* Department of Pathology and Department of Hepatology, Graduate School of Medicine, Osaka City University Medical School, Osaka 545-8585, Japan
1 To whom correspondence should be addressed at Department of Pathology, Osaka City University Medical School, 143 Asahi-machi, Abeno-ku, Osaka 545-8585, Japan. E-mail: fukuchan{at}med.osaka-cu.ac.jp.
Received December 17, 2004; accepted February 7, 2005
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: estradiol-3-benzoate; thioacetamide; cirrhosis; alpha-smooth muscle actin; Stellate cell activation-associated protein.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
It has been reported that estrogens exert inhibitory effects on some liver diseases. In dimethylnitrosamine (DMN) and pig serum models, treatment with estradiol inhibited the activation of hepatic stellate cells (HSCs) in vivo and in vitro (Shimizu et al., 1999) and reduced fibrosis (Yasuda et al., 1999
). The hormone was also found to inhibit lipid peroxidation, and decrease expression of I
B-
and NF-
B in rat liver cell culture (Omoya et al., 2001
). However, in some situations, estrogens have negative roles on the progress of liver disease. It was reported estradiol in combination with epidermal growth factor increased growth and induced c-fos mRNA expression at early times in cell culture, which ultimately culminated in enhanced DNA synthesis (Lee and Edwards, 2001
). Estrogens also stimulate proliferation of intrahepatic biliary epithelium (Alvaro et al., 2000
), and estrogens antagonist treatment during bile duct ligation (BDL) decreased fibrosis (Alvaro et al., 2002
).
It is known that estrogens can act as potent endogenous antioxidants, reducing lipid peroxidation levels in liver and serum (Lacort et al., 1995), and induce antioxidant enzymes such as copper-zinc SOD and glutathione peroxidase (Lu et al., 2004
).
Some of the many actions of estradiol may not be caused by estradiol per se, but may result from the formation of active estrogen metabolite(s) (Zhu and Conney, 1998). Among the metabolites, catechol estrogens can be oxidized to semiquinones, which in the presence of molecular oxygen are oxidized to quinones with formation of superoxide and subsequently hydroxyl radicals (Cavalieri et al., 2000
), and estradiol-derived metabolites, 2- and 4-hydroxyestradiol, can exert either pro- or antioxidant actions (Martinez et al., 2002
). These data let us set the hypothesis that some metabolites of estrogens might increase oxidative stress in some diseases which are related to the formation of reactive oxygen species.
Thioacetamide (TAA) causes liver cirrhosis at medium-term treatment (Muller et al., 1988) and hepatic neoplasms at long term treatment in animals (Becker, 1983
). Because this is associated with decreased catalase and glutathione peroxidase (Sanz et al., 1995
), we here tested the hypothesis that estrogen treatment may enhance oxidative stress and act as an oxidant or pro-oxidant in TAA-treated animals.
For this purpose we investigated the action of estradiol-3-benzoate (EB) on parameters of liver cirrhosis, as well as expression of alpha-smooth muscle actin (alpha-SMA) as a marker of activated HSCs and stellate cell activation-associated protein (STAP), which was recently discovered to be a kind of haemoprotein activated in fibrosis (Asahina et al., 2002; Kawada et al., 2001
). Modulation of ER alpha and ER beta expression by EB treatment was also assessed.
![]() |
MATERIAL AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
At 6 weeks of age, the rats were divided into six groups. Animals of groups 14 (n = 20 for each group) received TAA (0.03% in drinking water) for 12 weeks, and animals of groups 5 and 6 (10 per group) received drinking water without TAA. During this exposure period, EB pellets were subcutaneously implanted to give doses of 0 (groups 1 and 5), 1 (group 2), 10 (group 3), and 100 µg (groups 4 and 6). The EB pellets were produced by the method described previously (Kang et al., 2004). Briefly, after mixing 0.132, 1.32, or 13.2 mg of EB with 2 g of cholesterol and 1.7 ml of olive oil, the preparation was introduced into medical grade silastic tubes (Silicon Medical Tube No. 2, 1002N; Kaneka Medix Corporation, Japan). The total content of EB in each 1-cm tube was estimated as approximately 1, 10, or 100 µg. EB pellets were replaced with new ones every 4 weeks.
Body weights of all animals were measured every week. All animals were sacrificed at week 12 under ether anesthesia. At necropsy, liver weights were measured. Liver tissues were fixed in 10% phosphate-buffered formalin and routinely processed for embedding in paraffin, and staining of 4 µm sections with hematoxylin, and eosin staining for histopathological examination. The amount of total estradiol in serum was measured by 125I-radioimmunoassay kit (Coat-A-Count® Estradiol, Diagnostic Product Corporation, CA) as recommended protocol provided by producers. Detection limit of this kit is 10 pg/ml.
Fibrosis was categorized with the following criteria: +, portal fibrosis, characterized by mild fibrous expansion of portal tracts; ++, periportal fibrosis showing fine strands of connective tissue in zone 1 with only rare portalportal septa; +++, septal fibrosis manifested by connective tissue bridges that link portal tracts and central veins, minimally distorted architecture, but no regenerative nodules. Liver cirrhosis was diagnosed on the basis of bridging fibrosis and the presence of regenerative hepatic nodules. Samples of liver from all animals were also snap-frozen in liquid nitrogen for biochemical and molecular analysis.
Estimation of collagen content.
Two sections of liver were cut approximately 15-µm thick, deparaffinized and hydrated. They were then place in distilled water at 4°C and incubated in Fast green FCF (Sigma), and subsequently in Fast green FCF and Sirius red F3B (Aldrich). After adding 0.05 N NaOH in 50% aqueous methanol, eluted color was read in a spectrophotometer (Ultraspec 3000, UV/Visible Spectrophotometer; Pharmacia Biotech, Tokyo, Japan) at 530 nm and 605 nm. The collagen content was calculated according to the previously described method (Gascon-Barre et al., 1989). Data are the mean ± SD from ten samples per group and two independent experiments.
Quantification of lipid peroxidation.
Frozen livers were homogenized in sodium phosphate buffer, with addition of trichloroacetic acid (TCA, nacalai tesq, Japan). After centrifuge, the supernatant were mixed with 2-thiobarbituric acid (TBA, nacalai tesq, Japan), and the samples were boiled at 100°C for 10 min. They were mixed with butanol and were centrifuged, and the absorbance was measured using a spectrophotofluorometer (Hitachi F4500, Japan), and 2-thiobarbituric acid-reacting substances (TBARS), expressed as malondialdehyde equivalent (MDA eq) values, were calculated from a standard curve, with reference to protein content measured by the Lowry method. Data are the mean ± SD from five samples per group and three independent experiments.
Quantification of 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation.
DNA samples isolated from pieces of frozen liver weighing 500 mg were digested into deoxynucleosides by combined treatment with nuclease P1 and alkaline phosphatase. Levels of 8-OHdG were determined by high-performance liquid chromatography as described earlier (Nakae et al., 1997) and expressed as the number of 8-OHdG residues/105 total deoxyguanosines (dG). Data are the mean ± SD from ten samples per group and two independent experiments.
RNA preparation.
Total RNA was isolated from frozen liver using ISOGEN (Nippon Gene Co. Ltd, Tokyo, Japan), isopropanol precipitated, dissolved in DEPC-treated distilled water, and stored at 80°C until use. RNA concentrations were determined with a spectrophotometer (Ultraspec 3000, UV/Visible Spectrophotometer; Pharmacia Biotech, Tokyo, Japan). For cDNA synthesis, 3 µg of total RNA was heated to 70°C for 10 min and then placed immediately on ice for 10 min. To each sample, 4 µl of 5x first strand buffer, 2 µl of 0.1 M DTT, 4 µl of 2 mM each dNTP mix, 1 µl of oligo(dT) primer, and 1 µl of Superscript II reverse transcriptase (Invitrogen, CA) were added. Reverse transcription was then carried out at 42°C for 50 min, followed by heating to 70°C for 15 min, and cDNA samples were stored at 20°C until assayed.
RT-PCR for Alpha-SMA mRNA, STAP mRNA, ER Alpha mRNA, ER Beta mRNA, and Beta-Actin mRNA.
cDNAs were amplified using specific oligonucleotide primers for rat alpha-SMA, STAP, ER alpha, ER beta, and beta-actin as follows: rat alpha-SMA sense, 5'-ACT GGG ACG ACA TGG AAA AG-3' and antisense, 5'-CAT CTC CAG AGT CCA GCA CA-3'; rat STAP sense, 5'-ATG GAG AAA GTG CCG GGC GAC-3', antisense, 5'-TGG CCC TGA AGA GGG CAG TGT-3'; rat ER alpha, sense, 5'-CTG CCA AGG AGA CTC GCT ACT G-3', antisense, 5'-TCT TCC TCC GGT TCT TAT CGA TGG-3'; rat ER beta, sense 5'-AAC AAG GGC ATG GAA CAT CTG CT-3', antisense, 5'-TCC GCC TCA GGC CTG GCC ATC A-3'; and rat beta-actin, sense: 5'-ACC ACA GCT GAG AGG GAA ATC G-3', antisense, 5'-AGA GGT CTT TAC GGA TGT CAA CG-3'.
The PCR program cycles were set as follows: for alpha-SMA and beta-actin, initial denaturing at 95°C for 9 min, followed by 28 cycles or 24 cycles (95°C for 1 min, 58°C for 1 min, and 72°C for 1 min), respectively, and a final extension at 72°C for 5 min; for STAP, initial denaturing at 95°C for 9 min, following by 34 cycles (95°C for 1 min, 68°C for 1 min, and 72°C for 1 min), and a final extension at 72°C for 5 min; for ER alpha, initial denaturing at 95°C for 9 min, followed by 30 cycles (95°C for 1 min, 60°C for 1 min, and 72°C for 1 min), and a final extension at 72°C for 5 min. For ER beta, the PCR program cycle was set to denature at 95°C for 30 sec, to anneal at 65°C for 15 sec, and to extend at 72°C for 15 sec for a total of 20 cycles, the annealing temperature being reduced 0.5 °C in every cycle, and then set to denature at 95°C for 30 sec, to anneal at 51°C for 15 sec, and to extend at 72°C for 15 sec for a total of 30 cycles. For confirmation of ER beta PCR product, DNA was recovered using EasytrapTM Ver. 2 (Takara, Japan) from gel slices with the manufacturer's protocol, and purified in a Microspin S-300 HR column (Amersham Bioscience, NJ) for examination of the sequence by ABI PRISM 3100-Avant (Applied Biosystem, USA).
Beta-actin mRNA was employed as an internal standard, and alpha-SMA, STAP, ER alpha, and ER beta mRNA expression were determined by quantitative PCR and normalized against beta-actin mRNA levels. The PCR products were electrophoresed on a 2% Nusieve agarose gel and stained with ethidium bromide. The gels were then scanned and analyzed using a FLA-5100 and Multi Gauge Ver 2.0 software (Fujifilm, Japan). All PCR products were amplified in a linear cycle. Data are the mean ± SD from five samples per group and three independent experiments.
Statistical analysis.
Statistical analyses were performed with the Tukey-Kramer method using the JMP program (SAS Institute, Cary, NC). For all comparisons, probability values less than 5% (p < 0.05) were considered to be statistically significant.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The results are thus not in line with the reported antioxidant action of estrogen (Lacort et al., 1995) and the induction of antioxidant enzymes (Lu et al., 2004
). In DMN and pig serum models, treatment with estradiol resulted in suppression of hepatic fibrosis (Shimizu et al., 1999
) and reduced hepatic collagen deposition (Yasuda et al., 1999
), and inhibition of lipid peroxidation in rat liver cell culture has been documented (Omoya et al., 2001
). However, estrogen treatment enhanced fibrosis or cirrhosis in BDL model (Alvaro et al., 2000
, 2002
), as in the TAA model in this study. This difference in action appears to reflect variation in metabolic activation and interaction with the hepatotoxin.
It should be remembered that catechol estrogens can exert pro-oxidant activities (Martinez et al., 2002), and the fact that TAA treatment causes decrease in catalase and glutathione peroxidase, with glutathione depletion (Sanz et al., 1995
), might have played a role. In this study, estrogen actually enhanced collagen content, lipid peroxidation, and alpha-SMA and STAP expression in TAA-treated animals. Reduction of intracellular glutathione and increase of lipid peroxidation in biliary epithelial damages were evident in the BDL model (Tsuneyama et al., 2002
), in which antiestrogen treatment inhibited cholangiocyte proliferation and biliary fibrosis (Alvaro et al., 2000
).
Hepatic fibrosis and cirrhosis are considered to result from direct injury to hepatocytes or bile ducts, with excess deposition of extracellular matrix (ECM) components that are produced by HSCs (Friedman, 2000). Upon activation, HSCs may undergo proliferation and differentiation, including a phenotypic shift to myofibroblastic-like cells that are positive for alpha-SMA (Friedman, 2000
, 2003
). Activation of HSCs is associated with oxidative stress and change of composition and organization of ECM (Eng and Friedman, 2000
). Since EB treatment here enhanced lipid peroxidation in liver, this may have been the main cause of increase of alpha-SMA expression. It has been reported that STAP, recently renamed as cytoglobulin/STAP (Cygb/STAP) (Nakatani et al., 2004
), is activated under fibrotic and cirrhotic conditions (Asahina et al., 2002
; Kawada et al., 2001
). Cygb/STAP is a cytoplasmic protein that is induced during the activation of HSCs which are fibulin-2 positive (Tateaki et al., 2004
).
At the molecular level, estrogens can lead to the formation of DNA adducts (Shimomura et al., 1992) and have been shown to induce 8-hydroxylation of guanine bases in kidney and liver DNA in male Syrian hamsters (Han and Liehr, 1994
) and 8-OHdG formation in a breast cancer cell line (Mobley and Brueggemeier, 2004
). It has been reported that some synthetic estrogens have promoting properties (Yager and Liehr, 1996
), and estrogen has been considered a genotoxic carcinogen (Cavalieri et al., 2000
). However, in the present study EB treatment did not enhance 8-OHdG production in normal animals, so that this action could be dependent on a disease-specific background.
Liver lesions from groups 3 and 4 showed a similar pattern, and significant decrease of final body weight was found in groups 3 and 4 as compared to group 1. Treatment of high-dose EB is too toxic in TAA-treated animals, which may influence induction and severity of fibrosis and cirrhosis. However, there was also a decrease of final body weight in group 6 compared to group 5. Thus, it appears that body weight is not a major factor for enhancing cirrhosis by EB treatment.
It has been reported that estrogen treatment enhances ER levels in isolated hepatocytes (Vickers and Lucier, 1991), and endothelial and Kupffer cells (Vickers and Lucier, 1996
). The ER level was significantly correlated with CuZn-SOD level and inversely proportional to MDA production (Shimizu et al., 2001
). In our study, EB treatment induced ER alpha expression significantly in normal animals, but in TAA-treated animals there was a tendency for increase. Because surface receptor molecules that allow cells to respond to hormones and cytokines can be inactivated during lipid peroxidation (Halliwell and Gutteridge, 1999
), there may be a retardation of estrogen signal transduction under certain conditions.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Alvaro, D., Onori, P., Metalli, V. D., Svegliati-Baroni, G., Folli, F., Franchitto, A., Alpini, G., Mancino, M. G., Attili, A. F., and Gaudio, E. (2002). Intracellular pathways mediating estrogen-induced cholangiocyte proliferation in the rat. Hepatology 36, 297304.[CrossRef][ISI][Medline]
Asahina, K., Kawada, N., Kristensen, D. B., Nakatani, K., Seki, S., Shiokawa, M., Tateno, C., Obara, M., and Yoshizato, K. (2002). Characterization of human stellate cell activation-associated protein and its expression in human liver. Biochim. Biophys. Acta 1577, 471475.[ISI][Medline]
Becker, F. F. (1983). Thioacetamide hepatocarcinogenesis. J. Natl. Cancer Inst. 71, 553558.[ISI][Medline]
Becker, U., and Gluud, C. (1991). Sex, sex hormones and chronic liver diseases. Dig. Dis. 9, 916.[ISI][Medline]
Bosch, F. X., Ribes, J., and Borras, J. (1999). Epidemiology of primary liver cancer. Semin. Liver Dis. 19, 271285.[ISI][Medline]
Cavalieri, E., Frenkel, K., Liehr, J. G., Rogan, E., and Roy, D. (2000). Estrogens as endogenous genotoxic agentsDNA adducts and mutations. J. Natl. Cancer Inst. Monogr. 7593.
De Maria, N., Manno, M., and Villa, E. (2002). Sex hormones and liver cancer. Mol. Cell. Endocrinol. 193, 5963.[CrossRef][ISI][Medline]
Eng, F. J., and Friedman, S. L. (2000). Fibrogenesis I. New insights into hepatic stellate cell activation: The simple becomes complex. Am. J. Physiol. Gastrointest. Liver Physiol. 279, G7G11.
Francavilla, A., Polimeno, L., DiLeo, A., Barone, M., Ove, P., Coetzee, M., Eagon, P., Makowka, L., Ambrosino, G., Mazzaferro, V., et al. (1989). The effect of estrogen and tamoxifen on hepatocyte proliferation in vivo and in vitro. Hepatology 9, 614620.[ISI][Medline]
Friedman, S. L. (2000). Molecular regulation of hepatic fibrosis, an integrated cellular response to tissue injury. J. Biol. Chem. 275, 22472250.
Friedman, S. L. (2003). Liver fibrosisfrom bench to bedside. J Hepatol. 38 (Suppl. 1), S38S53.[CrossRef][ISI][Medline]
Gascon-Barre, M., Huet, P. M., Belgiorno, J., Plourde, V., and Coulombe, P. A. (1989). Estimation of collagen content of liver specimens. Variation among animals and among hepatic lobes in cirrhotic rats. J. Histochem. Cytochem. 37, 377381.[Abstract]
Green, S., Walter, P., Kumar, V., Krust, A., Bornert, J. M., Argos, P., and Chambon, P. (1986). Human oestrogen receptor cDNA: Sequence, expression and homology to v-erb-A. Nature 320, 134139.[CrossRef][ISI][Medline]
Halliwell, B., and Gutteridge, J. M. C. (1999). Oxidative stress: Adaptation, damage, repair and death. In Free Radicals in Biology and Medicine (B. Halliwell and J. M. C. Gutteridge, Eds.), 3rd ed., pp. 246350. Oxford University Press, New York.
Han, X., and Liehr, J. G. (1994). 8-Hydroxylation of guanine bases in kidney and liver DNA of hamsters treated with estradiol: Role of free radicals in estrogen-induced carcinogenesis. Cancer. Res 54, 55155517.[Abstract]
Kang, J. S., Kim, S., Che, J. H., Nam, K. T., Kim, D. J., Jang, D. D., and Yang, K. H. (2004). Inhibition of mammary gland tumors by short-term treatment of estradiol-3-benzoate associated with down-regulation of estrogen receptor ERalpha and ERbeta. Oncol. Rep. 12, 689693.[ISI][Medline]
Kawada, N., Kristensen, D. B., Asahina, K., Nakatani, K., Minamiyama, Y., Seki, S., and Yoshizato, K. (2001). Characterization of a stellate cell activation-associated protein (STAP) with peroxidase activity found in rat hepatic stellate cells. J. Biol. Chem. 276, 2531825323.
Kuiper, G. G., Enmark, E., Pelto-Huikko, M., Nilsson, S., and Gustafsson, J. A. (1996). Cloning of a novel receptor expressed in rat prostate and ovary. Proc. Natl. Acad. Sci. U.S.A. 93, 59255930.
Lacort, M., Leal, A. M., Liza, M., Martin, C., Martinez, R., and Ruiz-Larrea, M. B. (1995). Protective effect of estrogens and catecholestrogens against peroxidative membrane damage in vitro. Lipids 30, 141146.[ISI][Medline]
Lee, C. H., and Edwards, A. M. (2001). Stimulation of DNA synthesis and c-fos mRNA expression in primary rat hepatocytes by estrogens. Carcinogenesis 22, 14731481.
Lu, G., Shimizu, I., Cui, X., Itonaga, M., Tamaki, K., Fukuno, H., Inoue, H., Honda, H., and Ito, S. (2004). Antioxidant and antiapoptotic activities of idoxifene and estradiol in hepatic fibrosis in rats. Life Sci. 74, 897907.[CrossRef][ISI][Medline]
Martinez, R., Quintana, K., Navarro, R., Martin, C., Hernandez, M. L., Aurrekoetxea, I., Ruiz-Sanz, J. I., Lacort, M., and Ruiz-Larrea, M. B. (2002). Pro-oxidant and antioxidant potential of catecholestrogens against ferrylmyoglobin-induced oxidative stress. Biochim. Biophys. Acta 1583, 167175.[ISI][Medline]
Mobley, J. A., and Brueggemeier, R. W. (2004). Estrogen receptor-mediated regulation of oxidative stress and DNA damage in breast cancer. Carcinogenesis 25, 39.
Muller, A., Machnik, F., Zimmermann, T., and Schubert, H. (1988). Thioacetamide-induced cirrhosis-like liver lesions in ratsusefulness and reliability of this animal model. Exp. Pathol. 34, 229236.[ISI][Medline]
Nakae, D., Kobayashi, Y., Akai, H., Andoh, N., Satoh, H., Ohashi, K., Tsutsumi, M., and Konishi, Y. (1997). Involvement of 8-hydroxyguanine formation in the initiation of rat liver carcinogenesis by low dose levels of N-nitrosodiethylamine. Cancer Res. 57, 12811287.[Abstract]
Nakatani, K., Okuyama, H., Shimahara, Y., Saeki, S., Kim, D. H., Nakajima, Y., Seki, S., Kawada, N., and Yoshizato, K. (2004). Cytoglobin/STAP, its unique localization in splanchnic fibroblast-like cells and function in organ fibrogenesis. Lab. Invest. 84, 91101.[CrossRef][ISI][Medline]
Omoya, T., Shimizu, I., Zhou, Y., Okamura, Y., Inoue, H., Lu, G., Itonaga, M., Honda, H., Nomura, M., and Ito, S. (2001). Effects of idoxifene and estradiol on NF-kappaB activation in cultured rat hepatocytes undergoing oxidative stress. Liver 21, 183191.[CrossRef][ISI][Medline]
Sanz, N., Diez-Fernandez, C., Fernandez-Simon, L., Alvarez, A., and Cascales, M. (1995). Relationship between antioxidant systems, intracellular thiols and DNA ploidy in liver of rats during experimental cirrhogenesis. Carcinogenesis 16, 15851593.[Abstract]
Shimizu, I., Mizobuchi, Y., Yasuda, M., Shiba, M., Ma, Y. R., Horie, T., Liu, F., and Ito, S. (1999). Inhibitory effect of oestradiol on activation of rat hepatic stellate cells in vivo and in vitro. Gut 44, 127136.
Shimizu, I., Inoue, H., Yano, M., Shinomiya, H., Wada, S., Tsuji, Y., Tsutsui, A., Okamura, S., Shibata, H., and Ito, S. (2001). Estrogen receptor levels and lipid peroxidation in hepatocellular carcinoma with hepatitis C virus infection. Liver 21, 342349.[CrossRef][ISI][Medline]
Shimomura, M., Higashi, S., and Mizumoto, R. (1992). 32P-postlabeling analysis of DNA adducts in rats during estrogen-induced hepatocarcinogenesis and effect of tamoxifen on DNA adduct level. Jpn. J. Cancer Res. 83, 438444.[ISI][Medline]
Tateaki, Y., Ogawa, T., Kawada, N., Kohashi, T., Arihiro, K., Tateno, C., Obara, M., and Yoshizato, K. (2004). Typing of hepatic nonparenchymal cells using fibulin-2 and cytoglobin/STAP as liver fibrogenesis-related markers. Histochem. Cell Biol. 122, 4149.[ISI][Medline]
Tsuneyama, K., Harada, K., Kono, N., Sasaki, M., Saito, T., Gershwin, M. E., Ikemoto, M., Arai, H., and Nakanuma, Y. (2002). Damaged interlobular bile ducts in primary biliary cirrhosis show reduced expression of glutathione-S-transferase-pi and aberrant expression of 4-hydroxynonenal. J. Hepatol. 37, 176183.[CrossRef][ISI][Medline]
Vickers, A. E., and Lucier, G. W. (1991). Estrogen receptor, epidermal growth factor receptor and cellular ploidy in elutriated subpopulations of hepatocytes during liver tumor promotion by 17 alpha-ethinylestradiol in rats. Carcinogenesis 12, 391399.[Abstract]
Vickers, A. E., and Lucier, G. W. (1996). Estrogen receptor levels and occupancy in hepatic sinusoidal endothelial and Kupffer cells are enhanced by initiation with diethylnitrosamine and promotion with 17alpha-ethinylestradiol in rats. Carcinogenesis 17, 12351242.[Abstract]
Yager, J. D., and Liehr, J. G. (1996). Molecular mechanisms of estrogen carcinogenesis. Annu. Rev. Pharmacol. Toxicol. 36, 203232.[CrossRef][ISI][Medline]
Yasuda, M., Shimizu, I., Shiba, M., and Ito, S. (1999). Suppressive effects of estradiol on dimethylnitrosamine-induced fibrosis of the liver in rats. Hepatology 29, 719727.[CrossRef][ISI][Medline]
Zhu, B. T., and Conney, A. H. (1998). Functional role of estrogen metabolism in target cells: Review and perspectives. Carcinogenesis 19, 127.[Abstract]
|