Specific binding of polychlorinated biphenyls to rat liver cytosol protein

Target tissue selectivity and burdens of diverse classes of brominated and chlorinated contaminants in polar bears (Ursus maritimus) from East Greenland

The tissue-specific composition of sum classes of brominated and chlorinated contaminants and metabolic/degradation byproducts was determined in adult male and female polar bears from East Greenland. Significantly (p < 0.05) higher concentrations of sigma-PCBs, various other organochlorines such as sigma-CHL, p,p'-DDE, sigma-CBz, sigma-HCHs, octachlorostyrene (OCS), sigma-mirex, dieldrin, the flame retardants sigma-PBDEs, and total-(alpha)-hexabromocyclododecane (HBCD), sigma-methylsulfonyl (MeSO2)-PCBs and 3-MeSO2-p,p'-DDE, were found in the adipose and liver tissues relative to whole blood and brain. In contrast, sigma-hydroxyl (OH)-PCB, 4-OH-heptachlorostyrene and sigma-OH-PBDE concentrations were significantly highest (p < 0.05) in whole blood, whereas the highest concentrations of sigma-OH-PBBs were found in the adipose tissue. Based on the total concentrations of all organohalogens in all three tissues and blood, the combined body burden was estimated to be 1.34 +/- 0.12 g, where > 91% of this amount was accounted for by the adipose tissue alone, followed by the liver, whole blood, and brain. These results show that factors such as protein association and lipid solubility appear to be differentially influencing the toxicokinetics, in terms of tissue composition/ localization and burden, of organohalogen classes with respect to chemical structure and properties such as the type of halogenation (e.g., chlorination or bromination), and the presence or absence of additional phenyl group substituents (e.g., MeO and OH groups). The tissue- and blood-specific accumulation (or retention) among organohalogen classes indicates that exposure and any potential contaminant-mediated effects in these polar bears are likely tissue or blood specific.

Effects of polychlorinated biphenyls on thyroid hormones and liver type I monodeiodinase in the chick embryo

Polychlorinated biphenyls (PCBs) are widespread environmental contaminants which can biomagnify to higher tropic level organisms including birds. Circulating thyroid hormones (TH) and growth are decreased by PCB exposure. The first set of studies investigated the effects of PCBs on an enzyme responsible for TH homeostasis, hepatic type I monodeiodinase (MDI) in chicken embryos. Fertile chicken eggs were injected with Aroclor 1242, Aroclor 1254, 2,2',6, 6'-tetrachlorobiphenyl (TCB), 3,3',4,4'-TCB, or 3,3',5,5'-TCB on Day 0 and studies were terminated on Incubation Day 21. Hepatic MDI activity was reduced in embryos treated with the Aroclor mixtures. No effects on MDI activities were observed after PCB isomer treatment. Liver weights from embryos treated with Aroclor 1242 were decreased. In the second study, chick embryos were exposed to these same PCBs in order to evaluate their effect on circulating THs and growth. Treatment with PCBs had no effect on body weight. Femur length were decreased with Arcolor 1242 treatment. A decrease in plasma concentration of thyroxine was observed after treatment with Aroclor 1242 and Aroclor 1254. Based on these findings, it is evident that PCBs alter the thyroid axis. Bird circulating TH levels, which are generally reported, may not be a good biomarker for low-dose exposure to PCBs. However, the reduction in MDI activity was more sensitive to PCB mixture exposure and may be a useful biomarker.

Intranuclear distribution of 2,2',4,4',5,5'-hexachlorobiphenyl and 2,3,7,8,-tetrachlorodibenzo-p-dioxin

The in vitro intranuclear distribution of the chlorinated aromatic hydrocarbon compounds 2,2',4,4',5,5'-hexachlorobiphenyl and 2,3,7,8-tetrachlorodibenzo-p-dioxin was determined in isolated rat liver cell nuclei. Suspended nuclei were incubated with the 3H-labeled congeners, and the incubation terminated by brief UV irradiation. High-intensity UV irradiation at 254 nm changes the reversible association between macromolecules and ligands into covalent linkages and thus stabilizes the equilibrium distribution. The nuclei were then fractionated with the radioactive congeners covalently linked to the purified fractions. The intranuclear distribution of the model compounds was not uniform. The majority of either chemical was attached to the nuclear envelope and to the chromatin fraction. Much lower amounts were bound to nucleoli. The nuclear matrix was almost devoid of the chemicals. Minute amounts of either compound were detected in association with DNA, none with nuclear RNA. The substantial association of these chlorinated hydrocarbon model compounds with chromatin may bear more general biological relevance and point to detrimental effects on the genetic apparatus. The presented method yields an unequivocal profile of the genuine nuclear distribution of photoactivatable chemicals.

Partial purification and characterization of a rat liver polychlorinated biphenyl (PCB) binding protein

A protein capable of specifically binding polychlorinated biphenyls (PCB) was partially purified from rat liver cytosol. After labeling with [3H]2,2',4,4',5,5'-hexachlorobiphenyl (6-CB), protein enrichment was guided by monitoring the protein-bound radioactivity through a sequence of purification steps including ion exchange chromatography and preparative gel electrophoresis. In addition, specific binding tests of individual fractions were carried out. An average 100-fold enrichment of the 40 kDa protein was achieved. A variety of ligands were tested in competitive binding studies with 6-CB. Whereas penta- and hexachloro-PCB congeners are high affinity competitors, the 3,3',4,4'-tetrachlorobiphenyl congener does not compete for 6-CB binding. Studies on the species and tissue distribution suggest a prevalence of the binding protein in tissues of the rat. Since the natural physiological ligand of the protein has not yet been identified, the function of the protein can only be speculated on.