Biomedical subjects

Robert R Maronpot

Publications and source records attributed to Robert R Maronpot.

At least 19 recordsLinked to original sources

PubMed2006

Orphan nuclear receptor constitutive active/androstane receptor-mediated alterations in DNA methylation during phenobarbital promotion of liver tumorigenesis.

Altered DNA methylation is an epigenetic mechanism that plays a key role in the carcinogenesis process, and the nongenotoxic rodent hepatocarcinogen phenobarbital (PB) alters the methylation status of DNA in mouse liver. The constitutive active/androstane nuclear receptor (CAR) mediates half of the PB-induced hepatic gene expression changes and it is essential for liver tumor promotion in PB-treated mice. Here, a technique involving methylation-sensitive restriction digestion, arbitrarily primed PCR, and capillary electrophoresis was utilized to detect PB-induced regions of altered DNA methylation (RAMs) in CAR wildtype (WT) mice that are sensitive to promotion by PB and resistant CAR knockout (KO) mice. The CAR WT mice developed preneoplastic lesions after 23 weeks of PB treatment (precancerous) and liver tumors after 32 weeks, while the CAR KO mice did not develop tumors (Y. Yamamoto, et al., 2004, Cancer Res. 64, 7197-7200). Our goal was to discern those RAMs which are playing important roles in tumor formation by comparing the RAMs that form in sensitive and resistant groups of mice. Using this novel approach, 42 unique RAMs were identified in the precancerous as compared to the CAR KO, 23-week PB-treated tissue. Of these 42 RAMs, 14 carried forward to the tumor tissue, and additionally, 104 total unique RAMs were observed in the tumor tissue. These results indicate that there are unique RAMs occurring in the sensitive CAR WT mice and that a portion of these are seen in both the precancerous and tumor tissue. We hypothesize that these unique RAMs may be facilitating the tumorigenesis process, and these data support the view that DNA methylation plays a causative role in PB-induced tumorigenesis.

Analysis of Variance↗

PubMed2006

Application of magnetic resonance imaging in developmental neurotoxicity testing: a pilot study.

In a pilot developmental neurotoxicity study, a protocol was designed to utilize three-dimensional magnetic resonance (MR) images for linear and volumetric measurements of the developing rat brain. MR imaging, because of its non-destructive nature, provides a complement to traditional optical microscopy. Sprague-Dawley dams received 0, 1.25, 4.0 or 7.5mg/kg methylazoxymethanol acetate (MAM) by intraperitoneal injection during gestation days 13-15. At postnatal days (PND) 23 and 60, brains from representative male and female rats from two dams in each dose group were fixed with 10% neutral buffered formalin by transcardial perfusion for in situ MR imaging. A 7T small animal magnet system was used to obtain isotropic images at 100 microm resolution for PND 23 and 150 microm resolution for PND 60. Data from a rapid screening method based on midpoint MR slices of whole brain, cerebrum, cerebellum, and hippocampus showed a dose-related decreased volume of whole brain, cerebrum, and hippocampus in treated rats. Subsequent volumetric estimates using the Cavalieri method confirmed these findings. The brains were subsequently removed and processed for conventional histologic examination of hematoxylin and eosin-stained sections. It is concluded that MR imaging in rat developmental neurotoxicity studies offers the advantages of in situ volumetric measurements of brain structures while preserving the samples for conventional optical microscopy.

Animals↗

PubMed2006

Estrogen receptor alpha mediates 17alpha-ethynylestradiol causing hepatotoxicity.

Estrogens are known to cause hepatotoxicity such as intrahepatic cholestasis in susceptible women during pregnancy, after administration of oral contraceptives, or during postmenopausal replacement therapy. Enterohepatic nuclear receptors including farnesoid X receptor (FXR), pregnane X receptor (PXR), and constitutive active/androstane receptor (CAR) are important in maintaining bile acid homeostasis and protecting the liver from bile acid toxicity. However, no nuclear receptor has been implicated in the mechanism for estrogen-induced hepatotoxicity. Here Era(-/-), Erb(-/-), Fxr(-/-), Pxr(-/-), and Car(-/-) mice were employed to show that Era(-/-) mice were resistant to synthetic estrogen 17alpha-ethynylestradiol (EE2)-induced hepatotoxicity as indicated by the fact that the EE2-treated Era(-/-) mice developed none of the hepatotoxic phenotypes such as hepatomegaly, elevation in serum bile acids, increase of alkaline phosphatase activity, liver degeneration, and inflammation. Upon EE2 treatment, estrogen receptor alpha (ERalpha) repressed the expression of bile acid and cholesterol transporters (bile salt export pump (BSEP), Na(+)/taurocholate cotransporting polypeptide (NTCP), OATP1, OATP2, ABCG5, and ABCG8) in the liver. Consistently, biliary secretions of both bile acids and cholesterol were markedly decreased in EE2-treated wild-type mice but not in the EE2-treated Era(-/-) mice. In addition, ERalpha up-regulated the expression of CYP7B1 and down-regulated the CYP7A1 and CYP8B1, shifting bile acid synthesis toward the acidic pathway to increase the serum level of beta-muricholic acid. ERbeta, FXR, PXR, and CAR were not involved in regulating the expression of bile acid transporter and biosynthesis enzyme genes following EE2 exposure. Taken together, these results suggest that ERalpha-mediated repression of hepatic transporters and alterations of bile acid biosynthesis may contribute to development of the EE2-induced hepatotoxicity.

Animals↗

PubMed2006

Differential attenuation of oxidative/nitrosative injuries in early prostatic neoplastic lesions in TRAMP mice by dietary antioxidants.

BACKGROUND: Dietary antioxidants with yet unproven efficacies in averting prostate cancer (PCa) are widely used in the United States as preventives. Experimental evidence establishing a causal relationship between oxidative and nitrosative stress (OS/NS) and PCa development and showing its modulation by dietary antioxidants would help justify their usage. METHODS: The TRAMP (Transgenic Adenocarcinoma of the Mouse Prostate) mouse model was used to demonstrate the OS/NS-associated damage, as evident by 8-hydroxy-2'-deoxyguanosine (8-OHdG), 4-hydroxynonenal (4-HNE)-protein-adducts and nitrotyrosine (Ntyr), in prostatic premalignant lesions, and to evaluate the antioxidant efficacy of various dietary supplements [natural antioxidant (NAO) from spinach extracts, (-) epigallocatechin-3-gallate (EGCG), or N-acetylcystein (NAC)] during the early PCa development. RESULT: We show, for the first time, that oxidative/nitrosative damages of genomic DNA and cellular proteins were discretely localized in premalignant lesions, but not in adjacent morphologically normal epithelia, of TRAMP prostates; these injuries were absent in age-matched nontransgenic littermates. The extent of OS/NS-related injuries correlated well with the tempo of development and prevalence of premalignant lesions in various prostatic lobes and exhibited a clear trend of increase from 12 to 20 weeks of age. Treatment of TRAMP mice with various antioxidants as dietary supplements resulted in differential alleviation of OS/NS-related prostatic injuries. The antioxidant potencies of the dietary supplements did not fully correlate with their documented antiPCa actions, suggest that they may exert additional "nonantioxidant," antitumor effects in this model. CONCLUSIONS: Our data indicate that in TRAMP mice, OS/NS injuries are likely involved in early prostatic tumorigenesis and can be modulated by various antioxidants.

Adenocarcinoma↗

PubMed2006

Precancer in mice: animal models used to understand, prevent, and treat human precancers.

We present a status report from the NCI Mouse Models of Human Cancers Consortium (MMHCC) Precancers Workshop held November 8 and 9, 2004. An expert panel, the Mouse Models Group (MMG) evaluated the status of mouse models of precancer emphasizing genetically engineered mouse models, especially of lining epithelium and their utilitarian value to human carcinogenesis. An outline of the background for the panel's considerations is provided with examples of past and current precancerous lesions in mice. The experimental use of oncogenic viruses and chemical carcinogens in mice led to operational definitions of initiation, promotion, and preneoplasia Preneoplastic and precancerous lesions are found in these models. In this precancer concept, most preneoplastic lesions are considered as potentially precancerous or at least an earlier stage in cancer development than typical pre-invasive epithelial lesions, which are often seen in these mouse models. Genetically engineered mice, used to test the oncogenicity of individual genes, develop precancers that are initiated by defined molecular and histopathologic changes. The mouse can be used to isolate and study precancers in detail, thereby providing a level of biological understanding not readily available in clinical disease. These studies suggest that genetically engineered mice are very useful preclinical models for chemoprevention and therapy.

Animals↗

PubMed2005

Lung tumors in 2 year old strain A/J mice exposed for 6 months to tobacco smoke.

Young adult strain A/J mice were exposed for 6 months in a whole-body inhalation chamber to a mixture of 89% sidestream and 11% mainstream cigarette smoke generated from Kentucky 1R4F research cigarettes. Chamber concentrations of smoke constituents were 158mg/m(3) of total suspended particulate matter (TSP). After an additional 4 months in air, some of the animals were killed. Lung tumor multiplicities in the smoke exposed animals were 1.8+/-0.2 versus 0.9+/-0.2 in controls. In animals kept beyond the age of 12 months, lung tumor multiplicities increased in both groups, but remained at all times twice the control values in the smoke exposed animals compared to controls (4.3+/-0.7 vs. 2.1+/-0.5 tumors per lung in 24 months old animals). Histopathology showed that, in 2 year old animals, still about 80% of tumors were of benign nature. No tumors were found in the nasal passages. It was concluded that tobacco smoke exposure not simply accelerates the development of lesions that eventually would have developed spontaneously, but induced de novo formation of lung tumors in A/J mice.

Animals↗

PubMed2005

New insights into functional aspects of liver morphology.

The liver is structurally and functionally complex and has been considered second only to brain in its complexity. Many mysteries still exist in this heterogeneous tissue whose functional unit of the lobule has continued to stump morphologists for over 300 years. The primary lobule, proposed by Matsumoto in 1979, has been gaining acceptance as the functional unit of the liver over other conceptual views because it's based on vessel architecture and includes the classic lobule as a secondary feature. Although hepatocytes comprise almost 80% of the liver, there are at least another dozen cell types, many of which provide "cross-talk" and play important functional roles in the normal and diseased liver. The distribution and functional roles of all cells in the liver must be carefully considered in both the analysis and interpretation of research data, particularly data in the area of genomics and "phenotypic anchoring" of gene expression results. Discoveries regarding the functional heterogeneity of the various liver cell types, including hepatocytes, hepatic stellate cells, sinusoidal endothelia, and Kupffer cells, are providing new insights into our understanding of the development, prevention and treatment of liver disease. For example, functional differences along zonal patterns (centrilobular or periportal) have been demonstrated for sinusoidal endothelium, Kupffer cells, and hepatocytes and can explain the gradients and manifestations of disease observed within lobules. Intralobular gradients of bile uptake, glycogen depletion, glutamine synthetase, and carboxylesterase by hepatocytes; widened fenestrations in centrilobular sinusoidal lining cells; and differences in the components of centrilobular extracellular matrix or function of Kupffer cells have been demonstrated. Awareness of the complexities and heterogeneity of the liver will add to a greater understanding of liver function and disease processes that lead to toxicity, cancer, and other diseases.

Animals↗

PubMed2005

Microarray data analysis of mouse neoplasia.

Microarray gene expression analysis offers great promise to help us understand the molecular events of experimental carcinogenesis, but have such promises been fulfilled? Studies of gene expression profiles of rodent are being published and demonstrate that yes, indeed, gene array data is furthering our understanding of tumor biology. Recent studies have identified differentially expressed genes in rodent mammary, colon, lung, and liver tumors. Although relatively few genes on the rodent arrays have been fully characterized, information has been generated to better identify signatures of histologic type and grade, understand invasion and metastasis, identify candidate biomarkers of early development, identify gene networks in carcinogenesis, understand responses to therapy, and decifer overlap with molecular events in human cancers. Data from mouse lung, mammary gland, and liver tumor studies are reviewed as examples of how to approach and interpret gene array data. Methods of gene array data analysis were also applied for discovery of genes involved in the regression of mouse liver tumors induced by chlordane, a nongenotoxic murine hepatocarcinogen. Promises are beginning to be fulfilled and it is clear that pathologists and toxicologists, in collaboration with molecular biologists, bioinformatists,and other scientists are making great strides in the design, analysis, and interpretation of microarray data for cancer studies.

Animals↗

PubMed2005

An investigation of the effects of late-onset dietary restriction on prostate cancer development in the TRAMP mouse.

In our previous work we showed that dietary restriction initiated at puberty reduced prostate cancer development in the TRAMP mouse model. The current study was conducted to ascertain whether a dietary restriction regime would similarly reduce lesion development if imposed once tumor development was well established. Male TRAMP mice were maintained on an ad libitum diet until 20 weeks of age when proliferative prostate lesions are clearly evident. Mice were then subjected to a 20% restriction in dietary calories compared to matched controls, which were continued on ad libitum feeding. Mice were sacrificed at 20, 24, 32, and 39 weeks of age and proliferative epithelial lesions of the prostate were assessed using an established grading scheme. In this study, although dietary restriction reduced mean sex pluck weight (prostate and seminal vesicles), and mean grade of epithelial proliferative lesions in the dorsal and lateral lobes of the prostate, the effect was not as pronounced as was the case with dietary restriction from puberty. There was no relationship between serum insulin like growth factor (IGF-1) and prostate lesion grade. Additionally, we also report the relationship between lobe specific lesion development and SV40 immunostaining and, the occurance of neuroendocrine tumors (NETs) in the ventral prostate and urethra of the TRAMP mouse. NETs stained with high specificity and sensitivity for the neuroendocrine markers, synaptophysin and neuron-specific enolase (NSE), less for serotonin, but not for chromogranin A. NETs did not stain for cyclo-oxygenase-2 (COX-2) nor androgen receptor (AR). SV40 positive tubulo-acinar tumors seen occasionally in the kidney, did not stain for synaptophysin nor NSE.

Adenocarcinoma↗

PubMed2004

Cadmium at a non-toxic dose alters gene expression in mouse testes.

The testes are important targets of cadmium (Cd)-induced toxicity and carcinogenicity in rodents. Exposure to Cd at environmentally relevant low levels is a significant human health concern, but the effects of Cd on the rodent testes at doses that do not cause overt lesions are poorly defined. We used cDNA microarray and quantitative real-time RT-PCR assays to determine gene expression profiles in the testes of CD-1 mice 12-72 h after a single s.c. injection of 5 micromol/kg CdCl2. This dose of Cd did not produce overt histopathological changes, but clearly altered the expression of some genes that are likely to be important in toxicity responses. The most significant changes in gene expression occurred 24 h after treatment, corresponding to when the highest level of Cd was detected in the testes. Increased expression of the C-myc and Egr1 genes strongly suggests acute stress responses. Repressed expression of cell cycle-regulated cyclin B1 and CDC2 proteins indicates a potential for causing G2/M arrest and disturbance of meiosis. Decreased expression of pro-apoptotic genes, particularly Casp3, and DNA repair genes possibly contributes to Cd-induced carcinogenesis. These results indicate that changes in gene expression occur well before overt effects of Cd-induced testicular toxicity and carcinogenicity are apparent.

Animals↗

PubMed2004

Neurotoxicity of carbonyl sulfide in F344 rats following inhalation exposure for up to 12 weeks.

Carbonyl sulfide (COS), a high-priority Clean Air Act chemical, was evaluated for neurotoxicity in short-term studies. F344 rats were exposed to 75-600 ppm COS 6 h per day, 5 days per week for up to 12 weeks. In rats exposed to 500 or 600 ppm for up to 4 days, malacia and microgliosis were detected in numerous neuroanatomical regions of the brain by conventional optical microscopy and magnetic resonance microscopy (MRM). After a 2-week exposure to 400 ppm, rats were evaluated using a functional observational battery. Slight gait abnormality was detected in 50% of the rats and hypotonia was present in all rats exposed to COS. Decreases in motor activity, and forelimb and hindlimb grip strength were also detected. In rats exposed to 400 ppm for 12 weeks, predominant lesions were in the parietal cortex area 1 (necrosis) and posterior colliculus (neuronal loss, microgliosis, hemorrhage), and occasional necrosis was present in the putamen, thalamus, and anterior olivary nucleus. Carbonyl sulfide specifically targeted the auditory system including the olivary nucleus, nucleus of the lateral lemniscus, and posterior colliculus. Consistent with these findings were alterations in the amplitude of the brainstem auditory evoked responses (BAER) for peaks N3, P4, N4, and N5 that represented changes in auditory transmission between the anterior olivary nucleus to the medial geniculate nucleus in animals after exposure for 2 weeks to 400 ppm COS. A concentration-related decrease in cytochrome oxidase activity was detected in the posterior colliculus and parietal cortex of exposed rats as early as 3 weeks. Cytochrome oxidase activity was significantly decreased at COS concentrations that did not cause detectable lesions, suggesting that disruption of the mitochondrial respiratory chain may precede these brain lesions. Our studies demonstrate that this environmental air contaminant has the potential to cause a wide spectrum of brain lesions that are dependent on the degree and duration of exposure.

Air Pollutants↗

PubMed2004

The orphan nuclear receptor constitutive active/androstane receptor is essential for liver tumor promotion by phenobarbital in mice.

Hepatocellular carcinoma (HCC) is known to progress through a step often called tumor promotion. Phenobarbital (PB) is the prototype of nongenotoxic cacinogens that promote HCC in rodents. The molecular target of PB to elicit the promotion has been the subject of intense investigations over the last 30 years since it was discovered. The nuclear receptor constitutive active/androstane receptor (CAR) is activated by PB as well as by various other xenobiotics such as therapeutic drugs and environmental pollutants. CAR activation results in the transcriptional induction of numerous hepatic genes including those that encode xenobiotic-metabolizing enzymes such as a set of cytochrome P450s. In addition to PB, many CAR activators are nongenotoxic carcinogens, but the role of CAR in liver tumor promotion remains unexplored. Using Car(-/-) mice, we have here examined tumor promotion by chronic treatment with PB in drinking water after tumor initiation with a single dose of the genotoxic carcinogen diethylnitrosamine. None of the Car(-/-) mice developed either eosinophilic foci or advanced liver tumors, whereas all Car(+/+) mice developed HCC and/or adenoma by 39 weeks. The results indicate that CAR is the molecular target of promotion by PB and that activation of this receptor is an essential requirement for liver tumor development.

Animals↗

PubMed2004

Carcinogen-specific targeting of chromosome 12 for loss of heterozygosity in mouse lung adenocarcinomas: implications for chromosome instability and tumor progression.

Genotoxic carcinogens exert their tumorigenic effects in part by inducing genomic instability. We recently showed that loss of heterozygosity (LOH) on chromosome 12 associates significantly with the induction of chromosome instability (CIN) by the likely human lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and vinyl carbamate (VC) during mouse lung carcinogenesis. Here, we demonstrate the carcinogen specificity of this event and its effect on lung tumor evolution. LOH on chromosome 12 was observed in 45% of NNK-induced, 59% of VC-induced, 58% of aflatoxin B1 (AFB1)-induced, 14% of N-ethyl-N-nitrosourea (ENU)-induced and 12% of spontaneous lung adenocarcinomas. The frequency of LOH in each of the carcinogen-induced groups, except ENU, was significantly higher than in the spontaneous group (P<0.001). Deletion mapping revealed four potential candidate regions of 1-4 centiMorgans suspected to contain targeted tumor suppressor genes, with at least one expected to have a role in CIN. The relationship between LOH on chromosome 12 and additional chromosomal alterations occurring during lung tumor progression was also examined. LOH on chromosomes 1 and 14 were moderately frequent during malignant progression in tumors from all treatment groups, occurring in 21-35 and 18-33% of tumors. However, these alterations showed significant concurrence with LOH on chromosome 12 in VC-, NNK- and AFB1-induced tumors (P<0.05). The results suggest that a carcinogen-selective mechanism of lung cancer induction involves the frequent inactivation of genes on chromosome 12, including a stability gene that evidently promotes the evolutionary selection of additional chromosomal alterations during malignant progression.

Adenocarcinoma↗

PubMed2004

Classification of proliferative pulmonary lesions of the mouse: recommendations of the mouse models of human cancers consortium.

Rapid advances in generating new mouse genetic models for lung neoplasia provide a continuous challenge for pathologists and investigators. Frequently, phenotypes of new models either have no precedents or are arbitrarily attributed according to incongruent human and mouse classifications. Thus, comparative characterization and validation of novel models can be difficult. To address these issues, a series of discussions was initiated by a panel of human, veterinary, and experimental pathologists during the Mouse Models of Human Cancers Consortium (NIH/National Cancer Institute) workshop on mouse models of lung cancer held in Boston on June 20-22, 2001. The panel performed a comparative evaluation of 78 cases of mouse and human lung proliferative lesions, and recommended development of a new practical classification scheme that would (a) allow easier comparison between human and mouse lung neoplasms, (b) accommodate newly emerging mouse neoplasms, and (c) address the interpretation of benign and preinvasive lesions of the mouse lung. Subsequent discussions with additional experts in pulmonary pathology resulted in the current proposal of a new classification. It is anticipated that this classification, as well as the complementary digital atlas of virtual histological slides, will help investigators and pathologists in their characterization of new mouse models, as well as stimulate further research aimed at a better understanding of proliferative lesions of the lung.

Animals↗

PubMed2004

Chorioallantoic fusion defects and embryonic lethality resulting from disruption of Zfp36L1, a gene encoding a CCCH tandem zinc finger protein of the Tristetraprolin family.

The mouse gene Zfp36L1 encodes zinc finger protein 36-like 1 (Zfp36L1), a member of the tristetraprolin (TTP) family of tandem CCCH finger proteins. TTP can bind to AU-rich elements within the 3'-untranslated regions of the mRNAs encoding tumor necrosis factor (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), leading to accelerated mRNA degradation. TTP knockout mice exhibit an inflammatory phenotype that is largely due to increased TNF secretion. Zfp36L1 has activities similar to those of TTP in cellular RNA destabilization assays and in cell-free RNA binding and deadenylation assays, suggesting that it may play roles similar to those of TTP in mammalian physiology. To address this question we disrupted Zfp36L1 in mice. All knockout embryos died in utero, most by approximately embryonic day 11 (E11). Failure of chorioallantoic fusion occurred in about two-thirds of cases. Even when fusion occurred, by E10.5 the affected placentas exhibited decreased cell division and relative atrophy of the trophoblast layers. Although knockout embryos exhibited neural tube abnormalities and increased apoptosis within the neural tube and also generalized runting, these and other findings may have been due to deficient placental function. Embryonic expression of Zfp36L1 at E8.0 was greatest in the allantois, consistent with a potential role in chorioallantoic fusion. Fibroblasts derived from knockout embryos had apparently normal levels of fully polyadenylated compared to deadenylated GM-CSF mRNA and normal rates of turnover of this mRNA species, both sensitive markers of TTP deficiency in cells. We postulate that lack of Zfp36L1 expression during mid-gestation results in the abnormal stabilization of one or more mRNAs whose encoded proteins lead directly or indirectly to abnormal placentation and fetal death.

Allantois↗

PubMed2003

Inhibition of the enzymatic activity of prostate-specific antigen by boric acid and 3-nitrophenyl boronic acid.

BACKGROUND: Prostate specific antigen (PSA) is a well-established marker of prostate cancer, but it can also degrade extracellular matrix proteins such as fibronectin and could be involved in tumor progression and metastasis. In this study, we have addressed the use of boric acid and 3-nitrophenyl boronic acid (NPBA) as PSA inhibitors in vitro. METHODS: The inhibition of PSA by boric acid was studied by using specific fluorogenic substrates. Fibronectin, a biologically relevant substrate for PSA, was used as a substrate in a zymographic assay, and the degradation of fibronectin by PSA in the presence of boric acid and NPBA was followed by Western Blot. RESULTS: Low concentrations of boric acid partially inhibited the proteolytic activity of PSA toward a synthetic fluorogenic substrate. Also, by Western blot, we have found significant inhibition in the proteolysis of fibronectin by PSA in the presence of boric acid as well as NPBA. Results indicate that the boronated compounds used in this study can be used for the modulation of PSA activity. CONCLUSION: PSA activity is inhibited in vitro by boric acid and NPBA. If degradation of fibronectin by PSA were, in fact, an important step in the progression of prostate cancer, then borate-induced inhibition of PSA activity should help reduce the development and proliferation of prostate carcinomas.

Blotting, Western↗

PubMed2003

Bromoethane, chloroethane and ethylene oxide induced uterine neoplasms in B6C3F1 mice from 2-year NTP inhalation bioassays: pathology and incidence data revisited.

Chloroethane, bromoethane and ethylene oxide represent a unique set of chemicals that induce endometrial neoplasms in the uterus of B6C3F1 mice following an inhalation route of exposure. The results of the NTP's chronic bioassays with these three compounds resulted in an unusually high incidence of uterine epithelial neoplasms in B6C3F1 mice (chloroethane 86%, bromoethane 56%) and a lower incidence for ethylene oxide (10%). The uterine neoplasms were classified as adenomas, adenocarcinomas, and squamous cell carcinomas for bromoethane, and as adenocarcinomas for both chloroethane and ethylene oxide. The adenocarcinomas and squamous cell carcinomas were invasive into the myometrium and the serosa, and metastasized to a wide variety of organs. Metastatic sites included most commonly the lung, lymph nodes, and ovary at unusually high rates of metastases (79% for chloroethane and 38% for bromoethane). Because of the dramatically high rates of uterine neoplasms (induced by chemicals given by the inhalation route) and metastases, a re-evaluation of the pathology and incidence data was undertaken. The earlier results were confirmed. The mechanism of uterine carcinogenesis by chloroethane, bromoethane and ethylene oxide is unclear.

Adenocarcinoma↗

PubMed2003

Perturbations of the Ink4a/Arf gene locus in aflatoxin B1-induced mouse lung tumors.

Lung tumors from AC3F1 mice treated with aflatoxin B(1) (AFB(1)), were examined for loss of alleles, point mutations and hypermethylation of CpG sites within the promoters of the two genes in the Ink4a/Arf gene locus. Loss of microsatellite alleles in the Ink4a/Arf region occurred in 22 of 74 (30%) AFB(1)-induced lung tumors. Fifty-one of 61 (83%) tumors had at least partial methylation of CpG sites within the p16Ink4a promoter-exon 1alpha region. At least partial methylation of CpG sites was observed in 43 of 49 (88%) tumors analyzed for p19Arf promoter hypermethylation, with methylation of identified transcription factor binding sites or consensus sequences occurring in 21 tumors (DMP1/Ets in two tumors, CTCF in four tumors, E2F in three tumors, Sp1 in 16 tumors). Two tumors contained point mutations in the p19Arf promoter. Nuclear staining for p19(Arf) was decreased by 80-100% in 41 of 71 (58%) tumors. The concordance between p19Arf molecular perturbations and altered protein expression was 63%. However, upon comparing p19Arf promoter perturbations (i.e. methylation of functional transcription factor binding sites and point mutations) and altered p19(Arf) expression, the concordance was 86%, suggesting a mechanism for changes in protein expression in some tumors. There was an absence of a mutually exclusive relationship between disruption of p53 and p19(Arf), since the concordance was 62%. Similarly, no evidence was found of inverse relationships between perturbation of p16Ink4a and p19(Arf) (43% concordance) or p16Ink4(a) and p53 (37% concordance), suggesting that inactivation of these genes occurs independently and provides evidence that, although these genes may participate in cooperative cellular pathways, they also have functions in independent pathways that are important in mouse lung tumorigenesis.

Aflatoxin B1↗