Induction of liver tumor in Sherman strain female rats by polychlorinated biphenyl aroclor 1260.

Sherman strain female rats (200) were fed 100 ppm of polychlorinated biphenyl (Aroclor 1260) for apporximately 21 months, and 200 female rats were kept as controls. The rats were killed when 23 months old. Twenty-six of 184 experimental animals and 1 of 173 controls had hepatocellular carcinomas. None of the controls but 146 of 184 experimental rats had neoplastic nodules in their livers, and areas of hepatocellular alteration were noted in 28 of 173 controls and 182 of 184 experimental animals. Thus the polychlorinated biphenyl Aroclor 1260, when fed in the diet, had a hepatocarcinogenic effect in these rats. The incidence of tumors in other organs did not differ appreciably between the experimental and control groups.     

Induction of liver tumors in female Sherman strain rats by polybrominated biphenyls

Noninbred Sherman strain rats were given the polybrominated biphenyl mixture Firemaster FF-1 (PBB). Rats given a single dose of 1,000 mg PBB/kg or 12 doses of 100 mg PBB/kg body weight in corn oil by gavage had final (when less than or equal to 26 mo old) liver PBB concentrations of 17.1 and 34.8 mg/kg (wet wt), respectively. The respective incidence of hepatocellular carcinomas was 41.4 and 67.8%. No difference in PBB concentrations was found between hepatocellular carcinomas and surrounding liver tissue. In addition, most livers of PBB-dosed rats had adenofibrosis of the liver. Livers of controls were essentially normal. Rats given a single dose of 200 mg PBB/kg as above had a 31.2% incidence of neoplastic nodules, whereas none were seen in the controls. The mean PBB concentrations (when 26 mo old) were 2.68 mg/kg in liver, 244 mg/kg in adipose tissue, and 0.22 mg/kg in blood.     

Promoting effects of polychlorinated biphenyls (Aroclor 1254) and polychlorinated dibenzofuran-free Aroclor 1254 on diethylnitrosamine-induced tumorigenesis in the rat

The hepatic tumor-promoting activity of a commercial polychlorinated biphenyl mixture, Aroclor 1254 (AR 1254), with and without its intrinsic polychlorinated dibenzofuran (PCDF) impurities, was investigated. Male Sprague-Dawley non-inbred albino rats were treated with 66 microgram diethylnitrosamine (DENA)/ml drinking water for 5 weeks and subsequently given a control diet or a diet supplemented (100 ppm for 18 wk) with either AR 1254 or AR 1254 from which the PCDF moieties were removed (AR 1254-PCDF). Of those animals receiving DENA alone, 16% exhibited hepatocellular carcinomas. Of those rats treated with DENA followed by administration of AR 1254 or AR 1254-PCDF, 64 or 84%, respectively, developed hepatocellular carcinomas. Thus promotion with either AR 1254 or AR 1254-PCDF significantly (P less than 0.05) increased the incidence of DENA-initiated hepatocellular carcinomas. Administration of AR 1254 or AR 1254-PCDF alone did not induce hepatic tumors. Therefore, PCDF impurities were not necessary for the promoting activity of AR 1254.     

Promotion by polychlorinated biphenyls of lung and liver tumors in mice

Polychlorinated biphenyls (PCB), which are tumor promoters,have been found in human tissues for decades. Their contributionto cancer risk may only now start to appear, due to long humancancer latency and the nature of tumor promotion. Epidemiologicalassociations have been seen between PCB exposure or tissue contentand cancer at several sites. In rodents, tumor promotion byPCBs has been little studied in tissues other than liver. Previously,in an experiment modeling infant carcinogen exposure followingPCBs received in milk, lung and liver tumors, initiated neonatallyin mice by the environmental nitrosamine N-nitrosodimethylamine(NDMA), were promoted by later treatment with Aroclor 1254.The present study was undertaken to confirm and characterizethe effects of Aroclor 1254 on tumor number, latency, size andmalignancy. Male Swiss mice were given NDMA on postnatal day4 and Aroclor 1254 (250 mg/kg) on day 8, and killed at intervals.Eight PCB congeners were quantified in the carcasses. Incidencesof mice with NDMA-initiated lung tumors at 28 weeks of age wereincreased 2.5-fold by PCBs. Multiplicities of lung tumors wereenhanced four-fold by PCBs at 28 and 52 weeks. By 72 weeks tumornumbers were similar in the NDMA-only and NDMA–PCB groups.Liver tumors first occurred in significant numbers at 52 weeksand only in mice receiving both NDMA and PCBs. As for the lung,at 72 weeks the incidence was high in both the NDMA-only andNDMA–PCB groups. Sizes of tumors and liver carcinoma incidencewere not altered by PCB treatment. Carcass analysis revealeda significant positive association between lung tumor numbersat 28 weeks and relative percentage of 2,2',4,4',5-pentachlorobiphenyl,with no other correlations. The results confirm that PCBs promotelung as well as liver tumors, by triggering the early appearanceof latent initiated tumors otherwise presenting in old age.     

Effects of polychlorinated biphenyls on lung and liver tumors initiated in suckling mice by N-nitrosodimethylamine

A mixture of polychlorinated biphenyls (PCB), Aroclor 1254, was administered ip (500 mg/kg) to pregnant Swiss noninbred CD-1 mice on the 19th day of gestation. The suckling offspring of these mice and of controls were then treated ip with 5 mg N-nitrosodimethylamine (DMN)/kg on postnatal day 4 or day 14. The progeny were killed at 28 weeks or 18 months of age. The DMN treatment caused lung and liver tumors. Among the mice given DMN on day 14, exposure also to PCB resulted in a lower tumor incidence in some of the treatment groups. This protective action was most evident for lung tumors in both sexes at 18 months of age and for liver tumors in males at 28 weeks. However, the PCB exposure also led to significant increases in the percentage of mice with extensive DMN-initiated liver tumors at 18 months of age compared to the results obtained when only DMN was given. This effect was most pronounced in mice given DMN on postnatal day 4.     

Induction of mesothelioma by intraperitoneal injections of ferric saccharate in male Wistar rats

Iron appears to play a major role in catalysing free radical production, leading to lipid peroxidation and DNA damage. We, therefore, investigated the effect of colloidal iron deposited in the peritoneum. Wistar male rats were given either ferric saccharate, ferric saccharate and nitrilotriacetic acid (NTA), NTA or saline. NTA was shown previously to 'free' iron to promote lipid peroxidation and an iron chelate of NTA is known to be carcinogenic to the kidney. Iron at a dose of 5 mg kg-1 day-1, and saline at a dose of 0.5 ml day-1 were injected i.p. for 3 months. NTA at a dose of 83.5 mg kg-1 day-1 was give i.p. for 5 months. All the rats were killed about a year later for histological examination. In nine of the 19 rats treated with ferric saccharate, mesothelial tumors were induced in the serosa of the tunica vaginalis or the length of the spermatic cord. Among rats treated with ferric saccharate and NTA, seven had localised mesotheliomas in the above locations and six had wide-spread peritoneal mesotheliomas. No mesothelial tumors developed in either NTA treated or saline treated rats. No pleural mesotheliomas were found in any group. These findings add to the evidence that iron is involved in some carcinogenic processes.     

Promotion by polychlorinated biphenyls of enzyme-altered foci in rat liver

Aroclor 1254 is a complex mixture of polychlorinated biphenyls (PCB) that upon prolonged administration has been reported to produce hepatic tumors in mice and rats. The ability of Aroclor 1254 to promote enzyme-altered foci was determined in an initiation/promotion bioassay in rat liver. Initiation was accomplished in rats that received a 2/3 partial hepatectomy followed in 24 h by diethylnitrosamine (DENA). Aroclor 1254 was administered to each rat 7, 28 and 49 days after the DENA and some of the rats were killed 21 days after each dose of Aroclor. The liver of rats that received Aroclor 1254 on either day 7 or on day 7 and 28 contained an increased incidence of gamma-glutamyltranspeptidase (GGTase)-positive foci compared to partial hepatectomized and DENA treated rats given tricaprylin (the solvent for Aroclor 1254). Therefore, Aroclor 1254 was demonstrated to enhance the appearance of enzyme-altered foci after only a single oral dose.     

Induction of liver tumors in F344 rats by crotonaldehyde

The tumorigenic activities in F344 rats of crotonaldehyde, a representative alpha, beta-unsaturated carbonyl compound, and N-nitrosopyrrolidine, which could produce crotonaldehyde upon metabolism, were compared. Groups of rats were treated with either crotonaldehyde (0.6 mM or 6.0 mM) or N-nitrosopyrrolidine (0.6 mM) in their drinking water for 113 or 84 weeks, respectively. At the 0.6 mM dose, crotonaldehyde induced neoplastic lesions of the liver in 9 of 27 rats; 2 rats had hepatocellular carcinomas, and 9 rats had neoplastic nodules. It also caused altered liver cell foci in 23 of 27 rats. The incidences of tumors and foci were significantly higher than those of the control group. N-Nitrosopyrrolidine induced hepatocellular carcinomas in 20 of 23 rats, liver neoplastic nodules in 16 of 23 rats, and altered liver cell foci in 23 of 23 rats. Thus, crotonaldehyde appears to be a weaker tumorigen than N-nitrosopyrrolidine. At the 6.0 mM dose, crotonaldehyde treatment caused moderate to severe liver damage in 10 of 23 rats. No preneoplastic or neoplastic lesions were observed in these rats. The remaining 13 rats of this group developed altered liver cell foci. The tumorigenicity of crotonaldehyde suggests that alpha, beta-unsaturated carbonyl compounds, which are ubiquitous in the human environment and can be formed endogenously, may be an important class of potential carcinogens.     

Comparison of transplacental and neonatal initiation of mouse lung and liver tumors by N-nitrosodimethylamine (NDMA) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and promotability by a polychlorinated biphenyls mixture (Aroclor 1254)

We have previously shown a positive tumor-promoting effect ofa single dose of Aroclor 1254 on lung and liver tumors initiatedneonatally in the mouse by N-nitrosodimethylamine (NDMA). Inthis study, we have confirmed and extended this observationwith NDMA and the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyI)-1-butanone(NNK) given either transplacentally or postnatally, followedby a single dose of Aroclor 1254 on day 56. This polychlorinatedbiphenyl (PCB) mixture was an effective promoter of both lungand liver tumors; however, there were specific initiator andsex-related differences in this response. Aroclor administrationsignificantly increased the incidence of lung tumors initiatedtransplacentally by NDMA or NNK in male mice. Neither nitrosamineinitiated tumors transplacentally in females, but lung tumorsinitiated with NNK and liver tumors caused by NDMA in neonatalfemales were promoted by PCBs. Both liver and lung tumors initiatedneonatally by NDMA in male animals, but not NNK-initiated tumors,were promoted by PCBs. These data confirm that PCBs are ableto promote both NDMA- and NNK-initiated tumors, but with chemical-,sex- and age-dependent difference; this suggests influencesof both quantitative and qualitative factors in susceptibilityto tumor promotion.     

Induction of colon tumors in 1,2-dimethylhydrazine-resistant Lobund Wistar rats by methylazoxymethanol acetate.

Sprague-Dawley and Lobund Wistar rats, which were sensitive and resistant to induction of colon tumors by 1,2-dimethylhydrazine (DMH), respectively, were treated with methylazoxymethanol (MAM), the product of DMH metabolism by the microsomal mixed-function oxidase system. Although the colon tissue in both stocks of rats had similar NAD+-dependent dehydrogenase activities that are considered necessary to activate MAM to an ultimate carcinogen, still a sevenfold greater incidence of colon tumors was found in the Sprague-Dawley rats, and their tumors were more extensive. The results indicated that the difference in susceptibility to colon tumor induction between the rat stocks was partially related to metabolic activation of the DMH and to other, as yet undetermined, endogenous factors.     

Induction of liver tumors in rats by nitrosodiethanolamine at low doses

Nitrosodiethanolamine was given to male and female F344 ratsin drinking water at three concentrations, 160, 64 and 28 mg/l.The highest dose was given for 50 weeks, the middle dose for50 weeks and for 100 weeks, and the lowest dose for 100 weeks,the last to a group of 39 rats of each sex. The principal neoplasmsthat could be attributed to the treatment were hepatocellularcarcinomas and neoplastic nodules in the liver. All of the femalerats and 70% of male rats drinking 160 mg/l had hepatocellularneoplasms. At 64 mg/l the incidence of hepatocellular neoplasmswas higher after 100 weeks administration than after 50 weeks,and was significantly higher than in controls after 100 weeksin both sexes. At 28 mg/ml there was a greater incidence ofhepatocellular neoplasms than among controls only in the femalerats. Nitrosodiethanolamine appears to be carcinogenic to F344rats at quite low concentrations.     

Induction of free radicals and tumors in the kidneys of Wistar rats by ferric ethylenediamine-N,N'-diacetate

An iron chelate, ferric ethylenediamine-N,N’-diacetate[Fe(III)-EDDA], was found to produce hydroxyl radicals withhydrogen peroxide, as determined by both a deoxyribose degradationtest and electron spin resonance. Hydroxyl radical productionwas inhibited not only by adding hydroxyl radical scavengersand catalase, but also by adding superoxide dismutase to thereaction mixture, suggesting that superoxide anion may be involvedin the hydroxyl radical production. A single injection of Fe(III)-EDDA(10 mg Fe/kg body wt) to Wistar rats induced thiobarbituricacid reactivity in the kidneys and liver. Repeated Injectionsof Fe(III)-EDDA (10 mg Fe/kg body wt, twice weekly for 3 months)induced a 40% incidence of renal tumors, including renal adenocarcinomaand renal adenoma, 1 year later. These results suggest thatFe(III)-EDDA is an effective free radical producer in vitroand in vivo and that it may be useful in preparing animal modelsrelated to iron-dependent free radical damage. The results supportour hypothesis that endogenous or exogenous iron, complexedwith certain kinds of chelators, promotes free radical-dependenttissue damage and ultimately leads to carcinogenesis in theaffected tissue.     

Induction of ductal carcinomas by intraductal administration of 7,12-dimethylbenz(a)anthracene in Wistar rats

Summary Postpartum Wistar inbred rats (weaned on the 9th puerperal day) were injected intraductally in one mammary gland with 7,12-dimethylbenze (a) anthracene (DMBA) to selectively induce ductal carcinoma. The incidence of ductal hyperplasia increased with time until it peaked at 7 weeks (12/13 animals) and then decreased. Ductal carcinoma first developed at 9 weeks in 3/12 (2 non-invasive and 1 invasive lesion) and the incidence increased with time until invasive ductal tumors were observed in 9/11 at 20 weeks. Tumors developed only in the DMBA-treated mammary glands and no systemic effects of the carcinogen were observed. Degeneration and detachment of epithelioglandular cells were seen here and there in the ducts and terminal ducts, and epithelioglandular cells proliferated in terminal duct until 2 weeks. Residual trace DMBA powder was detected in terminal ducts and the epithelioglandular layer until 7 weeks. This trace DMBA was considered to be the cause of the development of atypical epithelial cells, inducing ductal carcinomas.     

Effects of a single dose of polychlorinated biphenyls to infant mice on N-nitrosodimethylamine-initiated lung and liver tumors

Polychlorinated biphenyls (PCBs) are widespread, chemically-stable environmental contaminants; some congeners are commonly found in human adipose tissue and breast milk. We investigated the effects of a single dose of one PCB mixture (Aroclor 1254) on tumors initiated by N-nitrosodimethylamine (NDMA), also a common environmental agent. Infant outbred Swiss male mice were treated with NDMA (5 mg/kg) i.p. on the 4th day of life, to initiate lung and liver tumors. Four days later each received a single intragastric dose of PCBs (50, 250, or 500 mg/kg of Aroclor 1254) or oil. Groups were killed 16 and 28 weeks later. At both endpoints the mice given 500 mg/kg PCBs after NDMA developed twice as many lung tumors (alveologenic adenomas) as those treated with NDMA only, a significant difference. The PCBs alone did not cause lung tumors. This is the first demonstration of tumor promotion by PCBs in an extrahepatic organ, and it occurred after a single exposure. There were also complex, multiple effects on NDMA-caused liver tumors (adenomas and carcinomas) and on focal hepatocellular proliferative lesions: PCB treatment after the NDMA was associated with decreased number but increased size of these tumors and foci. All of these changes were accompanied by retention in the bodies of 0.1-6 ppm PCBs, as indicated by gas chromatography with electron capture detection. Of this, 80% or more consisted of 2,4,5,2',4',5'-and 2,3,4,2',4',5'-hexachlorobiphenyls in about equal amounts for periods up to 28 weeks. These results point to a need for both experimental and epidemiological studies of the effect of PCB body burden on tumor development.