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

Polychlorinated biphenyl quinone induced the acquisition of cancer stem cells properties and epithelial-mesenchymal transition through Wnt/β-catenin

Polychlorinated biphenyls (PCBs) are persistent industrial pollutants that have been linked to breast cancer progression. However, their molecular mechanism(s) are currently unclear. Our previous assessment suggested that the highly reactive PCB metabolite 2,3,5-trichloro-6-phenyl-[1,4]-benzoquinone (PCB29-pQ) induces the metastasis of breast cancer. Here, our data illustrate that PCB29-pQ increases cancer stem cell (CSC) marker expression, resulting in an increase in the epithelial-mesenchymal transition (EMT) in MDA-MB-231 breast cancer cells; further, the Wnt/β-catenin pathway also becomes activated by PCB29-pQ. When the Wnt/β-catenin pathway is inhibited, the promotion of CSC properties and EMT by PCB29-pQ were accordingly reversed. In addition, the overproduction of reactive oxygen species (ROS) mediated by PCB29-pQ plays a key role in Wnt/β-catenin activation. Collectively, our current data designated the regulatory role of Wnt/β-catenin in PCB29-pQ-triggered acquisition of CSC properties and EMT.

Prediagnostic serum polychlorinated biphenyl concentrations and primary liver cancer: A case-control study nested within two prospective cohorts

BACKGROUND

Polychlorinated biphenyls (PCBs) were used in electrical equipment and a range of construction materials. Although banned in the United States and most of Europe in the 1970s, they are highly persistent in the environment and bioaccumulate. Whether PCBs are associated with liver cancer risk at general population levels is unknown.

METHODS

This study consisted of 136 incident liver cancer cases and 408 matched controls from the Kaiser Permanente Northern California Multiphasic Health Checkup (MHC) cohort and 84 cases and 252 matched controls from the Norwegian Janus cohort. Sera collected in the 1960s-1980s were measured for 37 PCB congeners and markers of hepatitis B (HBV) and C (HCV) infection. Odds ratios (OR) and 95% confidence intervals (CI) for tertiles of each lipid-adjusted PCB were estimated from conditional logistic regression. We also examined the molar sum of congeners in groups: total PCBs; low, medium, and high chlorination; and Wolff functional groups.

RESULTS

Concentrations of individual congeners from the 1960s/1970s sera ranged from 1.3-123.0 and 1.4-116.0 ng/g lipid among MHC cases and controls, respectively, and from 1.9-258.0 and 1.9-271.0 ng/g lipid among Janus cases and controls, respectively. Among MHC participants with sera from the 1960s, collected an average of 27 years before diagnosis among cases, the top tertile of PCBs 151, 170, 172, 177, 178, 180, and 195 was significantly associated with elevated odds of liver cancer (OR range = 2.01-2.38); most of these congeners demonstrated exposure-response trends. For example, OR_{tertile 3vs1} = 2.38 (95% CI: 1.22-4.64, p-trend = 0.01) for PCB 180. As a group, Wolff group 1b congeners, which are biologically persistent and weak phenobarbital inducers, were associated with increased odds. In MHC participants, ever vs. never HBV or HCV infection modified the PCB-liver cancer associations. There was little evidence of an association between PCBs and odds of liver cancer among the Janus cohort.

DISCUSSION

We observed associations between a number of PCB congeners and increased odds of liver cancer among MHC, but not Janus, participants with sera from the 1960s/1970s.

Associations between functional polychlorinated biphenyls in adipose tissues and prognostic biomarkers of breast cancer patients

BACKGROUND

Exposure to polychlorinated biphenyls (PCBs) has been shown to influence expression of some biomarkers that are predictive/prognostic for breast cancer. Therefore, our study was conducted to further investigating associations of different functional PCBs in adipose tissue with breast cancer prognostic biomarkers.

METHODS

Two hundred and five breast cancer patients were recruited in Shantou, China. Breast adipose tissues were collected during their resection surgery and levels of 7 PCB congeners were analyzed by gas chromatography-mass spectrometry (GC-MS). The PCB congeners were divided into 4 groups according to structure-activity. Socio-demographic, clinical and pathological information were obtained from questionnaire and digital medical records. Odds ratios (ORs) for associations between prognostic biomarkers and PCB levels (tertile 3 [T3], tertile 2 [T2] vs. tertile 1) were estimated from logistic regression models.

RESULTS

Most PCB congeners were detectable, with a highest level (22.06 ng/g lipid) of PCB153. As for estrogenic PCBs, increased PCB52 exposure was positively associated with PR expression (OR_T2 = 2.36, P_trend = 0.054), but higher PCB101 level was negatively associated with HER-2 (OR_T3 = 0.24, P_trend = 0.029) and tumor size (OR = 0.43). Limited dioxin-like PCB138 exposure was positively associated with ER (OR_T2 = 3.23, OR_T3 = 3.77, P_trend = 0.047) but negatively with Top-IIα expression (OR_T2 = 0.35, OR_T3 = 0.28, P_trend = 0.080). Higher PCB153 (CYP inducer) level was negatively associated with ER (OR_T2 = 0.32, OR_T3 = 0.19, P_trend = 0.038) but positively with Ki-67 expression (OR_T2 = 1.43, OR_T3 = 3.60, P_trend = 0.055). Higher neurotoxic PCB28 was positively associated with HER-2 (OR_T3 = 5.43, P_trend = 0.006) and tumor size (OR = 2.37). Moreover, total PCBs exposure was positively associated with VEGF-C (OR_T2 = 76.91, OR_T3 = 97.96, P_trend = 0.041) and tumor metastasis (OR = 2.25).

CONCLUSIONS

Different functional PCB congeners have different associations (both positive and negative) with breast cancer prognostic biomarkers, as well as tumor classification stage. Therefore, the development and aggressiveness of breast cancer may depend upon exposure to specific structure-activity of PCBs.

Aroclor 1254 inhibits cell viability and induces apoptosis of human A549 lung cancer cells by modulating the intracellular Ca(2+) level and ROS production through the mitochondrial pathway

To study the acute toxic effects of PCBs on airway exposure, the cell viability, apoptosis and mitochondrial functions of human lung cancer cell line A549 were measured and compared after Aroclor 1254 exposure for different time. The results showed that Aroclor 1254 could inhibit cell viability and increase cell apoptosis in a concentration- and time-dependent manner. The mitochondrial apoptosis pathway was confirmed playing an important role. ROS elevation was an early response within 1h treatment of Aroclor 1254. Then after 4 h of Aroclor 1254 exposure, the intracellular calcium level increased and mitochondrial transmembrane potential (ΔΨm) collapsed, accompanying with Cytochrome c (Cyt-c) leakage, boosting expression of Bax, Apaf-1 and miRNA155, which were involved in the mitochondrial apoptosis pathway. After 24 h of Aroclor 1254 exposure, ROS returned to normal level, but cell apoptosis rate was higher than that at 4 h with ΔΨm continued collapsing and intracellular calcium increased. In conclusion, Aroclor 1254 could suppress cell viability and induce apoptosis in A549 cells, which was associated with ROS over-production and elevated cellular Ca(2+) level, which may result in mitochondrial dysfunction, inducing expression of Bax/Cyt-c/Apaf-1 and miRNA155.

Carcinogenicity of "non-dioxinlike" polychlorinated biphenyls

Complex technical mixtures of polychlorinated biphenyls (PCBs) cause liver and thyroid neoplasms in rodents, whereas very few data are available on the carcinogenic potency of single non-dioxinlike (NDL) PCB congeners. In most genotoxicity assays technical PCB mixtures and individual congeners were inactive, suggesting that PCBs act as indirect, nongenotoxic carcinogens. Various mechanisms, including suppression of apoptosis in preneoplastic cells or inhibition of intercellular communication, have been suggested to be active in liver tumor promotion by PCBs. A decrease in thyroid hormone levels after PCB treatment has been suggested to play a role in the development of thyroid neoplasms in rats; however, other mechanisms may also be involved. Results from a chronic carcinogenicity study in rats indicate that not the dose of total PCBs but the total TCDD or toxic equivalents (TEQs) associated with "dioxinlike" (DL) constituents within a technical mixture are mainly if not exclusively responsible for the development of liver neoplasms in female rats. Quantitative comparison reveals almost identical dose-response curves for the total TEQs in various technical PCB mixtures and for TCDD as inducers of hepatic neoplasms in female rats. Tumor promotion experiments have shown, however, that, after initiation with a genotoxic carcinogen, technical PCB mixtures and individual DL-and NDL-PCBs act as liver tumor promoters in rodents. Based on these data, a weak carcinogenic potency of individual NDL-PCB congeners cannot be excluded. In epidemiological studies, increased mortality from cancers of the liver, gallbladder, biliary tract, gastrointestinal tract, and from brain cancer and malignant melanoma were observed in workers exposed to a series of technical PCB mixtures. A significant association between PCB concentrations in adipose tissue and non-Hodgkins lymphoma was found in another study. While in all human studies mixed exposure to DL-and NDL-PCBs occurred, no comprehensive data are available on the relative contribution of NDL-PCBs to the overall external and/or internal PCB exposure in those cohorts.

Tumor promoting potency of PCBs 28 and 101 in rat liver

Only few data are available on the carcinogenic potency of individual PCB congeners. In this study, we tested the 'non-dioxinlike' congeners PCB 28 and 101 for their potency as liver tumor promoters in female rats which received diethyl-N-nitrosamine as an initiator. After 8 or 16 weeks of PCB treatment (50 and 150 micromol/kg body weight per week), each congener was recovered in the liver according to the dose levels applied, with PCB 28, at the same dose level, showing nine- to 16-fold higher hepatic levels than PCB 101 (approximately, 44 micromol/kg versus 5 micromol/kg liver at low dose, 145 micromol/kg versus 9 micromol/kg liver at high dose). PCB 28 was found to mildly induce hepatic EROD activity, while both congeners induced PROD activity. With each congener, no significant increase in the number of ATPase-deficient or GSTP-positive preneoplastic foci was obtained, while a significant increase in the relative hepatic volume of ATPase-deficient foci was found in the livers of DEN pre-treated animals having received 50 micromol/kg body weight of PCB 101 per week over 16 weeks. Our results revealed that neither the accumulative PCB 28 nor the more readily metabolisable PCB 101 was an efficacious tumor promoter in the livers of female rats.

Carcinogenic effects of polychlorinated biphenyls

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of an important section of the Toxicological profile for polychlorinated biphenyls [ATSDR. 2000: Toxicological profile for polychlorinated biphenyls. Atlanta, GA: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry.] into the scientific literature. This article focuses on the carcinogenic effects of this group of synthetic organic chemicals (polychlorinated biphenyls) in humans and animals. Information on other health effects, toxicokinetics, mechanisms of toxicity, biomarkers, interactions, chemical and physical properties, potential for human exposure, and regulations and advisories is detailed in the profile.

Coexposure to ethanol with N-nitrosodimethylamine or 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone during lactation of rats: marked increase in O(6)-methylguanine-DNA adducts in maternal mammary gland and in suckling lung and kidney

Use of alcoholic beverages increases risk of cancer at several target sites, including the breast. Of several possible mechanisms for this effect, competitive inhibition by ethanol of hepatic clearance of nitrosamines, resulting in increased dose delivery to posthepatic tissues, gives the quantitatively most pronounced enhancement. We investigated whether this effect would pertain to the mammary gland, and to ethanol and nitrosamines delivered translactationally to sucklings. Ethanol (1.6 g/kg) was administered by gavage to nursing Sprague-Dawley rats 10 min before 5 mg/kg N-nitrosodimethylamine (NDMA) or 50 mg/kg 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK); treatment was on postnatal days 1, 7, or 14. Tissues taken 4 h later for analysis of O(6)-methylguanine in DNA were liver, blood, and mammary glands from the mothers, and liver, lung, kidney, and blood from the sucklings. Ethanol cotreatment resulted in a marked, 10-fold increase in O(6)-methylguanine adducts from NDMA in mammary gland, as well as smaller but significant increases in this tissue from NNK and in maternal blood cells from both chemicals; adducts in maternal liver decreased slightly. In the sucklings, ethanol cotreatment also lowered adducts in liver after NDMA or NNK treatment. After NDMA, adducts were also detected in suckling lung and kidney and were increased five- to 10-fold after ethanol coexposure. Adducts from either chemical, with or without ethanol, decreased markedly in all suckling tissues with development from postnatal day 1 to day 14. Thus ethanol coexposure with nitrosamines increases O(6)-methylguanine DNA adducts in mammary gland and strongly influences adduct formation in suckling tissues after translactational delivery.

Parental smoking and neonatal serum levels of polychlorinated biphenyls and hexachlorobenzene

Polychlorinated biphenyls (PCB) and hexachlorobenzene (HCB) are ubiquitous compounds that have tumor-promoting properties if applied together with tobacco-specific carcinogens. It was the purpose of the present study to investigate whether parental smoking by itself will increase the prenatal uptake of such organochloric compounds. With the informed consent of the parents, blood samples were taken from 80 full-term neonates before the first oral feeding. Six PCB congeners (PCB 28, 52, 101, 138, 153, and 180) and HCB were analyzed with capillary gas chromatography. Information about parental smoking behavior, the geographic origin of the parents, and their actual and previous working places was recorded. We composed three study groups for statistical analyses: active smoking mothers (n = 12), passive smoking mothers (n = 33), and nonsmoking families (n = 35). Neonates born to active smoking mothers had the highest PCB and HCB concentrations compared with children of passive or nonsmoking mothers. These differences were statistically significant (p < 0.01) in the cases of PCB 138, total PCB, and HCB. Newborns of passive smoking mothers had higher PCB and HCB concentrations than children of nonsmoking families but lower values than those of active smoking mothers. These differences were statistically significant for all compounds with the exception of PCB 180. It is concluded that active and passive maternal smoking increases the neonatal burden with PCB and HCB.

Animal studies addressing the carcinogenicity of TCDD (or related compounds) with an emphasis on tumour promotion

Dioxin and certain structurally related compounds increase the incidence of liver neoplasms in rodents upon chronic bioassay. Short-term studies indicate the lack of direct DNA-damaging effects including covalent binding to DNA; however, secondary mechanisms may be important in the observed carcinogenicity as these chemicals affect a number of pathways necessary for maintenance of normal growth control and differentiation status. Studies with TCDD in the mouse skin support a lack of initiating activity but an ability to promote the growth of previously initiated lesions indicative of a promoting agent. Mouse skin tumour promotion studies indicate that Ah receptor activation may be involved in promotion by TCDD and selected structurally related compounds. While the mechanism of carcinogenicity induced by TCDD is unknown, the processes involved have a no-effect level, which in the rat liver is at an exposure level below 10 ng TCDD/kg/day. At least for the rodent liver, the relative effective dose for cytochrome P450 induction is not a good indicator of promotion potency. Studies on liver tumour promotion in the female rat liver support a non-genotoxic mechanism for the induction of neoplasms by TCDD. The ability of TCDD to enhance proliferation and inhibit apoptotic processes in focal hepatic lesions further supports an indirect mechanism of carcinogenicity.

Promotion by Helicobacter hepaticus-induced hepatitis of hepatic tumors initiated by N-nitrosodimethylamine in male A/JCr mice

A new murine Helicobacter species, Helicobacter hepaticus, infects the livers of mice, causing a progressive chronic active hepatitis culminating in hepatocellular tumors. To examine the role of chronic H. hepaticus infection in carcinogenesis, H. hepaticus-infected male infant mice of A/JCr strain were given a single i.p. dose of N-nitrosodimethylamine (NDMA). Noninfected A/J mice similarly treated with NDMA served as controls. The effect of hepatitis induced by H. hepaticus was studied for 64 wk. At 31-36 wk, the incidence of hepatocellular adenomas in infected mice was significantly higher than in noninfected mice (82 vs 52%; p = 0.05). The multiplicity of hepatocellular tumors was also significantly higher in infected mice compared to noninfected mice (3.2 +/- 0.09 vs 0.09 +/- 0.2; p = 0.03). At 51-64 wk, many (10/18) infected mice developed hepatocellular carcinomas while only 2 of 19 control mice developed such tumors (p = 0.005). Overexpression of cyclin D was observed in hepatocytes as well as adenomas induced by NDMA in H. hepaticus-infected mice, suggesting its role in inflammation, abnormal cell growth, and early neoplasia. High molecular weight keratins were highly expressed in hyperplastic oval cells in hepatitis and in liver tumors in mice with hepatitis, establishing a reliable marker for oval cells in formalin-fixed, paraffin-embedded tissue. Thus, chronic H. hepaticus infection significantly stimulated cyclin D expression, accelerated the development of liver tumors, increased the multiplicity of such lesions, and enhanced the progression of benign to malignant tumors.

Effect of dietary Aroclor 1254 exposure on lung and kidney cytochromes P450 in female rats: evidence for P4501A2 expression in kidney

In this report, we have investigated the effect of dietary exposure to Aroclor 1254 (1-100 ppm) given chronically or discontinuously over an 84-day time interval to the female F344 rat. Cytochrome P4501A was quantified in lung and kidney by measuring the dealkylation of ethoxyresorufin substrate and by Western immunoblotting. P4501A displayed a dose- and time-dependent increase in both extrahepatic organs. The kidney appeared to be more responsive to induction than lung at all doses (maximum of 500-fold induction following 84 days exposure to 100 ppm). Further, there was evidence by enzymatic activity, immunoblotting and Northern analysis of total RNA for the presence of 1A2 in the most highly induced kidneys. The decline in 1A induction observed following discontinuous exposure was more prominent in the kidney than in the lung. These data demonstrate the sensitivity of kidney to P4501A induction capacity as compared to lung, although the persistence of the induction response was evident in lung and not kidney.

Suppression of pulmonary P4502b and induction of hepatic, intestinal and kidney P4501a-1 and 1a-2 in the Ah-responsive and non-responsive mouse by Aroclor 1254

1. Investigations in our laboratory have demonstrated a rapid suppression of the P4502b isoform in mouse lung, concomitant with significant induction of this enzyme in liver from these same animals. The current study was designed to determine whether the suppression by polychlorinated biphenyls of pulmonary P4502b required the presence of a functional Ah receptor, and additionally to delineate the time course of the induction responses to Aroclor 1254 in the liver, kidney, and intestine of the AH-responsive and non-responsive mouse. 2. P450s were quantified by specific enzyme assay and immunoblot in liver (1a-1, 1a-2, 2b), lung (1a-1, 1a-2), kidney (1a-1, 1a-2, 2b) and small intestine (1a-1, 2b) of C57 and DBA animals at varying times (48 h-12 weeks) following a single intraperitoneal dose of Aroclor 1254 (250 mg/kg). 3. The suppression of constitutive P4502b in the lung by Aroclor was observed in both strains, but was more prominent over a longer time course in the non-responsive animals. P4502b enzyme activity was increased in the liver and intestine of both strains of mouse; however, there was a significantly greater response to Aroclor in the C57 animals. These data indicate that the AH receptor does not participate in the suppression of pulmonary P4502b, and suggests that the regulation of inducible P4502b in liver and intestine is quantitatively different between these two strains of mouse. 4. P4501a was predictably induced in all tissues examined from the C57 animal, but was largely unaffected by PCBs in the DBA strain. P4501a-2, which is also regulated by the Ah receptor, was highly induced in the liver of the responsive strain, and also increased approximately two-fold in the liver of the non-responsive animals. Kidney P4501a-2 was also modestly increased by Aroclor, only in the responsive mouse.

Organochlorine compounds in relation to breast cancer, endometrial cancer, and endometriosis: an assessment of the biological and epidemiological evidence

There is an increasing public and scientific concern that certain chlorinated compounds, recognized as environmental pollutants, may cause estrogen-related neoplastic disease in humans. The main hypothesis has been that certain organochlorines, through their estrogenic actions, might cause breast cancer. From experimental studies, both in vitro and in vivo, there is evidence that certain organochlorine compounds may cause estrogenic effects, whereas others may cause antiestrogenic effects. In limited studies, some of these compounds in high doses have also been shown to increase and reduce the frequency of estrogen-related tumors in animals. The epidemiological findings regarding the association between organochlorines and breast cancer are inconclusive. However, the largest and best designed study has been interpreted as negative with respect to DDT and polychlorinated biphenyls (PCB) in relation to breast cancer. Associations between organochlorine exposure and endometrial cancer or endometriosis have even more limited empirical basis. The hypothesis that human exposure to environmental levels or organochlorines would favor an estrogenic overactivity leading to an increase in estrogen-dependent formation of mammary or endometrial tumors is not supported by the existing in vitro, animal and epidemiological evidence. It can, however, not be conclusively rejected on the basis of available data.

Chemical contaminants, pharmacokinetics, and the lactating mother

We review the commonly occurring persistent pesticides and industrial chemicals in breast milk. These chemicals are dichlorodiphenyl trichloroethane as dichlorodiphenyl dichloroethene dieldrin, chlordane as oxychlordane, heptachlor, polychlorinated biphenyls, polychlorinated dibenzofurans, and polychlorinated dibenzodioxins. We present a worked example of the kinds of pharmacokinetic assumptions and calculations necessary for setting regulatory limits of contaminants in the food supply, calculating dose of chemical contaminants to the nursed infant, converting risks from lifetime exposure in laboratory animals to risks for short-term exposure in humans, and estimating the excess cancer risk to the nursed infant.

Dissimilar frequency of hepatoblastomas and hepatic cystadenomas and adenocarcinomas arising in hepatocellular neoplasms of D2B6F1 mice initiated with N-nitrosodiethylamine and subsequently given Aroclor-1254, dichlorodiphenyltrichloroethane, or phenobarbital

Aroclor-1254 (Ar-1254) and dichlorodiphenyltrichloroethane (DDT) were compared to phenobarbital (PB) for their ability to promote hepatocellular proliferative lesions to hepatocellular adenomas and carcinomas and to hepatoblastomas in D2B6F1 male mice initiated with N-nitrosodiethylamine (NDEA). Hepatocellular neoplasms developed in all mice given NDEA and were more numerous in mice fed promoters. Multiplicities decreased in the order Ar-1254 > PB > DDT, indicating that Ar-1254 was more potent than either PB or DDT at the dosage levels used. PB was the most effective of the 3 agents in stimulating the evolution of hepatocellular neoplasms to hepatoblastoma. The incidence of hepatoblastomas in the NDEA.PB group was 72% but was only 27% in NDEA-initiated, DDT-promoted mice and 33% in low-dose and only 9% in high-dose Ar-1254-promoted mice. In contrast, lesions resembling benign and malignant cholangiocellular neoplasms were frequently found within hepatocellular tumors in Ar-1254-promoted mice but not in mice fed PB or DDT, either alone or after NDEA. Some cystic glandular structures in Ar-1254-promoted mice contained mucous cells, argentaffin cells, and Paneth cells and thus constituted intestinal metaplasia. Hepatoblastoma and intestinal metaplasia/cholangiocellular tumor morphology appear to constitute different patterns of genetic programming induced by certain promoters in expanding clones of initiated hepatocytes, on favorable genetic backgrounds such as that of D2B6F1 male mice.

Persistent effects of a single dose of Aroclor 1254 on cytochromes P450IA1 and IIB1 in mouse lung

The polychlorinated biphenyl mixture Aroclor 1254 has been shown to elicit prolonged biochemical responses in several rodent species, particularly induction of mixed function oxygenases in hepatic tissue. Lung is also of interest since a single dose of Aroclor 1254 has been demonstrated to have a tumor promoting effect, increasing the numbers of lung tumors in Swiss mice initiated with N-nitrosodimethylamine. To investigate the enzyme induction response in lung, male Swiss mice were given a single 100 or 500 mg/kg dose of Aroclor 1254 and euthanized at time intervals ranging from 48 hr to 30 weeks. Both cytochromes P450IA1 and IIB1 were followed by use of specific enzyme activities and Western immunoblotting. The IA1 isoform, as quantified by ethoxyresorufin-O-deethylase activity and immunoblotting with monoclonal antibody 1-7-1, was significantly elevated for 30 weeks after both doses. In contrast, benzyloxy-resorufin-O-dealkylase activity (P450IIB1 specific), which is constitutively expressed in rodent lung, was unaffected by Aroclor treatment at the lower dose at early time points, but induced twofold at 30 weeks. At the higher dose, however, enzymatic activity was decreased to 50% of control values, an effect which persisted for 4 weeks postexposure. These changes were confirmed by Western immunoblotting utilizing monoclonal antibody 2-66-3. Concomitantly, content of individual PCB congeners in lungs and carcass was quantified by gas chromatography with electron capture detection. One congener, 2,3,3',4,4'-pentachlorobiphenyl, was selectively retained in lung compared to carcass. Lack of correlation between changes in lung content of PCBs and levels of the P450 isoforms suggested interactions between congeners in control of P450 induction and repression. These data confirm a prolonged P450 induction response in nonhepatic tissue following Aroclor exposure, and further suggest a bidirectional role for certain PCB congeners in the regulation of P450IA1 and P450IIB1 expression in lung tissue.

Tumorigenicity of the tobacco-specific carcinogen 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone in infant mice

The tobacco-specific nitrosamine, 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is a potent carcinogen in adult rodents and variably effective transplacentally, depending on species. In pursuit of the thesis that human infants may be especially vulnerable targets for tumor initiation by tobacco smoke constituents, we tested the efficacy of NNK as a tumor initiator in infant mice. Cr:NIH(S) (NIH Swiss outbred) mice were given 50 mg/kg NNK i.p. on postnatal days 1, 4, 7, 10 and 14, with saline to controls. At an average age of 13-15 months, 57% of the NNK-exposed male offspring had hepatocellular tumors, with a multiplicity of 1.15 +/- 1.4, including 4 with carcinoma. Liver tumors including 2 carcinomas were found in 8 (14%) of the NNK-exposed female offspring. There were no hepatocellular neoplasms in any control. A significant increase in primary lung tumors also occurred in the NNK-treated males, with an incidence of 30/55 (57%) and a multiplicity of 0.7 +/- 0.2, vs. 7/33 (21%), multiplicity 0.3 +/- 0.6, in controls (P less than 0.025). An apparent increase in the incidence of lung tumors in NNK-treated females, 21/57 (37%) vs. 7/32 (22%) in controls, approached significance (P less than 0.1). Thus NNK was a moderately potent neonatal carcinogen for liver and lung in infant Swiss mice and more efficacious in this regard than when received transplacentally by mice of the same strain.

Should the presence of carcinogens in breast milk discourage breast feeding?

Pollutant chemicals are commonly found in human milk at levels that would prevent its sale as a commercial food for infants. The chemicals found most commonly are dichlorodiphenyl-dichloroethene, polychlorinated biphenyls, dieldrin, chlordane, heptachlor, and polychlorinated dibenzodioxins. In general, the regulatory levels for these chemicals have been set to prevent cancer in adult humans from lifetime exposure. We compared lives saved in the postneonatal period by breast feeding to the estimated excess cancer deaths attributable to the contaminants in breast milk. The results of this analysis suggest that only extreme levels of contaminants in breast milk represent more of a hazard than failure to breast feed, but clinical considerations in individual cases might override this conclusion. Our analysis depends on assumptions about how the chemicals might cause cancer in humans and on whether breast feeding prevents some postneonatal mortality. Noncarcinogenic hazards from chemical exposure, other hazards from breast feeding such as transmission of viruses, and benefits of breast feeding other than reduction in mortality were not considered.

Promotion of mouse lung tumors by bioaccumulated polychlorinated aromatic hydrocarbons

Lung tumors initiated in infant Swiss mice by N-nitrosodimethylamine (NDMA) were promoted by a single dose of a mixture of polychlorinated biphenyls (PCBs), Aroclor 1254 (250 or 500 mg/kg) given 4 days later. The tumors were typical alveologenic adenomas, and their number increased gradually over the course of 1 year to a maximum 4-fold enhancement in average tumor number compared with those given NDMA alone. The time course pattern suggested continuous tumor stimulation by the nonmetabolized PCB congeners retained in the tissues. Content of the nine major bioretained PCB congeners in carcass, liver, and lung was determined at intervals after treatment. Several showed tissue-specific retention patterns: 2,3,3',4,4'-PCB was selectively retained in lung and liver, and 2,2',3,4,4', 5'-HCB in lung. In tests of the tumor-promoting ability of individual congeners, the 2,2',3,4,4',5'-HCB, an Ah receptor agonist, promoted lung tumors when given singly, whereas another prominent bioretained congener, the 2,2',4,4',5,5'-HCB, an Ah receptor antagonist, did not promote, and in fact abrogated the positive effect of the 2,2',3,4,4',5'-HCB. In a parallel examination of persistent biochemical effects, a single low dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (5 nmole/kg) resulted in significant elevation of immunochemically detected protein and enzymatic activity of cytochrome P450 IA1 in lung for at least 12 weeks; these parameters were elevated for at least 30 weeks after a single dose of Aroclor 1254 (500 mg/kg). Taken together these results suggest that Ah-receptor-dependent induction of cytochrome P450 IA1 in mouse lung is correlated with and possibly causally involved in promotion of tumors by retained congeners.

Short-term effects of the tumor promoting polychlorinated biphenyl mixture, Aroclor 1254, on I-compounds in liver, kidney and lung DNA of male Sprague-Dawley rats

The effects of a tumor promoting polychlorinated biphenyl mixture, Aroclor 1254, on I-compounds (tissue, species and sex dependent DNA modifications that increase with age in untreated rodents) were studied by 32P-postlabeling in male Sprague-Dawley rat liver, kidney, and lung DNA. Aroclor 1254 was dissolved in corn oil and intraperitoneally (i.p.) injected (2 x 500 mg/kg, 2 weeks apart) into 3-month-old rats. Control rats were given corn oil. Groups of 3 animals were sacrificed at 2 and 6 weeks after the second injection of corn oil or Aroclor 1254. At both time points Aroclor 1254-treated rats had significantly lower body weights and higher liver weights while kidney and lung weights were unaffected. Thymidine incorporation into liver and lung DNA was significantly increased at both time points, while kidney DNA showed a small decrease at 2 weeks. Treatment resulted in significant reductions (ranging from 29 to 100%) of each of nine liver I-spots at 2 and 6 weeks. In treated rats there was no decrease in kidney I-spots at 2 weeks, while the levels of only two out of ten kidney spots were reduced by 42-91% at 6 weeks. At 2 weeks three out of seven and at 6 weeks four out of seven lung I-spots were lowered by 51-100% in the Aroclor 1254-treated rats. Thus the effects decreased in the order liver greater than lung greater than kidney. Since Aroclor 1254 has been reported to be a tumor promoter in liver and lung but not kidney, these results suggest a correlation between organ specific promotion of carcinogenesis by Aroclor 1254 and the reduction of DNA I-compounds.

Effect of pretreatment with beta-naphthoflavone on tumorigenesis by N-nitrosoethylurea in five mouse strains

The non-carcinogenic inducer of the Ah locus, beta-naphthoflavone (beta NF), was administered to females of 5 mouse strains at a dose of 150 mg/kg 48 h before treatment with a tumorigenic dose of the direct-acting carcinogen, N-nitrosoethylurea (ENU), once weekly for 4 weeks. The strains used were C57BL/6, C3H/He and NIH Swiss (responsive to Ah locus induction) and AKR and DBA/2 (induction-non-responsive). The ENU caused primary lung tumors in all strains and in some cases smaller numbers of other neoplasms, including lymphomas, sarcomas and hepatocellular tumors. The beta NF pretreatment did not reduce the numbers of any of the tumors, compared with mice given ENU alone. This result is in contrast to previous findings of a strong protective effect of beta NF against tumorigenesis in Ah-responsive strains by the metabolism-dependent carcinogens, benzo[a]pyrene and 3-methylcholanthrene and confirms that this protection is directly related to enzyme induction. beta NF treatment caused a significant doubling in the number of lung tumor bearers among the ENU-exposed C57BL/6 mice but in no other strain, suggesting the possibility of strain-specific tumor promotion.

Differential enzyme induction of mouse liver and lung following a single low or high dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The induction response of cytochrome P-450-dependent enzyme activities to a single low (5 nmol/kg) or high (50 nmol/kg, intraperitoneal [ip] dose of TCDD was examined in liver and lung homogenates over a 12-week time course in an outbred, Ah-responsive strain of mice (National Institutes of Health [NIH] Swiss). Total hepatic cytochrome P-450 was quantified, and the dealkylation of ethoxy- and benzyloxyresorufin (activities of P-450 IA1 and IIB1, respectively) were measured in both tissues at 48 and 96 hr and at 1, 4, and 12 weeks post-TCDD administration. Western immunoblotting with monoclonal antibody 1-7-1 was conducted to confirm the specific IA1-inductive effects of each dose of TCDD over the same time course. Following the low dose, specific IA1 induction was apparent in liver at the earliest time point, was maximal at 1 week, and declined to control values at 12 weeks. Pulmonary IA1 was near-maximally induced at 48 hr, and remained at that level for 4 weeks. In contrast, a tenfold higher dose of TCDD elicited similar IA1 induction profiles for both tissues, with a maximum at 1 week and a progressive loss at 4 and 12 weeks postexposure. P-450 IIB1 activity was elevated in TCDD-treated animals by enzymatic assay; however, Western immunoblotting did not confirm this finding. These data demonstrate persistent dose-dependent P450 induction over many weeks by a single TCDD dose, with significant organ-specific differences: (a) lung is more sensitive than liver to a nonmaximal inducing dose of TCDD, and (b) at a maximally inducing dose of TCDD, lung is very similar to liver in both the level and time course of IA1 induction.

Carcinogenicity of polyhalogenated biphenyls: PCBs and PBBs

Polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) are compounds whose physical/chemical properties led to their widespread commercial use. Although their production has been banned or severely limited in most countries since the 1970s, the persistence and stability of these compounds have resulted in a worldwide distribution, especially of PCBs. PBB contamination is limited principally to the state of Michigan, where a series of tragic errors eventually resulted in the accumulation of residues in livestock and the general human population. Long-term exposure to PCBs and PBBs in animals has been associated with the induction of neoplastic nodules in the liver and in some cases hepatocellular carcinoma. This review discusses the role of PCBs and PBBs in the process of carcinogenesis. The mutagenicity/genotoxicity of these compounds, as well as their initiation/promotion potential is discussed. The epidemiology of PCB and PBB exposure is reported along with an estimation of the risk of cancer to humans. Finally, possible molecular mechanisms of action are suggested for polyhalogenated biphenyls in cancer development.

Polychlorinated biphenyls (PCBs): mutagenicity and carcinogenicity

The potential mutagenicity and carcinogenicity of commercial PCBs has been investigated in both in vivo and in vitro systems and several conclusions can be drawn from these studies. (1) PCBs can covalently adduct DNA both in vivo and in vitro (using a source of metabolic activation); the more highly chlorinated biphenyls are poorly metabolized and these compounds tend to exhibit very low binding to DNA. Based on the structure-activity relationships for PCBs (Safe, 1984) it is unlikely that the more toxic compounds such as 3,3',4,4',5-penta- and 3,3',4,4',5,5'-hexachlorobiphenyl, would form covalent adducts with DNA. (2) PCB mixtures and individual compounds exhibit minimal mutagenic activity in most assay systems. (3) The more highly chlorinated PCB mixtures (i.e. greater than 50% Cl by weight) are hepatocarcinogens in rodents whereas data from a limited number of studies suggest that the lower chlorinated mixtures are not carcinogenic. (4) In some model systems, the higher chlorinated PCB mixtures act as promoters of preneoplastic lesions and hepatocellular carcinomas in rodents treated with a variety of initiators. (5) Aroclor 1254 acts as a promoter of skin papilloma formation in HRS/J hairless mice and structure-activity and genetic studies suggest that the Ah receptor is necessary but not sufficient for the activity of halogenated aryl hydrocarbons as promoters in hairless mice. (6) Individual PCB congeners and higher chlorinated commercial mixtures also exhibit anti-carcinogenic activity in the CD-1 mouse skin cancer model. (7) Results from occupational studies suggest that individuals exposed to PCBs may have an excess of cancer at some sites, however, the most comprehensive study (Brown, 1987) suggests that there are no significant increases in the overall cancer rate in workers exposed to PCBs. Follow-up and continuing epidemiological studies on the PCB-exposed workers are required to further clarify the potential carcinogenic effects of PCBs on humans. In several strains of rats and mice, there is a high incidence of hepatic preneoplastic lesions and carcinomas and these lesions can be induced by diverse promoting agents (Schulte-Hermann et al., 1983; Weinstein, 1984). Since PCBs are not mutagenic and do not readily form covalent adducts with cellular DNA, it is likely that the higher chlorinated biphenyls are not genotoxic and act as promoters of carcinogenesis in rodents. A comparable mechanism has been suggested for 2,3,7,8-TCDD (Shu et al., 1987; Weinstein, 1984). For PCBs, the role of the Ah receptor in mediating their activity as promoters has not been delineated.(ABSTRACT TRUNCATED AT 400 WORDS)