Involvement of Peroxisome Proliferator-Activated Receptor-Alpha in Liver Tumor Production by Permethrin in the Female Mouse.

The nongenotoxic pyrethroid insecticide permethrin produced hepatocellular tumors in CD-1 mice but not in Wistar rats. Recently, based on findings of a Pathology Working Group involving an expert panel of pathologists, it was concluded that permethrin increased liver tumors at 2500 and 5000 ppm in female mice, but no treatment-related tumorigenic response occurred in male mice at dose levels examined in the 2-year bioassay. To evaluate a possible mode of action (MOA) for the permethrin female CD-1 mouse hepatocellular tumors, a number of investigative studies were conducted. In time-course studies in female CD-1 mice, permethrin increased relative liver weight and enhanced hepatocyte proliferation within 1 week. Treatment with permethrin resulted in marked increases in CYP4A enzyme activities and mRNA levels, but only slightly increased CYP2B markers, suggesting that permethrin primarily activates the peroxisome proliferator-activated receptor alpha (PPARα) and to a much lesser extent the constitutive androstane receptor. The effects of permethrin on relative liver weight, hepatocyte proliferation and CYP4A enzyme activities and mRNA levels were dose-dependent and were reversible within 5 weeks after cessation of treatment. The hepatic effects of permethrin observed in wild-type female mice were markedly reduced in PPARα knockout female mice. These results demonstrate that the MOA for hepatocellular tumor formation by permethrin in female mice involves activation of PPARα resulting in a mitogenic effect. The MOA for permethrin-induced mouse liver tumor formation due to PPARα activation is considered to be not plausible for humans. This conclusion is strongly supported by available epidemiological data for permethrin.

Identification of a Novel Bone Marrow Cell-Derived Accelerator of Fibrotic Liver Regeneration Through Mobilization of Hepatic Progenitor Cells in Mice.

Granulocyte colony stimulating factor (G-CSF) has been reported to ameliorate impaired liver function in patients with advanced liver diseases through mobilization and proliferation of hepatic progenitor cells (HPCs). However, the underlying mechanisms remain unknown. We previously showed that G-CSF treatment increased the number of bone marrow (BM)-derived cells migrating to the fibrotic liver following repeated carbon tetrachloride (CCl4 ) injections into mice. In this study, we identified opioid growth factor receptor-like 1 (OGFRL1) as a novel BM cell-derived accelerator of fibrotic liver regeneration in response to G-CSF treatment. Endogenous Ogfrl1 was highly expressed in the hematopoietic organs such as the BM and spleen, whereas the liver contained a relatively small amount of Ogfrl1 mRNA. Among the peripheral blood cells, monocytes were the major sources of OGFRL1. Endogenous Ogfrl1 expression in both the peripheral blood monocytes and the liver was decreased following repeated CCl4 injections. An intrasplenic injection of cells overexpressing OGFRL1 into CCl4 -treated fibrotic mice increased the number of HPC and stimulated proliferation of hepatic parenchymal cells after partial resection of the fibrotic liver. Furthermore, overexpression of OGFRL1 in cultured HPC accelerated their differentiation as estimated by increased expression of liver-specific genes such as hepatocyte nuclear factor 4α, cytochrome P450, and fatty acid binding protein 1, although it did not affect the colony forming ability of HPC. These results indicate a critical role of OGFRL1 in the mobilization and differentiation of HPC in the fibrotic liver, and administration of OGFRL1-expressing cells may serve as a potential regenerative therapy for advanced liver fibrosis. Stem Cells 2019;37:89-101.

Combining Genomics To Identify the Pathways of Post-Transcriptional Nongenotoxic Signaling and Energy Homeostasis in Livers of Rats Treated with the Pregnane X Receptor Agonist, Pregnenolone Carbonitrile.

Transcriptomic, proteomic, phosphoproteomic, and metabolomic analyses were combined to determine the role of pregnane X receptor (PXR) in nongenotoxic signaling and energy homeostasis in liver after rats were repeatedly orally dosed with the PXR agonist pregnenolone carbonitrile (PCN) for 7 days. Analyses of mRNAs and proteins in the supernatant, membrane, and cytosolic fractions of enlarged liver homogenates showed diverse expression profiles. Gene set enrichment analysis showed that the synchronous increase in mRNAs and proteins involved in chemical carcinogenesis and the response to drug was possibly mediated by the PXR pathway and proteasome core complex assembly was possibly mediated by the Nrf2 pathway. In addition, levels of proteins in the endoplasmic reticulum lumen and involved in the acute-phase response showed specific increase with no change in mRNA level, and those composed of the mitochondrial inner membrane showed specific decrease. The analysis of phosphorylated peptides of poly(A) RNA binding proteins showed a decrease in phosphorylation, possibly by casein kinase 2, which may be related to the regulation of protein expression. Proteins involved in insulin signaling pathways showed an increase in phosphorylation, possibly by protein kinase A, and those involved in apoptosis showed a decrease. Metabolomic analysis suggested the activation of the pentose phosphate and anaerobic glycolysis pathways and the increase of amino acid and fatty acid levels, as occurs in the Warburg effect. In conclusion, the results of combined analyses suggest that PXR's effects are due to transcriptional and post-transcriptional regulation with alteration of nongenotoxic signaling pathways and energy homeostasis.

Editor's Highlight: Mode of Action Analysis for Rat Hepatocellular Tumors Produced by the Synthetic Pyrethroid Momfluorothrin: Evidence for Activation of the Constitutive Androstane Receptor and Mitogenicity in Rat Hepatocytes.

High dietary levels of momfluorothrin, a nongenotoxic synthetic pyrethroid, induced hepatocellular tumors in male and female Wistar rats in a 2-year bioassay. The mode of action (MOA) for rat hepatocellular tumors was postulated to occur via activation of the constitutive androstane receptor (CAR), as momfluorothrin is a close structural analogue of the pyrethroid metofluthrin, which is known to produce rat liver tumors through a CAR-mediated MOA. To elucidate the MOA for rat hepatocellular tumor formation by momfluorothrin, this study was conducted to examine effects on key and associative events of the CAR-mediated MOA for phenobarbital based on the International Programme on Chemical Safety framework. A 2-week in vivo study in Wistar rats revealed that momfluorothrin induced CYP2B activities, increased liver weights, produced hepatocyte hypertrophy and increased hepatocyte replicative DNA synthesis. These effects correlated with the dose-response relationship for liver tumor formation and also showed reversibility upon cessation of treatment. Moreover, momfluorothrin did not increase CYP2B1/2 mRNA expression and hepatocyte replicative DNA synthesis in CAR knockout rats. Using cultured Wistar rat hepatocytes and the RNA interference technique, knockdown of CAR resulted in a suppression of induction of CYP2B1/2 mRNA levels by momfluorothrin. Alternative MOAs for liver tumor formation were excluded. A global gene expression profile analysis of the liver of male Wistar rats treated with momfluorothrin for 2 weeks also showed similarity to the prototypic CAR activator phenobarbital. Overall, these data strongly support that the postulated MOA for momfluorothrin-induced rat hepatocellular tumors as being mediated by CAR activation.

An Evaluation of the Human Relevance of the Lung Tumors Observed in Female Mice Treated With Permethrin Based on Mode of Action.

Permethrin increased the incidence of bronchiolo-alveolar adenomas in female mice but not male mice or female or male rats. Studies were conducted to determine whether permethrin has mitogenic activity in Club cells in mouse lung as the basis for the mode of action (MOA) for the lung adenoma induction. Several short-term experiments focusing on time-course, dose-response, reversibility, sex difference, strain difference, and species difference were evaluated for Club cell proliferation and morphology. The findings demonstrated that permethrin slightly and continuously enhanced Club cell proliferation at tumor-associated dose levels in female mice, but did not increase proliferation in male mice or in female rats. Electron microscopic examination demonstrated that permethrin produced morphological alterations in Club cells prior to increasing the Club cell proliferation. There was no evidence of increased cell death. These alterations in Club cells were also observed with a close structural analog cypermethrin. Taken together, the present studies provide evidence that the MOA for induction of mouse lung adenomas by permethrin involves slight morphological effects on Club cells, sustained Club cell proliferation, and eventually hyperplasia and bronchiolo-alveolar adenoma in susceptible mice. The potential human carcinogenic hazard of permethrin based on the tumorigenic MOA for lung tumors in mice was evaluated using the International Programme on Chemical Safety Human Relevance Framework. As humans are quantitatively much less sensitive to agents that increase Club cell proliferation and tumor formation in mice, it is not likely permethrin will lead to an increase in susceptibility to lung tumor development in humans. Epidemiological data for permethrin strongly supports this conclusion.

Candidate genes responsible for early key events of phenobarbital-promoted mouse hepatocellular tumorigenesis based on differentiation of regulating genes between wild type mice and humanized chimeric mice.

Phenobarbital (PB) is a nongenotoxic hepatocellular carcinogen in rodents. PB induces hepatocellular tumors by activating the constitutive androstane receptor (CAR). Some previous research has suggested the possible involvement of epigenetic regulation in PB-promoted hepatocellular tumorigenesis, but the details of its molecular mechanism are not fully understood. In the present study, comprehensive analyses of DNA methylation, hydroxymethylation and gene expression using microarrays were performed in mouse hepatocellular adenomas induced by a single 90 mg kg-1 intraperitoneal injection dose of diethylnitrosamine (DEN) followed by 500 ppm PB in the diet for 27 weeks. DNA modification and expression of hundreds of genes are coordinately altered in PB-induced mouse hepatocellular adenomas. Of these, gene network analysis showed alterations of CAR signaling and tumor development-related genes. Pathway enrichment analysis revealed that differentially methylated or hydroxymethylated genes belong mainly to pathways involved in development, immune response and cancer cells in contrast to differentially expressed genes belonging primarily to the cell cycle. Furthermore, overlap was evaluated between the genes with altered expression levels with 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) alterations in mouse hepatocellular adenoma induced by DEN/PB and the genes with altered expression levels in the liver of CD-1 mice or humanized chimeric mice treated with PB for 7 days. With the integration of transcriptomic and epigenetic approaches, we detected candidate genes responsible for early key events of PB-promoted mouse hepatocellular tumorigenesis. Interestingly, these genes did not overlap with genes altered by the PB treatment of humanized chimeric mice, thus suggesting a species difference between the effects of PB in mouse and human hepatocytes.

An improved model of predicting hepatocarcinogenic potential in rats by using gene expression data.

Carcinogenicity studies using animals are expensive and time consuming. Therefore, the development of a highly accurate carcinogenicity prediction system to interpret short-term test results would be beneficial. The Ames test is popular for mutagens; however, it cannot detect non-genotoxic carcinogens. Previously, we reported a prediction system using gene expression data obtained from a short-term (28-day) study that screened candidate compounds for testing in long-term carcinogenicity studies. In this study, our system was improved by adding more gene expression data. To establish our new system, we used the data of 93 test compounds (41 hepatocarcinogens and 52 non-hepatocarcinogens). Analysis of liver gene expression data by dividing compounds into 'for training' and 'for test' categories (20 cases assigned randomly) using Support Vector Machine (SVM) identified a set of marker probe sets that could be used to predict hepatocarcinogenicity. The assigned 42 probe sets have included the cancer- or c-Myc-related genes such as Hsp90, Pink1, Hspc111, Fbx29, Hepsin, Syndecan2 and Synbindin. Compared with the older version, the improved system had a higher concordance rate with the training data and a good performance with the external test data.

Human hepatocytes support the hypertrophic but not the hyperplastic response to the murine nongenotoxic hepatocarcinogen sodium phenobarbital in an in vivo study using a chimeric mouse with humanized liver.

High doses of sodium phenobarbital (NaPB), a constitutive androstane receptor (CAR) activator, have been shown to produce hepatocellular tumors in rodents by a mitogenic mode of action (MOA) involving CAR activation. The effect of 1-week dietary treatment with NaPB on liver weight and histopathology, hepatic CYP2B enzyme activity and CYP2B/3A mRNA expression, replicative DNA synthesis and selected genes related to cell proliferation, and functional transcriptomic and metabolomic analyses was studied in male CD-1 mice, Wistar Hannover (WH) rats, and chimeric mice with human hepatocytes. The treatment of chimeric mice with 1000-1500-ppm NaPB resulted in plasma levels around 3-5-fold higher than those observed in human subjects given therapeutic doses of NaPB. NaPB produced dose-dependent increases in hepatic CYP2B activity and CYP2B/3A mRNA levels in all animal models. Integrated functional metabolomic and transcriptomic analyses demonstrated that the responses to NaPB in the human liver were clearly different from those in rodents. Although NaPB produced a dose-dependent increase in hepatocyte replicative DNA synthesis in CD-1 mice and WH rats, no increase in replicative DNA synthesis was observed in human hepatocyte-originated areas of chimeric mice. In addition, treatment with NaPB had no effect on Ki-67, PCNA, GADD45ß, and MDM2 mRNA expression in chimeric mice, whereas significant increases were observed in CD-1 mice and/or WH rats. However, increases in hepatocyte replicative DNA synthesis were observed in chimeric mice both in vivo and in vitro after treatment epidermal growth factor. Thus, although NaPB could activate CAR in both rodent and human hepatocytes, NaPB did not increase replicative DNA synthesis in human hepatocytes of chimeric mice, whereas it was mitogenic to rat and mouse hepatocytes. As human hepatocytes are refractory to the mitogenic effects of NaPB, the MOA for NaPB-induced rodent liver tumor formation is thus not relevant for humans.

Expression of the clustered NeuAcα2-3Galß O-glycan determines the cell differentiation state of the cells.

Human embryonic stem cells (hESCs) are pluripotent stem cells from early embryos, and their self-renewal capacity depends on the sustained expression of hESC-specific molecules and the suppressed expression of differentiation-associated genes. To discover novel molecules expressed on hESCs, we generated a panel of monoclonal antibodies against undifferentiated hESCs and evaluated their ability to mark cancer cells, as well as hESCs. MAb7 recognized undifferentiated hESCs and showed a diffuse band with molecular mass of >239 kDa in the lysates of hESCs. Although some amniotic epithelial cells expressed MAb7 antigen, its expression was barely detected in normal human keratinocytes, fibroblasts, or endothelial cells. The expression of MAb7 antigen was observed only in pancreatic and gastric cancer cells, and its levels were elevated in metastatic and poorly differentiated cancer cell lines. Analyses of MAb7 antigen suggested that the clustered NeuAcα2-3Galß O-linked oligosaccharides on DMBT1 (deleted in malignant brain tumors 1) were critical for MAb7 binding in cancer cells. Although features of MAb7 epitope were similar with those of TRA-1-60, distribution of MAb7 antigen in cancer cells was different from that of TRA-1-60 antigen. Exposure of a histone deacetylase inhibitor to differentiated gastric cancer MKN74 cells evoked the expression of MAb7 antigen, whereas DMBT1 expression remained unchanged. Cell sorting followed by DNA microarray analyses identified the down-regulated genes responsible for the biosynthesis of MAb7 antigen in MKN74 cells. In addition, treatment of metastatic pancreatic cancer cells with MAb7 significantly abrogated the adhesion to endothelial cells. These results raised the possibility that MAb7 epitope is a novel marker for undifferentiated cells such as hESCs and cancer stem-like cells and plays a possible role in the undifferentiated cells.

Metabolomic and transcriptomic profiling of human K-ras oncogene transgenic rats with pancreatic ductal adenocarcinomas.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most debilitating malignancies in humans, and one of the reasons for this is the inability to diagnose this disease early in its development. To search for biomarkers that can be used for early diagnosis of PDAC, we established a rat model of human PDAC in which expression of a human K-ras(G12V) oncogene and induction of PDAC are regulated by the Cre/lox system. In the present study, transgenic rats bearing PDAC and control transgenic rats with normal pancreatic tissues were used for metabolomic analysis of serum and pancreatic tissue by non-targeted and targeted gas chromatography-mass spectrometry and transcriptomic analysis of pancreatic tissue by microarray. Comparison of the metabolic profiles of the serum and pancreatic tissue of PDAC-bearing and control rats identified palmitoleic acid as a metabolite, which was significantly decreased in the serum of PDAC-bearing animals. Transcriptomic analysis indicated that several transcripts involved in anaerobic glycolysis and nucleotide degradation were increased and transcripts involved in the trichloroacetic acid cycle were decreased. Other transcripts that were changed in PDAC-bearing rats were adenosine triphosphate citrate lyase (decreased: fatty acid biosynthesis), fatty acid synthase (increased: fatty acid biosynthesis) and arachidonate 5-lipoxygenase activating protein (increased: arachidonic acid metabolism). Overall, our results suggest that the decreased serum levels of palmitoleic acid in rats with PDAC was likely due to its decrease in pancreatic tissue and that palmitoleic acid should be investigated in human samples to assess its diagnostic significance as a serum biomarker for human PDAC.

Toxicogenomics discrimination of potential hepatocarcinogenicity of non-genotoxic compounds in rat liver.

Long-term carcinogenicity testing of a compound is exceedingly time-consuming and costly, and requires many test animals, whereas the Ames test, which is based on the assumption that any substance that is mutagenic may also exert carcinogenic potential, is useful as a short-term screening assay but has major drawbacks. Although, in fact, 90% of compounds that give a positive Ames test cause cancer in laboratory animals, a good proportion of compounds that give a negative Ames test are also carcinogens; that is, there is no good correlation between carcinogenicity and negative Ames test results. As an alternative to these two approaches, we have tried applying toxicogenomics to predict the carcinogenicity of a compound from the gene expression profile induced in vivo. To establish our model, male Sprague-Dawley rats were orally administered test compounds (12 hepatocarcinogens and 26 non-hepatocarcinogens) for 28 days. Analysis of liver gene expression data by Support Vector Machines (SVM) dividing compounds into 'for training' and 'for test' (20 cases assigned randomly) allowed a set of marker genes to be tested for prediction of hepatocarcinogenicity. The developed prediction model was then validated with reference to the concordance rate with training data and test data, and a good performance was obtained. We will have new gene expression data and continue the validation of our model.

Circulating microRNAs in serum of human K-ras oncogene transgenic rats with pancreatic ductal adenocarcinomas.

OBJECTIVES: Novel biomarkers for pancreatic ductal adenocarcinoma (PDAC) are urgently needed because of its poor prognosis. We have previously established an animal model for human PDAC using transgenic rats in which expression of a human K-ras(G12V) oncogene is regulated by the Cre/lox system. Using this model, we searched for candidate circulating microRNAs (miRNAs) for use as novel clinical diagnostic biomarkers for PDAC. METHODS: Rats bearing PDACs were generated using our model. MicroRNA expression in serum and pancreatic tissues of PDAC and control rats was compared by microarray analysis. Rat serum levels of 28 miRNAs identified by microarray analysis and 4 miRNAs previously reported to be high in plasma of PDAC patients were quantified by real-time quantitative reverse transcription polymerase chain reaction. RESULTS: Quantification by real-time quantitative polymerase chain reaction revealed that miR-155, miR-21, and miR-210 were higher in serum of PDAC rats, similar to plasma of patients with PDAC. In addition, miR-18a, miR-203, miR-30b-5p, miR-31, miR-369-5p, miR-376a, and miR-541 were higher and miR-375 was lower in the serum of PDAC rats. CONCLUSION: We identified 4 previously unreported miRNAs (miRNA-203, miRNA-369-5p, miRNA-376a, and miRNA-375) whose expression is significantly different in PDAC rats compared to control rats. These miRNAs need to be quantitated in humans as potential novel clinical diagnostic biomarkers for PDAC.

New short term prediction method for chemical carcinogenicity by hepatic transcript profiling following 28-day toxicity tests in rats.

We have previously shown the hepatic gene expression profiles of carcinogens in 28-day toxicity tests were clustered into three major groups (Group-1 to 3). Here, we developed a new prediction method for Group-1 carcinogens which consist mainly of genotoxic rat hepatocarcinogens. The prediction formula was generated by a support vector machine using 5 selected genes as the predictive genes and predictive score was introduced to judge carcinogenicity. It correctly predicted the carcinogenicity of all 17 Group-1 chemicals and 22 of 24 non-carcinogens regardless of genotoxicity. In the dose-response study, the prediction score was altered from negative to positive as the dose increased, indicating that the characteristic gene expression profile emerged over a range of carcinogen-specific doses. We conclude that the prediction formula can quantitatively predict the carcinogenicity of Group-1 carcinogens. The same method may be applied to other groups of carcinogens to build a total system for prediction of carcinogenicity.

Circulating microRNAs, possible indicators of progress of rat hepatocarcinogenesis from early stages.

MicroRNAs (miRNAs), a class of small noncoding RNAs that regulate gene expression at the posttranscriptional level, are believed promising biomarkers for several diseases as well as a novel target of drugs, including cancer. In particular, miRNAs might allow detection of early stages of carcinogenesis. The present study was conducted to provide concrete evidence using chemical-induced hepatocarcinogenesis in rat as a model. We thereby observed aberrant fluctuation of circulating miRNAs in the serum of rats not only with neoplastic lesions such as hepatocellular adenoma (HCA) and hepatocellular carcinoma (HCC), but also with preneoplastic lesions, such as foci of hepatocellular alteration (FHA). Additional qRT-PCR analysis revealed gradual elevation of some circulating miRNAs (i.e., let-7a, let-7f, miR-34a, miR-98, miR-331, miR-338 and miR-652) with progress of hepatocarcinogenesis. Interestingly, increased levels of let-7a, let-7f and miR-98 were statistically significant even in the serum of rats at very early stages. These findings provide the first evidences that circulating miRNAs have the potential to predict carcinogenesis at earlier stages, preneoplastic lesions than with previous biomarkers and that they might be utilized to monitor the progress of tumor development.

Discrimination of carcinogens by hepatic transcript profiling in rats following 28-day administration.

This study aimed at discriminating carcinogens on the basis of hepatic transcript profiling in the rats administrated with a variety of carcinogens and non-carcinogens. We conducted 28-day toxicity tests in male F344 rats with 47 carcinogens and 26 non-carcinogens, and then investigated periodically the hepatic gene expression profiles using custom microarrays. By hierarchical cluster analysis based on significantly altered genes, carcinogens were clustered into three major groups (Group 1 to 3). The formation of these groups was not affected by the gene sets used as well as the administration period, indicating that the grouping of carcinogens was universal independent of the conditions of both statistical analysis and toxicity testing. Seventeen carcinogens belonging to Group 1 were composed of mainly rat hepatocarcinogens, most of them being mutagenic ones. Group 2 was formed by three subgroups, which were composed of 23 carcinogens exhibiting distinct properties in terms of genotoxicity and target tissues, namely nonmutagenic hepatocarcinogens, and mutagenic and nonmutagenic carcinogens both of which are targeted to other tissues. Group 3 contained 6 carcinogens including 4 estrogenic substances, implying the group of estrogenic carcinogens. Gene network analyses revealed that the significantly altered genes in Group 1 included Bax, Tnfrsf6, Btg2, Mgmt and Abcb1b, suggesting that p53-mediated signaling pathway involved in early pathologic alterations associated with preceding mutagenic carcinogenesis. Thus, the common transcriptional signatures for each group might reflect the early molecular events of carcinogenesis and hence would enable us to identify the biomarker genes, and then to develop a new assay for carcinogenesis prediction.

Mode of action analysis for the synthetic pyrethroid metofluthrin-induced rat liver tumors: evidence for hepatic CYP2B induction and hepatocyte proliferation.

Two-year treatment with high doses of Metofluthrin produced hepatocellular tumors in both sexes of Wistar rats. To understand the mode of action (MOA) by which the tumors are produced, a series of studies examined the effects of Metofluthrin on hepatic microsomal cytochrome P450 (CYP) content, hepatocellular proliferation, hepatic gap junctional intercellular communication (GJIC), oxidative stress and apoptosis was conducted after one or two weeks of treatment. The global gene expression profile indicated that most genes with upregulated expression with Metofluthrin were metabolic enzymes that were also upregulated with phenobarbital. Metofluthrin induced CYP2B and increased liver weights associated with centrilobular hepatocyte hypertrophy (increased smooth endoplasmic reticulum [SER]), and induction of increased hepatocellular DNA replication. CYP2B1 mRNA induction by Metofluthrin was not observed in CAR knockdown rat hepatocytes using the RNA interference technique, demonstrating that Metofluthrin induces CYP2B1 through CAR activation. Metofluthrin also suppressed hepatic GJIC and induced oxidative stress and increased antioxidant enzymes, but showed no alteration in apoptosis. The above parameters related to the key events in Metofluthrin-induced liver tumors were observed at or below tumorigenic dose levels. All of these effects were reversible upon cessation of treatment. Metofluthrin did not cause cytotoxicity or peroxisome proliferation. Thus, it is highly likely that the MOA for Metofluthrin-induced liver tumors in rats is through CYP induction and increased hepatocyte proliferation, similar to that seen for phenobarbital. Based on analysis with the International Life Sciences Institute/Risk Science Institute MOA framework, it is reasonable to conclude that Metofluthrin will not have any hepatocarcinogenic activity in humans, at least at expected levels of exposure.

Characteristic upregulation of glucose-regulated protein 78 in an early lesion negative for hitherto established cytochemical markers in rat hepatocarcinogenesis.

Previously, we reported α(2)-macroglobulin (α(2)M) to be a novel marker characteristic of rat hepatocellular preneoplastic and neoplastic lesions negative for hitherto well-established markers. In the present study, we further examined other candidate markers with specificity for the same type of lesions. Glutathione S-transferase-placental form (GST-P)-negative hepatocellular altered foci (HAF) were generated using a two-stage (initiation and promotion) carcinogenesis protocol with N,N-diethylnitrosamine (DEN) and either Wy-14,643 or clofibrate, two peroxisome proliferators. Microarray analysis using total RNAs isolated from laser-microdissected GST-P-negative HAF (amphophilic cell foci) and adjacent normal tissues was conducted along with immunohistochemistry and real-time RT-PCR. Staining for glucose-regulated protein 78 (GRP78) was detected in GST-P-negative HAF and hepatocellular adenomas, and slightly increased GRP78 mRNA expression was observed in the lesions by real-time RT-PCR analysis. Thus, an early increase of GRP78 expression in hepatocarcinogenesis is likely a feature of the amphophilic subset of HAF.

Molecular cloning of estrogen receptors from fathead minnow (Pimephales promelas) and bluegill (Lepomis macrochirus) fish: limited piscine variation in estrogen receptor-mediated reporter gene transactivation by xenoestrogens.

Estrogen receptors (ERs) play essential roles in estrogen function. Because they may be targets of environmental chemicals, concern exists that exposure to some anthropogenic agents may result in disruption of endocrine systems in human and wildlife populations. Various kinds of ERs have been reported, and a number of in vitro assays have been established to test hormone-like activity of chemicals. In the present study, cDNAs encoding ERs from fathead minnow (Pimephales promelas) and bluegill (Lepomis macrochirus) fish, which are useful for environmental monitoring, were cloned and sequenced. Four complete, full-length ERalpha and ERbeta cDNA sequences could be derived, with an ATG start site and a TGA termination signal included in each. Fathead minnow ERalpha has 602 amino acid residues, bluegill ERalpha1 has 582, bluegill ERalpha2 has 506, and bluegill ERbeta has 554. When the cDNAs were inserted into the pRc/RSV vector and transfected into HeLa cells (derived from cervical cancer cells) with a reporter plasmid, the encoding proteins were confirmed to be functional through interaction of the receptor-ligand complex with the estrogen-responsive element (ERE). Here, we report the analysis of piscine differences in ER-dependent transactivation with some chemicals using reporter gene assays. In agonist assays, fold-induction of luciferase activity significantly varied among ERs, but responsiveness to each chemical demonstrated certain similarities. These reporter gene assays appear to be very useful for estimating adverse effects of chemicals, including hormone-like or antihormone-like activity, in fish.

A comparative study of gene expression profiles in rat liver after administration of alpha-hexachlorocyclohexane and lindane.

Alpha-hexachlorocyclohexane (alpha-HCH) is a stereoisomer of gamma-HCH, the active ingredient of lindane (> 99% gamma-HCH). In the present study, cDNA microarray technology was employed to identify changes in gene expression associated with toxicity in livers of male Fischer 344 rats after treatment with alpha-HCH (2, 20 mg/kg/day) and lindane (1, 10 mg/kg/day) by daily oral gavage for up to 28 days. Liver samples were obtained after 1, 3, 7, 14 and 28 days and compared for gene expression profiles. The dose of the alpha-HCH was higher than that of lindane and toxicity was greater, but the numbers of probe sets with differences in expression were fewer for the alpha-HCH-treated group except on Day 3. Only very few probe sets with differences in expression overlapped between alpha-HCH and lindane at each time point and the gene expression profiles were very dissimilar. Important liver-based differences in expression between alpha-HCH and lindane might possibly account for hepato-carcinogenicity of alpha-HCH.

Optimization of an animal test protocol for toxicogenomics studies (I); requirement study of a protocol.

Toxicogenomics is a promising new tool for prediction of chemical toxicities including carcinogenicity in a relatively short period. However, it is important to develop a reliable animal test protocol for toxicogenomics studies. The preparation of RNA and tissues is also crucial, since it greatly influences outcomes of gene expression analysis. In the present study, we examined an animal test protocol by comparing gene expression data from different conditions and proposed a reliable animal test protocol for toxicogenomic studies. With regard to the preparation of tissues and RNA, here we present evidence that quality of RNA and tissues is well-preserved even after freezer storage for up to 2.5 years. Gene expression levels were compared using a GeneChip System (RGU34A, Affymetrix, Santa Clara, CA, USA) between RNA samples that were freshly prepared, stored at -80 degrees C or re-prepared from tissue kept at -20 degrees C. None showed degradation and no significant differences in expression were evident among the three sets of samples. The data demonstrate that gene expression analysis by DNA microarray is suitable for RNA or tissues that have been stored at an appropriate temperature.