The significance of DNA and protein adducts in human biomonitoring studies

The Use of Biomarkers as Alternatives to Current Animal Tests on Food Chemicals

Recent developments in biomarkers relating to the interrelationship of diet, disease and health were surveyed. Most emphasis was placed on biomarkers of deleterious effects, since these are of greatest relevance to the subject of this review. The area of greatest activity was found to be that relating to biomarkers of mutagenic, genotoxic and carcinogenic effects. This is also one of the major areas of concern in considerations of the beneficial and deleterious effects of dietary components, and also the area in which regulatory testing requires studies of the longest duration. A degree of progress has also been made in the identification and development of biomarkers relating to certain classes of target organ toxicity. Biomarkers for other types of toxicity, such as immunotoxicity, neurotoxicity, reproductive toxicity and developmental toxicity, are less developed, and further investigation in these areas is required before a comprehensive biomarker strategy can be established. A criticism that recurs constantly in the biomarker literature is the lack of standardisation in the methods used, and the lack of reference standards for the purposes of validation and quality control. It is encouraging to note the growing acknowledgement of the need for validation of biomarkers and biomarker assays. Some validation studies have already been initiated. This review puts forward proposals for criteria to be used in biomarker validation. More discussion on this subject is required. It is concluded that the use of biomarkers can, in some cases, facilitate the implementation of the Three Rs with respect to the testing of food chemicals and studies on the effects of diet on health. The greatest potential is seen to be in the refinement of animal testing, in which biomarkers could serve as early and sensitive endpoints, in order to reduce the duration of the studies and also reduce the number of animals required. Biomarkers could also contribute to establishing a mechanistic basis for in vitro test systems and to facilitating their validation and acceptance. Finally, the increased information that could result from the incorporation of biomarker determinations into population studies could reduce the need for supplementary animal studies. This review makes a number of recommendations concerning the prioritisation of future activities on dietary biomarkers in relation to the Three Rs. It is emphasised, however, that further discussions will be required among toxicologists, epidemiologists and others researching the relationship between diet and health.

Detection of Aromatic DNA Adducts in Human Cells and Fish Liver

Both nuclease PI treatment and reverse-phase high-performance liquid chromatography (HPLC) were used to enrich hydrophobic/bulky DNA adducts in DNA digests. 32P-postlabeling procedures and thin layer chromatography were then used to detect and quantitate aromatic/bulky DNA adducts. For both human and fish DNA from individuals exposed to environmental carcinogens, the nuclease PI and HPLC enrichment procedures generally gave similar results. The bottom sediments of the Buffalo and Detroit rivers are contaminated with polycyclic aromatic hydrocarbon carcinogens, and brown bullheads in these rivers show a high rate of liver cancer. Compared to DNA from control fish raised in aquariums, DNA of livers of brown bullheads from the polluted rivers exhibited elevated levels of DNA adducts. DNA from human oral mucosal cells and lymphocytes exhibited DNA adducts, but adducts levels did not differ significantly in smokers and nonsmokers. Adduct levels in DNA from human lung biopsy tissue, however, were elevated in smokers compared to nonsmokers. In former smokers, adducts levels were highest in those who had recently quit, and lowest in those who had not smoked for 10 years or more. Measurement of DNA adducts by 32P-postlabeling appears to be a useful and particularly direct procedure for assessing genetic damage from environmental carcinogens.

Dose-response relationships of polycyclic aromatic hydrocarbons exposure and oxidative damage to DNA and lipid in coke oven workers

Polycyclic aromatic hydrocarbons (PAHs) are known to induce reactive oxygen species and oxidative stress, but the dose-response relationships between exposure to PAHs and oxidative stress levels have not been established. In this study, we recruited 1333 male coke oven workers, monitored the levels of environmental PAHs, and measured internal PAH exposure biomarkers including 12 urinary PAH metabolites and plasma benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydotetrol-albumin (BPDE-Alb) adducts, as well as the two oxidative biomarkers urinary 8-hydroxydeoxyguanosine (8-OHdG) and 8-iso-prostaglandin-F2α (8-iso-PGF2α). We found that the total concentration of urinary PAH metabolites and plasma BPDE-Alb adducts were both significantly associated with increased 8-OHdG and 8-iso-PGF2α in both smokers and nonsmokers (all p < 0.05). This exposure-response effect was also observed for most PAH metabolites (all p(trend) < 0.01), except for 4-hydroxyphenanthrene and 8-OHdG (p(trend) = 0.108). Furthermore, it was shown that only urinary 1-hydroxypyrene has a significant positive association with both 8-OHdG and 8-iso-PGF2α after a Bonferroni correction (p < 0.005). Our results indicated that urinary ΣOH-PAHs and plasma BPDE-Alb adducts can result in significant dose-related increases in oxidative damage to DNA and lipids. Furthermore, when a multianalyte method is unavailable, our findings demonstrate that urinary 1-hydroxypyrene is a useful biomarker for evaluating total PAHs exposure and assessing oxidative damage in coke oven workers.

Signalling mechanisms of RhoGTPase regulation by the heterotrimeric G proteins G12 and G13

G protein-mediated signal transduction can transduce signals from a large variety of extracellular stimuli into cells and is the most widely used mechanism for cell communication at the membrane. The RhoGTPase family has been well established as key regulators of cell growth, differentiation and cell shape changes. Among G protein-mediated signal transduction, G12/13-mediated signalling is one mechanism to regulate RhoGTPase activity in response to extracellular stimuli. The alpha subunits of G12 or G13 have been shown to interact with members of the RH domain containing guanine nucleotide exchange factors for Rho (RH-RhoGEF) family of proteins to directly connect G protein-mediated signalling and RhoGTPase signalling. The G12/13-RH-RhoGEF signalling mechanism is well conserved over species and is involved in critical steps for cell physiology and disease conditions, including embryonic development, oncogenesis and cancer metastasis. In this review, we will summarize current progress on this important signalling mechanism.

Dose-response relationship, kinetics of formation, and persistence of S-[2-(N7-guanyl)-ethyl]glutathione-DNA adduct in livers of channel catfish (Ictalurus punctatus) exposed in vivo to ethylene dichloride

Formation of DNA adducts by reactive chemicals or their metabolites are often a precursor of mutagenesis and other adverse effects. Studies in juvenile channel catfish (Ictalurus punctatus) were conducted to determine the dose-response, kinetics of formation, and persistence of S-[2-(N7-guanyl)ethyl]glutathione hepatic-DNA adducts following a 4-h in vivo aqueous exposure to ethylene dichloride (EDC) at several dose levels. S-[2-(N7-guanyl)ethyl] glutathione adducts were detectable in liver tissue after 2 h of exposure and were still detectable three weeks after a single pulse exposure (detection limit=approximately 10 fmol, approximately 1 DNA adduct in 10(7) bases). Pretreatment of catfish with the glutathione-depleting agent diethylmaleate significantly reduced the level of tissue glutathione levels and, as a result, DNA adducts were not detected in pretreated fish. Catfish may serve as a useful sentinel species for detecting DNA-reactive chemicals in aquatic systems.

Genotoxic thresholds, DNA repair, and susceptibility in human populations

It has been long assumed that DNA damage is induced in a linear manner with respect to the dose of a direct acting genotoxin. Thus, it is implied that direct acting genotoxic agents induce DNA damage at even the lowest of concentrations and that no "safe" dose range exists. The linear (non-threshold) paradigm has led to the one-hit model being developed. This "one hit" scenario can be interpreted such that a single DNA damaging event in a cell has the capability to induce a single point mutation in that cell which could (if positioned in a key growth controlling gene) lead to increased proliferation, leading ultimately to the formation of a tumour. There are many groups (including our own) who, for a decade or more, have argued, that low dose exposures to direct acting genotoxins may be tolerated by cells through homeostatic mechanisms such as DNA repair. This argument stems from the existence of evolutionary adaptive mechanisms that allow organisms to adapt to low levels of exogenous sources of genotoxins. We have been particularly interested in the genotoxic effects of known mutagens at low dose exposures in human cells and have identified for the first time, in vitro genotoxic thresholds for several mutagenic alkylating agents (Doak et al., 2007). Our working hypothesis is that DNA repair is primarily responsible for these thresholded effects at low doses by removing low levels of DNA damage but becoming saturated at higher doses. We are currently assessing the roles of base excision repair (BER) and methylguanine-DNA methyltransferase (MGMT) for roles in the identified thresholds (Doak et al., 2008). This research area is currently important as it assesses whether "safe" exposure levels to mutagenic chemicals can exist and allows risk assessment using appropriate safety factors to define such exposure levels. Given human variation, the mechanistic basis for genotoxic thresholds (e.g. DNA repair) has to be well defined in order that susceptible individuals are considered. In terms of industrial exposures to known mutagens, knowing the dose relationships and protective mechanisms involved, offers the possibility of screening workers for susceptibility to mutation through examining DNA repair gene polymorphisms. Hence, thresholds may exist for certain mutagens, but there will undoubtedly be human subpopulations who are more at risk from low dose exposures than others and who should not be exposed, if possible. By studying polymorphisms in DNA repair genes, susceptible individuals may be identified, and additional safety factors appropriately targeted to these populations.

Societal and ethical issues in human biomonitoring--a view from science studies

BACKGROUND

Human biomonitoring (HBM) has rapidly gained importance. In some epidemiological studies, the measurement and use of biomarkers of exposure, susceptibility and disease have replaced traditional environmental indicators. While in HBM, ethical issues have mostly been addressed in terms of informed consent and confidentiality, this paper maps out a larger array of societal issues from an epistemological perspective, i.e. bringing into focus the conditions of how and what is known in environmental health science.

METHODS

In order to analyse the effects of HBM and the shift towards biomarker research in the assessment of environmental pollution in a broader societal context, selected analytical frameworks of science studies are introduced. To develop the epistemological perspective, concepts from "biomedical platform sociology" and the notion of "epistemic cultures" and "thought styles" are applied to the research infrastructures of HBM. Further, concepts of "biocitizenship" and "civic epistemologies" are drawn upon as analytical tools to discuss the visions and promises of HBM as well as related ethical problematisations.

RESULTS

In human biomonitoring, two different epistemological cultures meet; these are environmental science with for instance pollution surveys and toxicological assessments on the one hand, and analytical epidemiology investigating the association between exposure and disease in probabilistic risk estimation on the other hand. The surveillance of exposure and dose via biomarkers as envisioned in HBM is shifting the site of exposure monitoring to the human body. Establishing an HBM platform faces not only the need to consider individual decision autonomy as an ethics issue, but also larger epistemological and societal questions, such as the mode of evidence demanded in science, policy and regulation.

CONCLUSION

The shift of exposure monitoring towards the biosurveillance of human populations involves fundamental changes in the ways environment, health and disease are conceptualised; this may lead to an individualisation of responsibilities for health risks and preventive action. Attention to the conditions of scientific knowledge generation and to their broader societal context is critical in order to make HBM contribute to environmental justice.

ACB-PCR measurement of K-ras codon 12 mutant fractions in livers of Big Blue(R) rats treated with N-hydroxy-2-acetylaminofluorene

K-ras codon 12 GGT-->GAT and GGT-->GTT mutations are the most frequently observed K-ras point mutations in human and rodent tumors and therefore are implicated in carcinogenesis for many tissues. Measurement of these mutations in rat models and human tissue could facilitate a more logical extrapolation of rodent tumorigenesis data to human disease. We have developed allele-specific competitive blocker PCR (ACB-PCR) assays for rat K-ras codon 12 GGT-->GTT and GGT-->GAT mutations that parallel the already published assays for human K-ras codon 12 mutations. Liver K-ras codon 12 mutant allele fractions were measured in vehicle-treated and N-hydroxy-2-acetylaminofluorene (N-OH-AAF)-treated Big Blue rats. The average K-ras codon 12 GGT-->GTT mutant fraction (MF) for four control rats was 50 x 10(-6) (95% CI: 27 x 10(-6), 95 x 10(-6)) and for four treated rats was 165 x 10(-6) (95% CI: 87 x 10(-6), 312 x 10(-6)), indicating a 3.3-fold increase with treatment (95% CI: 1.3-8.1). The average MF of K-ras codon 12 GGT-->GAT for control rats was 1320 x 10(-6) (95% CI: 498 x 10(-6), 3500 x 10(-6)) and for treated rats was 8450 x 10(-6) (95% CI: 3180 x 10(-6), 22 400 x 10(-6)), indicating a 6.4-fold increase with treatment (95% CI: 1.6-25.4). These transgenic rats were part of a study that included analysis of liver lacI mutations. Although data from lacI determinations show that this compound induces mostly G-->T mutations, using the ACB-PCR method both K-ras codon 12 GGT-->GTT and GGT-->GAT MFs were significantly increased in treated rats versus control rats. This data raises the possibility that N-OH-AAF may not only induce mutations by a genotoxic mechanism, but also by amplification of both de novo and pre-existing K-ras mutation.

Do dose response thresholds exist for genotoxic alkylating agents?

The demonstration and acceptance of dose response thresholds for genotoxins may have substantial implications for the setting of safe exposure levels. Here we test the hypothesis that direct-acting DNA reactive agents may exhibit thresholded dose responses. We examine the potential mechanisms involved in such thresholded responses, particularly in relation to those of alkylating agents. As alkylating agents are representative model DNA reactive compounds with well characterized activities and DNA targets, they could help shed light on the general mechanisms involved in thresholded dose responses for genotoxins. Presently, thresholds have mainly been described for agents with non-DNA targets. We pay particular attention here to the contribution of DNA repair to genotoxic thresholds. A review of the literature shows that limited threshold data for alkylating agents are currently available, but the contribution of DNA repair in thresholded dose responses is suggested by several studies. The existence of genotoxic thresholds for alkylating agents methylmethanesulfonate is also supported here by data from our laboratory. Overall, it is clear that different endpoints induced by the same alkylator, can possess different dose response characteristics. This may have an impact on the setting of safe exposure levels for such agents. The limited information available concerning the dose response relationships of alkylators can nevertheless lead to the design of experiments to investigate the mechanisms that may be involved in threshold responses. Through using paired alkylators inducing different lesions, repaired by different pathways, insights into the processes involved in genotoxic thresholds may be elucidated. Furthermore, as alkyl-guanine-DNA transferase, base excision repair and mismatch repair appear to contribute to genotoxic thresholds for alkylators, cells deficient in these repair processes may possess altered dose responses compared with wild-type cells and this approach may help understand the contribution of these repair pathways to the production of thresholds for genotoxic effects in general. Finally, genotoxic thresholds are currently being described for acute exposures to single agents in vitro, however, dose response data for chronic exposures to complex mixtures are, as yet, a long way off.

HPRT gene alterations in umbilical cord blood T-lymphocytes in newborns of mothers exposed to tobacco smoke during pregnancy

Prenatal exposure to tobacco smoke has been associated with an increased risk of pediatric malignancies, yet the transplacental induction of genetic alterations by tobacco smoke carcinogens and their implication to childhood diseases remain poorly understood. We characterized mutations in the HPRT gene in umbilical cord blood T-lymphocytes of self-reported 103 never-smoking mothers and 104 smoking mothers (54 mothers smoked throughout and 50 mothers quit smoking during pregnancy). The results showed the illegitimate V(D)J recombinase-mediated deletion of HPRT exons 2-3 was the most prominent alteration occurring in 48.2% (26/54) of mutants from neonates of the smoking mothers who smoked during pregnancy, compared with 28.0% (14/50) from those of smoking mothers who quit smoking during pregnancy (p=0.035, Fisher's exact test), 34.9% (36/103) from never-smoking mothers (p=0.08), or 32.7% (50/153) of those of neonates born from the latter two groups of mothers combined (p=0.043). There was no significant difference in the frequency of this deletion between neonates of the never-smoking mothers and the smoking mothers who quit smoking during pregnancy (34.9% versus 28.0%, respectively, p=0.39). The results show an increase in illegitimate V(D)J recombinase-mediated deletion of HPRT exons 2-3 in cord blood T-lymphocytes of newborns of mothers who smoked during pregnancy, compared with the group of mothers who did not smoke during pregnancy, implying an increase in illegitimate V(D)J recombinase-mediated alteration, a genetic recombination event associated with childhood malignancies, may be induced in utero during pregnancy by maternal exposure to tobacco smoke-derived genotoxicants.

Polycyclic aromatic hydrocarbon-deoxyribonucleic acid (PAH-DNA) adduct levels and exposure to coke oven emissions among workers in Taiwan

In this study, the authors evaluated the relationship between polycyclic aromatic hydrocarbon-deoxyribonucleic acid (PAH-DNA) adduct levels in workers' peripheral white blood cells (WBCs) and their occupational exposures to coke oven emissions (measured by air and urinary 1-hydroxypyrene [1-OHP]). Personal exposures to smoking, charbroiled food, changing clothes in the workplace, and respirator use were determined by questionnaire. Eighty-nine coke oven workers were divided into 3 exposure groups on the basis of job description: topside workers, cokeside workers, and plant office staff. Referent subjects comprised 63 individuals from the same company who worked at a site remote from the coking plant. The geometric mean (GM) PAH-DNA adduct levels determined from the WBCs of the exposed groups were 6.86, 1.56, and 0.90 adducts/10(8) nucleotides, respectively (referents = 0.38 adducts/10(8) nucleotides). GM personal benzene soluble fraction (BSF) exposures for the exposed groups were 483.2 microg/m3, 70.1 microg/m3, and 43.2 microg/m3, respectively (referents = 10.7 microg/m3). There was a significant correlation (p < 0.05) between individual BSF and PAH-DNA adduct levels for the exposed groups. The authors also found a significant correlation (p < 0.05) between urinary 1-OHP levels from the day 2 samples of the exposed groups and their PAH-DNA adduct levels. The logistic-regression model revealed that PAH-DNA adduct levels were significantly different between job categories. The results of this study indicate that BSF exposure is the primary contributor to PAH-DNA adduct levels determined from WBCs.

Exposure of human primary colon carcinoma cells to anti-Fas interactions influences the emergence of pre-existing Fas-resistant metastatic subpopulations

Fas, an important death receptor-mediated signaling pathway, has been shown to be down-regulated during human colon tumorigenesis; however, how alterations in Fas expression influence the metastatic process remains unresolved. In mouse models, loss of Fas function was found to be both necessary and sufficient for tumor progression. In this study, we investigated the link between functional Fas status and malignant phenotype using a matched pair of naturally occurring primary (Fas-sensitive) and metastatic (Fas-resistant) human colon carcinoma cell lines in both in vitro and in vivo (xenograft) settings. Metastatic sublines were produced in vitro from the primary tumor cell line by functional elimination of Fas-responsive cells. Conversely, sublines derived from the primary tumor in vivo at distal metastatic sites were Fas-resistant. In contrast, simply disrupting the Fas pathway by molecular-based strategies in the Fas-sensitive primary tumor failed to achieve the same metastatic outcome. Interestingly, both in vitro- and in vivo-produced sublines resembled the naturally occurring metastatic population, based on functional and morphologic studies and genome-scale gene expression profiling. Overall, using this human colon carcinoma model, we: 1) showed that loss of Fas function was linked to, but alone was insufficient for, acquisition of a detectable metastatic phenotype; 2) demonstrated that metastatic subpopulations pre-existed within the heterogeneous primary tumor, and that anti-Fas interactions served as a selective pressure for their outgrowth; and 3) identified a large set of differentially expressed genes distinguishing the primary from metastatic malignant phenotypes. Thus, Fas-based interactions may represent a novel mechanism for the biologic or immunologic selection of certain types of Fas-resistant neoplastic clones with enhanced metastatic ability.

Role of DNA mismatch repair in apoptotic responses to therapeutic agents

Deficiencies in DNA mismatch repair (MMR) have been found in both hereditary cancer (i.e., hereditary nonpolyposis colorectal cancer) and sporadic cancers of various tissues. In addition to its primary roles in the correction of DNA replication errors and suppression of recombination, research in the last 10 years has shown that MMR is involved in many other processes, such as interaction with other DNA repair pathways, cell cycle checkpoint regulation, and apoptosis. Indeed, a cell's MMR status can influence its response to a wide variety of chemotherapeutic agents, such as temozolomide (and many other methylating agents), 6-thioguanine, cisplatin, ionizing radiation, etoposide, and 5-fluorouracil. For this reason, identification of a tumor's MMR deficiency (as indicated by the presence of microsatellite instability) is being utilized more and more as a prognostic indicator in the clinic. Here, we describe the basic mechanisms of MMR and apoptosis and investigate the literature examining the influence of MMR status on the apoptotic response following treatment with various therapeutic agents. Furthermore, using isogenic MMR-deficient (HCT116) and MMR-proficient (HCT116 3-6) cells, we demonstrate that there is no enhanced apoptosis in MMR-proficient cells following treatment with 5-fluoro-2'-deoxyuridine. In fact, apoptosis accounts for only a small portion of the induced cell death response.

Effect of the dithiocarbamate pesticide zineb and its commercial formulation, the azzurro. V. Abnormalities induced in the spindle apparatus of transformed and non-transformed mammalian cell lines

Abnormalities induced in the mitotic spindle by zineb and azzurro (1.0-25.0 micro g/ml, 24h) were evaluated in Chinese hamster ovary (CHO) and HeLa cells, and in non-transformed human fibroblasts (NTHF). Spindles were stained with FITC-conjugated anti-beta tubulin. Treatment with 10.0 micro g/ml of zineb induced complete inhibition of cell viability in NTHF cells while 10.0 micro g/ml of azzurro decreased cell growth down to 62%. Higher doses of both compounds induced cell death. In HeLa and CHO cells, 15.0 micro g/ml of zineb and 10.0-15.0 micro g/ml of azzurro decreased viability, whereas 25.0 micro g/ml of both compounds was cytotoxic. A significantly decreased mitotic index (MI) was observed in NTHF treated with 5.0 micro g/ml zineb or azzurro, whereas 10.0 micro g/ml of both chemicals were necessary to induce the same phenomenon in HeLa and CHO cells. Treatment with 1.0-5.0 micro g/ml of zineb or azzurro induced a dose-dependent increase of degenerated spindles in NTHF and the number of degenerated or multipolar spindles in HeLa and CHO cells increased in a dose-dependent manner with 1.0-10.0 micro g/ml zineb and azzurro. Although zineb and azzurro were able to induce mitotic spindle abnormalities in all cell types, non-transformed cells were less resistant than immortalized cells.

Effect of dithiocarbamate pesticide zineb and its commercial formulation, azzurro. III. Genotoxic evaluation on Chinese hamster ovary (CHO) cells

The in vitro genotoxicity exerted by the dithiocarbamate fungicide zineb, and its commercial formulation azzurro, were studied in Chinese hamster ovary (CHO) cells by the analysis of the sister chromatid exchange (SCE), cell-cycle progression and single cell gel electrophoresis (SCGE) assays. Both zineb and azzurro activities were tested within the range of 0.1-100.0 microg/ml. Concentrations of 0.1-25.0 microg/ml of zineb or azzurro induced a significant dose-dependent increase in SCE frequency over control values. For both test compounds, while doses ranging from 0.1 to 1.0 microg/ml did not alter the rate of cell proliferation, a significant delay in cell-cycle progression was observed within the 5.0-25.0 microg/ml dose-range. A regression test showed that either the proliferative replication index or the mitotic activity of cultures decreased as a function of the pesticide concentration within the 1.0-25.0 microg/ml dose-range. Doses higher than 50.0 microg/ml were cytotoxic. SCGE assay revealed an increase in zineb-induced DNA damage by enhancing the proportion of slightly damaged cells in the 25.0-100.0 microg/ml dose-range and by increasing in a dose-dependent manner the proportion of damaged cells within the 1.0-100.0 microg/ml dose-range. Overall, image analysis showed statistically significant positive relationships between zineb concentration and DNA damage (expressed by image length and width) and between length and width of the damaged cells. In azzurro-treated cells, only when 100.00 microg/ml was employed a significant increase in the frequency of damaged cells over control values affecting the totality of the cells was observed only when 100.0 microg/ml was employed. When lower doses were employed, no DNA damage was revealed. Based on these results, the evaluation of zineb as a genotoxic/non-genotoxic compound for human health should be reconsidered. Even though we demonstrate that the pesticide induces large DNA alterations in vitro, does no necessarily mean that the chemical should be considered clastogenic.notoxic

Human breast cancer cells generated by oncogenic transformation of primary mammary epithelial cells

A number of genetic mutations have been identified in human breast cancers, yet the specific combinations of mutations required in concert to form breast carcinoma cells remain unknown. One approach to identifying the genetic and biochemical alterations required for this process involves the transformation of primary human mammary epithelial cells (HMECs) to carcinoma cells through the introduction of specific genes. Here we show that introduction of three genes encoding the SV40 large-T antigen, the telomerase catalytic subunit, and an H-Ras oncoprotein into primary HMECs results in cells that form tumors when transplanted subcutaneously or into the mammary glands of immunocompromised mice. The tumorigenicity of these transformed cells was dependent on the level of ras oncogene expression. Interestingly, transformation of HMECs but not two other human cell types was associated with amplifications of the c-myc oncogene, which occurred during the in vitro growth of the cells. Tumors derived from the transformed HMECs were poorly differentiated carcinomas that infiltrated through adjacent tissue. When these cells were injected subcutaneously, tumors formed in only half of the injections and with an average latency of 7.5 weeks. Mixing the epithelial tumor cells with Matrigel or primary human mammary fibroblasts substantially increased the efficiency of tumor formation and decreased the latency of tumor formation, demonstrating a significant influence of the stromal microenvironment on tumorigenicity. Thus, these observations establish an experimental system for elucidating both the genetic and cell biological requirements for the development of breast cancer.

Role of Ras isoforms in the stimulated proliferation of human renal fibroblasts in primary culture

The proliferation of renal fibroblasts is implicated in the pathophysiologic processes of renal fibrosis. Many of the growth factors involved in proliferation are known to activate intracellular signaling pathways that converge on Ras monomeric GTPases. Although three ras family genes exist, their functional specificity is not yet known. Using antisense oligonucleotides, a role for Kirsten (Ki)-Ras in the stimulated proliferation of a primate renal fibroblast cell line was previously demonstrated. This study examines Ras in primary cultures of adult human renal fibroblasts. Using reverse transcription-PCR, mRNA for Harvey (Ha)-ras, Ki(4B)-ras, and neural (N)-ras, but not Ki(4A)-ras, were detected. Antisense oligonucleotides targeting Ha-, Ki-, and N-ras mRNA, which were used for liposomal transfection at 100 to 200 nM, were demonstrated to be active and isoform-specific in quantitative reverse transcription-PCR assays. Cellular Ras protein levels, as estimated using isoform-specific monoclonal antibodies, indicated that Ki-Ras was the predominantly expressed isoform (>95% of total Ras protein) under both serum-containing and serum-free conditions, with N- and Ha-Ras being detected in small amounts. Consistent with this finding, the antisense oligonucleotide directed against Ki-Ras reduced total cellular Ras levels by >70%, whereas Ha-Ras, N-Ras, and control oligonucleotides had no significant effect. Proliferation of oligonucleotide-transfected cells was measured using epidermal growth factor (EGF) and serum stimulation. The Ki-Ras oligonucleotide at 100 nM reduced serum-stimulated proliferation by >50% and EGF-stimulated proliferation by 25%, compared with data obtained with the control oligonucleotide (P: < 0. 01). The N-Ras oligonucleotide was not active, compared with the control oligonucleotide. The Ha-Ras oligonucleotide was not significantly active at 100 nM but reduced serum-stimulated proliferation by 13% and EGF-stimulated growth by 40% at 200 nM (P: < 0.01). These results demonstrate that Ki-Ras(4B) is the predominantly expressed Ras isoform in human renal fibroblasts in primary culture and is important for both serum- and EGF-stimulated proliferation. Ha-Ras appears to be expressed at low levels but may also play a distinct role in stimulated proliferation.

Differential role of Fas/Fas ligand interactions in cytolysis of primary and metastatic colon carcinoma cell lines by human antigen-specific CD8+ CTL

We have previously identified mutated ras peptides reflecting the glycine to valine substitution at position 12 as HLA-A2-restricted, CD8+ CTL neo-epitopes. CTL lines produced against these peptide epitopes lysed the HLA-A2+ Ag-bearing SW480 primary colon adenocarcinoma cell line, although IFN-gamma treatment of the targets was necessary to achieve efficient cytotoxicity. Here, we compared the lytic phenotype of the SW480 cell line to its metastatic derivative, SW620, as an in vitro paradigm to further characterize the nature of a HLA class I-restricted, Ag-specific CTL response against neoplastic cell lines of primary and metastatic origin. Although both colon carcinoma cell lines were lysed by these Ag-specific CTL following IFN-gamma pretreatment, the mechanisms of lysis were distinct, which reflected differential levels of sensitivity to the Fas pathway. Whereas IFN-gamma pretreatment rendered SW480 cells sensitive to both Fas-dependent and -independent (perforin) pathways, SW620 cells displayed lytic susceptibility to Fas-independent mechanisms only. Moreover, pretreatment of SW480 cells with the anti-colon cancer agent, 5-fluorouracil (5-FU), led to enhanced Fas and ICAM-1 expression and triggered Ag-specific CTL-mediated lysis via Fas- and perforin-based pathways. In contrast, these phenotypic and functional responses were not observed with SW620 cells. Overall, these data suggested that 1) IFN-gamma and 5-FU may enhance the lytic sensitivity of responsive colon carcinoma cells to immune effector mechanisms, including Fas-induced lysis; 2) the malignant phenotype may associate with resistance to Fas-mediated lysis in response to Ag-specific T cell attack; and 3) if Ag-specific CTL possess diverse lytic capabilities, this may overcome, to some extent, the potential "escape" of Fas-resistant carcinoma cells.

Increase in mutation frequency in lung of Big Blue rat by exposure to diesel exhaust

Exposure to diesel exhaust (DE) is known to cause lung tumors in rats. To clarify the mutagenicity of DE, we estimated mutant frequency (MF) and determined the mutation spectra in rat lung after exposure to DE using lambda/lacI transgenic rats (Big Blue system). Male Big Blue rats (6 weeks old) were exposed for 4 weeks to 1 or 6 mg/m(3) DE, which contains suspended particulate matter. Control rats were maintained in filtered clean air. After exposure to 6 mg/m(3) DE, MF in lung was 4.8-fold higher than in control rats (P < 0.01), but no increase in MF was observed in rats exposed to 1 mg/m(3) DE. Sixty-nine mutants were identified after exposure to 6 mg/m(3) DE. The major mutations were A:T-->G:C (18 mutations) and G:C-->A:T (19 mutations) transitions. Remarkably, G-->T transversion of the lacI gene at site 221 was a hot-spot induced by exposure to DE, and there were complex mutations in which multiple mutations occurred in a single mutant, especially in the rats exposed to 6 mg/m(3) DE. DNA adducts formed by DE were analyzed using a (32)P-post-label TLC method and the amount of 8-hydroxydeoxyguanosine (8-OHdG) was measured using HPLC. Relative adduct level and amount of 8-OHdG were significantly increased in the rats exposed to 6 mg/m(3) DE compared with the controls (3.0- and 2.2-fold, respectively; P < 0.01). The level of cytochrome P450 1A1 mRNA was shown by northern blot analysis to be significantly increased in the lungs of rats exposed to 6 mg/m(3) DE (5.5-fold; P < 0.01). These results indicate that DE causes lesions in genomic DNA and acts as a mutagen in rat lung.

Evidence of a role for Ki-Ras in the stimulated proliferation of renal fibroblasts

Progressive renal fibrosis is driven by a range of cytokines that act via membrane receptors and intracellular signaling cascades to evoke gene transcription events and related responses. The Ras family of GTPases has been implicated in many of these signaling cascades in model systems such as 3T3 fibroblasts. However, the roleof the specific Ras isoforms Ki, Ha, and N in the stimulation of renal fibroblasts has not been defined. In this study, Ras has been inhibited in primate renal fibroblasts (vero cells) using specific phosphorothioate oligodeoxynucleotides (oligos) targeting the three isoforms. Lipofectin transfection with 200 to 400 nM Ki-Ras oligo inhibited the epidermal growth factor- and fibroblast growth factor-stimulated proliferation of vero cells by 25 to 35% with a lesser effect on serum-stimulated growth. Oligos against Ha-Ras and N-Ras were inactive with respect to control oligo. Total cellular Ras protein (estimated by Western blotting) was reduced by 60 to 90% 24 h after transfection with Ki-Ras oligo. N-Ras, Ha-Ras, and control oligos were inactive. Total Ras synthesis over 4 h measured using [35S]-cys/met pulse chase was reduced by approximately 70% by Ki-Ras oligo and not altered by other oligos. The fractional prenylation of Ras was quantified from the discrete bands on polyacrylamide gel electrophoresis and was increased by the Ki-Ras oligo alone. These data demonstrate that these renal fibroblasts predominantly express the Ki isoform of Ras and that this GTPase plays a role in the stimulated proliferation of these cells. Ras GTPases may be a target for the inhibition of processes leading to renal fibrosis.

Molecular epidemiology in cancer research

The use of molecular biomarkers in epidemiological investigations brings clear advantages of economy, speed and precision. Epidemiology--the study of the factors that control the patterns of incidence of disease--normally requires large numbers of subjects and/or long periods of time, because what is measured (the occurrence of disease) is a rare event. Biomarkers are measurable biological parameters that reflect, in some way, an individual's risk of disease-because they indicate exposure to a causative (or protective) agent, or because they represent an early stage in development of the disease, or because they allow an assessment of individual susceptibility. Biomarkers must be usable on one of the few materials available for biomonitoring of humans, i.e. blood, urine, exfoliated epithelial cells and, with some difficulty, biopsies. The approach of molecular epidemiology has a great potential is several areas of cancer research: investigating the aetiology of the disease; monitoring cancer risk in people exposed to occupational or environmental carcinogens; studying factors that protect from cancer; and assessing intrinsic factors that might predispose to cancer. The biomarkers most commonly employed in cancer epidemiology include: measurements of DNA damage--DNA breaks, altered bases, bulky adducts--in lymphocytes; the surrogate marker of chemical modifications to blood proteins, caused by agents that also damage DNA; the presence of metabolites of DNA-damaging agents (or the products of DNA damage themselves) in urine; chromosome alterations, including translocations, micronuclei and sister chromatid exchange, resulting from DNA damage; mutations in marker genes; DNA repair; and the differential expression of a variety of enzymes, involved in both activation and detoxification of carcinogens, that help to determine individual susceptibility. The molecular approach has been enthusiastically employed in several studies of occupational/environmental exposure to carcinogens. While the estimation of biological markers of exposure has certainly shown the expected effects in terms of DNA damage and adducts, the detection of the biological effects of exposure (e.g. at the level of chromosome alterations) has not been so clear-cut. This is true also when smokers are examined as a group compared with non-smokers. Several markers (especially of chromosome damage and mutation) show a strong correlation with age-indicating either an increasing susceptibility to damage with age, or an accumulation of long-lived changes. DNA repair--a crucial player in the removal of damage before it can cause mutation--may vary between individuals, and may be modulated by intrinsic or extrinsic factors, but limited data are available because of the lack of a reliable assay. Information on other enzymes determining individual susceptibility does exist, and some significant effects of phenotypic or genotypic polymorphisms have emerged, although the interactions between various enzymes make the situation very complex. The important question of whether oxidative DNA damage in normal cells is decreased by dietary antioxidants (vitamin C, carotenoids etc., from fruit and vegetables) has been tackled in antioxidant supplementation experiments. The use of poorly validated assays for base oxidation has not helped us to reach a definitive answer; it seems that, in any case, the level of oxidative damage has been greatly exaggerated. DNA-damaging agents lead to characteristic kinds of base changes (transitions, transversions, deletions). The investigation of the spectrum of mutations in cancer-related genes studied in tumour tissue should lead to a better understanding of the agents ultimately responsible for inducing the tumour. Similarly, studying mutations in a neutral marker gene (not involved in tumorigenesis) can tell us about the origins of the 'background' level of mutations. So far, interpretation of the growing databases is largely speculative. (ABSTRACT

Requirement of NF-kappaB activation to suppress p53-independent apoptosis induced by oncogenic Ras

The ras proto-oncogene is frequently mutated in human tumors and functions to chronically stimulate signal transduction cascades resulting in the synthesis or activation of specific transcription factors, including Ets, c-Myc, c-Jun, and nuclear factor kappa B (NF-kappaB). These Ras-responsive transcription factors are required for transformation, but the mechanisms by which these proteins facilitate oncogenesis have not been fully established. Oncogenic Ras was shown to initiate a p53-independent apoptotic response that was suppressed through the activation of NF-kappaB. These results provide an explanation for the requirement of NF-kappaB for Ras-mediated oncogenesis and provide evidence that Ras-transformed cells are susceptible to apoptosis even if they do not express the p53 tumor-suppressor gene product.

K-ras is an essential gene in the mouse with partial functional overlap with N-ras

Mammalian ras genes are thought to be critical in the regulation of cellular proliferation and differentiation and are mutated in approximately 30% of all human tumors. However, N-ras and H-ras are nonessential for mouse development. To characterize the normal role of K-ras in growth and development, we have mutated it by gene targeting in the mouse. On an inbred genetic background, embryos homozygous for this mutation die between 12 and 14 days of gestation, with fetal liver defects and evidence of anemia. Thus, K-ras is the only member of the ras gene family essential for mouse embryogenesis. We have also investigated the effect of multiple mutations within the ras gene family. Most animals lacking N-ras function and heterozygous for the K-ras mutation exhibit abnormal hematopoietic development and die between days 10 and 12 of embryogenesis. Thus, partial functional overlap appears to occur within the ras gene family, but K-ras provides a unique and essential function.

Measurement of DNA adducts in humans after complex mixture exposure

In contrast to acute or chronic dosing experiments with a single chemical in animals, man is exposed to thousands of chemicals during a lifetime. Each of these may act alone, additively, synergistically or antagonistically in terms of biological effects, but most current risk assessment procedures fail to recognize such interactions. In carcinogenesis, a mutational process that is thought to occur through DNA damage by endogenous and/or exogenous agents, a wide variety of host factors is involved in disease outcome. These include absorption of chemicals, their distribution, metabolism and excretion. In addition, once metabolic activation has occurred, there is an array of protective mechanisms that cells have evolved to maintain DNA integrity, such as DNA repair, genetic redundancy and programmed cell death. One approach to risk assessment is to regard all DNA-damaging events as potentially leading to cancer and to measure DNA damage as the biologically relevant endpoint. The main method, if not the only method, presently available to assay a wide range of DNA adducts is 32P-postlabelling. This method has high sensitivity (limit of detection > 1 adduct per 10(10) nucleotides) and is capable of visualizing many different DNA adducts in a single analysis. Postlabelling is best suited for detecting hydrophobic adducts--low molecular weight adducts usually need a preliminary separation procedure prior to being postlabelled. This chromatographic procedure has been used to study DNA samples from human tissues of cigarette smokers, occupationally exposed groups and individuals living in polluted environments. Correlations have been found between the severity of exposure and the level of DNA adducts detected for human samples. However, most studies are single-time point studies, whereas for risk assessment purposes it may be better to use more quantitative and representative measures of long-term exposure, for example the number of adducts formed per annum. This article reviews methods of DNA adduct measurement, with particular reference to the 32P-postlabelling technique, which has been used to determine DNA adduct levels in populations exposed to complex mixtures.

N-alkylvaline levels in globin as a new type of biomarker in risk assessment of alkylating agents

Adducts with the N-terminal valine of erythrocyte globin can serve as individual biomarkers of systemic and cellular exposure to endogenous and exogenous alkylating agents. In contrast to "detoxification markers" of this kind of mecapturic acids derived from alkylation of glutathione, individual N-alkylations of valine in globin reflect the formally "toxifying" part of the stress due to alkylating agents transformed into the ultimate toxicant. Thus, in contrast to the traditional methods of biological monitoring this approach enables a better evaluation of systemic exposure to reactive agents, adapted more sensibly to the exposure situation over the whole life span of erythrocytes, and it can serve as a specific biomarker of exposure for the purpose of health surveillance in occupational medicine. An individual evaluation of exposures in comparison with the range of corresponding background levels is discussed from the point of view of supplementary risk assessment in medical surveillance of occupationally exposed persons.

Future approaches to genetic toxicology risk assessment

Short-term genetic toxicology tests were developed for the purpose of identifying chemical carcinogens in the environment. After two decades of development and validation, the tests are well-established in routine testing schemes, but our views of their utility for safety evaluation have undergone re-assessment. The correlation between identified mutagens and identified carcinogens has turned out to be significantly less than one. Processes or mechanisms that are not directly genotoxic appear to play a role in carcinogenesis. While short term test data are still components of the assessment of carcinogenic risk, genetic damage also has been recognized as important in its own right, in relation to heritable genetic risk and other health-related effects, such as aging, reproductive failure and developmental toxicity. The revolution in molecular biology and genetic analysis occurring over the past 20 years has contributed to the wealth of new information on the complexities of cell regulation, differentiation, and the carcinogenic process. These technologies have provided new experimental approaches to genetic toxicology assessments, including transgenic cell and animal models, human monitoring, and analysis of macromolecular interactions at environmentally relevant exposures. The potential exists for the development of more efficient and more relevant genetic toxicology testing schemes for use assessing human safety. A delineation of contemporary needs, a modern view of the elements of cancer induction, and an examination of new assays and technologies may provide a framework for integrating new approaches into current schemes for evaluating the potential genetic and carcinogenic risk of environmental chemicals.

Future research directions for evaluating human genetic and cancer risk from environmental exposures

The utility of biomarkers for evaluating the genotoxicity of environmental exposures is well documented. Biomarkers of both exposure and effect provide bases for assessing human-genotoxicant interactions and may be indicative of future disease risk. At present, there is little information on the predictive value of these assays for either a population or the individuals tested. This paper describes some aspects of biomarker assays, the possible use of susceptibility measures in biomonitoring protocols, and the need for evaluation of disease relevance. A population study involving epidemiologists, geneticists, toxicologists, statisticians, and physicians is proposed to determine the disease relevance of these biomarkers.

Cancer risk in asphalt workers and roofers: review and meta-analysis of epidemiologic studies

Twenty epidemiologic studies have described cancer risk in asphalt workers and roofers in various countries. A current concern for these workers is the potential carcinogenicity posed by inhalation of bitumen fumes or dermal exposure to bitumens. Bitumens are chemically different from many carcinogenic coal-tar based materials. Both have been employed in road paving and waterproofing. We examined and combined the results of the epidemiologic studies conducted on asphalt workers and roofers. We examined the cancer risk separately in three broad job categories: 1) roofers (exposed to bitumen fumes and previously often to coal-tar fumes); 2) highway maintenance workers (HMWs) and road pavers (exposed to bitumen fumes as well as possibly coal-tar fumes previously); and 3) miscellaneous and unspecified bitumen/asphalt workers. In roofers, an increased risk was suggested for cancers of the lung (aggregated relative risk 1.8, 95% confidence interval 1.5-2.1), stomach (1.7, 1.1-2.5), nonmelanoma skin (4.0, 0.8-12), and leukemia (1.7, 0.9-2.9). Some of the excesses may be attributable to polycyclic aromatic hydrocarbons (PAH) from coal-tar products. The aggregated relative risks in road pavers and HMWs were consistently lower than in roofers for cancers of the lung (0.9, 0.8-1.0), stomach (1.1, 0.8-1.5), bladder (1.2, 0.7-1.8), skin (2.2, 1.2-3.7), and leukemias (1.3, 0.9-1.8). Their risk of skin cancer was significantly increased, based on one study. Miscellaneous and unspecified workers had a significant excess (1.5, 1.2-1.8) of lung cancer. The data were poorly focused to address the carcinogenicity of bitumen fumes, as contrasted with tar-derived exposures. For the prospect of shedding more light on the bitumen-cancer controversy, the feasibility of a powerful multicenter cohort is currently being studied by the International Agency for Research on Cancer (IARC).

5-methylcytosine attack by free radicals arising from bromotrichloromethane in a model system: structures of reaction products

The interaction between free radicals derived from the catalytic decomposition of bromotrichloromethane and 5-methylcytosine (5MC) under different conditions were studied. The structures of the reaction products formed was established by the GC/MS analysis of their trimethylsilyl derivatives. Under anaerobic conditions, the formation of the following products was found: (1) thymine; (2) 5-hydroxymethyl uracil. Under aerobic conditions, the following reaction products were identified: (1) The same two products formed under anerobic conditions. (2) Monohydroxylated thymine. Precise location of the hydroxyl group was not established but probably corresponds to the six position isomer. (3) Two monochloro monohydroxy thymines. It is suggested that they are cis-trans isomers whose substituents are located at the 5-methyl and six positions of the base. (4) The trimethylsilyl derivative of thymine glycol. (5) Two monobromo monohydroxy adducts of thymine. One of them was detected as its underivatized form in the hydroxyl group position. (6) A partially silylated dihydroxythymine. When benzoyl peroxide was omitted from aerobic incubation mixtures, the compounds formed changed. No longer observable were: thymine; the two monochloro monohydroxy derivatives of thymine; thymine glycol, and one monohydroxythymine. On the other hand, two new reaction products were formed instead: a partially silylated monochloro-monohydroxy thymine and 5-hydroxymethyl-cytosine. If similar or equivalent reaction products were formed in DNA during CBrCl3 or CCl4 poisoning, results might be of relevance, because the 5MC content in DNA from eukaryotes is related to differentiation, gene control, and to carcinogenesis.

Immunoaffinity concentration of human lung DNA adducts using an anti-benzo[a]pyrene-diol-epoxide-DNA antibody. Analysis by 32P-postlabelling or ELISA

DNA, isolated from 15 human lung autopsy samples, was examined for the presence of polycyclic aromatic hydrocarbon (PAH) DNA adducts. Using the nuclease P1 modification of the 32P-postlabelling technique, between 1 and 12 adducts/10(8) nucleotides were detected prior to immunoconcentration. Autoradiograms from most of the samples revealed a diagonal smear of radioactivity consistent with complex mixture (cigarette smoking) DNA damage. The DNA samples were digested to oligonucleotides, made single-stranded and subsequently applied to immunoaffinity columns containing immobilised anti-benzo[a]pyrene (B(a)P)-7,8-diol-9,10-epoxide (BPDE) DNA polyclonal rabbit antibody. The material remaining bound to the column, in addition to that passing through, was analysed using both ELISA and 32P-postlabelling techniques. Column-bound adducts comprised between 0% and 78% of any particular sample. Immunoconcentration, followed by 32P-postlabelling of the material which had been bound to the column, revealed the presence of a number of discrete adduct spots in autoradiograms of the more heavily adducted samples. Sample DNA not retained by the columns was also analysed; the chromatographic pattern obtained was a dense zone of radioactive material migrating from the origin. This evidence suggests that the composition of PAH-DNA adducts found in human lung samples exhibits wide inter-individual variation.

Production and characterization of monoclonal antibodies to N7-phenylguanine

N7-Phenylguanine, a base adduct possibly formed after arylation of DNA by benzene oxide, the first reaction metabolite during benzene metabolism, was synthesized in our laboratory and used as reference for the production and characterization of monoclonal antibodies. 2-Hydroxymethyl-7-phenylhypoxanthine, a molecule structurally similar to N7-phenylguanine, was coupled by a linker molecule to different carrier proteins. The resulting conjugate was used to immunize BALB/c mice, the spleen cells of which were fused with mouse P3X63-Ag8.653 myeloma cells to obtain monoclonal antibodies. Several hybridoma lines were cultivated in defined media and characterized as to sensitivity and specificity by an enzyme-linked immunosorbent assay (ELISA). Competitive ELISA demonstrated that all antibodies showed a very high affinity for N7-phenylguanine but had a lower affinity towards various other samples including N7-chlorophenylguanines and C8-, N2-and O6-phenylguanine. As little as about 20 pg N7-phenylguanine could be detected with one of the most sensitive antibodies, CE6/G11, with a colorimetric end point while the detection limit could be lowered to about 10 pg N7-phenylguanine when a fluorescent end point was used. The detection limit of other methods used to determine N7-phenylguanine so far is 10 ng for gas-chromatography/mass-spectrometry and 1 ng for high-pressure liquid chromatography. Thus the use of specific monoclonal antibodies seems to be the most sensitive method for the detection of N7-phenylguanine.

Molecular epidemiology in cancer risk assessment and prevention: recent progress and avenues for future research

Molecular epidemiology is increasingly being applied in studies of cancer risks derived from exposure to environmental carcinogens of both endogenous and exogenous origins. Analytical methods have been developed that are capable of detecting and quantifying levels of covalent adducts of several important classes of carcinogens with cellular DNA and blood proteins. Methods of sufficient sensitivity and specificity to detect ambient levels of exposure are in current use. These are being used in studies related to tobacco use (polycyclic aromatic hydrocarbons, aromatic amines, tobacco-specific nitrosamines); dietary exposures (aflatoxins, N-nitrosamines, heterocyclic amines); medicinal exposures (cisplatin, alkylating agents, 8-methoxypsoralen, ultraviolet photoproducts); occupational exposures (aromatic amines, polycyclic aromatic hydrocarbons, oxides of ethylene and styrene, and vinyl chloride); and oxidative damage (8-hydroxyguanine, thymine glycol). Methodologic improvements together with their expanded use in feasibility studies continue to produce results that support the validity of this approach for detecting and quantifying exposure to carcinogens. Genetic markers are also being used to detect early biological responses in efforts to link carcinogen exposure to initiating events in the carcinogenesis process. These include, in addition to traditional cytogenetic markers (e.g., chromosomal aberrations, sister chromatid exchange, micronuclei), other alterations in chromosomal structure such as restriction fragment length polymorphisms, loss of heterozygosity, and translocation markers. Specific genetic changes have recently been identified as critical molecular events in the initiation and development of many cancers. Important among these are activation of oncogenes, especially those of the ras family, and inactivation of tumor-suppressor genes (e.g., p53 and Rb) by point mutations and/or chromosomal deletions and other structural changes. Although some of these changes are known to occur in chemically induced tumors of experimental animals, the possible role of chemical carcinogens in the induction of genetic abnormalities in human cancers has yet to be determined. Continuing investigations employing the methods of molecular epidemiology promise to provide further evidence concerning these relationships. Future investigations employing newly developed molecular biological methods, in particular those based on polymerase chain reaction amplification of DNA, to identify alterations in DNA and chromosomal structure, combined with methods for characterizing exposure to carcinogens and early effects, have great potential for further elucidating the role of genotoxic agents in the etiology of human cancers and also for the development of strategies for their prevention.

Development of fast atom bombardment mass spectral methods for the identification of carcinogen-nucleoside adducts

An analytical strategy using fast atom bombardment (FAB) ionization and tandem mass spectrometry has been developed to determine the molecular weight and major fragment ions, and to provide limited structural characterization of low picomole levels of carcinogen-nucleoside adducts. This strategy consists of three main components: (1) the sensitivity for analysis by FAB combined with mass spectrometry is increased via chemical derivatization; (2) the nucleoside adducts are selectively detected by using constant neutral loss scans; and (3) structurally characteristic fragments are obtained by using daughter ion scans. Trimethylsilyl derivatized arylamine-nucleoside adducts have been detected at levels as low as a few picomoles by using this approach. After experimental determination of the mass of the BH 2 (+) fragment ion, daughter ion spectra have been used to probe the structure specificity associated with collision-activated decomposition of this fragment. With model C-8 substituted arylamine adducts [N-(deoxyguanosin-8-yl)-4-aminobiphenyl, N-(deoxyadenosin--yl)-4-aminobiphenyl, and N-(deoxyguanosin-8-yl)-2-aminofluorene], nucleoside-specific and carcinogen-specific fragmentation have been observed in daughter ion spectra.

High-dose combination alkylating agents with autologous bone-marrow support in patients with breast cancer: preliminary assessment of DNA damage in individual peripheral blood lymphocytes using the single cell gel electrophoresis assay

The single cell gel (SCG) assay is a sensitive electrophoretic technique for detecting the presence of DNA single strand breaks and alkali-labile damage in individual cells. This technique was used to evaluate the levels of DNA damage in cryopreserved peripheral blood lymphocytes (PBLs) from 11 breast cancer patients treated with high doses of cyclophosphamide and cisplatin and provided autologous bone marrow transplantation after treatment. PBL specimens for the SCG study were obtained just prior to treatment, following the administration of cyclophosphamide and cisplatin for 2 days, and upon lymphocytic recovery. Based on a concurrent analysis of DNA damage in cryopreserved and non-cryopreserved PBL samples from three patients, the mean level of DNA migration or the dispersion of damage among cells was not affected by the process of cryopreservation. The pre-treatment samples of several patients contained PBL with increased levels of DNA damage, presumably reflecting persistent DNA damage induced by previous treatment regimens. Chemotherapy resulted in a significant but variable increase in DNA damage in PBL samples from all patients. In this limited study, the level of damage did not correlate with serum levels of cyclophosphamide or with lymphocyte toxicity. Among the post-treatment samples, increased levels of DNA damage were absent in most but not all patients. The presence of damaged cells in the post-treatment samples may be indicative of an inadequate therapy regimen or of DNA damage resulting from non-therapy related processes. Because of its simplicity and short processing time, the SCG assay can be used to evaluate levels of DNA damage during the course of therapy, allowing the dose schedule to be altered to achieve a desired effect level.

Mercapturic acids, protein adducts, and DNA adducts as biomarkers of electrophilic chemicals

The possibilities and limitations of using mercapturic acids and protein and DNA adducts for the assessment of internal and effective doses of electrophilic chemicals are reviewed. Electrophilic chemicals may be considered as potential mutagens and/or carcinogens. Mercapturic acids and protein and DNA adducts are considered as selective biomarkers because they reflect the chemical structure of the parent compounds or the reactive electrophilic metabolites formed during biotransformation. In general, mercapturic acids are used for the assessment of recent exposure, whereas protein and DNA adducts are used for the assessment of semichronic or chronic exposure. 2-Hydroxyethyl mercapturic acid has been shown to be the urinary excretion product of five different reactive electrophilic intermediates. Classification of these electrophiles according to their acid-base properties might provide a tool to predict their preference to conjugate with either glutathione and proteins or with DNA. Constant relationships appear to exist in the cases of 1,2-dibromoethane and ethylene oxide between urinary mercapturic acid excretion and DNA and protein adduct concentrations. This suggests that mercapturic acids in some cases may also play a role as a biomarker of effective dose. It is concluded that simultaneous determination of mercapturic acids, protein and DNA adducts, and other metabolites can greatly increase our knowledge of the specific roles these biomarkers play in internal and effective dose assessment. If the relationship between exposure and effect is known, similar to protein and DNA adducts, mercapturic acids might also be helpful in (individual) health risk assessment.

Biomarkers in styrene-exposed boatbuilders

14 fiberglass-reinforced plastics (FRP) boatbuilders were compared with 9 unexposed controls with respect to several chemical specific and nonspecific biomarkers measured in peripheral blood. Biomarkers included styrene-hemoglobin adducts (styrene-Hb), sister-chromatid exchanges (SCEs), micronuclei (MN), single-strand breaks (SSBs) and N-acetoxy-2-acetylaminofluorene-induced DNA binding (NA-AAF binding) as a measure of susceptibility to DNA damage. Workers' exposures averaged 11 ppm (8-h TWA; geometric mean) and ranged from 0.6 to 44 p.p.m. Mandelic acid levels were measured in end-of-shift urine samples and reflected an average styrene exposure equivalent to 15 p.p.m. There was a large though not significant difference in levels of styrene-Hb adducts among exposed workers and controls, largely the consequence of a single heavily-exposed individual with an extremely high level of adducts. Significant differences between biomarker levels in exposed workers and controls were observed with MN, SSBs and NA-AAF binding. No significant differences were seen in mean levels of SCEs nor in the incidence of cells with a high frequency of SCEs. The data suggest that exposure to levels of styrene in occupational settings near or below the current OSHA standard (50 p.p.m.) can induce damage at the cellular/molecular level. Appropriately-selected panels of biomarkers can be useful in identifying potentially harmful exposures.

DNA adducts in bronchial biopsies

To investigate the feasibility of measuring DNA-carcinogen adducts in the lungs of non-surgical patients, endobronchial biopsies were obtained from 78 patients undergoing routine diagnostic bronchoscopy. Lung cancer was present in 37 (47%) of the patients. DNA was isolated from the tissues and analyzed by HPLC- or nuclease-PI-enriched 32P-postlabelling, using procedures selective for aromatic adducts. Chromatograms from all 28 current smokers showed a distinctive diagonal adduct zone which was present in only 24 of 40 ex-smokers and 4 of 10 lifetime non-smokers. Adduct levels and chromatographic patterns were similar in bronchial tissue from different lobes of the lung, in bronchial and alveolar tissue, and in tumor and non-tumor bronchial tissue taken from the same subject. Bronchial DNA adduct levels were strongly associated with cigarette smoking status and dropped rapidly after smoking ceased. Higher levels of DNA adducts seen in the lung-cancer patients were mainly due to cigarette smoking. Frequent alcohol intake was the only dietary factor associated with higher levels of bronchial DNA adducts. We conclude that the level of bronchial DNA adducts is strongly associated with cigarette-smoking history and with alcohol intake, but is not associated with lung cancer independently from its relation to smoking. The results indicate the feasibility of using 32P-postlabelling to detect and quantitate genetic damage in bronchial biopsy specimens.

Carcinogen adducts as an indicator for the public health risks of consuming carcinogen-exposed fish and shellfish

A large variety of environmental carcinogens are metabolically activated to electrophilic metabolites that can bind to nucleic acids and protein, forming covalent adducts. The formation of DNA-carcinogen adducts is thought to be a necessary step in the action of most carcinogens. Recently, a variety of new fluorescence, immunochemical, and radioactive-postlabeling procedures have been developed that allow the sensitive measurement of DNA-carcinogen adducts in organisms exposed to environmental carcinogens. In some cases, similar procedures have been developed for protein-carcinogen adducts. In an organism with active metabolic systems for a given carcinogen, adducts are generally much longer lived than the carcinogens that formed them. Thus, the detection of DNA- or protein-carcinogen adducts in aquatic foodstuffs can act as an indicator of prior carcinogen exposure. The presence of DNA adducts would, in addition, suggest a mutagenic/carcinogenic risk to the aquatic organism itself. Vertebrate fish are characterized by high levels of carcinogen metabolism, low body burdens of carcinogen, the formation of carcinogen-macromolecule adducts, and the occurrence of pollution-related tumors. Shellfish, on the other hand, have low levels of carcinogen metabolism, high body burdens of carcinogen, and have little or no evidence of carcinogen-macromolecule adducts or tumors. The consumption of carcinogen adducts in aquatic foodstuffs is unlikely to represent a human health hazard. There are no metabolic pathways by which protein-carcinogen or DNA-carcinogen adducts could reform carcinogens. Incorporation via salvage pathways of preformed nucleoside-carcinogen adducts from foodstuffs into newly synthesized human DNA is theoretically possible.(ABSTRACT TRUNCATED AT 250 WORDS)

Ah locus-associated differences in induction of sister-chromatid exchanges and in DNA adducts by benzo[a]pyrene in mice

The effect of alleles of the Ah locus on the induction of sister-chromatid exchanges (SCE) was studied in C57Bl/6 and in DBA/2 mice treated twice intragastrically with benzo[a]pyrene (BP, 100 or 10 mg/kg b.w.). To measure the changes in the frequency of SCE, 2 protocols were used: in vivo in bone marrow cells after implantation of 5-bromodeoxyuridine (BrdU) tablets and in vivo/in vitro in spleen lymphocytes cultured with BrdU. On day 5 mice were killed and SCEs estimated in bone marrow cells. BP-DNA adducts in bone marrow and spleen were analyzed on day 5 after the same exposure to BP. In the spleen lymphocytes SCE frequencies were analyzed after an additional 48 h of culture. We found that at both doses of BP, the number of SCEs and BP-DNA adducts in bone marrow and in spleen cells was significantly higher in aryl hydrocarbon hydroxylase (AHH)-non-inducible (DBA/2) mice than in AHH-inducible (C57BL/6) mice. Only marginal induction of SCE was noted after the high dose of BP in C57BL/6 mice in bone marrow in vivo, whereas a highly significant increase in the frequency of SCEs was found in splenocytes in the in vivo/in vitro test. The spleen cells contained larger amounts of BP-DNA adducts and demonstrated higher absolute levels of SCEs than bone marrow cells. The sensitivity of both the in vivo/in vitro and the in vivo SCE test is high enough for assessment of Ah locus-linked differences in BP genotoxicity in mice at the prolonged time between treatment and cell preparation. The present data confirm the influence of inducibility of AHH in the intestine on the genotoxicity of BP to distal tissues after oral exposure to BP.

Distribution of methyl and ethyl adducts following alkylation with monofunctional alkylating agents

Alkylating agents, because of their ability to react directly with DNA either in vitro or in vivo, or following metabolic activation as in the case of the dialkylnitrosamines, have been used extensively in studying the mechanisms of mutagenicity and carcinogenicity. Their occurrence is widespread in the environment and human exposure from natural and pollutant sources is universal. Since most of these chemicals show varying degrees of both carcinogenicity and mutagenicity, and exhibit compound-specific binding patterns, they provide an excellent model for studying molecular dosimetry. Molecular dosimetry defines dose as the number of adducts bound per macromolecule and relates the binding of these adducts to the human mutagenic or carcinogenic response. This review complies DNA alkylation data for both methylating and ethylating agents in a variety of systems and discusses the role these alkylation products plays in molecular mutagenesis.

Development and application of biomarkers exploitable for human exposure monitoring

The objectives, applications and limitations of laboratory methods for assessing human exposure to carcinogens are concisely discussed. The available technologies include cytological, cytogenetic and molecular analyses, somatic cell mutation, carcinogen-DNA or carcinogen-protein adducts, metabolic markers, and chemical or biological analyses of expired air, body fluids, and excreta.