Einfluß der Gehirnerschütterung auf den Übertritt von Methylenblau aus dem Blut in das Gehirn bei der Katze

Schwere Gehirnerschütterungen verringern bei der Katze den Übergang von Methylenblau aus dem Blut in das Hirngewebe. Durch Cocain wird diese Wirkung nicht beeinflußt. Die Ursache des verringerten Farbstoffübertrittes ist nicht auf eine Abdichtung der Blut-Hirn-Schranke, sondern wahrscheinlich auf eine trauma-bedingte, langanhaltende Stoffwechselstörung, welche die Reduktionsgeschwindigkeit von Methylenblau zu Leukomethylenblau herabsetzt, zurückzuführen.

A 32P-postlabeling assay for the oxidative DNA lesion 8,5'-cyclo-2'-deoxyadenosine in mammalian tissues: evidence that four type II I-compounds are dinucleotides containing the lesion in the 3' nucleotide

8,5'-Cyclopurine-2'-deoxynucleotides, which are strong blocks to mammalian DNA and RNA polymerases, represent a novel class of oxidative DNA lesion in that they are specifically repaired by nucleotide excision repair but not by base excision repair or direct enzymatic reversion. Previous studies using thin layer chromatography of (32)P-postlabeled DNA digests have detected several bulky oxidative lesions of unknown structure, called I-compounds, in DNA from normal mammalian organs. We investigated whether any of these type II I-compounds contained 8,5'-cyclo-2'-deoxyadenosine (cA). Two previously detected type II I-compounds were found to be dinucleotides of the sequence pAp-cAp and pCp-cAp. Furthermore, a modification of the technique resulted in detection of two additional I-compounds, pTp-cAp and pGp-cAp. Each I-compound isolated from neonatal rat liver DNA matched authentic (32)P-labeled cA-containing chromatographic standards under nine different chromatographic conditions. Their levels increased significantly after normal birth. The (32)P-postlabeling technique used here is capable of detecting 1-5 lesions/diploid mammalian cell. Thus, it should now be possible to detect changes of cA levels resulting from low level ionizing radiation and other conditions associated with oxidative stress, and to assess cA levels in tissues from patients with the genetic disease xeroderma pigmentosum who are unable to carry out nucleotide excision repair.

Effects of dietary transition metals on oxidative DNA lesions in neonatal rats

Bulky endogenous oxidative lesions (type II I-compounds) reflect DNA damage associated with oxidative stress. As shown by 32P-postlabeling, their levels are enhanced by pro-oxidant genotoxins and also shortly after normal birth in several rat tissues as a function of time and the maternal diet. In order to elucidate which dietary components contribute to postnatal DNA damage, we have focused, herein, on the possible role of transition metals (iron, copper, and nickel). Pregnant Fischer 344 (F344) rats were fed AIN-93G purified diet containing different amounts of iron, copper, and nickel, or Purina-5001 natural-ingredient diet (which contains relatively high concentrations of these metals). Type II I-compounds were estimated by nuclease P1-enhanced 32P-postlabeling in liver and lung DNA of fetuses and at 24h and day 9 post-partum. Increased postnatal oxidative damage was detected in liver but not lung DNA of neonates exposed to higher amounts of dietary transition metals. There were significant positive linear correlations between maternal transition metal intake and neonatal, but not fetal and maternal type II I-compound levels. The results show that transition metals in the maternal diet affect perinatal oxidative DNA damage, presumably via a Fenton-type reaction. They also provide evidence for optimal levels in the maternal diet of transition metals, which on one hand, are essential for life, but on the other, can cause potentially deleterious DNA alterations in the offspring.

Effects of different diets and dietary restriction on perinatal endogenous DNA adducts. Time dependence of oxidative and presumptive nonoxidative lesions

Type II I-compounds (indigenous DNA adducts) denote a class of bulky oxidative DNA lesions that are detectable by 32P-postlabeling and represent useful biomarkers of DNA damage induced by oxidative stress. Their levels are increased in tissue DNA under pro-oxidant conditions, for example, as previously shown, in newborn rat organs. Here we have investigated whether the maternal diet affects perinatal type II I-compound levels. Pregnant F344 rats were fed Purina-5001 natural-ingredient or AIN-93G purified diet from day 11 of gestation. Type II I-compounds were measured in liver DNA at three different developmental stages, i.e., fetus, and 24 h and 9 days postnatally. Higher adduct levels were detected in the Purina-5001 group at each stage. In a second experiment, pregnant F344 rats were subjected to dietary restriction (DR) (by 40%; Purina-5001) from day 12 of gestation. At 24 h postpartum hepatic type II I-compound levels were decreased compared to parallel ad libitum (AL) fed controls. As an unrelated observation, fetal lung, but not liver, kidney, and skin DNA contained a different pattern of nonpolar, apparently nonoxidative adducts, which were not diet-dependent. These spots were not detectable 24 h after birth and were observed at much reduced levels and only in a few samples at 9 days. The main results show for the first time that the maternal nutrition modulated levels of oxidative lesions in fetal and neonatal DNA, but the underlying mechanisms (e.g., differences in metal or caloric content of the diets) still need to be determined. The dietary effects were apparently transmitted through both placenta and the mother's milk.

Acute elevation by short-term dietary restriction or food deprivation of type I I-compound levels in rat liver DNA

Type I I-compounds are bulky endogenous DNA modifications detectable by 32P postlabeling that exhibit age, species, tissue, genotype, gender, and diet dependence. Their formation appears unrelated to oxidative stress. In fact, several lines of indirect evidence suggest that many type I I-compounds may represent normal functional DNA modifications. For example, long-term dietary restriction (DR), which retards the development of age-related diseases including cancer and extends median and maximum life spans, unexpectedly elicits significant increases rather than decreases in the levels of many I-compounds in different rodent tissues. Positive linear correlations have been observed between such levels and median life spans of the animals. In the present work we have investigated 1) whether elevation of I-compound levels does not depend on chronic DR, i.e., occurs after a short period of DR or fasting, and 2) whether I-compound levels return to control values after the animals are returned to unrestricted feeding after food deprivation. Female Fischer 344 rats (approx 140 g each) were randomized into three groups. Group I was fed a natural ingredient (Purina 5001) diet ad libitum (AL) throughout the study, Group 2 was switched to 60% of the AL amount (40% DR) at 0 hour, and Group 3 was given no food for up to 72 hours and then returned to AL feeding until the end of the experiment. Liver DNA of individual rats (n = 4) was isolated for I-compound analysis at 24, 72, and 240 hours. Restricted and food-deprived rats showed elevated levels of hepatic I-compounds, with fasting eliciting the highest levels. These effects were seen as early as the 24-hour time point. Refeeding after 72 hours of food deprivation restored the levels to control values, measured at 240 hours. Our observations are discussed in relation to carcinogenesis and tumor promotion. The almost instantaneous changes of endogenous DNA modifications showed their exquisite sensitivity to nutritional factors and provided strong new evidence for precise regulation of their formation and removal.

Endogenous formation and significance of 1,N2-propanodeoxyguanosine adducts

The detection of 1,N2-propanodeoxyguanosine adducts in the DNA of rodent and human tissues as endogenous lesions has raised important questions regarding the source of their formation and their roles in carcinogenesis. Both in vitro and in vivo studies have generated substantial evidence which supports the involvement of short- and long-chain enals derived from oxidized polyunsaturated fatty acids (PUFAs) in their formation. These studies show that: (1) the cyclic propano adducts are common products from reactions of enals with DNA bases; (2) they are formed specifically from linoleic acid (LA; omega-6) and docosahexaenoic acid (omega-3) under in vitro stimulated lipid peroxidation conditions; (3) the levels of propano adducts are dramatically increased in rat liver DNA upon depletion of glutathione; (4) the adduct levels are increased in the liver DNA of the CCl4-treated rats and the mutant strain of Long Evans rats which are genetically predisposed to increased lipid peroxidation; and (5) adduct levels are significantly higher in older rats than in newborn rats. These studies collectively demonstrate that tissue lipid peroxidation is a main endogenous pathway leading to propano adduction in DNA. The possible contribution from environmental sources, however, cannot be completely excluded. The mutagenicity of enals and the mutations observed in site-specific mutagenesis studies using a model 1,N2-propanodeoxyguanosine adduct suggest that these adducts are potential promutagenic lesions. The increased levels of the propano adducts in the tissue of carcinogen-treated animals also provide suggestive evidence for their roles in carcinogenesis. The involvement of these adducts in tumor promotion is speculated on the basis that oxidative condition in tissues is believed to be associated with this process.

Bulky endogenous DNA modifications (I-compounds) -possible structural origins and functional implications

I-compounds are bulky covalent DNA modifications which increase with age in tissues of unexposed laboratory animals and are derived from endogenous DNA-reactive intermediates of nutrient and oxygen metabolism. They have been classified into 2 major groups, i.e., type I and type II. Profiles and levels of type I I-compounds show considerable variation depending on species, strain, tissue, and gender, but are also affected by diet and chemical and hormonal exposures, indicating their formation to be determined by genetic and environmental factors. For example, sex hormones, dietary oat lipids, and isoprenoids affect their profiles and/or levels in tissue DNA. A gradual depletion of many type I I-compounds occurs during carcinogenesis, as many carcinogens/tumor promoters significantly reduce their levels, and neoplasms display very low levels, apparently independent of growth rate, indicating a loss of the ability to form these modified nucleotides. Conversely, dietary restriction, the most effective method to retard carcinogenesis and aging, significantly elevates type I I-compound levels, as compared to age-matched ad libitum-fed animals. Levels of many liver and kidney I-compounds exhibit genotype- and diet-dependent positive linear correlations with median life span. Formation of high levels of oat-related type I I-compounds has been associated with reduced formation of carcinogen-induced preneoplastic hepatic foci. These results suggest that such DNA modifications may not represent DNA lesions but may rather be functionally important. This view is supported by circadian rhythms displayed by some I-compounds. Thus, certain type I I-compounds may play a protective role against carcinogenesis and age-associated degenerative processes. Type II I-compounds, on the other hand, represent DNA damage and include several bulky lesions, which are enhanced by pro-oxidant carcinogens such as ferric nitrilotri- acetate (Fe-NTA) in target organ (kidney) DNA of rodents and are identical to products generated by oxidizing DNA or oligonucleotides under Fenton reaction conditions in vitro. Some of these products appear to be base-base or base-sugar intrastrand crosslinks. Notably, Fe-NTA reduces the levels of type I I-compounds in renal DNA. Type II I-compound levels are increased in tissue DNA of normal newborn rats. The formation of oxidative DNA lesions in neonates is most likely caused by oxidative stress associated with the sudden increase of partial oxygen pressure in arterial blood and tissues at birth. In view of the rapid cell replication at this developmental stage, endogenous oxidative DNA lesions sustained early in life may contribute to the development of cancer and degenerative diseases later in life.

Genotoxicity of complex PAH mixtures recovered from contaminated lake sediments as assessed by three different methods

Although human exposure generally occurs to mixtures of chemicals, limited toxicological information is available to characterize the potential interactions of the components of environmental mixtures. This study was conducted to compare the genotoxicity of chemically characterized polycyclic aromatic hydrocarbon (PAH) mixtures using in vitro and in vivo techniques. A total of three extracts (E1-E3) were selected from sediment samples collected from a lake adjacent to an abandoned coal gasification site. Sediments were collected on a grid moving downstream and away from the most likely source of PAH contamination, with E1 collected closest to the shore, E2 at an intermediate distance, and E3 furthest from the shore. The sediment samples were extracted in methylene chloride and methanol, dried, and redissolved in an appropriate solvent for evaluation in a battery of genotoxicity assays. Samples were evaluated for their ability to produce point mutations in bacteria and DNA adducts in vitro without metabolic activation or in vivo. Samples were also analyzed using GC/MS. Sample E1 had both the highest concentration of benzo(a)pyrene (BP) (46.5 ppm) and carcinogenic PAHs and, using 32P-postlabeling, induced the highest adduct levels overall in vitro and in vivo. Sample E2, which had a BP concentration of 14 ppm, induced the greatest number of revertants in the bacterial mutagenicity assay. Sample E3, which had the lowest level of carcinogenic PAHs and BP, induced the lowest adduct levels. However, E3 was capable of inducing a positive genotoxic response in bacteria (with S9), although the slope of the response at lower doses was less than that of E2. The in vivo data showed that the major adduct formed by E1 and E2 was a BP adduct. This information could not have been obtained with the Salmonella or in vitro postlabeling tests. Among internal organs, the extracts of all three samples induced the greatest adduct levels in the lung, similarly to previous complex PAH mixtures studied. These data demonstrate the limitations of predicting genotoxic or carcinogenic potential based on chemical analysis or a single biological test. The results suggest that mixture interactions, cytotoxicity and metabolism are likely to have an influence on the potential of a complex mixture of chemicals to produce a carcinogenic effect. In addition, the concentration of genotoxic PAHs and both in vitro and in vivo DNA adduct formations were decreased with increasing distance from the shoreline.

High levels of endogenous DNA adducts (I-compounds) in pig liver. Modulation by high cholesterol/high fat diet

I (indigenous)-compounds are bulky endogenous DNA adducts which are detected by 32P-postlabeling in unexposed animals. I-compound levels in rodents depend on age, species, strain, gender, tissue, diet, and chemical exposure. There are two classes of I-compounds, type I and type II. While many type I I-compounds may not reflect DNA damage, type II I-compounds have been identified as oxidative DNA lesions some of which can be produced in vitro under Fenton reaction conditions. In rats, caloric restriction (CR) increases the levels of many type I I-compounds compared with ad libitum fed animals, while high fat diet has the opposite effect. Here, we have tested whether hepatic DNA of a non-rodent mammal, the pig, contains I-compounds and whether feeding a high cholesterol/high fat (HC/HF) diet modulates their levels, assuming this would affect the formation of lipid-related precursors and cause oxidative stress. Male Yorkshire pigs aged 2 months old, were fed either control or HC/HF diet (control diet supplemented with 2% cholesterol and 19% lard) for 2 months. Pig liver DNA contained at least 19 type I and five type II I-compounds. Among the former, only five matched corresponding spots in rat liver DNA, while all the latter DNA lesions were detected in both species. The levels of both types of DNA modifications were six to eight-fold higher in pig DNA. HC/HF diet reduced levels of many type I I-compounds up to several fold but had little effect on the oxidative lesions. Several type I I-compounds showed negative linear correlations with serum cholesterol levels, while this association was positive for total type II I-compounds. The substantially elevated steady-state levels of bulky endogenous DNA adducts in the species with the longer life expectancy were surprising. Thus, for the first time, an intimate link between nutritional status and endogenous DNA modifications has been established in a non-rodent system. We propose that in order to explain our observations, differences in diet composition, antioxidant defenses, and DNA repair, as well as cytochrome P450 modulation of precursor levels and hormonal effects need to be considered.

Partial characterization of two major liver I-compounds as unstable adducts which are readily hydrolyzed to unmodified guanine nucleotides

I-compounds are endogenous bulky DNA modifications which are detected by nuclease P1-enhanced 32P-post-labeling in tissue DNA of animals not knowingly exposed to carcinogens. Their profiles and levels depend inter alia on animal age, species, strain, tissue, gender, diet and exposure to chemicals such as cytochrome P450 inducers and carcinogens. Due to lack of sufficient material obtainable from in vivo sources, chemical structures of I-compounds and their parent normal bases have not yet been identified. In this report we provide 32P-post-labeling and chromatographic evidence that two prominent I-compounds, herein called C1 and C2, which occur at relatively high levels in pig liver DNA are guanine derivatives. This result was obtained by showing that both compounds, isolated from 32P-post-labeling thin-layer maps, were chemically unstable, i.e. they could be readily hydrolyzed to 32P-post-labeled deoxyguanosine 3',5'-bisphosphate by heating in water. C1 appeared particularly labile, undergoing hydrolysis during thin-layer chromatography at pH 3.3 without heating. Several other I-compounds and adducts, as well as the four normal DNA nucleotides, were, however, highly resistant to hydrolysis under the conditions used here. The possible significance of these findings will be briefly discussed.

Inhibition of CYP1A1-dependent activity by the polynuclear aromatic hydrocarbon (PAH) fluoranthene

Polynuclear aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants, and recently bioassay-based induction studies have been used to determine exposures to complex mixtures of PAHs. Induction of CYP1A1-dependent activity in H4IIE rat hepatoma cells has been used extensively as a bioassay for halogenated aromatic hydrocarbons and more recently for PAHs. Fluoranthene (FL) is a prevalent PAH contaminant in diverse environmental samples, and FL did not induce CYP1A1-dependent ethoxyresorufin O-deethylase (EROD) activity significantly in H4IIE cells. However, in cells cotreated with 2 x 10(-5) M FL plus the potent inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or benzo[k]fluoranthene (BkF) (2 x 10(-8) M), there was a significant decrease in EROD activities. Furthermore, treatment of TCDD-induced rat microsomes with FL caused an 80% decrease in EROD activity. Studies showed that FL did not affect induction of CYP1A1 protein or mRNA levels in H4IIE cells, and analysis of enzyme inhibition data using microsomal CYP1A1 indicated that FL noncompetitively inhibited CYP1A1-dependent activity. 32P-Postlabeling revealed no significant FL-DNA adduct formation in H4IIE cells treated with FL. However, in cells cotreated with FL plus BkF or benzo[a]pyrene (BaP), certain PAH-DNA adducts were induced 2-fold. This study demonstrated that FL is an inhibitor of CYP1A1-dependent enzyme activity in rat hepatoma H4IIE cells and that the genotoxic potency of some carcinogenic PAHs may be modulated by FL in mixtures containing relatively high levels of this compound.

Comparison of immunoaffinity chromatography enrichment and nuclease P1 procedures for 32P-postlabelling analysis of PAH-DNA adducts

32P-postlabelling analysis for detecting DNA adducts formed by polycyclic aromatic compounds is one of the most widely used techniques for assessing genotoxicity associated with these compounds. In cases where the formation of adducts is extremely low, a crucial step in the analysis is an enrichment procedure for adducts prior to the radiolabelling step. The nuclease P1 enhancement procedure is the most established and frequently used of these methods. An immunoaffinity procedure developed for class specific recognition for polycyclic aromatic hydrocarbon (PAH)-DNA adducts has therefore been compared with the nuclease P1 method for a range of DNA adducts formed by PAHs. The evaluation was carried out with skin DNA from mice treated topically with benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene, 5-methylchrysene or chrysene. The immobilised antibody had the highest affinity for adducts structurally similar to the BPDE-I-deoxyguanosine adduct ([+/-]-N2-(7r,8t,9r-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-1 0t-yl)-2'-deoxyguanosine) against which the antibody had been raised. Of the PAH-modified DNAs evaluated, the maximum adduct recovery was obtained for DNA containing the BPDE I-deoxyguanosine adduct. With DMBA-modified DNA, the profiles of adducts recovered from the column were similar when the column material was treated either with a digest of DMBA-modified DNA or with 32P-labelled DMBA adducts. I-compounds (endogenous adducts in tissue DNA of unexposed animals), which had similar chromatographic properties to PAH-DNA adducts, were not enriched by the immunoaffinity procedure. Compared to the simple nuclease P1 enhancement procedure, the immunoaffinity methods were lengthier and more labour intensive. Advantages of the immunoaffinity procedure include: specificity, allowing the selective detection of a certain class of adducts: efficient adduct enrichment, providing a viable alternative to other enrichment procedures; adequate sensitivity for model studies and the potential to purify adducts for further characterisation. However, as a general screen for detecting the formation of DNA adducts, the nuclease P1 procedure was viewed as the initial method of choice since it was capable of detecting a wider range of PAH-DNA adducts.

Enhanced levels in neonatal rat liver of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-hydroxydeoxyguanosine), a major mutagenic oxidative DNA lesion

The purpose of this study was to determine whether the level of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-hydroxy-2'-deoxyguanosine) (8-oxo-dG), a major mutagenic DNA oxidation product, is enhanced in newborn rat liver DNA as a consequence of oxidative stress incurred during the early postnatal period. 32P-postlabeling showed this adduct to increase approximately 2-fold from the 20th day of gestation (2 days before birth) to a peak level at 50-53 h after birth. Postnatal levels exceeded fetal levels at all time points investigated, i.e. 0.5-1, 8, 24, 50-53, 100, 216 and 432 h after birth. Increased formation of this mutagenic DNA lesion during the critical postnatal phase when there is rapid cell proliferation in all tissues is proposed to contribute to carcinogenesis in susceptible tissues later in life.

Organ-specific oxidative DNA damage associated with normal birth in rats

Mammalian DNA contains bulky endogenous DNA modifications (I-compounds), which increase with age in unexposed animals, as shown by 32P-postlabeling. We have examined the perinatal formation of a subclass (type II) of I-compounds in rat liver, kidney, skin and lung. These I-compounds represent bulky oxidative DNA lesions, defined herein as intrastrand base-base and base-sugar cross-links, adducts of lipid peroxidation products and DNA-protein cross-links. We observed a rapid increase in the levels of five bulky oxidative DNA lesions during the first hours after normal birth of rats, with total levels increasing 4.2-, 3.0- and 1.3-fold, respectively, in liver, kidney and skin. This effect was not noted in lung. The results were consistent with oxidative stress induced by the known sudden increase in partial oxygen pressure at birth in blood and tissues, implying inadequate antioxidant defenses in the affected neonatal organs. Hepatic oxidative damage appeared intensified by increased concentrations of pro-oxidants and reduced concentrations of antioxidants in the maternal diet. The postnatal DNA lesions are postulated to be premutagenic, as indicated by their bulky nature and persistence. Pathophysiological effects of oxidative DNA damage would be exacerbated by rapid cell proliferation in neonatal tissues and consequent fixation as mutations. In addition to inherited mutations, DNA lesions acquired as a consequence of normal birth may play a hitherto unrecognized role in spontaneous carcinogenesis and age-related degenerative diseases.

DNA adducts and chronic degenerative disease. Pathogenetic relevance and implications in preventive medicine

Chronic degenerative diseases are the leading causes of death in developed countries. Their control is exceedingly difficult due to their multiplicity and diversity, the interconnection with a network of multiple risk factors and protective factors, the long latency and multistep pathogenesis, and the multifocal localization. Adducts to nuclear DNA are biomarkers evaluating the biologically effective dose, reflecting an enhanced risk of developing a mutation-related disease more realistically than the external exposure dose. The localization and accumulation of these promutagenic lesions in different organs are the composite result of several factors, including (a) toxicokinetics (first-pass effect); (b) local and distant metabolism; (c) efficiency and fidelity of DNA repair; and (d) cell proliferation rate. The last factor will affect not only the dilution of DNA adducts but also the possible evolution towards either destructive processes, such as emphysema or cardiomyopathies, or proliferative processes, such as benign or malignant tumors at various sites. They also include heart tumors affecting fetal myocytes after transplacental exposure to DNA-binding agents, blood vessel tumors, and atherosclerotic plaques. In this article, particular emphasis is given to molecular alterations in the heart, which is the preferential target for the formation of DNA adducts in smokers, and in human aorta, where an extensive molecular epidemiology project is documenting the systematic presence of adducts to the nuclear DNA of smooth muscle cells from atherosclerotic lesions, and their significant correlation with known atherogenic risk factors. Exocyclic DNA adducts resulting from lipid peroxidation, and age-related indigenous adducts (I-compounds) may also originate from endogenous sources, chronic infections and infestations, and inflammatory processes. Type II I-compounds are bulky DNA lesions resulting from oxidative stress, whereas type II-compounds are presumably normal DNA modifications, which display positive correlations with median life span and are decreased in cancer and other pathological conditions. Profiles of type II-compounds strongly depend on diet and are related to the antidegenerative effects of caloric/ dietary restriction. Even broader is the possible meaning of adducts to mitochondrial DNA, which have been detected in rodents exposed to genotoxic agents and complex mixtures, as well as in untreated rodents, in larger amounts when compared to the nuclear DNA of the same cells. Mutations in mitochondrial DNA increase the number of oxidative phosphorylation-defective cells, especially in energy-requiring postmitotic tissues such as brain, heart and skeletal muscle, thereby playing an important role in aging and a variety of chronic degenerative diseases. A decreased formation of DNA adducts is an indicator of reduced risk of developing the associated disease. Therefore, these molecular dosimeters can be used as biomarkers in the prevention of chronic degenerative diseases, pursued either by avoiding exposure to adduct-forming agents or by using chemopreventive agents. Interventions addressed to the human organism by means of dietary measures or pharmacological agents have encountered a broad consensus in the area of cardiovascular diseases, and are deserving a growing interest also in cancer prevention. The efficacy of chemopreventive agents can be assessed by evaluating inhibition of nuclear DNA or mitochondrial DNA adduct formation in vitro, in animal models, and in phase II clinical trials in high-risk individuals.

Effects of cytochrome P450 inducers on tamoxifen genotoxicity in female mice in vivo

We recently reported that administration of the antiestrogen tamoxifen (TAM) gives rise to two groups of DNA adducts in female mouse liver in vivo, as measured by 32P-postlabeling, and provided evidence that 4-hydroxytamoxifen and alpha-hydroxytamoxifen are proximate carcinogenic metabolites leading to group I and group II adducts, respectively (Randerath et al., Carcinogenesis 15: 2087-2094, 1994). Because cytochrome P450 (CYP) enzymes play an important role in TAM metabolism, in this investigation we tested the hypothesis that induction of liver CYP enzymes may affect TAM metabolism profoundly, resulting in increased or decreased TAM-DNA adduct formation in vivo. To this end, we treated female ICR mice with TAM either alone or in combination with one of several classic CYP inducers, i.e. phenobarbital (PB), beta-naphthoflavone (BNF), and pregnenolone-16 alpha-carbonitrile (PCN), and determined the levels of 32P-postlabeled TAM-DNA adducts and the activities of several CYP-dependent enzymes. Each of the inducers greatly diminished levels of group II, but did not affect group I adducts. TAM elicited induction of benzphetamine N-demethylase activity in liver, while activities of other enzymes were not affected. TAM, when given in combination with BNF, elicited a synergistic induction of ethoxyresorufin O-deethylase (EROD) (CYP1A1) and methoxyresorufin O-demethylase (MROD) (CYP1A2) activities. Likewise, PCN given along with TAM caused synergistic induction of EROD and ethylmorphine N-demethylase activities. There was no synergism between PB and TAM, however. Overall, the results further support the existence of two pathways of TAM metabolism to DNA-reactive electrophiles and strongly suggest that the classic CYP inducers tested enhance detoxication of TAM to non-genotoxic metabolites.

Comparative 32P-postlabeling analysis of exogenous and endogenous DNA adducts in mouse skin exposed to a wood-preserving waste extract, a complex mixture of polycyclic and polychlorinated chemicals

Wood preserving waste (WPW) sites contain numerous toxic compounds, including phenols, polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins, and dibenzofurans. Previous in vitro and in vivo 32P-postlabeling studies showed the induction of multiple carcinogen-DNA adducts by WPW extracts. We now have tested the hypothesis in a mouse skin bioassay that a WPW extract not only causes the formation of exogenous, xenobiotic-derived DNA adducts, but also alters the levels of endogenous DNA modifications. Skin DNA of female ICR mice treated topically with an organic WPW extract was found by 32P-postlabeling to contain significantly increased levels of bulky oxidative DNA lesions (type II I-compounds), in addition to exogenous PAH-derived adducts. The mechanism of this increase is postulated to proceed through electrophilic quinoid compounds, which presumably were formed from phenols by chemical reactions of waste material or biologically by oxidative metabolism. On the other hand, the levels of another class of endogenous DNA adducts (type I I-compounds) were reduced significantly in exposed skin DNA. This effect was explained by the presence of cytochrome P450 inducers in the extract. All three types of DNA alterations observed may play a significant role in carcinogenesis. Our results imply that in addition to exogenous carcinogen-DNA adducts, alterations of endogenous DNA modifications may need to be considered in evaluating carcinogenic risk from toxic chemical wastes and the effects of remediation measures.

DNA adducts and chronic degenerative disease. Pathogenetic relevance and implications in preventive medicine

Chronic degenerative diseases are the leading causes of death in developed countries. Their control is exceedingly difficult due to their multiplicity and diversity, the interconnection with a network of multiple risk factors and protective factors, the long latency and multistep pathogenesis, and the multifocal localization. Adducts to nuclear DNA are biomarkers evaluating the biologically effective dose, reflecting an enhanced risk of developing a mutation-related disease more realistically than the external exposure dose. The localization and accumulation of these promutagenic lesions in different organs are the composite result of several factors, including (a) toxicokinetics (first-pass effect); (b) local and distant metabolism; (c) efficiency and fidelity of DNA repair; and (d) cell proliferation rate. The last factor will affect not only the dilution of DNA adducts but also the possible evolution towards either destructive processes, such as emphysema or cardiomyopathies, or proliferative processes, such as benign or malignant tumors at various sites. They also include heart tumors affecting fetal myocytes after transplacental exposure to DNA-binding agents, blood vessel tumors, and atherosclerotic plaques. In this article, particular emphasis is given to molecular alterations in the heart, which is the preferential target for the formation of DNA adducts in smokers, and in human aorta, where an extensive molecular epidemiology project is documenting the systematic presence of adducts to the nuclear DNA of smooth muscle cells from atherosclerotic lesions, and their significant correlation with known atherogenic risk factors. Exocyclic DNA adducts resulting from lipid peroxidation, and age-related indigenous adducts (I-compounds) may also originate from endogenous sources, chronic infections and infestations, and inflammatory processes. Type II I-compounds are bulky DNA lesions resulting from oxidative stress, whereas type II-compounds are presumably normal DNA modifications, which display positive correlations with median life span and are decreased in cancer and other pathological conditions. Profiles of type II-compounds strongly depend on diet and are related to the antidegenerative effects of caloric/ dietary restriction. Even broader is the possible meaning of adducts to mitochondrial DNA, which have been detected in rodents exposed to genotoxic agents and complex mixtures, as well as in untreated rodents, in larger amounts when compared to the nuclear DNA of the same cells. Mutations in mitochondrial DNA increase the number of oxidative phosphorylation-defective cells, especially in energy-requiring postmitotic tissues such as brain, heart and skeletal muscle, thereby playing an important role in aging and a variety of chronic degenerative diseases. A decreased formation of DNA adducts is an indicator of reduced risk of developing the associated disease. Therefore, these molecular dosimeters can be used as biomarkers in the prevention of chronic degenerative diseases, pursued either by avoiding exposure to adduct-forming agents or by using chemopreventive agents. Interventions addressed to the human organism by means of dietary measures or pharmacological agents have encountered a broad consensus in the area of cardiovascular diseases, and are deserving a growing interest also in cancer prevention. The efficacy of chemopreventive agents can be assessed by evaluating inhibition of nuclear DNA or mitochondrial DNA adduct formation in vitro, in animal models, and in phase II clinical trials in high-risk individuals.

Organ-specific oxidative DNA damage associated with normal birth in rats

Mammalian DNA contains bulky endogenous DNA modifications (I-compounds), which increase with age in unexposed animals, as shown by 32P-postlabeling. We have examined the perinatal formation of a subclass (type II) of I-compounds in rat liver, kidney, skin and lung. These I-compounds represent bulky oxidative DNA lesions, defined herein as intrastrand base-base and base-sugar cross-links, adducts of lipid peroxidation products and DNA-protein cross-links. We observed a rapid increase in the levels of five bulky oxidative DNA lesions during the first hours after normal birth of rats, with total levels increasing 4.2-, 3.0- and 1.3-fold, respectively, in liver, kidney and skin. This effect was not noted in lung. The results were consistent with oxidative stress induced by the known sudden increase in partial oxygen pressure at birth in blood and tissues, implying inadequate antioxidant defenses in the affected neonatal organs. Hepatic oxidative damage appeared intensified by increased concentrations of pro-oxidants and reduced concentrations of antioxidants in the maternal diet. The postnatal DNA lesions are postulated to be premutagenic, as indicated by their bulky nature and persistence. Pathophysiological effects of oxidative DNA damage would be exacerbated by rapid cell proliferation in neonatal tissues and consequent fixation as mutations. In addition to inherited mutations, DNA lesions acquired as a consequence of normal birth may play a hitherto unrecognized role in spontaneous carcinogenesis and age-related degenerative diseases.

Monophosphate 32P-postlabeling assay of DNA adducts from 1,2:3,4-diepoxybutane, the most genotoxic metabolite of 1,3-butadiene: in vitro methodological studies and in vivo dosimetry

Among the main DNA-reactive metabolites of 1,3-butadiene (BD), both 1,2:3,4-butadiene diepoxide (BDE) and 1,2-epoxy-3-butene (BME) have been reported in mice and rats exposed to BD, but blood and tissue levels of these metabolites are much higher in mice than in rats under similar exposure conditions. BDE, being more reactive and genotoxic than BME, is thought to be responsible for the greater susceptibility of mice to BD carcinogenicity. While BDE is a DNA-alkylating agent and some BDE adducts have been characterized, no sufficiently sensitive method has been reported for studying BDE-DNA binding in vivo. In the present investigation, a modified dinucleotide/monophosphate version of the 32P-postlabeling assay was applied to detect BDE-DNA adducts, which were prepared by reacting BDE with calf thymus DNA or deoxyribooligonucleotides [(AC)10, (AG)10, (CCT)7 and (GGT)7] in vitro or with skin DNA of mice in vivo upon topical treatment. Optimal resolution by 2-D PEI-cellulose TLC of the highly polar 5'-monophosphate adducts was achieved at +4 degrees C using 0.3 M LiCI (DI) and 0.4 M NaCl, 0.04 M H3BO3, pH 7.6 (D2). The profiles of the 32P-postlabeled adducts were similar for calf thymus and skin DNA, with 3 major spots being detected. Adducts obtained in in vitro and in vivo experiments were compared by re- and cochromatography in 4 or 5 different solvents, and these experiments provided evidence that corresponding BDE adducts, for the most part, were identical and represented adenine derivatives. Guanine adducts were not detected by this method although literature data indicate their formation. Quantitatively, the assay responded linearly to adduct concentration, as shown in an experiment where BDE-modified skin DNA was serially diluted up to 81-fold with control DNA. The limit of detection was approximately 1 adduct in 10(8) normal nucleotides. Further, in an in vivo dosimetry study, skin DNA from groups of 8 individual mice treated with different doses of BDE (1.9, 5.7, 17, 51 and 153 mumol/mouse) for 3 days exhibited a linear relationship (r > or = 0.992) between adduct levels and dose. The results suggest that the 32P-postlabeling assay described herein will have utility in mechanistic studies and biomonitoring of DNA adduct formation from BDE and possibly other polar epoxides.

32P-postlabeling of 1,3-butadiene and 4-vinyl-1-cyclohexene metabolite-DNA adducts: in vitro and in vivo applications

Epoxides of 1,3-butadiene, i.e. 1,2-epoxy-3-butene and 1,2:3,4-diepoxybutane are DNA-reactive metabolites. No methods have been reported for detecting DNA adducts of these compounds in exposed animals or humans. The purpose of this study has been to develop a 32P-postlabeling assay for adducts of 1,3-butadiene and its dimer, 4-vinyl-1-cyclohexene. The assay was applied to skin DNA of mice exposed topically to diepoxides of these dienes. A dose-dependent increase in in vivo adduct formation was observed for both compounds. The newly developed assay will find applications in mechanistic studies on these and related compounds and in human biomonitoring.

Pentachlorophenol enhances 9-hydroxybenzo [a] pyrene-induced hepatic DNA adduct formation in vivo and inhibits microsomal epoxide hydrolase and glutathione S-transferase activities in vitro: likely inhibition of epoxide detoxication by pentachlorophenol

We recently reported that co-administration to female mice of tamoxifen or 4-hydroxytamoxifen (4-OH-tamoxifen) with pentachlorophenol (PCP), but not with 2,6-dichloro-4-nitrophenol (DNCP) results in strong intensification of a specific subgroup, termed group I, of tamoxifen-DNA adducts in female mouse liver. As both PCP and DCNP are sulfotransferase inhibitors, we concluded that the intensification of tamoxifen group I adducts is probably not due to inhibition of sulfation by these phenols of a tamoxifen metabolite. Since epoxide derivatives of 4-OH-tamoxifen are potential candidates involved in tamoxifen-induced DNA damage, the hypothesis was developed and tested that PCP inhibits epoxide detoxication. As 4-OH-tamoxifen metabolites were unavailable to us, we employed indirect approaches to test this hypothesis. In the first set of experiments we determined whether PCP would augment DNA adduct formation from the benzo[a]pyrene metabolite, 9-hydroxybenzo[a]pyrene (9-OH-BP), as 9-OH-BP-4,5-epoxide is known to be involved in the metabolic activation of this compound. Female mice were given a single i.p. dose of 9-OH-BP (50 mumol/kg) either alone or in combination with PCP (75 mumol/kg), and hepatic DNA adducts were measured 24 h later by nuclease P1-enhanced bisphosphate 32P-postlabeling. Co-administration of PCP with 9-OH-BP resulted in a statistically significant 1.5- to 1.7-fold increase in 9-OH-BP adduct levels versus 9-OH-BP controls. In order to determine whether PCP inhibits the enzymatic detoxication of epoxides in vitro, in a second set of experiments, the effects of PCP on liver microsomal epoxide hydrolase (mEH) and purified equine liver glutathione S-transferase (GST) activities were studied using, respectively, styrene-7,8-oxide and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. Incubation of mouse liver microsomes with PCP (10-100 microM) strongly inhibited (by 21-97%) mEH activity in a dose-dependent manner, the IC50 being 35 microM. DCNP was ineffective as a mEH inactivator. PCP also inhibited purified equine liver GST activity, with an IC50 of 23.5 microM. Taken together, the results of this study strongly support the hypothesis that PCP inhibited enzymatic detoxication of epoxides in vivo and in vitro. By this mechanism PCP would lead to enhancement of DNA damage caused by 9-OH-BP, and possibly other drugs and their metabolites, which undergo epoxidation prior to DNA binding.

DNA damage induced in mouse tissues by organic wood preserving waste extracts as assayed by 32P-postlabeling

Numerous wood preserving waste (WPW) sites in the United States pose genotoxic hazards. WPWs consist of complex mixtures containing toxic, including genotoxic, compounds which are derived from the preservatives coal tar creosote and pentachlorophenol (PCP) and other polychlorinated aromatics. The genotoxicity of WPW extracts, which has not been tested in mammals, cannot be evaluated on the basis of data for individual components because of possible compound interactions. Therefore, whole extracts need to be assayed. 32P-postlabeling represents a powerful tool to determine DNA adduct formation by complex genotoxic mixtures, such as cigarette smoke, diesel exhaust, and coke oven and foundry emissions in experimental animals and humans. In the present study, a mouse bioassay was used in combination with 32P-postlabeling to determine DNA adduct formation induced by hexane/acetone extracts of two samples from a WPW site. Female ICR mice were treated dermally with extract corresponding to 3 mg residue or vehicle control once per day for 2 days and killed 24 h later. Skin, lung, liver, kidney, and heart DNA preparations were assayed by nuclease P1-enhanced postlabeling. Adduct profiles were tissue-specific and displayed a multitude of non-polar DNA adducts with levels amounting to one adduct in 1.6 x 10(6) DNA nucleotides in skin (both extracts) and one adduct in 3.2 x 10(7) or 1.2 x 10(7) DNA nucleotides in liver (extract 1 or extract 2). Based on their chromatographic properties, these adducts appeared largely derived from polycyclic aromatic hydrocarbons (PAHs) present in the extracts. One of the major adducts was identified as the 32P-labeled derivative of the reaction product of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7, 8,9,10-tetrahydrobenzo[a]pyrene (BPDE I) with N2 of deoxyguanosine. Total non-polar DNA adduct levels were highest in skin and lung, amounting to 17.4 and 24.0% of the skin values for extracts 1 and 2, respectively, in lung while the corresponding levels in liver were 5.0 and 12.6%. These results were in accord with the carcinogenic potencies of PAHs in these organs. Extract 2 induced higher adduct levels in internal organs, although its PAH concentrations were lower than those of extract 1, i.e. lung, liver, kidney, and heart had 1.4, 2.5, 1.9, and 1.7 times higher total adduct levels and 1.6, 3.3, 1.6, and 1.9 times higher benzo[a]pyrene adduct levels. With the exception of total adducts in lung, the differences between the two extracts were all significant, suggestive of compound interactions. The benzo[a]pyrene adduct levels in the five tissues correlated linearly with total adduct levels and thus represented a surrogate for the latter. Overall, the results suggest that DNA adducts in mouse tissues, as analyzed by 32P-postlabeling, are suitable biomarkers and dosimeters of the genotoxicity of WPW extracts.

In vitro and in vivo (32)P-postlabeling analysis of 4-vinyl-1-cyclohexene (butadiene dimer) diepoxide-DNA adducts

4-Vinyl-1-cyclohexene diepoxide (VCD), and industrial chemical, and its parent compound, 4-vinyl-1-cyclohexene (VCH), are potential health hazards, a they destroy oocytes in follicles in rodents. VCD is also a skin carcinogen at the site of application in both female and male mice and rats and after gavage, induces ovarian tumors in mice and forestomach tumors in rats. A (32)P-postlabeling assay was developed for the detection and measurement of VCD-DNA adducts. VCD, a direct-acting carcinogen, was reacted with DNA in vitro, as well as through mouse skin painting for 3 days with different doses of VCD. (32)P-Labeled adducts were separated by polyethyleneimine (PEI)-cellulose TLC and detected by screen-enhanced autoradiography. Comparable adduct profiles were obtained in vitro and in vivo. At higher doses (36-225 micro mol/mouse), adduct levels in vivo showed a linear dose response, while there was no difference between 14 and 36 micro mol/mouse. The limit of detection was estimated to be 1-3 adducts in 10(8) DNA nucleotides. The results show that VCD exposure gives rise to (presumably pre-mutagenic) DNA adducts in vivo and that (32)P-postlabeling can be applied to biomonitoring of VCD exposure.

Structural origins of bulky oxidative DNA adducts (type II I-compounds) as deduced by oxidation of oligonucleotides of known sequence

Bulky DNA adducts, previously termed type II I-compounds, are detected by 32P-postlabeling following treatment of DNA with several Fenton-type oxygen radical-generating reagents, i.e., mixtures of Fe(II) or Ni(II) and H2O2. In an attempt to characterize the chemical nature and mechanism(s) of formation of these novel adducts, 16 single-stranded deoxyribooligonucleotides (20- and 21-mers) of known sequence were oxidized with Fe(II) or Ni(II) and H2O2, and the products were analyzed by 32P-postlabeling. Eight adducts were obtained reproducibly by oxidation of DNA and test oligonucleotides in a sequence-dependent manner. One major adduct (2) was formed only if the test oligonucleotide contained two adjacent adenine residues. Similarly, adducts 3 and 8 specifically originated in AC and CA sequences, respectively. Adduct 6 required a 5'-C-purine-3' sequence. On the other hand, GN sequences (where N is any normal nucleotide) gave rise to adduct 1, another major product, and adduct 7. Similarly, adducts 4 and 5 were produced by the oxidation of AN sequences. These observations are most readily explained if the oxidation reactions caused intrastrand cross-links between adjacent nucleotides, leading to dimer formation. The observation that adducts 1, 4, 5, and 7 did not require a specific 3'-nucleotide was consistent with the notion that these nucleotides lacked a 3'-base, suggesting the presence of a 5'-->3' purine-sugar cross-linked in the oxidized products. The majority of the lesions came from AA and 5'-purine-N-3' sequences. The effects of Fe(II) and Ni(II) were qualitatively similar; however, higher yields of products were observed with Fe(II) as the catalyst. The definition of the chemical origins of these bulky DNA modifications, which represent a new type of DNA damage, is expected to contribute to a better understanding of the mechanism of metal carcinogenesis and to shed light upon the origins of certain endogenous DNA lesions. Recently, some of the major oxidative DNA adducts characterized here were detected by 32P-postlabeling in the renal DNA of male rats treated with ferric nitrilotriacetate, a known potent prooxidative kidney carcinogen in these animals.

Tamoxifen metabolic activation: comparison of DNA adducts formed by microsomal and chemical activation of tamoxifen and 4-hydroxytamoxifen with DNA adducts formed in vivo

One of our laboratories recently showed by 32P-postlabeling that administration of tamoxifen to mice induces two groups of hepatic DNA adducts comprising two major spots, nos. 3 and 5, respectively. 4-Hydroxytamoxifen and alpha-hydroxytamoxifen appear to be the proximate metabolites of groups I and II adducts, respectively. The relative significance of these two adduct groups for tamoxifen carcinogenicity remains to be established. To determine the activation mechanism(s) of tamoxifen and 4-hydroxytamoxifen, in vivo adducts were compared by 32P-postlabeling with adducts generated by microsomal or chemical activation in vitro. Microsomal activation of 4-hydroxytamoxifen and tamoxifen, respectively, in the presence of DNA and cumene hydroperoxide, induced two adducts, which mapped similarly to the corresponding in vivo adduct spots 3 and 5. Chemical oxidation of 4-hydroxytamoxifen with silver(II) oxide, followed by incubation of the product(s) with DNA, elicited the formation of a major spot (Q1), while tamoxifen itself did not react. Rechromatographic analyses revealed that in vitro fractions 3 and Q1 (from 4-hydroxytamoxifen) matched the major in vivo group I adduct fraction 3, consistent with the hypothesis that 4-hydroxytamoxifen is a precursor for adduct fraction 3 in vivo. The in vitro adduct fraction 5 (from tamoxifen) was identical to that formed in vivo, indicating that the metabolic pathway for the formation of group II adducts did not involve 4-hydroxytamoxifen. In conclusion, the results support a model where primary metabolites of tamoxifen undergo secondary metabolism to form DNA adducts, which are detected in vivo after treatment with tamoxifen or 4-hydroxytamoxifen.

Effects of a single dose of the cytochrome P450 inducer, beta-naphthoflavone, on hepatic and renal covalent DNA modifications (I-compounds)

I-compounds are age-dependent covalent DNA modifications, which occur in rodent tissues without known carcinogen exposure. A number of studies from our laboratory indicate that I-compounds may serve as biomarkers of carcinogenesis. Recently, we demonstrated significant lowering of liver I-compound levels in rats that were exposed to different cytochrome P450 inducers. In order to gain further mechanistic insights into the possible relationship between P450 induction and I-compound reduction, female Sprague-Dawley rats were administered a single dose of the CYP1A1 inducer, beta-naphthoflavone (BNF) (80 mg/kg), in corn oil (CO) (2 ml/kg) or CO only (2 ml/kg) as vehicle control. Liver and kidney microsomal P450 contents and P450-related enzyme activities and DNA I-compounds were determined at 4, 24, and 48 h after treatment. Liver and kidney I-compounds were analyzed by nuclease P1-enhanced 32P-postlabeling. DNA synthesis was determined by measuring [3H]methylthymidine incorporation. Liver and kidney microsomal P450 contents were elevated by BNF at 24 and 48 h. Ethoxyresorufin-O-deethylase (EROD) and methoxyresorufin-O-demethylase (MROD) were significantly elevated at all time points, with the former displaying a much higher extent of induction. BNF treatment resulted in significant diminution of the levels of several individual and total I-compounds in liver at 48 h, but few effects were seen at the earlier time-points. Kidney I-compounds were also markedly affected by BNF at 48 h, albeit to a lesser extent than in liver. In both tissues, P450 induction preceded I-compound reduction. Taken together, the results of this investigation demonstrate significant diminution of I-compound levels by a single dose of BNF, a CYP1A1 inducer, in a time-dependent manner, suggesting the participation of a specific biochemical process, possibly involving CYP1A1, in the metabolic regulation of these endogenous DNA adducts.

Evidence from 32P-postlabeling and the use of pentachlorophenol for a novel metabolic activation pathway of diethylstilbestrol and its dimethyl ether in mouse live: likely alpha-hydroxylation of ethyl group(s) followed by sulfate conjugation

Diethylstilbestrol (DES), a synthetic stilbene estrogen, is a potent development toxin and carcinogen in humans and rodents. A number of 32P-postlabeling studies suggest that genotoxic effects of DES substantially contribute to these biological effects. The mechanisms involved in DES-mediated genotoxicity are not completely understood, however. As reported here, the structural resemblance of tamoxifen to DES led to the hypothesis that DES may be hydroxylated and sulfated at the allylic C2 and/or C5 of the ethyl side chains in analogy to alpha-hydroxylation and sulfation of and DNA adduct formation by tamoxifen. Female ICR mice were administered 500 mumol/kg DES or its dimethyl ether derivative (DiMeDES), either alone or in combination with the sulfotransferase inhibitor pentachlorophenol (PCP) (75 mumol/kg), once daily for 4 days. Liver DNA adducts were measured 24 h after the last dose by dinucleotide/monophosphate 32P-postlabeling. Administration of DES or DiMeDES led to the formation of a unique and novel pattern of several major DNA adducts which were absent in vehicle controls. With minor exceptions the pattern was qualitatively similar for the two compounds, suggesting rapid O-demethylation of DiMeDES to DES in vivo followed by metabolic activation. Adducts formed in vivo did not chromatographically match DES quinone adducts synthesized in vitro. Co-administration of PCP with DES or DiMeDES significantly decreased adduct formation from either compound, by 33-61%. Taken together, these results are consistent with a hitherto unrecognized pathway of metabolic activation and DNA adduct formation by DES involving the putative hydroxylation of the allylic alpha-carbon of the ethyl side chain(s), followed by formation of DNA-reactive sulfuric acid esters. DES is now known to induce DNA damage in vivo by at least four different mechanisms. It is postulated that this multiplicity of mechanisms in itself explains why this drug elicits such a plethora of unique and complex pathophysiological effects in adults and off-spring of different species.

DNA adducts induced by lipids and lipid peroxidation products: possible relationships to I-compounds

A methanol-extractable lipid fraction of oats has been found previously to induce three specific I-compounds (age-dependent covalent DNA modifications) in female rat liver DNA, as detected by the 32P-postlabeling assay. The current report used an in vitro system to explore the possible mechanisms involved in the formation of these DNA derivatives. Ground oats or commercial oatmeal were extracted with methanol, and the extracts were incubated with rat lung DNA in vitro. DNA was recovered and analyzed by the nuclease P1-enhanced version of the 32P-postlabeling assay. A number of adducts were induced by the in vitro reaction but none of them was identical by chromatographic analysis to oats-specific I-compounds detected in vivo. Addition of rat liver microsomes and cofactors (NADPH or cumene hydroperoxide) to the in vitro reaction also failed to induce any of the oats-specific I-compounds. Pretreatment of oat lipids with soybean lipoxidase and oxygen enhanced formation of most adducts formed in vitro in a dose- and time-dependent manner. Several of these adducts were related to peroxide derivatives of linoleic acid. Chromatographic evidence suggests that one of the major adducts is derived from 4-hydroxynonenal, a reactive intermediate lipid peroxidation product. This adduct was detectable in liver and kidney DNA of untreated rats and its level increased with age. These results were in line with previous in vivo results, suggesting that the oats-specific I-compounds are presumably formed via an indirect mechanism rather than by direct binding of oats components to DNA.

Rapid decreases in indigenous covalent DNA modifications (I-compounds) of male Fischer-344 rat liver DNA by diquat treatment

I-compounds are indigenously appearing covalent DNA modifications that can be detected by 32P-postlabeling assay in tissues of normal animals without known exposure to any carcinogens or toxins. Although these compounds have not been structurally identified, indirect evidence from earlier work suggested the possibility of involvement of molecular fragments derived from lipid peroxides. Diquat is a herbicide that stimulates lipid peroxidation and massive intrahepatic oxidant stress through redox cycling-mediated generation of reactive oxygen species. In the present study, we examined the effects of diquat on hepatic I-compounds of male Fischer-344 rats. Two groups of rats, approximately 14 weeks and 8 weeks old, were given a hepatotoxic dose (0.1 mmol/kg) of diquat or equal volumes of saline, i.p. Two and 6 h later plasma alanine aminotransferase (ALT) activities were measured and hepatic DNA I-compound levels were examined by nuclease P1-enhanced 32P-postlabeling. Elevated ALT activities were observed in some animals in both groups, at both time points, but considerable inter-animal variation was seen. A total of 15-16 I-compound fractions were measured in control and in diquat-treated animals, but no extra spots indicative of treatment-induced adducts were detected. Despite the qualitative similarities, the quantities of individual I-compounds were markedly decreased at 2 h in diquat-treated animals of both age groups. In 14 week old rats the hepatic I-compound contents were decreased at 2 h by 22-59%, which was statistically significant (ANOVA, P < 0.05) for all of the 9 polar I-compound fractions and none of the non-polar fractions. Eleven I-spots from this group showed significant negative linear correlations (P < 0.05) with ALT values. In 8 week old rats treated with diquat a 22-43% depletion in I-compound contents was statistically significant for 4 of the 7 nonpolar and 2 of the 8 polar adduct fractions, but there was no significant correlation of I-compound contents with ALT values at the 2 h time point. By 6 h most of the I-spot levels had returned to normal or above normal values in both groups of animals. While most I-spots from 14 week old rats did not correlate with ALT levels at 6 h, two I-spots displayed positive correlations in the 8 week group. Overall, the susceptibility to diquat-associated DNA alterations appeared to differ with age.(ABSTRACT TRUNCATED AT 400 WORDS)

Intensification and depletion of specific bulky renal DNA adducts (I-compounds) following exposure of male F344 rats to the renal carcinogen ferric nitrilotriacetate (Fe-NTA)

The effects of the renal carcinogen ferric nitrilotriacetate (Fe-NTA) on kidney DNA of male F344 rats were studied to determine whether bulky DNA oxidation products (putative intrastrand crosslinks) could be detected by 32P-postlabeling in the target organ of carcinogenesis. Rats (10-11 weeks old) were given a single dose of Fe-NTA (15 mg Fe/kg body weight) i.p. at 3:00 pm. After 5 h, renal DNA from Fe-NTA-treated and vehicle control animals was assayed by 32P-postlabeling. Thin-layer chromatography and quantitative analysis of two labeled nucleotide fractions of increasing polarity, L and C, showed that three spots (L1, L2, and C3) were intensified 3.5- to 4.2-fold in treated animals. L1 consisted of subfractions L1a, L1b, and L1c, which could be resolved chromatographically. L1c, L2, and C3 were identical to DNA oxidation products generated by the Fenton reaction in vitro, while L1a and L1b apparently did not arise by this mechanism. DNA damage and toxicity appeared reduced in younger animals and animals treated in the morning, presumably due to differences in antioxidant defenses. Liver and lung (non-target organs) DNA did not exhibit enhanced L1, L2, and C3 spots. In addition to augmenting renal I-compounds, Fe-NTA reduced the levels of three major polar kidney I-compounds (C4, C5, and C6) to 22-53% of control. This reduction did not appear to arise by direct oxidative DNA damage, resembling the previously documented loss of liver I-compounds induced by numerous hepatocarcinogens. Two of these I-compounds (C4 and C5) have been reported to exhibit positive linear correlations with median lifespan of male F344 rats. The pleiotropic response of kidney I-compound levels to Fe-NTA was consistent with different roles of different types (I and II) of I-compounds in Fe-NTA-mediated renal carcinogenesis. The results strongly support a causal relationship between oxidative DNA lesions and Fe-NTA-mediated carcinogenesis.

Tamoxifen: evidence by 32P-postlabeling and use of metabolic inhibitors for two distinct pathways leading to mouse hepatic DNA adduct formation and identification of 4-hydroxytamoxifen as a proximate metabolite

Exposure to pentachlorophenol (PCP) strongly intensifies the formation of mouse hepatic DNA adducts elicited by oral administration of tamoxifen (TAM), as previously shown by 32P-postlabeling. To explain this effect, PCP was proposed to interfere with the detoxication by sulfate conjugation of an as yet unidentified hydroxylated proximate TAM metabolite. A comparison of the present and earlier results shows that the hepatic TAM adduct pattern in female ICR mice depended on the route of administration of TAM (120 mumol/kg), with oral administration primarily eliciting formation of more polar adducts (termed group I adducts), while after i.p. administration less polar adducts (group II) predominated over group I adducts by a factor of 17.5. All these adducts were also formed in female Sprague-Dawley rats after i.p. dosing with TAM, but total adduct levels were 3.5- to 5-fold higher than in mice. After four daily i.p. treatments, TAM adducts accumulated in mouse liver DNA in a non-linear fashion. Adduct levels were 30-50 times lower in mouse kidney and lung than in liver. The phenolic metabolite 4-hydroxy TAM (120 mumol/kg) exclusively led to formation of polar (group I) hepatic adducts, and this process was stimulated 8-fold by co-administration of PCP (75 mumol/kg). Co-administration of PCP with the parent compound led to an 11-fold enhancement of group I adduct formation; simultaneously, levels of group II adducts were suppressed 6-fold. Another inhibitor of sulfate conjugation, 2,6-dichloro-4-nitrophenol, unlike PCP, had no effect on group I adducts, but it reduced group II adduct formation 2.2-fold. The PCP metabolite 2,3,5,6-tetrachlorohydroquinone (75 mumol/kg) did not significantly affect any major TAM adduct, suggesting that PCP itself was the active compound. Similar to group II TAM adducts, the formation of hepatic safrole-DNA adducts was inhibited in female ICR mice by both sulfotransferase inhibitors, consistent with the proposal that metabolic alpha-hydroxylation of the ethyl group of TAM followed by sulfate conjugation represented a mechanism of TAM activation. On the other hand, the strong intensification of group I adducts by PCP and the lack of this effect by 2,6-dichloro-4-nitrophenol suggested that inhibition of sulfate conjugation may not have been the primary mechanism underlying the intensification of group I adducts formed from TAM or 4-hydroxy TAM. The results presented herein demonstrate conclusively that TAM was activated to DNA-reactive compounds along two distinct pathways which contrasted in their responses to metabolic inhibitors.

32P-postlabeling of bile components: bulky adduct-like behavior in polyethyleneimine-cellulose thin layer chromatography

The 32P-postlabeling assay has been used widely in carcinogen-DNA adduct analysis because of its sensitivity and reproducibility. Cloned T4 polynucleotide kinase (PNK), routinely used in this assay, phosphorylates the 5'-OH groups of adducted nucleotides in the presence of [gamma-32P]ATP. However, as an exception to this property, PNK has been reported to phosphorylate non-adducted carcinogen metabolites, such as tetrol derivatives of benzo[a]pyrene and chrysene. Also, PNK phosphorylates both 5'-OH and 3'-OH groups of safrole-adducted deoxydinucleoside monophosphates having an unmodified purine in the 3'-position. In the present study we show that T4 PNK catalyzed the transfer of [32P]phosphate from [gamma-32P]ATP to rat bile components or purified bile acids (derivatives of 3 alpha-hydroxy-5 beta-cholanic acid) in the absence of nucleic acids or nucleases. However, labeling of the bile acids appeared over 100,000-fold less efficient than labeling of 2'-deoxyadenosine-5'-monophosphate. There was no reaction in the absence of bile components or PNK. Dehydrocholic acid, which lacks hydroxyl groups, was resistant to phosphorylation. On polyethyleneimine-cellulose TLC maps, 32P-labeled rat bile extract gave an array of non-polar radioactive spots which resembled carcinogen-DNA adducts, while 32P-labeled purified bile acids each gave a single spot. These 32P-labeled products liberated 32Pi upon incubation with prostatic acid phosphatases. Two of the radioactive spots obtained from rat bile were identified as phosphorylated taurocholic and taurodeoxycholic acids by co-chromatography with 32P-labeled standards. These findings demonstrate for the first time that PNK is able to phosphorylate natural products other than nucleotides and further emphasize the need to rule out contamination with bile acids and possibly other bulky/hydrophobic alcohols when analyzing DNA samples by 32P-postlabeling.

DNA damage induced by wood preserving waste extracts in vitro without metabolic activation, as assayed by 32P-postlabeling

Aqueous wood preserving waste (WPW) extracts were tested for their ability to damage DNA in vitro without metabolic activation. Two extracts were prepared from a surface tar and a surface clay soil sample of a WPW site. As assayed by 32P-post-labelling incubation of DNA with these extracts gave rise to highly complex, extract-specific profiles of DNA adducts whose formation depended on the concentration of WPW material. Most of the adducts appeared to be derived from polycyclic aromatic hydrocarbons (PAHs). Three mg organic WPW residue gave rise to total adduct levels of 13.8 (extract 1) and 66.2 (extract 2) DNA modifications in 10(7) DNA nucleotides, corresponding to 13.9 and 26.9 modifications, respectively, per 10 mg of soil. Thus, extract 2 was more active, although the parent residue had a 1.4-times lower PAH content as determined by gas chromatography/mass spectrometry (GC/MS). DNA adduct formation presumably was a consequence of (i) free radical reactions, possibly involving semiquinones and oxygen free radicals, and (ii) reaction of direct-acting electrophiles, derived from metabolism of WPW toxicants by soil microorganisms. These reactions appeared to be more active in sample 2. The results suggest that ground water at WPW sites contains DNA-reactive compounds posing a cancer hazard to humans. The in vitro DNA adduct assay represents a novel tool to readily assess this type of hazard and the possible effects of remediation measures.

Chemical structure- and time-dependent effects of polycyclic aromatic hydrocarbon-type inducers on rat liver cytochrome P450, DNA adducts, and I-compounds

It is well documented that cytochrome P450IA1 (CYP1A1) plays an important role in carcinogen activation. CYP1A1/1A2 induction may serve as a biomarker of exposure to environmental toxins. In order to explore a specific role of CYP1A1 in metabolism of I-compounds (age-dependent indigenous DNA modifications), 2-month-old female Sprague-Dawley rats were treated ip with corn oil (2 ml/kg) or with one of several CYP1A1 inducers, i.e., dibenz[a,c]anthracene (DBA) (93 mumol/kg), benzo[a]pyrene (BP) (93 mumol/kg), naphthacene (NAP) (93 mumol/kg), or beta-naphthoflavone (BNF) (140 mumol/kg), once daily for 4 days. Levels of total cytochrome P450 and activities of CYP1A1-associated enzymes, i.e., ethoxycoumarin O-deethylase (ECD) and ethoxyresorufin O-deethylase (EROD), were determined in liver microsomes at 1, 8, or 15 days after the last treatment. DNA adducts and I-compounds were analyzed by nuclease P1-enhanced 32P-postlabeling. DNA synthesis rate was determined by measuring [3H]methylthymidine incorporation into DNA. Each inducer significantly elevated the total P450 level at 1 day. The enzyme levels in BP-, NAP-, and BNF-treated animals gradually returned to control by 8 and 15 days, but elevated levels persisted in DBA-treated rats. Similar trends were observed for ECD and EROD activities. DBA and BP, but not NAP and BNF, gave rise to several measurable DNA adducts, which persisted throughout the period of study. All P450 inducers, irrespective of adduct formation, strongly depleted both nonpolar and polar I-compounds, the effects being most pronounced at 1 and 8 days. These results imply a specific role for CYP1A1 in the regulation of I-compound metabolism, in addition to PAH activation.

Strong intensification of mouse hepatic tamoxifen DNA adduct formation by pretreatment with the sulfotransferase inhibitor and ubiquitous environmental pollutant pentachlorophenol

Although negative in assays for mutagenicity, the clinically important antiestrogen tamoxifen induces hepatic DNA adduct formation in mice, rats and hamsters, as indicated by 32P-postlabeling, and is a potent hepatocarcinogen in rats. Both phenolic and alcoholic metabolites of tamoxifen have been reported. As these metabolites are potential candidates for sulfate conjugation, we examined whether the sulfotransferase inhibitor pentachlorophenol, a ubiquitous environmental contaminant, modulates hepatic tamoxifen adduct formation in vivo. Female ICR mice were given tamoxifen (45 mg/kg) daily per os for up to 4 days, with and without i.p. pretreatment with pentachlorophenol (20 mg/kg) 1 h before dosing with tamoxifen. At days 1, 2 and 4, liver DNA was analyzed 5 h after tamoxifen administration by a modified monophosphate version of the 32P-postlabeling assay. At day 4, pentachlorophenol pretreatment led to a large increase (13- to 17-fold) of the levels of four tamoxifen adduct fractions, while two adducts appeared unaffected, resulting in an approximately 7-fold enhancement of overall adduct formation. Significant pentachlorophenol related increases were also observed at day 1 and day 2. The mechanism of this effect has not yet been determined, but may involve the inhibition of sulfation of a tamoxifen metabolite(s) involved in the detoxication of the drug to nonelectrophilic derivatives. It was also apparent that there are two pathways of metabolic activation of tamoxifen, one being sensitive and the other resistant to pentachlorophenol.

Effect of Ni(II) on tissue hydrogen peroxide content in mice as inferred from glutathione and glutathione disulfide measurements

Studies on Ni(II)-induced carcinogenesis have suggested that oxidative damage caused by Ni(II) may in part be due to increased tissue H2O2 formation. However, there is lack of evidence in vivo. Because of limitations of available methods for direct measurement of the in vivo rate of H2O2 formation in animals, Ni(II)-induced production of H2O2 was estimated from changes in the rate of glutathione disulfide (GSSG) formation. Male B6C3F1 mice (6-8 wk old) were injected i.p. with 170 mumol NiAc2/kg. Biliary efflux and liver, kidney, and lung levels of glutathione (GSH and GSSG) were determined 0-2 h after treatment. In spite of slight increases in tissue GSSG levels by Ni(II), there was no significant change in the biliary efflux of GSSG. Pretreatment with 50 mg/kg (i.p.) of bis-chloroethyl-nitrosourea (BCNU), an inhibitor of GSSG reductase, did not augment the effects of Ni(II) on GSSG formation significantly. Based on these observations, it was apparent that Ni(II) did not change the concentration of H2O2 significantly in vivo.

Biomarkers of aging: correlation of DNA I-compound levels with median lifespan of calorically restricted and ad libitum fed rats and mice

I-compounds are species-, tissue-, genotype-, gender-, and diet-dependent bulky DNA modifications whose levels increase with animal age. While a few of these DNA modifications represent oxidation products, the majority of I-compounds appear to be derived from as yet unidentified endogenous DNA-reactive intermediates other than reactive oxygen species. Circadian rhythms of certain I-compounds in rodent liver imply that levels of these DNA modifications are precisely regulated. Caloric restriction (CR), the currently most effective method available to retard aging and carcinogenesis, has been previously shown to elicit significant elevations of I-compound levels in tissue DNA from Brown-Norway (BN) and F-344 rats as compared to age-matched ad libitum fed (AL) animals. The present investigation has extended this work by examining liver and kidney DNA I-compound levels in three genotypes of rats (F-344, BN, and F-344 x BN) and two genotypes of mice (C57BL/6N and B6D2F1) under identical experimental conditions in order to determine whether correlations exist between I-compound levels, measured in middle-aged animals, and median lifespan. Levels of a number of liver and kidney I-compounds were found to display genotype- and diet-dependent, statistically significant positive linear correlations with median lifespan in both species. In particular, the longer-lived hybrid F-344 x BN rats and B6D2F1 mice tended to exhibit higher I-compound levels than the parent strains. CR enhanced I-compound levels substantially in both rats and mice. Thus, I-compounds, measured at middle age, reflected the functional capability ('health') of the organism at old age, suggesting their predictive value as biomarkers of aging. The positive linear correlations between levels of certain I-compounds (designated as type I) and lifespan suggest that these modifications may be functionally important and thus not represent endogenous DNA lesions (type II), whose levels would be expected to correlate inversely with lifespan.

Effects of polychlorinated dibenzofurans on compounds in hepatic DNA of female Sprague-Dawley rats: structure dependence and mechanistic considerations

Previous work indicated that covalent age-dependent DNA modifications of endogenous origin termed I-compounds may represent useful biomarkers for tumor promotion/carcinogenesis, as various tumor promoters/carcinogens, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and phenobarbital, reduce rat I-compound levels in liver, the target organ. The present study addressed the question as to whether polychlorinated dibenzofurans (PCDFs), which are related to TCDD and its congeners with regard to their toxic and biochemical properties, would also affect hepatic I-compound patterns and levels, and whether such effects would be chemical structure-dependent. Female Sprague-Dawley rats were treated once a week with a single dose (100 micrograms/kg) of 1,2,3,7,8-pentachlorodibenzofuran (1,2,3,7,8-PeCDF), 1,2,4,7,8-PeCDF, 2,3,4,7,8-PeCDF, or 2,3,4,6,7,8-hexachlorodibenzofuran (2,3,4,6,7,8-HeCDF) for 4 weeks and liver DNA was analyzed at the end of the last week by 32P-postlabeling assay. No carcinogen-DNA adducts were detected; however, levels of both non-polar and polar I-compounds were reduced in a structure-dependent manner. Potencies increased in the order, control (100%, 122 modifications in 10(9) DNA nucleotides = 1,2,4,7,8-PeCDF (104%) < 1,2,3,7,8-PeCDF (80%) < 2,3,4,7,8-PeCDF (61%) and 2,3,4,6,7,8-HeCDF (61%). Structure-activity relationships for total I-compounds, therefore, paralleled those reported for Ah receptor agonist activity, i.e., compounds that exhibit high cytosolic Ah receptor binding affinities and are also potent inducers of aryl hydrocarbon hydroxylase activity (1,2,3,7,8-PeCDF, 2,3,4,7,8-PeCDF, and 2,3,4,6,7,8-HeCDF) were active, while 1,2,4,7,8-PeCDF, which is a less potent Ah receptor agonist, was inactive. Polar I-compounds responded to a greater extent than did non-polar ones and, in general, individual I-compounds were affected differentially, thus decreased formation or increased removal of I-compounds played a role in the observed effects of the toxins on DNA. It is proposed that Ah receptor-mediated enzyme induction, particularly of cytochrome P450, is involved in reduced hepatic I-compound formation and that subnormal I-compound levels may contribute to tumor promotion.

Altered fidelity of a nucleic acid modifying enzyme, T4 polynucleotide kinase, by safrole-induced DNA damage

Mouse liver DNA adducted with metabolites of the spice constituent safrole (1-allyl-3,4-methylenedioxybenzene), when analyzed via the bisphosphate version of the 32P-postlabeling assay, exhibits two major adducts, which had been previously identified as N2-(trans-isosafrol-3'-yl)2'-deoxyguanosine 3',5'-bisphosphate (adduct 1) and N2-(safrol-1'-yl)2'-deoxyguanosine 3',5'-bisphosphate (adduct 2). However, analysis of the same DNA preparation by the dinucleotide/monophosphate version of the assay gave two additional spots on PEI-cellulose TLC whose nature was clarified in the present study. Several enzymes (T4 polynucleotide kinase, nuclease P1, venom phosphodiesterase and spleen phosphodiesterase) were utilized to hydrolyze these compounds, and the products co-chromatographed on PEI-cellulose thin layers with radiolabeled and non-radioactive nucleotides of known structure. The additional spots were found to be adducted dinucleotides carrying 32P-label at both the 5'- and 3'-hydroxyls. T4 polynucleotide kinase-catalyzed 3'-phosphorylation was highly specific in that only dinucleoside monophosphate derivatives of adduct 1, with an unmodified purine in the 3'-position, were susceptible to both 5'- and 3'-phosphorylation by the enzyme. Thus, the structures of the two additional 32P-labeled safrole derivatives were pX1pAp and pX1pGp where X1 denotes N2-(trans-isosafrol-3'-yl)2'-deoxyguanosine. The official name of T4 polynucleotide kinase, ATP:5'-dephosphopolynucleotide 5'-phosphotransferase (EC 2.7.1.78), denotes the specific action of this enzyme as a 5'-phosphokinase. Although the enzyme has 3'-phosphatase activity at acidic pH, no 3'-kinase reaction has been previously reported. Possible implications for chemical carcinogenesis of the finding that carcinogen-DNA adducts can specifically alter the fidelity of protein-nucleotide interactions are discussed.

Formation and persistence of safrole-DNA adducts over a 10,000-fold dose range in mouse liver

The spice constituent safrole (1-allyl-3,4-methylenedioxybenzene) and related allylbenzenes form DNA adducts and are rodent carcinogens. This study examined both dose and time dependence of hepatic safrole-DNA adduct formation over a 10,000-fold dose range up to 30 days after single administration. Female CD-1 mice were treated with safrole i.p. at 0.001, 0.01, 0.1, 1.0, and 10.0 mg/mouse in 0.2 ml tricaprylin or with vehicle alone. Liver DNA was analyzed at 0.5, 1, 2, 3, 7, 15 and 30 days via the dinucleotide/monophosphate version of the 32P-postlabeling assay. An approximately 10-fold increase in total safrole adduct levels with each successive 10-fold increase in dose was observed, giving relative adduct labeling (RAL) values of 10(-9)-10(-5). Each dose elicited identical kinetics of adduct formation, showing peak levels at 2 days and only slight decreases thereafter. The time course of adduct persistence was independent of the dose (0.01-10 mg/mouse). An in vitro experiment established that the assay responded in strictly linear fashion to adduct concentration over a 10,000-fold range, and thus was suitable for in vivo dosimetry. DNA synthesis, as measured by [3H]thymidine incorporation, was enhanced only for the 10.0 mg dose at 2, 3 and 7 days. These results indicate a linear response of safrole-DNA adduct formation and persistence in mouse liver following administration of minute (0.001 mg/mouse) to high (10.0 mg/mouse) doses of the carcinogen.

3-Methylcholanthrene-inducible liver cytochrome(s) P450 in female Sprague-Dawley rats: possible link between P450 turnover and formation of DNA adducts and I-compounds

The hepatic cytochrome P450s are mixed-function oxidases which metabolize a wide variety of xenobiotics and endobiotics, and also bioactivate carcinogens such as 3-methyl-cholanthrene (MC) to reactive metabolites capable of forming DNA adducts. To investigate possible relationships between cytochrome P450 induction and covalent DNA modifications (adducts and I-compounds), female Sprague-Dawley rats were i.p. treated with MC (25 mg/kg) in corn oil (CO), once daily for 4 days. Controls received CO only. Animals were euthanized at 1, 8, 15, 28 and 45 days after the last MC treatment, and liver microsomal cytochrome P450, ethoxycoumarin O-deethylase (ECD) and ethoxyresorufin O-deethylase (EROD) activities were determined. Liver DNA adducts and I-compounds were analyzed by 32P-postlabeling. A significant induction of the levels of P450, ECD and EROD activities was noted in MC-treated rats, and elevated enzyme levels persisted for about 6 weeks after cessation of MC administration. Linear decay of total P450, ECD and EROD activities as a function of time was observed. MC induced 11 DNA adducts in liver, which were resolved by thin-layer chromatography (TLC) and persisted at high levels throughout the study. On the other hand, MC elicited a significant depletion of both non-polar and polar I-compounds (age-dependent DNA modifications detectable by 32P-postlabeling in rodent tissues without known exposure to carcinogens). Level of most I-compounds returned to normal at 45 days, and this paralleled the return of P450-related activities to normal. These results suggest a possible link between P450 turnover, DNA adduct formation, and I-compound depletion.

Flavor constituents in cola drinks induce hepatic DNA adducts in adult and fetal mice

Mice given one of several widely consumed cola drinks in place of drinking water for up to 8 weeks developed significant levels of covalent liver DNA adducts in a time dependent manner, as measured by 32P-postlabeling. These adducts were not detected in mice given tap water or one of 3 non-cola beverages. Adducts chromatographically identical to those induced by cola drinks were detected in mice treated with extracts of nutmeg or mace, spices from the nutmeg tree (Myristica fragrans Houttuyn), or with myristicin (1-allyl-5-methoxy-3,4-methylenedioxybenzene), the major spice constituent of nutmeg. In addition, small amounts of adducts derived from the hepatocarcinogen safrole (1-allyl-3,4-methylenedioxybenzene), a minor constituent of nutmeg, were observed. Liver DNA adducts were also detected in fetal liver when pregnant mice were intubated with myristicin. Possible implications of these findings for human health are discussed.

Bulky DNA-adduct formation induced by Ni(II) in vitro and in vivo as assayed by 32P-postlabeling

Various small oxidation products (e.g. 8-hydroxydeoxyguanosine) can be induced in DNA by nickel compounds. In this study, the 32P-postlabeling assay was applied to determine whether Ni(II) compounds are able to induce bulky DNA-adduct formation in vitro and in vivo. In vitro studies detected two major and several minor adducts in DNA incubated with NiCl2 and H2O2 at 37 degrees C for 1 h. Formation of the two major adducts increased with incubation time (0-24 h) and NiCl2 concentration (0-800 microM). Adduct levels were greatly reduced by hydroxyl free-radical scavengers, i.e. 0.4 M sodium formate or 0.05 M p-nitrosodimethylaniline, and by a singlet oxygen scavenger, 0.05 M sodium azide. The in vitro effects of NiCl2 on DNA were significantly enhanced by (1) addition of 3 mM ascorbic acid, (2) replacement of H2O with D2O in the reaction, and (3) prior denaturation of DNA. Adduct formation presumably involved a Fenton-type reaction, in which DNA crosslinks may arise by reaction with hydroxyl free radicals and singlet oxygen. For in vivo studies, male 6-8 wk old B6C3F1 mice were used. In untreated mice, several I-compounds (putative indigenous DNA modifications that increase with age) were detected in liver, kidney, and lung. Two of these (spots 1 and 2) were chromatographically identical to the two major spots induced by Ni(II) in vitro. The intensities of spots 1 and 2 in kidney and of some other spots in liver and lung were increased 1 and 2 h after i.p. injection with a single dose of 170 mumols/kg NiAc2. The effects of NiAc2 were reduced or undetectable in the three tissues 24 h after treatment. These observations indicate the capacity of Ni(II) to induce and modulate bulky DNA modifications both in vitro and in vivo.