DDT stimulates c-erbB2, c-met, and STATS tyrosine phosphorylation, Grb2-Sos association, MAPK phosphorylation, and proliferation of human breast epithelial cells

Signs of carcinogenicity induced by parathion, malathion, and estrogen in human breast epithelial cells (Review)

Cancer development is a multistep process that may be induced by a variety of compounds. Environmental substances, such as pesticides, have been associated with different human diseases. Organophosphorus pesticides (OPs) are among the most commonly used insecticides. Despite the fact that organophosphorus has been associated with an increased risk of cancer, particularly hormone-mediated cancer, few prospective studies have examined the use of individual insecticides. Reported results have demonstrated that OPs and estrogen induce a cascade of events indicative of the transformation of human breast epithelial cells. In vitro studies analyzing an immortalized non-tumorigenic human breast epithelial cell line may provide us with an approach to analyzing cell transformation under the effects of OPs in the presence of estrogen. The results suggested hormone-mediated effects of these insecticides on the risk of cancer among women. It can be concluded that, through experimental models, the initiation of cancer can be studied by analyzing the steps that transform normal breast cells to malignant ones through certain substances, such as pesticides and estrogen. Such substances cause genomic instability, and therefore tumor formation in the animal, and signs of carcinogenesis in vitro. Cancer initiation has been associated with an increase in genomic instability, indicated by the inactivation of tumor-suppressor genes and activation of oncogenes in the presence of malathion, parathion, and estrogen. In the present study, a comprehensive summary of the impact of OPs in human and rat breast cancer, specifically their effects on the cell cycle, signaling pathways linked to epidermal growth factor, drug metabolism, and genomic instability in an MCF-10F estrogen receptor-negative breast cell line is provided.

Toxicologic Evaluation for Amorphous Silica Nanoparticles: Genotoxic and Non-Genotoxic Tumor-Promoting Potential

Amorphous silica nanoparticles (SiO₂NPs) have been widely used in medicine including targeted drug/DNA delivery, cancer therapy, and enzyme immobilization. Nevertheless, SiO₂NPs should be used with caution due to safety concerns associated with unique physical and chemical characteristics. The objective of this study was to determine the effects of SiO₂NPs on genotoxic and non-genotoxic mechanisms associated with abnormal gap junctional intercellular communication (GJIC) in multistage carcinogenesis. The SiO₂NPs exhibited negative responses in standard genotoxicity tests including the Ames test, chromosome aberration assay, and micronucleus assay. In contrast, the SiO₂NPs significantly induced DNA breakage in comet assay. Meanwhile, SiO₂NPs inhibited GJIC based on the results of scrape/loading dye transfer assay for the identification of non-genotoxic tumor-promoting potential. The reduction in expression and plasma membrane localization of Cx43 was detected following SiO₂NP treatment. Particularly, SiO₂NP treatment increased Cx43 phosphorylation state, which was significantly attenuated by inhibitors of extracellular signal-regulated kinases 1/2 (ERK1/2) and threonine and tyrosine kinase (MEK), but not by protein kinase C (PKC) inhibitor. Taken together, in addition to a significant increase in DNA breakage, SiO₂NP treatment resulted in GJIC dysregulation involved in Cx43 phosphorylation through the activation of mitogen-activated protein kinase (MAPK) signaling. Overall findings of the genotoxic and non-genotoxic carcinogenic potential of SiO₂NPs provide useful toxicological information for clinical application at an appropriate dose.

In Utero Exposure to Bisphenol a Promotes Mammary Tumor Risk in MMTV-Erbb2 Transgenic Mice Through the Induction of ER-erbB2 Crosstalk

Bisphenol A (BPA) is the most common environmental endocrine disrupting chemical. Studies suggest a link between perinatal BPA exposure and increased breast cancer risk, but the underlying mechanisms remain unclear. This study aims to investigate the effects of in utero BPA exposure on mammary tumorigenesis in MMTV-erbB2 transgenic mice. Pregnant mice were subcutaneously injected with BPA (0, 50, 500 ng/kg and 250 µg/kg BW) daily between gestational days 11–19. Female offspring were examined for mammary tumorigenesis, puberty onset, mammary morphogenesis, and signaling in ER and erbB2 pathways. In utero exposure to low dose BPA (500 ng/kg) induced mammary tumorigenesis, earlier puberty onset, increased terminal end buds, and prolonged estrus phase, which was accompanied by proliferative mammary morphogenesis. CD24/49f-based FACS analysis showed that in utero exposure to 500 ng/kg BPA induced expansion of luminal and basal/myoepithelial cell subpopulations at PND 35. Molecular analysis of mammary tissues at PND 70 showed that in utero exposure to low doses of BPA induced upregulation of ERα, p-ERα, cyclin D1, and c-myc, concurrent activation of erbB2, EGFR, erbB-3, Erk1/2, and Akt, and upregulation of growth factors/ligands. Our results demonstrate that in utero exposure to low dose BPA promotes mammary tumorigenesis in MMTV-erbB2 mice through induction of ER-erbB2 crosstalk and mammary epithelial reprogramming, which advance our understanding of the mechanism associated with in utero exposure to BPA-induced breast cancer risk. The studies also support using MMTV-erbB2 mouse model for relevant studies.

DMBA promotes ErbB2‑mediated carcinogenesis via ErbB2 and estrogen receptor pathway activation and genomic instability

Environmental factors, including 7,12‑dimethylbenz[a]anthracene (DMBA) exposure, and genetic predisposition, including ErbB2 overexpression/amplification, have been demonstrated to increase breast cancer susceptibility. Although DMBA‑ and ErbB2‑mediated breast cancers are well‑studied in their respective models, key interactions between environmental and genetic factors on breast cancer risk remain unclear. Therefore, the present study aimed to investigate the effect of DMBA exposure on ErbB2‑mediated mammary tumorigenesis. MMTV‑ErbB2 transgenic mice exposed to DMBA (1 mg) via weekly oral gavage for 6 weeks exhibited significantly enhanced mammary tumor development, as indicated by reduced tumor latency and increased tumor multiplicity compared with control mice. Whole mount analysis of premalignant mammary tissues from 15‑week‑old mice revealed increased ductal elongation and proliferative index in DMBA‑exposed mice. Molecular analyses of premalignant mammary tissues further indicated that DMBA exposure enhanced epidermal growth factor receptor (EGFR)/ErbB2 and estrogen receptor (ER) signaling, which was associated with increased mRNA levels of EGFR/ErbB2 family members and ER‑targeted genes. Furthermore, analysis of tumor karyotypes revealed that DMBA‑exposed tumors displayed more chromosomal alterations compared with control tumors, implicating DMBA‑induced chromosomal instability in tumor promotion in this model. Together, the data suggested that DMBA‑induced deregulation of EGFR/ErbB2‑ER pathways plays a critical role in the enhanced chromosomal instability and promotion of ErbB2‑mediated mammary tumorigenesis. The study highlighted gene‑environment interactions that may increase risk of breast cancer, which is a critical clinical issue.

Direct effect of p,p'- DDT on mice liver

ABSTRACT Contact with the pesticide dichlorodiphenyltrichloroethane (p,p′-DDT) can be the cause of various harmful effects in humans, wildlife, and the environment. This pesticide is known to be persistent, lipophilic, resistant to degradation, and bioaccumulive in the environment and to be slowly released into bloodstream. Growing evidence shows that exposure to DDT is linked to type 2 diabetes mellitus. Individuals exposed to elevated levels of DDT and its metabolite have an increased prevalence of diabetes and insulin resistance. To evaluate these possible relationships, experiments were performed on eight-week-old female mice, divided into three groups (n = 10 per group): Group 1 received a vehicle-control intraperitoneal (i.p.) injection of sesame oil; Groups 2 and 3 received an i.p. dose of 50 and 100 µg/g p,p′-DDT respectively, dissolved in sesame oil. All groups were treated once daily for four days. Real-time PCR analysis of several genes was undertaken. Additionally, biochemical parameters and histopathological changes were measured. NQO1, HMOX1, NR1I3 and NR3C1 were up-regulated in DDT-exposed animals compared to the vehicle control group, while only SREBP1 was down-regulated in the 100 µg/g group. MTTP and FABP5, not previously reported for DDT exposure, but involved in regulation of fatty acid fluxes, could also function as biomarkers cross-talking between these signaling pathways. These results suggest that beyond epidemiological data, there is increasing molecular evidence that DDT may mimic different processes involved in diabetes and insulin resistance pathways.

Exometabolom analysis of breast cancer cell lines: Metabolic signature

Cancer cells show characteristic effects on cellular turnover and DNA/RNA modifications leading to elevated levels of excreted modified nucleosides. We investigated the molecular signature of different subtypes of breast cancer cell lines and the breast epithelial cell line MCF-10A. Prepurification of cell culture supernatants was performed by cis-diol specific affinity chromatography using boronate-derivatized polyacrylamide gel. Samples were analyzed by application of reversed phase chromatography coupled to a triple quadrupole mass spectrometer. Collectively, we determined 23 compounds from RNA metabolism, two from purine metabolism, five from polyamine/methionine cycle, one from histidine metabolism and two from nicotinate and nicotinamide metabolism. We observed major differences of metabolite excretion pattern between the breast cancer cell lines and MCF-10A, just as well as between the different breast cancer cell lines themselves. Differences in metabolite excretion resulting from cancerous metabolism can be integrated into altered processes on the cellular level. Modified nucleosides have great potential as biomarkers in due consideration of the heterogeneity of breast cancer that is reflected by the different molecular subtypes of breast cancer. Our data suggests that the metabolic signature of breast cancer cell lines might be a more subtype-specific tool to predict breast cancer, rather than a universal approach.

DDT Exposure in Utero and Breast Cancer

CONTEXT

Currently no direct evidence links in utero dichlorodiphenyltrichloroethane (DDT) exposure to human breast cancer. However, in utero exposure to another xenoestrogen, diethylstilbestrol, predicts an increased breast cancer risk. If this finding extends to DDT, it could have far-reaching consequences. Many women were heavily exposed in utero during widespread DDT use in the 1960s. They are now reaching the age of heightened breast cancer risk. DDT exposure persists and use continues in Africa and Asia without clear knowledge of the consequences for the next generation.

HYPOTHESIS

In utero exposure to DDT is associated with an increased risk of breast cancer.

DESIGN

This was a case-control study nested in a prospective 54-year follow-up of 9300 daughters in the Child Health and Development Studies pregnancy cohort (n = 118 breast cancer cases, diagnosed by age 52 y and 354 controls matched on birth year).

SETTING AND PARTICIPANTS

Kaiser Foundation Health Plan members who received obstetric care in Alameda County, California, from 1959 to 1967, and their adult daughters participated in the study.

MAIN OUTCOME MEASURE

Daughters' breast cancer diagnosed by age 52 years as of 2012 was measured.

RESULTS

Maternal o,p'-DDT predicted daughters' breast cancer (odds ratio fourth quartile vs first = 3.7, 95% confidence interval 1.5-9.0). Mothers' lipids, weight, race, age, and breast cancer history did not explain the findings.

CONCLUSIONS

This prospective human study links measured DDT exposure in utero to risk of breast cancer. Experimental studies are essential to confirm results and discover causal mechanisms. Findings support classification of DDT as an endocrine disruptor, a predictor of breast cancer, and a marker of high risk.

The evaluation of p,p'-DDT exposure on cell adhesion of hepatocellular carcinoma

Many studies have found a positive association between the progression of hepatocellular carcinoma and DDT exposure. These studies mainly focus on the effect of DDT exposure on cell proliferation and epithelial to mesenchymal transition (EMT) promotion. However, the influence of DDT on cell adhesion of hepatocellular carcinoma remains to be unclear. The aim of our study was to determine the effect of p,p'-DDT on cell adhesion of hepatocellular carcinoma in vitro and in vivo. The data showed that p,p'-DDT, exposing HepG2 cells for 6 days, decreased cell-cell adhesion and elevated cell-matrix adhesion. Strikingly, p,p'-DDT increased reactive oxygen species (ROS) content, and this was accompanied by the activation of JAK/STAT3 pathway. Moreover, ROS inhibitor supplement reversed these effects significantly. However, the addition of ER inhibitor, ICI, had no effect on the p,p'-DDT-induced effects. p,p'-DDT altered the mRNA levels of related adhesion molecules, including inhibition of E-cadherin and promotion of N-cadherin along with CD29. Interestingly, the p,p'-DDT-altered adhesion molecules could be reversed with JAK inhibitor or STAT3 inhibitor. Likewise, p,p'-DDT stimulated the JAK/STAT3 pathway in nude mice, as well as altered the mRNA levels of E-cadherin, N-cadherin, and CD29. Taken together, these results indicate that p,p'-DDT profoundly promotes the adhesion process by decreasing cell-cell adhesion and inducing cell-matrix adhesion via the ROS-mediated JAK/STAT3 pathway. All these events account for the carcinogenic potential of p,p'-DDT in liver.

Antiestrogenic activity of flavonoid phytochemicals mediated via the c-Jun N-terminal protein kinase pathway. Cell-type specific regulation of estrogen receptor alpha

Flavonoid phytochemicals act as both agonists and antagonists of the human estrogen receptors (ERs). While a number of these compounds act by directly binding to the ER, certain phytochemicals, such as the flavonoid compounds chalcone and flavone, elicit antagonistic effects on estrogen signaling independent of direct receptor binding. Here we demonstrate both chalcone and flavone function as cell type-specific selective ER modulators. In MCF-7 breast carcinoma cells chalcone and flavone suppress ERα activity through stimulation of the stress-activated members of the mitogen-activated protein kinase (MAPK) family: c-Jun N-terminal kinase (JNK)1 and JNK2. The use of dominant-negative mutants of JNK1 or JNK2 in stable transfected cells established that the antiestrogenic effects of chalcone and flavone required intact JNK signaling. We further show that constitutive activation of the JNK pathway partially suppresses estrogen (E2)-mediated gene expression in breast, but not endometrial carcinoma cells. Our results demonstrate a role for stress-activated MAPKs in the cell type-specific regulation of ERα function.

Two-generation reproduction toxicity study in rats with methoxychlor

A two-generation reproduction toxicity study was conducted in rats with a reference estrogenic pesticide, methoxychlor, to validate the sensitivity and competency of current guidelines recommended by the United States Environmental Protection Agency; Japanese Ministry of Agriculture, Forestry and Fisheries; and Organisation for Economic Co-operation and Development for predicting reproductive toxicity of the test compound based on estrogenic endocrine disrupting effects. Both sexes of SD rats were exposed to methoxychlor in the diet at concentrations of 0, 10, 500 and 1500 ppm for two successive generations. The present study has successfully detected estrogenic activities and reproductive toxicities of methoxychlor, as well as its systemic toxicity. Body weights, body weight gains and food consumption of both sexes of animals were suppressed significantly in the 500 and 1500 ppm groups. Typical reproductive toxicities observed in females of these groups included, but were not limited to, prolonged estrous cycle, reduced fertility, decreased numbers of implantation sites and newborns, decreased ovary weights and/or increased incidences of cystic ovary. Uterine weights of weanlings increased significantly in these groups, suggesting that the sensitivity of this parameter for predicting estrogenic ability of the test compound is comparable to that of the uterotrophic assay. Reproductive toxicities of methoxychlor seemed less potent in males than in females. Methoxychlor delayed preputial separation and significantly reduced sperm counts and reproductive organ weights of males of the 500 and/or 1500 ppm groups; however, most males that failed to impregnate females in the same group showed normal fertility when they were re-mated with untreated females. Neither systemic nor reproductive toxicities appeared in the 10 ppm group.

Ascorbic acid 6-palmitate suppresses gap-junctional intercellular communication through phosphorylation of connexin 43 via activation of the MEK-ERK pathway

Although the health benefits of dietary antioxidants have been extensively studied, their potential negative effects remain unclear. L-Ascorbic acid 6-palmitate (AAP), a synthetic derivative of ascorbic acid (AA), is widely used as an antioxidant and preservative in foods, vitamins, drugs, and cosmetics. Previously, we found that AA exerted an antitumor effect by protecting inhibition of gap-junctional intercellular communication (GJIC), which is closely associated with tumor progression. In this study, we examined whether AAP, an amphipathic derivative of AA, has chemopreventive effects using a GJIC model. AAP and AA exhibited dose-dependent free radical-scavenging activities and inhibited hydrogen peroxide (H(2)O(2))-induced intracellular reactive oxygen species (ROS) production in normal rat liver epithelial cells. Unexpectedly, however, AAP did not protect against the inhibition of GJIC induced by H(2)O(2); instead, it inhibited GJIC synergistically with H(2)O(2). AAP inhibited GJIC in a dose-dependent and reversible manner. This inhibitory effect was not due to the conjugated lipid structure of AAP, as treatment with palmitic acid alone failed to inhibit GJIC under the same conditions. The inhibition of GJIC by AAP was restored in the presence of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126, but not in the presence of other signal inhibitors and antioxidant (PKC inhibitors, EGFR inhibitor, NADPH oxidase inhibitor, catalase, vitamin E, or AA), indicating the critical involvement of MEK signaling in the GJIC inhibitory activity of AAP. Phosphorylation of ERK and connexin 43 (Cx43) was observed following AAP treatment, and this was reversed by U0126. These results suggest that the AAP-induced inhibition of GJIC is mediated by the phosphorylation of Cx43 via activation of the MEK-ERK pathway. Taken together, our results indicate that AAP has a potent carcinogenic effect, and that the influence of dietary antioxidants on carcinogenesis may be paradoxical.

Nitric oxide inhibits an interaction between JNK1 and c-Jun through nitrosylation

Nitric oxide (NO) has been shown to negatively regulate c-Jun N-terminal kinase (JNK) through S-nitrosylation. Here, we show that disruption of an interaction between JNK and its substrate c-Jun is an important mechanism underlying the NO-mediated inhibition of JNK signaling. Endogenous NO, which was generated by interferon-gamma treatment, suppressed anisomycin-stimulated JNK activity in microglial BV-2 cells. The interferon-gamma-induced suppression of JNK1 activation in BV-2 cells was prevented completely by treatment with N(G)-nitro-l-arginine, an inhibitor of NO synthase. A NO donor S-nitro-N-acetyl-dl-penicillamine (SNAP) inhibited JNK activity in vitro, and this inhibition was reversed by a thiol-reducing agent, dithiothreitol. Nitric oxide disrupts a physical interaction between JNK and its substrate c-Jun both in vitro and in intact cells without affecting an interaction between SEK1 and JNK. Collectively, our results suggest that the inhibition of the interaction between JNK and c-Jun may be an integral part of the mechanism underlying the negative regulation of the JNK signaling pathway by NO.

Two-generation reproduction toxicity study in rats with 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT)

DDT, an organochlorine pesticide, has been cited as a representative chemical suspected of having endocrine disrupting effects. In this study, the potential endocrine disrupting activities of p,p'-DDT, a major component of DDT, were investigated in rats in a 2-generation reproduction toxicity study in accordance with the most current test guidelines of the Ministry of Agriculture, Forestry and Fisheries in Japan, Organization for Economic Cooperation and Development (OECD) and United States Environmental Protection Agency (USEPA) with some modifications and additions. p,p'-DDT was given to parental rats at dietary levels of 0, 5, 50 or 350 ppm. Systemic toxicities in the parental animals consisted of tremors and subsequent deaths (females only) and/or pathological alterations of the liver (both sexes of animals) of the 2 higher dose groups. Reproductive and postnatal developmental toxicities were not evident up to the highest dose level except for the decreased pup viability index on postnatal day 21 in the 350 ppm group. Changes in serum estradiol and progesterone levels and/or a delay in male sexual maturation were noted in the 2 higher dose groups in a dose-dependent fashion, suggesting alterations of endogenous endocrine functions. However, these changes never resulted in substantial reproductive disorders.

Xenobiotic-induced TNF-alpha expression and apoptosis through the p38 MAPK signaling pathway

Some xenobiotics, such as dichlorodiphenyltrichloroethane (DDT), bind to and activate estrogen receptors (ERs), eliciting estrogenic effects in both wildlife and humans. However, our laboratory and others have demonstrated that DDT and DDT-like compounds target non-ER pathways. In search for a molecular mechanism we recently established that DDT and its metabolites stimulate activator protein-1 (AP-1)-mediated gene expression through the p38 mitogen-activated protein kinase (MAPK) cascade. Here, we determined that DDT-induced p38 activity produces a novel environmental signaling pathway in endometrial Ishikawa and human embryonic kidney (HEK) 293 cells. Xenobiotic exposure stimulates expression of the death ligand, tumor necrosis factor-alpha (TNF-alpha) as demonstrated using RT-PCR and reporter gene assays. Furthermore, DDT-induced p38 activity led to the release of cytochrome c from the mitochondria and activation of caspase-3/7. Ultimately, DDT-treated cells underwent cell death. Taken together, these data demonstrate DDT induces both the expression of the death ligand TNF-alpha and apoptosis through a p38 MAPK-dependent mechanism.

Additional Repression of Activity-Dependent c-fos and BDNF mRNA Expression by Lipophilic Compounds Accompanying a Decrease in Ca2+ Influx Into Neurons

Recently, it has been proposed that a variety of environmental disruptors (EDs) disturb the neonatal development of the brain in mammals because of their lipophilic characteristics. Therefore, the synergism of these lipophilic compounds is important when evaluating the risk from EDs. In mouse cerebellar granule cells (CGCs), the activity-dependent expression of the brain-derived neurotrophic factor (BDNF) gene is activated through an influx of calcium ions (Ca2+) into CGCs caused by membrane depolarization, which is involved in the activity-dependent development of not only the cerebellum but also other regions of the brain after birth. In our previous study, we reported that permethrin and some other pyrethroid insecticides, which are suspected of being EDs, repressed the induction of c-fos and BDNF mRNA expression, accompanying a reduction of Ca2+ influx at doses non-toxic to CGCs. In the present study, we investigated whether other lipophilic compounds influenced the Ca2+ signal-induced expression of both genes as permethrin did and, if so, whether these effects were synergistic or additional. Pretreatment with p,p'-DDT, diethylstilbestrol (DES) or bisphenol A dose-dependently repressed the induction of both genes as well as the increase in the uptake of Ca2+ by CGCs. Simultaneous exposure of CGCs with permethrin, p,p'-DDT and DES, in addition, revealed an additional repression on the induction of the genes and the Ca2+ uptake. These results suggest that toxic effects of EDs might, at least additionally, occur in the brain even if the concentration of each compound is lower than the effective dose for humans.

Differential c-myc expression profiles in normal human bronchial epithelial cells following treatment with benzo[a]pyrene, benzo[a]pyrene-4,5 epoxide, and benzo[a]pyrene-7,8-9,10 diol epoxide

Bronchial epithelial cells are often exposed to airborne mutagens that have the potential to induce genetic changes involved in the development of lung cancer. Although lung tumors often display alterations in the expression of oncogenes and/or tumor suppressor genes, the role of specific chemicals and/or metabolites in causing these alterations is not well defined. The polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P), a by-product of combustion, is a prevalent airborne environmental mutagen and a constituent of cigarette smoke. The primary objective of this study was to compare the effect of B[a]P and two of its reactive metabolites, benzo[a]pyrene diol epoxide (BPDE or bay region epoxide) and benzo[a]pyrene-4,5-dihydroepoxide (BPE or K-region epoxide), on expression of the proto-oncogene c-myc in normal human bronchial epithelial (NHBE) cells using a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method. Changes in c-myc gene expression were compared with DNA adduct formation, growth inhibition, and cell-cycle progression as determined by (32)P-postlabelling, neutral red (NR), and flow cytometric analyses, respectively. None of the three test compounds altered the levels of 18S ribosomal RNA or beta-actin at the concentrations evaluated for c-myc expression, indicating that nonspecific changes in gene expression induced by cytotoxicity, for example, were not present at the concentrations evaluated. Cells exposed to B[a]P exhibited a dose-dependent increase in c-myc expression; conversely, a dose-dependent decrease in c-myc expression was observed following BPDE exposure. A marginal but concentration-dependent increase in c-myc mRNA levels was observed following exposure to the K-region epoxide. Our results demonstrated that, although B[a]P and its metabolites alter c-myc expression, the parent compound and its metabolites produce unequal and contrasting effects on the expression of this gene.

Cannabinoids inhibit gap junctional intercellular communication and activate ERK in a rat liver epithelial cell line

Many tumor promoters suppress the immune system; however, the direct effect of immunosuppressants on the tumorigenic pathways of nonimmune cells in solid tissue has not been well documented. Cannabinoids were chosen to explore this question further. Cannabinoids are immune modulators that affect specific intracellular signaling pathways in leukocytes. Since these compounds are nongenotoxic, any tumorigenic effect that might be associated with these compounds would need to occur through an epigenetic mechanism. Therefore, we determined the effect of Delta(9)-THC and CBN, 2 plant-derived cannabinoids, on 2 key epigenetic markers of tumor promotion: inhibition of GJIC, which is essential in removing a cell from growth suppression, and activation of the ERK-MAPK pathway, which is crucial in activating the appropriate genes for mitogenesis. Both Delta(9)-THC and CBN reversibly inhibited GJIC at noncytotoxic doses (15 microM) in a normal diploid WB rat liver epithelial oval cell line within 20 min and activated ERK1 and ERK2 within 5 min. Inhibition of MEK with PD98059 prevented the inhibition of GJIC by either cannabinoid, suggesting that inhibition of GJIC was MEK-dependent. Based on RT-PCR analysis and employment of an antagonist of CB1 and CB2, the effects on GJIC and MAPK were independent of both cannabinoid receptors. Cannabinoids affected crucial epigenetic pathways associated with cell proliferation in a rodent liver epithelial cell model system.

Dichlorodiphenyltrichloroethane suppresses neurite outgrowth and induces apoptosis in PC12 pheochromocytoma cells

It is well known that dichlorodiphenyltrichloroethane (DDT) is used as an insecticide and prevents many people in the tropical zone from devastating malaria. On the other hand, a number of reports have indicated that it may act as an endocrine disruptor and also has possible carcinogenic effects. However, the effects of DDT on the neural cells remain to be investigated. In this study, therefore, we observed the effects of p,p'-DDT, o,p'-DDT and its major metabolite p,p'-DDE on the differentiation and survival of PC12 pheochromocytoma cells. After stimulation with nerve growth factor, PC12 cells exhibited remarkable neurite outgrowth, suggesting that neuronal differentiation was induced by this growth factor. p,p'-DDT and o,p'-DDT suppressed this neurite outgrowth dose dependently, and p,p'-DDE also revealed a similar effect but to a lesser extent. Apoptotic cell death was induced within 3-6 h after treatment with p,p'-DDT and o,p'-DDT. Again p,p'-DDE showed a weaker apoptosis-inducing effect. In the organochlorine-treated PC12 cells phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) was upregulated, whereas phosphorylation bands were not detected in any kinases of other MAPK groups such as p38 MAPK and SAPK/JNK. A kinase assay on p44/42 MAPK revealed that the extent of phosphorylation of Elk-1 substrates well correlated with the suppressive effect on neuronal differentiation and apoptosis-inducing activity. These results suggest that p,p'-DDT and o,p'-DDT exerted their effects on neuronal cells by the stimulation of p44/42 MAPK, and p,p'-DDE had less effects than the other two organochlorines.

Effects of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (p,p'-DDT) on 3T3-L1 and 3T3-F442A adipocyte differentiation

Based upon our initial observations that 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (p,p'-DDT) induces a concentration-dependent increase in 3T3-L1 adipocyte differentiation, the mechanism of the p,p'-DDT-induced adipocyte differentiation was studied, using 3T3-L1 and 3T3-F442A cells. Since, it is known that the differentiation of the 3T3-L1 adipocyte cell line involves the induction of the transcription factors CCAAT enhancer binding protein beta (C/EBPbeta), peroxisome proliferator-activated receptor gamma (PPARgamma), and C/EBPalpha, the possible role of these factors in p,p'-DDT-induced adipocyte differentiation had to be examined. It was found that p,p'-DDT-treated 3T3-L1 cells showed a concentration-dependent increase in the nuclear levels of both PPARgamma and C/EBPalpha protein. On the other hand, treatment with p,p'-DDT (20 microM) did not affect the expression pattern of C/EBPbeta protein during differentiation. Gel shift analysis of nuclear proteins for binding to the C/EBP recognition site of DNA showed an increase in binding activity at day 2 of differentiation in p,p'-DDT-treated cells. Supershift analysis revealed that this rise was caused mainly by a dramatic increase in the abundance of the C/EBPalpha-DNA complex. Similar increases were observed at days 4 and 7 after the induction of differentiation. Tumor necrosis factor alpha induced a strong inhibition of adipocyte differentiation, which was reversed by co-treatment with troglitazone, an activator of PPARgamma. p,p'-DDT was unable to reverse the inhibitory effect of tumor necrosis factor alpha on adipocyte differentiation in 3T3-L1 cells. 3T3-F442A is another preadipocyte cell line that can be induced to differentiate into adipocytes in the presence of insulin and fetal bovine serum. p,p'-DDT (20 microM) induced an alteration in the morphology of these cells at day 2 after the induction of differentiation. These cells however, were unable to become fully differentiated adipocytes. These data showed, therefore, the ability of p,p'-DDT to alter the differentiation process of adipocyte cell lines through the modification of transcription factors regulating this event.

Foci formation of MCF7 cells as an in vitro screening method for estrogenic chemicals

Previously we reported a novel phenomenon that some organochlorine compounds mainly act through activation of c-Neu tyrosine kinase without being strong agonists for the estrogen receptor. In this study we tested the possibility of developing an assay system to identify estrogenic compounds acting through this c-Neu-mediated mechanism. We describe herein an assay that utilizes foci formation of MCF7 cells as an endpoint, antibody 9G6 to neutralize the c-Neu-mediated pathway and 4-hydroxytamoxifen to block the ER. Aroclors 1242 and 1248, 2,2',3,5',6-pentachlorobiphenyl (PCB 95), 2,2'-dichlorobiphenyl (PCB), cis- and trans- permethrins, and chlorothalonil were found to render estrogenic effects through this c-Neu-mediated mechanism, while α and β- endosulfans appeared to act through a pathway independent of the c-Neu-mediated one. Pentachloronitrobenzene was found to be capable of antagonizing the 17β-estradiol effect, which has never been reported previously.

On the rumors about the silent spring. Review of the scientific evidence linking occupational and environmental pesticide exposure to endocrine disruption health effects

Occupational exposure to some pesticides, and particularly DBCP and chlordecone, may adversely affect male fertility. However, apart from the therapeutic use of diethylstilbestrol, the threat to human reproduction posed by "endocrine disrupting" environmental contaminants has not been supported by epidemiological evidence thus far. As it concerns other endocrine effects described in experimental animals, only thyroid inhibition following occupational exposure to amitrole and mancozeb has been confirmed in humans. Cancer of the breast, endometrium, ovary, prostate, testis, and thyroid are hormone-dependent, which fostered research on the potential risk associated with occupational and environmental exposure to the so-called endocrine-disrupting pesticides. The most recent studies have ruled out the hypothesis of DDT derivatives as responsible for excess risks of cancer of the reproductive organs. Still, we cannot exclude a role for high level exposure to o,p'-DDE, particularly in post-menopausal ER+ breast cancer. On the other hand, other organochlorine pesticides and triazine herbicides require further investigation for a possible etiologic role in some hormone-dependent cancers.

Estrogens and environmental estrogens

The natural female sex hormone estrogens binds once inside the cell to a protein receptor to form a 'ligand-hormone receptor complex'. The binding activates the hormone receptor, which triggers specific cellular processes. The activated hormone receptor then turns on specific genes, causing cellular changes that lead to responses typical of a ligand-hormone receptor complex. Estrogens (especially estradiol) bring out the feminine characteristics, control reproductive cycles and pregnancy, influence skin, bone, the cardiovascular system and immunity. Natural hormones are more potent than any of the known synthetic environmental estrogens (except drugs such as diethylstilbestrol [DES]). Estrogen production varies according to different factors (gender, age and reproductive cycles). Women produce more estrogen than men and the production is more abundant during fetal development than in the postmenopausal period. Most natural estrogens are short-lived, do not accumulate in tissue and are easily broken down in the liver. In contrast to natural estrogens, estrogenic drugs such as ethynylestradiol diethylstilbestrol (DES), synthetic environmental estrogens such as beta-hexachlorocyclohexane (beta-HCH), polychlorinated biphenyls (PCBs), o, p, p'DDT, 4-nonylphenol (NP) and phytoestrogens such as isoflavones or lignans, are more stable and remain in the body longer than natural estrogens. Because most of these compounds are lipophilic, they tend to accumulate within the fat and tissue of animals and humans. Thus, depending on the natural estrogen levels, environmental estrogens may have different influences (mimicking, blocking or cancelling out estrogen's effects) on estrogen activities.

Steroid hormone receptors and dietary ligands: a selected review

Members of the nuclear steroid hormone superfamily mediate essential physiological functions. Steroid hormone receptors (SHR) act directly on DNA, regulate the synthesis of their target genes and are usually activated by ligand binding. Both endogenous and exogenous compounds and their metabolites may act as activators of SHR and disruptors of endocrine, cellular and lipid homeostasis. The endogenous ligands are generally steroids such as 17beta-oestradiol, androgens, progesterone and pregnenolone. The exogenous compounds are usually delivered through the diet and include non-steroidal ligands. Examples of such ligands include isoflavanoids or phytooestrogens, and food contaminants such as exogenous oestrogens from hormone-treated cattle, pesticides, polychlorinated biphenyls and plasticisers. Certain drugs are also ligands; so nuclear receptors are also important drug targets for intervention in disease processes. The present review summarises recent reports on ligand-activated SHR that describe the selective regulation of a tightly-controlled cross-talking network involving exchange of ligands, and the control of major classes of cytochrome P450 (CYP) isoforms which metabolise many bioactive exogenous compounds. Many CYP have broad substrate activity and appear to be integrated into a coordinated metabolic pathway, such that whilst some receptors are ligand specific, other sensors may have a broader specificity and low ligand affinity to monitor aggregate levels of inducers. They can then trigger production of metabolising enzymes to defend against possible toxic nutrients and xenobiotic compounds. The influence of dietary intakes of nutrients and non-nutrients on the human oestrogen receptors (alpha and beta), the aryl hydrocarbon receptor, the pregnane X receptor, the constitutive androstane receptor, and the peroxisome proliferator-activated receptors (alpha and gamma), can be examined by utilising computer-generated molecular models of the ligand-receptor interaction, based on information generated from crystallographic data and sequence homology. In relation to experimental and observed data, molecular modelling can provide a scientifically sound perspective on the potential risk and benefits to human health from dietary exposure to hormone-mimicking chemicals, providing a useful tool in drug development and in a situation of considerable public concern.

Inhibition of cell death in human mammary epithelial cells by the cooked meat-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mammary gland carcinogen present in the human diet in cooked meat. To examine if PhIP and its reactive metabolite N-hydroxy-PhIP inhibit apoptosis in human mammary epithelial MCF-10A cells, confluent cultures deprived of serum and growth factors were incubated for 24 h with either compound. The percentages of dead cells (mean +/- SEM, n = 3) as measured by trypan blue exclusion were 5.7 +/- 0.6, 3.4 +/- 0.3, 2.7 +/- 0.3, and 0.2 +/- 0.003%, in control, 1 microM N-hydroxy-PhIP-, 5 microM N-hydroxy-PhIP-, and 100 microM PhIP-treated dishes, respectively. The expression of Bcl-2 and Bcl-x(L) as quantitated by Western blotting was 1.2- to 1.9-fold higher in the treated groups. PhIP-DNA adducts induced by N-hydroxy-PhIP in MCF-10A cells measured by the (32)P-postlabeling assay were low (<1 x 10(7), relative adduct labeling). No adducts were detected after incubation with PhIP. Western blot analysis indicated that PhIP increased ERK2 phosphorylation concomitant with Bcl-2. The results suggest that the inhibition of cell death in mammary epithelial cells by PhIP occurs independently of PhIP-DNA adducts and may involve enhanced signaling through the MAP kinase pathways.

Effects of environmental estrogens on tumor necrosis factor alpha-mediated apoptosis in MCF-7 cells

Environmental estrogens represent a class of compounds which have been shown to mimic the effects or activity of the naturally occurring ovarian hormone 17beta-estradiol. Given the role of 17beta-estradiol in cell survival in a number of systems, we wished to determine if environmental estrogens protect MCF-7 cells from apoptosis. Here we demonstrate that the organochlorine pesticides o, p' DDT and alachlor, like 17beta-estradiol, have the ability to suppress tumor necrosis factor alpha (TNF)-induced apoptosis in estrogen receptor (ER)-positive MCF-7 breast carcinoma cells. These compounds, however, did not affect TNF-induced apoptosis of the ER-negative MDA-MB-231 cell line. The ability of these compounds to suppress apoptosis in MCF-7 cells was correlated with an ER-dependent increase in Bcl-2 expression. Taken together these results demonstrate that estrogenic organochlorine pesticides like o, p' DDT and alachlor may partially mimic the primary endogenous estrogen, 17beta-estradiol, and function to suppress apoptosis in ER-responsive cells.

Differential spatiotemporal regulation of lactoferrin and progesterone receptor genes in the mouse uterus by primary estrogen, catechol estrogen, and xenoestrogen

Many xenobiotics are considered reproductive toxins because of their ability to interact with the nuclear estrogen receptors (ERalpha and ERbeta). However, there is evidence that these xenobiotics can regulate gene expression in the reproductive targets by mechanisms that do not involve these ERs. To examine this further, we compared the effects of estrogenic (o,p'-DDT [1-(o-chlorophenyl)-1-(p-chlorophenyl)2,2,2-trichloroethane] and Kepone, chlordecone) and nonestrogenic (p,p'-DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane], a metabolite of p,p'-DDT) xenobiotics with those of 17beta-estradiol (E2) and 4-hydroxyestradiol-17beta (4-OH-E2), a catechol metabolite of E2, on uterine expression of lactoferrin (LF) and progesterone receptor (PR). These genes are estrogen responsive in the mouse uterus. Normally, LF is expressed in the uterine epithelium, whereas PR is expressed in both the epithelium and stroma in response to estrogenic stimulation. Ovariectomized mice were injected with xenobiotics (7.5 mg/kg), E2 (10 microg/kg), 4-OH-E2 (10 microg/kg), or the vehicle (oil, 0.1 ml/mouse), and uterine tissues were processed for Northern blot and in situ hybridization. The pure antiestrogen ICI-182780 (ICI; 1 or 20 mg/kg) was used to interfere with estrogenic responses that were associated with the ERs. The results of Northern and in situ hybridization demonstrated increased uterine levels of PR and LF messenger RNAs (mRNAs) by all of these xenobiotics, but quantitatively the responses were much lower than those induced by E2 or 4-OH-E2. The results further showed that the E2-inducible epithelial LF mRNA accumulation was markedly abrogated by pretreatment with ICI (20 mg/kg). In contrast, this treatment retained the epithelial expression of PR mRNA, but down-regulated the stromal expression. In contrast, ICI had negligible effects on LF and PR mRNA responses to 4-OH-E2, indicating that this catechol estrogen exerted its effects primarily via a mechanism(s) other than the ERs. The heightened accumulation of LF mRNA in the epithelium in response to Kepone and o,p'-DDT was also severely compromised by pretreatment with ICI, but this antiestrogen had little effect on responses to p,p'-DDD. Similar to E2, Kepone increased the expression of PR mRNA in both uterine epithelium and stroma. However, pretreatment with ICI decreased stromal cell expression, whereas epithelial cell expression remained unaltered or increased. These responses were not noted in mice treated with o,p'-DDT or p,p'-DDD. Collectively, the results demonstrate that catechol estrogens or xenobiotics can alter uterine expression of estrogen-responsive genes by mechanisms that are not totally mediated by the classical nuclear ERs, and these alterations are cell type specific. We conclude that an interaction of a compound with the nuclear ERalpha and/or ERbeta is not an absolute requirement for producing specific estrogen-like effects in the reproductive target tissues.

Interactions between hormones and chemicals in breast cancer

Development of breast cancer in women is dependent on diverse factors, including genetic predisposition, exposure to both exogenous and endogenous chemicals, which can modulate initiation, promotion and progression of this disease, and the timing of exposure to these agents. Several compounds--including 16 alpha-hydroxyestrone (16 alpha-OHE1), catecholestrogens, and aromatic amines--have been proposed as initiators of mammary carcinogenesis in humans; however, their role as genotoxins is unconfirmed. Lifetime exposure to estrogens has been established as an important risk factor for breast cancer, and it has been suggested that xenoestrogens may directly add to the hormonal risk or indirectly increase risk by decreasing 2-hydroxyestrone (2-OHE1)/16 alpha-OHE1 metabolite ratios. Results of recent studies suggest that chemical-induced modulation of 2-OHE1/16 alpha-OHE1 metabolite ratios is not predictive of xenoestrogens or mammary carcinogens. Moreover, based on current known dietary intakes of natural and xenoestrogenic/antiestrogenic chemicals, it is unlikely that xenoestrogens contribute significantly to a woman's overall lifetime exposure to estrogens. More information is required on the identities and serum levels of both natural and xenoendocrine active compounds, their concentrations in serum, and the mammary gland and levels of these compounds at critical periods of exposure.