Neoplasms observed in untreated and corn oil gavage control groups of F344/N rats and (C57BL/6N X C3H/HeN)F1 (B6C3F1) mice

Control data on F344/N rats and (C57BL/6N X C3H/HeN)F1 (B6C3F1) mammary tumor virus-free mice from the National Toxicology Program (NTP) were examined to determine if animals receiving corn oil by gavage showed tumor incidences that differed from those of untreated control animals. Analyses of these data were adjusted for interlaboratory variability, time-related trends, and supplier effects. Two biologically significant effects were found: Male F344/N control rats receiving corn oil by gavage showed a higher (P less than .05) incidence of pancreatic acinar cell adenoma and a lower (P less than .001) incidence of leukemia (primarily mononuclear cell leukemia) than did the corresponding untreated controls. The increased incidences of pancreatic acinar cell adenoma seen in male rats administered corn oil by gavage were associated with elevated body weights observed in these animals relative to untreated controls. Female F344 rats and male and female B6C3F1 mice showed little or no evidence of a difference in tumor incidence between corn oil gavage-treated and untreated controls. A review of nearly 300 carcinogenesis studies done by the National Cancer Institute (NCI) and the NTP revealed that there were no corn oil gavage studies in which increased incidences of pancreatic acinar cell tumors or leukemia in male F344/N rats were the sole evidence of the carcinogenicity of a test chemical. Thus use of corn oil appears to have little impact on the interpretation of NCI-NTP carcinogenicity studies.     

Necrotizing effect of ethanedimethanesulfonate on spontaneously occurring Leydig cell tumors in old F344 rats

Thirty 18-month-old male F344/DuCrj rats were divided into the following groups: 10 untreated controls; eight vehicle-injected controls; and 12 ethanedimethanesulfonate (EDS)-injected rats. Untreated controls were killed immediately to check for testicular tumor incidence. In rats of the test group, a 75-mg/kg dose of EDS dissolved in dimethyl sulfoxide:water (1:3) was injected i.p. At intervals of 1, 2, 3, and 10 days after injection, two vehicle-injected control rats and three EDS-injected rats were sacrificed, and the testes were fixed by vascular perfusion. The midsagittal sections of all the fixed testes were examined to determine the incidence of macroscopic Leydig cell tumors, and some tumor tissues of the injection-treated groups were also investigated ultrastructurally. In 28 of 30 animals, a total of 78 Leydig cell tumors could be distinguished. Extensive and severe necrotic alterations accompanying fresh, multiple hemorrhages in early stages and reparative changes in later stages could be observed in a total of 78% of the 32 tumors examined from the EDS-injected group. The tumor cells exhibited ultrastructurally degenerative changes such as chromatin condensation and cytoplasmic vacuolation from 1 day after EDS injection. Therefore, EDS may be a necrotic agent for rat Leydig cell tumor.     

Influence of dietary fat on the induction of mammary tumors by N-nitrosomethylurea: associated hormone changes and differences between Sprague-Dawley and F344 rats

A single iv dose of N-nitrosomethylurea (NMU, 50 mg/kg) given to 50-day-old F344 and Sprague-Dawley rats was sufficient to induce mammary adenocarcinomas. The Sprague-Dawley rats were more sensitive to the carcinogenic action of NMU than were the F344 rats. Moreover, regardless of strain, tumors developed in greater numbers and with a shorter latent period in animals fed a high-fat (HF) diet compared with animals fed a low-fat (LF) diet. The tumor-enhancing effect of HF diet was not related to body weight, since the mean body weight of the rats on the two diets was similar. In addition, no correlation was found between body weight and tumor incidence in individual rats under either dietary regimen. Since the most pronounced difference in tumor incidence between groups fed HF and LF diets was exhibited by the F344 rats, hormone analyses were performed on this group. At termination of the experiment, prolactin levels in the group fed an HF diet were significantly higher than those in the group fed an LF diet. Total estrogen levels were also significantly higher in the group fed an HF diet, compared with the group fed an LF diet, but this difference was seen only at the metestrus-diestrus stage. Regardless of diet or estrous cycle, when animals with tumors were compared with those without tumors, the former exhibited higher prolactin-estrogen (P/E) ratios. The results suggested a relationship between the ingestion of high levels of dietary fat, a high P/E ratio, and increased mammary tumor incidence.     

Inhibition of spontaneous testicular Leydig cell tumor development in F-344 rats by dehydroepiandrosterone.

The incidence of spontaneous Leydig cell tumors of testis is very high in old F-344 rats. We have examined the effect of dehydroepiandrosterone (DHEA), a steroid hormone with antimitotic and anticarcinogenic properties, on spontaneous Leydig cell tumorigenesis. Fifteen-week-old male F-344 rats were fed a diet containing DHEA (0.45% w/w) for 84 weeks. At the termination of experiment none of the 13 rats had Leydig cell hyperplasia or Leydig cell tumors. All the eight control rats of comparable age had Leydig cell tumors. These findings suggest that DHEA is a potent inhibitor of spontaneous Leydig cell tumors of testis in aged rats.     

Influence of age at inoculation on avian oncornavirus-induced brain tumor incidence, tumor morphology, and postinoculation survival in F344 rats.

Intracranial neoplasms were induced by intracerebral inoculation of a standardized, cell-free inoculum of the Bratislava-77 strain of avian sarcoma virus in F344 rats at 1, 9,97 to 99, and 528 days of age. Deaths from diseases that occur spontaneously in aged F344 rats complicated assessment of tumor incidence in rats inoculated at 528 days; 20 of 30 rats inoculated at this age developed brain tumors. All rats inoculated at age 1 day (47 rats), at age 9 days (37 rats), and at 97 to 99 days of age (41 rats) developed brain tumors. The incidence of animals developing tumors was 100% in these three groups, but the incidence of multiple tumors declined with increasing age at inoculation. The mean and variance of postinoculation survival increased from 83.8 +/- 21.5 days for rats inoculated at 1 day of age to 284.6 +/- 151.5 days for rats inoculated at 97 to 99 days of age. Poorly differentiated astrocytomas and astrocytomas of mixed morphology were common among rats inoculated as neonates. Solitary, pilocytic astrocytomas were the most common tumors among rats inoculated as adults.     

Effect of Konjac mannan on 1,2-dimethylhydrazine-induced intestinal carcinogenesis in Fischer 344 rats

The effect of Konjac mannan (KM) on 1,2-dimethylhydrazine (DMH-induced intestinal carcinogenesis was studied in male F344 rats. Rats were fed a diet containing 5% KM at 5 weeks of age. At 6 weeks of age, all animals were given a weekly intraperitoneal injection of 20 mg DMH/kg body wt for 13 weeks and autopsied 13 weeks after the last injection of DMH. The weight gain was lower in rats fed the KM diet than in rats fed the control diet throughout the experiment (P less than 0.05). The incidence of DMH-induced colon tumors was lower in animals fed the KM diet compared to animals fed the control diet (P less than 0.05). The number of colon adenocarcinoma per animal was also lower in animals fed the KM than in animals fed the control diet (P less than 0.05). However, the incidence of tumors of the small intestine did not significantly differ between the groups fed the KM and control diets. The present study demonstrated that colon tumorigenesis induced by DMH in F344 rat was inhibited by maintaining the KM diet.     

Elevated Serum Growth Hormone Accelerates Gastric Tumorigenesis in F344 Rats after Treatment with N-Methyl-N-nitrosourea in Their Drinking Water

We examined the effects of growth hormone on tumorigenesis in F344 rats treated with N -methyl- N -nitrosourea (MNU). Four-week-old male F344 rats were exposed to 100 ppm MNU in their drinking water for 15 weeks. Thereafter Group II animals received 100 μCi/100 g body weight of ¹³¹I (radiothyroidectomy, Tx) injected i.p. and Group III rats were implanted with pituitary tumors (MtT) secreting growth hormone while Group I received no further treatment after MNU. Non-carcinogen control animals received MtT, Tx or no treatment. Animals were killed at 39 weeks after starting MNU administration. Gastric tumors were present in 13 of 31 (43%), 15 of 32 (47%) and 17 of 32 (53%) rats in Groups I to III, respectively. All tumors were of well-differentiated type. Spinal cord tumors appeared in 15 of 31 (47%) in Group I, 10 of 32 (32%) in Group II and 10 of 32 (32%) in Group III, most being malignant schwannomas. Thymic lymphornas also appeared in 10 of 31 (32%), 5 of 32 (16%) and 6 of 32 (19%) animals in Groups I to III, respectively. There were no significant differences among the groups. However, tumors in Group III developed significantly earlier than in Groups I or II. This was mainly due to gastric tumors, and cumulative incidence curves for spinal cord tumors or thymic lymphomas were similar in all groups. The results indicate that gastric tumors induced by MNU in F344 male rats are influenced by elevated levels of growth hormone.     

Relationship between calculus formation and carcinogenesis in the urinary bladder of rats administered the non-genotoxic agents thymine or melamine.

Urinary bladder lesions induced by administration of thymine or melamine were investigated in male F344 rats. Animals, 6 weeks old at the beginning of the experiment, received either 3.0 or 1.0% thymine or 3.0, 1.0 or 0.3% melamine in the diet for 36 weeks followed by a 4 week period without chemicals, the total observation time being 40 weeks. Carcinomas of the urinary bladder were observed in 1/20 (5%) rats in each of the 3.0% thymine and 1.0% melamine groups, and in 15/19 (79%) animals given the 3.0% melamine treatment. Papillomas were induced in 9/20 (45%), 12/19 (63%) and 1/20 (5%) among rats receiving the 3.0% thymine, 3.0% and 1.0% melamine treatments respectively. Exploratory laparotomy at the end of week 36 revealed calculus formation in 9/10 (90%), 10/10 (100%) and 7/10 (70%) rats in these groups. In the ureter of the 3.0% melamine treated group, a carcinoma and papillomas were induced in 1/19 (5%) and 3/19 (16%) animals respectively. However, no tumors were observed in the renal pelvis in any of the other treated groups. Thus, administration of 3.0% thymine in the diet results in calculus formation in the urinary bladder of F344 rats, and is associated with development of tumors. It was also confirmed that a 3.0% dose level of melamine in the diet induces tumors in both the urinary bladder and the ureter.     

Effect of carcinogen dose fractionation, diet and source of F344 rat on the induction of colonic aberrant crypts by 2-amino-3-methylimidazo[4,5-f]quinoline

Carcinogen dose fractionation, diet and source of laboratory animal were examined as variables in the induction of colonic aberrant crypt foci (ACF) by the heterocyclic amine 2-amino-3-methylimidazo [4, 5-f]quinoline (IQ). In the first experiment, male F344 rats from the National Cancer Institute (NCI rats) were fed AIN-93G diet and, starting in the third week, IQ was given by gavage on alternating days, the total carcinogen dose of 105 mg being fractionated proportionally over 2, 4, 8 or 14 weeks. Only the high dose (2 week) treatment with IQ was effective for the induction of ACF at 16 weeks, producing on average 3.8 ACF/colon versus 0.5 ACF/colon in all other groups (P < 0.05). The 2 week IQ dosing protocol was used in a second experiment in which male F344 rats from Simonsen Laboratories (SN) or NCI were fed AIN-93G, AIN-76A or chow diet. On average, SN rats on chow diet had twice the number of aberrant crypts compared with NCI rats given the same diet and three to four times as many aberrant crypts as NCI rats fed AIN diets. Hepatic cytochrome P4501A1 (CYP1A1) levels were essentially unaffected by diet, but methoxyresorufin O-demethylase activities and CYP1A2 protein levels were increased 2- to 3-fold in animals fed chow versus AIN diets. During the 2 week period of carcinogen administration, IQ markedly induced CYP1A proteins and negated the differences among groups related to diet. No consistent diet-related changes were detected in the activities of aryl sulfotransferase or N-acetyltransferase, but UDP-glucuronosyltransferase activities were elevated 2- to 3-fold in rats given chow versus AIN diets. In summary, high dose treatment with IQ was required for the induction of ACF, rats on the chow diet had more aberrant crypts than those given AIN diets and male F344 rats purchased from different vendors and fed chow diet differed with respect to their sensitivity to induction of ACF.     

Large intestinal carcinogenesis. I. Promotional effect of dietary fatty acid isomers in the rat model

For evaluation of the promotional effects of dietary trans-fatty acids on large intestinal carcinogenesis, 120 inbred female F344 rats were divided into 6 groups and fed a 25% elaidic acid diet, a 25% oleic acid diet, or a regular (4.5% fat) chow diet. Ninety animals, 30 per dietary group, received weekly im injections of azoxymethane (2 mg/kg; CAS: 25843-45-2). None of the 30 saline-injected control animals, 10 per dietary group, fed any of the three diets developed tumors. There were twice as many animals with adenocarcinoma of the large intestine from the trans-fatty acid diet group as compared with either the cis-fatty acid diet group or regular diet groups. Chi-square analysis showed that the difference between the incidence of large intestinal carcinomas was not significant between the cis- and trans-fatty acid diets. The difference between the regular diet and trans-fatty acid diet groups was not significant at the 5% level (P = .08). A higher, but nonstatistically significant, incidence of nephroblastomas and squamous ear duct neoplasms was also observed in carcinogen-treated animals maintained on each of the high-fat diets as compared with the incidence of both in treated animals fed the regular chow diet.     

The effect of 4-substitution on the carcinogenicity of nitrosopiperidine

Nitrosopiperidine and three derivatives substituted in the 4-positionwere fed to female F 344 rats in drinking water at equimolarconcentration. The substituents were phenyl, cyclohexyl andtertiary-butyl. Like nitrosopiperidine, the t-butyl- and phenyl-derivativesinduced tumors of the upper gastrointestinal tract (esophagus,forestomach and tongue), but the animals given nitrosopiperidinedied earlier and after a smaller total dose. The rats given4-phenylnitrosopiperidine also had a high incidence of tumorsof the liver, both hepatocellular carcinomas and angiosarcomas.These tumors were absent from untreated animals of this strain.In contrast, no induced tumors were observed in rats treatedwith 4-cyclohexylnitrosopiperidine.     

Effect of intestinal microflora on 2,2'-dimethyl-4-aminobiphenyl-induced carcinogenesis in F344 rats.

The effect of intestinal microflora on colon and breast carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) was studied with the use of germfree and conventional F344 rats of both sexes. At 7 weeks of age, all animals except controls were given 20 weekly sc injections of DMAB in corn oil (100 mg/kg body wt/wk). Male animals were autopsied 15 weeks after the last injection, whereas female animals were autopsied 10 weeks after the last injection. Tumors were induced in the colons, duodena, breasts, ear ducts, salivary glands, and skin of conventional rats, and in the colons, breasts, ear ducts, salivary glands, and skin of germfree rats. No consistent difference was found in the incidence of tumors in the ear ducts, salivary glands, and skin between the germfree and conventional rats. None of the germfree rats showed duodenal tumors, whereas 13% of the female and 53% of the male conventional rats developed duodenal tumors. The incidence of intestinal tumors was lower in the germfree rats than in conventional animals. The mammary tumor incidence was lower in germfree female rats than in the conventional female rats than in the conventional females. DMAB induced fewer intestinal and breast tumors in germfree rats than in conventional rats.     

High incidences of pheochromocytomas after long-term administration of retinol acetate to F344/DuCrj rats

The carcinogenicity of retinol acetate [(RAC) CAS: 127-47-9], a synthetic derivative of retinol, was tested by continuous oral administration in the drinking water of F344/DuCrj rats for 104 weeks. Groups of 50 male and 50 female rats were given solutions of 0.25 or 0.125% RAC in the form of gelatinized beadlets suspended in distilled water. Control groups consisting of the same numbers of rats were given 0.25% of placebo beadlets. All of the surviving animals were killed at 108 weeks, 4 weeks after the cessation of the RAC treatments. The survival rates were 72-84% and were sufficiently high for statistical comparison of all groups. Inhibition of body weight gain was marked in females of the high-dose group. Higher incidences of malignant pheochromocytomas, benign pheochromocytomas, and hyperplasias of the adrenal medulla were observed in the RAC-treated groups. The combined incidences of tumors of the adrenal medulla in males and females of the high-dose groups and the incidence in females of the low-dose group were significantly higher than the incidence in the controls. Conversely, statistically significant decreases were found in the incidences of the mammary gland tumors in males of the high-dose group, of thyroid tumors in females of the high-dose group, and of clitoral gland tumors in females of both high- and low-dose groups. It was concluded that RAC given orally possesses potential for increasing the incidence of pheochromocytomas in male and female F344 rats in a dose-related manner under the conditions of this bioassay.     

Morphologic changes in the urinary bladder and stomach after long-term administration of sodium saccharin in F344 rats

The effects of long-term administration of sodium saccharin on the urinary bladder and stomach of F344 rats were investigated. Sixty-eight male F344 rats, aged 7 weeks at the beginning of the experiment, were maintained on diet supplemented with 5% sodium saccharin for 112 weeks. Animals were killed periodically and investigated for gross and microscopic lesions in the urinary bladder and stomach. Papillary or nodular hyperplasia was evident in the urinary bladder epithelium from 8 weeks onwards although no papillomas or transitional cell carcinomas developed. Lesions observed in the bladders of control animals fed the basal diet without the saccharin supplement were limited throughout the experiment to a few areas of simple hyperplasia. While no changes were apparent in the stomach of control animals, a 100% incidence of hyperkeratosis at the limiting ridge of the forestomach was observed after 80 weeks administration of saccharin, 5 of 20 animals also having papillomas. Furthermore, erosion was pronounced in the glandular stomach of saccharin-treated animals with 4 cases of atypical gland being observed. No histopathological lesions were apparent in the liver, kidneys or spleen of either control or experimental groups.     

A study of betel quid carcinogenesis--VIII. Carcinogenicity of 3-(methylnitrosamino)propionaldehyde in F344 rats.

In assays of Areca-specific N-nitrosamines, 3-(methylnitrosamino)propionaldehyde (MNPA) exhibits higher cytotoxicity than nitrosoguvacine (NGC), nitrosoguvacoline (NG) and 3-(methylnitrosamino)propionitrile (MNPN). NGC is not mutagenic. However, NG is a weak carcinogen in F344 rats while MNPN is a potent carcinogen; MNPA had thus far not been tested. In this study MNPA was injected s.c. at a dose of 6.57 mg three times weekly for 15 weeks (total dose 2.6 mmol/rat). During the 100 weeks of the bioassay, the treated F344 rats, and especially the females, showed significantly less weight gain than the control animals, indicating high toxicity for MNPA at the tested dose. Upon termination of the bioassay, the MNPA-treated animals were found to have tumors of the lung, liver, nasal cavity, forestomach and kidneys. The control animals showed no tumors in these organs. The incidence of lung tumors in the MNPA group was statistically significant (P less than 0.025). The results of this study show that MNPA is a carcinogen in F344 rats.     

The presence of alpha 2u-globulin is necessary for d-limonene promotion of male rat kidney tumors.

In a 2-year carcinogenesis bioassay, d-limonene (dL) induced kidney tumors in male F344 rats, but not in female F344 rats or either sex of mice, d-Limonene-1,2-oxide, a metabolite of dL, has been shown to bind reversibly the male rat-specific urinary protein, alpha2u-globulin (alpha 2u-G), lysosomal degradation than alpha 2u-G alone. This reduced degradation of alpha 2u-G-chemical complex leads to an accumulation of this protein in the proximal convoluted tubules of the male rat kidney and to the morphological changes characteristic for alpha 2u-globulin nephropathy. The only male rat strain known to be resistant to this renal disease is the alpha 2u-G deficient NCI-Black-Reiter (NBR) rat. The objectives of this study were to determine whether or not dL causes sustained increases in cell proliferation and has promoting activity for renal adenomas in male rats and if the male rat-specific urinary protein, alpha 2u-G, is required. In a 32-week initiation-promotion assay, male F344 and NBR rats were treated with either 0 or 500 ppm N-ethyl-N-hydroxyethylnitrosamine (EHEN) in the drinking water for 2 weeks. Experimental groups of 31 to 38 rats then received 0 or 150 mg d-limonene/kg/day in corn oil for 30 weeks by p.o. gavage 5 days/week. Cell proliferation in the proximal tubules was assessed via 5-bromo-2'-deoxyuridine-filled osmotic mini-pumps and immunohistochemistry after 7 weeks (2 weeks EHEN + 5 weeks dL) and at the end of the study (2 weeks EHEN + 30 weeks dL). Preneoplastic and neoplastic lesions were quantified in perfusion-fixed kidneys. A 5-fold increase in the labeling index of P2-cells was found after 5 weeks and 30 weeks of promotion in all dL-treated F344 rats, whereas no difference between treatment groups was detected in NBR rats. No increase in tumors or preneoplastic lesions was detected in dL-treated NBR rats, whereas a 10-fold increase in renal adenomas and atypical hyperplasias was found in the EHEN-dL-treated F344 rats compared with F344 rats treated with EHEN-corn oil. d-Limonene treatment alone caused a significant increase in the number of atypical tubules and atypical hyperplasias in F344 rats when compared with the F344 vehicle control. On the other hand, a significantly lower incidence of liver tumors was found in EHEN-dL-treated F344 rats compared with F344 rats treated with EHEN-corn oil, suggesting a chemopreventative effect of dL on EHEN-induced liver carcinogenesis in F344 rats.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of butylated hydroxyanisole pretreatment on low dose N-methyl-N'-nitro-N-nitrosoguanidine- or N,N-dibutylnitrosamine-induced rat forestomach or esophageal carcinogenesis

The effects of butylated hydroxyanisole (BHA) pretreatment on subsequent low dose N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N,N-dibutylnitrosamine (DBN) treatment on forestomach or esophageal carcinogenesis were investigated in male F344 rats. Groups of animals were pretreated with 2% BHA or basal diet alone for 24 weeks and then were given 20 mg/kg body wt MNNG once every 2 weeks, 0.025% DBN in drinking water continuously or basal diet alone for the subsequent 24 weeks. Further groups of rats were similarly treated with BHA or basal diet alone for 24 weeks, placed on basal diet for the next 24 weeks and then treated with MNNG, DBN or basal diet alone for the subsequent 24 weeks. Animals were killed 48 or 72 weeks after the beginning of the experiment. Histopathological examination showed that the incidence of forestomach tumors was not significantly affected by the BHA pretreatment in the MNNG-treated groups. On the other hand, the incidence of esophageal squamous cell carcinomas was lower in the group pretreated with BHA followed by DBN than in that treated with basal diet followed by DBN (48 week experiment). There was no significant difference in esophageal tumor incidence in the 72 week experiment. The results thus indicate that continuous treatment with 2% BHA for 24 weeks does not exert initiating activity on forestomach and esophageal epithelia.     

Studies of a deuterium isotope effect in carcinogenesis by N-nitroso-N-alkylurethanes in rats

Nitroso-N-methylurethane and nitroso-N-ethylurethane were administered to groups of 20 female F344 rats in corn oil solution by gavage. Each rat received once a week 0.2 ml of solution containing 7 mg/ml or 1.75 mg/ml of the methyl compound or 8 mg/ml or 2 mg/ml of the ethyl compound for 20 weeks. In parallel with these treatments additional groups of rats were given equimolar dose of nitrosomethylurethane and nitrosoethylurethane fully labeled with deuterium in the N-alkyl groups. All animals were allowed to die naturally. The total doses received by the rats were 0.2 mmol at the higher concentration and 0.05 mmol at the lower concentration. Almost all of the treated rats died with papillomas and carcinomas of the forestomach (non-glandular stomach), and the other induced tumors of significance were carcinomas and papillomas of the esophagus in rats given the 7 mg/ml dose of nitrosomethylurethane, both labeled and unlabeled. There was no significant difference in tumor incidence or rate of mortality from tumors that would indicate a difference in carcinogenic effectiveness between the nitrosoalkylurethanes and their deuterium-labeled counterparts. Apart from the esophageal tumors induced only by nitrosomethylurethane at the higher dose, there was no significant difference in carcinogenic effectiveness between the methyl and ethyl nitrosourethanes.     

Forestomach and kidney carcinogenicity of caffeic acid in F344 rats and C57BL/6N x C3H/HeN F1 mice

The carcinogenic potential of caffeic acid was investigated in both sexes of F344 rats and C57BL/6N x C3H/HeN F1 mice. After groups of 30 animals received diet containing 0 and 2.0% caffeic acid for 104 weeks in rats or 96 weeks in mice, detailed histopathological examination revealed induction of forestomach squamous cell papillomas or carcinomas in rats at high incidence (77% for males; 80% for females) and in mice at low incidence (13% for males; 3% for females). Invasion to the abdominal cavity of these squamous cell carcinomas was observed in three rats and two mice. In addition, renal tubular cell hyperplasias and adenomas, clearly related to toxic lesions, were found in treated rats at high incidence for males (73 and 13%) and low incidence for females (20 and 0%). In mice, renal tubular cell hyperplasias and tumors also occurred in treated females (97 and 28%), and at a lower incidence in treated males (27 and 3%). No toxic renal injuries were apparent in mice. Alveolar type II cell tumors also developed in treated male mice (27%) with statistical significance. Thus, the current investigation showed caffeic acid to exert carcinogenic activity for the forestomach squamous cell epithelium in both sexes of F344 rats and C57BL/6N x C3H/HeN F1 mice, for the renal tubular cell in male rats and female mice, and for the alveolar type II cell in male mice.     

Induction of oral cavity tumors in F344 rats by tobacco-specific nitrosamines and snuff

The tumorigenic activities toward the oral cavity of snuff, its extracts, and two of its major nitrosamines, N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were evaluated in male F344 rats. In one protocol, groups of 21-30 rats were treated beginning at age 10 weeks by chronic application to the oral cavity for 131 weeks of either H2O, an H2O extract of snuff, an H2O extract of snuff enriched with ten times its indigenous concentration of NNN and NNK, or with NNN and NNK in H2O. The incidence of oral cavity tumors in the rats treated with NNN and NNK was 8 of 30, compared to 0 of 30 in controls (P less than 0.05). These results demonstrate that NNN and NNK can induce tumors locally in the oral cavity of F344 rats. Oral cavity tumors were also observed in 3 of 30 rats treated with snuff extract enriched with NNN and NNK, but not in the rats treated with snuff extract alone. In a second protocol, a test canal was surgically created in the lower lip of groups of 21-32 rats, and either snuff, H2O-extracted snuff, or snuff enriched with its own H2O extract was inserted in the test canal 5 times weekly for 116 weeks. A group of 10 control rats had surgery only. Among the 32 rats treated with snuff, 3 had oral cavity tumors; one was a squamous cell carcinoma originating in the test canal and invading the gingiva, one was a papilloma of the test canal, and one was a papilloma of the hard palate. Oral cavity tumors were also observed in 2 of 21 rats treated with H2O-extracted snuff and 1 of 32 rats treated with snuff enriched with its H2O extract. Oral tumors were not observed in control rats. The results of this study indicate that snuff and individual nitrosamines present in snuff can induce oral cavity tumors in F344 rats and support the epidemiological observations which indicate that snuff dipping causes oral cancer in man.