Inhibition of the promotion of hepatocarcinogenesis by 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) by the deletion of the p50 subunit of NF-kappa B in mice

Ceramide/protein phosphatase 2A axis is engaged in gap junction impairment elicited by PCB153 in liver stem-like progenitor cells

The widespread environmental pollutant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) is a non-dioxin-like toxicant. It is a potential carcinogen compound able to induce gap junction (GJ) intercellular communication impairment, probably the first non-genomic event leading to tumor promotion. Although PCBs have been known for many years, the molecular mode of PCB153 action is still unclear. Recent studies from our research group have shown that the toxicant elicits a transient modulation of connexin (Cx) 43-formed GJs in hepatic stem-like WB-F344 cells involving sphingosine 1-phosphate (S1P) path. Taking into account that other strictly related bioactive sphingolipids, such as ceramide (Cer), may have different effects from S1P, here we aim to clarify the signaling paths engaged by PCB153 in the control of GJs, focusing primarily on the role of Cer. Accordingly, we have achieved a combined biomolecular and electrophysiological analysis of GJs in cultured WB-F344 cells treated with PCB153 at different time points. We have found that the toxicant elicited a time-dependent regulation of GJs formed by different Cx isoforms, through a transient modulation of Cer/Cer kinase (CerK) axis and, in turn, of protein phosphatase 2A (PP2A). Our new findings demonstrate the existence of a specific molecular mechanism downstream to Cer, which distinctly affects the voltage-dependent and -independent GJs in liver stem-like cells, and open new opportunities for the identification of additional potential targets of these environmental toxicants.

PCB153 reduces apoptosis in primary cultures of murine pituitary cells through the activation of NF-κB mediated by PI3K/Akt

Polychlorinated biphenyls (PCBs) are persistent pollutants involved in human tumorigenesis. PCB153 is a ubiquitous non-dioxin-like PCB with proliferative and anti-apoptotic effects. To explore the impact of PCB153 in the survival of pituitary cells, we exposed murine pituitary primary cells to PCB153 10 μM for 24 h. Apoptosis was assessed by RT-qPCR, Western-blot, immunoprecipitation, caspase activity, and immunofluorescence. We found that PCB153 decreased pituitary apoptosis through both the extrinsic and intrinsic pathways. PCB153 reduced the level of the pro-apoptotic protein p38-MAPK. Otherwise, PCB153 activated PI3K/Akt and Erk1/2 pathways and enhanced the expression and nuclear translocation of NF-κB. Cotreatments with specific inhibitors revealed that only PI3K/Akt changed the caspase-3 expression and NF-κB activation induced by PCB153. Also, PCB153 decreased the expression of the pro-apoptotic and pro-senescent cyclins p53 and p21. In summary, exposure to PCB153 leads to a downregulation of apoptosis in the pituitary driven by a PI3K/Akt-mediated activation of NF-κB.

Britanin Exhibits Potential Inhibitory Activity on Human Prostate Cancer Cell Lines Through PI3K/Akt/NF-κB Signaling Pathways

Britanin, a natural pseudoguaiacane sesquiterpene lactone, has significant antioxidant and anti-inflammatory activity, but little is known about its tumor inhibitory activity and the underlying mechanism. Here, we demonstrated in vitro and in vivo that britanin inhibited the growth of human prostate cancer cell lines (PC-3, PC-3-LUC, and DU-145). Through in vitro study, the results showed that britanin significantly decreased cell proliferation, migration, and motility. The moderate toxicity of britanin was determined with an acute toxicity study. A luciferase-labeled animal tumor xenograft model and bioluminescence imaging were applied, combining with biological validation for assessing the tumor progression. In vivo results demonstrated that britanin inhibited the growth of PC-3-LUC. The interleukin-2 level in mice was upregulated by britanin, which indicated that britanin induced antitumor immune activation. In addition, britanin downregulated the expression of nuclear factor (NF)-κB p105/p50, pp65, IκBα, pIκBα, phosphoinositide 3-kinase, pPI3k, Akt (protein kinase B, PKB), and pAkt proteins and upregulated expression of Bax. We discovered that britanin inhibits the growth of prostate cancer cells both in vitro and in vivo by regulating PI3K/Akt/NF-κB-related proteins and activating immunity. These findings shed light on the development of britanin as a promising agent for prostate cancer therapy.

Associations between functional polychlorinated biphenyls in adipose tissues and prognostic biomarkers of breast cancer patients

BACKGROUND

Exposure to polychlorinated biphenyls (PCBs) has been shown to influence expression of some biomarkers that are predictive/prognostic for breast cancer. Therefore, our study was conducted to further investigating associations of different functional PCBs in adipose tissue with breast cancer prognostic biomarkers.

METHODS

Two hundred and five breast cancer patients were recruited in Shantou, China. Breast adipose tissues were collected during their resection surgery and levels of 7 PCB congeners were analyzed by gas chromatography-mass spectrometry (GC-MS). The PCB congeners were divided into 4 groups according to structure-activity. Socio-demographic, clinical and pathological information were obtained from questionnaire and digital medical records. Odds ratios (ORs) for associations between prognostic biomarkers and PCB levels (tertile 3 [T3], tertile 2 [T2] vs. tertile 1) were estimated from logistic regression models.

RESULTS

Most PCB congeners were detectable, with a highest level (22.06 ng/g lipid) of PCB153. As for estrogenic PCBs, increased PCB52 exposure was positively associated with PR expression (OR_T2 = 2.36, P_trend = 0.054), but higher PCB101 level was negatively associated with HER-2 (OR_T3 = 0.24, P_trend = 0.029) and tumor size (OR = 0.43). Limited dioxin-like PCB138 exposure was positively associated with ER (OR_T2 = 3.23, OR_T3 = 3.77, P_trend = 0.047) but negatively with Top-IIα expression (OR_T2 = 0.35, OR_T3 = 0.28, P_trend = 0.080). Higher PCB153 (CYP inducer) level was negatively associated with ER (OR_T2 = 0.32, OR_T3 = 0.19, P_trend = 0.038) but positively with Ki-67 expression (OR_T2 = 1.43, OR_T3 = 3.60, P_trend = 0.055). Higher neurotoxic PCB28 was positively associated with HER-2 (OR_T3 = 5.43, P_trend = 0.006) and tumor size (OR = 2.37). Moreover, total PCBs exposure was positively associated with VEGF-C (OR_T2 = 76.91, OR_T3 = 97.96, P_trend = 0.041) and tumor metastasis (OR = 2.25).

CONCLUSIONS

Different functional PCB congeners have different associations (both positive and negative) with breast cancer prognostic biomarkers, as well as tumor classification stage. Therefore, the development and aggressiveness of breast cancer may depend upon exposure to specific structure-activity of PCBs.

A novel natural product, britanin, inhibits tumor growth of pancreatic cancer by suppressing nuclear factor-κB activation

Pancreatic cancer has a high mortality rate and poor prognosis. The development of novel medicines for pancreatic cancer therapy is urgently need. Britanin is a bioactive sesquiterpene lactone, that exhibits excellent anti-inflammatory and antioxidant effects. However, the potential anti-tumour activity of britanin is also considerable. Hence, in this study, the in vitro and in vivo anti-pancreatic cancer effects of britanin were investigated. Several pancreatic cancer cell lines were applied to evaluate inhibition of proliferation, migration and NF-κB pathway in vitro. Then in vivo toxicity of britanin was evaluated in BALB/c mice. The in vivo inhibitory effects of britanin were investigated by bioluminescence imaging, traditional methods and histological analysis in a pancreatic cancer xenograft mouse model. The results showed that britanin exhibited effective anti-tumour actions both in vitro and in vivo. The IC₅₀ values in PANC-1, BxPC-3 and MIA CaPa-2 cell lines were 1.348, 3.367 and 3.104 μmol/L, respectively, and cell proliferation and migration were significantly inhibited by britanin treatment. Western blotting demonstrated that NF-κB family proteins, such as P50, P65, and P-P65 were affected by britanin treatment. It is worth noting that the P-P65 protein, which regulates the expression of multiple factors downstream, was significantly decreased in britanin treated group. In vivo experiments verified that britanin could suppress the tumour progression in a pancreatic cancer xenograft mouse model, while the compound did not exhibit intolerable toxicity. In conclusion, britanin has remarkable potential treatment effects against pancreatic cancer, and it could be developed as a new agent for pancreatic cancer chemotherapy.

Periodic monitoring of persistent organic pollutants and molecular damage in Cyprinus carpio from Büyük Menderes River

Concentrations of persistent organic pollutants (POPs) were quantified in river water and sediment, as well as in the liver and muscle tissues of Cyprinus carpio that were sampled four times in a year at three stations in the Büyük Menderes River (BMR). Potential biomarkers of possible cellular molecular damage, namely lipid peroxidation (LPO) degradation products, protein carbonyls (PCO) and DNA repair product 8-hydroxy-2'-deoxyguanosine (8-OHdG), were analysed. All the targeted pollutants were measurable both in biotic and abiotic samples. Interestingly, the results suggested that there was recent organochlorine pesticide (OCP) input into the river water in the first two sampling periods in all stations in contrast to prohibition, while input of polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs) was not detected. Liver POP concentrations were higher than in muscle, as expected, and were found to decrease from the first to the fourth sampling period in all stations, except PBDEs. Levels of LPO degradation products in the liver and in muscle tissues decreased from the first to the fourth sampling period. This suggests that these markers reflect the lipid damage in respective tissues due to the tissue burden of targeted POPs. Protein carbonyls were the highest in the first sampling period, followed by a dramatic decrease in the second, and then a gradual increase towards the fourth sampling period in all stations. 8-OHdG levels were lower in Sarayköy station in the first sampling period. Among the measured biomarkers, only several LPO degradation products were significantly correlated with OCPs and PCBs in liver tissue.

Non-dioxin-like organic toxicant PCB153 modulates sphingolipid metabolism in liver progenitor cells: its role in Cx43-formed gap junction impairment

The non-dioxin-like environmental toxicant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153), member of a group of persistent organic pollutants wide-spread throughout the environment, reduces gap junction intercellular communication (GJIC), an event possibly associated with tumor promotion. Since very few studies have investigated the signaling effectors and mode(s) of action of PCB153, and it is known that the gap junction (GJ) protein Cx43 can be regulated by the bioactive sphingolipid (SL) sphingosine 1-phosphate (S1P), this in vitro study mainly addresses whether SL metabolism is affected by PCB153 in rat liver epithelial WB-F344 cells. PCB153 treatment obtained significant changes in the S1P/ceramide (Cer) ratio, known to be crucial in determining cell fate. In particular, an increase in S1P at 30 min and a decrease of the bioactive lipid at 3 h were observed, whereas Cer level increased at 1 h and 24 h. Notably, a time-dependent modulation of sphingosine kinase (SphK), the enzyme responsible for S1P synthesis, and of its regulators, ERK1/2 and protein phosphatase PP2A, supports the involvement of these signaling effectors in PCB153 toxicity. Electrophysiological analyses, furthermore, indicated that the lipophilic environmental toxicant significantly reduced GJ biophysical properties, affecting both voltage-dependent (such as those formed by Cx43 and/or Cx32) and voltage-independent channels, thereby demonstrating that PCB153 may act differently on GJs formed by distinct Cx isoforms. SphK down-regulation alone induced GJIC impairment, and, when combined with PCB153, the acute effect on GJ suppression was additive. Moreover, after enzyme-specific gene silencing, the SphK1 isoform appears to be responsible for down-regulating Cx43 expression, while being the target of PCB153 at short-term exposure. In conclusion, we provide the first evidence of novel effectors in PCB153 toxic action in rat liver stem-like cells, leading us to consider SLs as potential markers for preventing GJIC deregulation and, thus, the tumorigenic action elicited by this environmental toxicant.

Association between NFKB1 -94ins/del ATTG Promoter Polymorphism and Cancer Susceptibility: An Updated Meta-Analysis

Nuclear factor-κB is associated with the pathogenesis of numerous malignancies, and the functional polymorphism −94ins/del ATTG (rs28362491) in the human NFKB1 gene is associated with cancer risk. Previous studies on the association between the −94ins/del ATTG polymorphism and cancer risk reported conflicting results. To clarify this relationship, we performed a meta-analysis of 21 case-control studies involving 6127 cases and 9238 controls. We used pooled odds ratios (ORs) with their 95% confidence intervals (95% CIs) to assess the association. We found that the NFKB1 promoter −94ins/del ATTG polymorphism was significantly associated with cancer risk in four genetic models (ins/ins versus del/del, OR = 1.47, 95% CI = 1.11–1.93; dominant model, OR = 1.26, 95% CI = 1.03–1.53; recessive model, OR = 1.26, 95% CI = 1.05–1.51; ins allele versus del allele, OR = 1.19, 95% CI = 1.05–1.35). Stratified analyses revealed a significant association between the polymorphism and ovarian, oral, and prostate cancers. Similar results were determined in an Asian population and not in a Caucasian population. Thus, our results suggested that the polymorphism can contribute to cancer risk. Moreover, the polymorphism can exert race- and cancer-specific effects on cancer risk. Further large-scale and functional studies are necessary to elucidate this possible effect.

Biological and tumor-promoting effects of dioxin-like and non-dioxin-like polychlorinated biphenyls in mouse liver after single or combined treatment

To assess the impact of a mixture containing dioxin-like and non-dioxin-like polychlorinated biphenyls (PCBs), male mice were initiated with N-nitroso-diethylamine and subsequently treated with PCB126, an Ah-Receptor agonist, and PCB153, acting via activation of the constitutive androstane receptor. The two congeners were given at two dose levels: the low dose was adjusted to induce ~150-fold increases in cytochrome P450 (Cyp)1a1 (PCB126) and Cyp2b10 mRNAs (PCB153), and the high dose was chosen as twice the low dose. To keep the liver PCB levels constant, mice were given initial loading doses followed by weekly maintenance doses calculated on the basis of the PCBs' half-lives. Mice were treated with the individual congeners (low and high dose) or with a mixture consisting of the low doses of the 2 PCBs. The following results were obtained: (1) the 2 PCBs produced dose-dependent increases in Cyp1a1 and Cyp2b10 mRNA, protein, and activity when given individually; (2) combined treatment caused more than additive effects on Cyp1a1 mRNA expression, protein level, and ethoxyresurofin activity; (3) changes in the levels of several proteins were detected by proteome analysis in livers of PCB-treated mice; (4) besides these biological responses, the individual PCBs caused no significant increase in the number of glucose-6-phospatase (G6Pase)-deficient neoplastic lesions in liver, whereas a moderate significant effect occurred in the combination group. These results suggest weak but significant response-additive effects of the 2 PCBs when given in combination. They also suggest that the Cyp biomarkers tend to overestimate the carcinogenic response produced by the PCBs in mouse liver.

Parental exposure to natural mixtures of POPs reduced embryo production and altered gene transcription in zebrafish embryos

Determination of toxicity of complex mixtures has been proposed to be one of the most important challenges for modern toxicology. In this study we performed genome wide transcriptome profiling to assess potential toxicant induced changes in gene regulation in zebrafish embryos following parental exposure to two natural mixtures of persistent organic pollutants (POPs). The mixtures used were extracted from burbot (Lota lota) liver originating from two lakes (Lake Mjøsa and Lake Losna) belonging to the same freshwater system in Norway. The dominating groups of contaminants were polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane metabolites (DDTs). Because both mixtures used in the present study induced similar effects, it is likely that the same toxicants are involved. The Mjøsa mixture contains high levels of PBDEs while this group of pollutants is low in the Losna mixture. However, both mixtures contain substantial concentrations of PCB and DDT suggesting these contaminants as the predominant contributors to the toxicity observed. The observed effects included phenotypic traits, like embryo production and survival, and gene transcription changes corresponding with disease and biological functions such as cancer, reproductive system disease, cardiovascular disease, lipid and protein metabolism, small molecule biochemistry and cell cycle. The changes in gene transcription included genes regulated by HNF4A, insulin, LH, FSH and NF-κB which are known to be central regulators of endocrine signaling, metabolism, metabolic homeostasis, immune functions, cancer development and reproduction. The results suggest that relative low concentrations of the natural mixtures of POPs used in the present study might pose a threat to wild freshwater fish living in the lakes from which the POPs mixtures originated.

Effect of vitamin E on hepatic cell proliferation and apoptosis in mice deficient in the p50 subunit of NF-κB after treatment with phenobarbital

Phenobarbital (PB) is an efficacious and well-studied hepatic tumor promoting agent. Nuclear factor-κB (NF-κB) is a transcription factor activated by reactive oxygen and is involved in cell proliferation and apoptosis. We previously found that PB activates NF-κB and that dietary vitamin E is effective in decreasing PB-induced NF-κB DNA binding. We therefore hypothesized that dietary vitamin E influences PB-induced changes in cell proliferation and apoptosis through its action on NF-κB. NF-κB1 deficient mice (p50-/-) and wild-type B6129 mice were fed a purified diet containing 10 or 250ppm vitamin E (α-tocopherol acetate) for 28days. At that time, half of the wild-type and half of the p50-/- mice were placed on the same diet with 0.05% PB for 10days. Compared to wild-type mice, the p50-/- mice had higher levels of cell proliferation and apoptosis. Cell proliferation was significantly increased by PB, but vitamin E did not affect hepatic cell proliferation. Apoptosis was not changed in mice fed PB, and there was no significant difference in apoptosis between control and high vitamin E treated mice. Thus, vitamin E does not appear to influence cell growth parameters in either wild-type or p50-/- mice.

Comparison of combinatory effects of PCBs (118, 138, 153 and 180) with 17 beta-estradiol on proliferation and apoptosis in MCF-7 breast cancer cells

We analyzed whether polychlorinated biphenyls (PCBs) interfere with the activity of 17 β-estradiol in the proliferation and apoptosis of the MCF-7 cell line. MCF-7 cells were cultured in Dulbecco's modified Eagle's medium (DMEM) without phenol red supplemented with 5% charcoal-treated fetal bovine serum (CD-FBS) for 3 days with 10 nM 17 β-estradiol or 0.1 µM, 0.5 µM and 1 µM of the tested PCB congeners (118, 138, 153 and 180), or both. Cell proliferation was determined by measuring 5-bromo-2'-deoxyuridine (BrdU) incorporation, and cell apoptosis was measured by caspase-9 activity. From the PCB congeners tested, PCB138 and 153 had the highest stimulatory effects on basal cell proliferation as well as the highest inhibitory actions on basal caspase-9 activity. The proliferative and anti-apoptotic actions of PCB138 and 153 were still observed in the presence of 17 β-estradiol, while the actions of PCB118 and 180 were reversed. In conclusion, the results of this study suggest the possibility that PCB138 and 153 contribute to the action of endogenous 17 β-estradiol on cell proliferation and apoptosis in the breast cancer cell line MCF-7.

PCB-153 exposure coordinates cell cycle progression and cellular metabolism in human mammary epithelial cells

2,2',4,4',5,5'-Hexachlorobiphenyl (PCB-153) is a non-metabolizable environmental chemical contaminant commonly found in breast milk of PCB exposed individuals, suggesting that chronic exposure to PCB-153 could have adverse health effects. We have shown previously that PCB-153 increased reactive oxygen species levels in non-tumorigenic MCF-10A human mammary epithelial cells, which were associated with DNA damage, growth inhibition, and cytotoxicity. This study investigates the hypothesis that PCB-153 exposure coordinates cell cycle progression and cellular metabolism by inhibiting cyclin D1 accumulation. PCB-153 treated MCF-10A cells exhibited a dose and time dependent decrease in cyclin D1 protein levels. The decrease in cyclin D1 protein levels was associated with an inhibition in AKT and GSK-3beta phosphorylation, which correlated with an increase in cyclin D1-T286 phosphorylation. Fibroblasts carrying a mutant form of cyclin D1 (T286A) were resistant to PCB-153 induced degradation of cyclin D1. Pre-treatment of cells with a proteasome inhibitor (MG132) suppressed PCB-153 induced decrease in cyclin D1 protein levels. Interestingly, suppression in cyclin D1 accumulation was associated with an increase in cellular glucose consumption, and hexokinase II and pyruvate kinase protein levels. These results suggest that cyclin D1 coordinates cell cycle progression and cellular metabolism in PCB-153 treated non-tumorigenic human mammary epithelial cells.

Polychlorinated biphenyls disrupt blood-brain barrier integrity and promote brain metastasis formation

BACKGROUND

Polychlorinated biphenyls (PCBs) comprise a ubiquitous class of toxic substances associated with carcinogenic and tumor-promoting effects as well as neurotoxic properties in the brain. However, the effects of PCBs on the development of tumor metastases are not fully understood.

OBJECTIVE

We evaluated the hypothesis that exposure to individual PCB congeners can facilitate the development of brain metastases in immunocompetent mice via the disruption of the integrity of the blood-brain barrier (BBB).

METHODS

C57/Bl6 mice were exposed to individual PCBs by oral gavage, and 48 hr later they were injected with luciferase-labeled K1735 M2 melanoma cells into the internal carotid artery. The development of metastatic nodules was monitored by bioluminescent imaging. In addition, we evaluated the functional permeability of the BBB by measuring permeability of sodium fluorescein across the brain microvessels. Expression and colocalization of tight junction (TJ) proteins were studied by Western blotting and immunofluorescence microscopy.

RESULTS

Oral administration of coplanar PCB126, mono-ortho-substituted PCB118, and non-coplanar PCB153 (each at 150 micromol/kg body weight) differentially altered expression of the TJ proteins claudin-5, occludin, and zonula occludens-1 in brain capillaries. These alterations were associated with increased permeability of the BBB. Most importantly, exposure to individual PCB congeners enhanced the rate of formation and progression of brain metastases of luciferase-tagged melanoma cells.

CONCLUSIONS

Our results show for the first time that exposure to individual PCBs can facilitate the formation of bloodborne metastases via alterations of the integrity of the brain capillary endothelium.

The biological functions of NF-kappaB1 (p50) and its potential as an anti-cancer target

Nuclear factor-kappaB (NF-kappaB) is a key transcriptional factor family that consists of five members in mammalian cells, including NF-kappaB1 (p50), NF-kappaB2 (p52), RelA (p65), RelB and c-Rel. NF-kappaB is implicated in multiple physiological and pathological processes, including cell proliferation and differentiation, inflammatory and immune response, cell survival and apoptosis, cellular stress reactions and tumorigenesis. Recent studies by our group and others have highlighted the novel functions of the p50 protein. In this review, we will focus on the regulation and functions of NF-kappaB p50.

Effect of antioxidant phytochemicals on the hepatic tumor promoting activity of 3,3',4,4'-tetrachlorobiphenyl (PCB-77)

Polychlorinated biphenyls (PCBs) have promoting activity in the liver, which may be brought about in part by the induction of oxidative stress. In this study we examined the effects of several antioxidant phytochemicals on the tumor promoting activity of 3,3',4'4-tetrachlorobiphenyl (PCB-77). Female Sprague Dawley rats were first injected with diethylnitrosamine (DEN, 150 mg/kg) and one week later the rats were fed an AIN-93 based purified diet or the same diet containing ellagic acid (0.4%), beta-carotene (0.5%), curcumin (0.5%), N-acetyl cysteine (NAC, 1.0%), coenzyme CoQ10 (CoQ10, 0.4%), resveratrol (0.005%), lycopene (10% as Lycovit, which contains 10% lycopene), or a tea extract (1%, containing 16.5% epigallocatechin-3-gallate [EGCG] and 33.4% total catechins). Rats were fed the diets for the remainder of the study. After three weeks, 2/3 of the control rats and all of the antioxidant diet-fed rats were injected i.p. with PCB-77 (300 micromol/kg) every other week for four injections. All rats were euthanized ten days after the last PCB injection. The rats that received PCB-77 alone showed an increase in the number and size of placental glutathione S-transferase (PGST)-positive foci in the liver. Lycopene significantly decreased the number of foci, while curcumin and CoQ10 decreased the size of the foci. In contrast, ellagic acid increased the number but decreased the size of the foci. All of the other phytochemicals showed only slight or no effects. Compared with the PCB-77 group, CoQ10 increased cell proliferation in normal hepatocytes, whereas the other antioxidants had no effect in either normal or PGST-positive hepatocytes. These findings show that none of the antioxidant phytochemicals produced a clear decrease in the promoting activity of PCB-77.