High incidence of hepatocellular carcinomas after synthetic estrogen administration in Syrian golden hamsters fed alpha-naphthoflavone: a new tumor model

The association between circulating oestradiol levels and severity of liver disease in males with hepatitis B virus infection

BACKGROUND

Males have a strikingly increased risk of advanced liver disease. This study was designed to investigate the association between sex hormone levels and different disease states in hepatitis B virus (HBV)-infected male patients.

METHODS

Two hundred and fifty-two male patients, including 30 with acute hepatitis B (AHB), 127 with chronic hepatitis B (CHB) and 95 with chronic severe hepatitis B (CSHB), and 48 healthy controls (HCs) were enroled in this study. All patients were followed for 4 months. The primary end point was in-hospital mortality at the end of 90 days. At study entry, a blood sample was collected from all subjects to examine liver function, renal function and sex hormone levels (serum total testosterone and oestradiol). A total of nine clinical chemistry and biochemical variables were analyzed for possible association with outcomes by using Cox proportional hazards and multiple regression models.

RESULTS

We demonstrated that in CSHB and CHB patients, oestradiol levels were significantly increased compared with HCs and AHB patients, whereas no significant differences were observed in AHB patients and HCs. All male patients had normal levels of testosterone which were not significantly different compared with those of HCs. Increased oestradiol levels were clinically associated with severe liver disease, and increased 3-month mortality rate. Multivariate analysis demonstrated that oestradiol and the model for end-stage liver disease (MELD) score were independent predictors for mortality (both P < 0.001).

CONCLUSION

Oestradiol levels are significantly increased in male patients with hepatitis B, and were associated with the severity of liver disease. Moreover, elevation of oestradiol is an independent predictive factor for the 3-month mortality rate in male patients with hepatitis B.

Vitamin C and alpha-naphthoflavone prevent estrogen-induced mammary tumors and decrease oxidative stress in female ACI rats

The mechanisms underlying the pathogenesis of estrogen-induced breast carcinogenesis remain unclear. The present study investigated the roles of estrogen metabolism and oxidative stress in estrogen-mediated mammary carcinogenesis in vivo. Female August Copenhagen Irish (ACI) rats were treated with 17beta-estradiol (E(2)), the antioxidant vitamin C, the estrogen metabolic inhibitor alpha-naphthoflavone (ANF), or cotreated with E(2) + vitamin C or E(2) + ANF for up to 8 months. E(2) (3 mg) was administered as an subcutaneous implant, ANF was given via diet (0.2%) and vitamin C (1%) was added to drinking water. At necropsy, breast tumor incidence in the E(2), E(2) + vitamin C and E(2) + ANF groups was 82, 29 and 0%, respectively. Vitamin C and ANF attenuated E(2)-induced alterations in oxidative stress markers in breast tissue, including 8-iso-prostane F(2alpha) formation and changes in the activities of antioxidant enzymes superoxide dismutase and glutathione peroxidase. Quantification of 2-hydroxyestradiol (2-OHE(2)) and 4-hydroxyestradiol (4-OHE(2)) formation in breast tissue confirmed that ANF inhibited 4-hydroxylation of E(2) and decreased formation of the highly carcinogenic 4-OHE(2). These results demonstrate that antioxidant vitamin C reduces the incidence of estrogen-induced mammary tumors, increases tumor latency and decreases oxidative stress in vivo. Further, our data indicate that ANF completely abrogates breast cancer development in ACI rats. The present study is the first to demonstrate the inhibition of breast carcinogenesis by antioxidant vitamin C or the estrogen metabolic inhibitor ANF in an animal model of estrogen-induced mammary carcinogenesis. Taken together, these results suggest that E(2) metabolism and oxidant stress are critically involved in estrogen-induced breast carcinogenesis.

Sex hormones and risk of liver tumor

The liver is morphologically and functionally modulated by sex hormones. Long-term use of oral contraceptives (OCs) and anabolic androgenic steroids (AASs) can induce both benign (hemangioma, adenoma, and focal nodular hyperplasia [FNH]) and malignant (hepatocellular carcinoma [HCC]) hepatocellular tumors. Hepatic adenomas (HAs) are rare, benign neoplasms usually occurring in young women, the development and the complications of which have been related to the strength of OCs and the duration of their use. HA incidence has fallen since the introduction of pills containing smaller amounts of estrogens. FNH is a benign lesion, most commonly seen in young women, which is thought to represent a local hyperplastic response of hepatocytes to a vascular abnormality. Because of the female predominance and the young age at onset, a role of female hormones has been suggested. Furthermore, a large proportion of women with FNH (50-75%) are OC users. Liver hemangiomas (LHs) are the most common benign liver tumors and are seen more commonly in young adult females. The female predilection and clinical observations of LH growth under conditions of estrogenic exposure suggest a possible role for estrogen in the pathogenesis of LHs. HCC has become one of the most widespread tumors in the world in recent years, representing the sixth leading cancer and the third most common cause of death from cancer. Apart from liver cirrhosis, numerous other factors responsible for its onset have been proposed: hepatitis infections from virus B (HBV) and C (HCV), alcohol, smoking, and aflatoxin. However, regardless of etiology, chronic liver diseases progress at unequal rates in the two sexes, with the major sequelae, such as cirrhosis and HCC, being more frequent in men than in women. These epidemiological data have prompted researchers to investigate the relationship between sex hormones and liver tumors. The human liver expresses estrogen and androgen receptors and experimentally both androgens and estrogens have been implicated in stimulating hepatocyte proliferation and may act as liver tumor inducers or promoters.

Tamoxifen induces suppression of cell viability and apoptosis in the human hepatoblastoma cell line HepG2 via down-regulation of telomerase activity

BACKGROUND/AIMS

Antiproliferative action of tamoxifen in the estrogen receptor-alpha-negative human hepatoblastoma cell line HepG2 was investigated.

METHODS

HepG2 cells, seeded at different densities (4000-36 000 cells/cm(2)), were incubated with tamoxifen (1, 10, or 20 microM) or the telomerase inhibitor 3'-azido-3'-deoxythymidine (AZT) (0.6-3.0 mM) up to 72 h. Cell viability was assessed (MTT-test), flow cytometric analysis was performed, and telomerase activity was measured (telomeric repeat amplification protocol assay).

RESULTS

Ten or 20 microM tamoxifen induced a reduction of cell viability. Basically reduction of viability was related to an increase in the fraction of G0/1-phase. When tamoxifen was present at higher concentration (20 microM) or at low cell density (4000/cm(2)) an additional increase of the rate of apoptotic cells occurred with a delay, aggravating the effect of tamoxifen on cell viability substantially. When apoptosis was induced a significant suppression of telomerase activity preceded regularly. Direct inhibition of telomerase activity with AZT resulted in a decrease of cell viability and apoptosis.

CONCLUSION

The tamoxifen-induced reduction of cell viability in HepG2 cells depends on drug concentration and cell density and is due to cytostatic and cytocide effects. The latter may be mediated by a down-regulation of telomerase activity.

Naphthalene and beta-naphthoflavone effects on Anguilla anguilla L. hepatic metabolism and erythrocytic nuclear abnormalities

The effects of a polycyclic aromatic hydrocarbon (PAH) such as naphthalene (NAP)--an environmental contaminant--and beta-naphthoflavone (BNF)--a model substance (PAH-like compound)--were investigated in European eel (Anguilla anguilla L.) over 3-, 6-, and 9-day exposure (0.1-2.7 microM). Both xenobiotics revealed to be strong biotransformation (phase I) inducers. After 3-day exposure, liver ethoxyresorufin O-deethylase (EROD) activity was significantly increased by all NAP and BNF tested concentrations. At 6 and 9 days, liver EROD activity was significantly induced mainly by the highest NAP and BNF concentrations. Liver cytochrome P450 content was significantly induced after 3-day exposure to 0.9 and 2.7 microM BNF and 9-day exposure to 0.1, 0.3 and 0.9 microM NAP. Liver alanine transaminase (ALT) activity was measured as an indicator of hepatic health condition, revealing a significant decrease after 6-day exposure to 0.9 microM BNF. Genotoxicity measured as erythrocytic nuclear abnormalities (ENA) was detected in all BNF treated fish on day 6, whereas on day 9, ENA frequencies returned to control levels, significantly decreasing at 0.9 microM BNF exposure. Immature erythrocytes (IE) frequency demonstrated a decreasing tendency along the BNF experiment and concomitantly with the above ENA response. The present experimental results elect EROD activity in A. anguilla as a useful short- to medium-term biomarker of exposure to both PAH and PAH-like compounds. However, some problems can emerge in the presence of high xenobiotic concentrations. Concerning genotoxicity, it is hypothesized that ENA response depends on different factors such as the exhaustion of the detoxification process, the balance erythropoiesis/erythrocytic catabolism and the DNA repairing capacity.

Tamoxifen inhibits hepatoma cell growth through an estrogen receptor independent mechanism

BACKGROUND/AIMS

Tamoxifen has previously been shown to prolong the survival of patients with advanced stages of hepatocellular carcinoma and it has been suggested that it inhibits the growth of hepatoma cells through an estrogen receptor-dependent mechanism. We have studied the effects of the synthetic estrogen, mestranol, and the antiestrogen, tamoxifen, on the growth regulation of hepatoma cells in vitro.

METHODS

Cells were maintained under fully estrogenized conditions and were deprived of estrogen shortly before conducting experiments.

RESULTS

In the human hepatoma cell line Hep 3B, tamoxifen inhibited cell growth in a concentration and time-dependent manner with effective concentrations ranging from 0.1 microM to 10 microM. Mestranol inhibited cell growth at a concentration of 10 microM and had an additive effect with tamoxifen on growth inhibition. Expression of estrogen receptors in hepatoma cells was not detected by enzyme immunoassay, Northern blot analysis or reporter gene expression assay. Furthermore, the introduction of estrogen receptors into Hep 3B cells did not alter the effect of tamoxifen and mestranol on cell growth.

CONCLUSIONS

This study suggests that tamoxifen inhibits the growth of Hep 3B hepatoma cells through an estrogen receptor-independent mechanism.

Prospective controlled trial with antiestrogen drug tamoxifen in patients with unresectable hepatocellular carcinoma

Clinical and experimental evidence indicates that estrogens are involved in the control of hepatocyte proliferation both in normal and in neoplastic conditions. Thirty-two cirrhotic patients with unresectable or otherwise untreatable hepatocellular carcinoma were allocated to receive either tamoxifen (30 mg/day) or no treatment. The patients in the two groups were matched for age, male/female ratio, Child-Pugh class, approximate tumor volume (US and CT scan), and etiology of the underlying cirrhosis. Survival of the tamoxifen-treated patients (life-table, Wilcoxon-Breslow) was significantly prolonged (P = 0.0038), with 35% (vs 0%) survival at 12 months. No difference was observed between males and females or between alcoholic and nonalcoholic cirrhosis. In 40% of tamoxifen-treated patients, the levels of alpha-fetoprotein declined. In conclusion, the antiestrogen tamoxifen appears to be effective in the palliative treatment of hepatocellular carcinoma. An initial decline in alpha-fetoprotein levels may represent an early favorable prognostic sign.

Chemiexcitation in the peroxidative metabolism of diethylstilbestrol. Metabolic products

In the presence of the surfactant hexadecyltrimethyl ammonium bromide (CTAB) a cascade of electronically excited states accompanies the successive steps in the peroxidative metabolization of the strong estrogenic and tumourogenic diethylstilbestrol. Reversing the order by necessity, we report in this first paper results with the metabolites. Exposure of 4-hydroxypropiophenone, Z,Z-dienestrol or E,E-dienestrol to horseradish peroxidase and H2O2 promotes oxygen uptake and spectral alterations. Light emission is observed provided that the surfactant CTAB is present. With the three substrates, 4-hydroxybenzoic acid and a new metabolite, p-benzoquinone, have been identified. With both dienestrol isomers, 1-(4'-hydroxyphenyl)-propan-1-on-2-ol has been identified. In all cases the emission spectrum indicates the presence of several emitters. Possible chemiexcitation routes are pointed out. From the dramatic increase of the emission by enhancers, values as high as 1 x 10(-5) are inferred for the product of the quantum yields of chemiexcitation and energy transfer.

Unresectable hepatocellular carcinoma: a prospective controlled trial with tamoxifen

The liver is an estrogen responsive organ. Clinically, estrogens may play a role in the induction of liver tumors and, experimentally, estrogens are involved in the control of hepatocyte proliferation. The results of a prospective controlled clinical trial using an anti-estrogen, tamoxifen, in patients with unresectable hepatocellular carcinoma (HCC) are presented below. Thirty-eight consecutive cirrhotics with HCC were allocated to either 30 mg/day tamoxifen or no treatment. The two groups of patients were matched for mean age, male/female ratio, Child-Pugh risk group, approximate tumor volume (US and/or CT scan) and etiology of the underlying cirrhosis. The drug appeared to have no side effects. Survival was significantly prolonged in tamoxifen-treated patients with 22% (vs. 5%) survival at 12 months. No differences were observed between males and females or alcoholic and non-alcoholic cirrhosis. In 53% of tamoxifen-treated patients the levels of alpha-fetoprotein dropped and, in this subgroup, survival was further prolonged. Tumor volume, lactate dehydrogenase (LDH) and alkaline phosphatase slowly increased, suggesting a slower, but continuous, progression of the disease. In conclusion, anti-estrogen treatment appears effective in the palliation of unresectable or otherwise untreatable HCC. A reduction in alpha-fetoprotein levels appears to be a favorable prognostic index.

Estrogen induction of hepatocellular carcinomas in Armenian hamsters

Liver tumors were found in most Armenian hamsters (Cricetulus migratorius) injected with on 15-mg pellet of diethylstilbestrol. The tumors were detectable as early as 1 1/2 mo after diethylstilbestrol administration and were usually present as multiple nodules that progressively increased in size. Histologically, the multicentric neoplasms were all hepatocellular carcinomas of varied degrees of differentiation and frequently (42.8%) contained Mallory bodies; preneoplastic lesions were not observed. This hepatocellular carcinoma hamster model is unique because estrogen alone without any other known mutagen is responsible for induction of hepatocellular carcinoma.

Effects of various inducers on diethylstilbestrol metabolism, drug-metabolizing enzyme activities and the aromatic hydrocarbon (Ah) receptor in male Syrian golden hamster liver

In order to elucidate the role of metabolic activation of the synthetic estrogen, diethylstilbestrol (DES), in the mechanism of liver tumor formation in male Syrian golden hamsters observed after combined treatment with DES and 7,8-benzoflavone (7,8-BF), the metabolism of DES and the concentrations and activities of various drug-metabolizing enzymes were studied in hamster liver microsomes after various pretreatments. The levels of the hepatic aromatic hydrocarbon (Ah) receptor were also determined. Pretreatment with 7,8-BF increased both P450 and cytochrome b5 levels, whereas phenobarbital (PB) and 3-methylcholanthrene (MC) induced P450 but not cytochrome b5. 7,8-BF pretreatment increased 7-ethoxyresorufin-O-deethylase (EROD) 3-fold and 7-pentoxyresorufin-O-dealkylase (PROD) 2.5-fold, whereas aromatic hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin-O-deethylase (ECOD) activities were only slightly induced by 7,8-BF. MC pretreatment increased EROD 8-fold and PROD activity 7-fold, whereas PB pretreatment enhanced AHH 4.5-fold and PROD activity 4-fold. In contrast to PB, pretreatment with 7,8-BF and MC reduced the oxidative metabolism of DES in hepatic microsomes, but the pattern of metabolites was identical with that in untreated controls. Treatment of hamsters with the inducers changed the hepatic Ah receptor level. PB and MC-pretreatment resulted in an increase of the receptor level 1.5-fold and 1.3-fold, respectively, whereas 7,8-BF-pretreatment leads to a 1.5-fold decrease. The dissociation constant Kd is 170 nM for the reaction of 7,8-BF with the hamster Ah receptor compared to 70 nM for 5,6-BF and 38 nM for 2,3,7,8-tetrachlorodibenzofuran (TCDF). The Kd-value is 3.6 nM for TCDF with the rat receptor protein. It is concluded from these data that metabolic activation of DES is not involved in the mechanism of hepatocarcinogenesis in this animal tumor model.

Multiple pathways for the oxidative metabolism of estrogens in Syrian hamster and rabbit kidney

Microsomal preparations from hamster kidney, a target tissue for the carcinogenic action of stilbene-type and steroidal estrogens, catalyze the oxidative metabolism of diethylstilbestrol (DES). The formation of the major metabolite Z,Z-dienestrol and of reactive intermediates capable of protein binding were mediated by enzyme activities requiring nicotinamide-adenine dinucleotide phosphate (reduced form-NADPH), cumene hydroperoxide, or arachidonic acid (ARA). In addition, hydroxylated DES metabolites were detected in NADPH-supplemented incubations. The NADPH-dependent oxidation of DES was inhibited by SKF 525A and metyrapone. Monooxygenase-catalyzed metabolism was apparently responsible for the majority of DES oxidation in microsomes from whole hamster kidneys in vitro and this activity is preferentially localized in the kidney cortex. However, ARA-dependent, i.e., prostaglandin H synthase (PHS) mediated oxidation of DES and of the catechol estrogen 2-hydroxyestrone was demonstrated as well in the medulla of both rabbit and hamster kidney. It is proposed that monooxygenase and PHS activities act in concert in the metabolic activation of carcinogenic estrogens. This appears to apply in particular to steroidal estrogens, since catechol estrogens formed by monooxygenases are further oxidized to reactive intermediates by PHS and other peroxidatic enzymes.

Effect of pretreatment of male Syrian golden hamsters with 7,8-benzoflavone and with diethylstilbestrol on P-450 isoenzyme activities and on microsomal diethylstilbestrol metabolism

Combined treatment of male Syrian golden hamsters with the synthetic estrogen diethylstilbestrol (DES) and 7,8-benzoflavone (7,8-BF) gives rise to a high incidence of hepatocellular carcinomas, whereas no such tumors are formed with DES alone nor with 7,8-BF alone. To determine whether alterations in DES metabolism may account for the observed hepatocarcinogenicity, we have studied the effect of pretreatment with 7,8-BF alone, DES alone and 7,8-BF plus DES on the levels of hepatic P-450 and cytochrome b5, on the activities of various P-450 isoenzymes and on microsomal DES metabolism. Hepatic P-450 content was significantly increased after pretreatment with 7,8-BF and decreased after DES, while combined pretreatment led to levels similar to those in untreated control animals. Hepatic cytochrome b5 was also elevated in 7,8-BF-treated hamsters; DES pretreatment had no effect, and combined pretreatment led to a slight increase. Four different substrates were used to probe P-450 isoenzyme activity. Aryl hydrocarbon hydroxylase (AHH), 7-ethoxycoumarin-O-deethylase (ECOD), 7-ethoxyresorufin-O-deethylase (EROD) and 7-pentoxyresorufin-O-dealkylase (PROD) were all elevated after 7,8-BF-pretreatment, while DES led to a decrease in these activities with the exception of AHH, where a transient increase which was observed after 8 and 20 weeks of pretreatment was back to control levels after 32 weeks. Combined pretreatment with 7,8-BF and DES led to an intermediate response (slight increase) with AHH, EROD and PROD, but not with ECOD, where a full induction comparable with that observed after 7,8-BF alone was elicited. In spite of the modulation of enzyme levels and activities observed after the various pretreatments, the metabolism of DES in microsomes from pretreated animals was virtually identical with that from controls. Therefore it is concluded that modulation of hepatic DES metabolism is not the reason for the observed hepatotumorigenicity; instead, it is speculated that 7,8-BF is the carcinogenic agent in this tumor model, and DES may act as a promotor.

Effect of pretreatment with 7,8-benzoflavone and diethylstilbestrol on the hepatic metabolism of diethylstilbestrol in the male Syrian golden hamster in vivo

Liver tumors are induced in male Syrian golden hamsters by the combined treatment with diethylstilbestrol (DES) and 7,8-benzoflavone (7,8-BF), but not with either substance alone. With the aim of clarifying whether metabolic activation of DES is involved in the mechanism of tumorigenesis in this animal model, we have studied the effect of pretreatment with 7,8-BF alone, DES alone, and 7,8-BF plus DES for 2, 8, 20 and 32 weeks on the hepatic in vivo metabolism of DES, using biliary metabolites collected from bile-duct cannulated male hamsters as probe. Formation of glucuronides and sulfates was not affected by treatment with 7,8-BF nor 7,8-BF plus DES. In contrast, animals pretreated with DES alone had a decreased amount of glucuronides and an increased proportion of unconjugated material in the bile. Oxidative metabolism of DES was not significantly altered in hamsters treated with 7,8-BF for up to 20 weeks, whereas pretreatment with DES alone and with 7,8-BF plus DES caused an enhancement of oxidative DES metabolism in vivo, leading mostly to highly polar, as yet unidentified products. From a consideration of various cytochrome P-450-associated enzyme activities, it is concluded that the observed effect on biliary DES metabolites is most likely to be due to an estrogen-induced intrahepatic cholestasis. Taken together, the data do not support a role for the metabolic activation of DES in this tumor model. Alternative mechanisms are proposed.

The effects of pretreatment with 7,8-benzoflavone on drug-metabolizing enzymes and diethylstilboestrol metabolism in male hamster liver microsomal preparations

1. Pretreatment of male Syrian golden hamsters with 7,8-benzoflavone (7,8-BF, 0.4% in the diet) for 4 and 20 weeks resulted in a significant increase in the amount of cytochrome P-450 and cytochrome b5 in hepatic microsomes. The activities of microsomal 7-ethoxycoumarin-O-deethylase (ECOD) and 7-ethoxyresorufin-O-deethylase (EROD) increased by a factor of 2 and 5, respectively, whereas aryl hydrocarbon hydroxylase (AHH) activity was only marginally enhanced. 2. Because the relative increase in cytochrome b5 exceeded that of cytochrome P-450, the ratio of P-450 to b5 decreased from 2.2 in controls to 1.6 in 7,8-BF-treated animals. 3. Hepatic microsomes from untreated and 7,8-BF-pretreated hamsters metabolize E-diethylstilboestrol (E-DES) to its stereoisomer Z-DES and to several oxidative metabolites, of which 3-hydroxy-DES and Z,Z-dienestrol were unambiguously identified by g.l.c.-mass spectrometry. 4. Pretreatment with 7,8-BF led to a marked decrease in the formation of all oxidative DES metabolites but not in the isomerization to Z-DES. The possible implication of these data for the mechanism of liver tumour formation by the combined treatment of hamsters with 7,8-BF and DES is discussed.

Inhibition of prostaglandin H synthase-catalyzed cooxidation of diethylstilbestrol by alpha-naphthoflavone and beta-naphthoflavone

Prostaglandin H synthase (PHS) has gained interest as a drug-metabolizing enzyme and has been shown to cooxidize and metabolically activate diethylstilbestrol (DES) in vitro. Both 7,8-benzoflavone (alpha-naphthoflavone, ANF) and 5,6-benzoflavone (beta-naphthoflavone, BNF) have now been studied for their effects on PHS from ram seminal vesicle microsomes by means of several in vitro assays. The PHS-catalyzed cooxidation of DES, as measured by high-performance liquid chromatography (HPLC) analysis, is inhibited by BNF and ANF at micromolar concentrations, with median inhibitory concentrations (IC-50) of less than 20 and 40 microM, respectively. The oxidation of DES is inhibited whether it is initiated by arachidonic acid or by hydrogen peroxide, indicating that the benzoflavones inhibit PHS by a mechanism different from that of indomethacin. Monitoring of cyclooxygenase activity in an oxygraph also reveals an inhibition of PHS by BNF which depends only weakly on arachidonic acid concentration; inhibition by ANF is less pronounced under these conditions. Since PHS-catalyzed conversion of the benzoflavone compounds was detected under conditions permitting cooxidation, the inhibition of PHS by benzoflavones in vitro could either be a direct effect or possibly mediated via metabolites. Our data imply that ANF and BNF, in addition to their well-known role as modifiers of mixed-function oxidases, can affect the PHS-catalyzed metabolism of xenobiotics. This is discussed in the context of adverse effects caused by DES in vivo and in cell culture and must be taken into account when interpreting the modifying effect of benzoflavones on these endpoints.

Metabolism of diethylstilbestrol in hamster hepatocytes

Under certain modulating conditions the liver of the male Syrian golden hamster is a target organ for the carcinogenic effect of the synthetic estrogen diethylstilbestrol (DES). As a basis for mechanistic studies aimed at elucidating the role of metabolic activation in the process of DES-induced neoplasia, the metabolism of 14C-DES was investigated in freshly isolated hamster hepatocytes. These oxidative metabolites of DES, viz. Z,Z-dienestrol,3'-hydroxy-DES and 1-hydroxy-E-DES, were formed in 14.2, 9.1, and 0.3% yield, respectively, when hepatocytes were incubated with 50 nmol DES/mg cellular protein for 60 min. Glucuronides (4.0%) and sulfates (2.8%) of DES and of the oxidative metabolites were also found, and non-extractable binding of radioactivity to cellular protein was observed indicating the formation of reactive intermediates. The capability of hamster hepatocytes to oxidize and conjugate DES should allow the investigation of the effects of modulators on the metabolic activation of DES in this cellular system in order to help clarify the mechanisms of DES-induced hepatocarcinogenesis.

Effect of 7,8-benzoflavone pretreatment on diethylstilbestrol metabolism, drug-metabolising enzymes and the aromatic hydrocarbon (Ah) receptor in male hamster liver

Pretreatment of male Syrian golden hamsters with 7,8-benzoflavone (7,8-BF) leads to a marked increase of cytochrome P450 and cytochrome b5 levels in the liver, whereas phenobarbital (PB) and 3-methylcholanthrene (MC) induce cytochrome P450 but not cytochrome b5 7,8-BF pretreatment has only minor effects on the activities of aryl hydrocarbon hydroxylase and 7-ethoxycoumarin-O-deethylase, but 7-ethoxyresorufin-O-deethylase is increased 3-fold. In contrast to PB, pretreatment with 7,8-BF or MC reduces the oxidative metabolism of diethylstilbestrol (DES) by hepatic microsomes in vitro. The cytosolic level of the aromatic hydrocarbon (Ah) receptor in hamster liver is decreased by 7,8-BF and slightly enhanced by MC pretreatment. PB increases the receptor level 1.5-fold. The affinity of 7,8-BF to the Ah receptor in vitro is of the same order of magnitude as that of the known ligands 5,6-benzoflavone and 2,3,7,8-tetrachlorodibenzofurane. PB and DES show no binding to the receptor protein.

Sex hormones and neoplasia: liver tumors in rodents

The association of liver tumors in women and men with the use of oral contraceptives and anabolics, respectively, has drawn attention to the hepatotumorigenic effects of sex hormones. The available evidence from long-term carcinogenicity studies in various strains of mice, rats and hamsters indicates that sex hormones are hepatotumorigenic agents, although the incidence of liver tumors is, in general, low even at doses exceeding human exposure by a factor of one hundred or more. Among the three rodent species, mice appear to be the least sensitive. Under certain modulating conditions, however, a 100% incidence of hepatocellular carcinomas can be obtained with some estrogens in male Syrian golden hamsters. The mechanism of the hepatotumorigenic effect of sex hormones is far from being clear. Whereas their tumor promoting activity is generally recognized, there is recent evidence suggesting that some sex hormones may also have initiating potential. Although the incomplete understanding of the mechanisms responsible for sex hormone induced liver neoplasia seriously hampers the assessment of the human risk, it appears to be clear that sex hormones are important modulating factors determining the incidence of hepatic tumors in rodents and possibly in humans.