S-transferase Placental Form Positive Foci Research Articles

Enriched Riceberry Bran Oil Exerts Chemopreventive Properties through Anti-Inflammation and Alteration of Gut Microbiota in Carcinogen-Induced Liver and Colon Carcinogenesis in Rats.

Simple SummaryRice bran oil is gaining popularity around the world due to its ability to improve lipid profiles. Recent in vitro studies have shown that the active compounds in colored rice bran oil exhibited anti-cancer properties in various cell lines. However, there has been a limited number of animal studies focusing on the anti-carcinogenic action of rice bran oil. In this study, Riceberry bran oil (RBBO) extracted from the bran of a Thai-pigmented rice variety, namely Riceberry, was investigated for its inhibitory mechanism on the early stages of liver and colorectal carcinogenesis using the dual carcinogens-induced rat model. RBBO was able to inhibit the biomarkers of rat liver cancer and colon cancer by forcing cells to undergo apoptosis, reducing inflammation, and changing the profiles of bacteria and their metabolites. These findings suggest that RBBO could be a promising source of high-value chemopreventive agents in terms of both cancer prevention and treatment.Riceberry has recently been acknowledged for its beneficial pharmacological effects. Riceberry bran oil (RBBO) exhibited anti-proliferation activity in various cancer cell lines. However, animal studies of RBBO on anti-carcinogenicity and its molecular inhibitory mechanism have been limited. This study purposed to investigate the chemopreventive effects of RBBO on the carcinogen-induced liver and colorectal carcinogenesis in rats. Rats were injected with diethylnitrosamine (DEN) and 1,2-dimethylhydrazine (DMH) and further orally administered with RBBO equivalent to 100 mg/kg body weight of γ-oryzanol 5 days/week for 10 weeks. RBBO administration suppressed preneoplastic lesions including hepatic glutathione S-transferase placental form positive foci and colorectal aberrant crypt foci. Accordingly, RBBO induced hepatocellular and colorectal cell apoptosis and reduced pro-inflammatory cytokine expression. Interestingly, RBBO effectively promoted the alteration of gut microbiota in DEN- and DMH-induced rats, as has been shown in the elevated Firmicutes/Bacteroidetes ratio. This outcome was consistent with an increase in butyrate in the feces of carcinogen-induced rats. The increase in butyrate reflects the chemopreventive properties of RBBO through the mechanisms of its anti-inflammatory properties and cell apoptosis induction in preneoplastic cells. This would indicate that RBBO containing γ-oryzanol, phytosterols, and tocols holds significant potential in the prevention of cancer.

Assessment of Systemic Toxicity, Genotoxicity, and Early Phase Hepatocarcinogenicity of Iron (III)-Tannic Acid Nanoparticles in Rats.

Iron-tannic acid nanoparticles (Fe-TA NPs) presented MRI contrast enhancement in both liver cancer cells and preneoplastic rat livers, while also exhibiting an anti-proliferative effect via enhanced autophagic death of liver cancer cells. Hence, a toxicity assessment of Fe-TA NPs was carried out in the present study. Acute and systemic toxicity of intraperitoneal Fe-TA NPs administration was investigated via a single dose of 55 mg/kg body weight (bw). Doses were then repeated 10 times within a range of 0.22 to 5.5 mg/kg bw every 3 days in rats. Furthermore, clastogenicity was assessed by rat liver micronucleus assay. Carcinogenicity was evaluated by medium-term carcinogenicity assay using glutathione S-transferase placental form positive foci as a preneoplastic marker, while three doses ranging from 0.55 to 17.5 mg/kg bw were administered 10 times weekly via intraperitoneum. Our study found that the LD50 value of Fe-TA NPs was greater than 55 mg/kg bw. Repeated dose administration of Fe-TA NPs over a period of 28 days and 10 weeks revealed no obvious signs of systemic toxicity, clastogenicity, and hepatocarcinogenicity. Furthermore, Fe-TA NPs did not alter liver function or serum iron status, however, increased liver iron content at certain dose in rats. Notably, antioxidant response was observed when a dose of 17.5 mg/kg bw was given to rats. Accordingly, our study found no signs of toxicity, genotoxicity, and early phase hepatocarcinogenicity of Fe-TA NPs in rats.

Improvement and validation of a medium-term gpt delta rat model for predicting chemical carcinogenicity and underlying mode of action

We have developed a new medium-term animal model, “GPG”, in which an in vivo mutation assay in partially hepatectomized tissue and a tumor-promoting assay were performed. The tumor-promoting assay measures glutathione S-transferase placental form positive foci induced by diethylnitrosamine (DEN) in the residual tissue. Given that a limitation of the original protocol is the potential interaction between the test chemical and DEN, the present study establishes a modified protocol that includes a test chemical washout period. Using CYP2E1 inhibitor and CYP1A or CYP2B inducers, a period of 2 weeks after cessation of exposure to the chemicals was confirmed to be sufficient to return their enzymatic activities to normal levels. Additionally, to avoid the effects of DEN on the pharmacokinetics of the test chemical, re-exposure to the test chemical started 1 week after DEN injection, in which tumor-promoting activities were clearly detected. Consequently, a modified protocol has been established with 2- and 1-week washout periods before and after DEN injection, respectively. The applicability of the modified protocol was demonstrated using the genotoxic hepatocarcinogen, estragole (ES), the genotoxic renal carcinogen, aristolochic acid (AA), and the non-genotoxic hepatocarcinogens, β-naphthoflavone and barbital. Furthermore, the increase of cell cycle-related parameters in ES-treated livers, but not in AA-treated livers, may indicate that the liver is not the carcinogenic target site of AA despite its genotoxic role. Thus, since various parameters related to carcinogenesis can be evaluated concurrently, the GPG model could be a rapid and reliable assay for the assessment of human cancer hazards.

Arachidonate-enriched triglyceride oil does not promote tumor development in a rat medium-term multi-organ carcinogenesis model

The modifying potential on tumor development of arachidonate-enriched triglyceride oil (ARA-oil) containing approximately 40% arachidonic acid was investigated in a medium-term multi-organ carcinogenesis bioassay using male and female F344 rats. The animals were sequentially given five carcinogens with different target sites in the first 4weeks, and then administered ARA-oil for 24weeks at dietary levels of 0% (control), 1.25%, 2.5% or 5.0%. No statistically significant differences in incidences and multiplicities of hyperplastic and neoplastic lesions were showed in the large intestine in either sex. In the liver, kidney, and lung in both sexes, and the mammary gland and uterus in females, tumor promoting potential was not evident with ARA-oil treatment. ARA-oil did not affect the quantitative data for glutathione S-transferase placental form positive foci of the liver. Increased induction of hyperplastic or neoplastic lesions in the urinary bladder and thyroid in ARA-oil-treated groups was without dose dependence. In addition, a second experiment with ARA-oil only administration for 8-week revealed no effects on cellular proliferation in the urinary bladder or thyroid in either sex. These results indicate that ARA-oil has no tumor promoting potential in any organs or tissues initiated with the five carcinogens applied in the present study.

Twenty-six-week oral toxicity of diheptyl phthalate with special emphasis on its induction of liver proliferative lesions in male F344 rats

The 26-week oral toxicity of diheptyl phthalate (DHP), a peroxisome proliferator-activated receptor α (PPARα) agonist, with special emphasis on the potential induction of hepatocellular proliferative lesions was investigated in this study. DHP was administered to male F344 rats via gavage at 0 (control), 1,000 or 2,000 mg/kg/day for 26 weeks. Body weight gain was significantly lower, whereas food and water consumption was significantly higher in DHP-treated rats compared with controls. DHP-treated rats exhibited decreases in blood triglyceride, total cholesterol, phospholipid and glucose levels, which were likely related to biological effects of the PPARα agonist. Absolute and relative organ weights of the livers with pale brown discoloration and dark brown spots significantly increased in DHP-treated rats. Histopathological examinations revealed remarkable diffuse hypertrophy of hepatocytes with ground-glass appearance, intracytoplasmic inclusion bodies and/or vacuolation in the DHP-treated groups. These findings were associated with increases in serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and γ-glutamyltranspeptidase. The number and area of glutathione S-transferase placental form positive foci, a marker of hepatocellular preneoplastic lesions in rats, significantly increased in DHP-treated groups. Additionally, proliferating cell nuclear antigen positive liver cell counts in DHP-treated groups were significantly higher than those of the controls. Testicular alterations were not detected histopathologically, whereas absolute and relative prostate weights significantly decreased at both doses. These results indicate that DHP induces liver pre-neoplastic foci, and suggest the possibility that DHP is a possible genotoxic carcinogen in the liver of rats.

Inhibition by licorice flavonoid oil of glutathione S-transferase–positive foci in the medium-term rat hepatocarcinogenesis bioassay

Licorice flavonoid oil (LFO) is a new functional food ingredient consisting of hydrophobic licorice polyphenols in medium-chain triglycerides. Recently, it was reported that licorice and its derivatives have anticarcinogenic activity in some types of tumors. However, the anticarcinogenic activity has not been identified in the liver, which is a major target organ for carcinogenesis in human. Therefore, we hypothesized that LFO has antihepatocarcinogenic activity, and we tested this hypothesis using the rat medium-term liver bioassay for carcinogens. Six-week-old male F344 rats (15 animals/group) received N-diethylnitrosamine (200 mg/kg by intraperitoneal injection) to initiate carcinogenesis. From the second week after initiation, animals received a 6-week regimen of either LFO concentrate solution (0, 150, 300, or 600 mg/kg) intragastrically or phenobarbital sodium salt in the diet (500 ppm) as a positive control. During the third week after initiation, animals were subjected to a two-thirds partial hepatectomy. During the eighth week of the treatment period, liver samples were taken from animals and examined immunohistochemically for expression of glutathione S-transferase placental form. No increase in the number of glutathione S-transferase placental form-positive liver foci was observed in all LFO groups compared with the negative control (solvent) group, and the number of foci in the 600 mg/kg LFO group was significantly lower than that in the negative control group. These results indicate that LFO concentrate solution has a significant inhibitory effect on liver carcinogenesis at 600 mg/kg.

Evidence of a Threshold-Effect for 2-Amino-3,8-dimethylimidazo-[4,5-f]quinoxaline Liver Carcinogenicity in F344/DuCrj Rats

To estimate potential human risk of exposure to a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), a 2-year carcinogenicity test was conducted using male F344 rats administered MeIQx-containing diet at doses of 0 (control), 0.001, 1, and 100 ppm. The lowest dose 0.001 ppm was established as equivalent to the daily intake of this carcinogen in humans (0.2 to 2.6 microg/man/day). Significant decreases of survival rate and body weight gain were observed in rats treated with 100 ppm MeIQx. Histopathological examination revealed significant induction of hepatocellular carcinomas, adenomas, and development of glutathione S-transferase placental form-positive foci with MeIQx at 100 ppm. Moreover, the incidences of Zymbal's glands carcinoma, mammary fibroadenoma, and subcutaneous fibroma were found significantly increased in a 100 ppm MeIQx group. However, no significant induction of altered preneoplastic hepatocellular foci was observed in 0.001 and 1 ppm groups as compared to the controls. 8-Hydroxy-2'-deoxyguanosine levels in the rat liver DNA of the 100 ppm-treated group were not elevated, but MeIQx-DNA adduct formation increased as compared with the 1 ppm case, albeit without significance. No significant induction of any other neoplastic lesions related to the carcinogen administration was found in MeIQx-administered groups except for 100 ppm. These results imply that 1 ppm may be a no-effect level for MeIQx carcinogenesis.

Harman and Norharman Suppressed but NaNO2 Enhanced the Development of Preneoplastic Liver Cell Foci in 2-Amino-3,8-Dimethylimidazo[4,5-f]Quinoxaline (MeIQx)-Treated Rats

The modifying potentials of two heterocyclic amines, harman and norharman, as well as sodium nitrite (NaNO2), on 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)-induced rat liver carcinogenesis were investigated using a medium-term liver bioassay system. Harman (500 ppm in diet), norharman (500 ppm in diet) or NaNO2 (0.1% in drinking water) were given with or without MeIQx (300 ppm in diet) for 6 weeks after initiation with a single dose of dimethylnitrosamine (DEN). The appearance of MeIQx-induced glutathione S-transferase placental form positive foci in the liver was significantly decreased in the harman and norharman cases (p< 0.001), but it was significantly increased by NaNO2 (p< 0.001). These chemicals, however, did not modify DEN-liver carcinogenesis in the absence of MeIQx. Neither harman nor norharman affected mRNA expression of CYP1A1 and 1A2 in the liver, with or without MeIQx administration, whereas NaNO2 significantly enhanced CYP1A1 mRNA levels together with MeIQx.

Induction of glutathione S-transferase placental form positive foci in liver and epithelial hyperplasia in urinary bladder, but no tumor development in male Fischer 344 rats treated with monomethylarsonic acid for 104 weeks

The carcinogenicity of monomethylarsonic acid (MMA(V)), a major metabolite of inorganic arsenics in human and experimental animals, was investigated in male Fischer 344 rats. A total of 129 rats at 10 weeks of age were randomly divided into three groups and received drinking water containing MMA(V) at doses of 0 (Control), 50, and 200 ppm ad libitum for 104 weeks. No significant differences were found between the control and the MMA(V)-treated groups regarding clinical signs, mortality, hematological, and serum biochemistry findings. Quantitative analysis of glutathione S-transferase placental form (GST-P) positive foci in liver revealed a significant increase of numbers and areas in the 200 ppm MMA(V)-treated group. In the urinary bladder MMA(V) induced simple hyperplasia and significantly elevated the proliferating cell nuclear antigen (PCNA)-positive index in the urothelium. A variety of tumors developed in rats of all groups, including the controls, but all were histologically similar to those known to occur spontaneously in F344 rats and there were no significant differences among the groups. Thus, it could be concluded that, under the present experimental conditions, MMA(V) induced lesions in the liver and urinary bladder, but did not cause tumor development in male F344 rats even after 2 years exposure.

Enhancing risk of ethanol on MeIQx-induced rat hepatocarcinogenesis is accompanied with increased levels of cellular proliferation and oxidative stress

We investigated promotion potential of ethanol after initiation of hepatocarcinogenesis in male, 21-day-old, F344 rats by exposure to 10 ppm 2-amino-3, 8-dimethylimidazo[4,5- f]quinoxaline pellet diet for 8 weeks. The rats in group 1 were then fed on liquid control diet for 16 weeks, group 2 receiving the same diet containing 5% ethanol for 8 weeks followed by 8 weeks on the control diet, while group 3 animals were given 5% ethanol containing liquid diet for the entire16 weeks. On sacrifice at the end of week 24, glutathione S-transferase placental form positive foci, putative preneoplastic lesions in the liver, cell proliferation as indicated by proliferating cell nuclear antigen immunohistochemical staining and levels of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, were significantly increased in the liver of group 3 along with non significant alteration of 8-oxoguanine DNA glycosylase mRNA expression. Lack of persistent increase of above parameters was found in transient ethanol exposure group. These results suggest that chronic consumption of ethanol promotes hepatocarcinogenesis by increasing oxidative stress and cell proliferation. It is also evident that abstinence of ethanol during the second stage stops its persistent promotion effect.

Promoting effects of monomethylarsonic acid, dimethylarsinic acid and trimethylarsine oxide on induction of rat liver preneoplastic glutathione S-transferase placental form positive foci: a possible reactive oxygen species mechanism.

Dimethylarsinic acid (DMA) is a major metabolite of inorganic arsenicals, which are epidemiologically significant chemicals in relation to liver cancer in mammals. The present study was conducted to determine the promoting effects of organic arsenicals related to DMA [monomethylarsonic acid (MMA) and trimethylarsine oxide (TMAO)] on rat liver carcinogenesis using a liver medium-term bioassay (the Ito test). Male, 10-week-old, F344 rats were given a single i.p. injection of diethylnitrosamine at a dose of 200 mg/kg b.w. as an initiator. Starting 2 weeks thereafter they received 100 ppm of MMA, DMA or TMAO in their drinking water, or no supplement as a control, for 6 weeks. All animals underwent 2/3 partial hepatectomy in week 3 after initiation. Quantification of glutathione S-transferase placental form (GST-P)-positive foci as preneoplastic lesions in liver sections revealed significantly increased numbers and areas in all 3 treated groups compared with controls. Hepatic microsome cytochrome P-450 content was markedly increased with all 3 arsenic treatments. Markedly elevated CYP 2B1 protein levels and CYP 2B1/2 mRNA levels were thus observed in all cases. The potency of promotion was similar for MMA, DMA and TMAO. Since hydroxyradicals were found to be generated in the relatively early phase while methylated arsenicals were metabolized in liver, the resultant oxidative stress might have promoted lesion development.

Chemopreventive effects of S-methylcysteine on rat hepatocarcinogenesis induced by concurrent administration of sodium nitrite and morpholine

The aim of the present study was to examine the chemopreventive efficacy of S-methylcysteine (SMC) on rat hepatocarcinogenesis induced by concurrent administration of sodium nitrite (NaNO2) and morpholine (Mor) using a medium-term rat liver carcinogenesis bioassay (Ito test). Administration of SMC caused significant reduction in the areas of glutathione S-transferase placental form positive foci along with a significant decrease of hepatocyte 5-bromo-2′-deoxyuridine (BrdU) labeling indices. These results demonstrated potent chemopreventive effects of SMC against hepatocarcinogenesis due to concurrent administration of Mor and NaNO2. SMC could thus be an effective chemopreventive agent for decreasing the risk of carcinogenicity from environmental precursors of N-nitroso compounds.

Changes in natural killer cell activity and prostaglandin E2 levels during the progression of diethylnitrosamine-induced hepatocarcinogenesis in Fischer 344 rats.

The sequential changes of natural killer cell (NK) activity and prostaglandin E2 (PGE2) during hepatocarcinogenesis induced by diethylnitrosamine (DEN) in male Fischer 344 rats were investigated. DEN at a concentration of 40 ppm was administered in drinking water for 10 weeks. At weeks 5, 10, 20 and 30, rats were autopsied and the development of glutathione S-transferase placental form positive foci (GST-P+ foci) at weeks 5 and 10 and hepatocellular tumors at weeks 20 and 30 were examined. The labeling index of bromodeoxyuridine (BrdU) an indicator of DNA synthesis, was also sequentially checked. GST-P+ foci were found to increase with age. Hepatocellular nodules increased until week 20, but by week 30 when the incidence of hepatocellular carcinoma was 100%, the incidence of nodules had decreased. BrdU positive cells also increased with age, and by week 30 when the incidence of hepatocellular carcinoma was 100%, the number of BrdU-positive cells had decreased. NK cell activity increased until week 10, but at week 20, was less than in the untreated control group. The level of PGE2 increased until week 5, but at week 10, levels were not significantly different from those seen in the untreated control group. On the basis of these results, we concluded that NK activity is closely related to the progression of hepatocarcinogenesis, but PGE2 levels show no significant change.

ENHANCING EFFECTS OF PHENOBARBITAL AND 3-METHYLCHOLANTHRENE ON GST-P-POSITIVE LIVER CELL FOCI DEVELOPMENT IN A NEW MEDIUM-TERM RAT LIVER BIOASSAY USING D-GALACTOSAMINE

The carcinogenic potential of phenobarbital (PB) and 3-methylcholanthrene (3-MC) was assayed in a new medium-term carcinogenicity bioassay using D-galactosamine (DCA) as a nonsurgical method to induce liver cell regeneration in place of partial hepatectomy (PH). Rats were initially given a single ip injection (200 mg/kg) of diethylnitrosamine (DEN) and after 2 wk on basal diet received 2 ip injections of DCA (300 mg/kg) at the end of wk 2 and 5. They were treated with one of the test compounds PB or 3-MC in the diet or fed basal diet for wk 3-8. Carcinogenic potential was assessed by comparing the numbers and areas per square centimeter of glutathione S-transferase placental form-positive (CST-P*) foci in the livers of test chemical-treated animals with those of the control animals given DEN/DCA alone. Positive estimations of carcinogenicity were obtained for PB, which is a nongenotoxic liver tumor promoter, and for 3-MC, which is a genotoxic nonliver carcinogen. Increases of liver/body weight ratios and serum total cholesterol were observed in rats treated with PB or 3-MC. Interestingly, interlobe differences were found on the development of CST-P* liver cell foci. Our results thus confirm that the present bioassay protocol with repeated administration of DCA instead of PH may offer a new and sensitive method to screen large numbers of environmental liver and nonliver carcinogens.

Enhancing effects of captafol on the development of GST-P-positive liver cell foci in a medium-term bioassay, and protection by L-cysteine of the enhancement in rats.

The modifying effects of captafol and protective effects of L-cysteine on the development of glutathione S-transferase placental form-positive (GST-P +) foci of the liver and expression of proliferating cell nuclear antigen (PCNA) in the kidney were investigated in a medium-term bioassay using D-galactosamine (DGA) in rats. Male 6-week-old F344 rats were initially given a single i.p. injection (200 mg/kg) of diethylnitrosamine (DEN) and after 2 weeks on basal diet, received two i.p. injections of DGA (300 mg/kg) at the ends of weeks 2 and 5, and were fed a diet supplemented with test chemicals for weeks 3-8. Animals in group 1 were given 1500 ppm captafol in the diet, while group 2 received 1500 ppm captafol in diet as well as 1500 ppm L-cysteine in drinking water, animals in control group being given basal diet alone. Positive results regarding increased numbers and areas of GST-P + liver cell foci were obtained in rats treated with captafol alone. On the other hand, significant reduction by L-cysteine in the areas of GST-P + liver cell foci initiated by DEN and promoted by captafol was observed. In addition, the PCNA-labelling indices of renal tubule cells were elevated in rats treated with captafol alone and significantly reduced in rats treated simultaneously with L-cysteine. The protocol used in the present study therefore allowed the in vivo determination of promoting effects of captafol and inhibitory influence of L-cysteine by analyzing GST-P + foci in the livers as marker lesions, within a relatively short period of 8 weeks. Thus, this bioassay protocol could have applicability as a new in vivo assay system for the screening of hepatic carcinogenic or anti-carcinogenic agents.

Lack of promoting activity of 7-methoxy-2-nitro-naphtho-[2,1- b]furan (R7000) in a medium-term rat liver bioassay

Among the nitro-naphthofurans, 7-methoxy-2-nitro-naphtho[2,1- b]furan (R7000) has proved to be a very potent mutagen that causes sarcomas at the subcutaneous injection site and carcinomas in the forestomach after p.o. administration. In the present study, possible promoting activity for diethylnitrosamine (200 mg/kg, i.p.)-initiated liver carcinogenesis was assessed in rats. R7000 dissolved in 5% ethanol solution at doses of 10 or 50 mg/l given as the drinking water for 6 weeks did not enhance development of pre-neoplastic glutathione S-transferase placental form positive foci. Thus, it was concluded that R7000 may not be carcinogenic for the rat liver under the present experimental conditions.

Enhancement by non-mutagenic pesticides of GST-P positive hepatic foci development initiated with diethylnitrosamine in the rat

The potential hepatocarcinogenicity of seven pesticides was examined using a rapid bioassay based on the induction of glutathione S-transferase placental form positive foci in the rat liver. Rats were initially injected with diethylnitrosamine and two weeks later were fed on diet supplemented with one of the pesticides for 6 weeks and then killed: all rats were subjected to a partial hepatectomy at week 3. Positive results were seen with chlorobenzilate (2000 ppm), vinclozolin (2000 ppm), malathion (4000 ppm), tecnazene (2000 ppm) and isoproturon (2000 ppm). S,S,S-tributylphosphorotrithioate (DEF, 200 ppm) and dicloran (2000 ppm) were negative in both number and area analyses. Although chlorobenzilate is carcinogenic in mice, malathion and vinclozolin have been reported as non-carcinogens in both rats and mice. Since the present system is based on the two-stage carcinogenesis hypothesis, it is possible that the chemicals showing positive results in this system possess at least tumor-promoting activity in the rat liver. This is very significant, as most carcinogens show tumor-promoting activity in their target organs.

Analysis of carcinogenic activity of some pesticides in a medium-term liver bioassay in the rat.

Eight pesticides were tested in a medium-term bioassay based upon the induction of preneoplastic lesions in the liver. Rats were initially given diethylnitrosamine intraperitoneally at a dose of 200 mg/kg body weight and 2 weeks later were treated with the pesticides for 6 weeks and then killed; all rats had a partial hepatectomy at week 3. Hepatocarcinogenic potential was assessed by comparing the number and area of glutathione S-transferase placental form positive foci in the liver with those of controls given diethylnitrosamine (DEN) alone. Positive results were seen with p,p-DDT and Triadimefon. Permethrin (mixture of 39% cis form and 61% trans form) showed borderline results. Permethrin (25/75), Deltamethrin, Cypermethrin (52/48), while Trimorphamide and Propineb gave negative results. Our findings provide experimental evidence to indicate that compounds active in this assay have a potential for liver carcinogenicity in rodents.

Enhancing effects of diallyl sulfide on hepatocarcinogenesis and inhibitory actions of the related diallyl disulfide on colon and renal carcinogenesis in rats.

It has been reported that diallyl sulfide (DS) and diallyl disulfide (DDS), major volatile compounds in garlic (Allium sativum), exert anticarcinogenic activity in several organs in rodents. The modifying effects of these two chemicals were therefore assessed using two-step liver and multi-organ carcinogenesis models. In experiment 1, male F344 rats were given a single i.p. injection of N-diethylnitrosamine (200 mg/kg body wt) and then received DS or DDS by intragastric intubation at doses of 200 and 50 mg/kg body wt, respectively, three times a week for 6 weeks. All rats were subjected to two-thirds partial hepatectomy at experimental week 3. In experiment 2, male F344 rats were sequentially treated with five carcinogens with different organ target sites for 4 weeks, and then administered DS or DDS as in experiment 1 for 24 weeks. DS demonstrated clear enhancing effects on the development of glutathione S-transferase placental form positive foci in both experiments. On the other hand, an inhibitory potential in colon and renal carcinogenesis was observed in rats treated with DDS. Therefore, while DDS may act as a chemopreventive agent, DS may promote hepatocarcinogenesis.

Inhibition of rat hepatic glutathione S-transferase placental form positive foci development by concomitant administration of antioxidants to carcinogen-treated rats

Inhibition potential of concomitant butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), catechol or sodium ascorbate (Na-AsA) administration on development of diethylnitrosamine (DEN) initiated glutathione S-transferase placental form (GST-P) positive foci in rat liver under the influence of 2-acetylaminofluorene (2-AAF) or 3′-methyl-4-dimethylaminoazobenzene (3′-Me-DAB) plus partial hepatectomy (PH) was investigated. Whereas BHA, BHT and catechol exerted marked inhibitory effects, Na-AsA lacked any modifying potential. The compounds that demonstrated inhibition also induced GST-P in the hepatic periportal areas, suggesting that development of GST-P positive foci is negatively influenced by extra-focal increase in this enzyme form observed with BHA, BHT or catechol.