Polychlorinated Biphenyls Metabolites Research Articles

Hydroxylated Polychlorinated Biphenyls (PCBs) Interact with Protein Disulfide Isomerase and Inhibit Its Activity

Protein disulfide isomerase (PDI) is a catalyst of isomerization of substrate protein intra- and extra-molecular disulfide bridges and also has 3,3',5-triiodo-l-thyronine (T(3))-binding activity and molecular chaperone-like activity. We previously found that halogenated derivatives of bisphenol A as well as bisphenol A itself bind to PDI and thereby suppress the oxidative refolding of reduced RNaseA by PDI. Polychlorinated biphenyls (PCBs) are environmental endocrine-disrupting chemicals that cause various abnormalities in many organs such as the central nervous system. PCBs are metabolized to hydroxylated compounds (HO-PCBs) in humans and other animals, and HO-PCBs gain toxicity by metabolism. In the present study, 2',3,3',4',5'-pentachlorobiphenyl (penCB), 2',3,3',5,5',6'-hexachlorobiphenyl (hexCB), and their 4-hydroxylated metabolites (HO-penCB and HO-hexCB, respectively) were used to examine whether they interact with PDI and inhibit its activity. HO-penCB and HO-hexCB markedly inhibited the binding of T(3) to PDI. However, nonhydroxylated PCBs did not show any interaction with PDI. The effects of PCBs and HO-PCBs on PDI activity were also investigated using an RNaseA refolding assay. Both HO-PCBs inhibited the oxidative refolding of reduced RNaseA by PDI. We also assessed the effects of HO-PCBs and PCBs on the chaperone activity of PDI, which was measured by a thermal aggregation assay, and found that neither HO-PCBs nor PCBs have significant inhibitory or promoting effects. These findings suggest that the metabolites of PCBs have the potential to cause defective protein folding via PDI.

Mono-hydroxylated polychlorinated biphenyls are potent aryl hydrocarbon receptor ligands in recombinant yeast cells

The toxicities of polychlorinated biphenyls (PCBs) are thought to be mediated mainly by the aryl hydrocarbon receptor (AhR). However, little is known about changes to AhR-mediated effects caused by metabolic conversion of PCBs. To investigate whether hydroxylation affects the affinity of PCBs for the AhR, we measured the AhR agonistic activity of mono-hydroxylated PCBs (mono-OH-PCBs) and their non-hydroxylated analogs (PCBs) using yeast cells transduced with the human AhR and its response pathway. Fifty-two of 84 tested OH-PCBs and 12 of 24 PCBs exhibited AhR agonistic effects. Of 49 OH-PCBs that had the same chlorination patterns as the tested PCBs, 26 had activities that were more than twice those of their analogous PCBs, or became activated if their non-hydroxylated analogs were inactive. In particular, 3′,4,5′-trichlorobiphenyl-2-ol and 3′,4,4′-trichlorobiphenyl-3-ol were 37- and 22-fold more potent than their non-hydroxylated analogs and were 1.42 times and 1.08 times, respectively, as active as a standard, β-naphthoflavone. The activities of only 5 OH-PCBs were reduced to less than half those of their non-hydroxylated counterparts. No tested PCBs were inactivated by the presence of a hydroxyl group. These findings underscore the need to rethink the toxicological evaluation of hydroxylated metabolites of PCBs and their abundance in the environment.

Improved syntheses of non-dioxin-like polychlorinated biphenyls (PCBs) and some of their sulfur-containing metabolites

Polychlorinated biphenyls (PCBs) are an important group of environmental pollutants that have been associated with adverse human health effects. Despite recent advances in their synthesis, the availability of PCB congeners in sufficient quantity and purity still represents one obstacle in the investigation of their biological effects. We report herein improved syntheses of PCB congeners (and their metabolites) containing two or more ortho-chlorine substituents. The Suzuki coupling reaction at 110 °C yielded PCB congeners with a 2,2′-substitution pattern in good yields (78–99%), but failed to give PCB congeners with 3 or 4 ortho chlorine substituents. Symmetrically substituted PCB congeners with multiple ortho chlorine substituents were obtained in 20–52% yields using a modified Ullmann coupling reaction. The yield of the coupling increased with increasing degree of chlorination of the starting material. The modified Ullmann coupling reaction employed much milder reaction conditions (copper–bronze/CuCl in N-methylpyrrolidinone, 110 °C) and, therefore, appears to be advantageous compared to the classical Ullmann coupling reaction (copper–bronze, no solvent, 230 °C). PCBs 136 and 155 prepared via the modified Ullmann coupling reaction were nitrated and reduced with Na 2S 2O 4 to the corresponding amino-PCBs. Subsequently, the amino-PCBs were converted into sulfur-containing PCB metabolites or PCB 184 via the corresponding diazonium salt. These modified reaction conditions allow the synthesis of large quantities of pure, non-dioxin-like PCB congeners and their sulfur-containing metabolites for environmental and toxicological studies by overcoming problems associated with classical PCB synthesis strategies.

Oxidative DNA adducts after Cu 2+-mediated activation of dihydroxy PCBs: Role of reactive oxygen species

Polychlorinated biphenyls (PCBs) are toxic industrial chemicals, complete carcinogens, and efficacious tumor promoters. However, the mechanism(s) of PCB-mediated carcinogenicity remains largely undefined. One likely pathway by which these agents may play a role in carcinogenesis is the generation of oxidative DNA damage by redox cycling of dihydroxylated PCB metabolites. We have now employed a new 32P-postlabeling system to examine novel oxidative DNA lesions induced by Cu 2+-mediated activation of PCB metabolites. 32P postlabeling of DNA incubated with various PCB metabolites resulted in over a dozen novel polar oxidative DNA adducts that were chromatographically similar for all active agents. The most potent metabolites tested were the hydroquinones (hydroxyl groups arranged para to each other), yielding polar oxidative adduct levels ranging from 55 to 142 adducts/10 6 nucleotides. PCB catechols, or ortho-dihydroxy metabolites, were up to 40% less active than their corresponding hydroquinone congeners, whereas monohydroxylated and quinone metabolites did not produce detectable oxidative damage over that of vehicle. With the exception of 2,4,5-Cl-2′,5′-dihydroxybiphenyl, this oxidative DNA damage seemed to be inversely related to chlorine content: no chlorine ≈ mono- > di- > trichlorinated metabolites. Importantly, copper, but not iron, was essential for activation of the PCB metabolites to these polar oxidative DNA adducts, because in its absence or in the presence of the Cu +-specific scavenger bathocuproine, no adducts were detected. Intervention studies with known reactive oxygen species (ROS) modifiers suggested that H 2O 2, singlet oxygen, hydroxyl radical, and superoxide may also be involved in this PCB-mediated oxidative DNA damage. These data indicate a mechanistic role for several ROS, in addition to copper, in PCB-induced DNA damage and provide further support for oxidative DNA damage in PCB-mediated carcinogenesis.

Chiral Polychlorinated Biphenyls Are Biotransformed Enantioselectively by Mammalian Cytochrome P-450 Isozymes to Form Hydroxylated Metabolites

In vitro incubations of purified rat cytochrome P-450 (CYP) 2B1 and human CYP 2B6 were performed to determine if CYP isozymes biotransform polychlorinated biphenyls (PCBs) enantioselectively. Enantioselective metabolism of chiral PCBs 45, 84, 91, 95, 132, and 136 and production of hydroxylated PCB metabolites (OH-PCBs) were observed, while no changes in PCB 183 atropisomer composition were observed for either isozyme. Enantiomer fractions (EFs) of parent PCBs, individually incubated as racemates at 25 ng/mL initial concentration, with rat CYP 2B1 ranged from 0.353 to 0.822. Enantioselectivity was also observed for PCBs 45 (EF = 0.437) and 132 (EF = 0.537) incubated at that concentration with human CYP 2B6. Both atropisomers of chiral PCBs appeared to be biotransformed simultaneously by rat CYP 2B1, except for (+)-PCB 132, but at different rates. Hydroxylated PCBs were identified using gas chromatography-high resolution mass spectrometry for all chiral PCBs enantioselectively transformed by CYPs. These metabolites did not correspond to any commercially available authentic standards, supporting the hypothesis that many unidentified OH-PCBs detected in wildlife may have arisen from in vivo biotransformation of chiral PCBs. A rough estimate suggested that more than half of the total congener metabolized by rat CYP 2B1 was converted to OH-PCBs. Similar concentration decreases were observed for congeners incubated with human CYP 2B6, but less OH-PCBs were formed. Formation of OH-PCBs via an enantioselective OH insertion mechanism was suggested, and may be a source of the unidentified OH-PCBs currently found in the environment.

Biotransformation of PCBs in Relation to Phase I and II Xenobiotic-Metabolizing Enzyme Activities in Ringed Seals (Phoca hispida) from Svalbard and the Baltic Sea

Polychlorinated biphenyls (PCBs) may induce activity of hepatic enzymes, mainly Phase I monooxygenases and conjugating Phase II enzymes, that catalyze the metabolism of PCBs leading to formation of metabolites and to potential adverse health effects. The present study investigates the concentration and pattern of PCBs, the induction of hepatic phase I and II enzymes, and the formation of hydroxy (OH) and methylsulfonyl (CH3SO2=MeSO2) PCB metabolites in two ringed seal (Phoca hispida) populations, which are contrasted by the degree of contamination exposure, that is, highly contaminated Baltic Sea (n=31) and less contaminated Svalbard (n=21). Phase I enzymes were measured as ethoxyresorufin-O-deethylation (EROD), benzyloxyresorufin-O-dealkylation (BROD), methoxyresorufin-O-demethylation (MROD), and pentoxyresorufin-O-dealkylation (PROD) activities, and phase II enzymes were measured as uridine diphosphophate glucuronosyl transferase (UDPGT) and glutathione-S-transferase (GST). Geographical comparison, multivariate, and correlation analysis indicated that sigma-PCB had a positive impact on Phase I enzyme and GST activities leading to biotransformation of group III (vicinal ortho-meta-H atoms and < or =1 ortho-chlorine (Cl)) and IV PCBs (vicinal meta-para-H atoms and < or =2 ortho-Cl). The potential precursors for the main OH-PCBs detected in plasma in the Baltic seals were group III PCBs. MeSO2-PCBs detected in liver were mainly products of group IV PCB metabolism. Both CYP1A- and CYP2B-like enzymes are suggested to be involved in the PCB biotransformation in ringed seals.

Chlorination Increases the Persistence of Semiquinone Free Radicals Derived from Polychlorinated Biphenyl Hydroquinones and Quinones

Polychlorinated biphenyls (PCBs) comprise a group of persistent organic pollutants that differ significantly in their physicochemical properties, their persistence, and their biological activities. They can be metabolized via hydroxylated and dihydroxylated metabolites to PCB quinone intermediates. We have recently demonstrated that both dihydroxy PCBs and PCB quinones can form semiquinone radicals (SQ(*-)) in vitro. These semiquinone radicals are reactive intermediates that have been implicated in the toxicity of lower chlorinated PCB congeners. Here we describe the synthesis of selected PCB metabolites with differing degrees of chlorination on the oxygenated phenyl ring, e.g., 4,4'-dichloro-biphenyl-2,5-diol, 3,6,4'-trichloro-biphenyl-2,5-diol, 3,4,6,-trichloro-biphenyl-2,5-diol, and their corresponding quinones. In addition, two chlorinated o-hydroquinones were prepared, 6-chloro-biphenyl-3,4-diol and 6,4'-dichloro-biphenyl-3,4-diol. These PCB (hydro-)quinones readily react with oxygen or via comproportionation to yield the corresponding semiquinone free radicals, as detected by electron paramagnetic resonance spectroscopy (EPR alias ESR). The greater the number of chlorines on the (hydro-)quinone (oxygenated) ring, the higher the steady-state level of the resulting semiquinone radical at near neutral pH.

The role of African American ethnicity and metabolism in sentinel polychlorinated biphenyl congener serum levels

Polychlorinated biphenyls (PCBs) are environmental contaminants found in the serum of human populations across the globe. A small set of sentinel PCB congeners (IUPAC# 101, 118, 138, 153, and 180) commonly sought in human serum are often used as markers of exposure. The Chicago Great Lakes cohort of pregnant African American women was developed to study organochlorine exposure through Great Lakes resources in a pregnant African American population and their children. Comparison of PCB serum concentrations in women reporting mixed race/ethnicity within the cohort shows significant elevations of serum PCB 101 and 118 in women reporting exclusive African American ancestry. Incubations were performed using pooled human liver microsomes followed by individual recombinant human CYP isoform microsomes to identify whether the other sentinel congeners are metabolized by human CYP 450. In human liver microsome metabolism experiments with the sentinel PCB congeners (IUPAC# 101, 118, 138, 153, and 180), only PCB 101 metabolism produced an identifiable metabolite. However, a significant loss of parent compound was observed for PCB 118 incubations with human liver microsomes. The loss of PCB 101 and PCB 118 in microsome experiments indicates they are likely metabolized in human liver. Therefore, CYP 450 mediated metabolic differences may contribute to differences in serum concentrations by race/ethnicity. PCB metabolism has an important impact on toxicity. PCB metabolites have been shown to differ significantly in toxicity profiles relative to parent compounds. Biomonitoring studies of PCB serum levels have correlated with toxicity for the metabolizable congeners such as PCB 101 and PCB 118. However, measurable amounts of metabolizable parent congeners such as PCB 101 may not be detectable in the serum of study participants. Because PCB 118 is metabolized, but is also readily found in human serum, it may be a better marker of metabolism related PCB toxicity. Human specific PCB metabolism is difficult to characterize but has important pathophysiological ramifications and deserves further study.

Biosensor discovery of thyroxine transport disrupting chemicals

Ubiquitous chemicals may interfere with the thyroid system that is essential in the development and physiology of vertebrates. We applied a surface plasmon resonance (SPR) biosensor-based screening method for the fast screening of chemicals with thyroxine (T4) transport disrupting activity. Two inhibition assays using the main thyroid hormone transport proteins, T4 binding globulin (TBG) and transthyretin (TTR), in combination with a T4-coated biosensor chip were optimized and automated for screening chemical libraries. The transport protein-based biosensor assays were rapid, high throughput and bioeffect-related. A library of 62 chemicals including the natural hormones, polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs) and metabolites, halogenated bisphenol A (BPA), halogenated phenols, pharmaceuticals, pesticides and other potential environmentally relevant chemicals was tested with the two assays. We discovered ten new active compounds with moderate to high affinity for TBG with the TBG assay. Strikingly, the most potent binding was observed with hydroxylated metabolites of the brominated diphenyl ethers (BDEs) BDE 47, BDE 49 and BDE 99, that are commonly found in human plasma. The TTR assay confirmed the activity of previously identified hydroxylated metabolites of PCBs and PBDEs, halogenated BPA and genistein. These results show that the hydroxylated metabolites of the ubiquitous PBDEs not only target the T4 transport at the TTR level, but also, and to a great extent, at the TBG level where most of the T4 in humans is circulating. The optimized SPR biosensor-based transport protein assay is a suitable method for high throughput screening of large libraries for potential thyroid hormone disrupting compounds.

Hydroxy-PCBs, Methoxy-PCBs and Hydroxy-Methoxy-PCBs: Metabolites of Polychlorinated Biphenyls Formed In Vitro by Tobacco Cells

While the metabolism of polychlorinated biphenyls (PCBs) in plant cells is a rarely studied field, hydroxy-PCBs have been detected in several studies involving the use of various plant species. The ability of the tobacco (Nicotiana tabacum) callus culture WSC-38 to metabolize six dichlorobiphenyls under aseptic conditions was studied, and the resulting PCB metabolites were analyzed. WSC-38 cultures were cultivated with individual dichlorinated PCB congeners. The metabolites were identified based on mass spectra characteristics after gas chromatography separation. In addition, metabolites of PCB 9 (2,5-dichlorobiphenyl) were identified by comparing their retention characteristics with the available standards. In most cases at least two hydroxy-PCBs were produced from each parent PCB. Methoxy-PCBs and hydroxy-methoxy-PCBs were other groups of metabolites produced. To the best of our knowledge, ours is the first report to determine the presence of methoxy- and hydroxy-methoxy-metabolites of PCBs in plants. The role of the O-methyltransferases (OMTs) in the methylation of hydroxy-PCBs is discussed. As methoxy-metabolites of acetophenone were found among our samples, we posit that the OMTs responsible for the methylation of these compounds are also involved in the metabolism of PCBs in cultures of WSC-38.

Glucuronidation of Polychlorinated Biphenylols and UDP-Glucuronic Acid Concentrations in Channel Catfish Liver and Intestine

Polychlorinated biphenylols (OH-PCBs) are potentially toxic polychlorinated biphenyl metabolites that can be eliminated by glucuronidation, catalyzed by UDP-glucuronosyltransferases (UGTs). OH-PCBs with a 3,5-dichloro-4-hydroxy substitution pattern have been detected in blood from humans and wildlife, suggesting slow elimination. In this study we assessed the glucuronidation of 4-OH-PCBs with zero, one, or two chlorine atoms flanking the 4-hydroxyl group and zero to four chlorine atoms in the aphenolic ring in microsomes from channel catfish liver and proximal intestine. Product formation was quantitated with [(14)C]UDP-glucuronic acid (UDPGA). Physiological concentrations of UDPGA were measured in preparations of liver and intestine. When the OH-PCB concentrations were varied in the presence of saturating UDPGA concentrations, glucuronidation V(max) values were higher in hepatic than in intestinal microsomes (0.40-3.4 and 0.12-0.78 nmol/min/mg of protein, respectively), whereas the K(m) values were generally lower for intestine (0.042-0.47 mM) than for liver (0.11-1.64 mM). In both tissues V(max) values with 3,5-dichloro-4-OH-PCBs were lower than with the corresponding 3-chloro-4-OH-PCBs. Varying the UDPGA concentrations in the presence of saturating concentrations of OH-PCB showed that the K(m) for UDPGA was lower in intestine (27 microM) than in liver (690 microM). The measured concentration of UDPGA in catfish liver (246-377 nmol/g) was lower than the K(m) for UDPGA, suggesting that in vivo rates of glucuronidation may be suboptimal, whereas in intestine the measured UDPGA concentration (71-258 nmol/g) was higher than the K(m) for UDPGA. Although liver has a greater glucuronidation capacity than proximal intestine, the properties of intestinal UGTs in channel catfish enable them to efficiently glucuronidate low concentrations of OH-PCBs.

Risk of Incidence of Selected Malignancies and Human Exposure to Polyhalogenated Hydrocarbons

ISEE-924 Objective: Findings regarding the carcinogenicity of polyhalogenated hydrocarbons are still inconclusive and even contradictory. We analyzed the incidence of selected malignancies in a population exposed to polychlorinated biphenyls (PCBs) by comparing data available in the Czech National Cancer Registry database for Czech Republic (∼10 million inhabitants), with data from the population of Uherské Hradišťe District (∼146,000 inhabitants). The District Uherské Hradišťe (UH) is recognized as the most heavily PCB-contaminated area in Czech Republic. Material and Methods: Cancer incidence data was analyzed for the 10-year period 1987–1996. The age adjusted world standard ratio (WSR), the over all (total) incidence of malignancies, and the incidence of thyroid, pancreatic, breast, ovarian, bladder, brain, prostate, and testicular tumors found in local populations were compared. Statistical significance was evaluated using two sample paired t-tests of the means in the STATISTICA 6.0 software. Results: The only statistically validated difference, between the UH District and the Czech Republic analyzed database, was a lower incidence of bladder malignancies both in men and women on the same level of significance (P < 0.01). This study does not confirm our previous experience from Eastern Slovakia. In a former study, which was respecting the same protocol in a population heavily exposed to PCBs, there was a lower incidence of breast (P < 0.01) and prostate malignancies (P < 0.03), in the local population (∼112,000 inhabitants), compared with the whole Slovakia (∼5 million inhabitants). Conclusions: Neither PCBs nor polychlorinated dibenzofurans (PCDFs) appear to contribute to the observed lower incidence of bladder cancer in men and women (P < 0.01) in the UH District. However, antiestrogenic and antiandrogenic properties have been described for hydroxylated and methylsulfonyl PCBs metabolites. Acknowledgement: This study is a continuation of the recently finished 5th FP PROJECT: Evaluating human health risk from low-dose and long-term PCB exposure QLK4-2000-00488 PCBRISK and currently supported by CASCADE NoE 6FP EC.

Perinatal Exposure to Brominated Flame Retardants and Polychlorinated Biphenyls in Japan

Brominated flame retardants (BFRs) are used to prevent combustion in consumer products. Examples of BFRs are polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA), and tribromophenol (TBP). These compounds are reported to have adverse effects on human health and endocrine disrupting effects. The purpose of this study was to identify the Japanese perinatal exposure to PBDEs, hydroxylated PBDE metabolites (OH-PBDEs), TBBPA, and TBP compared with polychlorinated biphenyls (PCBs) and hydroxylated PCB metabolites (OH-PCBs). We investigated the concentrations of these compounds in maternal blood, maternal milk, cord blood, and umbilical cords from 16 Japanese mother-infant pairs by HRGC/HRMS. PBDEs were detected in all samples of maternal blood (mean+/-SD; median=25+/-23 pg/g; 18 pg/g wet weight), maternal milk (140+/-220 pg/g; 59 pg/g wet weight), cord blood (4.8+/-6.5 pg/g; 1.6 pg/g wet weight), and umbilical cords (3.1+/-3.1 pg/g; 2.1 pg/g wet weight). The mothers were divided into two groups, a high-concentration group and a low-concentration group. The percentage of BDE-47 showed the greatest difference between the two groups. 6-OH-BDE-47, TBBPA, and TBP were detected in all umbilical cord samples (mean+/-SD; median=8.4+/-8.1 pg/g; 8.0 pg/g, 16+/-5.5 pg/g; 15 pg/g, and 33+/-8.2 pg/g; 32 pg/g wet weight respectively), but not in all maternal blood or cord blood samples. These results indicate that OH-PBDEs, TBBPA, and TBP, in addition to PBDEs, PCBs, and OH-PCBs, pass through the blood-placenta barrier and are retained in the umbilical cord.

Polychlorinated biphenyls (PCBs) and hydroxy-PCBs in adipose tissue of women in Southeast Spain

Polychlorinated biphenyls (PCBs) and hydroxylated PCBs (OH-PCBs) were investigated in human adipose tissue samples collected from 20 women undergoing surgery. Mean sum of PCB and sum of OH-PCB levels were 737 ng/g of lipid and 8 pg/g of lipid, respectively. Among PCBs, congeners 180, 153, 138 and 170 were the most frequent and abundant, and together constituted 72% of the total amount of PCBs in adipose tissue. The PCB congener pattern and the frequencies and concentrations of non-dioxin-like and non-hydroxylated congeners observed in adipose tissue were similar in distribution and order of magnitude to the profile previously published in Spain but lower than that found in other European countries. Among OH-PCB congeners studied, 4-OH-PCB 107/118 was found at the highest concentrations followed by 3′-OH-PCB 180 and 3-OH-PCB 138. To date, no information on levels of PCB metabolites in the Spanish population is available for comparison. These three predominant OH-PCBs contributed 97% of all OH-PCBs. Twelve dioxin-like PCBs contributed around 8% of the total PCB exposure, and all were present in all study subjects. Further research is required to determine trends in human exposure to PCBs and OH-PCBs and how existing banning measures affect exposure.

Placental transfer of polychlorinated biphenyls, their hydroxylated metabolites and pentachlorophenol in pregnant women from eastern Slovakia

The aim of the present study was to understand the placental transfer of polychlorinated biphenyls (PCBs), specific hydroxylated PCB metabolites (OH-PCBs), and pentachlorophenol (PCP) in blood serum, in a birth cohort from eastern Slovakia. During the period 2002–2004, cord blood specimens were collected in parallel with maternal specimens from women delivering in the two eastern Slovak districts of Michalovce and Svidnik/Stropkov. A total of 92 pairs of mother-cord specimens at delivery were selected for this study. 4-OH-CB107, 3-OH-CB153, 4-OH-CB146, 3′-OH-CB138, 4-OH-CB187, and 4′-OH-CB172 were quantified. The median concentrations of Σ 17PCBs, Σ 6OH-PCBs, and PCP in cord serum were 0.92, 0.33, and 0.69 ng/g wet wt., respectively and highly correlated with the corresponding maternal serum levels (correlations were R 2 = 0.61, 0.78, and 0.82, respectively). The median cord to mother ratios of the Σ 17PCBs, Σ 6OH-PCBs, and PCP were 0.18, 0.75, and 1.10, respectively. The median ratio of the Σ 6OH-PCBs to the Σ 17 PCBs in the cord serum was 0.38 from wet weight based concentrations, which was about four times higher than the ratio of these compounds in maternal serum (0.09). PCP was more abundant than any PCB or OH-PCB congener measured in cord serum. The higher cord to maternal ratios of OH-PCB metabolites as compared with the parent compounds suggests either a higher placental transfer rate or greater metabolism in the fetus as compared with the maternal compartment. These findings are consistent with their preferential binding to TTR that can cross the placenta. The cord to maternal ratio varies by congener (e.g., 4-OH-CB107 = 0.58, 4-OH-CB146 = 0.74, 3′-OH-CB138 = 1.01).

Maternal and cord serum exposure to PCB and DDE methyl sulfone metabolites in eastern Slovakia

Polychlorinated biphenyls (PCBs) were commercially produced between 1959 and 1984 in eastern Slovakia. Improper handling led to a highly contaminated local environment and high levels of PCBs in humans and wildlife in the Michalovce area. The aim of this study was to analyse serum for methylsulfonyl metabolites of PCB (MeSO 2-PCBs) and DDE (3-MeSO 2-DDE) in serum samples from pregnant women and in a selected number of paired cord blood samples to assess maternal sulfone levels and patterns, and transplacental transfer of these metabolites. The donating women were from two districts in eastern Slovakia. A liquid–liquid extraction method together with separation of substance groups and further clean-up on silica gel columns were applied prior to analysis by gas chromatography/mass spectrometry. 3-MeSO 2-DDE was the major methyl sulfone in most of the samples followed by a yet not identified MeSO 2-hexaCB, 4′-MeSO 2-CB101, 4′-MeSO 2-CB87 and 4-MeSO 2-CB149. The women from the contaminated area had three times higher concentrations of the MeSO 2-PCBs than women from the reference area. This is the first report on methyl sulfone metabolites of PCB and DDE in human cord serum. It is shown that these metabolites are transported through the placenta. The levels of MeSO 2-PCBs in the maternal serum were about 1.5 times higher than in the corresponding cord serum on a lipid weight basis. For 3-MeSO 2-DDE, the levels were about the same in maternal and cord serum. The difference in the maternal:cord ratio, comparing MeSO 2-PCBs with 3-MeSO 2-DDE might be due to differences in transport through the placenta caused by their different affinities for lipoproteins and plasma proteins.

Thyroid hormone status of newborns in relation to in utero exposure to PCBs and hydroxylated PCB metabolites

The associations between in utero exposure to polychlorinated biphenyls (PCBs) or hydroxylated PCB metabolites (OH-PCBs), and free thyroxin (fT4) or thyroid-stimulating hormone (TSH) status in the newborn were investigated as a pilot study of a large-scale epidemiologic study on in utero PCB or OH-PCB exposure and thyroid function of the newborns. Umbilical cord tissue was used as the media for the biological monitoring of PCBs/OH-PCBs exposure in utero. For the measurement of fT4 and TSH, a heel-prick blood sample spotted on filter paper, which is called Guthrie card, is collected from each neonate at day 4–6 postpartum for this study when the mass screening sampling was performed. We showed that the concentration of total OH-PCBs and one of the OH-PCB congeners (OH-PCB 187) was related significantly to higher fT4 level of newborns. On the other hand, the concentration of total PCBs and PCB congeners (PCB 118, 138, 153, and 180) showed no relationship with fT4 and TSH level of the newborns. The results obtained in this pilot study indicated the possibility that in utero OH-PCBs exposure affects thyroid hormone status of newborns.

Serum thyroid hormone concentrations and thyroid histomorphology as biomarkers in bowhead whales (Balaena mysticetus)

Serum thyroid hormone (TH) concentrations have been used alone or with other measurements to assess health status or effects of toxicant exposure in marine mammals. Histological sections from thyroid glands of the bowhead whale ( Balaena mysticetus L., 1758) were examined in conjunction with serological TH analyses. Serum was assayed for total and free triiodothyronine and total and free thyroxine via radioimmunoassay. Histomorphology of thyroid tissue was assessed by light microscopy and the utilization of an epithelial-follicular index (EFI). Age, sex, or season did not significantly affect serum TH levels. However, TH concentrations in pregnant or lactating females were found to be significantly lower than in the other sex and reproductive groups investigated. The EFI and epithelial height (EH) were greater in spring subadult and adult whales compared with those that were landed in the fall. No correlation was found between serum TH concentrations and serum, blubber, or liver levels of select polychlorinated biphenyl metabolites and organochlorine congeners examined. Low variability in concentrations of the serum THs across age, season, and sex and reproductive groups supports the existence of strong homeostatic mechanisms for maintaining TH concentrations in these presumably healthy animals. Departures from these ranges may indicate a disturbance in these regulatory mechanisms and may be a useful indication of toxicity or other health disorders.

Molecular cytotoxic mechanisms of catecholic polychlorinated biphenyl metabolites in isolated rat hepatocytes

Polychlorinated biphenyl (PCB) and PCB metabolites are highly lipophilic and accumulate easily in the lipid bilayer and fat deposits of the body. The molecular cytotoxic mechanisms of these metabolites are still not understood. The aim of the present study was to compare the cytotoxicity and toxicological properties of six dihydroxylated metabolites using isolated rat hepatocytes. All of the metabolites were more cytotoxic than 4-chlorobiphenyl (4-ClBP) and less cytotoxic than phenyl hydroquinone (PHQ). The order of cytotoxic effectiveness of catecholic metabolites expressed as LC 50 (2 h) was 3′,4′-diCl-2,3-diOH-biphenyl > PHQ > 4′-Cl-2,5-diOH-biphenyl, 4′-Cl-2,3-diOH-biphenyl > 2′,5′-diCl-3,4-diOH-biphenyl > 2′,3′-diCl-3,4-diOH-biphenyl > 3′,4′-diCl-3,4-diOH-biphenyl > 4′Cl-3,4-diOH-biphenyl > 4′-Cl-biphenyl; showing that the positions of hydroxyl and chlorine groups were important for their hepatotoxicity and that the two 2,3-diOH congeners were the most cytotoxic. Cytotoxicity for 3,4-diOH metabolites correlated with the number and position of chlorine atoms with the more chlorine atoms being more cytotoxic. The cytotoxic order of metabolites with two chlorine atoms being 2′,5′ > 2′,3′ > 3′,4′. Borneol, an uridine diphosphate glucuronosyltransferases (UGT) inhibitor, increased the cytotoxicity of all tested metabolites; suggesting that glucuronidation was a major mechanism of elimination of these compounds. On the other hand entacapone, a catechol- O-methyl transferase (COMT) inhibitor, only increased the cytotoxicity of 3′,4′-diCl-3,4-diOH-biphenyl, 3′,4′-diCl-2,3-diOH-biphenyl and 4′-Cl-2,3-diOH-biphenyl. Hepatocyte GSH was depleted (oxidized and conjugated) by these metabolites before cytotoxicity ensued in a similar order of effectiveness to their cytotoxicity with PHQ being the most effective. Hepatocyte mitochondrial membrane potential also decreased before cytotoxicity ensued with a similar order of effectiveness as their cytotoxicity. These results suggest that catecholic cytotoxicity can be attributed to mitochondrial toxicity and oxidative stress. Semiquinone or benzoquinone species were also important in the cytotoxicity of catecholic metabolites.

Prenatal Pesticide and PCB Exposures and Birth Outcomes

Evidence is inconsistent or poorly understood for links between polychlorinated biphenyls (PCBs), 1,1'-dichloro-2,2'-bis(4-chlorophenyl)ethylene (DDE), and organophosphate (OP) pesticides and adverse pregnancy outcomes, although they are known developmental toxicants. We measured biomarkers of maternal exposure to DDE, PCB, and OP metabolites in the third trimester of pregnancy among 404 mothers in a multiethnic cohort in New York City. We also determined maternal paraoxonase (PON1), butyrylcholinesterase (BuChe), and PON1Q192R gene variant. Higher multivariate-adjusted DDE levels (but not PCB) were associated with lower birth weight (-98 g/log10 DDE, p = 0.096) and head circumference (-0.54 cm/log10 DDE, p = 0.030). DDE and PCB levels were not related to birth length, Ponderal index, or gestational age. Birth length was shorter for mothers with PON192RR slow genotype compared with PON192QQ (p = 0.026), and head circumference was inversely associated with maternal PON1 activity (p = 0.004). With slow-activity PON1 or PON192, urinary diethylphosphates (SigmaDEPs) were associated with lower birth weight and dimethylphosphates (SigmaDMPs) with shorter birth length. No associations were found between birth outcomes and BuChe. In summary, we found suggestive relationships between prenatal environmental biomarkers and birth outcomes in this population. Maternal susceptibility factors including PON1 and maternal weight contributed to the observed effects.