Influence of polymorphisms of the human glutathione transferases and cytochrome P450 2E1 enzyme on the metabolism and toxicity of ethylene oxide and acrylonitrile

A cohort of 59 persons with industrial handling of low levels of acrylonitrile is being studied as part of a medical surveillance programme. Previously, an extended haemoglobin adduct monitoring (N-(cyanoethyl)valine and N-(hydroxyethyl)-valine) was performed regarding the glutathione transferases hGSTM1 and hGSTT1 polymorphisms but no influence of hGSTM1 or hGSTT1 polymorphisms on specific adduct levels was found. A compilation of case reports of human accidental poisonings had pointed to significant individual differences in human acrylonitrile metabolism and toxicity. Therefore, a re-evaluation of the industrial cohort included known polymorphisms of the glutathione transferases hGSTM3 and hGSTP1 as well as of the cytochrome P450 CYP2E1. A detailed statistical analysis revealed that exposed carriers of the allelic variants of hGSTP1, hGSTP1*B/hGSTP1*C, characterized by a single nucleotide polymorphism at nucleotide 313 which results in a change from Ile to Val at codon 104, had higher levels of the acrylonitrile-specific haemoglobin adduct N-(cyanoethyl)valine compared to the carriers of the codon 113 alleles hGSTP1*A and hGSTP1*D. The single nucleotide polymorphism at codon 113 of hGSTP1 (hGSTP1*A/hGSTP1*B versus hGSTP1*C/hGSTP1*D) did not show an effect, and also no influence was seen on specific haemoglobin adduct levels of the polymorphisms of hGSTM3 or CYP2E1. The data, therefore, point to a possible influence of a human enzyme polymorphism of the GSTP1 gene at codon 104 on the detoxication of acrylonitrile which calls for experimental toxicological investigation. The study also confirmed the impact of GSTT1 polymorphism on background N-(hydroxyethyl)-valine adduct levels in haemoglobin which are caused by endogenous ethylene oxide.

Procedures for health risk assessment in Europe

This report compares cancer classification systems, health risk assessment approaches, and procedures used for establishing occupational exposure limits (OELs), in various European countries and scientific organizations. The objectives were to highlight and compare key aspects of these processes and to identify the basis for differences in cancer classifications and OELs between various scientific organizations and countries. Differences in cancer classification exist in part due to differences in the ultimate purpose of classification and to the relative importance of different types of data (i.e., animal vs human data, mechanistic data, and data from benign vs malignant tumors). In general, the groups surveyed tend to agree on classification of chemicals with good evidence of carcinogenicity in humans, and agree less on classification of chemicals with positive evidence in animals and inadequate or limited evidence in humans. Most entities surveyed distinguish between genotoxic and nongenotoxic chemicals when conducting risk assessments. Although the risk assessment approach used for nongenotoxic chemicals is fairly similar among groups, risk assessment approaches for genotoxic carcinogens vary widely. In addition to risk assessment approaches, other factors which can affect OELs include selection of the critical effect, use of health-based vs technology-based exposure limits, and consideration of technological feasibility and socioeconomic factors.

N-acetyltransferase 2 phenotype in painters with bladder cancer and controls

AIM

This study was designed to evaluate the impact of N-acetyltransferase 2 (NAT2, substrate: aromatic amines) in painters with bladder cancer and controls.

BACKGROUND

Until the beginning of the 1960s, painters in Germany have used, among others, azo dyes based on carcinogenic aromatic amines.

MATERIALS AND METHODS

Sixteen painters with bladder cancer and 26 healthy painters (controls) who were from the same area in Germany and in the same age group (+/-5 years) were recruited into the study. All subjects were phenotyped for NAT2 by the molar ratio of two caffeine metabolites in the urine which was determined by the high performance liquid chromatography (HPLC) method. The number of years working as a painter, age at first exposure to paints and the life-time smoking habits of subjects were noted.

RESULTS

Fourteen cases and 23 controls had been exposed to paints before 1960. Age at first exposure to paint was 15.5 years (SD 5.3) in cases and 16.3 (SD 4.9) years in controls. Cases had worked 31.1 years (SD 15.0) and controls had worked 44.8 years (SD 7.2) as painters. Four cases and 7 controls were non-smokers. In this study, 88% of cases and 65% of controls were of the "slow" acetylation and phenotype,

CONCLUSION

The result point to and impact of the slow acetylation status as an individual risk factor for bladder cancer in persons occupationally exposed to amounts of carcinogenic aromatic amines released from water-soluble azo dyes.

Biological monitoring in workers in a nitrobenzene reduction plant: haemoglobin versus serum albumin adducts

The high priority of monitoring workers exposed to nitrobenzene is a consequence of clear findings of experimental carcinogenicity of nitrobenzene and the associated evaluations by the International Agency for Research on Cancer. Eighty male employees of a nitrobenzene reduction plant, with potential skin contact with nitrobenzene and aniline, participated in a current medical surveillance programme. Blood samples were routinely taken and analysed for aniline, 4-aminodiphenyl (4-ADP) and benzidine adducts of haemoglobin (Hb) and human serum albumin (HSA). Also, levels of methaemoglobin (Met-Hb) and of carbon monoxide haemoglobin (CO-Hb) were monitored. Effects of smoking were straightforward. Using the rank sum test of Wilcoxon, we found that very clear-cut and statistically significant smoking effects (about 3-fold increases) were apparent on CO-Hb (P = 0.00085) and on the Hb adduct of 4-ADP (P = 0.0006). The mean aniline-Hb adduct level in smokers was 1.5 times higher than in non-smokers; the significance (P = 0.05375) was close to the 5% level. The strongest correlation was evident between the Hb and HSA adducts of aniline (r(s) = 0.846). Less pronounced correlations (but with P values < 0.02) appeared between aniline-Hb and 4-ADP-Hb adducts (r(s) = 0.388), between 4-ADP and 4-ADP-HSA adducts (r(s) = 0.373), and between 4-ADP-Hb and aniline-HSA adducts (r(s) = 0.275). In view of the proposal for additional use of the aniline-HSA adduct for biological monitoring, particularly in cases of acute overexposures or poisonings, the strong correlation of the Hb and HSA conjugates is noteworthy; the ratio aniline-HSA:aniline-Hb was 1:42 for the entire cohort.

Real-time PCR analysis of the N-acetyltransferase NAT1 allele *3, *4, *10, *11, *14 and *17 polymorphism in squamous cell cancer of head and neck

Although tobacco smoke has been established as a main risk factor in the development of head and neck squamous cell cancer (HNSCC), genetic polymorphisms of xenobiotic metabolizing enzymes are supposed to modulate an individual's susceptibility to smoking-related HNSCC. N-acetyltransferase (NAT) 1 gene is known to be polymorphic and its protein product is implicated in the activation and detoxification of carcinogens, such as aromatic amines, present in tobacco smoke. We developed a rapid and reproducible LightCycler-assisted real-time polymerase chain reaction (PCR) for NAT1 genotyping, which allowed the parallel differentiation of NAT1*3, *4, *10 and *11 alleles and separately of NAT1*14 and *17 alleles within 60 min without the need for further post-PCR processing. In order to investigate the role of the NAT1 gene polymorphism as a risk-modifying factor in HNSCC, we tested for the presence of NAT1*3, *4, *10, *11, *14 and *17 alleles in a case-control study of 291 HNSCC patients and 300 healthy controls of Caucasian origin. Our findings suggest that in Caucasians, the risk of HNSCC is not associated with NAT1 polymorphism. The overall distribution of NAT1 allele frequencies was not significantly different among cases and controls. The presence of the fast acetylator NAT1*10 and NAT1*11 alleles did not significantly increase the risk of HNSCC and no modifying effect of NAT1*10 was observed among smokers. This new approach in NAT1 genotyping substantially increases throughput of sample analysis and, therefore, enhances opportunities to study NAT1 as a risk factor in different cancers in large-scale studies.

Re-evaluation of the effect of smoking on the methylation of N-terminal valine in haemoglobin

In view of the established extrapulmonary cancer sites targeted by smoking a multiplicity of compounds and mechanisms might be involved. It has been debated that smoking caused increased incidence of N-methylvaline at the N-terminus of haemoglobin. Because this could indicate a relevance of methylating nitrosamines in tobacco smoke, data are presented from an industrial cohort of 35 smokers and 21 non-smokers repeatedly monitored between 1994 and 1999. In general, N-methylvaline adduct levels in haemoglobin of smokers were approximately 50% higher than those of non-smokers. The smoking-induced methylation of haemoglobin is likely to be caused by dimethylnitrosamine (N-nitroso-dimethylamine), a major nitrosamine in side-stream tobacco smoke. The biomonitoring data emphasise the potential value of N-methylvaline as a smoking-related biomarker and call for intensified research on tobacco smoke compounds that lead to macromolecular methylation processes.

Pathological excretion patterns of urinary proteins in miners highly exposed to dinitrotoluene

A cohort of 161 underground miners who had been highly exposed to dinitrotoluene (DNT) in the copper-mining industry of the former German Democratic Republic was reinvestigated for signs of subclinical renal damage. The study included a screening of urinary proteins excreted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and quantitations of the specific urinary proteins alpha 1-microglobulin and glutathione-S-transferase alpha (GST alpha) as biomarkers for damage of the proximal tubule and glutathione-S-transferase pi (GST pi) for damage of the distal tubule. The exposures were categorized semiquantitatively (low, medium, high, and very high), according to the type and duration of professional contact with DNT. A straight dose-dependence of pathological protein excretion patterns with the semiquantitative ranking of DNT exposure was seen. Most of the previously reported cancer cases of the urinary tract, especially those in the higher exposed groups, were confined to pathological urinary protein excretion patterns. The damage from DNT was directed toward the tubular system. In many cases, the appearance of Tamm-Horsfall protein, a 105-kD protein marker, was noted. Data on the biomarkers alpha 1-microglobulin, GST alpha, and GST pi consistently demonstrated a dose-dependent increase in tubular damage, which confirmed the results of screening by SDS-PAGE and clearly indicated a nephrotoxic effect of DNT under the given conditions of exposure. Within the cluster of cancer patients observed among the DNT-exposed workers, only in exceptional cases were normal biomarker excretions found.

Association of CYP1B1 codon 432 mutant allele in head and neck squamous cell cancer is reflected by somatic mutations of p53 in tumor tissue

Tobacco use is causally associated with head and neck squamous cell cancer (HNSCC). Here, we present the results of a case-control study that investigated the effects that the genetic variants of the cytochrome (CYP)1A1, CYP1B1, glutathione-S-transferase (GST)M1, GSTT1, and GSTP1 genes have on modifying the risk of smoking-related HNSCC. Allelisms of the CYP1A1, GSTT1, GSTM1, and GSTT1 genes alone were not associated with an increased risk. CYP1B1 codon 432 polymorphism was found to be a putative susceptibility factor in smoking-related HNSCC. The frequency of CYP1B1 polymorphism was significantly higher (P < 0.001) in the group of smoking cases when compared with smoking controls. Additionally, an odds ratio (OR) of 4.53 (2.62-7.98) was discovered when investigating smoking and nonsmoking cases for the susceptible genotype CYP1B1*2/*2, when compared with the presence of the genotype wild type. In combination with polymorphic variants of the GST genes, a synergistic-effect OR was observed. The calculated OR for the combined genotype CYP1B1*2/*2 and GSTM1*2/*2 was 12.8 (4.09-49.7). The calculated OR for the combined genotype was 13.4 (2.92-97.7) for CYP1B1*2/*2 and GSTT1*2/*2, and 24.1 (9.36-70.5) for the combination of CYP1B1*2/*2 and GSTT1-expressors. The impact of the polymorphic variants of the CYP1B1 gene on HNSCC risk is reflected by the strong association with the frequency of somatic mutations of the p53 gene. Smokers with susceptible genotype CYP1B1*2/*2 were 20 times more likely to show evidence of p53 mutations than were those with CYP1B1 wild type. Combined genotype analysis of CYP1B1 and GSTM1 or GSTT1 revealed interactive effects on the occurrence of p53 gene mutations. The results of the present study indicate that polymorphic variants of CYP1B1 relate significantly to the individual susceptibility of smokers to HNSCC.

Real-time genotyping of cytochrome P4501A1 A4889G and T6235C polymorphisms

Single nucleotide polymorphisms, such as the cytochrome P450 1A1 (CYP1A1) A4889G and T6235C variants, have been reported to be associated with an increased cancer risk. In order to study their role in molecular-epidemiological studies, we developed a single-step procedure for genotyping these two CYP1A1 polymorphisms using real-time polymerase chain reaction (PCR) and subsequent melting curve analysis. Genotypes of 300 unrelated Caucasians, without prior history of cancer, were determined by real-time PCR and compared to genotypes obtained by restriction fragment length polymorphism PCR. In the population examined, the allele frequency of the CYP1A1 G allele at position 4889 was 0.042, and the frequency of the T allele at position 6235 was 0.10. Five percent of samples disagreed between methods. Sequence analysis of discordant samples revealed that the differences are likely attributed to incomplete digestion of amplicons by the RFLP method. These findings confirm the reliability and utility of real-time PCR as a method for large-scale genotyping.

European aspects of standard setting in occupational hygiene and medicine

Occupational standards concerning the allowable concentrations of chemical compounds in the ambient air of workplaces have been established in several countries at national levels. With the integration of the European Union, a need exists for establishing harmonized Occupational Exposure Limits. For analytical developments, it is apparent that methods for speciation or fractionation of carcinogenic metal compounds will be of increasing practical importance for standard setting. Criteria of applicability under field conditions, cost-effectiveness, and robustness are practical driving forces for new developments. When the European Union issued a list of 62 chemical substances with Occupational Exposure Limits in 2000, 25 substances received a 'skin' notation. The latter indicates that toxicologically significant amounts may be taken up via the skin. Similar notations exist on national levels. For such substances, monitoring concentrations in ambient air will not be sufficient; biological monitoring strategies will gain further importance in the medical surveillance of workers who are exposed to such compounds. Proceedings in establishing legal frameworks for a biological monitoring of chemical exposures within Europe are paralleled by scientific advances in this field. A new aspect is the possibility of a differential adduct monitoring, using blood proteins of different half-life or lifespan. This technique allows differentiation between long-term mean exposure to reactive chemicals and short-term episodes, for example, by accidental overexposure. For further analytical developments, the following issues have been addressed as being particularly important: New dose monitoring strategies, sensitive and reliable methods for detection of DNA adducts, cytogenetic parameters in biological monitoring, methods to monitor exposure to sensitizing chemicals, and parameters for individual susceptibilities to chemical toxicants.

Glutathione transferase activities in renal carcinomas and adjacent normal renal tissues: factors influencing renal carcinogenesis induced by xenobiotics

In general, the biological activation of nephrocarcinogenic chlorinated hydrocarbons proceeds via conjugation with glutathione. It has mostly been assumed that the main site of initial conjugation is the liver, followed by a mandatory transfer of intermediates to the kidney. It was therefore of interest to study the enzyme activities of subgroups of glutathione transferases (GSTs) in renal cancers and the surrounding normal renal tissues of the same individuals (n = 21). For genotyping the individuals with respect to known polymorphic GST isozymes the following substrates with differential specificity were used: 1-chloro-2,4-dinitrobenzene for overall GST activity (except GST theta); 7-chloro-4-nitrobenzo-2-oxa- 1,3-diazole for GST alpha; 1,2-dichloro-4-nitro-benzene for GST mu; ethacrynic acid and 4-vinylpyridine for GST pi; and methyl chloride for GST theta. In general, the normal tissues were able to metabolize the test substrates. A general decrease in individual GST enzyme activities was apparent in the course of cancerization, and in some (exceptional) cases individual activities, expressed in the normal renal tissue, were lost in the tumour tissue. The GST enzyme activities in tumours were independent of tumour stage, or the age and gender of the patients. There was little influence of known polymorphisms of GSTM1, GSTM3 and GSTP1 upon the activities towards the test substrates, whereas the influence of GSTT1 polymorphism on the activity towads methyl chloride was straightforward. In general, the present findings support the concept that the initial GST-dependent bioactivation step of nephrocarcinogenic chlorinated hydrocarbons may take place in the kidney itself. This should be a consideration in toxicokinetic modelling.

Comparative assessment of endocrine modulators with oestrogenic activity: I. Definition of a hygiene-based margin of safety (HBMOS) for xeno-oestrogens against the background of European developments

A novel concept - the hygiene-based margin of safety (HBMOS) - is suggested for the assessment of the impact of potential endocrine modulators. It integrates exposure scenarios and potency data for industrial chemicals and naturally occurring dietary compounds with oestrogenic activity. An HBMOS is defined as a quotient of estimated daily intakes weighted by the relative in vivo potencies of these compounds. The Existing Chemicals Programme of the European Union provides Human and Environmental Risk Assessments of Existing Chemicals which include human exposure scenarios. Such exposure scenarios, along with potency estimates for endocrine activities, may provide a basis for a quantitative comparison of the potential endocrine-modulating effects of industrial chemicals with endocrine modulators as natural constituents of human diet. Natural phyto-oestrogens exhibit oestrogenic activity in vitro and in vivo. Important phyto-oestrogens for humans are isoflavones (daidzein, genistein) and lignans, with the highest quantities found in soybeans and flaxseed, respectively. Daily isoflavone exposures calculated for infants on soy-based formulae were in the ranges of 4.5-8 mg/kg body wt.; estimates for adults range up to 1 mg/kg body wt. The Senate Commission on the Evaluation of Food Safety (SKLM) of the Deutsche Forschungsgemeinschaft has also indicated a wide range of dietary exposures. For matters of risk assessment, the SKLM has based recommendations on dietary exposure scenarios, implying a daily intake of phyto-oestrogens in the order of 1 mg/kg body wt. On the basis of information compiled within the Existing Chemicals Programme of the EU, it appears that a daily human exposure to nonylphenol of 2 microg/kg body wt. may be a worst-case assumption, but which is based on valid scenarios. The intake of octylphenol is much lower, due to a different use pattern and applications, and may be neglected. Data from migration studies led to estimations of the daily human uptake of bisphenol A of maximally 1 microg/kg body wt. On the basis of comparative data from uterotrophic assays in rats, with three consecutive days of oral applications involved, and taking the natural phyto-oestrogen daidzein as reference (= 1), relative uterotrophic activities in DA/Han rats follow the sequence: daidzein = 1; bisphenol A = 1; p-tertoctylphenol = 2; o, p'-DDT = 4; ethinyl oestradiol = 40,000. The derived values from exposure scenarios, as well as these relative potency values and bridging assumptions, led to calculations of HBMOS as a quantitative comparison of potential endocrine-modulating effects of industrial chemicals with those of natural constituents of human diet. HBMOS estimates for nonylphenol ranged between 250 and 500, dependent on bridging assumptions, and around 1000 for bisphenol A. The derivations of HBMOS were in full support of the conclusions reached by the SKLM of the Deutsche Forschungsgemeinschaft. The estimated HBMOS values for the industrial chemicals (nonylphenol, bisphenol A) appear sufficiently high to ensure the absence of a practical risk to human health under the present exposure conditions.

Biotransformation of trichloroethylene in collagen gel sandwich cultures of rat hepatocytes

The collagen gel sandwich culture of hepatocytes has been proposed as one of the most suitable culture models available for biotransformation studies of xenobiotics. It is a complex model which imitates the cascade of enzymatic events of in vivo biotransformation and allows investigation of biological endpoints under realistic conditions. The biotransformation of trichloroethylene (TRI) has been studied in this model using rat hepatocytes. Headspace gas chromatographic measurements revealed that hepatocytes, cultured for 4 days in this in vitro system, metabolised TRI into the major oxidative metabolites trichloroacetic acid (TCA) and trichloroethanol (TCE). Cultured hepatocytes were exposed either to TRI, or to TCA and TCE. Endpoints studied were albumin secretion and the cytochrome P450 (CYP)-dependent enzymatic activities ethoxyresorufin O-deethylase (EROD), pentoxyresorufin O-depentylase (PROD) and N-nitrosodimethylamine demethylase (NDMA). The results show that both the parent compound and its metabolites exert specific effects on different CYP-dependent mono-oxygenase activities, as seen in vivo. It is suggested that collagen gel sandwich cultures represent a useful in vitro model for the investigation of metabolism-linked toxicity studies.

Toxicokinetics of bisphenol A in female DA/Han rats after a single i.v. and oral administration

Bisphenol A [BPA; 2,2-bis-(4-hydroxyphenyl)-propane] is a monomer used in the manufacture of resins with a wide range of applications, e.g. plastic coatings in the food packaging industry. BPA has been shown to have a weak oestrogenic activity in vitro and in vivo. Despite its low oestrogenic potency there is concern that, as a consequence of slow clearance, BPA might reach biologically significant levels in humans and animals exposed to environmental levels. To address this concern, we assessed the kinetic behaviour of BPA in female DA/Han rats. Groups of female rats received 10 mg BPA/kg body weight intravenously or 10 or 100 mg BPA/kg body weight orally (by gavage). Blood samples were collected at different time-points and plasma was prepared. Free BPA in the samples was isolated by fluid-fluid extraction. BPA was measured by GC-MS which allowed the reliable determination of BPA concentrations as low as approximately 10 ng/ml plasma. Immediately after i.v. administration, the BPA plasma concentration was in the range of about 15 microg/ml and decreased rapidly within the first hour (to 700 ng/ml). The levels declined further (100 ng/ml at 2 h), and after 24 h the analytical detection limit was reached. BPA was detected in plasma as early as 10 min after gavage administration, indicating rapid initial uptake from the gastrointestinal tract. Absorption of BPA was variable. In animals receiving 10 mg/kg, maximal plasma levels were reached after 1.5 h (31 ng/ ml) and 6 h (40 ng/ml). In animals receiving 100 mg/kg, plasma levels reached maxima around 30 min (150 ng/ml) and 3 h (134 ng/ml) after administration. After 48 h BPA was at or below the detection limit in both dose groups. Fluctuations in the BPA plasma concentrations over time point to the possibility of enterohepatic recirculation and protracted absorption from the gastrointestinal tract. Using the area under the concentration-time curves (AUCs), low bioavailabilities of 16.4% and 5.6% were calculated for the 10 and 100 mg/kg dose groups, respectively. The toxicokinetic properties of BPA in DA/Han rats are in agreement with the hypothesis of a rapid first-pass elimination by the liver and efficient metabolic clearance of low oral doses. Only excessive doses may lead to bioaccumulation if detoxification pathways are saturated.

Toxicokinetics of the phytoestrogen daidzein in female DA/Han rats

Female DA/Han rats were given the phytoestrogen daidzein, either intravenously (10 mg/kg b.w.) or orally by gavage (10 or 100 mg/kg b.w.). The plasma concentration-time curve determined after i.v. administration of daidzein was fitted to a triexponential model, resulting in a final half-life (gamma-phase) of approximately 4 h. The oral bioavailability of 10 mg daidzein/kg was 9.7%, while that of 100 mg/kg was 2.2%; the higher dose (100 mg/kg) was apparently absorbed to a four- to fivefold lower extent than the smaller dose. The plasma concentration time curves after oral administration of daidzein to female DA/Han rats revealed pronounced interindividual differences and multiple peaks, pointing to extensive enterohepatic circulation and/or protracted absorption from the gastrointestinal tract. As shown in a separate experiment with bile duct-cannulated rats, daidzein (i.p. 10 mg/kg b.w.) is efficiently excreted with bile: glucuronide/sulfate metabolites amounting to approximately 30% of the dose in 8 h. Conjugates were also the main circulating metabolites upon i.v. or gavage administration of daidzein, indicating efficient phase II metabolism in female DA/Han rats. Since only few data have been published on tissue levels of isoflavones, their concentrations were measured in various organs and compared to plasma levels determined at the time the animals were killed, with one exception 32 or 48 h after rats had received a single dose of daidzein (i.v. or per os). As expected, the daidzein concentrations depended upon dose and administration route. Despite notable differences in the absolute amounts of total daidzein (free plus hydrolyzed conjugates), the levels were usually three- to fivefold higher in liver and kidney than in plasma; in most samples of uteri, the concentrations were similar, or up to twofold higher, than the respective plasma levels. These data point to an uptake and storage of isoflavones and metabolites in tissues. Experimental toxicokinetics appear to be a relevant subject that should be integrated into assessments of toxicological data for endocrine modulators.

Carcinogenicity and genotoxicity of ethylene oxide: new aspects and recent advances

Long-term inhalation studies in rodents have presented unequivocal evidence of experimental carcinogenicity of ethylene oxide, based on the formation of malignant tumors at multiple sites. However, despite a considerable body of epidemiological data only limited evidence has been obtained of its carcinogenicity in humans. Ethylene oxide is not only an important exogenous toxicant, but it is also formed from ethylene as a biological precursor. Ethylene is a normal body constituent; its endogenous formation is evidenced by exhalation in rats and in humans. Consequently, ethylene oxide must also be regarded as a physiological compound. The most abundant DNA adduct of ethylene oxide is 7-(2-hydroxyethyl)guanine (HOEtG). Open questions are the nature and role of tissue-specific factors in ethylene oxide carcinogenesis and the physiological and quantitative role of DNA repair mechanisms. The detection of remarkable individual differences in the susceptibility of humans has promoted research into genetic factors that influence the metabolism of ethylene oxide. With this background it appears that current PBPK models for trans-species extrapolation of ethylene oxide toxicity need to be refined further. For a cancer risk assessment at low levels of DNA damage, exposure-related adducts must be discussed in relation to background DNA damage as well as to inter- and intraindividual variability. In rats, subacute ethylene oxide exposures on the order of 1 ppm (1.83 mg/m3) cause DNA adduct levels (HOEtG) of the same magnitude as produced by endogenous ethylene oxide. Based on very recent studies the endogenous background levels of HOEtG in DNA of humans are comparable to those that are produced in rodents by repetitive exogenous ethylene oxide exposures of about 10 ppm (18.3 mg/m3). Experimentally, ethylene oxide has revealed only weak mutagenic effects in vivo, which are confined to higher doses. It has been concluded that long-term human occupational exposure to low airborne concentrations to ethylene oxide, at or below current occupational exposure limits of 1 ppm (1.83 mg/m3), would not produce unacceptable increased genotoxic risks. However, critical questions remain that need further discussions relating to the coherence of animal and human data of experimental data in vitro vs. in vivo and to species-specific dynamics of DNA lesions.

Endocrine disruptors: update on xenoestrogens

Endocrine disruptors and their possible impact on human and animal health have become a topic of discussion and an area of active research in toxicology. A focus has been on xenoestrogens, i.e., environmental chemicals with estrogenic activity. In principle, there is agreement that such compounds, in high doses, may cause developmental, reproductive and tumorigenic effects ("hazard"). A matter of controversy is the question of risks associated with xenoestrogens under realistic (low) exposure scenarios; this is due to uncertainty on how to assess the interactions of exogenous compounds with the endocrine system and its complex regulation. Our overview will address topics including: consequences from previous clinical use of the potent estrogen diethylstilbestrol with particular emphasis on dose-response relationships, other observations in humans exposed to estrogenic chemicals in an occupational context, and available information on exposure levels of synthetic and naturally occurring estrogens in the diet. Together with a critical appraisal of methods to detect and quantitate the estrogenic activity of synthetic and naturally occurring chemicals, novel aspects in the risk assessment for endocrine active compounds are discussed.

Glutathione S-transferase polymorphism in Parkinson's disease

Glutathione S-transferases (GSTs) are involved in the detoxification of endogenous or exogenous toxins, which may play a role in the pathogenesis of Parkinson's disease. We genotyped the Glutathione-S-Transferase isoenzymes GSTM1 and GSTT1 by polymerase chain reaction in order to evaluate different gene polymorphisms of these isoenzymes in 149 parkinsonian and 99 control subjects. No differences appeared between both groups regarding the frequencies of the homozygous deletion of GSTM1 (odds ratio 1.021; 95% CI [0.613; 1.699], p < 0.521 Fisher's exact test) and GSTT1 (odds ratio 1.514; 95% CI [0.811; 2.824], p < 0.127). Age of onset of PD did not correlate to GSTM1 and GSTT1 polymorphisms. These results do not support the hypothesis of a possible impact of GSTM1 and GSTT1 detoxification activities in the pathogenesis of Parkinson's disease.

Species differences in acrylonitrile metabolism and toxicity between experimental animals and humans based on observations in human accidental poisonings

The high acute toxicity of acrylonitrile may be a result of its intrinsic biological reactivity or of its metabolite cyanide. Intravenous N-acetylcysteine has been recommended for treatment of accidental intoxications in acrylonitrile workers, but such recommendations vary internationally. Acrylonitrile is metabolized in humans and experimental animals via two competing pathways; the glutathione-dependent pathway is considered to represent an avenue of detoxication whilst the oxidative pathway leads to a genotoxic epoxide, cyanoethylene oxide, and to elimination of cyanide. Cases of acute acrylonitrile overexposure or intoxication have occurred within persons having industrial contact with acrylonitrile; the route of exposure was by inhalation and/or by skin contact. The combined observations lead to the conclusion of a much higher impact of the oxidative metabolism of acrylonitrile in humans than in rodents. This is confirmed by differences in the clinical picture of acute life-threatening intoxications in both species, as well as by differential efficacies of antidotes. A combination of N-acetylcysteine with sodium thiosulfate seems an appropriate measure for antidote therapy of acute acrylonitrile intoxications. Clinical observations also highlight the practical importance of human individual susceptibility differences. Furthermore, differential adduct monitoring, assessing protein adducts with different rates of decay, enables the development of more elaborated biological monitoring strategies for the surveillance of workers with potential acrylonitrile contact.

Psychological effects upon exposure to polyhalogenated dibenzodioxins and dibenzofurans

Thirty workers who had been exposed to combustion products for several years due to testing of flame retarding qualities of building materials and 30 controls from the same facility were investigated. Concentrations found in samples taken from different places of the facility were up to 14,660 microg/kg for polybrominated dibenzofurans and up to 67.1 microg/kg for polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs). Physical examination, routine laboratory parameters, and blood fat concentrations of PCDDs and PCDFs revealed normal findings. Neurotoxic symptoms showed a weak tendency of overrepresentation among the exposed workers. The frequency of neurobehavioural symptoms increased significantly with trait anxiety independent of exposure to combustion products.

Renal toxicity and carcinogenicity of trichloroethylene: key results, mechanisms, and controversies

The discussion on renal carcinogenicity of trichloroethylene addresses epidemiological, mechanistic, and metabolic aspects. After trichloroethylene exposure of rats, renal cell tumors were found increased in males, and an increased incidence of interstitial cell tumors of the testes was reported. Studies on the metabolism of trichloroethylene in rodents and in humans support the role of bioactivation reactions for the development of tumors following exposure to trichloroethylene. Epidemiological cohort studies addressing the carcinogenicity of trichloroethylene with respect to the renal or urothelial target sites have been conducted, and no clear evidence for an elevated renal or urinary tract cancer risk in trichloroethylene-exposed groups was visible in exposed populations. However, a cohort study of 169 male workers having been exposed to unusually high levels of trichloroethylene in Germany within the period between 1956 and 1975 supported a nephrocarcinogenic effect of trichloroethylene in humans. The results of this study were discussed in the literature with considerable reserve; criticism was based mainly on the choice of the study group, which had been recruited from personnel of a company in which a cluster of four renal tumors was observed previously. Hence, a further case-control study was conducted in the same region. This study confirmed the results of the previous cohort study, supporting the concept of involvement of prolonged and high-dose trichloroethylene exposures in the development of renal cell cancer. Further investigations on patients with renal cell carcinoma and with histories of high trichloroethylene exposures, on the basis of excretion of marker proteins in the urine, pointed to toxic damage to the proximal renal tubules by trichloroethylene. The hypothesis of implication of a glutathione transferase-dependent bioactivating pathway of trichloroethylene, established in experimental animals, seems at least also plausible for humans. Apparently, the occurrence of renal cell carcinomas in man follows high-dose exposures to trichloroethylene that are also accompanied by damage to tubular renal cells. Development of renal cell carcinomas has been related to mutations in the vonHippel-Lindau (VHL) tumor suppressor gene. Renal cell carcinoma tissues of persons with histories of prolonged high-dose exposure to trichloroethylene were investigated for the occurrence of mutations of the vonHippel-Lindau (VHL) tumor suppressor gene. VHL gene mutations were found in the majority of renal cell tumors associated with high-level exposure to trichloroethylene. A specific mutational hot spot at the VHL nucleotide 454 was addressed as a unique mutation pattern of the VHL tumor suppressor gene. A synopsis of all experimental, clinical, and epidemiological data suggests that reactive metabolites of trichloroethylene, with likely involvement of dichlorovinyl-cysteine (DCVC), exert a genotoxic effect on the proximal tubule of the human kidney. This constitutes a tumor-initiating process of genotoxic nature, the initial genotoxic effect apparently being linked with mutational changes in the VHL tumor suppressor gene. However, there is compelling evidence that the full development of a malignant tumor requires continued promotional stimuli. Repetitive episodes of high peak exposures to trichloroethylene over a prolonged period of time apparently led to nephrotoxicity, visualized by the excretion of tubular marker proteins in the urine. This critical process of development of tubular damage by trichloroethylene must follow a "conventional" dose-dependence, implying a practical threshold. This view is much corroborated by the fact that the occurrence of human renal cell cancer is obviously confined to cases of unusually high trichloroethylene exposures in the past, with special characteristics of very high and repetitive peak exposures. Current instruments of regulation should be adjusted to allow adequate consideration of su

Fractionation of nickel species from airborne aerosols: practical improvements and industrial applications

Presently recommended methods for fractionation of airborne nickel dusts are laborious and time-consuming. A new method has been developed based on existing procedures of leaching nickel fractions from sample filters, and based on the principles of flow-injection analysis. A special sample filter holder has been constructed to be used in conjunction with the flow-injection system. In this system, soluble nickel compounds are extracted from the filter with ammonium citrate buffer, sulphidic nickel by peroxycitric acid, and metallic nickel by CuCl2/KCl. The final dissolution of the filter by HNO3/HCl results in the oxidic fraction. Endpoint determination of these fractions is performed by use of graphite-furnace atomic absorption spectrometry (GF-AAS). The analytical criteria of this method have been established, and the suitability of the method for application in the practice of industrial hygiene has been demonstrated.