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C D Davis

Publications and source records attributed to C D Davis.

At least 19 recordsLinked to original sources
PubMed2000

Changes in dietary zinc and copper affect zinc-status indicators of postmenopausal women, notably, extracellular superoxide dismutase and amyloid precursor proteins.

BACKGROUND: Zinc is an essential trace element for human health and well-being; however, methods currently available for the assessment of zinc status in humans are unsatisfactory. OBJECTIVE: The objective was to critically evaluate the use of various indicators of zinc status in humans in a controlled metabolic ward study. DESIGN: Indicators of zinc status were measured in 25 healthy postmenopausal women aged 64.9 +/- 6.7 y. After a 10-d equilibration period, volunteers consumed a diet with either a low (1 mg/d; n = 12) or a high (3 mg/d; n = 13) copper content based on a total energy content of 8.4 MJ. They received the same amount of copper throughout the study. Both groups were fed the basal diet (3 mg Zn/d) with no zinc supplement for one 90-d period, and the diet supplemented with 50 mg Zn/d for another 90-d period. RESULTS: Zinc supplementation significantly increased (P < 0.0001) extracellular but not erythrocyte superoxide dismutase activity. This increase was more apparent when subjects were fed the low-copper diet. Zinc supplementation in combination with the low-copper diet significantly decreased (P < 0.01) amyloid precursor protein expression in platelets. Other indicators of zinc status that were significantly elevated after zinc supplementation were as follows: plasma zinc and free thyroxine concentrations and mononuclear 5'-nucleotidase activity. CONCLUSION: The measurement of serum extracellular superoxide dismutase activity may be useful as a marker for the functional assessment of zinc status in humans.

5'-Nucleotidase↗
PubMed1999

In vivo mutagenicity and hepatocarcinogenicity of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in bitransgenic c-myc/lambda lacZ mice.

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is a mutagenic and carcinogenic heterocyclic amine found in cooked meat. Hepatic DNA adduct formation, in vivo mutagenicity, and hepatocarcinogenicity of MeIQx were examined in mice harboring the lacZ mutation reporter gene (Muta mice) and bitransgenic mice overexpressing the c-myc oncogene. C57Bl/lambda lacZ and bitransgenic c-myc (albumin promoter)/lambda lacZ mice were bred and weaned onto an American Institute of Nutrition-76-based diet containing 0.06% (w/w) MeIQx or onto control diet. After 30 weeks on diet, only male bitransgenic mice on MeIQx developed hepatocellular carcinoma (100% incidence). By 40 weeks, hepatic tumor incidence was 100%/75% (17%/0%) and 44%/17% (0%/0%) in male c-myc/lambda lacZ and C57Bl/lambda lacZ mice who were given MeIQx (or control) diet, respectively, supporting a synergism between MeIQx and c-myc overexpression in hepatocarcinogenesis. At either time point, mutant frequency in the lacZ gene was at least 40-fold higher in MeIQx-treated mice than in control mice of either strain. These findings suggest that MeIQx-induced hepatocarcinogenesis is associated with MeIQx-induced mutations. Elevated mutant frequency in MeIQx-treated mice also occurred concomitant with the formation of MeIQx-guanine adducts, as detected by the 32P-postlabeling assay. Irrespective of strain or diet, sequence analysis of the lacZ mutants from male mouse liver showed that the principal sequence alterations were base substitutions at guanine bases. Adenine mutations, however, were detected only in animals on control diet. MeIQx-fed mice harboring the c-myc oncogene showed a 1.4-2.6-fold higher mutant frequency in the lacZ gene than mice not carrying the transgene. Although there was a trend toward higher adduct levels in c-myc mice, MeIQx-DNA adduct levels were not significantly different between c-myc/lambda lacZ and C57Bl/lambda lacZ mice after 30 weeks on diet. Thus, it seemed that factors in addition to MeIQx-DNA adduct levels, such as the enhanced rate of proliferation associated with c-myc overexpression, may have accounted for a higher mutant frequency in c-myc mice. In the control diet groups, the lacZ mutant frequency was significantly higher in c-myc/lambda lacZ mice than in C57Bl/lambda lacZ mice. The findings are consistent with the notion that c-myc overexpression is associated with an increase in mutagenesis. The mechanism for the synergistic effects of c-myc overexpression on MeIQx hepatocarcinogenicity seems to involve an enhanced expression of MeIQx-induced mutations.

Animals↗
PubMed1999

Dietary selenium reduces the formation of aberrant crypts in rats administered 3,2'-dimethyl-4-aminobiphenyl.

Human epidemiologic studies suggest that low selenium status is associated with increased cancer risk and that selenium supplementation is associated with reduction in the incidence of several cancers, including colorectal cancer. Aromatic and heterocyclic amine carcinogens are thought to be important in the etiology of human colorectal cancer, but no information is available on the effects of selenium on aromatic amine-induced colon cancer. In order to investigate this effect, aberrant crypt foci (ACF), the putative preneoplastic lesions of colon cancer in humans and rodents, were used as a biomarker to test the hypothesis that selenium supplementation can reduce aromatic amine-induced colon carcinogenesis. Male weanling F344 inbred rats were fed a basal torula yeast selenium-deficient diet supplemented with 0, 0.1, or 2. 0 mg selenium/kg diet as selenite, selenate, or selenomethionine (SeMet). Animals were fed the diets for 4 weeks and then administered 1 sc injection/week for 2 weeks of 3, 2'-dimethyl-4-aminobiphenyl (DMABP; 100 mg/kg) or vehicle (peanut oil). At 12 weeks, the rats were euthanized and the colon and rectum were removed, opened longitudinally, and fixed in 70% ethanol. Glutathione peroxidase activities in erythrocytes and liver cytosol and selenium concentrations in the colon/rectum and kidney increased significantly (p < 0.05) and in a dose-dependent manner with each of the three selenium diets. No ACF were identified in vehicle-treated rats. In DMABP-treated rats, ACF frequencies decreased significantly (p < 0.05) in groups supplemented with 0.1 or 2.0 mg selenium/kg diet as selenite and selenate but not SeMet. There were no significant differences in ACF and aberrant crypts between rats fed 0.1 vs 2.0 mg selenium/kg diet. These results suggest that dietary selenium, depending on chemical form, can reduce aromatic amine-induced colon carcinogenesis.

Aminobiphenyl Compounds↗
PubMed1999

Manganese deficiency and toxicity: are high or low dietary amounts of manganese cause for concern?

Manganese is an essential trace element that is required for the activity of several enzymes. Manganese is also quite toxic when ingested in large amounts, such as the inhalation of Mn-laden dust by miners. This review examines Mn intake by way of the food supply and poses the question: Is there reason to be concerned with Mn toxicity or deficiency in free-living populations in North America? Although much remains to be learned of the functions of Mn, at present there are only a few vaguely described cases of Mn deficiency in the medical literature. Given the heterogeneity of the North American food supply, it is difficult to see the possibility of more than greatly isolated and unique instances of Mn deficiency. However, low Mn-dependent superoxide dismutase activity may be associated with cancer susceptibility, and deserves further study. There may be reasons, however, to be concerned about Mn toxicity under some very specialized conditions. Increasing numbers of young people are adopting a vegetarian lifestyle which may greatly increase Mn intake. Iron deficiency may increase Mn absorption and further increase the body-burden of Mn, especially in vegetarians. Mn is eliminated primarily through the bile, and hepatic dysfunction could depress Mn excretion and further contribute to the body burden. Would such a combination of events predispose substantial numbers of people to chronic Mn toxicity? At present, there is no definite proof of this occurring, but given the state of knowledge at the present time, more studies with longer time-frames and more sensitive methods of analysis are needed.

Animals↗
PubMed1999

The chemical form of selenium influences 3,2'-dimethyl-4-aminobiphenyl-DNA adduct formation in rat colon.

There is increasing evidence that selenium can protect against tumorigenesis or preneoplastic lesion development induced by chemical carcinogens. This study examined whether selenite, selenate or selenomethionine would be protective against 3, 2'-dimethyl-4-aminobiphenyl (DMABP)-DNA adduct formation in the liver and colon of rats and sought to delineate the mechanism for the protective effects of the different chemical forms of selenium against aberrant crypt formation, a preneoplastic lesion for colon cancer. After injection of DMABP, two DNA adducts were identified in the liver and colon of rats. Supplementation with either 0.1 or 2.0 mg selenium/kg diet as either selenite or selenate but not selenomethionine resulted in significantly fewer (53-70%; P < 0.05) N-(deoxyguanosin-8-yl)-(deoxyguanosin-8-yl)-3, 2'-dimethyl-4-aminobiphenyl (C8-DMABP)-DNA adducts in the colon but not the liver than in rats fed a selenium-deficient diet. Rats supplemented with selenomethionine had greater (P < 0.05) plasma and liver selenium concentrations and glutathione peroxidase activity than those supplemented with selenite or selenate; however, they also had more DMABP-DNA adducts. The protective effect of selenite and selenate against DMABP-DNA adduct formation apparently is not a result of alterations in plasma or liver selenium concentrations or altered glutathione peroxidase or glutathione transferase activities but may be related to differences in the metabolism of the different forms of selenium.

Aminobiphenyl Compounds↗
PubMed1999

Dietary copper, manganese and iron affect the formation of aberrant crypts in colon of rats administered 3,2'-dimethyl-4-aminobiphenyl.

Aberrant crypt foci (ACF) are preneoplastic lesions for colon cancer. Altered amounts of copper-zinc (CuZnSOD) and manganese (MnSOD) superoxide dismutases have been implicated in multistage carcinogesis of both rodents and humans. Dietary factors are potential modulators of both CuZnSOD and MnSOD activity. The purpose of this study was to investigate the interactive effects of dietary copper, manganese, and iron on 3,2'-dimethyl-4-aminobiphenyl (DMABP)-induced ACF and superoxide dismutase activities in weanling rats fed low or adequate copper (0.8 or 5.1 microg Cu/g diet), low or adequate manganese (0.6 or 17 microg Mn/g diet), and adequate or high iron (37 or 140 microg Fe/g diet). Twelve rats were allowed free access to each of these eight diets for 3.5 wk prior to DMABP administration and for an additional 8 wk after the first DMABP injection. Rats fed low dietary copper had 105% (P < 0.0001) higher formation of DMABP-induced ACF than those fed adequate dietary copper. Rats ingesting low rather than adequate dietary manganese had 23% higher formation of ACF, and rats ingesting high rather than adequate dietary iron had 18% higher formation of ACF. Heart total superoxide dismutase activity was significantly correlated with the number of ACF (r = -0.43, P < 0.0001) in rats administered DMABP. These results suggest that dietary alterations that affect superoxide dismutase activity may affect cancer susceptibility.

Aminobiphenyl Compounds↗
PubMed1999

Antibody response to heat shock proteins and histopathology in mice infected with Trypanosoma cruzi and maintained at elevated temperature.

Highly susceptible C3HeB/FeJ mice survive an otherwise lethal infection with a Brazil strain of Trypanosoma cruzi when held at an elevated environmental temperature of 36 C. The body temperature of these mice has been shown to increase 3-4 C to levels typical of a febrile response. In the present study, the synthesis of parasite heat shock proteins (hsp60, hsp70, and hsp90) was shown to be enhanced at a temperature of 39 C and the results of immunoprecipitation analysis indicated that parasite HSPs are highly immunogenic in T. cruzi-infected mice maintained at 36 C or room temperature (RT). Differences in the histopathology of cardiac and skeletal muscle in C3HeB/FeJ mice maintained at RT or 36 C at different times postinfection also were investigated in this study. The lower numbers of circulating parasites observed in mice maintained at 36 C were correlated with lower levels of tissue parasitism, inflammation, and tissue destruction. Finally, the transfer of infected mice from RT to an environment of 36 C at various times during infection was shown to increase the survival rate of infected mice and also resulted in a dramatic reduction in parasitemia levels. In light of the growing evidence for a beneficial effect of elevated temperature during experimental Chagas' disease, further studies seem warranted to determine if hyperthermia or fever therapy might also be beneficial in the treatment of humans infected with T. cruzi.

Animals↗
PubMed1998

Effect of biliary ligation on manganese accumulation in rat brain.

Neurologic and radiologic disorders have been reported to occur in miners inhaling manganese (Mn)-laden dust and in humans receiving long-term parenteral nutrition. These abnormalities have been attributed to Mn intoxication because of elevated serum Mn concentrations. Because the liver, by way of the bile, is the major route of Mn excretion, it is possible that anything that decreases biliary excretion could increase accumulation of Mn in the brain. The purpose of this study was to determine whether biliary ligation would increase Mn accumulation in the brain of rats that were exposed to deficient or adequate amounts of dietary manganese. The first experiment had a 2 x 3 factorial design, two levels of Mn (0 or 45 microg/g diet) and three surgical treatments (control, sham, or bile-ligation). Animals were sacrificed 10 d after being fed 54Mn. In experiment 2, animals that had a sham operation or bile-ligation were sacrificed at 8 time points after being injected intraportally with 54Mn complexed to albumin. The biliary-ligated animals had a significantly (p < 0.001) smaller percentage of the 54Mn in their brains (when expressed as a percentage of whole animal 54Mn) than the sham-operated animals. Mn deficiency had a similar effect. However, we did observe an increased accumulation of the radioisotope in the brain over time. Therefore, in short-term studies, biliary-ligated rats do not appear to be a good model for Mn accumulation in the brains of people with cholestatic liver disease.

Animals↗
PubMed1998

Proliferation, development and DNA adduct levels in the mammary gland of rats given 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and a high fat diet.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine derived from cooked meat that is a mammary gland carcinogen in rats. A carcinogenic dose-regimen of PhIP (75 mg/kg, p.o., 10 doses, once per day) was administered to 43-day old female Sprague-Dawley rats, and the rats were then placed on a defined high fat (23.5% corn oil) or low fat (5% corn oil) diet for up to 6 weeks. At various times after carcinogen and diet, and prior to carcinogenesis, we examined the percentage of proliferating cells in terminal end bud (TEB) epithelial structures of the rat mammary gland by proliferating cell nuclear antigen staining, mammary gland architecture by whole mounting, and PhIP-DNA adduct levels in mammary epithelial cells by the 32P-post-labeling assay. Immediately after dosing, the percentage of proliferating epithelial cells in TEBs was significantly higher in PhIP-treated rats than in control rats receiving vehicle only [7.5 +/- 0.9% (n = 99) versus 4.2 +/- 0.6% (n = 127), respectively]. The mammary glands of PhIP-treated rats showed a significantly lower density of alveolar buds (ABs) and a higher density of TEBs than control rats, which suggests that PhIP exposure partially inhibited the normal glandular differentiation of TEBs to ABs. After 6 weeks on the diet, proliferation in TEBs was statistically higher in rats given PhIP plus a high fat diet than in rats given vehicle plus a low fat diet. The mammary glands from rats on a high fat diet also showed a statistically higher density of TEBs when compared with rats on a low fat diet [2.08 +/- 0.34% versus 1.04 +/- 0.20%, respectively (n = 6)]. PhIP-DNA adduct levels were relatively high in mammary epithelial cells of treated rats. At 3 h after the last dose of PhIP, DNA adduct levels [relative adduct labeling (RAL) x 10(7), mean +/- SE] were 10.5 +/- 1.7 (n = 8) and 0.9 +/- 0.2 (n = 7) in epithelial cells isolated from mammary gland and in the liver, respectively. DNA adduct removal rates from the mammary gland were not different between rats on the high fat and low fat diets. Adducts were still detected after 6 weeks on either diet. Thus, events that occurred prior to neoplasia in the mammary glands of PhIP-treated rats include formation of PhIP-DNA adducts at relatively high levels, and enhanced proliferation in TEBs (putative sites of origin of mammary gland carcinomas) and partial inhibition of TEB differentiation. The high fat diet, a promoter of PhIP-induced mammary gland carcinogenesis, appeared to sustain the proliferative effect of PhIP in mammary gland TEBs at a time when PhIP-DNA adducts are still detectable. These early events may contribute to the targeting and carcinogenicity of PhIP to the mammary gland of rats.

Animals↗
PubMed1998

Beneficial effect of selenium supplementation during murine infection with Trypanosoma cruzi.

Selenium (Se) has been shown to function as an antioxidant that may enhance immunity during microbial infection. To investigate the effect of elevated levels of Se on the course of experimental Chagas' disease, 5 groups of C3HeB/FeJ mice were infected with 10(3) bloodform trypomastigotes of a Brazil strain of Trypanosoma cruzi while receiving supplements of 0 ppm, 2 ppm, 4 ppm, 8 ppm, or 16 ppm Se as sodium selenate in drinking water. After 64 days of infection, survival ranged from 0 to 60%, with groups receiving 4 ppm and 8 ppm Se exhibiting 60% survival and the group without Se exhibiting 0% survival. In addition, parasitemia levels of mice supplemented with Se were significantly lower (P<0.01) than in nonsupplemented mice. The results of the present study suggest that Se supplementation does have a beneficial effect during murine infection with T. cruzi, resulting in decreased parasitemias and increased longevity.

Animals↗
PubMed1997

Metabolism of food-derived heterocyclic amines in nonhuman primates.

During the cooking of meats, several highly mutagenic heterocyclic amines (HCAs) are produced. Three HCAs, IQ, MeIQx, and PhIP have been under study for carcinogenicity in cynomolgus monkeys, and to date, IQ has been shown to be a potent hepatocarcinogen. Concomitantly, the metabolic processing of these HCAs has been examined. Metabolism studies show that the potent hepatocarcinogenicity of IQ is associated with the in vivo metabolic activation of IQ via N-hydroxylation and the formation of DNA adducts. In monkeys undergoing carcinogen bioassay with IQ, N-hydroxylation was confirmed by the presence of the N-hydroxy-N-glucuronide conjugate of IQ in urine. The N-hydroxylation of IQ appears to be carried out largely by hepatic CYP3A4 and/or CYP2C9/10, and not by CYP1A2, an isoform not expressed in liver of this species. Notably MeIQx is poorly activated in cynomolgus monkeys and lacks the potency of IQ to induce hepatocellular carcinoma after a 5-year dosing period. The poor activation of MeIQx appears to be due to the lack of constitutive expression of CYP1A2 and an inability of other cytochromes P450, such as CYP3A4 and CYP2C9/10, to N-hydroxylate the quinoxalines. MeIQx is detoxified in monkeys largely by conjugation with glucuronide at the N-1 position. Although the carcinogenicity of PhIP is not yet known, the metabolic data suggest that PhIP will be carcinogenic in this species. PhIP is metabolically activated in vivo in monkeys by N-hydroxylation, as discerned by the presence of the N-hydroxy-N-glucuronide conjugate in urine, bile, and plasma. PhIP also produces DNA adducts that are widely distributed in tissues. The results from these studies support the importance of N-hydroxylation in the carcinogenicity of HCAs in nonhuman primates and by analogy, the importance of this metabolic activation step in the possible carcinogenicity of dietary HCAs in humans.

Amines↗
PubMed1997

Bioactivation and inactivation of aflatoxin B1 by human, mouse and rat liver preparations: effect on SCE in human mononuclear leucocytes.

The purpose of this study was to investigate the use of human and animal subcellular liver fractions in an in vitro evaluation of carcinogenic risk. The bioactivation and bioinactivation of the known genotoxic carcinogen aflatoxin B1 by human, mouse and rat liver preparations was investigated using the SCE assay in human lymphocytes as a genotoxic endpoint. There was a 10-fold variation in SCE response (1.1-11.6 SCE/Cell) in human mononuclear leucocytes (MNLs) after aflatoxin B1 was activated by human liver microsomes (n = 6). Activation correlated with the CYP1A2 phenotype of livers (r = 0.8; p < 0.05), but there was no correlation with either GST M1 genotype or epoxide hydrolase phenotype. Mouse liver microsomes activated aflatoxin B1 to a greater extent [(1 micro M) 12.8 +/- 2.51 SCE/Cell] than either rat [(10 micro M) 12.0 +/- 3.84 SCE/Cell or human (L25) [(10 micro M) 8.8 +/- 2.00 SCE/Cell liver microsomes. The addition of mouse liver cytosol and reduced glutathione (GSH) significantly (p < 0.001) reduced aflatoxin B1-dependent genotoxicity, whereas the addition of either human or rat cytosol (+GSH) was without effect. These data indicate that species variation in both bioactivation and bioinactivation can exist. Therefore there is a necessity for careful selection of activation systems from species whose biochemical profile reflects that of man.

Aflatoxin B1↗
PubMed1997

Hepatic tumor induction in c-myc mono-transgenic and TGF-alpha/c-myc double-transgenic mice.

Double transgenic mice bearing fusion genes consisting of mouse albumin enhancer/promoter-mouse c-myc cDNA and mouse metallothionein 1 promoter-human TGF-alpha cDNA were generated to investigate the interaction of these genes in hepatic oncogenesis and to provide a general paradigm for characterizing both the interaction of nuclear oncogenes and growth factors in tumorigenesis as well as to produce an experimental model to test how environmental chemicals might interact with these genes during the neoplastic process. Coexpression of c-myc and TGF-alpha as transgenes in the mouse liver resulted in a tremendous acceleration of neoplastic development in this organ as compared to expression of either of these transgenes alone. The two distinct cellular reactions that occurred in the liver of the double transgenic mice prior to the appearance of liver tumors were dysplastic and apoptotic changes in the existing hepatocytes followed by emergence of multiple focal lesions composed of both hyperplastic and dysplastic cell populations. These observations suggest that the interaction of c-myc and TGF-alpha, during development of hepatic neoplasia contributes to the selection and expansion of the preneoplastic cell populations which consequently increases the probability of malignant conversion. Treatment of the double transgenic mice with both genotoxic agents such as diethylnitrosamine and IQ as well as the tumor promoter phenobarbital greatly accelerated the neoplastic process. These results suggest that selective transgenic mouse models may provide important tools for testing both the carcinogenic potential of environmental chemicals and the interaction/cooperation of these compounds with specific genes during the neoplastic process.

Animals↗
PubMed1996

Characterisation of the toxic metabolite(s) of naphthalene.

The toxicity of naphthalene and its metabolites has been investigated in vitro. Both naphthalene and its metabolite 1-naphthol were bioactivated by human hepatic microsomes to metabolite(s) which were toxic to mononuclear leucocytes (MNL). However 1-naphthol was more cytotoxic than naphthalene (49.8 +/- 13.9% vs. 19.0 +/- 10.0% cell death; P < 0.01), indicating that the toxicity of naphthalene is dependent on the bioactivation of 1-naphthol. CYP2E1-induced rat liver microsomes increased metabolism of naphthalene by 13% compared to control microsomes with a concomitant increase in both 1-naphthol and dihydrodiol formation. The cytotoxicity of naphthalene but not of 1-naphthol was increased by CYP2E1 induction, indicating that separate enzymes are involved in the bioactivation of 1-naphthol. The metabolites of 1-naphthol, 1,2-naphthoquinone (51.4 +/- 6.6% cell death) and 1,4-naphthoquinone (49.1 +/- 3.4% cell death) were directly toxic to MNL and depleted glutathione to 1.0% of the control levels. Both quinones were also genotoxic to human lymphocytes. In contrast, the primary metabolite of naphthalene, the 1,2-epoxide (0-100 microM) was neither cytotoxic nor genotoxic, and did not deplete glutathione. In conclusion, our data suggests that the cytotoxicity and genotoxicity of naphthalene is associated with the formation of quinones from 1-naphthol rather than naphthalene-1,2-epoxide.

Adult↗
PubMed1996

In vivo mutagenicity and DNA adduct levels of heterocyclic amines in Muta mice and c-myc/lacZ double transgenic mice.

The cooked meat derived heterocyclic amines (HCAs) 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-9H-pyrido[2,3-b]indole (A alpha C) are established mutagens in the Salmonella assay and hepatocarcinogens in mice. The current study uses transgenic mice to examine hepatic HCA-DNA adduct formation and mutagenesis in vivo and the impact of hepatic overexpression of the c-myc oncogene on HCA-induced mutagenesis. C57B1/lacZ and c-myc/lacZ mice strains, produced by crossbreeding Muta Mice (carrying the lacZ mutation target gene) with either C57B1 control or c-myc transgenic mice, respectively, were treated with 10 daily doses of IQ, MelQx or A alpha C (20 micrograms/g, p.o.). Four weeks after dosing, the frequency of mutations in the lacZ gene in liver of either C57B1/lacZ or c-myc/lacZ mice was significantly higher in mice treated with any one of the three HCAs than in mice given vehicle only. In addition, all three HCAs formed hepatic DNA adducts, as measured by the 32P-postlabeling analysis 24 h after dosing. In both strains of mice, hepatic DNA adduct levels were 2-3-fold higher with A alpha C than with either IQ or MeIQx, although the mutant frequencies in the lacZ gene were 30-40% lower in mice dosed with A alpha C. These results suggest that A alpha C-DNA adducts may be less mutagenic in vivo than either IQ- or MeIQx-DNA adducts. The lacZ mutant frequencies observed with all three HCAs appeared to be influenced by c-myc transgene expression: after HCA treatment, transgenic mice carrying the c-myc gene showed a 30-40% higher lacZ mutant frequency than mice not carrying this transgene. Notably, lacZ mutant frequencies were not different among C57B1/lacZ and c-myc/lacZ mice that received vehicle control. DNA adduct studies showed that the levels of IQ- and MeIQx-DNA adducts were 2-3-fold higher in c-myc/lacZ mice than in C57B1/lacZ mice; however, A alpha C DNA adducts were not statistically different between the two strains. In addition, phase 1 metabolic activation of these HCAs, as assessed by hepatic microsomal mutagenic activation, was also similar in both strains of mice. These results support the notion that overexpression of the c-myc oncogene cooperates with the HCAs to enhance in vivo mutagenicity. Further studies are needed to assess the mechanisms of this cooperative effect.

Animals↗
PubMed1996

N-acetyltransferase expression and metabolic activation of the food-derived heterocyclic amines in the human mammary gland.

The heterocyclic amines (HCAs) found in cooked meat are procarcinogens that are metabolically activated by N-hydroxylation followed by O-acetylation by the N-acetyltransferases NAT1 and NAT2. Despite the importance of metabolic activation in HCA carcinogenicity and the finding that several HCAs are rodent mammary gland carcinogens, nothing was known about O-acetylation activity in the human mammary gland. The current study examines the expression and catalytic activity of NAT toward the N-hydroxy-HCAs 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP) and 2-hydroxy-amino-3-methylimidazo[4,5-f]quinoline (N-hydroxy-IQ) in the human mammary gland. Mammary gland cytosol from 10 women and lysates from a primary culture of human mammary epithelial cells metabolically activated 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-hydroxyamino-3-methylimidazo[4,5-f]quinoline by NAT-mediated 0-acetyltransferase, as measured by the acetyl CoA-enhanced binding of the N-hydroxylamines to calf thymus DNA in vitro. N-acetylation of p-aminosalicylic, an activity specific to NAT1, but not N-acetylation of sulfamethazine, an activity specific to NAT2, was detected in the mammary gland cytosols and human mammary epithelial cell lysates. Immunohistochemical analysis of human mammary gland sections showed positive staining for NAT1 protein in the epithelial cells lining the mammary gland ducts. Reverse transcription-PCR analysis showed that mRNA transcripts for both NAT1 and NAT2 were present in human mammary gland; however, no NAT2 catalytic activity was detectable. Our data demonstrate for the first time that the human mammary gland is catalytically active toward the metabolic activation of HCA food mutagens, and that this activity is most likely contributed by NAT1 expressed in the ductular epithelial cells of the mammary gland.

Acetylation↗
PubMed1996

Ahr locus phenotype in congenic mice influences hepatic and pulmonary DNA adduct levels of 2-amino-3-methylimidazo[4,5-f]quinoline in the absence of cytochrome P450 induction.

The potent food mutagen/carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) undergoes metabolic N-hydroxylation by cytochromes P450, including cytochrome P450 1A2, followed by generation of an unstable ester catalyzed by acetyltransferases; promutagenic DNA adducts result. Genetic polymorphisms in these enzymes have been implicated in human cancer risk related to arylamine exposure. We investigated the effects of Ahr locus and acetylator polymorphisms on 32P-postlabeled IQ/DNA adducts in lungs and livers of female C57BL/6 mice congenic for slow acetylation and/or Ahr-nonresponsiveness; some groups were pretreated with beta-naphthoflavone (beta NF), a cytochrome P450 1A inducer. Total adducts in lung were doubled by beta NF pretreatment in Ahr-responsive mice only and consisted of < or = 30% adduct 2 and < or = 60% adduct 3. In contrast, in Ahr-nonresponsive mice, adducts 2 and 3 were each < or= 7% of the total. Livers of noninduced Ahr-responsive mice formed 6-18-fold more adducts than those of nonresponsive mice. This striking difference was not due to altered levels of cyp1a-2, as indicated by specific enzyme assays and immunoblotting, and was not accompanied by a comparable increase in the ability of liver preparations to activate IQ to a mutagen in the Ames test. Pretreatment of responsive mice with beta NF to induce cyp1a-1 and cyp1a-2 led to a reduction in liver adduct levels. Acetylation phenotype also had a significant effect in Ahr-responsive mice, with 3-fold more adducts in slow than in rapid acetylators. These results indicate that in uninduced mice, the normal Ah receptor facilitates formation of IQ/DNA adducts in liver and alters the profile of adducts in lung, via an unknown mechanism, whereas the Ah receptor-dependent enzyme induction reduces adducts in liver, probably due to increased detoxification, but increases them in lung.

Acetylation↗