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

Cyclin-Dependent Kinase Inhibitor BMI-1026 Induces Apoptosis by Downregulating Mcl-1 (L) and c-FLIP (L) and Inactivating p-Akt in Human Renal Carcinoma Cells

Previous studies have investigated the inhibitory effect of BMI-1026 on cyclin-dependent kinase 1 in vitro. However, the molecular mechanisms by which BMI-1026 treatment leads to cancer cell death remain unclear. This study was conducted to investigate the anticancer mechanisms of BMI-1026 on human renal carcinoma Caki cells. BMI-1026 induced apoptosis in association with the cleavage of poly(ADP-ribose) polymerase and pro-caspase-3 and the release of apoptosis-inducing factor and cytochrome c from mitochondria in Caki cells. BMI-1026-induced apoptosis was inhibited by the pan-caspase inhibitor z-VAD-fmk. Furthermore, BMI-1026 downregulated Bcl-2 and X-linked inhibitor of apoptosis protein (XIAP) at the transcriptional level and Mcl-1 (L) and cellular FADD-like IL-1β-converting enzyme inhibitory protein (c-FLIP (L)) at the post-transcriptional level. Interestingly, Mcl-1 (L) and c-FLIP (L), but not Bcl-2 or XIAP, played important roles in BMI-1026-induced Caki cell apoptosis. Although the constitutively active form of Akt did not attenuate BMI-1026-induced apoptosis, blockade of the PI3K/Akt pathway using a subcytotoxic concentration of the PI3K/Akt inhibitor LY294002 enhanced Caki cell apoptosis induced by BMI-1026. Electrophysiological safety was confirmed by determining the cardiotoxicity of BMI-1026 via left ventricular pressure analysis. These results suggest that BMI-1026 is a potent multitarget anticancer agent with electrophysiological safety and should be further investigated.

Exercise influences the impact of polychlorinated biphenyl exposure on immune function

Polychlorinated biphenyls (PCBs) are environmental pollutants and endocrine disruptors, harmfully affecting reproductive, endocrine, neurological and immunological systems. This broad influence has implications for processes such as wound healing, which is modulated by the immunological response of the body. Conversely, while PCBs can be linked to diminished wound healing, outside of PCB pollution systems, exercise has been shown to accelerate wound healing. However, the potential for moderate intensity exercise to modulate or offset the harmful effects of a toxin like PCB are yet unknown. A key aim of the present study was to examine how PCB exposure at different doses (0, 100, 500, 1000 ppm i.p.) altered wound healing in exercised versus non-exercised subgroups of mice. We examined PCB effects on immune function in more depth by analyzing the concentrations of cytokines, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6) and granulocyte macrophage colony stimulating factor (GM-CSF) in these wounds inflicted by punch biopsy. Mice were euthanized at Day 3 or Day 5 after PCB injection (n = 3-6) and skin excised from the wound area was homogenized and analyzed for cytokine content. Results revealed that wound healing was not signficantly impacted by either PCB exposure or exercise, but there were patterns of delays in healing that depended on PCB dose. Changes in cytokines were also observed and depended on PCB dose and exercise experience. For example, IL-1β concentrations in Day 5 mice without PCB administration were 33% less in exercised mice than mice not exercised. However, IL-1β concentrations in Day 3 mice administered 100 ppm were 130% greater in exercised mice than not exercisedmice. Changes in the other measured cytokines varied with mainly depressions at lesser PCB doses and elevations at higher doses. Exercise had diverse effects on cytokine levels, but increased cytokine levels in the two greater doses. Explanations for these diverse effects include the use of young animals with more rapid wound healing rates less affected by toxin exposure, as well as PCB-mediated compensatory effects at specific doses which could actually enhance immune function. Future work should examine these interactions in more detail across a developmental time span. Understanding how manipulating the effects of exposure to environemntal contaminants using behavioral modification could be very useful in certain high risk populations or exposed individuals.

Exposure to Aroclor 1254 differentially affects the survival of pancreatic β-cells and α-cells in the male mice and the potential reason

Previous works showed that chronic exposure to Aroclor 1254 disrupted glucose homeostasis and induced insulin resistance in male mice. To further observe the different effects of Aroclor 1254 exposure on the pancreatic α-cells and β-cells, male mice were exposed to Aroclor 1254 (0, 0.5, 5, 50, 500 μg/kg) for 60 days, the pancreas was performed a histological examination. The results showed that the percentage of apoptosis cell (indicated by TUNEL assay) was increased in both α-cells and β-cells, as the Aroclor 1254 dose was increased; the proliferation (indicated by PCNA expression) rate of β-cells was elevated while that of α-cells was not affected, resulting in an increased β-cell mass and a decreased α-cell mass in a dose-depend manner. The number of Pdx-1 positive β-cells was significantly increased whereas that of Arx positive α-cells was markedly decreased, indicating an enhanced β-cell neogenesis and a weakened α-cell neogenesis. The drastically reduction of serum testosterone levels in all the treatments suggested an anti-androgenic potency of Aroclor 1254. The up-regulation of estrogen receptors (ERα and ERβ) and androgen receptor in β-cells might be responsible for the increased β-cell mass and neogenesis.

Identification of Sex-Specific Transcriptome Responses to Polychlorinated Biphenyls (PCBs)

PCBs are classified as xenoestrogens and carcinogens and their health risks may be sex-specific. To identify potential sex-specific responses to PCB-exposure we established gene expression profiles in a population study subdivided into females and males. Gene expression profiles were determined in a study population consisting of 512 subjects from the EnviroGenomarkers project, 217 subjects who developed lymphoma and 295 controls were selected in later life. We ran linear mixed models in order to find associations between gene expression and exposure to PCBs, while correcting for confounders, in particular distribution of white blood cells (WBC), as well as random effects. The analysis was subdivided according to sex and development of lymphoma in later life. The changes in gene expression as a result of exposure to the six studied PCB congeners were sex- and WBC type specific. The relatively large number of genes that are significantly associated with PCB-exposure in the female subpopulation already indicates different biological response mechanisms to PCBs between the two sexes. The interaction analysis between different PCBs and WBCs provides only a small overlap between sexes. In males, cancer-related pathways and in females immune system-related pathways are identified in association with PCBs and WBCs. Future lymphoma cases and controls for both sexes show different responses to the interaction of PCBs with WBCs, suggesting a role of the immune system in PCB-related cancer development.

PCB 118-induced endothelial cell apoptosis is partially mediated by excessive ROS production

Endothelial cell apoptosis, which may alter the integrity of the endothelium and lead to plaque instability, plays a critical role in the development and pathogenesis of atherosclerosis. Exposure of polychlorinated biphenyls (PCBs) is associated with increased risk of atherosclerosis and cardiovascular disease. In our present study, we explored whether exposure to PCB 118 influences endothelial cell apoptosis in vitro and the underlying mechanisms involved. As expected, exposure to PCB 118 increased the intracellular reactive oxygen species (ROS) levels in HUVECs. Increases in apoptosis and Bax/Bcl-2 ratios were observed in PCB 118-treated HUVECs. N-acetyl-l-cysteine (NAC), a ROS scavenger, partially reduced PCB 118-induced apoptosis and Bax/Bcl-2 ratios in HUVECs. Taken together, PCB 118-induced endothelial cell apoptosis was partially initiated by excessive ROS production.

Pollutants make rheumatic diseases worse: Facts on polychlorinated biphenyls (PCBs) exposure and rheumatic diseases

BACKGROUND

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that bioaccumulate in adipose tissue, disturbing its metabolism and the balance of adipokines, related to obesity. The altering secretion pattern of adipokines from the adipose tissue and the increasing mechanical load in weight-bearing joints presented in obesity condition, are risk factors for osteoarthritis development. The most prevalent rheumatic diseases, osteoarthritis and rheumatoid arthritis, are chronic conditions that target the whole joints, leading to increasing disability and health care cost. The goal of this focused review is to summarize the current knowledge on the role of PCBs in osteoarthritis and rheumatoid arthritis pathogenesis.

SEARCH STRATEGY

A PubMed search was managed using keywords as "rheumatic diseases", "polychlorinated biphenyls", "obesity" and "endocrine disruption".

MAIN RESULTS OF THE REVIEW

The incidence of rheumatoid arthritis has been reported to be increased especially in urban areas in industrialized countries, emphasizing the importance of environment in the pathogenesis of rheumatic diseases. Analysis of two cohorts exposed to PCBs food contamination showed high incidence of arthritis. In addition, PCBs in serum correlated positively with the prevalence of self-reported arthritis. Few studies support the hypothesis that osteoarthritis development could be related to PCBs induction of chondrocytes apoptosis.

CONCLUSION

Evidences have emerged for a relationship between PCBs and development of several types of arthritis. Further research is encouraged to determine the correlation between PCBs exposure and the development of rheumatic diseases.

Cytokine dysregulation in autism spectrum disorders (ASD): possible role of the environment

Autism spectrum disorders (ASD) are neurodevelopmental diseases that affect an alarming number of individuals. The etiological basis of ASD is unclear, and evidence suggests it involves both genetic and environmental factors. There are many reports of cytokine imbalances in ASD. These imbalances could have a pathogenic role, or they may be markers of underlying genetic and environmental influences. Cytokines act primarily as mediators of immunological activity but they also have significant interactions with the nervous system. They participate in normal neural development and function, and inappropriate activity can have a variety of neurological implications. It is therefore possible that cytokine dysregulation contributes directly to neural dysfunction in ASD. Further, cytokine profiles change dramatically in the face of infection, disease, and toxic exposures. Imbalances in cytokines may represent an immune response to environmental contributors to ASD. The following review is presented in two main parts. First, we discuss select cytokines implicated in ASD, including IL-1Β, IL-6, IL-4, IFN-γ, and TGF-Β, and focus on their role in the nervous system. Second, we explore several neurotoxic environmental factors that may be involved in the disorders, and focus on their immunological impacts. This review represents an emerging model that recognizes the importance of both genetic and environmental factors in ASD etiology. We propose that the immune system provides critical clues regarding the nature of the gene by environment interactions that underlie ASD pathophysiology.

2,3,7,8 Tetrachlorodibenzo-p-Dioxin (TCDD) Directly Enhances the Maturation and Apoptosis of Dendritic Cells In Vitro

2,3,7,8 Tetrachlorodibenzo-p-dioxin (TCDD) suppresses adaptive immune responses and modulates the function of numerous cells involved in these responses. Our laboratory has shown that dendritic cells (DCs), which are important for the initiation of T-cell-dependent immunity, from TCDD-exposed mice exhibited reduced cell numbers and had altered expression of costimulatory molecules that are critical for the activation of T-cells. To further characterize the effects of TCDD on DCs and to elucidate a potential mechanism of toxicity, we investigated the direct effects of TCDD on DC maturation and survival in vitro. DCs, derived from bone marrow cells, were exposed to TCDD and then treated with TNFalpha to induced maturation. Apoptosis of bone marrow derived DCs (bmDCs) was induced by activating CD95 on the surface of the cells and was measured by annexin V staining. The TCDD-mediated changes in the expression of genes associated with apoptosis were examined using a pathway-specific c-DNA microarray. The results demonstrate that TCDD-treatment of bmDCs enhanced TNFalpha-induced maturation, measured as an increase in the expression of major histocompatibility complex class II, CD86, CD40, and CD54. In addition, TCDD exposure significantly augmented CD95-mediated death of bmDCs and altered the transcription of several genes involved in apoptosis. These findings confirm and extend the in vivo effects of TCDD on DC activation, and suggest that TCDD induces these changes, at least in part, via direct effects on the DC.

Morphological alterations of Vero cell exposed to coplanar PCB 126 and noncoplanar PCB 153

Polychlorinated biphenyls (PCBs) are widespread, persistent environmental contaminants that display a complex spectrum of toxicological properties. Exposure to PCBs has been associated with morphological anomalies in cell cultures. However, most mechanistic studies of PCBs' toxic activity have been focused on coplanar congeners. It is of importance to determine whether PCB treatment would influence cell configuration and whether these changes would depend on the structural characteristics of PCBs. In this study, we investigated cell morphological alteration in Vero cell cultures after exposure to coplanar PCB 126 and noncoplanar PCB 153. The survival of Vero cells was measured through the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test. Cytotoxicity results suggested that PCB congeners had a toxic, antiproliferative effect on Vero cells. Morphological studies described structural modifications and provided evidence that apoptosis might be the main cell death pathway in PCB 153-treated cells. The comparison between PCB 126 and PCB 153 indicated that the cell death mechanisms involved in coplanar or noncoplanar PCB congener exposure were different in Vero cells.

Preclinical evaluation of azathioprine plus buthionine sulfoximine in the treatment of human hepatocarcinoma and colon carcinoma

AIM: To evaluate the efficacy and the safety of azathioprine (AZA) and buthionine sulfoximine (BSO) by localized application into HepG2 tumor in vivo.

METHODS: Different hepatoma and colon carcinoma cell lines (HepG2, HuH7, Chang liver, LoVo, RKO, SW-48, SW-480) were grown in minimal essencial medium supplemented with 10% fetal bovine serum and 1% antibiotic/antimycotic solution and maintained in a humidified 37 °C incubator with 5% CO₂. These cells were pretreated with BSO for 24 h and then with AZA for different times. We examined the effects of this combination on some proteins and on cellular death. We also studied the efficacy and the safety of AZA (6 mg/kg per day) and BSO (90 mg/kg per day) in HepG2 tumor growth in vivo using athymic mice. We measured safety by serological markers such as aminotransferases and creatine kinase.

RESULTS: The in vitro studies revealed a new mechanism of action for the AZA plus BSO combination in the cancer cells compared with other thiopurines (6-mercaptopurine, 6-methylmercaptopurine, 6-thioguanine and 6-methylthioguanine) in combination with BSO. The cytotoxic effect of AZA plus BSO in HepG2 cells resulted from necroptosis induction in a mitochondrial-dependent manner. From kinetic studies we suggest that glutathione (GSH) depletion stimulates c-Jun amino-terminal kinase and Bax translocation in HepG2 cells with subsequent deregulation of mitochondria (cytochrome c release, loss of membrane potential), and proteolysis activation leading to loss of membrane integrity, release of lactate dehydrogenase and DNA degradation. Some of this biochemical and cellular changes could be reversed by N-acetylcysteine (a GSH replenisher). In vivo studies showed that HepG2 tumor growth was inhibited when AZA was combined with BSO.

CONCLUSION: Our studies suggest that a combination of AZA plus BSO could be useful for localized treatment of hepatocellular carcinoma as in the currently used transarterial chemoembolization method.

Early life environment and developmental immunotoxicity in inflammatory dysfunction and disease

Components of the innate immune system such as macrophages and dendritic cells are instrumental in determining the fate of immune responses and are, also, among the most sensitive targets of early life environmental alterations including developmental immunotoxicity (DIT). DIT can impede innate immune cell maturation, disrupt tissue microenvironment, alter immune responses to infectious challenges, and disrupt regulatory responses. Dysregulation of inflammation, such as that observed with DIT, has been linked with an increased risk of chronic inflammatory diseases in both children and adults. In this review, we discuss the relationship between early-life risk factors for innate immune modulation and promotion of dysregulated inflammation associated with chronic inflammatory disease. The health risks from DIT-associated inflammation may extend beyond primary immune dysfunction to include an elevated risk of several later-life, inflammatory-mediated diseases that target a wide range of physiological systems and organs. For this reason, determination of innate immune status should be an integral part of drug and chemical safety evaluation.

Estimates of DNA strand breakage in bottlenose dolphin (Tursiops truncatus) leukocytes measured with the Comet and DNA diffusion assays

The analysis of DNA damage by mean of Comet or single cell gel electrophoresis (SCGE) assay has been commonly used to assess genotoxic impact in aquatic animals being able to detect exposure to low concentrations of contaminants in a wide range of species. The aims of this work were 1) to evaluate the usefulness of the Comet to detect DNA strand breakage in dolphin leukocytes, 2) to use the DNA diffusion assay to determine the amount of DNA strand breakage associated with apoptosis or necrosis, and 3) to determine the proportion of DNA strand breakage that was unrelated to apoptosis and necrosis. Significant intra-individual variation was observed in all of the estimates of DNA damage. DNA strand breakage was overestimated because a considerable amount (~29%) of the DNA damage was derived from apoptosis and necrosis. The remaining DNA damage in dolphin leukocytes was caused by factors unrelated to apoptosis and necrosis. These results indicate that the DNA diffusion assay is a complementary tool that can be used together with the Comet assay to assess DNA damage in bottlenose dolphins.

Oxidative stress and apoptosis of Carassius auratus lymphocytes induced by nonplanar (PCB153) and coplanar (PCB169) polychlorinated biphenyl congeners in vitro

Among all the 209 kinds of polychlorinated biphenyls (PCBs) congeners, nonplanar and coplanar PCB congeners have different levels of toxicity on mammal cells such as neuronal cells, but little is known about their toxicity on fish cells although PCB congeners usually have high bioaccumulation abilities in the detected fish bodies. This study showed that 2,2',4,4',5,5'-hexacholorbiphenyl (PCB153, nonplanar congener) and 3,3',4,4',5,5'-hexacholorbiphenyl (PCB 169, coplanar congener) caused apoptosis on the isolated crucian carp (Carassius auratus) lymphocytes and the induced cytotoxicity was structure-dependent. According to the laser confocal microscope observations, apoptosis was clearly distinguished by condensation of nucleus, shrinkage and formation of apoptotic bodies. DNA fragmentation was detected by agarose gel electrophoresis. These typical morphological and biochemical characteristics indicate the occurrence of apoptosis on fish lymphocytes. According to the flow cytometry analysis, after the cells were exposed to 10 micromol/L PCBs for 3 h, the apoptotic percentage induced by PCB153 was 23.41%, while that induced by PCB169 was even higher (31.03%). Furthermore, incubating PCBs with fish lymphocytes enhanced levels of reactive oxygen species (ROS) and malondialdehyde (MDA), clearly indicating the presence of oxidative stress and lipid peroxidation. Our data also demonstrate that the different cytotoxic effects induced by coplanar and nonplanar PCBs were correlated with their structural characteristics and the coplanar congener was more cytotoxic than nonplanar congener. This study suggests that cytotoxicity mechanisms of the PCB congeners on fish lymphocytes depend on their planarity and chemical structures.

Environmental toxicity, oxidative stress and apoptosis: ménage à trois

Apoptosis is an evolutionary conserved homeostatic process involved in distinct physiological processes including organ and tissue morphogenesis, development and senescence. Its deregulation is also known to participate in the etiology of several human diseases including cancer, neurodegenerative and autoimmune disorders. Environmental stressors (cytotoxic agents, pollutants or toxicants) are well known to induce apoptotic cell death and to contribute to a variety of pathological conditions. Oxidative stress seems to be the central element in the regulation of the apoptotic pathways triggered by environmental stressors. In this work, we review the established mechanisms by which oxidative stress and environmental stressors regulate the apoptotic machinery with the aim to underscore the relevance of apoptosis as a component in environmental toxicity and human disease progression.

In vitro investigations for the QSAR mechanism of lymphocytes apoptosis induced by substituted aromatic toxicants

The objective of this study was to assess the chemicals-induced apoptosis effects on fish lymphocytes and to use the QSAR model to interpret the relationships between apoptotic effects and chemical structures to identify the immune toxicology mechanism. By the use of a simple in vitro toxicological assay, the measured apoptotic parameter (EC50) is used in a QSAR to interpret the apoptotic effects of 25 substituted benzenes at low exposure levels. The apoptotic effects of all tested substituted aromatic chemicals with Carassius auratus lymphocytes were confirmed by DNA ladder and nucleus condensation. For both chlorobenzenes and PCBs, the EC50 values increase with increasing Cl number in the molecule, a result reflecting probably the increased p-pi conjugation of the C-Cl bonds that lowers the molecular reactivity. Furthermore, the apoptotic EC50 data were best correlated with the dipole moment (mu) and the energy of the lowest unoccupied molecular orbital (ELUMO) such that: log(1/EC50)=0.325+0.222 micro-0.163(ELUMO) (with R(2)=0.879). The dependence on the electronic ELUMO factor of the established correlation suggests that during the apoptotic process the ROS (reactive oxygen substance) produced by cells acts as a Lewis base in substituted nucleophilic reactions with toxic chemicals behaving as an electron acceptor. On the basis of the test results, the present toxicological assay offers a rapid tool for assessing the toxic effects of chemicals at low exposure levels.

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.

CYP1A1 and MT1K are congener specific biomarker genes for liver diseases induced by PCBs

We have identified two most significant biomarker genes, CYP1A1 (69.81 up-regulation) and MT1K (14.66 up-regulation), showing highest overexpression at p-value <0.005. These were selected out of several hundred genes induced in vitro, using PCB exposed human liver (HepG2) cells. Over expression of the CYP1A1 (cytochrome P450) gene was specific to PCB-77 and MT1K (Metallothionein) to PCB-153. Affymetrix oligonucleotide microarrays (mRNA) were used to screen the entire genome of human liver cells in a time-dependent exposure and were further validated by quantitative real-time RT-PCR.

Altered protein expressions in chronic PCB-153-induced human liver (HepG2) cells

Polychlorinated biphenyls (PCBs) are a group of persistent and widely distributed environmental pollutants that have various deleterious effects, e.g., neurotoxic, endocrine disruption and reproductive abnormalities, including cancers. Chronic exposure to environmentally hazardous chemicals like PCBs is of great concern to human health. It has been reported earlier that apoptotic proteins change in rats under chronic PCB treatment. It is of importance to determine if chronically exposed human cells develop a different protein expression. In the present study, the authors chronically exposed metabolically competent human liver (HepG2) cells at 50 to 100 microM to examine the role of the well-known environmentally hazardous pollutant non-coplanar 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) to study cell death. After 12 weeks of exposure these cells showed significant changes in apoptotic death in subsequent trypan blue growth assay, fluorescence microscopy, DNA fragmentation, and immunoblotting studies. Interestingly, chronically exposed cells showed marked differences in apoptotic and/or death-related proteins (e.g., Bcl2, Bak, and the pro and active forms of caspase-9, which were up-regulated), in contrast to acutely exposed (i.e., 48-h PCB-153 exposed) cells, which maintained linear growth despite repeated exposures. Similarly, tumor suppressor protein p53, proto-oncogene c-myc, and cell cycle regulator protein p21 were also up-regulated compared to nonchronically exposed HepG2 Cells. The results indicated that PCB-153-induced chronic exposure significantly altered different apoptotic (e.g., Bcl2, Bak, caspase-3) and tumor suppressor (e.g., p21, p53, and c-myc) proteins in the cellular model. These results suggest that chronic exposure to PCB-153 can induce cell survival by altering several apoptotic and tumor suppressor proteins.

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.

Differential effects of PCBs on the induction of apoptosis machinery and PKCα translocation in rat renal tubular cell cultures

We have demonstrated previously [Pérez-Reyes, P.L., Sánchez-Alonso, J.A., López-Aparicio, P., Recio, M.N., Pérez-Albarsanz, M.A., 2001. Different molecular capacity in the induction of apoptosis by polychlorinated biphenyl congeners in rat renal tubular cell cultures. Biosci. Rep. 6, 765-778] that the polychlorinated biphenyls (PCBs) cause loss of cell viability and accelerate apoptosis in cell kidney cultures. Further investigations are necessary to elucidate the mechanism of apoptosis induction. In this way, we have analyzed in the present work the effects of PCBs on protein kinase C (PKC, a protein family intimately involved in the regulation of cell survival) and the expression of two proapoptotic (caspase-3 and Bax) and one antiapoptotic (Bcl-2) proteins. Aroclor 1248 (a commercial PCB mixture with 48% chlorine by weight), PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl, a di-ortho-substituted nonplanar congener) and PCB 77 (3,3',4,4'-tetrachlorobiphenyl, a non-ortho-substituted planar congener), significantly increased PKCalpha activity compared to control cells in the cytosolic and particulate cell fractions, and increased the PKCalpha protein content in the particulate fraction. The nonplanar PCB 153 showed stronger effects than the coplanar congener PCB 77. In addition, Aroclor 1248 decreased both, procaspase-3 levels and the Bcl-2/Bax protein ratio. These findings indicate that PCBs, particularly nonplanar congeners, can induce apoptosis in primary renal tubular cells through the PKCalpha, caspase-3 and Bcl-2/Bax pathway.

Apoptosis in bovine cumulus-oocyte complexes after exposure to polychlorinated biphenyl mixtures during in vitro maturation

Aroclor-1254 (A-1254) is a commercial mixture of coplanar (dioxin-like) and non-coplanar (non dioxin-like) polychlorinated biphenyls (PCBs) affecting bovine oocyte in vitro maturation (IVM) and developmental competence. In the present study, the role of cumulus cell apoptosis in mediating the toxic effects of PCBs during in vitro maturation has been investigated. Results indicate that exposure of cumulus-oocyte complexes (COCs) to A-1254 significantly induced apoptosis of cumulus cells. Furthermore, A-1254 significantly increased the expression of the pro-apoptotic gene, Bax, concomitantly reducing the level of the anti-apoptotic gene, Bcl-2, in the cumulus cell compartment. The effects of pure mixtures of coplanar (PCB 77, 126 and 169) or non-coplanar (PCB 52, 101 and 153) PCBs were examined. Exposure of COCs to coplanar PCBs affected maturation at doses as low as 100.6 pg/ml. Furthermore, a significant increase in apoptosis and in Bax mRNA expression was observed. No variations in maturation or apoptosis were observed in the non-coplanar PCB group. To further analyze the role of cumulus cells, COCs and denuded oocytes (DOs) have been exposed to A-1254 or coplanar PCBs during IVM. Exposure of COCs significantly reduced the percentage of matured oocytes after 24 h of culture in both treatments. In contrast, exposure of DOs significantly decreased the maturation rate only at the highest dose investigated (100-fold greater than that affecting COCs). Taken together, the results indicate a direct role of cumulus cell apoptosis in mediating PCB toxicity on bovine oocytes, and a direct relationship between congener planarity and toxicity in bovine oocytes is suggested.

Polychlorinated biphenyl mixtures (Aroclors) induce apoptosis via Bcl-2, Bax and caspase-3 proteins in neuronal cell cultures

Polychlorinated biphenyls (PCBs) are a group of persistent and widely dispersed environmental pollutants, some of which may be neurotoxic. In the present study, we have investigated the effect of PCB commercial mixtures (Aroclors) on neuronal cell cultures by assessing cell viability and apoptotic cell death. We have combined morphological and biochemical techniques to establish the relevance of apoptosis in neuronal cell death induced by Aroclors. Treatment with both Aroclor 1248 and Aroclor 1260 caused the loss of cell viability and accelerated apoptosis both in a concentration- and time-dependent manner. However, the extent of apoptosis resulted greater for Aroclor 1248 than for Aroclor 1260. This is correlated with the loss of cell viability since Aroclor 1248 is more cytotoxic. The apoptosis induced by Aroclors involves the increase of caspase-3 activity. To correlate the caspase-3 activity with respect to changes in protein processing, caspase-3 precursor protein (procaspase-3) was evaluated by Western blot analysis. Also, Bcl-2 and Bax protein were assessed in order to elucidate the cell death machinery induced in cortical neuronal cell cultures by Aroclor 1248. The results indicate that the increase in Aroclor-induced apoptosis correlates with a reduction in the expression of antiapoptotic Bcl-2 and an increase in the expression of proapoptotic Bax. These results suggest that, with our experimental conditions, Aroclors induce apoptosis in primary cultures of cortical neurons via proteins of the Bcl-2 and caspase families.

VEGF regulates PCB 104-mediated stimulation of permeability and transmigration of breast cancer cells in human microvascular endothelial cells

Polychlorinated biphenyl (PCB) congeners, a group of worldwide, persistent environmental contaminants, are known to cause carcinogenesis and tumor promotion, and may also affect the development of cancer metastasis. Because vascular endothelial cells create a selective barrier to the passage of cancer cells, we hypothesize that specific PCB congeners can disrupt endothelial integrity and increase the transendothelial migration of tumor cells. To examine this hypothesis, we elucidated the effects of 2,2',4,6,6'-pentachlorobiphenyl (PCB 104), a representative of highly ortho-substituted non-coplanar PCB congeners, on the endothelial permeability and transendothelial migration of MDA-MB-231 breast cancer cells. Exposure of human microvascular endothelial cell 1 (HMEC-1) to PCB 104 induced endothelial hyperpermeability and markedly increased transendothelial migration of MDA-MB-231 cells. These effects were associated with overexpression of vascular endothelial growth factor (VEGF). PCB 104-mediated elevation of VEGF expression was induced by phosphatidylinositol 3-kinase (PI3K) but not affected by co-treatments with antioxidants or the NF-kappaB inhibitor SN50. In addition, the PI3K-dependent pathway was involved in PCB 104-induced activation of AP-1, a transcription factor implicated in the regulation of VEGF gene expression. The VEGF receptor (KDR/Flk-1) antagonist SU1498 and the PI3K inhibitor LY294002 inhibited PCB 104-induced hyperpermeability. These results indicate that PCB 104 may contribute to tumor metastasis by inducing VEGF overexpression that stimulates endothelial hyperpermeability and transendothelial migration of cancer cells.

Effect of PCB 126 and PCB 153 on incidence of apoptosis in cultured theca and granulosa cells collected from small, medium and large preovulatory follicles

The aim of the presented study was to evaluate the effects of PCB 126 and PCB 153 on granulosa and theca cell apoptosis. Granulosa and theca cells were collected from small, medium, and large preovulatory porcine follicles and cultured as monolayers. Cells were initially cultured for 24 h to allow attachment to the plates. Media were changed and 100 pg/ml PCB 126 or 100 ng/ml PCB 153 were added. After 48 h, granulosa and theca cells were fixed for assessment of the number of apoptotic cells utilizing a Hoechst staining technique or frozen for measurement of caspase-3 activity. Media were collected for testosterone concentration analysis from theca cell cultures or estradiol from granulosa cell cultures. Neither PCB 153 nor PCB 126 had an effect on testosterone secretion by theca cells collected from small and medium size follicles, while both PCBs decreased testosterone secretion by large follicles. The decrease in testosterone secretion by large follicles under the influence of both PCBs was paralleled by a suppression of caspase-3 activity and a decreased incidence of apoptotic bodies. Neither of the PCBs had an effect on estradiol secretion by granulosa cells collected from small and medium size follicles, while both PCBs increased estradiol in granulosa cells collected from large follicles. PCB-associated increased estradiol secretion by granulosa cells collected from large follicles was accompanied by suppression of caspase-3 activity and a decreased incidence of apoptotic bodies. In conclusion, we have presented evidence that in preovulatory follicles PCBs inhibit both theca and granulosa cells apoptosis. Therefore, an exposure to PCBs may cause alterations in the pattern of terminal differentiation of follicles and attenuate spontaneous elimination of atretic follicles.

2,2',4,6,6'-pentachlorobiphenyl (PCB 104) induces apoptosis of human microvascular endothelial cells through the caspase-dependent activation of CREB

It has been proposed that endothelial integrity can play an active regulatory role in the extravasation of tumor cells during cancer metastasis. Since polychlorinated biphenyls (PCBs) have been shown to cause endothelial cell activation or injury and to lead to various diseases that involve dysfunction of the vascular endothelium, the present study was designed to determine the cellular and molecular signaling mechanisms of PCB-induced apoptosis in human microvascular endothelial cells (HMEC-1). A significant and marked decrease in cell viability was observed in HMEC-1 treated with 2,2',4,6,6'-pentachlorobiphenyl (PCB 104) in a time- and dose-dependent manner. Exposure of HMEC-1 to PCB 104 also dramatically induced internucleosomal DNA fragmentation. However, the caspase inhibitor zVAD-fmk significantly reversed the PCB 104-induced DNA fragmentation in HMEC-1, suggesting that endothelial cell death induced by PCB 104 exposure is, at least in part, due to caspase-dependent apoptotic pathways. To elucidate the molecular signaling mechanisms of PCB 104-induced apoptotic cell death in human microvascular endothelial cells, the present study focused on the effects of acute exposure of PCB 104 on the activation of several transcription factors, such as cAMP responsive element-binding protein (CREB), activator protein-1 (AP-1), nuclear factor-kappaB (NF-kappaB), and signal transducers and activators of transcription (STAT1), which have been known to play a pivotal role in the molecular signaling cascades for the induction of apoptosis. A series of electrophoretic mobility shift assay showed that PCB 104 specifically increased only CREB DNA-binding activity in a dose-dependent manner. AP-1, NF-kappaB, and STAT1, however, were not activated. In addition, zVAD-fmk significantly and dose-dependently blocked the CREB activation enhanced by PCB 104 exposure. These results suggest that PCB-induced death of human microvascular endothelial cells is mediated, at least in part, via the caspase-dependent apoptotic pathways and that the selective activation of CREB is involved in this process.

Polycyclic aromatic hydrocarbons inhibit differentiation of human monocytes into macrophages

Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BP) are ubiquitous environmental carcinogenic contaminants exerting deleterious effects toward cells acting in the immune defense such as monocytic cells. To investigate the cellular basis involved, we have examined the consequences of PAH exposure on macrophagic differentiation of human blood monocytes. Treatment by BP markedly inhibited the formation of adherent macrophagic cells deriving from monocytes upon the action of either GM-CSF or M-CSF. Moreover, it reduced expression of macrophagic phenotypic markers such as CD71 and CD64 in GM-CSF-treated monocytic cells, without altering cell viability or inducing an apoptotic process. Exposure to BP also strongly altered functional properties characterizing macrophagic cells such as endocytosis, phagocytosis, LPS-triggered production of TNF-alpha and stimulation of allogeneic lymphocyte proliferation. Moreover, formation of adherent macrophagic cells was decreased in response to PAHs distinct from BP such as dimethylbenz(a)anthracene and 3-methylcholanthrene, which interact, like BP, with the arylhydrocarbon receptor (AhR) known to mediate many PAH effects. In contrast, benzo(e)pyrene, a PAH not activating AhR, had no effect. In addition, AhR was demonstrated to be present and functional in cultured monocytic cells, and the use of its antagonist alpha-naphtoflavone counteracted inhibitory effects of BP toward macrophagic differentiation. Overall, these data demonstrate that exposure to PAHs inhibits functional in vitro differentiation of blood monocytes into macrophages, likely through an AhR-dependent mechanism. Such an effect may contribute to the immunotoxicity of these environmental carcinogens owing to the crucial role played by macrophages in the immune defense.

Polychlorinated biphenyl-induced apoptosis of murine spleen cells is aryl hydrocarbon receptor independent but caspases dependent

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants and many of their toxic effects, including their immunotoxicities, are mediated by the activation of aryl hydrocarbon receptor (AhR). We previously reported that Aroclor 1254, one of the most widely used PCB mixtures, increased DNA fragmentation in mouse spleen cells, suggesting that apoptosis was correlated with the immunotoxicity of PCB (Yoo et al., Toxicol. Lett. 91, 83-89, 1997). In the present study we investigated the mechanism by which PCB induces apoptosis and the involvement of AhR in the PCB-mediated apoptosis of mouse spleen cells. Aroclor 1254 induced DNA fragmentation without AhR activation, and the apoptosis was unaffected by alpha-naphtoflavone, a well-known antagonist of AhR. Moreover, the PCB congeners (PCB 47, 52, 128, and 153), which have little affinity for AhR, induced DNA fragmentation, whereas congeners (PCB 77, 126, and 169) that have high affinity for AhR did not induce fragmentation. The di-ortho form of PCB (PCB 153) and Aroclor 1254 induced DNA fragmentation in the spleen cells of both AhR knockout mice and Ah low-response mice, whereas the non-ortho form of PCB (PCB 126) did not induce DNA fragmentation. In the light of these findings, it is evident that AhR is not involved in PCB-mediated apoptosis. PCB 153 significantly increased caspase-3 activity in both spleen cells and human leukemia cells, and z-VAD-fmk, a general inhibitor of caspases, prevented PCB-induced DNA fragmentation. Based on our findings, the most likely mechanism that can account for this biological effect involves the induction of caspase-dependent apoptotic cell death.

Recent advances in understanding the mechanisms of TCDD immunotoxicity

TCDD is a highly immunosuppressive chemical that induces potent suppression of immune responses in laboratory animals. However, apart from the requisite role of the AhR and the identification of bone-marrow-derived cells as critical AhR-expressing targets, the specific cells and the underlying biochemical mechanisms by which TCDD disrupts immunological functions remain unclear. Recent data suggest that a new paradigm for the mechanism of immunotoxic action of TCDD may be more accurate, moving from one focused on the suppression of immune functions to one focused on the inappropriate activation of cells, leading to anergy or death, and the consequent premature termination of the immune response. Enhanced activation of B cells, DC and CD4+ T cells by TCDD has been described as well as the earlier disappearance of the latter two populations from peripheral lymphoid organs. Although much remains to be learned about how inappropriate cellular activation via the AhR induces immune suppression, deducing this mechanism of action and the signaling pathways involved, should lead to new insight into basic mechanisms of immune regulation.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Phospholipase A2-mediated Ca2+ influx by 2,2',4,6-tetrachlorobiphenyl in PC12 cells

Polychlorinated biphenyls (PCBs) are a group of persistent and widespread environmental pollutants, and known to affect signaling molecules. Phospholipase A2 (PLA2) mediates cellular destructive processes as well as normal physiological responses in neuronal cells. In this study, we examined whether PLA2 can be activated by PCBs in PC12 cells. Of the congeners tested, ortho-substituted PCBs were found to induce PLA2 activation. PLA2 activation by 2,2',4,6-tetrachlorobiphenyl (TeCB), the most potent congener, was inhibited by bromoenol lactone (BEL), a calcium-independent PLA2 (iPLA2) inhibitor, and methyl arachidonyl fluorophosphonate (MAFP), a cytosolic PLA2 and iPLA2 inhibitor. In the case of Ca2+, although 2,2',4,6-TeCB increased [Ca2+]i in the presence of extracellular Ca2+, PLA2 activation was not inhibited by EGTA and 1,2-bis (o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra (acetoxy-methyl) ester, an extracellular and an intracellular Ca2+ chelator, respectively. On the other hand, 2,2',4,6-TeCB-induced Ca2+ increase was partially inhibited by BEL and MAFP. In addition, 2,2',4,6-TeCB induced apoptotic cell death in these cells. Taken together, our results suggest that ortho-substituted PCBs might induce apoptosis through PLA2-mediated Ca2+ influx, which provides a clue to understand the mechanism of neurotoxic effects of ortho-substituted PCBs.

Aroclor 1254 alters morphology, survival, and gene expression in Xenopus laevis tadpoles

PCBs are persistent environmental contaminants that cause a variety of adverse health effects in wildlife and humans. This article describes the use of signature gene expression patterns that link increased PCB exposure with progressive, adverse biological effects. Developing Xenopus laevis tadpoles of two age classes were exposed to the PCB mixture Aroclor 1254 for 2 days. Real-time PCR was used to quantitate mRNA expression for 11 physiologically relevant, potential bioindicator genes. Younger tadpoles (5 days postfertilization) were resistant to Aroclor 1254 and showed few changes in gross morphology, swimming behavior, survival, or gene expression. Older tadpoles (11 days postfertilization) were more susceptible to Aroclor 1254. Exposure to 25 and 50 ppm Aroclor 1254 caused alterations in gross morphology and swimming behavior and statistically significant decreases in survival. These tadpoles showed statistically significant decreases in gene expression for 9 out of the 11 genes measured. Tadpoles exposed to 10 ppm showed incipient health changes but had gene expression profiles similar to the tadpoles treated with higher doses of Aroclor 1254. Tadpoles exposed to 1 ppm did not exhibit any observable adverse health effects, yet statistically significant decreases in gene expression occurred in these tadpoles (4 out of 11 genes). After prolonged exposure, tadpoles exposed to 1 and 10 ppm Aroclor 1254 exhibited health effects similar to those exposed to higher concentrations. Therefore, changes in expression of specific genes may serve not only as molecular bioindicators of Aroclor 1254 exposure but also as predictors of impending adverse health effects.