Polybrominated biphenyl toxicosis in the rat and mouse

Brominated flame retardants and other organobromines in Norwegian predatory bird eggs

A set of 62 unhatched eggs was collected from six different predatory bird species throughout Norway after incubation period was completed. They were analysed for PBDE, PBB, TBBP A and naturally occurring halogenated compounds. BDE 47, 99 and 153 were the dominating congeners, with species dependent PBDE patterns. BDE 153 was observed as the most abundant congener in eggs of peregrine falcon, golden eagle and merlin. The highest PBDE level (sum of nine congeners) was found in eggs of white-tailed sea eagle with up to 800ng/gww (median sumPBDE: 184ng/gww), followed by eggs of peregrine falcon and osprey (median sumPBDE: 155 and 105ng/gww, respectively). Golden eagle eggs showed the lowest concentration of all species (median sumPBDE: 3ng/gww). The levels in the peregrine falcon are similar to those found earlier in the Baltic region [Lindberg, P., Sellstrom, U., Haggberg, L., de Wit, C.A., 2004. Higher brominated diphenyl ethers and hexabromocyclododecane found in eggs of peregrine falcons (Falco peregrinus) breeding in Sweden. Environmental Science & Technology. 38 (1), 93-96]. The differences between species are not fully explainable, due to lack of data from the major food species. BB 101 and 153 were found in eggs of all investigated bird species. Especially in samples of white-tailed sea eagle, peregrine falcon and goshawk additional unknown penta- and hexabrominated biphenyls were detected. TBBP A was detected in all of eight eggs analysed sampled from four different bird of prey species. The naturally occurring halogenated compounds Q1, the dibromotrichloro monoterpene MHC-1, and 2,4,6-tribromoanisole (TBA) were detected in all of seven analysed samples except for one peregrine falcon egg.

A comparison of the properties of the major commercial PBDPO/PBDE product to those of major PBB and PCB products

Decabromodiphenyl oxide (DBDPO), a highly effective polybrominated diphenyl oxide (PBDPO) flame retardant (FR) used primarily in electrical and electronic equipment, is the second highest volume brominated flame retardant (BFR) and accounts for 82% of the PBDPO usage globally. The apparent similarities in chemical structure between the DBDPO, polychlorinated and polybrominated biphenyl (PCB, PBB) molecules have led to the presumption that these substances also share similar toxicological and environmental properties. However, DBDPO's physical/chemical properties, applications, environmental release, and toxicology differ substantially from the former PCB/PBB products. DBDPO is a heavier and larger molecule than components of the predominant PCB/PBB products used in the past, and the commercial DBDPO product has a lower water solubility and vapor pressure than the former PCB and PBB products. DBDPO's detection in the environment is generally in sediments near known point sources, and its primary use in thermoplastics limits its environmental release from end products. PBB environmental release has been primarily associated with one accident occurring in the US in 1973. The PCBs, used in applications with a high potential for environmental release, were detected in diverse locations around the world as early as in the 1970s. Current releases of PCB are considered related to an environmental cycling process of congeners previously released into the environment; however, DBDPO's physical/chemical properties do not indicate a similar potential. Extensive testing of the DBDPO commercial product has demonstrated that it is toxicologically and pharmacokinetically different from the predominant PCB and PBB products used in the past. Thus, although the chemical structures of DBDPO, PBB, and PCB appear similar, the properties of DBDPO are distinctly different.

2,2',4,4',5,5'-hexabromobiphenyl: its toxicokinetics, biotransformation and porphyrinogenic action in rats

The porphyrinogenic action of 2,2',4,4',5,5'-hexabromobiphenyl and its toxicokinetics were studied in female Wistar rats that were treated every other day for 6 wk with oral doses of 112 mg/kg body weight. Subsequently, the animals were kept for a further period of 22.5 months but without supply of the brominated biphenyl. 10.5 months after cessation of treatment the compound reached a maximum concentration in the adipose tissue followed by a gradual decline of its content. In the liver the concentration of the substance started to decrease 3 months after cessation of treatment. In the excreta, hexabromobiphenylol and two pentabromobiphenyls were detected as metabolites. The rate of biotransformation amounted to about 5%. At the end of the dosing period no alterations in the content and profile of the hepatic porphyrins were observed. Urinary porphyrins and their precursors delta-aminolaevulinic acid and porphobilinogen were slightly elevated. The urinary porphyrin pattern and faecal porphyrin content and pattern did not differ from those of the controls. 15 and 18 months after cessation of treatment (16.5 and 19.5 months after the start of treatment) two animals were found to have marked alterations in the content and profile of hepatic porphyrins with uro- and heptacarboxyporphyrin predominating. It was concluded that there is an extreme delayed individual porphyric response to 2,2',4,4',5,5'-hexabromobiphenyl in female rats.

Short-term oral administration of polybrominated biphenyls enhances the development of hepatic enzyme-altered foci in initiated rats

FireMaster BP-6 (FM), a commercial mixture of polybrominated biphenyls (PBB), has been shown to act as a tumor promoter in hepatocarcinogenesis assays in rats. Most hepatic tumor promoters must be administered for many weeks or months. Because FM is highly persistent in animal tissues, it was hypothesized that very short-term administration of FM would result in tumor promotion. Female Sprague-Dawley rats weighing 185-215 g were initiated by a two-thirds partial hepatectomy followed by 10 mg diethylnitrosamine/kg body weight (BW) 24 h later. Thirty days later, rats were gavaged with FM in corn oil, at total doses of 0, 13, or 130 mg FM/kg BW. Half the dose was given on d 30, and the remaining half was given 24 h later. At 120 d after gavage the rats were killed and necropsied. Five liver sections from each animal were histochemically stained for gamma-glutamyl transpeptidase-positive enzyme-altered foci (EAF). EAF were significantly increased over control values in initiated rats given 130 mg FM/kg. In animals given 13 mg FM/kg, EAF were increased to a lesser extent but not significantly above controls. Enhancement of these EAF in initiated rats reflects tumor-promoting activity. In this study, 24-h administration of FM in initiated rats was sufficient to enhance hepatic EAF measured 120 d later in an rats was sufficient to enhance hepatic EAF measured 120 d later in an initiation-promotion protocol, and a dose of 13 mg FM/kg was apparently close to a possible no-effect threshold level for enhancement of EAF.

The murine aromatic hydrocarbon responsiveness locus: a comparison of receptor levels and several inducible enzyme activities among recombinant inbred lines

The aromatic hydrocarbon responsiveness (Ah) locus has been correlated with genetic differences in the risk of drug toxicity, teratogenesis, chemical carcinogenesis, and mutagenesis. Hepatic cytosolic Ah receptor levels, 2-amino-5-chlorobenzoxazole (zoxazolamine) paralysis time following beta-naphthoflavone treatment and aryl hydrocarbon hydroxylase (AHH3, acetanilide 4-hydroxylase (Ac4H), and NAD(P)H:menadione oxidoreductase (NMOR)4, induction by 3-methylcholanthrene were studied in (a) the progenitors C57BL/6J (Ahb/Ahb) and DBA/2J (Ahd/Ahd) and 25 BXD recombinant inbred lines, (b) the progenitors C57BL/6N and C3H/HeN and 14 B6NXC3N recombinant inbred lines, and (c) the progenitors C57BL/6J and C3H/HeJ and 12 BXH recombinant inbred lines. The Ahb phenotype exhibits greater than 5 femtomole receptor/mg of cytosolic protein, less than or equal to 15 minutes zoxazolamine paralysis time, and twofold to 15-fold induction of these three hepatic enzyme activities; the Ahd phenotype exhibits less than or equal to 2 fmol receptor/mg protein, greater than 15 minutes zoxazolamine paralysis time, and less than 30% induction of these three activities. Among the BXD lines but especially among the B6NXC3N and BXH lines, high frequencies of recombination were found; the phenotype of each of the five parameters did not segregate with the phenotype of each of the other parameters in four or more recombinant lines. This report shows for the first time that AHH induction by 3-methylcholanthrene can occur in the Ahd phenotype mouse. These data underline the complexity of this genetic system when genes from C57BL/6 and DBA/2 are combined and particularly when genes from C57BL/6 and C3H/He inbred mouse strains are combined.

Mechanism of benzo(a)pyrene induction of alpha-human chorionic gonadotropin gene expression in human lung tumor cells

Human lung cells (ChaGo) derived from a bronchogenic carcinoma synthesize and secrete in the culture medium the alpha subunit of the glycoprotein hormone, human chorionic gonadotropin (alpha-hCG). The synthesis of alpha-hCG by ChaGo cells could be further stimulated by treatment with sublethal concentrations of the polycyclic aromatic hydrocarbons (PAHs), benzo(a)pyrene (BaP), or dimethylbenzanthracene. The production of alpha-hCG could be correlated to the levels of alpha-hCG-specific mRNA sequences in control and PAH-treated cells. Further analysis of the RNA species (Northern blot) revealed that the level of the mature (approximately 1.0 kb) and the high molecular weight alpha-hCG specific nuclear RNA sequences (approximately 2.2 and 5 kb) were all greater in PAH-treated cells. Addition of [3H]BaP (0.25 microgram/ml) in the culture medium of ChaGo cells led to immediate uptake of the radioactive compound apparently by simple diffusion. SDS PAGE and subsequent fluorography revealed that the radioactive compound interacted and formed covalent complexes with cytoplasmic and nuclear proteins. This covalent interaction of the [3H]BaP molecule with cellular proteins could be significantly inhibited by either inhibiting the activity of the enzyme aryl hydrocarbon hydroxylase with 7,8-benzoflavone or by reducing the cellular concentration of the enzyme by simultaneous incubation with cycloheximide. These results suggested that in ChaGo cells, the observed covalent complexes were formed by the interaction of the BaP metabolites with cellular proteins. The concentrations at which 7,8-benzoflavone or cycloheximide inhibited formation of metabolites from [3H]BaP and their covalent interaction with cell protein did not affect the BaP-induced stimulation of alpha-hCG gene expression. However, the cytotoxic effects of BaP in ChaGo cells seemed to be exerted by the metabolism of the compounds. Results presented in this report suggest that BaP metabolism and the interaction of the metabolites with cell proteins were not essential for the BaP-induced modulation of alpha-hCG gene expression.

The PBB episode in Michigan: an overall appraisal

Polybrominated biphenyls (PBB) were used as a fire retardant. In common with other halogenated hydrocarbons, PBBs are lipophilic and resistant to chemical and metabolic degradation. Cattle on about 25 Michigan farms were exposed to as much as 250 g per head of PBB when it was accidentally mixed in cattle feed in 1973 to 1974. Livestock exposures several orders of magnitude lower occurred on several hundred other farms because of carryover and equipment contamination in feed mills. Approximately 85% of the Michigan population received some exposure to PBB because dairy product marketing involves mixing milk from many farms. A few cases of high human exposure, which may have been as great as 10 g, occurred when residents of the more highly exposed farms consumed their own products. Although numerous clinical signs and pathological changes were reported in exposed cattle, only anorexia, lacrimation, emaciation, hyperkeratosis, and kidney damage were confirmed in controlled studies. The acute toxicity of PBB in laboratory animals is low, but a variety of subacute effects have been reported. Induction of microsomal enzymes, enlargement and histopathological changes of the liver, fetotoxicity, and immunosuppression are among the more significant. Epidemiological studies of exposed humans have revealed no pattern of clinical signs or symptoms that were related to PBB exposure. A complete evaluation of the human consequences of exposure to PBB await the conclusion of long-term epidemiological studies.

Acute response of rat liver microsomal lipids, lipid peroxidation, and membrane anisotropy to a single oral dose of polybrominated biphenyls

Liver microsomal lipids and lipid peroxidation activities were examined in adult male rats at intervals over a 2-mo period after the administration of a single oral dose of 0 or 500 mg/kg of FireMaster BP-6 in corn oil. Microsomal lipids were markedly altered in the polybrominated biphenyl- (PBB-) dosed animals at the earliest time examined (1 wk), and these changes persisted throughout the remainder of the study. An early decrease in the cholesterol-phospholipid ratio was noted, which probably contributed to the significant decrease in the steady-state fluorescence anisotropy demonstrable in both intact microsomes and in liposomes prepared from microsomal lipid extracts. Significant concentrations of PBBs were present in dosed rat microsomes, but the changes in anisotropy appeared to result from membrane lipid alterations rather than from a direct perturbation by PBBs. Iron ascorbate-induced peroxidation was also greatly enhanced in dosed rat microsomes, even when rats were maintained on a low-iron (25 ppm) diet. These early alterations in membrane fluidity and peroxidative capacity of microsomes may ultimately contribute to the hepatotoxicity of PBBs.

Hepatic tumor-promoting ability of 3,3',4,4',5,5'-hexabromobiphenyl: the interrelationship between toxicity, induction of hepatic microsomal drug metabolizing enzymes, and tumor-promoting ability

Female Sprague-Dawley rats were fed diets containing 0, 0.01, 0.1, or 1.0 mg/kg 3,3',4,4',5,5'-hexabromobiphenyl (345-HBB) for 140 days after a 70% partial hepatectomy and diethylnitrosamine administration (10 mg/kg body weight) to determine if 345-HBB had tumor-promoting ability in a two-stage hepatocarcinogenesis assay. Tumor-promoting ability was assessed by measuring enzyme-altered foci exhibiting gamma-glutamyl transpeptidase activity. Enhancement of enzyme-altered foci occurred only at a dietary concentration of 345-HBB (1.0 mg/kg) that was toxic. The toxic effects were decreased body weight gain, involution of the thymus, increased liver weight, histologic and ultrastructural alterations of the liver, and elevated serum concentrations of aspartate aminotransferase. 345-HBB is a strict 3-methylcholanthrene (MC) type of hepatic microsomal drug metabolizing enzyme inducer and caused a dose-related increase of cytochrome P-450. 345-HBB, at a dietary concentration of 0.1 mg/kg, caused a physiologic response in rats as determined by induction of hepatic microsomal drug metabolizing enzymes, but there was minimal evidence of toxicity and no evidence of tumor-promoting ability. Results indicate that there can be induction of MC type of hepatic microsomal drug-metabolizing enzymes without toxicity or tumor-promoting ability and that the tumor-promoting ability of 345-HBB was most likely the result of hepatic degeneration and necrosis. This finding is in contrast to previous studies in which a closely related congener, 2,2',4,4',5,5'-hexabromobiphenyl, enhanced the development of enzyme-altered foci at dietary concentrations that were not hepatotoxic.

The comparative biologic and toxic potencies of polychlorinated biphenyls and polybrominated biphenyls

Aroclor 1254 and fireMaster BP-6, two commercial polychlorinated biphenyl (PCB) and polybrominated biphenyl (PBB) preparations, exhibit comparable biologic and toxic effects. In the present study the commercial PBB was more active than Aroclor 1254 in causing thymic atrophy in male Wistar rats. However, a direct comparison of the relative effects of bromine vs chlorine substituents is not possible with the commercial PBB and PCB mixtures due to their complex congeneric composition. This study reports the synthesis and biologic and toxic effects of a series of laterally substituted 3,3',4,4'-tetrahalobiphenyls which contain the following variable molecular Cl/Br ratios; Br4, Br3Cl, Br2Cl2 (two isomers), BrCl3, and Cl4. 3,3',4,4'-Tetrabromobiphenyl and 3,4,4'-tribromo-3'-chlorobiphenyl (150 mumol/kg)-pretreated animals significantly inhibited the growth rate of and caused thymic atrophy in immature male Wistar rats whereas those isostereomers with reduced Br (and increased Cl) content were either less active or inactive. Pretreatment of male Wistar rats with 10 mumol/kg of the 3,3',4,4'-tetrahalobiphenyls and determination of their effects as inducers of the hepatic microsomal drug-metabolizing enzymes also illustrated the effects of the relative Cl/Br ratios on induction potencies. Both 3,3',4,4'-tetrabromo- and 3,4,4'-tribromo-3'-chlorobiphenyl maximally induced the cytochrome P-448-dependent monooxygenases, benzo[a]pyrene and 4-chlorobiphenyl hydroxylase; the order of potency of the other isostereomers was 4,4'-dibromo-3,3'-dichloro- congruent to 3,4-dibromo-3',4'-dichlorobiphenyl greater than 4-bromo-3,3',4'-trichloro- greater than 3,3',4,4'-tetrachlorobiphenyl. With few exceptions this order of potency was observed for the induction of benzo[a]pyrene hydroxylase and ethoxyresorufin O-deethylase in rat hepatoma cells in culture and for their relative binding affinities to the rat cytosolic receptor protein. The data clearly demonstrate that the biologic activities of this group of isosteric halogenated biphenyls are enhanced with increasing bromine substitution and also support the hypothesis that the activities of this class of chemicals are mediated through the receptor.

Effects of a polybrominated biphenyl mixture in the rat and mouse. II. Lifetime study

This study was undertaken to characterize the long-term toxic and carcinogenic potential of a polybrominated biphenyl (PBB) mixture in rats and mice of both sexes. Fischer 344 rats and B6C3F1 mice were given 125 po doses of PBB over a 6-month period at 0 (control), 0.1, 0.3, 1.0, 3.0, and 10.0 mg/kg body weight/day (5 days/week) and observed for an additional 23 months for rats and 24 months for mice (lifetime observation). The treatments (0.3 mg/kg or higher dosages) shortened the survival time in male rats whereas no such effect was observed in treated females. There was also evidence of shortened survival time in mice treated with 10.0 mg/kg PBB. As observed by uv light, hepatic porphyrin markedly increased at the 6-month observation, then tended to decrease, primarily in mice, following cessation of exposure. Significantly higher incidences of atypical hepatocellular foci, neoplastic nodules, hepatocellular carcinomas, and cholangiocarcinomas were observed in exposed rats. The incidence of hepatocellular carcinoma was also increased in both male (95%) and female (88%) mice (highest dose level) compared with control male (48%) and female (0%) mice. The incidence of hepatic neoplasms appeared to be dose dependent in both species. Liver tumors were observed primarily in those groups of animals to which PBB was given in doses sufficient to induce readily observable hepatic toxicity. Under the conditions of this experiment, polybrominated biphenyl mixture (Firemaster FF-1) was carcinogenic for Fischer 344 rats and B6C3F1 mice of both sexes. Lesions included neoplastic nodules, hepatocellular carcinomas, and cholangiocarcinomas in rats and hepatocellular carcinomas in mice. Other manifestations of toxicity included porphyrogenic effects and hepatotoxicity. A significantly higher incidence of chronic progressive nephropathy was observed in male rats of the 1.0, 3.0, and 10.0 mg/kg dosage groups when compared with control males. Gastric ulcers and hyperplastic gastropathy of the glandular portion of the stomach were observed more frequently in male rats, primarily in the high dosage groups.

Effects of a polybrominated biphenyl mixture in the rat and mouse. I. Six-month exposure

A 1973 environmental accident in Michigan resulted in exposure of humans via the food chain to polybrominated biphenyl (PBB). To better characterize the toxicity of the halogenated polycyclic aromatic hydrocarbon class of chemicals, rodents were dosed with PBB and their target organs examined for morphological, histological, biochemical, and selected endocrine changes. Male and female rats and mice were given 125 po doses of PBB over a 6-month period at 0.1, 0.3, 1.0, 3.0, and 10.0 mg/kg of body weight/day (5 days/week). There was a dose-related decrease in body weight gain in both male and female rats and male mice. Thymus weights were significantly decreased in all rats exposed to 0.3 mg/kg or more of PBB. Dose-related hepatotoxic effects were observed in both rats and mice characterized by marked increase in liver weight with accentuation of hepatic lobular markings. Microscopically, there were moderate to marked swelling, disorganization, and single cell necrosis of hepatocytes, fatty infiltration, bile duct proliferation, and presence of atypical hyperplastic foci. Hepatic porphyrin levels were markedly increased in both rats and mice primarily in females. There was a significant decrease in serum thyroxine (T4) and triiodothyronine (T3) suggesting that PBB may interfere with thyroid hormone secretion. There was a significant dose-related increase in serum cholesterol and gamma-glutamyl transpeptidase, and a decrease in serum glucose.

Toxicity of 3,3',4,4'- and 2,2',5,5'-tetrabromobiphenyl: correlation of activity with aryl hydrocarbon hydroxylase induction and lack of protection by antioxidants

3,3',4,4'-Tetrabromobiphenyl is a minor component of commercial polybrominated biphenyl (PBB) mixture fireMaster BP-6 and is a potent inducer of aryl hydrocarbon hydroxylase (AHH). A single ip dose of 3,3',4,4'-tetrabromobiphenyl (150 mumol/kg) caused significant reduction in the growth rate in the immature male Wistar rat, as well as pale enlarged livers and marked reduction in thymus size. Under light microscopy, hepatocytes were enlarged and vacuolated. The vacuoles, which were most prominent in the midzonal region of the lobule, corresponded to fat droplets in oil-red-O-stained sections. The thymus, especially the cortex, was markedly depleted of lymphocytes. Neither the reduced growth, altered organ weights nor the histopathology was reversed for the duration of the study by the coadministration of the antioxidants butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), or vitamin E. Vitamin E did, however counter the negative effect of 3,3',4,4'-tetrabromobiphenyl on growth during the first 5 d of the study. 2,2',5,5'-Tetrabromobiphenyl, also a minor component of fireMaster BP-6, is a weak phenobarbital-type inducer of cytochrome P-450. When administered at the same dose, 2,2',5,5'-tetrabromobiphenyl did not elicit any observed toxic effects. These data confirm the correlation between AHH induction and toxicity for these PBBs and suggest that 3,3',4,4'-tetrabromobiphenyl may significantly contribute to the toxicity of fireMaster BP-6. Although there is evidence that polychlorinated biphenyls, and perhaps 2,3,7,8-tetrachlorodibenzo-p-dioxin, exert certain toxic effects via a lipid peroxidation mechanism, the toxic changes measured during this study were not reversed by the administration of the antioxidants.

Inter-relation between environmental monitoring data, human exposure and health effects

To determine whether a population has been affected by a chemical, evidence of exposure must be established. The mere presence of a chemical in the surroundings of a population may not, in all instances, result in actual exposure. Not all such exposures will cause health effects; nor is it always possible to establish that illness has or will result from exposure to chemicals. The inability to establish health effects in humans cannot a priori be translated to mean that a specific chemical is harmless. On the other hand, it must be determined whether health studies would be fruitful. If exposure was so minimal that no health effects are expected, then no health studies should be conducted.