Development of a synthetic PCB mixture resembling the average polychlorinated biphenyl profile in Chicago air

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.

Polychlorinated Biphenyls (PCBs) in the Environment: Occupational and Exposure Events, Effects on Human Health and Fertility

In the last decade or so, polychlorinated biphenyls (PCBs) garnered renewed attention in the scientific community due to new evidence pointing at their continued presence in the environment and workplaces and the potential human risks related to their presence. PCBs move from the environment to humans through different routes; the dominant pathway is the ingestion of contaminated foods (fish, seafood and dairy products), followed by inhalation (both indoor and outdoor air), and, to a lesser extent, dust ingestion and dermal contact. Numerous studies reported the environmental and occupational exposure to these pollutants, deriving from building materials (flame-retardants, plasticizers, paints, caulking compounds, sealants, fluorescent light ballasts, etc.) and electrical equipment. The highest PCBs contaminations were detected in e-waste recycling sites, suggesting the need for the implementation of remediation strategies of such polluted areas to safeguard the health of workers and local populations. Furthermore, a significant correlation between PCB exposure and increased blood PCB concentrations was observed in people working in PCB-contaminated workplaces. Several epidemiological studies suggest that environmental and occupational exposure to high concentrations of PCBs is associated with different health outcomes, such as neuropsychological and neurobehavioral deficits, dementia, immune system dysfunctions, cardiovascular diseases and cancer. In addition, recent studies indicate that PCBs bioaccumulation can reduce fertility, with harmful effects on the reproductive system that can be passed to offspring. In the near future, further studies are needed to assess the real effects of PCBs exposure at low concentrations for prolonged exposure in workplaces and specific indoor environments.

Fatty liver and impaired hepatic metabolism alter the congener-specific distribution of polychlorinated biphenyls (PCBs) in mice with a liver-specific deletion of cytochrome P450 reductase

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are linked to adverse health outcomes. PCB tissue levels are determinants of PCB toxicity; however, it is unclear how factors, such as an altered metabolism and/or a fatty liver, affect PCB distribution in vivo. We determined the congener-specific disposition of PCBs in mice with a liver-specific deletion of cytochrome P450 reductase (KO), a model of fatty liver with impaired hepatic metabolism, and wild-type (WT) mice. Eight-week-old male WT (M_WT, n = 3), male KO (M_KO, n = 5), female WT (F_WT, n = 4), and female KO mice (F_KO, n = 4) were exposed orally to Aroclor 1254. PCBs were quantified in adipose, blood, brain, and liver tissues by gas chromatography-mass spectrometry. The ΣPCB levels followed the rank order adipose > liver ∼ brain > blood in WT and adipose ∼ liver > brain > blood in KO mice. PCB levels were much higher in the liver of KO than WT mice, irrespective of the sex. A comparison across exposure groups revealed minor genotype and sex-dependent differences in the PCB congener profiles (cos Θ > 0.92). Within each exposure group, tissue profiles showed small differences between tissues (cos Θ = 0.85 to 0.98). These differences were due to a decrease in metabolically more labile PCB congeners and an increase in congeners resistant to metabolism. The tissue-to-blood ratio of PCBs decreased for adipose, increased for the brain, and remained constant for the liver with an increase in chlorination. While these ratios did not follow the trends predicted using a composition-based model, the agreement between experimental and calculated partition coefficients was reasonable. Although the distribution of PCBs differs between KO and WT mice, the magnitude of the partitioning of PCBs from the blood into tissues can be approximated using composition-based models.

Fatty liver and impaired hepatic metabolism alter the congener-specific distribution of polychlorinated biphenyls (PCBs) in mice with a liver-specific deletion of cytochrome P450 reductase

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are linked to adverse health outcomes. PCB tissue levels are determinants of PCB toxicity; however, it is unclear how factors, such as an altered metabolism and/or a fatty liver, affect PCB distribution in vivo. We determined the congener-specific disposition of PCBs in mice with a liver-specific deletion of cytochrome P450 reductase (KO), a model of fatty liver with impaired hepatic metabolism, and wild-type (WT) mice. Eight-week-old male WT (M_WT, n = 3), male KO (M_KO, n = 5), female WT (F_WT, n = 4), and female KO mice (F_KO, n = 4) were exposed orally to Aroclor 1254. PCBs were quantified in adipose, blood, brain, and liver tissues by gas chromatography-mass spectrometry. The ΣPCB levels followed the rank order adipose > liver ∼ brain > blood in WT and adipose ∼ liver > brain > blood in KO mice. PCB levels were much higher in the liver of KO than WT mice, irrespective of the sex. A comparison across exposure groups revealed minor genotype and sex-dependent differences in the PCB congener profiles (cos Θ > 0.92). Within each exposure group, tissue profiles showed small differences between tissues (cos Θ = 0.85 to 0.98). These differences were due to a decrease in metabolically more labile PCB congeners and an increase in congeners resistant to metabolism. The tissue-to-blood ratio of PCBs decreased for adipose, increased for the brain, and remained constant for the liver with an increase in chlorination. While these ratios did not follow the trends predicted using a composition-based model, the agreement between experimental and calculated partition coefficients was reasonable. Although the distribution of PCBs differs between KO and WT mice, the magnitude of the partitioning of PCBs from the blood into tissues can be approximated using composition-based models.

Gut Microbiota Modulates Interactions Between Polychlorinated Biphenyls and Bile Acid Homeostasis

The gut microbiome is increasingly recognized as a second genome that contributes to the health and diseases of the host. A major function of the gut microbiota is to convert primary bile acids (BAs) produced from cholesterol in the liver into secondary BAs that activate distinct host receptors to modulate xenobiotic metabolism and energy homeostasis. The goal of this study was to investigate to what extent oral exposure to an environmentally relevant polychlorinated biphenyl (PCBs mixture), namely the Fox River mixture, impacts gut microbiome and BA homeostasis. Ninety-day-old adult female conventional (CV) and germ-free (GF) C57BL/6 mice were orally exposed to corn oil (vehicle), or the Fox River mixture at 6 or 30 mg/kg once daily for 3 consecutive days. The PCB low dose profoundly increased BA metabolism related bacteria Akkermansia (A.) muciniphila, Clostridium (C.) scindens, and Enterococcus in the large intestinal pellet (LIP) of CV mice (16S rRNA sequencing/qPCR). This correlated with a PCB low dose-mediated increase in multiple BAs in serum and small intestinal content (SIP) in a gut microbiota-dependent manner (UPLC-MS/MS). Conversely, at PCB high dose, BA levels remained stable in CV mice correlated with an increase in hepatic efflux transporters and ileal Fgf15. Interestingly, lack of gut microbiota potentiated the PCB-mediated increase in taurine conjugated α and β muricholic acids in liver, SIP, and LIP. Pearson's correlation identified positive correlations between 5 taxa and most secondary BAs. In conclusion, PCBs dose-dependently altered BA homeostasis through a joint effort between host gut-liver axis and intestinal bacteria.

A comprehensive approach to actual polychlorinated biphenyls environmental contamination

Worldwide polychlorinated biphenyls (PCBs) pollution is due to complex mixtures with high number of congeners, making the determination of total PCBs in the environment an open challenge. Because the bulk of PCBs production was made of Aroclor mixtures, this analysis is usually faced by the empirical mixture identification via visual inspection of the chromatogram. However, the identification reliability is questionable, as patterns in real samples are strongly affected by the frequent occurrence of more than one mixture. Our approach is based on the determination of a limited number of congeners chosen to enable objective criteria for Aroclor identification, summing up the advantages of congener-specific analysis with the ones of total PCBs determination. A quantitative relationship is established between congeners and any single mixture, or mixtures combination, leading to the identification of the actual contamination composition. The approach, due to its generality, allows the use of different sets of congeners and any technical mixture, including the non-Aroclor ones. The results confirm that PCB environmental pollution in northern Italy is based on Aroclor. Our methodology represents an important tool to understand the source and fate of the PCBs contamination.

Environmental PCBs in Guánica Bay, Puerto Rico: implications for community health

Guánica Bay, located in southwestern Puerto Rico, has suffered oil spills and other pollution discharges since the 1960s. Previous research showed elevated concentrations of polychlorinated biphenyls (PCBs) in coral reef and sediment. This research examined PCB concentrations in sediment and fish. Sediment and fish sampling in the bay was facilitated by community members. This study identified the second highest reported PCB level (129,300 ng/g) in sediment in the USA. Fish samples also showed elevated concentrations (1623 to 3768 ng/g), which were higher than the thresholds of safe levels of PCBs in fish for human consumption. The alarmingly high concentration of PCBs calls for proactive community engagement to bring awareness about contamination of the bay and more extensive sampling to test for the concentration of PCBs in seafood and the people of Guánica. This study also underscores the value of the involvement of local communities during sampling design aimed at identifying hot spots of contaminants.

Human CYP2E1-dependent mutagenicity of mono- and dichlorobiphenyls in Chinese hamster (V79)-derived cells

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants with confirmed carcinogenicity to humans. Metabolic activation of lower chlorinated PCBs to genotoxic metabolites may involve hydroxylation and further oxidation, and some hydroxylated metabolites may be sulfo-conjugated. However, the genotoxicity of individual PCB compounds is largely unknown. In this study, 15 mono- and dichlorobiphenyls were investigated for genotoxicity using the micronucleus and Hprt mutagenicity assays in a Chinese hamster V79-derived cell line expressing both human cytochrome P450 (CYP) 2E1 and human sulfotransferase (SULT) 1A1 (V79-hCYP2E1-hSULT1A1). All tested compounds were inactive in both assays in V79 control cells. However, eight dichlorobiphenyls strongly induced micronuclei and other congeners were weakly positive for this endpoint in V79-hCYP2E1-hSULT1A1 cells. The effects of each PCB in V79-hCYP2E1-hSULT1A1 cells were abolished or reduced in the presence of a CYP2E1 inhibitor (1-aminobenzotriazole), or enhanced by pretreatment of the cells with (CYP2E1-inducing) ethanol, while the genotoxicity was not significantly affected by a SULT1 inhibitor (pentachlorophenol). As representative dichlorobiphenyls, PCB 5, 10, 8 and 11 (2,3-, 2,5-, 2,4'- and 3,3'-dichlorobiphenyl, respectively) strongly induced Hprt gene mutations in V79-hCYP2E1-hSULT1A1 cells in a concentration-dependent manner. This is the first indication that human CYP2E1 is capable of converting a series of dichlorobiphenyls to strong mutagens.

Toxicity Evaluation of Exposure to an Atmospheric Mixture of Polychlorinated Biphenyls by Nose-Only and Whole-Body Inhalation Regimens

The health risk of inhalation exposure to polychlorinated biphenyls (PCB) cannot be assessed with high confidence due to the lack of rigorous inhalation studies. One uncertainty rests on exposure regimen, as whole-body exposure systems allow oral PCB intake that confounds the exposure. We conducted contemporaneous PCB inhalation exposures with whole-body and nose-only exposure methods. Female Sprague-Dawley rats were concurrently exposed to vapor-phase PCBs (533 ± 93 μg/m(3)) generated from PCB11-supplemented Chicago Air Mixture resembling the Chicago airshed, 4 h/day, 6 days/week, for 4 weeks. Congener-specific analysis showed 1.5-fold higher ∑PCBs in the lungs of nose-only exposed than the whole-body exposed animals (p = 0.0024). Higher ∑PCB concentrations were also found in the sera, livers, brains, and adipose tissue of nose-only exposed animals (1.1-1.5-fold), but these increases were not statistically significant. Congener profiles of five tissue types were dominated by PCB 28/31 and higher-chlorinated congeners in both groups reflecting rapid metabolism of other lower-chlorinated PCBs. No toxicity was seen regarding metabolic enzyme expression, glutathione, or histopathology. However, diminished weight gain and reduced plasma total thyroxine levels were found in both groups compared with controls, after exposure to 76 μg/m(3) ∑PCBs as adjusted for continuous exposure. Hepatic lipid peroxidation was also elevated in the nose-only group. Our study shows that prolonged nose-only exposure was well-tolerated and eliminated the need for housing animals outside the vivarium, thus was preferred for long-term PCB inhalation studies.

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.

A new player in environmentally induced oxidative stress: polychlorinated biphenyl congener, 3,3'-dichlorobiphenyl (PCB11)

Recent analysis of air samples from Chicago and Lake Michigan areas observed a ubiquitous airborne polychlorinated biphenyl (PCB) congener, 3,3'-dichlorobiphenyl (PCB11). Our analysis of serum samples also revealed the existence of hydroxylated metabolites of PCB11 in human blood. Because PCBs and PCB metabolites have been suggested to induce oxidative stress, this study sought to determine whether environmental exposure to PCB11 and its 4-hydroxyl metabolite could induce alterations in steady-state levels of reactive oxygen species (ROS) and cytotoxicity in immortalized human prostate epithelial cells (RWPE-1). This study also examines if antioxidants could protect the cells from PCB11-induced cytotoxicity. Exponentially growing RWPE-1 cells were exposed to PCB11 and its metabolite, 3,3'-dichlorobiphenyl-4-ol (4-OH-PCB11), as well as an airborne PCB mixture resembling the Chicago ambient air congener profile, every day for 5 days. Results showed that 4-OH-PCB11 could significantly induce cell growth suppression and decrease the viability and plating efficiency of RWPE-1 cells. 4-OH-PCB11 also significantly increased steady-state levels of intracellular superoxide, O₂•⁻), as well as hydroperoxides. Finally, treatment with the combination of polyethylene glycol-conjugated CuZn superoxide dismutase and catalase added 1h after 4-OH-PCB11 exposures, significantly protected RWPE-1 cells from PCB toxicity. The results strongly support the hypothesis that exposure to a hydroxylated metabolite of PCB11 can inhibit cell proliferation and cause cytotoxicity by increasing steady-state levels of ROS. Furthermore, antioxidant treatments following PCBs exposure could significantly mitigate the PCB-induced cytotoxicity in exponentially growing human prostate epithelial cells.

Subchronic inhalation exposure study of an airborne polychlorinated biphenyl mixture resembling the Chicago ambient air congener profile

Although inhalation of atmospheric polychlorinated biphenyls (PCBs) is the most universal exposure route and has become a substantial concern in urban areas, research is lacking to determine the body burden of inhaled PCBs and consequent health effects. To reflect the Chicago airshed environment and mimic the PCB profile in Chicago air, we generated vapors from a Chicago air mixture (CAM). Sprague-Dawley rats were exposed to the CAM vapor for 1.6 h/day via nose-only inhalation for 4 weeks, 520 ± 10 μg/m(3). Congener-specific quantification in tissue and air samples was performed by gas chromatography-tandem mass spectrometry (GC/MS/MS). In contrast to the lower-chlorinated congener-enriched vapor, body tissues mainly contained tri- to hexachlorobiphenyls. Congener profiles varied between vapor and tissues and among different organs. The toxic equivalence (TEQ) and neurotoxic equivalence (NEQ) were also investigated for tissue distribution. We evaluated a variety of end points to catalogue the effects of long-term inhalation exposure, including immune responses, enzyme induction, cellular toxicity, and histopathologic abnormalities. Glutathione oxidized/reduced ratio (GSSG/GSH) was increased in the blood of exposed animals, accompanied by elevation of hematocrit. This study demonstrated that inhalation contributed to the body burden of mostly tri- to hexachlorobiphenyls and produced a distinct profile of congeners in tissue, yet minimal toxicity was found at this exposure dose, estimated at 134 μg/rat.

Regulation of paraoxonase 1 (PON1) in PCB 126-exposed male Sprague Dawley rats

3,3',4,4',5-Pentachlorobiphenyl (PCB 126), an aryl hydrocarbon receptor (AhR) agonist and most potent dioxin-like PCB congener, significantly alters gene expression, lipid metabolism, and oxidative stress in the liver. PON1, an antioxidant and anti-atherogenic enzyme, is produced in the liver and secreted into the blood where it is incorporated into high density lipoprotein (HDL) and protects LDL and cellular membranes against lipid peroxidation. To explore the regulation of PON1, male Sprague-Dawley rats were treated with ip injections of corn oil or 1 μmol/kg or 5 μmol/kg PCB 126 and euthanized up to two weeks afterwards. Serum total and HDL-cholesterol were increased by low dose and decreased by high dose exposure, while LDL-cholesterol was unchanged. PCB 126 significantly increased hepatic PON1 gene expression and liver and serum PON1 activities. Liver and serum thiobarbituric acid reactive substances levels were not elevated except for high dose and long exposure times. Serum antioxidant capacity was unchanged across all exposure doses and time points. This study, the first describing the regulation of gene expression of PON1 by a PCB congener, raises interesting questions whether elevated PON1 is able to ameliorate PCB 126-induced lipid peroxidation and whether serum PON1 levels may serve as a new biomarker of exposure to dioxin-like compounds.

Dietary selenium as a modulator of PCB 126-induced hepatotoxicity in male Sprague-Dawley rats

Homeostasis of selenium (Se), a critical antioxidant incorporated into amino acids and enzymes, is disrupted by exposure to aryl hydrocarbon receptor (AhR) agonists. Here we examined the importance of dietary Se in preventing the toxicity of the most toxic polychlorinated biphenyl congener, 3,3',4,4',5-pentachlorobiphenyl (PCB 126), a potent AhR agonist. Male Sprague-Dawley rats were fed a modified AIN-93 diet with differing dietary Se levels (0.02, 0.2, and 2 ppm). Following 3 weeks of acclimatization, rats from each dietary group were given a single ip injection of corn oil (vehicle), 0.2, 1, or 5 μmol/kg body weight PCB 126, followed 2 weeks later by euthanasia. PCB exposure caused dose-dependent increases in liver weight and at the highest PCB 126 dose decreases in whole body weight gains. Hepatic cytochrome P-450 (CYP1A1) activity was significantly increased even at the lowest dose of PCB 126, indicating potent AhR activation. PCB exposure diminished hepatic Se levels in a dose-dependent manner, and this was accompanied by diminished Se-dependent glutathione peroxidase activity. Both these effects were partially mitigated by Se supplementation. Conversely, thioredoxin (Trx) reductase activity and Trx oxidation state, although significantly diminished in the lowest dietary Se groups, were not affected by PCB exposure. In addition, PCB 126-induced changes in hepatic copper, iron, manganese, and zinc were observed. These results demonstrate that supplemental dietary Se was not able to completely prevent the toxicity caused by PCB 126 but was able to increase moderately the levels of several key antioxidants, thereby maintaining them roughly at normal levels.

Airborne polychlorinated biphenyls (PCBs) reduce telomerase activity and shorten telomere length in immortal human skin keratinocytes (HaCat)

PCBs, a group of 209 individual congeners, are ubiquitous environmental pollutants and classified as probable human carcinogens. One major route of exposure is by inhalation of these industrial compounds, possibly daily from inner city air and/or indoor air in contaminated buildings. Hallmarks of aging and carcinogenesis are changes in telomere length and telomerase activity. We hypothesize that semi-volatile PCBs, like those found in inner city air, are capable of disrupting telomerase activity and altering telomere length. To explore this possibility, we exposed human skin keratinocytes to a synthetic Chicago Airborne Mixture (CAM) of PCBs, or the prominent airborne PCB congeners, PCB28 or PCB52 for up to 48 days and determined telomerase activity, telomere length, cell proliferation, and cell cycle distribution. PCBs 28, 52 and CAM significantly reduced telomerase activity from days 18-48. Telomere length was shortened by PCB 52 from day 18 and PCB 28 and CAM from days 30 on. All PCBs decreased cell proliferation from day 18; only PCB 52 produced a small increase of cells in G0/G1 of the cell cycle. This significant inhibition of telomerase activity and reduction of telomere length by PCB congeners suggest a potential mechanism by which these compounds could lead to accelerated aging and cancer.

Polychlorinated Biphenyl (PCB) carcinogenicity with special emphasis on airborne PCBs

Polychlorinated biphenyls (PCBs) are industrial chemicals used in various applications requiring chemical stabilityand have now become widely dispersed. Their characteristics of persistence, low water/higher lipid solubility, contribute to their ability to bioconcentrate and bioaccumulate. Traditionally PCBs have been regulated as food contaminants and the general population is primarily exposed by that route. PCBs in foodstuffs are generally higher chlorinated, resistant to metabolic breakdown, and elicit toxic changes that are thought to be predominantly receptor/parent PCB-driven. But for certain occupational exposures, and for those persons residing or working in contaminated buildings, and in large cities, an inhalation route of exposure may predominate. Airborne PCBs are, in contrast to foodborne PCBs, lower chlorinated, more volatile, and subject to metabolic attack. In this review, we have explored (geno-) toxic manifestations of PCBs typical of those found in air. Here metabolic conversion of the parent PCB to hydroxylated and other metabolic progeny appear to play a dominant role, especially in genotoxicity. We should be cognizant of the impact of exposures to airborne PCBs for those individuals who are occupationally exposed, for persons living near contaminated sites, for those who work or go to school in contaminated buildings, and especially cognizant of the young, the socio-economically disadvantaged and medically-underserved or nutritionally-deficient populations.

Polyploidy-induction by dihydroxylated monochlorobiphenyls: structure-activity-relationships

Recently semivolatile lower chlorinated biphenyls have been identified in inner city air, in public buildings like schools, and at many other sites. Inhalation exposure to these compounds, which are readily metabolized to mono- and dihydroxy-biphenyls and further to quinones, is of great concern in light of new studies revealing that at least one such compound, 4-monochlorobiphenyl (PCB3), has tumor initiating and mutagenic activity in rats. In vitro the quinone metabolites of PCB3 induced gene mutations, whereas its mono- and dihydroxylated metabolites increased micronuclei frequency. To gain further insight into the genotoxicity and possible structure-activity-relationships of the dihydroxy-metabolites, we measured the effects of the 2-chloro-, 3-chloro-, and 4-chloro-2',5'-dihydroxybiphenyl (PCB1-HQ, PCB2-HQ, and PCB3-HQ, respectively), and of 4-chloro-3',4'-dihydroxybiphenyl (PCB3-Cat) on cytotoxicity, sister chromatid exchange (SCE), cellular proliferation and chromosome number. Notably only PCB3-Cat caused a significant increase in SCE levels. Cell cycle progression during exposure, which is indicated indirectly in this assay by the occurrence of metaphases with Harlequin-stained chromosomes (cell underwent two S-phases) or uniformly dark-stained chromosomes (underwent less than two S-phases) was inhibited by PCB2-HQ and PCB3-HQ. Most surprising was the finding that up to 96% of metaphases from cells treated with PCB2- or PCB3-HQ were tetraploid, some of which had dark and some Harlequin-stained chromosomes. Neither PCB1-HQ nor PCB3-Cat or the negative (solvent) or positive control (ethylmethane sulfonate, EMS) induced this effect. The mechanism of this polyploidization is unknown. Nearly all cancer cells are hyperdiploid and polyploidization, followed by uneven chromosome loss, is hypothesized as one possible underlying mechanism of carcinogenesis. Thus different PCB metabolites may induce carcinogenesis by different mechanisms, including SCE induction or polyploidization. Understanding the mechanism(s) and structure-activity-relationships of these unexpected effects is needed before we can perform fully data-driven risk assessment of these compounds.

Spatial distribution of airborne polychlorinated biphenyls in Cleveland, Ohio and Chicago, Illinois

Passive samplers were deployed across Cleveland, OH and Chicago, IL to evaluate the spatial variability of airborne PCBs in urban areas. We measured SigmaPCB concentrations, the sum of 151 congeners or congener groups quantified using tandem mass spectrometry, spatial distributions, and congener profiles in two urban areas in the Great Lakes region. Mean SigmaPCB concentrations were significantly different between Cleveland (1.73 +/- 1.16 ng m(-3)) and Chicago (1.13 +/- 0.58 ng m(-3)) during the August 2008 sampling period. Mean congener profiles were compared with commercial Aroclor mixtures and found to be similar to Aroclor 1242 in Cleveland and similar to a mixture of 1242 and 1254 in Chicago. We observed large spatial variation in concentrations and weak or no significant autocorrelation between sites in both cities. "Hot spots" of high SigmaPCB concentrations were identified in both urban areas and the congener profiles at these locations were most strongly correlated to that of PCB Aroclor mixtures. Congener profiles showed important differences including the enrichment of dioxin-like congeners in Chicago.

Atmospheric PCB congeners across Chicago

We have measured PCBs in 184 air samples collected at 37 sites in the city of Chicago using an innovative system of high-volume air samplers mounted on two health clinic vans. Here we describe results of sampling conducted from November 2006 to November 2007. The samples were analyzed for all 209 PCB congeners using a gas chromatograph with tandem mass spectrometry (GC-MS/MS). The ΣPCBs (sum of 169 peaks) in Chicago ranged from 75 pg m(-3) to 5500 pg m(-3) and primarily varied as a function of temperature. The congener patterns are surprisingly similar throughout the city even though the temperature-corrected concentrations vary by more than an order of magnitude. The average profile resembles a mixture of Aroclor 1242 and Aroclor 1254, and includes many congeners that have been identified as being aryl hydrocarbon receptor (AhR) agonists (dioxin-like) and/or neurotoxins. The toxic equivalence (TEQ) and neurotoxic equivalence (NEQ) in air were calculated and investigated for their spatial distribution throughout the urban-industrial complex of Chicago. The NEQ concentrations are linearly correlated with ΣPCBs while the TEQ concentrations are not predictable. The findings of this study suggest that airborne PCBs in Chicago are widely present and elevated in residential communities; there are multiple sources rather than one or a few locations of very high emissions; the emission includes congeners associated with dioxin-like and neurotoxic effects and congeners associated with unidentified sources.

Minding the calcium store: Ryanodine receptor activation as a convergent mechanism of PCB toxicity

Chronic low-level polychlorinated biphenyl (PCB) exposures remain a significant public health concern since results from epidemiological studies indicate that PCB burden is associated with immune system dysfunction, cardiovascular disease, and impairment of the developing nervous system. Of these various adverse health effects, developmental neurotoxicity has emerged as a particularly vulnerable endpoint in PCB toxicity. Arguably the most pervasive biological effects of PCBs could be mediated by their ability to alter the spatial and temporal fidelity of Ca2+ signals through one or more receptor-mediated processes. This review will focus on our current knowledge of the structure and function of ryanodine receptors (RyRs) in muscle and nerve cells and how PCBs and related non-coplanar structures alter these functions. The molecular and cellular mechanisms by which non-coplanar PCBs and related structures alter local and global Ca2+ signaling properties and the possible short and long-term consequences of these perturbations on neurodevelopment and neurodegeneration are reviewed.

Aroclor 1254 induced cytotoxicity and mitochondrial dysfunction in isolated rat hepatocytes

Polychlorinated biphenyls (PCBs) are widespread persistent environmental contaminants that display a complex spectrum of toxicological properties, including hepatotoxicity. Although Aroclor 1254 is ubiquitous in the environment, its potential cytotoxic effect on rat hepatocytes and the mechanism underlines its cytotoxicity are not fully investigated. Therefore, the present study was conducted to investigate: (1) the potential cytotoxicity of Aroclor 1254 in rat hepatocytes, and (2) characterization of the molecular mechanisms involved in the Aroclor 1254-induced hepatotoxicity, particularly the role of mitochondria, possibly a primary target in such event, could greatly explain the cytotoxic effect of Aroclor 1254 in rat hepatocytes. Hepatocytes were isolated from adult male albino rats and incubated for 24h in a fresh media containing 0, 20, 30, 40, 50 or 60muM of Aroclor 1254. At the end of incubation, hepatocytes and hepatocyte mitochondria were used for the assay. Our results showed cytotoxicity of Aroclor 1254 in rat hepatocytes starting at a concentration of 30muM as manifested by increased lactate dehydrogenase (LDH) leakage, decreased cell viability (MTT assay) and increased lipid peroxidation. As mitochondria are known to be one possible site of the cell damage, the effects of Aroclor 1254 on hepatocyte mitochondria was investigated. Aroclor 1254 induced reactive oxygen species (ROS) generation in hepatocyte mitochondria, inhibited mitochondrial respiratory chain complexes I and III and beta-oxidation of free fatty acids, depletion of mitochondrial antioxidant enzymes GPx and GR and the non-enzymatic antioxidant reduced glutathione, inhibited mitochondrial membrane potential (Deltapsi(m)), decreased mitochondrial aconitase and cardiolipin content, and elevated levels of cytochrome P450 subfamily, CYP1A and CYP2B activities as indicated by ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin O-deethylase (PROD). Therefore, we can conclude that Aroclor 1254 induced rat hepatocyte toxicity and our findings provide evidence to propose that mitochondria are one of the most important and earliest cell targets in Aroclor 1254-mediated toxicity and delineate several mitochondrial processes at least, in part, by induction of oxidative stress. These findings can be useful in future cytoprotective therapy approaches. Since mitochondrial events appear to be targeted in hepatocellular damage induced by Aroclor 1254, an antioxidant therapy targeted to mitochondria may constitute an interesting strategy to ameliorate its toxicity.