Identification and localization of five CYP2Cs in murine extrahepatic tissues and their metabolism of arachidonic acid to regio- and stereoselective products

The CYP2C subfamily has been extensively studied in humans with respect to the metabolism of clinically important drugs, and polymorphisms have been identified in these enzymes. In the present study, a murine model was used to determine the possible physiological functions and extrahepatic distribution of CYP2Cs. Using the reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and immununohistochemistry, this report demonstrates that the mouse CYP2Cs are extensively distributed in extrahepatic tissues and localized to heart muscle, lung Clara and ciliated cells, kidney collecting ducts, the X-zone of female adrenals, reproductive organs, white blood cells, and eyes (in the optic nerve, rods, and cones). RT-PCR, subcloning, and sequencing of the products indicate that each CYP2C has a unique tissue distribution. Four cDNA fragments representing potentially new CYP2Cs were identified, each with its own organ-specific pattern of expression. Using a bacterial cDNA expression system, we found that recombinant proteins for each of the five full-length murine CYP2Cs metabolize arachidonic acid to different regio- and stereospecific products, including epoxyeicosatrienoic acids and hydroxyeicosatetraenoic acids. Regio- and stereospecific metabolites of arachidonic acid have been reported to affect important physiological functions such as inflammation, neutrophil activation, ion transport, cellular proliferation, and vascular tone. Our results suggest that the presence of CYP2C enzymes in heart muscle, aorta, kidney, lung, adrenals, eyes, and reproductive organs could regulate important physiological and/or pathological processes in these tissues.

Cytochrome P450 CYP2J9, a new mouse arachidonic acid omega-1 hydroxylase predominantly expressed in brain

A cDNA encoding a new cytochrome P450 was isolated from a mouse brain library. Sequence analysis reveals that this 1,958-base pair cDNA encodes a 57-58-kDa 502-amino acid polypeptide that is 70-91% identical to CYP2J subfamily P450s and is designated CYP2J9. Recombinant CYP2J9 was co-expressed with NADPH-cytochrome P450 oxidoreductase (CYPOR) in Sf9 cells using a baculovirus system. Microsomes of CYP2J9/CYPOR-transfected cells metabolize arachidonic acid to 19-hydroxyeicosatetraenoic acid (HETE) thus CYP2J9 is enzymologically distinct from other P450s. Northern analysis reveals that CYP2J9 transcripts are present at high levels in mouse brain. Mouse brain microsomes biosynthesize 19-HETE. RNA polymerase chain reaction analysis demonstrates that CYP2J9 mRNAs are widely distributed in brain and most abundant in the cerebellum. Immunoblotting using an antibody raised against human CYP2J2 that cross-reacts with CYP2J9 detects a 56-kDa protein band that is expressed in cerebellum and other brain segments and is regulated during postnatal development. In situ hybridization of mouse brain sections with a CYP2J9-specific riboprobe and immunohistochemical staining with the anti-human CYP2J2 IgG reveals abundant CYP2J9 mRNA and protein in cerebellar Purkinje cells. Importantly, 19-HETE inhibits the activity of recombinant P/Q-type Ca(2+) channels that are known to be expressed preferentially in cerebellar Purkinje cells and are involved in triggering neurotransmitter release. Based on these data, we conclude that CYP2J9 is a developmentally regulated P450 that is abundant in brain, localized to cerebellar Purkinje cells, and active in the biosynthesis of 19-HETE, an eicosanoid that inhibits activity of P/Q-type Ca(2+) channels. We postulate that CYP2J9 arachidonic acid products play important functional roles in the brain.

Effects of iodine on inducible nitric oxide synthase and cyclooxygenase-2 expression in sulfur mustard-induced skin

In a previous study we demonstrated the protective effect of topical iodine as postexposure treatment for sulfur mustard (SM) application. The iodine treatment results in significantly reduced inflammation and necrosis and increased epidermal hyperplasia. The expression and localization of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) in paraffin-embedded skin samples from that study were evaluated in the present investigation. We compared the immunoreactivity of iNOS and COX-2 using five samples from each of the following four test sites: untreated control sites, SM-exposed sites, sites treated with iodine mixture 15 min after SM exposure, and sites treated with iodine 30 min after SM exposure. All animals were killed 2 days after irritant exposure. iNOS immunoreactivity was present only in skin sites exposed to SM without iodine treatment. The ulcerated skin was covered with a relatively thick band of exudate composed of iNOS-immunostained polymorphonuclear cells and macrophages. In untreated skin, COX-2 immunostaining was limited to the thin suprabasal epidermal layer. In SM-exposed skin, induction of COX-2 was noted in inflammatory cells located close to the site of epidermal injury. In skin sites treated with iodine 15 or 30 min after SM exposure, the regenerating hyperplastic epithelium showed moderate cytoplasmic staining localized to the epithelium overlying the basal layer. This pattern of staining was also present in the nearby dermal fibroblasts. Thus, in contrast to the skin samples exposed to SM without iodine treatment, the epidermal layer expressing immunohistochemical positivity for COX-2 was thicker and corresponded to the epidermal hyperplasia noted in samples treated with iodine. It is well documented that prostaglandins (PGs) promote epidermal proliferation, thereby contributing to the repair of injured skin. That the induction of the COX-2 shown in our study may also play a role in the healing process is indicated by the present evidence. The results suggest that nitric oxide radicals (NO*) are involved in mediating the damage induced by the SM and that iodine-related reduction in acute epidermal inflammation is associated with reduced iNOS expression.

CYP2C40, a unique arachidonic acid 16-hydroxylase, is the major CYP2C in murine intestinal tract

We recently identified five different murine CYP2C cDNAs from a murine cDNA library. When expressed in a bacterial cDNA expression system, all five recombinant proteins metabolized arachidonic acid but produced distinctly different profiles. In addition, some CYP2C mRNAs were found in extrahepatic tissues, as well as in liver. Immunoblots with an antibody raised against recombinant CYP2C38, which recognizes all five murine CYP2Cs, demonstrated that among extrahepatic tissues, colon and cecum contained the highest amount of CYP2Cs. The highest concentration of CYP2Cs occurred in cecum and colon (cecum >/= proximal colon >> distal colon), with lower levels in duodenum, jejunum, and ileum. Immunohistochemical studies revealed that CYP2Cs were localized principally in epithelial cells and autonomic ganglia in gut and colon. Polymerase chain reaction amplification of reverse-transcribed mRNA using murine CYP2C-specific primers followed by cloning and sequencing identified CYP2C40 as the major CYP2C isoform expressed in murine intestinal tract. Recombinant CYP2C40 metabolized arachidonic acid in a regio- and stereospecific manner to 16(R)-HETE (hydroxyeicosatetraenoic acid) as the major product. To our knowledge, CYP2C40 is the first enzyme known to produce primarily 16-HETE. We conclude that CYP2C40 is one of the major cytochrome P450 proteins in the mouse intestinal tract. In the light of vasoactive and anti-neutrophilic effects of 16-HETE, we hypothesize that CYP2C40 may play an important role in endogenous biological functions in intestine.

Molecular cloning, enzymatic characterization, developmental expression, and cellular localization of a mouse cytochrome P450 highly expressed in kidney

A cDNA encoding a new cytochrome P450 was isolated from a mouse liver library. Sequence analysis reveals that this 1,886-base pair cDNA encodes a 501-amino acid polypeptide that is 69-74% identical to CYP2J subfamily P450s and is designated CYP2J5. Recombinant CYP2J5 was co-expressed with NADPH-cytochrome P450 oxidoreductase in Sf9 cells using a baculovirus system. Microsomal fractions of CYP2J5/NADPH-cytochrome P450 oxidoreductase-transfected cells metabolize arachidonic acid to 14,15-, 11,12-, and 8, 9-epoxyeicosatrienoic acids and 11- and 15-hydroxyeicosatetraenoic acids (catalytic turnover, 4.5 nmol of product/nmol of cytochrome P450/min at 37 degrees C); thus CYP2J5 is enzymologically distinct. Northern analysis reveals that CYP2J5 transcripts are most abundant in mouse kidney and present at lower levels in liver. Immunoblotting using a polyclonal antibody against a CYP2J5-specific peptide detects a protein with the same electrophoretic mobility as recombinant CYP2J5 most abundantly in mouse kidney microsomes. CYP2J5 is regulated during development in a tissue-specific fashion. In the kidney, CYP2J5 is present before birth and reaches maximal levels at 2-4 weeks of age. In the liver, CYP2J5 is absent prenatally and during the early postnatal period, first appears at 1 week, and then remains relatively constant. Immunohistochemical staining of kidney sections with anti-human CYP2J2 IgG reveals that CYP2J protein(s) are present primarily in the proximal tubules and collecting ducts, sites where the epoxyeicosatrienoic acids are known to modulate fluid/electrolyte transport and mediate hormonal action. In situ hybridization confirms abundant CYP2J5 mRNA within tubules of the renal cortex and outer medulla. Epoxyeicosatrienoic acids are endogenous constituents of mouse kidney thus providing direct evidence for the in vivo metabolism of arachidonic acid by the mouse renal epoxygenase(s). Based on these data, we conclude that CYP2J5 is an enzymologically distinct, developmentally regulated, protein that is localized to specific nephron segments and contributes to the oxidation of endogenous renal arachidonic acid pools. In light of the well documented effects of epoxyeicosatrienoic acids in modulating renal tubular transport processes, we postulate that CYP2J5 products play important functional roles in the kidney.

Frequency of Ha-ras-1 gene mutations inversely correlated with furan dose in mouse liver tumors

Liver tumors were induced in infant male B6C3F1 mice by preweaning administration of furan, either as a single dose of 400 mg/kg body weight or six doses of 200 mg/kg body weight. Six doses of 200 mg/kg furan resulted in an increased incidence and multiplicity of liver tumors relative to the multiple-dose vehicle control group and the single-dose furan group. In the single-dose group, there was an increase in overall tumor multiplicity but not prevalence of liver tumors. After polymerase chain reaction amplification of isolated DNA, slot-blot oligonucleotide hybridization was used to screen for mutations at known mutational hot-spots in the first three exons of Ha-ras-1 (Hras1). The relative frequency of Hras1 activation was 82% in the 28 tumors analyzed from the single-dose group and 32% in the 28 tumors analyzed from the multiple-dose group. The lack of histomorphologic evidence of chronic cytotoxicity in the livers and the pattern of Hras1 activation suggest that a genotoxic mode of action is responsible for at least part of the hepatocarcinogenicity of furan in B6C3F1 mice. These findings confirm previously documented hepatocarcinogenicity of furan in B6C3F1 mice and provide evidence that carcinogen dose may influence the frequency of Hras1 activation in mouse liver tumors.

Mechanism of skin tumorigenesis by contact sensitizers: the effect of the corticosteroid fluocinolone acetonide on inflammation and tumor induction by 2,4 dinitro-1-fluorobenzene in the skin of the TG.AC (v-Ha-ras) mouse

The effect of the corticosteroid fluocinolone acetonide (FA) on skin tumor induction and inflammation by the contact sensitizer dinitrofluorobenzene (DNFB) was examined. This study broadly relates to the question of whether contact sensitizers, as electrophilic chemicals that produce protein adduction, may constitute an environmental cancer hazard. The specific aim of this study was to evaluate the extent to which the immunogenic inflammatory response to DNFB, in contrast to DNFB cytotoxicity, might be responsible for tumor induction. Experiments were conducted on a transgenic (TG.AC) mouse, incorporating a mutated ras oncogene (v-Ha-ras) that responds rapidly and profusely with skin papillomas to tumor promoters as if it were genetically initiated. Various doses and patterns of DNFB and FA were applied to the skin in a 2-week period; DNFB was given four times and FA was given either with the DNFB or daily. The tumor response to DNFB was completed by 8 weeks from the first dose and was consistent with a dose-squared relationship. FA was not tumorigenic alone; when given with DNFB, it caused only a small reduction in inflammation and tumor yield. When given daily, FA increased ulcerative skin damage, inflammation, and the yield tumors. The results suggest that tumorigenesis by DNFB, in the high-dose short-term regimen used here, is mainly due to its cytotoxicity and not contact sensitization.

Protein tyrosine kinase inhibitors suppress the production of nitric oxide in mixed glia, microglia-enriched or astrocyte-enriched cultures

Nitric oxide (NO) produced by glial cells has been implicated in the neuropathogenesis of various diseases. However, the signaling transduction pathway(s) for the production of NO in these cells is not well understood. To test whether protein tyrosine kinases (PTKs) are required for signaling events of NO production in glial cells, this study examined the effects of genistein and tyrphostin A25, two potent inhibitors of PTKs, on the production of NO in mouse primary mixed glia, microglia-enriched or astrocyte-enriched cultures exposed to lipopolysaccharide (LPS) or a combination of LPS and interferon-gamma (IFN gamma). LPS induced a dose-dependent increase in NO production from the mixed glia cultures. The LPS-induced NO production was significantly enhanced by stimulating the cells with IFN gamma. Genistein or tyrphostin A25 inhibited the production of NO in both LPS- and IFN gamma/LPS-stimulated mixed glia cultures. The production of NO in the stimulated microglia-enriched or astrocyte-enriched cultures was also inhibited by tyrphostin A25. To verify the cellular sources of NO, immunocytochemical staining of inducible NO synthase (iNOS) was followed by staining with the microglia marker Mac-1 or the astrocyte marker glial fibrillary acid protein (GFAP) in microglia-enriched or astrocyte-enriched cultures. The expression of iNOS and the production of NO in microglia-enriched cultures were significantly higher than those in the identically stimulated astrocyte-enriched cultures. These results demonstrate that PTKs are involved in the signaling events of LPS-induced NO production in microglia and astrocytes, and that microglia are more responsive than astrocytes to stimuli which induce NO. These results may provide insights into therapeutic interventions in the pathway for NO production in the brain.

Induction of CYP1A1 and ALDH-3 in lymphoid tissues from Fisher 344 rats exposed to 2,3,7,8-tetrachlorodibenzodioxin (TCDD)

The immune system is a primary target for toxic insult by a number of drugs and environmental chemicals, many of which require activation to toxic metabolites by drug-metabolizing enzymes. We compared the induction of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1) and aldehyde dehydrogenase (ALDH), in lymphoid tissues of F344 rats following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). ALDH was induced in both the spleen and the thymus after TCDD treatment, with maximal expression at 9 and 15 days, respectively. Thymic microsomal preparations from TCDD-treated animals expressed elevated levels of inducible CYP1A1 as compared to microsomes from the spleens of treated animals or tissues from control rats. TCDD treatment also resulted in increased ethoxyresorufin-O-deethylase (EROD) activity in the thymus. There were no detectable mRNA transcripts for CYP1A1 in peripheral blood or splenic lymphocytes from treated animals; however, CYP1A1 transcripts were induced in isolated thymocytes, whole spleen, and whole thymus. In vitro exposure to TCDD did not result in induction of immunoreactive CYP1A1 in thymocytes unless simultaneously activated with the mitogen, phytohemagglutinin (PHA). Immunohistochemical localization of CYP1A1 in immune tissues indicated that cells other than the lymphoid populations are responsible for the increased CYP1A1 expression. The pattern of CYP1A1 induction was related to the expression of the Ah receptor (AhR) in immune tissues. Western blot analyses demonstrated less AhR present in peripheral blood lymphoid cells and spleen, as compared to whole tissues. These studies indicate that while drug-metabolizing enzymes are present in immune tissues, the induction of enzymes is selective in different lymphoid cells.

Persistence of TCDD-induced hepatic cell proliferation and growth of enzyme altered foci after chronic exposure followed by cessation of treatment in DEN initiated female rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent tumor promoter in two-stage models of hepatocarcinogenesis. This study focuses on the persistence or reversibility of TCDD-mediated changes in livers after 30 weeks of treatment and cessation of treatment. Diethylnitrosamine (DEN) initiated animals (175 mg/kg) were promoted bi-weekly with TCDD at a dose equivalent to 125 ng/kg/day for 30 weeks without or with a following waiting period of 32 weeks before necropsy. 2,3,7,8-Tetrachlorodibenzo-p-dioxin liver concentration decreased 300-fold above background. Induction of CYP1A1 dependent enzyme activity decreased according to TCDD tissue levels. In contrast, cell proliferation, as measured by BrdU-labeling index, was still 2.8-fold increased over controls in the TCDD group with waiting period compared to a 4-fold increase over controls at the end of the 30 week dosing period. Enzyme altered hepatic foci expressing the placental form of glutathione S-transferase decreased in number but the remaining foci were significantly increased in size and the percent of liver occupied by foci was higher at the end of the waiting period as compared to livers at the end of the dosing period. Liver tumor incidence at the end of the waiting period was 71% (5 of 7 animals) and the livers showed an increase in bile duct lesions with only mild toxicity. There was pronounced bile duct proliferation in DEN/TCDD treated animals after the waiting period with intense expression of TGF alpha in bile duct epithelial cells at detected by immunohistochemical methods. In comparison, at the end of the 30 week dosing period the livers showed more severe toxicity and only mild bile duct proliferation. Also, one small hepatocellular adenoma was observed. It is concluded that as opposed to CYP1A1 induction the more complex biological responses, cell proliferation and selective growth of certain preneoplastic foci, are persistent after prolonged TCDD treatment within the experimental framework of our study.

Loss of heterozygosity in spontaneous and chemically induced tumors of the B6C3F1 mouse

The B6C3F1 mouse is used worldwide to gauge the carcinogenic hazard posed by chemicals to humans. An assessment of the ability of this rodent model to predict human neoplasia requires an evaluation of similarities and differences in the genetics of tumor formation between these two species. We examined 142 spontaneous and chemically-induced liver tumors isolated from the B6C3F1 mouse for losses of heterozygosity (LOH) at 78 polymorphic loci and compared these results to genetic changes known to occur in human hepatocellular carcinoma. Approximately a third of the 142 mouse tumors exhibited LOH, suggesting that tumor suppressor gene inactivation may be involved in the formation of mouse liver tumors. Most of the LOH observed was restricted to seven chromosome sites and most of the tumors that underwent LOH lost alleles from only one of those seven sites. The relatively few losses seen in these mouse tumors distinguished them from clinical stage human tumors in that, in the mouse tumors, interstitial deletions appeared more frequently than losses of whole chromosomes. Only four mouse tumors lost a whole chromosome. LOH occurred at loci of the mouse genome syntenic to areas of the human genome known to harbor the Wilms', retinoblastoma, APC, MCC and DCC tumor suppressor genes; these genes have never been associated with hepatocellular carcinomas. Losses observed on chromosomes 5 and 8 (syntenic to human chromosomes 4 and 16) suggest tumor suppressor genes that are common to hepatocellular carcinomas from both species, while losses on chromosome 9 suggest involvement of a previously unidentified tumor suppressor gene.

Comparison of proliferating cell nuclear antigen to tritiated thymidine as a marker of proliferating hepatocytes in rats

Proliferating cell nuclear antigen (PCNA), an endogenous nuclear protein, has recently been used to identify replicating cells. PCNA was compared to tritiated thymidine ([3H]-TdR), a reliable and accurate exogenous labeling agent, to ascertain if PCNA gives comparable results for quantitative cell proliferation. Male F344 rats were treated with a single dose of 500 mg/kg 4-acetylaminofluorene (4-AAF), a known liver mitogen. Rats (n = 5) were euthanized and necropsied at 6, 12, 18, 24, 36, 48, 96, or 192 hr after treatment. Two hours before necropsy, rats were pulsed-dosed with [3H]-TdR (2 mCi/kg body weight). Livers were sectioned, autoradiography performed, and labeling indexes (LI), a measurement of the percentage of S-phase hepatocytes, determined. One and a half years after the completion of this study, the archival paraffin blocks of the liver tissue were sectioned and stained for PCNA by an immunohistochemical procedure. Immunocytochemical staining patterns of proliferating cell nuclear antigen antigen expression permitted the recognition of G1, S, G2, M, and quiescent cells. PCNA LI, generated by scoring only cells exhibiting S-phase staining patterns, was compared to the pulse [3H]-TdR LI for each animal. Similar periportal staining patterns of S-phase nuclei were detected by both markers. The [3H]-TdR LI and the PCNA LI exhibited a peak at 24 hr of approximately the same magnitude. However, while the [3H]-TdR LI had returned to near baseline at the 48-hr time point, the PCNA LI remained elevated until the 96-hr time point. This sustained elevation of the PCNA index cannot be explained at this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of p53 mutations in methylene chloride-induced lung tumors from B6C3F1 mice

Mutations of the p53 tumor suppressor gene are the most common defined genetic alterations seen in a wide variety of human cancers. In contrast, little is known about the importance of the p53 gene in chemically induced tumors of rodents, which are widely used as models for the evaluation of human health risks. In this study we examined 54 methylene chloride-induced and seven spontaneously arising lung tumors from female B6C3F1 mice for losses of heterozygosity (LOH) at markers near the p53 gene on chromosome 11. LOH was detected in seven methylene chloride-induced lung carcinomas by Southern analysis of a restriction fragment length polymorphism and PCR analysis of five simple sequence length polymorphisms. In each case allele loss was observed at all six markers; thus, these chromosomal alterations were likely to have resulted from mitotic nondisjunction. In contrast, LOH was not detected in 20 liver tumors from methylene chloride-treated mice at the Acrb locus, which is tightly linked to the p53 gene on chromosome 11. In addition single strand conformation polymorphism analysis was performed to screen for mutations in the most conserved regions of the p53 gene (exons 5 to 8). Consequently, potential mutations identified by direct sequencing, were only detected in four of the seven tumor samples with LOH, but not in any of the remaining lung tumors. Overexpression of the p53 protein by immunohistochemical staining was detected only in the four tumors that contained p53 point mutations and in a focal area of another tumor. Finally, using a simple sequence length polymorphism within the retinoblastoma tumor suppressor gene, LOH on mouse chromosome 14 was also detected in three lung carcinomas and one liver tumor. Inactivation of p53 and possibly the retinoblastoma tumor suppressor gene appear to be infrequent events in lung and liver tumors from methylene chloride treated mice.

Parental bias of Ki-ras oncogenes detected in lung tumors from mouse hybrids

A mouse strain with low lung tumor susceptibility (C3H) and a strain with high lung tumor susceptibility (A/J) were reciprocally crossed to produce C3A and AC3 F1 hybrid mice. Ki-ras oncogenes were detected in spontaneous and chemically induced lung tumors obtained from the C3A and AC3 mice. To further explore the genetics of the Ki-ras gene in mouse lung tumor susceptibility, the parental origin of Ki-ras oncogenes detected in lung tumors from the F1 hybrids was determined by a strategy based on a 37-base-pair deletion in the second intron of the A/J Ki-ras allele. Ki-ras oncogenes were derived from the A/J parent in 38 of 40 tumors obtained from C3A mice and 30 of 30 tumors from AC3 mice. The observation that the activated oncogene in hybrids originates from the susceptible parent suggests that the Ki-ras gene is directly linked to mouse lung tumor susceptibility. This finding may have implications for pulmonary adenocarcinoma development in humans, since Ki-ras oncogenes are detected in 35% of this human tumor type.

Ovarian hormones enhance 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated increases in cell proliferation and preneoplastic foci in a two-stage model for rat hepatocarcinogenesis

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent hepatocarcinogen in rodents. However, liver tumor incidence is increased by TCDD in female Sprague-Dawley rats but not male rats in chronic carcinogen bioassays. Our studies have investigated this finding by evaluating histological and biochemical parameters in a two-stage model for hepatocarcinogenesis in female Sprague-Dawley rats (intact and ovariectomized), using diethylnitrosamine (DEN) as the initiating agent and TCDD as the promoting agent. Increases in gamma-glutamyl transpeptidase-positive foci were greater in intact female rats than in ovariectomized (OVX) animals. For example, in intact rats receiving both DEN and TCDD, the percentage of liver occupied by gamma-glutamyl transpeptidase-positive foci was 0.37, compared to 0.08 in OVX rats. Values for intact or OVX rats receiving either DEN or TCDD only were 0.04 or less. Similar results were obtained when using placental glutathione S-transferase to detect hepatic preneoplastic lesions. Cell proliferation data, obtained using bromodeoxyuridine in osmotic minipumps, were consistent with preneoplastic foci data in that the hepatocyte labeling index was increased in DEN/TCDD intact rats but not in DEN/TCDD OVX rats. Analysis of data from individual animals revealed a strong correlation (P less than 0.01) between cell proliferation and placental glutathione S-transferase-positive foci/cm3 in liver. These findings did not reflect effects of ovariectomy on TCDD tissue distribution, since livers of OVX rats contained more TCDD than livers of intact rats, although both groups of rats received a dose of 1.4 micrograms TCDD/kg once every 2 weeks for 30 weeks. Hepatic cytochrome P-450d (IA2) was induced approximately 6-8-fold in all TCDD-treated groups, and the magnitude of induction was not influenced by ovariectomy. This cytochrome efficiently catalyzes metabolism of 17 beta-estradiol to catechol estrogens. Our data suggest that ovarian hormones (probably estrogen) play a significant role in the hepatocarcinogenic actions of TCDD.

Activation of K-ras by codon 13 mutations in C57BL/6 X C3H F1 mouse tumors induced by exposure to 1,3-butadiene

1,3-Butadiene has been detected in urban air, gasoline vapors, and cigarette smoke. It has been estimated that 65,000 workers are exposed to this chemical in occupational settings in the United States. Lymphomas, lung, and liver tumors were induced in female and male C57BL/6 X C3H F1 (hereafter called B6C3F1) mice by inhalation of 6.25 to 625 ppm 1,3-butadiene for 1 to 2 years. The objective of this study was to examine these tumors for the presence of activated protooncogenes by the NIH 3T3 transfection and nude mouse tumorigenicity assays. Transfection of DNA isolated from 7 of 9 lung tumors and 7 of 12 liver tumors induced morphological transformation of NIH 3T3 cells. Southern blot analysis indicated that the transformation induced by 6 lung and 3 liver tumor DNA samples was due to transfer of a K-ras oncogene. Four of the 7 liver tumors that were positive upon transfection contained an activated H-ras gene. The identity of the transforming gene in one of the lung tumors has not been determined but was not a member of the ras family or a met or raf gene. Eleven 1,3-butadiene-induced lymphomas were examined for transforming genes using the nude mouse tumorigenicity assay. Activated K-ras genes were detected in 2 of the 11 lymphomas assayed. DNA sequencing of polymerase chain reaction-amplified ras gene exons revealed that 9 of 11 of the activating K-ras mutations were G to C transversions in codon 13. One liver tumor contained an activated K-ras gene with mutations in both codons 60 and 61. The activating mutation in one of the K-ras genes from a lymphoma was not identified but DNA sequence analysis of amplified regions in proximity to codons 12, 13, and 61 demonstrated that the mutation was not located in or near these codons. Activation of K-ras genes by codon 13 mutations has not been found in any lung or liver tumors or lymphomas from untreated B6C3F1 mice. Thus, the K-ras activation found in 1,3-butadiene-induced B6C3F1 mouse tumors probably occurred as a result of genotoxic effects of this chemical. The oncogenes most frequently detected in human pulmonary adenocarcinomas are K-ras genes. Activated K-ras genes have also been found in some human lymphomas. This suggest that activation of K-ras may be important in the induction of human pulmonary adenocarcinomas and lymphomas.(ABSTRACT TRUNCATED AT 400 WORDS)

Dose-response relationships in promotion of rat hepatocarcinogenesis by 17 alpha-ethinylestradiol

One of the critical issues in risk assessment for chemical carcinogens is the evaluation of dose-response relationships for tumor promoters. In the studies reported here we have systematically investigated dose-response relationships for the liver tumor-promoting actions of 17 alpha-Ethinylestradiol (EE2) following a single injection of diethylnitrosamine (200 mg/kg) to ovariectomized female rats. Parameters measured included tumor incidence, gamma-glutamyltranspeptidase (GGT) positive foci, serum prolactin and serum EE2. The length of tumor promotion ranged from 30 to 60 wk. Results showed a linear increase in GGT-positive foci between doses of 16 and 90 micrograms EE2 kg/d for 30 wk. This was associated with corresponding increases in liver tumor incidence at 60 wk. Seventy-five percent of the animals had either hepatocellular adenoma or hepatocellular carcinoma in the group promoted with 90 micrograms EE2/kg for 60 wk. No liver tumors were evident in either controls or animals receiving estrogen only. Serum prolactin concentrations were elevated in all estrogen-treated groups. In summary, our studies have evaluated dose-response relationships for GGT-positive foci and tumor incidence in a two-stage model for hepatocarcinogenesis using EE2 as the promoting agent.

Quantitative stereological analysis of the effects of age and sex on multistage hepatocarcinogenesis in the rat by use of four cytochemical markers

Altered hepatic foci (AHF) were analyzed by quantitative stereology on frozen serial sections stained sequentially for gamma-glutamyltranspeptidase (GGT), canalicular adenosine triphosphate (ATPase), glucose-6-phosphatase (G6Pase), and the placental isoenzyme of glutathione S-transferase (GST). Livers for these analyses were obtained from both male and female rats of different ages which had been subjected to initiation with a nonnecrogenic dose of diethylnitrosamine following a 70% partial hepatectomy with subsequent phenobarbital (PB) feeding. Different combinations of these four marker alterations (from single marker to four-marker combinations) were used to analyze the data, and the results were compared for their ability to detect AHF. In rats on the above protocol, GST was the single most effective marker, exhibiting a high sensitivity for scoring both number and volume of foci. There was a high degree of overlap with GGT. The combination of the four different markers, GST/GGT/ATPase/G6Pase, scored 80% more foci in number and 60% more in volume than the routinely used GGT/ATPase/G6Pase method. When all four markers were used to score AHF, PB promotion was equally effective in both sexes at weaning and at 6 months of age, but at 1 year of age males showed a dramatic reduction in the effectiveness of PB as a promoting agent, both for number and volume percentage of liver occupied by AHF. On the other hand, initiation was more effective in the male at weaning and at 6 months of age, although by the 12-month point no distinction between the sexes could be made. When only GGT was used as a marker, promotion by PB appeared to be markedly less effective in males than in females at all ages. In the absence of PB administration, both the number and volume fraction of AHF in the livers of both males and female increased with age. Likewise, both the number of AHF per liver and their volume fractions increased with age in both sexes when uninitiated animals were fed PB, although only after a 6-month lag in females. These experiments demonstrate that the stages of initiation and promotion in hepatocarcinogenesis in the rat as monitored by the number and volume percentage occupied of AHF are altered by both the age and the sex of the animal. The combination of GGT and GST identified all AHF scored by the GST/GGT/ATPase/G6Pase set of markers and thus may be the most efficient combination of markers of AHF resulting from promotion by PB.

Quantitative stereologic study of the effects of varying the time between initiation and promotion on four histochemical markers in rat liver during hepatocarcinogenesis

The effects of varying the interval of time between initiation with diethylnitrosamine (DEN) and promotion by phenobarbital (PB) on the development of altered hepatic foci (AHF) and hepatomas in female Fischer 344 rats was investigated. The intervals between DEN initiation after a 70% partial hepatectomy and a subsequent 6 month period of promotion by feeding of PB were 1 day, 1 week, 1 month, 2 months, 6 months and 11 months. The number and volume percentage occupied by AHF were determined by quantitative stereologic methods on serial frozen sections stained for the markers gamma-glutamyltranspeptidase (GGT), canalicular adenosine triphosphatase (ATPase), glucose-6-phosphatase (G6Pase) and the placental form of glutathione S-transferase (GST-pi). The number of AHF was greatest when the initiation-promotion interval was only 1 day, and there was a tendency for the number of AHF to decrease as the interval between initiation with DEN and the start of PB promotion was extended. An 11 month delay between initiation and promotion resulted in only 20% fewer AHF than when promotion was begun 1 day after initiation. On the other hand, the volume percentage fraction of AHF did not change when the initiation-promotion interval was increased from 1 day to 2 months. An interval of 6 months roughly doubled the volume percentage fraction, but an interval of 11 months led to a 7- to 8-fold increase in the volume percentage of AHF over that from a 1 day interval. The phenotypic distribution of AHF was significantly lower in relation to certain markers, especially GGT and GST-pi, in those animals only initiated with DEN compared with those initiated with DEN and promoted with PB. When no exogenous promotion was given, there was still a nearly linear increase in both the number and volume percentage occupied by AHF in the liver of rats initiated with DEN. On the other hand, rats subjected to a 1 week interval between DEN initiation and PB promotion exhibited the greatest number of hepatocellular carcinomas 14 months after initiation, compared with other groups. These studies demonstrated a gradually decreasing effectiveness of PB as a promoting agent to stimulate the growth of all AHF initiated by DEN as the interval between initiation and promotion was extended.(ABSTRACT TRUNCATED AT 400 WORDS)

Critical parameters in the quantitation of the stages of initiation, promotion, and progression in one model of hepatocarcinogenesis in the rat

Critical parameters in the quantitation of altered hepatic foci (AHF) developing during multistage hepatocarcinogenesis in the rat include: 1) the enumeration of AHF induced by test agents as well as those AHF occurring spontaneously in livers of untreated animals; 2) the volume percentage or fraction of the liver occupied by all AHF as a reflection of the total number of altered cells within the liver and the degree of tumor promotion which has occurred; and 3) the phenotype of individual AHF as determined by multiple markers with serial sections. These parameters, especially the number of AHF, should be corrected by the presence of spontaneous AHF which increase with the age of the animal, more so in males than females. While accurate estimation of the background level of spontaneous AHF can be important in demonstrating that a carcinogenic agent does not possess the ability to increase the numbers of AHF above the background level, a better method to distinguish the effectiveness and relative potencies of agents as initiators or promoters is reviewed. The relative effectiveness of four different markers--gamma-glutamyltranspeptidase (GGT), a placental form of glutathione S-transferase (GST), canalicular ATPase, and glucose 6-phosphatase (G6Pase)--was described for the chemicals C.I. Solvent Yellow 14 and chlorendic acid as promoting agents in males and females. C.I. Solvent Yellow 14 is a more effective promoting agent in females than males, and AHF exhibit extremely low numbers scored by GGT. On the other hand, the numbers of AHF present in livers of male rats promoted by this agent are more than twice those seen in livers of female animals, possibly owing to the effectiveness of this agent as an initiator in the male but not the female. Very few AHF, especially in the male, are scored by GGT during chlorendic acid promotion. The distribution of phenotypes with these markers also differs in the spontaneous AHF appearing in the livers of animals fed 0.05% phenobarbital on either a crude NIH-07 or AIN-76 purified diet. Such studies emphasize the extreme dependence of the promoting stage of hepatocarcinogenesis on environmental factors of sex, diet, and the molecular nature of the promoting agent itself. The hallmark of the final stage of progression in the development of hepatocellular carcinomas is aneuploidy, which may be reflected by phenotypic heterogeneity within individual AHF, termed foci-in-foci. The implications of such quantitative analyses during hepatocarcinogenesis induced by specific agents in relation to the specific action of the agent at one or more of the stages of hepatocarcinogenesis are discussed.

Functional hepatocellular heterogeneity determined by the hepatotoxins allyl alcohol and bromobenzene in immature and adult Fischer 344 rats

Adult (male, 75-90 days old) and immature rats (both sexes, 11-12 days old) were treated with allyl alcohol or bromobenzene to induce periportal or centrilobular hepatic injury, respectively. Histologically confirmed liver lesions were produced in adult rats with both treatments. In adult rats, allyl alcohol decreased hepatic cytochrome P-450, benzphetamine N-demethylation, and ethoxyresorufin O-deethylation activities all by about 30%, whereas bromobenzene influenced these parameters differently: cytochrome P-450 was lowered by 55%, benzphetamine N-demethylation by 80%, and ethoxyresorufin O-deethylation by 90%. Cytochrome c reductase, 5'-nucleotidase, glucose-6-phosphatase, and glutamate-pyruvate transaminase activities were not significantly influenced. In immature rats, allyl alcohol did not produce histopathological alterations in liver, but did lower both cytochrome P-450 concentration (30%) and ethoxyresorufin O-deethylation (75%). Benzphetamine N-demethylation was not significantly affected. Bromobenzene produced typical centrilobular liver damage and a decrease of both cytochrome P-450 (20%) and ethoxyresorufin O-deethylation (50%). Benzphetamine N-demethylation was increased slightly, but not significantly. The differences in effects of the two hepatotoxins in adult vs immature rats seem to indicate that the hepatocellular heterogeneity of xenobiotic metabolism which is seen in adult liver (perivenous vs periportal areas) is not well developed in the immature animal.

Animal models for the study of dietary factors and cancer of the large bowel

Studies in metabolic epidemiology have shown a strong association between dietary fat intake, level of fecal anaerobic bacteria, fecal acid, and neutral sterols and the risk of colon cancer among different populations. Current concepts visualize that colonic bile acids and cholesterol metabolites play a modifying role in large bowel carcinogenesis, that these compounds are derived from dietary factors (directly or indirectly), and that they subsequently are modified by the intestinal bacteria. In the animal model, 2 bile acids (lithocholic and taurodeoxycholic) acted as colon tumor promoters. Rats fed a high-fat diet were more susceptible to colon tumor induction by 1,2-dimethylhydrazine compared to animals fed a normal-fat diet. The intestinal microflora also played a modifying role in enhancing colon tumor production by 1,2-dimethylhydrazine.

A study of tobacco carcinogenesis. XIV. Effects of N'-nitrosonornicotine and N'-nitrosonanabasine in rats

N'-Nitrosonornicotine (NNN) and N'-nitrosoanabasine (NAB) were synthesized and administered in drinking water to male Fischer rats for 30 weeks (total dose, 630 mg). 1,4-Dinitrosopiperazine (DNPI) served as the positive control. By 11 months, all surviving rats given NNN developed esophageal tumors (12/20); 1 had a pharyngeal tumor and 3 had invasive carcinomas originating in the nasal cavity. During the same time, only 1 of 20 rats given NAB developed esophageal tumors. Compared to the strong esophageal carcinogen DNPI, NNN was a moderately active and NAB a weak carcinogen. NNN (0.3-90 parts per million) in chewing tobacco was related to the observation that cancer of the oral cavity and esophagus in man was correlated with the chewing of tobacco.