2,3,7,8-Tetrachlorodibenzo-p-dioxin tissue distribution, excretion, and effects on clinical chemical parameters in guinea pigs

Binding characteristics of Ah receptors from rats and mice before and after separation from hepatic cytosols. 7-Hydroxyellipticine as a competitive antagonist of cytochrome P-450 induction

The Ah receptor, a soluble protein implicated in the mechanism of action of the toxic halogenated aryl hydrocarbons has been examined in rodent livers. Due to the difficulty of making reliable quantitative determinations on binding parameters for hydrophobic compounds in cytosols that contain several components, Ah receptors from livers of Sprague-Dawley rats and C57BL/6 mice have been separated, in a preparative manner, using sucrose density gradient centrifugation in a vertical rotor. The binding characteristics of Ah receptors, before and after separation, were assessed by competition of various chemicals as 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, 3-methylcholanthrene, benzo[a]pyrene, beta-naphthoflavone and ellipticines with [3H]3-methylcholanthrene and 2,3,7,8-tetrachloro[3H]dibenzo-p-dioxin as radioligands. The rationale of this approach is supported by the results obtained and the major conclusions are as follows. 1. The intrinsic binding characteristics of Ah receptors were dependent on the presence or absence of other cytosolic binding components (light-density component and 4-S carcinogen-binding protein). 2. In contrast with many previous unsuccessful attempts, the separation of the C57BL/6 Ah receptor allowed the unambiguous detection of a 9-S binding peak with [3H]benzo[a]pyrene as a radioligand. 3. The intrinsic binding characteristics of the separated Ah receptors of Sprague-Dawley rats and C57BL/6 mice were similar if not identical. 4. A good correlation exists between the competitive potency (IC50) of chemicals and their ability to induce aryl hydrocarbon hydroxylase activity, except for 7-hydroxyellipticine which binds to the Ah receptors of rat and mouse liver (IC50 approximately 5-10 microM) without inducing aryl hydrocarbon hydroxylase. 5. When coadministered with various inducers, 7-hydroxyellipticine antagonizes (from about 20% to 65%) the inducing ability of chemicals displaying similar (ellipticines) or weaker (chlorpromazine, phenothiazine) binding affinities for the Ah receptor.

Binding characteristics of 4-S proteins from rat and mouse liver. High affinity of ellipticines

The binding characteristics of 4-S components (carcinogen-binding protein) from livers of Sprague-Dawley rats, C57BL/6 and DBA/2 mice have been examined before and after separation from other binding components presents in the cytosol. Competitive potency of 3-methylcholanthrene, benzo[alpha]pyrene, beta-naphthoflavone and 20 ellipticines, a series of compounds differently substituted on the dimethyl-pyrido-carbazole nucleus and deprived of carcinogenic activity, has been determined with [3H]3-methylcholanthrene and/or [3H]benzo[a]pyrene as radioligands. The inducing ability of the same compounds for aryl hydrocarbon hydroxylase and for ethoxyresorufin-O-deethylase has been compared to their affinity for the 4-S protein and the Ah receptor respectively. The main results of this study are as follows. 1. The intrinsic binding characteristics of 4-S proteins were dependent on both the nature of the radioligand used and the presence or absence of other cytosolic binding components. 2. The heterocyclic ellipticines were revealed as strong ligands for the carcinogen-binding protein (stronger than benzo[alpha]pyrene for five derivatives substituted in the A ring of ellipticine), with IC50 values ranging from 0.047 microM (8-hydroxyellipticine) to 5.8 microM (N2-ethyl-9-hydroxyellipticinium). 3. When the affinity of ellipticines was plotted versus their inducing ability of aryl hydrocarbon hydroxylase and ethoxyresorufin-O-deethylase, it appears that a good correlation exists for the Ah receptor but not for the 4-S protein. It is concluded that these data, as well as the lack of enzymatic induction after benzo[alpha]pyrene treatment of DBA/2 mice, which display a high level of 4-S protein, do not support the implication of this binding component in the positive control of cytochrome P-450 induction.

The toxicological significance of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in human adipose tissue

Reports of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) in human tissues were reviewed to assess their toxicological significance. The predominance of 2,3,7,8-chlorinated congeners in human tissues and in the food chain, but not in other environmental matrices, suggests that the food chain is the major source of human residues. Exposures to unique distributions of congeners can result in recognizable patterns of excess 2,3,7,8-chlorinated PCDDs/PCDFs in humans. Current levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in the general population can be accounted for by an average level of 133 or 27 ppq (parts per quadrillion) in food based on an estimated half-life in humans of 1 or 5 yr, respectively. 2,3,7,8-TCDD is more persistent in humans than in rodents or lagomorphs, resulting in higher body burdens in humans at comparable levels in the diet. Taken alone, this toxicokinetic difference would increase risks estimated for humans from toxicity in laboratory animals. However, humans appear to be less susceptible due to the following: less food is ingested per body mass, more 2,3,7,8-TCDD is sequestered in adipose tissue and away from target organs, and tissue susceptibility appears to be lower than in the most sensitive rodents and lagomorphs. The body burden of 2,3,7,8-TCDD in a Seveso woman receiving an apparently nontoxic dose was approximately 180 times the average body burden of 2,3,7,8-TCDD equivalents in the general population of industralized societies. The body burden of prisoners who were exposed dermally to a suspension of 2,3,7,8-TCDD and who developed severe chloracne was estimated to be as much as 38 times that of the Seveso woman. These comparisons suggest a considerable margin of safety for the general population.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on guinea pig heart muscle

Cardiac effects of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) were examined using atrial muscle isolated from young or mature guinea pigs fed ad libitum, from young animals 10 or 20 days after a single ip injection of 1 microgram TCDD/kg body wt, and from control guinea pigs pair-fed to the TCDD-treated animals. Basal contraction force of left atrial muscle obtained from TCDD-treated and pair-fed control guinea pigs 10 days after treatment was significantly increased compared to atrial muscle obtained from ad libitum control animals. Atrial muscle from TCDD-treated animals 20 days after treatment had a significantly lower basal force of contraction while that from pair-fed animals was significantly higher relative to atrial muscle from ad libitum control animals. These results suggest that the TCDD-induced change in basal atrial contraction force is in part due to undernutrition and that prolonged exposure to TCDD inhibits this response observed in pair-fed animals. Furthermore, prolonged TCDD treatment shifted the dose-response curve for the positive inotropic effect of isoproterenol to the right with no statistically significant change in the maximal inotropic effect obtained with high concentrations of isoproterenol. The TCDD-induced changes in force of contraction and the dose-response curve for the positive inotropic effect of isoproterenol were similar in young TCDD-treated and mature control guinea pigs. TCDD did not alter the basal contraction frequency or the dose-response curve for the positive chronotropic effect of isoproterenol. There was no effect on cardiac lipoprotein lipase activity at 1 microgram/kg, but in animals administered 4 micrograms TCDD/kg activity was reduced. It was concluded that TCDD adversely affects atrial muscle of guinea pig heart.

Skeletal muscle glucocorticoid receptor and glutamine synthetase activity in the wasting syndrome in rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin

This study demonstrated specific changes in rat skeletal muscles after a single oral dose (100 micrograms/kg) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The development of the wasting syndrome was characterized by marked body weight loss, as well as atrophy of plantaris and gastrocnemius muscles. Fourteen days after administration of TCDD, gastrocnemius muscle cytosolic glucocorticoid receptor binding, measured at a single saturating concentration of [3H]triamcinolone acetonide, was significantly diminished, while plantaris muscle glutamine synthetase activity was strikingly elevated, indicating that specific biochemical alterations occur in skeletal muscle in the wasting syndrome.

Characterization of the in vitro stability of the rat hepatic receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The in vitro stability of the Ah receptor from rat hepatic cytosol was evaluated by [3H]TCDD binding studies, gel filtration, and sucrose density gradient ultracentrifugation. Thermal inactivation of unoccupied receptor followed first-order kinetics between 5 and 40 degrees C, with an estimated Ea for inactivation of approximately 35 kcal/mol. Protease inhibitors did not reduce and dilution slightly increased the inactivation rate at 20 degrees C. Recovery and 20 degrees C stability decreased with increasing ionic strength. The TCDD-receptor complex was less susceptible to degradation at 20 degrees C, even in the presence of 0.4 M KCl. Specific binding was markedly pH dependent, with maximum recovery at 7.6. Analysis of the pH curve suggested that cysteine sulfhydryl groups may be involved in TCDD binding. Dithiothreitol (1 mM) maximized recovery and 20 degrees C stability, and addition of the thiol largely reactivated binding sites lost from cytosol prepared without it. Removal of low molecular weight components of cytosol by gel filtration resulted in a rapid 20 degrees C inactivation rate that could not be lessened by dithiothreitol. Glycerol (10% v/v) and EDTA (1.5 mM) maximized recovery of specific binding, but both decreased 20 degrees C stability in a concentration-dependent manner. Calcium chloride (4 mM) increased stability at 20 degrees C by approximately 20%, and retarded the characteristic shift in sedimentation coefficient from approximately 9 to approximately 6 S in high-salt sucrose gradients. The fact that sodium molybdate (20 mM) decreased recovery and 20 degrees C stability when dithiothreitol was present but slightly increased stability in its absence suggested an antagonism between the two compounds. Molybdate mitigated the inactivation induced by 0.4 M KCl, an effect which may be related to the observation of dual peaks in molybdate-containing high-salt sucrose gradients. These data indicate that thermal inactivation of the unoccupied rat hepatic Ah receptor primarily may be due to physical rather than enzymatic processes; (ii) sulfhydryl oxidation, removal of low molecular weight cytosolic components, and high ionic strength result in rapid rates of inactivation at 20 degrees C; and (iii) the large degree of protection conferred by TCDD binding implies a very tight ligand-receptor interaction, and as such accords with TCDDs extraordinary potency and persistence in producing its toxic and biochemical effects.

Circadian alterations in prolactin, corticosterone, and thyroid hormone levels and down-regulation of prolactin receptor activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Studies were initiated to determine whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affects circadian rhythms of serum prolactin (PRL), corticosterone, thyroxine (T4), and triiodothyronine (T3) in male Sprague-Dawley rats. In addition, the effects of TCDD on PRL receptor activity, as assessed by the ability of PRL to induce ornithine decarboxylase (ODC), were determined. The earliest effect detected following TCDD administration was a significant decrease in the serum PRL concentration compared with that of pair-fed controls within 4 hr (p less than 0.05). This was followed by a significant decrease in serum T4 by 6 hr (p less than 0.05). By 8 hr the serum peak of corticosterone was shifted to 2 hr later in the TCDD-treated rats. This temporal sequence of hormonal changes suggests that the earlier alteration in PRL may be involved in the later alterations in the concentrations of serum T4 and corticosterone. The serum PRL concentration 7 days after TCDD administration was significantly higher (p less than 0.05) in TCDD-treated animals compared with that in pair-fed controls (mean of 20.5 +/- 3.7 vs 13.6 +/- 1.8 ng/ml serum, p less than 0.05, respectively). The elevation of ODC activity in response to PRL, 2 days after TCDD, was decreased in the order of thymus greater than adrenal greater than spleen greater than heart greater than kidney greater than liver. By 7 days, liver ODC activity in response to PRL was only 12% that detected in pair-fed controls. Liver ODC activity in response to dexamethasone and aminophylline was decreased to 25 and 22% of pair-fed controls, respectively, by 7 days after TCDD administration. However, in kidney, TCDD-treated rats had an increased ODC response to aminophylline to 191% of pair-fed controls by Day 7. These results suggest that the ability of TCDD to alter receptor coupling or the receptor number for diverse hormones may play a role in TCDD toxicity.

Changes in hamster hepatic cytochrome P-450, ethoxycoumarin O-deethylase, and reduced NAD(P): menadione oxidoreductase following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin. Partial dissociation of temporal and dose-response relationships from elicited toxicity

The temporal and dose-related characteristics of hepatic enzymes induced in the hamster by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were examined. Male Syrian golden hamsters received a single intraperitoneal injection of TCDD at a dose of 0-500 micrograms/kg. At various times up to 35 days, a number of variables were determined and compared: whole body, liver, and thymus weights; hepatic concentrations of cytochrome P-450 (P-450); and activities of 7-ethoxycoumarin O-deethylase (ECOD) and reduced NAD(P): menadione oxidoreductase (NMOR). Increased liver weights and decreased thymus weights were observed to be dose related. At day 7 following treatment, the approximate ED50 values for these responses were 15 and 100 micrograms/kg respectively. The ED50 values for the increase in hepatic P-450 concentrations and activities of ECOD and NMOR ranged from 0.5 to 2.0 micrograms/kg. At 10 and 500 micrograms/kg, NMOR activity remained maximally induced for up to 35 days. This was also the case for P-450 and ECOD activity at a dose of 10 micrograms/kg. At 500 micrograms/kg, both P-450 and ECOD demonstrated an induction up to day 4 followed by a decrease to near control levels by day 14. This decrease appeared to correlate with changes in hepatic morphology. These results demonstrate a dissociation of the induction of these hepatic enzymes from TCDD-induced lethality, in this species.

Toxicity and evidence for metabolic alterations in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated guinea pigs fed by total parenteral nutrition

The effect of total parenteral nutrition (TPN) on the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in male, Hartley-strain guinea pigs was determined. At a single dose of 2 micrograms TCDD/kg, TPN-fed guinea pigs maintained body weight at a level which was slightly, but consistently, below that of the TPN-fed control animals. However, despite the sustenance of body weight, TCDD-treated animals died or were sacrificed due to morbidity between Days 8 and 24 following treatment. Approximately 50% of this group demonstrated a profound loss of body weight within a few days prior to death or sacrifice. With the exception of the pattern of weight loss, the signs of toxicity in the TPN-fed, TCDD-treated animals were strikingly similar to those observed in TCDD-treated guinea pigs fed ad libitum. Although livers from TCDD-treated, TPN-fed animals demonstrated increased content of lipid and cytochrome P-450, this tissue appeared to be morphologically and functionally comparable to that from TPN-fed controls. Of the blood chemistry examined, only the serum concentrations of 3,5,3'-triiodothyronine were significantly decreased in the treated animals fed by TPN. Results were also compared to TCDD-treated guinea pigs fed ad libitum and respective pair-fed controls. Many of the physiological and biochemical responses observed in animals fed ad libitum following TCDD treatment could be explained by a decrease in food consumption. This study demonstrated that although food consumption clearly accounts for the major effect of TCDD on body weight loss in guinea pigs fed ad libitum, additional physiological and/or biochemical alterations occurred which also contribute to body weight loss, other signs of toxicity, and subsequent lethality.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) modulates epidermal growth factor (EGF) binding to basal cells from a human keratinocyte cell line

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) modulates the proliferation, differentiation, or both, of epidermal keratinocytes in vivo and in culture. The growth of epidermal cells in culture is regulated by several biochemical mediators including epidermal growth factor (EGF). In this report the actions of TCDD on EGF binding in a basal cell population from a human keratinocyte cell line were examined. TCDD decreased the specific binding of 125I-EGF to basal cells by 40% within 96 hr. This reduction in EGF binding could not be attributed to changes in the state of differentiation as assessed by cell size and morphology, and cornified envelope competence, a marker of terminal differentiation. Modulation of EGF binding by TCDD was concentration-dependent (EC50 = 1 nM) and stereospecific, suggesting involvement of the Ah receptor. Scatchard analysis of EGF binding to the basal cells indicated a single class of high-affinity sites in both control (Kd = 0.14 nM) and treated (Kd = 0.11 nM) cultures and confirmed a decrease in the number of these sites in response to TCDD. The reduction in EGF binding correlated with a decrease in EGF-stimulated DNA synthesis and cell proliferation. Comparison of differentiation-competent squamous cell carcinoma (SCC) lines treated with TCDD supported an association between modulation of EGF binding and enhanced differentiation. The data indicate that basal cells are a target for TCDD. We propose that the modulation of EGF binding in basal keratinocytes by TCDD is one of the critical regulatory events resulting in enhanced differentiation.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on lipid peroxidation in microsomal systems in vitro

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) when added to suspensions of rat hepatic microsomes in the presence of NADPH has little influence on the peroxidation of microsomal lipids unless the system also contains complexed ferric ion, in which case TCDD stimulates. This stimulation does not appear to require metabolism of the TCDD. Peroxidation was monitored by production of thiobarbiturate-reactive substances (malondialdehyde and dienals), production of conjugated dienes, and disappearance of polyunsaturated fatty acids. Stimulation of lipid peroxidation by TCDD in a mixed lysosome-microsome preparation resulted in significantly decreased 'leakage' of acid phosphatase into the medium, implying an effect on lysosomal membranes. Consideration both of the present results and data in the literature leads to the conclusion that it is premature to attempt to define the relationship between enzyme induction, lipid peroxidation and TCDD lethality.

Dose-related effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in C57BL/6J and DBA/2J mice

The dose-related effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were studied in B6D2F1/J (B6D), C57BL/6J (C57), and DBA/2J (DBA) mice. A 14-fold difference in lethality was observed in C57 and DBA mice, based upon 30-day LD50 values of 182 and 2570 micrograms TCDD/kg body wt, respectively. The 30-day LD50 for B6D mice was 296 micrograms TCDD/kg body wt. A progressive loss of body weight in all strains of mice was observed during the 30-day LD50 studies, with maximal weight losses of 24.7, 34.0, and 33.4% prior to death of C57, B6D, and DBA mice, respectively. In separate experiments, it was found that decreased feed consumption did not contribute to weight loss in C57 mice exposed to lethal or sublethal doses of TCDD until the animals were moribund. Time-course studies in C57 mice treated with 200 micrograms TCDD/kg body wt indicated that decreases in serum glucose and triglyceride concentrations and increases in hepatic triglyceride content occurred within 4 to 8 days of exposure, and were maximally altered within 17 to 21 days postexposure, concomitant with a 25% body weight loss. C57 mice fasted for 24 to 96 hr lost 18% of body weight and also exhibited alterations in glucose and lipid parameters; however, these changes were substantially different than the effects of TCDD exposure. In concert, these observations demonstrate that decreased feed consumption (hypophagia) does not account for weight loss and changes in carbohydrate and lipid metabolism in TCDD-treated C57 mice. Dose-response experiments resulted in comparable changes in glucose and lipid parameters when DBA mice were exposed to 10-fold higher doses of TCDD than C57 mice. Parallel LD50 responses and parallel changes in carbohydrate and lipid metabolism, at 10- to 15-fold differences in dose range, are indicative of a common mechanism of toxicity in TCDD-treated C57 and DBA mice.

Influence of phenobarbital and TCDD on the hepatic metabolism of TCDD in the dog

The influence of phenobarbital and TCDD pretreatment on the formation and biliary excretion of TCDD-metabolites following single doses of 3H-TCDD was investigated. Without pretreatment, 24.5% of the absorbed 3H-TCDD dose was excreted in the bile within 110 h. Phenobarbital did not influence this rate, whereas a single dose of 10 micrograms of unlabeled TCDD/kg b.wt nine days earlier resulted in a doubling of the amount of radioactive material eliminated in the bile (47.4%).

A hydroxylapatite microassay for receptor binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin and 3-methylcholanthrene in various target tissues

A "batch" hydroxylapatite assay for the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) receptor that does not require detergents is described. The receptor could be assayed in rat target tissues using either of the cytochrome P1-450 inducers [3H]TCDD or [3H]3-methylcholanthrene as radioligands. A phosphate buffer washing procedure was developed on the basis of chromatographic data and optimized to separate nonspecifically and specifically bound ligand. The assay was characterized with respect to washing efficiency, binding specificity, competition, adsorption time, amount of hydroxylapatite required to bind receptor complexes, sensitivity, and effects of detergents. Equilibrium binding parameters were determined. Receptor extracted with phosphate from hydroxylapatite was analyzed on sucrose gradients and was found to exhibit the same sedimentation properties as the receptor in crude cytosol. Furthermore, the applicability of the assay has been demonstrated in cytosolic preparations from three different target tissues: liver, lung, and thymus.

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) reduces lipoprotein lipase activity in the adipose tissue of the guinea pig

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) administered to young male guinea pigs at a dose of 1 microgram/kg (single intraperitoneal injection) caused a large reduction in adipose tissue lipoprotein lipase (LPL) activity. This effect occurred rapidly; a 70% decrease was noticed after 24 hour and 80% of LPL activity was lost by 48 hours when the serum triglyceride levels increased to 175% of control levels. LPL is known to play an important role in controlling the amount of free fatty acids supplied to adipose tissues. Administration of a large dose of glucose to fasted guinea pigs, which have shown a similar weight loss, but less LPL loss than TCDD-treated animals, had the effect of elevating their adipose LPL levels back to a near normal level, whereas the same treatment caused no significant increase in the LPL levels of TCDD-treated animals. Evidence indicates that the TCDD-caused decline in LPL activity is irreversible. As a consequence, the affected guinea pigs are incapable of responding to changes in nutritional status.

Lipid abnormalities in workers exposed to dioxin

Ten years after an incident in which workers were exposed to tetrachlorodibenzodioxin (TCDD) a controlled biochemical study showed statistically significant increases in the serum cholesterol and triglyceride concentrations of workers both with and without chloracne. Urinary excretion of D-glucaric acid was significantly higher for all workers.

Liver morphology in guinea pigs fed pyrolysis products of a polychlorinated biphenyl transformer fluid continuously for 90 days

After a fire involving a transformer, the State Office Building in Binghamton, New York, was contaminated with soot containing polychlorinated biphenyls, biphenylenes, naphthalenes, dioxins, and dibenzofurans. The toxicity of the soot and its effect on liver morphology after prolonged (subchronic) exposure were determined for both sexes of Hartley guinea pigs, which were fed soot continuously for 90 days. By light microscopy the observed alterations of the liver were predominantly centrilobular; they included hepatocyte hypertrophy, steatosis, increased glycogen and iron, focal necrosis, and bile duct proliferation with fibrosis. Cytoplasmic vacuoles and acidophilic hyalin-like bodies were observed. Electron microscopy of hepatocytes showed proliferated smooth endoplasmic reticulum (SER), cytoplasmic vacuoles, concentric membrane arrays (CMAs), glycogen bodies, and microdroplets of fat, often without limiting membranes. The vacuoles frequently contained membrane fragments and had a halo-like periphery composed of proliferated membranes. Cell debris, membrane fragments, and small CMAs were observed in the sinusoids. Membrane fragments were also observed in the bile canaliculi and bile ducts. Intoxicated bile duct cells contained more cytoplasmic myelin whorls and altered mitochondria. In contrast to the previously reported study of a single dose, these liver alterations showed a strong dose dependence, emphasizing the importance of time and method of administration. The cytoplasmic vacuoles, which were not pronounced in the previous study, are here a prominent alteration, probably originating from outpouchings of canaliculi and sinusoidal membranes. A hypothesis for the mechanism of hepatocyte detoxification based on the proliferated SER and ejection of membrane fragments is proposed.

Examination and rapid analysis of hepatic cytosolic receptors for 2,3,7,8-tetrachlorodibenzo-p-dioxin using gel-permeation high performance liquid chromatography

Gel-permeation high performance liquid chromatography was used to examine the molecular characteristics of the cytosolic and nuclear receptors for 2,3,7,8-tetrachlorodibenzo-p-dioxin. The physical properties for this receptor previously established by sucrose-density gradient analysis have been maintained by the technique. The high performance liquid chromatography method offers the advantages of rapid separation and reproducibility thus minimizing possible effects of proteolytic enzymes or dissociation of the ligand-receptor complex. The specific binding of [3H]2,3,7,8-tetrachlorodibenzo-p-dioxin as measured by this system also corresponds quantitatively to that determined by the hydroxyapatite method. These methods will facilitate a further understanding of the biochemical actions of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds, as well as an understanding of the physiological function of this receptor molecule.

Dioxin in soil: bioavailability after ingestion by rats and guinea pigs

Soil environmentally contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was given by gavage to guinea pigs and rats. The development of a characteristic clinicopathologic syndrome in guinea pigs, the induction of aryl hydrocarbon hydroxylase in rats, and the presence of TCDD in the livers of both species show that TCDD in soil exhibits high biological availability after ingestion.

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) causes reduction in the low density lipoprotein (LDL) receptor activities in the hepatic plasma membrane of the guinea pig and rat

Administration of 1 micrograms/kg (single intraperitoneal injection and studied after 10 days) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to young male guinea pigs was found to cause a significant reduction in binding of low-density lipoprotein (LDL) to its receptor on the hepatic plasma membrane. This reduction in LDL binding is not caused by the decrease of food intake by treated animals since pair-fed control animals had significantly higher LDL binding than treated animals. It was also found that primary hepatocytes from treated animals had a reduced ability to internalize LDL than controls. Such a change in the plasma membrane function may explain the resulting hyperlipidemia particularly hypercholesterolemia which occurs in this species as a result of TCDD administration.

Health implications of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) contamination of residential soil

Extrapolations from animal toxicity experiments (including carcinogenicity and reproductive effects) to possible human heath effects can be used to estimate a reasonable level of risk for 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). Extrapolations are derived from: (1) review of published studies, (2) a complex set of assumptions related to human exposure to contaminated soil, and (3) estimates of (a) a dose response curve, (b) appropriate margins of safety, and/or (c) applicable mechanisms of action. One ppb of 2,3,7,8-TCDD in soil is a reasonable level at which to begin consideration of action to limit human exposure for contaminated soil.

Health status of workers with past exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in the manufacture of 2,4,5-trichlorophenoxyacetic acid: comparison of findings with and without chloracne

Chloracne was found in 52% of 226 workers in a 1979 cross-sectional survey at a plant where 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) had been manufactured from 1948 to 1969. Mean duration of residual chloracne was 26 years, and in 29 subjects, it had been present for 30 years. A significant increased prevalence of abnormal gamma-glutamyl transpeptidase (GGT) and higher mean GGT were found in those with chloracne, compared to those without. Although mean triglyceride values were higher in those with chloracne, the difference was not statistically significant. Neurological examination showed a statistically significant higher prevalence of abnormal sensory findings in those with chloracne. Increased prevalence of angina and reported myocardial infarction in those with chloracne was not significant when age-adjusted. Increased prevalence of reported sexual dysfunction and decreased libido in those with chloracne compared to those without was statistically significant after age adjustment. No differences were found between those with and without chloracne in serum cholesterol, total urinary porphyrins, or in reproductive outcome.

Toxicity and distribution of 2,3,7,8-tetrachlorodibenzofuran in male guinea pigs

The toxicity of 2,3,7,8-tetrachlorodibenzofuran (TCDF) was studied in male Hartley guinea pigs after single or multiple oral treatment. In each animal studied, adipose tissue, liver, and skin were the major depots of TCDF and accounted for 50-74% of the total dose. The whole-body half-life of TCDF in guinea pigs was estimated to be approximately 40 d. This slow clearance of TCDF by guinea pigs may explain the high toxicity of TCDF for this species even when very low repeated doses were administered. Intervals of 1, 2, or 4 wk between doses had little effect on TCDF lethality, but did have an effect on the pattern of toxicity. Treatment of mature animals with high single doses of TCDF (10 or 15 micrograms/kg body weight) resulted in the immediate loss of weight and the eventual death of all treated animals within 2-4 wk after the loss of approximately 35% of their initial body weight. Treatment of immature animals with low multiple doses totaling cumulative doses of between 4 and 12 micrograms/kg resulted in the death of 75% of these animals, with the deaths occurring between 7 and 19 d after the initial appearance of quantitative toxic symptoms (loss of weight); however, weight loss was less dramatic following repeated low doses than after acute high doses. Concentration of TCDF in adipose tissue was generally proportional to dose of TCDF. With increasing time after dosage, there was a shift in distribution from adipose tissue to liver.

Subchronic oral toxicity in guinea pigs of soot from a polychlorinated biphenyl-containing transformer fire

We have previously described the acute po toxicity in guinea pigs of soot from a transformer fire at the State Office Building in Binghamton, New York. The soot was determined to contain polychlorinated biphenyls, biphenylenes, dibenzodioxins, and dibenzofurans. The present study evaluates soot toxicity in guinea pigs receiving 0, 0.2, 1.9, 9.3, or 46.3 ppm soot in the feed for 90 days or 231.5 ppm for 32 days. At 231.5 ppm, body weight loss, thymic atrophy, bone marrow depletion, skeletal muscle and gastrointestinal tract epithelial degeneration, and fatty infiltration of hepatocytes were observed. Mortality had reached 35% by Day 32 (when survivors were killed), with total soot consumption of approximately 400 mg/kg. At 46.3 or 9.3 ppm soot, a reduced rate of body weight gain was observed, and at 46.3 ppm, the mortality by Day 90 was 30%. Relative (to body) thymus weights were decreased in both groups, while relative spleen weights were increased at 46.3 ppm soot only. Salivary gland interlobular duct squamous metaplasia and focal lacrimal gland adenitis were detected histopathologically, while bone marrow depletion was noted only in females at the higher dose. Diminished serum alanine aminotransferase (ALT) activity in both sexes and decreased serum sodium levels in male and potassium levels in female animals were detected at both dose levels. decreased gamma-glutamyl transferase activity and red blood cell count and elevated serum creatinine and triglycerides were observed only in animals fed 46.3 ppm soot. At 1.9 ppm soot, salivary gland duct metaplasia was observed in both sexes, along with decreased relative thymus weights, ALT activity, and serum sodium levels in male animals only. No effects attributable to soot exposure were noted in animals receiving 0.2 ppm soot for 90 days. Total average soot consumption for male and female animals in the 0.2, 1.9, 9.3, and 46.3 ppm dosage groups was 1.2, 12, 55, and 275 mg/kg, respectively. Although many of the observed effects were typical of acute exposure of guinea pigs to the Binghamton soot or to polychlorinated aromatic hydrocarbons in general, salivary gland duct metaplasia has not been previously reported. Toxic effects of this subchronic exposure were observed at lower total doses than with acute exposure, although variations in absorption due to the effects of different vehicles (aqueous in the acute study versus the feed in this study) could account for some or all of this difference.

Liver morphology in guinea pigs administered either pyrolysis products of a polychlorinated biphenyl transformer fluid or 2,3,7,8-tetrachlorodibenzo-p-dioxin

A transformer cooled and insulated with a mixture of 65% Aroclor 1254 and 35% chlorinated benzenes located in the Binghamton State Office Building in Binghamton, New York, was involved in a fire, which produced soot containing polychlorinated biphenyls, biphenylenes, dioxins, and dibenzofurans. A single dose of either soot or 2,3,7,8-tetrachlorodibenzo-p-dioxin in aqueous methyl cellulose was administered by gavage to Hartley guinea pigs of both sexes. The liver tissue was examined 42 days after administration. By light microscopy hypertrophy of hepatocytes, steatosis, focal necrosis, and cytoplasmic hyalin-like bodies were observed as a result of both treatments. Bile duct proliferation (adenofibrosis) was observed only in the guinea pig groups administered soot. These animals also showed proliferation of the smooth endoplasmic reticulum, concentric membrane arrays (CMA), mitochondrial alterations, decreased rough endoplasmic reticulum, and autophagolysosomes by electron microscopy. The CMAs, which corresponded to the hyalin-like bodies, surrounded lipid droplets and cytoplasmic matrix containing mitochondria and degenerating organelles.

Fate of 2,3,7,8-tetrachlorodibenzo-p-dioxin metabolites from dogs in rats

1. Metabolites of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were extracted from the bile of TCDD-treated dogs and administered by gavage to bile-duct-cannulated rats and also to an intact rat. 2. Radioactivity of the TCDD metabolites was rapidly cleared from the body of the rats, indicating that bioaccumulation of these compounds does not occur. 3. Biliary excretion was the most important route of elimination in the cannulated rats and amounted to greater than 30% of the administered dose within 24h. TCDD metabolites were also eliminated to a minor extent by the kidneys. The combined recovery of radioactivity in faeces, bile and urine after 24h accounted for greater than 85% of the dose. 4. The intact animal exhibited a somewhat different kinetic behaviour in that only 13% dose was excreted in faeces and urine after 24h, which indicates enterohepatic circulation. The administered radioactivity was completely recovered after 72h. 5. Results from the present experiments indicate that metabolism of TCDD is the rate-limiting step in elimination of TCDD from the liver. Interspecies variability in the toxicity of TCDD may in part be attributable to different rates at which the species metabolize and excrete TCDD.

Utilization of blood analyses to evaluate metabolic changes in control and 1,2-dimethylhydrazine-treated adult male fischer rats

The synthetic compound 1,2-dimethylhydrazine is employed in carcinogenesis studies because of its reliable and specific ability to produce colon tumors in rodents. Male Fischer rats were treated at 7 weeks of age with a single oral dose of 1,2-dimethylhydrazine (35 mg/kg) and examined at autopsy 1.5 years later when the incidence of colon tumors is approximately 80%. Blood from control and 1,2-dimethylhydrazine-treated animals was taken at autopsy for routine hematoplazia analysis and for biochemical analysis with the Sequential Multiple Analyzer Computer multitest system. The results indicate that the induction of tumors with a single oral dose of this carcinogen is associated with statistically significant changes in the serum levels of some clinically useful metabolic parameters. Clinically significant changes in the serum chemistry were increases in the creatine phosphokinase (CPK) and albumin/globulin values without an increase in the total serum protein. The multitest system has not been previously employed to evaluate the blood chemistry profiles of tumor-bearing animals and, thus, this study provides an illustration of the potential for this technique to evaluate metabolic changes associated with exposure to carcinogens.

Transfer of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the mouse embryo and fetus

(1) Following the administration of the highly toxic agent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to pregnant mice, exceedingly low concentrations of this substance were found in the embryo and fetus between gestational days 11 and 18 (between 0.04 and 0.14% of the maternal dose/g tissue). (2) Tissue levels of tCDD in embryos on days 9 and 10 exceeded those of later gestational stages. (3) TCDD levels in fetal livers were 2--4 times higher than those in other fetal organs. (4) Maternal liver contained the highest concentrations of TCDD (4 -10% of the dose/g). A comparison of the results obtained following oral, s.c. and i.p. applications indicated that there was no major first pass effect involved following oral administration. (5) Placenta and other extrahepatic maternal organs exhibited TCDD levels, which were approximately 1, embryos and features 2 orders of magnitude lower than maternal liver concentrations. (6) Good correlation was found between the doses applied (5, 12.5 and 25 microgram/kg) and the tissue levels observed. (7) A single dose of 25 microgram/kg given on day 10 or 5 doses of 5 microgram/kg, 1/day from days 7-11, resulted in higher levels of TCDD in embryos on day 13 than did a singly dose of 25 microgram/kg on day 7; cleft palate was induced at different rates by these treatment schedules.