Toxicology of chlorinated dibenzo-p-dioxins

Blood clearance tests for detecting 2,3,7,8-tetrachlorodibenzo-p-dioxin hepatotoxicity in rats and rabbits

The objective was to determine if a blood clearance test would detect liver dysfunction in rats and rabbits treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Guinea pigs were included as a negative control, because TCDD does not produce detectable hepatotoxicity in this species. TCDD was given as a single dose to male rats (25 microgram/kg, po), rabbits (25 microgram/kg, ip) and guinea pigs (2 microgram/kg, ip) and liver function was assessed 10 days later by determining blood clearance of indocyanine green (ICG) and ouabain. Activity in serum of sorbitol dehydrogenase (SDH), glutamic pyruvic transaminase (SGPT) and gamma glutamyl transpeptidase (gamma GTP) were also measured and light microscopy performed on the liver. The results showed that hepatotoxicity in the rabbit could be detected by a reduction in ICG blood clearance and an elevation in SDH activity. In the rat, ouabain blood clearance was reduced and SDH activity elevated. None of the liver function tests were altered in the guinea pig. These results underline the usefulness of blood clearance tests using ICG and ouabain in detecting TCDD hepatotoxicity in animals.

Role of the endocrine system in the action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the thymus

Several experiments were conducted to study the involvement of the adrenal and the pituitary gland in the acute toxic effects of TCDD. Adrenalectomized or hypophysectomized rats were treated with a single oral dose of 10 or 20 microgram of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg body weight. The reduced growth rate, the hepatotoxic effects and thymic involution induced by TCDD were not prevented by the adrenalectomy. The pituitary gland did not appear to be involved in causing thymic involution. In fact, the thymic effects of TCDD intoxication were even somewhat increased in hypophysectomized rats. Treatment with growth hormone failed to prevent thymic involution or the influence of TCDD on the liver.

2,3,7,8-Tetrachlorodibenzo-p-dioxin toxic effects and tissue levels in animals from the contaminated area of Seveso, Italy

After the environmental contamination by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the area of Seveso, Italy, thousands of small domestic animals (mainly rabbits and poultry) died within a few weeks. Autopsies on dead animals showed various pathological signs, such as hepatic lesions and haemorrhage. TCDD was monitored in animal tissues by gas chromatography-mass fragmentography; rabbit liver levels corresponded fairly well to soil contamination, which indicated that this species can be used as a tool for tracking the presence of TCDD in the environment.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on indocyanine green blood clearance in rhesus monkeys

To assess effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on liver function adult male rhesus monkeys were treated with a single oral dose of acetone/corn oil (control) or 5, 25, or 75 micrograms/kg TCDD. Each monkey was used as its own control and indocyanine green (ICG) blood clearance and the following serum enzymes: glutamic pyruvate transaminase (SGPT), sorbitol dehydrogenase (SDH) and gamma glutamyl transpeptidase (gamma GTP), were measured at regular intervals for 4 weeks before and 17 weeks after treatment. In control monkeys ICG blood clearance and serum enzymes were similar before and after treatment. However, in the monkey that received 5 micrograms/kg TCDD there was a mild increase in ICG blood clearance followed by a slight decrease. The magnitude of this biphasic change was greater in monkeys that received 25 and 75 micrograms/kg TCDD and the decrease in clearance was invariably associated with a 1--2-week period before the monkeys died. SDH and SGPT activities were elevated at some time during the course of intoxication in all TCDD-treated monkeys but gamma GTP activity was not altered. The monkey treated with 5 micrograms/kg TCDD survived but monkeys treated with 25 and 75 micrograms/kg died 4--6 weeks after treatment. Light microscopy of the livers of TCDD-treated monkeys that died revealed fatty infiltration with minimal hepatocellular necrosis.

Metabolism of dibenzo[1,4]dioxan by a Pseudomonas species

Pseudomonas sp. N.C.I.B. 9816 strain 11, when grown on salicylate in the presence of dibenzo[1,4]dioxan, accumulated cis-1,2-dihydroxy-1,2-dihydrodibenzo[1,4]dioxan and 2-hydroxydibenzo[1,4]dioxan in the culture medium. Each metabolite was isolated in crystalline form and identified by a variety of conventional chemical techniques. Crude cell extracts prepared from the parental strain grown with naphthalene oxidized cis-1,2-dihydroxy-1,2-dihydrodibenzo[1,4]dioxan under both aerobic and anaerobic conditions to 1,2-dihydroxydibenzo[1,4]dioxan. Further degradation of this metabolite was not detected.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on splenic lymphocyte transformation in mice after single and repeated exposures

Male CD-1 mice were orally treated with 0.01, 0.1, 1 and 10 micrograms TCDD/kg body wt./week for up to 8 weeks. Randomly selected animals were sacrificed at 2, 4, and 8 weeks of exposure. An additional group was given orally 10 micrograms TCDD/kg and the animals similarly sacrificed. Splenic lymphocytes from these animals were cultured in vitro with or without the presence of phytomitogens, phytohemagglutinin, and pokeweed mitogen. The incorporation of 3H-thymidine was measured as an indication of relative blast formation. Exposure of animals to TCDD, even at the lowest level (0.01 microgram/kg/wk for 2 weeks) caused a marked increase in the thymidine uptake by cultured lymphocytes. The blastogenic response of mitogens was reduced at high levels of TCDD exposure, indicating an immunosuppressive effect. Following a single treatment with 10 micrograms TCDD/kg, the increase in the blast formation was noted at 2 weeks, the effect reduced at 4 weeks, and no difference noticed in treated vs. control cultures 8 weeks after the treatment. Small doses of TCDD stimulate the splenic lymphocyte transformation and this effect, although somewhat dose-related, can be reversed in a relatively short period of time.

Iron deficiency prevents liver toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes hepatocellular damage and porphyria in C57B1/6J mice, among a wide range of toxic effects. We compared the effect of TCDD toxicity in iron-deficient mice with that in mice receiving a normal diet. Porphyria did not develop in the iron-deficient animals, and these animals were also protected from hepatocellular damage and certain other toxic effects of TCDD.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on lipid profiles in tissue of the Fischer rat

Female Fischer 344 rats were given single oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 10, 50 or 100 microgram/kg, and sacrificed 1, 3, 10, 14 or 21 days later. The fatty livers caused by a sub-lethal dose of TCDD involved a temporary increase in triglyceride and free fatty acid levels, with a persistent decrease in levels of sterol esters. In contrast, the fatty livers resulting from a lethal dose of TCDD involved a large increase in cholesterol esters and free fatty acids, with little change in triglyceride levels. These changes appeared to result in part from damage sustained by lysosomes. TCDD also altered the lipoprotein composition of the serum, the fatty acid composition of various lipid classes in liver and serum, and the ultrastructure of the liver (formation of myeloid bodies). A rapid, dose-dependent effect of TCDD, was the elevation of levels of organic-soluble fluorescent pigment in the heart. This pigment was found to match a previously characterized fraction of lipofuscins in fluorescence spectrum and chromatographic properties. The relatioship of these observations to a possible mechanism of toxicity for TCDD involving radical-induced lipid peroxidation is discussed.

Overview of potential mutagenic problems posed by some pesticides and their trace impurities

This review principally addresses a number of aspects of usage of pesticides as well as populations at potential risk and attempts to highlight categories of pesticides whose structures or those of their metabolites and/or trace impurities, degradation and transformation products suggest an a priori mutagenic and/or carcinogenic risk. The pesticides considered include: DDT, hexachlorobenzene (HCB), 2,4,5-T, pentachlorophenol, and various herbicidal precursors (e.g., carbamates, triazines) of nitrosamines and nitroso derivatives. Structural features of a number of halo-unsaturated pesticides (e.g., dichloropropenes) were also reviewed from a viewpoint of contrasting their potential mutagenicity with that of vinyl chloride and vinylidene chloride. Additionally the mutagenicity of the organophosphorus pesticide Trichlorophon is contrasted with that of its degradation products.

Genetically mediated induction of drug-metabolizing enzymes associated with congenital defects in the mouse

Various polycyclic aromatic compounds induce certain monooxygenase activities, including aryl hydrocarbon (benzo[a]pyrene) hydroxylase (EC 1.14.14.2), and cytochrome P1-450 in the liver and many nonhepatic tissues of the mouse. This induction process is controlled by the Ah locus. Genetic differences that have been shown in the past to be associated with the Ah locus include an increased susceptibility to chemical carcinogenesis, mutagenicity in vitro, and drug toxicity--manifested as hepatic necrosis, aplastic anemia, or shortened survival time. Pregnant mice received a single injection of 3-methylcholanthrene or 7,12-dimethylbenz[a] anthracene between day 5 and day 13 of gestation, and the uterine contents were examined on day 18. Striking increases were observed in the incidence of MC-1 and DMBA-induced resorptions and congenital malformations in the aromatic hydrocarbon "responsive" C57BL/6N inbred strain, and of DMBA-induced resorptions in the "responsive" C3H/HeN and BALB/cAnN strains--when compared with the similarly treated genetically "nonresponsive" AKR/N strain. These data suggest but do not prove that an association exists between the Ah locus and developmental toxicity, i.e., teratogenesis. Although numerous teratogenic differences among inbred mouse strains have previously reported, this study is unique in that the genetic differences in teratogenicity observed were predicted in advance on the basis of known differences among these strains in polycyclic hydrocarbon metabolism regulated by the Ah locus.

3,4,3',4'-Tetrachloro azoxybenzene and azobenzene: potent inducers of aryl hydrocarbon hydroxylase

Two unwanted contaminants, 3,4,3',4'-tetrachloroazoxybenzene (TCAOB) and 3,4,3',4'-tetrachloroazobenzene (TCAB), formed in the commercial synthesis of 3,4-dichloroaniline or of herbicides made from 3,4-dichloroaniline, were responsible for three outbreaks of acne among chemical workers. TCAOB and TCAB are approximately isosteric to 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,7,8-tetrachlorodibenzofuran, two well-known contaminants that cause acne. All four of these agents are potent inducers of hepatic aryl hydrocarbon hydroxylase activity and compete for stereospecific binding sites in the hepatic cytosol, which are thought to be the receptor sites for the induction of this enzyme. Among the chlorinated azoxy and azobenzenes, the potency of a congener to induce aryl hydrocarbon hydroxylase activity correlates with its binding affinity for the hepatic cytosol specific binding sites and its capacity to induce acne; this relation between structure and activity parallels that observed for the chlorinated dibenzo-p-dioxins and dibenzofurans.

Pathological changes in the liver of mice given 2,3,7,8-tetrachlorodibenzo-p-dioxin

In C57BL/6 mice a single oral dose of 2,3,7,8-tetrachlorodibenzodioxin (LD50 126 mug/kg) results in loss of body weight and death with an enlarged fatty liver after ca. 21 days. A progressive necrotic centrilobular liver lesion is also seen.

Polychlorinated dibenzo-p-dioxins. Separation and identification of isomers by gas chromatography-mas spectrometry

Attempts were made to synthesize all polychlorinated dibenzo-p-dioxin isomers containing six to eight chlorine atoms by micro-scale pyrolysis of different polychlorophenates. Eight of the ten possible hexachlorodibenzo-p-dioxins, the two hepta- and the octachlorodibenzo-p-dioxin were observed and separated by gas chromatography using glass capillary columns. Without actual isolation of these toxic materials, isomers were characterized by gas chromatography and mass spectrometry. Commercial chlorinate phenols were analyzed for the presence of these isomers. The major hexachlorodibenzo-p-dioxin observed in two commerical products was the unexpected 1,2,3,7,8,9-substituted isomer, which was not formed as the main dioxin component in any of the pyrolysis experiments. The same isomer was reported to be isolated from toxic fat and identified by X-ray crystallography.

Tetrachlorodibenzodioxin: an accidental poisoning episode in horse arenas

Tetrachlorodibenzodioxin was identified as the apparent cause of an outbreak of poisoning in humans, horses, and other animals. Exposure was related to the spraying of contaminated waste oil on riding arenas for dust control. The contamination resulted from improper disposal of a toxic industrial waste. The pathologic effects and chemical identification of tetrachlorodibenzodioxin are described.

Induction and suppression of hepatic and extrahepatic microsomal foreign-compound-metabolizing enzyme systems by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on a number of hepatic and extrahepatic foreign-compound-metabolizing enzyme systems in microsomes from rats, rabbits and guinea pigs were investigated. Following TCDD treatment, the N-demethylation of benzphetamine, aminopyrine and ethylmorphine was suppressed in hepatic microsomes from male but not from female rats. However, both cytochrome P-450 and benzpyrene hydroxylase were significantly stimulated in hepatic microsomes from both male and female rats at doses as small as 1 mug TCDD/kg body weight. The inductive effect on rat hepatic microsomal enzymes was considerably more persistent than the suppressive effect. Following a single oral dose of 25 mug TCDD/kg weight, benzpyrene hydroxylase of male rat liver microsomes remained significantly elevated for 73 days but the suppression of benzphetamine N-demethylase had gone after 35 days. The induction of benzpyrene hydroxylase in male rat liver microsomes by TCDD was independent of the age of the rat and the levels to which this enzyme was increased was similar in male rats of all ages. However, the suppression of benzphetamine N-demethylase in male rat liver microsomes was age related: the suppression was seen only in adult animals and in the very young (10 days old) the enzyme was actually induced by TCDD. Inductive effects appeared in both smooth and rough-surfaced hepatic microsomes from male rats but the suppression of N-demethylation occurred only in the smooth-surfaced microsomes (SER). In microsomes from extrahepatic tissues of the rat, induction of mixed-function oxidases (MFOs) by TCDD occurred only in the kidney. However, UDPglucuronyltransferase was induced in microsomes from lung, kidney, intestine and brain but not testes. The response in the rabbit and guinea pig to TCDD differed considerably from that in the rat. Benzpyrene hydroxylase was unaffected in hepatic microsomes from the guinea pig and actually suppressed in microsomes from rabbit liver. Benzphetamine N-demethylase was also suppressed in rabbit liver microsomes. Glucuronyl-transferase was unaffected by TCDD in microsomes from liver, lung or kidney of the rabbit and guinea pig. The only lung enzyme responsive to TCDD was biphenyl 4-hydroxylase of the rabbit and guinea pig. Suppression was not observed in any of the extraheptic tissues studied and may be confined to only certain hepatic systems.

A survey of the embryotoxic effects of TCDD in mammalian species

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