* Departments of Physiology and Pharmacology,
Cancer Biology, and
Biochemistry, Comprehensive Cancer Center, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157; and
§ Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108
Received December 9, 1999; accepted February 4, 2000
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: Cyp1a1, Cyp1b1; glutathione S-transferase (GST); heterocyclic amines; IQ; transplacental.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Despite the well-documented role these dietary carcinogens play in the tumorigenic process in adults, very few studies have addressed the effects of these compounds on the unborn fetus. Brittebo et al. (1994) demonstrated that unmetabolized 2amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) could be found in fetuses and newborns following maternal exposure to this HA. In similar studies by Ghoshal and Snyderwine (1993), Davis et al. (1994), and Mauthe et al. (1998), PhIP metabolites and PhIP-DNA adducts were observed in pups exposed to lactating rats treated with this dietary compound. The importance of studying the effects of transplacental exposure to dietary carcinogens is further supported by reports, by several groups, of a direct link between maternal exposure to dietary and environmental carcinogens and an increased incidence of childhood, as well as adult, cancer (Greenberg and Shuster, 1985; Turusov and Tomatis, 1997
; Zahm and Devesa, 1995
). Moreover, an increasing amount of data suggests that neonates may be especially susceptible to the carcinogenic effects of these compounds. In a study by Dooley et al. (1992), hepatic adenomas were induced in newborn mice following an ip injection of a heterocyclic amine, PhIP, at a dose that was 5,00010,000 times lower than that found to be effective in adults. In addition, Paulsen et al. (1999) have recently demonstrated that neonatal exposure to PhIP results in an increased incidence of intestinal tumors in Min mice. Further, several studies have demonstrated the high sensitivity of the developing organism to the carcinogenic effects of dietary and environmental toxicants, and have provided evidence that transplacental exposure to these compounds may play an important role in the initiation of tumors during fetal development (Anderson et al., 1985
; Miller et al., 1990b
, 1994; Rice, 1979
; Wessner et al., 1996
).
It is well established that transplacental exposure to such environmental toxicants as polycyclic aromatic hydrocarbons (PAHs) results in the induction of cytochrome P4501A1 (CYP1A1), and that this is mediated by the aryl hydrocarbon (Ah) receptor (Miller, 1994). It is not certain, however, what role this receptor and the CYP1A1 isoform might play in transplacentally induced HA carcinogenesis. CYP1A1 is an inducible cytochrome P450 enzyme expressed primarily in extrahepatic tissues (Sesardic et al., 1990
), and is important at an early stage of development (Kimura et al., 1987
). Expression of the 1a1 gene has been detected as early as 10 days of gestational age in the mouse (Tuteja et al., 1985
), and intraperitoneal 3-methylcholanthrene (MC) treatment of pregnant mice has been shown to lead to transplacental induction of Cyp1a1 enzyme activity (Nebert and Gelboin, 1969
). Cyp1a2, on the other hand, is expressed constitutively in the liver (Kimura et al., 1986
) and its induction during development is minimally detectable until the neonatal period (Dey et al., 1989
; Miller et al., 1989
,1996).
Several studies have demonstrated that HAs are metabolized primarily by CYP1A2 (Boobis et al., 1994); however, few studies have looked at the CYP enzymes responsible for extrahepatic metabolism of HAs early in gestation. This appears important to study, considering that IQ has been shown to induce tumors in organs other than the liver, such as the lung and colon (Ohgaki et al., 1984
; Takayama et al., 1984
; Tanaka et al., 1985
). Accordingly, CYP1A1, the isoform expressed in extrahepatic tissues, may play a role in mediating the metabolic activation of IQ. Studies have shown that CYP1A1 is involved in HA bioactivation (Adachi et al., 1991
; Boobis et al., 1991
; Crofts et al., 1998
), but its exact involvement in this process remains unclear since others have reported conflicting results (Snyderwine and Battula, 1989
). In addition to CYP1A1, it is possible that other forms of the CYP1 family, such as CYP1B1, may be transplacentally induced following IQ exposure. CYP1B1 has recently been shown to be expressed in fetal tissues (Hakkola et al., 1997
), and to be involved in the activation of a number of environmental compounds including HAs (Shimada et al., 1996
).
A multitude of studies in the literature have investigated the carcinogenic effects of HAs in the adult model. However, despite the fact that ingestion of cooked meats during pregnancy may result in a significant level of exposure in the fetal compartment, very few studies have assessed the role of these compounds in transplacentally induced neoplasia. A congenic C57BL/6 mouse strain (Lin et al., 1991) was utilized in the present study to determine whether in utero exposure to a prototypical HA, IQ, results in the formation of tumors in treated offspring. Further, enzymatic and biochemical analyses were performed to evaluate whether transplacental exposure to HAs results in the induction of fetal Cyp1a1, Cyp1b1, and/or GST, and what role these metabolic enzymes might play in the tumorigenic process. In order to specifically assess the effects of fetal Cyp1a1 and 1b1 activity on the toxicity and carcinogenicity of IQ, a genetic cross was utilized that resulted in inducible fetuses residing in a noninducible mother in order to minimize the contributions of maternal metabolism.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals and treatment protocol.
A congenic C57BL/6 (B6) mouse strain was utilized in the present study to assess the transplacental carcinogenicity of IQ (Lin et al., 1991). C57BL/6 (AhdAhd or B6d,d) nonresponsive female mice were mated with C57BL/6 (AhbAhb or B6b,b) responsive male mice. On day 17 of gestation (day 1 being the day the vaginal plug was first detected), a single ip injection of either olive oil or 6.25, 12.5, or 25 mg/kg of IQ suspended in olive oil was administered. Three days after transplacental treatment with IQ, offspring were born and foster nursed by untreated mothers to avoid further carcinogen exposure through the mother's milk. The mice were housed for 13 months, with no further treatment, in a pathogen-free environment in plastic cages with hardwood shavings for bedding. The mice were allowed free access to water and food (AIN-76 Purified Rodent Diet, Dyets Inc., Bethlehem, PA) and a 12-h fluorescent light/dark cycle was maintained. At 13 months of age, mice were euthanized by cervical dislocation and all major organs except the brain (including the intestines) were examined grossly for lesions. Tissues were fixed in 10% formalin, embedded in paraffin, and 6 µ sections were cut with a microtome and stained with hematoxylin and eosin. Several sections of livers and lungs from all animals in the high-dose group were examined histologically, in addition to sections of the small and large intestine from selected animals, by a board-certified veterinary pathologist, using standard histopathologic criteria (Faccini et al., 1990
). Animal studies were approved by the Wake Forest University's Institutional Animal Care and Use Committee and followed all NIH guidelines for the care, use, and euthanasia of laboratory animals.
Preparation of 800 g and S9 supernatants.
Pregnant B6d,d nonresponsive mice were treated on day 17 of gestation with 25 mg/kg of IQ or olive oil and were euthanized by cervical dislocation 8, 24, and 48 h after injection. The fetuses were removed from the mother, decapitated, and placed on ice. Fetal livers and lungs were removed, pooled, and homogenized in a 20% wt/vol 0.1 M solution of potassium phosphate (pH 7.25) for 15 s using a Polytron homogenizer. Supernatant fractions were subjected to 3 cycles of freezing in an ethanol (EtOH)/dry ice bath and thawing in a room temp water bath. Supernatants were then isolated by centrifugation at 800 g for 10 min at 4°C in a Sorvall RT6000 refrigerated centrifuge. Samples were stored at 80°C until assayed for P450 catalytic activity. A 1/10 dilution of the supernatant was assayed for protein content by the method described by Bradford (1976).
Adult mice were treated with 25 mg/kg of IQ or olive oil and were euthanized by cervical dislocation 48 h after injection. Livers were removed and homogenized in 0.25 M potassium phosphate pH 7.25/0.15 M KCl for 30 s using a Polytron homogenizer at medium speed. Supernatant fractions were isolated by centrifugation at 9000 g for 20 min at 4°C in a Sorvall RC-58 refrigerated centrifuge and stored at 80°C until use. A 1/50 dilution of the supernatant was prepared for determination of protein concentration.
Determination of ethoxyresorufin O-deethylase (EROD) activity.
Supernatant fractions prepared from fetal liver and lungs were assayed for EROD activity by a modification of the assays described by Pohl and Fouts (1980) and Lubert et al. (1985). Specifically, 100800 µg of supernatant protein were added to a reaction mixture consisting of 1.0 M TrisHCl, 0.5 M MgCl2, 50 mM glucose-6-phosphate, 50 U/ml glucose-6-phosphate dehydrogenase, 2 mM dicumarol, and 10 mM NADPH. The reactions were started by the addition of ethoxyresorufin to a final concentration of 5 µM in a final volume of 2 ml and incubated for 15 min at 37°C in a shaking water bath. The reactions were stopped by the addition of methanol. Following the assay, precipitated protein was centrifuged for 5 min at 4°C at 2000 RPM in a RT6000 Sorvall centrifuge. The formation of resorufin, as measured by fluorescence, was determined using a SLM-AMINCO Luminescence Spectrometer (excitation wavelength, 522 nm; emission wavelength, 586 nm).
Determination of glutathione S-transferase (GST) activity.
Isolated fetal liver and lung tissues were sonicated briefly. An aliquot was removed, resonicated for an additional 15 s, and centrifuged at 12,000 RPM for 10 min at 4°C. Supernates were assayed for GST activity at 25°C by a standard spectrophotometric assay using 1 mM 1-chloro-2,4-dinitrobenzene (CDNB) and 1 mM GSH as substrates (Habig and Jakoby, 1981), and activities are expressed as nmol of substrate consumed/min/mg protein (mU/mg). Protein levels were measured with bicinchoninic acid protein assay reagent (Pierce Chemical, Rockford, IL).
Determination of GST protein expression levels.
Primary antibody to GST was prepared as described previously (Fields et al., 1998
). Cytosolic protein samples were boiled for 5 min prior to loading. Samples were electrophoresed on a 12% SDSPAGE gel and transferred by semi-dry electroblotting onto a nitrocellulose membrane. The blot was blocked with 5% nonfat dry milk in PBS, then probed with a 1:1000 dilution of affinity purified rabbit polyclonal anti-human GST
. The probed blot was washed 4 times in PBS, then incubated with a 1:3000 dilution of goat anti-rabbit HRP-conjugated IgG (Cappel/ICN, Costa Mesa, CA). The blot was washed again in PBS and developed using the Renaissance Chemiluminescence Kit (NEN Boston, MA).
Determination of Cyp1a1 and Cyp1b1 RNA expression levels.
Pregnant B6d,d nonresponsive mice were treated on day 17 of gestation with 25 mg/kg of IQ or olive oil and were euthanized by cervical dislocation 1, 2, 4, 8, 12, 16, 24, and 48 h after injection. The fetuses were removed from the mother, decapitated, and placed on ice. Fetal tissue RNA was purified using the standard guanidine isothiocyanate/CsCl density centrifugation method (MacDonald et al., 1987) as described previously for fetal tissues (Miller et al., 1989
,1990a,b).
Ribonuclease protection assays (RPA) were performed to determine expression levels of Cyp1a1 and Cyp1b1 in RNA isolated from fetal liver and lung tissue samples. Mouse P4501A1 and P4501B1 plasmids were kindly provided by Drs Daniel Nebert (Kimura et al., 1984) and Colin Jefcoate (Savas et al., 1994
), respectively. In order to synthesize a probe for the RPA assays, a 1 µl aliquot of plasmid DNA was subjected to the polymerase chain reaction (PCR) using the Perkin-Elmer GeneAmp PCR Reagent Kit. All reactions were carried out in 100 µl and consisted of reaction buffer (10 mM TrisHCl, pH 8.0/2.5 mM MgCl2/50 mM KCl), 200 µM dNTPs (dATP, dCTP, dGTP, dTTP), and 2 units of AmpliTaq Gold (Perkin Elmer). Primers for Cyp1a1 and Cyp1b1 (DNA Synthesis Core Laboratory, Comprehensive Cancer Center of Wake Forest University) were added at a final concentration of 0.2 µM for each primer. The first 27 nucleotides of antisense primers were specific for the SP6 promoter sequence (MAXIscript In vitro Transcription Kits, Ambion, Austin, TX). The primer sequences for Cyp1a1 were 5`-TGGGCCTCAGAGAACTCCTG-3`(sense) and 5`-GGATCCATTTAGGTGACACTATAGAAGGCAGTGTCATAAACCATTTG-3`(antisense). The primer sequences for Cyp1b1 were 5`-ATGCACAACTATCTAAGAAAG-3`(sense) and 5`-GGATCCATTTAGGTGACACTATAGAAGGAAGCATTTTTCCAAGCAAG-3`(antisense). The samples were overlaid with 100 µl of mineral oil to prevent evaporation and cross-contamination of the samples. The PCR cycle parameters consisted of an initial 2 min denaturation step at 94°C, followed by 40 cycles of 1 min at 94°C, 2 min at either 55°C (for Cyp1a1) or 51°C (for Cyp1b1), and 2 min at 72°C, with a final extension step of 72°C for 7 min.
[-32P]UTP RNA labeled probes were synthesized using an Ambion MAXIscript In Vitro Transcription Kit (Austin, TX) according to manufacturer's instructions. Briefly, reactions were carried out in a 20 µl solution of 10x transcription buffer (includes 100 mM DTT), 10 mM NTPs (ATP, CTP, GTP), 800 Ci/mmol [
-32P]UTP, 5 U/µl RNase inhibitor, 1 µg Cyp1a1 or Cyp1b1 template DNA, and 5 U/µl SP6 RNA polymerase. This reaction mixture was incubated at 37°C for 90 min. Two U/µl RNase-free DNase was added and the reaction was incubated at 37°C for 15 min to remove the template DNA. The 234 bp labeled probes were gel purified on a 5% acrylamide/8 M urea gel to separate out full-length transcripts from any prematurely terminated transcription products and unincorporated nucleotides.
Sample RNA and gel purified [-32P]UTP labeled RNA probe were hybridized using an Ambion RPA III Kit (Austin, TX) according to manufacturer's instructions. Briefly, 5 µg of sample RNA and 1.0 x 104 cpm of labeled probe were mixed together and concentrated by ethanol precipitation at 20°C for 15 min, followed by centrifugation at 4°C for 15 min. The EtOH was carefully removed and the samples were air dried for 5 min at room temp. The pellets were resuspended in Hybridization III Buffer, heated at 95°C for 4 min, and incubated at 50°C in a dry bath overnight to permit hybridization of the probe and complementary mRNA in the sample RNA. After hybridization, RNase III Digestion Buffer/RNase T1 Mix was added and the samples were incubated for 30 min at 37°C to degrade single-stranded, unhybridized probe. RNase Inactivation/Precipitation III Solution was then added to the mixture and samples were placed at 20°C for at least 15 min, followed by centrifugation at 4°C for 15 min. Samples were then incubated at 95°C for 4 min, separated on a 5% acrylamide/8 M urea gel at 26 W for 1 h at room temperature, and visualized by autoradiography on a Molecular Dynamics Phosphorimager 445SI (Sunnyvale, CA). Mouse glyceraldehyde-3-phosphate dehydrogenase (GAPDH) served as an internal control and MC-treated tissue served as experimental positive controls. Expression of Cyp1a1 and/or Cyp1b1 mRNAs was quantified using ImageQuant Software (Molecular Dynamics).
![]() |
RESULTS AND DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
An initial 6-week toxicity study was undertaken to determine the appropriate doses of IQ to be administered to pregnant mice. Doses of IQ greater than 25 mg/kg were shown to be highly toxic to the fetuses, resulting in a low rate of live births. Only 1 of the 6 litters born to mothers treated with a 50 mg/kg dose of IQ survived beyond 2 weeks. Three of the litters (50%) had no live births (all the pups born dead) while the neonates from 2 of the 3 remaining litters exhibited a "fail to thrive" syndrome, as evidenced by poor weight gain and a sickly appearance. These neonates were either euthanized or died prior to 2 weeks after birth. In contrast, 5 of 7 litters from the oil-treated and 5 of 6 litters from the 25 mg/kg dose group of IQ survived until the end of the 6-week study period. The 50 mg/kg dose group had only 12 live births out of a total of 26 pups born to 6 mothers, compared to 40 live births out of a total of 40 pups born to 6 mothers treated with 25 mg/kg of IQ, and 33 live births out of a total of 37 pups born to 7 mothers treated with olive oil. By the end of the 6-week study period, 31 of the 37 pups (84%) born to the oil-treated controls and 32 of the 40 pups (80%) born to the 25 mg/kg dose group were still alive. The body weights for the oil-treated and 25 mg/kg IQ dose groups were comparable and are shown in Table 1. Thus, the doses selected for the long-term tumorigenicity study were a high dose of 25 mg/kg, a medium dose of 12.5 mg/kg, and a low dose of 6.25 mg/kg. Pregnant mice were treated with the appropriate doses of IQ and the resultant carcinogenic effects in the offspring were determined.
|
|
To ensure that the EROD assays were performed properly and that these results were accurate, adult and fetal mice were exposed to MC, a well-documented inducer of Cyp1a1 (Conney, 1982). Supernatant fractions from these mice were assayed using the same reagents and under the same conditions used for the IQ-treated mice. In contrast to the results obtained with IQ, 8 h after treatment with MC induction of EROD activity was observed in both lungs and livers of transplacentally treated mice, reaching levels of 2.0 ± 0.82 and 26.6 ± 6.2 pmol of resorufin formed/min/mg of protein, respectively. In addition, treatment with MC resulted in a 74-fold increase in adult EROD activity over oil-treated controls (375 ± 151.7 vs. 5.1 ± 2.01 pmol of resorufin formed/min/mg of protein, respectively). These results are in excellent agreement with our previous studies utilizing the benzo[a]pyrene hydroxylase assay (Miller et al., 1989
,1990b), and suggest that transplacental exposure to IQ does not lead to a substantial induction of fetal Cyp1a1.
Fetal lung and liver tissues were also isolated for the determination of alterations in the levels of expression of Cyp1a1 and Cyp1b1 RNA. To test for the integrity of isolated RNA, all samples were separated and visualized on an agarose gel. Consistent with the results obtained from the EROD analyses, data from ribonuclease protection assays showed that the levels of Cyp1a1 RNA in liver (Figure I) and lung (data not shown) tissue from IQ-treated mice were identical to those found in olive oil-treated controls, using RNAs from two individual litters for each time point. Mouse glyceraldehyde-3-phosphate (GAPDH) was utilized in each experiment as an internal control to correct for any differences in the amounts of RNA added to each reaction sample. Four h MC-treated tissue served as a positive control since previous studies demonstrated maximal increases in Cyp1a1 RNA expression following a 4 h transplacental exposure period to MC (Miller et al., 1989,1990a,b). Accordingly, both the MC-treated liver and lung tissues exhibited, on average, a 20-fold increase in expression of Cyp1a1 RNA over oil- and IQ-treated samples (Fig. 1
).
|
|
The enzymatic activity of glutathione S-transferase (GST) was measured and utilized as a marker of electrophilic response element (ERE)-mediated induction. Fetal levels of GST activity in lung and liver tissue were assessed using 1-chloro-2,4-dinitrobenzene (CDNB). As shown in Figure 3, activity levels of GST in IQ-treated samples were similar to those found in olive oil-treated tissues. The average activity in oil-treated fetal lung was 57.0 ± 1.7 nmol of substrate consumed/min/mg protein (mU/mg), compared to an activity of 62.5 ± 1.1 mU/mg found in IQ-treated lung. Similarly, the average GST activity in fetal liver tissue treated with olive oil and IQ was 407 ± 36 and 410 ± 17 mU/mg, respectively. Western blot analysis additionally revealed that expression of GST
in fetal lung and liver tissue samples treated with IQ were the same as found in oil-treated tissues.
|
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
NOTES |
---|
2 To whom correspondence should be addressed. Fax: (336) 7160255; E-mail: msmiller{at}wfubmc.edu.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Adamson, R. H., Thorgeirsson, V. P., Snyderwine, E. G., Thorgeirsson, S. S., Reeves, J., Dalgard, D. W., Takayama, S., and Sugimura, T. (1990). Carcinogenicity of 2-amino-3-methyl-imidazo[4,5-f]quinoline in nonhuman primates: induction of tumors in three macaques. Jpn.. J. Cancer Res. 81, 1014.[ISI][Medline]
Anderson, L. M., Jones, A. B., Riggs, C. W., and Ohshima, M. (1985). Fetal mouse susceptibility to transplacental lung and liver carcinogenesis by 3-methylcholanthrene: positive correlation with responsiveness to inducers of aromatic hydrocarbon metabolism. Carcinogenesis 6, 13891393.[Abstract]
Boobis, A. R., Lynch, A. M., Murray, S., de la Torre, R., Solans, A., Farre, M., Segura, J., Gooderham, N. J., and Davies, D. S. (1994). CYP1A2-catalyzed conversion of dietary heterocyclic amines to their proximate carcinogens is their major route of metabolism in humans. Cancer Res. 54, 8994.[Abstract]
Boobis, A. R., Sesardic, D., Murray, B. P., Edwards, R. J., Davies, D. S. (1991). Specificity and inducibility of cytochrome P-450 catalyzing the activation of food-derived mutagenic heterocyclic amines. In N-oxidation of Drugs; Biochemistry, Pharmacology, Toxicology (P. Hlavica and L. A. Damani, Eds.), pp. 345355. Chapman and Hall, London.
Bradford, M. M. (1976). A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem. 72, 248254.[ISI][Medline]
Brittebo, E. B., Karlsson, A. A., Skog, K. I., and Jagerstad, I. M. (1994). Transfer of the food mutagen PhIP to foetuses and newborn mice following maternal exposure. Food Chem. Toxicol. 32, 717726.[ISI][Medline]
Conney, A. H. (1982). Induction of microsomal enzymes by foreign chemicals and carcinogenesis by polycyclic aromatic hydrocarbons: G. H. A. Clowes Memorial Lecture. Cancer Res. 42, 48754917.[ISI][Medline]
Crofts, F. G., Sutter, T. R., and Strickland, P. T. (1998). Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by human cytochrome P4501A1, P4501A2 and P4501B1. Carcinogenesis 19, 19691973.[Abstract]
Davis, C. D., Ghoshal, A., Schut, H. A., and Snyderwine, E. G. (1994). Metabolism of the food-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by lactating Fischer 344 rats and their nursing pups. J. Natl. Cancer Inst. 86, 10651070.[Abstract]
Dey, A., Westphal, H., and Nebert, D. W. (1989). Cell-specific induction of mouse Cyp1a1 mRNA during development. Proc. Natl. Acad. Sci. U S A 86, 74467450.[Abstract]
Dooley, K. L., Von Tungeln, L. S., Bucci, T., Fu, P. P., and Kadlubar, F. F. (1992). Comparative carcinogenicity of 4-aminobiphenyl and the food pyrolysates Glu-P-1, IQ, PhIP and MeIQx in the neonatal B6C3F1 male mouse. Cancer Lett. 62, 205209.[ISI][Medline]
Eisenbrand, G., and Tang, W. (1993). Food-borne heterocyclic amines. Chemistry, formation, occurrence and biological activities. A literature review. Toxicology 84, 182.[ISI][Medline]
Faccini, J. M., Abbott, D. P., and Paulus, G. J. J. (1990). Mouse Histopathology: A Glossary for Use in Toxicity and Carcinogenicity Studies, pp. 4862. Elsevier Scientific Publications, New York.
Fields, W. R., Morrow, C. S., Doss, A. J., Sundberg, K., Jernstrom, B., and Townsend, A. J. (1998). Overexpression of stably transfected human glutathione S-transferase P11 protects against DNA damage by benzo[a]pyrene diol-epoxide in human T47D cells. Mol. Pharmacol. 54, 298304.
Ghoshal, A., and Snyderwine, E. (1993). Excretion of food-derived heterocyclic amine carcinogens into breast milk of lactating rats and formation of DNA adducts in the newborn. Carcinogenesis 14, 21992203.[Abstract]
Greenberg, R. S., and Shuster, J. L., Jr. (1985). Epidemiology of cancer in children. Epidemiol. Rev. 7, 2248.[ISI][Medline]
Gressani, K. M., Leone-Kabler, S., O'Sullivan, M. G., Case, L. D., Malkinson, A. M., and Miller, M. S. (1999). Strain-dependent lung tumor formation in mice transplacentally exposed to 3-methylcholanthrene and postnatally exposed to butylated hydroxytoluene. Carcinogenesis 20, 21592165.
Habig, W. H., and Jakoby, W. B. (1981). Glutathione S-transferase (rat and human). Meth. Enzymol. 77, 218231.[Medline]
Hakkola, J., Pasanen, M., Pelkonen, O., Hukkanen, J., Evisalmi, S., Anttila, S., Rane, A., Mantyla, M., Purkunen, R., Saarikoski, S., Tooming, M., and Raunio, H. (1997). Expression of CYP1B1 in human and fetal tissues and differential inducibility of CYP1B1 and CYP1A1 by Ah receptor ligands in human placenta and cultured cells. Carcinogenesis 18, 391397.[Abstract]
Hasegawa,. R., Kimura, J., Yaono, M., Takahashi, S., Kato, T., Futakuchi, M., Fukutake, M., Fukutome, K., Wakabayashi, K., Sugimura, T., Ito, N., and Shirai, T. (1995). Increased risk of mammary carcinoma development following transplacental and trans-breast milk exposure to a food-derived carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), in Sprague-Dawley Rats. Cancer Res. 55, 43334338.[Abstract]
Kimura, S., Donovan, J. C., and Nebert, D. W. (1987). Expression of the mouse P1450 gene during differentiation without foreign chemical stimulation. J. Exp. Pathol. 3, 6174.[Medline]
Kimura, S., Gonzalez, F. J., and Nebert, D. W. (1984). The murine Ah locus. Comparison of the complete cytochrome P1-450 and P3-450 cDNA nucleotide and amino acid sequences. J. Biol. Chem. 259, 1070510713.
Kimura, S., Gonzalez, F. J., and Nebert, D. W. (1986). Tissue-specific expression of the mouse dioxin-inducible P1450 and P3450: differential transcriptional activation and mRNA stability in liver and extrahepatic tissue. Mol. Cell. Biol. 6, 14711477.[ISI][Medline]
Kleman, M. I., Overvik, E., Mason, G. G., and Gustafsson, J.-A. (1992). In vitro activation of the dioxin receptor to a DNA-binding form by food-borne heterocyclic amines. Carcinogenesis 13, 16191624.[Abstract]
Layton, D. W., Bogen, K. T., Knize, M. G., Hatch, F. T., Johnson, V. M., and Felton, J. S. (1995). Cancer risk of heterocyclic amines in cooked foods: an analysis and implications for research. Carcinogenesis 16, 3952.[Abstract]
Lin, F. H., Stohs, S. J., Birnbaum, L. S., Clark, G., Lucier, G. W., and Goldstein, J. A. (1991). The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the hepatic estrogen and glucocorticoid receptors in congenic strains of Ah responsive and Ah nonresponsive C57BL/6J mice. Toxicol. Appl. Pharmacol. 108, 129139.[ISI][Medline]
Lubert, R. A., Nims, R. W., Mayer, R. T., Cameron, J. W., and Schechtman, L. M. (1985). Measurement of cytochrome P-450 dependent dealkylation of alkoxyphenoxazones in hepatic S-9s and hepatocyte homogenates: effects of dicumarol. Mutat. Res. 142, 127131.[ISI][Medline]
MacDonald, R. J., Swift, G. H., Przybyla, A. E., and Chirgwin, J. M. (1987). Isolation of RNA using guanidinium salts. Methods Enzymol. 152, 219227.[ISI][Medline]
Malkinson, A. M. (1989). The genetic basis of susceptibility to lung tumors in mice. Toxicology 54, 241271.[ISI][Medline]
Mauthe, R. J., Snyderwine, E. G., Ghoshal, A., Freeman, S. P., and Turteltaub, K. W. (1998). Distribution and metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in female rats and their pups at dietary doses. Carcinogenesis 19, 919924.[Abstract]
Miller, M. S. (1994). Transplacental lung carcinogenesis: a pharmacogenetic mouse model for the modulatory role of cytochrome P4501A1 on lung cancer. Chem. Res. Toxicol. 7, 471481.[ISI][Medline]
Miller, M. S., Jones, A. B., Chauhan, D. P., and Anderson, L. M. (1990a). Role of the maternal environment in determining susceptibility to transplacentally induced chemical carcinogenesis in mouse fetuses. Carcinogenesis 11, 19791984.[Abstract]
Miller, M. S., Jones, A. B., Chauhan, D. P., Park, S. S., and Anderson, L. M. (1989). Differential induction of fetal mouse liver and lung cytochromes P-450 by ß-naphthoflavone and 3-methylcholanthrene. Carcinogenesis 10, 875891.[Abstract]
Miller, M. S., Jones, A. B., Park, S. S., and Anderson, L. M. (1990b). The formation of 3-methylcholanthrene-initiated lung tumors correlates with induction of cytochrome P450IA1 by the carcinogen in fetal but not adult mice. Toxicol. Appl. Pharmacol. 104, 235245.[ISI][Medline]
Miller, M. S., Juchau, M. R., Guengerich, F. P., Nebert, D. W., and Raucy, J. L. (1996). Drug metabolic enzymes in developmental toxicology. Fundam. Appl. Toxicol. 34, 165175.[ISI][Medline]
Nagao, M., Honda, M., Seino, Y., Yahagi, T., and Sugimura, T. (1977). Mutagenicities of smoke condensates and the charred surface of fish and meat. Cancer Lett. 2, 221226.[ISI][Medline]
Nebert, D. W., and Gelboin, H. V. (1969). The in vivo and in vitro induction of aryl hydrocarbon hydroxylase in mammalian cells of different species, tissues, strains, and developmental and hormonal states. Arch. Biochem. Biophys. 134, 7689.[ISI][Medline]
Ohgaki, H., Kusama, K., Matsukura, N., Morino, K., Hasegawa, H., Sato, S., Takayama, S., and Sugimura, T. (1984). Carcinogenicity in mice of a mutagenic compound, 2-amino-3-methylimidazo[4,5-f]quinoxaline, from broiled sardine, cooked beef and beef extract. Carcinogenesis 5, 921924.[Abstract]
Paulsen, J. E., Steffensen, I.-L., Andreassen, A., Vikse, R., and Alexander, J. (1999). Neonatal exposure to the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine via breast milk or directly induces intestinal tumors in multiple intestinal neoplasia mice. Carcinogenesis 20, 12771282.
Pohl, R. J., and Fouts, J. R. (1980). A rapid method for assaying the metabolism of 7-ethoxyresorufin by microsomal subcellular fractions. Anal. Biochem. 107, 150155.[ISI][Medline]
Raucy, J. L., and Carpenter, S. J. (1993). The expression of xenobiotic-metabolizing cytochrome P450 in fetal tissues. J. Pharmacol. Toxicol. Methods 29, 121128.[ISI][Medline]
Rice, J. M. (1979). Perinatal period and pregnancy: intervals of high risk for chemical carcinogens. Environ. Health Perspect. 29, 2327.[ISI][Medline]
Savas, U., Bhattacharyya, K. K., Christou, M., Alexander, D. L., and Jefcoate, C. R. (1994). Mouse cytochrome P-450EF, representative of a new 1B subfamily of cytochrome P-450s. Cloning, sequence determination, and tissue expression. J. Biol. Chem. 269, 1490514911.
Schut, H. A., and Snyderwine, E. G. (1999). DNA adducts of heterocyclic amine food mutagens: implications for mutagenesis and carcinogenesis. Carcinogenesis 20, 353368.
Sesardic, D., Pasanen, M., Pelkonen, O., and Boobis, A. R. (1990). Differential expression and regulation of the cytochrome P450IA gene subfamily in human tissues. Carcinogenesis 11, 11831188.[Abstract]
Shimada, T., Hayes, C. L., Yamazaki, H., Amin, S., Hecht, S. S., Guengerich, F. P., and Sutter, T. R. (1996). Activation of chemically diverse procarcinogens by human cytochrome P-450 1B1. Cancer Res. 56, 29792984.[Abstract]
Snyderwine, E. G., and Battula, N. (1989). Selective mutagenic activation by cytochrome P3450 of carcinogenic arylamines found in foods. J. Natl. Cancer Inst. 81, 223227.[Abstract]
Sugimura, T. (1997). Overview of carcinogenic heterocyclic amines. Mutat. Res., 376, 211219.[ISI][Medline]
Sugimura, T., Nagao, M., Kawachi, T., Honda, M., Yahagi, T., Seino, Y., Sato, S., and Matsukura, N. (1977). Mutagen-carcinogens in foods, with special reference to highly mutagenic pyrolytic products in broiled foods. In Origins of Human Cancer, Book C (H. H. Hiatt, J. D. Watson, and J. A. Winstein, Eds.), pp. 15611577. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY.
Takayama, S., Nakatsuru, Y., Masuda, M., Ohgaki, H., Sato, S., and Sugimura, T. (1984). Demonstration of carcinogenicity in F344 rats of 2-amino-3-methylimidazo[4,5-f]quinoline from broiled sardine, fried beef and beef extract. Gann. 75, 467470.[ISI][Medline]
Tanaka, T., Barnes, W. S., Williams, G. M., and Weisburger, J. H. (1985). Multipotential carcinogenicity of fried food mutagen 2-amino-3-methylimidazo-[4,5-f]quinoline in rats. Jpn. J. Cancer Res. 76, 570576.[ISI][Medline]
Turusov, V. S., and Tomatis, L. (1997). Transplacental and transgenerational carcinogenesis. Arkh. Pathol. 59, 712.
Tuteja, N., Gonzalez, F. J., and Nebert, D. W. (1985). Developmental and tissue-specific differential regulation of the mouse dioxin-inducible P1-450 and P3-450 genes. Dev. Biol. 112, 177184.[ISI][Medline]
Wakabayashi, K., Nagao, M., Esumi, H., and Sugimura, T. (1992). Food-derived mutagens and carcinogens. Cancer Res. 52, 2092s2098s.[Abstract]
Wessner, L. L., Fan, M., Schaeffer, D. O., McEntee, M. F., and Miller, M. S. (1996). Mouse lung tumors exhibit specific Ki-ras mutations following transplacental exposure to 3-methylcholanthrene. Carcinogenesis 17, 15191526.[Abstract]
Zahm, S. H., and Devesa, S. S. (1995). Childhood cancer: overview of incidence trends and environmental carcinogens. Environ. Health Perspect. 103(Suppl. 6), 177184.