Effect of some carcinogenic and non-carcinogenic polycyclic aromatic hydrocarbons on gap junction intercellular communication in hepatoma cell cultures

Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing

Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.

Effects of Environment and Lifestyle Factors on Premature Ovarian Failure

Premature ovarian insufficiency (POI) or primary ovarian failure is defined as a cessation of the menstrual cycle in women younger than 40 years old. It is strictly defined as more than 4 months of oligomenorrhea or amenorrhea in a woman <40 years old, associated with at least two follicle-stimulating hormone (FSH) levels >25 U/L in the menopausal range, detected more than 4 weeks apart. It is estimated that POI was affected 1 and 2% of women. Although 80% of POI cases are of unknown etiology, it is suggested that genetic disorder, autoimmune origin, toxins, and environmental factors, as well as personal lifestyles, may be risk factors of developing POI. In this section, we will discuss the influences of environmental and lifestyle factors on POI. Moreover updated basic research findings regarding how these environmental factors affect female ovarian function via epigenetic regulations will also be discussed.

Cigarette smoking and hormones

PURPOSE OF REVIEW

The purpose is to provide a summary of the effects of cigarette smoking on steroid hormone metabolism and how it affects female fertility.

RECENT FINDINGS

Components of tobacco smoke such as polycyclic aromatic hydrocarbons lead to transcriptional upregulation of a number of genes, including members of the cytochrome P450 (CYP) family, in particular CYP1B1 and CYP1A1. In humans, CYP1A1 and CYP1A2 are the primary enzymes catalyzing the 2-hydroxylation of estradiol. This pathway shunts available estrogen away from the more estrogenically potent 16α-hydroxylation to the production of catechol estrogens, mainly 2 and 4 hydroxyestradiol.

SUMMARY

Smoking has multiple effects on hormone secretion and metabolism. These effects are mainly mediated by the pharmacological action of tobacco alkaloids (nicotine and its metabolite cotinine). A strong body of evidence indicates that the negative effects of cigarette smoking on fertility compromises nearly every system involved in the reproductive process.

Ovotoxicity of cigarette smoke: A systematic review of the literature

This study reviews the scientific literature on the noxious effects of cigarette smoke on the ovarian follicle, and the cumulative data on the impact of smoking on in vitro fertilization (IVF) cycle outcome. There is a close association between tobacco smoke and accelerated follicle loss, abnormal follicle growth and impairment of oocyte morphology and maturation. There is an increasing amount of evidence indicating that smoke can directly derange folliculogenesis. Increased cellular apoptosis or autophagy, DNA damage and abnormal crosstalk between oocyte and granulosa cells have been implicated in the demise of ovarian follicles. It becomes increasingly clear that maternal smoking can exert multigenerational effects on the ovarian function of the progeny. Growing evidence suggests that cigarette smoke is associated with decreased results after IVF. Further research is needed to better define the molecular mechanisms behind smoking-induced ovarian disruption.

Impact of obesity on 7,12-dimethylbenz[a]anthracene-induced altered ovarian connexin gap junction proteins in female mice

The ovarian gap junction proteins alpha 4 (GJA4 or connexin 37; CX37), alpha 1 (GJA1 or connexin 43; CX43) and gamma 1 (GJC1 or connexin 45; CX45) are involved in cell communication and folliculogenesis. 7,12-dimethylbenz[a]anthracene (DMBA) alters Cx37 and Cx43 expression in cultured neonatal rat ovaries. Additionally, obesity has an additive effect on DMBA-induced ovarian cell death and follicle depletion, thus, we investigated in vivo impacts of obesity and DMBA on CX protein levels. Ovaries were collected from lean and obese mice aged 6, 12, 18, or 24 wks. A subset of 18 wk old mice (lean and obese) were dosed with sesame oil or DMBA (1mg/kg; ip) for 14days and ovaries collected 3days thereafter. Cx43 and Cx45 mRNA and protein levels decreased (P<0.05) after 18 wks while Cx37 mRNA and protein levels decreased (P<0.05) after 24 wks in obese ovaries. Cx37 mRNA and antral follicle protein staining intensity were reduced (P<0.05) by obesity while total CX37 protein was reduced (P<0.05) in DMBA exposed obese ovaries. Cx43 mRNA and total protein levels were decreased (P<0.05) by DMBA in both lean and obese ovaries while basal protein staining intensity was reduced (P<0.05) in obese controls. Cx45 mRNA, total protein and protein staining intensity level were decreased (P<0.05) by obesity. These data support that obesity temporally alters gap junction protein expression and that DMBA-induced ovotoxicity may involve reduced gap junction protein function.

The effects of cigarette smoke extract on ovulation, oocyte morphology and ovarian gene expression in mice

Cigarette smoking can harm fertility, but the existing research has targeted primarily on ovarian follicles, embryos or sex hormone. In this study, we tested cigarette smoke extract on ovulation, oocyte morphology and ovarian gene expression associated with inhibition of oxidative stress using C57BL/6 mice. Mice in the experimental group were administered a cigarette smoke extract (CSE) solution (2 mg/ml) orally daily, while the blank control group was given dimethylsulfoxide (DMSO). A positive control group (menadione) was used that received an intraperitoneal injection of 15 mg/kg menadione in oil solution daily. We found that the CSE group manifested a reduced diameter of zona pellucida-free oocyte (ZP-free OD) and a morphologically misshapen first polar body (PB). Our results suggest that CSE exposure is associated with a shrink size and poor quality of oocytes. Quitting smoking is a wise choice to ensure good fertility.

Characterization of a gap-junctional intercellular communication (GJIC) assay using cigarette smoke

Inhibition of gap-junctional intercellular communication (GJIC) via exposure to various toxic substances has been implicated in tumor promotion. In the present study, cigarette smoke total particulate matter (TPM), a known inhibitor of GJIC, were used to characterize a new GJIC screening assay in three independent experiments. The main features of this assay were automated fluorescence microscopy combined with non-invasive parachute technique. Rat liver epithelial cells (WB-F344) were stained with the fluorescent dye Calcein AM (acetoxymethyl) and exposed to TPM from the Kentucky Reference Cigarette 2R4F (a blend of Bright and Burley tobaccos) and from two single-tobacco cigarettes (Bright and Burley) for 3h. Phorbol-12-myristate-13-acetate (TPA) was used as positive control and 0.5% dimethyl sulfoxide (DMSO) as solvent control. The transfer of dye to adjacent cells (percentage of stained cells) was used as a measure of cellular communication. A clear and reproducible dose-response of GJIC inhibition following TPM exposure was seen. Reproducibility and repeatability measurements for the 2R4F cigarette were 3.7% and 6.9%, respectively. The half-maximal effective concentration values were 0.34ng/ml for TPA, 0.050mg/ml for the 2R4F, 0.044mg/ml for the Bright cigarette, and 0.060mg/ml for the Burley cigarette. The assay was able to discriminate between the two single-tobacco cigarettes (P<0.0001), and between the single-tobacco cigarettes and the 2R4F (P=0.0008, 2R4F vs. Burley and P<0.0001, 2R4F vs. Bright). Thus, this assay can be used to determine the activity of complex mixtures such as cigarette smoke with high throughput and high precision.

De novo reestablishment of gap junctional intercellular communications during reprogramming to pluripotency and differentiation

Gap junctional intercellular communication (GJIC) has been described in embryonic stem cells (ESCs) and various somatic cells. GJIC has been implicated in the regulation of cell proliferation, self-renewal, and differentiation. Recently, a new type of pluripotent stem cells was generated by direct reprogramming of somatic cells. Here, for the first time, we show that during reprogramming events GJIC is re-established upon reaching complete reprogramming. The opposite process of cell differentiation from the pluripotent state leads to the disruption of GJIC between pluripotent and differentiated cell subsets. However, GJIC is subsequently re-established de novo within each differentiated cell type in vitro, forming communication compartments within a histotype. Our results provide the important evidence that reestablisment of functional gap junctions to the level similar to human ESCs is an additional physiological characteristic of somatic cell reprogramming to the pluripotent state and differentiation to the specific cell type.

[Effects of cigarette smoking on female reproduction: from oocyte to embryo (Part I)]

Cigarette smoking is associated with lower fecundity rate, adverse reproductive outcomes and higher risk of IVF failure. Over the last decades, prevalence of smoking among women of reproductive age has increased. The aim of this work was to focus on the knowledge of the effects of cigarette smoking on all reproductive stages, from oocyte to embryo. For each reproductive functions human clinical and experimental studies were analysed in order to find hypothesis and explanations for effects observed. All reproductive functions are targets of smoke compounds and cigarette smoking impairs ovarian reserve, sexual steroids synthesis, Fallopian tubes functions and embryo development, leading to reduced fecundity. Some of smoke compounds were identified in ovarian tissue, in uterine fluid and in the embryo, suggesting direct toxicity.

Advanced glycation end products down-regulate gap junctions in human hepatoma SKHep 1 cells via the activation of Src-dependent ERK1/2 and JNK/SAPK/AP1 signaling pathways

Hyperglycemia and advanced glycation end products (AGEs) are associated with an elevated risk of developing several cancers in diabetic patients. However, the detailed mechanisms remain to be elucidated. The mechanism of AGE-bovine serum albumin (BSA) on gap junction intercellular communication in human hepatoma cell line, SKHep 1, was investigated. Both Cx32 and Cx43 are major gap junction forming proteins in the liver, the loss of which has been shown to facilitate tumorigenesis. Although the MTT assay results showed that AGE-BSA significantly increased cell growth by 31%, AGE-BSA down-regulated Cx32 and Cx43 expression in a dose- and time-dependent manner. The present study also demonstrated that ERK1/2 and JNK/SAPK were significantly activated by AGE-BSA and that Src, ERK1/2, and JNK/SAPK inhibitors significantly reversed the reduction of Cx32 and Cx43 proteins by AGE-BSA. Taken together, these results strongly support the hypothesis that Src-dependent ERK1/2 and JNK/SAPK/AP1 signaling pathways play a key role in AGE-BSA-mediated down-regulation of Cx32 and Cx43 protein expression in SKHep 1 cells.

Effects of cigarette smoking on reproduction

BACKGROUND Cigarette smoking is associated with lower fecundity rates, adverse reproductive outcomes and a higher risk of IVF failures. Over the last few decades, prevalence of smoking among women of reproductive age has increased. This review focuses on current knowledge of the potential effects of smoke toxicants on all reproductive stages and the consequences of smoke exposure on reproductive functions. METHODS We conducted a systematic review of the scientific literature on the impact of cigarette smoking and smoke constituents on the different stages of reproductive function, including epidemiological, clinical and experimental studies. We attempted to create hypotheses and find explanations for the deleterious effects of cigarette smoke observed in experimental studies. RESULTS Cigarette smoke contains several thousand components (e.g. nicotine, polycyclic aromatic hydrocarbons and cadmium) with diverse effects. Each stage of reproductive function, folliculogenesis, steroidogenesis, embryo transport, endometrial receptivity, endometrial angiogenesis, uterine blood flow and uterine myometrium is a target for cigarette smoke components. The effects of cigarette smoke are dose-dependent and are influenced by the presence of other toxic substances and hormonal status. Individual sensitivity, dose, time and type of exposure also play a role in the impact of smoke constituents on human fertility. CONCLUSIONS All stages of reproductive functions are targets of cigarette smoke toxicants. Further studies are necessary to better understand the deleterious effects of cigarette smoke compounds on the reproductive system in order to improve health care, help to reduce cigarette smoking and provide a better knowledge of the molecular mechanisms involved in reproductive toxicology.

Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity

Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.

Benzo[a]pyrene-dependent activation of transcription factors NF-κB and AP-1 related to tumor promotion in hepatoma cell cultures

The activation by the carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BP) of transcription factors NF-kappaB and AP-1 in hepatoma 27 and HepG2 cell cultures was studied. In contrast to the hepatoma HepG2 cells, cytochrome P450 isoforms and Ah-receptor are not expressed in the hepatoma 27 cells. The transcription factor NF-kappaB was activated only in the hepatoma 27 cells by BP treatment but not by its noncarcinogenic isomer benzo[e]pyrene (BeP). Conversely to NF-kappaB activation the transcription factor AP-1 was activated in the hepatoma HepG2 cells by cell treatment with BP but not in the hepatoma 27 cells. It is concluded that the NF-kappaB activation is caused by nonmetabolized BP molecule and not related to activation of the Ah-receptor. The transcription factor AP-1 seems to be activated as a result of the interaction of BP with the Ah-receptor. The realization of tumor promotion stage by carcinogenic PAHs treatment in dependence on the cytochrome P450 and Ah-receptor levels in the initiated cells is discussed.