Formation of Potential Antigens from Radiographic Contrast Media

The use of radiographic contrast media is occasionally accompanied by more or less serious adverse effects, evidently of complex etiology, following intravascular administration. Some of these reactions are suspected of having an allergic basis. The in vitro and in vivo formation of iodinated serum proteins following gamma irradiation in the presence of two commonly used radiographic contrast media is demonstrated. Non-toxic concentrations of ascorbate present during the irradiation is shown to prevent the formation of such iodo-proteins in vitro as well as in vivo. The amounts of potentially antigenic iodoprotein formed during radiographic procedures will certainly be very small, but this quantity may be sufficient to elicit a hypersensitivity reaction in cases when an individual has been previously sensitized to immunologically similar iodo-proteins, a mechanism that could account for certain rare and unpredictable reactions. The radiation induced formation of iodo-proteins may also serve as a model for the formation of iodine containing antigens mediated by a free radical mechanism, i.e. in the metabolism of iodinated compounds like erythrosine, a widely used colouring agent for certain foods.

Alkylating properties of dichlorvos (DDVP)

Dichlorvos (DDVP) is a methylating agent. In DNA from mice given 1.9 x 10(-6) mol/kg of DDVP, a degree of alkylation of guanine-N-7 amounting to 8 x 10(-13) mol methyl per g DNA, was found. From this, a rate of clearance of 29 hr-1 was estimated. This value is in reasonable agreement with the value (55 hr-1), calculated from published data on the concentration over time of DDVP in the brain after injection of the compound in mice. Applying a risk estimation on humans exposed to DDVP, the genetic risk connected with the methylating activity of DDVP is low or very low. Comparing the mutagenic effectiveness of DDVP with that of methyl methanesulfonate, indicates that DDVP is more effective than expected from reaction kinetic data. The possible contribution of the dichloroacetaldehyde formed in vivo from DDVP has to be evaluated before a complete risk estimate can be made for DDVP.

Reaction-kinetic parameters of glycidamide as determinants of mutagenic potency

Values for reaction-kinetic parameters of electrophiles can be used to predict mutagenic potency. One approach employs the Swain-Scott relationship for comparative kinetic studies of electrophilic agents reacting with nucleophiles. In this way glycidamide (GA), the putatively mutagenic/carcinogenic metabolite of acrylamide, was assessed by determining the rates of reaction with different nucleophiles. The rate constants (kNu) were determined using the "supernucleophile" cob(I)alamin [Cbl(I)] as an analytical tool. The Swain-Scott parameters for GA were compared with those of ethylene oxide (EO). The substrate constants, s values, for GA and for EO were found to be 1.0 and 0.93, respectively. The reaction rates at low values of nucleophilic strength (n=1-3), corresponding to oxygens in DNA, were determined to be 2-3.5 times higher for GA compared to EO. GA was also more reactive than EO towards other nucleophiles (n=0-6.4). The mutagenic potency of GA was determined in Chinese hamster ovary cells (hprt mutations in CHO-AA8 cells per dose unit with gamma-radiation as reference standard). The potency of GA was estimated to be about three mutations per 10(5) cells and mMh corresponding to about 40 rad-equ./mMh. A preliminary comparison of the mutagenic potency (per mMh and as rad-equivalents) of GA and EO shows an approximately seven times higher potency for GA. A higher mutagenic potency of GA compared to EO is compatible with expectation from reaction-kinetic data of the two compounds. The data confirmed that GA is not a strong mutagen, which is in line with what is expected for simple oxiranes. The present study shows the value of cob(I)alamin for the determination of reaction-kinetic parameters and their use for prediction of mutagenic potency.

Estimation of cancer risk caused by environmental chemicals based on in vivo dose measurement

Methods for estimating the risks, that is, the probabilities of contracting a disease, are required as a basis of decision-making regarding the needs for protection and risk reduction. A mechanism-based model has been developed for estimating the cancer risks from genotoxic chemicals using adducts to macromolecules for determining the in vivo dose. On the assumption that cancer is caused by an increased frequency of mutations in tissues, interacting with inherited or acquired growth-promoting factors, a simplified model has been proposed for estimating cancer risks from chemically reactive, that is, mutagenic agents. According to a multiplicative model, the risk increment (deltaP) is deltaP = beta x D x P0, proportional to the background incidence (P0) and linearly dependent on dose at low to intermediate doses (D); beta is the risk coefficient, which is approximately the same for different tumor sites and, probably, different species. This model is already in use for ionizing radiation and has been validated for a few mutagenic and carcinogenic chemical compounds. Inherent in this method is the measurement of dose. Sensitive chemical methods have been developed for determining reactive compounds and intermediates in vivo through their stable reaction products (adducts) with proteins, particularly hemoglobin. In humans or animals, the doses of genotoxic agents can be derived from measured levels of adducts and rates of adduct formation. This approach has been applied to various exposures such as air pollutants in occupational settings, carcinogens in foods, and tobacco smoke. By such methods, exposures to previously unknown mutagens and carcinogens may be detected and assessed in humans. Examples of this are epoxides (from endogenously produced alkenes) and compounds (such as acrylamide) formed in cooking foodstuffs.

Studies of dose distribution, premutagenic events and mutation frequencies for benzo[a]pyrene aiming at low dose cancer risk estimation

Cancer risk assessment of polycyclic aromatic hydrocarbons (PAH) is complicated by several of these compounds exerting a promoter action leading to high tumour incidences at high doses. Cancer risks at low doses corresponding to the uptake from air and food in the general environment would best be estimated on the basis of measurement of in vivo target doses of genotoxic (mutagenic) intermediates and a determination of mutation frequency per unit of dose. In experiments ultimately aiming at a risk assessment of environmental PAH from in vivo doses benzo[a]pyrene (BaP) was chosen as a model. gamma-Radiation has earlier been used as a reference standard in cancer risk estimation of genotoxic chemicals where dose equivalents (rad-equivalents) have been shown to give reliable risk estimates for several alkylating agents. Variation in dose of BaP diolepoxide between organs was studied by measurement of deoxyguanosine-N(2) adducts in DNA after administration of BaP by gavage to mice of a strain with reduced DNA repair (Xpa(-/-)). The adduct levels in spleen, forestomach, stomach and small intestine were approximately the same; with the adduct level in spleen as reference it was twice as high in liver and lung and about half as high in colon tissue. A chemical or radiation dose is proportional to the cumulative frequency of putatively premutagenic changes (premutagenic hits) in DNA. The mutation frequency per premutagenic hit (genotoxic chemicals) and per unit of dose (gamma-radiation) were calculated from acutely exposed V79 cells in order to determine the mutagenic effectiveness of each agent. Based on the mutagenic effectiveness determined in this study 10(-4) Gy can be regarded equally effective in causing phenotypically expressed HPRT mutations as the dose of BaP which causes the formation of one deoxyguanosine-N(2) adduct per cell.

Comparison of exhaust emissions from Swedish environmental classified diesel fuel (MK1) and European Program on Emissions, Fuels and Engine Technologies (EPEFE) reference fuel: a chemical and biological characterization, with viewpoints on cancer risk

Diesel fuels, classified as environmentally friendly, have been available on the Swedish market since 1991. The Swedish diesel fuel classification is based upon the specification of selected fuel composition and physical properties to reduce potential environmental and health effects from direct human exposure to exhaust. The objective of the present investigation was to compare the most stringent, environmentally classified Swedish diesel fuel (MK1) to the reference diesel fuel used in the "European Program on Emissions, Fuels and Engine Technologies" (EPEFE) program. The study compares measurements of regulated emissions, unregulated emissions, and biological tests from a Volvo truck using these fuels. The regulated emissions from these two fuels (MK1 vs EPEFE) were CO (-2.2%), HC (12%), NOx (-11%), and particulates (-11%). The emissions of aldehydes, alkenes, and carbon dioxide were basically equivalent. The emissions of particle-associated polycyclic aromatic hydrocarbons (PAHs) and 1-nitropyrene were 88% and 98% lower than those of the EPEFE fuel, respectively. The emissions of semi-volatile PAHs and 1-nitropyrene were 77% and 80% lower than those from the EPEFE fuel, respectively. The reduction in mutagenicity of the particle extract varied from -75 to -90%, depending on the tester strain. The reduction of mutagenicity of the semi-volatile extract varied between -40 and -60%. Furthermore, the dioxin receptor binding activity was a factor of 8 times lower in the particle extracts and a factor of 4 times lower in the semi-volatile extract than that of the EPEFE fuel. In conclusion, the MK1 fuel was found to be more environmentally friendly than the EPEFE fuel.

The multiplicative model for cancer risk assessment: applicability to acrylamide

According to a multiplicative model for prediction of cancer risk for genotoxic agents the incremental cancer risk is, for low-intermediate exposures, proportional to target doses of the genotoxic substance and to the background risk in control groups. This model has been applied to evaluate cancer tests of acrylamide in rodents. Because of its reactivity toward DNA, glycidamide is assumed to be the causative genotoxic metabolite of acrylamide. Evaluation of experimental data according to the multiplicative model shows that mice, compared with rats, are of the order of 10 times more sensitive per administered dose of acrylamide. The US EPA procedure would, however, generally predict rats to be about twice as sensitive as mice to carcinogenic chemicals, because their estimates are based on scaling of the dose per square meter body surface area, as a surrogate for metabolic differences between the species. The comparison of rats and mice with respect to observed cancer incidence is at a key position in the evaluation of the usefulness of risk models for extrapolation between species. In the present study mice and rats were compared, with respect to in vivo doses of acrylamide and the metabolite glycidamide, after exposure to acrylamide. The relative in vivo doses were inferred from levels of hemoglobin adducts. The adduct levels from glycidamide were, per administered dose of acrylamide, approximately 3-10 times higher in mice than in rats. In combination with the above mentioned higher sensitivity of mice than rats in cancer tests of acrylamide this is compatible with the concept that glycidamide is the key genotoxic factor in acrylamide exposure. Furthermore, it is shown that the multiplicative, i.e. relative, risk model and measurements of the dose of the genotoxic factor give good prediction of the observed risk from acrylamide in cancer tests with rats and mice.

Transalkylation of phosphotriesters using Cob(I)alamin: toward specific determination of DNA-phosphate adducts

The supernucleophilic cobalt compound, cob(I)alamin, has been kinetically characterized with respect to its ability to bring about transalkylation of adducts to DNA phosphates (phosphotriesters). The reactivity of cob(I)alamin toward different phosphotriesters (model compounds and methylated DNA), as well as its specificity toward DNA-phosphate adducts, has been investigated. Through nucleophilic displacement on the alkyl by cob(I)alamin, the alkyl groups (methyl and ethyl) were transferred from phosphotriesters within minutes at room temperature. In contrast, methylated nucleosides (base adducts) were stable in the presence of cob(I)alamin.

Characterization of hemoglobin adducts from a 4, 4'-methylenedianiline metabolite evidently produced by peroxidative oxidation in vivo

4,4'-Methylenedianiline (MDA) is a widely used mutagenic and carcinogenic industrial chemical. It is also a metabolite of 4, 4'-methylenediphenyl diisocyanate (MDI), which is used in the manufacturing of polyurethane foams. Biomonitoring of MDA, like other aromatic amines, is mainly carried out by GC/MS measurement of cysteine adducts in Hb from the nitroso metabolite, released by alkaline hydrolysis. In the present study it was investigated whether the formation of Hb adducts from non-nitroso metabolites of MDA can be used for the dosimetry of MDA. The study was carried out by treatment of mice with MDA and tritiated MDA or deuterated MDA and by identification of their products of reaction with Hb, after enzymatic hydrolysis of the globin and enrichment of the adducts. The main adduct, about 50% of the total amount of MDA associated with Hb, was characterized by MS and was shown to be a reaction product of MDA and the amino group of N-terminal valine in Hb, the derived structure being 1-[(4-imino-2, 5-cyclohexadien-1-ylidene)methyl]benzene-4-azo-2-isovaleric acid. It is likely that this quinonoid MDA imine adduct to valine was formed by an attack of a metabolite formed through peroxidative oxidation of MDA, in analogy with earlier observed oxidation of some other aromatic amines, e.g., benzidine. The reactive intermediate is suggested to be [(4-imino-2, 5-cyclohexadien-1-ylidene)methyl]-4-aminobenzene. The formation of the adduct was confirmed by incubating MDA with valine methyl ester in vitro in the presence of H2O2 and lactoperoxidase. Further, the same adduct was detected in MDI-exposed and control rats, the level in the exposed animals being about 60 times higher than in the controls. This study indicates that, at least in the mouse, extrahepatic peroxidative metabolism is an important pathway for the bioactivation of MDA, possibly leading to a genotoxic reactive intermediate. This study also demonstrates the usefulness of Hb adduct analysis for the identification of reactive intermediates in vivo.

Studies of transalkylation of phosphotriesters in DNA: reaction conditions and requirements on nucleophiles for determination of DNA adducts

Reactive compounds form adducts at several sites in DNA. One of these sites, the phosphate groups, forms phosphotriesters (PTE) which are both chemically stable and little repaired. A measurement of PTE in DNA could therefore be advantageous for the determination of doses in vivo of mutagens/cancer initiators. In this paper, the possibilities of utilizing the weakly alkylating properties of PTE for the transfer of adducts to strong nucleophiles have been investigated. Model compounds, thymidine 3'-[thymidine 5'-(methyl phosphate)], TpMeT, and thymidine 3'-[thymidine 5'-(2-hydroxyethyl phosphate)], TpHOEtT, were incubated with thiosulfate, a relatively strong nucleophile and the formation of dealkylated model PTE, thymidine 3'-(thymidine 5'-phosphate), TpT, was followed by HPLC. Transalkylation to thiosulfate or aniline of methyl PTE in DNA alkylated by [3H]N-methyl-N-nitrosourea was demonstrated. The methyl groups transferred, forming methyl thiosulfate and N-methylaniline, respectively, were determined by HPLC. These experiments demonstrate that it is possible to transfer alkyls from DNA phosphate to nucleophiles. Kinetic aspects of the transalkylation and requirement on nucleophiles for a practically useful method for determination of DNA adducts are discussed. Constants of reaction rates are presented.

Relevance of different biological assays in assessing initiating and promoting properties of polycyclic aromatic hydrocarbons with respect to carcinogenic potency

The results from assays that describe biological effects of polycyclic aromatic hydrocarbons (PAH) were explored using multivariate methods. Based on the availability of data, 29 PAH were included in the study. Five variables described the carcinogenic potency in rodents of the PAH. Biological effects were assayed using 14 variables. These included bacterial mutagenicity, enhancement and inhibition of bacterial mutagenicity, Ah receptor (AhR) affinity, and induction of enzymes that bioactivate many PAH to proximal bacterial mutagens. A principal components analysis (PCA) showed that the highest correlations with the cancer data were observed for variables describing AhR affinity, whereas bacterial mutagenicity data were poorly correlated with cancer data. When a partial least squares (PLS) regression analysis was applied, only one bacterial mutagenicity variable, but all AhR affinity variables were statistically relevant to describe carcinogenic potency. The latter variables were also correlated with the inhibition of bacterial mutagenicity of benzo[a]pyrene. It was concluded that structural requirements for AhR affinity are the same as those required for metabolism by enzymes that bioactivate benzo(a)pyrene. Negative correlations between mutagenicity and induction of enzymes were observed. The roles of cancer initiation and cancer promotion are discussed regarding the biological properties studied. It is proposed that bacterial mutagenicity reflects the cancer initiation potency, whereas the AhR affinity reflects the promotive effect of some PAH at the high doses applied in rodent carcinogenicity tests. It is thus indicated that initiation and promotion are provoked by different chemical species: reactive metabolites and the parent hydrocarbons, respectively. At doses reflecting a normal human exposure situation the effects of initiation may be more important in the course of chemical carcinogenesis. The mechanisms of cancer initiation and cancer promotion should therefore be studied in more detail for reliable quantitative risk assessments.

In vivo dosimetry of ethylene oxide and propylene oxide in the cynomolgus monkey

In mammals, including the cynomolgus monkey, a striking difference between the potencies of ethylene oxide (EO)* and propylene oxide (PO) with respect to induction of certain clastogenic effects has previously been observed. In order to clarify to what extent such differences can be ascribed to a difference in detoxification rate, cynomolgus monkeys were administered an equimolar mixture of the two epoxides at two dose levels, and the blood doses were determined by measurement of the degree of alkylation of N-terminal valines in hemoglobin (Hb). For the highest exposure a saturation in the detoxification of PO was evident from a marked increase in adduct level. At the lower exposure, the dose in blood resulting from exposure to PO was about one fourth of that from EO. Although playing a great role, differences in detoxification rate, therefore, cannot fully account for the much lower clastogenic potency of PO, which has been found in earlier studies. Furthermore, the determination of doses in blood gives data on relationship between in vivo dose and exposure dose (accounting for detoxification), with relevance for risk estimation.

Retrospective dose estimates in Estonian Chernobyl clean-up workers by means of FISH

The present study deals with retrospective estimation of radiation doses, among Estonian Chernobyl clean-up workers, by means of scoring stable translocations using the FISH technique. All persons investigated in this study were sent to the area in 1986 and the majority of them were selected to be among those with the presumably highest exposure doses. In spite of the selection the estimated average dose is between 0.2-0.3 Gy, thus not clearly above the officially permitted dose level of 0.25 Gy. Due to unforseen conditions during transport of the blood samples, both the number of persons available for analysis and the number of metaphases available for scoring were substantially reduced. However, unless this selection is linked with the potential aberration frequency of the cells involved, no bias is expected.

DNA damage and repair in mutagenesis and carcinogenesis: implications of structure-activity relationships for cross-species extrapolation

Previous studies on structure-activity relationships (SARs) between types of DNA modifications and tumour incidence revealed linear positive relationships between the log TD50 estimates and s-values for a series of mostly monofunctional alkylating agents. The overall objective of this STEP project was to further elucidate the mechanistic principles underlying these correlations, because detailed knowledge on mechanisms underlying the formation of genotoxic damage is an absolute necessity for establishing guidance values for exposures to genotoxic agents. The analysis included: (1) the re-calculation and further extension of TD50 values in mmol/kg body weight for chemicals carcinogenic in rodents. This part further included the checking up data for Swain-Scott s-values and the use of the covalent binding index (CBI); (2) the elaboration of genetic toxicity including an analysis of induced mutation spectra in specific genes at the DNA level, i.e., the vermilion gene of Drosophila, a plasmid system (pX2 assay) and the HPRT gene in cultured mammalian cells (CHO-9); and (3) the measurement of specific DNA alkylation adducts in animal models (mouse, rat, hamster) and mammalian cells in culture. The analysis of mechanisms controlling the expression of mammalian DNA repair genes (alkyltransferases, glycosylases) as a function of the cell type, differentiation stage, and cellular microenvironment in mammalian cells. The 3 classes of genotoxic carcinogens selected for the project were: (1) chemicals forming monoalkyl adducts upon interaction with DNA; (2) genotoxins capable of forming DNA etheno-adducts; and (3) N-substituted aryl compounds forming covalent adducts at the C8 position of guanine in DNA. In general, clear SARs and AARs (activity-activity relationships) between physiochemical parameters (s-values, O6/N7-alkylguanine ratios, CBI), carcinogenic potency in rodents and several descriptors of genotoxic activity in germ cells (mouse, Drosophila) became apparent when the following descriptors were used: TD50 estimates (lifetime doses expressed in mg/kg b.wt. or mmol/kg b.wt.) from cancer bioassays in rodents; the degree of germ-cell specificity, i.e., the ability of a genotoxic agent to induce mutations in practically all cell stages of the male germ-cell cycle of Drosophila (this project) and the mouse (literature search), as opposed to a more specific response in postmeiotic stages of both species; the Mexr-/Mexr+ hypermutability ratio, determined in a repair assay utilizing Drosophila germ cells; mutation spectra induced at single loci (the 7 loci used in the specific-locus test of the mouse (published data), and the vermilion gene of Drosophila); and doubling doses (DD) in mg/kg (mmol/kg) for specific locus test results on mice. By and large, the TD50 values, the inverse of which can be considered as measures of carcinogenic potency, were shown to be predictable from knowledge of the in vivo doses associated with the absorbed amounts of the investigated alkylators and with the second-order constant, kc, reaction at a critical nucleophilic strength, nc. For alkylating agents kc can be expressed as the second-order rate constant for hydrolysis, kH2O, and the substrate constant s:kH2OTD50 is a function of a certain accumulated degree of alkylation, here given as the (average) daily increment, ac, for 2 years exposure of the rodents. The TD*50 in mmol/kg x day) could then be written: [formula: see text] This expression would be valid for monofunctional alkylators provided the reactive species are uncharged. This is the case for most SN2 reagents. Although it appears possible to predict carcinogenic potency from measured in vivo doses and from detailed knowledge of reaction-kinetic parameter values, it is at present not possible to quantify the uncertainty of such predictions. One main reason for this is the complication due to uneven distribution in the body, with effects on the dose in target tissues. The estimation can be impro

Macromolecule adducts as biomarkers of exposure to environmental mutagens in human populations

A cancer epidemiologist recently said that "adduct measurement has so far been of little use to epidemiological research." This remark gives us a starting point for the discussion of the purposes of measuring macromolecule adducts that originate from electrophilic compounds or metabolites in humans and animals. Historically, methods for adduct monitoring were developed as a means of determining target doses that, combined with measurements of genotoxic potencies, could be used for risk assessment. With mass spectrometric methods, adducts can be quantified at levels that are thousands of times lower than those in which the cancer incidence associated with this exposure is detectable in disease-epidemiological studies. Furthermore, mass spectrometric techniques permit identification of the chemical structure of the adduct, particularly in the case of hemoglobin adducts. Adduct measurement therefore constitutes not only a means of risk estimation but it may be used as a complement of disease epidemiology in situations in which, for statistical reasons, the risk is too low to be detectable--which does not signify that the risk is acceptably low. It also gives a possibility of identification of the dangerous components in mixed exposures and of the relevant reactive intermediates in cases of complex metabolism.

Thiols, recA induction and radiosensitivity in Escherichia coli

Induction by gamma-radiation, UV radiation or hydroxyurea of RecA gene product synthesis in Escherichia coli, monitored as beta-D-galactosidase in recA-lacZ fusion strains, was shown to be inhibited if 2-mercaptoethylamine (MEA) was added before treatment with the inducing agents. If cysteine (Cys) at low concentrations was added at the same time as MEA it counteracted the action of MEA. The effect of MEA may be described as a competitive inhibition of an inducing or conducting effect of Cys. In E. coli GE499 (uvrA+), complete inhibition by 30-mmol dm-3 MEA of recA induction was associated with about five times higher radio-resistence. Both of these effects of MEA were completely reversed by 0.3-mmol dm-3 Cys. As shown in parallel experiments with E. coli GE500 (uvrA-), these effects of MEA and Cys were shown to be independent of excision-repair proficiency. Treatment of bacteria with MEA and/or Cys was shown not to lead to increased intracellular concentrations of these thiols. Instead, treatment with them appeared to provoke conspicuous increases in glutathione levels, which are, however, probably not directly involved in the studied action of MEA and Cys.

The research background for risk assessment of ethylene oxide: aspects of dose

Data for relationships between in vivo doses inferred from levels of hemoglobin (Hb) or DNA adducts and administered (by inhalation or injection) doses of ethylene oxide (EO) in mice, rats and humans are reviewed. At low absorbed doses or dose rates these relationships appear to be linear, whereas at higher dose rates deviations from linearity due to saturation kinetics of detoxification and of DNA repair as well as certain toxic effects have to be allowed for. If these factors are taken into consideration, a rather consistent picture is obtained for animal studies, with a variation by less than a factor 2 between estimates of adduct level increments or in vivo dose increments per unit of administered dose. Although the value for in vivo dose per unit of exposure dose (ppm-hour) in humans is uncertain because of unreliable data for the time-weighted average exposure level, the most likely value for this relationship, supported by data for ethene, agrees with data for the rodents. In the animal species testis doses are approximately one-half of the blood doses inferred from Hb adducts.

Ethylene oxide: evaluation of genotoxicity data and an exploratory assessment of genetic risk

A risk estimate of the heritable effects of ethylene oxide exposure, using the parallelogram approach, as suggested by Frits Sobels, is described. The approach is based on available data on the ethylene oxide-induced responses for the same genetic endpoint in somatic cells of both laboratory animals and humans, and for germ cell mutations in the same laboratory animal. Human germ cell effects are estimated. The available data sets for this approach were evaluated. We consider this as complementary to the genetic risk assessment carried out by U.S. EPA scientists, in which the risk from heritable (reciprocal) translocations induced by ethylene oxide was estimated. In the present study we restricted our assessment to dominant mutations. The sensitivity factor relating mouse to man was based on ethylene oxide-induced HPRT mutant frequencies in lymphocytes in vivo. From this comparison, it could be concluded that occupational exposure for 1 year to 1 ppm ethylene oxide would lead to a risk of a dominantly inherited disease in the offspring of 4 x 10(-4) above the background level. The uncertainty interval of this figure is quite large (0.6-28) x 10(-4). The values are compatible with the existing estimates of the corresponding risk from exposure to low LET radiation when the genotoxic potency ratio of ethylene oxide and radiation is considered. This risk estimation approach has allowed us to identify additional data that are required for a more complete risk estimation of the heritable effects of ethylene oxide, or indeed any mutagenic chemical.

Effects of variation in detoxification rate on dose monitoring through adducts

1. Föst et al. (Human & Experimental Toxicology 1991; 10: 25) have shown that ethylene oxide (EO) added to human blood gave rise to a higher level of adducts to haemoglobin (Hb) when the donors were deficient in an erythrocytic glutathione S-transferase (GST, later found to be GST-theta) than in blood from persons possessing this enzyme, and drew the conclusion that this polymorphism in detoxification rendered Hb adducts less suitable for biological monitoring. 2. By fitting a kinetic model to the data, the present study shows that the Hb adduct level gives a correct measure of the dose (concentration integrated over time) relevant to risk estimation. 3. It does illustrate, however, the importance of knowing an individual's detoxification efficiency, when Hb adduct measurements are used to assess environmental exposure, for example in occupational surveillance.

On cancer risk estimation of urban air pollution

The usefulness of data from various sources for a cancer risk estimation of urban air pollution is discussed. Considering the irreversibility of initiations, a multiplicative model is preferred for solid tumors. As has been concluded for exposure to ionizing radiation, the multiplicative model, in comparison with the additive model, predicts a relatively larger number of cases at high ages, with enhanced underestimation of risks by short follow-up times in disease-epidemiological studies. For related reasons, the extrapolation of risk from animal tests on the basis of daily absorbed dose per kilogram body weight or per square meter surface area without considering differences in life span may lead to an underestimation, and agreements with epidemiologically determined values may be fortuitous. Considering these possibilities, the most likely lifetime risks of cancer death at the average exposure levels in Sweden were estimated for certain pollution fractions or indicator compounds in urban air. The risks amount to approximately 50 deaths per 100,000 for inhaled particulate organic material (POM), with a contribution from ingested POM about three times larger, and alkenes, and butadiene cause 20 deaths, respectively, per 100,000 individuals. Also, benzene and formaldehyde are expected to be associated with considerable risk increments. Comparative potency methods were applied for POM and alkenes. Due to incompleteness of the list of compounds considered and the uncertainties of the above estimates, the total risk calculation from urban air has not been attempted here.

Uptake and metabolism of ethene studied in a smoke-stop experiment

Knowledge of the relationships between exposure levels and levels of hemoglobin adducts are essential when the latter are to be used for exposure monitoring or risk estimation, the hygienic control being based on measurements of exposure. These ratios are mostly very uncertain, mainly due to difficulties of determining the time-weighted average exposure concentration. A solution to this problem has been suggested involving adduct measurement before and after two consecutive periods of about 1 week, the first with absence from exposure, the second with careful measurement of exposure. This model was tested in two smokers who abstained from smoking for one week. Analysis of inhaled ethene and of adducts from ethylene oxide (EO) to N-terminal valine of hemoglobin are compatible with metabolism of 2% of inhaled ethene to EO and a detoxification rate of 1 h-1 of EO.

Comparative two-stage cancer tests of ethylene oxide, N-(2-hydroxyethyl)-N-nitrosourea and X-rays

Mutagenicity tests have shown that the potencies of ethylene oxide and other alkylating agents relative to that of low-LET ionising radiation are approximately the same in different biological systems. In the present study this relationship, the radiation-dose equivalence ("rad-equivalence") of doses of genotoxic chemicals, was tested for the induction of tumours in skin and lung of mice using different initiation-promotion protocols. The initiators used were X-rays, ethylene oxide and N-(2-hydroxyethyl)-N-nitrosourea (HOENU). This short-term treatment was followed by treatment with the "promoters" 12-O-tetradecanoylphorbol 13-acetate (TPA) and carbon tetrachloride. Unexpectedly, the animals treated with carbon tetrachloride did not show treatment-related liver tumours, but exhibited precocious death, mostly with lung tumours. According to estimates from in vitro tests the total in vivo dose from exposure to 400 ppm for 4 x 5 h corresponds to 700 rad-equivalents. Although still with great statistical uncertainty, this ratio is supported by the observed time-dependent frequencies of animals with papillomas (in the TPA series) and lung tumours (in the carbon tetrachloride series). Animals treated with HOENU exhibited high incidences of tumours of both these types in approximate agreement with the higher rad-equivalence of the treatments with this compound.

Genotoxic effects of ethylene oxide and propylene oxide in mouse bone marrow cells

Ethylene oxide and propylene oxide are high-volume reactive alkylating agents used primarily as intermediates in the chemical industry. Studies were undertaken to investigate the ability of these alkylating agents to induce chromosomal aberrations, micronuclei and sister-chromatid exchanges in mouse bone marrow cells. The mice were exposed to these chemicals by intraperitoneal injection. The data show that both compounds are effective in inducing chromosomal alterations. Our studies confirm the findings reported by different investigators that ethylene oxide is more cytotoxic than propylene oxide. This difference is to a large extent due to a faster detoxification of propylene oxide than of ethylene oxide.

Degree of alkylation of macromolecules in vivo from variable exposure

Measurements of adducts formed with blood proteins, particularly haemoglobin, are increasingly being used to monitor human exposures to genotoxic chemicals. Information about the relationships between levels of genotoxic chemicals in the environment, e.g., concentration in the air, and levels of protein adducts in the blood is particularly important in setting safety standards and assessing risks. This paper describes the relationships between level of exposure to alkylating agents and level of haemoglobin adducts, considering the zero-order kinetics of the disappearance of these adducts. For comparison the corresponding relationship for adducts to macromolecules subjected to turnover, with first-order kinetics of disappearance, is described. For chemically stable and unstable adducts different exposure situations are considered: acute, chronic, intermittent and varying exposure levels. It is shown how an optimum solution of the problem of establishing the relationship between long-term exposure at varying levels (e.g., in work environments) and adduct level can be reached. Through mathematical derivations, which are given, expressions applicable to various exposure patterns are obtained and presented.

Use of biomarkers in epidemiology: quantitative aspects

Cancer initiators (mutagens) present, due to the absence of definable no effect threshold, a special problem in toxicology, requiring a high sensitivity of detection methods. Disease epidemiology aiming at identification of carcinogens and quantification of associated risks has a low resolving power, the detectable incidence or mortality increments being often orders of magnitude larger than those which are of public concern. Other drawbacks of disease epidemiology is the long latency times and the influence of confounders. The use of genetic endpoints as biomarkers suffers from low cause specificity, although this drawback seems to be overcome, partly at least, by emerging methods for determination of mutation spectra at the DNA level. Proximal cancer initiators/mutagens are electrophilic compounds or metabolites that can react with nucleophilic atoms in nucleic acids and proteins. These reactions lead to 'adducts' that can be identified and quantified, e.g. in lymphocytes and erythrocytes in blood samples. The shift from biological observations to chemical analysis permits sufficient sensitivity, and measurement can be done shortly after onset of exposure. The well-defined life span of the adducts to hemoglobin (Hb) offer possibilities of dose calculation and risk estimation. For these reasons the measurement of adducts to Hb and DNA constitutes a powerful epidemiological tool, applications of which has been initiated in work environments and the general environment and also in the search for a priori unknown carcinogens.

Risk assessment of urban air pollution

Urban air pollution, originating in western countries mainly from automotive engine exhausts, contains thousands of components, many of which are genotoxic, i.e. are putative cancer initiators. Other pollution components, such as NO2 and certain particles, may have cocarcinogenic/promotive effects, at least at higher exposure levels. Cancer risk assessment of this complex mixture has to combine data from the exposure history, from epidemiological studies as well as from animal carcinogenicity tests, and from in vitro studies of fractions and individual components. Data for metabolism and pharmaco-kinetics have also to be considered. A multiplicative linear model is assumed to be valid for cancer initiation at low levels. Attempts are being made to determine the target dose from ultimate carcinogens (reactive metabolites) via macromolecule adduct levels, and to base the risk assessment on the radiation-dose equivalent to the chemical dose. So far this has been possible only for simple alkenes, which are metabolized to epoxides, and indirectly, via benzo(a)pyrene (BaP), for particle-bound polycyclic aromatic hydrocarbons (PAH). The lifetime risk of cancer (all sites) from ethene is estimated accordingly to 1.4 x 10(-4) per microgram m-3, and from PAH to 12 x 10(-4) per ng m-3 BaP. For other components indicated to give risk contribution (NOx, volatile PAH, benzene, aldehydes, butadiene) essential data are lacking and only very rough estimates can be given at this time.

On the bioactivation and genotoxic action of fluoranthene

Fluoranthene (FA) was studied with respect to possible mechanisms of its high mutagenicity but low carcinogenicity, in comparison with the corresponding properties of benzo[a]pyrene (BaP), and with regard to the synergism of these two compounds shown by van Duuren and Goldschmidt (J Natl Cancer Inst 56, 1976, 1237). FA and BaP activated by S9 from Aroclor 1254 (PCB)-treated rats induce HPRT mutations in CHO cells with about equal effectiveness at the same exposure doses, which also lead to the same frequencies of repairable DNA adducts, enzyme-induced strand breaks being used as an indirect measure of adducts to DNA. FA was also shown to be an efficient inducer of SCE in human peripheral lymphocytes cocultivated with PCB-treated HepG2 cells or with liver cells from PCB-pretreated rats. For the induction of SCE, FA and BaP were shown to act additively. From metabolic studies with liver microsomes from C57Bl/6 mice it is concluded that, whereas BaP induces the metabolism of BaP to the mutagenic epoxide, neither BaP nor FA is able to induce the metabolism of FA. In mutation experiments with V79 cells (XEM2) constitutive for P450 IA1 activity, BaP 7,8-diol but not FA 2,3-diol provokes a high frequency of HPRT mutations. In cells constitutive for P450 IA2 enzymatic activity FA and BaP are but weakly mutagenic and practically nonmutagenic, respectively. Due to the additivity of the genotoxic effects of FA and BaP, induction of an error-prone condition by the latter compound seems to be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of recA induction by the radioprotector 2-mercaptoethylamine

Our earlier finding that the radioprotective action of 2-mercaptoethylamine (MEA) is counteracted by ascorbate suggests a biochemical mechanism of action, which is supported by observations that MEA is not radioprotective in Rec- E. coli strains. In this study we show that MEA inhibits the induction of the recA gene by UV- or gamma-irradiation or by nalidixic acid in Escherichia coli strain GE94, which contains a recA-lacZ fusion. This effect, which may be counteracted by cysteine, indicates that in general MEA inhibits the induction of SOS functions.

Pharmacokinetics of ethylene in man; body burden with ethylene oxide and hydroxyethylation of hemoglobin due to endogenous and environmental ethylene

The inhalation pharmacokinetics and the endogenous production of ethylene has been determined in healthy volunteers with respect to the formation of the carcinogen ethylene oxide. Ethylene showed a low degree of accumulation in the body determined in six subjects, the thermodynamic partition coefficient "body/air" being 0.53 +/- 0.23 (mean +/- SD) and the accumulation factor "body/air" at steady-state being 0.33 +/- 0.13 (mean +/- SD). The rate of metabolism was directly proportional to the exposure concentration. Only 2% of ethylene inhaled was metabolized to ethylene oxide, whereas 98% of ethylene was exhaled unchanged. The rate of the endogenous production of ethylene was 32 +/- 12 nmol/h (mean +/- SD), as calculated from exhalation data from 14 subjects. The resulting body burden was 0.44 +/- 0.19 nmol/kg (mean +/- SD). By analyzing published data on ethylene oxide in man its half-life was estimated to be 42 min. Using the pharmacokinetic parameters of ethylene and ethylene oxide, the body burden of ethylene oxide due to the sum of the exposure to environmental ethylene of about 15 ppb and to endogenous ethylene exposure of 0.44 nmol/kg was predicted to be 0.25 nmol/kg. In the blood of five non-smokers and one smoker the hemoglobin adduct resulting from the reaction of ethylene oxide with the N-terminal valine, N-(2-hydroxyethyl)valine, was quantified by gas chromatography/mass spectrometry. The value of 20 +/- 5 pmol/g Hb (mean +/- SD) found in the non-smokers corroborated the steady-state level of 18 +/- 3 pmol/g Hb (mean +/- SD) calculated from the pharmacokinetic approach.

Genotoxic effects of ethylene oxide and propylene oxide: a comparative study

The two alkylating agents ethylene oxide (EO) and propylene oxide (PO) were compared for genotoxic effectiveness in various test systems. The study was undertaken partly to shed light on the difference between the compounds found after chronic exposure of monkeys (Lynch et al., 1984) where EO but not PO was able to induce SCE and chromosomal aberrations. In the present study EO was found to be 5-10 times more effective than PO with respect to gene conversion and reverse mutation in Saccharomyces cerevisiae D7 and sister-chromatid conversion in S. cerevisiae RS112. In contrast, the abilities of the two compounds to induce point mutation in S. typhimurium strains and SCE in human lymphocytes were approximately equal. One possible cause of EO being more effective than PO in certain respects, discussed on the basis of inference from earlier studies, is an expected difference in ability to cause strand breaks via alkylation of DNA-phosphate groups.

Studies of biological and chemical monitoring of low-level exposure to ethylene oxide

Ten sanitary workers exposed to concentrations of ethylene oxide below 1 ppm were studied to determine whether effects could be observed at low exposure levels. A significant increase in the number of sister chromatid exchanges in cultured lymphocytes was found only for five subjects with relatively high exposure in the sterilization area. However, it was not possible to separate clearly the effect of smoking from that of ethylene oxide exposure. No increase in the frequencies of micronuclei in lymphocytes and buccal cells was found. The level of 2-hydroxyethyl adducts to the N-terminal valines in hemoglobin responded in a reliable fashion to chronic ethylene oxide exposure and smoking. Furthermore, measurement of levels of 2-hydroxyethyl adducts to the N-terminal valines in hemoglobin made it possible to reconstruct the dynamics of a leakage of ethylene oxide which involved three workers.

Human health risk assessment and biological reactive intermediates: hemoglobin binding

There is ample evidence to show that the demonstration of adducts to hemoglobin and other proteins of electrophilically reactive compounds or biological reactive intermediates (BRI) is a relevant indication of the formation of the corresponding DNA adducts, and also that the rates of formation of protein- and DNA adducts are proportional. Measurement of hemoglobin and DNA adducts are therefore complementary. The former has so far been used mainly in the monitoring of low-mol.wt alkylators and BRI whereas DNA adduct monitoring has been applicable mostly to bulky compounds. Since dose-response curves are presumably linear, demonstration of adducts should be taken as identification of genotoxic risk factors. The fast development of analytical methods renders quantification of associated risks increasingly important: For instance, using adduct analysis in the search for a priori unknown carcinogens/mutagens, analytical procedures should be developed towards a power permitting detection of unacceptable risks, at the same time as unnecessary banning of factors originating from beneficial procedures should be avoided.

Epidemiological studies of geographic variations of cancer incidence in Sweden. Choice of variables and statistical units

The Swedish Cancer-Environment Registry has been used for studies of the parts of cancer incidences and of their variations between subpopulations, which, in a statistical sense, can be 'explained' by environmental variables. In previous studies the dependence of age-standardized incidences in municipalities (279 in Sweden) on population density, socio-economic variables, smoking habits and a variable for 'diagnostic intensity', assumed to allow for variations in under-diagnosing and under-reporting, was studied in, i.a., multiple-regression analyses. Due to intrinsic variation in potentially etiologic factors and in size, municipalities are less suitable as geographic units. Therefore a system was developed to build up, from parishes (about 2,600), pseudo-municipalities standardized with respect to size and some environmental variable(s), in the present study population density. This paper shows, for a number of cancer diseases and for total cancer, the superiority of pseudo-municipalities to municipalities with respect to power of explaining variation and, preliminarily, also incidence.

Unsaturated lipids and intestinal bacteria as sources of endogenous production of ethene and ethylene oxide

Studies of adducts to hemoglobin (Hb) have revealed levels of hydroxyethylations of i.a. N-terminus (valines) in knowingly unexposed animals and persons (non-smokers). This paper describes some exploratory experiments with mice, carried out with the aim of tracing the origin of these background levels. It is shown that the hydroxyethylvaline content in Hb is higher in animals fed unsaturated lipids and lower in bacterium-free as compared to control animals. Lipid peroxidation and metabolism of intestinal bacteria, giving rise to ethene, precursor of ethylene oxide, are thus indicated to be sources of observed background hydroxyethylations.

Note on ethene and other low-molecular weight hydrocarbons in environmental tobacco smoke

Levels of ethene and propene, together with those of some other light hydrocarbons (propane, butane, isobutane and ethyne), have been measured under realistic conditions in environmental tobacco smoke (ETS) as a step towards the elucidation of the sources of 2-hydroxyethyl and 2-hydroxypropyl adducts of hemoglobin observed in non-smokers. These adducts may reflect in vivo doses of carcinogenic epoxides that are metabolites of the respective alkenes. The data show that 2.0 mg ethene, 1.4 mg propene, and 0.7 mg propane together with smaller amounts of butane, isobutane and ethyne are released per cigarette smoked (0.66 g tobacco) of a common Swedish brand. The alkenes in ETS should be considered as contributing factors to a risk of systemic cancer from passive smoking. With regard to alkene intake, even a relatively mild exposure to ETS (2 cigarettes per h for 5 h per day in a 33 m3 room with one air change per hour is estimated to correspond to the active smoking of about one cigarette per day.

Hemoglobin adducts in animals exposed to gasoline and diesel exhausts. 1. Alkenes

Blood samples from rats and hamsters exposed to automotive engine exhausts in the Committee of Common Market Automobile Constructors long-term inhalation study at Battelle-Geneva were analysed for the levels of 2-hydroxyethylvaline (HOEtVal) and 2-hydroxypropylvaline (HOPrVal) in hemoglobin (Hb). These adducts to the N-terminus of the Hb chains were determined by gas chromatography-mass spectrometry of derivatives obtained by a modified Edman degradation that specifically cleaves off alkylated N-terminal amino acids (valine in Hb). The adduct levels found correspond to the metabolic conversion of about 5-10% of inhaled ethene and propene to ethylene oxide and propylene oxide, respectively, in agreement with results from earlier studies on mice inhaling radio-labelled alkenes. It is concluded that the alkenes, via epoxides, are the main sources of the observed HOEtVal and HOPrVal. From calculated doses and estimates of genotoxic potency the contribution from ethene in urban air to human cancer risk is discussed.

Methylations in human hemoglobin

Levels of N-Methylvaline (MeVal) and N tau-methylhistidine (MeHis) were measured in male smokers and non-smokers in a program aimed at mapping background alkylations of hemoglobin (Hb) as potential indicators of doses of exogenous and endogenous genotoxic agents. MeVal was also determined in Hb from rats, Syrian golden hamsters, mice and chickens. MeVal was found to occur at levels around 0.5 nmole/g Hb, with relatively little variation between individuals and species. MeVal was not significantly affected by smoking. This result contrasts with elevated levels of N-hydroxyethylvaline (HOEtVal) measured in the same persons (Törnqvist et al., 1986b). Levels of S-methylcysteine (MeCys) (Bailey et al., 1981) and MeHis were much higher than those of MeVal. The high levels of MeCys and MeHis may be due partly to misincorporation during protein synthesis and to artifacts. S-Adenosylmethionine and formaldehyde are possible endogenous sources of MeVal. One individual (smoker) out of 21 selected for measurement of MeVal was an outlier, with raised levels of both MeVal and HOEtVal, as would be expected in case of a defective detoxification system.

Formation of potential antigens from radiographic contrast media

The use of radiographic contrast media is occasionally accompanied by more or less serious adverse effects, evidently of complex etiology, following intravascular administration. Some of these reactions are suspected of having an allergic basis. The in vitro and in vivo formation of iodinated serum proteins following gamma irradiation in the presence of two commonly used radiographic contrast media is demonstrated. Non-toxic concentrations of ascorbate present during the irradiation is shown to prevent the formation of such iodo-proteins in vitro as well as in vivo. The amounts of potentially antigenic iodoprotein formed during radiographic procedures will certainly be very small, but this quantity may be sufficient to elicit a hypersensitivity reaction in cases when an individual has been previously sensitized to immunologically similar iodo-proteins, a mechanism that could account for certain rare and unpredictable reactions. The radiation induced formation of iodo-proteins may also serve as a model for the formation of iodine containing antigens mediated by a free radical mechanism, i.e. in the metabolism of iodinated compounds like erythrosine, a widely used colouring agent for certain foods.