Toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Histopathological Alterations in the Livers of Chronic Hepatitis Patients Exposed to Agent Orange/Dioxin in Vietnam

We investigated changes in some laboratory indices and the liver histology of chronic hepatitis patients who were exposed to dioxin. In 2014, we collected liver biopsy samples for histopathological examination from 33 chronic hepatitis patients living around the Da Nang Airbase, which is a dioxin-contaminated area due to the herbicide spraying in Vietnam. Dioxin exposure was measured by its levels in the blood. METAVIR classification was used to clarify the liver fibrosis stage. Laboratory tests included ten biochemical and six hematological indices that were measured in the blood. A regression linear model and binary logistic regression were used for data analysis. The observed alterations in the liver at the histological level mainly comprised hydropic degenerative hepatocytes, lymphocytes and polynuclear leukocytes surrounding the liver cells and granular and lipoic degeneration. In addition, increased TCDD levels were associated with increasing aminotransferase (AST), alanine aminotransferase, protein and total bilirubin levels and liver fibrosis stage. Similarly, increased TEQ-PCDD/Fs levels were associated with higher levels of AST and protein and liver fibrosis stage. In conclusion, dioxin exposure altered the liver histology and increased some biochemical marker indices and the liver fibrosis stage of chronic hepatitis patients living in dioxin-contaminated areas in Da Nang, Vietnam.

Risk for animal and human health related to the presence of dioxins and dioxin-like PCBs in feed and food

The European Commission asked EFSA for a scientific opinion on the risks for animal and human health related to the presence of dioxins (PCDD/Fs) and DL-PCBs in feed and food. The data from experimental animal and epidemiological studies were reviewed and it was decided to base the human risk assessment on effects observed in humans and to use animal data as supportive evidence. The critical effect was on semen quality, following pre- and postnatal exposure. The critical study showed a NOAEL of 7.0 pg WHO2005-TEQ/g fat in blood sampled at age 9 years based on PCDD/F-TEQs. No association was observed when including DL-PCB-TEQs. Using toxicokinetic modelling and taking into account the exposure from breastfeeding and a twofold higher intake during childhood, it was estimated that daily exposure in adolescents and adults should be below 0.25 pg TEQ/kg bw/day. The CONTAM Panel established a TWI of 2 pg TEQ/kg bw/week. With occurrence and consumption data from European countries, the mean and P95 intake of total TEQ by Adolescents, Adults, Elderly and Very Elderly varied between, respectively, 2.1 to 10.5, and 5.3 to 30.4 pg TEQ/kg bw/week, implying a considerable exceedance of the TWI. Toddlers and Other Children showed a higher exposure than older age groups, but this was accounted for when deriving the TWI. Exposure to PCDD/F-TEQ only was on average 2.4- and 2.7-fold lower for mean and P95 exposure than for total TEQ. PCDD/Fs and DL-PCBs are transferred to milk and eggs, and accumulate in fatty tissues and liver. Transfer rates and bioconcentration factors were identified for various species. The CONTAM Panel was not able to identify reference values in most farm and companion animals with the exception of NOAELs for mink, chicken and some fish species. The estimated exposure from feed for these species does not imply a risk.

Protective effect of prostacyclin against pre-cardiac edema caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin and a thromboxane receptor agonist in developing zebrafish

The role of prostaglandin pathways has been suggested in some toxicological responses to dioxins. Cyclooxygenase type 2b (COX2b), thromboxane synthase, and the thromboxane receptor (TP) pathway have been implicated in mediating 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced pre-cardiac edema in developing zebrafish at 55 h post fertilization (hpf). Pre-cardiac edema refers to edema located in a small cavity between the heart and body wall of zebrafish eleutheroembryos. In the present study, we assessed the role of prostacyclin, which counteracts some biological effects of thromboxane, in TCDD-induced pre-cardiac edema. Pre-cardiac edema induced by TCDD exposure (0.5 and 1 ppb) beginning at 24 hpf was markedly inhibited by exposure to beraprost (5 and 10 μM), a prostacyclin receptor (IP) agonist, beginning at 33 hpf. The preventive effect of beraprost was reduced by exposure to CAY10441 (10 μM), an IP antagonist starting at 33 hpf. Knockdowns of the IP receptor (IP-KD) with two different morpholinos caused edema by themselves and enhanced pre-cardiac edema caused by the low concentration of TCDD (0.5 ppb). On the other hand, short exposure beginning at 48 hpf to U46619 (7.5-30 μM), a thromboxane receptor agonist caused pre-cardiac edema, which was inhibited by exposure beginning at 48 hpf to both ICI-192,605 (24 μM), a TP antagonist, and beraprost. Expression of prostacyclin synthase was increased from fertilization, plateaued by 48 hpf, and was maintained until at least 96 hpf. Overall, the results demonstrate a preventive effect of prostacyclin on TCDD-induced pre-cardiac edema in developing zebrafish.

Dioxin-Produced Alteration in the Profiles of Fecal and Urinary Metabolomes: A Change in Bile Acids and Its Relevance to Toxicity

This study investigated dioxin-induced changes in metabolomes in pubertal rat excrement. The administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or restricting dietary intake (pair-fed group) markedly altered the metabolomic profile including lipids, hormones, and vitamins in the urine and feces. TCDD caused an increase in the fecal chenodeoxycholic acid and taurocholic acid content and in urinary adrenaline and 17β-estradiol, while the urinary melatonin level was reduced by TCDD. These changes were not observed in the pair-fed group. In accordance with the elevated level of fecal bile acids, TCDD reduced the intestinal expression of the apical sodium-dependent bile salt transporter, which plays a role in resorbing bile acids from the bile duct. In addition, CYP7A1, a rate-limiting enzyme for bile acid biosynthesis, was attenuated by TCDD treatment, although TCDD induced hepatic CYP8B1, an enzyme essential for cholic acid synthesis. Supplying cholic acid or chenodeoxycholic acid to TCDD-exposed rats tended to restore the TCDD-produced reduction in serum triglycerides, whereas no similar trend was observed in wasting syndrome and lipid accumulation in the liver. These results suggest that: 1) TCDD alters the circulating levels of bile acids and hormones via a mechanism distinct from an attenuation in dietary intake, although the majority of TCDD-induced changes in nutrient contents in the excrement is due to a reduction in food intake; and 2) TCDD facilitates the excretion of bile acids and disrupts their biosynthesis, resulting in the disturbance of lipid homeostasis.

[Environmental dioxin compounds as the cause of endometriosis and other diseases]

There has been much debate of late about whether or not dioxin, an industrial toxin, could be a causative agent in the onset of endometriosis, a gynaecological disease associated with infertility and pain. Studies found either no difference in serum dioxin concentrations when cases were compared to controls or a non-significant increase, or reached low statistical power. The introductory results on Rhesus monkey contradict with the observations on mice fed with dioxin and oestrogen simultaneously. Genetic comparison shows that human belongs to the dioxin resistant races so dioxin concentrations measured in the population could not cause disease especially not an oestrogen dependent one, like endometriosis.

The topical application of 2,3,7,8-tetrachlorodibenzo-p-dioxin lacks skin tumor-promoting potency but induces hepatic injury and tumor necrosis factor-alpha expression in ICR male mice

One of the most toxic environmental pollutants known to man is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). There is growing evidence that indicates TCDD is a potent tumor promoter in rat and mouse liver, as well as in mouse skin. The mouse skin carcinogenesis model has been used extensively to assess whether a chemical or physical agent carries a carcinogenic hazard to humans and to define the mechanism involved with the carcinogenic effects. We applied the mouse skin model to ICR male mice and the results showed that following the application of DMBA, repeated dorsal application of all doses of TCDD produced no papillomas. These findings imply that the ICR male mouse is an extremely insensitive strain as a TCDD-induced two-stage mouse skin carcinogenesis model. However, severe hepatic injuries and wasting syndrome were seen in mice treated topically with TCDD. Meanwhile, serum TNF-alpha levels increased during the experimental periods. Inflammatory cell infiltration, fatty liver, and nodule formation could be observed in damaged livers. Elevated hepatic EROD activity and urinary 8-epi-PGF2alpha were also observed in mice with short-term exposure of TCDD.

Basis for a proposed reference dose (RfD) for dioxin of 1-10 pg/kg-day: a weight of evidence evaluation of the human and animal studies

The dioxins have been perhaps the most studied of all chemicals to which humans are routinely exposed. It has been reported that more than 5,000 scientific papers have been published that have evaluated the toxicology of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Although the cancer hazard posed by this chemical has probably received the bulk of attention over the past 20 years, the U.S. Environmental Protection Agency (EPA) and the recent U.S. EPA Science Advisory Board (SAB) that reviewed the "Reassessment" have suggested that the noncancer hazard may well be more important than the cancer hazard at current background doses to the general public. The World Health Organization (WHO) and U.K. Food Standards Agency (FAO) committee (JECFA) on dioxins has reached similar conclusions. This article reviews the published studies involving laboratory animals and humans that address the noncancer effects. Based on our review, developmental toxicity is the most sensitive effect of TCDD consistently seen in mice and rats. Specifically, of the various studies, a no-observed-adverse-effects level (NOAEL) of 13 ng/kg (maternal body burden) was identified as the most pertinent for deriving a reference dose (RfD) for humans. Although more than a dozen different adverse effects have been reported in various studies of humans over the past 25 years, the most consistent clinically important adverse effect of human exposure appears to be chloracne. Following a review of all published studies, we concluded that the best estimate of a LOAEL for production of chloracne is approximately 160 ng/kg (body burden). Based on our analysis, an RfD of between 1 and 10 pg/kg-d (TCDD TEQ) is consistent with the objectives of this risk criterion. Maintaining a lifetime average daily dose below this concentration, based on what is known today, should prevent noncancer effects in virtually all persons. This value is consistent with the JECFA recommendation of 70 pg/kg-mo.

Biochemical and toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in immature male and female chickens

It has been reported that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced body wasting in mammals is associated with decreased adipose tissue lipoprotein lipase (LPL) and glucose transporting (GT) activity with differential sensitivity between genders. This study extends those findings to chickens as an avian model. A significant decrease in body weight gain was demonstrated in immature male and female chickens 10 days after treatment with a single intraperitoneal (i.p.) dose of 10 and 100 microg TCDD/kg. Body weight gain decrease was associated with hepatomegaly and induction of hepatic CYP1A enzymes in both genders. The increase in liver/body weight ratio (48%) and the decreased LPL activity (28%) were significant only in females at 10 microg TCDD/kg. However, the increase in liver/body weight ratio (31%) and the decrease in LPL activity (26%) were significantly demonstrated in males at 100 microg TCDD/kg. Levels of GT were significantly decreased in females (46%) and in males (48%) following treatment with 10 microg TCDD/kg and 100 microg TCDD/kg, respectively. Therefore, in chickens, as in mammals, the TCDD-induced body wasting is accompanied with decreased LPL activity and decreased GT activity and the magnitude of these changes is gender dependent. In contrast to mammals, this study suggests that female chickens are equally, if not more responsive to TCDD toxicity than males.

Interaction of estrogen and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with hepatic fatty acid synthesis and metabolism of male chickens (Gallus domesticus)

This study tested the hypothesis that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) antagonizes estrogen-induced hepatic lipid synthesis and metabolism in birds. Twenty immature male chickens (Gallus domesticus) were divided evenly into four groups: (1) vehicle control; (2) estrogen alone (1.0 mg/kg estradiol cypionate injected on three consecutive days); (3) TCDD alone (50 microg/kg injected on the fourth day); and (4) a combination of the estrogen and TCDD treatments. On day 14, liver samples were collected for quantitative fatty acid analysis by capillary gas chromatography. Birds treated with estrogen alone had increased total triacylglyceride concentrations with specific increases in the Delta9 desaturase products 16:1n7, 18:1n7, 18:1n9, and 20:1n9. In addition, estrogen treatment specifically increased 22:6n3 concentrations in both triacylglycerides and phospholipids. However, these increases in Delta9 desaturase products or 22:6n3 did not occur for birds treated with estrogen in combination with TCDD. TCDD and estrogen plus TCDD treatments increased phospholipid concentrations of the diet-derived polyunsaturated fatty acids 18:2n6, 18:3n6, 20:3n6, 18:3n3, and 20:5n3, although only the estrogen plus TCDD group had significantly increased total phospholipids. In cholesterol esters, all three treatments decreased concentrations of total fatty acids, saturated fatty acids, and Delta9 desaturase products compared to the control group.

Expression of the aryl hydrocarbon receptor (AhR) and AhR nuclear translocator during chick cardiogenesis is consistent with 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced heart defects

We examined cardiotoxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the chick embryo and the cardiac expression of transcription factors, the aryl hydrocarbon receptor (AhR) which binds TCDD, and its dimer partner, the AhR nuclear translocator (Arnt). Chicken eggs were injected with control (triolein) or 1.0 pmol TCDD/g egg prior to incubation and collected on Day 10 when cardiomorphogenesis is complete. Relative to controls, TCDD increased heart wet weight (27.2 +/- 0.5 versus 36.6 +/- 1.3 mg, p < 0.001) and dry weight (2.7 +/- 0.1 versus 3.1 +/- 0.1 mg, p < 0.01), and tended to increase heart myosin content (3.5 +/- 0.6 versus 6.3 +/- 2.5 microg, p < 0.07), suggesting an increase in cardiac muscle mass and edema. Histologic and morphometric analyses revealed that 10/13 TCDD-exposed hearts exhibited enlarged right and left ventricles, thickened ventricular septum, and a thinner left ventricular wall with increased trabeculation, and 4/13 exhibited ventricular septal defects compared to controls (0/23). To evaluate AhR and Arnt expression, untreated chick embryos were collected on Days 2.2, 3, 4, 5, and 8 of incubation, preserved in Bouin's fixative, sectioned, and stained with AhR and Arnt antibodies. The AhR was expressed ubiquitously in cardiac myocytes, while Arnt expression was restricted to myocytes overlying developing septa: atrioventricular canal, outflow tract, and atrial and ventricular septa. Both proteins were absent from endocardium and endocardial-derived mesenchyme. In addition, cardiac expression of an AhR/Arnt target, cytochrome P4501A1, was restricted to myocardium coexpressing AhR and Arnt. Thus, the spatial and temporal expression of AhR and Arnt suggests that the developing myocardium and cardiac septa are potential targets of TCDD-induced teratogenicity, and such targets are also consistent with cardiac hypertrophy and septal defects observed following TCDD exposure.

Characterization of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced brain serotonin metabolism in the rat

It has previously been shown that a lethal dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increases the brain concentrations of serotonin precursor, tryptophan, and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in TCDD-susceptible Long-Evans but not in TCDD-resistant Han/Wistar rats. In the present study, TCDD (50 micrograms/kg; LD100 for Long-Evans and nonlethal for Han/Wistar rats) enhanced de novo biosynthesis of serotonin in the brain of Long-Evans but not Han/Wistar or food-restricted Long-Evans rats 10 days after exposure. Furthermore, TCDD increased the plasma level of free tryptophan in Long-Evans rats alone, which may be causally related to the observed effects of TCDD on brain tryptophan levels. Administration of hemin modified the time course of TCDD-induced anorexia although 10 day cumulative food consumption was not altered. Hemin tended to attenuate TCDD-elicited increases in brain serotonin turnover, whereas a beta-adrenergic blocker, propranolol, did not. In the majority of Long-Evans rats, TCDD inhibited the main tryptophan degrading enzyme in the liver, tryptophan pyrrolase, but the rest exhibited augmented activities; these effects were not altered by hemin. TCDD increased the plasma levels of nonesterified fatty acids in Long-Evans (five-fold) but not in Han/Wistar rats. A slight elevation (two-fold) was also seen in food-restricted Long-Evans rats. It is concluded that TCDD selectively promotes brain serotonin turnover in Long-Evans rats and this acceleration is related to increased plasma levels of free tryptophan. The inhibition of tryptophan catabolism in the liver and elevation of plasma nonesterified fatty acids may contribute to these changes.

Developmental and reproductive toxicity of dioxins and related compounds: cross-species comparisons

Developmental toxicity to TCDD-like congeners in fish, birds, and mammals, and reproductive toxicity in mammals are reviewed. In fish and bird species, the developmental lesions observed are species dependent, but any given species responds similarly to different TCDD-like congeners. Developmental toxicity in fish resembles "blue sac disease," whereas structural malformations can occur in at least one bird species. In mammals, developmental toxicity includes decreased growth, structural malformations, functional alterations, and prenatal mortality. At relatively low exposure levels, structural malformations are not common in mammalian species. In contrast, functional alterations are the most sensitive signs of developmental toxicity. These include effects on the male reproductive system and male reproductive behavior in rats, and neurobehavioral effects in monkeys. Human infants exposed during the Yusho and Yu-Cheng episodes, and monkeys and mice exposed perinatally to TCDD developed an ectodermal dysplasia syndrome that includes toxicity to the skin and teeth. Toxicity to the central nervous system in monkey and human infants is a potential part of the ectodermal dysplasia syndrome. Decreases in spermatogenesis and the ability to conceive and carry a pregnancy to term are the most sensitive signs of reproductive toxicity in male and female mammals, respectively.

Toxicity and reproductive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in ring-necked pheasant hens

Hen pheasants (Phasianus colchicus) injected with graded single doses of TCDD (6.25, 25, or 100 micrograms/kg) exhibited delayed-onset body weight loss and mortality--classic signs of the wasting syndrome. The lowest single dose of TCDD to produce this effect was 25 micrograms/kg. When hen pheasants were treated weekly with far lower doses of TCDD (0.01-1.0 microgram/kg/wk) for 10 wk, signs of the wasting syndrome and mortality were also produced. The lowest cumulative TCDD dose required to produce the response, using a weekly dosing regimen, was 10 micrograms/kg. Furthermore, using this dosing regimen, egg production by hens treated with a cumulative TCDD dose of 10 micrograms/kg was reduced, as was hatchability of their eggs. We conclude that hen pheasants are responsive to the overt toxic effects of TCDD and that the lowest cumulative dose of TCDD that produces overt signs of toxicity, 10 micrograms/kg, also reduces egg production and egg hatchability.

Chloracne caused by ingestion of olive oil contaminated with PCDDs and PCDFs

1. All members of a Spanish family (father, mother and six children) developed chloracne. 2. The causative agent was found to be the family's stock of olive oil, which had become contaminated with polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), pentachlorophenol, and hexachlorobenzene. 3. The more highly chlorinated PCDDs, in particular octachlorodibenzo-p-dioxin, were the predominant congeners in the oil. 4. Three members of the family exhibited either an overt or a sub-clinical disturbance of kidney function. The father also had a chronic respiratory problem. These changes could not be unequivocally attributed to the PCDDs. 5. Experimental toxicity of the oil was limited to the development of an hepatic porphyria in mice. 6. A serum sample, taken 5 years after consumption of the oil ceased, contained high levels of the PCDDs and PCDFs. Extrapolation back to ingested dose was used to validate dosage estimates. 7. The use of toxicity equivalence factors (TEFs) provided estimates of cumulative dosage to produce chloracne as 0.13-0.31 micrograms 2378-TCDD kg-1 (using EPA TEFs) or 6.7-16 micrograms 2378-TCDD kg-1 (using Nordic/NATO TEFs). 8. This is the first incident in which human toxicity is related primarily to ingestion of PCDDs and for which estimates of dosage can be made.

Pleiotropic effect of the gene hairless on hepatotoxicity of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin in mice

Treatment of mice of the A2G-hr/+ congenic line with 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in the development of hepatic porphyria over a period of 4 weeks. Female mice responded to a lesser extent than did males. The degree of porphyria in haired heterozygotes (hr/+) was less than in the corresponding hairless homozygotes (hr/hr) and the haired mice had lower resting metabolic rates than hairless mice. Adaptation of mice of either genotype to a 32-33 degrees C environment resulted in a decrease in resting metabolic rate and a reduction in hepatic porphyrin levels. Histologically-demonstrated necrotic changes in livers were accompanied by increased activity of alanine aminotransferase and sorbitol dehydrogenase in the plasma; however, there was no clear temporal trend in plasma enzyme levels. Elevated environmental temperature reduced the plasma alanine aminotransferase activity. The study provided evidence for a pleiotropic effect of variation at the hr locus being expressed in TCDD hepatotoxicity. Suggestions for mechanisms whereby the effect can be mediated through alterations in resting metabolic rate are made.

Effect of a sublethal dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin on interscapular brown adipose tissue of rats

The effect of a sublethal dose (15 micrograms/kg) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was studied in selected tissues of male Sprague-Dawley rats by histological techniques 1, 3, 7 and 14 days after TCDD dosage. Histology of the heart, muscle, white adipose tissue, pancreas and the thyroid was unremarkable and that of the liver was found in agreement with previous reports. However, considerable changes were seen in interscapular brown adipose tissue (IBAT) of TCDD-treated rats. Initial accumulation followed by depletion of lipids, appearance of glycogen, cellular, mitochondrial and nuclear transformations were observed. In conjunction with other experiments it is concluded that a sublethal dose of TCDD alters fat and glucose metabolism in IBAT.

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.

Relationship of the wasting syndrome to lethality in rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin

Young adult male Sprague-Dawley rats treated with a LD95 dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibited a progressive reduction in feed intake and body weight until death occurred 15 to 32 days post-treatment. The time course and magnitude of weight loss and lethality of pair-fed control rats were essentially identical to that of TCDD-treated rats with each pair-fed control animal dying within 3 days of its TCDD-treated partner. Body composition analysis of the dead animals revealed that the total amounts of protein, fat, water, and ash in the carcasses of TCDD-treated and pair-fed control rats were each reduced to a similar extent. The temporal pattern of daily feed intake in TCDD-treated and pair-fed control rats (3 meals/day) or (1 meal/day) did not influence the results. Studies conducted at LD25-62 doses of TCDD in male Sprague-Dawley rats of different ages--weanling (90 g), young adult (275 g), and mature (450 g)--showed that the severity of the wasting syndrome in all age groups was greatest for animals that died. Also, young adult rats treated with a LD25 dose of TCDD that died displayed the same degree of hypophagia and weight loss prior to death as rats administered a LD95 dose. Histopathology of the liver and gastrointestinal tract was compared in TCDD-treated (LD95 dose) and pair-fed control rats killed 1 day before they otherwise would have died. Hepatocytes of TCDD-treated rats were enlarged relative to those of pair-fed control rats and contained nuclei that varied in size and number. Pair-fed control rats exhibited atrophy of the liver cords due to a decrease in the cytoplasmic volume of their hepatocytes. The stomach and small intestine of TCDD-treated rats were histologically similar to those of ad libitum-fed controls. In contrast, the glandular mucosa of the stomach of pair-fed control rats was ulcerated and the intestinal mucosa was atrophied. Stomach ulcers were the source of clotted blood found throughout the gastrointestinal tract of pair-fed control rats but not that of TCDD-treated animals. These findings demonstrate that hypophagia-induced weight loss is one of perhaps several responses that contribute to the death of TCDD-treated rats. That other responses are also involved is suggested by differences between pair-fed control and TCDD-treated rats in the weight and histopathology of certain organs. In addition, gastrointestinal blood loss contributes to the death of pair-fed control rats but not TCDD-treated animals.

Continued depression of hepatic uroporphyrinogen decarboxylase activity caused by hexachlorobenzene or 2,3,7,8-tetrachlorodibenzo-p-dioxin despite regeneration after partial hepatectomy

Hepatic uroporphyrinogen decarboxylase activity in male C57BL/10 mice was maintained in regenerated liver after recovery from two-thirds hepatectomy. In contrast, there was little increase in enzyme activity in regenerated liver from animals previously treated with hexachlorobenzene (HCB) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). These chemicals initially cause depression of uroporphyrinogen decarboxylase activity over a time much longer than the period allowed for regeneration. Estimation of HCB levels showed that there was only a small amount of redistribution to the liver during regrowth. The results demonstrate that HCB and TCDD induce either formation of a toxic metabolite or some other inhibitory process and that this can be sustained for a long period which delays recovery to the normal state.

Prevention of TCDD toxicity in laboratory rodents by addition of charcoal or cholic acids to chow

The mortalities of mice, rats and guinea-pigs given a single lethal dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were substantially reduced by feeding them with chows containing 2.5 or 5% activated charcoal, which presumably enhances elimination of the toxic agent from the organism. Chows with 0.25 or 0.5% cholic acid and dehydrocholic acid added had a similar protective action on mice intoxicated with TCDD. Since no treatment is currently available for this type of poisoning, charcoal-whose safe clinical use is well established-is worth considering in view of its potential benefit to humans acutely exposed to TCDD.

Incomplete correlation of 2,3,7,8-tetrachlorodibenzo-p-dioxin hepatotoxicity with Ah phenotype in mice

Pretreatment of male mice of the inbred strains A2G, BALB/c, C57BL/10, and AKR with iron dextran synergized the action of a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 75 micrograms/kg) in causing hepatic porphyria and necrosis 35 days later. There was no effect in DBA/2 mice. Increased porphyrin levels were associated with decreased hepatic activity of uroporphyrinogen decarboxylase. Iron alone had no effect on porphyrin levels or decarboxylase activity. In male BALB/c mice given TCDD alone there was a delay in the onset of porphyria. Female BALB/c, AKR, and AKR X DBA/2 F1 mice were more resistant to the porphyrinogenic effect of TCDD than males. Development of porphyria did not correlate with Ah phenotype of the mice. The inheritance of sensitivity to TCDD in crosses of the AKR and DBA/2 strains, both Ah nonresponsive, was studied by a biometrical genetic analysis. The inheritances of increased porphyrin levels and of increased plasma activity of enzymes indicative of hepatic necrosis were both complex. Segregation of alleles at more than one locus was required to explain the data. A lack of correlation of porphyrins with plasma enzyme levels in the F2 generation suggested that the expression of these traits was determined independently. Genes other than Ah influence the development of TCDD-induced hepatotoxicity in mice.

Characterization of the wasting syndrome in rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin

Treatment of male rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes a dose-dependent decrease in body weight, feed intake, resting and total oxygen consumption, and spontaneous motor activity. In animals treated with a nonlethal dose (5 or 15 micrograms/kg), feed intake and oxygen consumption recover within 3 weeks post-treatment to levels appropriate for the reduced weight of the animals. Rats treated with a lethal dose (50 micrograms/kg) lose weight continuously after treatment and typically die at a body weight approximately half that of age-matched, control rats. The similar dose and time dependencies for reduction of feed intake and weight suggest that hypophagia is the major factor responsible for weight loss in TCDD-treated rats. To determine if this hypophagia is a primary or secondary effect of TCDD treatment, rats whose body weights were reduced by food restriction prior to treatment (25 micrograms/kg) were studied. When allowed to feed ad libitum immediately after treatment, these animals exhibited relative hyperphagia and weight gain demonstrating that TCDD did not impair their capacity to feed. This finding suggests that the primary effect of TCDD is not on a system that controls feed intake, but rather on one that regulates body weight. It is proposed, as a heuristic model of the wasting syndrome, that TCDD treatment lowers a "set point" for regulated body weight in the rat in a dose-dependent fashion and that hypophagia serves, as a secondary response, to reduce the animal's weight to the lower regulation level determined by the dose administered.

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.

Excretion and distribution of two occupational toxicants, tetrachloroazobenzene and tetrachloroazoxybenzene in the rat

The clearance profile and tissue distribution of 2 occupational toxicants, 3,3',4,4'-tetrachloroazobenzene (TCAB) and 3,3',4,4'-tetrachloroazoxybenzene (TCAOB), were examined in male Sprague-Dawley rats. TCAB was found to be cleared from the body more rapidly than TCAOB when a single dose of 14C-labeled TCAB or TCAOB was administered orally. While 66% of the administered TCAB dose was excreted via the urine and feces within the first 24 h, TCAOB-treated animals were only able to clear 37% of the administered dose by the same elimination route. The half-lives for elimination of TCAB and TCAOB were estimated to be 18 h and 34 h, respectively. Examination of the tissue distribution of the remaining radioactivity indicated that, for both compounds, the adipose tissue contained the highest level of radioactivity. The rapid elimination of TCAB and TCAOB by rats may explain in part the reduced toxicity of these 2 compounds to whole animals in comparison to the isosteric 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Natural history of TCDD-induced liver lesions in rats as observed by transmission electron microscopy during a 32-week period after a single intraperitoneal injection

Forty-two male rats were injected with a single intraperitoneal dose of TCDD in acetone and corn oil and sacrificed after 2, 4, 8, 16, 24, and 32 weeks, to study the long-term effects of a single injection. The liver lesions become progressively worse up to the 16th week and appear thereafter to slowly regress.

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.

Effects of halogenated dibenzo-p-dioxins on plasma disappearance and biliary excretion of ouabain in rats

A single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7-tribromodibenzo-p-dioxin (2,3,7-TBDD), 1,2,3,7,8,9-hexachlorodibenzo-p-dioxin (1,2,3,7,8,9-HCDD), 1,2,4,6,7,9-hexachlorodibenzo-p-dioxin (1,2,4,6,7,9-HCDD), or 1,3,6,8-tetrachlorodibenzo-p-dioxin (1,3,6,8-TCDD) was given to male rats (25 micrograms/kg, p.o.) and plasma concentration and biliary excretion of ouabain assessed 10 days later. Treatment of TCDD, 2,3,7-TBDD and to a lesser extent 1,2,3,7,8,9-HCDD increased the plasma concentration of ouabain and decreased its excretion into ouabain. TCDD, 2,3,7-TBDD and to a lesser extent, 1,2,3,7,8,9-HCDD decreased the bile flow. Liver wet weight was increased in TCDD and 2,3,7-TBDD treated rats. The magnitude of depression in ouabain excretion by those compounds was closely related to the reported relative binding affinity of the compound to liver cytosol and their induction potency of aryl hydrocarbon hydroxylase activity.

Toxicity of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)

In summary, the toxicity of TCDD has been comprehensively examined in multiple acute, subchronic, and chronic studies. Acute toxicity studies have shown marked species differences, with up to a 10,000-fold difference between the single oral LD50 dose for the guinea pig and hamster. TCDD is capable of causing an acnegenic response in man and a similar skin response in certain animals. It is also a potent inducer of microsomal enzymes in some but not all species. A dose-related suppression of cell-mediated immunity has been observed at higher dose levels in laboratory animals but not in humans manifesting TCDD-induced acnegenic response. TCDD causes a dose-related teratogenic response in mice, with the no-adverse-effect level of 0.1 micrograms TCDD/kg/day. In rats, TCDD causes embryo- and fetotoxicity above the no-adverse-effect level of 0.03-0.125 micrograms/kg/day. Dose-related reproductive effects have also been noted in monkeys at doses that elicit maternal toxicity, and additional long-term studies are presently underway. A multigeneration reproduction study as well as a lifetime chronic toxicity study have been completed with TCDD in rats; in both studies, the no-adverse-effect level was found to be 0.001 microgram TCDD/kg/day. Numerous mutagenic studies have been performed using in vitro plant and microbial test systems as well as in vivo tests in mammals and man. A mutagenic response was noted in a few of the vitro test systems, but there are no definitive in vivo correlates of TCDD mutagenicity in higher mammals or man. TCDD has been studied for carcinogenic potential in rats and mice. There is good correlation of the results, with a carcinogenic response noted in both species only after long-term ingestion of higher dose levels that induce toxicity. No carcinogenic response occurred at continuous dose levels of 0.001-0.0014 micrograms/kg/day in rats and 0.001-0.03 micrograms/kg/day in mice. Data presently available are more supportive of a nongenetic (?promotor) rather than a genetic mechanism of carcinogenesis. The most recent research, some of which is still underway, indicates that the biologic uptake and toxicity of TCDD may be significantly decreased if the TCDD is adsorbed onto carbon or soil particles. This information is helpful in hazard assessment of exposure to TCDD.

Biochemical and morphological changes induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin in the rat liver cell plasma membrane

The administration of single oral doses of 200 micrograms kg-1 of 2,3,7,8-tetrachlorodibenzo-p-dioxin to females of the outbred, Lac : P strain of rat results in the formation of hepatic multinucleate cells by cell fusion. Liver cell plasma membranes isolated 6 or 11 days after dosing show two distinct changes. The first is a decrease of the activity of K+-Mg2+-ATPase, which confirms histochemical observations. The second is the formation, in those animals showing a more severe intoxication, of a population of plasma membranes which are less dense than usual and which consist of extended membrane sheets. It is suggested that these alterations are consequent on a disturbance of lipid metabolism in the hepatic cells and that they represent early manifestations of the toxic process which leads to the formation of multinucleate cells.

Intestinal absorption of nutrients in rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Impairment of active intestinal absorption of glucose and leucine was observed in rats 2-3 wk after oral treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (5 and 100 mg/kg). At the higher dose level used this response was complicated by the effects of severely reduced food consumption. Malabsorption of specific nutrients may help occasion the body wasting seen in many animals after acute exposure to TCDD.

The morphology of early trophoblast after dioxin poisoning in the Seveso area

The placental morphology in 22 cases of induced abortion performed one to three months after the Seveso disaster is described. In 15 cases no gross histological or ultrastructural alterations were observed. In seven cases there were many prominent microprecipitates beneath the trophoblastic basement membrane at various distances from the fetal capillaries. Intermediate patterns between simple dense bodies, already well known, and complex pluri-stratified giant structures not previously reported have been described. Combined ultrastructural and x-ray investigations (EDAX analysis) have recorded calcium- and iron-related emissions from these structures. The significance of these findings and their possible relationship to dioxin poisoning has been discussed.

Review of the dioxin problem. Mass spectrometric analyses of tetrachlorodioxins in environmental samples

Major concern over the chemical group of chlorodioxins has arisen since 2,3,7,8-tetrachlorodibenzo-p-dioxin with its extremely toxic and teratogenic properties has been found in widely distributed pesticides such as the herbicide 2,4,5-trichlorophenoxy acetic acid. Because of its chemical stability and lipophilic nature, 2,3,7,8-tetrachlorodibenzo-p-dioxin released into the environment has the potential of accumulation in the food chain. Mass spectrometry in its various forms has been the method of choice to detect and confirm low parts per billion of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Recently, a Consensus Forum held at the National Center for Toxicological Research amongst the various United States Government agencies (Food and Drug Administration, Environmental Protection Agency, US Department of Agriculture and National Institute of Environmental Health Sciences), eloquently demonstrated the potential, as well as the shortcomings, of the various techniques applied. In particular, the availability of a stable 13C labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin has proved to be an essential component to achieve low level quantitation. A brief review of the findings of the Consensus Forum is presented together with a detailed survey of the application of atmospheric pressure ionization mass spectrometry to TCDD analysis at the National Center for Toxicological Research/Food and Drug Administration.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the hepatic storage of retinol in rats with different dietary supplies of vitamin A (retinol)

The effect of various dietary sources of vitamin A on liver storage of retinol has been investigated in Sprague-Dawley rats treated with single oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): 0,0.1,1.0, or 10 microgram.kg-1. Each dose group consisted of 3 subgroups, each comprising 10 rats which received a diet with normal, low or high retinol content. The animals were killed 4 weeks after TCDD administration. Analyses of retinol were performed by high pressure liquid chromatography and glucuronosyltransferase activities were determined spectrophotometrically. A dose-dependent decrease in hepatic storage of retinol was evident. The high retinol diet did not fully compensate for the reduction caused by the highest TCDD-dose. Glucuronosyltransferase activity increased directly in relation to the TCDD-dose but in inverse proportion to the retinol content of the diet.

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.

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.

Responses of the D-glucuronic acid pathway in rat tissues to treatment with tetrachlorodibenzodioxin

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was administered to rats to study its effects on the enzyme activities of the D-glucuronic acid pathway in the liver, small intestine and kidney. 2. The UDP-glucuronosyl transferase activity of male albino rats given TCDD (80 mug/kg, one dose, i.p.) 6 days before killing was significantly increased in all tissues examined, and UDP-glucuronic acid pyrophosphatase activity was markedly decreased in the liver. D-Glucuronolactone and L-gulonate dehydrogenase activities in the liver and small intestine were slightly decreased after TCDD treatment. 3. The activities of UDP-glucose dehydrogenase and beta-glucuronidase were unchanged. 4. The 24 h urinary excretion of L-ascorbic acid was enhanced 8-fold, although no difference was detected in the excretion of D-glucaric acid between the control and experimental animals. 5. These results suggest an increased capacity for glucuronide conjugation after treatment with TCDD. 6. The lack of increase in the urinary excretion of D-glucaric acid further challenges its use as a reliable indicator of enhanced drug metabolism.