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R R Maronpot

Publications and source records attributed to R R Maronpot.

At least 55 records · Page 3Linked to original sources
PubMed1995

High frequency of K-ras mutations in spontaneous and vinyl carbamate-induced lung tumors of relatively resistant B6CF1 (C57BL/6J x BALB/cJ) mice.

The murine K-ras proto-oncogene is hypothesized to be a pulmonary adenoma susceptibility gene. This postulate is supported by the previous demonstration of a preference for mutation of the K-ras allele from the susceptible parent in lung tumors of A/J x C3H F1 mice. We have examined K-ras activation in control and vinyl carbamate (VC) (single dose 0.03 mumol/g i.p.) treated B6CF1 mice, the progeny of resistant C57BL/6J and intermediately sensitive BALB/cJ parents. Thirty-four of 37 tumors from VC-treated mice and 17 of 23 from controls contained activating K-ras mutations. The spectra of mutations in codons 12 and 61 of K-ras were similar for the two groups, except that 7 tumors from VC-treated mice had A-->T transversions in the second base of codon 61; none were observed in tumors from saline-treated animals. PCR-based genotyping of first exon K-ras mutations revealed that the vast majority (15 of 18) of the mutations were in the BALB/cJ allele. Furthermore, the three tumors with mutated C57BL/6J K-ras were among the smallest tumors analyzed. These results are consistent with previous findings in other mouse hybrids showing parental bias for K-ras mutations and suggest that mutation of the allele of the susceptible parent may provide a growth advantage to the tumor.

Alleles↗
PubMed1995

H-ras oncogene mutation spectra in B6C3F1 and C57BL/6 mouse liver tumors provide evidence for TCDD promotion of spontaneous and vinyl carbamate-initiated liver cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent environmental toxin which has been found to be non-genotoxic in short term in vitro tests but strongly carcinogenic in two stage models of hepatocellular carcinogenesis in female rats. Many recent studies have shown that after treatment of mice with various genotoxic or non-genotoxic compounds, the H-ras oncogene mutational patterns exhibited by hepatocellular tumors appear to vary specifically with the chemical. To gain insight into the mechanism of TCDD-associated carcinogenesis, susceptible B6C3F1 mice and resistant C57BL/6 mice were treated with a single dose of vinyl carbamate (VC) or vehicle, and TCDD was administered once every 2 weeks for 1 year to half of the animals in each group. Liver tumor prevalence was assessed and found to be highest in the VC + TCDD treatment groups, reaching nearly 100% at 600 days in both sexes and both strains of mice. DNA was isolated from 20 or more frozen liver tumors (if available) from each exposure group and analyzed for H-ras mutations in codon 61 by sequencing after PCR amplification of exon 2. Fifty-one percent of tumors analyzed from B6C3F1 mice treated with TCDD alone had H-ras codon 61 mutations with a pattern similar to that detected in spontaneous tumors. Seventy-eight percent of tumors from B6C3F1 mice treated with both VC and TCDD had codon 61 mutations, and most mutations were A-->T transversions in the second base as observed similarly with VC alone. In the C57BL/6 strain comparable results were found in the respective exposure groups. These data suggest that TCDD is acting as a promoter of lesions previously initiated either spontaneously or by VC. Moreover, the intrinsic resistance of both male and female C57BL/6 mice to liver tumor formation seemed to disappear after treatment with TCDD.

Animals↗
PubMed1995

Bile duct-specific lectins, Dolichos biflorus agglutinin and peanut agglutinin, as probes in mouse hepatocarcinogenesis.

BACKGROUND: It is well established that alterations in the expression of cell surface glycoproteins occur during the course of tumorigenesis and can be detected immunohistochemically. However, no consistent markers of malignancy in mouse hepatocellular tumors have yet been identified. EXPERIMENTAL DESIGN: Lectin histochemistry, using three bile duct-specific lectins, Dolichos biflorus agglutinin (DBA), peanut agglutinin (PNA) and soybean agglutinin (SBA), and anti-epidermal keratin immunohistochemistry, was conducted on formalin-fixed, paraffin-embedded tissues of a spectrum of benign and malignant hepatocellular proliferative lesions of mice, including hepatocholangiocarcinomas. DBA- and PNA-binding glycoproteins in normal livers and in bile and liver tumors of mice were verified by SDS-PAGE and Western blot analysis. RESULTS: Normal bile duct cells stained strongly with DBA but minimally to moderately with PNA and SBA. DBA-positive tumor cells were present in 96% of hepatocholangiocarcinomas, 89% of hepatocellular carcinomas, and 35% of hepatocellular adenomas. In comparison, 43% of hepatocholangiocarcinomas, 37% of hepatocellular carcinomas, and 24% of hepatocellular adenomas exhibited PNA staining. SBA did not specifically stain tumor cells. Normal hepatocytes and those in altered foci were consistently negative for these three lectins. Keratin-positive staining was found only in normal bile ductular cells and ductal elements in 70% of hepatocholangiocarcinomas. Electrophoresis and Western blot analysis demonstrated that, in normal livers, DBA and PNA bound to the 13- to 16-kDa and 27- to 30-kDa glycoproteins believed to be of bile duct cell origin and commonly present in hepatocellular adenomas, hepatocellular carcinomas, and hepatocholangiocarcinomas, with strongest expression in the last. In addition, hepatocholangiocarcinomas had the same high molecular mass glycoprotein (> 200 kDa) labeled with DBA as detected in bile. CONCLUSIONS: Our results suggest that some malignant hepatocytes, especially in mouse hepatocholangiocarcinomas, have the potential of biliary differentiation. DBA is a sensitive marker for malignant hepatocytes in mice.

Adenoma↗
PubMed1995

Considerations concerning the murine hepatocarcinogenicity of selected chlorinated hydrocarbons.

Of the chlorinated hydrocarbons discussed above, all six are associated with induction of hepatocellular neoplasia in mice. None of the six is considered to be potent mutagen and most are without any significant genotoxic activity as assessed by conventional in vitro testing schemes. Although some of the agents have biological effects in common (see Figure 4), there is no single biological response (mode of action) that they all share to provide a mechanistic basis for the observed murine hepatocarcinogenicity. Based upon the information currently available for each of the chlorinated hydrocarbons discussed above, it is probable that some modes of action may be more contributory to the rodent carcinogenic response than others; however, no mode of action, pathway, or mechanism should be considered to be mutually exclusive. The murine hepatocarcinogenic effect of TriCE is most probably contingent upon its species-specific metabolism to trichloroacetic acid and DCA. There is fairly consistent evidence that cytotoxicity and reparative hyperplasia are associated with doses of TriCE that cause induction of liver neoplasms. The possibility that peroxisome proliferation is playing a role in the induction of mouse hepatocellular neoplasia remains a tempting explanation, since higher intracellular steady states of H2O2 production would be consistent with observed enhanced cellular proliferation as well as the possibility of in vivo DNA damage. The mouse hepatocarcinogenicity associated with TetCE most probably is associated with species-specific metabolic production of trichloroacetic acid. As with TriCE, cytotoxicity and reparative hyperplasia may represent a potential mode of action for the observed hepatocarcinogenicity. Once again, the potential for enhanced peroxisome proliferation is consistent with enhanced cell proliferation and oxygen radical damage would help explain the random point mutations in ras proto-oncogenes documented in DNA from TetCE-induced mouse liver tumors. DCA-induced mouse hepatocellular neoplasia is probably influenced by cytotoxicity and reparative hyperplasia, but there is also recent evidence that DCA may directly damage DNA, implying an in vivo genotoxic mechanism may be operational. Likewise, altered expression of several genes suggests that subversion of signal transduction may play a role in the induction or progression of liver tumor development. As with TetCE and TriCE, a role for peroxisome proliferation is still a consideration, although the liver tumor response is obvious at doses too low to cause peroxisome proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Allelotype analysis of mouse lung carcinomas reveals frequent allelic losses on chromosome 4 and an association between allelic imbalances on chromosome 6 and K-ras activation.

We generated allelotypes of 38 methylene chloride-induced lung carcinomas from female C57BL/6J x C3H/6J F1 (hereafter called B6C3F1) mice. Two or more polymorphic markers per autosome, most of them microsatellites, were examined for loss of heterozygosity. Allelic losses throughout the genome were generally infrequent except for markers on chromosome 4, which were lost in approximately one-half of the carcinomas. Analysis of lung adenomas indicated that chromosome 4 loss was associated with malignant conversion. In addition, chromosome 4 loss were specific for lung carcinomas based on comparison to methylene chloride-induced liver tumors and additional studies of lung tumors from a variety of treatment protocols and different mouse strains. Preferential loss of the maternal chromosome 4 was observed in B6C3F1 carcinomas. Analyses of additional tumors induced in mice from two reciprocal crosses, A/J x C3H/HeJ F1 (hereafter called AC3F1) and C3H/HeJ x A/J F1 (hereafter called C3AF1), provided evidence for the inactivation of one allele of the putative chromosome 4 tumor suppressor gene by parental imprinting. Most B6C3F1 tumors lost all chromosome 4 markers examined, suggesting nondisjunction events. In contrast, several C3AF1 and AC3F1 tumors appeared to have interstitial deletions that defined the smallest region of overlap as a 9-cM interval between Ifa-2 and D4Nds2. The homologous region on human chromosome 9p21-22 is frequently lost in a variety of tumors including lung cancers. A candidate tumor suppressor gene, MTS1, is located in this region, which is homozygously deleted or mutated in cell lines derived from a variety of human tumors. Finally, an association between K-ras gene activation and allelic imbalances on chromosome 6 was observed for B6C3F1 lung tumors.

Alleles↗
PubMed1994

Regulation of apoptosis by low serum in cells of different stages of neoplastic progression: enhanced susceptibility after loss of a senescence gene and decreased susceptibility after loss of a tumor suppressor gene.

A cell culture model system has been used to study the susceptibility of cells to apoptotic cell death during different stages of neoplastic progression. This system consists of normal diploid Syrian hamster embryo (SHE) cells, two preneoplastic cell lines [tumor suppressor stage I (sup +I) and non-tumor suppressor stage II (sup -II)], and hamster tumor cell lines. Stage I preneoplastic cells are nontumorigenic immortal clones that suppress tumorigenicity when hybridized to tumor cells, whereas stage II cells have lost the ability to suppress tumorigenicity in cell hybrids. We refer to these two types of preneoplastic cells as sup +I and sup -II, respectively. Neoplastic progression is generally associated with cellular alterations in growth factor responsiveness. Therefore, to study the regulation of apoptosis in the system described above, cells were cultured in low serum (0.2%) as a means of withdrawing growth factors. In low serum, normal SHE cells were quiescent (labeling index of 0.2%), with little cell death. The sup +I cells showed a relatively low labeling index (1.6%) but, in contrast to the normal cells, died at a high rate (55% cell loss after 48 h) by apoptosis, as evidenced by morphology, DNA fragmentation, and in situ end-labeling of fragmented DNA. The apoptotic cells did not go through a replicative cycle while in low serum, implying that apoptosis was initiated in the G0/G1 phase of the cell cycle. The sup -II cell line showed a high labeling index (40%) after 48 h, but cell growth was balanced by cell death that occurred at approximately the same rate. The cells died, however, predominantly by necrosis. The tumor cell lines continued to proliferate in low serum, with high labeling indices (ranging from 27% to 43%) and a low level of apoptotic or necrotic cell death. To determine the relative ability of these cells to survive in vivo, normal SHE cells, sup +I cells, and sup -II cells were injected s.c. into nude mice. At 5 or 21 days after injection, the normal SHE cells were readily retrieved from the mice and grew well in culture. In contrast, few sup +I cells were retrieved 5 days after injection and no viable cells were retrieved after 21 days. Sup -II cells were not retrieved at either the 5-day or 21-day harvest, and histological examinations of the sites of injection showed the presence of macrophages, eosinophils, and neutrophils, indicating an inflammatory response associated with necrotic cell death.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Studies on bromobenzene-induced hepatotoxicity using in vivo MR microscopy with surgically implanted RF coils.

Using surgically implanted RF coils at 300 MHz, three-dimensional microscopic MR images of rat liver were obtained in vivo to follow the development of pathology induced by bromobenzene exposure. Formalin fixed specimens of liver from these animals were also imaged using in vitro MR microscopy, followed by conventional optical microscopy. All MR images were acquired using a spin-warp pulse sequence with TR = 950 ms and TE = 23 ms. The in vivo images were reconstructed as 256(2) x 32 arrays with a voxel size of (50 microns)2 x 219 microns, while the in vitro images were reconstructed as 256(2) x 128 arrays, giving an isotropic resolution at (39 microns)3. Based on results from six animals, we have found in all animals exposed to bromobenzene, image intensity decreased in specific hepatic tissue regions. These regions were well correlated to low signal intensity areas observed in in vitro MR images at higher resolution. Conventional optical microscopy indicated that the low signal intensity regions corresponded to areas of necrosis. The decrease in signal intensity is consistent with increased local diffusion coefficients as a result of necrosis. This study demonstrates that MR microscopy with implanted RF coils can be successfully used to follow tissue pathological changes in living tissues.

Animals↗
PubMed1994

Early responses of the liver of B6C3F1 mice to the hepatocarcinogen oxazepam.

Oxazepam has recently been shown to induce hepatocarcinogenicity in B6C3F1 mice. Due to the widespread human exposure to this anxiolytic compound and other structurally similar benzodiazepines, we conducted toxicity and cell proliferation studies on oxazepam to determine possible mechanisms whereby this nonmutagenic chemical may have exerted a carcinogenic effect. Male B6C3F1 mice (10 per dose-time group) received diets containing oxazepam at 0, 25, 125, 2500, and 5000 ppm. Mice were treated for 15, 30, 45, or 90 days, at which time they were evaluated for feed consumption, liver/body weight ratios, clinical pathology, serum oxazepam levels, and histopathology of the liver. During the final 7 days before sacrifice, the mice were exposed to BrDU via osmotic minipump to quantify hepatocellular replicative DNA synthesis. Few effects were observed resulting from chronic exposure to oxazepam other than statistically significant, dose-related increases in liver/body weight ratios. Replicative DNA synthesis was significantly increased in a dose-related manner at the 15-day time point in the 125, 2500, and 5000 ppm dose groups, and attained levels of four- to five-fold above control levels which returned to control levels by 30 days. The lack of significant toxicity, sustained increased liver/body weight ratios, and the rapid and transient induction of replicative DNA synthesis are similar to the effects reported for exposure to another widely used therapeutic agent shown to be a nongenotoxic carcinogen, phenobarbital.

Animals↗
PubMed1994

Di-(2-ethylhexyl) phthalate suppresses estradiol and ovulation in cycling rats.

Di-(2-ethylhexyl) phthalate (DEHP) is a known reproductive toxicant and a carcinogen in rodent animal models. DEHP may also be a reproductive toxicant in women. Its action in female animal models is undetermined, although its potential to target the ovary has recently been shown. We have identified the ovarian toxicity and target cells of DEHP in the female rat. Adult, regularly cycling Sprague-Dawley rats were dosed daily with 2 g/kg DEHP in corn oil by gavage for 1 to 12 days. Ovarian morphology and serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, and progesterone levels were analyzed. DEHP exposure resulted in prolonged estrous cycles. Specifically, 35 of 42 DEHP-treated rats had 5- or 6-day cycles and only 7 of 42 had a 4-day cycle compared to 44 of 45 control rats with 4-day cycle lengths. DEHP treatment also suppressed or delayed ovulations by the first proestrus/estrus after metestrus-initiated dosing. Microscopic evaluation of the ovaries determined that 7 of 10 DEHP-exposed rats had not ovulated by vaginal estrus, whereas 13 of 13 control rats had ovulated by vaginal estrus. Thus, DEHP treatment significantly altered natural ovulation times. Preovulatory follicles were also quantitatively smaller in DEHP-exposed rats than in controls because the granulosa cells were smaller. The mean control rat preovulatory follicle granulosa cell area was 16 +/- 3 x 10(3) microns, whereas the mean DEHP-treated rat preovulatory follicle granulosa cell area was 12 +/- 4 x 10(3) microns. DEHP exposure significantly suppressed preovulatory follicle granulosa cell estradiol production over 8 days of exposure. Suppressed serum estradiol levels caused secondary increases in FSH levels and did not stimulate the LH surge necessary for ovulation. Consequently, ovulation did not occur in DEHP-treated rats, although DEHP-treated rats ovulated after treatment with human chorionic hormone. Vaginal lavage cytology from rats treated with DEHP did not detect the ovarian toxicity as shown by histology and hormone analysis. In summary, exposure to DEHP resulted in hypoestrogenic anovulatory cycles and polycystic ovaries in adult female rats.

Analysis of Variance↗
PubMed1994

ras proto-oncogene activation in dichloroacetic acid-, trichloroethylene- and tetrachloroethylene-induced liver tumors in B6C3F1 mice.

The frequency and mutation spectra of proto-oncogene activation in hepatocellular neoplasms induced by tetrachloroethylene, trichloroethylene and dichloroacetic acid were examined to help define the molecular basis for their carcinogenicity. H-ras codon 61 activation was not significantly different among dichloroacetic acid- and trichloroethylene-induced and combined historical and concurrent control hepatocellular tumors (62%, 51% and 69% respectively). The mutation spectra of H-ras codon 61 mutations showed a significant decrease in AAA and increase in CTA mutations for dichloroacetic acid- and trichloroethylene-induced tumors when compared to combined controls. The H-ras codon 61 mutation frequency for tetrachloroethylene-induced tumors was significantly lower (24%) than that of combined controls and also that of the two other chemicals. Mutations at codons 13 and 117 plus a second exon insert contributed 4% to the total H-ras frequencies for trichloroethylene and tetrachloroethylene. There was also a higher incidence of K-ras activation (13%) in tetrachloroethylene-induced tumors than in the other chemically induced or control tumors. Four liver tumors were found to contain insertions of additional bases within the second exon of K- or H-ras. These findings suggest that exposure to dichloroacetic acid, trichloroethylene and tetrachloroethylene provides a selective growth advantage to spontaneously occurring mutations in codon 61 of H-ras and, at the same time, is responsible for a small number of unique molecular lesions suggestive of either a random genotoxic mode of action or a non-specific result of secondary DNA damage. However, the absence of ras activation in many of the liver neoplasms suggests that alternative mechanisms are also important in B6C3F1 mouse hepatocarcinogenesis.

Animals↗
PubMed1994

Activation of H-ras is prevalent in 1,3-butadiene-induced and spontaneously occurring murine Harderian gland tumors.

Treatment of B6C3F1 mice with concentrations of 62.5-625 p.p.m. 1,3-butadiene by inhalation for up to 2 years causes a significantly increased incidence of Harderian gland (HG) neoplasms over untreated controls (Melnick,R., Huff,J., Chou,B.J. and Miller,R.A. Cancer Res., 50, 6592-6599, 1990). Since a specific K-ras mutation (codon 13 GGC-->CGC) had previously been described in lung and liver tumors from 1,3-butadiene-treated B6C3F1 mice, we analyzed 23 adenomas and six adenocarcinomas of the HG from mice exposed to 1,3-butadiene for this mutation and mutations in the H-ras gene. We also examined ras activation in 16 spontaneously occurring HG adenomas and one adenocarcinoma. DNA samples were prepared from paraffin-embedded tissues and analyzed by PCR followed by direct sequencing methods. Only one 1,3-butadiene-induced HG tumor contained the K-ras codon 13 mutation previously detected in lung and liver tumors. However, 16/29 HG tumors from the treated B6C3F1 mice contained H-ras codon 61 mutations. The mutations detected were: 12 CAA-->CGA transitions, two CAA-->CTA and two CAA-->AAA transversions. Eleven of 17 spontaneous HG tumors contained mutations in H-ras codon 61: five CAA-->CGA transitions, two CAA-->CTA transversions and four CAA-->AAA transversions. While the spectrum of ras mutations did not differ between the spontaneously occurring and chemically induced tumors, these data indicate that activation of H-ras contributes to the process of HG tumorigenesis in both groups of these neoplasms.

Animals↗
PubMed1994

Low frequency of H-ras mutations in hepatocellular adenomas and carcinomas and in hepatoblastomas from B6C3F1 mice exposed to oxazepam in the diet.

Oxazepam has been the subject of recent toxicological and carcinogenesis studies because it is a commonly prescribed tranquilizer and has been shown to cause tumors in rodents. In this study, male and female B6C3F1 mice received 0, 125, 2500 or 5000 p.p.m. oxazepam in the diet for up to 2 years. Hepatocellular adenomas and carcinomas, as well as hepatoblastomas, which developed in these mice, were examined for the presence of activated ras proto-oncogenes. DNA was isolated from 20 or more tumors from each exposure group and analyzed by oligonucleotide hybridization, single-stranded conformation polymorphism analysis and direct sequencing of PCR-amplified H-ras gene fragments for codon 61 mutations. Thirteen of 37 (35%) hepatocellular adenomas and carcinomas from the 125 p.p.m. exposure group had mutations in codon 61, while mutations were detected in only 2 of 25 or 8% of the liver tumors from the 2500 p.p.m. exposure group and none of the 22 tumors from the 5000 p.p.m. group. This compares to 63% of 126 historical control liver tumors and 55% of 20 liver tumors from unexposed B6C3F1 mice in this study. In addition, 12 hepatoblastomas from the two high dose groups were examined for H-ras mutations at codon 61, but none were detected. No tumor DNAs from any of the exposure groups tested had mutations in codons 12, 13 or 117 of the H-ras gene or codons 12 or 13 of the K-ras gene, the other known hotspots for ras activation in mouse liver tumors. These results, together with those from the National Toxicology Program study showing no evidence of cytotoxicity or genotoxicity by oxazepam, suggest that oxazepam preferentially promotes cells that have activating lesions other than ras.

Adenoma↗
PubMed1994

Ras mutations in methylclofenapate-induced B6C3F1 and C57BL/10J mouse liver tumours.

The majority of genotoxic carcinogen-induced liver tumours of the sensitive B6C3F1 mouse contain activated H-ras oncogenes. Such mutations also occur in hepatocarcinogenesis-resistant strains. In order to determine whether this is true of non-genotoxic carcinogen-induced tumours, liver tumours induced in B6C3F1 and C57BL/10J mice by methylclofenapate (MCP) were compared. Polymerase chain reaction (PCR) analysis revealed H-ras codon 61 mutations in 11/46 B6C3F1 and 4/31 C57BL/10J liver tumours. The nude mouse tumorigenicity (NMT) assay was used to analyse tumours without codon 61 mutations. Of the 12 B6C3F1 liver tumour DNAs subjected to this assay, one contained a H-ras codon 117 mutation. Further PCR analysis on frozen tumour samples (46 B6C3F1 and 15 C57BL/10J) revealed no codon 12 mutations; one additional codon 117 mutation was identified in a B6C3F1 tumour. Overall, then, H-ras codon 61 mutations were detected in MCP-induced B6C3F1 tumours less frequently than in genotoxin-induced tumours. Two B6C3F1 tumours contained codon 117 mutations similar to those previously found in tumours induced by ciprofibrate, furan and furfural, and in at least one spontaneous tumour. Ras mutations were also detected in some C57BL/10J tumours, providing further evidence that ras oncogenes can participate in hepatocarcinogenesis in resistant mice.

Alleles↗
PubMed1994

"Lipomatous" lesions of unknown cellular origin in the liver of B6C3F1 mice.

The gross, microscopic, and ultrastructural features of lipomatous lesions in the liver of B6C3F1 mice are described. The cases were selected from a database of 45,406 male and 45,674 female mice used as treated, control, or vehicle-control animals in the National Cancer Institute's Bioassays or the National Toxicology Program's 2-year carcinogenicity studies. Thirteen hepatic lesions identified from cases within the database were re-evaluated microscopically and selected for further study. These lesions were present in ten males and three females that were between 85 and 113 weeks of age at the time of death. Grossly, the liver lesions were described as white to yellow or red to brown nodules/masses or foci that ranged from 2.0 to 25 mm in diameter. The lesions commonly involved the median and left lateral hepatic lobes. Microscopically, many of the lesions closely resembled lipomas described in the liver of human beings, and they consisted of nonencapsulated mature adipose-like tissue with irregular margins. The majority of the cells that comprised the lipomatous lesions were signet-ring shaped. These cells were positive for lipid as evidenced with oil red-O. The lipid droplets were also present within the hepatocytes that comprised the hepatic plates trapped within or surrounding many of the lipomatous lesions. At the margins of many of the lesions there were spindle-shaped cells that contained small intracytoplasmic lipid vacuoles. These cells were often within a stromal matrix that had focal areas of collagen and mucopolysaccharides, as evidenced by weak staining with Masson's trichrome and periodic acid-Schiff's stains, respectively. There was also disruption of the reticulum fibers in many of the lesions, as noted with a Gomori's reticulum stain. Ultrastructurally, cytoplasmic organelles, such as rough endoplasmic reticulum, free ribosomes and small lipid vacuoles, were present in the spindle-shaped cells, whereas signet-ring-shaped cells had few discernible organelles due to peripheral compression of the cytoplasm by single large vacuoles occupying the cytoplasmic space. The spindle-shaped cells were free of lysosomes. Thin collagen fibers were seen in contact with some of the spindle-shaped cells and were located between these cells and adjacent hepatocytes, or endothelial cells lining sinusoidal capillaries. A distinct basal lamina was not associated with spindle- or signet-ring-shaped cells. Similar lipomatous lesions were not found in other visceral organs. The exact cellular origin of the hepatic lesions described here is not known.

Animals↗
PubMed1993

Comparison of pulmonary O6-methylguanine DNA adduct levels and Ki-ras activation in lung tumors from resistant and susceptible mouse strains.

The role of O6-methylguanine (O6MG) DNA adduct formation and persistence in the formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors from resistant C57BL/6 and susceptible A/J mice was investigated. In addition, the frequencies of pulmonary tumor formation and Ki-ras activation were defined in C57BL/6 mice treated with NNK or vinyl carbamate (VC), and the role of the p53 gene in pulmonary carcinogenesis in these resistant mice was examined. One day after treatment with 100 mg/kg NNK, O6MG adduct concentrations were twofold to eightfold higher in Clara cells and type II cells than in small cells or whole lungs from both mouse strains. The concentrations of O6MG in isolated cells decreased at a similar rate in the two strains of mice. Lung tumors were detected by 27 mo of age in 18% of the C57BL/6 mice after a single 100 mg/kg dose of NNK and in 46% of these mice after a single 60 mg/kg dose of VC. In contrast, the tumor incidence in untreated C57BL/6 mice was 4%. Only one of 22 lung tumors from C57BL/6 mice treated with NNK contained an activated Ki-ras gene that was associated with an O6MG DNA adduct, whereas previous studies detected activated Ki-ras oncogenes in most of the NNK-induced lung tumors analyzed from susceptible A/J and resistant C3H mice. The small differences in formation and persistence of the O6MG adduct in whole lung or isolated lung cells from A/J and C57BL/6 strains do not account for the differences in either susceptibility for tumor formation or activation of the Ki-ras gene between these strains. In contrast to the low number of NNK-induced tumors with Ki-ras mutations in the resistant mice, 11 of 20 lung tumors from VC-treated mice contained activated Ki-ras genes. Neither p53 tumor suppressor gene mutations nor overexpression of the p53 protein were detected in spontaneous or chemically induced lung tumors in C57BL/6 mice. Thus, although Ki-ras activation was detected in some tumors, pathways independent of ras activation and p53 inactivation also appear to be involved in lung tumorigenesis in this resistant mouse strain.

Animals↗
PubMed1993

ras mutations in 2-amino-3-methylimidazo-[4,5-f]quinoline-induced tumors in the CDF1 mouse.

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is a very potent mutagen that is carcinogenic in rodents and nonhuman primates. IQ-induced CDF1 mouse lung and liver tumors were examined for activated Ki-ras and Ha-ras genes, respectively. Polymerase chain reaction (PCR)-amplified target DNAs were analyzed for mutations of codons 12, 13, and 61 by single-strand conformation polymorphism (SSCP) and direct sequencing methods. All mutations were localized to codon 61 of the ras genes. Forty-nine of 54 lung tumors induced by IQ possessed activating Ki-ras mutations, as did 20 of 26 lung tumors from the vehicle-treated animals; 80% and 75% of these mutations, respectively, were A-->T transversions of the second nucleotide redundant. One lung adenoma from the IQ-treated group contained a tandem duplication of the sequence corresponding to codons 50-57 of the Ki-ras gene (unpublished observations). In addition, seven of 34 IQ-induced liver tumors harbored activating Ha-ras mutations: five were C-->A (G-->T) transversions at the first nucleotide, and two were A-->T transversions at the second nucleotide of codon 61. None of the 15 liver tumors collected from the vehicle-treated mice possessed Ha-ras mutations in codon 12, 13, or 61. These data indicate that IQ induces Ha-ras gene activation in CDF1 mouse liver tumors. The mechanisms of lung tumor induction by IQ, however, is obscured by the high frequency of Ki-ras A-->T mutations observed in both the IQ-induced and spontaneous lung tumors. The different ras mutational spectra in lung and liver tumors may suggest either that two different pathways of IQ metabolism exist in these organs or that IQ contributes to CDF1 lung tumorigenesis by a mechanism other than its direct interaction with the Ki-ras gene.

Adenoma↗