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.

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.

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.

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.

Interactions between clinically used drugs and oral contraceptives

Metabolism of contraceptive compounds may be influenced by various drugs. Of clinical importance is induction by barbiturates, by diphenylhydantoin, and especially by rifampicin, of enzymes that are responsible for degradation of estrogens. The major target is the hepatic microsomal estrogen-2-hydroxylase (cytochrome P450 3A4). Another type of interaction of drugs with disposition and effectiveness of estrogens is impairment of their enterohepatic circulation. This may be due to absorption of biliary estrogen conjugates (e.g., by cholestyramine) or to insufficient cleavage of the conjugate by intestinal bacteria, the latter being observed after administration of antibiotics (e.g., ampicillin, neomycin).

[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.

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.

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)

Macromolecular adducts in the use of methyl bromide as fumigant

An HPLC method for analysis of blood protein adducts of methyl bromide was developed. With this method, the alkylated amino acid S-methylcysteine can be quantified both in globin and in serum albumin. The determination of these adducts was implemented in a field study on fumigators who use methyl bromide for the control of insects, nematodes and fungi. Sister chromatid exchange (SCE) was determined in the lymphocytes of the fumigators as an additional biomonitoring parameter. Exposure of persons living in the vicinity of fumigated objects to methyl bromide has been repeatedly reported in the past. The new method for determination of blood protein adducts can be applied for evaluation of such environmental exposure.

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.

A note on distribution of human plasma levels of ascorbic and dehydroascorbic acid

Ascorbic acid concentrations in 102 human plasma samples ranged from 1 to 15 micrograms ml-1 with a mean concentration at about 8 micrograms ml-1, corresponding to the results of other authors. Dehydroascorbic acid was found only in traces, independent of ascorbic acid concentrations. The ascorbic acid concentrations in plasma of four persons, examined twice with a four-years interim period revealed no obvious differences over time. It is suggested that the variability of plasma ascorbic acid concentrations is mainly determined by long-term dietary habits.

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.

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.

Genetic and individual differences in the process of biotransformation and their relevance for occupational medicine

Genetically determined differences in biotransformation of xenobiotics have been identified which are important for occupational medicine. This review highlights the following topics: (i) genetic polymorphisms in the activity of cholinesterases; (ii) polymorphisms in the cytochrome P-450 isozymes CYP2D6 and CYP2E1; (iii) polymorphisms in the N-acetyltransferase NAT-2; (iv) polymorphisms in the glutathione-S-transferases mu and theta. From the view-point of occupational medicine, these genetic polymorphisms may affect the toxicity of industrial and workplace chemicals, such as organophosphates (i), major solvents and monomers for plastics (ii), aromatic amines (iii), and compounds like styrene/styrene oxide, methyl halides, dichloromethane and ethylene oxide (iv). Individual differences in biotransformation linked with genetic polymorphisms also have a considerable influence on biological monitoring strategies and on human risk assessment.

[DNA methylation of monohalogenated methanes of F344 rats]

Monohalogenated methanes (methyl chloride, methyl bromide and methyl iodide) are mutagenic and carcinogenic. The possible mechanism of these effects, DNA methylation, was studied. DNA adducts from organs of F344 rats exposed to these chemicals were separated and identified with high performance liquid chromatography (HPLC) and gas-chromatography/mass-spectrometry (GC/MS). DNA adducts, 7-methylguanine (7-MeG) and O6-Methylguanine(0(6)-MeG), incorporation of 14C into de novo synthesis of nucleobases could be observed in enzymatic DNA hydrolysates by HPLC and determination of the radioactivity in the fractions. The formation of DNA adducts in the studied organs was only quantitatively different. The formation of O6-MeG was further proved by analysing the acidic hydrolysates using HPLC with non-radioactive O6-MeG as internal standard. 7-MeG and 3-MeA were identified with GC/MS analysis.

Polymorphism of glutathione conjugation of methyl bromide, ethylene oxide and dichloromethane in human blood: influence on the induction of sister chromatid exchanges (SCE) in lymphocytes

A hitherto unknown glutathione-S-transferase in human erythrocytes displays polymorphism: three quarters of the population ("conjugators") possess, whereas one quarter ("non-conjugators") lack this specific activity. A standard method for the identification of conjugators and non-conjugators with the use of methyl bromide and gas chromatography (head space technique) is described. Three substrates of the polymorphic enzyme, methyl bromide, ethylene oxide and dichloromethane (methylene chloride), were incubated in vitro with individual whole blood samples of conjugators and non-conjugators. All three substances led to a marked increase of sister chromatid exchanges (SCE) in the lymphocytes of the non-conjugators but not in those of conjugators. A protective effect of the glutathione-S-transferase activity in human erythrocytes for the cytogenetic toxicity of these chemicals in vitro is thus confirmed. Since the enzyme activity is not found in erythrocytes of laboratory animals, species extrapolations for risk assessment of methyl bromide, ethylene oxide and dichloromethane should be reconsidered.