Detection of carcinogen-DNA adducts in human cells and antibodies to these adducts in human sera

Immunologic detection of benzo(a)pyrene-DNA adducts

The binding of chemical carcinogens to DNA is well established as the initiating step in the process of carcinogenesis. While early studies in animals or cells in culture took advantage of radiolabeled model carcinogens such as benzo(a)pyrene, interest in measuring DNA damage levels in humans necessitated the development of alternative methods. Among these, immunologic methods using polyclonal or monoclonal antibodies to carcinogen-DNA adducts have proven extremely useful in monitoring human exposure as well as being applicable to animal and cell culture studies. Here we describe the use of antibodies for immunohistochemical analysis of tissue sections, biopsies, or intact cells and for quantitation of carcinogen binding in DNA isolated from blood and tissues by enzyme-linked immunosorbent assays.

Biological monitoring exposure of workers from plant producing carbon electrodes: quantification of benzo[a]pyrene DNA-adducts in leukocytes, by a 32P-postlabelling method and an immunoassay

The levels of benzo[a]pyrene were monitored for blood DNA-benzo[a]pyrene adducts in 17 workers from a plant producing carbon electrodes, with high exposure to benzo[a]pyrene (575-902-1149 ng m(-3)). Two different techniques, a 32P-postlabelling method and a competitive immunoassay using polyclonal antibodies obtained from rabbits immunised with DNA modified by benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide were used. For each worker, urinary 1-hydroxypyrene, a potential indicator of exposure to polycyclic aromatic hydrocarbons, was measured. The effect of tobacco by urinary cotinine measurement was also considered. The postlabelling and immunoassay detection limits for DNA-benzo[a]pyrene adducts were respectively 0.15 and 10 fmol 50 microg(-1) of DNA. The results obtained by the two methods demonstrated a good detection of DNA-benzo[a]pyrene adducts, but no direct relationship between the quantity of adducts and the concentration of benzo[a]pyrene in air-borne was noted in the studied plant. The levels of DNA-benzo[a]pyrene adducts obtained by immunoassay were significantly higher than those obtained by the 32P-postlabelling (P < 0.001). For several workers, variations due to professional or non professional factors must be taken into account in interpreting the results. In conclusion, the two methods used proved very efficient in determining DNA-benzo[a]pyrene adducts, and may be useful in monitoring human exposure to known and previously unidentified environmental genotoxic agents.

Detection of benzo[a]pyrene-DNA adducts in human placenta and umbilical cord blood

Placenta constitutes a vital organ of exchange between mother and foetus. In addition to this favourable effect for foetal development, placenta indirectly may allow transfer of several maternal blood xenobiotics. Human placenta and umbilical cord blood are interesting models for investigating maternal environment and the metabolism, the bioactivation and the transfer of carcinogens such as polycyclic aromatic hydrocarbons. We used them to assess the effect of a woman's smoking on the foetus. Few studies cover this subject. In pregnant women who have continued to smoke, benzo[a]pyrene compound of cigarette smoke is metabolically activated to diol-epoxide derivative: benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide, ultimate carcinogen (BPDE-I). This derivative is covalently fixed on DNA and gives BPDE-I-DNA adducts. By a competitive immunoassay technique, we determined BDPE-I-DNA adducts in 20 samples of placenta and umbilical cord blood from women who smoked (n = 15) and who did not (n = 10). Tobacco consumption was checked by urinary cotinine determination. In the group of smokers levels of adducts were found in 13 specimens of placenta (from 10 to 60 fmol/50 micrograms of DNA) and 12 umbilical cord blood (from 10 to 22.15 fmol/50 micrograms of DNA) samples. These results indicate that a mother's tobacco consumption is linked to the accumulation of BPDE-I-DNA adducts in the placenta, which are seen in smaller quantities in the umbilical cord blood, probably because of the metabolic capacity of the placenta and the transfer of B[a]P from the mother to the foetus.

A sensitive color ELISA for detecting polycyclic aromatic hydrocarbon-DNA adducts in human tissues

Human exposure to polycyclic aromatic hydrocarbons (PAHs) has been determined by measurement of DNA adducts in human tissues. Competitive enzyme-linked immunosorbent assays (ELISAs) using antisera recognizing benzo[a]pyrenediol-epoxide-modified DNA (BPDE-I-DNA) and color of fluorescence endpoint detection have been used extensively for quantifying PAH-DNA adducts. The fluorescence ELISA (limit of detection 1 adduct/10(8) nucleotides) was previously reported to be more sensitive than the color ELISA (1/10(7)) for measuring PAH adducts (Santella et al. (1988) Carcinogenesis, 9, 1265-1269). However, the fluorescence assay has the disadvantages of greater variation among the replicates and higher background levels than the color assay. Using a newly developed antiserum against BPDE-I-DNA, we have modified the color of ELISA so that it has the same sensitivity as the fluorescence ELISA and requires only 33% of the sample quantity needed for the fluorescence ELISA. The modifications included preincubation of the antiserum with the samples, using microtiter plates with half-size, flat bottom wells, and optimizing the assay conditions. The improved color ELISA was used to analyze DNA samples from human autopsy tissues, including heart, lung, liver, kidney, spleen, pancreas and stomach from smokers and nonsmokers. With the exception of spleen and stomach, all tissues from smokers showed higher PAH-DNA adducts (ranging from 0.3 to 19.0 adducts/10(7) nucleotides) than the tissues from the nonsmokers (0.3 to 3.7 adducts/10(7) nucleotides) in two separate experiments. Among the tissues from smokers, heart showed the highest level of DNA adducts. This study demonstrates that a stable color ELISA with high sensitivity can be useful in assessing human exposure to PAH.

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.

Antisera specific for carcinogen-DNA adducts and carcinogen-modified DNA: applications for detection of xenobiotics in biological samples

The development of immunoassays and immunoaffinity chromatography methods for determination of carcinogen-DNA adducts and carcinogen-modified DNA samples rests upon eliciting and characterizing polyclonal and monoclonal antisera against these haptens. The use of such antisera has widespread application in investigating chronic carcinogen administration in animal models and in monitoring human tissues for evidence of carcinogen exposure. Radioimmunoassays and enzyme-linked immunosorbent assays developed with carcinogen-DNA adduct antisera are exceedingly sensitive, measuring 1 adduct in 10(8) nucleotides. Not only can DNA damage be quantified directly by immunoassay, but the antisera have also been used to isolate DNA adducts of a particular chemical class by immunoaffinity chromatography before application of more chemically-specific end-points. Both of these methodological approaches have made seminal contributions to the newly-emerging field of molecular epidemiology. This chapter will focus on methods for preparing immunogens, the establishment of immunoassays, characterization of antisera and specific problems encountered with biological samples in addition, the use of immunoaffinity chromatography for preparative concentration of DNA adducts of a particular class will be included.

Interception of reactive, DNA adduct-forming metabolites present in rodent serum following carcinogen exposure: implications for use of body fluids in biomonitoring

The detection of adduct-forming metabolites in the serum of carcinogen treated animals by 32P-postlabeling was evaluated as a novel approach to overcome the stringent requirement of obtaining DNA from tissues in human biomonitoring assessments. Benzo[a]pyrene (BP) was given i.p. to B6C3F1, C57B1/6, ICR, and DBA/2 mouse strains as well as Sprague-Dawley rats. Three adducts related to BP were detected in the liver and/or lung of Sprague-Dawley rats or B6C3F1, C57B1/6, and ICR mice; a single adduct was detected in the liver and lung of the DBA/2 mouse strain. Adducts chromatographically similar to those found in these tissues were also detected when salmon sperm DNA was incubated with the serum of BP-treated animals. Benzidine treatment induced the formation of one adduct in the liver of B6C3F1 mice, which was chromatographically similar to dG-C8-N'-acetylbenzidine. An identical adduct was detected in the salmon sperm DNA incubated with the serum of these mice. Cyclopenta[cd]pyrene treatment produced four major and three minor adducts in the liver or lung of B6C3F1 mice, all but two of which were detected in DNA incubated with serum of cyclopenta[cd]pyrene-treated animals. Large interstrain differences in the serum level of BP adduct-forming metabolites as well as tissue DNA adducts were found which correlated with previously observed strain-specific trends in sensitivity to PAH-mediated carcinogenesis. Thus, levels of BP adduct-forming metabolites were found in the following descending order: B6C3F1, C57B1/6, ICR, and DBA/2. BP-derived adduct-forming metabolites were detectable as late as 2 d and 5 d post-treatment in the serum of C57B1/6 mice or Sprague-Dawley rats, respectively, which seems to coincide well with the reported species-specific turnover of serum albumin; a protein know to be involved in the transport of reactive metabolites throughout the systemic circulation. The results obtained clearly indicate the presence of adduct-forming carcinogen metabolites in the serum of treated animals, which seemingly irrespective of their chemical nature, can be intercepted with exogenous DNA and detected by 32P-postlabeling. Successful application of a serum-based approach coupled with the use of the generally applicable, ultrasensitive 32P-postlabeling assay could evade the need for obtaining DNA from tissues, currently the major impediment in human biomonitoring studies.

Monitoring human exposure to carcinogens by DNA adduct measurement

Sensitive immunologic techniques are now available for the detection and quantitation of carcinogen-DNA adducts. We have developed a number of specific monoclonal antibodies which recognize DNA modified by particular carcinogens, including benzo[a]pyrene, aminopyrene, 8-methoxypsoralen plus UVA light and vinyl chloride. These antibodies can be used in competitive enzyme-linked immunosorbent assays to quantitate adducts in DNA isolated from biological samples. Samples from treated animals as well as from humans with occupational or environmental exposure to carcinogens have been studied. In addition, antibodies can be used in indirect immunohistochemical studies to localize adduct formation in various tissues or cell types.

Detection of benzo[a]pyrene diol epoxide-DNA adducts in human placenta

Human placenta is a readily available organ that responds to maternal environmental insult and has been previously used to investigate metabolism and bioactivation of procarcinogens, for example, benzo[a]pyrene. HPLC in combination with synchronous fluorescence spectroscopy was used to examine 28 placentas for the presence of benzo[a]pyrene diol epoxide-DNA adducts, and 10 of these were found to be positive. DNA samples from these placentas were subsequently pooled and subjected to partial enzymatic digestion to oligonucleotide fragments. Concentration of those DNA fragments containing benzo[a]pyrene diol epoxide-DNA adducts was achieved by immunoaffinity chromatography with polyclonal antibodies raised against these adducts. Column eluates were hydrolyzed under mild acid conditions and extracted with an organic solvent. The presence of benzo[a]pyrene-7,10/8,9-tetrahydrotetrol residues in the extracts was determined by HPLC and synchronous fluorescence spectroscopy and was confirmed by GC/MS. The results unequivocally confirm bioactivation and formation of DNA adducts from benzo[a]pyrene in human placenta in vivo and establish a methodological approach to direct measurement of carcinogen-DNA adducts that are formed as a result of human environmental exposure.

Application of new techniques for the detection of carcinogen adducts to human population monitoring

Several techniques have recently been developed for the detection and quantitation of carcinogen-DNA or -protein adducts without the requirement for radioactive carcinogens. These assays can be used to detect adducts in animals or cultured cells exposed to test compounds or in humans exposed to environmental carcinogens. Immunologic, 32P-postlabeling and fluorescence techniques, used on human samples for DNA adduct measurement, are reviewed here. Methods for the detection of carcinogen-protein adducts on human samples are also summarized.

Chemical carcinogenesis: from animal models to molecular models in one decade

During the last decade, progress in chemical carcinogenesis research has been substantial, and understanding the cellular changes and molecular causes of initiation, promotion, and malignant conversion appears to be within reach. Cancer begins as a carcinogen-induced genetic change in a single cell. The interaction of a particular carcinogen with specific genetic sites results, in part, from selectivity of metabolically activated carcinogens for particular nucleosides or gene sequences. In turn, modification of the molecular structure at specific genetic loci will have tissue-specific and species-specific consequences dependent on the expression of a particular gene, its sequence, and the function of the gene product in the target cell. It is likely that inactivation of regulatory regions, genomic rearrangements, and point mutations in coding sequences all can result in an altered cell phenotype. The rasH gene (and perhaps other members of the ras gene family) appears to be a common target for coding sequence mutations in the initiation of carcinogenesis in several organ sites and species by specific carcinogens. Whatever genetic mechanisms are involved, an initiated cell phenotype common to many epithelial cell types is observed. Initiated cells have an altered program of terminal differentiation, are resistant to cytotoxic substances or show altered requirements for specific growth factors or nutrients. These cells would have a selective growth advantage in cytostatic or cytotoxic situations or under conditions favoring terminal differentiation. Tumor promoters, some acting through specific cellular receptors, produce a tissue environment conductive to the selective clonal outgrowth of the initiated cell population resulting in a clinically evident premalignant lesion. The tissue specificity for most promoters depends on the ability of a particular agent to produce the selective conditions required for the initiated phenotype of that organ. At the molecular level, phorbol ester tumor promoters bind to and activate protein kinase C and transduce signals through this second-messenger pathway. Heterogeneity in the species of protein kinase C molecule expressed by normal and initiated epidermal cells could account for the differential response pattern observed in these cell types during skin tumor promotion. Malignant conversion of benign tumors requires further genetic changes in the tumor cell. Such changes could result from inherent instability in the genome of initiated cells, from spontaneous mutations more likely to occur in the expanding population of proliferating benign tumor cells, or by additional exposure to exogenous genotoxic agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical and molecular epidemiology of human cancer: indicators of carcinogen exposure, DNA damage, and genetic predisposition

The primary goal of biochemical and molecular epidemiology is to identify individuals at high cancer risk by obtaining evidence of high exposure to carcinogens, leading to pathobiological lesions in target cells, and/or increased oncogenic susceptibility due to either inherited or acquired host factors. This emerging and multidisciplinary area of cancer research combines epidemiological and laboratory approaches. Because DNA is considered to be an important target for modification by mutagens and carcinogens, damage to DNA can be used as an internal, molecular dosimeter of carcinogen exposure. The reactive species of these carcinogens may directly bind to DNA to form adducts and may indirectly cause secondary DNA lesions, e.g., via induction of free radicals and aldehydes. Highly sensitive and specific methods have been developed to measure the minute amounts of DNA lesions and DNA repair products found in biological specimens from humans exposed to carcinogens. For example, DNA adducts have been measured in cells and tissues from people occupationally exposed to carcinogenic polycyclic aromatic hydrocarbons. Antibodies recognizing carcinogen-DNA adducts have also been detected in human sera. Inherited predisposition to cancer has been revealed by recent advances in molecular genetics, including restriction-fragment-length polymorphism. For example, the hypothesis that rare alleles of the Ha-ras proto-oncogene are associated with an increased risk of lung cancer is currently being tested. These approaches afford the potential of biochemical and molecular epidemiology to predict disease risk for individual persons, instead of for populations, and before the onset of clinically evident disease.