Comparative histochemical investigation of the glutathione S-transferase placental form and gamma-glutamyltranspeptidase during N-nitrosobis(2-hydroxypropyl)amine-induced pancreatic carcinogenesis in hamsters

Multi-step lung carcinogenesis model induced by oral administration of N-nitrosobis(2-hydroxypropyl)amine in rats

N-Nitrosobis(2-hydroxypropyl)amine (BHP) was first synthesized by Krüger et al. (1974), and has been shown to primarily induce pancreatic duct adenocarcinomas by a subcutaneous injection in Syrian hamsters. By contrast, the carcinogenic effect of BHP has been indicated at the different target organs in rats, namely the lung. When rats are received by an oral administration of BHP in drinking water for 25 weeks, a high incidence of lung carcinomas are induced, which include adenocarcinomas, squamous cell carcinomas and combined squamous cell and adenocarcinomas. So many similarities are observed in terms of not only histological appearances but also gene alterations between human and BHP-induced rat lung cancers. Moreover, the step by step development of lung lesions, from preneoplastic lesions to cancers in rat lung carcinogenesis by BHP offers a good model to investigate the mechanisms underlying the pathogenesis of lung cancers. Because data for genetic and epigenetic alterations have indeed been accumulated during the BHP-induced rat lung carcinogenesis, we will introduce them in this review and hence demonstrate that this lung carcinogenesis model provides a useful opportunity for the research on the pathogenesis of lung cancers of both humans and rats.

Combination of vitamin K2 and the angiotensin-converting enzyme inhibitor, perindopril, attenuates the liver enzyme-altered preneoplastic lesions in rats via angiogenesis suppression

BACKGROUND/AIMS

Chemoprevention should be a promising approach to improve the prognosis of the patients with hepatocellular carcinoma (HCC). Angiogenesis is now recognized as a crucial step not only in tumor growth, but also in early carcinogenesis. The aim of this study was to elucidate the combination effect of the clinically used vitamin K(2) (VK) and the angiotensin-converting enzyme inhibitor, perindopril (PE), on hepatocarcinogenesis, especially in conjunction with angiogenesis.

METHODS

In a diethylnitrosamine-induced rat hepatocarcinogenesis model, the effects of VK and PE on the development of liver enzyme-altered preneoplastic lesions and angiogenesis were examined.

RESULTS

Treatment with both VK and PE markedly inhibited the development of preneoplastic lesions in association with suppression of neovascularization in the liver. The combination treatment with VK and PE exerted a more potent inhibitory effect as compared with the single agent treatments. The in vitro study demonstrated that VK and PE inhibited the endothelial cell (EC) tubular formation. VK also suppressed the EC proliferation in a dose-dependent manner.

CONCLUSIONS

The combination of VK and PE exerted a chemopreventive effect against rat liver carcinogenesis via suppression of angiogenesis. Since both agents are widely used in the clinical practice, this combination therapy may represent a potential new strategy for chemoprevention against HCC in the future.

Inhibition of renin-angiotensin system attenuates liver enzyme-altered preneoplastic lesions and fibrosis development in rats

BACKGROUND/AIMS

It is suggested that the renin-angiotensin system (RAS) is involved in tumor development and fibrogenesis. The aim of the present study was to examine the effect of RAS inhibition on the liver enzyme-altered preneoplastic lesions and fibrosis development.

METHODS

The effects of the clinically used angiotensin-I converting enzyme inhibitor (ACE-I), perindopril (PE), on two different rat model of liver carcinogenesis models induced separately by diethylnitrosamine (DEN) and a choline-deficient L-amino acid-defined (CDAA) diet were studied. This CDAA model was also used to elucidate the effect of PE on liver fibrosis development.

RESULTS

The immunohistochemical evaluation revealed that the glutathione S-transferase placental form (GST-P), and gamma-glutamyltransferase (GGT)-positive preneoplastic foci significantly decreased in the livers of the PE-treated groups. In CDAA-induced liver fibrosis model, PE revealed a marked inhibitory effect of liver fibrosis development. The hepatic hydroxyproline, serum fibrosis markers, alpha-smooth muscle actin (alpha-SMA) immunopositive cells in number, and alpha-(III) pro-collagen mRNA expression were significantly suppressed by PE treatment. These inhibitory effects of PE were achieved even at a clinically comparable dose (2 mg/kg per day).

CONCLUSIONS

These results suggested that the RAS is involved in liver carcinogenesis and fibrosis development.

Enhancement of hepatocarcinogenesis initiated with diethylnitrosamine or N-nitrosobis(2-hydroxypropyl)amine by a choline-deficient, L-amino acid-defined diet administered prior to the carcinogen exposure in rats

Effects of pre-administration of a choline-deficient, L-amino acid-defined (CDAA) diet on hepatocarcinogenesis initiated with diethylnitrosamine (DEN) or N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats were investigated. A pre-administrating period was set as 1 week, because CDAA diet induces liver injuries by this time-point. In a time-course study, male Fischer 344 rats, 6 weeks old, received a 1-week pre-administration of choline-supplemented, L-amino acid-defined (CSAA) or CDAA diet, DEN at a dose of 100 mg/kg body weight by a single intraperitoneal injection, then CSAA or CDAA diet for up to 8 weeks, and were sacrificed 4, 6 and 8 weeks after DEN. CDAA diet administered only after DEN significantly increased the numbers of glutathione S-transferase placental form (GST-P)-positive lesions 4, 6 and 8 weeks after DEN and their sizes 6 and 8 weeks after DEN. CDAA diet administered both before and after DEN similarly increased the numbers and sizes of GST-P-positive lesions, but with a significantly greater degree than obtained by the diet administered only after DEN. In a dose response study, rats received vechicle or DEN, at a dose of 0.001, 0.01, 0.1, 1, 10, 20, 50, 100 or 200 mg/kg body weight, 1 week after the commencement of CSAA or CDAA diet, and sacrificed 8 weeks after vehicle or DEN. The significant increases of the numbers of GST-P-positive lesions were obtained after 50-200 mg/kg body weight of DEN under the CSAA diet administration, whereas those were detected after 10-200 mg/kg under CDAA diet administration. Sizes became significantly larger with only 200 mg/kg body weight of DEN in the CSAA case but with 50-200 mg/kg in the CDAA case. Male Wistar rats received a 1-week pre-administration of CSAA or CDAA diet, vehicle or BHP, at a dose of 600 or 1200 mg/kg body weight, by a single intraperitoneal injection, then CSAA or CDAA diet for 8 weeks, and were then sacrificed. The numbers of GST-P-positive lesions demonstrated significant increment with 1200 mg/kg body weight of BHP by CDAA diet administered only after BHP and, to a significantly greater degree, by the diet administered both before and after BHP. While CDAA diet administered only after BHP did not alter the sizes of GST-P-positive lesions, the diet administered both before and after 600 and 1200 mg/kg body weight of BHP significantly increased the sizes of the lesions. These results indicate that the pre- plus post-administration of CDAA diet enhances hepatocarcinogenesis initiated with DEN or BHP, more than the post-administration only, thus providing a sensitive model to detect weak liver carcinogenic potency of environmental chemicals.

Inhibition of early-phase exogenous and endogenous liver carcinogenesis in transgenic rats harboring a rat glutathione S-transferase placental form gene

Hepatocarcinogenesis initiated with N-nitrosodiethylamine (DEN) and that initiated by feeding of a choline-deficient, L-amino acid-defined (CDAA) diet were compared in transgenic male Wistar rats harboring a rat glutathione S-transferase placental form (GST-P) gene (GST-P-Tg rats) and non-transgenic (N-Tg) rats. Eight-week-old GST-P-Tg and N-Tg rats were administered DEN intraperitoneally at 100 mg/kg body weight, subjected to a selection procedure with 2-acetylaminofluorene and CCl4, and killed at the end of weeks 5 and 12. Other groups were fed the CDAA diet for 12 weeks and killed. Five weeks after the DEN treatment, numbers and sizes of gamma-glutamyltransferase (GGT)- or GST-P-positive lesions and 8-hydroxyguanine (8-OHG) levels in the livers were significantly less in GST-P-Tg rats than in N-Tg rats. The lesion numbers were unchanged between the ends of weeks 5 and 12 in GST-P-Tg rats, but decreased in N-Tg rats. The lesion sizes were increased in GST-P-Tg rats, but unchanged in N-Tg rats. While the proliferating cell nuclear antigen labeling indices (PCNA L.I.) in and surrounding the lesions were decreased, more prominently in GST-P-Tg rats than in N-Tg rats, the 8-OHG levels were also decreased but similarly in both cases. After 12 weeks on the CDAA diet, the lesion incidences, numbers and sizes, 8-OHG levels, PCNA L.I. in and surrounding the lesions, and liver injury were significantly less in GST-P-Tg rats than in N-Tg rats. These results indicate that insertion of a rat GST-P transgene alters the early phase of exogenous and endogenous rat hepatocarcinogenesis, presumably due to enhanced detoxification by GST-P expressed both transiently during the initiation and chronically in the altered hepatocyte populations.

Inhibition by green tea extract of diethylnitrosamine-initiated but not choline-deficient, L-amino acid-defined diet-associated development of putative preneoplastic, glutathione S-transferase placental form-positive lesions in rat liver

The effects of green tea extract (GTE) on exogenous and endogenous models of rat liver carcinogenesis using diethylnitrosamine (DEN) and a choline-deficient, L-amino acid-defined (CDAA) diet were studied. For the exogenous carcinogenesis study, male Fischer 344 rats, 6 weeks old, were given a single intraperitoneal dose of 200 mg/kg body weight of DEN, partially hepatectomized at week 3, and administered GTE at doses of 0, 0.01 and 0.1% in the drinking water from week 2 for 10 weeks. For the endogenous carcinogenesis study, rats were fed the CDAA diet and simultaneously given GTE for 12 weeks. All rats were killed at the end of week 12. After DEN-initiation, the apparent numbers of glutathione S-transferase placental form-positive foci, assayed as putative preneoplastic lesions, were decreased by the administration of GTE, though their sizes were not altered. In contrast, GTE did not significantly reduce the numbers of the lesions induced by the CDAA diet or affect their sizes. While the levels of 8-hydroxyguanine, a parameter of oxidative DNA damage, were reduced by the GTE administration in both experimental models, GTE did not protect against the CDAA-diet-associated liver tissue damage in terms of either histology or plasma marker enzyme levels. We conclude that, while GTE may be a possible chemopreventive agent for nitrosamine-initiated hepatocarcinogenesis in the absence of chronic hepatocyte damage, it does not significantly inhibit lesion development in hepatocarcinogenesis associated with the CDAA diet, a cirrhosis-associated model.

Comparative changes in the liver of female Fischer-344 rats after short-term feeding of a semipurified or a semisynthetic L-amino acid-defined choline-deficient diet

Groups of female Fischer-344 rats were fed a semipurified choline-deficient (CD) diet, or a semisynthetic L-amino acid-defined choline-deficient (CDAA) diet, for up to 12 wk and effects of the 2 diets on the liver were compared. Steatosis was diffuse and more severe throughout in rats fed the CDAA diet than in rats fed the CD diet. Greater elevations in serum aspartate and alanine aminotransferase activities were also present in the former rats, along with higher 2-bromodeoxyuridine labeling indices in the liver. Discrete amounts of 8-hydroxyguanine were detected in liver DNA, but were not significantly different in rats fed the 2 diets, or from those present in a group of control rats killed at 0 time. Glutathione S- transferase placental form-positive focal lesions were not observed in any of the rats. The results show that the CDAA diet causes more severe degrees of steatosis and liver cell death and proliferation than the CD diet, raising the possibility that it may, in contrast to the CD diet, result in the eventual induction of hepatocellular carcinomas in female Fischer-344 rats.

Different roles of 8-hydroxyguanine formation and 2-thiobarbituric acid-reacting substance generation in the early phase of liver carcinogenesis induced by a choline-deficient, L-amino acid-defined diet in rats

The present study was performed to assess the roles of hepatocellular oxidative damage to DNA and constituents other than DNA in rat liver carcinogenesis caused by a choline-deficient, L-amino acid-defined (CDAA) diet by examining the effects of the antioxidant N,N'-diphenyl-p-phenylenediamine (DPPD). The parameters used for cellular oxidative damage were the level of 8-hydroxy-guanine (8-OHGua) for DNA and that of 2-thiobarbituric acid-reacting substance (TBARS) for constituents other than DNA. A total of 40 male Fischer 344 rats, 6 weeks old, were fed the CDAA diet for 12 weeks with or without DPPD (0.05, 0.10 or 0.20%) or butylated hydroxytoluene (BHT, 0.25%). In the livers of the rats, the numbers and sizes of glutathione S-transferase (EC 2.5.1.18) placental form (GSTP)- and/or gamma-glutamyltransferase (GGT, EC 2.3.2.2)-positive lesions and levels of 8-OHGua and TBARS were determined. The GSTP-positive lesions of 0.08 mm2 or larger were all stained positively for GGT as well in cross-sectional area, whereas the smaller lesions were generally negative for GGT. DPPD and BHT reduced the size of the GSTP-positive lesions without affecting their total numbers. At the same time, they reduced TBARS generation without affecting 8-OHGua formation in DNA. The present results indicate that oxidative DNA damage (represented by 8-OHGua formation) and damage to constituents other than DNA (represented by TBARS generation) may play different roles in rat liver carcinogenesis caused by the CDAA diet; the former appears to be involved in the induction of phenotypically altered hepatocyte populations while the latter may be related to the growth of such populations.

Glutathione S-transferases in the organ of Corti of the rat: enzymatic activity, subunit composition and immunohistochemical localization

Glutathione S-transferases (GSTs), a family of ubiquitous cytosolic isozymes, catalyze the detoxification of electrophilic substrates with reduced glutathione and participate in intracellular binding and transport of lipophilic substances. This study measured GST activity biochemically in the inner ear of the rat; determined the isozyme profile by Western blotting; and identified, immunohistochemically, the distribution of the mu and pi class GSTs in the organ of Corti. GST enzymatic activity in inner ear tissues ranged from 117 to 348 nmoles glutathione converted/min/mg protein, values somewhat higher than those found in brain (130) and much lower than in liver (1011). Of the GST isoforms, the pi class (identified by antibodies against the Yp subunit) was most prominent, the mu class (Yb1 subunit) clearly evident while the alpha class (Y(a) subunit) was barely detectable on Western blots. Immunocytochemical analysis showed differential distribution of the Yb1 and Yp subunits. The Yb1 subunit was present in the sensory cells, while supporting cells were not specifically stained. At the subcellular level, the isozyme was localized in the apical zones of inner (IHCs) and outer hair cells (OHCs) close to the cuticular plate. The extent of staining, however, varied between OHCs and IHCs. In the OHCs, staining appeared in discrete spots in the apical areas only, whereas in IHCs staining extended further towards the center of the cells. The Yp subunit was mainly localized to Deiters cell processes and pillar cells. Both Yb1 and Yp colocalized with tubulin-specific antibody. The functional significance of GST in the cochlear receptor cells is speculative. However, a role analogous to that in other tissues (detoxification, prostaglandin synthesis) can be assumed. In addition, an association of GST with the microtubule system is possible based on immunohistochemical colocalization with tubulin.

Development of glutathione S-transferase placental form (GST-P) stained foci during hamster buccal pouch mucosa carcinogenesis

The expression of the placental form of glutathione S-transferase (GST-P) using anti-rat liver GST-P antibody was investigated in hamster buccal pouch mucosa (HBPM) treated with 0.5% dimethylbenz[a]anthracene (DMBA) biweekly for 12 weeks. This preliminary study showed that the anti-rat liver GST-P antibody is applicable to the HBPM model and that DMBA treatment induced GST-P positive foci. These foci are randomly distributed and frequently involved the hyperplastic and dysplastic segments of the epithelium, as well as squamous cell carcinoma. Further study is needed to explore the kinetics of these GST-P positive foci.

Monoclonal antibodies to glutathione S-transferase pi-immunohistochemical analysis of human tissues and cancers

Mouse monoclonal antibodies (MAb) have been generated against the anionic isozyme of human glutathione S-transferase (GST pi). MAb AGST I can inhibit 50-70% of GST pi enzymatic activity and reacts with a 3-dimensional epitope which includes a putative glutathione binding site on GST pi. A sandwich enzyme-immunoassay established using MAb AGST I and a polyclonal antibody displayed a sensitivity of 0.5 ng/ml. Immunohistochemical analysis of human tissues demonstrated marked increases in GST pi levels in cancers of the brain, cervix, endometrium, colon, rectum and testis and in fibro- and chondrosarcomas.

Differential localization of glutathione-S-transferase Yp and Yb subunits in oligodendrocytes and astrocytes of rat brain

Glutathione-S-transferase Yb subunits were recently identified in rat brain and localized to astrocytes, ependymal cells lining the ventricles, subventricular zone cells, and tanycytes. Another isoform, Yp (pi family), was detected in rat brain by immunoblotting, and its mRNA was detected by Northern hybridizations. Double immunofluorescence localized Yb and Yp in different glial cells. The strongly Yp-positive cells were identified as oligodendrocytes by virtue of their arrangement in rows in white-matter tracts, colocalization in strongly carbonic anhydrase-positive cells, and association with myelinated tracts in the corpus striatum. Ependymal cells in the choroid plexus and ventricular lining were also strongly Yp positive, whereas Yb was not detected in the choroid plexus. The occurrence of Yp at low levels in astrocytes was indicated after immunostaining by a sensitive peroxidase-antiperoxidase method, which revealed weak staining of those cells in the molecular layer of the cortex. The data suggest that Yb and Yp subunits are primarily localized to astrocytes and oligodendrocytes, respectively, and that both are absent from neurons. The glutathione-S-transferase in oligodendrocytes may participate in the removal of toxins from the vicinity of the myelin sheath. The finding of glutathione-S-transferases in ependymal cells and astrocytes in the brain also suggests that this enzyme could be a first line of defense against toxic substances.

Glutathione transferases in rat hepatoma cells. Effects of ascites cells on the isoenzyme pattern in liver and induction of glutathione transferases in the tumour cells

Rat hepatoma cells grown intraperitoneally as an ascites tumour were analysed with respect to their contents of cytosolic glutathione transferases. In contrast with normal liver tissue, the hepatoma cells were dominated by the class Pi glutathione transferase 7-7. All the major hepatic enzyme forms were down-regulated to almost undetectable concentrations. Livers of rats bearing ascites-hepatoma cells expressed low, but significant, amounts of protein which, by electrophoretic and immunochemical properties, appeared identical with transferase 7-7. This enzyme is not detectable in normal hepatocytes. Treatment of rats with trans-stilbene oxide induced the expression of transferase 7-7 in the livers of normal rats as well as in hepatoma-cell-bearing animals. In addition, a 2-fold induction of transferase 7-7 was measured in the hepatoma ascites cells. No significant elevation of any other enzyme forms in the hepatoma cells was noted.

Early pancreatic duct adenocarcinoma

A 68-year-old Japanese woman presented with complaints of appetite and weight loss. Early pancreatic duct adenocarcinoma was diagnosed by endoscopic retrograde cholangiopancreatography (ERCP), which revealed partial obstruction of the main pancreatic duct. Pancreatoduodenectomy with lymph node dissection was performed. Macroscopically, no pancreatic tumor was detected. Histologically, the pancreatic lesion showed continuous changes consisting of duct epithelial cell hyperplasia, carcinoma in situ, and invasive carcinoma. Immunohistochemical stains for carcinoembryonic antigen and CA19-9 were positive in cancer cells.

Histochemical studies on gamma-glutamyltranspeptidase activity of pancreatic acinar cell lesions induced by 4-hydroxyaminoquinoline 1-oxide and/or azaserine in rats

The utility of gamma-glutamyltranspeptidase (gamma-GTP) as an enzyme marker during pancreatic acinar cell carcinogenesis in rats was assessed by measuring its enzyme-histochemical performance in pancreatic acinar cell lesions induced by 4-hydroxyaminoquinoline 1-oxide (4-HAQO) and/or azaserine in partially-pancreatectomized Fischer 344 and Wistar rats. Rats were given a single intravenous injection of 4-HAQO (10 or 7 mg/kg body weight) 3 days after partial pancreatectomy followed by intraperitoneal injections of azaserine (30 mg/kg) once a week for 10 weeks, or the same treatment without azaserine. The animals were sacrificed at 3, 6, 10, 12 and 18 months. 4-HAQO predominantly induced basophilic foci in Fischer rats, while in Wistar rats acidophilic foci and acidophilic hyperplastic nodules were predominant. A preferential enhancement of the induction of acidophilic foci and hyperplastic nodules was exhibited in Fischer rats following co-administration with azaserine. Normal acinar cells were positive for gamma-GTP. 90 to 100% of basophilic foci were either negative or slightly positive for gamma-GTP, whilst 68 to 98% of acidophilic foci were positive. The gamma-GTP activities of acidophilic hyperplastic nodules were more variable between nodules than within nodules, and either co-administration of azaserine or extension of experimental duration time appeared to increase the gamma-GTP positive nodules. Between the gamma-GTP positive and decreased nodules, no histological but some morphometrical differences were observed. As far as the nodules induced by 4-HAQO in Fischer rats were concerned, all of the gamma-GTP decreased nodules had thin fibrous capsules and exhibited ultrastructurally more atypia than the positive ones. Present study thus revealed that gamma-GTP is neither a useful nor invariable enzyme marker during pancreatic acinar cell carcinogenesis in rats.