeCDF (approximately 2%) was eliminated. Results indicate that the dermal absorption of these compounds is incomplete and that systemic toxicity following acute dermal exposure to levels found in the environment is unlikely.     

The Acute Toxicity of 2,3,4,7,8-Pentachlorodibenzofuran (4PeCDF) in the Male Fischer Rat

The Acute Toxicity of 2,3,4,7,8-Pentachlorodibenzofuran (4PeCDF)in the Male Fischer Rat. Brewster, D. W., Uraih, L. C, and Birnbaum,L. S. Fundam. Appl. Toxicol. 11, 236-249 Polychlorinated dibenzofuransare ubiquitous environmental pollutants which have great potentialfor human exposure. To characterize the toxicity of 2,3,4,7,8-pentachlorodibenzofuran(4PeCDF), male F344 rats were administered a single oral doseof 0, 100, 250, 500, 1000, or 2000 µg 4PeCDF/kg. A progressiveand dose-dependent loss of body weight was evident by 3 daysafter treatment. Signs of toxicity included piloerection, hairloss, hypoactivity, morbidity, and death. Death occurred assoon as 14 days after treatment and continued throughout the35-day observation period. The LD5O/35 was estimated to be 916µgAg with a 95% confidence interval of 565–1484µgAg. Dose-dependent increases were observed in serumcholesterol, tri-glyceride, and bile acid concentrations andin sorbitol dehydrogenase and aspartate aminotrans-ferase activities.The hematocrit, hemoglobin, mean corpuscular volume, and meancorpuscular hemoglobin concentrations were depressed in a dose-dependentfashion. Hepatic ethoxyresoru-fin-O-deethylase (EROD) activitywas increased in all treatment groups approximately 25 timesabove that of control animals. Lymphoid depletion in the thymusand spleen was observed in the three highest doses and thymicatrophy was present at all dose levels. Absolute liver weightand the livenbody weight ratio were significantly increasedabove controls. Hepatotoxicity was dose-dependent and was characterizedby lipid accumulation resulting in hepatocytomegaly. Epithelialhyperplasia and focal ulcerations of the forestomach was observedin animals administered 500 µg 4PeCDF/kg. Spontaneouscardiomyopathy was exacerbated by treatment with 2000 µgKg.Since 4PeCDFand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) producea similiar spectrum of toxic effects, the biochemical mechanism(s)of toxicity for these chemicals may be Similar.     

Developmental Toxicity of 2,3,4,7,8-Pentachlorodibenzofuran in the Fischer 344 Flat

Developmental Toxicity of 2,3,4,7,8-Pentachlordibenzofuran inthe Fischer 344 Rat. COUTURE, L. A,, HARRIS, M. W., AND BIRNBAUM,L. S. (1989). Fundam Appl Toxicol 12, 358–366. Fischer344 rats were exposed acutely to 2,3,4,7,8-pentachlordibenzofuran(4-PeCDF) during the organogenic period to evaluate its potentialas an inducer of teratogenic and embryolethal effects. All damswere treated by gavage with a single dose of 0, 30, 100, or300 µg 4- PeCDF/kg body wt on gestation Day (gd) 8, 10,or 12. An additional treatment group was included on gd 12 andadministered 10µg 4-PeCDF/kg body wt po. All animals werekilled on gd 20 and maternal and fetal toxicities were assessed.Determination of embryotoxicity involved both soft tissue andskeletal examinations. 4-PeCDF induced a dose-related decreasein corrected maternal weight gain following treatment on gd8 and 10, as well as resulted in a concomitant Increase in theliver/body weight ratios, first evident at 30 µg/kg forall 3 days of exposure. The maternal thymus weight decreasedrelative to body weight compared with those of controls. Embryo-fetaltoxicity was evident from the high mortality (>80%) observedat 300 µg/kg for all 3 days of exposure. Mean fetal weight,a sensitive indicator of fetal toxicity, decreased comparedto that of controls at 30, 100, and 300 µg/kg followingtreatment on either gd 8, 10, or 12. 4- PeCDF induced cleftpalate in survivors at a dose of 300 µg/kg for all 3 daysof exposure. In conclusion, 4-PeCDF is maternally and fetallytoxic regardless of the gestation day of exposure, but inducedterata only at doses where overt maternal and fetal toxicitywere observed, in contrast to previously reported studies inthe mice where teratogenic effects were observed at nonfetotoxicdose levels. Thus, the mouse may be a more sensitive model forevaluating specific toxic responses induced prenatally followingexposure to the structurally related polyhalogenated aromatichydrocarbons which include the dioxins, furans, biphenyls, andnaphthalenes.     

Absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) after low dose dermal exposure

Human dermal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) occurs through contact with soil and paper products. In a previous study, relative percutaneous absorption of TCDD increased as the dose decreased (Brewster et al., 1989). To determine the rate of absorption of a low dose of TCDD, absorption, distribution, and elimination were examined at 1, 4, 8, 12, 24, 48, 72, and 120 hr after dermal application of 200 pmol (111 pmol/cm2) [3H]TCDD to 10-week-old male Fischer 344 rats. The compound was applied over a 1.8 cm2 area of the interscapular region of the back in 60 microliters acetone and covered with a perforated cap; animals were held in individual metabolism cages. Within 120 hr after dosing, 82 pmol (26 ng) of TCDD was absorbed. Absorption kinetics appeared to be first-order; the absorption rate constant was 0.005 hr-1. At each time point, greater than 70% of the radioactivity detected in the application site could be removed by swabbing with acetone. The time-related increase in the amount of TCDD in liver and fat closely paralleled the amount absorbed, while the percentage of the administered dose detected in the blood was never greater than 0.3%. Thus, absorption of a low dose of TCDD through the skin is extremely slow and appears to be a first-order process.     

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     

Estimation of Octanol-Water Partition Coefficients and Correlation with Dermal Absorption for Several Polyhalogenated Aromatic Hydrocarbons

n-Octanol-Water partition coefficients (K_ow)were experimentallyestimated for: 2,3,7,8-tetrachloro- and 2,3,7,8-tetrabromodibenzo-p-dioxin;2,3,7,8-tetrachloro-, 2,3,7,8-tetrabromo-, and 1,2,7,8- tetrabromodibenzofuran;1,2,3,7,8- pentachioro-, 1,2,3,7,8-pentabromo-, 2,3,4,7,8-pentachloro-,and 2,3,4,7,8- pentabromodibenzofuran; 1,2,4,6,8,9-hexachlorodibenzofuran(HxCDF), and 3,4,3',4'-tetrachlorobiphenyl (3,4,3',4'-TCB).The method involved correlation of literature K_ow with reversephasehigh-performance liquid chromotography (RP-HPLC) retention timefor a series of 23 calibration standards and estimation of K_owfor test compounds from measured RP-HPLC retention. Retentiontimes for all standards and test chemicals were measured induplicate on the same octadecasilane (C₁₈ reverse-phase columnwith an isocratic 85:15 methanol:water mobile phase; soluteswere detected by uv absorbance (254 nm). Literature log K_owvalues used for the calibration standards had been measuredexclusively by the generator column method. Log K_ow estimatesfor the test compounds in the present study ranged from 5.45for 3,4,3',4'-TCB to 6.81 for HxCDF. K_ow estimates were thenplotted against laboratory data for the in vivo 3-day dermalabsorption of single equimolar doses (200 pmol and 20 nmol,or 1 nmol/kg and 0.1 µmol/kg) of selected test compoundsin male F344 rats. Strong inverse correlations were found betweenoctanol-water partition coefficient estimates and single-dosedermal absorption for most of the compounds studied. In addition,RP-HPLC retention time itself appeared to be as equally suitedas K_ow to such correlations with dermal absorption. The structure-activityrelationships suggested in this study were sought in order toexplain observed differences in the dermal absorption of polyhalogenateddibenzo-p-dioxin, dibenzofuran, and biphenyl congeners differingin number, position, and/or type (Cl or Br) of halogen substituents.Moreover, these results should be of predictive value in therisk assessment of dermal exposure to polychlorinated dibenzo-p-dioxins,dibenzofurans, biphenyls, and their brominated analogues.     

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.     

Toxicity and disposition of 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) in the rhesus monkey (Macaca mulatta)

The toxicity and disposition of 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF), a ubiquitous and acutely toxic environmental contaminant, was examined in three adult male Rhesus monkeys administered a single iv dose of 34 micrograms (0.1 mumol)/kg. Within 20 min, 4PeCDF was eliminated from the blood and was distributed to the liver, skin, adipose, and muscle tissues. Excretion occurred primarily via the feces with a minimum whole body half-life approximately 38 days. Within 7-14 days after administration, the packed cell volume and serum triglyceride and bile acid concentrations were significantly increased while serum cholesterol, protein, and albumin concentrations were decreased relative to pretreatment levels. Thyroid hormone levels were also altered with an increase in TSH and a decrease in T3 and T4 concentrations. After 28 days, two monkeys began exhibiting alopecia, hyperkeratinization of the toe and finger nails, facial chloracne-like lesions, and loss of body weight. They subsequently died 40 and 48 days after treatment. Similar symptoms of toxicity were observed in the third animal 58 days after 4PeCDF administration, but this animal appeared to fully recover and was administered 4PeCDF orally and [3H]1,2,3,7,8-pentachloro-dibenzofuran (1PeCDF) dermally 238 days after the initial iv dose. In this animal, approximately 2% of an oral dose of [14C]-4PeCDF was absorbed from the stomach and small intestine in 6 hr and was distributed mainly to the muscle and skin and less than 99% of a dermal dose of 1PeCDF remained at the site of application. Pathological findings in the monkeys that died indicated hyperplastic and metaplastic changes in the gastric mucosa, the Meibomian glands of the eyelid, and the ceruminous glands of the ear. Regression of these lesions was present in the surviving animal. Therefore, 4PeCDF produces dioxin-like toxicity in the monkey similar to that reported for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in the same dose range.     

Bioavailability of Soil-Bound TCDD: Dermal Bioavailability in the Rat

Bioavailability of Soil-Bound TCDD: Dermal Bioavailability inthe Rat. SHU, H., TEITELBAUM, T., WEBB, A. S., MARPLE, L., BRUNCK,B. DEI ROSSI, D., MURRAY, J., AND PAUSTENBACH, D. (1988). Fundam.Appl. Toxicol. 10, 335-343. 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD), an unwanted by-product formed during the manufactureof hexachlorophene and phenoxyherbicides, has been found asan environmental contaminant in many U.S. and Western Europeansites. This study examines in the rat the degree of dermal absorptionof TCDD bound to soil. Such information would assist regulatoryagencies in evaluating the degree of exposure of humans whocome in contact with TCDD-contaminated soil. Several parameterswhich may influence dermal absorption were studied, includingTCDD dose, duration of contact, presence of crankcase oil asa co-contaminant, and environmentally contaminated vs laboratory-preparedsoil. The dermal penetration of TCDD following 4 hr of contactwith skin was approximately 60% of that following 24 hr of contact(P 0.05). Following 24 hr of contact with the skin, the degreeof dermal uptake of TCDD contaminated soil was approximately1% of the administered dose. Under the conditions of the presentstudy, the degree of uptake does not appear to be influencedto any significant extent by the concentration of TCDD on soil,the presence of crankcase oil as co-contaminants, or by environmentallyvs laboratory-contaminated soil. Although a number of parametersexamined in this study did not significantly influence the degreeof dermal absorption of TCDD in the rat following 24 hr of contactwith the contaminated soil, the unqualified use of the 1% valueto estimate human exposure would overestimate human exposure,since there is general agreement among researchers that ratskin tends to be more permeable than human skin to highly lipid-solublecompounds such as TCDD.     

Ethoxyresorufin O-deethylase induction by TCDD,PeCDF and TCDF in ring-necked pheasant and Japanese quail hepatocytes: Time-dependent effects on concentration–response curves

Ethoxyresorufin O-deethylase (EROD) activity was measured in primary cultures of ring-necked pheasant (Phasianus colchicus) and Japanese quail (Coturnix japonica) embryonic hepatocytes exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) for 12, 24, 36 and 48 h. In ring-necked pheasant hepatocytes there was a significant time-dependent increase in the EROD-inducing potency of TCDD, PeCDF and TCDF (i.e. decrease of the EC50). In Japanese quail hepatocytes there was no time-dependent change in the EROD-inducing potency of TCDD, PeCDF and TCDF. There was no time-dependent change in the relative potency of PeCDF and TCDF (i.e. compared to the potency of TCDD) in ring-necked pheasant hepatocytes and of PeCDF in Japanese quail hepatocytes. The results indicate that the relative potencies of these compounds at 24 h are representative of their relative potencies between 12 and 48 h. However, in Japanese quail hepatocytes, the relative potency of TCDF decreased in a time-dependent manner (up to 3.6-fold difference). These results suggest that the effect of time on the EROD-inducing potency of TCDD, PeCDF and TCDF in ring-necked pheasant and Japanese quail hepatocytes is compound- and species-specific, but experimental conditions could also be involved in the differences observed.     

Relative liver tumour promoting activity and toxicity of some polychlorinated dibenzo-p-dioxin- and dibenzofuran-congeners in female Sprague-Dawley rats.

The polychlorinated dibenzo-p-dioxins/dibenzofurans 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) were studied for liver tumour promoting activity in a medium-term altered foci assay in nitrosamine-initiated female Sprague-Dawley rats. The congeners under study were administered by weekly subcutaneous injections at three dose levels for 20 weeks. Evaluation of gamma-glutamyltranspeptidase (GGT+), altered hepatic foci development, showed that all congeners studied acted as potent promoters of hepatocarcinogenesis. TCDD and PeCDD were virtually equipotent as enhancers of foci development while PeCDF displayed approximately ten per cent of the activity of the dioxins. Analysis of the dioxin- and furan-congeners by gas chromatography/mass spectroscopy (GC/MS) technique showed that the retention of PeCDD and PeCDF in liver tissue was approximately 7 and 20 times, respectively, as high as the retention of TCDD. Based on the concentration of the respective congener in liver tissue, PeCDD and PeCDF were 0.14 and 0.007 times as active as TCDD as promoters of foci development. The dose related enhancement of GGT+ foci development induced by the PCDD/PCDF congeners was accompanied by an increased incidence of histological changes in the liver.     

The Effect to Pretreatment on the Biliary Excretion of 2,3,7,8-Tetrachlorodibenzo-p-dioxin, 2,3,7,8-Tetrachlorodibenzofuran, and 3,3',4,4'-Tetrachlorobiphenyl in the Rat

The Effect of Pretreatment on the Biliary Excretion of 2,3,7,8-Tetrachlorodibenzo-p-dioxin,2,3,7,8-Tetrachlorodibenzofuran, and 3,3',4,4'-Tetrachlorobiphenylin the rat. MCKINLEY, M. K., KEDDERIS, L. B., and BIRNBAUM,L. S. (1993). Fundam. Appl. Toxicol. 21, 425–432. The laterally halogenated chemicals 2,3,7,8-tetrachlorodibenzofuran(TCDF) and 3,3',4,4'-tetrachlorobiphenyl (TCB) exhibit the samespectrum of toxic effects as 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD), the prototype and most toxic member of the halogenatedaromatic hydrocarbon family. Metabolism of all three compoundsappears to be the rate-limiting step for excretion, which isprimarily via the bile into the feces. Therefore, the biliaryelimination of TCDF, TCDD, and TCB was examined as an indirectmeasure of metabolism. Male F344 rats were anesthetized withpentobarbital, the bile duct was cannulated, and 0.1 µmol[³H]TCDD, [¹⁴C]TCDF, or [¹⁴C]TCB/kg body wt was administerediv. Bile was collected for 0–8 hr while the animals werekept under anesthesia. To determine if TCDF was able to induceits own metabolism in vivo, a single dose of 1.0 µmolTCDF/kg was administered to rats by oral gavage 3 days priorto iv injection of 0.1 or 0.3 µmol [¹⁴C]TCDF/kg. Biliaryexcretion and hepatic concentrations of [¹⁴C]TCDF were significantlyincreased in the pretreated animals. These results suggest anautoinduction of TCDF metabolism. Essentially all biliary [¹⁴C]TCDFradioactivity was attributable to metabolites. High-pressureliquid chromatography profiles of biliary radioactivity from0 to 4 hr were qualitatively different between naive and pretreatedrats. To determine if pretreatment with TCDD altered the metabolismof TCDF and vice versa, a single dose of 1.0 µmol TCDF/kgor 0.1 µmol TCDD/kg was administered by oral gavage 3days prior to iv injection of 0.1 µmol [³H]TCDD or [¹⁴C]TCDF/kg,respectively. TCDD pretreatment increased the metabolism andhepatic concentrations of [¹⁴C]TCDF in pretreated rats, whilebiliary elimination and hepatic concentrations of [³H]TCDD wereunaffected by pretreatment with TCDF. In a fourth experiment,the ability of TCDD to alter the metabolism of TCB, a laterallysubstituted polychlorinated biphenyl (PCB), was examined. Pretreatmentwith TCDD increased the metabolism of [¹⁴C]TCB by approximatelytwofold, but no differences in hepatic concentrations were seendue to the rapid elimination of TCB. Rats pretreated with Aroclor1254, a commercial mixture of PCBs, demonstrated significantlyincreased metabolism of [¹⁴C]TCB compared to the naive group.Therefore, under these experimental conditions, induction ofTCDF metabolism occurred in the rat upon pretreatment with eitherTCDD or TCDF at doses which also elicited enhanced hepatic uptake.TCDD and Aroclor 1254 induced the metabolism of TCB. These findingssuggest that repeated exposure to a chemical or to a mixtureof these halogenated aromatic hydrocarbons can result in morerapid metabolism and elimination from the body than followinga single, acute exposure.     

Disposition of 1,2,3,7,8-pentachlorodibenzofuran in the rat

1,2,3,7,8-Pentachlorodibenzofuran (1PeCDF) is one of several toxic polychlorinated dibenzofurans (PCDFs) which are ubiquitous environmental contaminants. Related in structure and toxicity to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), PCDFs have been detected in municipal and industrial effluents, PCB mixtures, and in a variety of antiseptics and preservative solutions. The objective of this study was to evaluate the distribution and elimination of 1PeCDF in the rat and to compare these parameters with that of 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) and 2,3,7,8-tetrachlorodibenzofuran (TCDF). After iv administration of 0.1 mumol [3H]1PeCDF/kg, 1PeCDF was rapidly cleared from the blood and distributed to the liver, muscle, skin, and adipose tissue in a manner similar to that for other dibenzofurans. The initial pool sizes of 1PeCDF-derived radioactivity in the liver, muscle, skin, and adipose tissue were 43,35,10, and 7% of the administered dose, respectively. In all cases, loss of radioactivity from these tissues could be described by exponential decay and the initial half-lives for these tissues were 1.36, 0.03, 13, and 1 day, respectively. After redistribution from the muscle, skin, and adipose tissues to the liver, 1PeCDF was metabolized to a polar metabolite(s) and excreted from the body via the bile into the feces. No parent compound was detected in the bile and fecal excretion was the major route of elimination. Most of the radioactivity in the urine was excreted within the first day, after which less than 0.5% of the dose/day was detected. More than half of the administered dose was excreted in the urine and feces within 2 days. The whole-body half-life of related compounds is 4PeCDF much greater than 1PeCDF greater than or equal to TCDF. Therefore, persistence appears to be inversely related to the metabolism of these compounds and metabolism is inhibited by chlorine-substituted carbon atoms adjacent to the oxygen atom in the dibenzofuran ring.     

Cytochrome P4501A induction in primary cultures of embryonic European starling hepatocytes exposed to TCDD, PeCDF and TCDF

Novel methods that predict the sensitivity of avian embryos to the toxic effects of dioxin-like compounds (DLCs) using either (1) knowledge of the identity of amino acids at key sites within the ligand binding domain of aryl hydrocarbon receptor 1 (AHR1) or (2) a luciferase reporter gene assay that measures AHR1 activation were recently reported. Results from both methods predict that European starling (Sturnus vulgaris) and domestic chicken (Gallus gallus domesticus) embryos have similar sensitivity to the biochemical and toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 2,3,7,8-tetrachlorodibenzofuran (TCDF). Chicken embryos are highly sensitive to DLC toxicity, and the prediction that starlings are equally sensitive is surprising given their widespread distribution and large population size. In an attempt to learn more about starling sensitivity to DLCs, we determined concentration-dependent effects of TCDD, PeCDF and TCDF on cytochrome P4501A4 and 1A5 (CYP1A4 and 1A5) mRNA levels in primary cultures of hepatocytes prepared from embryonic European starlings. It has been demonstrated that the sensitivity of avian hepatocytes to CYP1A4/5 induction is well correlated with LD₅₀ values of DLCs for several avian species. The results of the present study indicate that European starling hepatocytes are indeed as sensitive as chicken hepatocytes to CYP1A4/5 induction after exposure to TCDD. However, starling hepatocytes are less sensitive than chicken hepatocytes to CYP1A4/5 induction by PeCDF and TCDF.     

Relative Liver Tumour Promoting Activity and Toxicity of some Polychlorinated Dibeiizo-p-dioxin- and Dibenzofuran-Congeners in Female Sprague-Dawley Rats

Abstract: The polychlorinated dibenzo-p-dioxins/dibenzofurans 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) were studied for liver tumour promoting activity in a medium-term altered foci assay in nitrosamine-initiated female Sprague-Dawley rats. The congeners under study were administered by weekly subcutaneous injections at three dose levels for 20 weeks. Evaluation of γ-glutamyl-transpeptidase (GGT⁺), altered hepatic foci development, showed that all congeners studied acted as potent promoters of hepatocarcinogenesis. TCDD and PeCDD were virtually equipotent as enhancers of foci development while PeCDF displayed approximately ten per cent of the activity of the dioxins. Analysis of the dioxin- and furan-congeners by gas chromatography/mass spectroscopy (GC/MS) technique showed that the retention of PeCDD and PeCDF in liver tissue was approximately 7 and 20 times, respectively, as high as the retention of TCDD. Based on the concentration of the respective congener in liver tissue, PeCDD and PeCDF were 0.14 and 0.007 times as active as TCDD as promoters of foci development. The dose related enhancement of GGT⁺ foci development induced by the PCDD/PCDF congeners was accompanied by an increased incidence of histological changes in the liver.     

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.     

Species Differences in 2,3,7,8-Tetrachlorodibenzo-p-dioxin Toxicity and Biotransformation in Fish

Species Differences in 2,3,7,8-Tetrachlorodibenzo-p-dioxin Toxicityand Biotransformation in Fish. KLEEMAN, J. M., OLSON, J. R.,AND PETERSON, R. E. (1988). Fundam. Appl. Toxicol 10, 206-213.Rainbow trout, yellow perch, carp, bluegill, largemouth bass,and bullhead were treated with graded doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD; 1, 5, 25, or 125 µg/ kg) or vehicle, ip. The lethalpotency of TCDD tended to be greater in yellow perch, carp,and bullhead than in the other three species (LD50 80 days post-treatment,3-5 versus 10-16 µg/kg, respectively). All species treatedwith the highest dose of TCDD (125 µg/kg) displayed alatency period of 1-4 weeks prior to death; longer latency periodswere produced by lower lethal doses. Effects of TCDD treatmenton body weight were both species-dependent and dose-dependent.Fin necrosis was observed in all fish species; however, cutaneoushemorrhage was observed only in TCDD-treated perch, carp, andbluegill, and cutaneous hyperpigmentation only in TCDD-treatedcarp and largemouth bass. Gallbladder bile was analyzed forTCDD and its metabolites 7 days after fish were injected with[¹⁴C]TCDD (60 µg/kg, ip). At least three TCDD metabolitesin addition to the parent compound were found in the gallbladderbile of all six species. In addition, the retention time ofthe major biliary TCDD metabolite (determined by HPLC) was similarin all species except yellow perch. ß-Glucuronidasetreatment of the bile from largemouth bass and bluegill suggestedthat at least two of the TCDD metabolites were glucuronide conjugates.Thus, species differences exist in the lethal potency, signsof overt toxicity, and biotransformation of TCDD among freshwaterfish.     

Lack of Neuropathologic Consequences of Repeated Dermal Exposure to 2,4-Dichlorophenoxyacetic Acid in Rats

Lack of Neuropathologic Consequences of Repeated Dermal Exposureto 2,4-Dichlorophen- oxyacetic Acid in Rats. MATTSSON, J. L.,JOHNSON, K. A., AND ALBEE, R. R. (1986). Fundam. Appl. Toxicol.6, 175–181. A 24% aqueous solution of the dimethylaminesalt of 2,4-dichioro-phenoxyacetic acid (2,4-D amine) was appliedto the legs of male Fischer 344 rats 2 hr/day, 5 days/week,for 2 weeks. Because this concentration caused severe skin lesions,a second group of rats was treated similarly with a 12% solutionof 2,4-D amine for 3 weeks. The 12% solution caused only mildskin changes. The plasma 2,4-D content, at the end of exposure,was nearly five times greater in the rats exposed to the 24%solution than to the 12% solution (323 vs 66.5 µg/ml).The severe skin changes probably facilitated absorption in therats treated with the 24% solution. Rats treated with eitherconcentration weighed less than controls. Although histologicallynormal, kidneys of treated rats weighed more than controls.The increased kidney weights were attributed to physiologicaladaptation due to active excretion of absorbed 2,4-D. Lightmicroscopic examination of tissues, other than skin, revealedno differences between treated and control animals. There wereno nervous system pathologic changes although the rats wereexposed to sufficient amounts of 2,4-D amine to cause severeskin lesions, decreased body weights, and increased kidney weights.     

Age-Related Percutaneous Penetration of 2-sec-Butyl-4,6-dinitrophenol (Dinoseb) in Rats

[¹⁴C]Dinoseb was applied to previously clipped back skin of33- and 82-day-old female Fischer 344 rats at a dosage rangeof 210–2680 nmol/cm². Radioactivity in the treated skin,tissues, urine, and feces was determined at 1, 6, 24, 48, 72,and 120 hr following dermal application. In vitro dermal absorptionof [¹⁴C]dinoseb was also measured in rats of the same age bystatic and flow-through methods. In vivo dermal absorption inboth young and adults appeared biphasic with 55.6 and 82.7%of the recovered dose, respectively, penetrating in 72 hr. Invitro measurements of skin absorption at 72 hr with static cellsshowed higher values in young and lower values in the adultcompared to in vivo dermal absorption values, In vitro flow-throughmeasurements at 72 hr gave lower dermal absorption values forboth young and adult rats, compared to In vivo values. Followingin vivo application, adults excreted about 70% of the totalrecovered dose in urine, 16% in feces, and retained 7% in thebody at 120 hr. HPLC analysis of urine collected at 24 hr fromadults administered [¹⁴C]dinoseb showed extensive metabolismof parent. Excretion and retention results for young were about80% of the adult values, which also was the young to adult ratioof dermal penetration. Blood had the highest concentration ofdinoseb-derived radioactivity of the tissues examined. The kidneyto blood ratio averaged 0.60 in young and 0.41 in adults, whilethe liver and carcass to blood ratio averaged 0.18 in youngand 0.11 in adult. Dermal absorption in young rats was slightlyless than that in adults, and the subsequent kinetics of retentionand excretion appeared different, In vitro dermal penetrationof dinoseb was usually lower than In vivo absorption.     

Target Tissue Morphology and Serum Biochemistry following 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Exposure in a TCDD-Susceptible and a TCDD-Resistant Rat Strain

Target Tissue Morphology and Serum Biochemistry following 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) Exposure in a TCDD-Susceptible and a TCDD-Resistant RatStrain. POHJANVIRTA, R., KULJU, T., MORSELT, A. F. W., TUOMINEN,R., JUVONEN, R., ROZMAN, K.,MÄNNISTÖ, P., COLLAN,Y., SAINIO, E.-L., AND TUOMISTO, J. (1989). Fundam. Appl. Toxicol.12, 698–712. The mode of action of the highly toxic environmentalcontaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is unknown.It was recently discovered that two strains of rat, Long-Evans(L-E) and Han/Wistar (H/W), differ widely in susceptibilityto TCDD. Employing this strain divergence as a probe, the presentstudy set out to assess the role of various biochemical andmorphological effects in TCDD lethality. In the main experiment,the rats were treated once ip with 0, 5, 50, or (H/W) 500 µg/kgTCDD and killed 1 to 16 days postexposure. Several target organswere evaluated by light microscopy and a number of serum lipidand carbohydrate parameters as well as a few major regulatoryhormones were analyzed. The results demonstrated that most alterationscaused by TCDD were essentially similar in both strains. TCDDreduced circulating thyroxine to a slightly greater extent andmore permanently in the sensitive L-E strain. Moreover, a highlysignificant interaction on thyroid-stimulating hormone was foundamong strain, dose. and time. Serum concentrations of corticosteroneand free fatty acids were increased only in the L-E rats given50 µg/kg TCDD, i.e., at an apparent LDl00 dose level forthis strain. Yet, the most striking interstrain difference wasseen in the liver which was distinctly affected after Day 4in L-E rats given 50 µg/kg TCDD but only marginally affectedin rats from any H/W group. The lesion, while showing no necroticcell changes, was suggestive of plasma membrane damage, possiblyreflecting the production of free radicals. The relation ofthe findings to possible mechanisms of TCDD action is discussed.