Human GSH-transferase in risk assessment.
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Animals↗
Biomedical subjects
H M Bolt
Publications and source records attributed to H M Bolt.
Genetic predisposition in occupational toxicology.
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Acetyltransferases↗
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.
Erythrocytes↗
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.
Carcinoma, Renal Cell↗
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.
Adult↗
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.
Administration, Oral↗
Glutathione S-transferase GSTM1 and GSTT1 null genotypes as potential risk factors for urothelial cancer of the bladder.
One-hundred-and-thirteen patients with cancer of the urinary bladder (cases) were examined with respect to the frequency of null genotypes of the polymorphic glutathione S-transferases GSTM1 and GSTT1. The allelic background in the German population of the area was evaluated by analysing 170 newborns (controls). The frequency of GSTM1 and GSTT1 null genotypes in this population, using methods based upon internal standard controlled polymerase chain reaction (PCR), was 0.54 and 0.18 respectively. An elevated relative bladder cancer risk of GSTM1 null genotype carriers was indicated by comparison of this background with the data of the bladder cancer cases (OR = 1.81; 95% CI [1.10, 2.98]; p = 0.019). The frequencies of the GSTT1 null genotype in the total group of bladder cancer cases versus controls did not differ statistically. However, a significantly higher relative risk of bladder cancer for the GSTT1 null genotype was detected in the cases-subgroup of non-smokers (OR = 3.84; 95% CI [1.21, 12.23]; p = 0.023). Thus, the GSTT1 null genotype might represent a minor risk factor for human bladder cancer which should be further investigated.
Adult↗
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.
Acetylation↗
Sister chromatid exchange frequency in cultured isolated porcine urinary bladder epithelial cells (PUBEC) treated with ochratoxin A and alpha.
The mycotoxin ochratoxin A (OTA) and its metabolite ochratoxin alpha (OT-alpha) were investigated, to examine their potency to induce sister chromatid exchanges (SCE) in cultured porcine urinary bladder epithelial cells (PUBEC) (primary culture). Serum-free cultured PUBEC were incubated for 5 h with either OTA or OT-alpha, respectively, and subsequently cultured in the presence of 5-bromo-2-deoxyuridine (BrdU). After two cell cycles, mitosis was inhibited by the colchicine derivative Colcemid, cells were fixed and chromosomes were prepared for SCE analysis. For OTA, a dose-dependent increase in SCE frequency was measured in concentrations between 100 pM and 100 nM OTA. At 100 nM OTA, SCE frequency increased by about 41%, compared to the base SCE level (7.27 SCEs per chromosome set, solvent control). Higher concentrations of OTA were cytotoxic. The metabolite OT-alpha also increased SCE frequency, but at higher concentrations. At a concentration of 10 microM OT-alpha, an increase of about 55% was detected. OT-alpha showed no cytotoxic effect. These results indicate that OTA is genotoxic in this in vitro system, which represents the urinary bladder epithelium, a target organ of OTA in vivo. It could also be shown that OT-alpha, which is said to be non-toxic, is genotoxic in this assay at higher concentrations.
Animals↗
Glutathione-S-transferase (GST) theta polymorphism influences background SCE rate.
Polymorphism of glutathione S-transferase theta (GSTT1) modulates the toxicity of halogenated alkanes and epoxides in humans. The enzymatic activity of glutathione S-transferase theta and its corresponding gene is lacking in about 30% of the central European population. It has now been demonstrated that the background rate for sister chromatid exchange (SCE) is affected by this particular polymorphism. Smoking as a known inducer of SCE was taken into account. A group of GSTT1-positive subjects exhibited lower SCE rates than GSTT1-negative individuals (7.55 +/- 0.77 versus 8.74 +/- 1.24 SCE/mitosis, respectively, p < 0.005). Non-smoking GSTT1-positive individuals showed the lowest SCE rate (7.26 +/- 0.71 SCE/mitosis), significantly lower than the rates of smoking GSTT1-positive and non-smoking GSTT1-negative subjects (8.14 +/- 0.55 SCE/mitosis and 8.12 +/- 0.88 SCE/mitosis, respectively, p < 0.025 in both cases). Smoking GSTT1-negative subjects exhibited the highest SCE rates (9.28 +/- 1.3 SCE/mitosis). It is hypothesized that GSTT1 is protective against background genotoxic damage. Since ethylene oxide is a proven substrate of GSTT1, the detoxification of this epoxide arising from endogenous ethylene may modulate SCE background rates.
Adult↗
Comparative mutagenicity of 2-methylpropene (isobutene), its epoxide 2-methyl-1,2-epoxypropane and propylene oxide in the in vitro micronucleus test using human lymphocytes.
2-Methylpropene (isobutene), a gaseous compound widely used in chemical industries, is metabolized to the epoxide 2-methyl-1,2-epoxypropane. The parent compound has previously been shown to be non-mutagenic in a modified Ames test, whereas the epoxide metabolite gave a positive result. In this study, both compounds have been tested in the in vitro micronucleus test using human lymphocytes. Propylene oxide, a well known mutagenic compound, served as a positive control. It was found that 2-methylpropene had no mutagenic effect, whereas its epoxide induced a statistically significant dose-dependent increase in the number of micronuclei. The effect observed was comparable with that obtained for propylene oxide.
Alkenes↗
[Urothelial diseases as an occupational disease].
The number of urothelial tumors of the lower urinary tract caused by occupational exposure is expected to markedly exceed the number of diseases which are actually compensated. The German compensation system for diseases is explained using the example of disease number 1301 which applies to bladder diseases due to aromatic amines. A standard procedure for the evaluation of the percentage of disability ("MdE") caused by tumors of the urinary bladder is presented. Important working areas which are associated with an elevated tumor risk of the lower urinary tract are mentioned. Cancerogenic aromatic amines can also be liberated in the human organism from soluble, i. e. bioavailable, azo dyes by reductive cleavage. Therefore, as a first step, a detailed work history (starting from the beginning of apprenticeship) must be obtained in all cases of urothelial tumors because of the very long latency time of tumors of the urothelium which can be up to fourty years and higher.
Carcinoma, Transitional Cell↗
Human glutathione S-transferase theta (GSTT1): cDNA cloning and the characterization of a genetic polymorphism.
In humans, glutathione-dependent conjugation of halomethanes is polymorphic, with 60% of the population classed as conjugators and 40% as non-conjugators. We report the characterization of the genetic polymorphism causing the phenotypic difference. We have isolated a cDNA that encodes a human class Theta GST (GSTT1) and which shares 82% sequence identity with rat class Theta GST5-5. From PCR and Southern blot analyses, it is shown that the GSTT1 gene is absent from 38% of the population. The presence or absence of the GSTT1 gene is coincident with the conjugator (GSST1+) and non-conjugator (GSTT1-) phenotypes respectively. The GSTT1+ phenotype can catalyse the glutathione conjugation of dichloromethane, a metabolic pathway which has been shown to be mutagenic in Salmonella typhimurium mutagenicity tester strains and is believed to be responsible for carcinogenicity of dichloromethane in the mouse. In humans, the enzyme is found in the erythrocyte and this may act as a detoxification sink. Characterization of the GSTT1 polymorphism will thus enable a more accurate assessment of human health risk from synthetic halomethanes and other industrial chemicals.
Amino Acid Sequence↗
Intervention study on the influence of reduction of occupational exposure to styrene on sister chromatid exchanges in lymphocytes.
An intervention study was performed on 28 workers exposed by inhalation to styrene in the reinforced plastics industry and 20 controls not occupationally exposed to the compound. The workers involved were 14 laminators exposed to a time-weighted average of approximately 40 ppm styrene and 14 formers exposed to an average of about 10 ppm styrene. Ambient air monitoring data and the concentration of mandelic acid in the urine were used for the assessment of exposure. From each subject, peripheral blood lymphocytes were analysed for sister chromatid exchanges (SCEs). In the laminators, the mean SCE frequency was significantly higher than in the controls in both the group of smokers (9.59 +/- 0.77 SCEs/cell vs 7.23 +/- 1.00 SCEs/cell) and the group of non-smokers (10.25 +/- 1.08 SCEs/cell vs 5.98 +/- 0.60 SCEs/cell). The mean SCE frequency of the formers (7.42 +/- 128 SCEs/cell in smokers) did not differ statistically from the controls (7.23 +/- 1.00 SCEs/cell in smokers). No evaluation was made for non-smoking formers since all but one worker in this group were smokers. In order to comply with a lowering of the occupational exposure limit (MAK value) for occupational exposure to styrene in the Federal Republic of Germany from 100 ppm to 20 ppm, considerable technical and hygienic improvements were made at the work site of the laminators. This intervention led to a reduction of average exposure of these workers by inhalation from 40 ppm to approximately 20 ppm. One year after these improvements were made, a second investigation was performed. In all but one of the laminators, the concentration of mandelic acid in urine had dropped considerably. The SCE frequency in blood lymphocytes of the laminators had likewise dropped significantly to 7.74 +/- 0.59 SCEs/cell in the non-smokers. In the smokers, it was also lower than on the first occasion (9.02 +/- 1.19), yet statistical evaluation was not possible due to insufficient numbers. Overall, the results of the intervention study show that the lowering of the occupational exposure limit for styrene to 20 ppm in Germany was justified and that a reduction of occupational exposure to the chemical has led to a prevention of adverse cytogenetic effects.
Adult↗
Early health effects and biological monitoring in persons occupationally exposed to tetraethyl lead.
Dependent on the level of occupational exposure to tetraethyl lead, the occurrence of early signs of toxicity and the urinary excretion of triethyl lead, diethyl lead and total lead compounds were investigated. This was done in the following cohorts in the province of Hubei, China: 277 workers at gasoline depots exposed to gasoline, 36 traffic policemen exposed to automobile exhaust and 342 public office workers (virtually non-exposed controls). Mean external tetraethyl lead exposure concentrations were 84.8 micrograms/m3 (as Pb) for the gasoline depot workers, 5.2 micrograms/m3 for traffic police and 1.1 microgram/m3 for the controls. No significant subclinical indications of organic lead toxicity were found in the group of traffic policemen compared with the controls. In the cohort of gasoline workers, however, there was a statistical increase (vs controls) in the frequency of appearance of tremor and of sinus bradycardia. When the cohort of gasoline workers was divided into subgroups of different ranges of exposure, dose-dependence was noted. In general, the urinary excretion of triethyl lead was very low compared to that of diethyl lead, which appears to be a sensitive and specific indicator of exposure to tetraethyl lead; total lead excretion did not correlate well with actual external tetraethyl lead exposure. On the basis of these data it seems that current occupational exposure limits for tetraethyl lead are inadequate and need to be revised. In addition, a biological limit, based on urinary diethyl lead excretion, may be proposed.
Adult↗
DNA binding study with inhaled [14C]2-methylpropene (isobutene)
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Administration, Inhalation↗
Bacterial mutagenicity of 2-chloro-1,3-butadiene (chloroprene) caused by decomposition products.
Since the literature on genotoxicity of 2-chloro-1,3-butadiene (chloroprene) is controversial, the mutagenicity of this compound was reinvestigated with respect to its chemical stability. Because of the volatility of chloroprene, Ames tests with S. typhimurium TA 100 were carried out with gas-tight preincubation. Propylene oxide, a volatile direct mutagen, served as a positive control. Benzo[a]pyrene was used as a control for an indirect mutagen. Using this experimental regimen, freshly distilled chloroprene was not mutagenic. However, a mutagenic effect occurred linearly with increasing age of the chloroprene distillates. Aged chloroprene gave the same positive results whether preincubation was gas-tight or not. Analysis by gas chromatography (GC) revealed several decomposition products in aged chloroprene distillates. The direct mutagenicity towards TA 100 correlated with the integrated amounts of four of these substances; these substances always occurred in the same relative ratio. When chloroprene was kept under anaerobic conditions, products occurred with time which were partly different from those obtained under aerobic conditions. The direct mutagenicity of anaerobically aged chloroprene was only weak, but the mutagenic effect was enhanced about two- to threefold by addition of S9 mix. Partial identification of chloroprene decomposition products was done by gas chromatography-mass spectrometry (GC-MS): major byproducts of chloroprene, probably responsible for mutagenic properties of aged chloroprene samples, were cyclic chloroprene dimers.
Chloroprene↗
New scientific arguments for regulation of ethylene oxide residues in skin-care products.
Ethylene oxide (EO) occurs as a contaminant of skin-care products because current commercial preparations of polyglycol ethers may contain ethylene oxide monomer residues, up to the order of 1 ppm. Using current regulatory worst-case assumptions, the presence of EO in skin-care products might lead to a maximal human daily external ethylene oxide dose of about 2.8 micrograms, and a consecutive maximal daily absorbed dose of 0.39 microgram. Two methods of toxicokinetic analysis have been used to compare this possible EO load by use of skin-care products with the inevitable load of EO which is produced endogenously in the organism. On the basis of a previous assessment of the endogenous production of ethylene and ethylene oxide (Filser et al. 1992) it is inferred that the absorbed EO dose of 0.39 microgram is about 1/30 of the unavoidable human endogenous load by endogenous EO. Alternatively, for a second calculation molecular dosimetry data have been used which were based on experimental quantification of the hydroxyethyl adduct of EO to the N-terminal valine of hemoglobin (HOEtVal) in rats. If the worst-case assumptions for human EO absorption from skin-care products are transferred to the rat species, the associated internal EO doses are about 1/110 of the internal EO doses which were calculated from the background HOEtVal concentrations observed in untreated animals. The divergence between both lines of calculation is mainly due to differences in HOEtVal background concentrations between man and rat.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗