Toxicity of 2,2',4,4',5,5'-hexachlorobiphenyl in rats: effects following 90-day oral exposure

Concentration of polychlorinated biphenyls and risk assessment in finless porpoises from the East China Sea

Polychlorinated biphenyls (PCBs) are bioaccumulative persistent organic pollutants with a great impact on cetaceans. To examine the content of PCBs and their risks to finless porpoises, this study determined the concentrations of seven typical PCB congeners in 56 tissue samples of East Asian finless porpoises (EAFPs) sampled in 2009-2012 from Ningbo (29.8835° N, 122.0644° E), Pingtan (25.5133° N, 119.8172° E) and Lvsi (32.1035° N, 121.6078° E). PCB138, PCB153 and PCB101 were the predominant congeners, accounting for 31.15%, 18.59% and 15.75%, respectively, of all PCBs detected. The content of PCBs increased with age in males but decreased from juveniles to adults in females due to transfer to calves by reproduction and lactation. EAFPs in Ningbo and Pingtan accumulated more PCBs than those in Lvsi Port. The trophic positions of EAFPs from Lvsi, Pingtan and Ningbo were 9.41, 8.95 and 9.43, respectively. PCB concentrations did not accumulate significantly with increasing trophic levels. The risk quotient index indicated that the risk of trichlorobiphenyl (3-PCB), tetrachlorobiphenyl (4-PCB), pentachlorobiphenyls (5-PCB), and hexachlorobiphenyls (6-PCB) to EAFPs in the East China Sea was generally low and within safe limits thus far.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00221-0.

Dose-dependent toxicological effects in rats following a 90-day dietary exposure to PCB-156 include retinoid disruption

The toxicity of PCB-156 (2,3,3',4,4',5-hexachlorobiphenyl) was investigated in rats following subchronic dietary exposure. Groups of 10 male and female Sprague-Dawley rats were administered PCB-156 in the diet at 0, 0.01, 0.1, 1 or 10 ppm for 90 days. Dose-dependent increases were detected for the liver, lung and kidney weights, as well as for the liver EROD, PROD and UDPGT enzyme activities and liver uroporphyrin concentration. Dose-dependent decreases were observed in final body weight, body weight gain, and thymus weight. Apolar retinoid concentrations were decreased in the liver and lungs and increased in the kidneys. Histopathological examination of the liver, thyroid, and thymus showed mild to moderate dose-related changes. A LOAEL of 0.01 ppm was established, based on reduced apolar liver retinoid concentration. Benchmark dose-modelling corroborated the sensitivity of liver retinoid endpoints. The lower confidence limits (BMDL) for a 5% decrease in apolar liver retinoid concentrations were 0.0009 and 0.0007 ppm, respectively, in males and females, corresponding to a daily dose of 0.06 μg PCB-156 per kg body weight. Organizing dose-response data for the individual hepatic endpoints along the PCB-156 dosing scale revealed a sequence of events compatible with a causal link between depletion of apolar retinoids and the other liver biochemistry and pathology findings. Taken together, data suggest that the retinoid endpoints should be further evaluated for a causal relationship to PCB-induced liver toxicity and that retinoid system endpoints are identified and characterized to support health risk assessment in the emerging research fields of endocrine disruption and mixture toxicology.

Polychlorinated biphenyl toxicity in the thyroid gland of wild ungulates: an in vitro model

Polychlorinated biphenyls (PCBs) are carcinogens causing endocrine disruption. While production of PCBs is now banned, wildlife exposure still occurs due to environmental contamination. We investigated thyroid toxicity in wild ungulates using three-dimensional primary thyrocyte cultures exposed to PCB 138 for 24, 48, and 72 h at concentrations ranging within 0–3000 ng/ml. Thyrocyte viability ranged within 78.71–118.34%, 98.14–104.45%, and 84.16–106.70% in fallow deer-, mouflon-, and roe deer-derived cells, respectively. Viability decreased significantly in fallow deer (P = 0.012) and roe deer (P = 0.002) thyrocytes exposed for 48 h at 30 ng/ml. While cytotoxicity ranged within 2.36–16.37%, 3.19–9.85%, and 2.76–11.21% in fallow deer, mouflon, and roe deer, respectively, only roe deer displayed significantly higher cytotoxicity at a 3 ng/ml exposure (P < 0.05) and lower cytotoxicity at 30 ng/ml (P < 0.01). Exposure to 30 ng/ml for 24 and 48 h induced reactive oxygen species in fallow deer. Iodide uptake at 30 ng/ml exposure increased after 24 h in fallow and roe deer, but showed a significant drop after 48 and 72 h in fallow deer, mouflon, and roe deer. Thyroxine T4 release at 30 ng/ml exposure decreased significantly after 48 and 72 h; 24, 48 and 72 h; and 48 h in fallow deer, mouflon, and roe deer, respectively. Our findings indicate time- and species-dependent effects of PCB on performance and thyrocyte function. Use of cell culture models reduces the number of experimental specimens, increases test species welfare and replaces whole organisms with specific target cells.

Juvenile Male Rats Exposed to a Low-Dose Mixture of Twenty-Seven Environmental Chemicals Display Adverse Health Effects

Humans are exposed to a large number of environmental chemicals in their daily life, many of which are readily detectable in blood or urine. It remains uncertain if these chemicals can cause adverse health effects when present together at low doses. In this study we have tested whether a mixture of 27 chemicals administered orally to juvenile male rats for three months could leave a pathophysiological footprint. The mixture contained metals, perfluorinated compounds, PCB, dioxins, pesticides, heterocyclic amines, phthalate, PAHs and others, with a combined dose of 0.16 (Low dose), 0.47 (Mid dose) or 1.6 (High dose) mg/kg bw/day. The lowest dose was designed with the aim of obtaining plasma or urine concentrations in rats at levels approaching those observed in humans. Some single congeners were administered at doses representative of combined doses for chemical groups. With this baseline, we found effects on weight, histology and gene expression in the liver, as well as changes to the blood plasma metabolome in all exposure groups, including low-dose. Additional adverse effects were observed in the higher dosed groups, including enlarged kidneys and alterations to the metabolome. No significant effects on reproductive parameters were observed.

Compound- and sex-specific effects on programming of energy and immune homeostasis in adult C57BL/6JxFVB mice after perinatal TCDD and PCB 153

Early life exposure to endocrine disrupting compounds has been linked to chronic diseases later in life, like obesity and related metabolic disorders. We exposed C57BL/6JxFVB hybrid mice to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the constitutive androstane receptor/pregnane X receptor agonist polychlorinated biphenyl 153 (PCB 153) in an experimental design relevant for human exposure. Exposure occurred during gestation and lactation via maternal feed to a wide dose range (TCDD: 10-10,000 pg/kg body weight/day; PCB 153: 0.09-1406 μg/kg body weight/d). Then exposure was ceased and offspring were followed up to 1 year of age. Metabolic parameters like body weight, fat pad weights, glucose tolerance, endocrine serum profile, and neurobehavioral and immunological parameters were determined. Body weight was transiently affected by both compounds throughout the follow-up. TCDD-exposed males showed decreased fat pad and spleen weights and an increase in IL-4 production of splenic immune cells. In contrast, females showed increased fat pad weights and production of IFNγ. PCB 153-exposed males showed an increase in glucose, whereas females showed an increase in glucagon, a decrease in pancreas weight, and an increase in thymus weight. In conclusion, early life exposure to TCDD appears to affect programming of energy and immune homeostasis in offspring, whereas the effects of perinatal PCB 153 were mainly on programming of glucose homeostasis. Both compounds act sex-specifically. Lowest derived BMDLs (lower bounds of the (two sided) 90%-confidence interval for the benchmark dose) for both compounds are not lower than current tolerable daily intakes.

Toxicological profile of ultrapure 2,2',3,4,4',5,5'-heptachlorbiphenyl (PCB 180) in adult rats

PCB 180 is a persistent non-dioxin-like polychlorinated biphenyl (NDL-PCB) abundantly present in food and the environment. Risk characterization of NDL-PCBs is confounded by the presence of highly potent dioxin-like impurities. We used ultrapure PCB 180 to characterize its toxicity profile in a 28-day repeat dose toxicity study in young adult rats extended to cover endocrine and behavioral effects. Using a loading dose/maintenance dose regimen, groups of 5 males and 5 females were given total doses of 0, 3, 10, 30, 100, 300, 1000 or 1700 mg PCB 180/kg body weight by gavage. Dose-responses were analyzed using benchmark dose modeling based on dose and adipose tissue PCB concentrations. Body weight gain was retarded at 1700 mg/kg during loading dosing, but recovered thereafter. The most sensitive endpoint of toxicity that was used for risk characterization was altered open field behavior in females; i.e. increased activity and distance moved in the inner zone of an open field suggesting altered emotional responses to unfamiliar environment and impaired behavioral inhibition. Other dose-dependent changes included decreased serum thyroid hormones with associated histopathological changes, altered tissue retinoid levels, decreased hematocrit and hemoglobin, decreased follicle stimulating hormone and luteinizing hormone levels in males and increased expression of DNA damage markers in liver of females. Dose-dependent hypertrophy of zona fasciculata cells was observed in adrenals suggesting activation of cortex. There were gender differences in sensitivity and toxicity profiles were partly different in males and females. PCB 180 adipose tissue concentrations were clearly above the general human population levels, but close to the levels in highly exposed populations. The results demonstrate a distinct toxicological profile of PCB 180 with lack of dioxin-like properties required for assignment of WHO toxic equivalency factor. However, PCB 180 shares several toxicological targets with dioxin-like compounds emphasizing the potential for interactions.

Alteration of serotonin system by polychlorinated biphenyls exposure

Although commercial production of polychlorinated biphenyls (PCBs) was banned in 1979, PCBs continue to be an environmental and health concern due to their high bioaccumulation and slow degradation rates. In fact, PCBs are still present in our food supply (fish, meat, and dairy products). In laboratory animals, exposure to single PCB congener or to mixtures of different congeners induces a variety of physiological alterations. PCBs cross the placenta and even exposure at low level is harmful for the foetus by leading to neurodevelopment alterations. Serotonin system which regulates many physiological functions from platelet activation to high cerebral processes and neurodevelopment is one of the targets of PCBs toxicity. The effects of PCBs exposure on serotonin system have been investigated although to a lesser extent compared to its effect in other neurotransmitter systems. This review provides a summary of the results concerning the impact of PCBs exposure (in vitro and in vivo) on serotonin system. Further research is needed to correlate specific deficits with PCB-induced changes in the serotonin system.

Development of TEFs for PCB congeners by using an alternative biomarker--thyroid hormone levels

Polychlorinated biphenyls (PCBs) are ubiquitous toxic contaminants. Health risk assessment for this class of chemicals is complex: the current toxic equivalency factor (TEF) method covers dioxin-like (DL-) PCBs, dibenzofurans, and dioxins, but excludes non-DL-PCBs. To address this deficiency, we evaluated published data for several PCB congeners to determine common biomarkers of effect. We found that the most sensitive biomarkers for DL-non-ortho-PCB 77 and PCB 126 are liver enzyme (e.g., ethoxyresorufin-O-deethylase, EROD) induction, circulating thyroxine (T4) decrease, and brain dopamine (DA) elevation. For DL-ortho-PCB 118 and non-DL-ortho-PCB 28 and PCB 153, the most sensitive biomarkers are brain DA decrease and circulating T4 decrease. The only consistent biomarker for both DL- and non-DL-PCBs is circulating T4 decrease. The calculated TEF-(TH), based on the effective dose to decrease T4 by 30% (ED(30)) with reference to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is identical to both TEF-(WHO98) and TEF-(WHO05) for TCDD and DL-PCBs (correlation coefficients are r=1.00, P<0.001; and r=0.99, P<0.001, respectively). We conclude that T4 decrease is a prospective biomarker for generating a new TEF scheme which includes some non-DL-congeners. The new TEF-(TH) parallels the TEF-(WHO) for DL-PCBs and, most importantly, is useful for non-DL-PCBs in risk assessment to address thyroid endocrine disruption and potentially the neurotoxic effects of PCBs.

Effect of PCB153 on BaP-induced genotoxicity in HepG2 cells via modulation of metabolic enzymes

Benzo(a)pyrene (BaP) is a representative environmental carcinogen and is metabolically activated by several cytochrome P450 (CYP) enzymes to become the ultimate carcinogen. Numerous studies have indicated that 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) could effectively alter the activity of xenobiotic metabolizing enzymes (XMEs). Therefore, we propose that PCB153 may affect BaP-induced genotoxicity mediated by XMEs. In the present study, we treated HepG2 cells with BaP (50 microM) or PCB153 (0.1, 1, 10 and 100 microM), or pretreated the cells with PCB153 for 48 h followed by treatment with a combination of both BaP and PCB153. CYP1A1 activity was dramatically increased in cells treated with either BaP or PCB153. Glutathione-S-transferase (GST) activity was increased in BaP-treated cells, but decreased in PCB153-treated cells. In parallel to studies on enzyme activity, the micronuclei (MN) assay was used to assess the genotoxic damage caused by BaP and PCB153. BaP and PCB153 at 100 microM enhanced MN formation. In contrast to BaP treatment alone, treatment with both BaP and PCB153 significantly enhanced the activity of CYP1A1 and the formation of MN, but reduced the activity of GST. alpha-Naphthoflavone (ANF), an inhibitor of CYP1A1, inhibited MN formation in the presence of both BaP and PCB153. In addition, there was a positive correlation between CYP1A activity and MN formation (r(2)=0.794, P<0.001). Our observations suggest that co-exposure to BaP and PCB153 may increase BaP-induced genotoxicity, possibly through the induction of CYP1A1 and inhibition of GST.

Alteration of brain neurotransmitters in female rat offspring induced by prenatal administration of 16 and 64 mg/kg of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153)

PCB153 (2,2',4,4',5,5'-hexachlorobiphenyl), a non-coplanar PCB and the congener most widely distributed in the environment, was orally administered to pregnant Sprague-Dawley (Crj: CD (SD) IGS) rats from gestation day 10 through 16 at doses of 0 (control), 16 and 64 mg/kg body weight. Female pups were sacrificed at 1, 3, 6, and 9 wk, and at 1 yr of age to evaluate the differences in brain neurotransmitters and their metabolites between PCB153-exposed and control groups. Brain levels of norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5HT), 5-hydroxyindoleacetic acid (5HIAA), acetylcholine (ACh), and choline (Ch) in discrete brain regions or in whole brain were measured. At 1 to 3 wk after birth, brain levels of DA, DOPAC, HVA, 5HT and 5HIAA in PCB-exposed groups were higher than those of the control group. At 9 wk after birth, DA turnover was reduced in half of the four brain areas examined (forebrain and hindbrain), and 5HIAA levels were increased in all brain areas in the PCB-treated group compared to those of the control group. At 1 yr after birth, the levels of DA, DOPAC, and HVA in the hippocampus, hypothalamus, and medulla oblongata were lower in the PCB-exposed groups than in the control group. Prenatal exposure to PCB153 stimulated the turnover of 5HT neurons in the brain of female offspring at early stages (1 to 9 wk) of development. On the other hand, the turnover of DA neurons in the PCB-exposed groups was reduced in late stages (9 wk to 1 yr) of development compared with that of the control group. The brain neurotransmitters of dams treated with PCB were assayed at 3 wk after delivery (15 wk old), and decreases in DA, DOPAC, and HVA were observed. PCB153 reduced the activity of DA neurons in the brain of dams. These results are discussed in relation to health effects observed in humans exposed to PCBs.

beta-Naphthoflavone and benzo(a)pyrene alter dopaminergic, noradrenergic, and serotonergic systems in brain and pituitary of rainbow trout (Oncorhynchus mykiss)

In the present study we evaluate for the first time the potential of the flavonoid compound beta-naphthoflavone (BNF) and the high molecular weight- Polycyclic aromatic hydrocarbon (PAH) benzo(a)pyrene (BaP) to alter brain neurotransmitter metabolism in fish. Fish of three different groups were intraperitoneally (i.p.) injected (2 microl g(-1)) with vegetable oil alone (control) or containing BNF or BaP (10 mg kg(-1)) and sacrificed 3, 24, and 72 h after treatment. Contents of dopamine (DA), noradrenaline (NA) and serotonin (5HT), as well as the amine oxidative metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindole-3-acetic acid (5HIAA) were assayed in telencephalon, hypothalamus, preoptic region, optic tectum, and brain stem, as well as the pituitary. Fish treated with PAHs showed after 3h decreases in 5HT content in telencephalon, hypothalamus, preoptic region (with both BNF and BaP), and pituitary (with BaP), resulting in increased 5HIAA/5HT ratio. An increased ratio was also observed in hypothalamus 24h after BaP, and in preoptic region 72 h after BNF, in both cases due to an increased 5HIAA content. In other brain regions PAHs effects on 5-HT metabolism were less consistent. With respect to the dopaminergic system, changes induced by PAHs mainly occurred after 24 and 72 h of treatment, with increased DOPAC/DA ratio in preoptic region and brain stem. In hypothalamus, tectum, and pituitary, changes in DA metabolism showed strong variability. Finally, a decreased content of NA was evident in preoptic region (3h) and in telencephalon (24h) after both BNF and BaP treatments. Therefore, both BNF and BaP seem to act in rainbow trout brain by impairing 5HT availability at short term (3h) and increasing neuronal metabolic utilization of both 5HT and DA after 24 and 72 h. Data collected in the present study suggest that brain monoamine neurotransmitters are potential targets of BNF and BaP, and their alteration could have a role in known effects of PAHs on several neuroendocrine processes that are centrally regulated or modulated by brain monoamines.

Effects of in utero exposure to 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) on somatic growth and endocrine status in rat offspring

Exposure to polychlorobiphenyl (PCB) mixtures at an early stage of development has been reported to affect endocrine glands; however, little is known about the precise toxicological properties of individual PCB. The present study was undertaken to determine whether prenatal exposure to 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153), a di-ortho-substituted non-coplanar congener, affects postnatal development in rat offspring. Pregnant Sprague-Dawley rats (Crj: CD (SD) IGS) were given PCB 153 (0, 16, or 64 mg/kg/day) orally from gestational day (GD) 10 through GD 16, and developmental parameters in the male and female offspring were examined. We found no dose-dependent changes in body weight, body length (nose-anus length), tail length, or the weights of kidneys, testes, ovaries and uterus in offspring at 1 or 3 weeks of age. Liver weights were increased in the PCB 153-treated groups, although we observed a significant difference only in males. Anogenital distance was unaffected in the PCB 153-treated groups. We observed a significant dose-dependent decrease in the plasma concentrations of thyroxine and tri-iodothyronine, whereas those of thyroid-stimulating hormone were not significantly changed. In addition, there were no dose-dependent changes in plasma concentrations of growth hormone and insulin-like growth factor-I in any dose group. These findings suggest that prenatal exposure to PCB 153 (GD 10-16, 16-64 mg/kg/day) may alter the thyroid status in rat offspring to some extent without affecting somatic growth or its related hormonal parameters.

Associations between prenatal exposure to polychlorinated biphenyls and neonatal thyroid-stimulating hormone levels in a Mexican-American population, Salinas Valley, California

BACKGROUND

Studies have reported that prenatal exposure to polychlorinated biphenyls (PCBs) may alter neurodevelopment in both humans and animals. Furthermore, prenatal exposure to some PCB congeners and commercial mixtures has been shown to decrease free and total thyroxine (T(4)) blood levels in animals. Because thyroid hormones (TH) are essential for normal neurologic development, it has been suggested that the deleterious neurodevelopmental effect of PCBs may occur through TH disruption. PCBs may in turn affect TH levels by inducing the microsomal enzyme uridinediphosphate glucuronosyltransferase (UDP-GT), which is involved in TH elimination.

OBJECTIVES

Our goals were to group PCB congeners based on their potential to induce microsomal enzymes in animals, and to examine the relationship between neonatal TSH levels and prenatal exposure to PCB congeners grouped according to their structure and potential mechanisms of action.

METHODS

We measured the concentration of 34 PCB congeners in serum samples collected from 285 pregnant women and the thyroid-stimulating hormone (TSH) levels in their children's blood collected shortly after birth.

RESULTS

We found no association between the sum of PCB congeners, the toxic equivalents, or structure-based groupings (mono- or di-ortho substituted congeners), and TSH blood concentration. However, we found a positive association between the sum of congeners suspected to be UDP-GT inducers (more specifically cytochrome P450 2B inducers) in animals and neonatal TSH levels. In individual congener analyses, PCBs 99, 138, 153, 180, 183, 187, 194, and 199 were positively associated with neonatal TSH levels after adjustment for covariates. PCBs 194 and 199 remained significant after adjustment for multiple hypothesis testing.

CONCLUSIONS

Our results support grouping PCB congeners based on their potential mechanism of action of enzyme induction when investigating associations with TH. Findings also suggest that PCBs affect TH homeostasis even at the low background level of exposure found in the CHAMA-COS (Center for the Health Assessment of Mothers and Children of Salinas) population.

Early embryonic exposure to polychlorinated biphenyls disrupts heat-shock protein 70 cognate expression in zebrafish

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that have documented neurological effects in children exposed in utero. To better define neuronally linked molecular targets during early development, zebrafish embryos were exposed to Aroclor 1254, a mixture of PCB congeners that are common environmental contaminants. Microarray analysis of the zebrafish genome revealed consistent significant changes in 38 genes. Of these genes, 55% (21) are neuronally related. One gene that showed a consistent 50% reduction in expression in PCB-treated embryos was heat-shock protein 70 cognate (Hsc70). The reduction in Hsc70 expression was confirmed by real-time polymerase chain reaction (PCR), revealing a consistent 30% reduction in expression in PCB-treated embryos. Early embryonic exposure to PCBs also induced structural changes in the ventro-rostral cluster as detected by immunocytochemistry. In addition, there was a significant reduction in dorso-rostral neurite outgrowth emanating from the RoL1 cell cluster following PCB exposure. The serotonergic neurons in the developing diencephalon showed a 34% reduction in fluorescence when labeled with a serotonin antibody following PCB exposure, corresponding to a reduction in serotonin concentration in the neurons. The total size of the labeled neurons was not significantly different between treated and control embryos, indicating that the development of the neurons was not affected, only the production of serotonin within the neurons. The structural and biochemical changes in the developing central nervous system following early embryonic exposure to Aroclor 1254 may lead to alterations in the function of the affected regions.

2,2',4,4'-Tetrachlorobiphenyl upregulates cyclooxygenase-2 in HL-60 cells via p38 mitogen-activated protein kinase and NF-kappaB

Polychlorinated biphenyls (PCBs) are ubiquitous, persistent environmental contaminants that affect a number of cellular systems, including neutrophils. Among the effects caused by the noncoplanar PCB 2,2',4,4'-tetrachlorobiphenyl (2244-TCB) in granulocytic HL-60 cells are increases in superoxide anion production, activation of phospholipase A(2) with subsequent release of arachidonic acid (AA) and upregulation of the inflammatory gene cyclooxygenase-2 (COX-2). The objective of this study was to determine the signal transduction pathways involved in the upregulation of COX-2 by 2244-TCB. Treatment of HL-60 cells with 2244-TCB led to increased expression of COX-2 mRNA. This increase was prevented by the transcriptional inhibitor actinomycin D in cells pretreated with 2244-TCB for 10 min. The increase in COX-2 mRNA was associated with release of (3)H-AA, phosphorylation of p38 and extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinases, increased levels of nuclear NF-kappaB and increased superoxide anion production. Bromoenol lactone, an inhibitor of the calcium-independent phospholipase A(2), reduced (3)H-AA release but had no effect on COX-2 mRNA, protein or activity. Pretreatment with SB-202190 or SB-203580, inhibitors of the p38 MAP kinase pathway, prevented the 2244-TCB-mediated induction of COX-2 and phosphorylation of p38 and ERK MAP kinases. These inhibitors did not alter (3)H-AA release. Treatment with PD 98059 or U 0126, inhibitors of the MAP/ERK (MEK) pathway, prevented the 2244-TCB-mediated activation of ERK but had no effect on COX-2 induction or p38 phosphorylation. 2244-TCB treatment did not affect c-Jun N-terminal kinase (JNK) phosphorylation. 2244-TCB exposure increased the amount of nuclear NF-kappaB. This increase was prevented by pretreatment with p38 MAP kinase inhibitors, but not by pretreatment with MEK inhibitors. Pretreatment with inhibitors of NF-kappaB prevented the 2244-TCB-mediated induction of COX-2 mRNA. 2244-TCB-mediated increases in superoxide anion were prevented by the NADPH oxidase inhibitor apocynin or the free radical scavenger 4-hydroxy TEMPO, but neither of these inhibitors affected the 2244-TCB-induced changes in COX-2 mRNA levels or (3)H-AA release. Taken together these data suggest that p38 MAP kinase-dependent activation of NF-kappaB is critical for the 2244-TCB-mediated upregulation of COX-2 mRNA.

Epidemiology of Parkinson's disease

This chapter discusses the epidemiology of Parkinson's disease (PD). Classically, PD refers to progressive parkinsonism caused by loss of pigmented aminergic brainstem neurons without an identifiable cause, while parkinsonism refers simply to the syndrome of bradykinesia, resting tremor, rigidity and postural reflex impairment. Over nearly two centuries, Parkinson's clinical description has provided the framework for clinical investigations, including epidemiologic ones. Descriptions of PD were limited to selected clinical settings until the middle of the 20th century. Since then, epidemiologic approaches have been used not only to investigate the population distribution of PD, but also as a way to glean clues as to the cause of this “idiopathic” disorder. Because PD is relatively infrequent, a large base population must be surveyed to identify sufficient numbers of cases for a study. In some instances, PD cases can be identified through health service rosters within defined geographic areas or in enumerated populations. In others, cases of PD are sought independently of the health care system, such as through door-to-door surveys. While the latter approach is theoretically least likely to exclude cases, the time and cost involved are also greatest using this approach.

Brain monoaminergic neurotransmission parameters in weanling rats after perinatal exposure to methylmercury and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB153)

The individual and joint effects of methylmercury (MeHg; 1 mg/kg body weight/day, GD7-PND7) and PCB153 (20 mg/kg body weight/day, GD10-GD16), administered orally to rat dams, were explored in 21-day-old rat offspring brain in terms of monoamine oxidase B (MAO-B) activity and regional content of dopamine (DA), serotonin (5-HT), 5-hydroxy-indole-3-acetic acid (5-HIAA) and homovanillic acid (HVA). Neither treatment altered MAO-B in striatum, hippocampus, cerebellum and cerebral cortex of female pups. In males the cerebellum displayed a significantly reduced enzyme activity (25-45%) following all treatments. Concerning biogenic amines, 5-HT levels were decreased by 30-50% in the cerebral cortex of males and females by PCB153 alone and combined with MeHg, without changes in 5-HIAA and dopaminergic endpoints. In cerebellum of all pups, MeHg enhanced 5-HIAA levels, whereas PCB153, either alone or combined with MeHg, did not affect this endpoint. In striatum, PCB153 reduced the content of DA, HVA and 5-HIAA (respective control values: 2-3; 60-80; 8-10 ng/mg protein) to a similar extent when administered alone or together with MeHg (20-40%). Perinatal exposure to MeHg and/or PCB153 results in regionally and/or gender-specific alterations in the central dopaminergic and serotonergic systems at weaning. The combined treatment with MeHg and PCB153 does not exacerbate the neurochemical effects of the individual compounds.

PCB congener-specific disruption of reproductive neuroendocrine function in Atlantic croaker

Exposure of Atlantic croaker to Aroclor 1254 has been shown to impair reproductive neuroendocrine function in this species. In addition, we have identified hypothalamic tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin synthesis, as a target of PCB neuroendocrine toxicity. A previous study in rats has implicated di-ortho-substituted non-coplanar PCB congeners in the inhibition of a similar enzyme, tyrosine hydroxylase, which is the rate-limiting enzyme in dopamine synthesis. Therefore, the present study was designed to investigate whether di-ortho-substituted congeners (PCB 47, PCB 153) or a coplanar congener (PCB 77) present in Aroclor 1254 could be responsible for the reproductive impairment observed in croaker exposed to the PCB mixture. Fish were exposed to PCB 47 and PCB 153 in the diet (0, 0.2 and 1.0 mg/kg body weight/day) for 30 days and to PCB 77 (0.01 and 0.1 mg/kg body weight/day) for 15 days. Neither PCB 47 nor PCB 153 altered hypothalamic TPH activity or gonadal growth at doses similar to the effective doses of the Aroclor 1254 mixture. Therefore, these ortho-substituted PCB congeners known to be neurotoxic in mammalian systems are unlikely to contribute to Aroclor 1254-induced reproductive neuroendocrine disruption in croaker. In contrast, PCB 77 significantly inhibited hypothalamic TPH activity and gonadal growth at doses much lower than the effective doses of Aroclor 1254. The results provide the first evidence for PCB congener-specific disruption of reproductive neuroendocrine function in a vertebrate species.

Fatty liver and hepatic function for residents with markedly high serum PCDD/Fs levels in Taiwan

This study was designed to examine the associations between serum polychtorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) levels and adverse hepatic-related health outcomes. Residents living in the vicinity of a closed pentachlorophenol (PCP) manufacturing factory (exposure area) and other areas nearby (control area) were identified from prior investigation of serum PCDD/Fs measurements. A total of 85 subjects were recruited for the study, 52 from exposure area and 33 from control, respectively. Average level of serum PCDD/Fs was 80.1 6 50.9 pg WHO-TEQ/g lipid for those residing in exposure area, and 25.5 6 18.2 in control area. Statistically higher odds ratio (ORs) for fatty liver and gamma-glutamyltransferase (GGT) activity was found in subjects with higher serum PCDD/Fs levels and high body mass index (BMI) as compared to those with lower PCDD/Fs levels and less BMI. Data suggest that dioxin exposure and high lipid content affect the prevalence of fatty liver in exposed subjects. Future study should be directed to prevent continuous exposure to environmental PCDD/Fs from the defunct PCP factory, and to characterize prospectively, with a larger study sample size, the potential long-term consequences on hepatic function associated with contaminant exposure.

Effect of anaesthetics[sol ]terminal procedures on neurotransmitters from non-dosed and aroclor 1254-dosed rats

Subtle effects of low-dose exposure to environmental toxicants may be altered or masked by an inappropriate choice of anaesthesia prior to manipulation or termination of experimental animals. This study was designed to investigate effects of various anaesthetics and terminal procedures on neurotransmitters from male Sprague-Dawley rats. Significant changes in neurotransmitters were observed in the caudate nucleus, nucleus accumbens, hippocampus and substantia nigra but not the frontal cortex upon exposure to isoflurane, an Equithesin-like mixture or carbon dioxide relative to control animals that were decapitated without anaesthesia. Terminal use of any of these three anaesthetics also masked or altered some of the changes induced by exposure to Aroclor 1254. These results suggest that it is critical to avoid anaesthetizing experimental animals and that decapitation is the preferred method for euthanasia when conducting neurochemical studies.

Polychlorinated biphenyls are not substrates for the multidrug resistance transporter-1

The multidrug resistance (MDR) transporter is a phosphorylated glycoprotein (P-gp) that has been implicated in the efflux of a large variety of xenobiotics, thereby protecting vital organs. This study examines the hypothesis that the multidrug resistance transporter is involved in restricting the entry of polychlorinated biphenyls (PCBs) into the brain. Three test systems were used. First, the ATPase activity of the human P-gp was measured as an indicator of the interaction of PCBs with the MDR transporter. PCB congeners and metabolites included in the study were PCB 153, PCB 169, PCB 77, and the 4-hydroxy and 4,4'-dihydroxy metabolites of PCB 77. An increase in ATPase activity was observed for all the PCBs tested except the 4-hydroxy metabolite of PCB 77. Second, we studied the transport of (14)C-PCB 77 and (14)C-PCB153 in a cell-culture model using porcine kidney cells expressing the human MDR1 or the mouse mdr1a gene and compared it to the transport in control cells. No difference in directional transport due to P-gp was observed with either of the congeners in any of the cell lines. Finally, the distribution pattern of (14)C-PCB 77 in mdr1a knockout mice and genetically matched wild-type mice was measured. No significant differences in tissue distribution, especially in the brain tissue, were observed between wild-type and mdr1a knockout mice. These results suggest that some PCB congeners can bind to the MDR1 transporter; however, they may not be transported by it.

Attention-deficit/hyperactivity disorder (ADHD) behaviour explained by dysfunctioning reinforcement and extinction processes

Inattentiveness, overactivity and impulsiveness are presently regarded as the main clinical symptoms of attention-deficit/hyperactivity disorder (ADHD). Inattention is, however, a characteristic of most psychiatric disorders. It is argued that the ADHD Inattentive subtype may have heterogeneous origins and be qualitatively different from the ADHD Hyperactive/Impulsive subtype. At the neurobiological level, ADHD symptoms may to a large extent be caused by a dysfunctioning dopamine system: A dysfunctioning meso-limbo-cortical dopamine branch will produce altered reinforcement and extinction processes, on a behavioural level giving rise to deficient sustained attention, hyperactivity, motor and cognitive impulsiveness. A dysfunctioning nigro-striatal dopamine branch will cause 'extrapyramidal' symptoms. Our model disentangles the behaviours usually explained by 'executive functions' into cognitive impulsiveness, motor impulsiveness and deficient motor control. The various dopaminergic branches may not be equally dysfunctional in all individuals with ADHD. Etiologically, dopamine dysfunctioning will probably mainly be genetically determined while sometimes be induced by environmental factors like drugs of abuse or pollutants, which may explain geographical differences in prevalence rates.

Effects of polychlorinated biphenyls on development and reproduction

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article, which constitutes the release of an important section of the Toxicological Profile for Polychlorinated Biphenyls (ATSDR 2000) into the scientific literature, focuses on the developmental and reproductive effects of this group of synthetic organic chemicals (PCBs) in humans and animals. Information on other health effects, toxicokinetics, mechanisms of toxicity, biomarkers, interactions, chemical and physical properties, potential for human exposure, and regulations and advisories is detailed in the profile. Interested readers are encouraged to consult the original toxicological profile for more information. Profiles can be requested from ATSDR's Information Center by telephone (1-888-42-ATSDR [1-888-422-8737] or E-mail: (atsdric@cdc.gov).

Disruption of neuroendocrine control of luteinizing hormone secretion by aroclor 1254 involves inhibition of hypothalamic tryptophan hydroxylase activity

Mechanisms governing the effect of polychlorinated biphenyl (PCB) toxicity on hypothalamic serotonergic function and the neuroendocrine system controlling LH secretion were investigated in Atlantic croaker (Micropogonias unulatus) exposed to the PCB mixture Aroclor 1254 (1 microg x g body weight(-1) x day(-1)) in the diet for 30 days. PCB treatment caused a decrease in hypothalamic 5-hydroxytryptamine (5-HT) concentrations and significant inhibition of hypothalamic tryptophan hydroxylase (TPH), the rate-limiting enzyme in 5-HT synthesis, but did not alter the activity of monoamine oxidase, the catabolic enzyme. Further, PCB treatment caused significant decreases in GnRH content in the preoptic-anterior hypothalamic area. Significant decreases in pituitary GnRH receptor concentrations and the LH response to the GnRH analogue (GnRHa) were also observed in PCB-exposed fish, possibly as a consequence of a decline in GnRH release. The possible association between impaired serotonergic and neuroendocrine functions after PCB treatment was explored using serotonergic drugs. Treatment of croaker with p-chlorophenylalanine, an irreversible TPH inhibitor, mimicked the effects of PCB on the GnRH system and the LH response to GnRHa. Bypassing the TPH-dependent hydroxylation step with the administration of 5-hydroxytryptophan restored 5-HT to control levels and prevented the deleterious effects of PCB on the neuroendocrine parameters. Moreover, slow-release GnRH implants prevented the PCB-induced decline in GnRH receptors and restored the LH response to GnRHa, suggesting that GnRH therapy can reverse PCB-induced disruption of LH secretion. These results demonstrate that TPH is one of the targets of PCB neurotoxicity and indicate that a decrease in 5-HT availability in PCB-exposed croaker results in disruption of the stimulatory 5-HT/GnRH pathway controlling LH secretion.

Effects of polychlorinated biphenyls on the nervous system

The neurological effects of polychlorinated biphenyls (PCBs) have been extensively investigated in humans and in animals. The main focus in human studies has been on the effects in neonates and young children, although studies of adults have also been conducted. A great deal of concern exists that even low levels of PCBs transferred to the fetus across the placenta may induce long-lasting neurological damage. Because PCBs are lipophilic substances, there is also concem that significant amounts might be transferred to nursing infants via breast milk. Studies in humans who consumed large amounts of Great Lakes fish contaminated with environmentally persistent chemicals, including PCBs. have provided evidence that PCBs are important contributors to subtle neurobehavioral alterations observed in newborn children and that some of these alterations persist during childhood. Some consistent observations at birth have been motor immaturity and hyporeflexia and lower psychomotor scores between 6 months and 2 years old. There is preliminary evidence that highly chlorinated PCB congeners, which accumulate in certain fish, are associated with neurobehavioral alterations seen in some newbom children. Subtle neurobehavioral alterations have also been observed in children bom to mothers in the general population with the highest PCB body burdens. Because of the limitations of epidemiological studies, these effects cannot be attributed entirely to PCB exposure. In one general population study, there was strong evidence that dioxins, as well as PCBs, were contributors to the neurobehavioral effects seen in exposed children. Children born to women who accidentally consumed rice oil contaminated with relatively high amounts of PCBs and chlorinated dibenzofurans (CDFs) during pregnancy also had neurodevelopmental changes. Studies in animals support the human data. Neurobehavioral alterations have been also observed in rats and monkeys following prenatal and/or postnatal exposure to commercial Aroclor mixtures, defined experimental congener mixtures, single PCB congeners, and Great Lakes contaminated fish. In addition, monkeys exposed postnatally to PCB mixtures of congeneric composition and concentration similar to that found in human breast milk showed learning deficits long after exposure had ceased. A few other generalizations can be made from the data in animals. It appears that ortho-substituted PCB congeners are more active than coplanar PCBs in modifying cognitive processes. In addition, one effect observed in both rats and monkeys--deficits on delayed spatial alternation--has been known to be induced by exposure to ortho-substituted PCBs, defined experimental mixtures, and commercial Aroclors. Both dioxin-like and non-dioxin-like PCB congeners have been shown to induce neurobehavioral alterations in animals. Changes in levels of neurotransmitters in various brain areas have also been observed in monkeys, rats, and mice. Of all the observed changes, the most consistent has been a decrease in dopamine content in basal ganglia and prefrontal cortex, but further research is needed before specific neurobehavioral deficits can be correlated with PCB-induced changes in specific neurotransmitters in specific brain areas.

Dioxin-like and non-dioxin-like toxic effects of polychlorinated biphenyls (PCBs): implications for risk assessment

Polychlorinated biphenyls (PCBs) are persistent, bioaccumulative, and toxic contaminants in the environment. Individual PCB congeners exhibit different physicochemical properties and biological activities that result in different environmental distributions and toxicity profiles. The variable composition of PCB residues in environmental matrices and their different mechanisms of toxicity complicate the development of scientifically based regulations for the risk assessment. In this article various approaches for the assessment of risks of PCBs have been critically examined. Recent developments in the toxic equivalency factor (TEF) approach for the assessment of toxic effects due to dioxin-like PCBs have been examined. PCB exposure studies that describe non-dioxin-like toxic effects, particularly neurobehavioral effects and their effective doses in animals were compiled. A comparative assessment of effective doses for dioxin-like and non-dioxin-like effects by PCBs has been made to evaluate the relative significance of non-ortho-and ortho-substituted PCBs in risk assessment. Using mink as an example, relative merits and implications of using TEF and total PCB approaches for assessing the potential for toxic effects in wildlife was examined. There are several advantages and limitations associated with each method used for PCB risk assessment. Toxic effects due to coplanar PCBs occur at relatively smaller concentrations than those due to non-dioxin-like PCBs and therefore the TEF approach derives the risk assessment of PCBs, in the environment. The need for the refinement of TEF approach for more accurate assessment of risks is discussed.

Interactive effects of three structurally different polychlorinated biphenyls in a rat liver tumor promotion bioassay

Interactive effects between the non-ortho-substituted 3,3', 4,4', 5-pentachlorobiphenyl (PCB126), the mono-ortho-substituted 2,3,3',4, 4'-pentachlorobiphenyl (PCB105), and the di-ortho-substituted 2,2',4, 4',5,5'-hexachlorobiphenyl (PCB153) were studied in an initiation/promotion bioassay. Female Sprague-Dawley rats were injected with 30 mg/kg ip of N-nitrosodiethylamine 24 h after partial hepatectomy. Five weeks later, weekly sc administrations of the three PCBs in 15 systematically selected dose combinations started. After 20 weeks of administration, the animals were killed and the livers were analyzed for areas expressing placental glutathione-S-transferase as a marker of preneoplastic foci. In addition, concentration of liver and kidney retinoids and plasma retinol was analyzed, as well as body and organ weights, plasma transaminases, and induction of hepatic cytochrome P450 1A1/2 (CYP1A1/2) and CYP2B1/2 activities. Data were analyzed with a multivariate method. At the doses applied in this study, weak antagonism was observed between PCB126 and PCB153 for effects on volume fraction of foci, number of foci/cm3, concentration of plasma retinol and liver retinoids, relative liver weight, and induction of CYP2B1/2 activity. Weak antagonism was also observed between PCB126 and PCB105 for effects on volume fraction of foci, number of foci/cm3, and plasma retinol concentration. No interactions other than pure additivity were observed between PCB105 and PCB153. Synergism was not observed within the dose ranges investigated in this study. Knowledge of interactive effects is important for risk assessment of environmental mixtures of dioxin-like compounds. Antagonism between congeners generally results in risk assessments that overestimate human risk. The significance to human risk assessment of the relatively weak antagonism observed in this study is however unclear, considering many other uncertainties involved in the toxic equivalency factor (TEF) concept. A change of the TEF concept for risk assessments of dioxin-like substances is not motivated based on the results of this study.

Subchronic toxicity of 2,2',3,3',4,4'-hexachlorobiphenyl in rats

The subchronic toxicity of 2,2',3,3',4,4'-hexachlorobiphenyl (PCB 128) was investigated in rats following dietary exposure at 0, 0.05, 0.5, 5, or 50 ppm for 13 wk. The growth rate was not affected by treatment and no apparent clinical signs of toxicity were observed. There was a significant increase in liver weight in the 50 ppm females. The liver ethoxyresorufin deethylase (EROD) activity was increased by five- and fourfold in the highest dose males and females, respectively, while aminopyrine demethylase (ADPM) activity was significantly increased only in the highest dose females. Liver vitamin A was significantly reduced in the highest dose females. No other biochemical or hematological effects were observed. Treatment-related histopathological changes were seen in the thyroid and liver, and to a lesser extent in the bone marrow and thymus. Residue data showed a dose-dependent accumulation of PCB 128 in the following tissues: fat, liver, kidney, brain, spleen, and serum, with the highest concentration being found in fat followed by liver and kidney. Based on these data, the no-observable-adverse-effect level of PCB 128 was judged to be 0.5 ppm in diet or 42 micrograms/kg body weight.

Toxicity of PCB 105 in the rat liver: an ultrastructural and biochemical study

PCB 105 (2,3,3',4,4'-pentachlorobiphenyl) congener was fed to weanling Sprague-Dawley rats in a diet combined with 4% corn oil. The animals were distributed randomly into 10 groups, each of which contained 10 males and 10 females, and rats in 8 groups received diets containing PCB at concentrations of 0.05, 0.5, 5, and 50 ppm. Animals in the other 2 groups served as controls. After 13 weeks, the animals were humanely killed and liver samples were obtained and prepared for transmission electron microscopy. Ultrastructural alterations revealed in the hepatocytes of animals fed the PCB included smooth endoplasmic reticulum proliferation, atypical mitochondrial cristae, and augmentation of peroxisome numbers (in animals fed high PCB concentrations). Biochemical alterations were estimated by using hepatic microsomal pentoxyresorufin-O-dealkylase (PROD) and ethoxyresorufin-O-deethylase (EROD) activities. A dose-dependent increase in EROD and PROD activities was discovered; only in the animals of highest PCB dose group, however, was EROD found to be significant (p < .05). Based on our previous work, this congener is relatively less toxic than PCB 126, 118, and 153 and is similar in toxicity to 156.