Occurrence of urinary tract tumors in miners highly exposed to dinitrotoluene

Between 1984 and 1997, six cases of urothelial cancer and 14 cases of renal cell cancer occurred in a group of 500 underground mining workers in the copper-mining industry of the former German Democratic Republic, with high exposures to explosives containing technical dinitrotoluene. Exposure durations ranged from 7 to 37 years, and latency periods ranged from 21 to 46 years. The incidences of both urothelial and renal cell tumors in this group were much higher than anticipated on the basis of the cancer registers of the German Democratic Republic by factors of 4.5 and 14.3, respectively. The cancer cases and a representative group of 183 formerly dinitrotoluene-exposed miners of this local industry were interviewed for their working history and grouped into four exposure categories. This categorization of the 14 renal cell tumor cases revealed no dose-dependency concerning explosives in any of the four exposure categories and was similar to that of the representative group of employees, whereas the urothelial tumor cases were predominantly confined to the high-exposure categories. Furthermore, all identified tumor patients were genotyped by polymerase chain reaction, using lymphocyte DNA, regarding their genetic status of the polymorphic xenobiotic metabolizing enzymes, including the N-acetyltransferase 2 and the glutathione-S-transferases M1 and T1. This genotyping revealed remarkable distributions only for the urothelial tumor cases, who were exclusively identified as "slow acetylators." This points to the possibility of human carcinogenicity of dinitrotoluene, with regard to the urothelium as the target tissue.

Determination of glutathione transferase (GSTT1-1) activities in different tissues based on formation of radioactive metabolites using 35S-glutathione

A new system has been developed to determine enzyme activities of glutathione transferase theta (GSTT1-1) based on radiometric product detection resulting from the enzymic reaction of methyl chloride with 35S-labelled glutathione. In principle, the method is universally applicable for determination of glutathione transferase activities towards a multiplicity of substrates. The method distinguishes between erythocyte GSTT1-1 activities of human 'non-conjugators', 'low conjugators' and 'high conjugators'. Application to cytosol preparations of livers and kidneys of male and female Fischer 344 and B6C3F1 mice reveals differential GSTT1-1 activities in hepatic and renal tissues. These ought to be considered in species-specific modellings of organ toxicities of chlorinated hydrocarbons.

Renal cell cancer correlated with occupational exposure to trichloroethene

A previous cohort-study in a cardboard factory demonstrated that high and prolonged occupational exposure to trichloroethene (C2HCl3) is associated with an increased incidence of renal cell cancer. The present hospital-based case/control study investigates occupational exposure in 58 patients with renal cell cancer with special emphasis on C2HCl3 and the structurally and toxicologically closely related compound tetrachloroethene (C2Cl4). A group of 84 patients from the accident wards of three general hospitals in the same area served as controls. Of the 58 cases, 19 had histories of occupational C2HCl3 exposure for at least 2 years and none had been exposed to C2Cl4; of the 84 controls, 5 had been occupationally exposed to C2HCl3 and 2 to C2Cl4. After adjustment for other risk factors, such as age, obesity, high blood pressure, smoking and chronic intake of diuretics, the study demonstrates an association of renal cell cancer with long-term exposure to C2HCl3 (odds ratio 10.80; 95% CI: 3.36-34.75).

Glutathione transferase T1 and M1 genotype polymorphism in the normal population of Shanghai

Glutathione transferases are known to be important enzymes in the metabolism of xenobiotics. In humans genetic polymorphisms have been reported for the hGSTM1 and hGSTT1 genes leading to individual differences in susceptibility towards toxic effects, such as cancer. This study describes the distribution of the two polymorphisms of hGSTT1 and hGSTM1 in the normal Chinese population of Shanghai. Out of 219 healthy individuals having been genotyped for GSTT1 and GSTM1, 108 (49%) were identified to be homozygously deficient for the GSTT1 gene and 107 (49%) for the GSTM1 gene.

Mutagenic properties of 1,2,3,4-tetrahydronaphthaline-1-hydroperoxide, a model compound for organic peroxides in Diesel exhaust

The genotoxicity of the organic peroxide 1,2,3,4-tetrahydronaphthaline-1-hydroperoxide (or tetraline-1-hydroperoxide, THP) was investigated in the Ames assay without a metabolic activating system using Salmonella typhimurium strains TA 98, TA 100, and TA 102. THP served as a model compound for higher organic peroxides, which can arise from autoxidation of hydrocarbons, e.g. in Diesel exhaust. While THP induced no mutagenic response in S. typhimurium TA 98, it was directly mutagenic in strains TA 100 and TA 102. These data, along with findings on mutagenic properties of other alkyl hydroperoxides, suggest that such compounds deserve further investigation regarding their genotoxic potential and occurrence in the environment.

The carcinogenic risk of ethene (ethylene)

On occasion of the 25th year of publication of Toxicologic Pathology, the Editor has asked for a report about recent progress in the area addressed by an article entitled “Olefinic Hydrocarbons: A First Risk Estimate,” one of the top 10 most frequently cited papers of the journal (3). Because general issues of risk assessment have very recently been addressed in this journal (6), I will focus on new specific aspects of ethene carcinogenicity.

Urothelial cancer of the bladder in an area of former coal, iron, and steel industries in Germany: a case-control study

In a case-control study performed in an area of former coal, iron, and steel industries, the professional and lifestyle histories of 412 male urothelial bladder cancer inpatients (cases) and 414 inpatients with benign prostatic hyperplasia (controls) were investigated. Smoking habits were identified as the main confounder for occupational bladder cancer risk. Two hundred and forty (58.3%) of the bladder cancer inpatients and 146 (35.3%) of the inpatients with benign prostatic hyperplasia were smokers. The percentage of ex-smokers in the bladder cancer cases was 10.2%; the percentage of ex-smokers in the controls was 9.7%. Smoking-adjusted Mantel-Haenszel estimates of the odds ratios (OR&infMH;) for bladder cancer were elevated in underground hard-coal miners (OR&infMH; =2. 54, 95% CI =[1.64; 3.93]), chemical workers (OR&infMH; =2.16, 95% CI =[0.87; 5.38]), painters/varnishers (OR&infMH; = 2.42, 95% CI =[1. 05; 5.57]), technicians (OR&infMH; = 1.99, 95% CI =[0.95; 4.16]), and foundry workers (OR&infMH; = 2.22, 95% CI = [0.53; 9.08]). Administrative officers had significantly lower smoking-adjusted odds ratios (OR&infMH; = 0.61, 95% CI = [0.42; 0.88]). Although statistically not significant, the results of the Breslow-Day test of homogeneity of the odds ratios over the strata are compatible with interactions between tobacco smoking and the occupations of underground hard-coal miners (chi(2)&infBD; = 4.91, p=0.07) and chemical workers (chi(2)&infBR; = 3.32, p=0.06).

Modulation of prostaglandin H synthase-2 mRNA expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice

Prostaglandin endoperoxide H synthases (PGHS-1 and PGHS-2) catalyze an intermediate step in the biosynthesis of prostaglandins and thromboxanes. Recently, it was observed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) modulates the expression of PGHS-2 mRNA in different cell lines. The main aim of this study was to examine whether PGHS-2 mRNA expression can be changed by acute TCDD in vivo and, second, we were also interested in whether modulation of PGHS-2 is mediated by the aryl hydrocarbon receptor (AhR) which is known to be involved in the transcriptional control of TCDD-induced phase 1 and phase 2 enzymes. Initially C57BL/6J mice were treated with a single dose of 10,000 ng TCDD/kg and the PGHS-1 and PGHS-2 mRNAs were analyzed in liver, lung, thymus, kidney, and spleen. In all tissues examined the expression of PGHS-1 mRNA was not affected by TCDD. However, TCDD treatment enhanced the PGHS-2 mRNA levels in lung and spleen. No effect of TCDD on PGHS-2 expression was found in liver and kidney. For dose-response studies C57BL/6J and DBA/2J mice were treated for 24 h with various doses of TCDD (1-50,000 ng/kg) and the PGHS-2 mRNA increases were analyzed in lungs and spleens. A significant increase of PGHS-2 mRNA in lungs of C57BL/6J mice was found at a dose of 100 ng TCDD/kg, whereas a nearly 100-fold higher TCDD dose was needed to increase PGHS-2 in DBA/2J mice. A similar dose-dependent induction of PGHS-2 was found in spleens of C57BL/6J mice; however, no significant increase of PGHS-2 was found in spleens of DBA/2 mice. These results indicate an involvement of AhR in TCDD-mediated changes of PGHS-2 expression. This suggestion is supported by studies in AhR-deficient animals which showed that TCDD had no effect on PGHS-2 mRNA. When changes of PGHS-2 mRNA expression are compared with those of CYP1A1 between 4 and 72 h after TCDD, it is noteworthy that TCDD led to a delayed and more transient increase of PGHS-2. These data suggest that the mechanism of modulation of both genes by TCDD may be different.

A note on the physiological background of the ethylene oxide adduct 7-(2-hydroxyethyl)guanine in DNA from human blood

A newly developed high-performance liquid chromatography (HPLC) method involves derivatization with phenylglyoxal and fluorescence detection, using 7-methylguanine as internal standard. The physiological background of the adduct 7-(2-hydroxyethyl)guanine in DNA isolated from human blood was determined by this method. In five persons the range of the adduct was between 2.1 and 5.8 pmol/mg DNA (mean 3.2). This finding is consistent with previous data obtained by others, using different analytical methods, and points to an intrinsic carcinogenic risk due to endogenous ethylene oxide.

N-Acetyltransferase 2 (NAT2) and Glutathione S-Transferase µ (GSTM1) in Bladder-cancer Patients in a Highly Industrialized Area

The study was designed to assess occupational and non-occupational risk factors in patients with urothelial carcinomas in an area of former coal, iron, and steel industries, with special regard to the impacts of polymorphic enzymes involved in the metabolism of aromatic amines (N-acetyltransferase 2, NAT2) and of polycyclic aromatic hydrocarbons (glutathione S-transferase µ, GSTM1). Inpatients with bladder cancer (n = 179) were interviewed for occupations ever engaged in for more than six months, and for bladder cancer risk factors in general. NAT2 was phenotyped by high-pressure liquid chromatography of caffeine metabolites in urine. The NAT2 status was additionally evaluated by genotyping 88 of these patients. Eighty-nine patients were genotyped for GSTM1. Of the 179 bladder-cancer patients, 115 (64%) were slow acetylators. In 70% of the subgroup of 89 patients, GSTM1 was negative, suggesting an impact of polycyclic aromatic hydrocarbons (PAHs) in bladder-cancer carcinogenesis in the general population in this area. Contrary to an ordinary distribution of the acetylator status in underground coal miners (18 slow acetylators out of 32), GSTM1 was negative in 16 of 19 of these coal miners. Five of six coke-oven workers were slow acetylators; GSTM1 was negative in all four genotyped coke-oven workers. Twelve of 17 patients formerly exposed to colorants were slow acetylators. Distributions of NAT2 (59% slow acetylators) and GSTM1 (54% GSTM1 negative) were normal in businessmen and administrative officers among the occupationally non-exposed bladder-cancer patients. The results are consistent with the view that a slow-acetylator status and lack of the GSTM1 gene are individual risk factors for bladder cancer in persons occupationally exposed to aromatic amines and PAHs. Aromatic amines may be connected with induction of bladder cancer in persons who have been in contact with azo dyes and in coke-oven workers. PAHs may also contribute to elevated bladder-cancer risks in coke-oven workers and in underground coal miners.

[Clinical relevance of acetylator phenotyping in 196 urothelial tumor patients]

A total of 196 patients with urothelial tumours were phenotyped for N-acetyltransferase 2 by the molar ratio of two caffeine metabolites excreted in urine. The proportion of "slow" acetylators, who are genetically predisposed to urothelial tumours if they have been exposed to aromatic amines in the past, in the entire group was 55%, within the range in a normal population. Among 40 patients with assumed former occupational exposure to aromatic amines, 65% were "slow" acetylators. Invasiveness, histopathological grading of the urothelial tumour at the time of first diagnosis, and course were not related to acetylator phenotype.

Influence of polymorphisms of GSTM1 and GSTT1 for risk of renal cell cancer in workers with long-term high occupational exposure to trichloroethene

Suspected nephrocarcinogenic effects of trichloroethene (TRI) in humans are attributed to metabolites derived from the glutathione transferase (GST) pathway. The influence of polymorphisms of GSTM1 and GSTT1 isoenzymes on the risk of renal cell cancer in subjects having been exposed to high levels of TRI over many years was investigated. GSTM1 and GSTT1 genotypes were determined by internal standard controlled polymerase chain reaction. Fourty-five cases with histologically verified renal cell cancer and a history of long-term occupational exposure to high concentrations of TRI were studied. A reference group consisted of 48 workers from the same geographical region with similar histories of occupational exposures to TRI but not suffering from any cancer. Among the 45 renal cell cancer patients, 27 carried at least one functional GSTM1 gene (GSTT1 +) and 18 at least one functional GSTT1 gene (GSTT1 +). Among the 48 reference workers, 17 were GSTM1 + and 31 were GSTT1 +. Odds ratio for renal cell cancer were 2.7 for GSTM1 + individuals (95% CI, 1.18-6.33; P < 0.02) and 4.2 for GSTT1 + individuals (95% CI, 1.16-14.91; P < 0.05), respectively. The data support the present concept of the nephrocarcinogenicity of TRI.

Experimental designs and risk assessment in combination toxicology: panel discussion

Advancing our knowledge on the toxicology of combined exposures to chemicals and implementation of this knowledge in guidelines for health risk assessment of such combined exposures are necessities dictated by the simple fact that humans are continuously exposed to a multitude of chemicals. A prerequisite for successful research and fruitful discussions on the toxicology of combined exposures (mixtures of chemicals) is the use of defined terminology implemented by an authoritative international body such as, for example, the International Union of Pure and Applied Chemistry (IUPAC) Toxicology Committee. The extreme complexity of mixture toxicology calls for new research methodologies to study interactive effects, taking into account limited resources. Of these methodologies, statistical designs and mathematical modelling of toxicokinetics and toxicodynamics seem to be most promising. Emphasis should be placed on low-dose modelling and experimental validation. The scientifically sound so-called bottom-up approach should be supplemented with more pragmatic approaches, focusing on selection of the most hazardous chemicals in a mixture and careful consideration of the mode of action and possible interactive effects of these chemicals. Pragmatic approaches may be of particular importance to study and evaluate complex mixtures; after identification of the 'top ten' (most risky) chemicals in the mixture they can be examined and evaluated as a defined (simple) chemical mixture. In setting exposure limits for individual chemicals, the use of an additional safety factor to compensate for potential increased risk due to simultaneous exposure to other chemicals, has no clear scientific justification. The use of such an additional factor is a political rather than a scientific choice.

Risk assessment of mixtures and standard setting: working towards practical compromises

Basic concepts of 'dose/concentration additivity' and 'response addition/independence' may be applied to evaluate chemical mixtures in human toxicology, as well as in ecotoxicology. In the case of compounds that cause the same toxicological effect by the same mechanism, 'dose addition' is a more plausible form of joint action than 'response addition'. Data on the effects of halogenated hydrocarbons on the kidney, the effects of organic solvents on the central nervous system, and the effects of organophosphates on cholinesterase, are the basis of this assumption. For such compounds, response addition will generally underestimate risk. None the less, both dose addition and response addition are 'non-interactive' forms of joint action. As such, neither additivity assumption will accurately predict risk for compounds that exhibit toxicological interactions regardless of the primary mechanism(s) of toxicity. More often, the additivity approach overestimates the risk of a combination of chemicals. From a public health perspective, such results over-protect the public; hence this approach can be used for standard setting. The introduction of a special safety factor of 10 for the standard setting for mixtures in addition to those normally used for deriving acceptable daily intakes, reference doses or minimal risk levels is not supported by data. Instead, each exposure scenario should be considered on a case-by-case basis. Furthermore, considerations of multiple endpoints, including multiple organs, multiple effects, multiple mechanisms and potential interactions between such mechanisms, are very desirable for overall toxicity and risk assessment of chemical mixtures. In conclusion, additivity could be used to estimate potential risks for a combination of chemicals: only if scientific data support independence of effects can response independence be used as an alternative for standard setting.

Butadiene and isoprene: future studies and implications

Based on the symposium on 1,-3-butadiene and isoprene at Blaine, WA, the following areas need special attention for future research: (1) discrepancies in PBPK modelling by different groups should be solved; (2) potential human target tissues (bone marrow, lymphatic tissues) should be better integrated into PBPK models; (3) the present rapid development in research on human genetic interindividual differences in 1,3-butadiene metabolism and toxicity should be supported, with the intention to determine human subgroups of differential susceptibility and to integrate this into epidemiological research; (4) further validation of past exposures in the epidemiologically studied corhorts is very desirable; (5) the question of possibly differential effects in 1,3-butadiene monomer workers and styrene-butadiene-rubber workers (lymphosarcoma?, reticulosarcoma?, leukemia?) should be resolved in future epidemiological studies; (6) potential human target tissues (bone marrow, lymphatic tissues) should be better integrated into PBPK modelling; (7) risk assessment of isoprene and, by quantitative comparison, of 1,3-butadiene in humans should consider the physiological background of endogenous isoprene production; and (8) future research on biomarkers should establish practical tools for medical surveillance of presently exposed persons.

Biological formation of the 1,3-butadiene DNA adducts 7-N-(2-hydroxy-3-buten-1-yl)guanine, 7-N-(1-hydroxy-3-buten-2-yl)guanine and 7-N-(2,3,4-trihydroxy-butyl)guanine

Male mice (B6C3F1) and male Wistar rats were exposed to [1,4-(14)C] butadiene in a closed all-glass desiccator jar system, and liver DNA was obtained. After acid hydrolysis and HPLC chromatography radioactive 7-N-(1-hydroxy-3-buten-2-yl)guanine and 7-N-(2,3,4-trihydroxybutyl)guanine were identified as radioactive DNA adducts. The same DNA adducts were identified upon incubation of calf thymus DNA, rat liver microsomes, [1,4-(14)C]butadiene and an NADPH-regenerating system. In this system, a third radioactive adduct was found which was identified as 7-N-(2-hydroxy-3-buten-yl)guanine.

Differential reactivities of the mono- and di-epoxide of 1,3-butadiene

The acid-catalysed (perchloric acid) hydrolysis of 1,2-epoxybutene-3 (EB) and of 1,2:3,4-diepoxybutane (DEB), two reactive epoxide metabolites of 1,3-butadiene (BD), was determined based on reaction of unchanged epoxide with 1-nitro-4-pyridyl-benzene (NBP). Related to different epoxide concentrations, both reactions were of first order. Related to different proton concentrations, second-order rate constants were obtained (approximately 10 s-1 M-1 perchloric acid for EB; approximately 0.01 s-1 M-1 perchloric acid for DEB). These data show a much higher chemical stability of DEB compared to EB. Moreover, EB and DEB were reacted at pH 7.2 in 10 mM TRIS buffer with deoxyguanosine (dG), guanosine (G) or calf thymus DNA. The unreacted epoxides (EB or DEB) present in the incubation mixtures with time were determined by gas chromatography. Consistent with the results of the acid-catalysed hydrolysis, the second-order rate constants for reaction with dG, G or DNA were more than 10-fold higher with EB, compared to those with DEB.

Occupational history and genetic N-acetyltransferase polymorphism in urothelial cancer patients of Leverkusen, Germany

OBJECTIVES

The study was designed to realize possible shifts in the ratio of slow to fast acetylators within a group of 196 urothelial cancer patients in an area with earlier benzidine production.

METHODS

The subjects were interviewed for occupational and nonoccupational risk factors. The patients were phenotyped for N-acetyltransferase 2 (NAT2) by Grant's caffeine test. A subgroup of 54 patients was additionally genotyped for NAT2.

RESULTS

The antimode in the NAT2 phenotyping with the caffeine test (AFMU: IX ratio) was 1.0, as evidenced by additional genotyping of the subgroup of 54 patients. The prevalence of slow acetylators in the entire group of bladder cancer patients was 55%, in accordance with published figures for European populations. In a subgroup of 40 patients with occupational histories as workers in chemical or rubber industries 65% were slow acetylators. In a further subgroup of 28 cases having specifically worked at chemical production sites of the local chemical industry, 68% were slow acetylators.

CONCLUSIONS

In contrast to earlier studies, this study shows no increased prevalence of slow acetylators among urothelial cancer patients in comparison with the normal population. However, in subgroups of cases with a likelihood of past occupational contacts with aromatic amines, there was a trend towards a higher representation of slow acetylators. This finding is in accordance with observations of others that the percentage of slow acetylators in urothelial cancer patients is generally decreasing, possibly because the production of benzidine and benzidine-based dyes ceased in the early 1970s.

Quantification of endogenous carcinogens. The ethylene oxide paradox

Although ethylene oxide is a proven genotoxic carcinogen in experimental animals, its human carcinogenicity is still being debated. Alkylations (hydroxyethylation) of DNA and proteins by ethylene oxide are well established. Ethylene oxide is metabolically formed from ethylene, which is a natural body constituent. Thus, endogenous sources of ethylene/ethylene oxide contribute to background alkylations of physiological macromolecules. There are now experimentally well established data sets on the background hydroxyethylations of the N-terminal valine of hemoglobin and of the 7-N position of guanine in DNA, in laboratory animals as well as in humans: A review of these data leads to the conclusion that these background levels display remarkable consistency between the different species studied and, as far as DNA adducts are concerned, also between different tissues. From the existing database it can be deduced that in rats a hemoglobin alkylation, equivalent to the level of normal background, would be caused by repetitive external atmospheric exposures to ethylene oxide (6 hr/day, 5 days/week for several weeks) of about 30 ppb. On the contrary, in the same species, a DNA alkylation, equivalent to the level of normal background, would be caused by similar repetitive exposures to ethylene oxide at about 1-2 ppm. This paradox is unresolved. It points, however, to the biological importance of endogenous DNA alkylations and questions current regulatory procedures of assessing the risk of minute doses of exogenous carcinogens.

Purification and characterization of a new glutathione S-transferase, class theta, from human erythrocytes

A new polymorphic form of glutathione S-transferase (GST), metabolising monohalogenated methanes, ethylene oxide and dichloromethane, has been purified from human erythrocytes and characterized. Several characteristics, such as similar elution patterns on different chromatographic matrices, KM-values and activity towards antibodies, confirm a previous assumption that this novel GST is a class theta enzyme. Although the presence or absence of the enzyme activity in human red blood cells is parallel with the polymorphism of the human GST T1 gene, the new GST theta in red blood cells may differ from the known GST T1-1 enzyme from other tissues in terms of substrate specificity, since established GST T1-1 substrates [1,2-epoxy-3-(p-nitro-phenoxy)propane and p-nitro-benzyl chloride] are not metabolized. The substrate specificity of the new enzyme in erythrocytes resembles more closely that of GST T2-2, most likely due to a common N-terminal modification which modifies substrate binding. The new polymorphic GST-isoform in human red blood cells therefore may be considered to represent an N-terminally modified isoform of GST T1-1.

Comparative genotyping and phenotyping of glutathione S-transferase GSTT1

Only limited information is available so far concerning the human glutathione S-transferase isoenzyme class theta encoded by the GSTT1 gene. The aim of the study was to characterize individuals in respect to a polymorphic deletion of the GSTT1 gene and to validate these results with the phenotypical determination of the "conjugator status" according to Hallier et al. (1993). Determination of the GSTT1 genotype was done in 40 healthy adults by using an assay based on internal standard controlled polymerase chain reaction. The GSTT1-1 phenotype was determined by measuring the erythrocyte conjugating activity towards methyl chloride using a gas chromatographic assay. Genotypically, 34 individuals out of 40 were classified as GSTT1 positive; the remainder were negative. These results could be confirmed by phenotyping in all but one case. In the present study the frequency of "nonconjugators" was 15%. Our study demonstrates the reliability of the suggested PCR assay for GSTT1 genotyping which is easier to perform than the phenotyping assay and is not affected by confounding factors.

Toxicokinetics of p-tert-octylphenol in male Wistar rats

Only weak oestrogenic activity has been reported for p-alkylphenols compared with the physiological hormone 17 beta-estradiol. Despite the low potency, there is concern that due to bioaccumulation oestrogenically efficient blood levels could be reached in humans exposed to trace levels of p-alkylphenols. To address these concerns, toxicokinetic studies with p-tert-octylphenol [OP; p-(1,1,3,3-tetramethylbutyl)-phenol] as a model compound have been conducted in male Wistar rats. OP blood concentrations were determined by GC-MS in rats receiving either single oral (gavage) applications of 50 or 200 mg OP/kg body wt or a single intravenous injection of 5 mg/kg body wt. The OP blood concentration was approximately 1970 ng/ml immediately after a single intravenous application, decreased rapidly within 30 min, and was no longer detectable 6-8 h after application. The curve of blood concentration vs time was used to calculate an elimination half-life of 310 min. OP was detected in blood as early as 10 min after gavage administration, indicating rapid initial uptake from the gastrointestinal tract; maximal blood levels reached 40 and 130 ng/ml after applications of 50 and 200 mg/kg, respectively. Using the area under the curve (AUC) of blood concentration vs time, low oral bioavailabilities of 2 and 10% were calculated for the 50 and 200 mg/kg groups, respectively. OP toxicokinetics after repeated administration was investigated in male Wistar rats receiving daily gavage administrations of 50 or 200 mg OP/kg body wt for 14 consecutive days. Profiles of OP blood concentration vs time determined on day 1 and day 14 were similar, indicating that repeated oral gavage administration did not lead to increased blood concentrations. Another group of rats received OP via drinking water saturated with OP (approximately 8 mg/l, corresponding to a mean daily dose of approximately 800 micrograms/kg) over a period of up to 28 days. OP was not detected in any blood sample from animals treated via drinking water (detection limit was 1-5 ng/ml blood). OP concentrations were also analysed in tissues obtained from the repeated gavage (14 days) and drinking water groups (14 and 28 days). In the 50 mg/kg group, low OP concentrations were detected in fat and liver from some animals at average concentrations of 10 and 7 ng/g tissue, respectively. OP was not detected in the other tissues analysed from this group. In the 200 mg/kg group, OP was found in all tissues analysed except testes (fat, liver, kidney, muscle, brain and lung had average concentrations of 1285, 87, 71, 43, 9 and 7 ng/g tissue, respectively). OP was not detected in tissues of animals receiving OP via drinking water for 14 or 28 days, except in muscle and kidney tissue of one single animal receiving OP for 14 days. Using rat liver fractions it was demonstrated that OP was conjugated via glucuronidation and sulphation in vitro. A Vmax of 11.24 nmol/(min * mg microsomal protein) and a Km of 8.77 mumol/l were calculated for enzyme-catalysed OP glucuronidation. For enzyme-catalysed sulphation, a Vmax of 2.85 nmol/(min * mg protein) and a Km of 11.35 mumol/l were calculated. The results indicate that OP does not bioaccumulate in rats receiving low oral doses, in agreement with the hypothesis of a rapid first-pass elimination of OP by the liver after oral ingestion, via glucuronidation and sulphation. Only if these detoxification pathways are saturated may excessive doses lead to bioaccumulation.

Preexistence of chronic tubular damage in cases of renal cell cancer after long and high exposure to trichloroethylene

Substantially more cases of tubular damage were found among renal cell carcinoma patients who had been exposed to high levels of trichloroethylene over many years than among renal cell carcinoma patients who had not been exposed to trichloroethylene. This supports the hypothesis (Goeptar et al. 1995) that chronic tubular damage may be regarded as a necessary precondition for trichloroethylene to exert a nephrocarcinogenic effect. The findings also indicate that the urine protein patterns identified with SDS-PAGE may represent a valuable parameter for effect biomonitoring of persons exposed to high levels of trichloroethylene over many years.