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Over the last few years there has been an increasing effort in identifying environmental and occupational carcinogenic agents and linking them to the incidence of a variety of human cancers. The carcinogenic process itself is multistage and rather complex involving several different mechanisms by which various carcinogenic agents exert their effect. Amongst them are epigenetic mechanisms often involving silencing of tumor suppressor genes and/or activation of proto-oncogenes, respectively. These alterations in gene expression are considered critical during carcinogenesis and have been observed in many environmental- and occupational-induced human cancers. Some of the underlying mechanisms proposed to account for such differential gene expression include alterations in DNA methylation and/or histone modifications. Throughout this article, we aim to provide a current account of our understanding on how the epigenetic pathway is involved in contributing to an altered gene expression profile during human carcinogenesis that ultimately will allow us for better cancer diagnostics and therapeutic strategies., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Although we have greatly benefited from the use of traditional epidemiological approaches in linking environmental exposure to human disease, we are still lacking knowledge in to how such exposure participates in disease development. However, molecular epidemiological studies have provided us with evidence linking oxidative stress with the pathogenesis of human disease and in particular carcinogenesis. To this end, oxidative stress-based biomarkers have proved to be essential in revealing how oxidative stress may be mediating toxicity induced by many known carcinogenic environmental agents. Therefore, throughout this review article, we aim to address the current state of oxidative stress-based biomarker development with major emphasis pertaining to biomarkers of DNA, lipid and protein oxidation., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Blood and urine were obtained from male Sprague-Dawley rats and B6C3F1 mice exposed to either a single 6 h or multiple daily (5 x 6 h) nose-only doses of 1,3-[2,3- (14)C]-butadiene at atmospheric concentrations of 1, 5 or 20 ppM. Globin was isolated from erythrocytes of exposed animals and analyzed for total radioactivity and also for N-(1,2,3-trihydroxybut-4-yl)-valine adducts. The modified Edman degradation procedure coupled with GC-MS was used for the adduct analysis. Linear relationships were observed between the exposures to 1,3-[2,3-(14)C]-butadiene and the total radioactivity measured in globin and the level of trihydroxybutyl valine adducts in globin. A greater level of radioactivity (ca. 1.3-fold) was found in rat globin compared with mouse globin. When analyzed for specific amino acid adducts, higher levels of trihydroxybutyl valine adducts were found in mouse globin compared with rat globin. Average levels of trihydroxybutyl valine adduct measured in globin from rats and mice exposed for 5 x 6 h at 1, 5 and 20 ppM 1,3-[2,3-(14)C]-butadiene were, respectively, for rats: 80, 179, 512 pM/g globin and for mice: 143, 351, 1100 pM/g globin. The profiles of urinary metabolites for rats and mice exposed at the different concentrations of butadiene were obtained by reverse phase HPLC analysis on urine collected 24 h after the start of exposure and were compared with results of a previous similar study carried out for 6 h at 200 ppM butadiene. Whilst there were qualitative and quantitative differences between the profiles for rats and mice, the major metabolites detected in both cases were those representing products of epoxide hydrolase mediated hydrolysis and glutathione (GSH) conjugation of the metabolically formed 1,2-epoxy-3-butene. These were 4-(N-acetyl-l-cysteine-S-yl)-1,2-dihydroxy butane and (R)-2-(N-acetyl-l-cystein-S-yl)-1-hydroxybut-3-ene, 1-(N-acetyl-l-cystein-S-yl)-2-(S)-hydroxybut-3-ene, 1-(N-acetyl-l-cystein-S-yl)-2-(R)-hydroxybut-3-ene, (S)-2-(N-acetyl-l-cystein-S-yl)-1-hydroxybut-3-ene, respectively. The former pathway showed a greater predominance in the rat. The profiles of metabolites were similar at exposure concentration in the range 1-20 ppM. There were however some subtle differences compared with results of exposure to the higher 200 ppM concentrations. Overall the results provide the basis for cross species comparison of low exposures in the range of occupational exposures, with the wealth of data available from high exposure studies.

Male Sprague-Dawley rats and B6C3F1 mice were exposed to either a single 6h or a multiple (5) daily (6h) nose-only dose of 1,3-[2,3-(14)C]-butadiene at exposure concentrations of nominally 1, 5 or 20 ppm. The aim was to compare the results with those from a similar previous study at 200 ppm. DNA isolated from liver, lung and testis of exposed rats and mice was analysed for the presence of butadiene related adducts, especially the N7-guanine adducts. Total radioactivity present in the DNA from liver, lung and testis was quantified and indicated more covalent binding of radioactivity for mouse tissue DNA than rat tissue DNA. Following release of the depurinating DNA adducts by neutral thermal hydrolysis, the liberated depurinated DNA adducts were measured by reverse phase HPLC coupled with liquid scintillation counting. The guanine adduct G4, assigned as N7-(2,3,4-trihydroxybutyl)- guanine, was the major adduct measured in liver, lung and testis DNA in both rats and mice. Higher levels of G4 were detected in all mouse tissues compared with rat tissue. The dose-response relationship for the formation of adduct G4 was approximately linear for all tissues studied for both rats and mice exposed in the 1-20 ppm range. The formation of G4 in liver tissue was about three times more effective for mouse than rat in this exposure range. Average levels of adduct G4 measured in liver DNA of rats and mice exposed to 5 x 6 h 1, 5 and 20 ppm 1,3-[2,3-(14)C]-butadiene were, respectively, for rats: 0.79 +/- 0.30, 2.90 +/- 1.19, 16.35 +/- 4.8 adducts/10(8) nucleotides and for mice: 2.23 +/- 0.71, 12.24 +/- 2.15, 48.63 +/- 12.61 adducts/10(8) nucleotides. For lung DNA the corresponding values were for rats: 1.02 +/- 0.44, 3.12 +/- 1.06, 17.02 +/- 4.07 adducts/10(8) nucleotides, and for mice: 3.28 +/- 0.32, 14.04 +/- 1.55, 42.47 +/- 13.12 adducts/10(8) nucleotides. Limited comparative data showed that the levels of adduct G4 formed in liver and lung DNA of mice exposed to a single exposure to butadiene in the present 20 ppm study and earlier 200 ppm study were approximately directly proportional across dose, but this was not observed in the case of rats. From the available evidence it is most likely that adduct G4 was formed from a specific isomer of the diol-epoxide metabolite, 3,4-epoxy-1,2-butanediol rather than the diepoxide, 1,2,3,4-diepoxybutane. Another adduct G3, possibly a diastereomer of N7-(2,3,4-trihydroxybutyl)-guanine or most likely the regioisomer N7-(1-hydroxymethyl-2,3-dihydroxypropyl)-guanine, was also detected in DNA of mouse tissues but was essentially absent in DNA from rat tissue. Qualitatively similar profiles of adducts were observed following exposures to butadiene in the present 20 ppm study and the previous 200 ppm study. Overall the DNA adduct levels measured in tissues of both rats and mice were very low. The differences in the profiles and quantity of adducts seen between mice and rats were considered insufficient to explain the large difference in carcinogenic potency of butadiene to mice compared with rats.

The lipid peroxidation (as malondialdehyde, MDA), activities of superoxide dismutase (SOD) and catalase (CAT), and benzo[a]pyrene (BaP) metabolites were investigated in sera and erythrocytes of male Sprague-Dawley rats treated with BaP (20 mg per rat). MDA levels were significantly increased in sera (16.98+/-3.29 nmol/ml serum, P<0.05) 12 h after BaP treatment and persisted up to 96 h (13.80+/-1. 65 nmol/ml serum, P<0.05), but no significant change in NIDA levels was observed in erythrocytes. SOD and CAT activities were significantly increased in erythrocytes shortly after BaP exposure, and they were slightly decreased in sera, indicating an inverse correlation between lipid peroxidation and antioxidant enzyme activity. BaP and BaP-quinones (BaP-1,6-quinone and BaP-3,6-quinone) were measured in sera during the study period. A rapid increase of unmetabolized BaP was observed in sera (41.27+/-4.14 pmol/ml serum) 3 h after BaP treatment, reaching a peak at 6 h (48.56+/-4.62 pmol/ml serum) followed by a sharp decrease. Formation of the BaP-1, 6-quinone and BaP-3,6-quinone started in sera 3 h after BaP treatment, reached a peak at 24 h (7.23+/-1.02 pmol/ml serum) and 12 h (9.20+/-0.98 pmol/ml serum), respectively, and then decreased gradually. The time-dependent pattern of serum lipid peroxidation and the level of erythrocyte antioxidant enzymes were shown to be related to the concentrations of the BaP-quinone metabolites. These results suggest that BaP treatment, probably via the formation of BaP-quinones, oxidatively altered lipids and antioxidant enzymes in the blood, and might be associated with BaP-related vascular toxicity including carcinogenesis.

Certain finfish species living in chemically polluted environments exhibit a high incidence of gastrointestinal tract tumors. Carnivorous fish in such environments are likely to consume invertebrates which contain chemical procarcinogens and the invertebrate biotransformation products of these compounds. The retention in tissues, extent of DNA adduct formation in liver and intestine, and metabolite composition of bile was investigated in southern flounder following gavage with pure [3H]- or [14C]benzo[a]pyrene (BaP), pure [14C]benzo[a]pyrene-7,8-dihydrodiol (BaP-7,8D), or hepatopancreas from spiny lobsters previously dosed with [3H]- or [14C]BaP (Metab.HP). Metab.HP contained mainly polar conjugates of BaP diols, triols and tetraols. BaP-7,8D was retained in fish tissues and bile at 24 h to a greater extent (33.6% of the dose), than either BaP (19.00%) or Metab.HP (6.6%). Hepatic and intestinal DNA isolated from all dosed fish contained covalently bound radioactivity, but exposure to BaP-7,8D or BaP resulted in significantly higher binding in both tissues than exposure to Metab.HP. Hepatic DNA from BaP and BaP-7,8D-dosed flounder contained 0.24 +/- 0.07 and 0.33 +/- 0.06 pmol BaP equivalents/mg DNA respectively (mean +/- S.E.), while hepatic DNA isolated from Metab.HP-dosed flounder contained 0.006 +/- 0.002 pmol BaP equivalents/mg DNA. Binding of radioactivity to intestinal DNA was significantly higher than to hepatic DNA for flounder dosed with Metab.HP (0.026 +/- 0.003) or with BaP (0.76 +/- 0.27) but not for flounder dosed with BaP-7,8D (0.44 +/- 0.09). These studies show that dietary BaP, and metabolites likely to be present in invertebrates, can be absorbed by the southern flounder and form DNA adducts in target organs.

Polynuclear aromatic hydrocarbons (PAH), some of which are potent carcinogens, are common environmental pollutants. The transport processes for these hydrophobic compounds into cells and between intracellular membranes are diverse and are not well understood. A common mechanism of transport is by spontaneous desorption and transfer through the aqueous phase. From the partitioning parameters, we have inferred that the rate limiting step involves solvation of the transfer species in the interfacial water at the phospholipid surface. Transfer of 10 PAH (pyrene, 3,4-benzophenanthrene, triphenylene, chrysene, 1,2-benzanthracene, 1,1'-binaphthyl, 9-phenylanthracene, 2,2'-binaphthyl, m-tetraphenyl and 1,3,5-triphenylbenzene) out of phosphatidylcholine vesicles has been examined. Our results show that the molecular volume of the PAH is a rate-determining factor. Moreover, high performance liquid chromatography (HPLC) data confirms the hypothesis that the rate of transfer is correlated with the size of the molecule and with the partitioning of the molecule between a polar and hydrocarbon phase. The kinetics and characteristics of the spontaneous transfer of carcinogens are likely to have a major impact on the competitive processes of PAH metabolism within cells.