Exposure to the polychlorinated biphenyl mixture Aroclor 1254 alters melanocyte and tail muscle morphology in developing Xenopus laevis tadpoles

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have damaging effects on both ecosystem and human health. Numerous studies have shown that exposure to PCBs can alter growth and development of aquatic organisms, including frogs. In this report, developing Xenopus laevis tadpoles were exposed to the PCB mixture Aroclor 1254. Tadpoles were exposed from 5 through 9 d postfertilization to either 0, 1, 10, 50, or 100 ppm Aroclor 1254. Exposure to an acute, high concentration of Aroclor 1254 (10, 50, and 100 ppm) caused statistically significant reductions in survival and body size. In addition, tadpoles exposed to these higher concentrations showed histological abnormalities, including aberrant tail tip, myotomal, and melanocyte morphologies. Described adverse health effects associated with PCB exposure of developing frogs will serve as useful health endpoints in ongoing and future molecular-based studies that correlate health effects with changes in gene expression.     

Polychlorinated biphenyls (PCBs) exert thyroid hormone-like effects in the fetal rat brain but do not bind to thyroid hormone receptors

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants routinely found in human and animal tissues. Developmental exposure to PCBs is associated with neuropsychologic deficits, which may be related to effects on thyroid hormone (TH) signaling in the developing brain. However, PCBs may interfere with TH signaling solely by reducing circulating levels of TH, or they may exert direct effects on TH receptors (TRs). Therefore, we tested whether maternal exposure to a commercial PCB mixture, Aroclor 1254 (A1254), exerts effects in the fetal brain by one or both of these mechanisms. Dams were dosed daily with 0, 1, or 4 mg/kg A1254 from gestational day 6 (GD6) until they were sacrificed on GD16. A1254 significantly reduced circulating levels of triiodothyronine (T3) and thyroxine (T4) in pregnant rats but increased the expression of several TH-responsive genes in the fetal cortex, including neuroendocrine-specific protein A (NSP-A), RC3/neurogranin, and Oct-1. These findings are consistent with a direct action of PCBs on TRs. However, we did not identify parent PCB congeners or metabolites that bound to rat TRs isolated from hepatic nuclei. These findings indicate that PCBs can interfere with TH signaling in the fetal brain by direct actions on the fetus rather than by producing maternal hypothyroidism.     

Bioavailability of PCBs to Male Laboratory Rats Maintained on Litters of Contaminated Soils: PCB Burden and Induction of Alkoxyresorufin O-Dealkylase Activities in Liver and Lung

Male rats from the Sprague-Dawley laboratory strain were maintained in the laboratory during 3 days and 1 night on litters containing a reference soil and different amounts of a soil, mainly polluted by PCBs (207 ppm expressed in Aroclor? 1254; SIII soil). Two categories of biomarkers of exposure were measured in both liver and lung of these rats: PCB burdens and activities of microsomal liver and lung cytochrome P450–dependent mono-oxygenases, namely ethoxy-, pentoxy-, and benzoxy-resorufin O-dealkylase activities (EROD, PROD, and BROD, respectively). PCB burdens in liver and lung of rats exposed to SIII soil were 1,845 and 241 ppb, respectively (expressed in Aroclor? 1254 equivalents). EROD, PROD, and BROD were significantly induced in the liver of rats exposed to SIII soil, while only EROD activity was induced in the lung. Induction of hepatic EROD activity was ∼3- to 5.4-fold; pulmonary EROD activity was induced by 9- to 12-fold. In the lung, PROD and BROD activities were inhibited. When rats were exposed to SIII soil diluted with various amounts of standard ISO soil, a nearly linear dose-response relationship was found between the level of PCBs in the litter and EROD activity in both liver and lung. A nonlinear dose-response relationship exists with hepatic BROD activity; no dose-response relationship was observed with hepatic PROD and pulmonary PROD and BROD activities. EROD activity measurement in both liver and lung of rats maintained on a litter of PCB polluted soil was used to assess the bioavailability to mammals of PCBs. Received: 16 December 1996/Accepted: 18 November 1997     

Assessing the effects of polychlorinated biphenyls (Aroclor 1254) on a scleractinian coral (Stylophora pistillata) at organism, physiological, and molecular levels

Polychlorinated biphenyls (PCBs) are a group of widespread contaminants, and accumulation of PCBs has been observed in corals in the field. However, the toxic effects of PCBs on corals have not been investigated. In this study, we tested short and long term toxicity of Aroclor 1254, a commercial PCB mixture, on the scleractinian coral Stylophora pistillata. Coral nubbins were incubated in either control seawater or seawater dosed with PCBs (approximately 300ng/L) for 96h. The effect of PCB exposure on coral gene expression at 4h post exposure was tested with the suppression subtractive hybridization (SSH) and quantitative PCR methods. Photosystem II activity of the zooxanthellae was measured at 96h. After the exposure, nubbins were moved into clean seawater and their survival and growth were observed for another 50 days. All nubbins survived during the exposure and the following 50-d recovery period. Photosystem II activity and coral growth were not affected by PCB exposure in this study. Fifty-four clones were sequenced for gene expression analysis, and 15% of these sequences were identified, including genes involved in general stress response, peptide metabolism, cellular receptor, cytoskeleton organization, membrane trafficking, and oxidative stress response. However, the quantitative PCR did not show significant difference in the five selected genes. In conclusion, acute exposure of S. pistillata to Aroclor 1254 at 300ng/L did not affect coral survival, photosynthesis or growth but may alter the expression of certain genes involved in various important cellular functions. The nubbin technique proved to be an efficient approach to simultaneously characterize the impact of PCBs on the corals at multiple biological levels.     

Neurobehavioral and somatic effects of perinatal PCB exposure in rats

Developing rats were exposed to PCBs via provision of diets containing 0.02 (no PCB added), 2.5, 26, or 269 ppm Aroclor 1254 to sperm-positive female rats from mating to weaning of their pups. Provision of the 269 ppm diet decreased the number of impregnated rats that delivered a litter and lowered pup birth weight, and most pups died within 7 days of birth. Pregnancy success, pup birth weight, and dam body weight and food intake were not altered in the 2.5 and 26 ppm conditions. Preweaning pup growth was reduced in the 26 ppm condition and slightly reduced in the 2.5 ppm condition. The ontogeny of negative geotaxis, auditory startle, and air righting was delayed in pups from the 26 ppm condition. Pups in the 2.5 ppm condition had slightly delayed development of auditory startle. PCB exposure did not affect the duration of forepaw suspension or age at eye opening. Maximal electroshock seizure tests on postweaning rats showed that perinatal PCB exposure decreased seizure severity of both the 2.5 and 26 ppm groups as indicated by increased durations of forelimb and hindlimb flexion and decreased duration of hindlimb extension. PCB exposure increased pup liver weights at birth and dam and pup liver weights at weaning. Spleen and thymus weights were lower in PCB-exposed pups, while brain weights were unaffected. Analytical determination of PCB levels in brain showed greater maternal transfer of PCBs during lactation than during gestation. Elevated PCB levels were detectable in brains of perinatally exposed adult rats. The results indicate that perinatal PCB exposure of rats alters neurobehavioral and somatic ontogeny.     

Adenofibrosis in the Rat Liver

Fifty male Sherman strain rats were fed 500 ppm of a polychlorinated biphenyl (PCB) (Aroclor 1254) for six months. Five each were killed zero, one, two, three, four, six, eight, and ten months after exposure to Aroclor had ceased. The livers of these rats were examined by light and electron microscopy. Liver lesions persisted although exposure to PCBs ceased.

Ten months after exposure ceased, 1,192 ppm PCBs were still present in the rats’ adipose tissue and 22.65 ppm in the rat livers.

Aroclor patterns found in the tissues by electron capture gas chromatography differed from patterns of dietary Aroclors. Mass spectral analysis of liver and adipose tissue revealed three major Aroclor components with masses of 324, 358, and 392. These contained isotopic clusters indicative of the presence of C1₅, C1₆, and C1₇, respectively.     

Polychlorinated biphenyls alter extraneuronal but not tissue dopamine concentrations in adult rat striatum: an in vivo microdialysis study

Polychlorinated biphenyls (PCBs) reduce tissue dopamine (DA) concentrations and increase media DA concentrations in both in vitro preparations of bovine adrenal chromaffin cells and adult rat striatal tissue. To determine whether these changes also occur in the intact animal, we used in vivo microdialysis to determine changes in concentrations of DA in striatal dialysates from freely moving adult male rats after exposure to 25 mg/kg/day Aroclor 1254 for varying periods of time. We also determined DA concentrations in striatal tissue obtained postmortem from similarly treated animals. The effects of PCBs on dialysate DA concentrations depended on the length of exposure; DA concentrations were significantly elevated after 3 days of exposure and were significantly reduced after exposure for periods of 1 week or longer. On the other hand, striatal tissue concentrations of DA, determined postmortem in rats exposed to PCBs for the same periods of time, were not significantly altered. We suggest that these time-dependent alterations in dialysate DA concentrations a) reflect PCB-induced alterations of both plasma membrane and vesicular DA transporter function; b) provide a more sensitive index of altered central DA function after exposure to PCBs than does measurement of postmortem tissue DA concentrations; and c) play an important role in mediating some PCB-mediated changes in behavior.     

Tilapia Larvae Aroclor 1254 Exposure: Effects on Gonads and Circulating Thyroid Hormones During Adulthood

Aroclor 1254 a polychlorinated biphenyls (PCBs) mixture, when administrated through the diet, was previously found to inhibit adult tilapia (Oreochromis niloticus) reproduction. Since fish larvae can be more sensitive to contaminants, the objectives of this study were to evaluate in adults the impact in gonad development and in thyroid function of Aroclor 1254 administrated at larvae stages. Aroclor 1254 exposed tilapia presented both ovary and testicular alterations and a decline in T4 plasma concentration while T3 remained unaltered. This work shows exposure to Aroclor 1254 during tilapia early life stages causes a disruption of the reproductive axis that enables reproduction.     

Levels of polychlorinated biphenyls (PCBs) in fish: the influence on local decision making about fish consumption

In 1989, the level of Aroclor 1254 (a mixture of polychlorinated biphenyls with 42 percent chlorine by weight) in fish collected from a recreational pond in Toledo, Ohio, was reported to be 44.4 milligrams per kilogram (mg/kg), prompting local health officials to declare a "no fishing advisory" for the pond. A second study conducted in 1990 did not identify elevated levels of polychlorinated biphenyls (PCBs) in fish tissue. In other words, the two studies gave conflicting results. The purpose of this study was to determine the level of Aroclor in fish tissues and then evaluate whether consumption of fish from the pond would pose a serious health risk. Fish samples collected on several occasions in 1998 and 1999 were filleted, and tissues were analyzed, as composite or individual samples, with gas chromatography. The levels of Aroclor 1254 ranged from 0.2 mg/kg in white crappies to 1.0 mg/kg in carp. These levels, while far less than the level reported in 1989, nevertheless were greater than 0.05 mg/kg, which is the maximum level established by the Great Lakes Fish Advisory Task Force for "no restriction in fish consumption." Levels of other Aroclor formulations ranged from less than the 0.02 mg/kg (the minimum detectable limit) to 0.1 mg/kg. Given current knowledge about the potential health consequence of exposure to PCBs and the results of this study, the authors have recommended that local health officials develop a new fish consumption guideline for PCBs. Any decisions about maintaining or lifting the restrictions on the pond, however, should be based on additional studies that determine the levels of other chemicals that are present in the pond and deemed hazardous to human health.     

Acute ozone-induced differential gene expression profiles in rat lung

Ozone is an oxidant gas that can directly induce lung injury. Knowledge of the initial molecular events of the acute O3 response would be useful in developing biomarkers of exposure or response. Toward this goal, we exposed rats to toxic concentrations of O3 (2 and 5 ppm) for 2 hr and the molecular changes were assessed in lung tissue 2 hr postexposure using a rat cDNA expression array containing 588 characterized genes. Gene array analysis indicated differential expression in almost equal numbers of genes for the two exposure groups: 62 at 2 ppm and 57 at 5 ppm. Most of these genes were common to both exposure groups, suggesting common roles in the initial toxicity response. However, we also identified the induction of nine genes specific to 2-ppm (thyroid hormone-beta receptor c-erb-A-beta; and glutathione reductase) or 5-ppm exposure groups (c-jun, induced nitric oxide synthase, macrophage inflammatory protein-2, and heat shock protein 27). Injury markers in bronchoalveolar lavage fluid (BALF) were used to assess immediate toxicity and inflammation in rats similarly exposed. At 2 ppm, injury was marked by significant increases in BALF total protein, N-acetylglucosaminidase, and lavageable ciliated cells. Because infiltration of neutrophils was observed only at the higher 5 ppm concentration, the distinctive genes suggested a potential amplification role for inflammation in the gene profile. Although the specific gene interactions remain unclear, this is the first report indicating a dose-dependent direct and immediate induction of gene expression that may be separate from those genes involved in inflammation after acute O3 exposure.     

Effects of chronic polychlorinated biphenyls exposure on reproductive success of white-footed mice (peromyscus leucopus)

Reproductive success was impaired in white-footed mice (Peromyscus leucopus) chronically exposed to food treated at a rate of 10 ppm (g/g) polychlorinated biphenyls (PCBs) (Aroclor® 1254). Mice in which PCBs exposure was initiated at adulthood (wild-caught and subsequently paired) and laboratory-raised mice paired and first exposed to PCBs-treated food at 16 weeks of age weaned significantly smaller numbers of young. Other parameters of reproductive success (interval between births, litter size at birth) were unaffected.Laboratory-raised white-footed mice paired and first exposed to PCBs-treated food at 12 weeks of age exhibited longer intervals between births, smaller litter sizes at birth, and smaller litter sizes at weaning.These results suggest that exposure to PCBs-contaminated natural foods can contribute to declines in natural populations of white-footed mice by reducing the number of young mice entering the breeding population.     

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

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

Combined Effects of Repeated Administration of 2,3,7,8-Tetrachlorodibenzo-<Emphasis Type="Italic">p</Emphasis>-dioxin and Polychlorinated Biphenyls on Kidneys of Male Rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) are persistent environmental contaminants that exist as complex mixtures in the environment, but the possible interactions of TCDD and PCBs have not been systematically investigated. The main objective of this study was to investigate the combined nephrotoxic effects of TCDD and PCBs on rats and to reveal the potential interactions between TCDD and PCBs. Male Sprague–Dawley rats were intragastrically administered TCDD (10 μg/kg), PCBs (Aroclor 1254, 10 mg/kg), or the combination (10 μg/kg TCDD + 10 mg/kg Aroclor 1254). After 12 consecutive days of exposure, all treatments induced nephrotoxicity, as evidenced by significant increases in the levels of serum creatinine and blood urea nitrogen, changes of kidney histopathology, and significant renal oxidative stress. Most of these effects were more remarkable in the combined-exposure group. Furthermore, all treatments induced renal cytochrome P450 1A1 (CYP1A1) protein expression, and the induction was more conspicuous in the combined-exposure group. These findings suggested that the nephrotoxicity induced by TCDD and PCBs in the present study might be attributable to the high expression of CYP1A1. In addition, the result of the two-way analysis of variance revealed that the combined effects of TCDD and PCBs were complicated, being additive, synergistic, or antagonistic depending on the selection of toxicity end points under the present experimental condition. This study demonstrates that combined exposure to TCDD and PCBs induced significant nephrotoxicity in rats, and there were complicated interactions between the two pollutants on the nephrotoxicity.     

Cardiovascular and hematological parameters affected by feeding various polychlorinated biphenyls to the single comb white leghorn cockerel

The effect of dietary PCBs (50–200 ppm) on some cardiovascular and hematological parameters in the SCWL cockerel was investigated. Heart rate was significantly reduced by PCB 1242 and 1254 at 100 ppm and was not altered by PCB 1221 or 1260 at 150 ppm. A significant decrease in arterial blood pH was observed with PCB 1254 at 150 ppm. Mean blood pressure was unaffected by any treatment used. Hemoglobin concentration, HCT, and total erythrocyte count were found to be significantly decreased by PCBs 1242 and 1254 at 50 ppm. These same parameters were not affected by PCB 1221 or 1260 at any level used. It was concluded that the anemia observed was due solely to a decrease in total erythrocyte concentration. The possibility that these changes may be due to a decrease in erythropoiesis is discussed. Pericardial fluid volume was increased with PCBs 1242 and 1254; however, there was no correlation between the magnitude of the bradycardia and the amount of pericardial fluid.Michigan Agricultural Experiment Station Journal Article 6411.     

Liver mixed function oxidases in chickens: Induction by polychlorinated biphenyls and lack of induction by DDT

Microsomal hydroxylase and demethylase activities were compared in livers from White Leghorn cockerels fed polychlorinated biphenyls (PCBs) containing 21 to 68% chlorine, orp,p′-DDT. The higher chlorinated PCBs, Aroclor 1254 and 1268, were potent inducers of hepatic enzyme activity while DDT did not induce these enzymes. Aroclor 1254 was the most potent inducer because feeding 5 ppm increased liver aminopyrine demethylase activity 1.5X but did not affect liver weight. Feeding 50 and 500 ppm of Aroclor 1254 and 1268 increased liver weight and demethylase activity per mg of protein. A differential response in the two enzymes occurred. Only 500 ppm of Aroclor 1268 increased hydroxylase activity. Aroclor 1242 had no effect on liver enzyme concentration but 50 and 500 ppm of Aroclor 1242 increased liver weights and consequently increased total enzyme activity. Our data demonstrated that in the avian species DDT and PCB did not have the same effect on hepatic microsomal enzyme activity.     

Liver mixed function oxidases in chickens: induction by polychlorinated biphenyls and lack of induction by DDT.

Microsomal hydroxylase and demethylase activities were compared in livers from White Leghorn cockerels fed polychlorinated biphenyls (PCBs) containing 21 to 68% chlorine, or p,p'-DDT. The higher chlorinated PCBs, Aroclor 1254 and 1268, were potent inducers of hepatic enzyme activity while DDT did not induce these enzymes. Aroclor 1254 was the most potent inducer because feeding 5 ppm increased liver aminopyrine demethylase activity 1.5X but did not affect liver weight. Feeding 50 and 500 ppm of Aroclor 1254 and 1268 increased liver weight and demethylase activity per mg of protein. A differential response in the two enzymes occurred. Only 500 ppm of Aroclor 1268 increased hydroxylase activity. Aroclor 1242 had no effect on liver enzyme concentration but 50 and 500 ppm of Aroclor 1242 increased liver weights and consequently increased total enzyme activity. Our data demonstrated that in the avian species DDT and PCB did not have the same effect on hepatic microsomal enzyme activity.     

The effects of polychlorinated biphenyls (Aroclors® 1016 and 1254) on mortality,reproduction, and regeneration inHydra oligactis

Budding and tentacle regeneration were observed inHydra oligactis following exposure to the commercial PCB mixtures Aroclor 1016 and 1254. The acute toxicity of these PCB s was also compared by determining their respective 72-hr LC50s. The animals were exposed to the PCBs as a component of an artificial pond water medium with PCB dilutions being made from a 49:1, reagent grade acetone:PCB solution. All exposures were continuous with the medium being replaced daily. Animals used in studying the effects of these chemicals on tentacle regeneration had their heads transected at the time of initial exposure to the PCBs. Observation were taken at 24, 48, 72, and 96-hr of incubation at 19 ±0.2°C.Aroclor 1016 was more toxic than the more widely occurring 1254, with 72-hr LC50s of 5 mg/L and 20 mg/L, respectively. The two chemicals suppressed bud initiation equally, however, Aroclor 1254 had a significantly greater inhibitory effect on bud detachment when equal concentrations of the two PCBs were compared. As was the case with mortality, Aroclor 1016 had four times the suppressive effect of Aroclor 1254 on tentacle regeneration, with 50% inhibition occurring at 1 mg/L and 4 mg/ L, respectively. The quantitatively different effects on the two PCBs on mortality and tentacle regeneration may have been due to structural differences between the two PCBs or the different aqueous solubility properties (1016 being more soluble) of these chemicals. The results on bud initiation and detachment indicated that this developmental process may have been affected by the PCB through a different mechanism than was mortality and tentacle regeneration.Registered trademark, Monsanto Co., St. Louis, MO     

Useful biomarkers for assessing the adverse health effects of PCBs in allergic children: pediatric molecular epidemiology

The incidences of childhood allergies have been increasing in recent years in many parts of the world. The development of allergic disorders is attributed to a complex series of interactions between individuals’ genetic backgrounds and their immune and psychoneurotic responses to environmental factors. Among the various possible environmental causes of childhood allergies, the early exposure of developing infants to air pollutants and the presence of persistent chemical pollutants such as pesticides have been suggested most frequently. Therefore, it is very important to obtain epidemiological evidence of direct associations between clearly defined adverse health effects and exposure to low levels of pollutants. However, there are no useful biomarkers for assessing such associations. Thus, we planned to establish reliable health-related biomarkers that could be used to investigate these relationships in children. The serum concentrations of several sub-types of polychlorinated biphenyl (PCB) congeners were found to be significantly correlated with interleukin (IL)-8 mRNA expression among asthmatic children. In addition, IL-22 mRNA expression was found to be particularly useful for detecting the effects of environmental pollutants, especially PCB congeners, in a sub-population of vulnerable children who exhibited positive immunoglobulin E (IgE) responses to milk or egg. Furthermore, we detected significant differences in IL-22 mRNA expression between the IgE-negative non-asthmatic subjects and the asthmatic children who exhibited positive IgE reactions toward egg or milk. In conclusion, IL-8 and IL-22 mRNA expressions could be useful biomarkers for detecting sub-populations of children who are particularly vulnerable to the adverse health effects of environmental pollutants, especially PCBs.