Inhibitory effect of celery seeds extract on chemically induced hepatocarcinogenesis: modulation of cell proliferation, metabolism and altered hepatic foci development

The chemopreventive activity of methanolic extract of Apium graveolens seeds (celery seeds) has been investigated against Solt Farber protocol of hepatocarcinogenesis, oxidative stress and induction of positive foci of gamma-GT in the liver of Wistar rats. The prophylactic treatment of celery seeds extract protected dose dependently against diethylnitrosoamine (DEN)+2-acetylaminofluorine (AAF)+partial hepatectomy (PH) induced hepatocarcinogenesis and other related events such as induction of gamma-GT positive foci (P<0.001). 2-AAF administration in diet with PH in rats resulted in increased hepatic ornithine decarboxylase (ODC) activity and a consequent increase in the rate of DNA synthesis when compared to saline treated control group while pretreatment of rats with celery seeds extract resulted in inhibition of aforementioned parameters dose dependently. The augmentation of quinone reductase (QR), glutathione-S-transferase (GST) and serum gamma-glutamyl transpeptidase (GGT) activities; and depletion of the tissue GSH content after 2-AAF (i.p. injection) for five consecutive days was prevented with the administration of celery seed extract. On the basis of the above results it can be said that A. graveolens is a potent plant against experimentally induced hepatocarcinogenesis in Wistar rats.     

Chemopreventive Potential of Neem Flowers on Carcinogen-induced Rat Mammary and Liver Carcinogenesis

We have previously reported that dietary neem flowers (Azadirachta indica A. Juss var. siamensis Valeton) caused ‍a marked increase in glutathione S-transferase (GST) activity in the liver, while resulting in a significant reduction ‍in the activities of some hepatic P450-dependent monooxygenases. These results strongly indicate that neem flowers ‍may have chemopreventive potential. In the present study, we examined the inhibitory effects of neem flowers on ‍9,10-dimethyl-1,2-benzanthracene (DMBA)-induced mammary gland carcinogenesis in female Sprague Dawley rats ‍and on aflatoxin B ‍1 ‍(AFB1)-induced hepatocarcinogenesis in male Wistar rats. Young animals were fed with AIN-76 ‍purified diets containing either 10-12.5% ground freeze-dried neem flowers for 1 week prior to, during, and for 1 ‍week after the administration of each carcinogen. Interestingly, it was found that neem flowers resulted in a marked ‍reduction of the incidence of mammary gland (about 35.2%) and liver tumors (61.7% and 80.1% for benign and ‍malignant tumors, respectively). Furthermore, the multiplicity of tumors per rats was also lower in the neem flower ‍groups, i.e. those for mammary gland tumors and benign and malignant liver tumors were reduced to 44.0%, ‍87.9% and 88.9%, respectively. These results clearly demonstrated that neem flowers contain some chemopreventive ‍agents capable of inhibiting AFB1 and DMBA induced liver and mammary gland carcinogenesis in rats.     

Dietary Administration of Inositol and/or Inositol-6-phosphate Prevents Chemically-induced Rat Hepatocarcinogenesis

Chemoprevention is considered a rational strategy for dietary approaches to prevention of cancer. Multiple lines ‍of evidence suggest that many of our dietary principles are able to intervene in the multistage carcinogenesis process ‍and phytic acid (inositol hexaphosphate, IP6), a phytochemical present in a variety of plant species, has been shown ‍to prevent various cancers, including those of the mammary gland, colon and liver. However, the mechanism of ‍chemoprevention by IP6 has not been fully elucidated. In the present study, we examined the effects of inositol and/ ‍or IP6 supplementation on rat hepatocarcinogenesis initiated by diethylnitrosamine (DEN) and promoted by partial ‍hepatectomy (PH). Supplementation with either inositol or IP6, or their combination, starting one week prior to ‍administration of DEN, resulted in a significant decrease in both the area and the number of placental glutathione Stransferase ‍positive (GST-P+) foci, a preneoplastic marker for DEN-initiated hepatocarcinogenesis. The administration ‍of inositol and/or IP6 in drinking water caused marked enhancement in the glutathione S-transferase (GST) activity. ‍In addition, the production of thiobarbituric acid reactive substances and the catalase activity were significantly ‍reduced in rats supplemented with inositol and /or IP6. Based on these findings, it is likely that the chemopreventive ‍effects of inositol and/or IP6 on rat hepatocarcinogenesis initiated by DEN and promoted by PH are associated with ‍induction of GST activity and suppression of lipid peroxidation.     

Inhibitory Effects of Crude α-Mangostin,a Xanthone Derivative,on Two Different Categories of Colon Preneoplastic Lesions Induced by 1, 2-dimethylhydrazine in the Rat

The purpose of this study was to examine whether crude á-mangostin (a major xanthone derivative in mangosteen ‍pericarp (Garcinia mangostana)) has short-term chemopreventive effects on putative preneoplastic lesions involved ‍in rat colon carcinogenesis. The crude preparation was obtained by simple recrystallization of an ethylacetate ‍extract of mangosteen pericarps. A total of 33 five-week-old male F344 rats were randomly divided into 5 experimental ‍groups. Rats in groups 1-3 were given a subcutaneous injection of 1,2-dimethylhydrazine (DMH)(40 mg/kg body ‍weight) once a week for 2 weeks. Starting one week before the first injection of DMH, rats in groups 2 and 3 were fed ‍a diet containing 0.02% and 0.05% crude á-mangostin, respectively, for 5 weeks. Rats in group 4 also received the ‍diet containing 0.05% crude á-mangostin, while rats in group 5 served as untreated controls. The experiment was ‍terminated 5 weeks after the start. Dietary administration of crude á-mangostin at both doses significantly inhibited ‍the induction and/or development of aberrant crypt foci (ACF) (P<0.05 for 0.02% crude á-mangostin, P<0.01 for ‍0.05% crude á-mangostin), when compared to the DMH-treated group (group 1). Moreover, treatment of rats with ‍0.05% crude á-mangostin significantly decreased dysplastic foci (DF) (P<0.05) and â-catenin accumulated crypts ‍(BCAC) (P<0.05), to below the group 1 values. The proliferating cell nuclear antigen (PCNA) labeling indices of ‍colon epithelium and focal lesions in groups 2 and 3 were also significantly lower than in group 1 and this effect ‍occurred in a dose dependent manner of the crude á-mangostin. This finding that crude á-mangostin has potent ‍chemopreventive effects in our short-term colon carcinogenesis bioassay system suggests that longer exposure might ‍result in suppression of tumor development. ‍     

Quinone Reductase Inducers in Azadirachta indica A. Juss Flowers,and their Mechanisms of Action

We have previously shown that the flowers of neem tree (Azadirachta indica A. Juss, family Meliaceae), Thai ‍variety, strongly induced the activity of glutathione S-transferase (GST) while resulting in a significant reduction in ‍the activities of some cytochrome P450-dependent monooxygenases in rat liver, and possess cancer chemopreventive ‍potential against chemically-induced mammary gland and liver carcinogenesis in rats. In the present study, 2 ‍chemicals possessing strong QR inducing activity were fractionated from neem flowers using a bioassay based on ‍the induction of QR activity in mouse hepatoma Hepa 1c1c7 cultured cells. Spectroscopic characteristics revealed ‍that these compounds were nimbolide and chlorophylls, having CD (concentration required to double QR specific ‍activity) values of 0.16 and 3.8 ìg/ml, respectively. Nimbolide is a known constituent of neem leaves, but was found ‍for the first time here in the flowers. Both nimbolide and chlorophylls strongly enhanced the level of QR mRNA in ‍Hepa 1c1c7 cells, as monitored by northern blot hybridization, indicating that the mechanism by which these ‍constituents of neem flowers induced QR activity is the induction of QR gene expression. These findings may have ‍implication on cancer chemopreventive potential of neem flowers in experimental rats previously reported.     

Pituitary regulation of cytochrome P-450-mediated metabolism of steroids and xenobiotics in rat liver microsomes

In a previous paper we reported on the influence of sex andpituitary hormones on the selection of diethylnitrosamine-initiated,enzyme-altered cells by 0.02% (w/w) 2-acetylamino-ftuorene (2-AAF)and partial hepatectomy in the resistant hep-atocyte model (RH-raodel).The islands of enzyme-altered cells in this model grew fasterin male than in female rat liver and the growth rate was markedlydecreased in male rats bearing ectopic pituitary grafts duringthe 2-AAF selection period. Male rats are also generally moresusceptible to 2-AAF carcinogenesis than female rats. In orderto investigate whether the sex differentiated response to 2-AAFselection and 2-AAF carcinogenesis might be due to pituitarycontrol of xenobiotk metabolism, as previously shown for ratliver metabolism of steroid hormones, we have studied the influenceof age, sex and pituitary hormones on the cytochrome P-450-mediatedhydroxylations of 2-AAF and benzo[a]pyrene (B[a]P), O-de-ethylationof 7-ethoxyresorufin and the metabolism of 4-androstene-3, 17-dione(androstenedione) in rat liver microsomes. Microsomes from prepubertalrats had a generally higher capacity to metabolize the xenobioticcompounds whereas the capacity for androstenedione hydroxylationwas low. In adult rats pronounced sex differences and a markedinfluence of pituitary hormones were observed in the mkro-somalformation of several 2-AAF metabolites as well as in B[a]P andandrostenedione metabolism. The results clearly show that atleast the oxidative pathways of 2-AAF and B[a]P metabolism arecontrolled by pituitary hormones in a similar way to the ratliver metabolism of steroids. These data do not, however, provideany explanation for the previously mentioned sex differencesin the RH-model or in 2-AAF carcinogenesis. We therefore suggestthat the pituitary regulation of other pathways of 2-AAF metabolismmust be considered in order to clarify the biochemical backgroundbehind sexually differentiated 2-AAF carcinogenesis in rat liver.     

Ethanolic Neem Leaf Extract Protects Against N-methyl –N’- nitro-N-nitrosoguanidine-induced Gastric Carcinogenesis in Wistar Rats

We evaluated the effects of ethanolic neem leaf extract on N-methyl-N’-nitro-N-nitrosoguanidine (MNNG)-induced ‍gastric carcinogenesis in Wistar rats. The extent of lipid peroxidation and the status of the antioxidants superoxide ‍dismutase (SOD), catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GPx), and glutathione-Stransferase ‍(GST) in the stomach, liver and erythrocytes were used as biomarkers of chemoprevention. Animals ‍were divided into four groups of six animals each. Rats in group 1 were given MNNG (150 mg/kg bw) by intragastric ‍intubation three times with a gap of 2 weeks in between the treatments. Rats in group 2 administered MNNG as in ‍group 1, in addition received intragastric intubation of ethanolic neem leaf extract (200 mg/kg bw) three times per ‍week starting on the day following the first exposure to MNNG and continued until the end of the experimental ‍period. Group 3 animals were given ethanolic neem leaf extract alone, while group 4 served as controls. All the ‍animals were killed after an experimental period of 26 weeks. Diminished lipid peroxidation in the stomach tumour ‍tissue was associated with enhanced antioxidant levels. In contrast to tumour tissue, enhanced lipid peroxidation ‍with compromised antioxidant defences was found in the liver and erythrocytes of tumour bearing animals. ‍Administration of ethanolic neem leaf extract significantly reduced the incidence of stomach tumours, modulated ‍lipid peroxidation and enhanced antioxidant status in the stomach, liver and blood. From the results of our study, we ‍suggest that ethanolic neem leaf extract may exert its chemopreventive effects by modulating lipid peroxidation and ‍enhancing the antioxidant status in the stomach, liver and erythrocytes. ‍     

Inhibition of Azoxymethane-induced Colon Carcinogenesis in Rats due to JTE-522, a Selective Cyclooxygenase-2 Inhibitor

Prostaglandin E2, which is produced by cyclooxygenase (COX) during arachidonic acid metabolism, is considered ‍to be related to colon carcinogenesis and selective COX-2 inhibitors may be effective for chemoprevention without ‍the adverse side effects of non-selective, nonsteroid anti-inflammatory drugs. Therefore, the influence of JTE-522 ‍(4-(4-cyclohexyl-2-methyloxazol-5-yl)-2-fluorobenzensulfonamide), a selective COX-2 inhibitor, was examined in ‍azoxymethane(AOM)-induced rat colon carcinogenesis. A total of 40 male F344 rats were randomly divided into ‍two groups. Group 1 received diet containing 0.015% JTE-522 and group 2 the normal diet without supplement as ‍a control group; one week later, all rats were administered axozymethane (AOM) s.c. at a dose of 15 mg/kg body ‍weight once a week for 3 successive weeks. At the termination of the experiment (30 weeks after the start), the ‍multiplicity of colon cancer in group 1 was significantly less than that of group 2. The proliferating cell nuclear ‍antigen (PCNA) indices for non-neoplastic cells of the colon mucosa in group 1 were also lower. These data thus ‍suggest that JTE-522 has chemopreventive potential against colon carcinogenesis with decrease of mucosal cell ‍proliferation in rats. ‍     

Chemomodulatory Effect of Moringa Oleifera,Lam, on Hepatic Carcinogen Metabolising Enzymes,Antioxidant Parameters and Skin Papillomagenesis in Mice

The modulatory effects of a hydro-alchoholic extract of drumsticks of Moringa oliefera Lam at doses of 125 mg/ ‍kg bodyweight and 250 mg/ kg body weight for 7 and 14 days, respectively, were investigated with reference to drug ‍metabolising Phase I (Cytochrome b5 and Cytochrome P450 ) and Phase II (Glutathione-S- transferase) enzymes, ‍anti-oxidant enzymes, glutathione content and lipid peroxidation in the liver of 6-8 week old female Swiss albino ‍mice. Further, the chemopreventive efficacy of the extract was evaluated in a two stage model of 7,12 – ‍dimethylbenz(a)anthracene induced skin papillomagenesis. Significant increase (p<0.05 to p<0.01) in the activities ‍of hepatic cytochrome b5, cytochrome P450, catalase, glutathione peroxidase ( GPx ), glutathione reductase (GR), acid ‍soluble sulfhydryl content (-SH ) and a significant decrease ( p<0.01 ) in the hepatic MDA level were observed at ‍both dose levels of treatment when compared with the control values. Glutathione-S- transferase ( GST )activity was ‍found to be significantly incr eased (p<0.01 ) only at the higher dose level. Butylated hydr oxyanisol (BHA ) fed at a ‍dose of 0.75% in the diet for 7 and 14 days (positive control ) caused a significant increase (p<0.05 to p<0.01) in the ‍levels of hepatic phase I and phase II enzymes, anti- oxidant enzymes, glutathione content and a decrease in lipid ‍peroxidation. The skin papillomagenesis studies demonstrated a significant decrease (p<0.05 ) in the percentage of ‍mice with papillomas, average number of papillomas per mouse and papillomas per papilloma bearing mouse when ‍the animals received a topical application of the extract at a dose of 5mg/ kg body weight in the peri-initiation phase ‍7 days before and 7 days after DMBA application, Group II ), promotional phase (from the day of croton oil application ‍and continued till the end of the experiment, Group III ) and both peri and post initiation stages (from 7 days prior ‍to DMBA application and continued till the end of the experiment, Group IV) compared to the control group (Group ‍I ). The percentage inhibition of tumor multiplicity has been recorded to be 27, 72, and 81 in Groups II, III, and IV, ‍respectively. These findings are suggestive of a possible chemopreventive potential of Moringa oliefera drumstick ‍extract against chemical carcinogenesis.     

Alternative methods of selecting rat hepatocellular nodules resistant to 2-acetylaminofluorene

Dietary 2-acetylaminofluorene (2-AAF) coupled with a stimulus for cell proliferation such as a 2/3 partial hepatectomy (PH) or a necrotizing dose of carbon tetrachloride is frequently employed to generate nodules of resistant ("initiated") rat hepatocytes. This regimen is a useful model for experimental analysis of alterations in hepatocytes during carcinogenesis, and also as an assay for initiation by various carcinogens. Because of the decreasing availability of carcinogen-containing diets from commercial sources, we have developed alternative methods of 2-AAF administration to generate nodules in rats initiated with N-nitrosodiethylamine. This study compared the nodule-selecting and cancer-promoting efficacy of 2-AAF administered by the Solt-Farber procedure (0.02% in diet for 2 weeks) with 2-AAF administered by gavage, as a suspension in 1% aqueous carboxymethyl-cellulose (CMC). Three or 4 daily administrations of 2-AAF by gavage (20 mg/kg/day) followed by PH on day 4 were equivalent to the dietary regimen in generating early resistant nodules, late persistent nodules and hepatocellular carcinomas. These regimens were similar to the dietary regimen of 2-AAF in inhibiting virtually all normal hepatocyte proliferation. These regimens permit control over the duration and level of 2-AAF exposure and the resulting size of selected nodules.     

Induced drug resistance inhibits selection of initiated cells and cancer development

Compounds exerting a mitoinhibitory effect on normal hepatocytes are potent promoters in the resistant hepatocyte model of chemical carcinogenesis in combination with stimulation of regenerative growth by partial hepatectomy or treatment with carbon tetrachloride. 2- Acetylaminofluorene (2-AAF) almost completely inhibits liver cell regeneration after partial hepatectomy, allowing only resistant cells to participate in regenerative growth. After initiation by diethylnitrosamine and promotion with 2-AAF and partial hepatectomy (PH), focal growth of initiated cells generates liver lesions which occupy 40% of the hepatic volume three weeks after PH. In this work the mechanism for the anti promoting effects of phenobarbital and 3- methylcholantrene were investigated as well as their effects on the development of malignant hepatocellular carcinoma in the resistant hepatocyte model. Treatment with phenobarbital or, especially, 3- methylcholanthrene rendered normal rat hepatocytes resistant to the mitoinhibitory effect of 2-AAF. In combination with 2-AAF/PH, 3- methylcholanthrene shortened the regenerative growth period to less than one week. In the Solt-Farber protocol for experimental hepatocarcinogenesis, treatment with phenobarbital or 3- methylcholanthrene during promotion with 2-AAF/PH permitted hepatocytes surrounding the focal lesions to respond with regenerative growth. The foci and surrounding liver grew until the liver/body mass index reached the control value. With phenobarbital treatment the total focal volume was 20% of the liver volume three weeks after PH, whereas the corresponding value in the case of 3-methylcholanthrene was only 1%. Labelling index data supported the conclusion that growth of the liver lesions in the resistant hepatocyte model was dependent on differential inhibition of normal hepatocyte growth by the promoter and that the size of the foci obtained was related to the length of time after PH required to complete liver regeneration. 3-methylcholanthrene induced 2- AAF resistance prevented the development of large persistent nodules and hepatocellular carcinoma while phenobarbital delayed cancer development with several month. The data thus supports the idea that the degree of clonal expansion during promotion determines the size of the population at risk for malignant transformation, as well as the final frequency of carcinomas.      

Anticarcinogenic Effects of an Aqueous Infusion of Cloves on Skin Carcinogenesis

Spices and flavouring agents are now receiving incresaing attention as many of them have been shown to have ‍anticarcinogenic properties. Cloves, sundried unopened flower buds from the plant Syzygium aromaticum L, are ‍commonly used as a spice and food flavour. The present study was designed to investigate the chemopreventive ‍action of aqueous infusion of cloves on 9,10-dimethyl benz(a)anthracene (DMBA) and croton oil induced skin ‍carcinogenesis in Swiss mice. The results indicate protection against skin papilloma formation in a dose dependent ‍manner. It has been shown that oral administration of aqueous infusions of clove at a dose of 100ìl/ mouse/day not ‍only delays the formation of papilloma but also reduces the incidence of papilloma as well as the cumulative number ‍of papillomas per papilloma bearing mouse. Our observations suggest a promising role for cloves in restriction of ‍the carcinogenesis process.     

Growth hormone modifies the growth rate of enzyme-altered hepatic foci in male rats treated according to the resistant hepatocyte model

Male and female Wistar rats were given an initiating i.p. injectionof diethylnitrosamine (DEN; 200 mg/kg body wt). Two weeks laterthe rats were given a diet containing 0.02% (w/w) 2-acetylaminofluorene(2-AAF) for 2 weeks. In the middle of the 2-AAF treatment a70% partial hepatectomy (PH) was performed. In order to identifythe pituitary hormone responsible for the previously observedsex difference (male > female) in and influence of ectopicpituitary grafts on focal growth during 2-AAF/PH selection ofenzyme-altered foci, male rats were treated with a continuousinfusion of bovine growth hormone (bGH; 6 µg/h) or ovineprolactin (oPrl; 6 µg/h) by way of osmotic minipumps.Hormonal treatment was started 1 week after initiation and wasfinished 1 week after the 2-AAF selection period. All rats werekilled 6 weeks after initiation and liver sections were stainedfor -ghitamyttransferase. The number of foci/cm² as well asthe area per focus and area ratio (mm² foci/cm² liver section)were calculated. Whereas no significant differences in the numberof foci /cm² were observed between the different groups of rats,bGH treatment of male rats decreased both the area/focus andthe area ratio down to the female level. No significant effectswere seen following oPrl administration when compared with controlmales. In vitro studies of subcellular preparations from theliver lobes obtained at PH showed that the sexually differentiatedN-hydroxy-2-AAF sulfotransferase activity (male > female)in male rats was ‘feminized’, i.e. decreased, bybGH administration, but not by infusion of oPrl. The presentinvestigation strengthens the view of growth hormone as an importantdeterminant of sex differences in chemical carcinogenesis inrat liver, possibly via an influence on carcinogen metabolism.     

Chemopreventive Action of Emblica Officinalis on Skin Carcinogenesis in Mice

Chemoprevention with food phytochemicals is currently regarded as one of the most important strategies for ‍cancer control. Emblica officinalis (Family: Euphorbiaceae) indigenous to India, is valued for its unique tannins and ‍flavanoids, which contain very powerful antioxidant properties. The inhibition of tumor incidences by fruit extract ‍of this plant has been evaluated on two-stage process of skin carcinogenesis in Swiss albino mice, induced by a single ‍application of 7, 12-dimethyabenz(a)anthrecene (100 ìg/ 100 ìl acetone), and two weeks later, promoted by repeated ‍application of croton oil (1% in acetone/thrice a week) till the end of the experiment (16 weeks). The tumor incidence, ‍tumor yield, tumor burdon and cumulative number of papillomas were found to be higher in the control (without ‍EO treatment) as compared to experimental animals (EO treated). The differences in the values of the results of ‍experimental groups were statistically analysed and found to be significant in comparison to the control group (p< ‍0.05). The present study demonstrates the chemopreventive potential of Emblica officinalis fruit extract on DMBA ‍induced skin tumorigenesis in Swiss albino mice. ‍     

Ethanolic Neem (Azadirachta indica) Leaf Extract Induces Apoptosis in the Hamster Buccal Pouch Carcinogenesis Model by Modulation of Bcl-2, Bim,Caspase 8 and Caspase 3

Induction of apoptosis is one of the most active strategies in cancer chemoprevention and the ability of medicinal ‍plants in this regard has attracted major research interest. The present study was designed to investigate the apoptosis ‍inducing capacity of an ethanolic neem leaf extract (ENLE) during 7,12-dimethylbenz[a]anthracene (DMBA)-induced ‍hamster buccal pouch carcinogenesis using the apoptosis-associated proteins Bcl-2, Bim, caspase 8 and caspase 3 as ‍markers. Topical application of DMBA to the hamster cheek pouch for 14 weeks resulted in well developed squamous ‍cell carcinomas associated with increased expression of Bcl-2 and decreased expression of Bim, caspase 8 and caspase ‍3. Administration of ENLE inhibited DMBA-induced hamster buccal pouch (HBP) carcinogenesis, as revealed by ‍the absence of neoplasms, with induction of Bim and caspases 8 and 3 and inhibition of Bcl-2 expression. Our results ‍suggest that the chemopreventive effects of ENLE may be mediated by induction of apoptosis.     

Cleistocalyx nervosum Extract Ameliorates Chemical-Induced Oxidative Stress in Early Stages of Rat Hepatocarcinogenesis

Purpose: To study the effect of Cleistocalyx nervosum extract (CE) on diethylnitrosamine (DEN) andphenobarbital (PB) induced oxidative stress in early stages of rat hepatocarcinogenesis. Materials and Methods:Male Wistar rats were divided into 4 groups, with Group 1 as a negative control and Group 2 was a positivecontrol receiving DEN injections once a week and PB in drinking water for 6 weeks. Two weeks before DENinitiation and PB treatment, Groups 3 and 4, were fed with 500 and 1000 mg/kg of CEs, respectively, for 8weeks. Results: A number of GST-P-positive foci, preneoplastic lesions, in the liver were markedly increased incarcinogen administered rats, but was comparatively decreased in rats treated with 1000 mg/kg of CE. The CEreduced malondialdehyde in serum and in the livers of rats treated with DEN and PB. Moreover, CE significantlyincreased the activities of glutathione peroxidase and catalase in rat liver. Conclusions: CE appeared to exertits chemopreventive effects by modulating antioxidant status during DEN and PB induced early stages ofhepatocarcinogenesis in rats.     

Changes in levels of ADP-ribose polymers in rat liver during 2-acetylaminofluorene-induced hepatocarcinogenesis

The exposure of rats to the carcinogen 2-acetylaminofluorene(2-AAF) results in the accumulation of DNA-damaging adducts.The inability of cells to repair such damage adequately is aputative causal event in chemical carcinogenesis. It has beenshown that one cellular response to DNA damage that leads toDNA repair is poly(ADP-ribosyl)ation of nuclear proteins. Toexamine the possible existence of an altered poly(ADP-ribosyl)ationresponse to 2-AAF-mediated damage of rat liver DNA, tissue ADP-ribosepolymer levels were determined during various stages of 2-AAF-mediatedcarcinogenesis. 2-AAF was administered to rats in a discontinuousfeeding regimen comprised of five consecutive cycles, each cycleconsisting of 3 weeks on 2-AAF diet followed by 1 week of recoveryon a control diet without 2-AAF. During cycle one of 2-AAF administration,rat liver ADP-ribose polymer levels increased 3-fold over thatfound in livers of rats fed only the control diet. In contrast,when rats were administered the non-genotoxic liver mitogen4-AAF for one cycle, no significant elevation occurred in ADP-ribosepolymer levels. Elevated ADP-ribose polymer production was alsoobserved during cycles two and three of 2-AAF administration.However, during cycles four and five of 2-AAF administration,a period when rats administered 2-AAF acquire a high risk forhepatocarcinogenesis, an altered pattern of ADP-ribose polymerproduction occurred in rat livers. ADP-ribose polymer levelsin these rat livers remained low, similar to levels found incontrol rat livers, despite the administration of 2-AAF. Whenthe livers from rats fed either one or five cycles of 2-AAFwere analyzed for possible decreases in the levels of tissueNAD+, the substrate for poly(ADP-ribose) polymerase, no changesin relative abundance were found. In addition, analysis of poly(ADP-ribose)polymerase activity showed no decrease at five cycles of 2-AAFadministration. These results indicated that at late stagesof 2-AAF-induced hepatocarcinogenesis, 2-AAF does not inducean expected increase in ADP-ribose polymer levels, and suggestedthat significant changes in DNA repair may occur at a time justpreceding an increased risk for developing liver cancer.     

Modulation of altered hepatic foci induction by diallyl sulphide in Wistar rats.

Diallyl sulphide (DAS) is a sulphur-containing volatile compound present in garlic (Allium sativum). It has been shown to inhibit a number of chemically induced forms of cancer in experimental animals. The present study demonstrates the inhibitory effect of DAS on the development of diethylnitrosamine (DEN) initiated and 2-acetyl-aminofluorene (2-AAF) promoted preneoplastic altered hepatic foci (AHF) in Wistar rats. AHF were scored and analysed by quantitative stereology using the Image Analysis system from frozen liver sections stained for biological markers, namely glutathione S-transferase, placental form (GST-P), gamma-glutamyl transpeptidase (GGT), adenosine triphosphatase (ATPase), glucose-6-phosphatase (G6 Pase) and alkaline phosphatase (AlkPase). DAS-supplemented rats were found to restore the near-normal levels of enzymes GST-P and GGT when exposed to DEN and 2-AAF. DAS administration following DEN and 2-AAF exposure led to the restoration of enzymic activity of ATPase, G6 Pase and AlkPase, as evident by number and area of the foci. These findings suggest the protective role of DAS in rat hepatocarcinogenesis, by suppressing DEN- and 2-AAF-induced AHF development.     

Low selection of preneoplastic hepatocytes after treatment with the 2-acetylaminofluorene diet-partial hepatectomy regimen in the liver of hepatocarcinogenesis-resistant DRH strain rats

In hepatocarcinogenesis-resistant DRH rats, preneoplastic hepatocytic lesions are smaller than those of usual rats during carcinogenesis. When preneoplastic hepatocytes from DRH and Donryu (original strain of DRH) were reciprocally transplanted into the livers of DRH and Donryu treated with 2-acetylaminofluorene (2-AAF) diet/two-thirds hepatectomy (PH), the Donryu cells formed small colonies within the DRH liver, whereas the DRH cells formed large colonies within the Donryu liver. The DRH liver showed less degree of oval cell proliferation after treatment with 2-AAF and PH, and DRH hepatocytes were more resistant to the growth-inhibitory effect of 2-AAF after PH. Furthermore, DRH hepatocytes were generally resistant to cytotoxicity of hepatotoxins. The tissue environment of the DRH liver, therefore, is less effective for selective growth of preneoplastic hepatocytes during the carcinogen treatment, which is probably a major cause of the hepatocarcinogenesis-resistance in DRH rats.