Identification of sulfated metabolites of 4-chlorobiphenyl (PCB3) in the serum and urine of male rats

Elucidating the Metabolism of Chiral PCB95 in Wildtype and Transgenic Mouse Models with Altered Cytochrome P450 Enzymes Using Intestinal Content Screening

Polychlorinated biphenyls (PCBs), such as 2,2',3,5',6-pentachlorobiphenyl (PCB95), are persistent organic pollutants associated with adverse health outcomes, including developmental neurotoxicity. PCB95 is a chiral neurotoxic PCB congener atropselectively metabolized to potentially neurotoxic metabolites in vivo. However, the metabolic pathways of most PCB congeners, including PCB95, remain unknown. To address this knowledge gap, we analyzed the intestinal contents of mice exposed to PCB95 to elucidate the PCB95 metabolism pathway and assess if genetic manipulation of hepatic drug-metabolizing enzymes affects PCB95 metabolism. Our study exposed male and female wildtype (WT), Cyp2abfgs-null (KO), and CYP2A6-transgenic/Cyp2abfgs-null (KI) mice orally to 1.0 mg/kg body weight of PCB95. Intestinal content was collected 24 h after PCB administration. aS-PCB95 was enriched in all intestinal content samples, irrespective of sex and genotype. Gas chromatography-tandem mass spectrometry (GC-MS/MS) analyses identified 5 mono- (OH-PCB95) and 4 dihydroxylated PCB (diOH-PCB95) metabolites. Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) identified 15 polar hydroxylated, methoxylated, and sulfated PCB95 metabolites, including 3 dechlorinated metabolites. A sex difference in the relative OH-PCB95 levels was observed only for KO in the LC-HRMS analysis. Genotype-dependent differences were observed for female, but not male, mice, with OH-PCB95 levels in female KO (FKO) mice tending to be lower than those in female WT (FWT) and KI (FKI) mice. Based on the GC-MS/MS analysis, these differences are due to the unknown PCB95 metabolites, X1-95 and Y1-95. These findings demonstrate that combining GC-MS/MS analyses and LC-HRMS subject screening of the intestinal content of PCB95-exposed mice can significantly advance our understanding of PCB95 metabolism in vivo.

Significant metabolic alterations in mouse dams exposed to an environmental mixture of polychlorinated biphenyls (PCBs) during gestation and lactation: Insights into PCB and metabolite profiles

Polychlorinated biphenyls (PCBs) and their metabolites are linked to developmental neurotoxicity, but their levels in the gestational and lactational environment remain unexplored. This study investigated the effects of dietary exposure to the Fox River Mixture (FRM) on serum levels of PCBs and their metabolites in female C57BL/6 J mice. Mice were exposed to 0.1, 1.0, or 6.0 mg/kg body weight/day of FRM beginning two weeks before mating and throughout gestation and lactation. Serum samples collected from the dams at weaning were analyzed using gas chromatograph-tandem mass spectrometry and nontarget liquid chromatography-high resolution mass spectrometry. Results showed complex and dose-dependent differences in PCB and metabolite profiles. Untargeted metabolomics revealed alterations in metabolites involved in glucuronidation. Network analysis suggested disturbances in heme and amino acid metabolism associated with higher chlorinated PCBs. These findings suggested that PCBs and metabolites present in the gestational and lactation environment of mice may contribute to developmental neurotoxicity in rodents.

Distribution of 2,2',5,5'-Tetrachlorobiphenyl (PCB52) Metabolites in Adolescent Rats after Acute Nose-Only Inhalation Exposure

Inhalation of PCB-contaminated air is increasingly recognized as a route for PCB exposure. Because limited information about the disposition of PCBs following inhalation exposure is available, this study investigated the disposition of 2,2',5,5'-tetrachlorobiphenyl (PCB52) and its metabolites in rats following acute, nose-only inhalation of PCB52. Male and female Sprague-Dawley rats (50-58 days of age, 210 ± 27 g; n = 6) were exposed for 4 h by inhalation to approximately 14 or 23 μg/kg body weight of PCB52 using a nose-only exposure system. Sham animals (n = 6) were exposed to filtered lab air. Based on gas chromatography-tandem mass spectrometry (GC-MS/MS), PCB52 was present in adipose, brain, intestinal content, lung, liver, and serum. 2,2',5,5'-Tetrachlorobiphenyl-4-ol (4-OH-PCB52) and one unknown monohydroxylated metabolite were detected in these compartments except for the brain. Liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis identified several metabolites, including sulfated, methoxylated, and dechlorinated PCB52 metabolites. These metabolites were primarily found in the liver (7 metabolites), lung (9 metabolites), and serum (9 metabolites) due to the short exposure time. These results demonstrate for the first time that complex mixtures of sulfated, methoxylated, and dechlorinated PCB52 metabolites are formed in adolescent rats following PCB52 inhalation, laying the groundwork for future animal studies of the adverse effects of inhaled PCB52.

New Perspectives on the Risks of Hydroxylated Polychlorinated Biphenyl (OH-PCB) Exposure: Intestinal Flora α-Glucosidase Inhibition

Polychlorinated biphenyls (PCBs) are a group of colorless and odorless environmental pollutants with a wide range of toxic effects. Some PCBs, especially less chlorinated ones, will rapidly undergo phase I metabolism after entering the body, and hydroxylated polychlorinated biphenyls (OH-PCBs) are the main metabolites of PCBs. Intestinal flora α-glucosidase is a common carbohydrate-active enzyme which is ubiquitous in human intestinal flora. It can convert complex dietary polysaccharides into monosaccharides, assisting the body in degrading complex carbohydrates and providing energy for the survival and growth of bacterial flora. The present study aims to investigate the inhibition of the activity of intestinal flora α-glucosidase by OH-PCBs. 4-Nitrophenyl-α-D-glucopyranoside (PNPG) was used as a probe substrate for α-glucosidase, and in vitro incubation experiments were conducted to study the inhibition of 26 representative OH-PCBs on α-glucosidase. Preliminary screening of in vitro incubation was performed with 100 μM of OH-PCBs. The results showed that 26 OH-PCBs generally exhibited strong inhibition of α-glucosidase. The concentration-dependent inhibition and half inhibition concentrations (IC50s) of OH-PCBs on α-glucosidase were determined. 4'-OH-PCB 86 and 4'-OH-PCB 106 were chosen as representative OH-PCBs, and the inhibition kinetic parameters (Kis) of inhibitors for α-glucosidase were determined. The inhibition kinetic parameters (Kis) of 4'-OH-PCB 86 and 4'-OH-PCB 106 for α-glucosidase are 1.007 μM and 0.538 μM, respectively. The silico docking method was used to further analyze the interaction mechanism between OH-PCBs and α-glucosidase. All these results will help us to understand the risks of OH-PCB exposure from a new perspective.

Complex roles for sulfation in the toxicities of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic toxicants derived from legacy pollution sources and their formation as inadvertent byproducts of some current manufacturing processes. Metabolism of PCBs is often a critical component in their toxicity, and relevant metabolic pathways usually include their initial oxidation to form hydroxylated polychlorinated biphenyls (OH-PCBs). Subsequent sulfation of OH-PCBs was originally thought to be primarily a means of detoxication; however, there is strong evidence that it may also contribute to toxicities associated with PCBs and OH-PCBs. These contributions include either the direct interaction of PCB sulfates with receptors or their serving as a localized precursor for OH-PCBs. The formation of PCB sulfates is catalyzed by cytosolic sulfotransferases, and, when transported into the serum, these metabolites may be retained, taken up by other tissues, and subjected to hydrolysis catalyzed by intracellular sulfatase(s) to regenerate OH-PCBs. Dynamic cycling between PCB sulfates and OH-PCBs may lead to further metabolic activation of the resulting OH-PCBs. Ultimate toxic endpoints of such processes may include endocrine disruption, neurotoxicities, and many others that are associated with exposures to PCBs and OH-PCBs. This review highlights the current understanding of the complex roles that PCB sulfates can have in the toxicities of PCBs and OH-PCBs and research on the varied mechanisms that control these roles.

A green deep eutectic solvent based dispersive liquid-liquid microextraction for the quantitative analysis of 21 polychlorinated biphenyl metabolites in food of animal origin using injector port silylation-gas chromatography-tandem mass spectrometry

An analytical method was developed for the quantitative determination of 21 polychlorinated biphenyls (PCBs) metabolites (17 were -OH, 1 -MeO, and 3 were MeSO2) in foods of animal origin using deep eutectic solvent (DES) based dispersive liquid-liquid microextraction followed by injector port silylation-gas chromatography-tandem mass spectrometry. The type of DES (thymol: camphor, 1:1 molar ratio) and optimum volume of DES (300 µL), pH (7.0), and disperser solvent (acetonitrile) were optimized to attain the maximum extraction efficiency. The limit of detection, limit of quantification, and percent recovery were found to be in the range of 0.12-0.23 ng/mL, 0.40-0.76 ng/mL, and 80.1-111.4%, respectively. The expanded uncertainty was observed to be in the range of 7.2-22.8% for the targeted analytes. The proposed method was applied to real food samples (milk, meat, fish, and egg) and the levels were found to be in the range of 0.64-32.14 ng/g. This is first of its kind method using green solvent based method for the analysis of PCB metabolites (-OH, MeO, and MeSO2) and will find extensive application in routine testing for foods of animal origin.

Ten years after: findings from the medical surveillance program on Health Effects in High-Level Exposure to PCB (HELPcB)

After the detection of high environmental and occupational exposure to polychlorinated biphenyls (PCBs) in a German recycling company for transformers and capacitors in 2010, the multidisciplinary medical surveillance program "HELPcB" (Health Effects in High-Level Exposure to PCB) was established for former PCB-exposed workers of the company, their family members, employees of surrounding companies, and area residents to investigate potential adverse health effects by PCB exposure in a longitudinal study approach with up to seven examination time points between 2010 and 2019. More than 300 individuals were enrolled into the program. Assessments particularly included plasma and urine concentrations of PCB congeners and their metabolites, clinical laboratory parameters, Comet assay, analysis of telomere length, neuropsychological examinations, psychological screening, abdominal and thyroid ultrasound examination. This review summarizes the main results of the studies conducted in the HELPcB program yielding relevant new data on potential adverse effects of PCB exposure in humans and potential mechanisms that underlie these effects. Even larger studies in PCB-exposed individuals are warranted to confirm the results of this program and to further establish causality between PCB exposure and clinical effects in humans.

Environmental fate of sulfonated-PCBs: Soil partitioning properties, bioaccumulation, persistence, and mobility

Two new classes of PCB metabolites were recently discovered: sulfonated-polychlorinated biphenyls (sulfonated-PCBs) and hydroxy-sulfonated-polychlorinated biphenyls (OH-sulfonated-PCBs). These metabolites, originating from PCB degradation, seem to possess more polar characteristics than their parent compounds. However, no other information, such as their chemical identity (CAS number) or their ecotoxicity or toxicity, is available so far, although more than about one hundred different chemicals were observed in soil samples. In addition, their physico-chemical properties are still uncertain since only estimations are available. Here we show the first evidence on the fate of these new classes of contaminants in the environment, producing results from several experiments, to evaluate sulfonated-PCBs and OH-sulfonated-PCBs soil partition coefficients, degradation in soil after 18 months of rhizoremediation, uptake into plant roots and earthworms, as well as a preliminary analytical method to extract and concentrate these chemicals from water. The results give an overview of the expected environmental fate of these chemicals and open questions for further studies.

Metabolism of 3-Chlorobiphenyl (PCB 2) in a Human-Relevant Cell Line: Evidence of Dechlorinated Metabolites

Lower chlorinated polychlorinated biphenyls (LC-PCBs) and their metabolites make up a class of environmental pollutants implicated in a range of adverse outcomes in humans; however, the metabolism of LC-PCBs in human models has received little attention. Here we characterize the metabolism of PCB 2 (3-chlorobiphenyl), an environmentally relevant LC-PCB congener, in HepG2 cells with in silico prediction and nontarget high-resolution mass spectrometry. Twenty PCB 2 metabolites belonging to 13 metabolite classes, including five dechlorinated metabolite classes, were identified in the cell culture media from HepG2 cells exposed for 24 h to 10 μM or 3.6 nM PCB 2. The PCB 2 metabolite profiles differed from the monochlorinated metabolite profiles identified in samples from an earlier study with PCB 11 (3,3'-dichlorobiphenyl) under identical experimental conditions. A dechlorinated dihydroxylated metabolite was also detected in human liver microsomal incubations with monohydroxylated PCB 2 metabolites but not PCB 2. These findings demonstrate that the metabolism of LC-PCBs in human-relevant models involves the formation of dechlorination products. In addition, untargeted metabolomic analyses revealed an altered bile acid biosynthesis in HepG2 cells. Our results indicate the need to study the disposition and toxicity of complex PCB 2 metabolites, including novel dechlorinated metabolites, in human-relevant models.

Interconversion between methoxylated, hydroxylated and sulfated metabolites of PCB 3 in whole poplar plants

Methoxylated polychlorinated biphenyls (MeO-PCBs) are overlooked metabolites of PCBs. In general, they are more toxic to plants than their parent congeners. However, information on the fate of MeO-PCBs and the relationship between methoxylated, hydroxylated and sulfated metabolites of PCBs in plants is scarce. In this work, poplar plants (Populus deltoides × nigra, DN34) were hydroponically and separately exposed to 4'-methoxy-4-monochlorobiphenyl (4'-MeO-PCB 3) and 4'-PCB 3 sulfate for 10 days to investigate the uptake, translocation and metabolism of MeO-PCBs and the relationship between methoxy-PCBs, hydroxyl-PCBs and PCB sulfates within plants. Results showed that 4'-MeO-PCB 3 and 4'-PCB 3 sulfate were taken up by the roots of poplar plants and translocated from roots to shoots and leaves. 4'-OH-PCB 3 and 4'-PCB 3 sulfate were identified as the hydroxylated metabolite and sulfate metabolite of 4'-MeO-PCB 3 in poplar, respectively. In the backward reaction, 4'-OH-PCB 3 and 4'-MeO-PCB 3 were found as metabolites of 4'-PCB 3 sulfate. For exposure groups, the yields of 4'-OH-PCB 3 produced from 4'-MeO-PCB 3 and 4'-PCB 3 sulfate were 1.29% and 0.13% respectively. The yield of 4'-PCB 3 sulfate which originated from 4'-MeO-PCB 3 in wood and root samples of exposure groups was only 0.02%. Only 0.04% of the initial mass of 4'-PCB 3 sulfate was transformed to 4'-MeO-PCB 3 in the exposure groups. The sulfation yield of 4'-OH-PCB 3 was higher than hydrolysis yield of 4'-PCB 3 sulfate, indicating that formation of PCB sulfates was predominant over the reverse reaction, the formation of hydroxy-PCBs. These results provide new perspective on the transport, metabolism, and fate of MeO-PCBs, and also help to better understand sources of OH-PCBs and PCB sulfates in the environment. This study provides the first evidence of interconversion of sulfate metabolites from methoxy-PCBs and methoxy-PCBs from PCB sulfates.

Characterization of the Metabolic Pathways of 4-Chlorobiphenyl (PCB3) in HepG2 Cells Using the Metabolite Profiles of Its Hydroxylated Metabolites

The characterization of the metabolism of lower chlorinated PCB, such as 4-chlorobiphenyl (PCB3), is challenging because of the complex metabolite mixtures formed in vitro and in vivo. We performed parallel metabolism studies with PCB3 and its hydroxylated metabolites to characterize the metabolism of PCB3 in HepG2 cells using nontarget high-resolution mass spectrometry (Nt-HRMS). Briefly, HepG2 cells were exposed for 24 h to 10 μM PCB3 or its seven hydroxylated metabolites in DMSO or DMSO alone. Six classes of metabolites were identified with Nt-HRMS in the culture medium exposed to PCB3, including monosubstituted metabolites at the 3'-, 4'-, 3-, and 4- (1,2-shift product) positions and disubstituted metabolites at the 3',4'-position. 3',4'-Di-OH-3 (4'-chloro-3,4-dihydroxybiphenyl), which can be oxidized to a reactive and toxic PCB3 quinone, was a central metabolite that was rapidly methylated. The resulting hydroxylated-methoxylated metabolites underwent further sulfation and, to a lesser extent, glucuronidation. Metabolomic analyses revealed an altered tryptophan metabolism in HepG2 cells following PCB3 exposure. Some PCB3 metabolites were associated with alterations of endogenous metabolic pathways, including amino acid metabolism, vitamin A (retinol) metabolism, and bile acid biosynthesis. In-depth studies are needed to investigate the toxicities of PCB3 metabolites, especially the 3',4'-di-OH-3 derivatives identified in this study.

Detection and Quantification of Polychlorinated Biphenyl Sulfates in Human Serum

Polychlorinated biphenyls (PCBs) are persistent toxic chemicals with both legacy sources (e.g., Aroclors) and new sources (e.g., unintentional contaminants in some pigments and varnishes). PCB sulfates are derived from further metabolism of hydroxylated PCBs (OH-PCBs), which are oxidative metabolites of PCBs. While OH-PCBs and PCB sulfates are implicated in multiple toxicological effects, studies of PCB sulfates in human serum have been limited by available analytical procedures. We have now developed a method for extraction of PCB sulfates from serum followed by differential analysis with, and without, sulfatase-catalyzed hydrolysis to OH-PCBs. A sulfatase from Helix pomatia was purified by affinity chromatography, and it displayed broad specificity for PCB sulfates without contaminant glucuronidase activity. Following sulfatase-catalyzed hydrolysis of the PCB sulfates extracted from serum, the corresponding OH-PCBs were derivatized to methoxy-PCBs and quantitated by GC-MS/MS. In a pooled sample of human serum, we identified 10 PCB sulfates, with three PCB sulfate congeners exhibiting the highest concentrations from 1200 to 3970 pg/g of serum. In conclusion, we have developed a sensitive and specific method for the determination of PCB sulfates in human serum.

Nontarget analysis reveals gut microbiome-dependent differences in the fecal PCB metabolite profiles of germ-free and conventional mice

Mammalian polychlorinated biphenyl (PCB) metabolism has not been systematically explored with nontarget high-resolution mass spectrometry (Nt-HRMS). Here we investigated the importance of the gut microbiome in PCB biotransformation by Nt-HRMS analysis of feces from conventional (CV) and germ-free (GF) adult female mice exposed to a single oral dose of an environmental PCB mixture (6 mg/kg or 30 mg/kg in corn oil). Feces were collected for 24 h after PCB administration, PCB metabolites were extracted from pooled samples, and the extracts were analyzed by Nt-HRMS. Twelve classes of PCB metabolites were detected in the feces from CV mice, including PCB sulfates, hydroxylated PCB sulfates (OH-PCB sulfates), PCB sulfonates, and hydroxylated methyl sulfone PCBs (OH-MeSO₂-PCBs) reported previously. We also observed eight additional PCB metabolite classes that were tentatively identified as hydroxylated PCBs (OH-PCBs), dihydroxylated PCBs (DiOH-PCBs), monomethoxylated dihydroxylated PCBs (MeO-OH-PCBs), methoxylated PCB sulfates (MeO-PCB sulfates), mono-to tetra-hydroxylated PCB quinones ((OH)_x-quinones, x = 1-4), and hydroxylated polychlorinated benzofurans (OH-PCDF). Most metabolite classes were also detected in the feces from GF mice, except for MeO-OH-PCBs, OH-MeSO₂-PCBs, and OH-PCDFs. Semi-quantitative analyses demonstrate that relative PCB metabolite levels increased with increasing dose and were higher in CV than GF mice, except for PCB sulfates and MeO-PCB sulfates, which were higher in GF mice. These findings demonstrate that the gut microbiome plays a direct or indirect role in the absorption, distribution, metabolism, or excretion of PCB metabolites, which in turn may affect toxic outcomes following PCB exposure.

Atropselective Partitioning of Polychlorinated Biphenyls in a HepG2 Cell Culture System: Experimental and Modeling Results

Cell culture models are used to study the toxicity of polychlorinated biphenyls (PCBs); however, it is typically unknown how much PCB enters the cells and, for chiral PCBs, if the partitioning is atropselective. We investigated the partitioning of racemic PCB 91, PCB 95, PCB 132, and PCB 136 in HepG2 cells following a 72 h incubation. PCBs were present in the cell culture medium (60.7-88.8%), cells (8.0-14.6%), and dishes (2.3-7.8%) and displayed atropisomeric enrichment in the cells (enantiomeric fraction [EF] = 0.55-0.77) and dishes (EF = 0.53-0.68). Polyparameter linear free energy relationships coupled with a composition-based model provided a good estimate of the PCB levels in the cells and cell culture medium. The free concentration was subsequently used to extrapolate from the nominal cell culture concentration to PCB tissue levels and vice versa. This approach can be used for in vitro-in vivo extrapolations for all 209 PCB congeners. However, this model (and modified models based on descriptors incorporating atropselective interactions, i.e., relative retention times on chiral columns) did not predict the atropselective partitioning in the cell culture system. Improved chemical descriptors that account for the atropselective binding of PCBs to biological macromolecules are, therefore, needed to predict the atropselective partitioning of PCBs in biological systems.

3,3'-Dichlorobiphenyl Is Metabolized to a Complex Mixture of Oxidative Metabolites, Including Novel Methoxylated Metabolites, by HepG2 Cells

3,3'-Dichlorobiphenyl (PCB 11) is a byproduct of industrial processes and detected in environmental samples. PCB 11 and its metabolites are present in human serum, and emerging evidence demonstrates that PCB 11 is a developmental neurotoxicant. However, little is known about the metabolism of PCB 11 in humans. Here, we investigated the metabolism of PCB 11 and the associated metabolomics changes in HepG2 cells using untargeted high-resolution mass spectrometry. HepG2 cells were exposed for 24 h to PCB 11 in DMSO or DMSO alone. Cell culture media were analyzed with ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry. Thirty different metabolites were formed by HepG2 cells exposed to 10 μM PCB 11, including monohydroxylated, dihydroxylated, methoxylated-hydroxylated, and methoxylated-dihydroxylated metabolites and the corresponding sulfo and glucuronide conjugates. The methoxylated PCB metabolites were observed for the first time in a human-relevant model. 4-OH-PCB 11 (3,3'-dichlorobiphenyl-4-ol) and the corresponding catechol metabolite, 4,5-di-OH-PCB 11 (3',5-dichloro-3,4-dihydroxybiphenyl), were unambiguously identified based on liquid and gas chromatographic analyses. PCB 11 also altered several metabolic pathways, in particular vitamin B6 metabolism. These results demonstrate that complex PCB 11 metabolite profiles are formed in HepG2 cells that warrant further toxicological investigation, particularly since catechol metabolites are likely reactive and toxic.

Congener-specific determination of hydroxylated polychlorinated biphenyls by polar-embedded reversed-phase liquid chromatography-tandem mass spectrometry

This paper reports the development of an LC-ESI-MS² method for the sensitive determination of hydroxylated polychlorinated biphenyls (OH-PCBs) in human serum samples. Congener-specific separation was achieved by using a polar-embedded stationary phase, previously optimized for the working group, which provided better separation of isobaric compounds than the common octadecylsilane phases. MS fragmentation patterns and energies showed differences among OH-PCB congeners, mainly depending on the position of OH-group and the number of chlorine atoms in the molecule, although the most intense transitions were always those corresponding to the neutral loss of an HCl group from the quasi-molecular ion cluster. The method allowed the determination of OH-PCBs with good linearity (dynamic linear range of four orders of magnitude with R² higher than 0.995) and precision (relative standard deviations of absolute areas lower than 10%), and with better sensitivity than other similar methods previously described in the literature. Matrix effect has been evaluated and reduced to less than 10% by the addition of isotopically labeled standards and a 10-fold dilution of the final sample extract. The low iLODs provided by the developed method (from 1.2 to 5.4 fg µL^-1 for all the OH-PCBs studied, except 4'-OHCB108, whose iLOD was 61 fg µL^-1) allows dilution without losses of detected peaks. Finally, the applicability of the method has been demonstrated by analyzing human serum samples belonging to an interlaboratory exercise.

Metabolism of SCCPs and MCCPs in Suspension Rice Cells Based on Paired Mass Distance (PMD) Analysis

Short-chain and medium-chain chlorinated paraffins (SCCPs and MCCPs) are mixtures of complex chemical compounds with intensive usage. They are frequently detected in various environmental samples. However, the interaction between CPs and plants, especially the biotransformation behaviors of CPs within plants, is poorly understood. In this study, 1,2,5,6,9,10-hexachlorodecane (CP-4, a typical standard of individual SCCP congeners) and 52%-MCCP (a commercial mixture standard of MCCPs with 52% chlorine content by mass) were selected as representative chemicals to explore the metabolic behaviors of SCCPs and MCCPs using suspension rice cell culture exposure systems. Both 79.53% and 40.70% of CP-4 and 52%-MCCP were metabolized by suspension rice cells, respectively. A complementary suspected screening strategy based on the pair mass distances (PMD) analysis algorithm was used to study the metabolism of CPs mediated by the plant cells. Forty and 25 metabolic products for CP-4 and 52%-MCCP, respectively, were identified, including (multi-) hydroxylation, dechlorination, -HCl- elimination metabolites, (hydroxylation-) sulfation, and glycosylation conjugates. Here, we propose a comprehensive metabolic molecular network and provide insight on degradation pathways of SCCPs and MCCPs in plants for the first time, aiding in further understanding of the transformation behaviors of CPs.

Estrogen-related receptor γ is a novel target for Lower-Chlorinated Polychlorinated Biphenyls and their hydroxylated and sulfated metabolites

Airborne lower-chlorinated PCBs are vulnerable to metabolization to PCB sulfates through further sulfation of the hydroxylated metabolites (OH-PCBs). However, studies on the toxic effects and mechanisms of PCB sulfates are still very limited. Here, we investigated for the first time the potential endocrine disruption effects of PCB sulfates through estrogen-related receptor γ (ERRγ) in comparison with their OH-PCBs precursors and PCB parent compounds. The binding affinity of thirteen PCBs/OH-PCBs/PCB sulfates was measured by using fluorescence competitive binding assays based on fluorescence polarization (FP). All of the tested chemicals could bind to ERRγ with the K_d (dissociation constant) values ranging from not available (NA) to 3.2 μM 4'-OH-PCB 12 showed the highest binding affinity with K_d value of 3.2 μM, which was comparable to that of a synthetic ERRγ agonist GSK4716. The effects of the thirteen chemicals on the ERRγ transcriptional activity were determined by using the luciferase reporter gene assay. We found the PCBs/OH-PCBs/PCB sulfates acted as agonists for ERRγ, with the lowest observed effective concentration reaching 3 μM. The binding affinity and agonistic activity of PCBs towards ERRγ were both enhanced after hydroxylation, while further sulfation of OH-PCBs decreased the activity instead. Molecular docking simulation showed that OH-PCBs had lower binding energy than the corresponding PCBs and PCB sulfates, indicating that OH-PCBs had higher binding affinity theoretically. In addition, OH-PCBs could form hydrogen bonds with amino acids Glu316 and Arg247 while PCBs and PCB sulfates could not, which might be the main factor impacting the binding affinity and agonistic activity. Overall, ERRγ is a novel target for lower-chlorinated PCBs and their metabolites.

Binding and activity of sulfated metabolites of lower-chlorinated polychlorinated biphenyls towards thyroid hormone receptor alpha

There has been long-standing evidence that the lower-chlorinated polychlorinated biphenyls (LC-PCBs) can be metabolized to hydroxylated metabolites (OH-PCBs), which play important roles in the LC-PCBs induced toxicity. Recently, multiple studies have demonstrated the further metabolic transformation of OH-PCBs to LC-PCB sulfates in vitro and in vivo. Several studies found LC-PCB sulfates could bind with thyroid hormone (TH) transport proteins in the serum, indicating the potential relevance of these metabolites in the TH system disruption effects. However, the interaction of LC-PCB sulfates with the TH nuclear receptor (TR), another kind of important functional protein in the TH system, has not been explored. Here, by using a fluorescence competitive binding assay, we demonstrated that LC-PCB sulfates could bind with TRα. Moreover, the LC-PCB sulfates had higher binding potency than their corresponding OH-PCB precursors. By using a luciferase reporter gene assay, we found the LC-PCB sulfates showed agonistic activity towards the TRα signaling pathway. Molecular docking simulation showed all the tested LC-PCB sulfates could fit into the ligand binding pocket of the TRα. The LC-PCB sulfates formed hydrogen bond interaction with arginine 228 residue of TRα by their sulfate groups, which might facilitate the TR binding and agonistic activity. The present study suggests that interaction with the TR might be another possible mechanism by which LC-PCB sulfate induce TH system disruption effects.

Identification of Sulfonated and Hydroxy-Sulfonated Polychlorinated Biphenyl (PCB) Metabolites in Soil: New Classes of Intermediate Products of PCB Degradation?

In this paper we describe the identification of two classes of contaminants: sulfonated-PCBs and hydroxy-sulfonated-PCBs. This is the first published report of the detection of these chemicals in soil. They were found, along with hydroxy-PCBs, in soil samples coming from a site historically contaminated by the industrial production of PCBs and in background soils. Sulfonated-PCB levels were approximately 0.4-0.8% of the native PCB levels in soils and about twice the levels of hydroxy-sulfonated-PCBs and hydroxy-PCBs. The identification of sulfonated-PCBs was confirmed by the chemical synthesis of reference standards, obtained through the sulfonation of an industrial mixture of PCBs. We then reviewed the literature to investigate for the potential agents responsible for the sulfonation. Furthermore, we predicted their physicochemical properties and indicate that, given the low pK_a of sulfonated- and hydroxy-sulfonated-PCBs, they possess negligible volatility, supporting the case for in situ formation from PCBs. This study shows the need of understanding their origin, their role in the degradation path of PCBs, and their fate, as well as their (still unknown) toxicological and ecotoxicological properties.

Atropselective Disposition of 2,2',3,4',6-Pentachlorobiphenyl (PCB 91) and Identification of Its Metabolites in Mice with Liver-Specific Deletion of Cytochrome P450 Reductase

Hepatic cytochrome P450 enzymes metabolize chiral polychlorinated biphenyls (PCBs) to hydroxylated metabolites (OH-PCBs). Animal models with impaired metabolism of PCBs are one approach to study how the atropselective oxidation of PCBs to OH-PCBs contributes to toxic outcomes, such as neurodevelopmental disorders, following PCB exposure. We investigated the disposition of PCB 91, a para-substituted PCB congener, in mice with a liver-specific deletion of the cytochrome P450 reductase (cpr) gene (KO mice). KO mice and wild-type (WT) mice were exposed orally to racemic PCB 91 (30 mg/kg b.w.). Levels and enantiomeric fractions of PCB 91 and its hydroxylated metabolites were determined in tissues 3 days after PCB exposure and in excreta on days 1-3 after PCB exposure. PCB 91, but not OH-PCB levels were higher in KO compared to WT mice. The elevated fat and protein content in the liver of KO mice resulted in the hepatic accumulation of PCB 91. OH-PCBs were detected in blood, liver, and excreta samples of KO and WT mice. 2,2',3,4',6-Pentachlorobiphenyl-5-ol (5-91) was the major metabolite. A considerable percent of the total PCB 91 dose (%TD) was excreted with the feces as 5-91 (23%TD and 31%TD in KO and WT mice, respectively). We tentatively identified glucuronide and sulfate metabolites present in urine samples. The PCB 91 atropisomer eluting first on the chiral column (E₁-PCB 91) displayed genotype-dependent atropisomeric enrichment, with a more pronounced atropisomeric enrichment observed in WT compared to KO mice. E₁-atropisomers of 5-91 and 2,2',3,4',6-pentachlorobiphenyl-4-ol (4-91) were enriched in blood and liver, irrespective of the genotype; however, the extent of the enrichment of E₁-5-91 was genotype dependent. These differences in atropselective disposition are consistent with slower metabolism of PCB 91 in KO compared to WT mice and the accumulation of the parent PCB in the fatty liver of KO mice.

Hundreds of Unrecognized Halogenated Contaminants Discovered in Polar Bear Serum

Exposure of polar bears (Ursus maritimus) to persistent organic pollutants was discovered in the 1970s, but recent evidence suggests the presence of unknown toxic chemicals in their blood. Protein and phospholipid depleted serum was stirred with polyethersulfone capillaries to extract a broad range of analytes, and nontarget mass spectrometry with "fragmentation flagging" was used for detection. Hundreds of analytes were discovered belonging to 13 classes, including novel polychlorinated biphenyl (PCB) metabolites and many fluorinated or chlorinated substances not previously detected. All analytes were detected in the oldest (mid-1980s) archived polar bear serum from Hudson Bay and Beaufort Sea, and all fluorinated classes showed increasing trends. A mouse experiment confirmed the novel PCB metabolites, suggesting that these could be widespread in mammals. Historical exposure and toxic risk has been underestimated, and these halogenated contaminants pose uncertain risks to this threatened species.

Simultaneous detection of multiple hydroxylated polychlorinated biphenyls from biological samples using ultra-high-performance liquid chromatography with isotope dilution tandem mass spectrometry

We established a method for the separation and detection of nine hydroxylated polychlorinated biphenyls in whole blood and urine samples using ultra high performance liquid chromatography coupled with electrospray negative ionization tandem mass spectrometry. Clean-up procedures involved a filtration step, and optimization involved a pretreatment step consisting of a simple liquid-liquid extraction using hydrated silica-gel chromatography (5%). Nine hydroxylated polychlorinated biphenyls were separated on an ultra high performance liquid chromatography HSS T3 column using a gradient elution program of 2 mmol ammonium formate aqueous solution (A) and methanol (B). Recovery ranged from 84.0 to 105.4% for the nine different hydroxylated polychlorinated biphenyls in urine with three spiked levels of 0.1, 1, and 2 ng and from 73.5 to 98.6% for the blood with spiked levels of 0.2, 1, and 2 ng. The relative standard deviations were <8.7% (n = 6), and the limits of detection in urine and whole blood for the nine hydroxylated polychlorinated biphenyls were in the range of 1.5-4 and 20-100 pg/g, respectively. This analytical method may enable the simultaneous detection of various hydroxylated polychlorinated biphenyls from complex tissue matrices.

Telomerase gene expression bioassays indicate metabolic activation of genotoxic lower chlorinated polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are ubiquitously occurring pollutants with different chemical and toxicological properties. In this study we evaluated blood plasma samples of two PCB-exposed cohorts for their ability to alter telomerase (hTERT) gene expression. Blood plasma from PCB-exposed individuals inhibited hTERT expression depending solely on the concentration of lower chlorinated PCBs, with the lowest observed adverse effect level (LOAEL) at a plasma concentration between 0.5 and 2 µg/L of LC PCBs. Individual OH-metabolites derived from the WHO indicator congeners PCB 28 and PCB 101 mimicked these effects on hTERT expression in vitro with high toxicity, including DNA damage. However, by the combination of different OH-metabolites, the bio effective PCB concentration was reduced and the respective effects on hTERT expression could be increased. At a concentration which showed no toxic activity in MTT assay, hTERT inhibition reflected the interference of OH-PCBs with the mitochondrial respiratory chain, which could lead to the production of reactive oxygen species (ROS). As individual OH-metabolites already showed a much stronger inhibition of hTERT gene expression at a lower concentration than their parental compounds, the hTERT gene expression bioassay described in this study seems to indicate metabolic activation of LC PCBs rather than the mere effect of LC PCBs on their own. In summary, this study provides dose-response linkages between effects of lower chlorinated PCBs and their concentrations in human plasma.

Hydroxylated and sulfated metabolites of commonly observed airborne polychlorinated biphenyls display selective uptake and toxicity in N27, SH-SY5Y, and HepG2 cells

Although neurotoxicity and hepatotoxicity have long been associated with exposure to polychlorinated biphenyls (PCBs), less is known about the selective toxicity of those hydroxylated PCBs (OH-PCBs) and PCB sulfates that are metabolites derived from exposure to PCBs found in indoor air. We have examined the toxicity of OH-PCBs and PCB sulfates derived from PCBs 3, 8, 11, and 52 in two neural cell lines (N27 and SH-SY5Y) and an hepatic cell line (HepG2). With the exception of a similar toxicity seen for N27 cells exposed to either OH-PCB 52 or PCB 52 sulfate, these OH-PCBs were more toxic to all three cell-types than their corresponding PCB or PCB sulfate congeners. Differences in the distribution of individual OH-PCB and PCB sulfate congeners between the cells and media, and the ability of cells to interconvert PCB sulfates and OH-PCBs, were important components of cellular sensitivity to these toxicants.

Authentication of synthetic environmental contaminants and their (bio)transformation products in toxicology: polychlorinated biphenyls as an example

Toxicological studies use "specialty chemicals" and, thus, should assess and report both identity and degree of purity (homogeneity) of the chemicals (or toxicants) under investigation to ensure that other scientists can replicate experimental results. Although detailed reporting criteria for the synthesis and characterization of organic compounds have been established by organic chemistry journals, such criteria are inconsistently applied to the chemicals used in toxicological studies. Biologically active trace impurities may lead to incorrect conclusions about the chemical entity responsible for a biological response, which in turn may confound risk assessment. Based on our experience with the synthesis of PCBs and their metabolites, we herein propose guidelines for the "authentication" of synthetic PCBs and, by extension, other organic toxicants, and provide a checklist for documenting the authentication of toxicants reported in the peer-reviewed literature. The objective is to expand guidelines proposed for different types of biomedical and preclinical studies to include a thorough authentication of specialty chemicals, such as PCBs and their derivatives, with the goal of ensuring transparent and open reporting of scientific results in toxicology and the environmental health sciences.

Sources and toxicities of phenolic polychlorinated biphenyls (OH-PCBs)

Polychlorinated biphenyls (PCBs), a group of 209 congeners that differ in the number and position of chlorines on the biphenyl ring, are anthropogenic chemicals that belong to the persistent organic pollutants (POPs). For many years, PCBs have been a topic of interest because of their biomagnification in the food chain and their environmental persistence. PCBs with fewer chlorine atoms, however, are less persistent and more susceptible to metabolic attack, giving rise to chemicals characterized by the addition of one or more hydroxyl groups to the chlorinated biphenyl skeleton, collectively known as hydroxylated PCBs (OH-PCBs). In animals and plants, this biotransformation of PCBs to OH-PCBs is primarily carried out by cytochrome P-450-dependent monooxygenases. One of the reasons for infrequent detection of lower chlorinated PCBs in serum and other biological matrices is their shorter half-lives, and their metabolic transformation, resulting in OH-PCBs or their conjugates, such as sulfates and glucuronides, or macromolecule adducts. Recent biomonitoring studies have reported the presence of OH-PCBs in human serum. The occurrence of OH-PCBs, the size of this group (there are 837 mono-hydroxyl PCBs alone), and their wide spectra of physical characteristics (pKa's and log P's ranging over 5 to 6 orders of magnitude) give rise to a multiplicity of biological effects. Among those are bioactivation to electrophilic metabolites that can form covalent adducts with DNA and other macromolecules, interference with hormonal signaling, inhibition of enzymes that regulate cellular concentrations of active hormones, and interference with the transport of hormones. This new information creates an urgent need for a new perspective on these often overlooked metabolites.

Polychlorinated biphenyls and its potential role in endometriosis

With the progress of global industrialization and environmental deterioration, the relationship between human health and the living environment has become an increasing focus of attention. Polychlorinated biphenyls (PCBs, including dioxin-like polychlorinated biphenyls and non-dioxin-like polychlorinated biphenyls), as part of the organic chlorine contaminants, have been suspected as playing a role in the etiopathogenesis of endometriosis. Several population-based studies have proposed that exposure to PCBs may increase the risk of developing endometriosis, while some epidemiological studies have failed to find any association between PCBs and endometriosis. The purpose of this review is to discuss the potential pathophysiological relationship between endometriosis and PCBs with a focus on both dioxin-like polychlorinated biphenyls and non-dioxin-like polychlorinated biphenyls.

Identification of a sulfate metabolite of PCB 11 in human serum

Despite increasing evidence for a major role for sulfation in the metabolism of lower-chlorinated polychlorinated biphenyls in vitro and in vivo, and initial evidence for potential bioactivities of the resulting sulfate ester metabolites, the formation of PCB sulfates in PCB exposed human populations had not been explored. The primary goal of this study was to determine if PCB sulfates, and potentially other conjugated PCB derivatives, are relevant classes of PCB metabolites in the serum of humans with known exposures to PCBs. In order to detect and quantify dichlorinated PCB sulfates in serum samples of 46 PCB-exposed individuals from either rural or urban communities, we developed a high-resolution mass spectrometry-based protocol using 4-PCB 11 sulfate as a model compound. The method also allowed the preliminary analysis of these 46 human serum extracts for the presence of other metabolites, such as glucuronic acid conjugates and hydroxylated PCBs. Sulfate ester metabolites derived from dichlorinated PCBs were detectable and quantifiable in more than 20% of analyzed serum samples. Moreover, we were able to utilize this method to detect PCB glucuronides and hydroxylated PCBs, albeit at lower frequencies than PCB sulfates. Altogether, our results provide initial evidence for the presence of PCB sulfates in human serum. Considering the inability of previously employed analytical protocols for PCBs to extract these sulfate ester metabolites and the concentrations of these metabolites observed in our current study, our data support the hypothesis that total serum levels of PCB metabolites in exposed individuals may have been underestimated in the past.

Determination of hydroxylated polychlorinated biphenyls (OH-PCBs) in human urine in a highly occupationally exposed German cohort: New prospects for urinary biomarkers of PCB exposure

The present study evaluates for the first time the determination of 20 hydroxylated polychlorinated biphenyl (OH-PCB) congeners and their glucuronide and sulfate conjugates in urine as a biomarker of exposure to PCBs in humans. Thereby, a fast, sensitive and selective online solid phase extraction (SPE) method coupled to LC-MS/MS was validated for the determination of OH-PCBs in human urine, being previously successfully developed and applied for the separation and quantitation of OH-PCBs in human plasma. The lowest limit of quantification (LLOQ) ranged from 0.01 to 0.19ngmL^-1 and average extraction recoveries from 79 to 125% for all hydroxylated congeners. Within-run precision and between-run precision were between 2 and 17%. Extraction recovery tests were also performed in urine with different creatinine contents (0.52-3.92gL^-1) for an estimation of matrix influences and ranged between 69 and 125%. In order to evaluate the applicability of the method, the study was conducted in three different groups, which were distinctly separated as non-exposed to known sources of PCBs (N=21), low-to-moderate PCB-exposed individuals (N=25) and highly occupationally PCB-exposed individuals (N=25), which included workers of a transformer recycling plant, their relatives and workers of surrounding companies from a German cohort. As part of the biomonitoring program HELPcB (Health Effects in High-Level Exposure to polychlorinated biphenyls), urine and blood samples were collected annually from 2010 to 2014. In this way, OH-PCB elimination profile in urine over time, correlations between OH-PCB levels in human plasma and urine, and associations with their parent compounds in plasma of the studied PCB cohort could be also assessed. Tri-chlorinated OH-PCBs were the predominant congeners in urine with concentrations up to 174ngmL^-1. High chlorinated OH-PCBs (penta- through hepta-chlorinated OH-PCBs) were also frequently detected in urine samples from non-exposed and occupationally exposed individuals, although levels were in general very low or lower than LLOQ.

Tracing the biotransformation of polychlorinated biphenyls (PCBs) in common carp (Cryprinus carpio): Enantiomeric fraction and compound-specific stable carbon isotope analyses

Metabolites of polychlorinated biphenyls (PCBs) in fish are difficult to detect in vivo due to the complexity of biometabolism. In the present study, atropisomeric fraction analysis of chiral PCB congeners and compound-specific isotopic analysis (CSIA) were applied to trace the biotransformation of PCBs in fish by exposure of common carp (Cryprinus carpio) to the commercial PCB mixture Aroclor 1242. Stereoselective elimination of the chiral PCB congeners 91, 95, and 136 was observed, indicating a stereoselective biotransformation process. The δ(13)C values of PCBs 5/8, 18, and 20/33 in fish were increased compared with those in the spiked food, while PCBs 47/48 and 49 showed significant heavy isotope depletion. These results suggested a significant biotransformation of the corresponding individual PCB congeners although the potential PCB metabolites, hydroxylated PCBs (OH-PCBs) and methylsulfone PCBs (MeSO2-PCBs), were not detected in the fish tissue samples throughout this experiment. The results of the present study demonstrated that a combination of chiral analysis and CSIA is a promising new approach for investigating the biotransformation of PCBs in biota.

Sulfation of Lower Chlorinated Polychlorinated Biphenyls Increases Their Affinity for the Major Drug-Binding Sites of Human Serum Albumin

The disposition of toxicants is often affected by their binding to serum proteins, of which the most abundant in humans is serum albumin (HSA). There is increasing interest in the toxicities of environmentally persistent polychlorinated biphenyls (PCBs) with lower numbers of chlorine atoms (LC-PCBs) due to their presence in both indoor and outdoor air. PCB sulfates derived from metabolic hydroxylation and sulfation of LC-PCBs have been implicated in endocrine disruption due to high affinity-binding to the thyroxine-carrying protein, transthyretin. Interactions of these sulfated metabolites of LC-PCBs with HSA, however, have not been previously explored. We have now determined the relative HSA-binding affinities for a group of LC-PCBs and their hydroxylated and sulfated derivatives by selective displacement of the fluorescent probes 5-dimethylamino-1-naphthalenesulfonamide and dansyl-l-proline from the two major drug-binding sites on HSA (previously designated as Site I and Site II). Values for half-maximal displacement of the probes indicated that the relative binding affinities were generally PCB sulfate ≥ OH-PCB > PCB, although this affinity was site- and congener-selective. Moreover, specificity for Site II increased as the numbers of chlorine atoms increased. Thus, hydroxylation and sulfation of LC-PCBs result in selective interactions with HSA which may affect their overall retention and toxicity.

Hydroxylated polychlorinated biphenyls in human sera from adolescents and their mothers living in two U.S. Midwestern communities

Hydroxylated polychlorinated biphenyls (OH-PCBs) have been detected in human specimens and some are suspected as being more toxic than their parent compounds. We compared 58 OH-PCB congeners (in 51 chromatographic peaks) in serum samples from participants in the AESOP Study, a longitudinal cohort study of adolescents and their mothers living in urban and rural areas in the United States. We hypothesized that adolescents would have lower levels of OH-PCBs than their mothers and that serum concentration of OH-PCBs would be stable over a 3-year period. We found statistically significant differences in total OH-PCBs between age groups in both East Chicago (p = 0.001) and Columbus Junction (p < 0.001), with adolescents having lower concentrations than their mothers. We observed that lower-chlorinated OH-PCBs were rarely detected, suggesting that they are not retained in serum and/or rapidly biotransformed into other forms. Twelve OH-PCBs, including several that are rarely reported (4,4'-diOH-PCB 202, 4'-OH-PCB 208, and 4-OH-PCB 163) were detected in over 60% of participants. Lastly, from repeated measures within subject serum for three OH-PCBs, concentrations of 4-OH-PCB 107 and 4-OH-PCB 187 changed significantly over three years of the study.

Effects of thiol antioxidants on the atropselective oxidation of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) by rat liver microsomes

Chiral polychlorinated biphenyl (PCB) congeners, such as PCB 136, are atropselectively metabolized to various hydroxylated PCB metabolites (HO-PCBs). The present study investigates the effect of two thiol antioxidants, glutathione and N-acetyl-cysteine (NAC), on profiles and chiral signatures of PCB 136 and its HO-PCB metabolites in rat liver microsomal incubations. Liver microsomes prepared from rats pretreated with phenobarbital were incubated with PCB 136 (5 μM) in the presence of the respective antioxidant (0-10 mM), and levels and chiral signatures of PCB 136 and its HO-PCB metabolites were determined. Three metabolites, 5-136 (2,2',3,3',6,6'-hexachlorobiphenyl-5-ol), 4-136 (2,2',3,3',6,6'-hexachlorobiphenyl-4-ol), and 4,5-136 (2,2',3,3',6,6'-hexachlorobiphenyl-4,5-diol), were detected in all incubations, with 5-136 being the major metabolite. Compared to microsomal incubations without antioxidant, levels of 4,5-136 increased with increasing antioxidant concentration, whereas levels of PCB 136 and both mono-HO-PCBs were not affected by the presence of either antioxidant. PCB 136, 4-136, and 5-136 displayed significant atropisomeric enrichment; however, the direction and extent of the atropisomeric enrichment was not altered in the presence of an antioxidant. Because 4,5-136 can either be conjugated to a sulfate or glucuronide metabolite that is readily excreted or further oxidized a potentially toxic PCB 136 quinone, the effect of both thiol antioxidants on 4,5-136 formation suggests that disruptions of glutathione homeostasis may alter the balance between both metabolic pathways and, thus, PCB 136 toxicity in vivo.

Cytochrome c adducts with PCB quinoid metabolites

Polychlorinated biphenyls (PCBs) are a group of 209 individual congeners widely used as industrial chemicals. PCBs are found as by-products in dye and paint manufacture and are legacy, ubiquitous, and persistent as human and environmental contaminants. PCBs with fewer chlorine atoms may be metabolized to hydroxy- and dihydroxy-metabolites and further oxidized to quinoid metabolites both in vitro and in vivo. Specifically, quinoid metabolites may form adducts on nucleophilic sites within cells. We hypothesized that the PCB-quinones covalently bind to cytochrome c and, thereby, cause defects in the function of cytochrome c. In this study, synthetic PCB quinones, 2-(4'-chlorophenyl)-1,4-benzoquinone (PCB3-pQ), 4-4'-chlorophenyl)-1,2-benzoquinone (PCB3-oQ), 2-(3', 5'-dichlorophenyl)-1,4-benzoquinone, 2-(3',4', 5'-trichlorophenyl)-1,4-benzoquinone, and 2-(4'-chlorophenyl)-3,6-dichloro-1,4-benzoquinone, were incubated with cytochrome c, and adducts were detected by liquid chromatography-mass spectrometry (LC-MS) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI TOF). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was employed to separate the adducted proteins, while trypsin digestion and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were applied to identify the amino acid binding sites on cytochrome c. Conformation change of cytochrome c after binding with PCB3-pQ was investigated by SYBYL-X simulation and cytochrome c function was examined. We found that more than one molecule of PCB-quinone may bind to one molecule of cytochrome c. Lysine and glutamic acid were identified as the predominant binding sites. Software simulation showed conformation changes of adducted cytochrome c. Additionally, cross-linking of cytochrome c was observed on the SDS-PAGE gel. Cytochrome c was found to lose its function as electron acceptor after incubation with PCB quinones. These data provide evidence that the covalent binding of PCB quinone metabolites to cytochrome c may be included among the toxic effects of PCBs.

Estrogenicity and androgenicity screening of PCB sulfate monoesters in human breast cancer MCF-7 cells

Recent studies identified polychlorinated biphenyl (PCB) sulfate esters as a major product of PCB metabolism. Since hydroxy-PCBs (HO-PCBs), the immediate precursors of PCB sulfates and important contributors to PCB toxicity, were shown to have estrogenic activity, we investigated the estrogenicity/androgenicty of a series of PCB sulfate metabolites. We synthesized the five possible structural sulfate monoester metabolites of PCB 3, a congener shown to be biotransformed to sulfates, a sulfate ester of the paint-specific congener PCB 11, and sulfate monoesters of two HO-PCBs reported to interact with sulfotransferases (PCB 39, no ortho chlorines, and PCB 53, 3 ortho chlorines). We tested these PCB sulfates and 4'-HO-PCB 3 as positive control for estrogenic, androgenic, anti-estrogenic, and anti-androgenic activity in the E- and A-screen with human breast cancer MCF7-derived cells at 100 μM-1 pM concentrations. Only 4'-HO-PCB 3 was highly cytotoxic at 100 μM. We observed structure-activity relationships: compounds with a sulfate group in the chlorine-containing ring of PCB 3 (2PCB 3 and 3PCB 3 sulfate) showed no interaction with the estrogen (ER) and androgen (AR) receptor. The 4'-HO-PCB 3 and its sulfate ester had the highest estrogenic effect, but at 100-fold different concentrations, i.e., 1 and 100 μM, respectively. Four of the PCB sulfates were estrogenic (2'PCB 3, 4'PCB 3, 4'PCB 39, and 4'PCB 53 sulfates; at 100 μM). These sulfates and 3'PCB 3 sulfate also exhibited anti-estrogenic activity, but at nM and pM concentrations. The 4'PCB 3 sulfate (para-para' substituted) had the strongest androgenic activity, followed by 3'PCB 3, 4'PCB 53, 4PCB11, and 4PCB 39 sulfates and the 4'HO-PCB 3. In contrast, anti-androgenicity was only observed with the two compounds that have the sulfate group in ortho- or meta- position in the second ring (2'PCB 3 and 3'PCB 3 sulfate). No dose-response was observed in any screen, but, with exception of estrogenic activity (only seen at 100 μM), endocrine activity was often displayed at several concentrations and even at 1 pM concentration. These data suggest that sulfation of HO-PCBs is indeed reducing their cytotoxicity and estrogenicity, but may produce other endocrine disruptive activities at very low concentrations.

Identification of a novel hydroxylated metabolite of 2,2',3,5',6-pentachlorobiphenyl formed in whole poplar plants

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants consisting of 209 congeners. Oxidation of several PCB congeners to hydroxylated PCBs (OH-PCBs) in whole poplar plants has been reported before. Moreover, 2,2',3,5',6-pentachlorobiphenyl (PCB95), as a chiral congener, has been previously shown to be atropselectively taken up and transformed in whole poplar plants. The objective of this study was to determine if PCB95 is atropselectively metabolized to OH-PCBs in whole poplar plants. Two hydroxylated PCB95s were detected by high-performance liquid chromatography-mass spectrometry in the roots of whole poplar plants exposed to racemic PCB95 for 30 days. The major metabolite was confirmed to be 4'-hydroxy-2,2',3,5',6-pentachlorobiphenyl (4'-OH-PCB95) by gas chromatography-mass spectrometry (GC-MS) using an authentic reference standard. Enantioselective analysis showed that 4'-OH-PCB95 was formed atropselectively, with the atropisomer eluting second on the Nucleodex β-PM column (E2-4'-OH-PCB95) being slightly more abundant in the roots of whole poplar plants. Therefore, PCB95 can at least be metabolized into 4'-OH-PCB95 and another unknown hydroxylated PCB95 (as a minor metabolite) in whole poplar plants. Both atropisomers of 4'-OH-PCB95 are formed, but E2-4'-OH-PCB95 has greater atropisomeric enrichment in the roots of whole poplar plants. A comparison with mammalian biotransformation studies indicates a distinctively different metabolite profile of OH-PCB95 metabolites in whole poplar plants. Our observations suggest that biotransformation of chiral PCBs to OH-PCBs by plants may represent an important source of enantiomerically enriched OH-PCBs in the environment.

PROXIMAL: a method for Prediction of Xenobiotic Metabolism

Background

Contamination of the environment with bioactive chemicals has emerged as a potential public health risk. These substances that may cause distress or disease in humans can be found in air, water and food supplies. An open question is whether these chemicals transform into potentially more active or toxic derivatives via xenobiotic metabolizing enzymes expressed in the body. We present a new prediction tool, which we call PROXIMAL (Prediction of Xenobiotic Metabolism) for identifying possible transformation products of xenobiotic chemicals in the liver. Using reaction data from DrugBank and KEGG, PROXIMAL builds look-up tables that catalog the sites and types of structural modifications performed by Phase I and Phase II enzymes. Given a compound of interest, PROXIMAL searches for substructures that match the sites cataloged in the look-up tables, applies the corresponding modifications to generate a panel of possible transformation products, and ranks the products based on the activity and abundance of the enzymes involved.

Results

PROXIMAL generates transformations that are specific for the chemical of interest by analyzing the chemical’s substructures. We evaluate the accuracy of PROXIMAL’s predictions through case studies on two environmental chemicals with suspected endocrine disrupting activity, bisphenol A (BPA) and 4-chlorobiphenyl (PCB3). Comparisons with published reports confirm 5 out of 7 and 17 out of 26 of the predicted derivatives for BPA and PCB3, respectively. We also compare biotransformation predictions generated by PROXIMAL with those generated by METEOR and Metaprint2D-react, two other prediction tools.

Conclusions

PROXIMAL can predict transformations of chemicals that contain substructures recognizable by human liver enzymes. It also has the ability to rank the predicted metabolites based on the activity and abundance of enzymes involved in xenobiotic transformation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0241-4) contains supplementary material, which is available to authorized users.

Tissue Distribution, Metabolism, and Excretion of 3,3'-Dichloro-4'-sulfooxy-biphenyl in the Rat

Polychlorinated biphenyls (PCBs) with less chlorine atoms exhibit a greater susceptibility to metabolism than their more-chlorinated counterparts. Following initial hydroxylation of these less-chlorinated PCBs, metabolic sulfation to form PCB sulfates is increasingly recognized as an important component of their toxicology. Because procedures for the quantitative analysis of PCB sulfates in tissue samples have not been previously available, we have now developed an efficient, LC-ESI-MS/MS-based protocol for the quantitative analysis of 4-PCB 11 sulfate in biological samples. This procedure was used to determine the distribution of 4-PCB 11 sulfate in liver, kidney, lung, and brain as well as its excretion profile following its intravenous administration to male Sprague-Dawley rats. Following initial uptake of 4-PCB 11 sulfate, its concentration in these tissues and serum declined within the first hour following injection. Although biliary secretion was detected, analysis of 24 h collections of urine and feces revealed recovery of less than 4% of the administered 4-PCB 11 sulfate. High-resolution LC-MS analysis of bile, urine, and feces showed metabolic products derived from 4-PCB 11 sulfate. Thus, 4-PCB 11 sulfate at this dose was not directly excreted in the urine but was instead redistributed to tissues and/or subjected to further metabolism.

Metabolism and metabolites of polychlorinated biphenyls

Abstract The metabolism of polychlorinated biphenyls (PCBs) is complex and has an impact on toxicity, and thereby on the assessment of PCB risks. A large number of reactive and stable metabolites are formed in the processes of biotransformation in biota in general, and in humans in particular. The aim of this document is to provide an overview of PCB metabolism, and to identify the metabolites of concern and their occurrence. Emphasis is given to mammalian metabolism of PCBs and their hydroxyl, methylsulfonyl, and sulfated metabolites, especially those that persist in human blood. Potential intracellular targets and health risks are also discussed.

Evaluating health risks from inhaled polychlorinated biphenyls: research needs for addressing uncertainty

BACKGROUND

Indoor air concentrations of polychlorinated biphenyls (PCBs) in some buildings are one or more orders of magnitude higher than background levels. In response to this, efforts have been made to assess the potential health risk posed by inhaled PCBs. These efforts are hindered by uncertainties related to the characterization and assessment of source, exposure, and exposure-response.

OBJECTIVES

We briefly describe some common sources of PCBs in indoor air and estimate the contribution of inhalation exposure to total PCB exposure for select age groups. Next, we identify critical areas of research needed to improve assessment of exposure and exposure response for inhaled PCBs.

DISCUSSION

Although the manufacture of PCBs was banned in the United States in 1979, many buildings constructed before then still contain potential sources of indoor air PCB contamination. In some indoor settings and for some age groups, inhalation may contribute more to total PCB exposure than any other route of exposure. PCB exposure has been associated with human health effects, but data specific to the inhalation route are scarce. To support exposure-response assessment, it is critical that future investigations of the health impacts of PCB inhalation carefully consider certain aspects of study design, including characterization of the PCB mixture present.

CONCLUSIONS

In certain contexts, inhalation exposure to PCBs may contribute more to total PCB exposure than previously assumed. New epidemiological and toxicological studies addressing the potential health impacts of inhaled PCBs may be useful for quantifying exposure-response relationships and evaluating risks.

Modulating inhibitors of transthyretin fibrillogenesis via sulfation: polychlorinated biphenyl sulfates as models

Small molecules that bind with high affinity to thyroxine (T4) binding sites on transthyretin (TTR) kinetically stabilize the protein's tetrameric structure, thereby efficiently decreasing the rate of tetramer dissociation in TTR related amyloidoses. Current research efforts aim to optimize the amyloid inhibiting properties of known inhibitors, such as derivatives of biphenyls, dibenzofurans and benzooxazoles, by chemical modification. In order to test the hypothesis that sulfate group substituents can improve the efficiencies of such inhibitors, we evaluated the potential of six polychlorinated biphenyl sulfates to inhibit TTR amyloid fibril formation in vitro. In addition, we determined their binding orientations and molecular interactions within the T4 binding site by molecular docking simulations. Utilizing this combined experimental and computational approach, we demonstrated that sulfation significantly improves the amyloid inhibiting properties as compared to both parent and hydroxylated PCBs. Importantly, several PCB sulfates were of equal or higher potency than some of the most effective previously described inhibitors.

Hepatic metabolism affects the atropselective disposition of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) in mice

To understand the role of hepatic vs extrahepatic metabolism in the disposition of chiral PCBs, we studied the disposition of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) and its hydroxylated metabolites (HO-PCBs) in mice with defective hepatic metabolism due to the liver-specific deletion of cytochrome P450 oxidoreductase (KO mice). Female KO and congenic wild type (WT) mice were treated with racemic PCB 136, and levels and chiral signatures of PCB 136 and HO-PCBs were determined in tissues and excreta 3 days after PCB administration. PCB 136 tissue levels were higher in KO compared to WT mice. Feces was a major route of PCB metabolite excretion, with 2,2',3,3',6,6'-hexachlorobiphenyl-5-ol being the major metabolite recovered from feces. (+)-PCB 136, the second eluting PCB 136 atropisomers, was enriched in all tissues and excreta. The second eluting atropisomers of the HO-PCBs metabolites were enriched in blood and liver; 2,2',3,3',6,6'-hexachlorobiphenyl-5-ol in blood was an exception and displayed an enrichment of the first eluting atropisomers. Fecal HO-PCB levels and chiral signatures changed with time and differed between KO and WT mice, with larger HO-PCB enantiomeric fractions in WT compared to KO mice. Our results demonstrate that hepatic and, possibly, extrahepatic cytochrome P450 (P450) enzymes play a role in the disposition of PCBs.

Enantioselective transport and biotransformation of chiral hydroxylated metabolites of polychlorinated biphenyls in whole poplar plants

Hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) have been found to be ubiquitous in the environment due to the oxidative metabolism of their parent PCBs. With more polarity, OH-PCBs may be more toxic and mobile than their parent compounds. However, the behavior and fate of OH-PCBs have been neglected in the environment because they are not the original contaminants. Some of these hydroxylated metabolites are chiral, and chiral compounds can be used to probe biological metabolic processes. Therefore, chiral OH-PCBs were selected to study their uptake, translocation, transformation, and enantioselectivity in plants in this work. Poplars (Populus deltoides × nigra, DN34), a model plant with complete genomic sequence, were hydroponically exposed to 5-hydroxy-2,2',3,4',6-pentachlorobiphenyl (5-OH-PCB91) and 5-hydroxy-2,2',3,5',6-pentachlorobiphenyl (5-OH-PCB95) for 10 days. Chiral 5-OH-PCB91 and 5-OH-PCB95 were clearly shown to be sorbed, taken up, and translocated in whole poplars, and they were detected in various tissues of whole poplars. However, the enantioselectivity of poplar for 5-OH-PCB91 and 5-OH-PCB95 proved to be quite different. The second-eluting enantiomer of OH-PCB95, separated on a chiral column (Phenomenex Lux Cellulose-1), was enantioselectively removed in whole poplar. Enantiomeric fractions in the middle xylem, top bark, top xylem, and stem, reached 0.803 ± 0.022, 0.643 ± 0.110, 0.835 ± 0.087, and 0.830 ± 0.029, respectively. Therefore, 5-OH-PCB95 was significantly enantioselectively biotransformed inside poplar tissues, in contrast to nearly racemic mixtures of 5-OH-PCB95 remaining in hydroponic solutions. Unlike 5-OH-PCB95, 5-OH-PCB91 remained nearly racemic in most tissues of whole poplars during 10 day exposure, suggesting the enantiomers of 5-OH-PCB91 were equally transported and metabolized in whole poplars. This is the first evidence of enantioselectivity of chiral OH-PCBs and suggests that poplars can enantioselectively biotransform at least one chiral OH-PCB: namely, 5-OH-PCB95.