Differential effects of partial hepatectomy and carbon tetrachloride administration on induction of liver cell foci in a model for detection of initiation activity

In Vivo and In Vitro Models of Hepatocellular Carcinoma: Current Strategies for Translational Modeling

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the third leading cause of cancer-related death globally. HCC is a complex multistep disease and usually emerges in the setting of chronic liver diseases. The molecular pathogenesis of HCC varies according to the etiology, mainly caused by chronic hepatitis B and C virus infections, chronic alcohol consumption, aflatoxin-contaminated food, and non-alcoholic fatty liver disease associated with metabolic syndrome or diabetes mellitus. The establishment of HCC models has become essential for both basic and translational research to improve our understanding of the pathophysiology and unravel new molecular drivers of this disease. The ideal model should recapitulate key events observed during hepatocarcinogenesis and HCC progression in view of establishing effective diagnostic and therapeutic strategies to be translated into clinical practice. Despite considerable efforts currently devoted to liver cancer research, only a few anti-HCC drugs are available, and patient prognosis and survival are still poor. The present paper provides a state-of-the-art overview of in vivo and in vitro models used for translational modeling of HCC with a specific focus on their key molecular hallmarks.

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.

Antioxidant effects of flavonoids used as food additives (purple corn color, enzymatically modified isoquercitrin, and isoquercitrin) on liver carcinogenesis in a rat medium-term bioassay

To clarify the effects of purple corn color, enzymatically modified isoquercitrin (EMIQ), and isoquercitrin (IQ), registered as natural food additives in Japan, on liver carcinogenesis in vivo, a medium-term bioassay was employed. A total of 100 male F344 rats were divided into 5 groups; groups 1 to 4 were given a single intraperitoneal injection of diethylnitrosamine (200 mg/kg b.w.) on day 1. From weeks 2 to 8, they were administered basal diet purple corn color, EMIQ, or IQ as containing test chemicals at doses of 1.0% (groups 1 and 5), 0.1% (group 2), 0.01% (group 3), or 0% (group 4) (experiments 1, 4, and 5). All rats were subjected to two-thirds partial hepatectomy at week 3 and were sacrificed at week 8. Purple corn color exerted no significant modifying effects on GST-P positive foci, preneoplastic foci, development in the liver. However, serum of rats treated with purple corn color provided evidence of antioxidant power significantly by potential antioxidant (PAO) test in vivo (experiment 2). And microarray analyses showed purple corn color to induce RNA expression such as P450 (cytochrome) oxidoreductase, phosphatidylinositol 3-kinase, and phospholipase A2 (experiment 3). Higher doses of EMIQ or IQ with strong antioxidant power in vivo by PAO test treated groups were correlated with smaller numbers of GST-P positive foci, with Spearman's rank correlation coefficients of P= 0.002 and P= 0.049, respectively (experiments 4 and 5). Therefore, the tested food additives may be effective as antioxidants in vivo and have chemopreventive potential against liver preneoplastic lesion development.

Establishment of a bioassay model for lung cancer chemoprevention initiated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female A/J mice

AIMS

In order to prevent lung cancer development in people at high risk, identification of chemopreventive agents may be important. The present study was conducted to establish a bioassay model for this purpose. In particular, the time course of 4-(methylnitrosamno)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumor development was examined to determine the most appropriate shortest period to assess effects of test agents, with 8-methoxypsoralen (8-MOP) as a typical example.

METHODS

A total of 124 mice were separated into two groups (Group A: 60 mice, Group B: 64 mice), pretreated with 100ppm 8-MOP (Group A) or basal diet (Group B) for 3 days before receiving single doses of NNK (2mg/0.1ml saline/mouse i.p.) on days 0 and 7. Subgroups of 15 mice of each group were then sacrificed after 8, 10, 12, and 16 weeks.

RESULTS

Microscopically, the earliest time point when significant differences in data for hyperplasia, adenoma and hyperplasia and adenoma could be detected was 12 weeks. A trend was noted for 8-MOP to reduce adenomas to a greater extent than hyperplasia.

DISCUSSION

In conclusion, the results of this study showed that the double i.p. treatment with NNK and 12 weeks duration are effective for detection of lung cancer chemoprevention in our A/J mouse lung tumorigenesis model.

Hepatocarcinogenic susceptibility of rasH2 mice to troglitazone in a two-stage hepatocarcinogenesis model

Six-week-old rasH2 mice were injected intraperitoneally with N-diethylnitrosamine (DEN) after partial hepatectomy and administrated 0 or 6,000 ppm troglitazone (TRG) for 10 weeks. Relative liver weight of females increased significantly in the DEN + TRG group compared to the DEN-alone group. The numbers of gamma-glutamyltranspeptidase- and proliferating cell nuclear antigen (PCNA)-positive cells tended to increase in both the sexes in the DEN + TRG group; however, these changes were not significantly different from those in the DEN-alone group. Levels of gene expressions for vascular endothelial growth factor (VEGF) and VEGFB (related to angiogenesis), tropomyosin 1 (Tpm1) and transforming growth factor-beta (related to ras/MAPK cascade activation), and PCNA (related to cell proliferation) in females were significantly higher in the DEN + TRG than in the untreated control group but not in the DEN-alone group. Only Tpm1 gene had significantly higher expression in the DEN + TRG group than in the DEN-alone group. These results suggest that rasH2 mice are not susceptible to TRG in a two-stage hepatocarcinogenesis model.

Liver initiation activity of norfloxacin but not nalidixic acid, pipemidic acid, and ciprofloxacin on in vivo short-term liver initiation assay in rats

This study aimed to examine the in vivo initiation activity of the quinolone antimicrobials--nalidixic acid (NA), pipemidic acid (PPA), ciprofloxacin (CPFX), and norfloxacin (NFLX)--by using an in vivo short-term liver initiation assay. Rats were subjected to a two-thirds partial hepatectomy on day 0 and 12 h after completion of this procedure were treated once orally with each quinolone or vehicle. Subsequently, they were fed a basal diet for 14 days and a diet containing 0.015% of 2-acetylaminofluorene for the following 10 days. On day 19, a single oral dose of carbon tetrachloride at 0.8 mL/kg body weight was administered. On day 34, they were sacrificed under ether anesthesia, and liver slices were fixed in 10% neutral buffered formalin for immunohistochemical examination of glutathione S-transferase placental form (GST-P) positive foci. Administration of NFLX resulted in a significant increase in the mean number and area of GST-P positive foci; however, administration of the three other quinolones did not produce any increase. These results suggest that only NFLX has an initiation activity in rats under the conditions used in the present study.

Overexpression of NK2 inhibits liver regeneration after partial hepatectomy in mice

AIM

To investigate the in vivo effects of NK2 on liver regeneration after partial hepatectomy (PH).

METHODS

Survival after PH was observed with 21 NK2 transgenic mice and 23 wild-type (WT) mice over 10 d. Liver regeneration was analyzed using histology and immunohistochemistry. Expressions of genes were analyzed using Northern blot analysis, immunoprecipitation and immunoblotting, and reverse transcriptase polymerase chain reaction assay. Kaplan-Meier method and the log-rank test were used for analyzing the survival after PH. Differences in the results of immunohistochemistry and percentage of liver regeneration was determined by the Student's t-test.

RESULTS

More than half of NK2 transgenic mice died within 48 h after PH. After PH, increased deposition of small lipid droplets in hepatocytes was evident and hepatic proliferation was inhibited in NK2 transgenic mice. The hepatic expression and kinase activity of HGF receptor, c-Met, were unchanged among WT mice and NK2 transgenic mice after PH. The expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in liver tissues were prolonged in NK2 transgenic mice that died after PH.

CONCLUSION

Our findings indicate that over-expression of NK2 inhibits liver regeneration after PH.

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.

Absence of in vivo genotoxicity and liver initiation activity of dicyclanil

In order to clarify the in vivo genotoxicity of dicyclanil with the potential of hepatocarcinogenicity, the stomach, colon, liver, kidney, urinary bladder, lung, brain and bone marrow of male ddY mice given a single oral administration of 100 and 200 mg/kg body weight of dicyclanil were evaluated in an alkaline single-cell gel electrophoresis (comet) assay. In addition, to investigate its possible initiation activity, partially hepatectomized male F344 rats given a single oral administration of 75 mg/kg body weight of dicyclanil were examined by a short-term liver initiation assay. Three and 24 hr after administration, cell migration, as a marker of DNA damage in comet assay, was not observed in any of the tissues of dicyclanil-treated mice. There were no significant differences in the number and area of glutathione S-transferase placental form (GST-P) positive foci, as a marker of hepatocellular preneoplastic lesions in rats, between treated and control groups. These results indicate that dicyclanil has neither in vivo genotoxicity nor initiation activity, and suggest that the hepatocarcinogenicity in mice induced by dicyclanil is attributable to a non-genotoxic mechanism.

Lack of initiation activity in rat liver of low doses of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline

It has been generally accepted that genotoxic carcinogens have no threshold in exerting their potential for cancer induction. However, the non-threshold theory can be challenged for cancer risk assessment in humans. Here we examined low dose carcinogenicity of a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), using an in vivo medium-term bioassay to detect initiating activity for rat hepatocarcinogenesis. With MeIQx initiation at various doses followed by administration of phenobarbital, a well known hepatopromoter, no induction of glutathione S-transferase placental form-positive foci, assessed as preneoplastic lesions, was noted at doses of 0.001-1 ppm. The results imply a no-observed effect level for hepatocarcinogenicity with this genotoxic agent.

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.