Meeting report: international workshop on endocrine disruptors: exposure and potential impact on consumers health.

The French Agency for Food, Environmental and Occupational Health and Safety (Anses) hosted a two-day workshop on Endocrine Disruptors: Exposure and Potential Impact on Consumers Health, bringing together participants from international organizations, academia, research institutes and from German, Swedish, Danish and French governmental agencies. The main objective of the workshop was to share knowledge and experiences on endocrine disruptors (ED) exposure and potential impact on consumers' health, to identify current risk assessment practices and knowledge gaps and issue recommendations on research needs and future collaboration. The following topics were reviewed: (1) Definition of ED, (2) endpoints to be considered for Risk assessment (RA) of ED, (3) non-monotonic dose response curves, (4) studies to be considered for RA (regulatory versus academic studies), (5) point of departure and uncertainty factors, (6) exposure assessment, (7) regulatory issues related to ED. The opinions expressed during this workshop reflect day-to-day experiences from scientists, regulators, researchers, and others from many different countries in the fields of risk assessment, and were regarded by the attendees as an important basis for further discussions. Accordingly, the participants underlined the need for more exchange in the future to share experiences and improve the methodology related to risk assessment for endocrine disrupters.

Meta- and pooled analysis of GSTT1 and lung cancer: a HuGE-GSEC review.

Lung cancer is the most common malignancy in the Western world, and the main risk factor is tobacco smoking. Polymorphisms in metabolic genes may modulate the risk associated with environmental factors. The glutathione S-transferase theta 1 gene (GSTT1) is a particularly attractive candidate for lung cancer susceptibility because of its involvement in the metabolism of polycyclic aromatic hydrocarbons found in tobacco smoke and of other chemicals, pesticides, and industrial solvents. The frequency of the GSTT1 null genotype is lower among Caucasians (10-20%) than among Asians (50-60%). The authors present a meta- and a pooled analysis of case-control, genotype-based studies that examined the association between GSTT1 and lung cancer (34 studies, 7,629 cases and 10,087 controls for the meta-analysis; 34 studies, 7,044 cases and 10,000 controls for the pooled analysis). No association was observed between GSTT1 deletion and lung cancer for Caucasians (odds ratio (OR) = 0.99, 95% confidence interval (CI): 0.87, 1.12); for Asians, a positive association was found (OR = 1.28, 95% CI: 1.10, 1.49). In the pooled analysis, the odds ratios were not significant for either Asians (OR = 0.97, 95% CI: 0.83, 1.13) or Caucasians (OR = 1.09, 95% CI: 0.99, 1.21). No significant interaction was observed between GSTT1 and smoking on lung cancer, whereas GSTT1 appeared to modulate occupational-related lung cancer.

Glutathione transferase T1 phenotype affects the toxicokinetics of inhaled methyl chloride in human volunteers.

The aim of the present study was to investigate how the genetic polymorphism in glutathione transferase T1 (GSTT1) affects the metabolism and disposition of methyl chloride in humans in vivo. The 24 volunteers (13 males and 11 females) who participated in the study were recruited from a group of 208 individuals previously phenotyped for GSTT1 by measuring the glutathione transferase activity with methyl chloride in lysed erythrocytes ex vivo. Eight individuals with high (+/+), eight with medium (+/0) and eight with no (0/0) GSTT1 activity were exposed to methyl chloride gas (10 p.p.m.) in an exposure chamber for 2 h. Uptake and disposition was studied by measuring the concentration of methyl chloride in inhaled air, exhaled air and blood. A two-compartment model with two elimination pathways corresponding to exhalation and metabolism was fitted to experimental data. The average net respiratory uptake of methyl chloride was 243, 158, and 44 micromol in individuals with high, intermediate and no GSTT1 activity, respectively. Metabolic clearance was high (4.6 l/min) in the +/+ group, intermediate (2.4 l/min) in the +/0 group, and close to zero in 0/0 individuals, while the exhalation clearance was similar in the three groups. No exposure related increase in urinary S-methyl cysteine was detected. However, gender and the GSTTl phenotype seemed to affect the background levels. In conclusion, GSTT1 appears to be the sole determinant of methyl chloride metabolism in humans. Thus, individuals with nonfunctional GSTT1 entirely lack the capacity to metabolize methyl chloride.

CYP1A1 and GSTM1 polymorphisms affect urinary 1-hydroxypyrene levels after PAH exposure.

Certain human biotransformation enzymes have been implicated in the formation and scavenging of the ultimate reactive metabolites, the diolepoxides, from polycyclic aromatic hydrocarbons (PAHs). In the present study, performed on aluminum smelter workers, we have analyzed airborne PAH, the pyrene metabolite 1-hydroxypyrene (1-OHP) in urine, and genotypes for biotransformation enzymes involved in PAH metabolism. The aim was to evaluate the correlation between external exposure and biomarkers of exposure and to investigate to what extent genetic polymorphism in metabolic enzymes can explain interindividual variation in urinary 1-OHP levels. DNA was prepared from blood samples from 98 potroom workers and 55 controls and altogether eight polymorphisms in the CYP1A1, mEH, GSTM1, GSTP1 and GSTT1 genes were analyzed. The 1-OHP excretion was found to correlate significantly (P 100-fold) and univariate and multivariate regression analyses were used to find the variables that could determine differences in excretion. The variation could, to some degree, be explained by differences in exposure to airborne particulate-associated PAHs, the use of personal respiratory protection devices, smoking habits and genetic polymorphisms in the cytochrome P450 1A1, GSTM1 and GSTT1 enzymes. The part of the variance that could be explained by differences in biotransformation genotypes seemed to be of the same order of magnitude as the variance explained by differences in exposure. In the control group as well as in the occupationally exposed group, the highest 1-OHP levels were observed in individuals carrying the CYP1A1 Ile/Val genotype who were also of the GSTM1 null genotype. The results show that urinary 1-OHP is a sensitive indicator of recent human exposure to PAHs and that it may also to some extent reflect the interindividual variation in susceptibility to PAHs.

Influence of genetic polymorphisms of biotransformation enzymes on gene mutations, strand breaks of deoxyribonucleic acid, and micronuclei in mononuclear blood cells and urinary 8-hydroxydeoxyguanosine in potroom workers exposed to polyaromatic hydrocarbons.

OBJECTIVES: Airborne exposure to polycyclic aromatic hydrocarbons (PAH) in the potroom of an aluminum reduction plant was studied in relation to genotoxic or mutagenic effects, and the possibility of host genotypes of different metabolizing enzymes modifying associations between PAH exposure and genotoxic or mutagenic response was assessed. SUBJECTS AND METHODS: Ninety-eight male potroom workers and 55 male unexposed blue-collar workers constituted the study population. Micronuclei in CD4+ and CD8+ lymphocytes, DNA (deoxyribonucleic acid) single-strand breaks, hypoxanthine guanine phosphoribosyl transferase (HPRT) mutation frequency, and genotype for cytochrome P-4501A1, glutathione transferases M1, T1 and P1, and microsomal epoxide hydrolase were analyzed using peripheral mononuclear cells. Urine samples were collected for the analysis of 8-hydroxydeoxyguanosine. RESULTS: Micronuclei in peripheral CD4+ and CD8+ lymphocytes, DNA single-strand breaks, HPRT mutation frequency, and 8-hydroxydeoxyguanosine in urine did not differ between the potroom workers and the unexposed referents. With the exception of an observed exposure-response relationship for potroom workers with Tyr/Tyr genotype for microsomal epoxide hydrolase, between airborne PAH and CD8+ micronuclei, no correlations were found between any of the genotoxicity biomarkers and any of the exposure measures (airborne particulate PAH, airborne gas phase PAH, length of employment in the potroom, 1-hydroxypyrene in urine, or PAH-DNA adducts in peripheral lymphocytes), also when genotypes for biotransforamtion enzymes were considered. CONCLUSIONS: The results indicate that the employed biomarkers of mutagenic or genotoxic effects are not appropriate for surveillance studies of potroom workers exposed to current airborne levels of PAH. The significance of the correlation between airborne PAH and CD8+ micronuclei in Tyr/Tyr genotype subjects should be evaluated.

Radiographic changes and lung function in relation to activity of the glutathione transferases theta and mu among asbestos cement workers.

Experimental data indicate that active oxygen species may be casually involved in the development of asbestos-related disease. Thus, it was hypothesized that individual differences in glutathione transferase activity, which may affect the ability to inactivate molecules formed in relation to oxidative stress, could influence the biological response to asbestos exposure. We could, however, not demonstrate an increased risk for radiographic changes or reduced lung function among asbestos cement workers deficient for glutathione transferase theta (GSTT1), glutathione transferase mu (GSTM1), or having a combined deficiency of enzyme activity.

Resistance against ethacrynic acid in glutathione transferase 7-7 (GST-P)-positive hepatocytes isolated from carcinogen-treated rats: the role of cytoskeletal changes and ATP depletion.

Ethacrynic acid (Ea) is a substrate for glutathione transferase 7-7 (GST-P) in rat. Toxic effects of Ea have been related to its metabolism and GSH depletion, but resistance conferred by GSTP1-1 (the human homologue) has also been reported. Hepatocytes from enzyme altered foci (EAF) express GST-P, and a model for selection of resistant EAF cells has been developed using Ea as a toxic agent. In the present study the effects of Ea in this model have been characterized. Hepatocytes from foci-bearing rats were isolated. Isolated cells were exposed to Ea for 1-4 hr in suspension. They were then allowed to attach to collagen-coated plates in a serum-containing medium. Preferentially GST-P-positive cells attached after Ea treatment, thus increasing the number of positive cells per attached cells (GST-P-%). Extracellular GSH, as well as alpha-tocopherol, did not influence the Ea effect. However, the effect of Ea was counteracted by inhibitors of glutathione transferase activity. Taxol, a microtubule stabilizing agent, also counteracted the effect of Ea on GST-P-%. 1,2-Dichloro-4-nitrobenzene (DCNB, 0.4 mM), which is a substrate for other glutathione transferase isoenzymes than GST-P, also increased the GST-P-%. However, the effect of DCNB was not inhibited by taxol. It was also found that Ea induced a drop in ATP levels, but this effect, as well as cell leakage, came later than the loss of attachment. The data suggest that the critical effect of Ea was cytoskeletal changes, and that GST-P conferred resistance by detoxification of Ea.

Polymorphic distribution of glutathione transferase activity with methyl chloride in human blood.

Interindividual variation in the in vitro conjugation of methyl chloride with glutathione by erythrocyte glutathione transferase was investigated in 208 healthy males and females from the southern and central parts of Sweden. It was found that 11.1% of the individuals lacked this activity, whereas 46.2% had intermediate activity and 42.8% had high activity. This distribution of three phenotypes is compatible with the presence of one functional allele with a gene frequency of 0.659 and one defect allele with a gene frequency of 0.341. The proportion of non-conjugators in this Swedish material was considerably smaller than that previously found in Germany (Peter et al., Arch Toxicol 1989: 63, 351-355). The polymorphic distribution of another glutathione transferase, GST mu, was determined in the same individuals with a PCR method. No connection between the genotype for GST mu (GSTM1) and the glutatione conjugation with methyl chloride in erythrocytes was found.

Isolation of glutathione S-transferase P-positive hepatocytes from carcinogen treated rats by use of ethacrynic acid as selecting agent.

Rat liver responds to carcinogen treatment with growth of glutathione S-transferase P (GST-P)-positive enzyme-altered foci. In this paper a method is described where GST-P-positive hepatocytes are isolated from carcinogen-treated rats. The method utilizes ethacrynic acid, which is a good substrate for GST-P, and which induces toxicity mainly in GST-P-negative cells. The toxicity results in a loss of attachment to collagen. The method gives a 70% pure population of GST-P-positive cells attached to collagen-coated plates. Use of additional markers supports the conclusion that the GST-P-positive cells were derived from foci. Isolated GST-P-positive hepatocytes spread out and formed primary cultures of normal appearance. It was also shown that they synthesized DNA and did not respond to transforming growth factor beta 1. It is concluded that isolated GST-P-positive hepatocytes can be used for studies on alterations in enzyme-altered foci that cannot be done with in situ immunohistochemistry or in situ hybridization.

Selective toxicity in putative preneoplastic hepatocytes: a comparison of hydroquinone and duroquinone.

In this paper data is presented suggesting selective toxicity towards enzyme altered hepatocytes. Hydroquinone (HQ) treatment 24 or 48 h after diethylnitrosamine (DEN) initiation reduced the number of glutathione S-transferase-P (GST-P)-positive hepatocytes in situ. Furthermore, in experiments on primary cultures of hepatocytes from control rats a synergism in cell killing between DEN and HQ was observed. In another in vitro system the effect of HQ and duroquinone (DQ) on GGT-positive and -negative hepatocytes was investigated. DQ was shown to affect the GGT-positive cells, while HQ mainly affected GGT-negative cells. These results suggest that HQ can reduce the population of enzyme altered foci (EAF) precursor cells by synergistic interactions with DEN, but provide no support for the notion that HQ selectively damage cells in developed EAF. This conclusion is supported by previously published data on effects of HQ on the development of EAF.

Repetitive static muscle contractions in humans--a trigger of metabolic and oxidative stress?

Repetitive static exercise (RSE) is a repetitive condition of partial ischaemia/reperfusion and may therefore be connected to the formation of oxygen-derived free radicals and tissue damage. Seven subjects performed two-legged intermittent knee extension exercise repeating at 10 s on and 10 s off at a target force corresponding to about 30% of the maximal voluntary contraction force. The RSE was continued for 80 min (n = 4) or to fatigue (n = 3). Four of the subjects also performed submaximal dynamic exercise (DE) at an intensity of about 60% maximal oxygen uptake (VO2max) for the same period. Whole body oxygen uptake (VO2) increased gradually with time during RSE (P less than 0.05), indicating a decreased mechanical efficiency. This was further supported by a slow increase in leg blood flow (P less than 0.05) and leg oxygen utilization (n.s.) during RSE. In contrast, prolonged RSE had no effect on VO2 during submaximal cycling. Maximal force (measured in six additional subjects) declined gradually during RSE and was not completely restored after 60 min of recovery. After 20 and 80 min (or at fatigue) RSE phosphocreatine (PC) dropped to 74% and 60% of the initial value, respectively. A similar decrease in PC occurred during DE. Muscle and arterial lactate concentrations remained low during both RSE and DE. The three subjects who were unable to continue RSE for 80 min showed no signs of a more severe energy imbalance than the other subjects. A continuous release of K+ occurred during both RSE and DE.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of the induction of ornithine decarboxylase activity in primary cultures of adult rat hepatocytes by the phorbol ester 12-O-tetradecanoyl-13-acetate and other substances.

Hepatocytes from adult rats, cultivated for 4 days in RPMI 1640 medium, were used for studies on mechanisms of induction of ornithine decarboxylase (ODC). The activity of ODC was measured partially in situ by an assay method using (3)H-labelled ornithine and analysing of the labelled putrescine formed. The tumour-promoting phorbol ester 12-O-tetradecanoyl-13-acetate (TPA) induced ODC by several hundred percent in this system. No ODC activity remained after the cells were incubated for 4 hr with both TPA and cycloheximide, and no induction of ODC occurred when actinomycin D and TPA were present, although some ODC activity remained. Experiments with cyclohexidine and Actinomycin D (Act. D), respectively, indicated that the induction of ODC by TPA was totally dependent on protein synthesis and was also dependent on transcriptional events. Sphingosine and H-7 (1-(5-isoquinolinyl-sulphonyl)-2-methylpiperazine) inhibited the induction of ODC by TPA indicating the involvement of protein kinase C (PK-C) in this process. Pre-incubation of the hepatocytes with TPA, a procedure which down-regulates PK-C, decreased the induction of ODC by a subsequent new exposure to TPA, but had no effect on the induction of ODC caused by asparagine in this system. The induction caused by asparagine was additive to that caused by TPA. Studies with copper (diisopropylsalicylate)(2) and manganese(IV) desferrioxamine, and with prostaglandin D(2), respectively, gave no indication that activated oxygen or prostaglandins were involved in the induction of ODC by TPA. The results of this study are generally consistent with previously published in vivo data and show that a well defined hepatocyte in vitro system is suitable for mechanistic studies of ODC induction.

The role of GSH depletion and toxicity in hydroquinone-induced development of enzyme-altered foci.

Hydroquinone (HQ) may activate oxygen via redox cycles in biological systems and may also deplete glutathione (GSH). Both these reactions are potentially harmful, and we have studied their possible involvement in hydroquinone-induced development of gamma-glutamyltranspeptidase (GGT)-positive enzyme-altered foci in rat liver. The effect of HQ was compared to the effect of duroquinone, catechol, resorcinol and phenol. The dose was 100 mg/kg per day and the test substances were administered for 7-12 weeks in these foci experiments. HQ gave an increased number of foci and increased the foci volume, while none of the other compounds had any significant effect on these parameters. HQ, duroquinone and resorcinol were also tested at a higher dose level (200 mg/kg per day), but this dose gave a lower number of foci than the 100-mg dose. HQ, duroquinone and catechol induced single-strand breaks in hepatic DNA. Single doses of HQ (200 mg/kg) increased malondialdehyde excretion in urine, indicating in vivo lipid peroxidation. Duroquinone, phenol and resorcinol were negative with respect to malondialdehyde excretion. Catechol could not be properly tested as the 200-mg dose killed several animals. HQ and catechol induced hepatic ornithine decarboxylase activity. This effect was correlated to GSH depletion. An in vitro model for toxicity studies with hepatocytes from carcinogen-treated rats was also used. In this model HQ could be shown to be selectively toxic to GGT-negative cells in the presence of extracellular GSH. The toxicity was preceded by a rapid depletion of GSH. Catechol also depleted GSH and could be shown to be selectively toxic, but higher concentrations than those used for HQ had to be used. Duroquinone, phenol and resorcinol were not selectively toxic to GGT-negative cells. As duroquinone can be regarded as a more potent inducer of redox cycles than HQ, it can be concluded that the foci data provide no evidence for an involvement of redox cycles in HQ induced development of enzyme-altered foci. They suggest that GSH depletion may act to develop enzyme-altered foci, and the in vitro data indicate a mechanism by which GSH depletion and toxicity may induce this effect.

Studies of the role of DNA fragmentation in selenium toxicity.

The role of DNA damage in selenite cytotoxicity was studied in isolated hepatocyte model systems. An initial series of experiments, with hepatocytes in suspension, indicated that selenite-induced DNA fragmentation was oxygen dependent and could be inhibited by cyanide, HgCl2 and CuDIPS. These findings were interpreted to imply that selenite-induced redox cycles were involved in this effect. In a second series of experiments, the effect of inhibitors of poly(ADP-ribose)polymerase (3-aminobenzamide and theophylline) and DNA alkylating agents on selenite-induced cellular lysis was studied. These experiments were performed with hepatocytes in primary culture and 20-30 microM selenite lysed the cultured cells after about 20 hr exposure. It was found that alkylators added 20 hr before selenite acted synergistically with selenite, and that inhibitors of poly(ADP-ribose)polymerase antagonized lysis. Further studies also indicated NAD degradation before lysis. These data indicate a modulating role for DNA damage in selenite cytotoxicity mediated by poly(ADP-ribose)polymerase. Taken together with previously published data on, for example, potentially lethal oxidation of NADPH (Anundi et al., Chem. Biol. Interact. 50, 277, 1984) they also suggest that cell death resulted from interactions between several events that may deplete energy supplies. The results are compatible with a selective killing of DNA-damaged hepatocytes by low doses of selenite.

Conjugation of styrene oxide by the basic and acidic forms of glutathione transferase in the human fetal liver.

Two forms of glutathione transferase were isolated by means of isoelectric focusing of human fetal liver cytosol preparations. The enzyme activity was measured with 1-chloro-2,4-dinitrobenzene as the electrophilic substrate. One peak focused at pH 9-10 (basic form) and the other at pH 4-5 (acidic form). The basic and the acidic forms are representatives of glutathione transferase classes alpha and tau, respectively. These classes constitute two of the three classes defined for cytosolic forms of the enzyme in several mammalian species [Mannervik et al., Proc. natn. Acad. Sci. USA 82: 7202-7206, 1985]. Only the basic fraction isolated from human fetal liver catalyzed the conjugation of styrene oxide with glutathione at a significant rate. The kinetics of this form were studied keeping the concentration of styrene oxide constant (6 mM) and varying the glutathione concentration from 0.05 to 25 mM. The enzyme activity displayed non-Michaelis-Menten kinetics. The basic and acidic forms of glutathione transferase from a fetal liver were purified to homogeneity. Both purified forms catalyzed the conjugation of glutathione with styrene oxide. The kinetics were studied at varying glutathione concentrations and for both forms, it was found to be of a non-Michaelis-Menten type. The results are consistent with previous findings in the cytosolic fraction [Pacifici et al., Biochem. Pharmac. 30: 3367-3371, 1981] and show that the non-Michaelian kinetics observed with glutathione in human fetal liver cytosol are reflections of the intrinsic properties of the basic as well as the acid form of this enzyme and not primarily depending on the simultaneous catalytic action of the two forms.

Recovery of malondialdehyde in urine as a 2,4-dinitrophenylhydrazine derivative after exposure to chloroform or hydroquinone.

Malondialdehyde (MDA) excretion in urine as an index for toxicological effects of chloroform and hydroquinone was evaluated. In a first series of experiments three groups of rats were used: non-pretreated rats (group I), starved rats (group II) and starved plus phenobarbital pretreated rats (group III). Chloroform (0.15 or 0.30 ml/kg, p.o.) was given as a single dose. The MDA excretion was related to the pretreatment, and in group III to liver damage. In a second series of experiments control rats were administered hydroquinone (100 or 200 mg/kg, p.o.), which induced a dose-related MDA excretion. These data indicate that the MDA assay was a selective and accurate marker for toxicological effects induced by the tested compounds.

Detoxification of styrene oxide by human liver glutathione transferase.

Cytosolic glutathione transferase (GST) was investigated in four human livers. The profile of GST activity was determined by isoelectric focusing using 1-chloro-2,4-dinitrobenzene as the electrophilic substrate. Three livers contained at least one basic and a near-neutral isoenzyme (GST mu). GST mu was not detectable in the fourth liver. The kinetics of GST with styrene oxide as the electrophilic substrate were studied in the cytosolic fraction, with the pooled fractions from isoelectric focusing containing high activity of GST mu transferase, and with GST mu purified to homogeneity. The cytosol obeyed Michaelis-Menten kinetics when styrene oxide was used as the variable substrate. The average (+/- s.e.m.) of the Vmax and Km were 21.9 +/- 7.9 nmol min-1mg-1 and 4.9 +/- 0.4 mM, respectively. At varying concentrations of glutathione, the enzyme did not obey Michaelis-Menten kinetics. Such kinetics were also observed with the fractions from isoelectric focusing and with the homogeneous GST mu fraction. The Eadie-Hofstee plot showed two phases: one with a low and another with a high Km value. The apparent Km values for the cytosol were 0.035 +/- 0.022 and 0.88 +/- 0.36 mM. The kinetic pattern of purified GST mu is consistent with that found in the cytosol.

Purification and characterization of three distinct glutathione transferases from mouse liver.

Three distinct glutathione transferases in the liver cytosol fraction of male NMRI mice have been purified by affinity chromatography and fast protein liquid chromatofocusing. These enzymes account for approximately 95% of the activity detectable with 1-chloro-2,4-dinitrobenzene as electrophilic substrate. Differences between the three forms are manifested in isoelectric points, apparent subunit molecular mass values, amino acid compositions, N-terminal structures, substrate specificities, and sensitivities to inhibitors, as well as in reactions with specific antibodies raised against glutathione transferases from rat and human tissues. The results indicate strongly that the three mouse enzymes are products of different genes. A comparison of the mouse glutathione transferases with rat and human enzymes revealed similarities between the transferases from different species. Mouse glutathione transferases have been named on the basis of their respective subunit compositions.

Two distinct forms of glutathione transferase from human foetal liver. Purification and comparison with isoenzymes isolated from adult liver and placenta.

Isoelectric focusing of a cytosol fraction from human foetal liver revealed the existence of an acidic and a basic isoenzyme of GSH transferase. The acidic and basic forms of GSH transferase were purified in good yield by use of ion-exchange chromatography on DEAE-cellulose followed by affinity chromatography on S-hexyl-GSH coupled to epoxy-activated Sepharose 6B. The content of the acidic and the basic isoenzymes of GSH transferase together was calculated to constitute 1-2% of the soluble proteins in the hepatic cytoplasm. Physical, catalytic and immunological analyses of the acidic and the basic isoenzymes from foetal liver demonstrated unambiguously that the two forms are different structures with distinct properties. On the other hand, the results show clearly extensive similarities between the foetal acidic transferase and transferase pi from human placenta as well as between the foetal basic form and the basic isoenzymes isolated from adult liver. An exception is that both foetal enzymes seem to be considerably more efficient in catalysing the conjugation of GSH with styrene 7,8-epoxide than the corresponding adult forms of GSH transferase.