The pharmacokinetics of 2,2',5,5'-tetrachlorobiphenyl and 3,3',4,4'-tetrachlorobiphenyl and its relationship to toxicity

Polychlorinated biphenyls and organochlorine pesticides as intrinsic tracer tags of foraging grounds of bluefin tuna in the northwest Atlantic Ocean

Researchers have utilized chemical fingerprints in the determination of habitat utilization and movements of the aquatic animals. In the present effort, we analyzed polychlorinated biphenyl (PCB) congeners and organochlorine pesticides in the samples of juvenile bluefin tuna caught offshore of Virginia, and in larger bluefin tuna from the Gulf of Maine and near Nova Scotia. For a given specimen, or a given location, PCB concentrations were highest, followed by DDTs, and chlordanes. Average contaminant concentrations from fish captured from the three locations were not significantly different; and PCBs, DDTs, and chlordanes correlated well with each other. Trans-nonachlor/PCB 153 ratios in bluefin tuna of eastern Atlantic (i.e., Mediterranean) origin are low compared to the corresponding ratios in fish in the western Atlantic. As the former migrate to the western Atlantic, these ratios gradually turnover due to the accumulation of biomass from forage contaminated with higher trans-nonachlor/PCB 153 ratio reflecting dissimilar use of chlordane pesticides on two sides of the Atlantic Ocean. The trans-nonachlor/PCB 153 ratio indicated that one juvenile bluefin tuna from offshore of Virginia and one large bluefin tuna from Gulf of Maine in the present study originated from foraging grounds in the Mediterranean Sea, and that they have made the trans-Atlantic migrations. The remaining individuals were determined to be either spawned in the Gulf of Mexico or the trans-nonachlor/PCB 153 ratio for the putative Mediterranean bluefin tuna was completely turned over to resemble the ratio characteristic to the western Atlantic. Based on the turnover time for trans-nonachlor/PCB 153 ratio previously determined, the residence time of juvenile bluefin tuna offshore Virginia was estimated to be at least 0.8 to 1.6years. A discriminant function analysis (DFA) plot of total PCB normalized signatures of PCB congeners showed three separate clusters, which suggested that bluefin tuna from offshore Virginia, Gulf of Maine, and Nova Scotia could have had extended residences and foraging within the areas of capture to be able to sustain the stable signatures of PCB congeners. The DFA cluster results supported the concept of metapopulation theory of spatial ecology comprising discrete aggregates of local populations of bluefin tuna where the desired prey species are likely to be abundant. Despite their highly migratory trait and endothermic advantage of foraging in broader and colder habitats, the movements and mixing across the aggregation ranges related to feeding did not appear to be extensive. Advancement in the understanding of bluefin tuna population dynamics beyond the coarse concept of trans-Atlantic migrations to the metapopulation hypothesis provides a novel exploratory tool in the stock assessment and resource management. As the chemical tracer tags are fortified naturally and document the time- and space-integrated foraging history, they promise to serve as the low-cost alternatives to the high-cost electronic data recording tags employed for addressing the migratory movements of bluefin tuna. Between the different potential chemical tracer tags, a distinct advantage of PCB/pesticide analysis over the otolith micro-constituent analysis is that the muscle tissue of a given individual bluefin tuna can be sampled repeatedly for PCB/pesticide analysis over different spatial and temporal scales in a non-lethal manner.

The effect of olestra on the absorption, excretion and storage of 2,2',5,5' tetrachlorobiphenyl; 3,3',4,4' tetrachlorobiphenyl; and perfluorooctanoic acid

Mice were gavaged with either (14)C-labeled 2,2'5,5' tetrachlorobiphenyl; 3,3',4,4' tetrachlorobiphenyl; or perfluorooctanoic acid. Absorption of these compounds was determined by assay of feces collected for 48 h after the gavage. Part of the animals received test diets containing olestra during this 48-hour period to determine its effect on absorption of the compounds. Mice that received the diet without olestra during this period were divided into groups that either continued the diet without olestra or changed to a diet containing olestra. These diets were continued for 7 days, and a second 48-hour fecal collection was made to measure the effect of olestra on enterohepatic circulation of the compounds and their metabolites. The animals were sacrificed, and blood, fat, and liver concentrations of (14)C were measured. Olestra decreased the absorption of 2,2',5,5' tetrachlorobiphenyl. It also reduced tissue and blood concentrations of this compound. Olestra also decreased the absorption of 3,3',4,4' tetrachlorobiphenyl, but it did not alter enterohepatic circulation or tissue concentrations. Olestra significantly increased the excretion of perfluorooctanoic acid in the second 48-hour collection, suggesting an effect on enterohepatic circulation. It did not, however, alter tissue concentrations of perfluorooctanoic acid. These data are consistent with previously observed effects of olestra on the absorption and storage of lipophilic compounds.

Changes in antioxidant defense systems by 2,2',5,5'-tetrachlorobiphenyl exposure in neuronal SK-N-MC cells

Polychlorinated biphenyls (PCBs) are known to alter the mammalian antioxidant defense system. To determine whether similar detoxification processes are activated in human neuronal cells, we investigated activities of antioxidant enzymes and the glutathione status (i.e., the levels of reduced and oxidized glutathione, GSH and GSSG) in human neuronal SK-N-MC cells exposed to 2,2',5,5'-tetrachlorobiphenyl (PCB 52). Upon PCB 52 treatment, time- and concentration-dependent inhibitions of cell viability were observed. PCB 52 did not affect GSH contents upon increasing the concentration up to 15 microg/ml, but significant depletions in GSH were observed at the concentrations of 20 and 25 microg/ml. PCB 52 exposure increased GSSG levels in the SK-N-MC cells, while GSH levels were decreased, and these changes naturally modified the GSSG/GSH ratios. Cytosolic glutathione S-transferase (GST) activity with 1-chloro-2,4-dinitrobenzene as substrate was enhanced by two-fold in neuronal cells after exposure to PCB 52 versus controls. In contrast, neuronal cells showed a sustained decrease in glutathione peroxidase activity with increasing concentrations of PCB 52, and a sustained decrease in Cu/Zn-superoxide dismutase (SOD) activity with increasing concentrations of PCB 52. Catalase activity was increased until 12 h after exposure to PCB 52, but was decreased 24 h after exposure. Overall, these results imply a major effect of PCB 52 on GSH status and upon the activities of antioxidant enzymes in human neuronal SK-N-MC cells, and upon the overall process of detoxification in human neuronal cells.

Gestational and lactational exposure to TCDD or coplanar PCBs alters adult expression of saccharin preference behavior in female rats

Previous studies have shown that maternal doses of 1 microg/kg or less of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in late gestation can demasculinize and feminize reproductive behavior in male rats. However, it was not known whether coplanar polychlorinated biphenyls (PCBs) had similar effects, or whether non-reproductive sexually dimorphic behaviors such as saccharin preference behavior were also altered. We determined the effects of TCDD or coplanar PCBs on saccharin consumption and saccharin preference in male and female rats. Sprague-Dawley rats were dosed with 3,3',4, 4'-tetrachlorobiphenyl (PCB 77; 2 or 8 mg/kg/day), 3,3',4,4', 5-pentachlorobiphenyl (PCB 126; 0.25 or 1.0 microg/kg/day), TCDD (0. 025 or 0.10 microg/kg/day), or corn oil vehicle on days 10-16 of gestation. Maternal exposure to TCDD or coplanar PCBs did not change saccharin consumption or saccharin preference in male rats. However, TCDD and coplanar PCB-exposed females showed decreased saccharin consumption and saccharin preference. The results indicate that saccharin consumption is masculinized in female rats exposed to TCDD or coplanar PCBs during perinatal development. This effect could be related to the anti-estrogenic actions of these chemicals.

Effects of maternal exposure to 3,3',4,4'-tetrachlorobiphenyl or propylthiouracil in rats trained to discriminate apomorphine from saline

In the present experiment drug discrimination was examined in rats after maternal exposure to 3,3',4,4'-tetrachlorobiphenyl (PCB 77) using apomorphine (APO) as the training drug at a dose reported to act on dopamine D2 receptors. A group with maternal exposure to 6n-propyl-2-thiouracil (PTU) was included as a positive control for effects induced by PCB 77 on thyroid hormones. On gestational day (GD) 19 reduced levels of free and total thyroxine (FT4, TT4) and free triiodothyronine (FT3) were detected in dams exposed to PCB 77 or PTU. In the offspring decreases in levels of FT4 and TT4 were found in both treated groups on postnatal day (PND) 21, while reductions of FT3 were observed only in the PTU group. PTU-treated rats needed more daily sessions for successful discrimination between apomorphine and saline. There were no differences between groups in generalization tests and sessions with the D2/D3 agonist quinpirole, the D2 antagonist haloperidol plus APO, or with the GABAergic drug pentobarbital and only minor differences in sessions with the D1 agonist SKF-38393. Differences between controls and groups exposed to PCB 77 or PTU were detected in a blocking test using the mixed serotonin 5-HT1A agonist and partial D2 antagonist buspirone. This outcome suggests long-lasting effects by developmental exposure to PCB 77 on the interaction between dopaminergic and serotonergic processes which may be mediated by effects on thyroid hormone levels.

3,5,3',5'-tetrachlorobiphenyl is a weak oestrogen agonist in vitro and in vivo

Polychlorinated biphenyls (PCBs) are widespread, persistent environmental contaminants of which some congeners can act as endocrine disrupters. Previous work has shown that 3,4,3',4'-tetrachlorobiphenyl (PCB77) can act as an oestrogen with actions mediated through the oestrogen receptor. Here, oestrogenic actions have been assessed for two further tetrachlorobiphenyl isomers. Assays of oestrogenic action have involved (1) ligand regulation of oestrogen-sensitive gene expression; (2) ligand regulation of cell growth in oestrogen-dependent human breast cancer cell lines MCF7 McGrath and ZR-75-1; and (3) ligand activity in the immature mouse uterine weight bioassay in vivo. These results demonstrate that 3,5,3',5'-tetrachlorobiphenyl (PCB 80) can be considered to be a weak oestrogen agonist, but the 2,5,2',5'-congener (PCB 52) revealed no oestrogenic properties in any of these assays. Implications of these results are discussed in relation to structure-activity predictions for environmental oestrogens.

Tissue distribution, toxicokinetics and induction of hepatic drug metabolizing enzymes in male rats after a single s.c. dose of 3,4,3',4'-tetrachlorobiphenyl (PCB-77)

The tissue distribution and toxicokinetics of PCB-77 after a single s.c. dose of 6 mg/kg body weight was investigated in male adult rats as well as the concurrent induction of hepatic drug-metabolizing enzymes. During five days after treatment, the PCB-77 concentrations on fat weight basis in testis and in whole blood were found to be about in the same range as the concentrations in adipose tissue, whereas in liver fat PCB-77 accumulated. EROD and MROD activities were induced by about 8 and 4 times, respectively, during a period of two weeks after treatment. Concentrations in adipose tissue and in liver as well as the hepatic enzyme activities rapidly declined during the investigation period of eight weeks. An elimination half-life for PCB-77 of approximately 7-9 days was estimated.

Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and related compounds: environmental and mechanistic considerations which support the development of toxic equivalency factors (TEFs)

Halogenated aromatic compounds, typified by the polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and diphenylethers (PCDEs), are industrial compounds or byproducts which have been widely identified in the environment and in chemical-waste dumpsites. Halogenated aromatics are invariably present in diverse analytes as highly complex mixtures of isomers and congeners and this complicates the hazard and risk assessment of these compounds. Several studies have confirmed the common receptor-mediated mechanism of action of toxic halogenated aromatics and this has resulted in the development of structure-activity relationships for this class of chemicals. The most toxic halogenated aromatic is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and based on in vivo and in vitro studies the relative toxicities of individual halogenated aromatics have been determined relative to TCDD (i.e., toxic equivalents). The derived toxic equivalents can be used for hazard and risk assessment of halogenated aromatic mixtures; moreover, for more complex mixtures containing congeners for which no standards are available (e.g., bromo/chloro mixtures), several in vitro or in vivo assays can be utilized for hazard or risk assessment.