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

Fenofibrate, a peroxisome proliferator-activated receptor-alpha agonist, blocks steatosis and alters the inflammatory response in a mouse model of inflammation-dioxin interaction

2,3,7,8-Tetrachlorodibenzo-p-dioxin (dioxin; TCDD) is an environmental contaminant that elicits a variety of toxic effects, many of which are mediated through activation of the aryl hydrocarbon receptor (AhR). Interaction between AhR and the peroxisome proliferator-activated receptor-alpha (PPAR-α), which regulates fatty acid metabolism, has been suggested. Furthermore, with recognition of the prevalence of inflammatory conditions, there is current interest in the potential for inflammatory stress to modulate the response to environmental agents. The aim of this work was to assess the interaction of TCDD with hepatic inflammation modulated by fenofibrate, a PPAR-α agonist. Female, C57BL/6 mice were treated orally with vehicle or fenofibrate (250 mg/kg) for 13 days, and then were given vehicle or 30 μg/kg TCDD. Four days later, the animals received an i.p. injection of lipopolysaccharide-galactosamine (LPS-GalN) (0.05x10⁷ EU/kg and 500 mg/kg, respectively) to incite inflammation, or saline as vehicle control. After 4 h, the mice were euthanized, and blood and liver samples were collected for analysis. Livers of animals treated with TCDD with or without LPS-GalN had increased lipid deposition, and this effect was blocked by fenofibrate. In TCDD/LPS-GalN-treated mice, fenofibrate caused an increase in plasma activity of alanine aminotransferase, a marker of hepatocellular injury. TCDD reduced LPS-GalN-induced apoptosis, an effect that was prevented by fenofibrate pretreatment. LPS-GalN induced an increase in the concentration of interleukin-6 in plasma and accumulation of neutrophils in liver. TCDD exposure enhanced the former response and inhibited the latter one. These results suggest that fenofibrate counteracts the changes in lipid metabolism induced by TCDD but increases inflammation and liver injury in this model of inflammation-TCDD interaction.

Aspects of dioxin toxicity are mediated by interleukin 1-like cytokines

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) results in a broad spectrum of toxic effects. Most, if not all, of these responses are dependent upon the binding of dioxin to the aryl hydrocarbon receptor. Given their common roles in chemically induced toxicity, we asked whether interleukin 1 (IL1)-like cytokines play a role in acute aspects of the dioxin response. To test this idea, we employed a "triple-null" mouse model that lacks the two receptors for the tumor necrosis factors-alpha and -beta and the receptor for the IL1-alpha and IL1-beta cytokines. When triple null mice were treated with dioxin, there was significant attenuation in the levels of serum alanine aminotransferase, signifying reduced hepatocellular damage. In addition, the triple-null mice were protected from dioxin-induced liver inflammation. Loss of receptors for the IL1-like cytokines was not protective for all aspects of dioxin toxicity. Endpoints such as thymic involution, Cyp1a2 induction, hepatomegaly, and hydropic degeneration remain unchanged in this model.

Development of quantitative structure-activity relationship (QSAR) models for predicting risk of exposure from carcinogens in animals

Quantitative structure-activity relationship (QSAR) models capable of predicting acute toxicity and carcinogen potency of polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated hydrocarbons, and chlorinated insecticides have been formulated. Median lethal dose (LD50) for PCDD-exposed mice correlated negatively with polarity and positively with (H acceptor x 2 chi), whereas LD50 for PCDD-exposed guinea pigs correlated with (H acceptor x density). Both (H acceptor x 2 chi) and (H acceptor x density) exhibited parabolic relationship with log P (partition coefficient). Carcinogenic potency, determined from order of magnitude (OM) values, correlated negatively with log P and positively with (length x width). Thus, a hydrophobic mechanism plays a key role in the lethal effects of PCDD in mice, whereas both hydrophobic and electronic mechanisms are involved in the lethal effects of PCDD in guinea pigs. However, the molecule's lipophilicity, length, and width may play important roles in the carcinogenic effects of chlorinated compounds.

Toxicology of environmental chemicals in the flounder (Platichthys flesus) with emphasis on the immune system: field, semi-field (mesocosm) and laboratory studies

European flounder (Platichthys flesus) has shown an increased prevalence of liver tumors and lymphocystis disease (a viral infection) that correlated with pollution in field research in Dutch coastal and estuarine waters. Semi-field or mesocosm experiments confirmed the supposed causality. Although these types of research are highly relevant for the feral population, laboratory experiments are necessary to establish causal relationships between specific chemical pollutants and disease. Therefore, the effects on flounder of some of the potentially causative chemicals such as benzo[a]pyrene (BaP), dimethyl-benz[a]anthracene (DMBA), 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4',5 pentachlorobiphenyl (PCB-126), and bis(tri-n-butyltin)oxide (TBTO) were examined in several laboratory experiments. These effects were evaluated using general toxicological parameters and histopathology. For immune function assessment, attempts to develop an infection model with the lymphocystis virus were made, but appeared unsuccessful and immune function tests are not fully operational at the moment. Flounder has been successfully maintained and exposed to toxic substances in captivity in our laboratory. Short-term aqueous exposure to high levels of BaP or DMBA did not induce marked effects under our experimental conditions. Results of oral exposure of flounder to low levels of TCDD, PCB-126 or harbor sludge extract show significant induction of cytochrome P4501A (CYP1A) in hepatocytes. Oral exposure to high levels of TCDD or PCB-126 also significantly induced CYP1A immunoreactivity in epithelium in mesonephros and digestive tract and in endothelium in several organs. Remarkable was the induction of CYP1A in a distinct population of mononuclear cells in the mesonephros. Moreover, oral exposure to TCDD resulted in an increased mitotic activity and an increase of the hepatosomatic index in the 20 and 500 microgram TCDD/kg group respectively. Therefore, exposure to TCDD and related substances may promote the development of liver tumors in the field. Exposure to PCB-126 also significantly reduced the relative thymus volume, but other results indicate that flounder is relatively insensitive to this type of chemicals. Short-term aqueous exposure of flounder to TBTO, in concentrations that were in the same order of magnitude as upper TBT levels measured in the field, caused mortality after 7-12 days associated with gill lesions, and induced reduction of the non-specific resistance and decrease of the relative thymus volume. From these results we therefore conclude that TBTO might play a causal role in, for instance, increased prevalence of lymphocystis virus infections in the field

Reducing uncertainty in the derivation and application of health guidance values in public health practice. Dioxin as a case study

We were requested by the U.S. Environmental Protection Agency (EPA) to clarify the relationships among the minimal risk level (MRL), action level, and environmental media evaluation guide (EMEG) for dioxin established by the Agency for Toxic Substances and Disease Registry (ATSDR). In response we developed a document entitled "Dioxin and Dioxin-Like Compounds in Soil, Part I: ATSDR Interim Policy Guideline"; and a supporting document entitled "Dioxin and Dioxin-Like Compounds in Soil, Part II: Technical Support Document". In these documents, we evaluated the key assumptions underlying the development and use of the ATSDR action level, MRL, and EMEG for dioxin. We described the chronology of events outlining these different health guidance values for dioxin and identified the areas of uncertainty surrounding these values. Four scientific assumptions were found to have had a great impact on this process; these were: (1) the specific uncertainty factors used, (2) the toxicity equivalent (TEQ) approach, (3) the fractional exposure from different pathways, and (4) the use of body burdens in the absence of exposure data. This information was subsequently used to develop a framework for reducing the uncertainties in public health risk assessment associated with exposure to other chemical contaminants in the environment. Within this framework are a number of future directions for reducing uncertainty, including physiologically based pharmacokinetic modeling (PBPK), benchmark dose modeling (BMD), functional toxicology, and the assessment of chemical mixture interactions.

A chimeric aryl hydrocarbon receptor knockout mouse model indicates that aryl hydrocarbon receptor activation in hematopoietic cells contributes to the hepatic lesions induced by 2,3,7, 8-tetrachlorodibenzo-p-dioxin

Pathologic changes associated with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure have been reported in the livers of a wide range of species. While these changes have been extensively described, the mechanisms of toxic interaction(s) that produce these lesions remain unclear. Using an aryl hydrocarbon receptor (Ahr) knockout male mouse chimeric model, we investigated whether the presence of this receptor in hematopoietic and/or parenchymal cells affects TCDD-induced hepatotoxicity. Bone marrow chimeras were produced by hematopoietic reconstitution of irradiated mice. Specifically, chimeras were generated with aryl hydrocarbon receptor (AHR) positive hematopoietic and parenchymal cells (Ahr+/+ animal bone marrow cells into irradiated Ahr+/+ animals), AHR positive hematopoietic and negative parenchymal cells (Ahr+/+ into Ahr-/-), AHR negative hematopoietic and positive parenchymal cells (Ahr-/- into Ahr+/+), and AHR negative hematopoietic and parenchymal cells (Ahr-/- into Ahr-/-). Male wild-type (Ahr+/+) and knockout (Ahr-/-) animals were used as nonchimeric controls. Following TCDD treatment (30 microg/kg body wt), liver sections from mice in each control and chimeric group were histologically evaluated for necrotic and inflammatory changes. TCDD treatment produced moderate inflammation in Ahr+/+ controls and Ahr+/+ into Ahr+/+ chimeras. This response was mild in TCDD-treated Ahr-/-, Ahr-/- into Ahr-/-, Ahr+/+ into Ahr-/-, and Ahr-/- into Ahr+/+ animals and was not different from the corresponding vehicle-treated groups. Moderate necrosis was observed in all TCDD-treated controls or chimeras with AHR-positive parenchyma. No or mild necrosis was observed in TCDD- and vehicle-treated animals containing AHR-negative parenchyma. These data indicate that the presence of AHR in hepatic parenchyma alone is sufficient for TCDD induction of hepatic necrosis, and its presence in hematopoietic cells is necessary for the inflammatory response to TCDD-induced hepatic lesions.

A review of drug-induced lysosomal disorders of the liver in man and laboratory animals

Lysosomotropic agents are selectively taken up into lysosomes following their administration to man and animals [de Duve et al. (1974) Biochem. Pharmacol. 23:2494-2531] The effects of lysosomotropic drugs studied in vivo and in vitro can be used as models of lysosomal storage diseases. These agents include many drugs still used in clinical medicine: aminoglycosides used in antibiotics [Tulkens (1988)]; phenothiazine derivatives; such antiparasitic drugs as chloroquine and suramin; antiinflammatory drugs like gold sodium thiomalate; and cardiotonic drugs like sulmazol [Schneider (1992) Arch. Toxicol. 66:23-33]. Side-effects to these drugs can be caused by their lysosomotropic properties. In addition to drugs, other compounds to which man and animals are exposed (e.g., metals, cytostatics, vitamins, hormones) are also lysosomotropic. Liver cells, especially Kuppfer cells, are known to accumulate lysosomotropic agents. Here we review studies which evaluate lysosomal changes in the liver following administration of lysosomotropic agents to experimental animals, and relate them to toxic side-effects or pharmacological action, as was suggested by de Duve et al. (1974). Common features of lysosomal changes include, the overload of liver lysosomes by non-digestible material; increased size and number of liver lysosomes; inhibition of several lysosomal enzymes; secondary increase in the activity of some lysosomal enzymes; increased autophagy, and fusion disturbances. There was no significant change in endocytosis, except for an increase in the Triton WR 1339 model.

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

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

3,4,3',4'-tetrachlorobiphenyl-induced effects in the rat liver. I. Serum and hepatic retinoid reduction and morphologic changes

The distribution of 3,4,3',4'-tetrachlorobiphenyl (TCB), its effects on serum and hepatic retinoid, content and liver morphology were investigated in adult female WAG/Rij rats. Animals received a single intraperitoneal injection of either a corn oil vehicle, 15 or 200 mg TCB/kg body weight and were killed at 1, 3, 7, and 14 days after treatment. One rat of the high-dose group that had received 200 mg TCB/kg containing 1.85 mCi of 3H-TCB was sacrificed at each sampling time. There was a significant increase in liver weight when expressed as a percentage of body weight in the high-dose group at day 3 (122% of controls), day 7 (116% of controls), and day 14 (110% of controls). There was a rapid rise in the amount of 3H-TCB present in the liver that peaked at day 7 followed by a rapid decline in the amount of radiolabelled material by day 14. Greater than 90% of the radiolabelled material in the liver was parent compound. TCB treatment induced a significant decrease in serum retinol content in the high-dose group at day 3 (39% of controls) and day 7 (46% of controls) following exposure. There was a significant decrease in hepatic retinol content in the high-dose group at day 3 (34% of controls), day 7 (25% of controls), and day 14 (42% of controls) following exposure. TCB treatment induced a significant decrease in hepatic retinyl palmitate content in the high-dose group at day 7 (56% of controls) following exposure. Ultrastructural alterations in hepatocytes included the proliferation and vesiculation of endoplasmic reticulum, and mitochondrial enlargement with paracrystalline inclusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphologic lesions and acute toxicity in rainbow trout (Salmo gairdneri) treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin

To determine effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on growth, mortality, and morphologic lesions in rainbow trout, juvenile Shasta or Wytheville strain fish, obtained from 4 hatcheries, were administered graded single doses of TCDD, 0.1-125 micrograms/kg, ip. TCDD doses of 25 and 125 micrograms/kg caused 85% lethality 2-4 wk after treatment. At these high doses, death occurred before body weight loss could be detected. A lower dose of 5 micrograms/kg caused decreased growth and cumulative mortality of 20% after 11 wk. Stress associated with netting and weighing the fish at weekly intervals significantly shortened the delay period prior to TCDD-induced lethality. Gross and microscopic lesions were evident in rainbow trout treated with 10 micrograms TCDD/kg, but not in fish treated with 1 or 0.1 microgram/kg. Morphologic lesions occurred consistently in epithelial and lymphomyeloid tissues of TCDD-treated fish. Lymphomyeloid lesions included thymic involution, splenic lymphoid depletion, and hypocellularity of hematopoietic tissues in the head kidney and trunk kidney. In association with decreased hematopoiesis, peripheral leukopenia and thrombocytopenia occurred in Shasta strain yearling trout treated with 1 microgram/kg or more TCDD. Regarding epithelial lesions, all 4 hatchery strains treated with 10 micrograms/kg or more TCDD showed multifocal necrosis of gastric cardiac glandular mucosa, 3 of 4 hatchery strains showed vacuolar inclusions in exocrine pancreatic cells, and 2 of 4 hatchery strains showed fin necrosis. The severity and character of lesions in the liver and gastric mucosa varied markedly between hatchery strains of trout. One hatchery strain showed no hepatic lesions, two showed mild hepatocyte lesions, and one exhibited severe diffuse hepatopathy. In this severely affected hatchery strain, hyaline intracytoplasmic inclusions occurred in hepatocytes at 14 and 34 d after TCDD exposure, and bile-duct hyperplasia occurred at 34 d following TCDD exposure. One of 4 hatchery strains showed atrophy of serous gastric glands and 1 of 4 hatchery strains showed hyperplasia of these same glands at 25 and 34 d, respectively, following TCDD treatment. Thus, lymphomyeloid and epithelial tissues are the primary targets for TCDD-induced pathologic lesions in rainbow trout, and the incidence and severity of these lesions is influenced by the strain of trout used and the hatchery from which the trout were obtained.

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.