Initiated rat hepatocytes in primary culture: a novel tool to study alterations in growth control during the first stage of carcinogenesis

Differentiated and non-differentiated HepaRG™ cells: A possible in-vitro model system for early hepatocarcinogenesis and non-genotoxic carcinogens

Many xenobiotics are non-genotoxic carcinogens (NGC) in rodent liver. Their mode of action (MoA) and health risks for humans are unclear and no in-vitro tests are available to predict NGC. Human HepaRG™ cells in the differentiated (d-HepaRG) and non-differentiated state (nd-HepaRG) were studied as new approach methodology (NAM) for NGC. Cell-biological assays were performed with d-/nd-HepaRG and human hepatoma/hepatocarcinoma cell lines to characterize the benign/malignant phenotype. Reaction of d-/nd-HepaRG to several liver growth factors and NGC (phenobarbital, PB; cyproterone acetate, CPA; WY-14643) was compared to unaltered and premalignant rat hepatocytes in ex-vivo culture. Enzyme induction by NGC was checked by RT-qPCR/oligo-arrays. Growth, anchorage-independency, migration, clonogenicity, and in-vivo tumorigenicity of nd-HepaRG ranged between benign d-HepaRG and malignant hepatoma/hepatocarcinoma cells. All growth factors elevated DNA replication of d-/nd-HepaRG cells, similarly to unaltered/premalignant rat hepatocytes. NGC induced their prototypical enzymes in the rat and human cells, but elicited a growth response only in the unaltered/premalignant rat hepatocytes and not in human d-/nd-HepaRG cells. To conclude, a benign/premalignant phenotype of d-/nd-HepaRG cells and a reactivity towards several hepatic growth factors and NGC, as known from human hepatocytes, are essential components for an in-vitro model for early stage human hepatocarcinogenesis.The potential value as new approach methodology (NAM) for NGC is discussed.

Mesenchyme-derived factors enhance preneoplastic growth by non-genotoxic carcinogens in rat liver

Many frequently prescribed drugs are non-genotoxic carcinogens (NGC) in rodent liver. Their mode of action and health risks for humans remain to be elucidated. Here, we investigated the impact of two model NGC, the anti-epileptic drug phenobarbital (PB) and the contraceptive cyproterone acetate (CPA), on intrahepatic epithelial–mesenchymal crosstalk and on growth of first stages of hepatocarcinogenesis. Unaltered hepatocytes (HC) and preneoplastic HC (HC_PREN) were isolated from rat liver for primary culture. DNA replication of HC and HC_PREN was increased by in vitro treatment with 10 µM CPA, but not 1 mM PB. Next, mesenchymal cells (MC) obtained from liver of rats treated with either PB (50 mg/kg bw/day) or CPA (100 mg/kg bw/day), were cultured. Supernatants from both types of MC raised DNA synthesis of HC and HC_PREN. This indicates that PB induces replication of HC and HC_PREN only indirectly, via growth factors secreted by MC. CPA, however, acts on HC and HC_PREN directly as well as indirectly via mesenchymal factors. Transcriptomics and bio-informatics revealed that PB and CPA induce extensive changes in the expression profile of MC affecting many growth factors and pathways. MC from PB-treated rats produced and secreted enhanced levels of HBEGF and GDF15, factors found to suppress apoptosis and/or induce DNA synthesis in cultured HC and HC_PREN. MC from CPA-treated animals showed enhanced expression and secretion of HGF, which strongly raised DNA replication of HC and HC_PREN. In conclusion, our findings reveal profound effects of two prototypical NGC on the hepatic mesenchyme. The resulting release of factors, which suppress apoptosis and/or enhance cell replication preferentially in cancer prestages, appears to be crucial for tumor promotion by NGC in the liver.

Phenobarbital induces alterations in the proteome of hepatocytes and mesenchymal cells of rat livers

Preceding studies on the mode of action of non-genotoxic hepatocarcinogens (NGCs) have concentrated on alterations induced in hepatocytes (HCs). A potential role of non-parenchymal liver cells (NPCs) in NGC-driven hepatocarcinogenesis has been largely neglected so far. The aim of this study is to characterize NGC-induced alterations in the proteome profiles of HCs as well as NPCs. We chose the prototypic NGC phenobarbital (PB) which was applied to male rats for a period of 14 days. The livers of PB-treated rats were perfused by collagenase and the cell suspensions obtained were subjected to density gradient centrifugation to separate HCs from NPCs. In addition, HCs and NPC isolated from untreated animals were treated with PB in vitro. Proteome profiling was done by CHIP-HPLC and ion trap mass spectrometry. Proteome analyses of the in vivo experiments showed many of the PB effects previously described in HCs by other methods, e.g. induction of phase I and phase II drug metabolising enzymes. In NPCs proteins related to inflammation and immune regulation such as PAI-1 and S100-A10, ADP-ribosyl cyclase 1 and to cell migration such as kinesin-1 heavy chain, myosin regulatory light chain RLC-A and dihydropyrimidinase-related protein 1 were found to be induced, indicating major PB effects on these cells. Remarkably, in vitro treatment of HCs and NPCs with PB hardly reproduced the proteome alterations observed in vivo, indicating differences of NGC induced responses of cells at culture conditions compared to the intact organism. To conclude, the present study clearly demonstrated that PB induces proteome alterations not only in HCs but also in NPCs. Thus, any profound molecular understanding on the mode of action of NGCs has to consider effects on cells of the hepatic mesenchyme.

Detection of initiation activity of 1,2-dimethylhydrazine in in vivo medium-term liver initiation assay system using 4-week-old rats without hepatocellular proliferative stimuli during the test chemical treatment period

We have developed an in vivo medium-term liver initiation assay system to detect initiation activities of chemicals on multi-organ carcinogenesis. However, cell proliferation stimuli during the test chemical treatment period, required in the previously used assay models using adult rats, are laborious; moreover, those cause decrease of hepatic metabolic enzymes and psychological and physical discomfort to animals resulting in inaccurate interpretation. Therefore, we investigated the utility of another in vivo medium-term liver initiation assay model using 4-week-old rats without the cell proliferation stimuli. In this study, we confirmed that 4-week-old and 4.5-week-old male rats have high hepatocyte proliferation activity and similar enzyme activities of hepatic Cytochrome P450 subtypes as compared with 8-week-old male rats. Next, the in vivo medium-term liver initiation assay model using 4-week-old rats without cell proliferation stimuli was evaluated for the detection of the initiation activity of 1,2-dimethylhydrazine (DMH), which is a well-known genotoxic carcinogen. Four-week-old rats were orally administered DMH (single dose, 4 or 16 mg/kg; or 4-day repeat, 1 or 4 mg/kg); subsequently, these rats were treated promotion treatment consisted of administration of 2-acetylaminofluorene and carbon tetrachloride. Four weeks after the first DMH administration, the glutathione S-transferase placental form (GST-P)-positive foci induced by DMH in the liver was measured immunohistochemically. The inductions of GST-P-positive foci in all DMH-treated groups were dose-dependent, duration-dependent and significantly higher than that in non-DMH-treated group. From these results, our assay model was detected the initiation activity of DMH simply, and would be useful to evaluate the carcinogenicity of chemicals.

HB-EGF is a paracrine growth stimulator for early tumor prestages in inflammation-associated hepatocarcinogenesis

BACKGROUND/AIMS

We studied the impact of heparin-binding epidermal growth factor-like growth factor (HB-EGF) on inflammation-driven hepatocarcinogenesis.

METHODS

HB-EGF expression was determined by qRT-PCR and immunodetection in hepatocellular adenoma and carcinoma and in mesenchymal (MC) and parenchymal liver cells obtained from different models of inflammation. The functions of HB-EGF in early hepatocarcinogenesis were assessed in co-cultures of unaltered and initiated/premalignant hepatocytes.

RESULTS

In human and rat (pre)malignant liver lesions, HB-EGF levels were comparable to that of the surrounding tissue. In inflamed livers HB-EGF was expressed predominantly in MC and was further increased by pro-inflammatory lipopolysaccharide (LPS) or linoleic acid hydroperoxide (LOOH). In culture, DNA-replication occurred rather in initiated/premalignant than unaltered hepatocytes and was further elevated by LOOH- or LPS-stimulated MC-supernatants. The supernatant effects were abrogated by pre-incubation with HB-EGF-neutralizing antisera. HB-EGF itself induced DNA-replication and mitosis preferentially in the initiated/premalignant cells. When transducing hepatocytes with a dominant-negative ErbB1-construct, HB-EGF-induced DNA-replications were blocked completely in unaltered hepatocytes but incompletely in initiated/premalignant cells, which suggests elevated ErbB-mediated signal transduction in first stages of hepatocarcinogenesis.

CONCLUSIONS

Pro-inflammatory stimuli induce the release of HB-EGF from MC, which stimulates DNA-replication in initiated/premalignant hepatocytes. Similar mechanisms may contribute to carcinogenesis in human inflammatory liver diseases.

New cellular tools reveal complex epithelial-mesenchymal interactions in hepatocarcinogenesis

To enable detailed analyses of cell interactions in tumour development, new epithelial and mesenchymal cell lines were established from human hepatocellular carcinoma by spontaneous outgrowth in culture. We obtained several hepatocarcinoma (HCC)-, B-lymphoblastoid (BLC)-, and myofibroblastoid (MF)-lines from seven cases. In-depth characterisation included cell kinetics, genotype, tumourigenicity, expression of cell-type specific markers, and proteome patterns. Many functions of the cells of origin were found to be preserved. We studied the impact of the mesenchymal lines on hepatocarcinogenesis by in vitro assays. BLC- and MF-supernatants strongly increased the DNA replication of premalignant hepatocytes. The stimulation by MF-lines was mainly attributed to HGF secretion. In HCC-cells, MF-supernatant had only minor effects on cell growth but enhanced migration. MF-lines also stimulated neoangiogenesis through vEGF release. BLC-supernatant dramatically induced death of HCC-cells, which could be largely abrogated by preincubating the supernatant with TNFβ-antiserum. Thus, the new cell lines reveal stage-specific stimulatory and inhibitory interactions between mesenchymal and epithelial tumour cells. In conclusion, the new cell lines provide unique tools to analyse essential components of the complex interplay between the microenvironment and the developing liver cancer, and to identify factors affecting proliferation, migration and death of tumour cells, neoangiogenesis, and outgrowth of additional malignancy.

Hepatotoxicity induced by cyproterone acetate: A report of three cases

Cyproterone acetate (CPA) is a steroidal synthetic progestagen and anti-androgenic compound widely administered in prostate cancer which has been evidentially correlated with a severe hepatotoxic potency. Three male patients aged 78-83 years are presented, in whom severe hepatotoxic reactions emerged after CPA administration. Patients were treated with CPA at the doses of 200-300 mg/d for malignant prostate disease for 3-12 mo prior to the acute manifestation of the hepatic disease. Clinical features compatible with mixed hepatocellular and cholestatic liver disease including jaundice, white stools and dark urine, manifested in all three cases whereas encephalopathy and ascites were present in two of the patients. Other primary causes of hepatotoxicity (alcohol consumption and viral hepatitis) were also verified in two cases, and in those patients biopsy findings revealed the presence of cirrhotic lesions in liver parenchyma. Discontinuation of the therapeutic agent led to the amelioration of the clinical profile in all the patients whereas a patient died 40 d after hospital admission due to sepsis, despite acute liver disease improvement. The current article highlights the hepatotoxic potency of a widely administered therapeutic agent and illustrates the importance of clinical surveillance especially in patients with previous hepatic diseases. Three relevant cases are reported and a review of the published literature is made.

Deregulation of the activin/follistatin system in hepatocarcinogenesis

BACKGROUND/AIMS

Activins A and E negatively regulate hepatic cell number by inhibiting cell replication and inducing apoptosis. Follistatin and follistatin-like 3 bind activins and antagonise their biological activities. Aim of our study was to investigate, whether activins and follistatins may play a role in hepatocarcinogenesis.

METHODS

Expression levels of follistatin, follistatin-like 3, and activin subunits beta(A) as well as beta(E) were investigated in chemically induced rat and human liver tumours by real-time PCR and immunohistochemistry. In addition, the effects of follistatin and activin A on DNA synthesis of normal as well as preneoplastic hepatocytes and hepatoma cells were analysed.

RESULTS

Follistatin was overexpressed while both activin subunits were downregulated in the majority of rat and human liver tumours. Follistatin-like 3 expression was low in normal but enhanced in malignant rat liver. In human normal liver, in contrast, it was abundantly expressed but downregulated in liver cancer. Administration of follistatin to normal and preneoplastic hepatocytes stimulated DNA synthesis preferentially in preneoplastic rat hepatocytes, whereas activin A repressed it.

CONCLUSIONS

The balanced expression of follistatins and activins becomes deregulated during hepatocarcinogenesis. The sensitivity of preneoplastic hepatocytes to activin signals suggests the activin/follistatin system as promising target for therapeutic intervention.

Non-parenchymal liver cells support the growth advantage in the first stages of hepatocarcinogenesis

Hepatocellular carcinoma almost always arises in chronically inflamed livers. We developed a culture model to study the role of non-parenchymal cells (NPCs) for inflammation-driven hepatocarcinogenesis. Rats were treated with the carcinogen N-nitrosomorpholine, which induced initiated hepatocytes expressing the marker placental glutathione-S-transferase (GSTp). After 21 days two preparations of hepatocytes were made: (i) conventional ones (Hep-conv) containing NPCs and (ii) hepatocytes purified of NPCs (Hep-pur). Initiated hepatocytes, being positive for GSTp (GSTp-pos) were present in both preparations and were cultured along with normal hepatocytes, being negative for GSTp (GSTp-neg). Under any culture condition DNA synthesis was approximately 4-fold higher in GSTp-pos than in GSTp-neg hepatocytes demonstrating the inherent growth advantage of the first stages of hepatocarcinogenesis. Hepatocytes showed approximately 3-fold lower rates of DNA synthesis in Hep-pur than in Hep-conv, which was elevated above Hep-conv levels by addition of NPC or NPC-supernatant. Pretreatment of NPCs with proinflammatory lipopolysaccharide (LPS) further increased DNA synthesis. Thus, NPCs release soluble growth stimulators. Next we investigated the effect of specific cytokines produced by NPCs. Tumour necrosis factor alpha and interleukin 6 barely altered DNA synthesis, whereas hepatocyte growth factor (HGF), keratinocyte growth factor (KGF) and the heparin-binding epidermal growth factor-like growth factor (HB-EGF) were potent inducers of DNA replication in both, GSTp-neg and GSTp-pos cells. In conclusion, DNA synthesis of hepatocytes is increased by factors released from NPCs, an effect augmented by LPS-stimulation. NPC-derived cytokines, such as KGF, HGF and HB-EGF, stimulate DNA synthesis preferentially in initiated hepatocytes, presumably resulting in tumour promotion. Similar mechanisms may contribute to carcinogenesis in human inflammatory liver diseases.

Inherent growth advantage of (pre)malignant hepatocytes associated with nuclear translocation of pro-transforming growth factor alpha

The pro-peptide of transforming growth factor alpha (proTGFalpha) was recently found in hepatocyte nuclei preparing for DNA replication, which suggests a role of nuclear proTGFalpha for mitogenic signalling. This study investigates whether the nuclear occurrence of the pro-peptide is involved in the altered growth regulation of (pre)malignant hepatocytes. In human hepatocarcinogenesis, the incidence of proTGFalpha-positive and replicating nuclei gradually increased from normal liver, to dysplastic nodules, to hepatocellular carcinoma. ProTGFalpha-positive nuclei almost always were in DNA synthesis. Also, in rat hepatocarcinogenesis, proTGFalpha-positive nuclei occurred in (pre)malignant hepatocytes at significantly higher incidences than in unaltered hepatocytes. For functional studies unaltered (GSTp(-)) and premalignant (GSTp(+)) rat hepatocytes were isolated by collagenase perfusion and cultivated. Again, DNA synthesis occurred almost exclusively in proTGFalpha-positive nuclei. GSTp(+) hepatocytes showed an approximately 3-fold higher frequency of proTGFalpha-positive nuclei and DNA replication than GSTp(-) cells. Treatment of cultures with the mitogen cyproterone acetate (CPA) elevated the incidence of proTGFalpha-positive nuclei and DNA synthesis in parallel. Conversely, transforming growth factor beta1 (TGFbeta1) lowered both. These effects of CPA and TGFbeta1 were significantly more pronounced in GSTp(+) than in GSTp(-) hepatocytes. In conclusion, nuclear translocation of proTGFalpha increases in the course of hepatocarcinogenesis and appears to be involved in the inherent growth advantage of (pre)malignant hepatocytes.

Intraperitoneal injection ofd-galactosamine provides a potent cell proliferation stimulus for the detection of initiation activities of chemicals in rat liver

In an in vivo 5-week initiation assay model, chemical hepatectomy by hepato-toxicant administration was utilized as a cell proliferation stimulus as an alternative to the two-thirds partial hepatectomy. The study investigated the effect of an intraperitoneal (i.p.) injection of D-galactosamine (D-gal) for this purpose in a medium-term liver bioassay, with a further focus on cell proliferation kinetics and cytochrome P450 (CYP) expression. In experiment I, cell proliferation in rat liver after a single administration of D-gal (700 mg kg(-1), i.p.) was analysed by the bromodeoxyuridine (BrdU) labeling method, and CYP isozymes were quantified by immunoblotting. In experiment II, the induction of glutathione S-transferase placental form (GST-P) positive foci by 1,2-dimethylhydrazine (DMH) was evaluated in a modified in vivo 5-week initiation assay model. At 84 hours after single administration of d-gal (i.p.) the BrdU index was markedly elevated (27.5% +/- 9.5%). Although CYP 2E1 and 1A2 apoprotein contents decreased transiently to less than 20% of the control level, subsequently they recovered to 60% and 40% of the control level, respectively, at 84 hours. Induction of GST-P positive foci in the group given DMH at 84 hours after a single administration of d-gal was significantly greater than in the control group, correlating with the kinetics of cell proliferation. In conclusion, the sensitivity of the present initiation assay using D-gal i.p. is high, so that D-gal i.p. can be considered an effective cell proliferation stimulus.

Primary hepatocyte culture in collagen gel mixture and collagen sandwich

AIM: To explore the methods of hepatocytes culture in a collagen gel mixture or between double layers of collagen sandwich configuration and to examine the functional and cytomorphological characteristics of cultured hepatocytes.

METHODS: A two-step collagenase perfusion technique was used to isolate the hepatocytes from Wistar rats or newborn Chinese experimental piglets. The isolated hepatocytes were cultured in a collagen gel mixture or between double layers of collagen sandwich configuration respectively. The former was that rat hepatocytes were mixed with type I rat tail collagen solution till gelled, and the medium was added onto the gel. The latter was that swine hepatocytes were seeded on a plate precoated with collagen gel for 24 h, then another layer of collagen gel was overlaid, resulting in a sandwich configuration. The cytomorphological characteristics, albumin secretion, and LDH-release of the hepatocytes cultured in these two models were examined.

RESULTS: Freshly isolated rat hepatocytes were successfully mixed and fixed in collagen gel, and cultured in the gel condition. During the culture period, the urea synthesized and secreted by rat hepatocytes was detected throughout the period. Likewise, newborn experimental piglet hepatocytes were successfully fixed between the double layers of collagen gel, forming a sandwich configuration. Within a week of culture, the albumin secreted by swine hepatocytes was detected by SDS/PAGE analysis. The typical cytomorphological characteristics of the hepatocytes cultured by the above two culture models were found under a phase-contrast microscope. There was little LDH-release during the culture period.

CONCLUSION: Both collagen gel mixture and double layers of collagen sandwich configuration can provide cultural conditions much closer to in vivo environment, and are helpful for maintaining specific hepatic functions and cytomorphological characteristics. A collagen gel mixture culture may be more eligible for the study of bioartificial livers.

Distinction of carcinogens from mutagens by induction of liver cell foci in a model for detection of initiation activity

Initiating activities of 26 chemicals were investigated in an in vivo 5 week initiation assay model with evaluation of the induction of glutathione S-transferase placental form (GST-P) positive foci as end-point lesions. With the five genotoxic hepatocarcinogens (diethylnitrosamine, dimethylnitrosamine, 2-acetylaminofluorene, N-bis(2-hydroxypropyl)-nitrosamine and safrole) and 11 genotoxic non-hepatocarcinogens, (2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide, benzo[a]pyrene, N-butyl-N-(4-hydroxybutyl)nitrosamine, 7,12-dimethylbenz[a]anthracene, 1,2-dimethylhydrazine, N-ethyl-N-hydroxyethylnitrosamine, 3-methylcholanthrene, N-methyl-N-nitrosourea, N-methyl-N'-nitro-N-nitrosoguanidine, 4-nitroquinoline 1-oxide and 8-hydroxyquinoline), the numbers of GST-P positive foci were significantly higher than in the controls. On the other hand, the mutagenic non-carcinogens (quercetin, p-phenylenediamine dihydrochloride, 2-chloroethanol and 6-hydroquinoline) did not cause a significant increase. Similarly, non-genotoxic hepatocarcinogens of the hepatopromotor class and promotors which target organs other than the liver did not induce GST-P positive foci. The specificity was thus remarkable. Moreover, regardless of the target organ, mutagenic carcinogens were detected by this in vivo 5 week initiation assay, which therefore constitutes a powerful method for screening for carcinogenic potential, especially in the initiation stage of carcinogenesis.

A novel mechanism for mitogenic signaling via pro-transforming growth factor alpha within hepatocyte nuclei

Transforming growth factor (TGF) alpha, an important mediator of growth stimulation, is known to act via epidermal growth factor receptor (EGF-R) binding in the cell membrane. Here we show by immunohistology, 2-dimensional immunoblotting, and mass spectrometry of nuclear fractions that the pro-protein of wild-type TGF-alpha occurs in hepatocyte nuclei of human, rat, and mouse liver. Several findings show a close association between nuclear pro-TGF-alpha and DNA synthesis. (1) The number of pro-TGF-alpha+ nuclei was low in resting liver and increased dramatically after partial hepatectomy and after application of hepatotoxic chemicals or the primary mitogen cyproterone acetate (CPA); in any case, S phase occurred almost exclusively in pro-TGF-alpha+ nuclei. The same was found in human cirrhotic liver. (2) In primary culture, 7% of hepatocytes synthesized pro-TGF-alpha, which then translocated to the nucleus; 70% of these nuclei subsequently entered DNA replication, whereas only 2% of pro-TGF-alpha- hepatocytes were in S phase. (3) The frequency of hepatocytes coexpressing pro-TGF-alpha and DNA synthesis was increased by the hepatomitogens CPA or prostaglandin E(2) and was decreased by the growth inhibitor TGF-beta1. (4) Treatment with mature TGF-alpha increased DNA synthesis exclusively in pro-TGF-alpha- hepatocytes, which was abrogated by the EGF-R tyrosine kinase inhibitor tyrphostin A25. In conclusion, TGF-alpha gene products may exert mitogenic effects in hepatocytes via 2 different signaling mechanisms: (1) the "classic" pathway of mature TGF-alpha via EGF-R in the membrane and (2) a novel pathway involving the presence of pro-TGF-alpha in the nucleus.

The use of toxicokinetic and toxicodynamic data in risk assessment: an international perspective

Risk assessment of chemicals is a process which is usually based on data derived from animal testing in which the exposure of animals results in toxicological effects. By extrapolation, the dose/exposure in humans, which will not result in toxicological effects ('safe dose', 'safe exposure'), is estimated. Traditional approaches use 'safety factors' or 'uncertainty factors' to extrapolate from animal to man and from the 'mean' subject to the general population, including sensitive subgroups. Traditionally, a default factor of 10 has been used to account for interspecies variation. It is proposed that this factor be subdivided into a subfactor to address the toxicokinetic aspects and a second subfactor for the toxicodynamic aspects. Likewise, a default factor of 10 with subfactors is proposed to account for the intraspecies variability. In the framework of the International Program on Chemical Safety's (IPCS) project on the Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals, an activity has been initiated to provide guidance to risk assessors on the use of quantitative chemical specific data to account for interspecies variation and interindividual variability in risk assessment. To address the toxicokinetic aspects, the active species, the relevant internal exposure and the adequate metrics must be considered. Data quality and availability, in vitro or in vivo, the route of administration and the relevant dose level are relevant information for interspecies extrapolation. The availability of experimental data, including the relevance of the population studied, the number of subjects and/or samples obtained in the relevant group allow one to estimate the population distribution, e.g. difference between central tendency and given percentiles. In a similar fashion, the toxicodynamic data must be addressed. In addition to the identification of the active chemical species, the relevant endpoint must be determined. In extrapolation from animal to man, in most of the cases, the definitive endpoint (e.g. anemia) is lacking. It can be substituted by in vitro data (e.g. in vitro hemolysis) if it is a key event and relevant for the toxicity in animal as well as in humans. In extrapolating from animal to man, the dose-effect relationship plays an important role. To account for the toxicodynamic variability in the human population, similar aspects have to be taken into consideration, which have been discussed for toxicokinetics. The IPCS document is available at the IPCS website and risk assessors are invited to use the framework and report back their experience with it to enable revision and improvement.

Acute hepatitis induced by cyproterone acetate

OBJECTIVE

To report a case of acute hepatitis resulting from the use of cyproterone acetate, an adjuvant treatment for prostate cancer.

CASE SUMMARY

An 87 year-old white man, admitted to surgery for prostate cancer, received cyproterone acetate 300 mg/d orally and developed acute hepatitis, which initially was diagnosed clinically. A liver biopsy showed changes suggestive of acute cholestatic hepatitis. Cyprotorone was stopped immediately, and the patient was subsequently treated with corticosteroids. He then improved rapidly.

DISCUSSION

Cyproterone acetate is thought to be well tolerated, but some authors have reported severe hepatic reactions, in particular acute hepatitis, fatal fulminant hepatic failure, and hepatocellular carcinoma. The above-mentioned hepatotoxicity represents an idiosyncratic drug reaction, probably due to the hepatomitogen action of cyproterone, causing an increase of hepatocytes expressing placental glutathione S-transferase, which are considered preneoplastic elements.

CONCLUSION

This case suggests the possibility of hepatotoxicity from cyproterone.

The use of toxicodynamics in risk assessment

Risk assessment of xenobiotics is a qualitative and quantitative assessment of toxic properties conventionally based on data resulting from tests in animals exposed to the substance. The assessment of dose-effect relationship includes evaluation of exposure at the site of action. More recently, emphasis is put on understanding the relationship between exposure at the site of action and the resulting effect, i.e. toxicodynamic. In this respect, results from genotoxicity studies may be a measure for exposure and at the same time of an effect. Results of toxicodynamic endpoints such as binding to receptors or release of hormones have been used when replacing default values for interspecies extrapolation. It may also be envisaged to use toxicodynamic endpoints in order to get an estimate of intraspecies variability. It was demonstrated that this approach may be helpful only if the relationship between the toxicodynamic endpoint and the definite endpoint is known by using the example of bisphenol A. Whereas there are clear effects of bisphenol A in in vitro and ex vivo studies, the classical two generation study has not been able to detect an effect on reproduction and/or fertility. Looking in the future development of toxicodynamic endpoints, gene profiling and the analysis of proteins ('proteomics') may be helpful tools employed in screening and being related to the mode of action are explored for their suitability in terms of toxicodynamic endpoints.