Oxidative stress related DNA adducts in the liver of female rats fed with sunflower-, rapeseed-, olive- or coconut oil supplemented diets

Both animal and epidemiological studies support an effect of fatty acid composition in the diet on cancer development, in particular on colon cancer. We investigated the modulating effect of supplementation of the diet of female F344 rats with sunflower-, rapeseed-, olive-, or coconut oil on the formation of the promutagenic, exocyclic DNA adducts in the liver, an organ where major metabolism of fatty acids takes place. 1,N(6)-ethenodeoxyadenosine (etheno-dA), 3,N(4)-ethenodeoxycytidine (etheno-dC) and 1,N(2)-propandodeoxyguanosine from 4-hydroxy-2-nonenal (HNE-dGp) were determined as markers for DNA-damage derived from lipid peroxidation products and markers for oxidative stress. 8-Oxo-deoxyguanosine (8-Oxo-dG) was also measured as direct oxidative stress marker. The body weight of the rats was not influenced by the four diets containing the different vegetable oils during the 4-week feeding period. Highest adduct levels of etheno-dC (430 +/- 181 adducts/10(9) parent bases), HNE-dGp (617 +/- 96 adducts/10(9) parent bases) and 8-Oxo-dG (37,400 +/- 12,200 adducts/10(9) parent bases) were seen in rats on sunflower oil diet (highest linoleic acid content). Highest adducts levels of etheno-dA (133 +/- 113 adducts/10(9) parent bases) were found in coconut oil diet (lowest content of linoleic acid). Weakly positive correlations between linoleic acid content in the four diet groups were only observed for levels of HNE-dGp and 8-Oxo-dG. Neither the diet based on olive oil (which contains mainly oleic acid) nor the diet based on rapeseed oil (containing alpha-linolenic acid) exerted any significant protective effect against oxidative DNA damage. Our results indicate that a high linoleic acid diet may contribute to oxidative stress in the liver of female rats leading to a marginal increase in oxidative DNA-damage.

Unaltered brain levels of 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal in Alzheimer's disease

In recent years, an important role for the pathogenesis of Alzheimer's disease (AD) has been ascribed to oxidative stress. Trans-4-hydroxy-2-nonenal, a product of lipid peroxidation, forms stable adducts with a variety of nucleophilic substituents such as thiols or amino moieties. Here, we report the quantification of 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal (HNE-dGp) using the specific and very sensitive method of 32P-postlabeling of deoxyguanosine adducts derived from nuclear DNA in neuron rich areas of the hippocampus, the parietal cortex, and the cerebellum of postmortem brains from patients with AD and age matched controls. Adduct levels were highest in the hippocampus, followed by the cerebellum and parietal cortex irrespective of the disease. Neither age, postmortem delay time, gender, nor the extent of neurofibrillary deposits affected tissue adduct levels in the brain areas examined. Although distinctively present in the human brain, the level of HNE-dGp adducts appears not to be useful as a biomarker for AD.

DNA profiling: a valuable tool for quality control of sample logistics including occurrences of suspected sample confusion in a blood donation centre

BACKGROUND AND OBJECTIVES

A molecular method for analysing whole-blood samples should be established for quality control of plasma sample logistics.

MATERIALS AND METHODS

DNA profiles of retention samples (plasma) were compared to profiles of recent donations (whole blood). DNA extraction, amplification and detection were performed using the Qiagen DNA Blood Mini kit, the AmpFFISTR Profiler Plus Kit and capillary electrophoresis, respectively.

RESULTS

Matched pairs of full profiles were obtained for all samples investigated, therefore no deviation from the standardized procedures was detected.

CONCLUSIONS

Modified extraction and amplification protocols enabled DNA profiling to be used for the quality control of plasma samples. Hence, DNA profiling can be used in the blood bank as a safe and easy method for quality control of sample logistics.

Detection of 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal after gavage of trans-4-hydroxy-2-nonenal or induction of lipid peroxidation with carbon tetrachloride in F344 rats

The 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal (HNE-dGp-adducts) were quantitated in tissues of rats treated with trans-4-hydroxy-2-nonenal (HNE) or carbon tetrachloride, respectively, using a 32P-postlabeling method. The method development was based on chemically synthesized HNE-1,N2-propanodeoxyguanosine adduct standard, which was characterized by NMR and mass spectra. The adducts were enriched by Nuclease P1. They were subsequently reacted with gamma-32P-ATP to give the respective 3'-5'-bisphosphates, which were two-directionally separated on PEI-cellulose-TLC and quantitated by autoradiography. The labeling efficiency for the adduct standard was 27%, and the recovery of spiked amounts of adduct standard in the enzymatical procedure was about 80%. Internal standard was used to eliminate methodological variations. The determination of the limit of quantitation in DNA from rat tissues by spiking of HNE-dGp-adduct standard revealed a sensitivity of about 20 HNE-dGp-adducts/10(9) normal nucleotides. Background levels of HNE-dGp-adducts in tissues of rats including liver, kidney, lung, colon and forestomach were found in the range of 18-158 adducts/10(9) nucleotides with relatively high adduct levels in the liver and low adduct levels in kidney, lung and colon. These background levels were statistically significantly increased by the factor of 2 in liver, lung, colon and forestomach after induction of lipid peroxidation by carbon tetrachloride. The finding that background HNE-dGp-adduct levels may be in context with different metabolic activities of the tissues and the increase of HNE-dGp-adduct levels after application of carbon tetrachloride indicate that HNE-dGp-adducts are an endogenous lesion and that they are probably formed from radical initiated lipid peroxidation.

Cancer risk assessment for the environmental mutagen and carcinogen crotonaldehyde on the basis of TD(50) and comparison with 1,N(2)-propanodeoxyguanosine adduct levels

Humans are ubiquitously exposed to crotonaldehyde to a strongly varying extent, in particular, via food and alcoholic beverages. Like other alpha,beta-unsaturated carbonyl compounds, crotonaldehyde forms 1,N(2)-propanodeoxyguanosine adducts and is genotoxic, mutagenic, and carcinogenic. This study was designed to perform a cancer risk assessment on the basis of TD(50), which was available from a long-term cancer study with F-344 rats (F. L. Chung et al., Cancer Res., 46: 1285-1289, 1986), and the estimated daily intake via food and beverages. A relatively high cancer risk of 0.1-1 cancer incidence/10(3) humans was extrapolated on the basis of the TD(50) from the cancer study of Chung et al. for the estimated dietary intake and drinking wine. To compare the 1,N(2)-propanodeoxyguanosine DNA adduct levels of crotonaldehyde with the assessed cancer risk, we synthesized adduct standards and developed a (32)P-postlabeling method for DNA adducts of crotonaldehyde providing a detection limit of 3 adducts/10(9) nucleotides. Repeated gavages of 10 and 1 mg/kg were given to simulate the steady-state situation of the animal cancer study of Chung et al. and to estimate the adduct levels after intake of crotonaldehyde via food. The estimated adduct levels at these crotonaldehyde intakes were in the range of 3 adducts/10(9) nucleotides. The adducts persisted to a certain extent. The persistence is important for considering the steady-state situation after permanent intakes of crotonaldehyde via food. However, the adducts are repaired to some extent; 2 weeks after the last of repeated gavages, only 19% of the initial amount measured directly after the last gavage is left. According to our results, a steady-state concentration in the range of 3 adducts/10(9) nucleotides is responsible for the induction of cancer in the study of Chung et al., in the case that cancer from crotonaldehyde depends exclusively on the 1,N(2)-propanodeoxyguanosine adducts considered here. No propanodeoxyguanosine adducts of crotonaldehyde were found in the DNA of untreated animals in our studies.

On the role of alkylating mechanisms, O-alkylation and DNA-repair in genotoxicity and mutagenicity of alkylating methanesulfonates of widely varying structures in bacterial systems

The Ames test and the SOS-chromotest are widely used bacterial mutagenicity/genotoxicity assays to test potential carcinogens. Though the molecular mechanisms leading to backmutations and to the induction of SOS-repair are in principle known the role of alkylation mechanisms, of different DNA-lesions and of DNA-repair is in parts still unknown. In this study we investigated 14 monofunctional methanesulfonates of widely varying structures for mutagenicity in Salmonella typhimurium strain TA 1535 sensitive for O(6)-guanine alkylation for comparison with strain TA 100 in order to obtain additional information on the role of alkylation mechanisms, formation of the procarcinogenic DNA-lesion O(6)-alkylguanine and the role of DNA-repair in induction of backmutation. The substances were also tested in the SOS-chromotest with Escherichia coli strain PQ 37 and strain PQ 243 lacking alkyl base glycosylases important for base excision repair in order to examine the role of alkylation mechanisms, of base excision repair and the role of O-alkyl and N-alkyl DNA-lesions on the induction of SOS-repair. The secondary methanesulfonates with very high S(N)1-reactivity isopropyl methanesulfonate and 2-butyl methanesulfonate showed highest mutagenicities in both strains. The higher substituted methanesulfonates with very high S(N)1-reactivity had lower mutagenic activities because of reduced half lives due to their high hydrolysis rates. A clear increase in mutagenicities in strain TA 100 was observed for the primary compounds methyl methanesulfonate and allyl methanesulfonate with very high S(N)2-reactivity. The primary compound phenylethyl methanesulfonate has a relatively high mutagenicity in both Salmonella strains which can be explained by an increased S(N)1-reactivity and by low repair of the O(6)-phenylethylguanine. Highest SOSIPs (SOS inducing potency) in strains PQ 37 and PQ 243 were found for methyl methanesulfonate and for the secondary compounds with high S(N)1-reactivity. The ratios in the SOSIPs between strain PQ 243 and PQ 37, indirectly indicative for the role of O- and N-alkylation in the induction of SOS-repair, was high for the primary methanesulfonates and lower for the secondary, indicating that the SOS-repair is, to a certain extent, also induced by other lesions than O(6)-alkylation. The results indicate that O(6)-alkylation is also a predominant lesion for backmutation in strain TA 100 and that in the case of monofunctional alkylating agents high S(N)2-reactivities are required to induce error prone repair mediated backmutations. The O(6)-alkylguanine lesion is also important for induction of SOS-repair in the SOS-chromotest, however, other sites of alkylation which are repaired by the base pair excision repair system can also efficiently contribute to the induction of SOS-repair.

Mutagenicity of 2-alkylpropenals in Salmonella typhimurium strain TA 100: structural influences

alpha,beta-Unsaturated aldehydes are a class of mutagenic and carcinogenic compounds that form promutagenic 1,N(2)-propanodeoxyguanosine adducts. They are important industrial and environmental compounds, are formed endogenously, and are found in food. We recently published structure-mutagenicity relationships for 3-alkyl substituted alpha,beta-unsaturated aldehydes (beta-alkylacroleins) and here we present structural influences on the mutagenicity of the 2-alkyl substituted alpha,beta-unsaturated aldehydes (alpha-alkylacroleins), 2-methylacrolein, 2-ethylacrolein, 2-propylacrolein, and 2-butylacrolein, in Salmonella typhimurium TA 100. All four alkylacroleins are mutagenic without S9-mix; however, the results are strongly influenced by bacterial toxicity of the alkylacroleins. In general, toxicity increases with increasing length of the alkyl substituent. The increasing toxicity with increasing alkyl groups can be explained by increasing lipophilicity that allows the compounds to better penetrate into the bacterial cell. Other structural effects, such as steric hindrance of the deoxyguanosine binding (DNA-adduct formation) and the positive inductive effect of the alkyl groups, have only a slight effect on mutagenesis. Addition of S9-mix leads to an increase in the absolute revertant peak values but a decrease in mutagenic activities, as expressed by revertants per micromol. This effect is also observed with heat-inactivated S9-mix and does not depend on metabolic activation. The effect of S9-mix can be explained by partial detoxication of the substances by nucleophilic components of the S9-mix such as glutathione.

An approach to cancer risk assessment for the food constituent 2-hexenal on the basis of 1,N2-propanodeoxyguanosine adducts of 2-hexenal in vivo

2-Hexenal is formed by plants, and humans are regularly exposed to this mutagenic/genotoxic compound via vegetable foods. 2-Hexenal has not been tested for carcinogenicity, but it forms exocyclic 1,N2-propanodeoxyguanosine adducts like other carcinogenic alpha,beta-unsaturated carbonyl compounds. To quantify the respective DNA adducts as an approach to a theoretical cancer risk assessment, we used a newly developed 32P-postlabelling technique based on nuclease P1 enrichment, allowing a detection limit of 3 adducts per 10(8) nucleotides. Adduct levels were measured at different doses and the covalent binding index (CBI) was found to be dose-dependent. This can be explained by glutathione depletion at higher doses. The CBI at low doses was 0.06. A negligible cancer risk of 1-5 per 10(7) lives was estimated on the basis of TD50 values calculated from the correlation between CBI and TD50 of Lutz and on the daily intake of 2-hexenal via vegetable foods, fruit juices and black tea. A risk of 1.6-8.5 per 10(6) lives was estimated for the hypothetical case of glutathione depletion, e.g. due to consuming special medicaments. In every case, the benefit from eating fruit and vegetables is clearly higher than a possible low and unavoidable cancer risk. Utilization of 2-hexenal as a flavouring agent or as a fungicide, breeding fungus-resistant plants or technological gene construction of fungus resistance may lead to a high hypothetical cancer risk of 2-6 per 10(4) lives under certain circumstances which are avoidable and deserves special case-by-case consideration.

Development of a (32)P-postlabeling method for the detection of 1,N(2)-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal in vivo

A (32)P-postlabeling method was developed for the sensitive detection of 1,N(2)-propanodeoxyguanosine adducts of the lipid peroxidation product trans-4-hydroxy-2-nonenal in vivo. The method development was based on the chemically synthesized HNE-1, N(2)-propanodeoxyguanosine adduct standard, which was characterized by NMR and mass spectra. The adducts were enriched by nuclease P1. They were subsequently reacted with [gamma-(32)P]ATP to give the respective 3'-5'-bisphosphates, which were two-directionally separated on PEI-cellulose TLC and quantitated by autoradiography. The medium labeling efficiency for the mixture of the two pairs of diastereomers was 27%, and the recovery of spiked amounts of adduct standard in the enzymatical procedure was about 80%. The method is applicable for the separation and quantitation of HNE-dGp-propano adducts in vivo. It was applied to DNA from colon and brain tissue of untreated Fischer 344 rats and humans. The determination of the limit of quantitation in DNA from rat colon by spiking of adduct standard revealed a sensitivity of <21 adducts/10(9) nucleotides. The analytical quantitation of 4-HNE-dGp-propano adducts resulted in adduct-levels per 10(9) normal nucleotides +/- the standard deviation of 223.32 +/- 79.84 in rat colon tissue, 90.37 +/- 11.94 in rat brain tissue, 378.44 +/- 52.42 in human colon tissue, and 185.15 +/- 6.48 in human brain tissue. The results clearly demonstrate the applicability of this method for the sensitive detection of endogenously formed 1,N(2)-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal, a specific marker for the lipid peroxidation process.

The role of alcohols as solvents in the genotoxicity testing of alpha,beta-unsaturated ketones in the SOS chromotest

alpha,beta-Unsaturated ketones are bifunctional compounds which form promutagenic 1,N(2)-propanodeoxyguanosine adducts like carcinogenic alpha,beta-unsaturated aldehydes and are mutagenic and genotoxic like these aldehydes. They are important industrial chemicals, are found in our environment and are widespread in our food. We investigated the SOS repair inducing activities of five ketones in the SOS chromotest and compared these results with that of the Ames test. Alkyl substitution at the beta-position of the alpha, beta-unsaturated carbonyl moiety leads to a decrease or loss in genotoxicity. Genotoxicity is higher if using ethanol as solvent instead of dimethylsulfoxide (DMSO). An increasing effect is also observed with methanol and n-propanol. Addition of the alcohol dehydrogenase inhibitor 4-methylpyrazole does not significantly influence the genotoxicity indicating that it is unlikely that the solvent effect depends on competitive inhibition of alcohol dehydrogenase by the alcohols used as solvents. Since other possible explanations e.g. ketal formation or solubility effects are also unlikely, the mechanism of this solvent effect observed with three different E. coli PQ-strains remains unresolved. No significant difference in genotoxicity of ethyl vinyl ketone was found between the strains PQ 37 and PQ 243 indicating that base excision repair does not play a role in the repair of 1,N(2)-propanodeoxyguanosine adducts, the main adducts of the alpha,beta-unsaturated ketones.

Development of a 32P-postlabelling method for the detection of 1,N2-propanodeoxyguanosine adducts of crotonaldehyde in vivo

Crotonaldehyde is a genotoxic, mutagenic and carcinogenic alpha,beta-unsaturated carbonyl compound which forms 1,N2-propanodeoxyguanosine adducts. Humans are exposed to this compound at work places, and from tobacco smoke and air pollution, but also from food and beverages. Therefore crotonaldehyde can play a significant role in carcinogenesis. Since in vivo measurement of DNA adducts of crotonaldehyde can improve cancer risk assessment and contribute to the clarification of the role of crotonaldehyde in carcinogenicity, we developed, adapted and optimized a 32P-postlabelling technique for the adducts of crotonaldehyde based on nuclease P1 enrichment and on a polyethylene imine modified cellulose TLC to provide a detection sensitivity of three adducts per 10(9) nucleotides and a labelling efficiency of 80-90%. We also report a readily performable synthesis of adduct standards and demonstrated that DNA is completely digested to the 3'-monophosphate nucleotides under the conditions of our enzymatic DNA hydrolysis. We showed that the postlabelling method developed is appropriate for in vivo DNA-binding studies. Female Fischer 344 rats were treated by gavage with crotonaldehyde at doses of 200 and 300 mg/kg body weight, and 20 h after treatment adduct levels of 2.9 and 3.4 adducts per 10(8) nucleotides, respectively, were found in the liver DNA. Only 1.6 nucleotides per 10(8) nucleotides were found 12 h after treatment at 200 mg/kg body weight. Absolutely no adducts could be found in liver DNA of untreated rats with our method at the detection limit of three adducts per 10(9) nucleotides. In contrast to our group, the group of Chung have reported crotonaldehyde adduct levels in the range of 2.2 22 adducts per 10(8) nucleotides in DNA of untreated Fischer 344 rats. The clarification of this discrepancy is of importance for the elucidation of the role of crotonaldehyde in carcinogenicity, and both groups have decided to clarify this in cooperation in the near future.

Detection of 1,N(2)-propanodeoxyguanosine adducts in DNA of Fischer 344 rats by an adapted (32)P-post-labeling technique after per os application of crotonaldehyde

Crotonaldehyde is an important industrial chemical to which humans and animals are ubiquitously exposed. The main intake occurs via food, tobacco smoke and possibly also via beverages. Estimation of intake via the different routes is difficult since the data available on exposure are inconsistent. Crotonaldehyde is genotoxic, mutagenic and carcinogenic and forms 1,N(2)-propanodeoxyguanosine adducts as the main DNA adducts. We have developed a (32)P-post-labeling method for these adducts based on nuclease P1 enrichment and polyethyleneimine-cellulose TLC which allows reliable detection with a detection limit of 3 adducts/10(9) nucleotides, a labeling efficiency of 80-90% and a recovery of 38%. Using this method we found crotonaldehyde adducts in different organs of Fischer 344 rats after a single gavage of high doses of 300 and 200 mg/kg body wt in the range 0.3-3.2 +/- 0.4 adducts/10(8) nucleotides and after repeated gavage of low doses of 10 and 1 mg/kg body wt (five times a week for 6 weeks) 6.2 +/- 0.2 and 2.0 +/- 0.4 adducts/10(8)nucleotides, but not in untreated animals nor in calf thymus DNA not treated with crotonaldehyde. In contrast to our results, Chung and co-workers found adducts in tissue of untreated Fischer 344 rats. This discrepancy could depend on the different methods used but also on differences in exposure of the animals via food or due to animal housing, etc.

Cancer risk assessment for crotonaldehyde and 2-hexenal: an approach

Crotonaldehyde and 2-hexenal are bifunctional compounds that form 1,N2-propanodeoxyguanosine adducts and are mutagenic and genotoxic; crotonaldehyde is carcinogenic. Analysis of the mutations resulting from crotonaldehyde-induced DNA damage revealed the importance of deoxyguanosine adducts. Humans are exposed ubiquitously to these compounds by various routes. The highest daily intake of crotonaldehyde is assumed to be derived from cigarette smoke (31-169 micrograms/kg body weight), and the highest intake of 2-hexenal is probably from fruit and vegetables (31-165 micrograms/kg body weight per day). Because these compounds are suspected to play on important role in carcinogenicity, we developed sensitive 32P-postlabelling techniques for DNA adducts of crotonaldehyde and hexenal, in order to improve estimates of cancer risk. The respective standards were also synthesized and characterized spectroscopically. We report here the results of the 32P-postlabelling, e.g. the stability of the adducts in respect of nuclease P1 treatment, their labelling efficiencies, thin-layer chromatography of adduct spots and the recoveries and detection limits. In untreated male Fischer 344 rats, neither crotonaldehyde nor 2-hexenal adducts were detected, but crotonaldehyde adducts were found in the tissues of rats given single doses of 200 or 300 mg/kg body weight and in the livers of rats after repeated doses of 1 or 10 mg/kg body weight. The adduct levels were higher 20 h after gavage than after 12 h. The adducts persist to a certain extent. 2-Hexenal adducts were detected in tissues of male Fischer 344 rats after gavage with single doses of 50, 200 or 500 mg/kg body weight. The highest adduct levels were measured 48 h after gavage, but no adducts were found 8 h after gavage. Two approaches for cancer risk estimation are discussed. One is based on the correlation between the covalent binding index, calculated from adduct levels, and the median toxic dose (TD50) (Lutz, 1986) and showed a cancer risk of 1 per 10(7) lives for hexenal, assuming dietary intakes of 31-165 micrograms/kg body weight per day. The other is based on a cancer incidence of 0.07 at a dose of crotonaldehyde of 4.2 mg/kg body weight per day assessed from the study of Chung et al. (1986), which can be interpreted as a risk of 5.8-18 new cases per 10(4) smokers, assuming a consumption of 30 cigarettes per day. The latter approach may, however, lead to an overestimate of the cancer risk associated with exposure to crotonaldehyde; the estimate based on our binding studies resulted in a 20-fold lower estimate of the carcinogenic risk of crotonaldehyde.

Malignancies in patients treated with high doses of radium-224

Predominantly from 1945 to 1955, a group of patients in Germany was treated with multiple injections of the short-lived alpha-particle emitter (224)Ra. The patients suffered from ankylosing spondylitis, tuberculosis and in a few cases from other diseases. The "Spiess study" (study I) follows up the health of 899 of these patients; it includes most of the patients who were treated with high doses (mean bone surface dose: 30 Gy, mean specific activity: 0.66 MBq/kg), and nearly all of those treated under the age of 21 years. The most striking consequence of the (224)Ra injections was the occurrence of 56 malignant bone tumors. They appeared in a temporal wave that peaked around 8 years after exposure. A new analysis was recently performed, because a reassessment of the dosimetry resulted in changed bone surface doses, especially for the patients treated at younger ages. Averaged over all ages at exposure, the estimated risk coefficient is in general agreement with earlier analyses. However, there is now an increase in bone tumor risk that is significantly greater for younger ages at exposure. The earlier finding of an inverse protraction factor is confirmed. During the most recent years of follow-up, a significant excess of nonskeletal solid malignancies has become manifest. In 1998, a significant increase of breast cancer incidence, of soft tissue malignancies, of thyroid carcinomas, and of liver, kidney and bladder cancer was found. An eightfold increased risk of mammary cancers in those treated at a young age is particularly striking. Equally notable are two cases of breast cancer in male patients. To identify potential confounders, a control group of tuberculosis patients not treated with (224)Ra was established. The comparison confirms that the (224)Ra treatment is responsible for most of the excess of mammary cancer.

Detection of 1,N2-propanodeoxyguanosine adducts of 2-hexenal in organs of Fischer 344 rats by a 32P-post-labeling technique

2-Hexenal is an alpha,beta-unsaturated carbonyl compound which is mutagenic, genotoxic and forms cyclic 1,N2-propanodeoxyguanosine adducts like similar propenals for which carcinogenicity was shown, e.g. acrolein or crotonaldehyde. Since humans have a permanent intake of 2-hexenal via vegetarian food this genotoxic compound is considered to play a role in human carcinogenicity. The data base is, however, presently not sufficient for a cancer risk assessment. To date no long term carcinogenicity study on 2-hexenal has been published. Detection of respective DNA adducts of this substance in animals or humans could allow cancer risk assessment. Therefore, we have developed a 32P-post-labeling technique based on nuclease P1 enrichment and TLC separation of the labeled adducts. The respective adducts are stable over a wide pH range from pH 4 to pH 11 and relatively stable against nuclease P1. The detection limit was 0.03 adducts per 10(6) nucleotides and the recovery was 10%. With this method we have shown in vivo formation of 1,N 2-propanodeoxyguanosine adducts of 2-hexenal for the first time and found the respective DNA adducts in different organs of Fischer 344 rats after gavage of 500, 200 and 50 mg 2-hexenal/kg body wt. No adducts could be detected in the organs of untreated rats. There is a clear dependence of the adduct level and the CBI (covalent binding index) on the dose. The CBI of 2-hexenal calculated on the basis of our adduct levels is extremely low (0.06). Since intake of 2-hexenal via fruit and vegetables is very low the cancer risk from 2-hexenal intake via food must also be considered as very low according to a first raw estimation on the basis of CBI and intake. The situation deserves, however, a more precise risk assessment in the future.

Development of a 32P-postlabeling method for the detection of 1, N2-propanodeoxyguanosine adducts of 2-hexenal in vivo

2-Hexenal is an alpha,beta-unsaturated carbonyl compound which forms cyclic 1,N2-propano adducts in vitro. The adduct formation in vivo was not reported by others to date. Because this type of adduct is considered promutagenic (2-hexenal is actually mutagenic and genotoxic) and humans are permanently exposed to this compound via vegetarian food, 2-hexenal may play a role in carcinogenicity. To improve the cancer risk assessment, we developed a new 32P-postlabeling technique for this compound and optimized the different steps of the postlabeling procedure. The results of the postlabeling methods are shown. A labeling efficiency of 35%, a recovery of 10% for the synthesized standards, and a detection limit of three 2-hexenal adducts per 10(8) nucleotides was achieved. After gavage of 500 mg/kg of body weight to male Fischer 344 rats, the respective DNA adducts were detected in rat liver DNA. With this study, we demonstrate in vivo adduct formation of 2-hexenal for the first time. Highest adduct levels were found 2 days after gavage, and after 4 days, the level was even higher than after 1 day. No adducts were detected 8 h after gavage. The respective adducts could not be found as a background in tissues of untreated rats or in calf thymus DNA at the limit of detection.

Intraindividual variations of DNA adduct levels in humans

Reports on intraindividual changes of DNA adduct levels in humans are rare. Most of the data available in the literature are from polycyclic aromatic hydrocarbons (PAHs) and are measured in white blood cells with 32P-postlabeling or immunochemical assays. Surprisingly, environmental exposure can have a larger effect on PAH adduct levels than occupational exposure, food or smoking. Highest (13-fold) summer/winter increments, due to indoor heating were observed in Gliwice, Poland. Further studies of environmental PAH exposure confirm the environmental influence on intraindividual changes in PAHs-DNA adduct levels: studies of the Teplice program, (Czech Republic) and studies with US soldiers, stationed in Germany who went for a 8-week period of duty to Kuwait. Variations in occupational exposure, e.g., changing of anode material in aluminium plants (elevation factor 3.94), layoffs, reduced working hours in iron foundries or vacation also led to intraindividual changes in PAH adduct levels. Increase in PAH adduct levels after consumption of charcoal broiled meat evidently depends on individual susceptibility, e.g., polymorphism. In one person a 7.4-fold increment was observed. PAH adduct levels were not significantly influenced by smoking cessation whereas sister chromatid exchanges significantly decreased. Changes in occupational exposure to styrene in lamination plants, e.g., due to vacation, did not significantly influence styrene-O6-dG adduct levels in lymphocytes and granulocytes as determined by 32P-postlabeling. Increase of N7-methylguanine and O6-methylguanine levels were followed in white blood cells during treatment of cancer patients with dacarbazine and allowed insights into pharmacokinetic properties. According to a rough estimation the high increment in the PAHs-DNA adduct level of about 13 observed in Gliwice (see above) would result in a tentative increase in cancer risk from about 1 death/107 inhabitants to approximately 10 deaths/107 inhabitants which, in general, is considered as acceptable.

[Experiences with internal thoracic vessels in breast reconstruction with the free TRAM flap]

In breast reconstruction with free TRAM flaps, the thoracodorsal vessels are most commonly used as recipient vessels. In case of an irradiated and scarred axillary region, the internal thoracic vessels may be an alternative. In the pertinent literature it has been pointed out that the veins may be fragile and thin and, thus, not suitable for microvascular anastomosis. In a series of 31 breast reconstructions with free TRAM flaps, the internal thoracic vessels were dissected and evaluated in 24 cases in order to assess the value of this vascular system as a recipient site for free flap transplantation. In four cases, the veins were too small for anastomosis, and in one case the artery was severed during dissection. End-to-end anastomoses were performed in 19 cases (79%). The following complications were recorded: One marginal necrosis; one venous thrombosis, which was detected and salvaged by revision; one recurrent arterial thrombosis, resulting in flap loss; one pleural lesion healed uneventfully.

32P-Postlabeling analysis of DNA adducts of styrene 7,8-oxide at the O6-position of guanine

A 32P-postlabeling method was established for the quantitative characterization of 2'-deoxyguanosyl O6-adducts of styrene 7,8-oxide in DNA. The two regioisomeric adducts, O6-(2-hydroxyl-1-phenylethyl)-2'-deoxyguanosine 3'-phosphate (alpha-isomer) and O6-(2-hydroxyl-2-phenylethyl)-2'-deoxyguanosine 3'-phosphate (beta-isomer), were synthesized and used for optimizing and quantifying the various analytical steps. The adducts were stable at pH 7 and 10, but not at pH 4. The adducts were sensitive to dephosphorylation during the standard nuclease P1 (NP1) treatment. Within 30 min, 73 and 94% of the alpha- and beta-isomers were digested. Adducts could not be extracted into butanol, and micropreparative chromatography on reversed-phase thin layers resulted in a loss of adducts at low levels. Therefore, further methods of enrichment had to be investigated. Micropreparative reversed-phase HPLC chromatography on a C18 column resulted in a many thousand-fold purification from the normal nucleotides. Further enrichment was achieved with a mild NP1 treatment. The phosphorylation efficiency with polynucleotide kinase was 5 and 15% for the alpha- and beta-isomers, respectively. Adduct analysis was performed with reversed-phase TLC followed by contact transfer of the origin to a polyethyleneimine-cellulose sheet and two-dimensional development. Addition of various amounts of adduct standard to the hydrolysate of 30 microg of DNA isolated from a control rat liver showed limits of detection of three and two adducts per 10(7) nucleotides for the alpha- and beta-isomers, respectively. The applicability of the newly developed method was demonstrated by the DNA analysis of styrene-exposed rats.

Structures of acrolein-guanine adducts: a semi-empirical self-consistent field and nuclear magnetic resonance spectral study

The structures and conformations of adducts formed by reaction of guanosine with several mutagenic alpha,beta-unsaturated carbonyl compounds have been investigated by semi-empirical molecular orbital calculations and compared with NMR spectral results. Two cyclization processes taking place on the pyrimidine ring of guanine leading to two sets of regioisomers, 11-hydroxy- and 13-hydroxytetrahydropyrimidinoguanines (THPG), were considered. Relative stabilities and geometries of all configurations and conformations of adducts with acrolein, crotonaldehyde, and alpha-chloroacrolein were calculated by PM3, AM1, and MNDO methods. PM3 results were the most compatible with experimental structures based on 400-MHz 1H NMR spectroscopy. The most stable structures for the 11-hydroxy and 13-hydroxy THPG isomers from acrolein are predicted to have chair-like structures for the tetrahydropyrimidine ring and axial hydroxyl groups, as suggested by the NMR spectra of the isolated adducts. Of the possible isomers from guanine and crotonaldehyde, cis-11-hydroxy-13-methyl THPG with methyl and hydroxyl groups axial is predicted to be the most stable. The only isolated adduct is the trans-13-hydroxy-11-methyl THPG with methyl shown to be equatorial and hydroxyl axial by 1H NMR. This is completely consistent with the geometry predicted by PM3 for the 13-hydroxy regioisomer of crotonaldehyde. In the case of adducts of alpha-chloroacrolein, one stereoisomer predominates for each of the two possible regioisomers. For the 12-chloro-11-hydroxy isomer, the cis configuration with chlorine axial and hydroxyl quasi-axial is calculated to have the most stable geometry. In contrast, the 1H NMR spectrum supports a trans diaxial orientation, although the cis computed structure could also be accommodated by the spectrum. The 12-chloro-13-hydroxy regioisomer is unambiguously assigned as trans diaxial by PM3 calculations and 1H NMR spectroscopy.

Genotoxicity and mutagenicity of the alpha, beta-unsaturated carbonyl compound crotonaldehyde (butenal) on a plasmid shuttle vector

Crotonaldehyde is an alpha,beta-unsaturated carbonyl compound and an important environmental and industrial toxic substance. Its mutagenic and carcinogenic properties are related to its reactivity to DNA, where it forms different guanine adducts. In order to study the mutagenic consequences of this agent in intact human cells, we treated the shuttle vector plasmid pZ189 with different doses of crotonaldehyde at 37 degrees C for 2 h and then transfected the such damaged plasmid into the normal human lymphoblast cell line GM0621. Within these host cells the guanine adducts are repaired and the plasmids replicated by cellular enzymes. After 2.5 days replicated plasmids were purified from the cells and plasmid survival was quantitated by transformation ability. With increasing doses of crotonaldehyde, we found a significant decline of plasmid survival, reflecting a pronounced genotoxicity of crotonaldehyde-induced DNA damage in intact human cells. Using the plasmid encoded mutagenesis marker gene supF, we were able to screen for mutants and determine mutation frequency in recovered plasmids. A significant increase in mutation frequency with increasing doses of crotonaldehyde reflects mutagenicity of crotonaldehyde-induced DNA damage. Base sequence analysis of recovered mutants revealed 39% point mutations, 46% deletions, and 15% insertions and inversions. Most of the point mutations (82%) were located at G:C base pairs, which is well explained by the DNA damage profile of crotonaldehyde. Among deletions we found a frequent reoccurrence of two hot spot deletions, representing 62% of all deletions. The sites of breakpoints of these deletions hot spots and of other deletions within the plasmid were also found to be sites of DNA breaks, directly induced by crotonaldehyde, as seen in an endlabeled plasmid fragment, treated with crotonaldehyde. Further analysis of the flanking sequences around the deletion breakpoints revealed a high frequency of four different kinds of short sequence homologies of up to eight base pairs.

Comparative analysis of 8-oxo-2' -deoxyguanosine in DNA by 32P- and 33P-postlabeling and electrochemical detection

8-Oxo-2'-deoxyguanosine (8-oxo-dG) is emerging as a useful marker for oxidative DNA damage. Reported basal levels determined by 32P-postlabeling (PPL) method were 10-fold or more higher than those obtained with HPLC/electrochemical detection (ECD). This discrepancy was investigated. In commercial calf thymus DNA, levels of 4 +/- 1 and 64 +/- 14 8-oxo-dG per 10(6) 2'-deoxynucleosides (dN) were measured by the standard HPLC/ECD and PPL methods, respectively. DNA digestion by micrococcal nuclease/spleen phosphodiesterase and nuclease P1 (as used in the standard PPL method), followed by ECD analysis resulted in a level of 8 +/- 3. In calf thymus DNA spiked with chemically synthesized 8-oxo-dGp to give an increment of 9 8-oxo-dG/10(6) dN, the added standard produced a significant increase with HPLC/ECD but not PPL. After spiking the DNA with 90 8-oxo-dG/10(6) dN, the added 8-oxo-dGp was detectable also with PPL, with a labeling efficiency of 65%. In order to investigate the role of ionizing radiation from 32P for the higher 8-oxo-dG levels in PPL, incubation times and amounts of radioactivity in the phosphorylation reaction with commercial dGp were increased, and external irradiation of commercial dG with 32P was investigated. All modifications resulted in higher values of 8-oxo-dG measured, but the effect was not large enough to fully explain the discrepancy between PPL and HPLC/ECD. Using [gamma-33P]ATP instead of [gamma-32P]ATP or adding [33P]phosphate to a 32P-PPL assay resulted in even higher levels of 8-oxo-dG measured. The increase in 8-oxo-dG levels during the PPL workup is attributed to the presence and oxidation of unmodified dGp in the reaction mixture. For a determination of true basal levels, the PPL method will have to be modified, including the removal of dGp prior to the phosphorylation reaction.

Pneumothorax complicating laparoscopic ureterolysis

In a 71-year-old female marked left-sided ureteral stenosis secondary to retroperitoneal fibrosis was diagnosed. Since conservative therapy with cortisone had failed, laparoscopic ureterolysis was performed. Following tracheal intubation the lungs were ventilated with 40 vol% O2 in air and isoflurane 0.5-2%, using a positive end-expiratory pressure of 6 cm H2O. A CO2 pneumoperitoneum was established with a pressure-controlled high-flow insufflator; the intraabdominal pressure during the procedure was 14 mm Hg. Two hours after gas instillation, the peak airway pressure increased from 22 to 40 cm H2O, and the PaCO2 from 45 to 70 mm Hg. Breath sounds over the right lung were no longer heard, and subcutaneous emphysema was noted over the neck and face. An intraoperative chest X-ray confirmed a right pneumothorax. Following peritoneal gas evacuation, the PaCO2 returned to 35 mm Hg, the subcutaneous emphysema diminished, and a repeat chest X-ray showed complete resolution of the pneumothorax. The course of this event led us to the conclusion that the pneumothorax was due to diffusion of CO2 from the peritoneal to the pleural cavity through congenital defects in the diaphragm. Ureterolysis could be continued by laparotomy.

Crotonaldehyde: a carcinogenic and mutagenic air, water and food pollutant

Crotonaldehyde is mutagenic and carcinogenic and it is ubiquitous in our environment. The data base does, however, not allow an assessment of the carcinogenic risk. We have developed a sensitive 32P-postlabelling technique which allows the detection of specific DNA-adducts in animal tissues as markers for initiation of cancer cells. Adducts were found in several organs of F 344 rats after gavage and persisted to a certain extent. The determination of adduct levels in animal tissues after different exposure or even in human tissues can therefore be considered as an effect monitoring and would certainly improve the risk assessment.

Mutagenic and carcinogenic risk of oxygen containing chlorinated C-3 hydrocarbons: putative secondary products of C-3 chlorohydrocarbons and chlorination of water

Oxygen containing C-3 chlorohydrocarbons are secondary products of C-3 chlorohydrocarbons formed during oxidation at air, in the metabolism of pesticides and by chlorination of drinking water. These compounds are mutagenic, genotoxic and carcinogenic. 2-Chloroacroleins are extremely strong mutagens and genotoxins and form 1,N2-cyclic deoxyguanosine adducts. The role of such adducts in mutagenicity and carcinogenicity is discussed.

Genotoxicity of 2-halosubstituted enals and 2-chloroacrylonitrile in the Ames test and the SOS-chromotest

2-Chloroacrolein and 2-bromoacrolein are very potent direct mutagens not requiring metabolic activation in Salmonella typhimurium strains TA 100 and TA 1535. Mutagenic activities decrease with increasing degree of methyl substitution at carbon atom C-3 of the acrolein moiety from 2-chloroacrolein via 2-chlorocrotonaldehyde to 2-chloro-3,3-dimethylacrolein. With 2-chloroacrylonitrile equivocal results are obtained in strain TA 100 without S9-mix and unequivocal with S9-mix. In the SOS-chromotest the 2-chloroenals are also very strong genotoxins and the structure-activity relationships found in the Ames test are clearly confirmed. 2-Chloroacrylonitrile is not positive in the SOS-chromotest. The mutagenic mechanisms are discussed, and indications are provided that genotoxicity/mutagenicity depends on formation of DNA adducts, e.g., 1,N2-cyclic deoxyguanosine adducts.

Genotoxicity of 2-halocinnamaldehydes in two bacterial assays. Induction of SOS repair and frame-shift mutation

2-Chlorocinnamaldehyde and 2-bromocinnamaldehyde, compounds of practical interest, for example, as bacteriocides and fungicides or for utilization in light sensitive layers, were tested in the Ames preincubation test with various Salmonella typhimurium strains, and in the SOS chromotest with Escherichia coli PQ 37.2-Chlorocinnamaldehyde was clearly mutagenic in strain TA 100 (6081 revertants/mumol) and in strain TA 98 (3050 revertants/mumol) without S9 mix, and was clearly positive in the SOS chromotest (SOSIP = 0.181). 2-Bromocinnamaldehyde was a strong mutagen in strain TA 100 (105, 500 revertants/mumol), in strain TA98 (41567 revertants/mumol) and in strain TA 1538 (15825 revertants/mumol), and also unambiguously mutagenic in strain TA 1535 (2110 revertants/mumol) without S9 mix. The SOSIP in the SOS chromotest was 1.5. Addition of S9 mix led to a marked decrease in the mutagenic activity of 2-bromocinnamaldehyde in all strains tested. In the case of strain TA 1535, mutagenic activity was abolished or not significant in the presence of S9 mix. The possible primary mechanisms underlying these mutagenic effects are discussed. Frame-shift activity of these halocinnamaldehydes can be explained by their planar structure.

1,N2-cyclic deoxyguanosine adducts and guanine adducts of 2-haloacroleins. Isolation, characterization, isomerization and stability

The reaction of the mutagenic 2-haloacroleins, 2-fluoroacrolein, -2-chloroacrolein and 2-bromoacrolein, with nucleosides and 5'-mononucleotides was studied. We found two different regioisomers of 1,N2-cyclic deoxyguanosine adducts of 2-chloroacrolein and 2-bromoacrolein: type A, the 6-hydroxy, 7-haloadduct in which the OH-substituent is vicinal to the N2-atom of the guanine moiety and type B, the 8-hydroxy, 7-haloadduct in which the OH-group is adjacent to the N1-atom of the guanine moiety. The major adducts were the trans pairs of diastereomers of type A and type B in which the 6,7-substituents as well as the 7,8-substituents are in the energetically favoured diaxial position of the newly formed tetrahydropyrimidine ring. In the case of the type A regioisomers, the cis pairs of diastereomers (traces with chloroacrolein and about 4% with bromoacrolein) were also found in which the halosubstituent probably takes the equatorial position. Due to the anomeric effect, the OH-group takes the axial position in both regioisomers. No cis isomers of the type B regioisomers could be isolated. Acid hydrolysis of the deoxyguanosine adducts released deoxyribose, and the respective guanine adducts were isolated and characterized. Besides the vicinal halo, hydroxy adducts, trace amounts of the corresponding dihydroxy adducts were formed by hydrolysis of the chlorine or bromine substituents. The dihydroxy compounds possess the same structures and conformations in the newly formed tetrahydropyrimidine ring as do the halo, hydroxy adducts. Under our conditions no adducts other than those with deoxyguanosine and guanine could be identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and characterization of deoxyguanosine adducts of mutagenic beta-alkyl-substituted acrolein congeners

The reaction of the mutagenic beta-alkyl-substituted acroleins (E)-2-pentenal, (E)-2-hexenal, (E,E)-2,4-hexadienal, and 3,3-dimethylacrolein with nucleosides and 5'-mononucleotides was studied. We found two different types of adducts with deoxyguanosine and 2'-deoxyguanosine 5'-monophosphate. No adducts could be isolated with either nucleosides other than deoxyguanosine or nucleotides other than 2'-deoxyguanosine 5'-monophosphate. With pentenal, hexenal, and 3,3-dimethylacrolein, we identified and characterized 1,N2-cyclic adducts and 7,8-cyclic adducts. The 1,N2-adducts of pentenal and hexenal were mixtures of diastereomers, one pair in which the substituents in the newly formed ring were trans (6S,8S and 6R,8R) and another in which they were cis. The cis isomers were formed to a much lesser extent. In all cases, the regioisomer is formed in which the OH group is vicinal to the N-1 atom of the guanine moiety. In the case of the 7,8 adducts, the ribose cleaved spontaneously during the reaction, and a mixture of isomers in which the substituents were cis and trans in the newly formed tetrahydropyrrole ring was observed. Since these compounds form adducts in a similar way to crotonaldehyde and are also mutagenic like crotonaldehyde, it was proposed to regard them as carcinogenic, like crotonaldehyde, unless experimental examination demonstrates nonmutagenicity.

The possible role of alpha, beta-unsaturated carbonyl compounds in mutagenesis and carcinogenesis

alpha, beta-Unsaturated carbonyl compounds are industrially important compounds, ubiquitous in the environment and are formed endogenously. They interact with proteins and enzymes. Genotoxicity was found in eucaryotic cells and some compounds were carcinogenic. Unsaturated carbonyl compounds are considered to play an important role in human cancer. Insufficient and contradictory results were reported on mutagenicity. We demonstrated a clear mutagenic potential for these compounds and have shown interference of their bacterial toxicity with an adequate testing. Structure-mutagenicity relationships were confirmed by the results of the SOS-chromotest. The compounds induce DNA-strand breaks. However, we did not find indications for cross linking. With mutagenic alpha, beta-unsaturated carbonyl compounds we isolated and characterized 1,N2-cyclic deoxyguanosine adducts, 7,8-cyclic and 7-linear guanine adducts as well as 1,N2-7,8-biscyclic adducts and 1,N2-cyclic, 7-linear bisadducts. Reactivity of these compounds towards nucleosides runs in parallel with their mutagenic potential. Mutagenic and carcinogenic activities most probably depend on these reactions with DNA, and DNA adducts can be utilized as indicators for the role of these compounds in human carcinogenicity.

Biomonitoring studies and susceptibility markers for acrolein congeners and allylic and benzyl compounds

The importance of genotoxic acrolein congeners and allylic and benzyl compounds as industrial compounds, ubiquitous environmental pollutants, and naturally occurring substances necessitates the availability of adequate biomonitoring techniques. Endogenously formed acrolein congeners are considered to play an important role in carcinogenesis. Our studies have demonstrated that acrolein congeners react with DNA components and form adducts with the guanine moiety. We have identified and characterized cyclic 1,N2-deoxyguanosine adducts, cyclic 7,8-guanine adducts, linear 7-guanine adducts, 1,N2,7,8-bis-cyclic adducts, and 1,N2-cyclic, 7-linear bis adducts. Both the reactivity of the acroleins toward nucleosides and their mutagenicity in S. typhimurium TA100 decrease with increasing degree of alkyl substitution. Adducts are now available as reference substances for developing sensitive detection methods. Of the biomonitoring methods investigated for allylic and benzyl compounds, the detection of cysteine and histidine adducts isolated from hemoglobin seems to be the most sensitive. Gas chromatography with electron capture detection of heptafluorobutyric acid derivatives allows a detection limit in the femtomole range, HPLC-fluorescence detection of O-phthalic dialdehyde derivatives allows a limit in the picomole range, and detection of 9-fluorenylmethyl-chlorofomiate derivatives allows a limit in the femtomole range.

Identification and characterization of deoxyguanosine-crotonaldehyde adducts. Formation of 7,8 cyclic adducts and 1,N2,7,8 bis-cyclic adducts

Crotonaldehyde, a chemically reactive alpha,beta-unsaturated carbonyl compound, is an important industrial chemical and a ubiquitous environmental pollutant. It has been shown to be carcinogenic and mutagenic. We have studied the reaction of crotonaldehyde with nucleosides and 5'-mononucleotides and found three different types of adducts with deoxyguanosine and 2'-deoxyguanosine 5'-monophosphate. No adducts could be isolated either with nucleosides other than deoxyguanosine or with nucleotides other than 2'-deoxyguanosine 5'-monophosphate. With crotonaldehyde, deoxyguanosine produced 1,N2 and 7,8 adducts as well as 1,N2/7,8 bis-adducts. The 1,N2 adducts were mixtures of diastereomers: one pair in which the substituents in the newly formed ring were trans [adduct Ia (6S,8S) and (6R,8R)], about 94%, and another pair Ib in which they were cis. In the case of the 7,8-adducts IIa,b, the ribose was cleaved and a mixture of isomers in which the substituents were cis-IIa and trans-IIb (2:1) in the newly formed tetrahydropyrrole ring was observed. A 3:2 cis-IIIa and trans-IIIb mixture of 1,N2,7,8 bis-adducts was found with the isomerism in the newly formed tetrahydropyrrole ring in analogy to the 7,8 adducts IIa,b. The corresponding bis-adduct with the cis form in the newly formed tetrahydropyrimidine ring was not observed.

Mutagenicity of 2-methylacrolein, 2-ethylacrolein and 2-propylacrolein in Salmonella typhimurium TA100. A comparative study

The C2-alkylated acrolein derivatives 2-methylacrolein, 2-ethylacrolein and 2-propylacrolein are mutagenic in Salmonella typhimurium TA100. They are direct mutagens, their mutagenic potency being inversely proportional to the size of the alkylating substituent in the C2 position. In the presence of S9 mix, the mutagenicity of all these substances is considerably reduced; the reduction in mutagenicity is inversely proportional to the direct mutagenic potential of the substance. As shown for 2-methylacrolein, the reduction in mutagenicity is dependent on the concentration of S9 in the S9 mix and is not significantly influenced by heat inactivation of the S9 mix or by addition of TCPO, an inhibitor of epoxide hydrolase, to the testing system. There are no indications of enzymatic activation by the metabolizing microsomal system.

Genotoxicity of p-nitrocinnamaldehyde and related alpha, beta-unsaturated carbonyl compounds in two bacterial assays

Seventeen cinnamaldehydes, cinnamic acids, 2-furylacroleins and related compounds were tested in the Salmonella preincubation reversion assay and in the SOS chromotest. Of eight compounds containing nitrogroups, seven were clearly mutagenic in the presence of S9 mix and six in its absence; whereas none of the parent compounds not containing a nitrogroup and none of the congeners containing chlorine, methoxy or amino groups were mutagenic. Metabolic epoxidation was excluded in additional experiments using SKF525, an inhibitor of mono-oxygenases, and trichloropropene oxide, an inhibitor of epoxide hydrolases. Less or no mutagenicity was found in the nitroreductase deficient strains Salmonella typhimurium TA100NR or TA98NR and in the O-acetyltransferase deficient strains TA100/1,8-DNP6 or TA98/1,8-DNP6 except with 5-nitro-2-furylacrolein which exhibited decreased mutagenicity in TA100NR when compared with TA100 but the highest mutagenicity in TA100/1,8-DNP6. Less or no genotoxic activity was found in the SOS chromotest when using the nitroreductase deficient Escherichia coli strain PQ253 whereas all seven compounds tested were positive in strain PQ37. The results demonstrate the importance of the nitro group and that the compounds are activated either by bacterial nitroreductase or by the nitroreductase in the S9 mix. A chemical activation of the acrolein moiety by the negative inductive effect of the nitro group is unlikely. The genotoxicity of the cinnamyl compounds is dependent on the position of the nitro group in the phenyl ring. The genotoxicities of the p-nitro compounds were about two orders of magnitude higher than those of the ortho and meta congeners. The comparison between the Ames test and the SOS chromotest showed good agreement.

Genotoxic and cell-transforming properties of (trans,trans)-muconaldehyde

(trans,trans)-Muconaldehyde, a putative metabolite of benzene, should be expected to have mutagenic properties by virtue of its twin alpha,beta-unsaturated carbonylic function. It displayed definitely mutagenic properties in S. typhimurium TA100 without metabolic activation and with a 5-fold concentration of tester organisms in the preincubation assay and induced SOS response in E. coli. It induced micronucleus formation and morphological transformation in a dose-dependent manner in Syrian hamster embryofibroblasts. No DNA single-strand breaks or interstrand cross-links could be detected using the alkaline elution technique; however, strand-break generation by subsequent gamma-irradiation was found to be increased.

Theoretical structure-activity study of mutagenic allyl chlorides

Ab initio molecular orbital calculations at the STO-3G and 3-21G levels were used to clarify the mechanism of mutagenic action of various substituted allyl chlorides. Computed molecular properties were compared with experimental mutagenic potentials of these allylic compounds. In agreement with experiment, the computational results suggest that the primary mechanism of action involves the SN1 formation of allylic cations which then react with nucleophilic centers of nucleic acid bases. The usefulness of computed properties in estimating the degree of alkylating activity and mutagenicity was evaluated. In general, stability of the allylic carbocation intermediate and the degree of charge delocalization in the allyl system correlate well with observed mutagenic potentials.

Identification and characterization of deoxyguanosine adducts of methyl vinyl ketone and ethyl vinyl ketone. Genotoxicity of the ketones in the SOS Chromotest

The reaction of the alpha, beta-unsaturated ketones methyl vinyl ketone (MVK) and ethyl vinyl ketone (EVK) with nucleosides and 5'-mononucleotides was studied. The genotoxic activity of MVK and EVK in the SOS Chromotest was investigated. Three different types of adducts with deoxyguanosine were found and their structures elucidated: the cyclic 1,N2 adducts, the linear N7 adducts with one still-unreacted carbonyl function, and the cyclic 1,N2, linear N7, bis adducts. The spectroscopic and other relevant characterization data for the deoxyguanosine adducts and the corresponding guanine adducts are presented here together with details of the chromatographic methods used for isolation. The adducts described could also be isolated in the reactions of MVK and EVK with 2'-deoxyguanosine 5'-monophosphate. No adducts could be isolated either with nucleosides other than deoxyguanosine or with nucleotides other than 2'-deoxyguanosine 5'-monophosphate, indicating that the guanine moiety is the most reactive DNA constituent for MVK and EVK. MVK and EVK were clearly genotoxic in the SOS Chromotest according to the criteria of Quillardet and Hofnung. The formation of these adducts was proposed as the mechanism for the genotoxicity of MVK and EVK: all data available support the assumption that MVK and EVK represent a mutagenic and carcinogenic risk for mankind.

Genotoxicity of 1,3-dichloro-2-propanol in the SOS chromotest and in the Ames test. Elucidation of the genotoxic mechanism

1,3-Dichloro-2-propanol (1,3-DCP-OH, glycerol dichlorohydrin) is of great importance in many industrial processes and has been detected in foodstuffs, in particular in soup spices and instant soups. It has been shown to be carcinogenic, genotoxic and mutagenic. Its genotoxic mechanisms are, however, not yet entirely understood. We have investigated whether alcohol dehydrogenase (ADH) catalysed activation to the highly mutagenic and carcinogenic 1,3-dichloroacetone or formation of epichlorohydrin or other genotoxic compounds play a role for mutagenicity and genotoxicity. In our studies, no indications of ADH catalysed formation of 1,3-dichloropropane could be found, although we could demonstrate a clear activation by ADH in the case of 2-chloropropenol. Formation of allyl chloride could also be excluded. We found, however, clear evidence that epichlorohydrin formed chemically in the buffer and medium used in the test is responsible for genotoxicity. No indication was found that enzymatic formation of epichlorohydrin plays a role. Additional mutagenicity and genotoxicity studies with epichlorohydrin also confirmed the hypothesis that genotoxic effects of 1,3-DCP-OH depend on the chemical formation of epichlorohydrin.

Mutagenicity and genotoxicity of ethylvinyl ketone in bacterial tests

The mutagenic and genotoxic effects of ethylvinyl ketone were investigated. This alpha, beta-unsaturated carbonyl compound is widely distributed in the environment, in particular in food. Whereas ethylvinyl ketone shows only weak genotoxicity in the SOS Chromotest with Escherichia coli PQ37, it was distinctly mutagenic per se in the Salmonella preincubation assay with TA100. Using SKF 525 (an inhibitor of microsomal monooxygenase) and trichloropropene oxide (an inhibitor of epoxide hydrolase) we found indication for additional activation via epoxidation by S9 mix. The need for further investigation of the genotoxic, mutagenic and carcinogenic effects of this compound is strongly indicated.