Biomedical subjects

D C Wolf

Publications and source records attributed to D C Wolf.

At least 55 records · Page 3Linked to original sources

PubMed1996

A 90-day chloroform inhalation study in F-344 rats: profile of toxicity and relevance to cancer studies.

Chloroform acts via a nongenotoxic-cytotoxic mode of action to produce cancer if given in doses and at dose rates sufficiently high to produce organ-specific toxicity. In a recent study, chloroform failed to induce cancer in male or female F-344 rats when administered by inhalation for 2 years at 90 ppm, 5 days/week. The present study was undertaken to define the concentration-response curves for chloroform-induced lesions and regenerative cell proliferation in the F-344 rat when exposed by inhalation and to correlate those patterns of toxicity with the results from the inhalation cancer bioassay. Male and female F-344 rats were exposed to airborne concentrations of 0, 2, 10, 30, 90, or 300 ppm chloroform 6 hr/day, 7 days/week for 4 days or 3, 6, 13 weeks. Additional treatment groups were exposed 5 days/week for 13 weeks or were exposed for 6 weeks and held until Week 13. Bromodeoxyuridine was administered via osmotic pumps implanted 3.5 days prior to necropsy and the labeling index (LI, percentage of nuclei in S-phase) was evaluated immunohistochemically. A full-screen necropsy identified the kidney, liver, and nasal passages as the only target organs. This study confirmed that 300 ppm is extremely toxic and would be inappropriate for longer-term cancer studies. The primary target in the kidney was the epithelial cells of the proximal tubules of the cortex, with significantly elevated increases in the LI at concentrations of 30 ppm and above. However, only a marginal increase in the renal LI in the males was seen after exposures of 90 ppm, 5 days/week. Chloroform induced hepatic lesions in the midzonal and centrilobular regions with increases in the LI throughout the liver, but only at 300 ppm exposures. An additional liver lesion seen only at the highly hepatotoxic concentration of 300 ppm was numerous intestinal crypt-like ducts surrounded by dense connective tissue. Enhanced bone growth and hypercellularity in the lamina propria of the ethmoid turbinates of the nose occurred at the early time points at concentrations of 10 ppm and above. At 90 days there was a generalized atrophy of the ethmoid turbinates at concentrations of 2 ppm and above. Cytolethality and regenerative cell proliferation are necessary but not always sufficient to induce cancer because of tissue, sex, and species differences in susceptibility. A combination of a lack of direct genotoxic activity by chloroform, only a marginal induction of cell proliferation in the male rat kidney, and lower tissue-specific susceptibility in the female rat is apparently responsible for the reported lack of chloroform-induced cancer in a long-term inhalation bioassay with F-344 rats.

Administration, Inhalation↗

PubMed1996

Methyl tertiary butyl ether lacks tumor-promoting activity in N-nitrosodiethylamine-initiated B6C3F1 female mouse liver.

Methyl tertiary butyl ether (MTBE) is an additive in some formulations of unleaded gasoline (UG) that enhances octane and reduces carbon monoxide emissions from motor vehicles. MTBE in CD-1 mice and UG in B6C3F1 mice increased the incidence of liver tumors selectively in female mice in their chronic bioassays. Both agents were negative in in vitro tests of genotoxicity, and exhibit similar hepatic microsomal cytochrome P450 activity and hepatocyte proliferation after short-term exposure. We previously demonstrated that UG has hepatic tumor-promoting activity in DEN-initiated female B6C3F1 mice. Thus, we hypothesized that MTBE would have hepatic tumor-promoting activity in the same initiation-promotion model system in which UG was a hepatic tumor promoter. Twelve-day-old female B6C3F1 mice were initiated with a single i.p. injection of the mutagen N-nitrosodiethylamine (DEN) (5 mg DEN/kg, 7.1 ml/kg body weight) or saline. Beginning at 8 weeks of age, mice were exposed to 0 ppm or the hepatocarcinogenic dose of approximately 8000 ppm MTBE. After subchronic exposure, MTBE significantly increased liver weight and hepatic microsomal cytochrome P450 activity without hepatotoxicity or an increase in non-focal hepatocyte DNA synthesis. These are subchronic effects similar to those produced by UG. However, MTBE did not significantly increase the mean size of hepatic foci and volume fraction of the liver occupied by foci as compared to DEN-initiated controls at either 16 or 32 weeks. The lack of tumor-promoting ability of MTBE in DEN-initiated female mouse liver was unexpected and suggests that MTBE does not produce liver tumors through a tumor-promoting mechanism similar to that of UG.

Animals↗

PubMed1996

A non-bile duct origin for intestinal crypt-like ducts with periductular fibrosis induced in livers of F344 rats by chloroform inhalation.

To evaluate the toxic effects of prolonged exposure to chloroform vapors, female and male F344 rats were exposed to 0, 2, 10, 30, 90 and 300 p.p.m. chloroform by inhalation for 7 or 5 days/week for up to 13 weeks. The purpose of this study was to characterize a lesion that occurred in the livers of rats in the 300 p.p.m. exposure groups. Atypical glandular structures lined by intestinal-like epithelium and surrounded by dense connective tissue occurred in the livers of rats exposed to strongly hepatotoxic atmospheric concentrations of chloroform. Bile duct bromodeoxyuridine labeling indices as well as observations of the locations of the early lesions at the 3 and 6 week time points indicate that these lesions arose from a population of cells remote from the bile ducts. We refer to these lesions as intestinal crypt-like ducts with periductular fibrosis to distinguish them from true cholangiofibrosis. Here, intestinal crypt-like ducts with periductular fibrosis were seen only in rats exposed to 300 p.p.m. chloroform, and the multiplicity and severity of the lesions were greater in the right liver lobe. The lesion only occurred in association with liver necrosis and dramatic increases in hepatocyte labeling indices, while labeling indices in bile ducts in the same animals were not significantly different from controls. There was a treatment-related increase of transforming growth factor-alpha immunoreactivity in hepatocytes, bile duct epithelium, bile canaliculi and oval cells, and an increase in transforming growth factor-beta immunoreactivity in hepatocytes, bile duct epithelium and intestinal crypt-like ducts. Thus, intestinal crypt-like ducts with periductular fibrosis appeared to develop from a population of cells unrelated to bile ducts. Also, they occurred only in animals exposed to chloroform concentrations that induced significant hepatocyte necrosis and regenerative cell proliferation and were associated with increased growth factor expression or uptake.

Administration, Inhalation↗

PubMed1996

Cell proliferation and regulation of negative growth factors in mouse liver foci.

Foci of altered hepatocytes are preneoplastic lesions capable of progressing to hepatocellular carcinomas. To characterize the growth of preneoplastic hepatic lesions, size of hepatic foci was analyzed with regard to growth factor regulation and hepatocyte proliferation in focal and non-focal hepatocytes. Twelve-day-old female B6C3F1 mice were initiated with a single dose of the potent mutagen N-nitrosodiethylamine (DEN) (5 mg/kg body weight). Beginning at 6 weeks of age, mice were exposed for 16 weeks to 2038 p.p.m. unleaded gasoline (UG) vapor or 1 p.p.m. ethinyl estradiol (EE) in the diet. Analysis of hepatic foci demonstrated that UG significantly increased, but EE significantly decreased the size of DEN-initiated foci. Hepatic labeling index (LI), as measured by the incorporation of 5-bromo-2'-deoxyuridine, was similar in non-focal hepatocytes at 16 weeks in all groups (0.4-0.8%) and greatly increased in hepatic foci. Hepatocyte LI was significantly increased in DEN/UG foci (29%, n = 41) and significantly decreased in DEN/EE foci (6%, n = 23) relative to DEN/control focal hepatocytes (18%, n = 25). The mean LI of foci correlated with the focal size differences observed in the treatment groups. Immunohistochemical analysis with antibodies directed to the negative growth regulator transforming growth factor-beta 1 (TGF-beta1) demonstrated a consistent decrease of TGF-beta 1 in DEN/Ct and DEN/UG hepatic foci relative to non-lesion hepatocytes. Similar results were seen with mannose 6-phosphate/insulin-like growth factor-II receptor (M6P/IGF-II R), which facilitates activation of latent TGF-beta 1. In contrast, only 50% of DEN/EE foci had decreased levels of TGF-beta 1 and M6P/IGF-II R relative to non-focal hepatocytes. These data suggest that proliferative responses observed in hepatic foci may be correlated with foci size. In contrast, chemically induced proliferative responses in non-focal hepatocytes after subchronic exposure cannot necessarily be used to predict proliferative effects in preneoplastic cell populations. Furthermore, these studies suggest that hepatic foci may occur by M6P/IGF-II R enhancing activation of latent TGF-beta 1 in non-focal hepatocytes but not in the focal hepatocytes, thereby affording focal hepatocytes a selective growth advantage.

Air Pollutants↗

PubMed1995

Absence of p53 gene mutations in rat colon carcinomas induced by azoxymethane.

The K-ras and p53 genes are two of the most frequently mutated genes found in the human colonic tumors. Since azoxymethane (AOM) induced rat colonic neoplasms are similar to human colonic tumors in their histological features and proliferation characteristics, the rat has been used as an experimental model to study the pathogenesis of colon cancer in humans. Although the presence of K-ras point mutations has been reported in AOM induced rat colonic tumors, there are no reports describing the frequency for mutation of the p53 gene in these tumors. In this study, colon adenocarcinomas induced in rats by AOM were examined for the presence of point mutations in exons 5-8 of the p53 gene, using a combination of single strand conformation (SSCP) analysis, immunohistochemistry and direct DNA sequencing. SSCP analysis showed no differences in banding patterns between the normal mucosa and any of the 20 adenocarcinomas analyzed. Nuclear p53 immunoreactivity was absent in all tumors examined. Since p53 point mutations predominate in malignant colonic tumors, five adenocarcinomas with the greatest local invasiveness were analyzed by direct DNA sequencing of exons 5-8 of the p53 gene. Direct DNA sequencing did not reveal mutations in any of the adenocarcinomas analyzed, within the coding region of p53 gene that were sequenced. The results from the present study indicate that point mutations in the p53 gene, at least in the coding region (exons 5-8) are not involved in the development of colon cancer induced by AOM in the rat.

Adenocarcinoma↗

PubMed1995

Induced regenerative cell proliferation in livers and kidneys of male F-344 rats given chloroform in corn oil by gavage or ad libitum in drinking water.

These studies were designed to establish the dose response relationships for the induction of cytolethality and regenerative cell proliferation in the liver and kidneys of male F-344 rats given chloroform by gavage or in drinking water. Rats were administered oral doses of 0, 10, 34, 90 or 180 mg/kg/day chloroform dissolved in corn oil by gavage for 4 days or for 5 days/week for 3 weeks. A second group of rats was given chloroform ad libitum in the drinking water at concentrations of 0, 60, 200, 400, 900 or 1800 ppm for 4 days or 3 weeks. Bromodeoxyuridine (BrdU) was administered via an implanted osmotic pump 3.5 days prior to necropsy to label cells in S-phase. Cells having incorporated BrdU were visualized in tissue sections immunohistochemically and the labelling index (LI) evaluated as the percentage of S-phase cells. Rats treated with 90 or 180 mg/kg/day by gavage for 4 days had mild to moderate degeneration of renal proximal tubules and centrilobular hepatocytes. These alterations were absent or slight after 3 weeks of treatment. LI were increased in the kidney cortex only in the rats treated with 180 mg/kg/day for 4 days. A dose-dependent increase in LI was seen in rat liver after 4 days of treatment with 90 and 180 mg/kg/day by gavage, but the LI remained elevated after 3 weeks of treatment only at the 180 mg/kg/day dose. When chloroform was administered in the drinking water, no microscopic alterations were seen in the kidneys after 4 days of treatment. As a general observation, rats treated for 3 weeks with 200 ppm chloroform and greater had slightly increased numbers of focal areas of regenerating renal proximal tubular epithelium and cell proliferation than were noted in the controls, but no clear dose response relationship was evident. However, the overall renal LI was not increased at any dose or time point. Similarly, only mild hepatocyte vacuolation was observed in rats given 1800 ppm chloroform in the water for 3 weeks with no increase in the hepatic LI at any time point, even though the rats were consuming chloroform at a rate of 106 mg/kg/day at the 1800 ppm drinking water concentration. These data indicate more severe hepatic and renal toxicity when chloroform is administered by gavage than in the drinking water and a different pattern of regenerative proliferation in the kidney.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

p53 status in spontaneous and dimethylnitrosamine-induced renal cell tumors from rats.

Rats carrying the Eker tumor-susceptibility mutation (Eker rats) are predisposed to developing renal cell carcinoma. Rats heterozygous for the Eker mutation develop spontaneous multiple bilateral renal cell tumors by the age of 1 yr. In a previous study, Eker-mutation carrier and noncarrier rats were exposed to the renal carcinogen dimethylnitrosamine (DMN), and male rats carrying the Eker mutation exhibited a 70-fold increase in the induction of renal adenomas and carcinomas when compared with noncarrier rats. In this study, spontaneous and DMN-induced rat renal cell tumors (adenomas and carcinomas) were analyzed for mutations of the p53 gene by direct sequencing of cDNA polymerase chain reaction products. There were no mutations in p53 cDNA derived from renal tumors from six untreated rats. Mutations were found in one of 15 of the DMN-induced tumors: a transition at codon 140, CCT-->CTT, in a renal adenoma. Additionally, seven cell lines derived from spontaneous renal cell tumors did not contain mutations in p53. The low frequency of p53 mutations (one of 21 renal cell tumors and none of seven cell lines derived from renal cell tumors) indicates that the development of both spontaneous and carcinogen-induced renal tumors involved a non-p53-dependent pathway. As p53 is infrequently mutated in human renal cell carcinomas and in rat renal mesenchymal tumors, it is likely that a tumor suppressor gene or genes other than p53 are involved in the development of renal cancer.

Adenoma↗

PubMed1995

Two-year inhalation exposure of female and male B6C3F1 mice and F344 rats to chlorine gas induces lesions confined to the nose.

Chlorine gas is a respiratory irritant in both animals and humans that produces concentration-dependent responses ranging from minor irritation to death. Female and male B6C3F1 mice and F344 rats were exposed to chlorine gas for up to 2 years to determine chronic toxicity and carcinogenicity. Groups of approximately 70 each of female and male mice and rats were exposed to 0, 0.4, 1.0, or 2.5 ppm chlorine gas for 6 hr/day, 5 days/week (mice and male rats), or 3 alternate days/week (female rats) for 2 years, with an interim necropsy of rats at 12 months (10 rats/sex/concentration group). A complete necropsy was performed on all animals. Histological examination was performed on all organs from high-concentration and control animals and selected target organs from mid- and low-concentration groups. Exposure-dependent lesions were confined to the nasal passages in all sex and species groups. Chlorine-induced lesions, which were most severe in the anterior nasal cavity, included respiratory and olfactory epithelial degeneration, septal fenestration, mucosal inflammation, respiratory epithelial hyperplasia, squamous metaplasia and goblet cell hypertrophy and hyperplasia, and secretory metaplasia of the transitional epithelium of the lateral meatus. Intracellular accumulation of eosinophilic proteinaceous material was also a prominent response involving the respiratory, transitional, and olfactory epithelia, and in some cases the squamous epithelium of the nasal vestibule. Many of these nasal lesions exhibited an increase in incidence and/or severity that was related to chlorine exposure concentration and were statistically significantly increased at all chlorine concentrations studied. Male mice and female rats appeared more sensitive to chlorine than female mice and male rats, respectively. The reasons for the sex differences within a species were not determined. Interspecies differences in regional dosimetry and site-specific tissue susceptibility to chlorine exposure should be taken into account when using these data for accurate assessment of potential human health risks. The incidence of neoplasia was not increased by exposure, indicating that inhaled chlorine in rats and mice is an upper respiratory tract toxicant but not a carcinogen.

Administration, Inhalation↗

PubMed1995

Immunohistochemical localization of p53, PCNA, and TGF-alpha proteins in formaldehyde-induced rat nasal squamous cell carcinomas.

Mutation of the p53 tumor suppressor gene is a common event in many human cancers and has been specifically associated with invasive squamous cell carcinoma of the human skin and respiratory tract. Alterations in the p53 gene have also been identified in certain rodent tumors, including formaldehyde-induced nasal squamous cell carcinomas. Overexpression of transforming growth factor-alpha (TGF-alpha) is associated with carcinomas of the head and neck and respiratory tract in human patients and formaldehyde-induced rat nasal squamous cell carcinomas. Sections of rat noses containing tumors and other formaldehyde-induced lesions from rats exposed to 15 ppm formaldehyde vapor were examined using immunohistochemical techniques to detect and identify potential relationships between the presence and distribution of p53, proliferating cell nuclear antigen (PCNA), and TGF-alpha proteins. The five tumors that had p53 mutations were for mutant p53 protein by immunohistochemistry and three of six tumors with no detected p53 mutations were also immunoreactive for p53 protein. The presence, pattern, and distribution of p53 staining in tissue sections depended on the morphology of the lesion. PCNA immunoreactivity was strikingly similar in pattern and distribution to p53 immunoreactivity. The pattern and distribution of immunoreactivity for TGF-alpha did not directly correlate with the other markers. Mutation of the p53 tumor suppressor gene may be an important step in the progression of formaldehyde-induced nasal carcinogenesis in the rat. This study demonstrated that immunohistochemistry is a useful tool for the identification of sites within tumors that might have p53 mutations.

Animals↗

PubMed1995

Toxicity and cell proliferation in the liver, kidneys and nasal passages of female F-344 rats, induced by chloroform administered by gavage.

Dose-response relationships were determined for the induction of cytolethality and regenerative cell proliferation in the established target organs (liver, kidneys, and nasal passages) of female F-344 rats given chloroform daily by gavage. Rats were administered chloroform dissolved in corn oil at doses of 0, 34, 100, 200 or 400 mg/kg/day for 4 consecutive days or for 5 days/wk for 3 wk. Bromodeoxyuridine (BrdU) was administered through an implanted osmotic pump 3.5 days prior to autopsy to label cells in S-phase. Cells in S-phase were visualized immunohistochemically in tissue sections and the labelling index (LI) calculated as the percentage of cells in S-phase. Mild degenerative centrilobular changes and dose-dependent increases in the hepatocyte LI were observed after administration of 100 mg or more chloroform/kg/day. Rats given 200 or 400 mg/kg/day for 4 days or 3 wk had degeneration and necrosis of the proximal tubules of the renal cortex. Regenerating epithelium lining proximal tubules was seen histologically and as an increase in LI. Dose-dependent increases in LI were observed in the kidneys at doses of 100 mg or more chloroform/kg/day at both 4 days and 3 wk. Two distinct treatment-induced responses were observed in specific regions of the olfactory mucosa lining the ethmoid region of the nose. A peripheral lesion was seen at all doses used and included new bone formation, periosteal hypercellularity and increased cell replication. A central lesion was seen at doses of 100 mg or more chloroform/kg/day and was characterized by degeneration of the olfactory epithelium and superficial Bowman's glands. These observations define the dose-response relationships for the liver, kidneys and nasal passages as target organs for chloroform administered by gavage in the female F-344 rat.

Animals↗

PubMed1995

Hereditary renal cell carcinoma in the Eker rat: a unique animal model for the study of cancer susceptibility.

A class of genes, the so-called tumor suppressor genes or anti-oncogenes, was originally identified as being responsible for germ-line transmission of cancer susceptibility in humans. Tumor suppressor genes are recessive at the cellular level with respect to oncogenesis but often manifest as dominantly inherited familial cancer syndromes. This type of cancer syndrome arises in the Eker rat due to a genetic defect in the tuberous sclerosis 2 (Tsc2) gene. The Eker rat familial cancer syndrome serves as a unique animal model in which to study the molecular pathways of renal tubular epithelial carcinogenesis as well as a valuable tool for studies that examine how chemical carcinogens interact with cancer susceptibility genes.

Animals↗

PubMed1995

The role of regenerative cell proliferation in chloroform-induced cancer.

Chloroform produces cancer by a nongenotoxic-cytotoxic mode of action, with no increased cancer risk expected at noncytotoxic doses. The default risk assessment for inhaled chloroform relies on liver tumor incidence from a gavage study with female B6C3F1 mice and estimates a virtually safe dose (VSD) at an airborne concentration of 0.000008 ppm of chloroform. In contrast, a 1000-fold safety factor applied to the NOAEL for liver cytotoxicity from inhalation studies yields a VSD of 0.01 ppm. This estimate relies on inhalation data and is more consistent with the mode of action of chloroform.

Animals↗

PubMed1995

Preneoplastic and neoplastic lesions of rat hereditary renal cell tumors express markers of proximal and distal nephron.

Long-Evans (Eker) rats carry a mutation that predisposes them to develop spontaneous renal cell tumors of two morphologic patterns: solid chromophilic masses or cystic lesions lined by eosinophilic cells. Previous studies have suggested that these tumors arise from the proximal tubules. In the present study, lectin-binding characteristics and cytokeratin expression of various stages of hereditary rat renal epithelial neoplasia were examined to localize the portion of the nephron from which tumors arise. Lectin-binding histochemistry has been used as a marker of cell surface glycoprotein expression, thought to be important in the differentiation of benign from malignant epithelial lesions and in the determination of their cell of origin. The presence or absence of keratin intermediate filaments in the rat nephron has been used to identify nephron segments. The polyclonal antibody to high- and low-molecular-weight cytokeratin stained the cells of the collecting ducts but not the proximal or distal tubules. Binding to the proximal tubules by the lectins Conavalia ensiformis (Con A), Dolichas biflorus, Ricinus communis (RCA-1), and Triticum vulgare and to the distal tubules by Con A, RCA-1, Arachis hypogaea (PNA) with and without neuraminidase, and the antibody for cytokeratins was demonstrated. The lectin binding and cytokeratin staining patterns of rat hereditary renal cell carcinoma, adenoma and the preneoplastic lesions of atypical tubules and hyperplasias suggest that cystic adenomas arise from the distal nephron, principally the collecting duct, whereas the solid atypical tubules, hyperplasias, and adenomas arise from the proximal nephron, principally the proximal tubule.

Adenoma↗

PubMed1995

Rodent model of reproductive tract leiomyomata. Establishment and characterization of tumor-derived cell lines.

Uterine myometrial tumors are the most commonly found gynecological neoplasm in women. The underlying causes of uterine leiomyomata are poorly understood, a result in part of the absence of a good animal model system in which to study these tumors. This report describes a novel rat model (Eker rat) in which spontaneous gynecological smooth muscle tumors arise with a high frequency. Leiomyomas are the predominant reproductive tract tumor that arise in these animals, although leiomyosarcomas have also been observed. Cell lines have been established from both the benign and malignant lesions. All of the lines express smooth muscle-specific actin, and leiomyoma-derived cell lines express desmin. Two of the cell lines are tumorigenic in nude mice, and the lines are variable for expression of estrogen and progesterone receptors. These lines are the first rodent tumor-derived lines to be established from leiomyomata and are the only lines available from a hereditary form of these tumors. Together with Eker rats that spontaneously develop leiomyomata, they constitute an in vitro/in vivo model system for gaining insights into the mechanism of transformation of uterine smooth muscle cells and the role of steroid hormones and hormone receptors in myometrial tumorigenesis.

Actins↗

PubMed1995

Rodent model of reproductive tract leiomyomata. Clinical and pathological features.

Mesenchymal tumors of the lower reproductive tract of women are poorly understood at the molecular level as a result in part of the lack of relevant animal models. The present study describes a novel model of gynecological smooth muscle tumors in which these neoplasms arise in Eker rats as part of a familial cancer syndrome. The tumors develop as a result of a germline mutation in the tuberous sclerosis 2 (TSC2) gene, and predisposition to tumor development is inherited in an autosomal dominant fashion. Uterine and/or cervical tumors arise spontaneously as single or multicentric neoplasms and increase in incidence with increasing age. The tumors were classified into three phenotypic variants of leiomyoma/leiomyosarcoma and into stromal cervicovaginal tumors on the basis of cytological and histological features and immunostaining patterns for smooth muscle actin and desmin. Tumors histologically identical to the typical human myometrial leiomyoma arose, as did a subset of atypical leiomyomas having an epithelioid phenotype. Eker rats were found to develop both benign and malignant smooth muscle tumors. The high spontaneous incidence of smooth muscle tumors of uterus and cervix in this rodent model provides a unique opportunity to study the molecular mechanisms underlying the development of these clinically important gynecological neoplasms.

Animals↗

PubMed1994

Interactive effects of unleaded gasoline and estrogen on liver tumor promotion in female B6C3F1 mice.

We tested whether a concentration of unleaded gasoline (UG) vapor that was selectively hepatocarcinogenic in female mice in a chronic bioassay is antiestrogenic and whether liver tumor promotion by UG is secondary to antiestrogenicity. Twelve-day-old female C57BL/6 x C3H F1 mice (hereafter called B6C3F1) received i.p. injections of N-nitrosodiethylamine (5 mg/kg) or vehicle. Beginning at 5-7 weeks of age, mice were exposed to 0, 292, or 2056 ppm of PS-6 blend UG vapor for 6 h/day, 5 days/week for 16 weeks, 1 ppm ethinyl estradiol (EE2) in the diet, or 2056 ppm UG vapor and 1 ppm EE2 in the diet. Treatment with 2026 ppm UG but not 292 ppm UG increased relative liver weight, the number of macroscopic hepatic neoplasms, and the size and volume fraction of altered hepatic foci in N-nitrosodiethylamine-initiated mice. Treatment with 2056 ppm UG reduced relative uterus, ovary, and pituitary weights but did not change serum 17 beta-estradiol levels, uterine peroxidase activity, or uterine cytosolic estrogen receptor levels. EE2 treatment reduced the number and size of altered hepatic foci in N-nitrosodiethylamine-initiated mice, caused weight loss, anestrus, vaginal keratinization, decreased uterine peroxidase activity, and decreased uterine cytosolic estrogen receptor levels. UG/EE2 co-treatment attenuated the weight loss, anestrus, and vaginal keratinization caused by EE2 treatment alone but dramatically increased the number of macroscopic hepatic neoplasms and the size and volume fraction of altered hepatic foci as compared to UG treatment alone. Thus, in this two-stage model of carcinogenesis (a) 2056 ppm UG had antiestrogenic effects, particularly with respect to pharmacological actions of EE2; (b) 2056 ppm UG but not 292 ppm UG acted as a liver tumor promoter; (c) EE2 inhibited liver tumor promotion; and (d) EE2 strongly potentiated liver tumor promotion by UG. These data demonstrate significant individual and interactive effects of UG vapor and estrogens in liver tumor promotion in female mice.

Animals↗

PubMed1994

Induced cytotoxicity and cell proliferation in the hepatocarcinogenicity of chloroform in female B6C3F1 mice: comparison of administration by gavage in corn oil vs ad libitum in drinking water.

Chloroform increases the incidence of liver tumors in B6C3F1 mice when administered in by gavage in corn oil, but not when given in the drinking water at similar daily doses. Since cytotoxicity and regenerative cell proliferation have been implicated in the tumorigenic process for this nongenotoxic agent, these effects of chloroform in corn oil and drinking water were evaluated under conditions similar to the two bioassays. Female B6C3F1 mice were administered oral doses of 0, 3, 10, 34, 90, 238, or 477 mg/kg chloroform dissolved in corn oil 5 days/week for periods of 4 days or 3 weeks, or were continually exposed to chloroform in the drinking water at concentrations of 0, 60, 200, 400, 900, or 1800 ppm for 4 days or 3 weeks, at which time they were necropsied. 5-Bromo-2'-deoxyuridine (BrdU) was delivered via osmotic pumps implanted 3.5 days prior to necropsy. Cell proliferation was evaluated as the percentage of hepatocytes that entered S-phase over 3.5 days (labeling index, LI), measured by immunohistochemical detection of BrdU incorporated into the DNA. Dose-dependent changes included centrilobular necrosis and markedly elevated LI in mice given 238 or 477 mg/kg chloroform in corn oil (the average daily doses that produced tumors in the cancer bioassay). The no-observed-effect level for histopathological changes was 10 mg/kg/day and for induced cell proliferation was 34 mg/kg/day for chloroform given in corn oil. Chloroform given in the drinking water did not increase the hepatic LI after either 4 days or 3 weeks in any of the dose groups, nor were any microscopic alterations observed in the livers, even though the cumulative daily amount of chloroform ingested in the 1800-ppm exposure group was 329 mg/kg/day. The sustained increase in LI in the livers of mice administered hepatocarcinogenic doses of chloroform in corn oil, but not for chloroform in drinking water, is evidence that chloroform-induced mouse liver cancer is secondary to events associated with induced cytolethality and cell proliferation. The triggering of these effects appears to be dependent on both the rate and duration of chloroform delivery to the target tissues. Thus, the most straightforward risk assessment for chloroform for this tissue would assign no increased cancer risk for dosing regimens that do not induce cytolethality and cell proliferation.

Administration, Oral↗

PubMed1994

The toxicity of 1-week exposures to inhaled chloroform in female B6C3F1 mice and male F-344 rats.

Detailed quantitative descriptions of the toxicity of inhaled chloroform are lacking, despite the fact that the majority of environmental exposures occur by this route. We investigated the ability of chloroform vapors to produce toxicity and regenerative cell proliferation in the livers and kidneys, the principal target organs for carcinogenicity of female B6C3F1 mice and male F-344 rats, respectively. Nasal passages were also examined for toxic responses. Rodents were exposed to chloroform vapors at concentrations of 0, 1, 3, 10, 30, 100, or 300 ppm for 6 hr/day for 7 consecutive days and necropsied on Day 8. Animals were administered bromodeoxyuridine (BrdU) via implanted osmotic pump for the previous 3.5 days before necropsy. Cell proliferation was quantitated as the percentage of cells in S-phase (labeling index; LI) measured by immunohistochemical detection of BrdU-labeled nuclei. Mice exposed to 100 or 300 ppm exhibited centrilobular hepatocyte necrosis and severe vacuolar degeneration of midzonal and periportal hepatocytes, while exposure to 10 or 30 ppm resulted in mild to moderate vacuolar changes in centrilobular hepatocytes. Slight, dose-related increases in the hepatocyte LI were observed for exposure concentrations of 10 and 30 ppm, while the LI was increased more than 30-fold in the 100 and 300 ppm groups. The kidneys of mice were affected only at the 300 ppm exposure, with approximately half of the proximal tubules lined by regenerating epithelium and an increased LI of tubule cells of 8-fold over control. In rats, mild centrilobular vacuolation was observed only in the livers of rats exposed to 300 ppm. The hepatocyte LI in rats were increased only at 100 and 300 ppm, 3- and 7-fold over control, respectively. In the kidneys of the male rats exposed to 300 ppm, about 25 to 50% of the proximal tubules were lined by regenerating epithelium. The LI for tubule cells in the cortex was increased at 30 ppm and above. In the nasal passages of rats, chloroform concentrations of 10 ppm and above induced histopathological changes that exhibited clear concentration-related severity. These lesions consisted of respiratory epithelial goblet cell hyperplasia and degeneration of Bowman's glands in olfactory mucosa with an associated osseous hyperplasia of the endo- and ectoturbinates in the periphery of the ethmoid region. These nasal lesions were not observed in mice. Knowledge of the dose-dependent responses in rats and mice will be valuable in assessing the potential risks to humans posed by inhaled chloroform and in setting exposure concentrations for longer-term studies.

Administration, Inhalation↗