Regulatory mechanism of glutathione S-transferase P-form during chemical hepatocarcinogenesis: old wine in a new bottle

Aristolochic acid I promoted clonal expansion but did not induce hepatocellular carcinoma in adult rats

Aristolochic acid I (AAI) is a well-known nephrotoxic carcinogen, which is currently reported to be also associated with hepatocellular carcinoma (HCC). Whether AAI is a direct hepatocarcinogen remains controversial. In this study we investigated the association between AAI exposure and HCC in adult rats using a sensitive rat liver bioassay with several cofactors. Formation of glutathione S-transferase placental form-positive (GST-P+) foci was used as the marker for preneoplastic lesions/clonal expansion. We first conducted a medium-term (8 weeks) study to investigate whether AAI had any tumor-initiating or -promoting activity. Then a long-term (52 weeks) study was conducted to determine whether AAI can directly induce HCC. We showed that oral administration of single dose of AAI (20, 50, or 100 mg/kg) in combination with partial hepatectomy (PH) to stimulate liver proliferation did not induce typical GST-P+ foci in liver. In the 8-week study, only high dose of AAI (10 mg · kg-1 · d-1, 5 days a week for 6 weeks) in combination with PH significantly increased the number and area of GST-P+ foci initiated by diethylnitrosamine (DEN) in liver. Similarly, only high dose of AAI (10 mg· kg-1· d-1, 5 days a week for 52 weeks) in combination with PH significantly increased the number and area of hepatic GST-P+ foci in the 52-week study. No any nodules or HCC were observed in liver of any AAI-treated groups. In contrast, long-term administration of AAI (0.1, 1, 10 mg· kg-1· d-1) time- and dose-dependently caused death due to the occurrence of cancers in the forestomach, intestine, and/or kidney. Besides, AAI-DNA adducts accumulated in the forestomach, kidney, and liver in a time- and dose-dependent manner. Taken together, AAI promotes clonal expansion only in the high-dose group but did not induce any nodules or HCC in liver of adult rats till their deaths caused by cancers developed in the forestomach, intestine, and/or kidney. Findings from our animal studies will pave the way for further large-scale epidemiological investigation of the associations between AA and HCC.

Coffee consumption delays the hepatitis and suppresses the inflammation related gene expression in the Long-Evans Cinnamon rat

BACKGROUND AND AIMS

Large-scale epidemiological studies have shown that drinking more than two cups of coffee per day reduces the risks of hepatitis and liver cancer. However, the heterogeneity of the human genome requires studies of experimental animal models with defined genetic backgrounds to evaluate the coffee effects on liver diseases. We evaluated the efficacy of coffee consumption with one of experimental animal models for human disease.

METHOD

We used the Long Evans Cinnamon (LEC) rat, which onsets severe hepatitis and high incidence of liver cancer, due to the accumulation of copper and iron in livers caused by the genetic mutation in Atp7B gene, and leading to the continuous oxidative stress. We determined the expression of inflammation related genes, and amounts of copper and iron in livers, and incidence of the pre-neoplastic foci in the liver tissue of LEC rats.

RESULTS

Coffee administration for 25 weeks delayed the occurrence of hepatitis by two weeks, significantly improved survival, reduced the expression of inflammatory cytokines, and reduced the incidence of small pre-neoplastic liver foci in LEC rats. There was no significant difference in the accumulation of copper and iron in livers, indicating that coffee administration does not affect to the metabolism of these metals. These findings indicate that drinking coffee potentially prevents hepatitis and liver carcinogenesis through its anti-inflammatory effects.

CONCLUSION

This study showed the efficacy of coffee in the prevention of hepatitis and liver carcinogenesis in the LEC model.

Inhibition of 12-lipoxygenase reduces proliferation and induces apoptosis of hepatocellular carcinoma cells in vitro and in vivo

BACKGROUND

12-lipoxygenase (12-LOX) has been reported to be an important gene in cancer cell proliferation and survival, and tumor metastasis. However, its role in hepatocellular carcinoma (HCC) cells remains unknown.

METHODS

Expression of 12-LOX was assessed in a diethyl-nitrosamine-induced rat HCC model, and in SMMC-7721, HepG2 and L-02 cells using immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR). GST-π and Ki-67 were determined in vivo by immunohistochemical staining. Apoptosis was evaluated by TUNEL assay. Cell viability and apoptosis were determined by MTT assay and flow cytometry, respectively. Apoptosis-related proteins in SMMC-7721 and HepG2 cells were detected by Western blotting.

RESULTS

Immunohistochemical staining and RT-PCR showed that 12-LOX was over-expressed in rat HCC and two HCC cell lines, while the expression was inhibited by baicalein, a specific inhibitor of 12-LOX. Baicalein inhibited cell proliferation and induced apoptosis in rat HCC and both cell lines in a dose- and time-dependent manner. Our in vivo study demonstrated that baicalein also reduced neoplastic nodules. Mechanistically, baicalein reduced Bcl-2 protein expression coupled with a slight increase of the expression of Bax and activation of caspase-3. Furthermore, baicalein inhibited the activation of ERK-1/2 (phosphorylated). Interestingly, the effects of baicalein were reversed by 12(S)-HETE, a metabolite of 12-LOX.

CONCLUSIONS

Inhibition of 12-LOX leads to reduced numbers of HCC cells, partially caused by increased apoptosis. 12-LOX may be a potential molecular target for HCC prevention and treatment.

Diversity in antioxidant response enzymes in progressive stages of human nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), which occurs in approximately 17 to 40% of Americans, encompasses progressive stages of liver damage ranging from steatosis to nonalcoholic steatohepatitis (NASH). Inflammation and oxidative stress are known characteristics of NAFLD; however, the precise mechanisms occurring during disease progression remain unclear. The purpose of the current study was to determine whether the expression or function of enzymes involved in the antioxidant response, NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione transferase (GST), and glutamate cysteine ligase, are altered in the progression of human NAFLD. Human livers staged as normal, steatotic, NASH (fatty), and NASH (not fatty) were obtained from the Liver Tissue Cell Distribution System. NQO1 mRNA, protein, and activity tended to increase with disease progression. mRNA levels of the GST isoforms A1, A2, A4, M3, and P1 increased with NAFLD progression. Likewise, GST A and P protein increased with progression; however, GST M protein levels tended to decrease. Of interest, total GST activity toward the substrate 1-chloro-2,4-dinitrobenzene decreased with NAFLD progression. GSH synthesis does not seem to be significantly dysregulated in NAFLD progression; however, the GSH/oxidized glutathione redox ratio seemed to be reduced with disease severity, indicating the presence of oxidative stress and depletion of GSH throughout progression of NAFLD. Malondialdehyde concentrations were significantly increased with disease progression, further indicating the presence of oxidative stress. Nuclear immunohistochemical staining of nuclear factor E2-related factor 2 (Nrf2), an indicator of activation of the transcription factor, was evident in all stages of NAFLD. The current data suggest that Nrf2 activation occurs in response to disease progression followed by induction of specific Nrf2 targets, whereas functionality of specific antioxidant defense enzymes seems to be impaired as NAFLD progresses.

Characteristic gene expression profiles in the progression from liver cirrhosis to carcinoma induced by diethylnitrosamine in a rat model

Background

Liver cancr is a heterogeneous disease in terms of etiology, biologic and clinical behavior. Very little is known about how many genes concur at the molecular level of tumor development, progression and aggressiveness. To explore the key genes involved in the development of liver cancer, we established a rat model induced by diethylnitrosamine to investigate the gene expression profiles of liver tissues during the transition to cirrhosis and carcinoma.

Methods

A rat model of liver cancer induced by diethylnitrosamine was established. The cirrhotic tissue, the dysplasia nodules, the early cancerous nodules and the cancerous nodules from the rats with lung metastasis were chosen to compare with liver tissue of normal rats to investigate the differential expression genes between them. Affymetrix GeneChip Rat 230 2.0 arrays were used throughout. The real-time quantity PCR was used to verify the expression of some differential expression genes in tissues.

Results

The pathological changes that occurred in the livers of diethylnitrosamine-treated rats included non-specific injury, fibrosis and cirrhosis, dysplastic nodules, early cancerous nodules and metastasis. There are 349 upregulated and 345 downregulated genes sharing among the above chosen tissues when compared with liver tissue of normal rats. The deregulated genes play various roles in diverse processes such as metabolism, transport, cell proliferation, apoptosis, cell adhesion, angiogenesis and so on. Among which, 41 upregulated and 27 downregulated genes are associated with inflammatory response, immune response and oxidative stress. Twenty-four genes associated with glutathione metabolism majorly participating oxidative stress were deregulated in the development of liver cancer. There were 19 members belong to CYP450 family downregulated, except CYP2C40 upregulated.

Conclusion

In this study, we provide the global gene expression profiles during the development and progression of liver cancer in rats. The data obtained from the gene expression profiles will allow us to acquire insights into the molecular mechanisms of hepatocarcinogenesis and identify specific genes (or gene products) that can be used for early molecular diagnosis, risk analysis, prognosis prediction, and development of new therapies.

Glutathione in Cancer Biology and Therapy

The glutathione (GSH) content of cancer cells is particularly relevant in regulating mutagenic mechanisms, DNA synthesis, growth, and multidrug and radiation resistance. In malignant tumors, as compared with normal tissues, that resistance associates in most cases with higher GSH levels within these cancer cells. Thus, approaches to cancer treatment based on modulation of GSH should control possible growth-associated changes in GSH content and synthesis in these cells. Despite the potential benefits for cancer therapy of a selective GSH-depleting strategy, such a methodology has remained elusive up to now. Metastatic spread, not primary tumor burden, is the leading cause of cancer death. For patient prognosis to improve, new systemic therapies capable of effectively inhibiting the outgrowth of seeded tumor cells are needed. Interaction of metastatic cells with the vascular endothelium activates local release of proinflammatory cytokines, which act as signals promoting cancer cell adhesion, extravasation, and proliferation. Recent work shows that a high percentage of metastatic cells with high GSH levels survive the combined nitrosative and oxidative stresses elicited by the vascular endothelium and possibly by macrophages and granulocytes. ?-Glutamyl transpeptidase overexpression and an inter-organ flow of GSH (where the liver plays a central role), by increasing cysteine availability for tumor GSH synthesis, function in combination as a metastatic-growth promoting mechanism. The present review focuses on an analysis of links among GSH, adaptive responses to stress, molecular mechanisms of invasive cancer cell survival and death, and sensitization of metastatic cells to therapy. Experimental evidence shows that acceleration of GSH efflux facilitates selective GSH depletion in metastatic cells.

Development of glutathione S-transferase-P-negative foci accompanying nuclear factor-erythroid 2-related factor 2 expression during early stage of rat hepatocarcinogenesis

Glutathione S-transferase P (GST-P), a marker for rat hepatic preneoplastic lesions, is suggested to bind to Jun N-terminal kinase (JNK) to repress stress response, and GST-P gene expression is regulated by a transcription factor, nuclear factor-erythroid 2-related factor 2 (Nrf2). In this study, we examined by immunohistochemistry whether JNK2, p38 mitogen-activated protein kinase, and Nrf2 were expressed in GST-P-positive foci induced by the Solt-Farber protocol. At 2 weeks after partial hepatectomy, all GST-P-positive foci were negative for p38, and 86.4 +/- 5.6% and 64.7 +/- 6.3% of GST-P-positive foci were negative for JNK2 and Nrf2, respectively. Western blot analysis showed decreased p38 mitogen-activated protein kinase and JNK2 expression in livers treated with the protocol. In immunohistochemistry, besides GST-P-positive foci, GST-P-negative foci were detected as p38-negative foci in the surrounding tissues positive for p38. In contrast to GST-P-positive foci, most GST-P-negative foci showed enhanced Nrf2 expression. The number of GST-P-negative foci was 76 +/- 18/10 mm(2) of liver section at 2 weeks, but was undetectable at 1 week. The area of GST-P-negative foci was 0.09 +/- 0.05 mm(2), smaller than that of GST-P-positive ones (0.29 +/- 0.23). After treatment with carbon tetrachloride, small vacuoles due to liver injury were frequently observed inside GST-P-negative foci but less frequently in GST-P-positive foci. However, this treatment resulted in expression of JNK2, p38, and Nrf2 in both foci. These results showed development of GST-P-negative foci during the early stage of hepatocarcinogenesis and suggested that Nrf2 is not responsible for GST-P expression in rat hepatic preneoplastic foci.

Gene expression profile related to the progression of preneoplastic nodules toward hepatocellular carcinoma in rats

In this study, we investigated the time course gene expression profile of preneoplastic nodules and hepatocellular carcinomas (HCC) to define the genes implicated in cancer progression in a resistant hepatocyte model. Tissues that included early nodules (1 month, ENT-1), persistent nodules (5 months, ENT-5), dissected HCC (12 months), and normal livers (NL) from adult rats were analyzed by cDNA arrays including 1185 rat genes. Differential genes were derived in each type of sample (n = 3) by statistical analysis. The relationship between samples was described in a Venn diagram for 290 genes. From these, 72 genes were shared between tissues with nodules and HCC. In addition, 35 genes with statistical significance only in HCC and with extreme ratios were identified. Differential expression of 11 genes was confirmed by comparative reverse transcription-polymerase chain reaction, whereas that of 2 genes was confirmed by immunohistochemistry. Members involved in cytochrome P450 and second-phase metabolism were downregulated, whereas genes involved in glutathione metabolism were upregulated, implicating a possible role of glutathione and oxidative regulation. We provide a gene expression profile related to the progression of nodules into HCC, which contributes to the understanding of liver cancer development and offers the prospect for chemoprevention strategies or early treatment of HCC.

Nodularin-induced genotoxicity following oxidative DNA damage and aneuploidy in HepG2 cells

The problem of toxicity of Nodularia spumigena to animals and people is of increasing concern, as the incidence of such blooms grows. It was shown that nodularin is a liver carcinogen possessing both initiating and tumor-promoting activities. However, the mechanisms by which this toxin damages the DNA and induces liver cancer are not well understood. The aim of the present study was to investigate the DNA damaging properties of nodularin. The effect of different doses of nodularin (1-10 microg/ml) on DNA damage was determined in HepG2 cells after 6, 12, 24 and 48 h of the treatment. The modified comet assay in conjunction with Fpg (ROS-induced DNA damage) and FISH-micronucleus assay (clastogenic and/or aneugenic activities of nodularin) were applied. In addition the occurrence of apoptosis was estimated by the morphological analysis of chromatin condensation and the annexin method using flow cytometry. We found that nodularin induces oxidative DNA damage by oxidation of purines and increases the formation of centromere positive micronuclei due to aneugenic activity. In addition to genotoxic properties, nodularin exerts a cytotoxic activity by inducing apoptosis in HepG2 cells. These results suggest a causative role for nodularin in the process leading to the accumulation of genetic alterations which may be implicated in carcinogenesis.

Characterization of an Acute Molecular Marker of Nongenotoxic Rodent Hepatocarcinogenesis by Gene Expression Profiling in a Long Term Clofibric Acid Study

Evaluation of the nongenotoxic potential early during the development of a drug presents a major challenge. Recently, two genes were identified as potential molecular markers of rodent hepatic carcinogenesis: transforming growth factor-beta stimulated clone 22 (TSC-22) and NAD(P)H cytochrome P450 oxidoreductase (CYP-R) (1). They were identified after comparing the gene expression profiles obtained from the livers of Sprague-Dawley rats treated with different genotoxic and nongenotoxic compounds in a 5 day repeat dose in vivo study. To assess the potential of these two genes as acute markers of carcinogenesis, we investigated their modulation during a long-term nongenotoxic study in the rat using a classic initiation-promotion regime. Clofibric acid (CLO), which belongs to the broad class of chemicals known as peroxisome proliferators, was used as a nongenotoxic hepatocarcinogen. Male F344 rats were given a single nonnecrogenic injection of diethylnitrosamine (0 or 30 mg/kg) and fed a diet containing none or 5000 ppm CLO for up to 20 months. Necropsies of five rats per groups were performed at 18, 46, 102, 264, 377, 447 (control, DEN, and DEN + CLO rats), 524, and 608 days (for the CLO and control rats). Gross macroscopic and microscopic evaluation and gene expression profiling (on Affymetrix microarrays) were performed in peritumoral and tumoral liver tissues. Bioanalysis of the liver gene expression data revealed that TSC-22 was strongly down-regulated early in the study. Its underexpression was maintained throughout the study but disappeared upon CLO withdrawal. These modulations were confirmed by real-time polymerase chain reaction. However, CYP-R gene expression was not significantly altered in our study. Taken together, our results showed that TSC-22, but not CYP-R, has the potential to be an acute early molecular marker for nongenotoxic hepatocarcinogenesis in rodents.

Regulation of GST-P gene expression during hepatocarcinogenesis

Placental glutathione S-transferase (GST-P), a member of glutathione S-transferase, is known for its specific expression during rat hepatocarcinogenesis and has been used as a reliable tumor marker for experimental rat hepatocarcinogenesis. To explain the molecular mechanism underlying its specific expression concomitant with the malignant transformation, we have analyzed the regulatory element of the GST-P gene and the transcription factor that binds to this element. From the extensive analyses by the establishment of the transgenic rat lines having various regions of GST-P gene, we could identify the GPE1 as an essential enhancer element for specific GST-P expression. Next, we examined the transcription factor that binds and activates the GPE1, specifically in the early stage of hepatocarcinogenesis and in the hepatoma. Electrophoresis gel mobility shift assay, reporter transfection analysis, and the chromatin immunoprecipitation analysis indicate that the Nrf2/MafK heterodimer binds and activates GPE1 element in preneoplastic lesions and hepatomas but not in the normal liver cells. In this chapter, we describe details of the transgenic rat analyses and the identification of a factor responsible for the specific expression of the GST-P gene and discuss a possible molecular scenario for malignant transformation and tumor marker gene expression.