HPLC/fluorescence determination of anti-BPDE-DNA adducts in mononuclear white blood cells from PAH-exposed humans.
The aim of this study was to compare (+/-)-r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE)-DNA adduct levels in groups of humans subjected to various levels of polycyclic aromatic hydrocarbon (PAH) (benzo[a]pyrene) exposure. An HPLC/fluorescence method was applied to detect specifically anti-BPDE-DNA adducts in mononuclear white blood cells [lymphocyte plus monocyte fraction (LMF)] from humans exposed to PAHs. A total of 130 subjects comprised the sample population: 26 psoriatic patients (3 days after clinical coal tar treatment of the skin), 15 coke oven workers, 19 chimney sweeps, 36 aluminium anode plant workers and 34 non-occupationally PAH-exposed subjects (controls). PAH exposure was assessed in each group by means of the urinary excretion of 1-pyrenol (mean group levels: 1.2, 0.7, 0.3, 65.0 and 0.1 micromol/mol creatinine in coke oven workers, chimney sweeps, aluminium plant anode workers, psoriatic patients and non-occupationally PAH-exposed subjects, respectively). HPLC/fluorescence analysis of BPDE-DNA adducts showed that the percentage of subjects with adduct levels exceeding the 95 percentile control subject value (8.9 adducts/10(8) nucleotides) was significantly high in coke oven workers (46.7%) and chimney sweeps (21.0%) (chi2 test, P < 0.01 and P < 0.05, respectively) but not in aluminium plant workers (11.1%) and psoriatic patients (0%). The increase in BPDE-DNA adduct levels in LMF (Ln values) was significantly related to chronic inhalatory and high PAH exposure (linear multiple regression analysis, F = 6.37, P < 0.01; t = 4.2, P < 0.001). Skin acute (or short-term) and high PAH exposure, charcoal-grilled meat consumption and smoking habit did not seem to influence BPDE-DNA adduct formation in LMF. (+info
Structure-activity relationship of schisandrins in enhancing liver mitochondrial glutathione status in CCl4-poisoned mice.
AIM: To explore whether the methylenedioxy group and cyclooctadiene ring of the dibenzocyclooctadiene skeleton of schisandrins (Sch) play a role in the liver mitochondrial glutathione status enhancing activity. METHOD: The effects of three dibenzocyclooctadiene derivatives, Sch A, Sch B, Sch C, and a synthetic intermediate of Sch C, (dimethyl biphenyl dicarboxylate, DBD) on carbon tetrachloride (CCl4)-hepatotoxicity and liver mitochondrial glutathione status were examined in mice. RESULTS: Pretreating mice with intragastric Sch B, Sch C, or DBD 1.mmol.kg-1.d-1 for 3 d protected against CCl4-hepatotoxicity. The hepatoprotection afforded by Sch B or Sch C pretreatment was associated with increases in liver mitochondrial reduced glutathione (mtGSH) level and glutathione reductase (mtGRD) activity, an indication of enhanced mitochondrial glutathione status. In contrast, the hepatoprotective action of DBD was not accompanied by any detectable changes in mtGSH level and mtGRD activity. CONCLUSION: Both the methylenedioxy group and the cyclooctadiene ring of the dibenzocyclooctadiene molecule are important structural determinants in the enhancement of liver mitochondrial glutathione status. (+info
Dose-dependent preferential binding of polycyclic aromatic hydrocarbons to reiterated DNA of murine skin cells in culture.
The distribution of active metabolites of polycyclic aromatic hydrocarbons bound to reiterated or unique regions of murine DNA has been studied by a DNA-DNA renaturation technique. Murine skin cells were exposed to different doses of radioactive polycyclic aromatic hydrocarbons for 24 hr; then the hydrocarbon-labeled DNA was isolated, fragmented, and denatured. Renaturation kinetics and thermal stabilities of DNA-DNA duplexes were studied. At high carcinogen doses, polycyclic aromatic hydrocarbon adducts seem to be distributed equally among the DNA of all reiteration frequencies. At low carcinogen doses, however, a dose-dependent preferential binding to reiterated DNA sequences occurs. An inverse linear relationship appears to exist between the enrichment of hydrocarbon adducts in reiterated DNA sequences and the logarithm of the amount of total hydrocarbon bound to DNA. (+info
Cancer initiation by polycyclic aromatic hydrocarbons results from formation of stable DNA adducts rather than apurinic sites.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants with high carcinogenic potencies that have been linked to the etiology of human cancers through their presence in cigarette smoke and environmental mixtures. They are metabolically activated in cells by cytochrome P450 enzymes and/or peroxidases to reactive intermediates that damage DNA. One pathway of activation forms dihydrodiol epoxides that covalently bind to exocyclic amino groups of purines in DNA to form stable adducts. Another pathway involves formation of radical cations that bind to the N7 or C8 of purines to form unstable adducts that depurinate to leave apurinic (AP) sites in DNA. In the present study the proportions of stable DNA adducts and AP sites formed by the carcinogenic PAHs dibenzo[a,l]-pyrene (DB[a,l]P), 7,12-dimethylbenz[a]anthracene (DMBA), and benzo[a]pyrene (B[a]P) have been investigated in a target tissue for carcinogenesis, mouse epidermis. After topical application of the PAHs on the skin of female SENCAR mice epidermal DNA was isolated and the formation of stable DNA adducts was measured by (33)P-postlabeling and HPLC analysis. AP sites in DNA were measured with an aldehyde reactive probe in a slot-blot assay. At both 4 and 24 h after exposure, DB[a,l]P formed significantly higher amounts of stable DNA adducts than DMBA, and B[a]P exhibited the lowest level of binding. In contrast, the number of AP sites present in mice treated with these PAHs was in the order: DMBA > B[a]P >> DB[a,l]P. The level of AP sites was significantly lower than the level of stable adducts for each PAH. The most potent carcinogen, DB[a,l]P, induced the highest level of stable adducts and the lowest level of AP sites in epidermal DNA. These results indicate that stable DNA adducts rather than AP sites are responsible for tumor initiation by carcinogenic PAHs. (+info
Environmental pollution and human exposure to polycyclic aromatic hydrocarbons in the east Baltic region.
Environmental contamination by polycyclic aromatic hydrocarbons (PAH) and human exposure were surveyed in the east Baltic region. Polluted and heavily industrialized areas are upper Silesia in Poland, northern Bohemia in the Czech Republic, and the northeast part of Estonia. In Estonia the pollution is in a defined geographic area, where lung cancer incidence is higher than elsewhere. In Silesia, exposure of some 5 million people appears to be elevated; DNA (deoxyribonucleic acid) adduct levels in white blood cells are increased in groups of residents with apparently only environmental exposure. By extrapolation, some 150 annual lung cancer cases could be predicted due to PAH in Silesia. Air levels of benzo[a]pyrene were increased in northern Bohemia, and domestic heating and power plants using brown coal appeared to be major contributors to particulate air pollution in winter. Further studies are needed to assess health risks of PAH exposure in central and eastern Europe. (+info
Alternative pathways of polycyclic aromatic hydrocarbons activation: the formation of polar DNA adducts.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, and some are potent carcinogens in rodents. Carcinogenic PAHs are activated in the cells to metabolites that react with DNA to form covalent adducts. For most PAHs the reactive, electrophilic species which bind to DNA, are bay-region diol-epoxides. Application of 32P-postlabeling to PAH-DNA adducts analysis revealed that for some PAHs the adduct profiles generated in model systems are more complex and include adducts which are more polar than those formed by classic bay-region diol-epoxides. This minireview summaries the information gained on typical representatives of polar PAH-DNA adducts. Formation of triol-epoxide-DNA adducts was proposed for chrysene and a non-alterant PAH, benzo[b]fluoranthene (B[b]F). 5-OH-B[b]F, the precursor of B[b]F triol-epoxide, was found to be a potent tumor initiator in mouse skin. For planar PAHs such as dibenzanthracenes the possibility of bis-diol epoxide-DNA adducts formation was suggested. The most comprehensive data were obtained for dibenz[a,j]anthracene (DB[a,j]A). This hydrocarbon when applied to SENCAR mouse skin forms up to 23 species of adducts, most of which are polar. Among these polar adducts seven were identified as derived from DB[aj]A-3,4-10,11-bis-diol. Analysis of tumor-initiating activity showed, however, that this proximate metabolite was inactive in this respect. In contrast, an excellent correlation was observed between levels of less polar DNA adducts (i.e. those derived from bay-region diolepoxides) and skin tumor initiating activity of DB[a,j]A. Thus, while triol-epoxides seems to be involved in tumor initiating activity of the parent compound, non alterant B[b]F, the significance of bis-diol epoxide-DNA adducts, at least those derived from DB[aj]A, is minor. (+info
Mutability of different genetic loci in mammalian cells by metabolically activated carcinogenic polycyclic hydrocarbons.
The relationship between carcinogenesis and mutagenesis in mammalian cells has been determined with 10 polycyclic hydrocarbons with different degrees of carcinogenicity. Mutagenesis was determined in Chinese hamster cells with genetic markers that affect the surface membrane, nucleic-acid synthesis, and protein synthesis. The mutations were characterized by resistance to ouabain, 8-azaguanine, and temperature. Mutagenesis by the carcinogens required metabolic activation and this was provided by the presence of lethally irradiated metabolizing cells. The degree of carcinogenicity was related to the degree of mutagenicity for all three genetic markers. The most potent carcinogen, 7,12-dimethylbenz[a]anthracene, gave the highest mutagenicity and mutagenicity was obtained with 0.01 mug/ml. Treatment of the cells with aminophylline, which increases polycyclic hydrocarbon metabolism, increased mutagenesis by the carcinogens. It is suggested that such an experimental system with these and other mammalian cells should be useful as a sensitive assay for hazardous environmental chemicals. (+info
Effect of plant matrix and fluid ethanol concentration on supercritical fluid extraction efficiency of schisandrin derivatives.
An investigation of the effect of plant matrix on the supercritical fluid extraction efficiency of five schisandrin derivatives is reported, exhibiting a great difference with respect to extraction efficiency depending on the matrix. Pure supercritical CO2 at 60 degrees C and 34.0 MPa cannot fully recover schisandrin derivatives from the leaves as much as from the other matrices. Only 36.9% of these compounds are extracted from leaves of Schisandra chinensis by supercritical CO2 in comparison with organic solvent extraction. However, more than 80% of schisandrin derivatives are obtained from both stem and fruit parts. Ethanol addition also shows a different effect depending on plant matrix; that is, CO2 modified with 10% ethanol could enhance the yield of schisandrin derivatives from leaves by four times when compared with that of pure CO2, but it has little effect on both stems and fruits. (+info