Perfluorooctane sulfonate-induced apoptosis of cerebellar granule cells is mediated by ERK 1/2 pathway

Sodium p-perfluorinated noneoxybenzen sulfonate (OBS) induced neurotoxicity in zebrafish through mitochondrial dysfunction

Sodium p-perfluorous nonenoxybenzene sulfonate (OBS)-one of the main alternatives to perfluorooctane sulfonate-has been increasingly detected in both aquatic environments and human bodies. Therefore, the pathogenic risks of OBS exposure warrant attention, especially its central nervous system toxicity mechanism under long-term exposure. In this study, the effects and mechanisms of OBS on the zebrafish brain at 40 days post exposure were examined. The results demonstrated that at 3.2 μg/L, OBS had no significant effect on the zebrafish brain, but 32 μg/L OBS caused depression or poor social behavior in zebrafish and reduced both their memory and survival ability. These changes were accompanied by histological damage and cell apoptosis. Furthermore, OBS caused the accumulation of excessive reactive oxygen species in the fish brain, leading to oxidative stress and subsequently cell apoptosis. Moreover, an imbalance of both inflammatory factors (IL-6, IL-1β, IL-10, TNF-α, and NF-κB) and neurotransmitters (GABA and Glu) led to neuroinflammation. Additionally, 32 μg/L OBS induced decreases in mitochondrial membrane potential and Na+-K+-ATPase activity, leading to both mitochondrial structural damage and the emergence of mitochondrial autophagosomes, partly explaining the neurotoxicity of OBS. These results help to analyze the target sites and molecular mechanisms of OBS neurotoxicity and provide a basis for the scientific evaluation of its health risks to humans.

Role of intrinsic apoptosis in environmental exposure health outcomes

Environmental exposures are linked to diseases of high public health concern, including cancer, neurodegenerative disorders, and autoimmunity. These diseases are caused by excessive or insufficient cell death, prompting investigation of mechanistic links between environmental toxicants and dysregulation of cell death pathways, including apoptosis. This review describes how legacy and emerging environmental exposures target the intrinsic apoptosis pathway to potentially drive pathogenesis. Recent discoveries reveal that dynamic regulation of apoptosis may heighten the vulnerability of healthy tissues to exposures in children, and that apoptotic signaling can guide immune responses, tissue repair, and tumorigenesis. Understanding how environmental toxicants dysregulate apoptosis will uncover opportunities to deploy apoptosis-modulating agents for the treatment or prevention of exposure-linked diseases.

Astaxanthin ameliorates dopaminergic neuron damage in paraquat-induced SH-SY5Y cells and mouse models of Parkinson's disease

Parkinson's disease (PD) is the second largest neurodegenerative disorder caused by the decreased number of dopaminergic (DAc) neurons in the substantia nigra pars compacta (SNpc). There is evidence that oxidative stress can contribute degeneration of DAc neurons in SNpc which is mainly caused by apoptotic cell death. Thus, suppressing oxidative stress and apoptosis of DAc neurons is an effective strategy to mitigate the progress of PD. Astaxanthin (AST) is a carotenoid, which mainly exists in marine organisms and is a powerful biological antioxidant. In this study, we aimed to determine the neuroprotective effect of AST on paraquat (PQ) -induced models of PD in vitro and in vivo. Here, we showed that AST significantly enhanced cell survival of SH-SY5Y cells against PQ toxicity by suppressing apoptotic cell death and oxidative stress. Moreover, we found that AST significantly ameliorated PQ-induced behavioral disorders associated with PD in C57BL/6 J mice and the damage to DAc neurons in the SNpc of mice. Lastly, we found that the neuroprotective effects of AST were conducted through inhibiting PQ-induced activation of MAPK signaling. In conclusion, our study indicates that AST had a strong protective effect on PQ-induced oxidative stress and antagonized apoptotic cell death in SH-SY5Y cells and PQ-induced mice PD model, which might provide new insights of AST for PD treatment.

ERK: A Double-Edged Sword in Cancer. ERK-Dependent Apoptosis as a Potential Therapeutic Strategy for Cancer

The RAF/MEK/ERK signaling pathway regulates diverse cellular processes as exemplified by cell proliferation, differentiation, motility, and survival. Activation of ERK1/2 generally promotes cell proliferation, and its deregulated activity is a hallmark of many cancers. Therefore, components and regulators of the ERK pathway are considered potential therapeutic targets for cancer, and inhibitors of this pathway, including some MEK and BRAF inhibitors, are already being used in the clinic. Notably, ERK1/2 kinases also have pro-apoptotic functions under certain conditions and enhanced ERK1/2 signaling can cause tumor cell death. Although the repertoire of the compounds which mediate ERK activation and apoptosis is expanding, and various anti-cancer compounds induce ERK activation while exerting their anti-proliferative effects, the mechanisms underlying ERK1/2-mediated cell death are still vague. Recent studies highlight the importance of dual-specificity phosphatases (DUSPs) in determining the pro- versus anti-apoptotic function of ERK in cancer. In this review, we will summarize the recent major findings in understanding the role of ERK in apoptosis, focusing on the major compounds mediating ERK-dependent apoptosis. Studies that further define the molecular targets of these compounds relevant to cell death will be essential to harnessing these compounds for developing effective cancer treatments.

Perfluorooctane sulfonate and bisphenol A induce a similar level of mast cell activation via a common signaling pathway, Fyn-Lyn-Syk activation

Perfluoroalkyl compounds (PFCs) as food contaminants are widely distributed persistent organic pollutants (POPs) and have been suggested to induce immune dysfunction. However, their effects on immune function are not conclusive. Mast cells play a central role in allergic and non-allergic inflammatory responses. Therefore, we have examined the effects of PFCs (PFHxS, PFOA, PFOS) on mast cell-mediated inflammatory responses using in vitro mouse bone marrow-derived mast cells (BMMCs) and human mast cells (HMC-1) and in vivo mice model. The effects of PFCs were compared with those of bisphenol A (BPA), a well-studied environmental pollutant. Among PFCs tested, PFOS had the highest effects. Both PFOS and BPA increased degranulation and production of inflammatory eicosanoids in mast cells at a similar level, which subsequently led to increased skin edema and serum LTC₄ and PGD₂ in mice. Both PFOS and BPA increased not only downstream signaling (PLCγ1, AKT, ERK), but also upstream signaling (Fyn, Lyn, Syk/LAT) in mast cells. Taken together, PFOS and BPA induce mast cell-mediated inflammatory responses via a common signaling pathways. Our results may help establish the scientific basis for understanding the etiology of mast cell-mediated inflammatory responses and improve the immune dysfunction risk assessment for emerging POPs such as PFCs.

A human relevant mixture of persistent organic pollutants (POPs) and perfluorooctane sulfonic acid (PFOS) differentially affect glutamate induced excitotoxic responses in chicken cerebellum granule neurons (CGNs) in vitro

Primary cultures of cerebellar granule neurons (CGNs) derived from chicken embryos were used to explore the effects on developmental neurotoxicity by a complex defined mixture of persistent organic pollutants (POPs). Its chemical composition and concentrations were based on blood levels in the Norwegian/Scandinavian population. Perfluorooctane sulfonic acid (PFOS) alone, its most abundant compound was also evaluated. Different stages of CGNs maturation, between day in vitro (DIV) 1, 3, and 5 were exposed to the POP mixture, or PFOS alone. Their combination with glutamate, an excitatory endogenous neurotransmitter important in neurodevelopment, also known to cause excitotoxicity was evaluated. Outcomes with the mixture at 500x blood levels were compared to PFOS at its corresponding concentration of 20 μM. The POP mixture reduced tetrazolium salt (MTT) conversion at earlier stages of maturation, compared to PFOS alone. Glutamate-induced excitotoxicity was enhanced above the level of that induced by glutamate alone, especially in mature CGNs at DIV5. Glutathione (GSH) concentrations seemed to set the level of sensitivity for the toxic insults from exposures to the pollutants. The role of N-methyl-D-aspartate receptor (NMDA-R) mediated calcium influx in pollutant exposures was investigated using the non-competitive and competitive receptor antagonists MK-801 and CGP 39551. Observations indicate a calcium-independent, but still NMDA-R dependent mechanism in the absence of glutamate, and a calcium- and NMDA-R dependent one in the presence of glutamate. The outcomes for the POP mixture cannot be explained by PFOS alone, indicating that other chemicals in the mixture contribute its overall effect.

Neurotoxic effects of lactational exposure to perfluorooctane sulfonate on learning and memory in adult male mouse

The present study aims to examine the effect of early lactational perfluorooctane sulfonate (PFOS) exposures on learning and memory in male mice and reveal the underlying mechanisms involved. PFOS solution was orally administered to dams from the postpartum days 1-14, so that pups would be exposed through breast milk. At 8-10 weeks of age, we performed object location test (OLT), object recognition test (ORT), and pairwise visual discrimination (VD) task. We also performed in vivo microdialysis, and mRNA and protein analysis of genes responsible for hippocampal development and function. In both OLT and ORT, the performance of mice in the PFOS-exposed group was significantly lower than those in the control group. In the VD task, the PFOS-exposed group learned significantly slower than the control group. Concentrations of glutamate and gamma-aminobutyric acid in the dorsal hippocampus were significantly higher in the PFOS-exposed group than in the control group. No notable differences were shown in our mRNA and protein studies. The present study showed that lactational PFOS exposure has a profound, long-lasting neurotoxic effect in the hippocampus and consequently leads to learning and memory deficits.

Expression Levels of the Immune-Related p38 Mitogen-Activated Protein Kinase Transcript in Response to Environmental Pollutants on Macrophthalmus japonicus Crab

Environmental pollution in the aquatic environment poses a threat to the immune system of benthic organisms. The Macrophthalmus japonicus crab, which inhabits tidal flat sediments, is a marine invertebrate that provides nutrient and organic matter cycling as a means of purification. Here, we characterized the M. japonicus p38 mitogen-activated protein kinase (MAPK) gene, which plays key roles in the regulation of cellular immune and apoptosis responses. M. japonicusp38 MAPK displayed the characteristics of the conserved MAPK family with Thr-Gly-Tyr (TGY) motif and substrate-binding site Ala-Thr-Arg-Trp (ATRW). The amino acid sequence of the M. japonicus p38 MAPK showed a close phylogenetic relationship to Eriocheir sinensis MAPK14 and Scylla paramamosainp38 MAPK. The phylogenetic tree displayed two origins of p38 MAPK: crustacean and insect. The tissue distribution patterns showed the highest expression in the gills and hepatopancreas of M. japonicus crab. In addition, p38 MAPK expression in M. japonicus gills and hepatopancreas was evaluated after exposure to environmental pollutants such as perfluorooctane sulfonate (PFOS), irgarol, di(2-ethylhexyl) phthalate (DEHP), and bisphenol A (BPA). In the gills, p38 MAPK expression significantly increased after exposure to all concentrations of the chemicals on day 7. However, on day 1, there were increased p38 MAPK responses observed after PFOS and irgarol exposure, whereas decreased p38 MAPK responses were observed after DEHP and BPA exposure. The upregulation of p38 MAPK gene also significantly led to M. japonicus hepatopancreas being undertested in all environmental pollutants. The findings in this study supported that anti-stress responses against exposure to environmental pollutants were reflected in changes in expression levels in M. japonicusp38 MAPK signaling regulation as a cellular defense mechanism.

Prenatal and childhood exposure to poly- and perfluoroalkyl substances (PFAS) and cognitive development in children at age 8 years

BACKGROUND

Toxicological studies indicate that poly- and perfluoroalkyl substances (PFAS) may be neurotoxic, but human studies have yet to provide compelling evidence for PFAS' impact on cognitive abilities.

OBJECTIVE

To test whether prenatal and childhood PFAS are associated with cognitive abilities at 8 years and whether sex modifies these associations.

METHODS

We included 221 mother-child pairs from the Health Outcomes and Measures of the Environment (HOME) Study, a birth cohort in Cincinnati, OH (USA). We quantified PFAS in maternal serum at 16 ± 3 weeks gestation and in child serum at 3 and 8 years. We used the Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV) at age 8 years, assessing Full Scale IQ (FSIQ), verbal comprehension, perceptual reasoning, working memory, and processing speed. We used multiple informant models to estimate covariate-adjusted differences in WISC-IV scores by repeated ln-transformed PFAS.

RESULTS

Prenatal and childhood perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) were not associated with WISC-IV measures. We observed an increase of 4.1-points (95% CI 0.3, 8.0) and 5.7-points (95% CI 1.2, 10.2) in working memory with 1-ln unit increase in prenatal perfluorooctanoate (PFOA) and perfluorononanoate (PFNA), respectively. In addition, PFNA at 3 years was associated with better FSIQ and perceptual reasoning. Child sex modified the relationship between prenatal PFOA and FSIQ; the association was positive in females only. Sex also modified the association between concurrent PFOS and FSIQ, with males having higher scores.

CONCLUSION

We did not observe adverse associations between prenatal and childhood PFAS and cognitive function at age 8 years.

Potential health effects of emerging environmental contaminants perfluoroalkyl compounds

Environmental contaminants are one of the important causal factors for development of various human diseases. In particular, the perinatal period is highly vulnerable to environmental toxicants and resultant dysregulation of fetal development can cause detrimental health outcomes potentially affecting life-long health. Perfluoroalkyl compounds (PFCs), emerging environmental pollutants, are man-made organic molecules, which are widely used in diverse industries and consumer products. PFCs are non-degradable and bioaccumulate in the environment. Importantly, PFCs can be found in cord blood and breast milk as well as in the general population. Due to their physicochemical properties and potential toxicity, many studies have evaluated the health effects of PFCs. This review summarizes the epidemiological and experimental studies addressing the association of PFCs with neurotoxicity and immunotoxicity. While the relationships between PFC levels and changes in neural and immune health are not yet conclusive, accumulative studies provide evidence for positive associations between PFC levels and the incidence of attention deficit hyperactivity disorder and reduced immune response to vaccination both in children and adults. In conclusion, PFCs have the potential to affect human health linked with neurological disorders and immunosuppressive responses. However, our understanding of the molecular mechanism of the effects of PFCs on human health is still in its infancy. Therefore, along with efforts to develop methods to reduce exposure to PFCs, studies on the mode of action of these chemicals are required in the near future.

Protection of Taurine Against PFOS-Induced Neurotoxicity in PC12 Cells

As a new member of persistent organic pollutants, the potent neurotoxicity of perfluorooctane sulfonates (PFOS) found in epidemiological studies and laboratory research has drawn increasing attention around the world. Previous studies showed that apoptosis driven by oxidative stress and autophagy were both observed in PFOS-induced toxicity. Taurine has been demonstrated to exert potent protections against oxidative stress as an efficient antioxidant. Whether taurine could protect against the PFOS neurotoxicity is not known. In the present study, PC12 cells were treated with several concentrations of PFOS (31.25, 250 μM) for 24 h. 3-(4,5-Dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was applied to assess the cell viability. DCFH-DA detector was used to explore the production of ROS. Caspase 3 activity was used to reflect the possible apoptosis pathway. The lyso-tracker red dying was invited to evaluate the autophagy. Our data showed that taurine could significantly reverse the decreased viability and the increased ROS production in PC12 cells treated with PFOS. Moreover, the increased autophagy and apoptosis elicited by PFOS in PC12 cells could also be attenuated by taurine. Collectively, our results indicate that taurine may be an effective antioxidant in fighting against PFOS cytotoxicity and therefore could potentially serve as a preventative and therapeutic agent for environmental pollution-related toxicities.

Prenatal and childhood exposure to perfluoroalkyl substances (PFAS) and measures of attention, impulse control, and visual spatial abilities

BACKGROUND

Despite evidence from toxicological studies describing the potential neurotoxicity of perfluoroalkyl substances (PFAS), their role in neurodevelopment remains uncertain amid inconsistent findings from epidemiological studies.

METHODS

Using data from 218 mother-child dyads from the Health Outcomes and Measures of the Environment Study, we examined prenatal and childhood (3 and 8 years) serum concentrations of four PFAS and inattention, impulsivity, and visual spatial abilities. At 8 years, we used the Conners' Continuous Performance Test-II to assess attention and impulse control and the Virtual Morris Water Maze (VMWM) to measure visual spatial abilities.

RESULTS

In multiple informant models, there was no evidence to indicate that prenatal or childhood PFAS are associated with attention. However, there was an inverse association between prenatal ln-perfluorooctanoate (PFOA) and errors of commission (β = -2.0, 95% Confidence Interval [CI] -3.8, -0.3). Ln-perfluorononanoate (PFNA) at 3 years was associated with longer (poorer) VMWM completion times of 3.6 seconds (CI 1.6, 5.6). However, higher concurrent concentrations of ln-perfluorohexane sulfonate (PFHxS) (β = -2.4 s, 95% CI -4.4, -0.3) were associated with shorter (better) times. Higher prenatal PFHxS was positively associated with percentage of traveling distance in the correct quadrant (β = 4.2%, 95% CI 0.8, 7.7), indicating better performance.

CONCLUSION

Findings were mixed for prenatal and childhood PFAS concentrations and visual spatial abilities. There is not enough evidence to support that PFAS are associated with visual spatial abilities as assessed by the VMWM or CPT-II measures of inattention or impulsivity in children at age 8 years.

Childhood perfluoroalkyl substance exposure and executive function in children at 8 years

BACKGROUND

Toxicological studies highlight the potential neurotoxicity of perfluoroalkyl substances (PFAS) during fetal development. However, few epidemiological studies have examined the impact of childhood PFAS on neurodevelopment.

METHODS

We employed data from 208 children in the Health Outcomes and Measures of the Environment Study, a birth cohort (Cincinnati, OH), to examine associations of six serum PFAS concentrations measured at 3 and 8 years with executive function assessed at 8 years using the validated parent-completed Behavior Rating Inventory of Executive Function survey. We used multiple informant models to identify susceptible windows of neurotoxicity to PFAS and executive function. We investigated trajectories of PFAS concentrations and whether sex modified these associations.

RESULTS

Each ln-increase in perfluorononanoate (PFNA) at 8 years was associated with a 3.4-point increase (95% CI 0.4, 6.3) in metacognition score, indicating poorer function. Children with PFNA above the median at 8 years had poorer global executive functioning compared to children with concentrations consistently below median levels (β = 6.5, 95% CI 0.2, 12.9). Higher concurrent PFNA was associated with poorer behavior regulation among males, while associations among females were null (p_PFNA×sex = 0.018). Children with higher concurrent perfluorooctanoate (PFOA) had increased odds of being at risk of having clinical impairments in metacognition (OR = 3.18, 95% CI 1.17, 8.60). There were no associations between perfluorooctane sulfonate and perfluorohexane sulfonate and executive function.

CONCLUSIONS

PFNA and PFOA at 8 years, but not 3 years, may be related to poorer executive function at 8 years. Results need to be confirmed in cohort studies with larger sample sizes.

Perfluorobutanesulfonic acid (PFBS) potentiates adipogenesis of 3T3-L1 adipocytes

Perfluorobutanesulfonic acid (PFBS) is used as the replacement of perfluorooctanesulfonic acid (PFOS) since 2000 because of the concern on PFOS' persistence in the environment and the bioaccumulation in animals. Accumulating evidence has shown the correlation between the exposure to perfluorinated compounds and enhanced adipogenesis. There is no report, however, of the effect of PFBS on adipogenesis. Therefore, the present work aimed to investigate the role of PFBS in adipogenesis using 3T3-L1 adipocytes. PFBS treatment for 6 days extensively promoted the differentiation of 3T3-L1 preadipocytes to adipocytes, resulting in significantly increased triglyceride levels. In particular, the treatments of PFBS at the early adipogenic differentiation period (day 0-2) were positively correlated with increased the triglyceride accumulation on day 6. PFBS treatments significantly increased the protein and mRNA levels of the master transcription factors in adipocyte differentiation; CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator-activated receptor gamma (PPARγ), along with acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), the key proteins in lipogenesis. PFBS significantly activated the phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2) after 4-h treatment, and PFBS' effect on triglyceride was abolished by U0126, a specific MAPK/ERK kinase (MEK) inhibitor. In conclusion, PFBS increased the adipogenesis of 3T3-L1 adipocytes, in part, via MEK/ERK-dependent pathway.

Evaluation of PFOS-mediated neurotoxicity in rat primary neurons and astrocytes cultured separately or in co-culture

Perfluorooctane sulfonate (PFOS) is a potential neurotoxicant reported by epidemiological investigations and experimental studies, while the underlying mechanisms are still unclear. Astrocytes not only support for the construction of neurons, but also conduct neuronal functions through glutamate-glutamine cycle in astrocyte-neuron crosstalk. In the present study, the effect of PFOS exposure on rat primary hippocampal neurons or cortex astrocytes was evaluated. Then the role of the astrocytes in PFOS-induced toxic effect on neurons was explored with astrocyte-neuron co-culture system. Exposure of rat primary hippocampal neurons to PFOS has led to oxidation-antioxidation imbalance, increased apoptosis and abnormal autophagy. The adverse effect of PFOS on rat primary cortex astrocytes manifested in the form of altered extracellular glutamate and glutamine concentrations, decreased glutamine synthase activity, as well as decreased gene expression of glutamine synthase, glutamate transporters and glutamine transporters in the glutamate-glutamine cycle. Especially, the alleviation of PFOS-inhibited neurite outgrowth in neurons could be observed in astrocyte-neuron co-culture system, though the ability of astrocytes in fostering neurite outgrowth was affected by PFOS. These results indicated that both astrocytes and neurons might be the targets of PFOS-induced neurotoxicity, and astrocytes could protect against PFOS-inhibited neurite outgrowth in primary cultured neurons. Our research might render some information in explaining the mechanisms of PFOS-induced neurotoxicity.

ROS-mediated apoptosis of HAPI microglia through p53 signaling following PFOS exposure

Perfluorooctane sulfonate (PFOS), the most extensively studied member of perfluoroalkyl and polyfluoroalkyl substances (PFASs), has been thought to be toxic to the central nervous system (CNS) of mammals. However, the neurotoxic effects of PFOS remain largely unknown. In this study, the effect of PFOS on microglial apoptosis was examined. The results showed that PFOS could significantly reduce the cell viability and mediate cell apoptosis in HAPI microglia, which was closely accompanied with ROS production and p53 overexpression. Moreover, p53 interference significantly ameliorated PFOS-triggered cytotoxic effects in HAPI microglia, including the downregulation of cleaved PARP and cleaved caspase 3. Interestingly, NAC, a ROS inhibitor, inhibited p53 expression, and decreased the apoptosis of HAPI microglia. Taken together, these findings suggest that upregulated production of ROS plays a vital role in PFOS-mediated apoptosis in HAPI microglia via the modulation of p53 signaling.

PFOS Disturbs BDNF-ERK-CREB Signalling in Association with Increased MicroRNA-22 in SH-SY5Y Cells

Perfluorooctane sulfonate (PFOS), a ubiquitous environmental pollutant, is neurotoxic to mammalian species. However, the underlying mechanism of its neurotoxicity was unclear. We hypothesized that PFOS suppresses BDNF expression to produce its neurotoxic effects by inhibiting the ERK-CREB pathway. SH-SY5Y human neuroblastoma cells were exposed to various concentrations of PFOS to examine the role of the BDNF-ERK-CREB signalling pathway in PFOS-induced apoptosis and cytotoxicity. Furthermore, to ascertain the mechanism by which PFOS reduces BDNF signalling, we examined the expression levels of miR-16 and miR-22, which potentially regulate BDNF mRNA translation at the posttranscriptional level. Results indicated that PFOS significantly decreased cell viability and induced apoptosis in SH-SY5Y cells. In addition, BDNF and pERK protein levels decreased after PFOS treatment; however, pCREB protein levels were significantly elevated in PFOS treated groups. TrkB protein expression increased in the 10 μM and 50 μM PFOS groups and significantly decreased in the 100 μM PFOS group. Our results demonstrated that PFOS exposure decreased miR-16 expression and increased miR-22 expression, which may represent a possible mechanism by which PFOS decreases BDNF protein levels. PFOS may inhibit BDNF-ERK-CREB signalling by increasing miR-22 levels, which may, in part, explain the mechanism of PFOS neurotoxicity.

The potential for chemical mixtures from the environment to enable the cancer hallmark of sustained proliferative signalling

The aim of this work is to review current knowledge relating the established cancer hallmark, sustained cell proliferation to the existence of chemicals present as low dose mixtures in the environment. Normal cell proliferation is under tight control, i.e. cells respond to a signal to proliferate, and although most cells continue to proliferate into adult life, the multiplication ceases once the stimulatory signal disappears or if the cells are exposed to growth inhibitory signals. Under such circumstances, normal cells remain quiescent until they are stimulated to resume further proliferation. In contrast, tumour cells are unable to halt proliferation, either when subjected to growth inhibitory signals or in the absence of growth stimulatory signals. Environmental chemicals with carcinogenic potential may cause sustained cell proliferation by interfering with some cell proliferation control mechanisms committing cells to an indefinite proliferative span.

In vivo immunotoxicity of perfluorooctane sulfonate in BALB/c mice: Identification of T-cell receptor and calcium-mediated signaling pathway disruption through gene expression profiling of the spleen

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that is used worldwide and is continuously being detected in biota and the environment, thus presenting potential threats to the ecosystem and human health. Although PFOS is highly immunotoxic, its underlying molecular mechanisms remain largely unknown. The present study examined PFOS-induced immunotoxicity in the mouse spleen and explored its underlying mechanisms by gene expression profiling. Oral exposure of male BALB/c mice for three weeks followed by one-week recovery showed that a 10 mg/kg/day PFOS exposure damaged the splenic architecture, inhibited T-cell proliferation in response to mitogen, and increased the percentages of T helper (CD3(+)CD4(+)) and cytotoxic T (CD3(+)CD8(+)) cells, despite the decrease in the absolute number of these cells. A delayed type of PFOS immunotoxicity was observed, which mainly occurred during the recovery period. Global gene expression profiling of mouse spleens and QRT-PCR analyses suggest that PFOS inhibited the expression of genes involved in cell cycle regulation and NRF2-mediated oxidative stress response, and upregulated those in TCR signaling, calcium signaling, and p38/MAPK signaling pathways. Western blot analysis confirmed that the expressions of CAMK4, THEMIS, and CD3G, which were involved in the upregulated pathways, were induced upon PFOS exposure. Acute PFOS exposure modulated calcium homoeostasis in splenocytes. These results indicate that PFOS exposure can activate TCR signaling and calcium ion influx, which provides a clue for the potential mechanism of PFOS immunotoxicity. The altered signaling pathways by PFOS treatment as revealed in the present study might facilitate in better understanding PFOS immunotoxicity and explain the association between immune disease and PFOS exposure.

Connexin 43 mediates PFOS-induced apoptosis in astrocytes

Perfluorooctane sulfonate (PFOS) is a man-made environmental pollutant that is toxic to mammals. However, the neurotoxic effects of PFOS remain largely unexplored. In this study, we determined the role of an astrocyte specific gap junction protein, connexin 43 (Cx43), in PFOS-induced apoptosis. The rate of astrocyte apoptosis was higher in cortex astrocytes after PFOS treatment. These astrocytes also showed up-regulated expression of Cx43 and higher levels of cleaved caspase-3. Elevated ROS accumulation and decreased ΔΨm also confirmed the presence of PFOS-induced apoptosis. However, the exposure of astrocytes to PFOS together with carbenoxolone (CBX) significantly reduced both Cx43 and cleaved caspase-3 levels. These results indicate that Cx43 plays a proapoptotic role in PFOS-induced apoptosis in cortex astrocyte cells.

Reactive oxygen species mediate nitric oxide production through ERK/JNK MAPK signaling in HAPI microglia after PFOS exposure

Perfluorooctane sulfonate (PFOS), an emerging persistent contaminant that is commonly encountered during daily life, has been shown to exert toxic effects on the central nervous system (CNS). However, the molecular mechanisms underlying the neurotoxicity of PFOS remain largely unknown. It has been widely acknowledged that the inflammatory mediators released by hyper-activated microglia play vital roles in the pathogenesis of various neurological diseases. In the present study, we examined the impact of PFOS exposure on microglial activation and the release of proinflammatory mediators, including nitric oxide (NO) and reactive oxidative species (ROS). We found that PFOS exposure led to concentration-dependent NO and ROS production by rat HAPI microglia. We also discovered that there was rapid activation of the ERK/JNK MAPK signaling pathway in the HAPI microglia following PFOS treatment. Moreover, the PFOS-induced iNOS expression and NO production were attenuated after the inhibition of ERK or JNK MAPK by their corresponding inhibitors, PD98059 and SP600125. Interestingly, NAC, a ROS inhibitor, blocked iNOS expression, NO production, and activation of ERK and JNK MAPKs, which suggested that PFOS-mediated microglial NO production occurs via a ROS/ERK/JNK MAPK signaling pathway. Finally, by exposing SH-SY5Y cells to PFOS-treated microglia-conditioned medium, we demonstrated that NO was responsible for PFOS-mediated neuronal apoptosis.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: focus on the cancer hallmark of tumor angiogenesis

One of the important 'hallmarks' of cancer is angiogenesis, which is the process of formation of new blood vessels that are necessary for tumor expansion, invasion and metastasis. Under normal physiological conditions, angiogenesis is well balanced and controlled by endogenous proangiogenic factors and antiangiogenic factors. However, factors produced by cancer cells, cancer stem cells and other cell types in the tumor stroma can disrupt the balance so that the tumor microenvironment favors tumor angiogenesis. These factors include vascular endothelial growth factor, endothelial tissue factor and other membrane bound receptors that mediate multiple intracellular signaling pathways that contribute to tumor angiogenesis. Though environmental exposures to certain chemicals have been found to initiate and promote tumor development, the role of these exposures (particularly to low doses of multiple substances), is largely unknown in relation to tumor angiogenesis. This review summarizes the evidence of the role of environmental chemical bioactivity and exposure in tumor angiogenesis and carcinogenesis. We identify a number of ubiquitous (prototypical) chemicals with disruptive potential that may warrant further investigation given their selectivity for high-throughput screening assay targets associated with proangiogenic pathways. We also consider the cross-hallmark relationships of a number of important angiogenic pathway targets with other cancer hallmarks and we make recommendations for future research. Understanding of the role of low-dose exposure of chemicals with disruptive potential could help us refine our approach to cancer risk assessment, and may ultimately aid in preventing cancer by reducing or eliminating exposures to synergistic mixtures of chemicals with carcinogenic potential.

Reduction of progesterone, estradiol and hCG secretion by perfluorooctane sulfonate via induction of apoptosis in human placental syncytiotrophoblasts

INTRODUCTION

Perfluorooctane sulfonate (PFOS) is widely used as surfactants, lubricants, adhesives, fire retardants and propellants. Animal experiments have shown that PFOS can potentially influence reproductive function. The objective of the present study was to investigate the effects of PFOS on the endocrine function of human placental syncytiotrophoblasts.

METHODS

Primary human placental cytotrophoblasts were isolated from term placenta. After syncytialization, the levels of aromatase and apoptosis-related proteins including caspase3, Bcl-2 and Bax were examined after treatment with PFOS from 0.0001 μM to 1 μM or PFOS (0.1 μM) in the presence and absence of apoptosis inhibitor Z-VAD-FMK (30 μM) for 24 h.

RESULTS

PFOS suppressed aromatase level and the secretion of estradiol, hCG and progesterone in a concentration-dependent manner from 0.0001 μM to 1 μM with a significant inhibition at 0.001 μM and above in human placental syncytiotrophoblasts. Furthermore PFOS reduced cell viability and induced apoptosis in human placental syncytiotrophoblasts as revealed by increases of pro-apoptosis proteins such as Bax and cleaved-caspase3, and decreases of pro-caspase3 and anti-apoptosis protein Bcl-2. The apoptosis induced by PFOS was further illustrated by increased DNA fragmentation and nuclear condensation. Blocking apoptosis with pan-caspase inhibitor Z-VAD-FMK, the impairment of placental endocrine function by PFOS was restored.

DISCUSSION

These results indicate that PFOS may disrupt the secretion of hCG, progesterone and estradiol by human placental syncytiotrophoblasts via induction of apoptosis.

NMDA receptor-mediated ERK 1/2 pathway is involved in PFHxS-induced apoptosis of PC12 cells

Perfluorohexanesulfonate (PFHxS) is one of the major perfluoroalkyl compounds (PFCs) found in human blood and its possible neurotoxicity has been suggested. However, the neuronal responses to PFHxS are not much known. Many studies have demonstrated that the early exposure to environmental chemicals increases the risk of neurodegenerative diseases such as Parkinson's disease in later life. In this study, the effects of PFHxS on the neuronal cell death and the underlying mechanisms were examined using PC12 cells as a model of dopaminergic neuron. The treatment with PFHxS reduced cell viability in a dose-dependent manner. PFHxS increased cell apoptosis which was measured by caspase-3 activity and TUNEL staining. MK801, a NMDA receptor antagonist reduced PFHxS-induced apoptosis. PFHxS increased the activations of ERK1/2, JNK and p38 MAPK with different temporal activations. The treatment with PD98059, an ERK inhibitor, significantly reduced apoptosis, whereas SB203580, a p38 MAPK inhibitor, had no effect. JNK inhibition by SP600125 significantly increased apoptosis. PFHxS exposure also increased ROS formation, which was completely blocked by antioxidants, Trolox or N-acetylcysteine (NAC). However, neither Trolox nor NAC reduced PFHxS-increased apoptosis, suggesting that ROS may not be a critical mediator for PFHxS-induced apoptosis of cells. Moreover, ERK activation induced by PFHxS was blocked by MK801 but not antioxidants. Taken together, these results have demonstrated that PFHxS induces the apoptosis of dopaminergic neuronal cells, where NMDA receptor-mediated ERK pathway plays a pro-apoptotic role and JNK plays an anti-apoptotic role. Our results may contribute to understanding cellular mechanisms for PFHxS-induced neurotoxicity.

PFHxS induces apoptosis of neuronal cells via ERK1/2-mediated pathway

Perfluorohexanesulfonate (PFHxS) is one of the most widely distributed perfluoroalkyl compounds (PFCs) and its possible neurotoxicity has been suggested. However, the effects of PFHxS on neuronal function remain to be elucidated. In this study, the effects of PFHxS on neuronal cell death and the underlying mechanisms were examined. Cerebellar granule cells (CGCs) were isolated from 7-day old rat pups and maintained in culture for additional 7d. The apoptotic effects of PFHxS were determined by caspase-3 activity and TUNEL staining. PFHxS increased the apoptotic death of CGC in concentration-dependent manner. It also increased the activation of ERK1/2, JNK and p38 MAPK with different temporal activation. PD98059, an inhibitor of ERK1/2 pathway, completely blocked PFHxS-induced apoptosis whereas SP600125, a JNK inhibitor, significantly increased the apoptosis, showing their opposite roles in the apoptosis of CGCs. Treatment of antioxidants, Trolox or N-acetylcysteine (NAC), completely blocked ROS generation by PFHxS but neither of these antioxidants prevented PFHxS-induced apoptosis, suggesting that ROS may not play a key role in the process of apoptosis. PD98059 prevented ROS accumulation by PFHxS but the ERK1/2 activation was not affected by Trolox or NAC. These results indicate that ROS is one of downstream targets of ERK1/2, not vice versa. Taken together, PFHxS increased apoptosis of CGC in ERK1/2-dependent manner, where downstream pathway other than ROS may play a major role. This is a first report that PFHxS induces apoptosis of CGC isolated from the developing brain and its possible mode of action is associated with ERK1/2 pathway.

Neurotoxicity of perfluorooctane sulfonate to hippocampal cells in adult mice

Perfluorooctane sulfonate (PFOS) is a ubiquitous pollutant and found in the environment and in biota. The neurotoxicity of PFOS has received much concern among its various toxic effects when given during developing period of brain. However, little is known about the neurotoxic effects and potential mechanisms of PFOS in the mature brain. Our study demonstrated the neurotoxicity and the potential mechanisms of PFOS in the hippocampus of adult mice for the first time. The impairments of spatial learning and memory were observed by water maze studies after exposure to PFOS for three months. Significant apoptosis was found in hippocampal cells after PFOS exposure, accompanied with a increase of glutamate in the hippocampus and decreases of dopamine (DA) and 3,4-dihydrophenylacetic acid (DOPAC) in Caudate Putamen in the 10.75 mg/kg PFOS group. By two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) analysis, seven related proteins in the hippocampus that responded to PFOS exposure were identified, among which, Mib1 protein (an E3 ubiquitin-protein ligase), Herc5 (hect domain and RLD 5 isoform 2) and Tyro3 (TYRO3 protein tyrosine kinase 3) were found down-regulated, while Sdha (Succinate dehydrogenase flavoprotein subunit), Gzma (Isoform HF1 of Granzyme A precursor), Plau (Urokinase-type plasminogen activator precursor) and Lig4 (DNA ligase 4) were found up-regulated in the 10.75 mg/kg PFOS-treated group compare with control group. Furthermore, we also found that (i) increased expression of caspase-3 protein and decreased expression of Bcl-2, Bcl-XL and survivin proteins, (ii) the increased glutamate release in the hippocampus. All these might contribute to the dysfunction of hippocampus which finally account for the impairments of spatial learning and memory in adult mice.