Prevention of chemically induced mammary tumorigenesis by daidzein in pre-pubertal rats: the role of peroxidative damage and antioxidative enzymes

Isoflavones are biologically active plant derived compounds that have several health promoting effects. In the present study hitherto unknown effects of one of the well known isoflavonoids, daidzein, has been evaluated on its chemo-preventive action against breast cancers in pre-pubertal rats. Either daidzein (500 μg/g bwt) or vehicle, dimethyl sulphoxide (DMSO), was administered at 16th, 18th, and 20th day post-partum and the chemopreventive efficacy was evaluated in dimethylbenz[a]nthracene (DMBA) induced Sprague-Dawley rats, at 50th day. To elucidate the mechanism of action, the antioxidative status was also examined in the liver and mammary gland of prebubertal rats using two different doses of daidzein (0.5 mg/kg bwt and 50 mg/kg bwt, p.o.) for 10 days. The specific activity of antioxidant enzymes as well as reduced glutathione (GSH) level and peroxidative damage were evaluated spectrophotometrically, both in liver as well as in mammary gland. Animals treated with daidzein pre-pubertally, showed a significant reduction in the tumorigenesis of mammary gland up to 37.4% as compared to animals induced for tumors with DMBA. In animals treated with 50 mg/kg of daidzein, a significant increase in the specific activities of the antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione transferase (GST), DT-diaphorase (DTD), and in GSH content were observed in both liver and mammary gland. Expectedly, the specific activity of lactate dehydrogenase (LDH) and level of peroxidative damage was decreased, as compared to that of control group of animals. Our results suggest that, daidzein can be considered as a potent chemopreventive agent against mammary carcinogenesis in pre-pubertal animals, with modulation of antioxidant enzymes being one of its mechanisms of actions.     

Extrapolation of the relative risk of radiogenic neoplasms across mouse strains and to man

We have examined two interrelated questions: is the susceptibility for radiogenic cancer related to the natural incidence, and are the responses of cancer induction by radiation described better by an absolute or a relative risk model. Also, we have examined whether it is possible to extrapolate relative risk estimates across species, from mice to humans. The answers to these questions were obtained from determinations of risk estimates for nine neoplasms in female and male C3Hf/Bd and C57BL/6 Bd mice and from data obtained from previous experiments with female BALB/c Bd and RFM mice. The mice were exposed to 137Cs gamma rays at 0.4 Gy/min to doses of 0, 0.5, 1.0, or 2.0 Gy. When tumors that were considered the cause of death were examined, both the control and induced mortality rates for the various tumors varied considerably among sexes and strains. The results suggest that in general susceptibility is determined by the control incidence. The relative risk model was significantly superior in five of the tumor types: lung, breast, liver, ovary, and adrenal. Both models appeared to fit myeloid leukemia and Harderian gland tumors, and neither provided good fits for thymic lymphoma and reticulum cell sarcoma. When risk estimates of radiation-induced tumors in humans and mice were compared, it was found that the relative risk estimates for lung, breast, and leukemia were not significantly different between humans and mice. In the case of liver tumors, mice had a higher risk than humans. These results indicate that the relative risk model is the appropriate approach for risk estimation for a number of tumors. The apparent concordance of relative risk estimates between humans and mice for the small number of cancers examined encourages us to undertake further studies.     

Studies on the immunological cross-reactivity and physical properties of fatty acid synthetases

Fatty acid synthetase enzymes were purified from the liver, mammary gland, and adipose tissue of rats and the liver and mammary gland of mice. The enzymes from the liver and mammary gland of the same species have similar molecular weights and and dissociate into subunits at comparable rates.Rabbit antisera were prepared against the fatty acid synthetase from the lactating rat mammary gland. Cross-reactivity between different fatty acid synthetases was determined by immunodiffusion and immunoprecipitin tests. No differences in immunological cross-reactivity could be detected in liver, mammary gland, and adipose enzymes from the same species; fatty acid synthetases from the rat and mouse gave reactions of incomplete identity. Partially purified fatty acid synthetases from pigeon liver and rabbit mammary gland did not react with the antiserum.It is concluded that the immunochemical approach is useful in determining the degree of resemblance between fatty acid synthetases from different species. Within a given species, the liver and mammary gland fatty acid synthetases seem to be very similar, if not identical, proteins.     

Methylation and amplification of mouse mammary tumor virus DNA in normal, premalignant, and malignant cells of GR/A mice.

The methylation and amplification of mouse mammary tumor virus (MuMTV) proviral DNA was investigated in normal, premalignant, and malignant tissues of GR/A mice. The proviral methylation pattern was examined with the restriction enzyme HhaI, which fails to cleave methylated DNA. MuMTV proviral DNA from liver, kidney, and heart was highly methylated. Proviral DNA was somewhat undermethylated in mammary gland cells from virgin and lactating mice and extensively undermethylated in cells from premalignant outgrowths, pregnancy-dependent tumors, and pregnancy-independent tumors. The restriction enzyme SacI was used to detect additional proviruses in the same cells. No additional proviral copies of MuMTV were detected in liver, kidney, or heart cells or in mammary gland cells from virgin mice. Some mammary gland cells from lactating mice appeared to contain additional copies of the endogenous, highly oncogenic GT-MTV-2 provirus. Premalignant outgrowth, pregnancy-dependent tumor, and pregnancy-independent tumor cells contained an average of two to three additional copies per cell of the GT-MTV-2 provirus. Thus, neoplasia in GR/A mice was directly associated with quantized increases in MuMTV proviral DNA undermethylation and GR-MTV-2 proviral DNA amplification. Restriction enzyme analysis suggested that premalignant outgrowths and pregnancy-dependent tumors both consisted largely of heterogenous cell populations, although some evidence of clonal dominance was detected.     

Involvement of hepatocyte growth factor on hepatocarcinogenesis induced by peroxisome proliferators

Hepatocyte growth factor (HGF) has been known to enhance the growth of normal hepatocytes, but also to inhibit the growth of neoplastic cells. This article examines the involvement of HGF in the hepatocarcinogenesis caused by peroxisome proliferators (PPs). Up to 78 wk after male F-344 rats were orally given (4-chloro-6-[2,3-xylidino]-2-pyrimidinylthio) acetic acid (Wy-14,643), the hepatocarcinomas and (pre)neoplastic nodules in the livers were observed. At that time, the content of HGF and the expression of HGF mRNA in the liver tumors were significantly decreased. These changes were observed also in the liver of rats treated with other PPs, such as dehydroepiandrosterone and di(2-ethylhexyl)phthalate, but were not observed in tumors induced by genotoxic carcinogens (diethylnitrosamine-phenobarbital). In in vivo experiments, the formation of preneoplastic lesions and the tumors caused by Wy-14,643 administration were markedly suppressed by iv-injection of HGF in a dose-dependent manner. In the colony assay using (pre)neoplastic cells from livers of Wy-14,643-treated rats, HGF inhibited the colony formation of (pre)neoplastic cells in a dose-dependent manner. These findings may indicate that decreases in hepatic HGF levels are common and specific events induced by PPs, but not by genotoxic carcinogens, and that those changes play an important role in the promotion of neoplastic or preneoplastic cell growth induced by PPs.     

Elevated serum calcium concentrations in mammary tumor bearing C3H/Fg mice without bony metastases

Sera from eight adult C3H/Fg mice bearing spontaneous mammary gland tumors were analyzed for calcium content in two successive weekly samples. The sera from six mice were fount to have significantly elevated serum calcium concentrations while sera from two were normocalcemic. Intramuscular implantation of mammary gland tumors into 12, 3-month-old female C3H/Fg mice resulted in significant and progressive increases in serum calcium concentrations over a 4-week period. Subcutaneous implants had a similar effect, but gave less consistent results. These data supported the hypothesis that mammary gland tumors are capable of inducing elevated serum calcium concentrations in C3H/Fg mice. It was concluded that low grade elevation of serum calcium occasionally seen in adult female C3H/Fg mice may be caused by incipient mammary gland tumors.     

The role of IL-12 in the control of MCMV is fundamentally different in mice with a retroviral immunodeficiency syndrome (MAIDS)

The present study investigates the susceptibility of C57BL mice exhibiting T cell immunodeficiency and lymphadenopathy induced by LP-BM5 murine leukaemia virus (MAIDS) to murine cytomegalovirus (MCMV). Treatment of normal (M-) mice with anti-IL-12 increased the contribution of IgG1 to the hypergammaglobulinaemia induced by MCMV, consistent with a shift towards a Th2 phenotype. This impaired control of early MCMV replication in the liver, with little effect in the spleen. Control of hepatic infection correlated with a vigorous splenic NK cytotoxic response in a subgroup of IL-12-depleted M- mice that remained healthy, while others became moribund. Mortality in IL-12-depleted MAIDS (M+) mice given MCMV was ultimately greater than in M- controls, but was delayed despite high levels of MCMV in the liver. IL-12 was required for optimal control of MCMV replication in M+ mice. This may involve cytotoxic activity because similar levels of infection were seen in bg/bg M+ mice, where the beige mutation impairs the formation of cytotoxic granules. Hence the ability of M+ mice to tolerate high titres of MCMV during acute infection may enable innate cytotoxic responses to clear MCMV. Interleukin-12 depletion of M- mice also increased salivary gland MCMV titres and depressed delayed-type hypersensitivity responses to MCMV antigen, normally mediated by CD4+ T cells. These changes were not observed in IL-12-depleted M+ mice.     

Effects of soy oil on murine salivary tumorigenesis

Dietary fat influences dimethylbenzanthracene (DMBA)-induced tumorigenesis of several organs, including the salivary glands. There is not enough evidence to suggest that soy oil could also affect growth of salivary tumors. The main purpose of this work therefore was to study the effects of dietary soy oil on macroscopic parameters of chemically induced murine salivary gland tumors. Eighty BALB/c male mice were assigned to four groups: soy oil (SO), corn oil (CO, control), fish oil (FO) and olein (O). Two weeks later, tumors were induced by 9,10-dimethyl-1,2-benzanthracene (DMBA). At the 13th post-injection week, the animals were sacrificed. In vivo tumor diameter, gland volume (total resected mass), tumor volume (microscopically measured), tumor remission and tumor histopathology were analyzed. The initial in vivo tumor diameter, gland and tumor volume were significantly greater in soy oil than in fish oil group. 26.7% of animals on the soy oil diet showed tumor remission. Sarcomas were more often found in the SO group, carcinomas in FO and the mixed-type tumors both in SO and CO groups. This study shows that the soy oil treatment resulted in larger tumors, some of which later became undetectable. It is necessary to further investigate these divergent results.     

Augmented efficacy of tamoxifen in rat breast tumorigenesis when gavaged along with riboflavin, niacin, and CoQ10: effects on lipid peroxidation and antioxidants in mitochondria

Reactive oxygen species (ROS) play a major role in causing mitochondrial changes linked to cancer and metastasis. Uptake of antioxidants by tissue to reduce the ROS production could be instrumental in controlling cancer. Tamoxifen (TAM), a nonsteroidal anti-estrogen drug most used in the chemotherapy and chemoprevention of breast cancer. Riboflavin, niacin and coenzyme Q10 (CoQ10) are proved to be potent antioxidants and protective agents against many diseases including cancer. The objective of this research is to determine the therapeutic efficacy of combinatorial therapy on mammary carcinoma bearing rats in terms of the mitochondrial lipid peroxidation and antioxidant status especially MnSOD. Female albino rats of Sprague-Dawley strain were selected for the investigation. Mammary carcinoma was induced with 7,12-dimethyl benz(a)anthracene (DMBA: 25 mg), and the treatment was started by the oral administration of TAM (10 mg/kg body weight/day) along with riboflavin (45 mg/kg body weight/day), niacin (100 mg/kg body weight/day) and CoQ10 (40 mg/kg body weight/day) for 28 days. The levels of lipid peroxides, activities of enzymic and non-enzymic antioxidants were measured in the mitochondria isolated from the mammary gland and liver of control and experimental rats. Rats treated with DMBA showed an increase in mitochondrial lipid peroxidation (mammary gland 52.3%; liver 25.1%) accompanied by high malondialdehyde levels along with lowered activities of mitochondrial enzymic antioxidants [superoxide dismutase (mammary gland 19.9%; liver 24.8%), catalase (mammary gland 50%; liver 19.7%), glutathione peroxidase (mammary gland 47.8%; liver 31.1%)] and non-enzymic antioxidants [reduced glutathione (mammary gland 14.3%; liver 13.3%), Vitamin C (mammary gland 6.49%; liver 21.4%) and E (mammary gland 20.3%; liver 22.2%)]. Administration of combinatorial therapy restored lipid peroxide level and the activities of enzymic and non-enzymic antioxidants to near normalcy. In addition, antitumour activity was also found to be enhanced which is evident from the increased expression of tumour suppressor gene MnSOD thereby preventing cancer cell proliferation. These results suggested that TAM treatment is the most effective during co-administration of riboflavin, niacin and CoQ10 in terms of mitochondrial antioxidant and antitumour activity.     

Effect of monthly administration of GHRH (fragment 1-29) with osmotic pump on the rat anterior pituitary

Growth Hormone-Releasing Hormone (GHRH) is the main factor, which regulates GH secretion and somatotrope proliferation. However, its chronic effect on anterior pituitary gland is still unknown. It is known that excessive GHRH secretion in patients with gastroenteropancreatic tumors secreting GHRH results in acromegaly and somatotrope hyperplasia. In mice transgenic for GHRH somatotrope tumors develop. Thus, the aim of this paper was to examine the effect of GHRH chronic administration on somatotrope secretion, their percentage and cell proliferation in anterior pituitary gland in rats. The experiment was performed on male Fischer 344 rats weighing 200+/-20 g. The animals were divided into two groups: group I-controls (13 rats) received solvent for GHRH (5% ethanol in demineralized water); group II (10 rats) received GHRH (Growth Hormone Releasing Factor, fragment 1-29 amide) at a dose of 5 microg/day. The substances were given for 1 month via osmotic pump (ALZET), which were implanted subcutaneously in the dorsal region under ketamin anesthesia. After 4 weeks all rats were decapitated and the blood was collected. In the microscopic preparations of anterior pituitary gland the morphology of pituitary (Herlant staining) and the percentage of somatotrope cells and proliferation index based on PCNA staining were assessed. It was found that the chronic treatment with GHRH caused a statistically significant increase in serum rGH concentration and in percentage of somatotropes, but did not change proliferation index and did not induce pathological changes in the morphology of the anterior pituitary gland when compared to the control group. Summing up, monthly GHRH administration did not induce somatotrope adenomas but it caused serum GH level elevation, what seems to depend partially on the increase of somatotrope number.     

The carcinogenicity of acrylamide

Acrylamide is carcinogenic to experimental mice and rats, causing tumors at multiple organ sites in both species when given in drinking water or by other means. In mice, acrylamide increases the incidence of alveologenic lung tumors and initiates skin tumors after dermal exposures. In two bioassays in rats, acrylamide administered in drinking water consistently induced peritesticular mesotheliomas, thyroid follicular cell tumors, and mammary gland tumors, as well as primary brain tumors when all such tumors were included in data analysis. In one of the rat bioassays, increased numbers of adrenal pheochromocytomas, adenomas of pituitary and clitoral glands, papillomas of the oral cavity, and adenocarcinomas of the uterus also occurred. In both humans and experimental animals, a significant fraction of ingested acrylamide is converted metabolically to the chemically reactive and genotoxic epoxide, glycidamide, which is likely to play an important role in the carcinogenicity of acrylamide. No studies on the carcinogenicity of glycidamide have been published, but bioassays of this compound are in progress. Epidemiologic studies of possible health effects from exposures to acrylamide have not produced consistent evidence of increased cancer risk, in either occupationally exposed workers or the general populations of several countries in which acrylamide is present in certain foods and beverages. A doubling of risk for pancreatic cancer was observed in the most highly exposed workers within the largest industrial cohort, but no consistent exposure–response relationships were identified. Retrospective re-analyses of previously conducted case-control studies of cancer incidence in several European populations have identified no causal relationship between consumption of foods or beverages that contain acrylamide and the incidence of cancers at various sites including kidney, large bowel, urinary bladder, oral cavity, pharynx, larynx, esophagus, breast, and ovary. These retrospective studies of cancer incidence in relation to acrylamide in food have limited power to detect increased cancer risks, and have been criticized on various grounds, but they do indicate that no major cancer risks are attributable to intake of acrylamide in Western diets.     

Effects of astaxanthin supplementation on chemically induced tumorigenesis in Wistar rats

ABSTRACT: BACKGROUND: Astaxanthin (ASTA) is a fat-soluble xanthophyll with powerful antioxidant functions. It is extracted from e.g. salmon, an important food source for certain human populations known to have a reduced risk of tumor development. It is possible that ASTA plays a role in cancer chemoprevention in such populations. The purpose of this study was to investigate the effects of dietary ASTA on chemically induced mammary tumorigenesis using N-methyl-N-nitroso-urea (MNU) in immature Wistar rats. METHODS: Thirty-six 37 days old juvenile female Wistar rats were at random allocated to 4 groups of which Groups 1 and 2 received a single dose of 55 mg MNU/kg body weight. The effects of ASTA was evaluated by giving rats of Groups 2 and 4 a dose of 50 mg ASTA/kg/day for the entire duration of the study. Group 3 rats received feed added alimentary oil.Necropsy and histopathological examinations were carried out on each rat 14 months after the administration of MNU. Haematological values and antioxidative status were determined. Oxidative stress was evaluated by monitoring superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in hepatic tissue. Lipid peroxidation and carbonylation of proteins was determined in protein extracts from the liver. RESULTS: Tumor development occurred only in rats of Groups 1 and 2, i.e. MNU exposed animals. Frequency of tumor development in general and average number of tumors per animal were insignificant between these two groups. Mammary gland tumors developed in equal frequencies in Group 1 and 2 rats, respectively. Although only rather few tumors were found in the mammary glands, a substantial number of other tumors were found in Group 1 and 2 rats, but at equal rates.Biochemical analyses showed significant higher levels of GPx, malondialdehyde and dinitrophenylhydrazine in Group 1 rats that for rats in all other groups thus indicating protective effects of ASTA on MNU induced hepatic oxidative stress. CONCLUSIONS: Supplementation with ASTA did not reduce tumorigenesis induced by MNU in Wistar rats. However, supplementation with ASTA seemed to have anti-inflammatory effects.     

Histological changes of various organs in aged SD-JCL rats (author's transl)

Age-related histological changes were studied in various organs from SD-JCL rats reared throughout their lifespan. In aged-male rats examined at 5 to 36 months of age were frequently observed nephropathy, periarteritis, skeletal muscle degeneration, pigmentation of the follicular epithelium in the thyroid, fibrosis of the pancreatic islets, hyperplasia of the parathyroid epithelium, and changes of the acini in the extraorbital lacrymal gland. In aged-female rats sinusoid dilatation of the adrenal, and atrophy of the ovary were also noted. Perilobular fat deposition of the liver, dilatation of the gastric gland and severe hemosiderosis of the spleen were observed similar frequency in the both sexes. The nephropathy and cardiovasculopathy were major factors to cause death for males, while the main cause of death for females was tumors, especially of the mammary and pituitary glands. Enlargement of the parathyroid gland, bone resorption and metastatic calcification in the solf tissues were found in rats with severe nephropathy.     

Aryl hydrocarbon receptor (AhR)-mediated induction of xanthine oxidase/xanthine dehydrogenase activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an environmental contaminant, induced xanthine oxidase and xanthine dehydrogenase (XO/XDH) activities, in addition to ethoxyresorufin-O-dealkylase and methoxyresorufin-O-dealkylase activities in liver of mice. When TCDD was given to mice as a single oral dose of 40 microg/kg, the activities of XO and XDH increased about threefold within 3 days and the increased levels were maintained for 4 weeks. The treatment of mice with 3-methylcholanthrene also induced XO/XDH activities, but phenobarbital and dexamethasone had no effect. The level of aldehyde oxidase, a molybdenum flavoenzyme related to XO/XDH, in mouse liver was also enhanced about 1.5-fold by TCDD treatment. The inducing effect of TCDD and 3-methylcholanthrene was not observed in null mice (AhR(-/-)), which lack the AhR gene. XO and XDH activities were induced by TCDD in heterozygous mice (AhR(+/-)). The lipid peroxidation in liver was stimulated by TCDD. The induction of XO and XDH, which produces reactive oxygen species, may contribute to the various toxicities of TCDD.     

Carcinogenesis and nucleic acid alkylation by some oxygenated nitrosamines in rats and hamsters

A comparison has been made of the carcinogenic effects of nitroso-2,6-dimethylmorpholine and several hydroxylated acyclic nitrosodialkylamines derived from it or related to it in rats and Syrian hamsters. In rats nitrosodimethylmorpholine was the most potent, inducing mainly esophageal tumors. Nitrosodiethanolamine was the weakest of the five nitrosamines in both rats and hamsters. Tumors of the pancreas ducts were induced by four of the five compounds, but only in hamsters, and esophageal tumors appeared only in rats. Most of the nitrosamines induced tumors of liver and lung in both rats and hamsters. A study of alkylation of nucleic acids of the liver following treatment of rats and hamsters with the radiolabeled nitrosamines showed that nitrosodiethanolamine alkylated liver nucleic acids in rats to only a very small extent. The other four nitrosamines all gave rise to 7-methylation and O6-methylation of guanine residues in DNA of hamster liver and all but nitrosodimethylmorpholine in rat liver DNA, which corresponded quite well with the induction of liver tumors in the two species. Quantitatively, however, there was not a good correlation between liver DNA alkylation and the potency of the nitrosamine in inducing tumors.     

Inhibition of carbamoyl phosphate synthetase-I by dietary dehydroepiandrosterone.

Dehydroepiandrosterone (DHEA), administered per os, serves to prevent or retard the development of a variety of genetic and induced disorders in mice and rats. This treatment also results in the development of hepatomegaly, a change of liver color from pink to mahogany, peroxisome proliferation in hepatocytes and alterations in hepatocyte mitochondria morphology and respiration. We used one- and two-dimensional polyacrylamide gel electrophoresis (PAGE) to identify changes in the relative levels of liver proteins produced by DHEA treatment of rodents. In mouse liver, there were apparent increases in the levels of 26 proteins and decreases in the levels of 7 proteins. Of the induced proteins the most prominent had Mr approximately 72 K; this protein was identified in a previous study as enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase. Another protein of Mr approximately 28 K, of unknown nature, also was induced markedly by DHEA treatment of mice and rats. A protein of Mr approximately 160 K, which was identified as carbamoyl phosphate synthetase-I (CPS-I), was decreased markedly by DHEA action. This enzyme, which comprises approx. 15-20% of mitochondrial matrix protein, is involved in the entry and rate-limiting step of the urea cycle. The specific activity of CPS-I also was significantly decreased by DHEA, but serum urea levels were normal. To determine whether steroids other than DHEA also induced similar changes, mice were treated with various steroids for 14 days and, thereafter, liver proteins were evaluated by SDS-PAGE: estradiol-17 beta and isoandrosterone induced both the approximately 72 and approximately 28 kDa proteins, testosterone and androsterone induced the 28 kDa protein only, but etiocholanolone, pregnenolone and progesterone were without effect. The findings of this study serve to demonstrate that: (i) hepatic protein levels are affected by DHEA treatment of mice and rats; (ii) liver CPS-I activity is decreased significantly by DHEA treatment, but serum urea levels remain within the normal range; and (iii) sex steroids and some of their precursors, when administered per os, also alter liver protein levels.     

Mutagenicity and carcinogenicity of tea, Camellia sinensis

Aqueous, caffeine free and tannin fractions of commercial tea and tannic acid were tested for mutagenicity in Ames test. Tea fractions of tannic acid were non mutagenic in strains TA 100, TA 98, TA 1535 and TA 1538 of Salmonella typhimurium with or without metabolic activation (rat-S9 mix) at different doses tested. In strain TA 98 the above tea fractions and tannic acid inhibited the S9 mix mediated mutagenicity of tobacco in a dose dependent manner. The different tea fractions at 60 degrees C, did not increase the tumor incidence in Swiss mice by gavage feeding. They also failed to produce tumors when injected subcutaneously. Caffeine free tea extract decreased the tobacco induced liver tumors but had no effect on lung tumors. The same fraction was ineffective in hexachlorocyclohexane induced liver tumors in Swiss mice.     

Uroporphyria and hepatic carcinogenesis induced by polychlorinated biphenyls-iron interaction: absence in the Cyp1a2(-/-) knockout mouse

Aryl hydrocarbon receptor ligands, such as polychlorinated biphenyls (PCBs), cause inhibition of the heme biosynthesis enzyme, uroporphyrinogen decarboxylase; this leads to uroporphyria and hepatic tumors, which are markedly enhanced by iron overload in C57BL/10 and C57BL/6 strains of mice. Cyp1a2(-/-) knockout mice were used to compare the effects of CYP1A2 expression on uroporphyria and liver carcinogenesis. PCBs in the diet (100ppm) of Cyp1a2(+/+) wild-type mice caused hepatic uroporphyria, which was strongly increased by iron-dextran (800mg Fe/kg). In contrast, uroporphyria was not detected in Cyp1a2(-/-) knockout mice, although expression of CYP1A1 and CYP2B10 was greatly induced. After 57 weeks on this diet, hepatic preneoplastic foci and tumors were seen in the Cyp1a2(+/+) mice; numbers and severity were enhanced by iron. No foci or tumors were detected in Cyp1a2(-/-) mice, although evidence for other forms of liver injury was observed. Our findings suggest a link not only between CYP1A2, iron metabolism, and the induction of uroporphyria by PCBs, but also with subsequent hepatocarcinogenesis.     

The CYP inhibitor 1-aminobenzotriazole does not prevent oxidative stress associated with alcohol-induced liver injury in rats and mice

Cytochrome P450 (CYP) 2E1 is induced by ethanol and is postulated to be a source of reactive oxygen species during alcoholic liver disease. However, there was no difference in liver pathology and radical formation between wild-type and CYP2E1 knockout mice fed ethanol. Other CYP isoforms may contribute these effects if CYP2E1 is inhibited or absent. The purpose of this study was, therefore, to determine if blocking most of the P450 isoforms with 1-aminobenzotriazole (ABT; 100 mg/kg i.g.), has any effect on liver damage and oxidative stress due to alcohol in rats and mice. Male C57BL/6 mice and Wistar rats were fed either high-fat control or ethanol-containing enteral diet for 4 weeks. ABT had a significant inhibitory effect on many P450 isoforms independent of concomitant alcohol administration. However, ABT did not protect against liver damage due to alcohol in either species. Indices of oxidative stress and inflammation were also similar in livers from vehicle-treated and ABT-treated animals fed ethanol. In summary, suppression of P450 activity with ABT had no apparent effect on oxidative stress caused by alcohol in both rats and mice. These data support the hypothesis that oxidative stress and liver damage can occur independently of CYP activities in both rats and mice during early alcohol-induced liver injury.     

Dopamine receptors in rat pituitary and estradiol-induced pituitary tumor: effect of chronic treatment with bromocriptine

We have investigated dopamine (DA) receptors in estradiol-induced PRL-secreting pituitary tumors and intact pituitary tissue. Female rats were injected at 3-week intervals with 2 mg estradiol valerate (EV) or with diluent. After 21 weeks, adenomatous changes in the pituitary gland of EV-treated rats were seen and plasma PRL concentrations reached 2 micrograms/ml. Bromocriptine (2.5 mg/kg) was then administered for 1 month to half of the control rats and half of the rats bearing tumors. Anterior pituitary weight was increased in EV-treated rats compared to controls while the affinity and the density of DA receptors as assessed by [3H]spiperone binding remained unchanged. Bromocriptine (CB-154) induced a 70% decrease in the density of DA receptors without any change in affinity both in normal pituitaries and in tumors. Concurrently, the elevated plasma concentrations of PRL in the tumor bearing rats were decreased to control values following the CB-154 treatment. Our data suggest that rats with primary estrogen-induced PRL secreting tumors have normal pituitary DA receptors.