Structure-activity relations in promotion of rat urinary bladder carcinogenesis by phenolic antioxidants

The urinary bladder tumor-promoting potentials of the phenolic antioxidants, 2-tert-butyl-4-methylphenol (TBMP), propylparaben, catechol, resorcinol and hydroquinone, which are structurally related to butylated hydroxyanisole (BHA), were investigated in 170 male F344 rats. The animals were initially given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as an initiator in their drinking water for 4 weeks. Three days later, groups of 20 rats received diet containing 1.0% TBMP, 3% propylparaben, 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone or basal diet alone until the end of week 36. Significant increases in the incidences and average numbers of the putative preneoplastic lesions, papillary or nodular (PN) hyperplasia, and papillomas of the urinary bladder were only observed in the group given TBMP after BBN. Development of these lesions was not enhanced by diet containing the other test compounds and no induction was associated with any of the test chemicals alone. The results thus clearly showed that TBMP, which most closely resembles BHA, promoted urinary bladder carcinogenesis. The similar effects of TBMP and BHA on urinary bladder carcinogenesis suggest a direct link between chemical structure and biological potency.

Cellular differentiation and histogenesis of rat glandular stomach cancers

The gastric and intestinal phenotypic expressions of tumor cells in 18 adenomatous hyperplasias, 33 well-differentiated adenocarcinomas, and 16 undifferentiated adenocarcinomas (4 poorly differentiated adenocarcinomas, 10 signet-ring cell carcinomas and 2 mucinous adenocarcinomas) induced by N-methyl-N'-nitro-N-nitrosoguanidine or 4-nitroquinoline-1-oxide in the rat glandular stomach were studied by histochemical stainings for mucin and immunohistochemical staining for pepsinogen isozyme 1 (Pg 1). By histochemical staining for mucin [by the paradoxical concanavalin A method, the modified method with labeled peanut lectin, the galactose oxidase-Schiff (GOS) reaction, and the sialidase-GOS reaction] and immunohistochemical staining of Pg 1, gastric cancer cells of each histological group could be clearly classified into a gastric type, including mucous neck cell pyloric gland cell, and surface mucous cell subtypes, and an intestinal type, including goblet-cell, and intestinal absorptive cell subtypes. All tumors examined in this work consisted mainly of gastric-type cells but intestinal-type tumor cells were occasionally found among the gastric-type tumor cells. The incidences of intestinal-type cells in adenomatous hyperplasias (11.1%) and small well-differentiated adenocarcinomas (28.6%) were significantly less (P less than 0.05) than that in large well-differentiated adenocarcinomas (68.4%). The incidence of intestinal-type cells in small undifferentiated adenocarcinomas (25.0%) was also less than that in large ones (58.3%). The present results suggest the occurrence of change of phenotypic expression of tumor cells from the gastric type to the intestinal type during growth of tumors.

Gastric and intestinal phenotypic expression of human stomach cancers as revealed by pepsinogen immunohistochemistry and mucin histochemistry

Gastric and intestinal phenotypic expression in 223 surgically obtained primary gastric cancers and their histogenetic relationship to intestinal metaplasia in the surrounding gastric mucosa were studied by mucin histochemistry and pepsinogen (Pg) immunohistochemistry. Histochemical differentiation of mucins (paradoxical concanavalin A, the galactose oxidase-Schiff sequence and sialidase-galactose oxidase-Schiff) and immunohistochemical staining of Pgs I and II, allowed differentiation of gastric cancer cells from different histological categories into gastric elements including mucous neck cells, pyloric gland cells and surface mucous cells or intestinal elements including goblet cell and intestinal absorptive cell types. Of 122 papillary and tubular adenocarcinomas, 33 (27.1%) consisted mainly of gastric-type cells and 42 (34.4%) predominantly of intestinal-type cells. The remainder (38.5%) consisted of mixtures of gastric- and intestinal-type cells. Of 101 poorly differentiated adenocarcinomas, signet ring cell carcinomas and mucinous adenocarcinomas, 59 (58.4%) consisted mainly of gastric-type cells and 20 (19.8%) mainly of intestinal-type cells. Seven out of 35 papillary and tubular adenocarcinomas consisting mainly of gastric-type cancer cells were surrounded by mucosa with intestinal metaplasia. Conversely, 10 out of 40 papillary and tubular adenocarcinomas consisting mainly of intestinal-type cancer cells were observed in nonmetaplastic gastric mucosa. Thus no relationship as regards intestinal phenotypic expression was found between gastric cancers and surrounding gastric mucosa.

Increase in the active form of 3-hydroxy-3-methylglutaryl coenzyme A reductase in human hepatocellular carcinoma: possible mechanism for alteration of cholesterol biosynthesis

3-Hydroxy-3-methylglutaryl coenzyme A reductase activity and the rate of sterol biosynthesis are positively correlated with DNA synthesis and proliferation of mammalian cells. The total (active plus latent) activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase and the activity of its active form in hepatocellular carcinoma (HCC) from seven patients were measured and compared with those in liver tissue from five control subjects. The activity of the active form in HCC was 61 +/- 21 (SD) pmol/min/mg microsomal protein, while it was only 17 +/- 9.8 pmol/min/mg protein in the liver tissue from the controls; the difference was significant (P less than 0.005). The total activity of the reductase was also higher in HCC although the difference was not significant. The microsomal contents of the enzyme protein also were not significantly different. The rate of cholesterol biosynthesis was 307 +/- 81 pmol/h/mg tissue in HCC and 79.6 +/- 52 in normal liver tissue, indicating a significant increase in the rate in HCC (P less than 0.001). Thus, enhanced synthesis of cholesterol in human HCC seems to result partly from an increase in the active form of the reductase.

Enhancing effects of sodium phenobarbital and N,N-dibutylnitrosamine on tumor development in a rat wide-spectrum organ carcinogenesis model

A wide-spectrum organ carcinogenesis model for detection of cancer modifiers in various organs was assessed in F344 male rats. After sequential treatment with diethylnitrosamine, N-methylnitrosourea, and dihydroxy-di-N-propylnitrosamine, rats were fed 500 p.p.m. sodium phenobarbital (PB: carcinogen for the liver, promoter for the thyroid) in the diet or 50 p.p.m. N,N-dibutylnitrosamine (DBN: carcinogen for the upper digestive tract, liver and urinary bladder) in the drinking water. Upon histopathological investigation at experimental weeks 18 and 24, PB was found to increase significantly the incidences of hyperplasias and adenomas of the thyroid and the numbers and areas of placental glutathione S-transferase-positive foci in the liver. DBN increased the lung tumor incidences at week 18, and brought about significant increases in both numbers and areas of lung tumors per rat at week 24. Furthermore, DBN enhanced the occurrences of hyperplasias and papillomas of the esophagus as well as hyperplasia for the forestomach at both time points. In addition, significant numbers of esophageal carcinomas and lingual papillomas developed in the group given DBN after pretreatment with the three carcinogens at week 24. Assessment of lesion yield thus clearly revealed enhancement of carcinogenesis by the test chemicals in their respective target organs, indicating the advantage of the wide-spectrum organ carcinogenesis model for detection of cancer modifiers within a limited time period in multiple organs.

Epithelial cell proliferation in rat forestomach and glandular stomach mucosa induced by catechol and analogous dihydroxybenzenes

An investigation of antioxidant-induced lesions in stomach epithelia was performed using F344 rats of both sexes. Histopathological changes, levels of DNA synthesis and pepsinogen isozyme 1 altered pyloric gland (PAPG) induction were assessed following 4 weeks oral administration of catechol (CC) or analogs such as hydroxyhydroquinone (HHQ), protocatechuic acid (PCA), protocatechualdehyde (PCAH), dopamine and DL-dopa. While epithelial hyperplasia of the forestomach was only observed in the groups given CC, DNA synthesis in this epithelium was increased in groups of both sexes treated with CC, HHQ or dopamine. In the glandular stomach, CC induced submucosal growth of pyloric mucosal cells and an increase in crypt height associated with an elevation of DNA synthesis and numbers of PAPG. In contrast, dopamine brought about significant reduction in DNA synthesis in the pyloric mucosa of both sexes. The other CC analogs did not exert any obvious influence on glandular stomach mucosa. Since cell proliferation is well correlated to tumor promotion, the results suggested that HHQ and dopamine may have promoting potential for rat two-stage forestomach carcinogenesis in common with CC, while dopamine might be expected to inhibit glandular stomach carcinogenesis.

Duration of pressure overload alters regression of coronary circulation abnormalities

Using a rat model of ascending aortic banding and debanding, we examined how the duration of pressure overload affects reversibility in coronary circulation abnormalities after relief of pressure overload. Four-week banding increased left ventricular dry weight-to-body weight ratio to 158 +/- 8% of that of sham-operated controls. In isolated nonworking hearts perfused with crystalloid solution, peak mean coronary flow rate (CFR) was measured after brief ischemia. CFR and CFR/dry tissue weight significantly decreased (75 +/- 5 and 54 +/- 3% of that of controls at 100 mmHg of coronary perfusion pressure; 75 +/- 5 and 54 +/- 4% at 150 mmHg, respectively). Four weeks after debanding was performed, CFR and CFR/dry tissue weight increased to similar levels in controls. On the other hand, 10-wk banding produced the same degree of myocardial hypertrophy and decreases in CFR and CFR/dry tissue weight as in 4-wk banded rats. Four weeks after debanding was performed, CFR had not changed. CFR/dry tissue weight increased because of regression of myocardial hypertrophy but was significantly lower than that in rats debanded after 4 wk of banding. Thus the duration of pressure overload does not affect the degree of coronary circulation abnormalities in the progression process but does affect it in the regression process.

Preparation and opioid activities of N-methylated analogs of [D-Ala2,Leu5]enkephalin

Analogs of opioid pentapeptide [D-Ala2,Leu5]enkephalin were prepared using two kinds of N-methylation reactions, namely quaternization and amide-methylation. Quaternization reaction with CH3I-KHCO3 in methanol was applied to the deprotected N-terminal group of the pentapeptide derivatives affording trimethylammonium group-containing analogs. [Me3+Tyr1,D-Ala2,Leu5]enkephalin and its amide were found to show opioid activity on guinea pig ileium assay only slightly lower than the parent unmethylated peptides. Application of amide-methylation reaction using CH3I-Ag2O in DMF to the protected pentapeptide yielded a pentamethyl derivative in which all of the five N atoms were methylated. Deprotection of the derivative gave pentamethyl analogs of [D-Ala2,Leu5]enkephalin, which showed no significant activity on the guinea pig ileum assay and opiate-receptor binding assay.

Different carcinogenic responses in a variety of organs, including the prostate, of five different rat strains given 3,2'-dimethyl-4-aminobiphenyl

Tumorigenic response in the prostate of F344, ACI, Lewis, CD and Wistar rat strains to 3,2'-dimethyl-4-aminobiphenyl (DMAB) was examined in relation to development of other types of tumors. Rats of each strain aged 6 weeks were divided into two groups receiving DMAB s.c. at a dose of 50 mg/kg body wt once every other week for 10 times, with or without 1 week dietary ethynyl estradiol (EE) pretreatment. The experiment was terminated at week 60, carcinomas of the ventral prostate, all of microscopic size, being respectively found in 50, 17, 21, 15 and 0% of F344, ACI, Lewis, CD and Wistar strain animals treated with EE plus DMAB. The tumor yield correlated well with DMAB-DNA adduct formation. One invasive adenocarcinoma also developed in the periurethral part (occupying both of lateral and dorsal areas) of the prostate. The final survival rates were 46, 24, 65, 4 and 0% in F344, ACI, Lewis, CD and Wistar rats respectively. DMAB administration without EE pretreatment resulted in similar incidences of prostate tumors and mortalities. Tumors arose in greater than 14 different sites with strain dependency, lesions predominating in the skin/subcutis of ACI and F344, preputial gland of F344, urinary bladder of ACI, and mammary glands of CD rats respectively. Consideration of mortality and the relative incidence of prostate cancer and other types of tumors indicates the F344 rat strain to be the most appropriate for investigation of DMAB prostate carcinogenesis.

Effects of dietary perilla oil, soybean oil and safflower oil on 7,12-dimethylbenz[a]anthracene (DMBA) and 1,2-dimethyl-hydrazine (DMH)-induced mammary gland and colon carcinogenesis in female SD rats

The effects of diet supplemented with perilla oil, which contains a large amount of n-3 alpha-linolenic acid, and n-6 linoleic acid rich soybean and safflower oil supplemented diets on 7,12-dimethylbenz[a]anthracene (DMBA)- and 1,2-dimethylhydrazine (DMH)-induced mammary gland and colon carcinogenesis were investigated in female SD rats. Groups of 23 or 24, 5 week old animals were first given three s.c. injections of 40 mg/kg body wt DMH followed by a single intragastric administration of 50 mg/kg body wt DMBA within 2 weeks of the commencement. Starting 1 week after the DMBA treatment, they were administered pellet diet containing 10% perilla oil, soybean oil or safflower oil for the succeeding 33 weeks. Histological examination revealed that the resultant numbers of mammary tumors per rat were significantly lower in rats given perilla oil diet (4.4 +/- 2.5) than in the soybean oil diet group (6.5 +/- 3.9). Furthermore, colon tumor incidence was significantly lower in animals receiving the perilla oil supplement (18.2%) than in those given safflower oil diet (47.4%), and the numbers of colon tumors per rat tended to be lowest in rats administered perilla oil. Also the incidence of nephroblastomas in rats receiving perilla oil diet (0%) was significantly lower than that for the soybean oil diet group (23.8%). The results thus indicate that the alpha-linolenic acid (n-3)-rich perilla oil diet inhibits development of mammary gland, colon and kidney tumors as compared to linoleic acid (n-6)-rich safflower or soybean oil diet.

Correlation between medium-term liver bioassay system data and results of long-term testing in rats

The effects of hepatocarcinogens (ethionine, thioacetamide, phenobarbital), non-hepatocarcinogens [N-ethyl-N-(4-hydroxybutyl)nitrosamine (EHBN), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)] and a hepatoinhibitor [(butylated hydroxyanisole (BHA)] were compared in medium- and long-term in vivo systems. In experiment I, 2 weeks after a single injection of diethylnitrosamine (DEN) groups of male F344 rats received chemical administration for 6 weeks, combined with partial hepatectomy at week 3 and were killed at the end of week 8. In experiment II, animals were treated in the same manner and then given basal diet and tap water (group 1) or chemical continuously (group 2) until the 2 year timepoint. Numbers and areas of glutathione S-transferase placental form (GST-P)-positive foci developing in the liver under medium-term bioassay conditions (experiment I) were found to closely correlate with eventual hepatocellular carcinoma incidences after continuation of test chemical administration (experiment II). Thus all of the hepatocarcinogens enhanced both the induction of GST-P-positive focal lesions and liver tumors. While non-hepatocarcinogens exerted no such effects, their influence being limited to inducing lesions in their own respective target organs such as urinary bladder cancers in the EHBN case and glandular stomach adenocarcinomas with MNNG, BHA demonstrated inhibition potential in both experiments. The observed correlation between long- and medium-term results strongly indicates the applicability of our medium-term bioassay system for detection of liver carcinogens.

Comparison of initiation potential of 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in an in vivo carcinogen bioassay system

A new approach to low-dose assessment of carcinogenic potential was applied to food contaminant pyrolysis products. Single intragastric doses of the carcinogenic pyrolysates, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) or 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline MeIQx), were given 12 h after two-thirds partial hepatectomy (PH) to F344 male rats. Two weeks thereafter the animals were placed on a basal diet containing 0.05% phenobarbital (PB) for 6 weeks combined with an i.p. administration of D-galactosamine (300 mg/kg) to facilitate growth of initiated cells. Both IQ and MeIQx clearly caused initiation of hepatocarcinogenesis as revealed by induction of preneoplastic placental-form glutathione-S-transferase-positive (GST-P+) hepatocyte foci composed of more than three cells (approximately 30 microns in diameter). A similar protocol without performance of PH before pyrolysate administration gave a positive result only for the IQ-treated group indicating that cell proliferation is essential during the low-dose, one-shot initiation step. IQ was found to be two to three times more potent in inducing GST-P+ foci using both protocols. The current approach could find application in practical carcinogenicity screening of chemicals, for which only small amounts are available.

Immunohistochemical demonstration of carcinogen-DNA adducts in target and non-target tissues of rats given a prostate carcinogen, 3,2'-dimethyl-4-aminobiphenyl

An immunohistochemical procedure was applied which allows accurate localization of DNA lesions within organs and tissues of rats given 3,2'-dimethyl-4-aminobiphenyl (DMAB) using polyclonal antibodies against DMAB-DNA adducts. Dose-related nuclear staining was observed in organs regardless of DMAB-carcinogenic organotropism. In the male accessory sex organs, the lateral lobe of the prostate, a non-target site, demonstrated a similar staining intensity to that found for the ventral prostate and seminal vesicle, target sites. Orchiectomy and pretreatment with ethinyl estradiol resulted in a moderate to slight decrease in binding in the accessory sex organs. No observable decrease in staining intensity was evident in most organs 168 h after the administration of DMAB. These findings suggest that DNA adduct formation itself is not necessarily sufficient for tumor induction.

Selective induction of prostate carcinomas in F344 rats treated with intraperitoneal injections of N-hydroxy-3,2'-dimethyl-4-aminobiphenyl

Groups of F344 and Wistar rats were given an intraperitoneal injection of N-hydroxy-3,2'-dimethyl-4-aminobiphenyl (N-OH-DMAB) at a dose of 5 mg/kg body weight with a 1-week dietary pretreatment with ethinyl estradiol (EE), and this regimen was repeated 10 times at one-week intervals. Additional groups were given N-OH-DMAB 10 times without the dietary EE pretreatment. The total experimental period was 60 weeks. Carcinomas and atypical hyperplasias of the prostate developed in 8 (42%) and 16 (84%) of 19 F344 rats without the dietary EE treatment and in 1 (6%) and 7 (39%) of 18 rats with the EE diet, respectively. No prostatic tumors were found in Wistar rats, although atypical hyperplasias were observed in 6 of 18 rats with and 4 of 8 rats without the EE supplementation. Tumor yields in other organs were extremely low, resulting in good survival of the animals. A comparison of the results with those obtained for DMAB suggests that intraperitoneal administration of N-OH-DMAB in F344 provides a better induction method for models of prostate carcinogenesis.

Early proliferative responses of forestomach and glandular stomach of rats treated with five different phenolic antioxidants

The effects of 8 weeks of oral administration of five different phenolic antioxidants, e.g. catechol (CC), resorcinol, hydroquinone (HQ), 2-tert-butyl-4-methylphenol (TBMP) and propylparabene (PP), on forestomach and glandular stomach epithelium of male F344 rats were evaluated using a combined immunohistochemical and histopathological approach. Treatment with CC and TBMP induced a significant elevation of DNA synthesis in the forestomach epithelium, associated with hyperplasia. CC administration also brought about an increase of DNA synthesis in the pyloric gland mucosa, cell proliferation in this case being reflected by an increment in the crypt height. In addition to causing an increase in the pepsinogen-isozyme-1-altered pyloric glands (PAPG), which are considered to be putative preneoplastic precursor lesions in the rat glandular stomach, CC treatment was associated with submucosal growth of pyloric mucosal cells tending to decreased pepsinogen isoenzyme 1 binding. However, DNA synthesis values in these latter areas were lower than in pyloric glands of the control group. In contrast, other phenolic compounds, resorcinol, HQ and PP, did not induce any changes in the stomach mucosa. The present results demonstrated strong proliferative responses in the stomach epithelium for CC and TBMP, indicative of promoting potential in both cases, and suggest that CC and TBMP may exert detrimental effects leading to promotion of stomach carcinogenesis or cancer development via an early proliferative response.

Stomach carcinogenicity of caffeic acid, sesamol and catechol in rats and mice

The carcinogenic potential of caffeic acid, sesamol and catechol was examined in male and female F344 rats and B6C3F1 mice, groups of 30 animals being treated with diets containing 2% caffeic acid, 2% sesamol or 0.8% catechol for 104 weeks (rats) or 96 weeks (mice). Histological examination revealed that caffeic acid induced forestomach squamous cell carcinoma in 57% (P less than 0.001 vs. controls) and 50% (P less than 0.001) of male and female rats, respectively, whereas sesamol was associated with squamous cell carcinoma at incidences of 31% (P less than 0.001) in male rats, and 38% (P less than 0.001) and 17% (P less than 0.05) in male and female mice, respectively. Catechol induced glandular stomach adenocarcinomas in 54% (P less than 0.001) and 43% (P less than 0.001) of male and female rats, respectively. The results thus clearly demonstrated that all three antioxidants are carcinogenic in rodent stomach epithelia.

Modulation of c-myc expression by transforming growth factor beta 1 in human hepatoma cell lines

The effects of transforming growth factor beta 1 (TGF-beta 1) on cell proliferation of human hepatoma cell lines, PLC/PRF/5 and Mahlavu, were investigated under serum-free conditions. DNA synthesis was strongly inhibited in the PLC/PRF/5 cells by addition of TGF-beta 1 (0.5 to 4.0 ng/ml), but remained unchanged in the Mahlavu cells. Also the expression of c-myc mRNA was suppressed by the addition of TGF-beta 1 in the PLC/PRF/5 cells but not in the Mahlavu cells. These results indicate that TGF-beta 1 might regulate cell growth, in part, by modulating c-myc expression, although there is no direct proof that c-myc expression is really relevant to DNA synthesis mediated by TGF-beta 1.

Relationship between lectin binding properties and the expression of blood group ABH antigens in vascular endothelia and red blood cells from 18 primate species

The reactivity was examined of horseradish peroxidase labelled Ulex europaeus agglutinin-I (UEA-I) and Griffonia simplicifolia agglutinin I-B4 (GSAI-B4) with red blood cells and vascular endothelium in formalin-fixed, paraffin embedded tissues from 18 primate species. The expression of blood group ABH antigens in these cells as well as secretions from other tissues was also examined by the indirect immunoperoxidase method using monoclonal anti-ABH antibodies as primary antibodies. In Prosimians and New World monkeys which lack ABH antigens on both red blood cells and endothelial cells, but produce these antigens in other tissue secretions, GSAI-B4 always reacted with both red blood cells and endothelial cells. In Old World monkeys, which express blood group antigens on endothelial cells but not on red blood cells, neither GSAI-B4 nor UEA-I reactivity were observed, except the endothelial cells from blood group B or O individuals occasionally reacted with GSAI-B4 or UEA-I, respectively. Although UEA-I reactivity was not observed in the endothelial cells of gibbon, it reacted with these cells from chimpanzees. In these two anthropoid apes, both endothelial cells and red blood cells expressed ABH antigens as in humans. These results suggest the close evolutionary relationship between the expression of blood group ABH antigens and lectin binding properties of red blood cells and endothelial cells in primate species.

Modulatory interaction between initial clofibrate treatment and subsequent administration of 2-acetylaminofluorene or sodium phenobarbital on glutathione S-transferase positive lesion development

The effects of 2-acetylaminofluorene (2-AFF) or sodium phenobarbital (PB) treatment subsequent to clofibrate (CF) administration in terms of preneoplastic lesion development and induction of hepatocellular carcinomas (HCC) were studied using Fischer 344 rats. Animals received CF (0.3% in diet) for the initial 30 weeks, and then either 2-AAF (0.01% in diet), PB (0.05% in diet) or basal diet until week 78. Further groups were initially given basal diet, and then treated with 2-AAF or PB week 30. Two-thirds partial hepatectomy was carried out on all animals at week 3, sacrifice of representative groups being performed at weeks 30, 48 and 78. No glutathione S-transferase placental form positive (GST-P+) or negative focal or nodular lesions were apparent at the cessation of CF administration. The induction of GST-P+ focal lesions by 2-AAF was markedly decreased at week 48 in the group previously given CF (P less than 0.05) and furthermore, the respective incidences of HCC at week 78 were 4/17 (23.5%) in the CF----2-AAF group and 7/17 (41.2%) in the 2-AAF alone case. No significant differences between CF----PB and PB alone groups were evident with regard to either GST-P+ lesions and HCC at weeks 48 and 78. No CF-specific GST-P negative neoplastic nodules or HCC were observed in any of the experimental groups. These results suggest that pretreatment with CF may inhibit the induction of GST-P+ focal lesions and HCC by subsequently administrated 2-AAF and that CF demonstrates no initiating activity for liver carcinogenesis under the present condition.

Regression of butylated hydroxyanisole (BHA)-induced hyperplasia but not dysplasia in the forestomach of hamsters

The reversibility of butylated hydroxyanisole (BHA)-induced hamster forestomach hyperplasia was examined histopathologically. Groups of 10-15 male Syrian golden hamsters were treated with 2% BHA, for 12, 24 or 48 weeks and in each case then placed on basal diet until termination of the experiment at week 72, or treated with 2% BHA continuously for 72 weeks. Although sequential sampling revealed that BHA-induced hyperplasia reverted after cessation of antioxidant treatment, dysplastic lesions such as squamous cell dysplasia and basal cell dysplasia persisted and tended to increase with time on BHA. Basal cell dysplasia was observed in some hamsters later than squamous cell dysplasia, i.e. those treated with BHA for 24 weeks or more and killed up to 48 weeks later. Whereas the increase in labeling index evident in areas of hyperplasia during treatment returned to control level after cessation, this was not the case for the dysplastic lesions which continued to demonstrate elevated proliferation. The results thus suggest that basal cell dysplasia, including regions of squamous cell dysplasia, may be of particular importance as a precursor pre-neoplastic lesion.

Lack of hepatotoxicity or promotion of enzyme-altered liver foci development in rats treated with harman or norharman

The modifying effects of harman or norharman on liver carcinogenesis were investigated in male F344/DuCrj rats initially treated with N-nitrosodiethylamine (DEN). Two weeks after a single dose of DEN (200 mg/kg, intraperitoneally), rats were given harman or norharman at dietary levels of 1000 and 200 parts per million (ppm), or sodium phenobarbital (PB) at 500 ppm as a positive control, for 6 wk. At wk 3 following DEN administration, all animals were subjected to partial hepatectomy. Marked retardation of body weight gain was observed in rats treated with harman or norharman at 1000 ppm, but not at 200 ppm. Increased relative kidney but not liver weights were associated with harman or norharman treatment, especially in the higher dose groups. Although no toxicity-related hepatocyte lesions were found, severe renal toxic tubular lesions and regeneration were evident. Neither harman nor norharman significantly increased the numbers or areas of glutathione S-transferase placental form (GST-P) positive foci observed after DEN initiation, in clear contrast to PB. The results thus demonstrated that harman and norharman are nontoxic for the liver and lack modifying potential for liver carcinogenesis in our medium-term bioassay system.

Comparative sequential changes in serum and biliary levels of bile acid components after a single dose of D-galactosamine or partial hepatectomy in the rat

In order to characterize changes in bile acid profile during liver cell damage and regeneration, levels of bile acids in serum and bile were determined by high performance liquid chromatography (HPLC) in F344 rats treated with a single dose of D-galactosamine (galactosamine, 300 mg/kg, i.p.) or subjected to two-thirds partial hepatectomy (PH). In the serum, galactosamine caused elevation of conjugated bile acids such as taurocholic acid (TCA) and tauro-beta-muricholic acid (T beta MCA) at the 24 and 48-h time points, whereas unconjugated bile acids including cholic acid (CA) at 24 h and hyodeoxycholic acid (HDCA) at 48 h were increased after PH. In the bile, elevation of TCA showed most remarkable elevation at the 24-h time point in the galactosamine-treated group. All components of biliary bile acids showed rapid decreases from 24 to 48 h. The results demonstrated that while liver tissue damaged by galactosamine is able to conjugate bile acids it allows leakage into the blood stream. In contrast, the results for rats subjected to PH indicated that liver cells during DNA synthesis are not capable of conjugating all free bile acids with taurine although a similar leakage occurs. It is concluded that obvious elevation of serum TCA or CA and biliary T beta MCA could be a useful indicator of hepatocellular proliferation.

DNA-adduct formation in the forestomach of rats treated with 3-tert-butyl-4-hydroxyanisole and its metabolites as assessed by an enzymatic 32P-postlabeling method

Formation of DNA-adducts by 3-BHA or its metabolites, i.e., tert-butyl-1,4-benzoquinone (TBQ) and 5-methoxy-3-tert-butyl-1,2-benzoquinone (3-TBOQ), as well as DNA-adduct formation by 4-nitroquinoline-N-oxide (4NQO), in rat forestomach were examined by an enzymatic 32P-postlabeling assay. Four DNA-adducts were clearly detected in the forestomach after treatment of rats with 4NQO. The sensitivity was 1.9 certain adducts per 10(8) normal nucleotides. On the contrary, no DNA adducts were detected in the forestomach of rats given either a single or repeated oral administration (5 days) of 3-BHA, TBQ or 3-TBOQ. The analyses were carried out under conditions which could detect the DNA-adducts produced by reaction of TBQ with calf thymus DNA in vitro. The results suggest that formation of aromatic adducts in vivo by 3-BHA, TBQ or 3-TBOQ in the rat forestomach-DNA is not evident or at least below the detection limits of the current bioassay.