Polychlorinated biphenyl mixtures (Aroclors) inhibit LPS-induced murine splenocyte proliferation in vitro

New insight into the perplexing toxic features of PCBs: A study of nephrotoxicity in an animal model

The present study investigated the effects of PCBs on the rat kidneys with attention given to the determination critical effect dose (CED) using the Benchmark dose (BMD) approach. Male albino Wistar rats (7 animals per group) were given by oral gavage Aroclor 1254 dissolved in corn oil at doses of 0.0, 0.5, 1, 2, 4, 8, or 16 mg/kg b.w./day for 28 days. The PCB nephrotoxicity was manifested by a dose-dependent changes in serum urea levels. The study has also revealed PCB-induced oxidative stress induction in kidneys. The observed nephrotoxic effects can be partly explained by oxidative damage of lipids and proteins in the kidneys due to observed reduced CuZnSOD activity and disturbances in antioxidant protection. Аll the renal oxidative stress parameters showed dependence on PCB oral doses as well as internal, measure kidney PCB levels. Calculated BMDL values were lower than estimated no observed adverse effect levels (NOAEL) based on the study, suggesting the importance of BMD approach use in future risk assessment.

Toxic effects of polychlorinated biphenyls (Aroclor 1254) on human sperm motility

Polychlorinated biphenyls (PCBs) are common environmental contaminants that represent a considerable risk to reproductive toxicity in exposed human populations. Although some experimental studies have suggested an association between the levels of PCBs and semen quality, the direct effects of PCBs on human sperm parameters remain largely unexplored. To this aim, a short-term in vitro incubation experiment that better imitated the putative exposure of sperm to Aroclor 1254 (a commercial PCB mixture) in male reproduction tissue was conducted. Human sperm were incubated with various concentrations (0, 1, 5, or 25 mg l-1) of Aroclor 1254 for different amounts of time (3 and 6 h) in vitro. Sperm motility parameters were analyzed with computer-assisted sperm analysis (CASA). The proportion of sperm with high mitochondrial membrane potential (ΔΨm) and the levels of intracellular reactive oxygen species (ROS) were detected to explore the probable cause of sperm impairment. Human sperm exposed to continuous Aroclor 1254 exhibited: (i) reduced sperm motility and kinematic parameters, (ii) a proportion of sperm with high ΔΨm that decreased in a dose-dependent manner (P < 0.05), and (iii) increased levels of ROS compared with controls (P < 0.05). In conclusion, Aroclor 1254 can decrease sperm motility, which may culminate in increased ROS and general mitochondrial dysfunction, thus affecting the fertilization potential of sperm. Our findings suggest a broader understanding of the effect of Aroclor 1254 on human sperm.

Cadmium and chlorpyrifos inhibit cellular immune response in spleen of rats

Cadmium (Cd) and chlorpyrifos (CPF) are common pollutants coexisting in the environment, and both of them have been reported to have immunotoxicity to organisms. However, the joint effects of these two chemicals on the immune system are still unknown. In this study, we used CdCl₂ and CPF to study their combined effects on immune functions in the spleen of rats. In in vivo experiments, SD rats were exposed to different doses of CdCl₂ (0.7 and 6 mg kg^-1 body weight/day) and CPF (1.7 and 15 mg kg^-1 body weight/day) or their combinations for consecutive 28 days. The proliferation and cytokine production ability of the splenocytes isolated from the treated animals were assessed. In in vitro experiments, we used different concentrations of CdCl₂ and CPF to treat concanavalin A (Con A)-induced splenocytes isolated from untreated rats. We found that the combination of CPF and high dose of CdCl₂ had a synergistic inhibitory effect on production of IFN-γ by spleen cells induced by Con A. The in vitro results showed that two chemicals had different effects on the cell proliferation and cytokine production depending on the exposure doses and time. This result suggests that exposure to both CdCl₂ and CPF at the environmentally-relevant low dose may be potentially more hazardous than exposure to each individual toxicant.

Effects of co-exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and polychlorinated biphenyls on nonalcoholic fatty liver disease in mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) are persistent organic pollutants which coexist in environment, and human are co-exposed to these chemicals. Our present study was aimed to investigate the possible enhanced nonalcoholic fatty liver disease (NAFLD) in ApoE(-/-) mice co-exposed to TCDD and PCBs and to reveal the potential mechanisms involved in. Male ApoE(-/-) mice were exposed to TCDD (15 μg/kg) and Aroclor1254 (55 mg/kg, a representative mixture of PCBs) alone or in combination by intraperitoneal injection four times over a 6-week period. Those mice co-exposed to PCBs and TCDD developed serious liver steatosis, necrosis, and inflammatory stimuli. Interestingly, all treatment induced hepatic cytochrome P450 1A1 (CYP1A1) expression, but the maximal level of CYP1A1 was not observed in the co-exposure group. Furthermore, microarray analysis by ingenuity pathway analysis software showed that the nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response pathway was significantly activated following co-exposure to TCDD and PCBs. Our data demonstrated that co-exposure to TCDD and PCBs markedly worsen NAFLD in ApoE(-/-) mice.

Polychlorinated biphenyls as oxidative stress inducers in liver of subacutely exposed rats: implication for dose-dependence toxicity and benchmark dose concept

Hepatotoxicity is one of the well-documented adverse health effects of polychlorinated biphenyls (PCBs)-persistent organic pollutants widely present in the environment. Although previous studies suggest possible role of oxidative stress, the precise mechanisms of PCB-induced ROS production in liver still remain to be fully assessed. The aim of this study was to evaluate the effects of different doses of PCBs on the parameters of oxidative stress and to investigate whether these effects are dose dependent. Furthermore, a comparison between calculated benchmark doses (BMD) and estimated NOAEL values for investigated parameters, was made. Six groups of male albino Wistar rats (7 animals per group) were receiving Aroclor 1254 dissolved in corn oil in the doses of 0.5, 1, 2, 4, 8, 16 mg PCBs/kg b.w./day by oral gavage during 28 days while control animals were receiving corn oil only. The following parameters of oxidative stress were analyzed in liver homogenates: superoxide dismutase activity, glutathione, malondialdehyde (MDA) and total protein thiol levels. Hepatic enzymes AST, ALT, ALP and protein albumin were also determined in serum as clinical parameters of liver function. Collected data on the investigated parameters were analyzed by the BMD method. The results of this study demonstrate that subacute exposure to PCBs causes induction of oxidative stress in liver with dose-dependent changes of the investigated parameters, although more pronounced adverse effects were observed on enzymatic than on non-enzymatic components of antioxidant protection. The obtained values for BMD and NOAEL support the use of BMD concept in the prediction of health risks associated with PCBs exposure. Furthermore, our results implicate possible use of MDA in PCBs risk assessment, since MDA was the most sensitive investigated parameter with calculated low critical effect dose of 0.07 mg/kg b.w.

Aroclor 1254 impairs the development of ovarian follicles by inducing the apoptosis of granulosa cells

Aroclor 1254 impairs the development of follicle (primordial follicle excluded), possibly via the induction of apoptosis mainly in granulosa cells.

Effects of Aroclor 1254 on in vivo oocyte maturation in the mouse

Polychlorinated biphenyls (PCBs) are stable, lipophilic compounds that accumulate in the environment and in the food chain. Though some studies provided evidence that PCBs had adverse effects on reproductive function, most of these results were from in vitro models. Therefore we investigated the effect of Aroclor 1254 (a commercial PCBs mixture) treatments on in vivo maturation and developmental potential of mouse oocytes. In the present study, female ICR mice were treated with different doses (12.5, 25 and 50 mg/kg) of Aroclor 1254 (a commercial PCB mixture) once every 72 hours by intraperitoneal injection for 9 days. After three treatments of Aroclor 1254, the mice were superovulated to collect oocytes one day after the last exposure. The effects of Aroclor 1254 on oocyte maturation, fertilization, and preimplantation embryonic development were investigated. Immunofluorescence-stained oocytes were observed under a confocal microscope to assess the effects of Aroclor 1254 on spindle morphology. Parthenogenic activation and the incidence of cumulus apoptosis in cumulus-oocyte complexes were observed as well. Oocytes exposed to different doses of Aroclor 1254 in vivo were associated with a significant decrease in outgrowth potential, abnormal spindle configurations, and the inhibition of parthenogenetic activation of ovulated oocytes. Furthermore, the incidence of apoptosis in cumulus cells was increased after exposed to Aroclor 1254. These results may provide reference for the treatment of reproductive diseases such as infertility or miscarriage caused by environmental contaminants.

The Relationship Between Noncoplanar PCB-Induced Immunotoxicity and Hepatic CYP1A Induction in a Fish Model

Abundant literature exists demonstrating the immunomodulating effects of polychlorinated biphenyls (PCBs). To date, most of the research has focused on dioxin-like coplanar PCB congeners because of their high affinity for the aryl hydrocarbon receptor (AhR) and cytochrome P450-inducing capability. For this study, the impact of two structurally different PCB congeners on the immune responsiveness of bluegill sunfish (Lepomis macrochirus) was examined to evaluate the immunotoxic potential of each congener (as separate entities) and to relate effects on immune function with hepatic CYP1A induction. Fish received a single intraperitoneal injection of the: coplanar congener, PCB 126 (0.01 or 1.0 mug/g BW); noncoplanar PCB 153 (5.0 or 50.0 mug/g BW); or, the corn oil vehicle. PCB-induced effects on innate and cell-mediated immune parameters, and on hepatic CYP1A protein induction were evaluated in fish sacrificed 1, 3, 7, 14 or 21 days post-injection. In the absence of CYP1A induction, PCB 153 increased kidney phagocyte-mediated superoxide production 3 d post-injection, and at the highest dose suppressed B- and T-lymphocyte proliferation after 3 and 7 days, respectively. Treatment of fish with PCB 126 had no effect on oxyradical production, but altered B-lymphocyte proliferation after 1 day, also in the absence of CYP1A induction. Hepatic CYP1A was only induced in fish exposed to the highest PCB 126 dose; protein induction appeared at 3 d post-injection and persisted for up to 21 days. Taken together, these results demonstrate that exposure to different PCB congeners can alter immune function in the absence of CYP1A induction, suggesting that mechanisms other than the AhR pathway may play a role in PCB-induced immunotoxicity, particularly for the noncoplanar congeners.

Enhanced hepatotoxicity induced by repeated exposure to polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin in combination in male rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs) are among persistent polyhalogenated aromatic hydrocarbons that exist as complex mixtures in the environment worldwide. The present study was attempted to investigate the hepatotoxicity following repeated exposure to TCDD and PCBs in combination in male rats, and to reveal the involvement of potential mechanisms. Male Sprague-Dawley rats were exposed to TCDD (10 microg/kg) and Aroclor 1254 (10 mg/kg, a representative mixture of PCBs) alone or in combination by intragastric administration. After 12-day exposure, all treatments produced significant hepatotoxicity as characterized by changes of plasma biochemistry and histopathological changes. These effects were more prominent in the combined group. Furthermore, all treatments induced hepatic cytochrome P450 1A1 (CYP1A1) expression, and the maximal level of CYP1A1 expression was observed in the combined group, as in the case of the most severe hepatotoxicity evoked by the combined exposure. These findings indicated that the hepatotoxicity induced by TCDD and Aroclor 1254 might be ascribed to the high expression of hepatic CYP1A1. The present study demonstrates the enhanced hepatotoxicity after exposure to TCDD and PCBs in combination in rats.

Polybrominated Diphenyl Ethers Orally Administration to Mice Were Tansferred to Offspring during Gestation and Lactation with Disruptions on the Immune System

BACKGROUND

The present study was undertaken to examine the immunological effects of pentabrominated diphenyl ether (penta-BDE) and decabrominated diphenyl ether (deca-BDE) on the immune system of the dams and the developmental immune system of the offsprings.

METHODS

In this study, mated female C57BL/6J mice were orally administered penta-BDE, deca-BDE or corn oil for 5 weeks, from gestational day 6 to lactational day 21.

RESULTS

The body weight of PND21 exposed to penta-BDE was significantly decreased relative to control mice, but that of post-natal day 63 (PND63) were recovered. Orally dosed dams with penta-BDE had significantly smaller absolute and relative spleen masses than control mice. Absolute and relative spleen and thymus masses of PND21 exposed to penta-BDE were significantly decreased over control. The exposure of dams and PND21 with penta-BDE reduced the number of splenocytes and thymocytes. As results of hematologic analysis, percentage WBC and percentage neutrophils increased in dams with deca-BDE. Splenic T cell proliferation in dams and PND21 exposed to penta-BDE was increased, and there were no significant difference in splenic B cell proliferation in all treatment groups. As results of flow cytometric analysis of splenocyte, percentage total T cell, Th cell and Tc cell in PND21 exposed to penta-BDE was slightly increased, and percentage macrophage in dams and PND21 exposed to deca-BDE was decreased. The ELISA results of antibody production show no significant difference in all treatment groups relative to controls.

CONCLUSION

These results imply that PBDEs given to the dam were transferred to the offspring during gestation and lactation, and PBDEs transferred from the dam affect immune system of offspring.

Effects of PCBs 52 and 77 on Th1/Th2 Balance in Mouse Thymocyte Cell Cultures

Polychlorinated biphenyls (PCBs) are industrial chemicals that have been released into the environment, resulting in widespread and persistent contamination. PCBs exist as 209 different congeners depending on the chlorine substitution on the biphenyl rings, and the physical properties and toxic effects of different PCB congeners are structure-dependent. We have tested an ortho-substituted, noncoplanar congener, 2,2',5,5'-tetrachlorobiphenyl (PCB 52), and a non-ortho-substituted coplanar congener, 3,3',4,4'-tetrachlorobiphenyl (PCB 77), for their effects on the T helper 1 (Th1) and T helper 2 (Th2) lymphocyte balance. The experiments were performed in 10 microg/ml concanavalin A (Con A)-stimulated and nonstimulated thymocytes for determination of cytokine production profiles. Interferon-gamma (produced by Th1 cells) and interleukin (IL)-10 (produced by Th2 cells) concentrations were measured in the supernatants at 12 and 24 hr after treatment with PCBs. PCBs 52 and 77 caused significant increases in interferon-gamma levels at 12 and 24 hr in both Con A-stimulated and nonstimulated media. IL-10 levels were significantly reduced at two interval periods by PCBs 52 and 77 in cultures with and without Con A. Our results show that the cytokine production profile was significantly shifted to Th1 by both ortho-substituted and coplanar PCB congeners in mouse thymocyte cultures.

Neonatal bone marrow transplantation of ADA-deficient SCID mice results in immunologic reconstitution despite low levels of engraftment and an absence of selective donor T lymphoid expansion

Adenosine deaminase (ADA)-deficient severe combined immune deficiency (SCID) may be treated by allogeneic hematopoietic stem cell transplantation without prior cytoreductive conditioning, although the mechanism of immune reconstitution is unclear. We studied this process in a murine gene knockout model of ADA-deficient SCID. Newborn ADA-deficient pups received transplants of intravenous infusion of normal congenic bone marrow, without prior cytoreductive conditioning, which resulted in long-term survival, multisystem correction, and nearly normal lymphocyte numbers and mitogenic proliferative responses. Only 1% to 3% of lymphocytes and myeloid cells were of donor origin without a selective expansion of donor-derived lymphocytes; immune reconstitution was by endogenous, host-derived ADA-deficient lymphocytes. Preconditioning of neonates with 100 to 400 cGy of total body irradiation before normal donor marrow transplant increased the levels of engrafted donor cells in a radiation dose-dependent manner, but the chimerism levels were similar for lymphoid and myeloid cells. The absence of selective reconstitution by donor T lymphocytes in the ADA-deficient mice indicates that restoration of immune function occurred by rescue of endogenous ADA-deficient lymphocytes through cross-correction from the engrafted ADA-replete donor cells. Thus, ADA-deficient SCID is unique in its responses to nonmyeloablative bone marrow transplantation, which has implications for clinical bone marrow transplantation or gene therapy.

Effects of organochlorines, individually and in mixtures, on B-cell proliferation in marine mammals and mice

Organochlorines (OC) are lipophilic and stable, and therefore accumulate in tissues of top predators, such as marine mammals. While the immunomodulatory effects of individual OC have been studied in lab animals, their effects in other species (such as marine mammals) and the possible interactions between chemicals in mixtures are not well understood. This study investigated the immunomodulatory effects of four polychlorinated biphenyls (PCB, IUPAC numbers 138, 153, 169, and 180), as well as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), individually and in mixtures, in marine mammals and mice. Mitogen-induced B lymphocyte proliferation was mostly modulated by non-coplanar PCBs, for which general mechanisms underlying toxicity are poorly understood. Simple additive effects of OC in mixtures were found only in mice, while both synergistic and antagonistic interactions between OC were found in marine mammals. The toxic equivalency (TEQ) approach, which is currently used to assess the dioxin-like toxicity of OC mixtures, failed to predict immunotoxicity in mice and marine mammals, likely due to the complexity of interactions between OC and effects via dioxin-independent pathways. The commonly used mouse model failed to predict the immunotoxicity due to OC in the marine mammals tested. In addition, clustering data suggested that phylogeny might not help predict the toxicity of OC. Lymphoproliferative response was modulated in most species tested suggesting the possibility of increased susceptibility to infectious diseases in these animals. These findings may be helpful in more accurately characterizing the immunotoxic potential of OC in different target species and help in more relevant risk assessment.

Non-coplanar PCBs induce calcium mobilization in bottlenose dolphin and beluga whale, but not in mouse leukocytes

Polychlorinated biphenyls (PCBs) have been demonstrated to modulate marine mammal immune functions; however, the underlying mechanisms involved are poorly understood. Cytosolic calcium (Ca2+) is an important second messenger involved in numerous leukocyte functions. The direct effects of in vitro exposure to PCBs on Ca2+ mobilization were evaluated in leukocytes isolated from bottlenose dolphins, beluga whales, and B6C3F1 mice. Concentration- and time-response experiments with three non-coplanar PCBs (138, 153, 180), one coplanar PCB (169), and TCDD were tested. Exposure to the three non-coplanar PCBs significantly increased cytosolic Ca2+ in dolphin neutrophils, while PCB 180 significantly increased cytosolic Ca2+ in beluga neutrophils. Two non-coplanar PCBs (138 and 153) significantly increased Ca2+ in beluga monocytes, yet the response was delayed compared to that in neutrophils. Neither PCBs nor TCDD increased cytosolic Ca2+ in mouse neutrophils or monocytes. In experiments with Ca2+-free medium, only PCB 153 increased cytosolic Ca2+ in dolphin neutrophils, though the increase was less than that observed with Ca2+-supplemented medium, suggesting that extracellular Ca2+ was the predominant source for the rise in cytosolic Ca2+. Furthermore, in cells incubated with Ca2+-free medium, a significant increase in cytosolic Ca2+ was induced by thapsigargin following PCB exposure, indicating that intracellular Ca2+ was available, yet not mobilized by the PCBs, and further suggesting that PCBs mobilize extracellular Ca2+. These results demonstrate for the first time the direct effects of non-coplanar PCBs on Ca2+ mobilization in marine mammals, which may be involved in the modulation of phagocytosis previously observed in these species.

Immunomodulatory effects of in vitro exposure to organochlorines on T-cell proliferation in marine mammals and mice

Marine mammals bioaccumulate various environmental contaminants such as organochlorines (OCs), which biomagnify via the food web. While the immunomodulatory effects of individual OCs have been studied, the effects of mixtures are not well understood. The immunomodulatory effects of polychlorinated biphenyl (PCB) 138, 153, 169, and 180 as well as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and all possible mixtures were examined in marine mammals and mice. Lymphocyte proliferation was significantly modulated by OCs in all species tested, mostly by non-coplanar PCBs, as shown using regression analyses. Correlation analyses showed significant correlations (interpreted as additive effects) between OCs in mice, killer whales, and Steller sea lions. Nonadditive synergistic and antagonistic interactions between OCs were detected in most of the species tested. Toxic equivalency (TEQ) values used for OC toxicity assessment failed to predict the immunomodulatory effects measured in mice and marine mammals. The commonly used mouse model failed to predict immunomodulatory effects in other species. Clustering data suggested that phylogeny does not predict toxicity of OCs. Overall, our data suggest the presence of species-specific sensitivities to different mixtures, in which OCs interactions may be complex and that may exert their effects through dioxinlike or dioxin-independent pathways. Lastly, lymphocyte proliferation, an important part of adaptive immunity, was significantly modulated in mice and marine mammals, suggesting the possibility of increased susceptibility to diseases. These findings will be useful to better characterize the risk associated with OC exposure and possibly lead to new conservation and management strategies.

Non-coplanar PCB-mediated modulation of human leukocyte phagocytosis: a new mechanism for immunotoxicity

Organochlorine (OC) contaminants, notably polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are ubiquitous in all ecosystems and found in the tissues of humans and wildlife. Although the immunotoxicity of coplanar, dioxinlike PCBs is well documented, the adverse effects exerted by non-coplanar, non-dioxinlike PCBs have received little attention. Direct causal relationship between PCB and dioxin exposure and the observed detrimental effects on the immune system has yet to be fully established in humans. The immunomodulatory potential of toxic coplanar PCB 169 and TCDD and abundant non-coplanar PCBs 138, 153, and 180 on human leukocyte phagocytosis, an important innate immune function that initiates the clearance of pathogens, was tested upon in vitro exposure. Mixture and concentration-response experiments demonstrated a suppression of phagocytosis by non-coplanar PCBs suggesting a previously unrecognized aryl hydrocarbon receptor (AhR)-independent pathway. Regression analysis revealed that reduction of phagocytosis was mostly explained by the non-coplanar congeners. The effects on phagocytosis could not be accurately predicted by either the currently used toxic equivalence (TEQ) approach or the mouse model, thus undermining the use of the traditional models in the risk assessment for OC mixtures containing non-coplanar congeners. Our results are cause for concern as they suggest an AhR-independent pathway through which non-coplanar PCBs modulate phagocytosis, the immune system's first line of defense, possibly increasing the risk to developing infectious disease.

PCBs and TCDD, alone and in mixtures, modulate marine mammal but not B6C3F1 mouse leukocyte phagocytosis

Increasing evidence has supported the general hypothesis that organochlorines (OC) can produce immunotoxic effects in marine mammals. One important innate defense mechanism is phagocytosis, the ability of cells to ingest extracellular macromolecules. The present study is aimed at characterizing the immunomodulatory potential of mixtures of OCs on phagocytosis compared to that of individual compounds in different species of marine mammals and mice, the traditional model to study mammalian immunotoxicity. The ability of peripheral blood neutrophils and monocytes to engulf fluorescent microspheres was evaluated using flow cytometry. The immunomodulatory effects of three non-coplanar polychlorinated biphenyl (PCB) congeners, 138, 153, 180, one coplanar PCB, 169, as well as 2,3,7,8-TCDD, and all possible mixtures (26) were tested upon in vitro exposure. All species were not equally sensitive to the adverse effects of OCs on either neutrophils or monocytes phagocytosis. With the exception of harbor seals, all mixtures that significantly modulated neutrophil or monocyte phagocytosis contained at least one non-coplanar PCB. Regression analysis revealed that the non-coplanar congeners, more than the coplanar congeners, explained the variability in phagocytosis. Dendrograms revealed that phylogeny could not predict immunotoxicity. The currently used toxic equivalency (TEQ) approach and the traditional mouse model both failed to predict experimentally induced immunomodulatory effects in marine mammals tested, leading us to question the reliability of both TEQs and mouse model in risk assessment of OC mixtures. Testing the relative sensitivity to immunomodulatory effects of contaminants and contaminant mixtures between different species of marine mammals may have important implications for risk assessment as well as conservation and management strategies.

Estrogenic and toxic effects of polychlorinated biphenyls on cultured ovarian germ cells of embryonic chickens

Polychlorinated biphenyls (PCBs) are man-made ubiquitous pollutants that have detrimental effects on reproduction and endocrine functions in a variety of species. In the present study, estrogenic and toxic effects of PCBs on embryonic chicken ovarian development were evaluated by a germ-somatic cell co-culture system. Ovarian cells were cultured in serum-free medium and challenged with a mixture of PCBs (Aroclor 1254). Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) release. Results showed that lower PCBs (0.1-1 microg/ml) manifested mainly estrogenic effect to stimulate germ cell proliferation, while higher PCBs (10 microg/ml) imposed severe toxicity on germ and somatic cells. The toxic effect of PCBs could be attenuated by an antioxidant tocopherol. PCBs induced condensed nuclear chromosome in ovarian cells and caused cell exfoliation and breakdown within initial hours of treatment. After 24 h, the estrogenic effect of PCBs began to exhibit and the survived germ cells manifested proliferation. Inhibition of the estrogenic effect of PCBs by tamoxifen led to increased toxicity on germ cells and somatic cells. These results indicate that PCBs exposure may interfere with ovarian germ cell proliferation and cause reproductive disorder via both toxic and estrogenic actions in embryonic chickens.

The inhibition of LPS-induced splenocyte proliferation by ortho-substituted and microbially dechlorinated polychlorinated biphenyls is associated with a decreased expression of cyclin D2

Immunological effects of polychlorinated biphenyls (PCBs) have been demonstrated in our laboratories with the peferential inhibition of lipopolysaccharide (LPS)-induced splenocyte proliferation by ortho-substituted PCB congeners. An investigation of the mechanism behind this immunotoxicity revealed an interruption in the progression of murine lymphocytes from G0/G1 into S phase by Aroclor 1242 and the di-ortho-substituted congener, 2,2'-chlorobiphenyl (CB), whereas, a non-ortho-substituted congener, 4,4'-CB, did not affect cell cycle progression. This interruption of cell cycle progression by 2,2'-CB and Aroclor 1242 was associated with a decreased expression of the cell cycle regulatory protein, cyclin D2, while expression was not affected by exposure to the non-ortho-substituted 4,4'-CB. These results suggest the preferential inhibition of LPS-induced splenocyte proliferation by ortho-substituted congeners is a result of a decreased expression of cyclin D2, which leads to an interruption in cell cycle progression. In addition, PCB mixtures with an increased percentage of chlorines in the ortho position following an environmentally occurring degradation process inhibited LPS-induced proliferation, interrupted cell cycle progression, and decreased cyclin D2 expression. This study provides evidence for a mechanism of action of the immunological effects of ortho-substituted individual congeners as well as environmentally relevant mixtures enriched in congeners with this substitution pattern.

Inhibition of LPS-induced splenocyte proliferation by ortho-substituted polychlorinated biphenyl congeners

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants, and their ubiquitous nature has prompted studies of their potential health hazards. As a result of their lipophilic nature, PCBs accumulate in breast milk and subsequently affect the health of offspring of exposed individuals. Biological effects of PCBs in animals have mostly been attributed to coplanar congeners, although effects of ortho congeners also have been demonstrated. To investigate the relationship of immunotoxicity and chlorine substitution pattern, the effects of PCB congeners and mixtures of ortho and non-ortho-substituted constituents of Aroclor 1242 on splenocytes from C57B1/6 mice were examined. The immunotoxic endpoints investigated included splenocyte viability, lipopolysaccharide (LPS)-induced splenocyte proliferation, and LPS-induced antibody secretion. Congeners with multiple ortho chlorines preferentially inhibited splenocyte proliferation as compared with non- or mono-ortho-substituted congeners. However, mixtures of non- and mono-ortho-substituted congeners and multi-ortho-substituted congeners inhibited LPS-induced splenocyte proliferation and antibody secretion at similar concentrations. Exposure of splenocytes to these mixtures did not activate the aryl hydrocarbon receptor (AhR) signal transduction pathway. These results suggest individual multi-ortho-substituted congeners preferentially inhibit LPS-induced splenocyte proliferation, while congeners not exhibiting an effect individually may have additive effects in a mixture to produce an immunotoxic response through an AhR-independent pathway.

Effects of PCB congeners on the immune function of Mytilus hemocytes: alterations of tyrosine kinase-mediated cell signaling

Polychlorinated biphenyls (PCBs) are industrial chemicals which have been released into the environment resulting in widespread and persistent contamination. PCBs exist as 209 different congeners depending on the chlorine substitution on the biphenyl rings; the physical properties and the toxic effects of a PCB congener are structure-dependent. In this work, individual ortho-substituted non coplanar PCB congeners were tested for their effects on the function of mussel (Mytilus galloprovincialis Lam.) hemocytes. Moreover, the possibility that in mussel hemocytes different PCBs may affect the signal transduction pathways involved in the immune response was investigated, with particular regards to relevant components of tyrosine-kinase mediated cell signaling. The results were compared with those obtained with a model of non-ortho-substituted coplanar congener. The results demonstrate that the di-ortho-substituted, non coplanar PCB congeners P47 (2,2',4,4'-tetrachlorobiphenyl) and P153 (2,2',4,4',5,5'-hexachlorobiphenyl) can alter immune parameters of mussel hemocytes, such as microbicidal activity and lysosomal enzyme release, respectively. Both congeners, as well as the non-ortho, coplanar congener P77 (3,3',4,4'-tetrachlorobiphenyl) significantly reduced hemocyte lysosomal membrane stability; however, P77 had no effect on either bacterial killing or lysozyme release. P47, P153 and P77 affected different components of tyrosine kinase-mediated cell signalling; in particular, they lead to a time-dependent increase in the phosphorylation level of the stress activated p38 and JNK Mitogen Activated Protein Kinases (MAPKs), as evaluated by Western blotting of hemocyte protein extracts with specific anti-phospho-MAPK antibodies. P153 also increased the level of phosphorylated ERK (extracellularly regulated) MAPKs. Moreover, non coplanar P47 and P153 caused increased tyrosine phosphorylation of the transcription factor STAT5, thus possibly affecting gene expression, whereas coplanar P77 was ineffective. The results demonstrate that MAPKs, and in particular the stress-activated p38 and JNK MAPKs, that represents a key step in the response of mussel hemocytes to bacterial infection, are a target for different non coplanar and coplanar PCB congeners. The results also show functional differences between different PCB congeners with respect to the hemocyte functions. However, chlorine substitution at the ortho positions is not necessarily related to immunotoxicity: the hexachlorinated P128 (2,2',3,3',4,4'-hexachlorobiphenyl) had no significant effect on mussel hemocytes, whereas its isomer P153, that represents a major component of environmental PCBs, and that is accumulated in mussel tissues, significantly affected both aspects of the immune response and relevant signal transduction pathways. These are the first data on the effects and possible mechanisms of immunotoxicity of non coplanar PCBs in mussel hemocytes. The results support the hypothesis that the innate immune system is a sensitive target for these contaminants in both vertebrates and invertebrates. Moreover, when considering that non coplanar congeners are present both in commercial mixtures and, in higher proportions, in environmental samples, the results suggest that bivalve hemocytes represent a useful model for evaluating the potential immunotoxicity of PCB contamination.

Impact of polychlorinated biphenyls (PCBs) on the immune function of fish: age as a variable in determining adverse outcome

Polychlorinated biphenyls (PCBs) are a major contaminant of global extent in water resources and aquatic biota. Due to its high lipid solubility, PCBs fail to be degraded and, therefore, continue to bioaccumulate throughout the environment and food chain. To determine the impact of PCBs on the immune system of aged and juvenile Japanese medaka (Oryzias latipes), fish were injected with the coplanar PCB congener 126 and examined after 3 and 14 days. PCB 126 produced oxidative stress in both age groups of fish 14 days post-injection; however, juvenile medaka appeared more susceptible than aged fish. Humoral immunity, as determined by antibody forming cell (AFC) numbers, was significantly depressed for up to 14 days post-injection in both age groups. These results demonstrate the sensitivity of the fish immune response for predicting PCB-induced immunotoxicity and identify age as a variable in determining adverse outcome.

Cellular and molecular mechanisms mediating the effects of polychlorinated biphenyls on oocyte developmental competence in cattle

Polychlorinated biphenyls (PCBs) can interfere with normal reproductive functions acting as endocrine disruptors. Aroclor-1254 (A-1254), is a pool of more than 60 congeners used for in vitro studies because its composition is representative of PCBs environmental pollution. We previously demonstrated that the exposure of bovine oocytes to A-1254 during in vitro maturation (IVM) was detrimental not only to the maturation process but also induced a significant increase of polyspermy and a reduction of developmental competence. Therefore, we investigated whether A-1254 acts on two processes that occur during IVM and may be related with its negative effects: maternal mRNA polyadenylation and cortical granules (CGs) migration and exocytosis. Bovine cumulus-oocyte complexes (COCs) were exposed to 0.1 microg/ml of A-1254 during IVM, a level of exposure known to affect oocyte maturation, fertilization, and developmental competence. Oocyte exposure to A-1254 altered the poly(A) tail length of 5 out of 10 genes examined. PCBs effect on mRNA polyadenylation was different depending on the gene considered and resulted either in a shorter or in a longer poly(A) tail. At the end of maturation, Aroclor treated oocytes presented clustered CG in a significantly higher percentage than the control group. In addition, CG exocytosis after 8 hr of fertilization occurred at significantly lower extent in zygotes derived from the exposed group compared to control. Our results indicated that the lower developmental competence of oocytes exposed to PCBs during IVM can be related to the interaction of these contaminants with mechanisms regulating maternal mRNA storage in the ooplasm and normal CGs function.

In vitro reproductive toxicity of polychlorinated biphenyls: effects on oocyte maturation and developmental competence in cattle

Polychlorinated biphenyls (PCBs) are one of the most persistent and widespread group of endocrine disrupting compounds in the ecosystem. High concentrations of these substances are known to be present in sewage sludge from industrial, agricultural, and domestic origin that is spread in increasing amounts on arable land and pasture as fertilizer and is found in water, representing an increasing risk for the reproductive health of farm animals. Objective of this study was to determine the impact of PCBs on maturation and developmental competence of cattle oocytes. Since PCBs are a family of 209 molecules present in the environment as a mixture, Aroclor-1254, a pool of more than 60 congeners, was used in these experiments as its composition is considered to be environmentally relevant. Cumulus-oocytes complexes were exposed during IVM to serial concentrations of Aroclor-1254 (between 1 microg/ml and 0.0001 microg/ml) and compared with control groups. Aroclor decreased the percentage of oocytes that reached metaphase II stage after 24 hr, at doses as low as 0.01 microg/ml. Groups treated with 0.001 microg/ml or above, showed an impaired fertilization rate and a dramatic increase of polyspermy. Moreover, exposure during maturation resulted in a reduced proportion of oocytes that cleaved and developed until blastocyst stage although no differences in embryo cell numbers were observed. The present study indicates that very low PCBs concentrations are sufficient to disrupt bovine oocyte maturation, its fertilization, and developmental competence. These results also provide a set of reference data for the assessment of the risk posed by these substances to animal reproductive health, though further work will be necessary to equate in vitro doses to in vivo exposures.

2,2',4,6,6'-pentachlorobiphenyl induces apoptosis in human monocytic cells

Polychlorinatedbiphenyls (PCBs) are a group of persistent and widely dispersed environmental pollutants, some of which may be immunotoxic. In the present study, we investigated the effect of PCBs on immune system by assessing apoptotic cell death in human monocytic U937 cells. Among the various congeners tested, 2,2',4,6, 6'-pentachlorobiphenyl (PeCB), a highly ortho-substituted congener, specifically induced DNA fragmentation, a hallmark of apoptosis, while the other examined di-, tri-, tetra-, and pentachlorobiphenyls did not. To further study the 2,2',4,6,6'-PeCB-induced cell death, various features of apoptosis were examined. 2,2',4,6,6'-PeCB caused a decrease in cell viability and induced cellular morphologic features characteristic of apoptosis such as chromatin aggregation and apoptotic bodies. In addition, caspase-3, an executioner of apoptosis, was activated and its substrate, poly(ADP-ribose) polymerase (PARP), was cleaved during 2,2',4,6,6'-PeCB-induced apoptosis. In contrast, 3,3',4,4',5-PeCB, a congener of coplanar structure, as well as 2,3,7,8-TCDD did not induce apoptosis in these human monocytic cells, although they potently induced CYP 1A1 in human hepatoma Hep G2 cells. Taken together, the data indicate that 2,2',4,6,6'-PeCB induces apoptosis in human monocytic cells through a mechanism that is independent of the arylhydrocarbon receptor. This suggests a possibly separate mechanism by which PCBs cause immunosuppression.