Nonplanar Polychlorinated Biphenyls Research Articles

A structure-activity relationship linking non-planar PCBs to functional deficits of neural crest cells: new roles for connexins.

Migration of neural crest cells (NCC) is a fundamental developmental process, and test methods to identify interfering toxicants have been developed. By examining cell function endpoints, as in the 'migration-inhibition of NCC (cMINC)' assay, a large number of toxicity mechanisms and protein targets can be covered. However, the key events that lead to the adverse effects of a given chemical or group of related compounds are hard to elucidate. To address this issue, we explored here, whether the establishment of two overlapping structure-activity relationships (SAR)-linking chemical structure on the one hand to a phenotypic test outcome, and on the other hand to a mechanistic endpoint-was useful as strategy to identify relevant toxicity mechanisms. For this purpose, we chose polychlorinated biphenyls (PCB) as a large group of related, but still toxicologically and physicochemically diverse structures. We obtained concentration-dependent data for 26 PCBs in the cMINC assay. Moreover, the test chemicals were evaluated by a new high-content imaging method for their effect on cellular re-distribution of connexin43 and for their capacity to inhibit gap junctions. Non-planar PCBs inhibited NCC migration. The potency (1-10µM) correlated with the number of ortho-chlorine substituents; non-ortho-chloro (planar) PCBs were non-toxic. The toxicity to NCC partially correlated with gap junction inhibition, while it fully correlated (p < 0.0004) with connexin43 cellular re-distribution. Thus, our double-SAR strategy revealed a mechanistic step tightly linked to NCC toxicity of PCBs. Connexin43 patterns in NCC may be explored as a new endpoint relevant to developmental toxicity screening.

Sorption of polychlorinated biphenyls onto biochars derived from corn straw and the effect of propranolol

The sorption of three polychlorinated biphenyls (PCBs) in single-solute and bi-solute systems in the presence of propranolol was studied on biochars at pyrolyzing temperatures of 200°C (BC200) and 700°C (BC700). Hydrophobicity and molecular planarity played a major role in PCB sorption onto BC200 and BC700, respectively. The steric hindrance caused by non-planarity made the strong specific sorption sites on BC700 less accessible to nonplanar PCBs. In bi-solute systems for BC200, propranolol monomers at an initial concentration (Cinit) of 0.8mg/L inhibited the sorption of PCB4 by competing for sorption sites. Propranolol at Cinit larger than 1.2mg/L could form hemimicelle structures on the biochar surface, providing a favorable phase for PCB4 partitioning, thereby increasing Koc up to 1.15 times. For BC700, propranolol prohibited PCB4 sorption mainly by pore-blocking, with the log Koc being reduced from 4.92 to 3.94. This study informs the application of biochar in mixture-contaminated environment.

Effects of structurally different noncoplanar and coplanar PCBs on HELF cell proliferation, cell cycle, and potential molecular mechanisms.

Polychlorinated biphenyls (PCBs) are a group of chemicals that persist in the environment, indoors, and humans. Lung exposure to airborne and food contaminants, such as PCBs, may cause possible lung disorders, such as cancer. In the present study, we investigated the effects of structurally different lower chlorinated (≤4Cl), noncoplanar PCB40, and coplanar PCB77 on human lung fibroblast cell line (HELF) cell proliferation, cell cycle progression, and possible molecular mechanisms. Noncoplanar PCB40 and coplanar PCB77 exhibited concentration- and time-dependent biphasic dose-response effects on HELF cell proliferation. Noncoplanar PCB40 and coplanar PCB77 induced 23 and 45% cytotoxicity at higher concentrations than the control. The flow cytometry analysis showed that exposure to PCB40 caused a significant increase in time spent in the G1 phase but decreased length of the S phase in a concentration- and time-dependent manner, whereas PCB77 exposure decreased time spent in the G1 and S phases but increased time spent in the G2 phase. Western blot analysis indicated that PCB77 increased the expression of cyclin E, CDK2, p21, and caspase-9, while PCB40 decreased the expression of these proteins (except CDK2 and p21). An increase in CDK expression after exposure to PCB77 suggests that it may cause carcinogenic effects on HELF cells at higher doses. Our results also demonstrate that the different cytotoxic effects induced by coplanar and nonplanar PCBs were correlated with their structural characteristics; the coplanar congener was more cytotoxic than the nonplanar congener. The study elaborates threshold levels for these chemicals and suggests that the cytotoxicity mechanisms by which PCB congeners act on HELF cells depend on their planarity and chemical structures. Furthermore, the study will be important for developing antidotes to the adverse effects and risk assessment practices for PCBs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1183-1190, 2017.

Integrating structural and thermodynamic mechanisms for sorption of PCBs by montmorillonite.

Strong sorption of planar nonionic organic chemicals by clay minerals has been observed for important classes of organic contaminants including polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and dioxins, and such affinity was hypothesized to relate to the interlayer hydrophobicity of smectite clays. In batch sorption experiments of two trichlorobiphenyls on homoionic Na-, K-, Cs-montmorillonites, considerably greater sorption coefficient (Kw) was observed for coplanar 3,3',5-trichlorobiphenyl (PCB 36); log Kw for Na-, K-, and Cs-montmorillonite were 3.69, 3.72, and 4.53 for coplanar PCB 36 vs 1.21, 1.46, and 0.87 for the nonplanar 2,2',6-trichlorobiphenyl (PCB 19). MD simulations were conducted utilizing X-ray diffraction determined clay interlayer distances (d-spacing). The trajectory, density distribution, and radial distribution function of interlayer cation, water, and PCBs collectively indicated that the hydrophobic nature of the interlayer regions was determined by the hydration status of exchangeable cations and the associated d-spacing. The sorption free energies calculated for both coplanar and nonplanar PCB molecules by adaptive biasing force (ABF) method with an extended interlayer-micropore two-phase model consisting of cleaved clay hydrates and "bulk water" are consistent with the Gibbs free energies derived from the measured log Kw, manifesting enhanced sorption of coplanar PCBs was attributed to shape selectivity and hydrophobic interactions.

Enhanced PCBs sorption on biochars as affected by environmental factors: Humic acid and metal cations

Biochar plays an important role in the behaviors of organic pollutants in the soil environment. The role of humic acid (HA) and metal cations on the adsorption affinity of polychlorinated biphenyls (PCBs) to the biochars in an aqueous medium and an extracted solution from a PCBs-contaminated soil was studied using batch experiments. Biochars were produced with pine needles and wheat straw at 350 °C and 550 °C under anaerobic condition. The results showed that the biochars had high adsorption affinity for PCBs. Pine needle chars adsorbed less nonplanar PCBs than planar ones due to dispersive interactions and separation. Coexistence of HA and metal cations increased PCBs sorption on the biochars accounted for HA adsorption and cation complexation. The results will aid in a better understanding of biochar sorption mechanism of contaminants in the environment.

Levels and sources of planar and non-planar PCBs in pine needles across Poland

Under a small project, one-year-old Scots Pine needles collected from 25 spatially distant sites were examined in monitoring the extent of environmental diffusion and possible sources of polychlorinated biphenyls (PCBs) in ambient air, their depositions and uptake by plants in Poland. The congener-specific determination of planar and non-planar chlorobiphenyls was achieved by isotope dilution HRGC-HRMS method after a highly refined extraction on multi-layer column of silica gel and alumina layer and clean-up, and fractionations, followed by Hypercarb-HPLC and PYE-HPLC sub-fractionation steps. Contents of 117 chlorobiphenyls determined in pine needles varied for the 25 sites studied and is between 2.7 and 49 ng/g wet weight. The PCBs pollution and congener-specific composition of pine needles to some degree varied according to the site or region surveyed depending on population density and industrialization. Many of the country-side areas showed lower concentrations between 2.7 and 8.9 ng/g ww. Pine needles in areas close to well populated and industrial regions of Opole, Kutno, Włocławek and Dębica showed the highest PCB pollution with concentrations varying between 30 and 49 ng/g ww. The Kutno site showed the highest pollution and this fact probably can be explained by possible emission from transformer manufactures located at some distance west of the Kutno area. Factor analysis (FA) and depending on the site revealed on relationship of PCBs composition of pine needles both with highly chlorinated PCB constituents of the mixtures such as Chlorofen, Aroclor 1254, Aroclor 1268 and Sovol but also of lower chlorinated PCB constituents of Aroclor 1242, Aroclor 1248, Clophen A40 or Delor 103. Thermal processes were considered a less significant source of PCBs in ambient air over Poland compared to evaporative sources related to technical PCB formulations. Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Environmental Science and Health: Part A to view the free supplemental file.

Modeling polychlorinated biphenyl sorption isotherms for soot and coal

Sorption isotherms (pg–ng/L) were measured for 11 polychlorinated biphenyls (PCBs) of varying molecular planarity from aqueous solution to two carbonaceous geosorbents, anthracite coal and traffic soot. All isotherms were reasonably log-log-linear, but smooth for traffic soot and staircase-shaped for coal, to which sorption was stronger and more nonlinear. The isotherms were modeled using seven sorption models, including Freundlich, (dual) Langmuir, and Polanyi–Dubinin–Manes (PDM). PDM provided the best combination of reliability and mechanistically-interpretable parameters. The PDM normalizing factor Z appeared to correlate negatively with sorbate molecular volume, dependent on the degree of molecular planarity. The modeling results supported the hypothesis that maximum adsorption capacities ( Q max) correlate positively with the sorbent’s specific surface area. Q max did not decrease with increasing sorbate molecular size, and adsorption affinities clearly differed between the sorbents. Sorption was consistently stronger but not less linear for planar than for nonplanar PCBs, suggesting surface rather than pore sorption.

Gene expression profile of endothelial cells exposed to estrogenic environmental compounds: Implications to pulmonary vascular lesions

Aims The cardiovascular system is an important target of estrogenic compounds. Considering the recent studies that question previously reported cardio-protective effects of estrogen, there is a growing concern that estrogenic environmental compounds may contribute to the pathology of vascular lesion formation. Main methods Real-time quantitative PCR was used to monitor the expression of genes involved in vascularization. Using Bayesian network modeling, we determined a gene network that estrogenic chemicals modulate in human vascular endothelial cells. Key findings We showed that planar and coplanar polychlorinated biphenyls (PCBs) induce the expression of different genes compared to estradiol. Non-planar PCB congener 153 induced NOTCH3 which is a new finding as well as CCL2 and IL8 similar to what has been reported by other non-planar PCBs in endothelial cells. Our gene network indicated that experimental treatments signal a network containing TGF-β receptor and NOTCH3; molecules biologically relevant to signaling pulmonary vascular lesions. Significance We report in the present study that exposure of vascular endothelial cells to environmentally relevant concentrations of estrogenic PCBs induce gene networks implicated in the process of inflammation and adhesion. Our data suggest that PCBs can promote vascular lesion formation by activating gene networks involved in endothelial cell adhesion, cell growth, and pro-inflammatory molecules which were different from natural estrogen. Since inflammation and adhesion are a hallmark in the pathology of endothelial cell dysfunction, reconstructing gene networks provide insight into the potential mechanisms that may contribute to the vascular risks associated with estrogenic environmental chemicals.

PCBs and the energy cost of migration in the European eel ( Anguilla anguilla L.)

The effect of polychlorinated biphenyls (PCBs) on the energy consumption of fasting silver European eel ( Anguilla anguilla L.) was studied over a 27-day period during which the animals were at rest or were swimming 800 km in Blazka swim tunnels. Three-year-old female hatchery eels (silver stage) between 73 and 80 cm long weighing around 1 kg were dosed intraperitoneally with PCBs at a nominal dosage of 10× the consumption standard as a mixture representative for planar (7 μg PCB126/kg eel), non-planar (5 mg PCB153/kg eel) and metabolizable PCBs (50 μg PCB77/kg eel) found in wild eel, or only with the vehicle (corn oil, 10 ml/kg eel). Four major observations were made: (1) PCB-exposed animals lose less weight compared to their unexposed controls; (2) PCB-concentrations on a lipid basis are 2.8–14 times higher in swimming compared to resting animals; (3) the standard metabolic rate is significantly lower in the PCB-exposed animals than in unexposed controls. In addition, PCB-exposure significantly reduces oxygen consumption during swimming, and starting at 400 km (18 days) this effect increases with time; (4) the relative spleen and liver weight significantly increased in the PCB-swim animals but not in the PCB-rest animals. The swimming animals lost about 75% more weight compared to resting animals and had about 50% lower plasma fat content. Hematocrit, haemoglobin, plasma pH, ion levels (sodium and potassium), and plasma lactate were not affected by PCB-exposure or swimming. Apparently, the current levels of PCBs and other dioxin-like compounds may seriously impair the reproduction of the European eel.

Oxidative stress and apoptosis of Carassius auratus lymphocytes induced by nonplanar (PCB153) and coplanar (PCB169) polychlorinated biphenyl congeners in vitro

Among all the 209 kinds of polychlorinated biphenyls (PCBs) congeners, nonplanar and coplanar PCB congeners have different levels of toxicity on mammal cells such as neuronal cells, but little is known about their toxicity on fish cells although PCB congeners usually have high bioaccumulation abilities in the detected fish bodies. This study showed that 2,2',4,4',5,5'-hexacholorbiphenyl (PCB153, nonplanar congener) and 3,3',4,4',5,5'-hexacholorbiphenyl (PCB 169, coplanar congener) caused apoptosis on the isolated crucian carp (Carassius auratus) lymphocytes and the induced cytotoxicity was structure-dependent. According to the laser confocal microscope observations, apoptosis was clearly distinguished by condensation of nucleus, shrinkage and formation of apoptotic bodies. DNA fragmentation was detected by agarose gel electrophoresis. These typical morphological and biochemical characteristics indicate the occurrence of apoptosis on fish lymphocytes. According to the flow cytometry analysis, after the cells were exposed to 10 micromol/L PCBs for 3 h, the apoptotic percentage induced by PCB153 was 23.41%, while that induced by PCB169 was even higher (31.03%). Furthermore, incubating PCBs with fish lymphocytes enhanced levels of reactive oxygen species (ROS) and malondialdehyde (MDA), clearly indicating the presence of oxidative stress and lipid peroxidation. Our data also demonstrate that the different cytotoxic effects induced by coplanar and nonplanar PCBs were correlated with their structural characteristics and the coplanar congener was more cytotoxic than nonplanar congener. This study suggests that cytotoxicity mechanisms of the PCB congeners on fish lymphocytes depend on their planarity and chemical structures.

Availability of polychlorinated biphenyls in field‐contaminated sediment

Two chemical approaches, Tenax extraction and matrix solid phase microextraction (matrix-SPME), were evaluated as surrogates to estimate bioavailability of polychlorinated biphenyls (PCBs) from field-contaminated sediment. Aroclor 1254 was the primary contaminant found in sediment from Crab Orchard Lake in Marion, Illinois, USA, and a total of 18 PCB congeners were selected for study. Bioaccumulation was determined by exposing the freshwater oligochaete, Lumbriculus variegatus, to the sediment for 28 d. Differences in the rapidly desorbing fraction of PCBs and fraction desorbed within 6 h, defined by Tenax extraction, accounted for 39 and 31% of the differences among biota-sediment accumulation factor values, respectively. A better relationship (r2 = 0.95) was found between the oligochaete PCB body residues and the concentration of PCBs in the rapidly desorbing fraction of sediment. The degree of chlorination and planarity of the PCB congeners affected both desorption and bioaccumulation. The higher chlorine substituted and planar PCBs showed less chemical and biological availability, due to their stronger sorption to sediment, compared to the lower chlorinated and nonplanar PCBs. Accumulation of PCBs by L. variegatus correlated well (r2 = 0.88) with matrix-SPME fiber concentrations. The ratio of measured body residue to estimated body residue from the pore water concentration measured by matrix-SPME ranged from 0.4 to 1.3 with an average of 0.9. Overall, both Tenax and matrix-SPME approaches were useful surrogates of bioaccumulation for a field-contaminated sediment.

Rapid Method for Determination of Dioxin-Like Polychlorinated Biphenyls and Other Congeners in Marine Sediments Using Sonic Extraction and Photodiode Array Detection

A rapid method has been developed to measure dioxin-like polychlorinated biphenyl (PCB) congeners as well as other selected PCBs in sediment. The analytes were extracted from sediment by sonication with dichloromethane, and the PCBs were separated from interfering compounds on a gravity-flow cleanup column packed with acidic, basic, and neutral silica gels eluted with 1:1 hexane:pentane (v/v). Subsequently, the dioxin-like PCB congeners were resolved from nonplanar PCBs and other chlorinated compounds by high-performance liquid chromatography (HPLC). Two important advantages of PDA over conventional UV detection are the ability to identify individual analytes by comparing their UV spectra with those of reference standards and the ability to establish the spectral homogeneity (purity) of the analytes by comparing spectra within a peak to the apex spectrum. The HPLC-PDA method was tested with reference and marine sediment samples. Concentrations of selected dioxin-like PCBs, selected nonplanar PCBs, and summed PCBs in sediments and National Institute of Standards and Technology standard reference materials determined by our rapid HPLC-PDA method were comparable with the levels in the same samples analyzed by alternative comprehensive methods (i.e., gas chromatography-electron capture detection or high-resolution gas chromatography-high-resolution mass spectrometry).

Antagonism of TCDD-induced ethoxyresorufin- O-deethylation activity by polybrominated diphenyl ethers (PBDEs) in primary cynomolgus monkey ( Macaca fascicularis) hepatocytes

Polybrominated diphenyl ethers (PBDEs) are widespread environmental pollutants, and the levels of certain congeners have been increasing in biota and abiota in recent decades. Some PBDEs are lipophilic and persistent, resulting in bioaccumulation in the environment. Their structural similarity to other polyhalogenated aromatic hydrocarbons (PHAHs) such as polychlorinated biphenyls (PCBs) has raised concerns that PBDEs might act as agonists for the aryl hydrocarbon receptor (AhR). Recent studies in our laboratory with human and rat cell lines indicated no AhR mediated CYP1A1 induction for PBDEs. However, an earlier in vitro study by Van der Burght et al. (1999) [Van der Burght, A.S., Clijsters, P.J., Horbach, G.J., Andersson, P.L., Tysklind, M., van den Berg, M., 1999. Structure-dependent induction of CYP1A by polychlorinated biphenyls in hepatocytes of cynomolgus monkeys ( Macaca fascicularis). Toxicol. Appl. Pharmacol. 155, 13–23] indicated that in cynomolgus monkey ( M. fascicularis) hepatocytes PCBs with a non-planar configuration could induce CYP1A. As PBDEs show a structural similarity with non-planar ( ortho substituted) PCBs, our present study focused on the possible CYP1A induction by PBDEs (BDE-47, -99, -100, -153, -154, -183, and -77) in individual preparations ( n = 4) of primary hepatocytes of cynomolgus monkeys ( M. fascicularis). 7-Ethoxyresorufin- O-deethylase (EROD) was used as a marker for CYP1A-mediated catalytic activity. Cells were exposed for 48 h to various PBDE concentrations (0.01–10 μM), positive controls 2,3,7,8-TCDD (0.001–2.5 nM) and PCB-126 (0.01–10 nM), and negative control (DMSO vehicle alone). No statistically significant induction of CYP1A was observed in the hepatocytes after 48 h of exposure to all environmentally relevant PBDEs. After exposing hepatocytes to PBDEs in combination with TCDD, a concentration-dependent decrease in TCDD-induced EROD activity was observed. All PBDEs tested showed a similar reduction in each of four experiments, though quantitative differences were observed. The observed antagonism of TCDD-induced EROD activity by PBDEs occurred in both male ( n = 3) and female ( n = 1) hepatocytes and was not due to catalytic inhibition of EROD activity or cytotoxicity. However, based on the results of this study we do not expect these antagonistic effects of PBDEs on CYP1A induction at environmental relevant levels, since these in vitro interactive effects with TCDD were observed only at relatively high concentrations that are normally not seen, e.g. in the human body.

Differential effects of PCBs on the induction of apoptosis machinery and PKCα translocation in rat renal tubular cell cultures

We have demonstrated previously [Pérez-Reyes, P.L., Sánchez-Alonso, J.A., López-Aparicio, P., Recio, M.N., Pérez-Albarsanz, M.A., 2001. Different molecular capacity in the induction of apoptosis by polychlorinated biphenyl congeners in rat renal tubular cell cultures. Biosci. Rep. 6, 765–778] that the polychlorinated biphenyls (PCBs) cause loss of cell viability and accelerate apoptosis in cell kidney cultures. Further investigations are necessary to elucidate the mechanism of apoptosis induction. In this way, we have analyzed in the present work the effects of PCBs on protein kinase C (PKC, a protein family intimately involved in the regulation of cell survival) and the expression of two proapoptotic (caspase-3 and Bax) and one antiapoptotic (Bcl-2) proteins. Aroclor 1248 (a commercial PCB mixture with 48% chlorine by weight), PCB 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl, a di- ortho-substituted nonplanar congener) and PCB 77 (3,3′,4,4′-tetrachlorobiphenyl, a non- ortho-substituted planar congener), significantly increased PKCα activity compared to control cells in the cytosolic and particulate cell fractions, and increased the PKCα protein content in the particulate fraction. The nonplanar PCB 153 showed stronger effects than the coplanar congener PCB 77. In addition, Aroclor 1248 decreased both, procaspase-3 levels and the Bcl-2/Bax protein ratio. These findings indicate that PCBs, particularly nonplanar congeners, can induce apoptosis in primary renal tubular cells through the PKCα, caspase-3 and Bcl-2/Bax pathway.

COMPARATIVE METABOLISM OF POLYCHLORINATED BIPHENYLS AND TISSUE DISTRIBUTION OF PERSISTENT METABOLITES IN RATS, HAMSTERS, AND GUINEA PIGS

The present study was performed to compare the metabolite profiles of polychlorinated biphenyls (PCBs) in the liver and serum of rats, hamsters, and guinea pigs after exposure to a PCB mixture, Kanechlor 500 (100 mg/kg, i.p.). The percentage of contribution of major PCB residues in the liver 5 days after exposure indicated that nonplanar PCBs with 2,4- or 2,3,4-chlorine substitution were more abundant in the liver in the order rats (43% of total PCBs) > hamsters (20%) > guinea pigs (11%), whereas coplanar PCBs with 4-, 3,4-, or 3,4,5-chlorine substitution were predominant in guinea pigs (61%), followed by hamsters and rats (both 26%). The hepatic concentrations of methylsulfonyl metabolites (MeSO(2)-CBs) were higher in the order guinea pigs > rats > hamsters. Whereas hamsters formed minute amounts of MeSO(2)-CBs from 2,5-dichloro-substituted PCBs, guinea pigs formed higher levels of meta-MeSO(2)-CBs derived from 2,3,6-trichloro-substituted PCBs. In contrast, the serum concentrations of phenolic PCBs were higher in the order hamsters > rats > guinea pigs. Metabolites were predominated by 4-OH-2,3,5,3',4'-pentaCB (89% contribution) for rats, 3-OH-2,4,5,2',4'-pentaCB (56%) for guinea pigs, and dihydroxylated metabolites (39%) for hamsters. The reduced elimination of coplanar PCBs and the specific distribution of MeSO(2)- and phenolic PCBs may have implications for the differences in sensitivity to PCB toxicity among rats, guinea pigs, and hamsters.

Sorption of 2,4′‐dichlorobiphenyl and fluoranthene to a marine sediment amended with different types of black carbon

Recent studies demonstrate that sedimentary black carbon (BC) affects the sorption of some hydrophobic organic contaminants (HOCs) to a greater extent than sedimentary organic carbon (OC). Among HOC, polycyclic aromatic hydrocarbons (PAHs) are known to interact extensively with BC. Currently, data on the sorption of various kinds of HOCs to different types of BC are limited. In this study, we amended a marine sediment with BC from several different sources, humic acid, and inert sand. Equilibration studies with 14C fluoranthene and the polychlorinated biphenyl (PCB) 3H 2,4'-dichlorinated biphenyl were performed to determine the magnitude of sorption as a function of contaminant and BC type. The magnitude of sorption to the BC-amended sediments was greater for the PAH than the PCB as compared to the sediment alone, humic acid, and sand. For example, differences between the log partition coefficient (K(P)) for the PAH and PCB ranged from 0.41 to 0.69 log units for humic acid and sand treatments, while differences ranged from 0.88 to 1.57 log units for the BC-amended sediments. As a result, BC-normalized partition coefficients (log K(BC)) for the PAH averaged 6.41, whereas the PCB log K(BC) values averaged 5.33. These results demonstrate that PAH sorption and most likely bioavailability are influenced strongly by the presence of BC of different types, while sorption of a nonplanar PCB was affected to a lesser degree.

Excretion pattern of co-planar and non-planar tetra- and hexa-chlorobiphenyls in ovine milk and faeces

This study employed the gas chromatography with electron capture detection to determine residual levels and excretion patterns of two pairs of structurally diverse polychlorinated biphenyl (PCB) congeners (IUPAC Nos. 54, 80, 155, and 169) administered to lactating sheep by intramuscular injection. PCB levels and excretion patterns in blood, milk, and faeces were time-dependent and differed from the composition of PCB congeners administered. Lactational transfer substantially exceeded the faecal transfer. Between days 3 and 7, the amount of PCB congeners 54 and 169 excreted in milk was around 50- and 800-fold higher than the amount of these two congeners excreted via faeces. During the same period, the relative contribution of co-planar PCB congeners (80 and 169) in PCB pattern decreased in blood and increased in milk and faeces compared with non-planar PCBs (54 and 155). On day 3, the ratio PCB 169 to 54 was 7-fold higher in milk than in faeces. PCB congeners with log K ow values under 6.5 reached peaks of their excretion in milk within the first three days after administration, while the super-lipophilic PCB 169 congener with log K ow value of over 7 has not reached the plateau until day 10, but afterwards, its level remained relatively high throughout the observation period. During the 57-day follow-up period, the excretion of PCB 80, 155, and 169 in milk was 4.5-, 14-, and 46-fold greater compared with PCB 54. Differences in levels and patterns were explained with some physico-chemical properties of individual PCB congeners, such as lipophilicity, planarity, metabolic stability, sorption/diffusion properties.

Interaction between halogenated aromatic compounds in the Ah receptor signal transduction pathway

Many toxic and biochemical responses to halogenated aromatic compounds (HACs) such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (PCDDs) are mediated through the aryl hydrocarbon receptor (AhR), which is an intracellular cytosolic target for HACs. Environmental exposure to HACs almost always involves complex mixtures of congeners, some of which can antagonize the action of potent HACs such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In this work we studied TCDD and representative PCB congeners, alone and in mixture, for their effect on CYP1A gene transcription and protein levels in primary rat hepatocytes. Together with our previous work, our results suggest that formation of the Ah receptor-ligand-DRE (dioxin response element) complex is the principal point of divergence in the mechanism between an AhR agonist and an AhR antagonist. The coplanar PCBs 77 and 126 and the mono-ortho PCB 156 were full agonists toward CYP1A1 gene transcription and CYP1A protein levels, showing typical additive behavior with TCDD to the target molecule AhR. In contrast, the nonplanar PCB 153 antagonized the action of TCDD, even at concentrations that occupied a significant fraction of AhR molecules. Competitive inhibition explains the commonly reported decrease of ethoxyresorufin-O-deethylase (EROD) activity when PCBs are present in high concentrations and the antagonism of PCBs to the EROD activity of TCDD. The result is that Western blotting offers a much more reliable measure of CYP1A protein concentration than does the EROD assay, despite the greater convenience of the latter.

Inhibition of gap junctional intercellular communication by noncoplanar polychlorinated biphenyls: inhibitory potencies and screening for potential mode(s) of action.

Polychlorinated biphenyls (PCBs), a structurally diverse group of environmental pollutants, are effective promoters in two-stage cancer models, which implies that epigenetic mechanisms are involved. Inhibition of gap junctional intercellular communication (GJIC) belongs among critical epigenetic events of tumor promotion. We determined the relative potencies of a series of environmentally relevant PCB congeners to inhibit GJIC in vitro in a rat liver epithelial cell line with pluripotent oval cell characteristics. The nonplanar PCBs were potent inhibitors of GJIC, whereas the coplanar PCBs did not inhibit GJIC. We then compared the effects of the coplanar PCB 126 (3,3',4,4',5-pentachlorobiphenyl) and the noncoplanar PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl) with effects of two model GJIC inhibitors, a tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF). In contrast to TPA or EGF, PCB 153 elicited a long-term downregulation of GJIC (up to 48 h). Using Western blot analysis with phospho-specific antibodies, it was found that PCB 153, and not PCB 126, activated mitogen-activated protein kinases ERK1/2; however in contrast to TPA and EGF, this activation was observed at the time points subsequent to GJIC inhibition. Moreover, blocking of ERK1/2 activation did not prevent the GJIC inhibition induced by PCB 153. Therefore, additional intracellular signaling pathways potentially involved in the downregulation of GJIC by PCBs were screened by using specific chemical probes inhibiting serine/threonine kinases, tyrosine kinases, and phospholipases. The inhibition of diacylglycerol lipase partially blocked and the selective inhibition of Src kinases and phosphatidylcholine-specific phospholipase C (PC-PLC) completely blocked the inhibitory effects of the noncoplanar PCB on GJIC, indicating that PC-PLC or sphingomyelinase and Src might be upstream regulators of noncoplanar PCB-induced inhibition of GJIC.

Effect of 3,3′,4,4′-tetrachlorobiphenyl and 2,2′,4,4′,5,5′-hexachlorobiphenyl on the induction of hepatic lipid peroxidation and cytochrome P-450 associated enzyme activities in rats

Polychlorinated biphenyls (PCBs) are environmental contaminants that have been widely used for various industrial purposes. In spite of numerous studies on PCBs, however, their mechanism of toxicity remains unknown. The role of cytochrome P-450 in PCBs induced hepatic lipid peroxidation is controversial. Therefore, the present study was undertaken to study the mechanism of action of two PCBs and their role in cytochrome P-450 induction and lipid peroxidation, determined in vivo and during the incubation of subcellular fractions. We also examined whether agonist/antagonist activities between the two PCBs were occurring. Two PCBs were studied: 3,3′,4,4′-tetrachlorobiphenyl (PCB-77), a non- ortho-substituted, coplanar PCB; and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB-153), a di- ortho-substituted, non-planar PCB. Groups of male Sprague–Dawley rats were given a single i.p. injection of one of the two PCBs (at doses of 30, 150, or 300 μmol/kg), both PCBs (at doses of 30 or 150 μmol/kg), or vehicle alone. Rats were sacrificed after 2, 6, or 24 h; or 2, 6, or 10 days. Cytochrome P-450 induction occurred as early as 2 h with PCB-77 and 24 h with PCB-153. Significant increases in thiobarbituric acid reactive substances (TBARS) content in liver tissue occurred 2, 6 and 10 days after treatment with PCB-77 and PCB-153; it was unclear whether these PCBs were synergistic in their induction of TBARS formation. Liver microsomal fractions incubated with NADPH only showed increased TBARS formation at the highest doses of PCB-77 and PCB-153 after 6 days. The results indicate that both PCBs induced cytochrome P-450 enzymes and enhanced lipid peroxidation in liver and subcellular fractions but with different potencies and onsets of action. The results also indicate a larger time difference between cytochrome P-450 induction and lipid peroxidation for PCB-77. Thus, both PCB-77 and PCB-153 are toxic to cells, but may act via different mechanisms to induce their effects.