DNA adducts and P450 induction in human, rat and avian liver cells after exposure to polychlorobiphenyls

DNA damage in Arctic seabirds: Baseline, sensitivity to a genotoxic stressor, and association with organohalogen contaminants

Environmental contaminants are found throughout Arctic marine ecosystems, and their presence in seabirds has been associated with toxicological responses. However, there are few studies of genotoxicity in Arctic avian wildlife. The purpose of the present study was to quantify deoxyribonucleic acid (DNA) damage in lymphocytes of selected seabird species and to examine whether accumulation of organohalogen contaminants (ΣOHCs) affects DNA damage. Blood was sampled from common eider (Somateria mollissima), black guillemot (Cepphus grylle), black-legged kittiwake (Rissa tridactyla), glaucous gull (Larus hyperboreus), arctic skua (Stercorarius parasiticus), and great skua (Stercorarius skua) in Kongsfjorden, Svalbard (Norway). Contaminant concentrations found in the 6 species differed, presumably because of foraging ecology and biomagnification. Despite large differences in contaminant concentrations, ranging from ΣOHCs 3.3 ng/g wet weight in the common eider to ΣOHCs 895 ng/g wet weight in the great skua, there was no strong difference among the species in baseline DNA damage or sensitivity to a genotoxic stressor (hydrogen peroxide). Baseline levels of DNA damage were low, with median values ranging from 1.7% in the common eider to 8.6% in the great skua. There were no associations between DNA damage and contaminants in the investigated species, suggesting that contaminant concentrations in Kongsfjorden are too low to evoke genotoxic effects, or possibly that lymphocytes are resistant to strand breakage. Clearly, genotoxicity is a topic for future studies of Arctic seabirds. Environ Toxicol Chem 2018;37:1084-1091. © 2017 SETAC.

Estimation of uncertainty in the sampling and analysis of polychlorinated biphenyls and polycyclic aromatic hydrocarbons from contaminated soil in Brighton, UK

The heterogeneity of environmental samples is increasingly recognised, yet rarely examined in organic contamination investigations. In this study soil samples from an ex-landfill site in Brighton, UK were analysed for polychlorinated biphenyl (PCB) and polycyclic aromatic hydrocarbon (PAH) contamination by using a balanced sampling protocol. The analytical technique of gas chromatography-mass spectrometry was found to be fit for purpose by the use of duplicate samples and the statistical analysis of variances, as well as of certified reference materials. The sampling uncertainty was found to significantly overweigh the analytical uncertainty, by a factor of 3 and 6 for PCBs and PAHs, respectively. The soil samples showed a general trend of PCB concentration that was under the recommended target level of 20 ng/g dry weight. It is possible that one site alongside the main road may exceed the 20 ng/g target level, after taking into consideration the overall measurement uncertainty (70.8%). The PAH contamination was more severe, with seven sites potentially exceeding the effect-range medium concentrations. The soil samples with relatively high PCB and PAH concentrations were all taken from the grass verge, which also had the highest soil organic carbon content. The measurement uncertainty which was largely due to sampling can be reduced by sampling at a high resolution spacing of 17 m, which is recommended in future field investigations of soil organic contamination.

DNA double-strand breaks in relation to persistent organic pollutants in a fasting seabird

Lipophilic persistent organic pollutants (POPs) are released from fat reserves during fasting, causing increased blood concentrations. Thus, POPs represent a potential anthropogenic stressor during fasting periods. We analysed the blood of female common eiders (Somateria mollissima) by using agarose gel electrophoresis and image data analysis to quantify the DNA-fraction, of total DNA, that migrated into the gel (DNA-FTM) as a relative measure of DNA double strand-breaks (DSBs) during the fasting incubation period in the high arctic. In 2008 and in 2009 blood samples were obtained for analysis of 9 POPs and DNA-FTM at day 5 of the incubation period, and then in the same individuals at day 20. This unique study design gave us the opportunity to analyse the same individuals throughout two points in time, with low and high stress burdens. During the incubation period the body mass (BM) decreased by 21-24%, whereas the POP levels increased by 148-639%. The DNA-FTM increased by 61-67% (being proportional to the increase in DSBs). At day 5, but not day 20, DNA-FTM was positively correlated with most analysed POPs. The increase in DNA-FTM was positively correlated with the decrease in BM (g) during incubation. Thus, we suggest that fasting stress (BM loss) decreases DNA integrity and that stress caused by fasting on BM loss appeared to override the additional stress caused by concurrent increase in levels of the analysed POPs in the eiders. Blood levels of POPs in the eiders in Svalbard were relatively low, and additive and/or synergistic genotoxic effects of fasting stress and POP exposure may occur in populations with higher POP levels.

Polychlorinated biphenyls (PCBs) as initiating agents in hepatocellular carcinoma

PCBs are carcinogens, but for many decades it was assumed that PCBs may not possess initiating activity. Initiation is a process that involves changes in the DNA sequence, often, but not exclusively produced through DNA adduction by a reactive compound or reactive oxygen species (ROS). DNA adducts can be detected by (32)P-postlabeling, a method that Dr. Ramesh Gupta co-developed and refined. Today these types of assays together with other mechanistic studies provide convincing evidence that specific PCB congeners can be biotransformed to genotoxic and therefore potentially initiating metabolites. This review will provide an overview of our current knowledge of PCBs' genotoxic potential and mechanism of action, emphasizing the contributions of Dr. Ramesh Gupta during his tenures at the Universities of Kentucky and Louisville.

Oxidative stress and cell-cycle change induced by coexposed PCB126 and benzo(a) pyrene to human hepatoma (HepG2) cells

Benzo(a)pyrene (BaP) never exists in the environment as a single compound but always coexists with other chemicals. These chemicals may affect the toxicity of BaP. Our previous study confirmed that polychlorinated biphenyls (PCBs), which were recently found coexisting with BaP in various environmental media, dramatically enhanced the genotoxicity of BaP. But the known mechanisms associated with this phenomenon are limited. Because BaP's genotoxicity is highly associated with its ability to induce the oxidative stress, we propose that the coexistence of PCBs may enhance BaP's genotoxicity by affecting BaP-induced oxidative stress. In this study, the HepG2 cells were treated with either BaP (50 μM), 3,3',4,4',5-pentachlorobiphenyl (PCB126) (0.01, 0.1, 1, and 10 nM), or pretreated with PCB126 followed by a coexposure to BaP and PCB126. We found that the exposure to BaP alone effectively increased the level of reactive oxygen species (ROS), glutathione (GSH), malondialdehyde (MDA), and the percentage of cells in G0/G1 phase, but decreased the percentage of S-phase cells. Compared to BaP alone, coexposure to both BaP and PCB126 effectively enhanced the levels of ROS and MDA as well as the percentage of cells in S phase, but decreased the levels of GSH and percentage of cells in G0/G1 phase. Our findings suggest that increasing oxidative stress and impairing the normal cell-cycle control may be mechanisms by which PCB126 enhances the genotoxity of BaP exposure.

Cytogenotoxicity induced by PBDE-47 combined with PCB153 treatment in SH-SY5Y cells

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are important recalcitrant halogenated compounds that have been regarded as major environmental pollutants. Recently, their concurrent appearance in the environment and humans and their structural and toxicological profile similarities have sparked interest in the potential toxicologic consequences of their coexposure. The aim of the current study was to evaluate the cytogenotoxic effects induced by 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) combined with 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) treatment in human neuroblastoma cells (SH-SY5Y) in vitro. SH-SY5Y cells were exposed to different concentrations of PBDE-47 (0, 2, 4, 8 μM) with or without PCB153 (5 μM) for 24 h. Thereafter, the cell viability, DNA damage, chromosomal abnormalities, and DNA-protein crosslinks (DPC) were determined. The results show that PBDE-47 and PCB153 alone and in combination induce DNA damage, with an increase in the frequency of micronuclei (MN) and DPC formation with increasing PBDE-47 concentration. In cells coexposed to PBDE-47 and PCB153, the cell viability significantly decreased while the MN frequency, DNA damage and DPC formation were all obviously increased compared to those of cells treated with the corresponding concentrations of PBDE-47 or PCB153 alone. Factorial analysis suggests that there were interactions between PBDE-47 and PCB153. The results imply that PBDE-47 interacts with PCB153 to inhibit cell viability and induce DNA damage, DPC formation, and chromosome abnormalities.

Cisplatin and oxaliplatin inhibit gap junctional communication by direct action and by reduction of connexin expression, thereby counteracting cytotoxic efficacy

Cisplatin [cis-diamminedichloroplatinum(II)]/oxaliplatin [1,2-diamminocyclohexane(trans-1)oxolatoplatinum(II)] toxicity is enhanced by functional gap junctions between treated cells, implying that inhibition of gap junctions may decrease cytotoxic activity of these platinum-based agents. This study investigates the effect of gap junction modulation by cisplatin/oxaliplatin on cytotoxicity in a transformed cell line. The effects were explored using junctional channels expressed in transfected HeLa cells and purified hemichannels. Junctional channels showed a rapid, dose-dependent decrease in dye coupling with exposure to cisplatin/oxaliplatin. With longer exposure, both compounds also decreased connexin expression. Both compounds inhibit the activity of purified connexin hemichannels, over the same concentration range that they inhibit junctional dye permeability, demonstrating that inhibition occurs by direct interaction of the drugs with connexin protein. Cisplatin/oxaliplatin reduced the clonogenic survival of HeLa cells at low density and high density in a dose-dependent manner, but to a greater degree at high density, consistent with a positive effect of gap junctional intercellular communication (GJIC) on cytotoxicity. Reduction of GJIC by genetic or pharmacological means decreased cisplatin/oxaliplatin toxicity. At low cisplatin/oxaliplatin concentrations, where effects on connexin channels are minimal, the toxicity increased with increased cell density. However, higher concentrations strongly inhibited GJIC, and this counteracted the enhancing effect of greater cell density on toxicity. The present results indicate that inhibition of GJIC by cisplatin/oxaliplatin decreases their cytotoxicity. Direct inhibition of GJIC and reduction of connexin expression by cisplatin/oxaliplatin may thereby compromise the effectiveness of these compounds and be a factor in the development of resistance to this class of chemotherapeutic agents.

The Svalbard glaucous gull as bioindicator species in the European arctic: insight from 35 years of contaminants research

Biomonitoring survey conducted with glaucous gulls from Svalbard have demonstrated that this top-predator-scavenger species accumulates a wide array of chemicals of environmental concern, including organohalogens, trace elements, organometals, and several non-halogenated and non-metallic-compounds. Among these contaminants are those subjected to global bans or restrictions in North America and Europe (e.g., legacy OC's, penta-, and octa-PBDE technical mixtures and mercury). In addition, some currently produced chemicals were found in gulls that lack and global use regulation (e.g., deca-PBDE , HBCD, and other non-PBDE BFR additives, siloxanes, and selected PFASs). Svalbard glaucous gulls are also exposed to contaminant metabolites that, at time, are more bioactive than their precursors (e.g., oxychlordane, p,p'-DDE, OH- and MeSo2-PCBs, and OH-PBDEs) Concentrations of legacy OCs (PCBs, DDTs, CHLs, CBzs, dieldrin, PCDD/Fs, and mirec) in tissues, blood, and eggs of Svalbard glaucous gulls have displayed the highest contamination levels among glaucous gull populations that inhabit Greenland (Cleemann et al. 2000) Jan Mayen (Gabrielsen et al. 1997), Alaska (Vander Pol et al. 2009), and the Canadian Arctic (Braune et a. 2005). To date, measurements obtaines on more novel organohalogens (e.g., OH- and MeSo2-containing metabolites, BFRs and PFASs) in Svalbard glaucous gull samples generally confirm that the spatial and trophodynamic trends of the legacy OC concentrations, whereas no clear trend emerges from surveys of trace elements and organometals. Using the glaucous gull as biosentinel species provides clear evidence that Svalbard and the European Arctic environment is exposed to a complex mixture of legacy and more recently introduced PBT-like substances.

Influence of aroclor 1254 on benzo(a)pyrene-induced DNA breakage, oxidative DNA damage, and cytochrome P4501A activity in human hepatoma cell line

Both polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are important environmental pollutants. They coexist widely in the environment at very low levels. Numerous studies indicated that aroclor1254 (one of PCBs mixture) is the inducer of cytochrome P450 1A enzyme acitivity. Benzo(a)pyrene (BaP) can cause a variety of toxicities in vitro, such as oxidative DNA damage and genotoxicity. In the present study, HepG2 cells were treated with either BaP (50 microM) or aroclor1254 at concentrations of 11.5 (low), 23.0 (medium), and 46.0 microM (high) alone, or pretreated the cells with aroclor1254 (11.5, 23.0, and 46.0 microM), followed by BaP (50 microM). It was found that 7-ethoxyresorufin-O-deetylase (EROD) activities of HepG2 cells exposed to either BaP or aroclor 1254 increased. DNA damage measured by DNA migration and the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) also increased in cells exposed to BaP, but not in cells exposed to aroclor1254. Under the Aroclor 1254 pretreatment condition, BaP-induced EROD activities was enhanced in cells exposed to the medium and high concentrations of aroclor1254 (P < 0.01 for both), whereas in all pretreatment groups aroclor1254 significantly increased BaP-induced DNA migration (P < 0.01 for all) and the 8-OHdG formation (P < 0.05 for all). In addition, there was positive correlation between the EROD induction activity and Olive tail moment (r(2) = 0.958, P < 0.01) or the levels of 8-OHdG (r(2) = 0.992, P < 0.01). The findings suggest that under the experimental conditions aroclor1254 may enhance BaP-induced DNA migration and oxidative DNA damage in HepG2, due to inducing CYP1A enzyme activity.

Mutagenicity of 3-methylcholanthrene, pcb3, and 4-oh-pcb3 in the lung of transgenic bigblue rats

Recent findings of high levels of predominantly lower chlorinated biphenyls in indoor and outdoor air open the question of possible health consequences. Lower chlorinated biphenyls are more readily metabolized to reactive and potentially harmful intermediates, acting as mutagens and cancer initiators. The goal of this study was to assess the mutagenicity of PCB3 in the lungs of rats. Male BigBlue® 334 Fisher transgenic rats, which carry the bacterial lacI gene as a target of mutagenicity, were given intraperitoneal injections of corn oil, 3-methylcholanthrene (3-MC, positive control), 4-monochlorobiphenyl (PCB3) or its metabolite 4-hydroxy-PCB3 (4-OH-PCB3) weekly for 4 weeks. Lungs tissue was harvested to determine mutant frequencies, mutation spectra, and pathological changes. 3-MC caused a 15-fold increase in mutant frequency and an increase in transversion type mutations; a very early occurrence of this type of mutation in lung tissue was previously identified in Ki-ras oncogenes of lung tumors from 3-MC exposed mice. The 2-fold increase in the mutant frequency after treatment with PCB3 and 4-OH-PCB3 was not statistically significant, but a shift in the mutation spectra, especially with PCB3, and an increase in mutations outside of the hotspot region for spontaneous mutations (bp 1-400), suggest that PCB3 and possibly 4-OH-PCB3 are mutagenic in the rat lung.

Chromosome aberrations and DNA strand breaks in glaucous gull (Larus hyperboreus) chicks fed environmentally contaminated gull eggs

In this present laboratory study, our results suggest that a complex mixture of pollutants found in the marine environment exerts genotoxic effects on glaucous gull (Larus hyperboreus) chicks fed environmentally contaminated gull eggs. Chromosome aberrations, quantified by cytogenetic analysis of blood cells, and DNA strand breaks, quantified by agarose gel electrophoresis and image data analysis, were determined in glaucous gull chicks fed environmentally contaminated gull eggs (exposed group) and in chicks fed hen eggs (control group). For both female and male gulls, the fraction of damaged metaphases was quantitatively higher in exposed than in control groups. On the other hand, the differences between the control and the exposed groups were more relevant when the chromosomal aberration data were treated as group totals rather than at the individual level. Consistent results were obtained in the DNA strand break analyses. The control group appeared to display a greater median molecular length (MML) than the exposed group.

Cytochrome P4501A induction and DNA adduct formation in glaucous gulls (Larus hyperboreus), fed with environmentally contaminated gull eggs

This study indicates that complex mixtures of pollutants found in the Arctic marine environment have genotoxic effects in glaucous gulls (Larus hyperboreus). DNA adducts were quantified, by the (32)P-postlabeling technique, in liver samples from gulls fed with hen eggs (controls) and from gulls fed with environmentally contaminated gull eggs (exposed). All birds were grown and fed under laboratory conditions. Hepatic homologues to mammalian cytochrome P4501A (CYP1A) proteins were also determined by Western blotting. DNA adducts were detected in all but one liver sample, but the exposed birds had a significantly increased level of DNA adducts relative to that of the controls. There was no clear significant correlation between the DNA adduct level and the level of organochlorine compounds (OCs) in blood. The level of CYP1A protein was significantly higher in the liver of exposed male gulls than in the liver of control males and positively correlated, with significance, to the level of OC compounds measured in blood. There was no significant correlation between the level of DNA adducts and the CYP1A protein content.

Embryonic turkey liver: activities of biotransformation enzymes and activation of DNA-reactive carcinogens

Avian embryos are a potential alternative model for chemical toxicity and carcinogenicity research. Because the toxic and carcinogenic effects of some chemicals depend on bioactivation, activities of biotransformation enzymes and formation of DNA adducts in embryonic turkey liver were examined. Biochemical analyses of 22-day in ovo turkey liver post-mitochondrial fractions revealed activities of the biotransformation enzymes 7-ethoxycoumarin de-ethylase (ECOD), 7-ethoxyresorufin de-ethylase (EROD), aldrin epoxidase (ALD), epoxide hydrolase (EH), glutathione S-transferase (GST), and UDP-glucuronyltransferase (GLUT). Following the administration of phenobarbital (24 mg/egg) on day 21, enzyme activities of ECOD, EROD, ALD, EH and GLUT, but not of GST, were increased by two-fold or higher levels by day 22. In contrast, acute administration of 3-methylcholanthrene (5 mg/egg) induced only ECOD and EROD activities. Bioactivation of structurally diverse pro-carcinogens was also examined using (32)P-postlabeling for DNA adducts. In ovo exposure of turkey embryos on day 20 of gestation to 2-acetylaminofluorene (AAF), 4,4'-methylenebis(2-chloroaniline) (MOCA), benzo[a]pyrene (BaP), and 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx) resulted in the formation of DNA adducts in livers collected by day 21. Some of the DNA adducts had (32)P-postlabeling chromatographic migration patterns similar to DNA adducts found in livers from Fischer F344 rats exposed to the same pro-carcinogens. We conclude that 21-day embryonic turkey liver is capable of chemical biotransformation and activation of genotoxic carcinogens to form DNA adducts. Thus, turkey embryos could be utilized to investigate potential chemical toxicity and carcinogenicity.

Failure of the standard battery of short-term tests in detecting some rodent and human genotoxic carcinogens

Theoretical reasons and experimental evidence indicate that a no-effect level generally cannot be expected for genotoxic carcinogens; as a consequence, in quantitative risk assessment the capability of distinguishing genotoxic from non-genotoxic carcinogens is of fundamental importance in order to identify relevant levels of human exposure. According to generally accepted guidelines, the standard three-test battery for the detection of genotoxic compounds consists of: (i) an in vitro test for gene mutation in bacteria; (ii) an in vitro test in mammalian cells with cytogenetic evaluation of chromosomal damage and/or a test that detects gene mutations; (iii) an in vivo test for chromosomal damage using rodent hematopoietic cells. This test battery is designed to avoid the risk of false negative results for compounds with genotoxic potential, but it cannot be taken for granted that the risk is completely eliminated. As a matter of fact there are some chemicals, classified by the International Agency for Research on Cancer (IARC) as probably or possibly carcinogenic to humans, which gave consistent negative results in this test battery, and in contrast provided positive results in other not routinely employed genotoxicity assays. The failure of the standard test battery in detecting some genotoxic carcinogens is attributable to several causes, but the principal of them are the following ones: in vitro, the artificial metabolic activity of the liver S9-mix, and the different biotransformation of chemicals in cells of different type and from different animal species; in vivo, the pharmacokinetic behaviour of the test compound, and its possible species-, sex- and tissue-specificity.

DNA adducts in cultures of polychlorinated biphenyl-treated human hepatocytes

Polychlorinated biphenyls (PCBs) are persistent environmental chemicals that accumulate at the apex of food chains. Several scientific committees support its designation as a human carcinogen, even though the precise mechanism of carcinogenesis remains controversial. In view of its uncertain ability to cause DNA damage in human liver, we investigated the effects of Aroclor 1254, Aroclor 1016, and 4-chlorobiphenyl (4-CB) on DNA adduct formation in cultures of primary human hepatocytes from five donors. Based on (32)P-postlabeling assays, we detected DNA adducts in native human liver as well as untreated, i.e., control cultures of human hepatocytes. Treatment of human hepatocytes with Aroclor 1016 and Aroclor 1254 resulted in four-fold (NP1) and seven-fold (butanol) increases in DNA adduct formation. Further, two and six new adduct spots were detected by multidirectional thin-layer chromatography after nuclease P1 and butanol enrichment. Treatment of human hepatocyte cultures with 4-CB led to 209 adducts per 10(9) nucleotides at the 60 microM concentration, and we show metabolically activated PCBs to be more efficient in the production of DNA-binding species compared with higher chlorinated PCB mixtures. Our study is therefore highly suggestive for a link between PCB exposure and DNA insult in human hepatocytes.

Unexpected induction of the human connexin 43 promoter by the ras signaling pathway is mediated by a novel putative promoter sequence

Connexin 43 (Cx43) is essential for survival and is tightly regulated at the transcriptional and post-transcriptional levels. A number of previous studies have demonstrated altered expression in malignant tissues, and in the presence of carcinogenic factors. We examined the effect of protooncogenes of Cx43 expression, and found no effect on Cx43 promoter activity in cells transformed with Src or erbB2. On the other hand, we identified and characterized a novel sequence that mediates Cx43 promoter regulation in cell lines engineered to overexpress H-Ras. Compared with wild-type NIH3T3 cells, both Cx43 mRNA and protein levels are increased in NIH3T3-Ras cells. The H-Ras+ cells also have enhanced Cx43 promoter activation, which is inhibited by the MEK1 inhibitor 2'-amino-3'-methoxyflavone (PD98059), suggesting that Ras-mediated Cx43 overexpression is via the mitogen activated protein kinase kinase/extracellular signal-regulated pathway. Deletion analysis of the Cx43 promoter revealed a 200-bp region downstream of the Cx43 transcription start site as the minimal sequence essential for the Ras-mediated Cx43 up-regulation. Using this 200-base pair fragment in electrophoretic mobility shift assays, we identified one main protein complex that binds efficiently and is more abundant in nuclear extracts from NIH3T3-Ras and MCF7-Ras cells compared with their matched controls. This complex selectively recognizes a consensus sequence, AGTTCAATCA, located at positions +149 to +158 of the Cx43 promoter. Supershift assays identified the 90-kDa heat shock protein (HSP90) and c-Myc as constituents of this DNA-binding complex. Treatment of cells with the HSP90 inhibitor geldanamycin resulted in repression of the Cx43 promoter activity, and inhibits binding of the complex to the Cx43 promoter. Coimmunoprecipitation studies confirmed the interaction between endogenous HSP90 and c-Myc. This study provides evidence that the transcriptional up-regulation of Cx43 by Ras-Raf-MAPK is mediated via the interaction of a novel Cx43 promoter element with a protein complex that contains both HSP90 and c-Myc.

Cytochrome P450 (CYP1A) induction and DNA adducts in a rat hepatoma cell line (Fao), exposed to environmentally relevant concentrations of organic compounds, singly and in combinations

Cytochrome P4501A (CYP1A) induction and DNA adduct formation were evaluated in the rat hepatoma cell line Fao, as biomarkers of exposure to organic compounds. Cells were exposed to environmentally relevant concentrations of benzo[a]pyrene (B[a]P) or 3,3',4,4'-tetrachlorobiphenyl (TCB), and to combinations of B[a]P and TCB. Both B[a]P and TCB induced CYP1A proteins in a concentration-dependent relationship, up to concentrations of 10 and 1 μM, respectively, detected by Western blotting. DNA adducts, analyzed by (32)P-postlabeling, were found at the highest concentrations of B[a]P (1 and 10 μM). No adducts were found in cells exposed to 0.1 μM TCB alone. The cotreatment of TCB and B[a]P indicated an increase in DNA adduct formation, compared with B[a]P, but no further induction of CYP1A protein compared with TCB alone. This study suggests that Western blotting and (32)P-postlabeling might be suitable methods for detecting CYP1A protein induction and DNA adducts, respectively, after exposure to environmentally relevant concentrations of organic compounds.

DNA adduction by polychlorinated biphenyls: adducts derived from hepatic microsomal activation and from synthetic metabolites

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants and complete carcinogens in rodents. Metabolism of lower chlorinated congeners with rat liver microsomes was investigated in earlier studies and DNA adduction was also reported. The current study was designed to compare DNA adducts formed after bioactivation of PCBs with rat, mouse and human hepatic microsomes, and to investigate the role of quinoid PCB metabolites in DNA adduct formation. Eight congeners ranging from mono- to hexachlorinated biphenyls were tested. Metabolites obtained through microsomal bioactivation as well as synthetic quinoid metabolites of 4-monochlorobiphenyl (4-CB) were incubated with calf-thymus DNA (CT-DNA), and the resulting adducts were analyzed by the 32P-post-labelling method. DNA adducts were formed with mono- di- and tri-chlorinated congeners, but not with higher chlorinated congeners. Similar adduct patterns were observed for 2-monochlorobiphenyl (2-CB) activated with hepatic microsomes from rat, mouse and human, while 4-CB, 3,4-dichlorobiphenyl (3,4-CB) and 3,4,5-trichlorobiphenyl (3,4,5-CB) showed similar patterns for two out of the three microsomal systems tested. 4,4' -trichlorobiphenyl (4,4' -CB) showed different adduct patterns in all microsomal systems. Higher adduct levels were obtained with the rodent microsomes compared with human microsomes and were related to higher cytochrome P450 activity. When adducts derived from microsomal activation of 4-CB were compared by co-chromatography with those derived from the incubation of DNA with synthetic 2-(4' -chlorophenyl)-1,4-benzoquinone (4-BQ), one adduct co-migrated in three different chromatography systems. This study demonstrates that rodents as well as human hepatic enzymes metabolize lower chlorinated biphenyl congeners to reactive intermediates that form DNA adducts in vitro and shows that the para-quinone metabolites of PCBs are, in part, involved in direct DNA adduction.

Distribution and macromolecular binding of benzo[a]pyrene and two polychlorinated biphenyl congeners in female mice

PCBs are complete rodent carcinogens and their potent tumor promoting activity has been reported, but their tumor-initiating activity remains controversial. Macromolecular binding of PCB metabolites has been demonstrated in vitro, but this issue remains unclear in vivo. The purpose of this study was to determine the binding affinity of 4-chlorobiphenyl and 3,3',4,4'-tetrachlorobiphenyl to proteins and DNA in vivo. C57/BL6 female mice were treated intraperitoneally with hepatic enzyme inducers (phenobarbital and beta-naphthoflavone) and then with 14C-labelled polychlorinated biphenyls or benzo[a]pyrene. The short-term distribution of labeled compounds into liver, lungs and kidneys and into different sub-cellular fractions of these tissues was assessed and the DNA and proteins from the 700 x g pellet were further purified to assess covalent binding. All compounds were distributed in low amounts into the liver, kidneys and lungs, with the greatest accumulation in the liver, and the lowest in lungs. In all tissues, test compounds were mostly found in cytosols and organellar pellets (10,000 x g), and lower amounts were present in nuclear pellets (700 x g) and microsomes. In lungs and kidneys, only benzo[a]pyrene showed significant covalent binding to proteins. In the liver, protein binding indices were significant for all compounds (P<0.05), but no significant binding of the test compounds to DNA could be demonstrated with this approach. Our results suggest that at the 24 h time point, all compounds were activated to electrophilic intermediates prone to macromolecular binding. Hepatic proteins apparently act as a sink for PCB-derived electrophiles, thus preventing detectable levels of covalent binding to hepatic DNA or to proteins in less metabolically active tissues.

Use of a combined human liver microsome-estrogen receptor binding assay to assess potential estrogen modulating activity of PCB metabolites

Polychlorinated biphenyls (PCBs) are metabolized by hydroxylation; some of these hydroxylated metabolites exhibit estrogen-like activity in animal models. Because PCBs may have effects on human health, it is of interest to determine if human tissues also metabolize PCBs to potentially estrogenic metabolites. In this study metabolites of seven PCBs with different degrees and positions of chlorination, generated by human liver microsomal reaction mixtures (MRM) have been examined, and their affinity for human recombinant estrogen receptor-alpha (ER) has been tested before and after HPLC fractionation. Two of the three MRMs with di-chloro-biphenyls (BPs, 2,5BP and 3,4BP), one of the three MRMs with tetra-BPs (2,6,2',6'BP), and one hexa-BP (2,4,6,2',4',6'BP) generated metabolites that competed for ER. HPLC of the ER-binding MRMs generated fractions that also exhibited ER-binding. This study shows the usefulness of combining in vitro metabolism and an ER-binding assay in initial identification of PCBs with estrogen-modulating potential.

3,3',4,4'-Tetrachlorobiphenyl oxidation in fish, bird and reptile species: relationship to cytochrome P450 1A inactivation and reactive oxygen production

Previously we showed that the polychlorinated biphenyl 3,3',4,4'-tetrachlorobiphenyl (TCB) caused a release of reactive oxygen species (ROS) from cytochrome P450 1A (CYP1A) of the fish scup (Stenotomus chrysops), and from rat and human CYP1A1. This was linked to a TCB- and NADPH-dependent oxidative inactivation of the enzyme, which in scup and rat was inversely related to the rates of TCB oxidation. We examined the relationship between rates of TCB oxidation, CYP1A inactivation and ROS production in liver microsomes from additional vertebrate species, including skate (Raja erinacea), eel (Anguilla rostrata), killifish (Fundulus heteroclitus), winter flounder (Pleuronectes americanus), chicken (Gallus domesticus), cormorant (Phalacrocorax auritus), gull (Larus argentatus), and turtle (Chrysemys picta picta). TCB oxidation rates were induced in all fish and birds treated with aryl hydrocarbon receptor agonists. Induced rates of TCB oxidation were <1 pmol/min/mg microsomal protein in all fish, and 6-14 pmol/min/mg in the birds. In all species but one, TCB oxidation rates correlated positively with EROD rates, indicating likely involvement of CYP1A in TCB oxidation. Incubation of liver microsomes of most species with TCB+NADPH resulted in an immediate (TCB-dependent) inhibition of EROD, and a progressive loss of EROD capacity, indicating an oxidative inactivation of CYP1A like that in scup. NADPH stimulated production of ROS (H(2)O(2) and/or O(2)(-*)) by liver microsomes, slightly in some species (eel) and greatly in others (chicken, turtle). Among the birds and the fish, NADPH-stimulated ROS production correlated positively with EROD activity. TCB caused a significant stimulation of ROS production by liver microsomes of flounder, killifish, cormorant and gull, as well as scup. The stimulation of CYP1A inactivation and ROS generation indicates an uncoupling of CYP1A by TCB in many species, and when compared between species, the rates of CYP1A inactivation correlated inversely with rates of TCB oxidation. Some feature(s) of binding/active site topology may hinder TCB oxidation, enhancing the likelihood for attack of an oxidizing species in the active site.

Induction of DNA adducts by several polychlorinated biphenyls

It is known that lower-chlorinated biphenyls are metabolically activated to electrophilic quinoid species capable of binding to DNA. Also, certain metabolites are capable of redox cycling, thereby increasing oxidative stress in biological systems. In the present study, we tested mono-, di-, tri-, tetra-, penta-, hexa-, and heptachlorinated biphenyls for their ability to bind with DNA and to induce oxidative DNA damage. We present additional evidence that several PCB congeners form DNA adducts after metabolic activation, which can be detected by the nuclease P1- or butanol-enrichment procedures of the (32)P-postlabeling technique. Butanol and nuclease P1 enrichments showed different adduct recoveries, depending on the level of chlorination of the biphenyls. Application of the nuclease P1 enrichment showed that the incubation of 2-chloro-; 3, 4-dichloro-; 2,4,4'-trichloro-; 3,4,5-trichloro-; and 2,2',5, 5'-tetrachlorobiphenyl with calf thymus DNA and liver microsomes from rats treated with phenobarbital, followed by oxidation with a peroxidase, produced five to eight different DNA adducts. For these lower-chlorinated biphenyls, butanol enrichment generally showed a lower recovery. For some higher substituted congeners (3,3',4,4', 5-pentachloro-, 2,2',3,4,4',5'-hexachloro-, 2,2',4,4',5, 5'-hexachloro-, and 2,2',3,4,4',5,5'-heptachlorobiphenyl), after butanol enrichment a single dominant spot was observed, which was absent in the nuclease P1 procedure. After incubation of calf thymus DNA with either higher- or lower-chlorinated PCB congeners, we were not able to detect significantly increased levels of oxidative DNA damage above background levels, measured as 8-oxo-7, 8-dihydro-2'deoxyguanosine. In view of the carcinogenicity of PCB mixtures in animals and the ability of PCB metabolites to bind covalently to DNA, rats were orally treated with a mixture of PCBs (Aroclor 1242). PCB-DNA adduct levels were analyzed in PCB target organs: liver, thymus, glandular stomach, spleen, testes, seminal vesicles and prostate DNA. In vivo PCB-DNA adducts could not be detected by either the butanol- or by the NP1-enrichment procedure in rat target tissue DNA. Also, no differences in oxidative DNA damage could be observed between PCB-treated rats and controls. These results indicate a lack of DNA reactivity of PCB mixtures in vivo.

Dietary fat and prostate cancer: current status

Efforts to elucidate the causes of prostate cancer have met with little success to date. All that is known with certainty is that the incidence increases exponentially with age, varies by geography and by race or ethnicity, and is higher among men whose father or brother had the disease. Because the incidence changes in migrants and their offspring, exogenous factors certainly contribute to the risk of prostate cancer. Early epidemiologic studies implicated dietary fat as a likely causal factor for this cancer. However, scientific support for such an association has diminished in recent years as more epidemiologic evidence has accrued. Accordingly, we reviewed the relevant English language literature on this topic, including epidemiologic and animal studies, as well as current concepts regarding the involvement of fat in carcinogenesis to re-examine the fat-prostate cancer hypothesis. We conclude that dietary fat may indeed be related to prostate cancer risk, although the specific fat components that are responsible are not yet clear. Given the diverse effects of fatty acids on cellular biology and chemistry, it seems likely that the relationship is complex, involving the interplay of fat with other dietary factors, such as antioxidant vitamins and minerals, or with genetic factors that influence susceptibility. Some suggestions for further research are offered.

Cytochromes P-4501A, P-4503A and P-4502B in liver and heart of Mugil capito treated with CYP1A inducers

Hepatic microsomes of Aroclor 1254-treated Mugil capito showed a single protein band detected in immunoblot with monoclonal antibody 1-12-3 to teleost (scup) CYP1A. The hepatic CYP1A like protein was induced with dose dependency after exposure of the fish to β-naphthoflavone (BNF) as well as to Aroclor 1254. The induced mullet hepatic CYP1A protein was confined to a distinct fraction obtained by DE-52 anion exchange chromatography, and its relative content in that fraction increased in fish that were treated with higher doses of inducer. EROD (7-ethoxyresorufin O-deethylase) activity in hepatic microsomes from mullet treated with various doses of BNF correlated significantly (r(2)=0.81502, P<0.01) with CYP1A content. Treatment of the mullet with low dose of Aroclor 1254 (25 mg/kg) induced only traces of CYP1A in liver microsomes (5.1±4.8 mg/kg). However, in mullet treated with the high dose of Aroclor 1254 (100 mg/kg) there was a dramatic induction in CYP1A content (408±275 pmol/mg) and this hemoprotein comprised about 83% of the total P-450 content of liver microsomes. The total level of P-450, although induced in the liver tissue, was not induced in heart tissue of Aroclor 1254 treated mullet. On the other hand, P-4501A was induced in treated mullet to a level that comprised almost all of the cardiac P-450 content. EROD activity in the heart tissue of induced mullet was characterized by low V(max) and high K(m) values (K(m)=2.35 mM, V(max)=39.5 pmol/min per mg) compared to the values recorded for the enzyme from the liver (K(m)=1.0 mM, V(max)=288.0 pmol/min per mg). Cardiac CYP1A with low catalytic activity and repression of CYP-types other then CYP1A in heart of CYP1A induced fish may be part of a mechanism aimed to preserve crucial levels of electron donors and molecular oxygen in cardiac muscle of fish exposed to CYP1A inducers.