Molecular forms of glutathione S-transferase and UDP-glucuronyltransferase as hepatic preneoplastic marker enzymes

Effect of Boschniakia rossica on expression of GST-P, p53 and p21ras proteins in early stage of chemical hepatocarcinogenesis and its anti-inflammatory activities in rats

AIM: To investigate the effect of Boschniakia rossica (BR) extract on expression of GST-P, p53 and p21^ras proteins in early stage of chemical hepatocarcinogenesis in rats and its anti-inflammatory activities.

METHODS: The expression of tumor marker-placental form glutathione S-transferase (GST-P), p53 and p21^ras proteins were investigated by immunohistochemical techniques and ABC method. Anti-inflammatory activities of BR were studied by xylene and croton oil-induced mouse ear edema, carrageenin, histamine and hot scald-induced rat pow edema, adjuvant-induced rat arthritis and cotton pellet-induced mouse granuloma formation methods.

RESULTS: The 500 mg/kg of BR-H₂O extract fractionated from BR-Methanol extract had inhibitory effect on the formation of DEN-induced GST-P-positive foci in rat liver (GST-P staining was 78% positive in DEN+AAF group vs 20% positive in DEN+AAF+BR group, P < 0.05) and the expression of mutant p53 and p21^ras protein was lower than that of hepatic preneoplastic lesions (33% and 22% positive respectively in DEN+AAF group vs negative in DEN+AAF+BR group). Both CH₂Cl₂ and H₂O extracts from BR had anti-inflamatory effect in xylene and croton oil-induced mouse ear edema (inhibitory rates were 26%-29% and 35%-59%, respectively). BR-H₂O extract exhibited inhibitory effect in carrageenin, histamine and hot scald-induced hind paw edema and adjuvant-induced arthritis in rats and cotton pellet-induced granuloma formation in mice.

CONCLUSION: BR extract exhibited inhibitory effect on formation of preneoplastic hepatic foci in early stage of rat chemical-hepato-carcinogenesis. Both CH₂Cl₂ and H₂O extracts from BR exerted anti-inflammatory effect in rats and mice.

Inducibility of ethoxyresorufin deethylase and UDP-glucuronosyltransferase activities in two human hepatocarcinoma cell lines KYN-2 and Mz-Hep-1

Two human hepatoma cell lines, KYN-2 and Mz-Hep-1 were characterized in terms of glucuronidation capacity and inducibility of cytochrome P4501A1/1A2 and several UDP-glucuronosyltransferases (UGTs). Cytochrome P4501A1/1A2 activity was measured using 7-ethoxyresorufin and that of UGTs with 16 different substrates. The effects of dimethyl sulfoxide (DMSO), 3-naphthoflavone, alpha-naphthoflavone, and rifampicin on these drug-metabolizing enzyme activities were studied. DMSO treatment increased in a dose-dependent manner the ethoxyresorufin O-deethylase (EROD) activity in KYN-2 cells, while an opposite effect was observed in Mz-Hep-1 cells. In KYN-2 cells, EROD was more responsive toward beta-naphthoflavone treatment in combination with DMSO. This activity was enhanced in Mz-Hep-1 cells more than 83 times by beta-naphthoflavone. The enhancement of EROD activity by DMSO and beta-naphthoflavone treatments of KYN-2 cells was abolished by alpha-naphthoflavone treatment. In Mz-Hep-1, only the inducing effect of beta-naphthoflavone was abolished by alpha-naphthoflavone treatment. Rifampicin treatment of KYN-2 cells reversed both the DMSO and beta-naphthoflavone effects on the EROD activity. Glucuronidation of steroids, bile acids, fatty acids and drugs was effective in KYN-2 and Mz-Hep-1 cells. Both 1-naphthol glucuronidation and the level of UGT1*6 protein detected by immunoblot and supporting this activity were lowered by DMSO treatment and increased by beta-naphthoflavone treatment in KYN-2 cells. In Mz-Hep-1 cells, DMSO and beta-naphthoflavone had no effect on 1-naphthol glucuronidation activity. DMSO, beta-naphthoflavone and rifampicin also affected the glucuronidation of various substrates supported by different UGT isoforms. These results indicate that KYN-2 and Mz-Hep-1 cells can be used as new in vitro models for the studies of drug metabolism and the regulation of the corresponding enzymes.

Two-dimensional polyacrylamide gel electrophoresis in experimental hepatocarcinogenesis studies

High resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) in combination with computer-assisted densitometry was used to analyze sequential changes in polypeptide expression during chemically (aflatoxin Bl; AFB), spontaneously, and oncogene (v-Ha-ras, v-raf, and v-raflv-myc)-induced experimental rat hepatocarcinogenesis. Two-dimensional mapping of [35S]methionine and [32P]orthophosphate-labeled whole cell lysate and nuclear polypeptides revealed subsets of polypeptides specific for each transformation modality in the in vitro rat liver epithelial (RLE) transformation model. Many of the observed changes in whole cell lysate preparations were localized to specific subcellular organelles. Significant alterations in the expression of the extracellular matrix protein, fibronectin, as well as tropomyosin- and intermediate filament-related polypeptides (vimentin, beta-tubulin, cytokeratins 8, 14, and 18, and actin) were observed among the various transformant cell lines. Whereas alterations in the tropomyosin isoforms appeared to be transformation specific, concomitant modulation of intermediate filament expression was related more to the differentiation state of the individual cell lines than to the transformed phenotype. To integrate protein and DNA information of polypeptides believed to be critically involved during cellular transformation, N-terminal amino acid microsequencing of selected nuclear polypeptides was performed. Preliminary results suggest that N-terminal blockage of rat liver epithelial nuclear proteins to be minor (approximately 20%) with sequencing sensitivity of one pmol. These studies extend our on-going efforts toward the establishment of computerized database of rat liver epithelial cellular proteins (Wirth et al., Electrophoresis, 1991, 12, 931-954) to aid in the delineation of polypeptides critically involved in cellular growth and differentiation as well as transformation.

Vitamin E, glutathione S-transferase and gamma-glutamyl transpeptidase activities in cultured hepatocytes of rats treated with carcinogens

1. The effects of alpha-tocopherol and gamma-tocotrienol on glutathione S-transferase (GST) and gamma-glutamyl transpeptidase (gamma-GT) activities in cultured hepatocytes prepared from rats treated with diethylnitrosamine (DEN) and 2-acetylaminofluorene (AAF) were investigated. 2. Both the alpha-tocopherol and gamma-tocotrienol treated hepatocytes showed significantly higher (P < 0.05) GST activities than untreated hepatocytes prepared from the carcinogen treated rats in the first 3 days of culture. Treatment with alpha-tocopherol and gamma-tocotrienol generally resulted in a tendency to increase the GST activities above that in the untreated hepatocytes. 3. Treatment with high doses (125-250 microM) of alpha-tocopherol and low doses (12.5-25 microM) of gamma-tocotrienol generally resulted in a significant reduction in gamma-GT activities at 1-3 days. gamma-GT activities are reduced as the dose of alpha-tocopherol and gamma-tocotrienol are increased.

Ligandin binding phthalein complexone complex of technetium for hepatic function studies

In our pursuit for liver functional diagnosis, development of bifunctional radiopharmaceutical containing iminodiacetic acid (IDA), as the technetium chelating site along with phthalein or fluorescein structure, the skeleton of BSP and Rose Bengal, long used for the assessment of liver function is considered. Among the various PC, PPC, TPC and calcein IDA derivatives commercially available, 99mTc-PC (PC: 3,3'-bis(N, N-dicarboxymethylaminomethyl)o-cresolphthalein) showed the highest hepatobiliary excretion. The functionality of the various technetium labeled phthalein and fluorescein IDA derivatives was evaluated by competitive BSP binding studies and by comparative binding with the hepatocyte specific protein, ligandin.

Enzyme profile of rat bile ductular epithelial cells in reference to the resistance phenotype in hepatocarcinogenesis

An extensive bile ductular cell hyperplasia with the formation of well-differentiated bile ductules is the most prominent feature of rat liver at 6 to 15 weeks after bile duct ligation. We have improved our previous cell isolation procedure and are now routinely able to obtain from such livers high yields of viable bile ductular epithelial cells. These cells were characterized with respect to their specific activities of gamma-glutamyl transpeptidase and beta-glucuronidase and of select Phase I and Phase II enzymes of biotransformation. At the time of their isolation, only a very small number of the bile ductular epithelial cells were observed to be in DNA synthesis. In addition, in histological sections prepared from intact hyperplastic bile ductular tissue isolates, only the bile ductular epithelial cells exhibited histochemical staining for gamma-glutamyl transpeptidase activity. Typically, greater than 95% of the cells isolated from this tissue were also found to be histochemically positive for gamma-glutamyl transpeptidase activity, and no hepatocytes were seen contaminating this cell population. Biochemically, the isolated bile ductular cells exhibited a gamma-glutamyl transpeptidase specific activity that was 100 times higher than that of hepatocytes isolated at the same time from the bile duct-ligated rats and more than 300 times higher than the specific activity of the enzyme of freshly isolated normal rat hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the glucuronidation ability of liver microsomes from rats treated with 3-methylcholanthrene or phenolic antioxidants

1. UDP-glucuronyltransferase activity was studied in hepatic microsomal preparations isolated from female Sprague-Dawley rats treated with either 3-methylcholanthrene, butylated hydroxyanisole, propyl gallate, ethoxyquin or a combination of 3-methylcholanthrene and butylated hydroxyanisole. 2. The substrates p-nitrophenol, 1-naphthol and phenolphthalein were used. With p-nitrophenol all treatments, except propyl gallate, caused a significant increase in activity over the control value; the combined treatment of 3-methylcholanthrene and butylated hydroxyanisole gave an additive response when compared to each treatment used singly. With 1-naphthol as substrate, 3-methylcholanthrene and 3-methylcholanthrene + butylated hydroxyanisole caused 8-fold increases in activity compared to the 2-3 fold increased caused by the other treatments. When phenolphthalein was used, all treatments increased activity to the same extent. 3. When the assays were repeated with various concentrations of each substrate, the results revealed that, except where phenolphthalein was used, distinguishable differences in the activity of each microsomal preparation were discernible, the most significant being the bimodal response of each preparation to low and high concentrations of p-nitrophenol.

Differential induction profile of drug-metabolizing enzymes after treatment with hypolipidaemic agents

Various hypolipidaemic agents differentially induced microsomal drug-metabolizing enzymes. Clofibrate, clofibric acid, fenofibric acid and dulofibrate, which are mainly hypotriglyceridaemic, increased the content in cytochromes P-450 (77-185% over control), and especially cytochrome P-452-dependent lauric acid 12-hydroxylation (5.6- to 8.4-fold increase). Bilirubin glucuronidation was 2.1- to 2.8-fold stimulated; epoxide hydrolase activity (benzo(a)pyrene-oxide) was only slightly increased by the drugs. By contrast, F1379, which lowers plasma cholesterol only, did not change cytochromes P-450 content and slightly affected the 12-hydroxylation of lauric acid. It dramatically enhanced the epoxide hydrolase activity (7.6-fold), and increased (200%) the glucuronidation of planar group I substrates (4-nitrophenol, 4-methylumbelliferone, 1-naphthol). These effects were accompanied by a highly positive staining of gamma-glutamyltransferase in the liver characterized by a great number of intensively coloured foci in the periportal and perilobular area of the tissue. Treatment of rats for three weeks with F1379 did not modify this typical profile in enzyme induction. Such continuous effect could reveal some biochemical changes of hepatocytes with important toxicological relevance. Compared to the parent compound, treatment of rats with two metabolites of F1379 led to a decrease in the induction potency on epoxide hydrolase and on the forms I of UDP-glucuronosyltransferase; by contrast, the content in cytochromes P-450 was increased.

Cellular events during hepatocarcinogenesis in rats and the question of premalignancy

The cellular, biochemical, and genetic changes that occur in the liver of rats exposed to chemical hepatocarcinogens are reviewed. Multiple new cell types appear in the liver of carcinogen-treated rats including foci, nodules, ducts, oval cells, and atypical hyperplastic areas. The application of phenotypic markers for these cell types suggests that hepatocellular carcinomas may arise from more than one cell type, including a putative liver stem cell that proliferates following carcinogen exposure. Study of DNA, RNA, and proteins produced by hepatocellular carcinomas and putative premalignant cells has so far failed to identify a gene or gene product clearly associated with the malignant or premalignant phenotype. Understanding the cellular lineage from normal cell through putative premalignant cell to cancer is critical to understanding the process of carcinogenesis. Application of new immunological (monoclonal antibody, transplantation) and molecular biological (gene cloning, oncogene identification) approaches to this problem holds promise that the process of hepatocarcinogenesis will be better known in the near future.

Immunochemical studies of microsomal membranes of rat preneoplastic and neoplastic hepatocytes

Heterogenous rabbit antisera were prepared against microsomal proteins of hyperplastic hepatic nodules (HPN) induced by chemicals, and were utilized to assess the antigenic differences of microsomal polypeptides within a normal liver, HPN, and hepatocellular carcinomas (HCC), utilizing immunodetection of antigens separated electrophoretically and transferred to nitrocellulose. Although most antigens were common to all microsomes, differences (increase or decrease) were noted in some polypeptides not only between the normal liver and HPN, but also between HPN and HCC. On the other hand, monoclonal antibodies against epoxide hydrolase (EH), which was initially found as the PN antigen, reacted to a single polypeptide with a molecular weight of 49,000 in all the microsomes. These results suggested that there is little molecular modification of EH during hepatic carcinogenesis.

Purification, induction, and distribution of placental glutathione transferase: a new marker enzyme for preneoplastic cells in the rat chemical hepatocarcinogenesis

A polypeptide of Mr 26,000 and pI 6.7 that was markedly increased in rat livers bearing hyperplastic nodules (HNs) induced by chemical carcinogens was identified immunochemically as the subunit of neutral glutathione (GSH) transferase (GSHTase; RX:glutathione R-transferase, EC 2.5.1.18; also called GSH S-transferase) purified from placenta (GSHTase-P) and was demonstrated immunohistochemically to be localized in preneoplastic foci and HNs. In the present study, GSHTase-P has been purified from the HN-bearing liver, and the distribution and inducibility have been examined quantitatively using anti-GSHTase-P antibody. Elevation of GSHTase-P in the HN-bearing livers was also confirmed by in vitro translation of mRNAs isolated from the HN-bearing livers. The purified GSHTase-P was homogeneous in size but had two charge isomers on two-dimensional gel electrophoresis. In normal tissues, including liver, placenta, and fetal liver, the protein content of GSHTase-P was generally low but was significantly high in kidney and pancreas. In contrast, the amount of GSHTase-P in HN-bearing livers (primary hepatomas) and transplantable Morris hepatoma 5123D were several 10-fold higher than that in normal liver but were undetectably low in transplantable Yoshida ascites hepatoma AH 130. Different from ordinary drug-metabolizing enzymes, GSHTase-P was uninducible by administration of drugs and carcinogens prior to appearance of the preneoplastic foci and HNs. In addition, species specificity of GSHTase-P was low as it was crossreactive among rat, hamster, and human.